Application of physical vapor deposition technology for practical utilization of nano-size copper oxide for lead uptake from solution: kinetics, equilibrium, and recycling studies

Abstract

For the first time, copper oxide-coated glass beads (CuO-GBs) were fabricated using physical vapor deposition (PVD) technology for sequestrating Pb2+ ions from solution is addressed. Compared to other coating procedures, PVD offered high-stability uniform CuO nano-layers attached with 3.0-mm glass beads. Heating of copper oxide-coated glass beads after deposition was rather necessary to achieve the best stability of the nano-adsorbent. Detection of nano-size copper oxide on the beads was made by FTIR (intense peak at 655cm-1 for CuO bond stretching) and XRF (Cu peak at 8.0keV). Scanning electron micrographs taken at high magnification power indicated the presence of CuO in nano-range deposited over glass beads. The maximum deposited amount of CuO on the beads was 1.1% and accomplished at the following operational conditions: internal pressure 10-5mmHg, Ar flow rate 8.0mL/min, voltage 84V, pre-sputtering time 20s, total sputtering time 10.0min, and post-heating temperature 150°C for 3h. A univariate analysis indicated that the optimum Pb2+ uptake by CuO-GBs from solution was achieved at pH 7.0-8.0, 7 beads/50mL, 120-min contact time, and 15-mg/L initial concentration. Kinetic data for Pb2+ uptake was best presented by a pseudo-second-order model with a relative prediction error of 3.2 and 5.1% for GBs and CuO-GBs, respectively. On the other hand, Pb2+ equilibrium isotherms at 25°C were fairly presented by the Langmuir model, and the predicted saturation values were 5.48 and 15.69mg/g for GBs and CuO-GBs, respectively. CuO and CuO-GBs had similar Pb2+ saturation values (~ 16mg/g), although the latter demonstrated 4 times faster kinetic, thanks to fixation CuO on glass beads. Moreover, the chemical stability of copper oxide-coated glass beads was tested under different conditions. Recycling of copper oxide-coated glass beads was also investigated, and 90% of the surface was recovered using 0.01-M HNO3.