Nitrogen-doped hydrochars from shrimp waste as visible-light photocatalysts: Roles of nitrogen species.

The increasing shrimp waste production has caused severe environmental problems. In this study, nitrogen-doped hydrochars (NDHCs) were facilely synthesized from shrimp waste and glucose by one-pot hydrothermal carbonization (HTC). The characterizations showed that NDHCs had large surface areas of up to 30.5 m2 g-1 with numerous functional groups on their porous surfaces. The nitrogen content (1.3-2.8%) and species distribution in NDHCs were associated with the amount of added glucose. These NDHCs were applied as visible-light-induced photocatalysts, and their photocatalytic performances were evaluated by methylene blue (MB) degradation. The removal rate of MB reached 88.9% after 1 h of visible light radiation by NDHC-1, which was 2.3 times higher than that of glucose-derived hydrochar (GHC). The mechanism study showed that the improved photoactivity of NDHCs was attributed to the increased adsorption capacity by porous surface and the promoted formation of hydroxyl radicals by synergistic effects of quaternary N and pyrrolic N during photocatalysis. This study offered a green approach to preparing tunable, efficient, and low-cost photocatalyst from waste biomass and insight into the photocatalytic mechanism of hydrochar materials.