Geochemical and Physicochemical Characteristics of Clay Materials from Congo with Photocatalytic Activity on 4-Nitrophenol in Aqueous Solutions

Mukuna P Mubiayi; Adolph A Muleja; Sarre K M Nzaba; Bhekie B Mamba

doi:10.1021/acsomega.0c04295

Geochemical and Physicochemical Characteristics of Clay Materials from Congo with Photocatalytic Activity on 4-Nitrophenol in Aqueous Solutions

ACS Omega. 2020 Nov 13;5(46):29943-29954. doi: 10.1021/acsomega.0c04295. eCollection 2020 Nov 24.

Authors

Mukuna P Mubiayi¹, Adolph A Muleja¹, Sarre K M Nzaba¹, Bhekie B Mamba¹

Affiliation

¹ Nanotechnology and Water Sustainability (NanoWS) Research Unit, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1709, South Africa.

Abstract

This study investigated the geochemical and physicochemical characteristics of natural clay collected in the Democratic Republic of Congo. The optical properties of the sample collected in Golf (GOL) were tested in the removal of 4-nitrophenol in aqueous solution. The geochemical analysis depicted that all the samples are plotted within the shale quadrant. Furthermore, the Chemical Index of Alteration (CIA) indicated that the samples are extremely weathered. The particle size distribution ranged from 0.41 to 418.6 μm, while the pore diameters for all the samples were under 100 Å. A flake-like surface morphology was observed in all the samples. SiO₂, Al₂O₃, Fe₂O₃, K₂O, and TiO₂ were the major chemical compounds found in all the samples, while the XRD analysis showed the presence of quartz, kaolinite, magnetite, and illite. The presence of metal oxides (i.e., TiO₂ and Fe₂O₃) indicated that these natural clays can be used for photocatalytic oxidation of pollutants. The sample collected in Katuba (KAT) displayed the higher reflectance percentages for the selected wavelengths except at 200 nm. Interestingly, the GOL sample exhibited lower energy band gaps (2.68 and 3.94 eV) necessary for photocatalysis. The untreated GOL clay sample removed 99.13% of 4-nitrophenol from aqueous solution through the photodegradation process. The usage of the untreated GOL clay could be a cost-effective solution in the removal of 4-nitrophenol in wastewater.