Examining the Kinetics and Thermodynamics of Chlorpyrifos Adsorption unto Activated Mucuna pruriens Seed Shell

Abstract

The excessive use of pesticides (chlorpyrifos) in modern agriculture has increased chlorpyrifos in water. Hence, there is a need for imperative attention on alleviation of the negative impacts. This study evaluated the possible use of Mucuna pruriens seed shell (MPSS) as a bio-sorbent. MPSS was treated and activated by adding 1M of H₃PO₄, characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope-Energy dispersive X-ray (SEM-EDX) and Brunaer-emmett-teller (BET). The maximum efficiency of CLPF adsorption onto MPSS was 94.43% at optimum conditions of 30 mg/l adsorbate concentration, pH 6, and MPSS dosage of 0.5g/100ml. From the Isotherm results, all the models except Halsey describe the system well, but Temkin at 30 ^oC produced the best fit, with the highest correlation, R² of 0.9995 with the amounts adsorbed at 30, 35 and 40 ^oC to be 11.75 mg g^-1, 30.90 mg g^-1 and 51.29 mgg^-1 respectively. Pseudo second-order best described the kinetics study with the R² value of 0.9987. Thermodynamic parameters of ΔH⁰, ΔS⁰ and ΔG⁰ values at optimum temperature (40^oC) were -0.008 KJ/mol, -0.441 KJ/Kmol and +0.134 KJ/mol respectively. The adsorption process was practicable and accepted with cation exchange between the adsorbate and adsorbent as the rate-limiting phase. Experimental results illustrate that adsorption capacity increased with pH, sorbent dosage and concentration. Conclusively, MPSS is an efficient adsorbent for removing chlorpyrifos.