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TiO2-based catalysts with various surface heterostructures (0D, 1D, 2D, and 3D) have been widely researched owing to their cost-effectiveness, high stability, and environmentally friendly nature, and can be used for many applications in various fields, including hydrogen production and pollutant degradation. However, there are also many existing problems limiting their practical application, such as their large band gap and rapid electron–hole recombination rate. Owing to the abundance of recent achievements in materials science, we will summarize the recent structural engineering strategies which provide favorable photocatalytic activity enhancements, such as enhanced visible light absorption, stability, an increased charge–carrier separation rate and improved specific surface area. Among the various structural engineering methods in this review, we will introduce TiO2-based materials with different dimensional structures. Meanwhile, we also discuss recent achievements in synthesis methods and application of TiO2-based catalysts in various fields. We aim to display a comprehensive overview which can be a guide for the development of a new generation of TiO2-based catalysts according to their structural design for enhanced solar energy conversion. [ABSTRACT FROM AUTHOR]

This study details the rational design and synthesis of Cu2ZnSnS4 (CZTS)-doped anatase (A) heterostructures, utilizing earth-abundant elements to enhance the efficiency of solar-driven water splitting. A one-step hydrothermal method was employed to fabricate a series of CZTS–A heterojunctions. As the concentration of titanium dioxide (TiO2) varied, the morphology of CZTS shifted from floral patterns to sheet-like structures. The resulting CZTS–A heterostructures underwent comprehensive characterization through photoelectrochemical response assessments, optical measurements, and electrochemical impedance spectroscopy analyses. Detailed photoelectrochemical (PEC) investigations demonstrated notable enhancements in photocurrent density and incident photon-to-electron conversion efficiency (IPCE). Compared to pure anatase electrodes, the optimized CZTS–A heterostructures exhibited a seven-fold increase in photocurrent density and reached a hydrogen production efficiency of 1.1%. Additionally, the maximum H2 production rate from these heterostructures was 11-times greater than that of pure anatase and 250-times higher than the original CZTS after 2 h of irradiation. These results underscore the enhanced PEC performance of CZTS–A heterostructures, highlighting their potential as highly efficient materials for solar water splitting. Integrating Cu2ZnSnS4 nanoparticles (NPs) within TiO2 (anatase) heterostructures implied new avenues for developing earth-abundant and cost-effective photocatalytic systems for renewable energy applications. [ABSTRACT FROM AUTHOR]

The construction of semiconductor heterojunction photocatalysts that improve the separation and transfer of photoinduced charge carriers is an effective and widely employed strategy to boost photocatalytic performance. Herein, we have successfully constructed a CdS/Ag/Bi2WO6 Z-scheme heterojunction with an Ag-bridge as an effective charge transfer channel by a facile process. The heterostructure consists of both CdS and Ag nanoparticles anchored on the surface of Bi2WO6 nanosheets. The photocatalytic efficiency of the CdS/Ag/Bi2WO6 system was studied by the decontamination of tetracycline (TC) and Rhodamine B (RhB) under visible light irradiation (λ ≥ 420). The results exhibited that CdS/Ag/Bi2WO6 shows markedly higher photocatalytic performance than that of CdS, Bi2WO6, Ag/Bi2WO6, and CdS/Bi2WO6. The trapping experiment results verified that the •O2− and h+ radicals are the key active species. The results of photoluminescence spectral analysis and photocurrent responses indicated that the CdS/Ag/Bi2WO6 heterojunctions exhibit exceptional efficiency in separating and transferring photoinduced electron−hole pairs. Based on a series of characterization results, the boosted photocatalytic activity of the CdS/Ag/Bi2WO6 system is mostly due to the successful formation of the Ag-bridged Z-scheme heterojunction; these can not only inhibit the recombination rate of photoinduced charge carriers but also possess a splendid redox capacity. The work provides a way for designing a Z-scheme photocatalytic system based on Ag-bridged for boosting photocatalytic performance. [ABSTRACT FROM AUTHOR]

Photocatalytic technology based on the specific band structure of semiconductors offers a promising way to solve the urgent energy and environmental issues in modern society. In particular, hydrogen production from water splitting over semiconductor photocatalysts attracts great attention owing to the clean source and application of energy, which highly depends on the performance of photocatalysts. Among the various photocatalysts, TiO2 has been intensively investigated and used extensively due to its outstanding photocatalytic activity, high chemical stability, non-toxicity, and low cost. However, pure TiO2 has a wide band gap of approximately 3.2 eV, which limits its photocatalytic activity for water splitting to generate hydrogen only under ultraviolet light, excluding most of the inexhaustible sunlight for human beings. Fortunately, the band gap of semiconductors can be manipulated, in which introducing oxygen defects is one of the most effective measures to narrow the band gap of titanium oxides. This review considers the fundamentals of photocatalytic water splitting for hydrogen production over TiO2, discusses the latest progress in this field, and summarizes the various methods and strategies to induce oxygen defects in TiO2 crystals. Then, the next section outlines the modification approaches of oxygen-deficient titanium oxide (TiO2−δ) to further improve its photocatalytic performance. Finally, a brief summary and outlook of the studies on TiO2−δ photocatalysts for water splitting to produce hydrogen are presented. [ABSTRACT FROM AUTHOR]

