Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor–semiconductor heterojunction, the semiconductor–metal heterojunction, the semiconductor–carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degradation of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.

Many studies have shown the effect of solution chemistry on the environmental behavior of metal-based nanoparticles (NPs), except CuO NPs. Here, we investigated the agglomeration, sedimentation, dissolution, and speciation of CuO NPs by varying pH, ionic strength, ionic valence, and natural organic matter (NOM). The results showed that as the pH moved away from 6, the size of CuO agglomerates decreased, along with the enhanced NP suspension stabilization, due to the increase of electrostatic repulsive force. Increasing ionic strength and valence intensified the agglomeration and sedimentation of CuO NPs because of the compression of electrical double layers. The presence of humic acid and citric acid enhanced the dispersion and stabilization of CuO NP suspension, but l-cysteine showed a different impact. Decreasing pH, increasing ionic strength and all NOM improved the dissolution of CuO NPs, but the divalent electrolyte (CaCl₂) inhibited the Cu²⁺ release from CuO NPs compared to the monovalent electrolyte (NaCl). In addition, X-ray absorption near edge structure (XANES) analysis demonstrated that the presence of l-cysteine transformed more than 30% of CuO NPs to Cu(I)-cysteine by coordinating with thiol group. This study can give us an in-depth understanding on the environmental behavior and fate of CuO NPs in the aquatic environment.

A prerequisite for the development of photocatalysis techniques is to obtain photocatalysts with remarkable activity. Herein, we have reported BiOBr/WO₃ p–n heterojunctions as novel and efficient visible-light-driven photocatalysts. The BiOBr/WO₃ p–n heterojunctions have been prepared through an electrospinning–calcination–solvothermal method, and they all present a flower-like superstructure. The photocatalytic activities of these p–n heterojunctions are investigated by degrading rhodamine B (RhB), methyl orange (MO) and para-chlorophenol (4-CP) under visible light irradiation (λ > 400 nm), respectively. When RhB serves as the target pollutant, all BiOBr/WO₃ p–n heterojunctions with different theoretical molar ratios of BiOBr and WO₃ (1/0.5, 1/1, 1/2) exhibit higher photocatalytic activity than pure WO₃ or BiOBr. Especially, the BiOBr/WO₃ p–n heterojunction with a molar ratio of 1/1 displays the highest photocatalytic activity among all the as-synthesized catalysts, even higher than the activity from the mixture of two individual photocatalysts with the same weight of components (WO₃ and BiOBr). In addition, when MO or 4-CP acts as the target pollutant, the BiOBr/WO₃ p–n heterojunction with a molar ratio of 1/1 still exhibits excellent photocatalytic performance. Furthermore, the recycling experiment confirms that the BiOBr/WO₃ p–n heterojunction is essentially stable during the photocatalytic process. The enhanced photocatalytic activity of the BiOBr/WO₃ p–n heterojunction is predominantly attributed to the efficient separation of photogenerated electrons and holes. The photogenerated holes (h⁺) and superoxide radical anions (˙O₂ ⁻) have been found to be the primary reactive species responsible for the nearly complete mineralization of RhB dye in water.

This study, for the first time, rendered crab shell activated biochar modified by potassium hydroxide (KOH) impregnation (CSAB), revealing a new potential application in the removal of diesel oil from oily wastewater. The structural characteristics of crab shell biochar (CSB) and CSAB were investigated by SEM, and the crystal structure and optical properties of as-prepared samples were analyzed using XRD and FTIR. Results showed that CSAB had stratified surface structure morphology, abundant functional groups, and that its high specific surface area could reach up to 2441 m²/g, which was about eight times larger than that of untreated CSB (307 m²/g). An adsorption isotherm study indicated that the actual adsorption process both of CSAB and CSB were found to fit better with the Freundlich equation. Moreover, chemical interaction controlled the adsorption kinetics efficiency while the adsorption equilibrium capacity was 93.9 mg/g. Due to its highly developed pore structure, unique surface characteristics, and effective adsorption performance, this low-cost activated carbon had the potential to serve as an efficient adsorbent for water pollution purification.

A flower-like Bi₂S₃/Bi₂MoO₆ heterojunction has been prepared via a solvothermal method and it exhibits stable and remarkable enhanced photocatalytic activity.