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The status of photocatalytic (PC)/photoelectrochemical (PEC) water splitting as a promising approach to solar-to-chemical energy conversion has increased significantly over the past several decades for addressing the energy shortage. However, the overall energy conversion efficiency is still relatively poor due to the severe photocorrosion in photosensitive semiconductors. Herein, the review begins with the discussion of the photocorrosion mechanism with several typical semiconductors as examples. Then the feasible characterization methods used to evaluate the stability of semiconductors are summarized. Notably, most studies regarding water splitting focus on achieving high efficiency by improving the charge separation and transfer efficiency within the semiconductors. This review focuses on the recent advances in effective strategies for photocorrosion inhibition of semiconductor-based composites with respect to their intrinsic properties and interface charge transfer kinetics, including morphology/size control, heteroatom doping, heterojunction construction, surface modification, and reaction environment regulation. Furthermore, an in-depth investigation of photocorrosion pathways and mechanisms is critical to accurately and effectively address the photocorrosion of semiconductor-based composites to improve PC/PEC water splitting performance in the future.

Exploration of low-cost and earth-abundant photocatalysts for efficient photocatalytic H2 evolution from water is an attractive solution to the global energy and environmental problems. Although MoS2 has been proved as an efficient co-catalyst for the H2 evolution reaction (HER), controllably and accurately constructing MoS2-hybridized photocatalysts at where the electrons extracted still remains a challenge. Here, a facile two-step approach of photoetching-photodeposition has been developed to prepare MoSx/etched-CdS (Mo-Cd(e)-S) with heterostructure accurately constructed on the CdS surface defects. This structure can significantly accelerate photo-induced charge separation and transportation owing to the place of heterostructure construction matching well with that of electrons extracted, numerous active sites introduced, and shorter charge transfer path from bulk to surface. Therefore the charge recombination is significantly retarded. As a result, the Mo-Cd(e)-S exhibits outstanding photocatalytic performance with a state-of-the-art H2 generation rate of 22.5 mmol g−1 h−1 under visible light irradiation (λ ≥ 420 nm) which is 70 times higher than that of pristine CdS. This work opens a new avenue for the low-cost but high efficient photocatalysts development.

Metal organic frameworks (MOFs) have great potential for photocatalysis, but only possess moderate activity due to their slow charge transfer and low solar energy conversion. Herein, heterostructures photocatalysts constructed by boron nitride quantum dots (BNQDs) and MIL-100(Fe) (MNB) were successfully fabricated for overcoming these shortcomings. It was indicated that the composites possessed large surface area, mesoporous structure, and enhanced visible light absorption. The MNB photocatalysts exhibited excellent photocatalytic activity for tetracycline hydrochloride (TC-HCl) degradation under visible light irradiation. Compared with MIL-100(Fe), the photodegradation rate of TC-HCl by MNB-1 was 0.02383 min−1, which was 5.3 times higher than that of pure MIL-100(Fe). The close contact of MIL-100(Fe) with BNQDs and the synergistic effect between them were the main reasons for the improved photodegradation performance. This study reveals that a rational combination of MIL-100(Fe) and BNQDs can improve photocatalytic activity to enhance molecular oxygen activation. Therefore, it is reasonable to believe that quantum dots/MOFs photocatalysts have great potential in environmental remediation.

Spontaneous solar-driven water splitting to generate H2 with no pollution discharge is an ideal H2 generation approach. However, its efficiency remains far from real application owing to the poor light-harvesting and ultrafast charge recombination of photocatalysts. To address these issues, herein, we employed a novel but simple chemical bath deposition (CBD) method to construct CdS/SrTiO3 nanodots-on-nanocubes at room temperature (ca. 25 °C). The as-synthesized nanohybrids not only expand light absorption from ultraviolet (UV) to visible light but also significantly retard charge recombination owing to the well-defined heterostructure formation. As a result, the CdS/SrTiO3 exhibits high photocatalytic performance with H2 evolution rate of 1322 μmol g−1 h−1, which is 2.8 and 12.2 times higher than that of pristine CdS and SrTiO3, respectively. This work provides a universal approach for the heterostructure construction, and inspired by this, higher efficient photocatalysts for H2 evolution may be developed in the near future.