The presence of short-lived shallow trapping states in semiconductor-based photocatalysts hinders efficient utilization of charge carrier, which compromises the solar-to-hydrogen efficiency. Here, we presented an engineered graphitic carbon nitride (g-CN) nanosheets with long-lived shallow trapping states achieved through an n-π * electronic transition. This transition induces a significant red-shifted absorption edge at 600 nm, effectively extending the range of light absorption compared to pristine g-CN. Moreover, the engineered g-CN nanosheets exhibit lower exciton binding energies (36 meV) compared to pristine counterparts (50.1 meV), as revealed by temperature-dependent photoluminescence (PL) spectra. Femtosecond transient absorption spectroscopy (fs-TAS) confirms the presence of long-lived shallow trapping states (lifetime: 565.8 ps) in the engineered g-CN nanosheets. These states enable a greater participation of photoinduced electrons in photocatalytic reactions, resulting in significantly enhanced photoactivity. Notably, the g-CN sample with the n-π * transition achieves a remarkable photocatalytic H 2 production rate of 61.8 µmol h−1, which is a fivefold enhancement over pristine g-CN nanosheets. These findings highlight the crucial role of the n-π * transition in g-CN for prolonging shallow electron trapping and ultimately leading to superior photocatalytic performance. [Display omitted] • The n-π* transition expands g-CN's absorption edge to 600 nm. • The n-π* transition creates long-lived shallow trapping states in g-CN. • Engineered g-CN achieves 5-fold higher photocatalytic H 2 generation. [ABSTRACT FROM AUTHOR]

The serious problems of environmental pollution and energy shortage have pushed the green economy photocatalysis technology to the forefront of research. Therefore, the development of an efficient and environmentally friendly photocatalyst has become a hotpot. In this work, magnetic Fe3O4/C/MnO2/C3N4 composite as photocatalyst was synthesized by combining in situ coating with low-temperature reassembling of CN precursors. Morphology and structure characterization showed that the composite photocatalyst has a hollow core–shell flower-like structure. In the composite, the magnetic Fe3O4 core was convenient for magnetic separation and recovery. The introduction of conductive C layer could avoid recombining photo-generated electrons and holes effectively. Ultra-thin g-C3N4 layer could fully contact with coupled semiconductor. A Z-type heterojunction between g-C3N4 and flower-like MnO2 was constructed to improve photocatalytic performance. Under the simulated visible light, 15 wt% photocatalyst exhibited 94.11% degradation efficiency in 140 min for degrading methyl orange and good recyclability in the cycle experiment. [ABSTRACT FROM AUTHOR]

Ce/N co-doped TiO 2 /NiFe 2 O 4 /diatomite (CN-TND) hybrid catalyst was prepared via sol-gel method. This ternary composite combined the advantages of three components: adsorption capability of diatomite (Dt), visible-light-driven photoactivity of Ce/N co-doped TiO 2 (Ce/N-TiO 2 ), and magnetic recyclability of ferrite NiFe 2 O 4 . The physicochemical properties of CN-TND were characterized by various analytical methods. The visible-light-driven photoactivity of CN-TND was investigated by the degradation of tetracycline (TC) and disinfection of Escherichia coli ( E. coli ) under visible light irradiation, and the optimal amount of Ce dopant was determined. In addition, the kinetic data of the degradation process were obtained, and the mechanism of this process was proposed. Different scavengers detected the active species involved during the degradation process. CN-TND exhibited ferromagnetism, thus it could be simply separated from the reactor by an external magnet. The reusability test proved its excellent photocatalytic stability and recyclability. We consider it suitable for the application of wastewater treatment. [ABSTRACT FROM AUTHOR]

