Photocatalytic degradation of methyl violet in water using TiO2/Cellulose-N-MWCNTs

Mathebula, Xiluva
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ABSTRACT TiO2-carbon based composites are of great significance in a wide range of applications including photocatalytic degradation. This is attributed to the high photodecomposition efficiency of the composites as compared to independent TiO2. Carbon materials such as cellulose polymer and multiwalled carbon nanotubes (MWCNTs) are considered as good supports for TiO2 owing to their unique properties such as lightweight, large surface area and high aspect ratio. Lately, the study of cellulose-MWCNTs composite has been an area of academic interest due to its large mass fraction, and prowess to facilitate toughening mechanisms in fiber bridging. However, a cost-effective method that can improve the dispersion and interfacial adhesion of the MWCNTs in the polymer is still required. Thus different modification methods of MWCNTs have been explored to increase the binding sites of the material. In this study, it was hypothesized that the cellulose’s potential as a TiO2 support can be improved by hybridizing it with MWCNTs resulting in high TiO2-C photocatalytic activity through synergistic effect. A catalytic decomposition of Fe-Co/CaCO3 was used over C2H2 to fabricate the MWCNTs. Thereafter, the MWCNTs were functionalized by (1) acid-treatment (referred to as fMWCNTs), (2) nitrogen doping by in situ and ex situ methods (referred to as in situ N-MWCNTs and ex situ N-MWCNTs, respectively) and (3) both acid treatment and nitrogen doping (referred to as in situ fN-MWCNTs and ex situ fN-MWCNTs). Moreover, cellulose-N-MWCNTs (C@fN-MWCNTs) hybrid was prepared by electrospinning a solution of cellulose acetate/in situ fN-MWCNTs (11/0.115) in DMAc at 25 kv and 1 mL/h. The prepared MWCNTs and cellulosic materials were further used as support materials of TiO2 in the photodegradation of methyl violet (MV 6B). The supported TiO2 catalysts were prepared by a sol-gel method and then analyzed using various techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. iii TGA results revealed that in situ N-MWCNTs contained high impurities inclusive of as Fe, Co, Ca, and amorphous carbon which were identified by XRD analysis. Nevertheless, TGA, BET and TEM, showed that acid treatment of MWCNTs improves their purity, surface area and anchoring sites for the TiO2, respectively. Furthermore, SEM results showed that C@fNMWCNTs hybrid interacts with TiO2 better than cellulose fibers. This was in accord with the PL results which showed a reduction in the electron/hole recombination. However, the surface area of C@fN-MWCNTs was very low compared to cellulose fibers which resulted in low dye adsorption capacity by C@fN-MWCNTs. The photocatalytic degradation activity commercial TiO2 was enhanced by 3.7% and 5.6% after being supported on cellulose and C@fN-MWCNTs, respectively. Thus, incorporating in situ fNMWCNTs with cellulose did improve the cellulose’s potential as a TiO2 support. However, the overall photocatalytic degradation performance of TiO2/C@fN-MWCNTs was less than that of in situ TiO2/fN-MWCNTs. This may be due to the reduction in the surface area, which resulted in reduced adsorption and thus lowers degradation efficiency.
Mathebula, Xiluva (2018) Photocatalytic degradation of methyl violet in water using TiO2/cellulose-N-MWCNTs, University of the Witwatersrand, Johannesburg,