氧化钨富空穴的晶面与光照下空穴迁移的晶面

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Solar-light-driven photocatalysis is a green and efficient technology to immobilize high-toxic and radioactive uranium (U). However, a great challenge is to develop photocatalysts with simultaneous elevated conduction band (CB) potential and rapid charge carrier separation rate. Herein, spin-state engineering in d0 WO3 through (110) facet-confined oxygen vacancies (OVs) is proposed. Anchoring OVs at the symmetry-broken (110) facets induces low-spin WIII (d3) generation, delocalizing CB electrons and elevating CB by -0.86 V versus NHE due to higher electron occupancy in π antibonding orbitals. Density functional theory (DFT) calculations combined with femtosecond transient absorption spectroscopy (fs-TAS) reveal that triplet (T)-dominated spin-polarized electron delocalization significantly disrupts the charge carrier recombination pathway. Experiments and theoretical calculations confirm the enhanced interfacial charge transfer via O bridging between W 5d and U 5f provides a W 5d → U 5f directional electron transfer channel. Thus, the developed (110)-WO2.35 achieves high photocatalytic activity for U(VI) removal from water under simulated solar light, with a reduction efficiency of 98.0% (C0 = 10 mg L-1) and a reaction rate constant (k1) of 0.022 min-1, which is 4.1 times higher than the conventional WO3. This work pioneers atomic-scale spin-orbital synergy in d0 photocatalysis, offering a novel strategy for radionuclide remediation.

The development of water-splitting photocatalysts capable of generating green hydrogen (H2) from water and sunlight is crucial for achieving carbon neutrality. Further enhancement of the photocatalytic water-splitting activity is essential to realizing this objective. Photocatalysts with specific exposed crystal facets can facilitate efficient charge separation of electrons/holes, thereby achieving high activity for water splitting. However, there have been no reports of ultrafine (∼1 nm) cocatalysts being loaded onto specific crystal facets of photocatalysts, despite cocatalysts being the actual reaction sites for water splitting. This study establishes a novel method for achieving facet-selective loading of ultrafine H2-evolution cocatalysts onto the {100} facets, which are the H2-evolution facets, of a strontium titanate photocatalyst. The resulting photocatalyst exhibits the highest apparent quantum yield achieved to date for strontium titanate. This research holds the potential to further improve various types of advanced photocatalysts and is expected to accelerate the transition to carbon neutrality.

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Photoelectrochemical (PEC) performance of WO3 photoanode for water splitting is heavily influenced by the orientation of crystal facets. In this work, mono-particle-layer electrodes, assembled by particulate WO3 square plates with highly uniform alignment along (002) facet, improved PEC water oxidation kinetics and stability. Photo-deposition of Au along the cracks formed on the surface of the plates, which are the edges of {110} facets, was found to further enhance electron collection efficiency. Combination of these two strategies allowed the facet engineered WO3 electrode to produce significantly higher efficiencies in charge separation and transfer than the electrode prepared without facet orientation. This work has provided a facile route for fabricating structurally designed WO3 photoelectrode, which is also applicable to other regularly-shaped semiconductor photocatalysts with anisotropic charge migration.

Abstract Hydrogen generation via photoelectrochemical (PEC) technology is one of the most ideal strategies for providing sustainable fuel, in particular, from abundant natural resource (such as seawater). Herein, we demonstrate facet-controlled WO3 array decorated with reasonable distribution of dual-cocatalysts, which shows highly efficient and stable PEC H2 generation from natural seawater. The experimental and theoretical results illustrate that photo-generated electrons and holes accumulate directionally on different crystal facets of WO3 to achieve effective spatial separation, owing to the divergent energy levels of each crystal facet. Moreover, the charge utilization is further enhanced by selective modification of Ag nanoparticles and ZnFe-layered double hydroxide on different crystal facets reasonably, getting an average PEC H2 production of 38.18 μmol h−1 from natural seawater with excellent stability. This work opens up a new facet engineering pathway for the fabrication of novel photoelectrodes, which have potential applications in the fields of solar energy conversion and storage.

Photocatalytic reduction of CO2 into solar fuels is regarded as one of the most promising approaches to address the issues of global warming and the energy crisis. The promotion of spatial charge separation and transfer through crystal facet engineering could be conducive to improved photocatalytic activity. In this study, one-dimensional (1D) WO3 nanowires with a {110} dominant facet (WO3-110) and two-dimensional (2D) WO3 nanosheets with a {001} dominant facet (WO3-001) coupled with CuO nanoparticles are fabricated by a facile method and used for CO2 photoreduction. Its composition and structural characterizations suggest that the WO3–CuO hybrid features good contact between the WO3 and CuO nanostructures. Under light irradiation, the WO3 and WO3–CuO nanostructures are able to photoreduce CO2 into CH4. Notably, the prepared WO3–CuO nanohybrids with different exposed facets show improved CO2 reduction capability compared to pure WO3 and CuO. The heterojunction interface between the WO3 photocatalyst and the CuO cocatalyst through p–n contact can facilitate electron–hole pair separation and accordingly results in enhanced photocatalytic performance. With the assistance of the CuO cocatalyst, the {110} facet WO3–CuO hybrid displays superior photoreduction capability compared to the {001} facet WO3–CuO, which is attributed to the difference in the crystal facets in the heterostructure. The {110} facet WO3 nanowires have a more negative conduction band edge, contributing to the higher reduction capacity of this sample. On the other hand, it is shown that faster charge carrier transfer efficiency would enable more photoinduced electrons to participate in CO2 photoreduction, especially with the involvement of the nanoparticulate CuO cocatalyst. This work provides guidance for designing a hetero-photocatalyst–cocatalyst system through crystal facet engineering.

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Abstract The manipulation of the surface property of WO3 photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics. Here, we report a WO3(002)/m-WO3 homojunction film that is composed of an upper WO3 layer with predominant (002) facet (WO3(002)) and a lower WO3 layer with multi-crystal facets (m-WO3) as a photoanode for solar water oxidation. Due to the synergistic effect of WO3(002) layer and m-WO3 layer, better water oxidation activity and stability are achieved on the WO3(002)/m-WO3 homojunction film relative to the m-WO3 and WO3(002) film. Specifically, the improved water oxidation performance on the WO3(002)/m-WO3 homojunction film is attributed to the followings. In thermodynamics, the band position differences between WO3(002) layer and m-WO3 layer lead to the formation of WO3(002)/m-WO3 homojunction, which has positive function of improving their charge separation and transfer. In kinetics, the upper WO3(002) layer of the WO3(002)/m-WO3 film has superior activity in the adsorption and activation of water molecules, water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway, and the corrosion of photoanode from the H2O2 intermediate is restrained. The present work provides a new strategy to modify the WO3 photoanodes for thermodynamically and kinetically efficient water oxidation.

Abstract Systematical design and controllable assembly of nanostructured photocatalysts have received much attention in the field of CO2 reduction. The Cu2O decroted hexagonal WO3 nanosheets with and without dominant (0 0 1) facets (Cu2O/WO3-001 and Cu2O/WO3) were synthesized vertically on the surface of fluorine-doped stannic oxide (FTO) substrate and their photocatalytic performance for CO2 reduction were evaluated in the presence of H2O vapour under visible light irradiation (λ > 400 nm). The Cu2O/WO3-001 catalyst exhibited higher photocatalytic activity than those of Cu2O, WO3-001 and Cu2O/WO3. The maximal product yields of CO, O2 and H2 for Cu2O/WO3-001 after 24 h illumination reached 11.7, 5.7 and 0.7 μmol, respectively, and good cycling ability was discovered after 4 cycles. The (0 0 1) facet of hexagonal phase WO3 nanosheet was in favor of the H2O oxidation in the CO2 reduction process. Additionally, the Z-scheme charge transfer mode of Cu2O/WO3 heterojunction could promote photoinduced charge separation and enhance redox ability of the separated electrons and holes, leading to excellent photocatalytic CO2 reduction performance. The study may provide some insights into the coherent design of specific nanosheet photocatalysts with Z-scheme charge transfer for CO2 reduction.

