Cellulose titanium-dioxide composites for malachite green dye Photodegradation

Abstract

Textile industries largely contribute to water pollution by releasing their waste into streams, rivers, and other water bodies. With the rise in technology, researchers are discovering more ways of reducing water pollution in the environment. This research was aimed at extracting cellulose from a unique local plant source, Colophosperum mopane leaves. The process involved sodium hydroxide treatment, bleaching, and several washes to get the white fluffy cellulose. The cellulose was further used as a support material in making the cellulosetitanium dioxide composites which were synthesized using the hydrothermal method. Composites with 1-4% TiO2 catalyst loading were made. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) techniques were used. XRD results showed that Colophosperum mopane extracted cellulose to be semi-crystalline with crystallite size of 1.36 nm. The patterns of the titanium dioxide matched that of anatase which is known to be photoactive. Infrared spectroscopy mainly showed cellulose functional groups. The morphology of the fibers appeared smooth and with an average diameter of 1μm. TGA revealed that the titanium dioxide-cellulose composites were thermally stable up to 360 ℃. Titanium dioxide particles with average size of 100 nm were observed. Amongst the different catalyst compositions, the composite with 2% catalyst loading (Cell-TiO2-2) was found to be the most effective. The photo-degradability under ultra-violet and solar irradiation indicated that photodegradation under sunlight using the Cell-TiO2-2 catalyst, was higher than that done under UV light giving rise to percent degradations of 98.88 and 98.92% for that of solar, without adsorption contribution. Several scavengers were tested for their effectiveness in quenching the photoactivity. The presence of benzoquinone hindered the contribution effect of O2- radicals in the photocatalytic mechanism. The CellTiO2-2 was found to be still photoactive even after 4 cycles, thereafter reached plateaus. Adsorption played a role in the decolorization of the MG dye and cellulose proved to be a highly adsorptive material hence improving the catalytic effect of the composite. The kinetics of the photoactivity indicated a pseudo first-order reaction. The bandgap of 3.47 eV was recorded which provides the precise extent for the degradation process to occur. The results provided established the suitability of Colophosperum mopane as an active catalyst support.