In-situ active formation of carbides coated with NP–TiO₂ nanoparticles for efficient adsorption-photocatalytic inactivation of harmful algae in eutrophic water

Harmful algae pollution in eutrophic waters represents one of the most serious problems in natural water environment. Adsorption assisted photocatalytic inactivation is often considered as a promising method to achieve the clean-up of harmful algae and the remediation of eutrophic water. Here, we synthesize the NP–TiO₂ (nitrogen and phosphorous doped TiO₂)/C composites using a facile sol-gel method, and demonstrate successful achievement of efficient adsorption-photocatalytic performance via the in-situ formed carbides coated with NP–TiO₂ nanoparticles. We find that the composites have rough surfaces with porous structure, which can be tuned by the calcination temperature, and that such composites can be served to efficiently capture the algal cells. The N and P are successfully doped into the TiO₂ crystal lattices, and the cooperation of carbides and NP–TiO₂ particles enhances significantly light absorption, while inhibiting the recombination of the photogenerated charge carriers. Among all the NP–TiO₂/C composites, the NP–TiO₂/C system calcinated at 550 °C shows the best photocatalytic performance for the algal inactivation, presenting a removal rate of 92.6% following 6 h visible light irradiation. The destruction of cell structures is clearly observed in the photocatalytic process. Interestingly, the metabolic activities are also disturbed by the photogenerated radicals, which accelerates the death of algal cells. Moreover, the NP–TiO₂/C composite can effectively remove the cytotoxins from water, rendering the composite and the doping strategy promising in the remediation practice for eutrophic waters.