Abstract In this study, Pt@Cu2O/WO3 composite photocatalyst was constructed via coupling Cu2O onto the edged (200) and (020) facets of square-like WO3 nanoplates and followed by photodeposition of Pt onto Cu2O. The remarkably enhanced photocatalytic water oxidation activity over such assembled Pt@Cu2O/WO3 composite photocatalyst was observed. The superior photocatalytic performance can be attributed to intrinsic nature of charge separation between different facets of square-like WO3, highly efficient WO3-to-Cu2O electron transfer occurring at the intimate contact interface between WO3 and Cu2O, and Pt as reduction cocatalyst. This work will provide new deep insights into the design of crystal-based Z-scheme heterostructure photocatalysts by facet-preferentially coupling one semiconductor with another.

Self-assembled nanocomposites have gained much attention over the past decade due to their intriguing properties and functionalities. In this work, we developed a self-assembled nanocomposite photoanode composed of an epitaxial BiVO4 matrix embedded with WO3 mesocrystals for photoelectrochemical (PEC) applications in the visible-light regime. The orientation of the crystal facet and interface provides a superior template to understand the intimate contact between the two constituent phases. We demonstrate that the interfacial coupling of the mesocrystal and matrix improves the separation of photoexcited carriers and the properties of charge transfer, resulting in a greatly enhanced PEC performance compared with their parent compounds. The current study demonstrates that the utilization of the interface-to-volume ratio to optimize charge interactions in the nanocomposite is essential for the advanced design of novel mesocrystal-embedded nanocomposite photoelectrodes. Optimizing how two photocatalysts contact each other inside an amalgamated crystal may enhance solar energy conversion strategies. Bismuth vanadium oxide (BiVO4) is a bright yellow pigment that readily turns photons into electronic charges, which can be used to split water into hydrogen and oxygen gas. The team of Ying-Hao Chu from Taiwan's National Chiao Tung University has now found that embedding tungsten oxide (WO3) nanostructures into BiVO4 crystals makes it easier for photogenerated carriers to reach their target. Using pulsed laser deposition, the researchers grew bamboo-shaped nanotubes inside a BiVO4 matrix to produce numerous heterointerfaces. Band structure analysis and transport measurements showed that the improved charge separation at these interfaces provided more carriers for catalytic water splitting. The material's tunable structure makes it a promising tool for understanding surface-to-volume effects in other nanocomposites. We developed a self-assembled nanocomposite photoanode composed of epitaxial BiVO4 (BVO) matrix embedded with WO3 (WO) mesocrystal for photoelectrochemical (PEC) water splitting in the visible-light regime. The well-defined WO3-BiVO4 interface and controllable thickness provide a template for the fundamental understanding of photoactivity in the nanocomposite. The interfacial coupling of the mesocrystal and matrix improves the separation of photoexcited carriers and the properties of charge transfer, resulting in a significantly enhanced PEC performance. The utilization of the interface-to-volume ratio to optimize the charge interaction of the nanocomposite is essential for the advance design of novel mesocrystal-embedded nanocomposite photoelectrodes.

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Abstract General indirect transformation of methane into formaldehyde is based on methanol as intermediate yet leading to low selectivity. Herein, we report a direct photocatalytic conversion of methane to formaldehyde over gold modified cuboid-shaped tungsten trioxide with exposed (002), (020) and (200) facets containing crystal-O at room temperature (25 °C). Under light irradiation, high spin state crystal-O− ion as a hole can active C H bond in methane and subsequently be consumed to form formaldehyde, then renovated by the addition of oxygen. Isotopic 13CH4 and 18O2 tests reveal that formaldehyde indeed stems from the combination of methane and crystal-O on the exposed (002), (020) and (200) facets. Besides, metallic gold deposited on the surface of cuboid-shaped tungsten trioxide can extract the photoexcited electrons and further enhance the formation of crystal-O− ions. The productivity of formaldehyde over optimized catalyst can reach 7202 μmol g-1 with approximate 100 % selectivity within 24 h reaction time.

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Lanthanum-doped tungsten trioxide (La-WO 3 ) was synthesized via a solid-state reaction involving mechanical mixing of lanthanum hydroxide with WO 3 and tungstic acid, followed by calcination. The materials obtained were systematically analyzed through X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), ultraviolet-visible spectroscopy (UV-VIS) diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). Characterization revealed a well-defined block-like morphology with homogeneous La distribution. The incorporation of La was found to introduce defect states within the band gap and increase surface hydroxylation, which collectively improved visible-light harvesting and promoted the separation of photogenerated electrons and holes. The influence of La doping concentration on photocatalytic performance was examined, and an optimal formulation was identified. Specifically, the sample prepared with 0.5 g of a hydrothermally derived precursor and 0.05 g of La(OH) 3 (corresponding to 1% La doping) exhibited the highest activity in photocatalytic degradation tests. Based on experimental evidence, a plausible reaction mechanism for the enhanced photocatalysis is discussed.

Metal oxide photoanodes with exposure of specific facets generally exhibit distinct photoelectrochemical (PEC) performances; however, the critical role of facet-dependent hole transport in determining the overall efficiency remains underexplored. Herein, a high-performance WO3 photoanode is presented via a seed-mediated epitaxial growth strategy, featuring well-built nanosheet arrays with high percent {202} facets. Comparative studies reveal that a 320% increase of hole mobility along {202} facets relative to {200} ones, serves the trigger of efficient carriers' separation. Owing to this "hole highway" effect, {202}-dominated WO3 photoanode exhibits significantly enhanced PEC efficiency with excellent stability, delivering a remarkable photocurrent density of 3.87 mA cm-2 at 1.23 VRHE under AM 1.5G illumination, which reaches 96.8% of the theoretical maximum for the WO3 photoanode. First-principles calculation combined with characterizations further manifest the lowered activation energy barrier for fast water oxidation kinetics on {202} surface with tetra-coordinated W atomic configuration. Particularly, it promotes the rate-determining step (O* → OOH*) in oxygen evolution reactions (OER), and minimizing the accumulation of O* intermediates. This work proposes a novel design concept for facet-control of semiconductors, and establishes a viable pathway to develop efficiently solar-driven water splitting.

Abstract A highly faceted {001} TiO2 catalyst was hydrothermally synthesized by using Ti(IV)-isopropoxide precursor with aqueous HF addition. WO3 was synthesized by following a reported method. Coupled TiO2-WO3 samples were synthesized by adding the corresponding amount of WO3 to fluorinated TiO2 gel followed by a hydrothermal treatment. Additionally the synthesized systems were characterized by using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS) and N2-adsorption (BET) for specific surface area determination. The photocatalytic activity of the single and coupled oxides was measured by means of three model reactions: the photo-oxidation of phenol (as a colourless substrate) and methyl orange (as a dye) and the photoreduction of Cr(VI) as K2Cr2O7. The coupling of WO3 with a highly faceted {001} TiO2 makes it possible to optimize the photocatalytic properties of the faceted material. In fact, {001} faceted TiO2 by itself presents a substantial improvement with respect to commercial TiO2(P25), as it can implement its photoactivity after the incorporation of WO3 with promising results, which can reduce the limitations of TiO2 in terms of its photoactivity, taking advantage of a higher percentage of solar radiation.

