Biogenic magnesium oxide-rice husk biochar composite: synthesis, characterization, and optimization of pesticide sorption using response surface methodology

The use of pesticides in agriculture results in point and non-point pollution of ground and surface water bodies. Modifications of rice husk biochar to produce metal-biochar composites could exhibit high adsorption capacities. One pot synthesis of MgO doped rice husk biochar (MgO RHBC) composite was done to harness the benefits of both biochar and magnesium. The combination of 5 g of magnesium nitrate hexahydrate, 10 g of rice husk powder, and 200 mL of 5% purple-colored rice leaf extract (Crossa) were used to synthesize MgO RHBC for removal of three pesticides. Sorption kinetics study revealed that the Elovich, PSO, and PFO model had a better fit (R-2 similar to 0.999, lowest MSE, and chi(2) values) for the adsorption of thiamethoxam, chlorpyriphos, and fenpropathrin, respectively. Among the isotherm models, Sips isotherm model had a better fit (R-2 similar to 0.999, lowest MSE, and chi(2) values) for the adsorption of three pesticides. The calculated maximum adsorption capacity of MgO RHBC was 115.64, 89.47, and 78.73 mu g mg(-1) for thiamethoxam, chlorpyriphos, and fenpropathrin, respectively (total of 283.84 mu g mg(-1)) under the experimental conditions (dose, 30 mg; pH, 7; volume of adsorbate, 30 mL; contact time, 2 h; initial concentration, 130 mg L-1). Optimum conditions (dose, 23.70 mg in 30 mL; initial concentration, 75.00 mg L-1; and pH, 7.0) as obtained from response surface methodology using central composite design, resulted in 75.75, 79.65, and 77.66% removal of thiamethoxam, chlorpyriphos, and fenpropathrin, respectively. Thus, MgO RHBC could be an efficient and eco-friendly adsorbent for decontamination of pesticides from water.