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

[Display omitted] •Cl- and NO3– effect on HTCC configuration and photocatalytic ability was discussed.•Zn2+ catalysis promoted the SMX removal by hydrothermal carbon.•The effect of Zn2+ is not reduced by Cl- due to its absence in HTCC formation.•NO3– decimates the promotion role of Zn2+ by participating in glucose transformation. 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 Ca2+, Mn2+, Fe3+, Zn2+, and Ni2+ 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. Zn2+ 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 ZnCl2 catalyzed system, the promotion effect of Zn2+ was not influenced by anion due to Cl- absence in glucose transformation. While in Zn(NO3)2 catalyzed system, less levulinic acid (LA) led to less surface C = O, and NO3–, the powerful oxidant under acidic conditions was reduced to –NH2, 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 Zn2+.