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Using citric acid (CA) and 1,5-naphthalenedisulfonic acid (NDSA) as the structure-directing agent, a hierarchical flower-like Bi2O2CO3 product is successfully prepared via a simple one-step hydrothermal synthesis, which is spirally assembled by the {001} facet-dominated nanosheets. It is testified that the additive CA plays an important inducing role in forming the chemical composition of Bi2O2CO3, the nanosized sheet-type subunits, and the exposure of the {001} facet, while the NDSA greatly improves the dispersity and porous structure of the Bi2O2CO3 microflower. Due to the nano-size effect and distortion of surface Bi-O bonds, the Bi2O2CO3 microflower could be excited by the visible light to exhibit a superior photocatalytic performance in the degradation of tetracycline (TC). Besides, it is found the exposed {001} facet of Bi2O2CO3 would preferentially generate holes during the illumination process, thus enhancing the photooxidative activity of the Bi2O2CO3 microflower. Finally, the structural and optical features of the Bi2O2CO3 microflower have been discussed in detail, and its photocatalytic mechanism has also been proposed in this work.

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Thin layer fabrication and crystal facet engineering favor the prompt charge transfer from bulk to the surface of a material and spatial charge separation among different facets, tremendously benefitting photocatalytic activity. However, the thickness and surface facet composition are considered as two entwined characteristics of layered materials with well‐defined and tunable shapes, which possess great promise to achieve the simultaneous manipulation of charge transfer and spatial separation. Herein, it is demonstrated that one solution for the aforementioned issue by controllably regulating the surface {010}/{100} facet junctions of a layered thickness‐tunable bismuth‐based material, BiOIO3. The attenuation in thickness of BiOIO3 nanoplates shortens the diffusion pathway of charge carriers, and more importantly the tuning of nanolayer thickness renders the ratio variation of the top {010} facet to the lateral {100} facet, which dominates the spatial separation of photogenerated electrons and holes. As a result, the highest CO evolution rate from CO2 reduction over BiOIO3 nanoplates with the optimal thickness and ratio of exposed facets reaches 5.42 µmol g−1 h−1, over 300% that of the bulk counterpart (1.77 µmol g−1 h−1). This work paves a new way for governing charge movement behaviors on the basis of the synergistic engineering of layer structure and exposing facets.

To investigate the photochemical property of specific crystal facets, two well-defined CeVO4 dodecahedrons with exposed {101} and {100} facets are prepared, which have distinguishing appearances and unequal {101}/{100} area ratios (A{101}/A{100}), i.e., compressed dodecahedra (CeVO4 CD, A{101}/A{100} ≈ 1) and elongated dodecahedra (CeVO4 ED, A{101}/A{100} ≈ 0.3). During the visible-light-irradiated process, the {101} and {100} facets are certified to selectively deposit photogenerated holes (h+) and electrons (e-), thus exhibiting the photooxidability and photoreducibility, respectively. Meanwhile, a surface heterojunction could form at the adjacent facet interface and facilitate the spatial separation of carriers. Benefiting from the large exposure extent of the {101} facet and the rational A{101}/A{100} (∼1), the CeVO4 CD shows a superior photocatalytic performance for the degradation of tetracycline to the CeVO4 ED. Finally, simulation calculations reveal that the energy deviations of the valence band (VB) and conduction band (CB) between CeVO4{101} and CeVO4{100} impel the photogenerated h+ and e- to transfer in opposite directions, resulting in the facet-dependent photoactivity of the CeVO4 dodecahedron.

The spatial separation and transport of photogenerated charge carriers is crucial in building an efficient photocatalyst for solar energy conversion into chemical energy. A step-scheme CdS/MnOx-BiVO4 photocatalyst was synthesized by spatial deposition of MnOx and one-dimensional (1D) CdS nanowires on a three-dimensional (3D) decahedron BiVO4 surface. The photocatalytic activity of CdS/MnOx-BiVO4 for the overall water-splitting reaction was investigated without sacrificial reagent under visible light irradiation. The synthesized photocatalysts were thoroughly analyzed using high-end characterization techniques. The 5CdS/MnOx-BiVO4 exhibited the highest H2 and O2 production rates of 1.01 and 0.51 mmol g-1 h-1, respectively, with an apparent quantum yield of 11.3% in the absence of any sacrificial reagent. The excellent photoactivity is due to the presence of oxygen vacancies along with effective charge separation/transfer properties and strong interaction of cocatalysts (MnOx and Pt) with the photocatalysts (BiVO4 and CdS) in the 5CdS/MnOx-BiVO4 heterojunction. The significance of the presence of MnOx and Pt cocatalysts on the selective facets of BiVO4 for efficient overall water splitting reaction is highlighted in this work.

Efficient spatial separation of photogenerated charge carriers remains a formidable challenge in photocatalysis. Here, we employ in situ Kelvin probe force microscopy (KPFM) to reveal unexpected electron accumulation on nonpolar {01 1 ¯ ${\mathrm{\bar{1}}}$ 0} facets in wurtzite ZnO platelets (N-ZnO), which represents a dynamic "electron spillover" process beyond static facet confinement. Crucially, femtosecond transient absorption (fs-TA) spectroscopy directly captures interfacial electron transfer from polar Zn-terminated (0001) facets (Zn-ZnO) to N-ZnO with a lifetime of 60.82 ps. However, electrons spilling over from Zn-ZnO to N-ZnO recombine with the photogenerated holes inherent to N-ZnO, thereby turning it into a recombination center. Guided by this insight, we construct a dual-cocatalyst architecture (AuZnOCo): Au is selectively anchored on N-ZnO and Zn-ZnO to extract electrons, and Co3O4 is deposited on O-terminated (000 1 ¯ ${\mathrm{\bar{1}}}$ ) facets (O-ZnO) to trap holes. The loading of dual cocatalysts promotes charge separation and suppresses this electron spillover‑induced recombination. Quantitative analysis reveals ≈3739 holes localized on O-ZnO, ≈1771 electrons on Zn-ZnO, and ≈812 electrons on N-ZnO in AuZnOCo, while the electron diffusion length (L) increases from 81.41 to 121.77 nm. This work deciphers the spatiotemporal resolution of charge-carrier dynamics, offering a blueprint for rationally engineering anisotropic photocatalysts.

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Effective separation of photoexcited carriers and chemisorption of the N2 molecule are two key issues to efficient nitrogen photofixation. The spatial charge separation of BiVO4 with anisotropic exposed facets, namely the transfer of photoexcited electrons and holes to {010} and {110} facets, respectively, helps to enhance the separation ability of photogenerated carriers. Theoretical calculation results predict that a surface oxygen vacancy is easier to form on the (010) facet than on the (110) facet of BiVO4. Accordingly, in this study, enhanced N2 photofixation performance has been achieved for the first time by tuning the exposure of {010} facets of BiVO4.

Photogenerated charge separation is pivotal for effecting efficient photocatalytic reactions. Understanding this process with spatiotemporal resolution is vital for devising highly efficient photocatalysts. Here, we employed pump–probe transient reflection microscopy to directly observe the temporal and spatial evolution of photogenerated electrons and holes on the surface of facet-engineered bismuth vanadate (BiVO4) crystals. The findings suggest that the anisotropic built-in field of BiVO4 crystals propels the separation of photogenerated electrons and holes toward different facets through a two-step process across varying time scales. Photogenerated electrons and holes undergo ultrafast separation within ∼6 ps, with electrons transforming into localized small polarons toward the {010} facets of truncated BiVO4 octahedral crystals. However, the photogenerated holes prolong their separation up to ∼2000 ps in a drift–diffusion manner before ultimately accumulating on the {120} facets. This work provides a comprehensive visualization of spatiotemporal charge separation at the nano/microscale on semiconductor photocatalysts, which is beneficial for understanding the photocatalysis mechanism.

