Optimization and kinetic studies for degradation of insecticide monocrotophos using LR grade and P25 TiO₂ under UV/Sunlight conditions

Abstract

Photocatalytic degradation of monocrotophos (MCP), an organophosphorous insecticide, present as a severe contaminant in surface water was studied in slurry batch photoreactor by using Aeroxide P‐25 and LR (laboratory reagent) grade TiO2 as catalysts. Effect of varying parameters such as initial concentration, catalyst loading, area/volume ratio, pH of the solution, light conditions and intensities, and types of the catalyst has also been studied. Aeroxide P25 showed better degradation efficiency than LR grade TiO2 in both UV and sunlight conditions under optimized parameters. Optimum degradation of 25 ppm MCP was observed under UV light (30 W m−2), at solution pH 5 and catalyst loading of 2.5 g L−1 in both catalyst (LR & P25) cases. Chemical oxygen demand (COD) analysis of samples was performed in order to authenticate the mineralization of MCP. The disappearance of MCP in slurry reactor obeys first order kinetics. The rate of degradation shows a notable enhancement (15%) by the addition of small quantities of oxidant (H2O2) in sample solution with LR TiO2, under both UV and sunlight conditions. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1201–1208, 2014

Photocatalytic Reduction and Crystallization Hybrid System for Removal and Recovery of Lead (Pb)

“…At low photocatalyst concentration, the photoreduction reaction is primarily controlled by the active sites present on the surface of the photocatalyst, which are available on it for the sorption of light and heavy metals. However, at high concentration, the slurry induces increased solution turbidity, which causes a screening effect and consequently enhances the prevalence of light dispersion, thereby decreasing light transmission through the aqueous phase and resulting in lower photoreduction of Pb 2+ . ,,, Therefore, for further reduction experiments using TiO 2 , the optimal catalyst loading of 2 g L –1 was employed.…”

“…This is attributable to the fact that the photocatalyst active sites are easily occupied by Pb 2+ ions at low initial concentration, resulting in high efficiency, whereas high Pb 2+ ions saturate the available active sites and therefore reduce the photon absorption by the photocatalyst, resulting in a decrease in the photoreduction of lead ions (Pb 2+ ). In heterogeneous media, the Pb 2+ photoreduction rate was observed to obey the Langmuir–Hinshelwood rate equation with respect to the initial concentration of Pb 2+ . ,, where r o is the initial rate of reduction of lead, k r is the reaction rate constant, K is the equilibrium constant, and C o is the initial concentration. The initial reaction rates were evaluated at various initial lead concentrations from the concentration ( C ) versus time (t) curve (Figure ).…”

“…However, at high concentration, the slurry induces increased solution turbidity, which causes a screening effect and consequently enhances the prevalence of light dispersion, thereby decreasing light transmission through the aqueous phase and resulting in lower photoreduction of Pb 2+ . 18,29,34,35 Therefore, for further reduction experiments using TiO 2 , the optimal catalyst loading of 2 g L −1 was employed.…”

“…In a batch reactor, the solution was magnetically stirred throughout the entire experiment for 180 min. Our previous work describes the specifications and setup of the UV chamber used for carrying out this experimental work …”

“…Our previous work describes the specifications and setup of the UV chamber used for carrying out this experimental work. 29 For the reduction crystallization process, the prepared lead ion (Pb 2+ ) solution (concentration 100 mg L A specific quantity of hydrazine (2 M) was added to the solution when the temperature exceeded 50 °C. The pH of the metal solution was adjusted to 10 using the sodium hydroxide (1 M) solution.…”