Enhanced photocatalytic removal of Cd(II) from aqueous solution using Bi/S co-doped carbon quantum dots

Abstract

In this study, S and Bi Co-doped carbon quantum dots were synthesized and their application for Cd(II) removal was investigated. All the experiments were performed in batch mode and effect Bi/S ratio on pH was investigated. It was observed that 12 pH is most suitable for fast removal of Cd²⁺. The optimized Bi/S ratio was further investigated for effect of adsorbent dosage, initial concentration of Cd(II). Addition of four scavenger solvent namely formaldehyde, acetic acid, ethanediamine and methanol was investigated for enhancement in the photocatalytic activity. Maximum removal efficiency was observed with ethandiamine ∼94% at 300 ppm as compared to formaldehyde (∼90.3%), methanol (∼86.7%) and acetic acid(∼86.3%) indicating that amine group is more suitable as scavenger molecule. Adsorption isotherms of Cd(II) on Bi/S doped on CQD were fitted for different adsorption isotherm model namely Langmuir, Freundlich and Temkin isotherms. Both Lanmguir and Temkin isotherm were observed to fit well with R² value above 98% as compared to Freundlich with lower R² value (∼95.3%), indicating that a combination of chemisorption phenomenon as well as availability of energy of electron could be responsible for the Cd(II) removal. Thermodynamic parameters both enthalpy change and entropy change were estimated as −10.76 kJ/mol and −11.2 kJ/mol K. All three parameters were negative indicating that the process was spontaneous and exothermic.