Organophosphorus Diazinon Pesticide Removing from Aqueous Solution by Zero-Valent Iron Supported on Biopolymer Chitosan: RSM Optimization Methodology

Abstract

In this study, chitosan/zero-valent iron nanoparticle (CS/nZVI) composite was synthesized for the removal of diazinon as an organophosphorus pesticide from aqueous solution. Characterizations of the synthesized composite were identified by the scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometer (VSM), Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA), and differential scanning calorimetric (DSC). The surface area was obtained 90.164 m2 g−1 and 92.142 m2 g−1 by the BET method and Langmuir plot, respectively. The surface area, volume, and pore diameter of CS/nZVI were found 86.923 m2 g−1, 0.1623 cm3 g−1, and 1.85 nm, respectively from the pore size distribution curves using the Barrett–Joyner–Halenda (BJH) formula. The analysis of samples was accomplished with gas chromatography (GC). Response surface methodology (RSM) based on the central composite design (CCD) was applied to design the experiments, and survey the effects of factors on the adsorption efficiency. Analysis of variance (ANOVA) indicated that pH, adsorbent dosage, and initial concentration had a significant influence on the removal performance using the second-order polynomial model. The highest removal percent of the CCD method was equal to 96.95% in the optimum conditions. The effect of experimental variables such as contact time, pH, adsorbent dosage, and initial concentration of diazinon on the removal of diazinon was investigated. Results showed that the contact time of 20 min, pH 4.6, CS/nZVI dosage of 0.05 g, and initial diazinon concentration of 100 mg l−1 were achieved as optimum conditions. In addition, the adsorption data fitted well with the pseudo-second-order kinetic model (R2 = 0.9989) and Freundlich isotherm (R2 = 0.9629). Eventually, the results of diazinon removal from the aqueous real samples revealed the great applicability of CS–nZVI for the removal of diazinon.