In this work, ZnS microspheres with good dispersibility and high surface area have been successfully synthesized via a facile hydrothermal method in the absence of surfactant or template. The formation of ZnS microspheres were fully investigated by tuning the hydrothermal reaction time. The formation of ZnS microspheres could be attributed to oriented aggregation of nanoparticles followed by Ostwald ripening process. The band gap of ZnS microspheres was estimated to be 3.45 eV on the basis of UV-Vis spectrum. ZnS microspheres presented a wide and strong green emission centered at 522 nm. The photocatalytic results indicated that ZnS microspheres have superior ability of photodegradation organic pollutants. Moreover, the ZnS structures presented good antibacterial activity. It is believed that the obtained ZnS microspheres have huge potential in environmental protection and medical industry. [ABSTRACT FROM AUTHOR]

Porous TiO were assembled by evaporating or refluxing TiO colloid, which was obtained by dispersing the TiO nanoparticles with a crystallite size ( d) of 3.2 nm into water or ethanol without any additives. Porous transparent bulk TiO was obtained by evaporating the TiO-CHOH colloid at room temperature for 2 weeks, while porous TiO nanospheres were assembled by refluxing the TiO-HO colloid at 80 °C for 36 h. Both of the porous TiO architectures were pore-size-adjustable depending on the further treating temperature. Porous TiO nanospheres exhibited enhanced photocatalysis activity compared to the nanoparticles. [ABSTRACT FROM AUTHOR]

Porous ZnO nanosheets with exposed {0 0 1} facets coated on Zn foils have been synthesized by annealing sheet-like Zn 5 (OH) 8 Cl 2 ·H 2 O–Zn 2 OCl 2 ·2H 2 O precursor coated on Zn foils at 400 °C for 60 min. The precursors were synthesized by heating ZnCl 2 solution on zinc foil at 340 °C for 60 min. Photocatalytic activity of porous ZnO nanosheets in degradation of methyl orange was studied, and the results indicate that the porous ZnO nanosheets show superior photoreactivity, compared to ZnO nanorods as a benchmarking material. The superior photocatalytic activity is attributed to the exposed {0 0 1} facets and a high specific surface area. The exposed {0 0 1} facets were found to be polar surfaces by periodic density functional theory calculations, and thus a charge separation model between polar (0 0 1) and ( 0 0 1 ¯ ) surfaces was proposed. There is an internal electric field between positive Zn–ZnO (0 0 1) and negative O–ZnO ( 0 0 1 ¯ ) surfaces due to the spontaneous polarization. The internal electric field provides a driving force for charge separation. The reduction and oxidation reactions take place on the positive (0 0 1) and negative ( 0 0 1 ¯ ) polar surfaces, respectively. The charge separation model can deepen understanding of charge transfer in the semiconductor nanocrystal with highly photocatalytic activities and offer guidance to design more effective photocatalysts and new type of solar cells, photoelectrodes or photoelectric devices. [ABSTRACT FROM AUTHOR]

ZnO nanocrystals with various (0 0 2) orientations were synthesized via a solvothermal reaction of zinc acetate with n-butylamine (BA) and tetrahydrofuran at 140 °C for 12 h by varying the molar ratio of BA to Zn(II). The formation of the ZnO nanocrystals with various (0 0 2) orientations and shapes results from the selective adsorption of different amount of BA molecules on ZnO (0 0 1) surface. Photocatalytic activity of the as-prepared ZnO nanocrystals with various (0 0 2) orientations in degradation of methyl orange was studied, it was found that the exposed {0 0 1} facets are reactive facets. The structure and atomic charge distribution of the {0 0 1} facets were studied by periodic density functional theory calculations. Based on polar structure of the exposed {0 0 1} surfaces, a charge separation model between polar ZnO {0 0 1} surfaces was proposed. There is an internal electric field between positive Zn-ZnO (0 0 1) and negative O-ZnO ( 0   0   1 ¯ ) planes due to the spontaneous polarization. The internal electric field provides the driving force for charge separation. The reduction and oxidation reactions take place on the positive (0 0 1) and negative ( 0   0   1 ¯ ) polar planes, respectively. The charge separation model can deepen understanding of charge transfer in the semiconductor nanocrystal with highly photocatalytic activities and offer guidance to design more effective photocatalysts as well as new type solar cells, photoelectrodes or photoelectric devices. [ABSTRACT FROM AUTHOR]