Integrating solar-driven CO2 reduction with organic oxidation is regarded as an ideal strategy for achieving carbon neutrality. However, enhancement of photocatalytic efficiency is persistently blocked by low photogenerated carrier yields and unavoidable fast electron/hole recombination. Herein, we propose to design a plasmonic-ferroelectric heterojunction (WO3-x/K4Nb6O17), which enhances localized electromagnetic field and ferroelectric polarization field simultaneously through the cooperative coupling of localized surface plasmon resonance effect in WO3-x and ferroelectric polarization in K4Nb6O17, thereby not only promoting energetic hot-carriers generation, but also accelerating bulk charge separation. Ultimately, hot-electrons and photoelectrons are directionally transferred and extracted to K4Nb6O17 surface for CO2 reduction, whereas massive holes are accumulated in WO3-x for benzylicalcohol activation. Under mild-conditions, WO3-x/K4Nb6O17 exhibits superior CO yield (294.76µmol·g-1·h-1), which is 9.87 and 6.27-folds higher than that of K4Nb6O17 and WO3-x, respectively. Meanwhile, compared to the simple dehydrogenation of benzylicalcohol to benzaldehyde in K4Nb6O17 and WO3-x, WO3-x/K4Nb6O17 prefers to trigger benzylicalcohol C-C coupling for directed production of more value-added hydrobenzoin (313.15µmol·g-1·h-1). This work would open a conceptual vista for designing multi-field coupling structures to facilitate charge spatial separation and directional transfer, which would inspire further establishment of efficient novel photocatalysts and solar-to-fuel conversion systems to meet the green and sustainable development goals.

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Anisotropic facet engineering is an intriguing way to regulate the charge-separation behavior on a semiconductor photocatalyst. Here we show the morphology tailoring of cuprous oxide (Cu2O) from cubic to octahedral...

Crystal facet engineering has been recognized as a powerful strategy to finely modulate the charge separation behavior in semiconductor photocatalysis; however, disclosing the intrinsic roles that the morphologies and crystal facets play on photogenerated charge separation of semiconductor nanocrystals remains elusive. Herein, exemplified on the typical visible-light-responsive photocatalyst bismuth vanadate (BiVO4 ), for the first time, the successful fabrication is reported of well-defined BiVO4 square nanocrystals with precisely controllable (040)/(200) facet proportion, which undergo a dissolution-recrystallization-facet growth process accompanied with tetragonal to monoclinic phase transition. Spatial separation of photogenerated electrons and holes has been evidently demonstrated to take place between (040) and (200) facets of BiVO4 nanocrystals, on which the charge separation efficiency is verified to definitely depend on the facet proportion of (040)/(200). Further theoretical simulation reveals that the matching degree of charge collection length and crystal configuration is considered to be the major factor determining charge separation efficiency of BiVO4 nanocrystals. This study presents a strategy to fabricate morphology-tailored semiconductors, which will be favorable to advance the understanding of spatial charge separation in semiconductor photocatalysis.

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Poly(triazine imide)·Li+Cl– (PTI/Li+Cl–) as one of the most reported crystalline carbon nitrides has shown exciting potential for photocatalysis. However, understanding the role of Li+/Cl– in the photoexcited charge transfer in the time and space of PTI is a challenging problem. Here, we have investigated the nonradiative charge recombination of series ion intercalated PTI systems (PTI/Li+X–, where X = F, Cl, Br, and I) by performing the ab initio nonadiabatic molecular dynamics simulations. The results indicate that the intercalated anions in PTI/Li+Cl– and PTI/Li+Br– have the potential to trap holes, separate the electrons and holes, and prolong the nonradiative electron–hole recombination. In particular, ∼70% of holes in PTI/Li+Cl– can transport among interlayers toward the {0001} planes, while most of the electrons are transferred to the {101̅0} planes, exhibiting different transport pathways and directions. Furthermore, PTI/Li+Cl– has an electron–hole recombination time as long as 136 ns, which explains its excellent optoelectronic properties. This work provides a theoretical baseline for the reported facet engineering improvement of crystalline carbon nitride for overall water splitting.

In this work, we demonstrate an effective surface modulation strategy via facet-selective photodeposition coupled with oxygen vacancy-mediated size control of palladium (Pd) cocatalysts on monoclinic BiVO4 for efficient visible-light-driven H2O2 synthesis. By adjusting the pH during synthesis, a series of monoclinic BiVO4 with different degrees of oxygen vacancies is obtained; higher pH induces elevated vacancy levels, whereas only low to moderate pH preserves the decahedral structure with distinguished facets. Upon facet-selective photodeposition of Pd metal onto the (010) surface, increased oxygen vacancy concentrations enhance the electrostatic interactions with PdCl4 2- precursors, leading to the formation of smaller Pd nanoparticles with higher active-site density and accelerated surface reaction kinetics. However, the loss of well-defined facet geometry of the BiVO4 prepared under high pH weakens intrinsic spatial charge separation and compromises facet-selective Pd photodeposition, eventually diminishing photocatalytic activity. Thus, the optimized Pd/BiVO4 photocatalyst achieves an excellent H2O2 production rate of 2.35 mм/h, with an apparent quantum efficiency (AQE) of 19.2% at 420 nm, representing a significant performance advancement among BiVO4-based systems. This study not only sets a new benchmark but also offers valuable insights into the rational integration of defect and facet engineering for designing efficient metal/semiconductor composites for photocatalytic H2O2 production.

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Facet-engineered monoclinic scheelite BiVO4 particles decorated with various cocatalysts were successfully synthesized by selective sunlight photodeposition of metal or metal oxy(hydroxide) nanoparticles onto the facets of truncated bipyramidal BiVO4 monoclinic crystals coexposing {010} and {110} facets. X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning Auger microscopy revealed that metallic silver (Ag) and cobalt (oxy)hydroxide (CoOx(OH)y) particles were selectively deposited onto the {010} and {110} facets, respectively, regardless of the cocatalyst amount. By contrast, the nickel (oxy)hydroxide (NiOx(OH)y) photodeposition depends on the nickel precursor amount with an unprecedented selectivity for 0.1 wt % NiOx(OH)y/BiVO4 with a preferential deposition onto the {010} facets and the edges between the {110} facets. Moreover, these noble metal-free heterostructures led to remarkable photocatalytic properties for rhodamine B photodecomposition and sacrificial water oxidation reactions. For instance, 0.2 wt % CoOx(OH)y/BiVO4 led to one of the highest oxygen evolution rates, i.e., 1538 μmol h-1 g-1, ever described which is ten times higher than that found for bare BiVO4. The selective deposition of cobalt (oxy)hydroxide species onto the more electron-deficient facet of truncated bipyramidal monoclinic BiVO4 particles favors photogenerated charge carrier separation and therefore plays a key role for efficient photochemical oxygen evolution.

Controlling the exposure of anisotropic crystal facets provides a promising strategy to direct the migration of photogenerated charges and improve photocatalytic performance. Nevertheless, the underlying charge dynamics resulting from facet engineering in 2D Cs3Bi2Br9 vacancy‐ordered perovskite remain poorly understood. Herein, we synthesize two distinct morphologies of Cs3Bi2Br9 single crystals (nanosheets and nanostrips) with different ratios of exposed (001) to elucidate this mechanism. Surface photovoltage mapping, selective photodeposition, and DFT calculations jointly confirm the existence of anisotropic charge separation driven by an intrinsic facet junction electric field (∼180 meV). This electric field directs photogenerated holes to accumulate on the (001) facets for toluene activation, while electrons migrate to the (010) facets. Benefiting from this intrinsic facet junction, medium‐sized Cs3Bi2Br9 nanosheets with optimal (001) facet exposure achieve a high benzaldehyde production rate of 692 µmol·g−1·h−1 with 87% selectivity, significantly outperforming other morphologies. This work provides the first demonstration of facet engineering in Cs3Bi2Br9, establishing a crystal‐orientation design principle for efficient and selective photocatalytic organic transformations.