Metal-organic frameworks (MOFs) have been widely concerned for their excellent user-configuration flexibility to be capable of different tasks. A popular trend of their diversified development is pyrolyzing them to produce derived materials with improved stability, conductivity, and well-inherited characteristics. Thanks to these properties, prepared MOF derivatives are gradually testified as alternative catalysts in advanced oxidation processes (AOPs), involving Fenton reaction, sulfate radical-based AOPs (SR-AOPs) as well as photocatalysis for efficient pollutants degradation. Unfortunately, the introduction of the synthetic method of MOF derivatives is relatively rough yet and a comprehensive understanding of the differences in their application to different AOPs systems has not emerged. This review creatively details synthetic strategies of MOF derivatives by analyzing their special conditions and procedures. And starting with suitable MOF precursors, the review focuses on their changes in structure and component during derivation and associates them with performance improvements in AOPs. Besides, the related mechanisms are also discussed respectively by distinguishing the functional sites in different systems.

Herein, a facile in-situ topological transformation where BiVO4 nanosheets (NS) with open instead of closed and inert surface are used as template and original material for the preparation of ultrathin BiOCl NS is proposed. The BiOCl NS developed in this work not only inherits the two-dimensional nanosheet structure of the BiVO4 precursor, but also exhibits improved light-harvesting ability in the meantime as a result of the retention of oxygen vacancies during the topological transformation. The defect state mediated by oxygen vacancies under the conduction band endows BiOCl a narrower forbidden band width as compared to its bulk counterpart, which extends its light absorption range from ultraviolet to visible light region. More importantly, oxygen vacancies can also act as cocatalyst to accept photogenerated electrons excited from the valence band of BiOCl, which greatly suppresses the recombination of electron-hole pairs and prolongs the carrier lifetime, thereby promoting the activation of molecular oxygen into superoxide radicals ( O2−) under visible light irradiation. As expected, the optimal BiOCl-3 NS exhibits a 2.2-fold increase in the yield of O2− radicals compared with bulk-BiVO4. Furthermore, a large amount of free H+ in the waste acid wastewater can be tightly adsorbed with the terminal oxygen atoms of the (0 0 1) facet of BiOCl to compensate for its dangling bonds, which inhibits the crystal growth along the c axis, leaving highly reactive (0 0 1) facets as the dominant facets. Thanks to these merits, BiOCl-3 displays the highest photocatalytic performance towards ciprofloxacin (CIP) degradation among all samples, with the corresponding degradation rate of 4.51 times higher than that of the bulk-BiVO4, and the apparent quantum efficiency of 0.411%. Moreover, the as-developed BiOCl NS has excellent stability even after five successive cycles, with no significant changes in photocatalytic activity and structure, showing its good potential in practical applications.

Full solar spectrum active heterogenous photocatalysis for environmental applications remains highly challenging. Here we report the novel Cu2In2ZnS5/Gd2O2S:Tb (CG) hybrid photocatalysts via a facile solvothermal method for efficient Cr(VI) and CO2 reduction. The narrow band gap energies of the CG hybrid photocatalysts synthesized via a facile solvothermal method show excellent absorption and catalytic activity in the full solar spectrum. High Cr(VI) reduction rate of 90% and CH4 production rate of 57.73 μmol h−1 g−1 are achieved for CG hybrid photocatalyst with 1 wt.% Gd2O2S:Tb. The excellent performance is due to the fact that in the hybrid, Gd2O2S:Tb as cocatalyst, provides more active sites and inhibits the recombination of charge carriers due to the synergetic effect between Cu2In2ZnS5 and Gd2O2S:Tb, consequently improving the photocatalytic reduction activity. Financial support from the Province Natural Science Foundation of Zhejiang (No. LY18E060005, LY18E020007 and LQ18E030005), National Natural Science Foundation of China (No. 21401180) are gratefully acknowledged.

As an "up-and-coming" two-dimensional (2D) material, black phosphorus (BP) has attracted much attention due to its abundant metal-free properties and broad application prospects in photocatalysis. This study introduces a promising sunlight-driven metal-free photocatalyst for oxytetracycline hydrochloride degradation and hexavalent chromium reduction in water and wastewater. The roles of BP quantum dots (BPQDs) in the distribution of electrons and photocatalytic performances were well identified by experimental and density functional theory (DFT) calculations. As expected, the specially designed 0D/1D structure shows unusual photocatalytic efficiency toward the degradation of oxytetracycline hydrochloride (0.0276 min−1) and reduction of hexavalent chromium (0.0404 min−1). Reactive species, namely, O2− and h+ comprised the primary photocatalytic mechanisms for oxytetracycline hydrochloride degradation. This work highlights that the combination of tubular g-C3N4 (TCN) with BPQDs facilitates the charge spatial separation in the photocatalytic process, and provides alternative strategy for design of highly active and metal-free nanomaterials toward environmental remediation and sustainable solar-to-chemical energy conversion.

