Assessing the potential of modified rice husk-based Silica adsorbent for the removal of Atrazine from wastewater

Abstract

Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) or (2-chloro-4-(ethylamino)-6-(isopropylamino)-1,3,5-triazine) is a very common herbicide used on large scale farming to control weeds by farmers and it must be removed from the wastewater because of the serious harm it causes to the environment and its health risk to human. This research aimed at the use of modified rice husk derived silica adsorbent from waste agricultural biomass for atrazine removal from wastewater. The adsorbent was made by the process of pyrolysis, chemically activated with 7.5% Potassium Hydroxide. The characterisation results by the Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy showed that the modified rice husk-based silica adsorbent has good pore structure, oxygen containing functional groups and silica properties. The influence of contact time, adsorbent dosage, initial concentration and pH were investigated by use of a UV-Vis spectroscopy analysis. The adsorption studies were conducted in batch mode, and the results showed that the modified rice husk-based silica adsorbent exhibited high adsorption capacity for atrazine. The adsorption data were fit to several isotherm models such as Langmuir and Freundlich, and kinetic models such as pseudo-first order and pseudo-second-order reactions. The experiments showed that the adsorption process obeyed the Freundlich isotherm and pseudo-second order kinetic model, which means it followed a multi-layer adsorption mechanism and chemisorption which showed sharing of electrons between the adsorbate and the adsorbent. The highest adsorption capacity obtained was 702 mgg-1, which is like other reported adsorbents in the literature. The adsorbent was also discovered to be recyclable, suffering only a small decrement in adsorption capacity after five adsorption-desorption cycles. UV-visible spectrophotometer analysis confirmed the efficient removal of atrazine from wastewater using the modified rice husk-based silica adsorbent. In general, this research shows that the modified rice husk-based derived silica adsorbent can be used as a cheap and environmentally friendly material for the removal of atrazine from wastewater.