Efficient Ion Separation from Environmental and Biological Samples Using a Novel Sorbent Based on Ni-Substituted ZIF-67: Optimization, Equilibrium, Kinetic, and Thermodynamic Study

Abstract

After routine alkali treatment of industrial wastewaters, a subsequent purification step is required before discharging the resulting effluent due to the remaining trace amount of chromium(VI) at milligram per liter levels. In the present study, a simple one-step synthesis was carried out to fabricate a new adsorbent of NixCoyZIF-67 for adsorption and removal of wastewaters containing chromium(VI) efficiently. To find optimum adsorption conditions of chromium(VI), the sample pH effect, initial concentration of chromium(VI), temperature, contact time, and adsorbent amount were examined. At 298 K, an adsorption capacity of 30.3 mg/g was calculated. Analyzing the mechanism of removal indicated that the chromium(VI) uptake by NixCoyZIF-67 fits with the Langmuir and Dubinin–Radushkevich isotherms well and follows a pseudo-second-order kinetic approach. Also, a positive ΔG and negative ΔH and ΔS indicated adsorption that is endothermic and occurs spontaneously. Electrostatic attractions of chromium(VI) anions by the positively charged surface of the adsorbent and ion exchange with the hydroxyl groups of the adsorbent surface can be ascribed as the mechanism of adsorption. Under the optimized conditions, the detection limit was 0.003 mg/L, and the quantification limit was 0.010 mg/L. The linear range of the calibration plot was between 0.010 and 2.0 mg/L (R2 > 0.9900). The intraday and interday RSDs% at two concentration levels of 0.05 and 0.20 mg/L were less than 3.4%. Eventually, the applicability of the presented method was evaluated for measuring trace amounts of chromium(VI) in blood samples. Acceptable relative recoveries of 82–93% were achieved. Overall, it can be concluded that NixCoyZIF-67 can be introduced as a promising sorbent for the determination of chromium(VI) into complex biological fluids and its decontamination from industrial wastewaters.