Abatement of methylene blue and diazinon pesticide from synthetic solutions using magnetic biochar from pistachio shells modified with MOF-808.

This study develops a magnetic composite from pistachio shell biochar (PSBC/CoFe₂O₄) modified with MOF-808 for removing methylene blue (MB) dye and diazinon (DA) pesticide from water. The composite, with a surface area of 151.53 m/g and magnetic saturation of 19.653 emu/g, allowed easy separation from solutions. Key adsorption factors such as pH, temperature, contact time, adsorbent dosage, and initial pollutant concentration were optimized. Maximum removal efficiencies of 99.32% for MB and 99.14% for DA were achieved at adsorbent dosages of 1 g/L for MB and 1.5 g/L for DA, initial concentrations of 5 mg/L, temperatures of 55 °C, contact times of 60 min for MB and 80 min for DA, and pH levels of 9 for MB and 6 for DA. Thermodynamic analysis confirmed that the adsorption process is spontaneous and endothermic, with enthalpy values of 55.091 kJ/mol for MB and 42.028 kJ/mol for DA, while entropy values indicated increased randomness during adsorption. Kinetic studies revealed that adsorption involved both physical and chemical interactions, with intraparticle diffusion not being the rate-limiting step. The Freundlich isotherm model provided the best fit (R = 0.971 for MB and 0.988 for DA), highlighting heterogeneous surface interactions. The composite showed higher adsorption capacities for MB (31.44 mg/g) than for DA (21.49 mg/g) and exhibited excellent regeneration potential, performing better in deionized water due to the inhibitory effects of salts in non-deionized water.