Biosynthesized CS-MgO/zeolite hybrid material: An efficient adsorbent for chlorpyrifos removal - Kinetic studies and response surface methodology

The prevalence of organophosphate pesticides in aquatic environments raises severe concerns on a global scale. Chlorpyrifos, an insecticide, is included in a class of organophosphate pesticides. It is widely used on agricultural lands to control pests in cotton, fruit, and vegetables. The acute toxicity of chlorpyrifos is still dangerous to all aquatic living organisms. Then the treatment of water contaminated with chlorpyrifos is an important aspect. The recent decade has witnessed adsorption technology emerging as an advanced organophosphate pesticide wastewater treatment with great potential and a grand blueprint, in which the specific surface area and active sites of the adsorbent are considered to be the two most important characteristics largely impacting the adsorption performance. In this study, a CS-MgO/Zeolite composite was prepared by the microbial method as an effective adsorbent for the removal of chlorpyrifos from an aqueous solution. The adsorbent's properties were carefully characterized using X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The refinement of experimental conditions, encompassing variations in adsorbent dosage, contact time, and chlorpyrifos concentration at five discrete levels, was systematically undertaken through the utilization of a composite central design rooted in response surface methodology. The solution pH played a key role in chlorpyrifos removal, and a pH of 7.0 was selected according to its high adsorption ability. The highest removal (80.9%) of chlorpyrifos by CS-MgO/Zeolite was obtained at an optimum pH of 7, a contact time of 40 min, an adsorbent dosage of 0.4 g/L, and a chlorpyrifos concentration of 5 mg/L⁻¹. The adsorption results were highly fitted with the Freundlich adsorption isotherm model, and the maximum adsorption was 83.3 mg/g. Kinetic studies indicate that the removal of chlorpyrifos followed the pseudo-second-order model of adsorption (0.994). The thermodynamic parameters indicate the spontaneous and endothermic nature of chlorpyrifos sorption on CS-MgO/Zeolite sorbent. The results revealed that introducing chitosan could improve the adsorption capacity and rate effectively even though it sacrificed part of the specific surface areas of the MgO/Zeolite, indicating that active sites might play a dominant role during chlorpyrifos adsorption. The fabricated CS-MgO/Zeolite adsorbent nanocomposite displayed high reusability based on the elution and simultaneous regeneration ability. Therefore, as a cheap green nanocomposite adsorbent with high adsorption performance for chlorpyrifos, the CS-MgO/Zeolite nanocomposite adsorbent is expected to become one of the best candidate materials for chlorpyrifos removal aqueous solutions.