• Triphenylamine-porphyrin dyads are synthesized for photocatalysis. • XZP2/TiO 2 exhibits the most efficient charge separation as photoelectrode. • XZP2/TiO 2 performs the best in photodegradation of acid black and tetracycline. • Photocatalytic mechanism and interfacial charge transfer pathways are proposed. [Display omitted] Three triphenylamine (TPA) substituted dichromophoric zinc porphyrins XZP1–3 and a single zinc porphyrin ZP1 have been rationally designed to construct dye-sensitized TiO 2 nanoparticles to explore the feasibility of dichromophoric dye design for photocatalysis. TPA, N,N -diphenyl-(1,1′-biphenyl)− 4-amine and a carbazole-diphenylaniline derivative are attached to the meso -position of porphyrin core as the second chromophore. The electronic structure of the porphyrins is studied by density functional theory (DFT) calculations and the dye-sensitized composites are investigated using couples of spectral and electrochemical techniques. XZP2/TiO 2 exhibits the smallest charge transfer resistance and the longest electron lifetime among the investigated composites. The same catalyst performs the highest efficiency in photodegradation of both acid black (AB1) and tetracycline (TC) polluted water samples. Electronic paramagnetic resonance and radical quenching experiments reveal that the priority reactive species are superoxide radicals (•O 2 −) and holes (h+), suggesting the efficient charge separation at the porphyrin-sensitized TiO 2 interface. This work demonstrates the facilitated interfacial charge separation using dichromophoric dye-sensitized semiconductor particles for photodegradation and, the insights should aid in dyad design for photocatalysis application. [ABSTRACT FROM AUTHOR]

With the seriously environmental pollution, photocatalytic technology has been extensively studied for ensuring the continuous development of society. As a type of appealing semiconductor, bismuth-based materials have become a research hotspot in the field of photocatalysis due to their unique electronic structure, appropriate bandgap energy, high light quantum and outstanding electronic transmission efficiency. However, the separation and recovery of photocatalyst from reaction systems is difficult. The most promising strategy to facilitate separation process is to introduce a magnetic component. This review has mainly involved a classification, current challenges and prospects on the recent progress in fabrication of magnetic bismuth-based photocatalytic materials, as well as the list of their degrade object, dosage, initial concentration and reaction time. [ABSTRACT FROM AUTHOR]

Novel Bi2W2O9 and Bi2Mo2O9 with irregular polyhedron structure were successfully synthesized by a hydrothermal method. Compared to ordinary Bi2WO6 and Bi2MoO6, the modified structure of Bi2W2O9 and Bi2Mo2O9 were observed, which led to an enhancement of photocatalytic performance. To investigate the possible mechanism of enhancing photocatalytic efficiency, the crystal structure, morphology, elemental composition, and optical properties of Bi2WO6, Bi2MO6, Bi2W2O9, and Bi2Mo2O9 were examined. UV-Vis diffuse reflectance spectroscopy revealed the visible-light absorption ability of Bi2WO6, Bi2MO6, Bi2W2O9, and Bi2Mo2O9. Photoluminescence (PL) and photocurrent indicated that Bi2W2O9 and Bi2Mo2O9 pose an enhanced ability of photogenerated electron–hole pairs separation. Radical trapping experiments revealed that photogenerated holes and superoxide radicals were the main active species. It can be conjectured that the promoted photocatalytic performance related to the modified structure, and a possible mechanism was discussed in detail. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag+ was successfully doped into the imidazole ring of ZIF-8 via a simple etching and ion exchange approach. • The band gap energy of Ag-doped-ZIF-8 decreased efficiently. • A novel Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction was fabricated. • The Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction showed excellent photocatalytic activity. • AgCl/Ag-doped-ZIF-8 possessed good reusability and stability. It is of great importance to fabricate photocatalyst with high photocatalytic activity, and the formation of Z-scheme heterojunction photocatalyst has been proved to be an effective way to restrain the recombination of photo-induced carriers. In this work, Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction is synthesized via a two-step process involving appropriate amount of cationic Ag ion doping into the imidazole ring of ZIF-8 framework and the precipitation of AgCl onto this Ag-doped-ZIF-8. The successful doping of ZIF-8 which decreases the band gap energy, enhances the light harvesting. Besides, the separation efficiency of photo-induced carriers is further improved due to the formation of Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction, which is confirmed by photoelectrochemical experiments. As a result, the as-prepared AgCl/Ag-doped-ZIF-8 photocatalyst possesses excellent photocatalytic activity under visible light illumination. This work will provide a novel perspective for the design and construction of Z-scheme heterojunction for highly efficient photocatalysis. [ABSTRACT FROM AUTHOR]

