Enhanced photodegradation of methylene blue by silica coated ZnSe nanoparticles

Abstract

Herein, we report synthesis of silica-coated ZnSe nanoparticles (SZNPs), by varying the mass to volume ratio of ZnSe : TEOS i.e. mass to mass ratio of ZnSe : SiO₂ ranging from 0.0267 to 0.1071. These SZNPs showed enhanced photodegradation of methylene blue (MB) solution under visible light. Silica coating on ZnSe NPs  reduces the toxicity concerns for its wide use as photocatalyst. XRD of bare ZnSe NPs confirms hexagonal crystal structure, and TEM depicts size range of SZNPs around 7 nm. FTIR and Raman measurements confirm the presence of different chemical and silanol groups attached to bare ZnSe and SZNPs. Optical absorption and photoluminescence (PL) show a red shift due to silica coating on ZnSe NPs compared to bare ZnSe. This is due to silanization of ZnSe, as silica shell reduces the recombination of photon-generated electron and hole pairs. Photocatalytic experiments on methylene blue (MB) by bare and SZNPs have been conducted, optimal SZNPs i.e. 0.0535 sample (mass ratio of ZnSe:SiO₂) exhibits enhanced photo-generated free radicals. An increase in photodegradation of SZNPs, i.e. from 35 to 46% has been observed compared to bare counterparts (ZnSe). Stability decreased by only 7% after 4^th cycle of reuse, depicting efficacy of the SZNPs photocatalyst in the degradation of MB. A pseudo-first-order reaction kinetics has been observed for photodegradation of MB with highest rate constant of 8.6 × 10^-3 min^-1 for SZNPs (1.0000:0.0535) sample.