Effective Co2+ removal from aqueous solution and industrial wastewater using ZIF-7 and MnFe2O4-modified walnut shell biochar composite

In this study, we developed a novel magnetic composite of walnut shell biochar (WSB) and modified it with ZIF-7 for the purpose of removing Co 2+ ions. We conducted a comprehensive evaluation of its performance in Co 2+ removal, considering various factors such as contact time, temperature, adsorbent dose, pH, and initial Co 2+ concentration. Utilizing response surface methodology-central composite design (RSM-CCD), we examined the interactions between these variables. The specific surface area and magnetic saturation value of the WSB/MnFe 2 O 4 /ZIF-7 composite were determined as 170.560 m 2 .g −1 and 23.469 emu.g −1 , respectively. ANOVA analysis indicated that our model effectively captures the interactions between variables, with a high R 2 value of 0.9982, explaining 99.82 % of the experimental data. Optimal conditions for maximum Co 2+ adsorption efficiency (99.05 %) were identified as follows: a contact time of 44.82 min, pH of 6.04, adsorbent dose of 0.947 mg.L -1 , temperature of 25.55 °C, and Co 2+ concentration of 11.13 mg.g −1 . Kinetic studies revealed that the Pseudo 2nd order kinetic model provided the best fit to the experimental data. The negative entropy parameter indicated a decrease in disorderliness during the adsorption process, while the exothermic nature of adsorption was confirmed by enthalpy values of −92.751 and −40.511 kJ.mol −1 for WSB/MnFe 2 O 4 /ZIF-7 and WSB, respectively. Furthermore, the Langmuir isotherm model demonstrated excellent fitting to the isotherm results, suggesting the dominance of homogeneous surfaces in adsorption. The maximum adsorption capacities for Co 2+ using WSB/MnFe 2 O 4 /ZIF-7 and WSB were determined to be 29.26 and 22.39 mg.g −1 , respectively. The WSB/MnFe 2 O 4 /ZIF-7 magnetic composite demonstrates promising potential for efficiently removing Co 2+ from both natural water sources and industrial wastewater, highlighting its versatility and effectiveness in environmental remediation applications.