Fe@zeolite materials are widely applied in the production of ·OH by catalyzing Fenton-like reactions for degradation of recalcitrant organic pollutants due to their comprehensive sources, simple preparation and low environmental impact. However, the high cost of Fe@zeolite synthesis and the lack of Fe²⁺ regeneration strategy are serious issues that limit the application of Fe@zeolite as a Fenton-like catalyst in industrial-scale systems. In this study, the ash generated from activated sludge incineration treatment was utilized as raw material to selective recover Si, Al and Fe, preparing Fe²⁺-sodalite (FSD) material. Consequently, it was used as a Fenton-like catalyst to activate peroxyacetic acid (PAA) for the degradation of methylene blue (MB) in wastewater. Results indicated thatFSD was capable of effectively catalyzing PAA to generate various active oxygen species such as ·OH, ¹O₂ and R-O· in a wide pH range, thereby degrading MB through hydroxylation and sulfonation pathways. MB can be completely removed during 20 min under optimized conditions of 0.3 mmol/L PAA and 0.3 g/L FSD prepared with 0.5 mol/L Fe²⁺. In addition, the reductive S species in FSD can maintain its catalytical activity by enhancing Fe²⁺ regeneration, and the FSD/PAA system has been proven to be effective in the degradation of various organic pollutants under practical and complex environmental conditions.

Photocatalysis is widely employed to treat emerging pollutants in water, due to its well-organized attributes. Self-sensitive carbon nitride (SSCN) represents a novel class of non-metallic photocatalyst that has garnered significant attention for its distinctive properties in contrast with traditional graphitic carbon nitride (g-C₃N₄). However, their visible-light photodegradation effect remained still to be enhanced. Here, SiO₂ microspheres were initially synthesized by the Stöber method, followed by the preparation of SiO₂/SSCN composites through an in-situ hydrothermal process. Their microstructure, phase structure, and photoelectric properties were systematically investigated using a combination of characterization techniques. It is discovered that the SiO₂ within the composites effectively disperses in the SSCN. The obtained composite material was then applied to photocatalytic degradation of antibiotic pollutants in water, exhibiting enhanced degradation activity, which was closely correlated with the quantity of SiO₂. At mass ratio of SiO₂ to SSCN of 0.04 : 1, the composite achieved optimal photocatalytic activity and demonstrated good stability. After irradiation for 60 min, 42% of tetracycline hydrochloride was degraded, and the photocatalytic degradation efficiency remained at 38% after 5 cycles. Furthermore, incorporation of the SiO₂ component offers supplementary sites for the dispersion of SSCN, mitigating serious agglomeration phenomenon of SSCN. This facilitates the rapid decomposition of 1,3,5-triazine oligomers (TBO) on the surface of SSCN under light irradiation, and the optimizing content of TBO on surface active sites. Consequently, utilization efficiency of visible light on SSCN is significantly improved, and a higher separation rate of photogenerated electron-hole pairs is simultaneously observed. These attributes culminate in significantly improved photocatalytic activity for the degradation of tetracycline hydrochloride on SSCN under visible light irradiation. Above advantages may position the as-synthesized SiO₂ dispersed SSCN as prospective candidate for practical application. Therefore, this research offers a novel route for enhancing the photocatalytic activity and stability of catalysts.

TiO₂ nanomaterials are widely used photocatalysts due to high photocatalytic activity, good chemical stability, low cost, and nontoxicity. However, its lower photon utilization efficiency is still limited by larger bandgap width and higher recombination rate between photon and hole. In this study, two-dimensional TiO₂ nanosheets were synthesized via microetching, which were then inserted by ruthenium atoms to form an efficient photocatalyst Ru@TiO₂ with sandwich structure. The surface morphology, electronic structure, photoelectric properties, and photocatalytic degradation performance of tetracycline hydrochloride of Ru@TiO₂ sandwich structure were investigated using different measurements. Results indicated that the material’s photoresponse range extended from UV to visible- near-infrared regions, improving photon absorption and carrier separation efficiency while enhancing photocatalytic activity. Under simulated sunlight irradiation (AM 1.5 G, 100 mW·cm^-2) for 80 min, sandwich structured Ru@TiO₂ efficient photocatalyst exhibited superior degradation performance on tetracycline hydrochloride with a degradation efficiency up to 91.91%. This work offers an effective way for the construction of efficient TiO₂ based photocatalysts.

