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Correction for ‘Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts’ by Xiaoping Tao et al., Chem. Soc. Rev., 2022, 51, 3561–3608, https://doi.org/10.1039/d1cs01182k.

The photocatalytic conversion of carbon dioxide to fuels presents great promise for storing renewable energy and alleviating global warming. Herein, using the visible-light-responsive semiconductor bismuth tantalum oxyhalogen (Bi4TaO8X, X = Cl, Br) with suitable band structures, we realize the photocatalytic reduction of CO2 to selectively produce CO under visible light without introducing any sacrificial reagents. An isotope-labeling experiment clearly demonstrated that the produced CO originated from CO2 and, additionally, continuous water oxidation for O2 evolution was also detected during photocatalytic CO2 reduction. Further introducing crystal morphology modulation to prepare well-defined nanocrystals enables great enhancement of the photogenerated charge separation performance compared to that of irregular nanoparticles. Moreover, surface modification of the silver nanoparticles deployed as the CO2 reduction cocatalyst evidently facilitates the generation of intermediate species to promote the surface catalytic reaction. This work not only presents a potential semiconductor candidate for photocatalytic CO2 reduction, but it also provides a feasible strategy for designing artificial photosynthetic systems via combining morphology tailoring and suitable cocatalysts.

We experimentally demonstrated that spatial charge separation can take place between the {010} and {001} facets of Bi2WO6 microplates. Further assembly of the reduction and oxidation cocatalysts leads to a remarkable enhancement of photocatalytic water oxidation activity in the presence of Fe3+ ions while the reverse oxidation of Fe2+ to Fe3+ ions is totally inhibited. The origin of the driving force is theoretically proven to be the difference in surface work function between the co-exposed facets, which shows a feasible strategy for developing efficient photocatalysts for solar energy conversion.

A triple sequential junction by rationally combining anatase/rutile nanoparticle TiO2 heterophase (Ans/R) and rutile/rutile TiO2 homophase (Rns/R) junctions was fabricated as a proof of concept. Such a continuous charge separation and transfer channel resulted in a remarkable enhancement in the separation of photogenerated carriers and the photocatalytic activity.

Precise control of the size and distribution of noble metal nanoparticles exerts obvious effects on the performance of heterogeneous catalysts and has received tremendous interest. The photochemical deposition method has advantages in adjusting chemical states, morphology, etc., but the tuning of size and distribution remains a big challenge. In this work, via modulating the surface states and surface charges of the TiO2 support, the size and distribution of noble metals including Ag, Pt, Au and Pd were precisely controlled. We demonstrated that photoelectrons located in the conduction band tend to form larger noble metal nanoparticles, while surface state confined electrons could form smaller nanoparticles. The thus-prepared noble metals/TiO2 catalysts exhibit good potential in both photocatalytic H2 evolution and catalytic oxidation of HCHO. This work not only provides a green and effective method to control the particle size of noble metals on metal oxides, but also is helpful in understanding the role of surface states in photocatalytic processes.

Light-driven hydrogen production using semiconductor photocatalysts has gained much interest owing to their ability to store sunlight in the form of portable chemical fuel. The spatial separation of dual-cocatalysts onto different surfaces has been considered as a useful strategy for fabricating dynamic particulate photocatalysts to hinder charge recombination and reverse reactions. Herein, using one-dimensional (1D) semiconductors, CdSe nanorods as an example, we experimentally demonstrated that photogenerated electrons and holes can be effectively separated along different directions of a 1D semiconductor. Following this phenomenon, the reduction cocatalyst Pt and oxidation cocatalyst PdS were spatially deposited on different sites via an in situ photodeposition process, which drastically enhanced the photocatalytic activity for hydrogen production to more than 20 times, thus exhibiting an extremely high apparent quantum efficiency (AQE) of ∼45% at 420 nm. Further studies using photoluminescence spectroscopy indicated that the spatially separated dual-cocatalysts efficiently captured the photogenerated electrons and holes migrating to the surface, which greatly decreased the recombination of charge carriers and consequently led to superior photocatalytic performances. Our work provides an effective strategy for the rational construction of highly efficient photocatalyst systems based on (quasi) 1D semiconductors for artificial solar energy conversion.

