Laboratory and Commercial Synthesized Zinc Oxide Nanoparticles Adsorption onto Coconut Husk: Characterization, Isotherm, Kinetic, and Thermodynamic Studies

The accelerating application of zinc oxide nanoparticles (ZnO-NPs) has called for attention to their potential environmental and human health risks. This work aimed to investigate the sorption efficiency of laboratory and commercial synthesized nanocrystalline zinc oxide onto raw coconut husk in a batch adsorption study. Characterization of samples was performed by employing spectroscopies techniques such as X-ray Diffraction Spectroscopy, Field Emission Scanning Electron Microscopy, Transmission Electron Spectroscopy, Fourier transform IR Spectroscopy, and Brunauer–Emmett–Teller. A spherical shaped nanocrystalline ZnO with a mean crystallite and particle size of 14.7 nm and 24 nm by XRD and TEM was synthesized as compared to the commercial ZnO-NPs of size < 50 nm. The maximum percentage removal of 88% (0.13 mg/g) and 90% (0.16 mg/g) for laboratory synthesized and commercial ZnO-NPs respectively was recorded at an optimum contact time of 80 minutes. The data also indicated 2.0 g sorbent mass and pH of 8 as the optimum conditions for maximum percentage removal of these nanoparticles. Both Langmuir and Freundlich models fitted best for laboratory synthesized ZnO-NPs with a maximum capacity of 0.797 mg/g, whereas Langmuir isotherm model alone with a maximum capacity of 0.710 mg/g fitted well for commercial ZnO-NPs. The n-value from the Freundlich model, as well as separation factor (RL) were greater than unity suggesting a favorable adsorption process. The study obeyed pseudo-second-order, which was exothermic with a high degree of freedom of sorbent-sorbate interaction. The results suggested that coconut husk is potentially scalable for removing ZnO-NPs from wastewater.