Synthesis of z-scheme silver oxosalts-carbonaceous materials loaded on fibrous silica titania photocatalyst for degradation of 2-chlorophenol
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Date
2021
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Universiti Teknologi Malaysia
Abstract
Chlorophenols are undoubtedly a toxic pollutant that can cause serious threats to the ecological environment and human health. For instance, 2-chlorophenol (2-CP) can act as precursor to form unintentional by-product of dioxin and furan that are toxic and mutagenic. Photocatalytic degradation is an effective destructive method to remove 2-CP. Recently, fibrous silica titania (FST) catalyst synthesized by microemulsion method exhibited dendrimeric fiber morphology, which possesses high accessibility of active sites that can enhance the photocatalytic activity. However, the likelihood of photogenerated electron-hole pair recombination still could not be ruled out. Currently, a new type of heterostructure semiconductor known as Z-scheme system has been constructed in which the conduction band (CB)-electrons in the semiconductor I with lower energy combine with the valence band (VB)-holes in the semiconductor II, where only strong redox electron-hole will be retained to participate the photocatalytic reaction. These features induced the spatial isolation which inhibited the photogenerated electron-hole recombination. Carbonaceous materials are one of the suitable candidates for constructing Z-scheme mechanism. In this study, carbonaceous materials (graphitic carbon nitride, g-C3N4 (CN), graphene nanoplatelet, GNP (GN) and multi-wall carbon nanotube, MWCNT (CNT)) loaded on FST were successfully synthesized by solid-state method via microwave irradiation. The catalysts were characterized using X-ray diffraction, field emission scanning electron microscopy, nitrogen adsorption-desorption, transmission-electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance, Fourier transform infrared, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic performance of 2-CP over different carbonaceous materials loaded on FST were in the following order: g-C3N4 (CNFST) (70%) > GNP (GNFST) (47%) > MWCNT (CNTFST) (44%). This sequence could be attributed to the degree of dispersion of C and N elements on FST. The effect of loading (5-15 wt.%) of the best carbonaceous material, g-C3N4 loaded on FST was investigated for the degradation of 2-CP, which follows the trend of 10 wt.% CNFST (93%) > 15 wt. % CNFST (70%) > 5 wt.% CNFST (49%). This enhancement of photoactivity was due to high amount of oxygen vacancies, metal defects and Si-O-N/Si-O-C bonds. Next, further addition of silver oxosalts was introduced on 10 wt.% CNFST in order to enhance capability of redox reaction which resulted in this following sequence: silver sulphate, Ag2SO4 (AS-CNFST) (98%) > silver phosphate, Ag3PO4 (AP-CNFST) (86%) > silver carbonate, Ag2CO3 (AC-CNFST) (80%). The optimum performance was ascribed to the low negative VB energy level of Ag2SO4 which endow more hole with high oxidizing ability. This study highlighted the contribution of unique g-C3N4 and Ag2SO4 for dual Z-scheme FST-based photocatalyst that enhanced photocatalytic degradation of organic pollutants for wastewater treatment.
Description
Thesis (Ph.D (Chemistry))
Keywords
Chlorophenols, Photocatalysis