Biofabrication of highly effective and easily regenerated CuO nanoparticles as adsorbents for Congo red and malachite green removal

Abstract

An effective and easily regenerated adsorbent is the one for which scientists are making an effort to explore. In this study, copper oxide nanoparticles (CuO NPs) were synthesized in a green manner from a leaf extract of Moringa stenopetala and used for dye adsorption. XRD, FTIR, and SEM were employed for the characterization of CuO NPs. The crystallite size of the CuO NPs was calculated via Debye–Scherrer equation from the XRD data and was found to be 8.33 nm. The Cu–O bonding bending vibration at 1116 cm − 1 and stretching vibration at 1649 cm − 1 observed from the FTIR data strongly confirmed the formation of CuO NPs. SEM morphology analysis confirmed the formation of nanoparticles with a plate-like morphology and a spherically random orientation. The zero-point charge of CuO NPs was investigated and reported to be at pH 7. The adsorption of dyes on the greenly produced CuO NPs was studied by optimizing different adsorption parameters. The removal efficiencies of the green CuO NPs adsorbent were 99.54% at the optimum conditions (pH, 4; dye concentration, 30 mg/L; amount of adsorbent, 0.25 g; and contact time, 80 min) and 98.33% at the optimum conditions (pH, 11; dye concentration, 20 mg/L; amount of adsorbent, 0.4 g; and contact time, 80 min) for congo red and malachite green, respectively. The adsorption efficiency of the biosynthesized CuO NPs for the mixture of the two dyes was 92.3%. The green synthesized adsorbent was regenerated and able to work effectively for four cycles for the two dyes. The results of the kinetics-type investigation indicate that the adsorption of both dyes by the CuO NPs adsorbent best fits a pseudo-second-order model. The isotherm model-type investigation resulted in the fitting of the Langmuir adsorption isotherm for both the congo red and malachite green dyes.