Adsorption of hexavalent chromium from wastewater using polyaniline-coated microcrystalline cellulose nanocomposites

Lovejoy Dewa; Shepherd Masimba Tichapondwa; Washington Mhike

doi:10.1039/d3ra08027g

Adsorption of hexavalent chromium from wastewater using polyaniline-coated microcrystalline cellulose nanocomposites

RSC Adv. 2024 Feb 22;14(10):6603-6616. doi: 10.1039/d3ra08027g. eCollection 2024 Feb 21.

Authors

Lovejoy Dewa¹, Shepherd Masimba Tichapondwa², Washington Mhike¹

Affiliations

¹ Polymer Technology Division, Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology Pretoria 0001 South Africa MhikeW@tut.ac.za +27 12 382 5460.
² Water Utilization Division, Department of Chemical Engineering, University of Pretoria Pretoria 0001 South Africa.

Abstract

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 in situ 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 m² g^-1). 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^-1, an adsorbent dosage of 4 g L^-1 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^-1, at pH 7, in comparison to that of the MCC (3.92 mg g^-1 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.