The construction of photocatalytic systems that have strong redox capability, effective charge separation, and large reactive surfaces is of great scientific and practical interest. Herein, an edge‐connected 2D/2D Z‐scheme system that combines the facet junction and the interfacial heterojunction to achieve effective long‐range charge separation and large reactive surface exposure is designed and fabricated. The heterostructure is realized by the selective growth of 2D‐layered MoS2 nanoflakes on the edge‐sites of thin TiO2 nanosheets via an Au‐promoted photodeposition method. Attributed to the synergetic coupling of the facet junction and the interfacial heterojunction that assures the effective charge separation, and the tremendous but physically separated reactive sites offered by layered MoS2 and highly‐exposed (001) facets of TiO2, respectively, the artificial Z‐scheme exhibits excellent photocatalytic performance in photodegradation tests. Moreover, the junctional plasmonic Au nanoclusters not only act as electron traps to promote the edge‐selective synthesis but also generate “hot electrons” to further boost photocatalytic performance. The Z‐scheme charge‐flow direction in the heterostructure and the roles of electrons and holes are comprehensively studied using in situ irradiated X‐ray photoelectron spectroscopy and photodegradation tests. This work offers a new insight into designing high‐performance Z‐scheme photocatalytic systems.

Abstract Previously a silver–manganese dual cocatalyst loaded on a potassium hexatitanate crystal photocatalyst was reported to be efficient for photocatalytic reduction of CO2 to CO by using water as an electron source. In the present study, variously prepared silver–manganese dual cocatalysts were investigated to figure out their states and functions of Ag and MnOx species. Although an impregnation method provided various states of these species such as AgOx particles, core–shell structures, and oxidized aggregates, they gave negative effects on the photocatalytic activity. On the other hand, a simultaneous photodeposition method fabricated Ag and MnOx species on the long and short facets of the rod-like crystal, respectively, and these species functioned as each efficient promoter for the reductive and oxidative reactions in the photocatalysis. It was firstly evidenced that the clear separation of the reaction sites with the proper promoters is essential for the high efficiency in the photocatalytic CO2 reduction.

Rational assembly of cocatalysts on crystal‐based photocatalysts with anisotropic facets, namely the reduction cocatalyst on the reduction facets and oxidation cocatalyst on the oxidation facets, can enhance the photocatalytic activity remarkably. However, this strategy of selective loading of cocatalysts on crystal‐facet engineered photoelectrodes is rarely discussed in photoelectrocatalysis (PEC). Herein, we fabricated BiVO4 microcrystal photoanodes with simultaneous exposure of oxidation {110} and reduction {010} facets to study the effect of facet‐selective assembly of cocatalysts on the activity of PEC water oxidation. By elaborative photodeposition, identical cocatalysts of MnOx were selectively loaded on the reduction, the oxidation and all the facets of BiVO4 photoanodes (respectively designated as R‐BVO, O‐BVO and O/R‐BVO). We found that MnOx facilitates the charge separation in BiVO4 more significantly on the oxidation facets than on the reduction ones, contributing to the net increase in photocurrent of O‐BVO being as 5.2 and 2.2 times that of R‐BVO and O/R‐BVO, respectively. Surface photovoltage analysis reveals that the interaction between the inherent built‐in electric field in BiVO4 crystals and the additive electric filed induced by the MnOx was account for the difference. Our work emphasizes the effect of facet‐selective assembly of cocatalyst in PEC systems, which may guide the rational design of highly efficient photoelectrodes for solar energy conversion.

Uncovering the contribution of anisotropic crystal facets in single‐crystalline photocatalysts is still a challenge in fundamental study. Here, the mechanism underlying facet junction‐dependent photocharge separation in polyhedral Cu2O is demonstrated, which is beneficial for understanding why 50‐faceted Cu2O exhibiting quaternary {100}/{110}/{111}/{522} facet junction possesses an enhanced photodegradation activity toward tetracycline than that of the 26‐faceted Cu2O exhibiting ternary {100}/{110}/{111} and 18‐faceted Cu2O exhibiting binary {100}/{110} facet junction. Density functional theory (DFT) calculations and selective photodeposition results confirm that hierarchical facet junctions are formed in a 50‐faceted Cu2O, which could be regarded as one parallel connection between binary {110}/{111} and ternary {110}/{522}/{100} series facet junction for conduction band minimum, and another parallel connection between binary {100}/{522} and ternary {111}/{110}/{522} series facet junction for valence band maximum, leading to an unprecedented dual series‐parallel transfer pathway for more efficiently improved photocharge separation. Hopefully, this study would be a beneficial guideline for scientific researchers currently concentrating on the facet junction engineering of polyhedral photocatalysts.

The development of photocatalysts with wide spectral absorption and high charge separation efficiency has always been a pursued objective for photocatalytic solar energy conversion. Herein, we reported a wide-range visible-light-active Bi4TaO8Cl (BTOC) single crystal nanoplate with dominating {110} and {001} facets for enhancing the intrinsic charge separation efficiency. Insitu selective photodeposition of metals and metal oxides provides evidences of photogenerated electrons and holes spatially separated on {110} and {001} coexposed facets of BTOC, respectively. The intrinsic charge separation efficiency was demonstrated to be closely dependent on the crystal facets, which can be modulated by tuning the coexposed crystal facet ratio. Further surface modification of BTOC with suitable dual cocatalyst Ag and RuOx enables remarkable improvement of charge separation efficiency and photocatalytic water oxidation performance. Investigation by comparison between well-defined BTOC nanoplate and BTOC nanoparticles confirmed the significance of coexposed crystal facets for efficient spatial charge separation and the blocking of reverse reaction from Fe2+ to Fe3+ ions during water oxidation reaction, indicating that rational modulation of exposed crystal facets is significant for controlling the intrinsic charge separation efficiency on Bi4TaO8Cl photocatalyst for efficient photocatalytic water splitting.

Facet-engineered anatase TiO2 with NiO nanoparticles heterocontacts were successfully prepared by selective photodeposition of NiO nanoparticles onto the {101} facet of the top-truncated bipyramidal TiO2 anatase nanocrystals coexposed with {001} and {101} facets. The morphology and electronic properties of the resulting 0.1–10 wt % NiO-decorated TiO2 were investigated by X-ray diffraction, high-resolution electron microscopy, N2 sorption analysis, and UV–vis spectroscopy. Furthermore, a careful determination of the energy band alignment diagram was conducted by a model experiment using XPS and UPS to verify charge separation at the interface of the NiO−TiO2 heterostructure. The model experiment was performed by stepwise deposition of NiO onto oriented TiO2 substrates and in-situ photoelectron spectroscopy measurements without breaking vacuum. Core levels showed shifts of 0.58 eV toward lower binding energies, meaning an upward band bending in TiO2 at the NiO–TiO2 interface. Furthermore, 0.1 wt % NiO–TiO2 ...

Novel nano-zero-valent iron (Fe0)/MnOx/BiVO4 ternary magnetic assemblies are fabricated through hydrothermal and photo-deposition strategy. The assemblies are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. Fe0 as a reduction cocatalyst are deposited on surface of monoclinic BiVO4 decahedron supersturcture. Meanwhile, MnOx as an oxidation cocatalyst is selectively anchored on oxidative {110} facet of BiVO4 by photodeposition. The photogenerated electrons and holes can be transmitted to Fe0 and MnOx, respectively, which favors the spatial charge separation. The adjunction of Fe0 significantly enhances light absorption, and forms a photocatalysis-Fenton coupling system simultaneously. The assemblies with narrow band gap of 2.10 eV display an exceptional photocatalytic activity, and the visible-light-driven photocatalytic degradation ratio of 2,4-dichlorophenol and Bisphenol A are up to 95.4 and 91.4%, respectively, which are several times higher than that of pristine BiVO4. This is ascribed to the selective decoration of Fe0 and MnOx favoring the spatial charge separation, and the photocatalysis-Fenton coupling system enhancing degradation. Moreover, the superior magnetic property due to Fe0 decoration realizes magnetic separation of catalysts, which is favorable in practical applications.