Constructing a built-in electric field at the interface of semiconductors has been demonstrated to provide the driving force for spatial charge separation in photocatalysis. Although phase junctions (interfaces formed between two crystalline phases of the same semiconductor) have been demonstrated to be effective in spatial charge separation, regulation of the photocatalytic activity by precisely tuning the built-in electric fields is not yet well understood. In this work, taking anatase/rutile TiO2 phase junction as an example, the built-in electric field in the phase junction region was modulated via fabricating controllable anatase nanoparticles on rutile TiO2 surface to manipulate the interfacial contact area between anatase and rutile phases. We found that photocatalytic H2 evolution depends strongly on the interfacial contact area between anatase and rutile TiO2. The relation between the anatase/rutile phase junction interfacial contact area and the specific photocatalytic activity shows a typical volcano curve, that is, increasing the interfacial contact area results in enhancement of the driving force for spatial charge separation, allowing more electrons and holes to migrate to the surface and participate in redox reactions, but further increasing the interfacial contact area leads to decline of photocatalytic activity. The optimized interfacial contact is the most favorable balance between the strength of built-in electric field and transfer distance for photogenerated charge carriers for separation and transfer of photo-generated electrons and holes at the phase junction region. Our work provides new insight into the construction of built-in electric fields on the surface of semiconductor-based photocatalysts to boost spatial charge separation for solar energy conversion systems.

The selective conversion of alcohols to aldehydes under ambient conditions using semiconductor-based photocatalysts has attracted more and more attention in organic synthesis. In this work, bismuth vanadate (BiVO4) crystals with spatially separated dual-cocatalysts on different facets were introduced as photocatalysts for aerobic oxidation under visible light. It was found that the photocatalytic conversion of benzylalcohols to benzaldehydes was remarkably enhanced when Pt and MnOx are selectively deposited on the {010} and {110} facets of the BiVO4 crystal, acting as reduction and oxidation cocatalysts, respectively. The superior performance could be attributed to the spatial separation of the reduction and oxidation reactions so that the recombination and reverse reactions are greatly inhibited. We also found that adding a small amount of H2O in the system to increase the solubility of the photocatalysts at the interface of water and oil can remarkably boost the reaction rate of aerobic oxidation. Our work shows a useful strategy for the rational design and construction of highly efficient photocatalyst systems for the synthesis of organic compounds via photocatalytic processes.

The separation of photogenerated charge carries is a challenging issue in artificial photocatalyst systems for solar energy conversion. It has been reported that spatial charge separation can take place between different facets of semiconductor-based crystals with regular morphology and facets, which could be used to rationally deposit cocatalysts on the right facets. However, the spatial separation of photogenerated electrons and holes is still a big challenge for a particulate photocatalyst without regular morphology and specific facets. In this work, we demonstrated that photogenerated electrons and holes can be regularly separated on ferroelectric PbTiO3 photocatalyst even without regular morphology and facets. The reduction cocatalyst and oxidation cocatalyst could be selectively formed on different sites via an in situ photochemical deposition method. It is found that the photoactivity and hydrogen production for PbTiO3 with spatially separated dual-cocatalysts is remarkably enhanced to more than 100 times greater compared to native PbTiO3, which is much higher than that the case of dual-cocatalysts with a random distribution. The intrinsic electric fields and spontaneous electric polarization in the bulk of PbTiO3 are proposed to play important roles in the spatial distribution of active sites on irregular PbTiO3 particles. Our work emphasizes the essential roles of two important factors, efficient charge separation strategy and the location of dual-cocatalysts on the right sites, to construct integrated artificial photocatalyst systems for solar energy conversion.

One of the challenging issues in photocatalytic overall water splitting is to efficiently separate the photogenerated charges and the reduction and oxidation catalytic sites on semiconductor-based photocatalysts. It has been reported that the photogenerated charge can be separated between different facets of a semiconductor crystal with low symmetry. However, many semiconductor crystals possess high symmetry (such as the cubic phase) and expose isotropic facets, which are not suitable for charge separation between the facets. Herein, using a nanocrystal morphology tailoring strategy, we synthesized the exposed facets of high symmetry SrTiO3 nanocrystals from isotropic facets (6-facet SrTiO3) to anisotropic facets (18-facet SrTiO3), which leads to the exposure of different crystal facets. We found that the reduction and oxidation catalytic sites can be separately distributed only on the anisotropic facets of 18-facet SrTiO3 nanocrystals, but randomly distributed on every facet of 6-facet SrTiO3 nanocrystals. Based on these findings, the selective distribution of dual-cocatalysts on the anisotropic facets of 18-facet SrTiO3 nanocrystals leads to a fivefold enhancement of apparent quantum efficiency. The superior performance can be attributed to the charge separation between anisotropic facets and the separation of the reduction and oxidation catalytic sites to reduce the charge recombination. These findings will be instructive for the rational design of a high efficiency photocatalytic system for solar energy conversion.

New insight into junction-based designs for efficient charge separation is vitally important for current solar energy conversion research. Herein, an anatase–rutile phase junction is elaborately introduced into TiO2 films by rapid thermal annealing treatment and the roles of phase junction on charge separation and transfer are studied in detail. A combined study of transient absorption spectroscopy, electrochemical and photoelectrochemical (PEC) measurements reveals that appropriate phase alignment is essential for unidirectional charge transfer, and a junction interface with minimized trap states is crucial to liberate the charge separation potential of the phase junction. By tailored control of phase alignment and interface structure, an optimized TiO2 film with an appropriately introduced phase junction shows superior performance in charge separation and transfer, hence achieving ca. 3 and 9 times photocurrent density enhancement compared to pristine anatase and rutile phase TiO2 electrodes, respectively. This work demonstrates the great potential of phase junctions for efficient charge separation and transfer in solar energy conversion applications.

