A zinc oxide-coated nanoporous carbon adsorbent for lead removal from water: Optimization, equilibrium modeling, and kinetics studies

A zinc oxide-coated nanoporous carbon sorbent was prepared by acid modification and ZnO functionalization of mesoporous carbon. The synthesized materials, such as mesoporous carbon, oxidized mesoporous carbon and zinc oxide-coated nanoporous carbon, were characterized by nitrogen adsorption–desorption analysis, Fourier transform infrared spectra, scanning electron microscopy, and transmission electron microscopy. ZnO on oxidized mesoporous carbon gradually increased with increase in the number of cycles. Furthermore, the effects of agitation time, initial metal ions concentration, adsorbent dose, temperature and pH on the efficiency of Pb(II) ion removal were investigated as the controllable factors by Taguchi method. The value of correlation coefficients showed that the equilibrium data fitted well to the Langmuir isotherm. Among the adsorbents, zinc oxide-coated nanoporous carbon showed the largest adsorption capacity of 522.8 mg/g (2.52 mmol/g) which was almost close to that of the zinc oxide-coated (2.38 mmol/g), indicating the monolayer spreading of ZnO onto the oxidized mesoporous carbon. The results of the present study suggest that ZnO-coated nanoporous carbon can be effectively used for Pb(II) adsorption from aqueous solution, whereas a part of acidic functional groups may be contributed to binding the Pb(II) for the oxidized mesoporous carbon and mesoporous carbon. Kinetic studies indicated that the overall adsorption process of Pb(II) followed the pseudo-second-order model. The ZnO-coated nanoporous carbon was regenerated and found to be suitable of reuse of the adsorbent for successive adsorption–desorption cycles without considerable loss of adsorption capacity.