No abstract available

Facet-selective gold or platinum-nanoparticle deposition on decahedral-shaped anatase titania particles (DAPs) exposing {001} and {101} facets via photodeposition (PD) from metal-complex sources was reexamined using DAPs prepared with gas-phase reaction of titanium (IV) chloride and oxygen by quantitatively evaluating the area deposition density on {001} and {101} and comparing with the results of deposition from colloidal metal particles in the dark (CDD) or under photoirradiation (CDL). The observed facet selectivity, more or less {101} preferable, depended mainly on pH of the reaction suspensions and was almost non-selective at low pH regardless of the deposition method, PD or CDL, and the metal-source materials. Based on the results, the present authors propose that facet selectivity is attributable to surface charges (zeta potential) depending on the kind of facets, {001} and {101}, and pH of the reaction mixture and that this concept can explain the observed facet selectivity and possibly the reported facet selectivity without taking into account facet-selective reaction of photoexcited electrons and positive holes on {101} and {001} facets, respectively.

Bismuth vanadate (BiVO4) has been widely investigated as a photocatalyst or photoanode for solar water splitting, but its activity is hindered by inefficient cocatalysts and limited understanding of the underlying mechanism. Here we demonstrate significantly enhanced water oxidation on the particulate BiVO4 photocatalyst via in situ facet-selective photodeposition of dual-cocatalysts that exist separately as metallic Ir nanoparticles and nanocomposite of FeOOH and CoOOH (denoted as FeCoOx), as revealed by advanced techniques. The mechanism of water oxidation promoted by the dual-cocatalysts is experimentally and theoretically unraveled, and mainly ascribed to the synergistic effect of the spatially separated dual-cocatalysts (Ir, FeCoOx) on both interface charge separation and surface catalysis. Combined with the H2-evolving photocatalysts, we finally construct a Z-scheme overall water splitting system using [Fe(CN)6]3−/4− as the redox mediator, whose apparent quantum efficiency at 420 nm and solar-to-hydrogen conversion efficiency are optimized to be 12.3% and 0.6%, respectively. Artificial photosynthesis offers an integrated means to convert light to fuel, but efficiencies are often low. Here, authors report a Z-scheme system utilizing Ir and FeCoOx co-catalysts to enhance charge separation on BiVO4 facets that achieves high quantum efficiencies for overall water splitting.

No abstract available

Abstract A key component of the photocatalytic fuel cell (PFC) is a photoanode, typically based on highly stable semiconductor (e.g., TiO2) that is capable of effective photoelectrocatalytic oxidation of fuels. Notably, the photo(electro)catalytic activity of TiO2 materials can depend heavily on the microstructural morphology, so that tailored crystals with different shapes and exposed facets can show remarkably different, shape-dependent photoactivities. Herein, we study the PFC performance of photoanodes based on anatase crystals of various shapes – tetragonal truncated bipyramids, sheets and belts, which are characterized by different predominantly exposed facets: {1 0 1}, {0 0 1}, and {1 0 0}, respectively. We demonstrate that photoanodes based on belt-shaped crystals dominated by {1 0 0} facets, not observed in natural anatase crystals, exhibit superior performance. Analysis of open-circuit potential and impedance data suggests that this activity is related to faster transfer of photogenerated holes to methanol oxidation sites, avoiding thus the undesired surface trapping and Fermi level pinning effects that are the most likely reason of a poorer performance of materials dominated by {1 0 1} and {0 0 1} facets. This study highlights the importance of advanced crystal engineering and control over the surface catalytic properties of TiO2 materials for PFCs and other light-driven devices in which efficient alcohol photooxidation is crucial.

BiVO4 particles are attractive visible light-absorbing semiconductors to drive the water oxidation half reaction in a photoelectrochemical cell or for the overall water splitting reaction in a photocatalytic reactor. Ensemble-level and single particle-level measurements previously showed that photogenerated electrons and holes tend to accumulate and react at top {010} and lateral {110} facets, respectively. However, multiple possible surface terminations exist for these low-index facets, and it is unclear to what extent different surface facet terminations influence the overall current or reaction rate of a single BiVO4 particle. Here we use correlative scanning photoelectrochemical microscopy (SPCM), facet-dependent electrical measurements, electron beam induced current (EBIC) mapping, and mid-IR scattering scanning near-field optical microscopy (s-SNOM) measurements to quantify the water and sulfite oxidation photocurrent among different lateral and top facets of 62 BiVO4 particles. SPCM measurements confirmed that illuminating lateral {110} facets generates higher photocurrents for water and sulfite oxidation than top {010} facets. However, they also unexpectedly revealed that different lateral facets within the same particle produce varying photocurrents, despite electron microscopy images showing no clear structural differences between them. Facet-dependent electrical and EBIC measurements further indicated that no significant space charge regions form at inter-facet junctions or metal-BiVO4 contacts under vacuum. This result is significant because it is highly unlikely that photogenerated holes generated in the particle interior beneath the top {010} facet transport to the lateral {110} facets and contribute to the water/sulfite oxidation reaction. Additionally, nano-FTIR spectroscopy revealed that materials chemistry heterogeneity exists not only between particles but also within individual facets of a single particle. These findings suggest the presence of distinct surface termination chemistries across different facets, consistent with theoretical predictions, and emphasize the need to control atomic-level surface termination during sample growth to enhance photocatalytic performance.

No abstract available

Photocatalysis is a promising technology for purification of indoor air by oxidation of volatile organic compounds. This study provides a comprehensive analysis of the adsorption and photo‐oxidation of surface‐adsorbed acetone on three SrTiO3 morphologies: cubes (for which exclusively {100} facets are exposed), {110}‐truncated cubes, and {100}‐truncated rhombic dodecahedrons, respectively, all prepared by hydrothermal synthesis. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy shows that cubic crystals contain a high quantity of surface –OH groups, enabling significant quantities of adsorbed acetone in the form of η1‐enolate when exposed to gas phase acetone. Contrary, {110} facets exhibit fewer surface –OH groups, resulting in relatively small quantities of adsorbed η1‐acetone, without observable quantities of enolate. Interestingly, acetate and formate signatures appear in the spectra of cubic, surface η1‐enolate containing, SrTiO3 upon illumination, while besides acetate and formate, the formation of (surface) formaldehyde was observed on truncated cubes, and dodecahedrons, by conversion of adsorbed η1‐acetone. Time‐Resolved Photoluminescence studies demonstrate that the lifetimes of photogenerated charge carriers vary with crystal morphology. The shortest carrier lifetime (τ1 = 33 ± 0.1 ps) was observed in {110}‐truncated cube SrTiO3, likely due to a relatively strong built‐in electric field promoting electron transport to {100} facets and hole transport to {110} facets. The second lifetime (τ2 = 259 ± 1 ps) was also the shortest for this morphology, possibly due to a higher amount of surface trap states. Our results demonstrate that SrTiO3 crystal morphology can be tuned to optimize performance in photocatalytic oxidation.

