Synthesis and characterization of zinc stannate nanostructures for the adsorption of chromium (VI) ions and photo-degradation of rhodamine 6G

Abstract

The zinc stannate nanostructure was synthesized via sol-gel route and its physicochemical, adsorption and photocatalytic properties were studied. The specific surface area (S) was calculated by Brunauer–Emmett–Teller (BET) and Barrett, Joyner and Halenda (BJH) methods using N2 adsorption-desorption. The SBET and SBJH were found to be 105 and 138 m2 g−1 respectively with the average pore size of 2.5 nm. Based on diffraction data, cubic geometry was assigned to the crystallites with average size of 31.74 nm. The morphology of the particles was studied though transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and the average particles size as calculated from TEM was 21.6 nm. The band gap calculated from the diffuse reflectance spectrum was 3.36 eV. The percentage composition and purity were determined by energy dispersive X-ray (EDX), whereas surface functional moieties were detected by Fourier transform infrared (FTIR) spectroscopy. The batch method was used to study the adsorption of Cr(VI) ions by varying, initial electrolyte concentration, pH, and temperature of solution. The parameters extracted from Langmuir and Freundlich models shows that the adsorption process was more feasible at higher temperature and lower pH. The maximum sorption capacity of the adsorbent was found to be 32.81 mg g−1. The 1:1 exchange mechanism was proposed between Cr(VI) and surface protons while the thermodynamic study reveals the endodermic nature of the adsorption process. The photocatalytic performance of the zinc stannate was examined against Rhodamine 6G where 98.17% degradation was achieved in 390 min.