The effect of sodium formate mediated double regulation in TiO2 photocatalytic reduction of cadmium

Highlights: • The effect of sodium formate on the reduction of cadmium in the sodium formate-P25 system was investigated. • P25 is selective for cadmium ions in the sodium formate-P25 system. • The superior photocatalytic performance mechanism for P25 forms chelates only with sodium formate to adsorb and reduce Cd²⁺ is proposed. -- Abstract: Investigating on the effect of sodium formate mediated double regulation in TiO₂ photocatalytic reduction of cadmium is firstly reported. Multiple characterized methods were used to characterize and confirmed the successful reduction of Cd²⁺ to the form of metal elements by sodium formate-P25 system. The metal elements were attached to the surface of the composite photocatalyst were directly observed by SEM. The removal efficiency of Cd²⁺ for the composite photocatalyst was tested. When the addition of sodium formate was 1 g/L, the maximum removal rate of Cd²⁺ was 94.8% within 10 min. Further experiments showed the mechanism and activity of the combined catalysis of sodium formate and photocatalysis and the role of composite photocatalyst in photocatalytic activity. This is mainly due to the bidentate chelation between sodium formate and TiO₂ which makes it possible to adsorb heavy metal ions and the transfer of photo-generated electrons on the bidentate complex, which improves the survival time of the electrons and reduces the metal ions.