Peruíbe black mud based catalysts for the removal of organic pollutants in water

Abstract

Peruíbe black mud (BM) is a natural clay found on the coast of São Paulo state of Brazil; in this study, it was used as an eco-friendly catalyst for environmental remediation. For this purpose, the removal of two organic pollutants [phenol and methylene blue (MB) dye] in water was studied using catalysts based on BM (calcined, and also doped with TiO 2). The catalytic reactions were studied under the following conditions: adsorption, heterogeneous-photocatalysis (UV light), and photo-Fenton (UV light + traces of H 2 O 2). The catalysts were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, infrared spectroscopy, and adsorption-desorption of N 2. The characterization indicated that the calcined black mud (BM) is composed of muscovite and quartz (as majority components), and TiO 2 , among other minerals in trace amounts. The tests of removal of pollutants demonstrated that the BM has a notable photocatalytic activity to degrade the pollutants, the mixture of BM with small quantities of TiO 2 increased its photocatalytic activity; there was a kind of synergy between the BM and TiO 2 that was clearly observed in photo-Fenton reaction. The best way to remove phenol with the BM photocatalysts was by heterogeneous-photocatalysis and photo-Fenton reactions; while the best way for removing MB was by adsorption. In the photo-Fenton process, BM/TiO 2 mixture was better than the commercial catalyst (TiO 2). The catalytic tests, in general, demonstrated that the BM based catalysts could be used to remove organic pollutants in water to remediate polluted water, and consequently assist towards a better quality of the sedimentary environment. Keywords Black mud • Heterogeneous-photocatalysis • Photo-Fenton • Organic compounds • TiO 2 Abbreviations AOP Advanced oxidative processes BM Black mud CB Conduction band FTIR Fourier Transform infrared spectroscopy JCPDS Joint Committee on Powder Diffraction Standards MB Methylene blue Ph Phenol PCZ Point of zero charge VB Valence band XRD X-ray diffraction SEM Scanning electron microscopy List of symbols E Photon energy (eV) E bg Band gap energy (eV) h Planck's constant T Temperature (°C) UV radiation Wavelength (nm) Watt Power (W) Volt Electromotive force (V) (X%) Efficiency (X%) in the photodegradation (%) v Photon frequency (cm −1) Communicated by M. V. Alves Martins