Sol-gel synthesis of composite adsorbent coating from Prosopis juliflora–activated carbon for simultaneous adsorptive removal of Cd2+ and from wastewater

Abstract

To overcome the challenges associated with powdered activated carbon (PAC) in wastewater treatment, the efficacy of composite adsorbent coating (CAC) prepared using a simple sol-gel method with Prosopis juliflora–activated carbon for the simultaneous reduction of Cd2+ and Cr2O72- was investigated. The synthesized CAC was characterized by Fourier-transform infrared spectroscopy (C–H, C = O, and O–H stretching), pH point of zero charge (6–6.6), scanning electron microscopy (porous-rough surface), and Brunauer–Emmett–Teller surface area (10.6 m2/g) techniques. The analysis of variance results showed that pH and contact time were significant (p < 0.0001) for both Cd2+ and Cr2O72- removal. Generally, Cd2+ removal was higher than that of Cr2O72- at various operating conditions owing to the former's superior ionic properties. At the optimized operating parameters (pH = 8.5, adsorbent dosage = 0.25 g, initial concentration = 5 mg/L, contact time = 105 min, and temperature = 23.73°), the predicted and experimental ion removal efficiencies were 86.86 and 83.98% for Cd2+ and 94.26 and 58.08% for Cr2O72-, respectively. The Langmuir adsorption isotherm was the best-suited model (R2 > 0.99), while the metal ions removal was regulated by the pseudo-second-order Kinetic model (R2 > 0.999). The − ΔG°, +ΔH°, and +ΔS° values revealed the endothermic character and spontaneity of the adsorption process. The findings demonstrate the high potential of using CAC as an adsorbent for removal of metal ions to circumvent the PAC challenges in wastewater treatment.