Construction of heterojunction can effectively suppress the swift recombination of photogenerated electrons and holes in photocatalyst. In this study, a II/Z-type Bi₂MoO₆/Ag₂O/Bi₂O₃ heterojunction photocatalyst was synthesized using a solvothermal method combined with calcination. Various techniques were ultilized to examine the composition, morphology and photoelectrochemical properties of the as-prepared materials. The findings revealed that the optimal composition of the composite material was 25%ABOBM (with a mass ratio of Ag₂O/Bi₂O₃ and Bi₂MoO₆ of 1 : 4). Under visible light irradiation, the degradation efficiency of tetracycline (TC) by 25%ABOBM reached 85.6%, which was significantly higher than that of Ag₂O/Bi₂O₃ and Bi₂MoO₆, and maintained its good stability after three cycles of experiments. The enhanced photocatalytic performance of 25%ABOBM is attributed to the formation of heterojunctions and the unique morphologies among Ag₂O, Bi₂O₃ and Bi₂MoO₆. Both h⁺ and ·O₂^- are significant contributors, while ·OH and ¹O₂ have secondary roles in the degradation process of TC, as indicated by free radical capture experiment and electron paramagnetic resonance spectroscopy (EPR). Furthermore, the related photocatalytic mechanisms were explored, and the potential degradation pathways of TC were analyzed using liquid chromatography-mass spectrometry (LC-MS). This study offers a novel approach to the preparation of photocatalysts with dual heterojunctions and demonstrates their application in the degrading organic pollutants.

Preparation of alkali metal doped g-C₃N₄ materials is an important branch in the research of g-C₃N₄ semiconductor photocatalytic materials. However, there is still lack of study on g-C₃N₄ materials revealing mechanisms in photosensitizer-assisted photocatalytic degradation. In this study, Na⁺ doped g-C₃N₄ photocatalysts (Na⁺/g-C₃N₄) were prepared using solution synthesis, calcination, and solvothermal reaction methods.The doped position of Na⁺ in g-C₃N₄ and photoelectric performance were determined. The changes of morphological, specific surface area, and pore size of Na⁺/g-C₃N₄ materials were analyzed by scanning electron microscopy, N₂ adsorption and desorption experiments. In Na⁺/g-C₃N₄ materials, the Na⁺ loaded in a cyclic structure composed of three heptazine structural units, coordinating with N atoms. Na⁺/g-C₃N₄ changed the adsorption performance of g-C₃N₄, altered its bandgap width and position of conduction (valence) band, and increased its separation rate of photogenerated electrons and holes and charge transport rate of the material by affecting the π-conjugated system of g-C₃N₄. During the solvothermal reaction process for synthesis of Na⁺/g-C₃N₄, strong hydrolysis caused decomposition of unstable structures of g-C₃N₄ while the C-O^- bonds were formed at the edge of g-C₃N₄. The physical and chemical adsorption sites for methylene blue (MB) of Na⁺/g-C₃N₄ materials are confirmed by π-conjugated system and C-O^- bonds of Na⁺/g-C₃N₄, by which Na⁺/g-C₃N₄ materials can adsorb MB up to 93.25%, in contrast to the g-C₃N₄ materials’ adsorbtion only up to 24.50%. Under visible light irradiation, due to their strong adsorption capacity and photosensitivity to MB, Na⁺/g-C₃N₄ materials have constructed a unique photosensitive- photocatalytic degradation system with MB. MB not only acts as the photosensitizer for self degradation but also collaborates with Na⁺/g-C₃N₄ materials for photocatalytic degradation. At pH 6.0, the maximum degradation rate of MB is up to 96.40% in the photosensitive-photocatalytic system constructed with MB and Na⁺/g-C₃N₄ samples.

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.