Titanium dioxide (TiO2) is regarded as the benchmark semiconductor in photocatalysis, which possesses a suitable band structure and makes the overall water splitting reaction thermodynamically possible. However, photocatalytic overall water splitting (POWS) (2H2O → 2H2 + O2) can only take place on rutile but hardly on anatase and brookite TiO2. So obtaining the POWS on TiO2-based photocatalysts has remained a long-standing challenge for over 40 years. In this work, we found that the POWS on anatase and brookite TiO2 becomes feasible under prolonged UV light irradiation. Further investigation by means of electron spin resonance spectroscopy (EPR) and transient infrared absorption–excitation energy scanning spectroscopy (TRIRA-ESS) reveals that both kinetics and thermodynamics factors contributed to unique POWS activity for different phases of TiO2. Kinetically the process of photocatalysis differs on different phases of TiO2 due to the intermediates (˙OH radical for anatase and brookite TiO2, peroxy species for rutile TiO2) that are formed. Thermodynamically there are many trapped states lying near the valence band of anatase and brookite but not for rutile TiO2, which reduce the overpotential for water oxidation. These findings develop our understanding of why some semiconductors are inactive as POWS photocatalysts despite having thermodynamically suitable band structures for the proton reduction and water oxidation reactions.

Thiophene is one of the main sulfur-containing compounds in gasoline and difficult to be oxidized with the conventional oxidative processes. Herein for the first time we report that thiophene can be oxidized to SO3 on BiVO4 co-loaded with Pt and RuO2 co-catalysts (denoted as Pt-RuO2/BiVO4) under visible light irradiation with molecular oxygen as oxidant. The high activity of the catalyst can be achieved by only loading as low as 0.03 wt% of Pt and 0.01 wt% of RuO2 as dual co-catalysts on BiVO4. ESR measurements give the evidence that the active oxygen species (˙OH and O2˙−) generated by photocatalytic processes are involved in the photocatalytic oxidation of thiophene. The considerable enhancement of photocatalytic activity can be attributed to the simultaneous presence of the reduction and oxidation co-catalysts which are beneficial for the efficient separation and transfer of the photo-generated electrons and holes.

Overall water splitting on a TiO2-based photocatalyst has been extensively investigated. However, in most cases, the products are not in a stoichiometric ratio, thus the reaction is not really overall water splitting. In this work, we found that in the presence of Cl−, the evolution of O2 and H2 over Pt/TiO2 can be successfully achieved, and the activity can be enhanced up to 3 times compared to having no Cl− present. Furthermore, the H2 : O2 ratio can be close to 2.0, i.e. the stoichiometric ratio of overall water splitting. It is proposed that the Cl− ion is involved with the reaction intermediate of O2 evolution from water oxidation. Our work not only reported overall water splitting on a TiO2-based photocatalyst, but also provided experimental evidence for understanding the possible reaction process and the mechanism of photocatalytic water splitting.

Development of a photocatalyst with wide visible light absorption is of vital importance in solar-chemical energy conversion. In this work, we introduce a new nitrogen-doped layered oxide, Sr5Ta4O15−xNx, which exhibits a significantly extended absorption edge compared with the undoped oxide Sr5Ta4O15. The extension of the visible light absorption has been ascribed to the substitution of nitrogen for oxygen atoms as well as the formation of Ta–N bonds, which was confirmed by X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Judged by the first principle calculation, the N 2p states mixed with pre-existing O 2p states shift the valence band maximum upward and result in wide visible light absorption. Band structure analysis combined with UV-Vis diffuse reflectance spectrum (DRS) and Mott–Schottky (M–S) measurement shows that the conduction and valence bands of Sr5Ta4O15−xNx are sufficient for water reduction and oxidation, respectively. The photocatalytic water splitting performances of Sr5Ta4O15−xNx are strongly related to the deposited cocatalyst. With an optimized cocatalyst, the Sr5Ta4O15−xNx shows both H2 and O2 evolution activities under visible light irradiation using CH3OH and AgNO3 as scavengers respectively. Following the optimized cocatalyst deposition of the Sr5Ta4O15−xNx, the cocatalyst-modified nitrogen-doped tantalum-based layered oxides Sr2Ta2O7−xNx and Ba5Ta4O15−xNx also exhibit activities for both the water splitting half reactions. This work demonstrates that the nitrogen-doped tantalum-based layered oxides may be a new type of potential photocatalyst with wide visible light absorption for solar water splitting.