Efficient visible light-driven in situ photocatalytic destruction of harmful alga by worm-like N,P co-doped TiO2/expanded graphite carbon layer (NPT-EGC) floating composites

The bloom of harmful algae in water has adversely affected water quality, local economies, and human health. Efficient visible light driven floating photocatalysts, namely N, P co-doped TiO2/expanded graphite carbon layer (NPT-EGC) composites, were successfully synthesized using a sol-carbonization method, and then applied as algaecides. The synthesized photocatalysts were characterized by means of XRD, FESEM/EDS, TEM, FTIR spectroscopy, XPS, UV-vis DRS, and PL spectroscopy. The results show that the NPT-EGC composites have a worm-like structure with the N, P co-doped TiO2 particles immobilized on the surface. Among the NPT-EGC photocatalysts with different calcination temperatures, NPT-EGC450 exhibits the highest photocatalytic activity. The removal rate of the algal cells is 98.15% for NPT-EGC450 following 9 h of visible light irradiation. The photocatalytic destruction process can be divided into a rapid adsorption phase and a repeat of the cell reduction phase-lag phase. During the photocatalytic process, the algal cells were damaged as a result of photocatalysis induced oxidation and inhibition. In addition, we simulated the release of MC-LR in the photocatalytic destruction process for the algal cells. The results show that the photocatalyst can remove both the algal cells and MC-LR simultaneously with high efficiency. After three consecutive cycles, the removal rate of the algal cells is still more than 90% for NPT-EGC450, which demonstrates that the NPT-EGC photocatalyst has good reusability and stability.