Effect of accompanying anion on the formation pathway and photocatalytic performance of metal-modified hydrothermal carbon

Metal modification can elevate the photocatalytic ability of hydrothermal carbonization carbon (HTCC), but the effect of accompanying anions in precursor metal salts is unclear. Taking Ca 2+ , Mn 2+ , Fe 3+ , Zn 2+ , and Ni 2+ as metal examples, HTCCs modified with metal chloride and metal nitrate were fabricated through a simple hydrothermal process using glucose as raw material. The photocatalytic performance for sulfamethoxazole (SMX) removal by chloride catalyzed HTCC was superior to its nitrate modified counterpart. Zn 2+ catalysis was profitable for surface C = O generation and furan polymerization, which promoted the SMX removal by hydrothermal carbon via a photosensitization-like mechanism. In ZnCl 2 catalyzed system, the promotion effect of Zn 2+ was not influenced by anion due to Cl - absence in glucose transformation. While in Zn(NO 3 ) 2 catalyzed system, less levulinic acid (LA) led to less surface C = O, and NO 3 – , the powerful oxidant under acidic conditions was reduced to –NH 2 , which interrupted the original polymerization route of 5-hydroxymethylfurfural (HMF) by participating in the pseudo-Michael reaction, leading to the low polymerization of hydrothermal carbon, and these changes decreased the photocatalytic performance of nitrate-modified HTCCs, thus counteracting the promotion effect of Zn 2+ .