Photocatalysis is a green technology for the treatment of all kinds of contaminants and has advantages over other treatment methods. Recently, much effort has been devoted to developing new photocatalytic materials based on metal–organic frameworks for use in the degradation of many kinds of organic contaminants. With the aim of searching for more effective photocatalysts, the title three-dimensional coordination polymer, [Cd2(C8H4O4)2(C18H16N2O2)]n, was prepared. The asymmetric unit contains one CdIIcation, one benzene-1,2-dicarboxylate anion (denotedL2−) and half of a centrosymmetric 1,4-bis(pyridin-3-ylmethoxy)benzene ligand (denoted bpmb). Each CdIIcentre is five-coordinated by four carboxylate O atoms from twoL2−ligands and by one N atom from a bpmb ligand, forming a disordered pentagonal pyramidal coordination geometry. The CdIIcentres are interlinked byL2−ligands to form a one-dimensional [Cd2L2]nchain. Adjacent chains are further connected by bpmb linkers, giving rise to a two-dimensional network, and these networks are pillared by bpmb to afford a three-dimensional framework with a 33.42.63.71.81topology. Each grid in the framework has large channels which are filled mainly by the two other equivalent frameworks to form a threefold interpenetrating net. The compound exhibits relatively good photocatalytic activity towards the degradation of methylene blue in aqueous solution under UV irradiation.

Over the past decades, designing efficient photocatalysts represents a remarkable route to deal with energy crisis, environmental pollution issues and global warming problems. Zinc cadmium sulfide (ZnxCd1-xS) based photocatalysts have been explored extensively due to their continuously tunable band gap structure and outstanding absorption ability for visible light, and substantial satisfying contributions have been made. This work first summarizes recent progress on the synthesis of ZnxCd1-xS based materials. They also have various applications in photocatalytic area, including photocatalytic hydrogen evolution, pollutants degradation and carbon dioxide reduction. Especially, the mechanism of different pathways to improve the photocatalytic performance of ZnxCd1-xS based photocatalysts is discussed in detail, which has never been reported in any previous reviews up to now. Moreover, the current challenges and development ideas of ZnxCd1-xS based materials are proposed. It is expected that our review would be helpful for the application of ZnxCd1-xS based photocatalysts in future.

Considering that the crystal facet is highly correlated with the photocatalytic performance of the semiconductor, a novel BiVO4/Ag3PO4/PANI photocatalyst combined with facet engineering and heterojunction is prepared by depositing Ag3PO4 on the highly active (0 4 0) facet of BiVO4 and then incorporating polymer polyaniline (PANI). The synergistic modification of Ag3PO4 and PANI realizes excellent photocatalytic performance, with the degradation efficiency of 85.92% and the maximum rate constant of 0.00894 L mg−1 min−1, which is 10.1, 5.6 and 1.6 times than that of BiVO4, BiVO4/PANI and BiVO4/Ag3PO4, respectively. This enhanced photocatalytic performance is attributed to the following: (i) selective exposure of highly active BiVO4 (0 4 0) facet greatly improves the spatial separation efficiency of charge carriers; (ii) the (0 4 0) facet with preferentially exposed low-coordinated oxygen atoms provides sufficient binding sites for Ag+ anchoring, resulting in strong interfacial coupling between BiVO4 and Ag3PO4, which facilitates charge separation and transfer; (iii) the CB-electrons of Ag3PO4 can be timely consumed by the VB-holes of BiVO4 by the built-in electric field, thus preventing photo-corrosion of Ag3PO4; (iv) PANI acting as hole-transfer material can rapidly migrate holes accumulated in the VB of Ag3PO4 to the catalyst surface by its HOMO orbital, thereby achieving efficient charge separation; (v) the introduction of PANI results in a significant increase in visible light absorption efficiency. This work provides a novel design based on facet engineering and heterojunction, which can also be employed to other semiconductors to improve photocatalytic performance.

