article · RSC Advances
This research evaluates microcrystalline cellulose functionalised with polyaniline as a nanocomposite adsorbent for removing toxic hexavalent chromium from synthetic wastewater. Microcrystalline cellulose served as a scaffold for the chemical oxidative polymerisation of aniline, increasing the specific surface area relative to unmodified cellulose. In laboratory batch adsorption experiments, a nanocomposite containing 69 weight percent polyaniline achieved a 95 percent removal efficiency within 30 minutes under neutral conditions of pH 7. The material demonstrated a maximum adsorption capacity of 35.97 milligrams per gram, significantly outperforming plain microcrystalline cellulose. Analysis indicated that the removal process operates via electrostatic attraction, chemical reduction of hexavalent chromium to trivalent chromium, and subsequent precipitation on the surface of the nanocomposite.
Hexavalent chromium is a hazardous industrial water pollutant that poses serious environmental and public health risks. Most treatment materials only capture this contaminant in highly acidic wastewater, requiring costly chemical adjustments. Developing an effective adsorbent that operates efficiently at neutral pH simplifies water treatment processes, making the decontamination of industrial effluents safer and more practical.
The findings could support wastewater treatment applications, specifically targeting industries generating heavy metal effluents. Water treatment plant operators or industrial environmental managers could potentially use the material for effluent remediation. Currently, the work represents applied, laboratory-tested research based on synthetic wastewater, meaning further piloting, scale-up synthesis, and tests in real industrial effluents are required before commercial use.
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In this study, the effectiveness of microcrystalline cellulose (MCC) as an adsorbent for the removal of hexavalent chromium, Cr(vi), from synthetic wastewater was enhanced through functionalization with polyaniline (PANI). Scanning electron microscopy (SEM) showed that MCC was an effective scaffold for <i>in situ</i> chemical oxidative polymerization of aniline. Fourier transform infrared spectroscopy (FTIR) spectroscopy and X-ray diffraction confirmed successful PANI synthesis. The MCC/PANI nanocomposites exhibited relatively high specific surface areas, compared to that of the MCC (2.05 m<sup>2</sup> g<sup>-1</sup>). Batch adsorption studies showed that the optimal conditions for the removal of Cr(vi) from wastewater using the MCC/PANI-69 wt% nanocomposite were an initial Cr(vi) concentration of 100 mg L<sup>-1</sup>, an adsorbent dosage of 4 g L<sup>-1</sup> and a Cr(vi) solution pH of 7. The MCC/PANI-69 wt% required only 30 min to reach equilibrium and the equilibrium removal efficiency was 95%. FTIR spectroscopy and energy dispersive X-ray spectrometry results suggest that the Cr(vi) removal mechanism by the MCC/PANI-69 wt% nanocomposite at pH 7 was through electrostatic attraction of Cr(vi) species by PANI, reduction of Cr(vi) into Cr(iii) and precipitation of Cr(iii) on the nanocomposite surface. The kinetics for the removal of the Cr(vi) by the MCC/PANI-69 wt% nanocomposite were adequately described by the pseudo second order (PSO) kinetics model, whereas the Langmuir isotherm adequately described the equilibrium data. The MCC/PANI-69 wt% nanocomposite had a significantly improved maximum adsorption capacity of 35.97 mg g<sup>-1</sup>, at pH 7, in comparison to that of the MCC (3.92 mg g<sup>-1</sup> at pH 1). The study demonstrated that, whereas most of the reported adsorbents for Cr(vi) are only effective at low pH values, the MCC/PANI nanocomposite synthesized in this study was effective at pH 7.
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DOI: 10.1039/d3ra08027g
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