Preparation of highly efficient and stable photocatalysts is crucial for the development of photocatalysis technology. In this study, the method of ultrasonic-assisted deposition and low-temperature calcination was used to prepare MoS₂/g-C₃N₄ S-type heterojunction photocatalyst (MGCD). Effects of the phase structure, micro-morphology, optical absorption performance, X-ray photoelectron spectroscopy, electrochemical AC impedance, and photocurrent of the materials on the photocatalytic activity were comprehensively investigated. The results show that, after ultrasonic-assisted deposition-calcination treatment, MoS₂ microspheres were broken, dispersed and combined on the surface of g-C₃N₄ nanosheets, and formed a kind of heterojunction. Under visible light, the degradation rate of 5%MGCD (with 5% MoS₂ addition) for Rhodamine B (RhB) reached 99% in 20 min, and still reach 95.2% when the sample was reused for 5 times, showing good photocatalytic performance and stability. Further analysis from the point of view of the formation of built-in electric field shows that the band bending caused by built-in electric field, coupled with MoS₂ and g-C₃N₄ in heterojunction, can effectively guide the directional migration of carriers, which can efficiently promote the separation of photogenerated carriers, thus improving the efficiency of photocatalytic reaction. Free radical capture experiment of heterojunction photocatalyst reveals that O₂^- and ·OH are the main active species in the catalytic degradation of RhB, followed by H⁺.

Photocatalysis has received extensive attention due to its advantages of mild reaction conditions and direct conversion of solar energy to chemical energy. Improving the solar absorption range and reducing the recombination of photo-generated “electron-hole” pairs are the hot topics in the field of photocatalysis. In this work, the amorphous TiO₂ nanotube arrays (TiO₂NTs) were prepared by anodic oxidation, and indium-tin (In-Sn) alloy was pressed into the amorphous TiO₂NTs by a mechanical hydraulic method to make In_9.45Sn₁/TiO₂NTs, then the In_9.45Sn₁/TiO₂NTs were annealed in air to obtain indium tin oxide (ITO)/TiO₂NTs. The photocatalytic properties of the obtained TiO₂NTs, In_9.45Sn₁/TiO₂NTs and ITO/TiO₂NTs on the removal of methylene blue in aqueous solution were studied and compared. After 180 min visible light irradiation, the degradation efficiency of the ITO/TiO₂NTs reaches 96.14%. The applying UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) to explore the optical adsorption abilities of the samples shows the strongest absorbance of ITO/TiO₂NTs. Combining the results of transient photocurrent responses, photocurrent density-potential, electrochemical impedance spectroscopy, and Mott-Schottky plots, the ITO/TiO₂NTs have higher charge transfer capability and donor density than do other samples, which can reduce the recombination of holes and electrons, thus improving the visible-light catalytic performance. After five cycles, the degradation rate of the ITO/TiO₂NTs still maintains 90.28%. Results of free radicals trapping experiments reveal that •O₂^- and •OH are the main active substances for the photocatalytic degradation.

In this study, one-dimensional single-crystal TiO₂ nanobelt arrays with surface oxygen vacancies were constructed by Pd-catalyzed oxygen reduction method in anoxic environment to address the problems of insufficient surface active sites and slow reaction kinetics of TiO₂, low yield and poor selectivity of hydrocarbons in CO₂ reduction products. The effects of surface oxygen vacancies and hydrogen spillover of Pd on the separation and transport of photogenerated carrier and the selectivity of reduction product were investigated from morphological structure, carrier behavior and photocatalytic performance. With high CO₂ reduction activity of Pd-Ov-TNB, yields of CH₄, C₂H₆ and C₂H₄ are 40.8, 32.09 and 3.09 µmol·g^-1·h^-1, respectively, and selectivity of hydrocarbons is as high as 84.52%, showing great potential in C-C coupling. Its excellent photocatalytic activity is attributed to the one-dimensional single-crystal nanobelt structure that increases the active specific surface area and crystallinity of the material, provides more active sites for the CO₂ reduction and accelerates the segregated transport of photogenerated charges. Meanwhile, the oxygen vacancies enhance the surface accumulation of photogenerated charges, providing an electron-rich environment for CO₂ reduction. In addition, Pd nanoparticles increase concentration of H* in the reaction system, and then transfer H* to active sites of CO₂ adsorption on the catalyst surface through the hydrogen spillover effect, promoting the hydrogenation of reaction intermediates. Comprehensive advantages of Pd-nanoparticals contribute to the efficient conversion of CO₂ to hydrocarbons.