Coupling photocatalysis with membrane separation technology becomes one pioneering method to solve the membrane fouling. In this study, Ag@SnS photocatalyst was synthesized and blended with polyvinylidene fluoride (PVDF) to fabricate Ag@SnS/PVDF composite membranes via non-solvent induce phase separation (NIPS) method. The results show that with the addition of Ag@SnS, water flux of Ag@SnS/PVDF hybrid membranes increases due to the enhanced membrane hydrophilicity and increased porosity. The optimal hybrid membrane (MAS-2) exhibits the rejection rate of 97.0 % and 95.4 % for BSA and HA accompanied with a water permeance of 578.5 L m−2 h−1 bar−1. Moreover, MAS-2 membrane reveals excellent self-cleaning ability by photodegradation of HA on membrane surface, and its flux recovery rate (FRR) can achieve 91.7 % after UV irradiation and 95.8 % after 3 h natural sunlight irradiation via photocatalysis regeneration. The heterostructure of Ag@SnS can assist separation of photoinduced electrons and holes by transferring photoinduced electrons to Ag nanoparticles with enhanced photocatalytic activity. After three cycles, the FRR can still reach around 90.0 %, revealing its outstanding cleaning ability. Therefore, the Ag@SnS/PVDF membranes have a foreseeable potential in the field of water treatment due to its high flux performance, self-cleaning ability via photocatalysis process. [Display omitted] • Ag@SnS/PVDF photocatalytic membranes were revealed for the first time. • The membrane shows a PWP of 578.5 L m−2 h−1 bar−1 and BSA rejection of 97.0 %. • The fouled Ag@SnS/PVDF membranes can be regenerated via UV or sunlight irradiation. • Heterostructure of Ag@SnS enhanced the photocatalytic activity of the membranes. [ABSTRACT FROM AUTHOR]

Abstract: High efficient photocatalytic reduction of 4-nitroaniline to p-phenylenediamine over microcrystalline SrBi2Nb2O9 was observed upon purging with N2 under UV-light irradiation. Its photocatalytic activity was higher than that of sample P25 (commercial TiO2, Degussa Co.). The analysis results of X-ray diffraction and X-ray photoelectron spectroscopy revealed that microcrystalline SrBi2Nb2O9 had high stability for the photocatalytic reduction of 4-nitroaniline. Further experiments indicated that ammonium oxalate was indispensable for the photocatalytic reduction of 4-nitroaniline. Moreover, the high efficient photocatalytic reduction of 4-nitroaniline over microcrystalline SrBi2Nb2O9 might be ascribed to its relatively high conduction band. [Copyright &y& Elsevier]

• MnO 2 was designed as flower-like structure to obtain a larger surface area. • BiOBr and Bi metals were combined with MnO 2 to construct a heterojunction. • The magnetic core facilitated the recycling of the photocatalyst. • The core-shell structure can generate synergistic effects of different components. • Composite materials exhibited excellent dyes degradation capabilities. The flower-like Fe 3 O 4 /SiO 2 /MnO 2 /BiOBr-Bi magnetic composite photocatalyst was prepared in this work. The combination of BiOBr and Bi metal with flower-like MnO 2 constituted a heterojunction structure, which increased the specific surface area of the photocatalyst and promoted the separation of photo-generated carriers, resulting in the enhanced catalytic performance. The morphologies and the compositions of the photocatalyst were characterized in detail. Under simulated light, the degradation of organic dye methylene blue (MB) was used to research the photocatalytic activity. In the case of 15 mg photocatalyst, it was found that the photocatalytic degradation efficiency to the MB solution was 95.23% within 150 min. Moreover, the degradation rate of MB could still reach 81.11% after four cycles. The design of flower-like composites with magnetic core-shell structure provided a new method for fabricating photocatalysts having excellent catalytic performance and cyclic stability. [ABSTRACT FROM AUTHOR]

Two-dimensional Ag/WS 2 hybrid membranes were developed to improve separation performance of WS 2 membrane by in situ self-reduction of AgNO 3 on WS 2 nanoflakes. With the increase of Ag content in Ag/WS 2 hybrid membrane, water flux increased as well because of increased interlayer spacing and more irregular stacking of WS 2 nanoflakes, while the rejection rates for dye molecules decreased. The hybrid membrane containing 6.92 wt% of Ag nanoparticles (Ag/WS 2 -2) presented optimal separation performance, exhibiting a EB rejection rate around 90% and a water permeance higher than 500 L/m2·h·bar. Moreover, Ag/WS 2 -2 membrane revealed excellent UV-driven self-cleaning ability by photodegradation of contaminant on membrane surface, and its water flux recovery rate was higher than 99.0%. The formation of Ag/WS 2 heterostructure can assist separation of photoinduced electrons and holes by transferring photoinduced electrons to Ag nanoparticles with enhanced photocatalytic activity. [Display omitted] - 2D Ag/WS 2 hybrid membranes were developed by in situ self-reduction of AgNO 3. - Improved separation performances were achieved after Ag decorated. - Ag/WS 2 membrane presented excellent self-cleaning ability by photocatalysis. [ABSTRACT FROM AUTHOR]