No abstract available

Hydrogen peroxide is an important high-energy product widely used in various fields. Highly efficient semiconductor photocatalysts, especially those that can produce H2O2 both from water oxidation and O2 reduction, are eagerly desired. In this work, BiOCl nanosheets with preferentially exposed (001) and (010) facets were synthesized via a simple hydrothermal method. The facet-dependent photocatalytic H2O2 generation activities of these BiOCl nanosheets were assessed. The hydrogen peroxide evolution rate of BiOCl(001) is about 2-fold higher than that of BiOCl(010), which is assigned to the higher separation efficiency of photogenerated charge carriers. Interestingly, both the EPR study and active species trapping experiments demonstrate that the generation of H2O2 on the BiOCl(001) photocatalyst mostly originates from sequential two step single-electron O2 reduction, while there are two pathways for photocatalytic H2O2 production on BiOCl(010), from both oxygen reduction and water oxidation. This work offers a new strategy to pursue highly efficient semiconductor photocatalysts with two pathways for H2O2 production from both water oxidation and O2 reduction.

Abstract A series of flower-like BiOBr with exposed the (0 0 1) and (0 1 0) facets were successfully synthesized by pH adjustment method for gas-phase Hg0 photocatalytic oxidation. The physicochemical properties of the BiOBr were characterized by XRD, SEM, TEM, SAED, XPS, UV–vis DRS, PL, EIS and ESR analysis. It was found that BiOBr with the main exposed (0 1 0) facets exhibited better photocatalytic activity, and its best efficiency reached 65%. This can be attributed to the optimal ratio of dominant (0 1 0) facets exposed by pH adjustment to effectively promote the spatial separation of photo-generated charges. Finally, a possible photocatalytic reaction mechanism was proposed.

No abstract available

Abstract Bismuth chloride oxide (BiOCl) is a typical V-VI-VII ternary oxide material, which is one of the widely studied metal oxides due to its unique surface, electronic and photocatalytic properties. However, the broad bandgap and the large number of photogenerated electron-hole pair complexes of BiOCl limit its photocatalytic efficiency. Since the photocatalytic performance of BiOCl is highly dependent on its exposed crystallographic facets, research attention has increasingly focused on the different structures and properties possessed by different crystallographic facets of BiOCl. This article reviews the basic principles of using different crystalline surfaces of BiOCl materials to enhance photocatalytic activity, summarizes the applications of BiOCl single-crystal catalysts and composite catalysts in the environmental field, and provides an outlook on the challenges and new research directions for future development in this emerging frontier area. It is hoped that the crystalline surface-related photocatalysis of BiOCl can be used to provide new guidance for the rational design of novel catalysts for various energy and environment-related applications.

No abstract available

The charge migration mechanism across the surface heterojunction constructed on an anatase TiO2 nanocrystal is still under debate. To solve this longstanding question, we present a systematic study of the band edges (vs. standard hydrogen electrode, SHE) of aqueous TiO2 interfaces with anatase (101), (100) and (001) surfaces, using a combination of density functional theory-based molecular dynamics (DFTMD) and efficient computational SHE (cSHE) methods. Our calculations show that the conduction band minimum (CBM) of the (101) surface is lower than that of (001) and (100) surfaces, which is thermodynamically favorable for electrons migrating to the (101) surface through the surface heterojunction, while the hole preferentially accumulates on the (100) surface due to its highest valence band minimum (VBM). In addition, we qualitatively explore the facet-dependent photocatalytic activity of anatase TiO2. Due to the possession of both the beneficial atomic structure (with 100% undercoordinated Ti5c atoms at the surface) and electronic structure (more strongly oxidizing holes in the VBM and efficient electron-hole spatial separation separation), the (001) surface exhibits the most efficient photocatalytic performance for water oxidation. Furthermore, it is confirmed that the use of simplified theoretical models neglecting the detailed atomic structures of water at the aqueous interface is inadequate to predict the band alignment of semiconductors relative to water redox potentials, so that it may result in substantial errors in evaluating the photocatalytic performance of materials to be used for water splitting.

Developing bifunctional water-splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific-facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well-built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi4NbO8Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in-plane polarization from octahedral off-centering of Nb5+ and out-of-plane polarization from lone pair electron effect of anisotropic Bi3+, both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built-in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet-selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity-optimized Bi4NbO8Cl shows an excellent H2 and O2 evolution rate of 54.21 and 36.08 μmol·h-1 in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet-selective charge transfer process of photocatalysts.

The synthesis of photocatalysts with both broad light absorption and efficient charge separation is significant for a high solar energy conversion, which still remains to be a challenge. Herein, a narrow-bandgap Y2Ti2O5S2 (YTOS) oxysulfide nanosheet coexposed with defined {101} and {001} facets synthesized by a flux-assisted solid-state reaction was revealed to display the character of an anisotropic charge migration. The selective photodeposition of cocatalysts demonstrated that the {101} and {001} surfaces of YTOS nanosheets were the reduction and oxidation regions during photocatalysis, respectively. Density functional theory (DFT) calculations indicated a band energy level difference between the {101} and {001} facets of YTOS, which contributes to the anisotropic charge migration between them. The exposed Ti atoms on the {101} surface and S atoms on the {001} surface were identified, respectively, as reducing and oxidizing centers of YTOS nanosheets. This anisotropic charge migration generated a built-in electric field between these two facets, quantified by spatially resolved surface photovoltage microscopy, the intensity of which was found to be highly correlated with photocatalytic H2 production activity of YTOS, especially exhibiting a high apparent quantum yield of 18.2% (420 nm) after on-site modification of a Pt@Au cocatalyst assisted by Na2S-Na2SO3 hole scavengers. In conjunction with an oxygen-production photocatalyst and a [Co(bpy)3]2+/3+ redox shuttle, the YTOS nanosheets achieved a solar-to-hydrogen conversion efficiency of 0.15% via a Z-scheme overall water splitting. Our work is the first to confirm anisotropic charge migration in a perovskite oxysulfide photocatalyst, which is crucial for enhancing charge separation and surface catalytic efficiency in this material.

A crucial issue in artificial photosynthesis is how to modulate the behaviors of photogenerated charges of semiconductor photocatalysts. Here, using lead chromate (PbCrO4) as an example, we conducted the morphology tailoring from parallelepiped (p-PbCrO4) to truncated decahedron (t-PbCrO4) and elongated rhombic (r-PbCrO4), resulting in exposed anisotropic facets. The spatial separation of photogenerated charges closely correlates to the anisotropic facets of crystals, which can only be realized for t-PbCrO4 and r-PbCrO4 . The charge-separation efficiencies exhibit a quasilinear relation with the surface photovoltage (SPV) difference between anisotropic facets. The r-PbCrO4 gives an apparent quantum efficiency of 6.5% at 500 nm for photocatalytic water oxidation using Fe3+ ions as electron acceptors. Moreover, the oxidation reverse reaction from Fe2+ to Fe3+ ions was completely blocked with ~100% of Fe3+ conversion achieved on the anisotropic PbCrO4 crystals.

Multi-wall carbon nanotubes (MWCNTs) with high electrical conductivity are commonly accounted as the ideal additives to enhance the charge surface migration efficiency in photocatalysis. Theoretically, the MWCNTs-modified binary photocatalysts have potential for the change of nanocrystal structure. Herein, we reports an adjustable {312}/{004}facet heterojunction MWCNTs/Bi5O7I nanocomposite. Interestingly, the synergistic effect of {312}/{004}facet heterojunction and MWCNTs can effectively accelerate the spatial charge carriers transport. A novel {312}/{004}facet "S-scheme" pathway was proven to be the dominated pathway for the enhancement of spatial charge carriers. As a result, the MWCNTs-{312}/{004}Bi5O7I composites exhibited superior photocatalytic oxidation efficiency for a representative antibiotics ofloxacin photodegradation. Density functional theory (DFT) calculation and LC-MS/MS analysis confirmed that the possible dealkylation and oxidation pathways could be found in OFL degradation. This work provides novel insights for the relationship between charge carrier transport and facet structure-property.

