Environmental Advances (Jul 2024)
A comparative study of sol-gel process and chemical precipitation of NiO from fire assay waste: Structural characterization and insights into VOCs sensing application
Abstract
This study compares nickel oxide (NiO) derived from fire assay waste nickel sulphide (FA-NiS) and chemical precipitation and sol-gel process. This work reports the first time NiO prepared through chemical precipitation from the waste for VOC sensing purposes. Additionally, herein we provide insights into comparing the properties of NiO obtained through different methods and their potential for environmental sensing applications. Structural, morphological, and elemental characterizations are conducted, alongside preliminary investigation into their volatile organic compounds (VOCs) sensing application. After Cu extraction with 5,8-diethyl-7-hydroxydodecan-6-oxime, the nickel (Ni) raffinate was precipitated using lime (Ca(OH)2) at pH 2.5 and 6.5 conditions. Scanning electron microscope (SEM) -energy dispersive spectroscopy and X-ray photoelectron spectroscopy confirmed nickel and oxygen (O2) presence at pH 6.5, and iron (Fe), Ni, and O presence at pH 2.5. X-ray diffraction revealed a cubic crystal structure and high average crystallinity (39 - 41 nm) for both sol-gel process and chemical precipitation of NiO. SEM showed uniform, spherical particles for the sol-gel process while chemical precipitation displayed aggregated layered granules. NiO precipitated at pH 2.5 exhibited coalesced hexagonal particles with predominant Fe and Ni presence. Developed analytical methods for inductively coupled plasma optical emission and X-ray fluorescence demonstrated high purity NiO (≈75 %) with low relative standard deviation (RSD <0.05 %) and 90 % recovery using certified reference material. As compared to sol-gel process NiO, the NiO from fire essay waste displayed clear sensing responses at both 25 °C and 150 °C, with recovery times (80 and 120 seconds) even at the lowest concentration (1.5 ppm). The highest response (Rg/Ra = 1.198 for 45 ppm ethanol) occurred at 150 °C, indicating the potential NiO from the fire assay waste as a futuristic device for VOCs sensing under ambient conditions.
