Solar photocatalytic decomposition of two azo dyes on multi-walled carbon nanotubes (MWCNTs)/TiO2 composites

Abstract

Multi-walled carbon nanotubes (MWCNTs)/ TiO 2 composite photocatalysts with high photoactivity were prepared by sol-gel process and further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and UV-vis absorption spectra. Compared to pure TiO 2 , the combination of MWCNTs with titania could cause a significant absorption shift toward the visible region. The photocatalytic performances of the MWCNTs/TiO 2 composite catalysts were evaluated for the decomposition of Reactive light yellow K-6G (K-6G) and Mordant black 7 (MB 7) azo dyes solution under solar light irradiation. The results showed that the addition of MWCNTs enhanced the adsorption and photocatalytic activity of TiO 2 for the degradation of azo dyes K-6G and MB 7. The effect of MWCNTs content, catalyst dosage, pH, and initial dye concentration were examined as operational parameters. The kinetics of photocatalytic degradation of two dyes was found to follow a pseudo-first-order rate law. The photocatalyst was used for seven cycles with photocatalytic degradation efficiency still higher than 98%. A plausible mechanism is also proposed and discussed on the basis of experimental results.

Carbon quantum dot supported semiconductor photocatalysts for efficient degradation of organic pollutants in water: A review

“…CQDs are a new family of fluorescence carbon nanoparticles, firstly fabricated by Xu and co-workers in 2004 by accident and reported as side products in arc discharged soot generation in the synthesis of carbon nano-tubes (Namdari et al, 2017). CQDs comprise of distinct quasi-spherical nanoparticles with a 10-nm particle size (Chan et al, 2002;Wang et al, 2010). They are valuable materials due to small particle size, fine biocompatibility, low cost, abundant surface functional groups, chemical inertness, low toxicity, broad varying optical properties, and tunable PL behavior (Yang et al, 2011;Xu et al, 2004).…”

“…Because of outstanding charge carrier transfer, photosensitization and up-converted PL (UPCL) effect, CQDs have been utilized for modification of photocatalyst composite to raise their photocatalytic activity (Bajorowicz et al, 2018;Yu et al, 2007). After commencement of CQDs, expanded the range of photo responding and organized charge separation leads to enhancement in photocatalytic activity (Wang et al, 2010). The mechanism of excitation and photoactivity of CQDs modified photocatalysts are fully depended on band gap, valence band, and conduction band.…”

“…Wide band gap semiconductor such as TiO 2 , ZnO, BiOBr, etc. has been acknowledged as an excellent material for photocatalysis because of their large band gap, non-toxic nature, high photosensitivity, photochemical stability and low cost (Yu et al, 2012;Wang et al, 2010). Also, wide band gap of TiO 2 can only exploit from UV light of sunlight, which forms only a minor fraction of the whole solar spectra reaching the earth surface (Smith et al, 2009;Chai et al, 2018).…”