Abstract The work presents a combinative merit of non-metal ion doping and active facet effect of Bi2O2CO3 photocatalyst. Br-doped Bi2O2CO3 nanosheets with exposed {0 0 1} facets were facilely prepared via a one-step hydrothermal reaction with the assistance of cetyltrimethylammonium bromide (CTAB) at a mild temperature of 60 °C for 4 h. The presence of CTAB not only influences the growth of Bi2O2CO3 crystalline but also leads to a Br-doping. Based on the crystal structure and DFT calculation, bromine from CTAB as dopant interstitially incorporates into Bi2O2CO3 lattice, which alters the band gap positions of Bi2O2CO3 and generates delocalized impurity states at the Fermi level. The improved electronic structure endows Br-doped Bi2O2CO3 with a broadened light-harvesting and accelarated charge migration. In addition, the thin nanosheet means more exposure of {0 0 1} active facets and larger internal electric field, which would also benefit for the charge separation. The sample with a trace Br content of 1.17 wt% shows the best degradation efficiency for RhB with a rate constant k enhanced by 3.6 folds compared with that of pure Bi2O2CO3 under simulated solar irradiation. Combining the effective catalytic sites and the detected active species, a possible migration mechanism of photogenerated e−/h+ pairs on the surface of Br-doped Bi2O2CO3 nanosheet is proposed. The work provides some new insights into the rational design and synthesis of non-metal doped semiconductor photocatalyst with facet dependency.

Most photocatalysis research focuses on understanding the photogenerated charge transfer processes within the solid catalysts themselves. However, these studies often overlook the impact of the reaction environment on photogenerated charge separation and reactions. To address this gap, our study employed a sequential imaging methodology that integrates surface photovoltage microscopy (SPVM), in situ atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM) to track the transfer of photogenerated charges from the space charge region to the reactants at the nanoscale on individual BiVO4 particles. It identifies the key role that surface charges at the photocatalyst-electrolyte interface play in photogenerated charge transfer. Specifically, we demonstrated that the surface charge generates an additional driving force, which adjusts the interface electric field and reverses the photovoltage of {010} facet from 90 to -25 mV in a neutral electrolyte. This competitive or even larger driving force compels the photogenerated electrons, which are confined within the bulk, to migrate to the surface, ultimately leading to the redistribution of photogenerated charges. Furthermore, our findings uncovered that the difference between the solution pH and the isoelectric point of the facet serves as the origin of the interfacial electric field. Overall, our sequential imaging research fills an important gap in understanding the driving and influencing factors of charge transfer across the solid-liquid interface for photocatalytic reactions in solution. It provides significant insights into clarifying the bottleneck issue of charge separation in photocatalytic reactions.

Heterostructured photocatalysts can effectively facilitate the degradation of detrimental organic contaminants in wastewater, particularly bisphenol A (BPA) and methylene blue (MB); however, their catalytic performance often remains limited. Herein, we construct an S‐scheme ZnO/Zn3In2S6 (ZnO/ZIS) heterostructure with extensive interfacial coupling between the {001} facets of both phases. The distinct work functions and high surface atom densities of {001} ZnO and {001} ZIS generate elongated Zn─O bridges at the interface, facilitating directional charge migration along the S‐scheme pathway. Concurrently, abundant accessible Zn active sites and optimized adsorption toward pollutant molecules enhance photocatalytic efficiency. These structural and electronic features are confirmed via comprehensive in situ and ex situ characterizations, including scanning transmission electron microscopy, electron paramagnetic resonance, X‐ray absorption, and X‐ray photoelectron spectroscopy, supported by theoretical simulations. As a result, the heterostructure achieves remarkable mineralization rates of ∼86% for BPA and ∼96% for MB within a short treatment time, achieving rapid and thorough degradation without forming significant carbon‐based intermediates. This work demonstrates a feasible crystal‐plane engineering strategy for designing advanced photocatalysts for efficient wastewater purification.

Understanding the key factors that influence the interfacial transfer of charge carriers is crucial for improving the photocatalytic degradation of volatile organic compounds (VOCs). Herein, TiO2 samples with dominantly exposed (001) and (101) facets were synthesized. The density and types of hydroxyls on these facets were modified through alkali treatment. The surface photovoltage spectrum was measured in various atmospheres to analyze the interfacial charge transfer processes. The alkali treatment created additional terminal hydroxyls (OHt) on the (001) facets and bridging hydroxyls (OHb) on the (101) facets. OHt enhanced the migration of holes toward the (001) facets, and OHb facilitated the migration of electrons toward the (101) facets, thereby promoting charge separation. The accumulation of holes on the (001) facets was limited in the absence of OHt. H2O significantly enhanced charge separation in the presence of O2 and toluene, thereby improving both the adsorption and degradation of toluene. This work provides new insights into the interfacial processes involved in photocatalytic degradation of VOCs.

The manipulation of exposed anisotropic facets and surface microstructures facilitates the directional migration of photoinduced charge carriers, offering a promising strategy for enhancing the photocatalytic activity. However, the charge dynamics behavior associated with facet engineering remains unclear and elusive. Herein, the critical role of the {001}/{101} facet ratio on carrier lifetime was determined by precisely monitoring the charge redistribution in the micronano regions of individual TiO2 microcrystals via single-particle fluorescence spectroscopy in situ. The results demonstrate that TiO2 with a medium ratio of oxidative and reductive sites exhibits the longest PL lifetimes on both {001} and {101} facets due to the synergistic effect of the facets promoting efficient charge carrier migration. Correspondingly, the optimal utilization of electron-hole pairs was also demonstrated in the further toluene oxidation process. Furthermore, in situ monitoring of the fluorine (F) removal process via annealing of a single TiO2 particle confirms that the formation of oxygen vacancy (OV) after Ti-F bond breakage, rather than the removal of F, is the key factor in further promoting charge separation. In addition, real-time observation of toluene oxidation on a single TiO2 microcrystal was conducted at the single-particle level, indicating that the effective charge transfer between TiO2 and toluene is beneficial for the preferential formation of benzaldehyde on the TiO2-{101} facet. This work provides feasible monitoring methods and strong evidence for facet engineering to promote charge separation, which is beneficial for guiding the rational design of photocatalysts.

Urea is an essential chemical widely used in agriculture and consumer products, yet its conventional Bosch–Meiser synthesis is energy-intensive and carbon-intensive. Photocatalytic urea synthesis from N2, CO2, and H2O offers a sustainable alternative, but efficient C–N coupling is fundamentally limited by the trade-off between intermediate stability and surface migration needed for efficient C–N coupling processes. Strong adsorption of intermediates limits diffusion, whereas weak adsorption causes premature desorption, restricting the C–N coupling efficiency. Facet and spin-state engineering provide a promising route to balance intermediate stabilization, mobility, and interfacial charge transfer. Herein, we prepared oxygen-deficient WOx (x = 2.33–2.90) photocatalysts, including nanorods (WO2.33(100)) and nanosheets (WO2.90(001)), by a facile hydrothermal and plasma-treatment method. WO2.33(100) delivered a high photocatalytic urea production rate of 1451.38 μg g–1 h–1 under UV irradiation (λ = 365 nm) in a microflow reactor, representing a 3.2-fold enhancement over WO2.90(001) and ranking among the most efficient urea-synthesis photocatalysts reported to date. Mechanistic studies, including isotope labeling, in situ ATR-FTIR, and DFT calculations, reveal that facet-confined oxygen vacancies stabilize low-spin WIII (d3) centers, which simultaneously optimize N2 adsorption while preserving the surface mobility of *NO intermediates, thereby enabling efficient C–N coupling. This work establishes a facet-confined oxygen-vacancy strategy for spin-state regulation of surface intermediates and C–N coupling pathways, providing a general strategy for improved photocatalytic urea synthesis for smart agriculture.