Effective Uptake of Cadmium and Chromium from Wastewater Using Carbon-Based Capsicum annuum

Toxic metal ions such as cadmium-Cd(II) and chromium-Cr(VI) are toxic, do not degrade easily in nature, and can cause various disorders and diseases in humans. Removing and monitoring Cd(II) and Cr(VI) ions is necessary for improving water quality. This study aimed to produce an adsorbent from activated carbon of Capsicum annuum and assess its ability to adsorb Cd(II) and Cr(VI) ions from water. The results showed that the adsorbent from C. annuum was porous after its conversion to activated carbon. The pH(PZC) of carbon-based Capsicum annuum was acidic, with a pH of 2.68. The highest capacities for both metal ions were observed at a pH of 1 for Cr(VI) and pH 5 for Cd(II), with capacities of 18.38 and 29.48 mg/g, respectively. The Freundlich sorption model proved to be the most suitable method. The adsorption of Cr(VI) and Cd(II) increased when the initial concentrations were raised from 20 and 60 mg/L; thereafter, a decrease was observed. The data showed that the adsorption of Cd(II) was fast and reached a maximum in 40 min, while Cr(VI) increased with time up to 30 min; thereafter, the rate for Cr(VI) decreased, while equilibrium was reached for Cd(II) ions. The temperature effect showed that the adsorption of Cd(II) and Cr(VI) ions reached a maximum at 55 and 45 °C, respectively. The results of enthalpy change (ΔH°) showed that the uptake process was exothermic, while the change in thermodynamic values of Gibbs energy (ΔG°) indicated that the sorption process was spontaneous and achievable. The greatest adsorption capacities for Cd(II) and Cr(VI) ions were 34.34 and 15.24 mg/g, respectively. The activated carbon from C. annuum proved to be effective for the adsorption of Cd(II) and Cr(VI) from wastewater.