Enhanced Adsorptive Removal of Chlorpyrifos and Malathion by Functionalized Mesoporous Silica: A Detailed Insight Into Kinetics, Isotherm, and Statistical Surface Modeling

Chlorpyrifos and malathion are both widely used pesticides that pose significant hazards to the environment. Siliceous MCM-48 functionalized with 3-Aminopropyltriethoxysilane modification (AMCM-48) was employed as a highly efficient adsorbent, achieving removal capacities of 957 and 540 mg g^-1 for chlorpyrifos and malathion, respectively. The presence of characteristic XRD patterns in the range 2θ = 2-5°, along with BET surface areas of 787 and 593 m² g^-1, ascertained the retention of the mesoporous structure during functionalization. A subsequent drop in the surface area to 197 and 191 m² g^-1 indicates that chlorpyrifos and malathion are, respectively, adsorbed onto the internal pores of AMCM-48. FTIR and EDX characterization confirmed the uptake of pesticide molecules by AMCM-48. The maximum removal efficiency of CP (90.02%) was obtained within 27 min, when 90 mg L^-1 of CP was contacted with 40 mg of AMCM-48, at 31 °C. MTH uptake was 86.24% when 12 mg L^-1 was contacted with 35 mg of adsorbent at 41 °C, optimized by RSM-CCD. The adsorption parametric studies fitted well into the Langmuir model and pseudo-second order kinetics. The thermodynamic parameters (Δ<i>G</i>°, Δ<i>H</i>°, and Δ<i>S</i>°) indicated the exothermic and spontaneous nature of adsorption. The above analyses indicated that the adsorption was primarily driven by high surface area, hydrogen bonding, dipole-dipole interactions, and electrostatic forces. Desorption at higher pH achieved approximately 85% recovery, reflecting reversible physical interactions. AMCM-48 demonstrated excellent reusability, maintaining significant adsorption capacities for both pesticides over seven consecutive cycles. Overall, AMCM-48 is a simple and sustainable adsorbent for efficient pesticide removal.