Computational Exploration of Charge Transfer Dynamics in Dye Sensitized SnO2 and ZnS for Photocatalytic Applications

Abstract

A computational study of some novel charge transfer complexes, prepared by the adsorption of dyes on SnO2 and ZnS was carried out using semiempirical PM3 method. The two natural dyes, 1S,3R,4R,5R-3-(3,4-dihydroxyphenyl)acryloyloxy)-1,4,5-trihydroxycyclohexane carboxylic acid (DTC) and 2-Phenyl-4H-chromen-4-one (PHC) were adsorbed independently on to 1×1×1 SnO2 and ZnS crystals to form SnO2-DTC, SnO2‌-DTC-PHC and ZnS-DTC adsorption complexes. The theoretical electronic absorption spectra calculated via PM3 method revealed a large bathochromic shift to 958 nm and 577 nm for SnO2-DTC and SnO2-DTC-PHC, respectively, indicating the formation of charge transfer complex. Moreover, the bandgap was reduced to 1.29 and 2.15 eV as compared to 3.4 eV of pristine SnO2. Subsequently the adsorption of DTC on ZnS was accomplished and calculations were performed to determine the spectroscopic properties of the complex, where a considerable red shift was observed for ZnS-DTC as well. The semiempirical PM3 calculations evidenced stability of SnO2-DTC, SnO-DTC-PHC and ZnS-DTC as predicted from negative adsorption energy values. The positions of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) as obtained from single point energy calculations, were concomitant with proposed photocatalytic mechanisms.