With the development of industry, agriculture, and aquaculture, excessive ammonia nitrogen mainly involving ionic ammonia (NH₄⁺) and molecular ammonia (NH₃) has inevitable access to the aquatic environment, posing a severe threat to water safety. Photocatalytic technology shows great advantages for ammonia nitrogen removal, such as its efficiency, reusability, low cost, and environmental friendliness. In this study, CP (g-C₃N₄/CoP) composite materials, which exhibited high-efficiency ammonia nitrogen removal, were synthesized through a simple self-assembly method. For the optimal CP-10 (10% CoP) samples, the removal rate of ammonia nitrogen reached up to 94.8% within 80 min under visible light illumination. In addition, the nitrogen selectivity $S\left(N_2\right)$ is about 60% for all oxidative products. The high performance of the CP-10 photocatalysts can be ascribed to the effective separation and transmission of electron–hole pairs caused by their heterogeneous structure. This research has significance for the application of photocatalysis for the remediation of ammonia nitrogen wastewater.

Harmful algal blooms pose a serious threat to aquatic ecosystems and drinking water safety, calling for efficient and sustainable algal control strategies. In this study, the chitosan modified g-C₃N₄ photocatalyst was developed for visible light driven inactivation of Microcystis aeruginosa. Chitosan modification changed the surface charge of g-C₃N₄ from negative to positive, which strengthened the electrostatic interaction between the photocatalysts and negatively charged algal cells, which promoted close interfacial contact. Among the prepared samples, CNS-75 exhibited the best performance, achieving approximately 93% algal inactivation within 3 h under visible light. This enhanced activity was attributed to the combined effects of improved algal cell capture and enhanced in situ H₂O₂ generation. Evans blue staining and SEM observations indicated that the treated algal cells underwent membrane integrity loss and obvious morphological deformation. To further utilize the photocatalytic generated H₂O₂, MIL-88A was introduced to construct a self-supplied photocatalytic Fenton coupled system. The optimized coupled system achieved approximately 90% algal inactivation within 2.5 h, indicating accelerated inactivation compared with photocatalysis alone. Biochemical indicators in the coupled system further suggested enhanced oxidative damage to algal cells. The present work highlights the potential of photocatalysis-based technology for efficient algal remediation.

Harmful algal blooms (HABs) pose a serious threat to aquatic ecological security, necessitating efficient and sustainable algal cell inactivation technologies. In this study, a magnetic Fe3O4/MIL-88A(Fe) composite (Fe/M) was synthesized and integrated with ultrasound to enhance persulfate (PDS) activation for the efficient inactivation of Microcystis aeruginosa. The Fe/M/PDS system alone achieved 83% inactivation efficiency within 4 h, whereas an alternating stirring-ultrasonication protocol enhanced this to 99%. Ultrasound effectively disrupted the extracellular polymeric substances (EPS) barrier and facilitated oxidative species transport into cells, thereby mitigating interfacial mass transfer limitations. Quenching experiments and ESR spectroscopy confirmed SO4·- and O2·- as the dominant reactive species, with ·OH and 1O2 contributing synergistically. Cycling tests demonstrated robust composite stability, retaining 71% efficiency after three consecutive runs. This ternary ultrasound-Fe/M-PDS system integrates efficient oxidation, magnetic retrievability, and tolerance to water matrix variations, offering a promising approach for algal bloom remediation.