S-scheme heterojunction has been extensively investigated for hydrogen evolution and environmental pollution issues. In this study, a monoclinic WO₃/hydrothermally treated red phosphorus (HRP) S-scheme composite was prepared by hydrothermal method. XPS and EPR characterization confirmed that the monoclinic WO₃/HRP composite formed S-scheme heterojunction. 5%WO₃/HRP composite displayed the optimal photocatalytic activity under visible light irradiation, and its degradation rate of Rhodamine B (RhB) reached 97.6% after 4 min of visible light irradiation, while its hydrogen evolution rate reached 870.69 μmol·h^-1·g^-1 which was 3.62 times of that of pure HRP. This could be ascribed to the tight interfacial bonding between WO₃ and HRP, and the formation of S-scheme heterostructure, enabling rapid separation of photogenerated carriers and therefore improving the strong redox capacity. This study provided a promising RP-based photocatalyst to meet the demand for clean energy and drinking water.

One of the basic challenges of CO₂ photoreduction is to develop efficient photocatalysts. As an effective strategy, constructing heterostructure photocatalysts with intimate interfaces can enhance interfacial charge transfer for realizing high photocatalytic activity. Herein, a novel photocatalytic material, Bi₄O₅Br₂/CeO₂ composite fiber (B@C-x, x refers to the amount of reactant), was constructed by embeding CeO₂ nanofibers on Bi₄O₅Br₂ nanosheets via an electrospinning combined with hydrothermal method. Its composition, morphology and photoelectric properties were characterized. The results show that Bi₄O₅Br₂/CeO₂ heterojunction with appropriate Bi₄O₅Br₂ content can significantly improve the photocatalytic performance of CeO₂ nanofibers. Compared with pure Bi₄O₅Br₂ and CeO₂, B@C-2 exhibited the best photocatalytic activity under simulated sunlight. The Bi₄O₅Br₂/CeO₂ exhibited improved photocatalytic CO₂ reduction performance with a CO generation rate of 8.26 μmol·h⁻¹·g⁻¹ without using any sacrificial agents or noble co-catalysts. This can be attributed to the tight interfacial bonding between Bi₄O₅Br₂ and CeO₂ and the formation of S-scheme heterojunction, which enables the efficient spatial separation and transfer of photogenerated carriers. This work provides a simple and efficient method for directional synthesis of Bi-based photocatalytic composites with S-scheme heterojunction and illustrates an applicable tactic to develop potent photocatalysts for clean energy conversion.

A composite photocatalyst (TiHAP@g-C₃N₄) consisting of Ti doped hydroxyapatite and g-C₃N₄ was synthesized through hydrothermal route. Its structure and optical property were characterized by various means and photocatalytic activity was evaluated through methyl orange (MO) degradation experiments. Results show that short rod-shaped TiHAP in the sample grows on the surface of g-C₃N₄. Both TiHAP and g-C₃N₄ maintain their original crystal shape and chemical structure. As-prepared TiHAP@g-C₃N₄ is of high purity with specific surface area of 107.92 m²/g, which is increased about 135% and 44% as compared with sole TiHAP and sole g-C₃N₄, respectively. The highest MO degradation rate of 96.35% is achieved within 120 min by TiHAP@g-C₃N₄ at the concentration of 1.0 g/L and pH 7. More than 80.02% of MO was removed in every of three cyclic tests, demonstrating good and stable photocatalytic performance of TiHAP@g-C₃N₄. Holes (h⁺) play the largest role in the MO degradation process, followed by ·O₂^- and ·OH. The constructed TiHAP@g-C₃N₄ heterojunction enhances light absorption, improves separation efficiency of photoelectrons-h⁺, and preserves more redox-prone TiHAP valence band h⁺ and g-C₃N₄ conduction band electrons. Therefore, as-synthesized TiHAP@g-C₃N₄ can be a promising catalyst in photocatalytic degradation.

Photocatalysis is widely used for the removal of refractory organic pollutants in water, but the catalytic activity of semiconductor photocatalysts is significantly inhibited due to the high recombination rate of photogenerated electrons and holes. In this study, an S-scheme BiOBr/ZnMoO₄ composite was successfully prepared by a facile solvothermal method. The structure analysis, in-situ XPS, work function test, free radical capture and ESR experiment confirmed that the BiOBr/ZnMoO₄ composite formed an S-scheme heterojunction. The experimental results show that BiOBr/ZnMoO₄ heterojunction with appropriate ZnMoO₄ content can significantly improve the photocatalytic performance of BiOBr. Compared with pure BiOBr and ZnMoO₄, 15% BiOBr/ZnMoO₄ exhibits the best photocatalytic activity under visible light irradiation, and the photocatalytic degradation rate of bisphenol A reaches 85.3% (90 min). The rate constants of photodegradation of ciprofloxacin are 2.6 times that of BiOBr and 484 times that of ZnMoO₄, respectively. This can be attributed to the tight interfacial bonding between BiOBr and ZnMoO₄ and the formation of S-scheme heterojunction, which enables the efficient spatial separation and transfer of photogenerated carriers. This work provides a simple and efficient method for the directional synthesis of Bi-based S-scheme heterojunction photocatalytic materials, and provides a new theory and experimental basis for further understanding of the structure-activity relationship of Bi-based multi-heterojunction photocatalytic materials.

