Adsorption and photocatalysis kinetics of herbicide onto titanium oxide and powdered activated carbon

Abstract

The adsorption and photocatalysis kinetics of metsulfuron-methyl (MM) onto titanium oxide (TiO 2) and powdered activated carbon (PAC) were studied at varying adsorbent amount and MM concentration. The overall mass transfer in adsorption was estimated from concentration decay curves obtained in the batch adsorber. The maximum adsorption capacity decreased with increasing adsorbent amount in TiO 2 adsorption. The adsorption isotherms of MM could be plotted using the Langmuir isotherm model with a reasonable degree of accuracy having higher r 2 values rather than Freundlich isotherm model. Linear driving force approximation (LDFA) kinetic equation with Langmuir adsorption isotherm model was successfully applied to predict the adsorption kinetics data in various concentrations of MM in photobatch reactor. The estimated mass transfer coefficient was used to be 3.0 × 10 −5, 5.5 × 10 −5, 9.1 × 10 −5 m/s in PAC adsorption and 2.0 × 10 −5, 1.1 × 10 −5, 9.0 × 10 −6 m/s in TiO 2 adsorption for a different MM concentration of 20, 50 and 70 mg/L, respectively. Photocatalysis kinetics was same with TiO 2 of 0.2 g/L regardless of TiO 2 amounts and the MM degradation kinetics was enhanced by TiO 2 catalysis rather than only UV light degradation. Among the photocatalysis kinetics model with first-order, second-order and Langmuir–Hinshelwood (L–H) model, a second-order kinetic model was found to well present the experimental data of MM by TiO 2 catalyst for the range of various TiO 2 amounts and MM concentration studied.