An alternative to in situ photocatalytic degradation of microcystin-LR by worm-like N, P co-doped TiO2/expanded graphite by carbon layer (NPT-EGC) floating composites

•NPT-EGC floating photocatalyst was synthesized by a facile sol-carbonization method.•NPT-EGC can be an alternative to in situ degradation of MC-LR using solar light.•NPT-EGC450 achieved a high removal rate of MC-LR (99.4%) within 9 h.•Coexisting substances exhibit competitive adsorption or photosensitization effect.

In recent years, harmful algal blooms (HABs) frequently occur in eutrophic lakes all over the world. It causes the accumulation of microcystin-LR (MC-LR) in water, thus giving a great threat to aquatic animals and human beings. In this paper, a facile sol-carbonization method was used to synthesize N, P co-doped TiO2/expanded graphite by carbon layer (NPT-EGC) floating photocatalysts, which are designed for in situ photocatalytic degradation of MC-LR. XRD, N2 adsorption/desorption, FESEM/EDS, TEM, FTIR, XPS, UV-vis DRS and the PL spectrum were used to investigate the physicochemical and photoelectricity properties of the NPT-EGC photocatalysts. The results showed that NPT-EGC has a worm-like structure with N, P co-doped TiO2 particles distributed on the surface. The calcination temperatures have influences on the forming of TiO2 and carbon layer, specific surface area and photocatalytic activity. Among the different NPT-EGC photocatalysts, the photocatalyst calcined at 450 °C (NPT-EGC450) exhibited the strongest photo-absorption and the lowest recombination rate of photo-generated charge carrier. As a result, NPT-EGC450 achieved the highest removal rate of MC-LR (99.4%) following 9 h of irradiation, which is mostly attributed to photocatalytic degradation. LC-MS analysis showed most MC-LR molecules have been mineralized into small molecules. After three consecutive cycles, the NPT-EGC floating photocatalyst exhibited excellent reusability and stability, which indicates the floating photocatalysis is a promising technique for MC-LR degradation in the future.

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