The photocatalysts deactivation is one of the major issues, which lowers the usefulness of photocatalytic oxidation technology for the removal of low content volatile organic compounds (VOCs). Here, we carried out a series of experiments to demonstrate that the photocatalysts stability could be significantly improved via coupling the oxide base semiconductors, i.e., TiO₂ with 2D materials such as graphitic carbon nitride (g-C₃N₄). Initially, when Ag modified TiO₂ (AT) was used for the gaseous acetaldehyde degradation, a robust deactivation was observed within 60 min. The AT catalyst completely lost its activity when the reaction time was extended to 400 min. On the contrary, the g-C₃N₄ modified AT (CAT) showed superior photocatalytic performance and improved stability (600 min). The in-situ FT-IR, PL, and photocurrent studies suggested that the accumulation of reaction intermediates in the case of AT fundamentally caused the deactivation. However, the g-C₃N₄ provided excessive adsorption sites for the reaction by-products which improved the stability. Additionally, the PL and ESR studies suggested that the existence of g-C₃N₄ improved the charge separation and production of reactive oxygen species, which facilitated the photodegradation of acetaldehyde and ultimate reaction products. This study realizes the usefulness of 2D materials for developing stable and visible light active photocatalysts for applications in sustainable VOC abatement technology.

Graphitic carbon nitride (g-C₃N₄) is widely used in the field of photocatalysis due to its unique two-dimensional planar structure and suitable energy band structure. However, it has some disadvantages such as fast recombination of the electron-hole, low visible-light utilization efficiency and poor dispersion in water, which hinder its application. In this study, the hydrogel prepared by sodium alginate was used as matrix to improve the dispersion of Ag@C₃N₄ composite in water, and at the same time enhanced the separation efficiency of photoelectron-holes pairs, thus improving its photocatalytic performance. Firstly, g-C₃N₄ was synthesized by thermal polymerization and then exfoliated into nanosheets by ultrasound. Then, Ag nanoparticles were deposited in situ on the surface of g-C₃N₄ by solution method to prepare Ag@C₃N₄. Finally, hydrogel loaded with Ag@C₃N₄ (SA/Ag@C₃N₄) was obtained by using calcium ion as crosslinker and sodium alginate (SA) as precursor. The morphology, microstructure and phase composition of the as-prepared photocatalyst were characterized. The as-prepared SA/Ag@C₃N₄ exhibited a 1.5 times higher photocatalytic degradation rate of methyl orange than that of Ag@C₃N₄. The catalytic mechanism was investigated by photoluminescence spectrum, time resolved photoluminescence spectrum and electron paramagnetic resonance spectrum. The results showed that the surface plasmon resonance effect of silver nanoparticles together with the porous structure and mass transfer channel of sodium alginate hydrogel plays a synergistic role in the enhancement of photocatalytic performance.

Photocatalytic degradation is an eco-friendly and high-efficiency way to degrade dye pollutants which has broad application prospects in water pollution control. In this study, the multi-layer core-shell structure of SiO₂@Ag@SiO₂@TiO₂ was synthesized by different methods as a photocatalyst for pollutant degradation, with oxidation-reduction method, modified Stöber method and hydrothermal method in turn. Effect of silver nitrate (AgNO₃), tetraethyl orthosilicate (TEOS) and tetrabutyl titanate (TBOT) on the coating effect were discussed. Microstructure, phase structure, pore structure parameters and photoelectrical properties of SiO₂-based multi-layer core-shell structure were systematically analyzed by various characterization methods while its degradation performance of methylene blue (MB) was also studied and discussed. The results show that when the mass ratio of AgNO₃, TEOS and TBOT to SiO₂ is 5 : 2.4 : 6 : 1, each layer of the multi-layer cored shell structure achieves the optimal coating effect. Compared with SiO₂@TiO₂ and SiO₂@Ag@TiO₂, the core-shell structure of SiO₂@Ag@SiO₂@TiO₂ photocatalyst has the best photocatalytic activity. Its photocatalytic degradation efficiency is close to 93% after simulated visible light irradiation for 45 min, and degradation efficiency keeps at 90% after 4 cycles of recycling tests.