Effect of diethylene glycol and polyethylene glycol (M.W.600) on synthesis of TiO2 nanopowder and its application for chromium (VI) removal

Abstract

TiO₂ nanoparticles with different types of additive are prepared from alkoxide solutions via sol-gel method. The effects of diethylene glycol (DEG) and polyethylene glycol with molecular weight 600 (PEG 600) addition to the precursor solution on the TiO₂ properties and photocatalytic activity in chromium (VI) removal were studied. Results show that DEG and PEG 600 delayed the phase transformation from anatase to rutile phase. It was found that the long chain of PEG 600 can agglomerate the nanocrystal TiO₂ better than the short chain of DEG. Consequently, PEG 600 can accumulate the anatase and transform from the anatase to rutile phase in the lower temperature (500°C) comparing to DEG (600°C). Both DEG and PEG 600 also exerted the pronounced effect on reducing of nanocrystal size and increasing surface area of TiO₂ . The crystallite size of TiO₂ tends to increase with increasing of molecular weight of PEG as the PEG 600 can enhance the smaller size of TiO₂ as 18.84 nm comparing to 19.54 nm obtained from DEG. Adsorption characteristics for both of TiO₂ from DEG and PEG 600 are well described by Langmuir adsorption isotherm. For photocatalytic process, with initial concentration of chromium (VI) less than 50 mg/L, the kinetic pattern for both types of TiO₂ was followed zero order pattern. As the initial concentration of chromium (VI) was leveled up, the kinetic pattern was changed to be pseudo first order pattern. The intrinsic kinetic values of TiO₂ with DEG and PEG 600 were calculated with the value of the adsorption equilibrium constant (Kcr) was found to be 0.287 and 0.480 1/mg, respectively and the second-order rate constant (Kc) were obtained as 0.168 and 0.220 mg/1 min, respectively.