Facile and large-scale preparation of upconversion photocatalyst films is promising for the degradation of volatile organic compounds (VOCs), major component of the landfill gas stench. Herein, a spin-assisted layer-by-layer coating method is explored to fabricate the upconversion photocatalyst film of polyethylene terephthalate (PET)/Tm/Yb-doped NaYF4 (TYN)/P25/(CdSe/CdS) QDs (PET/TYN/P25/QDs). The near-infrared light energy passes through the top QDs and P25 layers to excite TYN, and the strong upconversion emissions of UV (290, 346, and 362 ​nm) and visible (452 and 476 ​nm) light are produced and absorbed by P25/QDs for photocatalysis. In the photocatalytic degradation of gaseous toluene, the removal efficiency over the PET/TYN/P25/QDs film reaches 83% after 1 ​h of simulated sunlight irradiation, which is much higher than that (40%) of the PET/TYN/P25 film. This better photocatalytic activity is ascribed to the large absorption edge of the CdSe/CdS QDs and the efficient electron-hole pair separation in the QDs-P25 heterostructure.

Microbial contamination and antibiotic pollutions diffusely exist in wastewater system, and contaminated water poses a threat to public health. Therefore, there is a need to effectively remove biohazard and antibiotic contamination from wastewater systems. In this paper, sulfur doped carbon quantum dots (S-CQDs)/hollow tubular g-C3N4 photocatalyst (HTCN-C), prepared via ultrasonic assisted synthesis strategy, was regarded as an efficient catalyst for the degradation of antibiotic (tetracycline) and destruction of a typical Gram-negative bacterium (Escherichia coli) in imitated wastewater system. The unique structures of hollow tubular g-C3N4 and loading of modified carbon quantum dots enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. Benefiting from these merits, the optimized catalysts (HTCN-C(2)) exhibited superior performance with a reaction rate of 0.0293 min−1 for tetracycline (TC) degradation and 99.99% destruction of Escherichia coli under visible-light irradiation. Moreover, the characterization of UV–Vis diffuse reflectance spectra, photoluminescence technique, transient photocurrent responses and electrochemical impedance spectroscopy also verified the good optical and electrochemical properties of resultant samples. Our current work indicates that HTCN-C has great potential in degradation of antibiotic and destruction of bacterium for practical wastewater treatment.

Photocatalytic H2 evolution from water splitting offers an attractive scientific and technological method to address the energy and environmental crisis. In this study, noble-metal-free Zn0.5Cd0.5S@MoS2 core@shell nanoheterostructures were elaborately designed and successfully synthesized. The visible-light-driven photocatalytic performance investigation shows that the Zn0.5Cd0.5S@MoS2 exhibits a state-of-the-art H2 evolution rate of 40.2 mmol g−1 h−1 far exceeding that of pristine Zn0.5Cd0.5S by more than 57 times. Moreover, thanks to the protection of MoS2 shells, the Zn0.5Cd0.5S@MoS2 can retain long-term stability in four-cycles of 24 h reactions. Furthermore, a tentative mechanism on H2 generation was systematically investigated and proposed, which contributes to understand the enhanced photocatalytic activity of the Zn0.5Cd0.5S@MoS2 heterostructures and may inspire the synthesis of other desirable catalytic systems.

Optofluidics may hold the key to greater success of photocatalytic water treatment. This is evidenced by our findings in this paper that the planar microfluidic reactor can overcome the limitations of mass transfer and photon transfer in the previous photocatalytic reactors and improve the photoreaction efficiency by more than 100 times. The microreactor has a planar chamber (5 cm×1.8 cm×100 μm) enclosed by two TiO(2)-coated glass slides as the top cover and bottom substrate and a microstructured UV-cured NOA81 layer as the sealant and flow input∕output. In experiment, the microreactor achieves 30% degradation of 3 ml 3×10(-5)M methylene blue within 5 min and shows a reaction rate constant two orders higher than the bulk reactor. Under optimized conditions, a reaction rate of 8% s(-1) is achieved under solar irradiation. The average apparent quantum efficiency is found to be only 0.25%, but the effective apparent quantum efficiency reaches as high as 25%. Optofluidic reactors inherit the merits of microfluidics, such as large surface∕volume ratio, easy flow control, and rapid fabrication and offer a promising prospect for large-volume photocatalytic water treatment.