Kinetics and mechanism of Paraquat’s degradation: UV-C photolysis vs UV-C photocatalysis with TiO2/SiC foams

Abstract

In this study, the photolytic and photocatalytic removal of the herbicide paraquat is investigated under UV-C (254 nm). For photocatalytic experiments, SiC foams were used with P25-TiO nanoparticles deposited by dip-coating. The foams were characterized by scanning electron microscopy and paraquat's degradation under UV-C photolysis or photocatalysis, followed by UV-vis spectroscopy, total organic carbon analyzer, LC-MS and ion chromatography. After 3 h of reactions by photolysis and photocatalysis, 4% and 91% of TOC removal were observed. An analysis of degradation by-products showed a similar degradation pathway with pyridinium ions observed by LC/MS and carboxylic acids (succinate, acetate, oxalate and formate) detected by ion chromatography. In conclusion, these two different photo-degradation processes are able to remove paraquat and produce similar by-products. However, the kinetics of degradation is rather slow during photolysis and it is recommended to combine the UV-C lightning with a TiO photocatalyst to improve the mineralization rate.

Carbon nanotube@silicon carbide coaxial heterojunction nanotubes as metal-free photocatalysts for enhanced hydrogen evolution

“…The main reason for this is the rapid recombination of the photoinduced electron-hole pairs in SiC photocatalysts [39,40]. Therefore, various engineering strategies, including the formation of unique SiC nanostructures (e.g., quantum dots [41], nanoparticles [42], nanowires [43], and hollow spheres [44]), construction of heterostructures (e.g., SiC-TiO2 [45], SiC-ZnS [46], SiC-MoS2 [47], SnO2-SiC [48,49], and SiC-CdS [50]), hybridization of SiC with metal co-catalysts (e.g., SiC-Pt [43], SiC-IrO2 [51]), and nanocarbon materials (e.g., SiC-graphene [52,53]), have been employed to promote the performance and durability of SiC photocatalysts since the initial research on water splitting in 1990 [54]. Further investigations show that the SiC-graphene nanoheterojunction with intimate interfacial contacts between SiC and graphene exhibits enhanced photoactivities for water splitting owing to the improved charge separation resulting from the formation of Schottky-junction interfaces [55].…”

The adsorption characteristics and degradation mechanism of tinidazole on an anatase TiO2 surface: a DFT study

“…Photocatalysis is a process of mineralizing these contaminants into CO 2 , H 2 O and other inorganic substances by generating strong oxidizing OH radicals. [14][15][16] It is considered to be a very effective method for the treatment of nitroimidazole residues. 17 Metal oxides or suldes are oen used as semiconductor photocatalysts to degrade residual contaminants, 18 such as TiO 2 , ZnO, GaO, CdS, ZnS.…”

A comparative study of the photocatalytic efficiency of metal oxide/hydroxyapatite nanocomposites in the degradation kinetic of ciprofloxacin in water

“…Among them, adsorption and photodegradation are considered the most widely used methods requiring effective support with good thermal stability, structural and surface properties [4,5]. Several natural and synthetic materials have been evaluated [6][7][8][9]. Among them, apatite efficiency is better versus various pollutants by controlling their porosity and the chemical composition of their surfacee.…”

“…Nevertheless, other oxides (ZnO, -Fe 2 O 3 , etc.) prepared under suitable synthesis conditions lead to satisfactory photocatalysis results but require a modification of their surface by using a porous systems such as silica or clays which accelerate the adsorption rate and consequently their photodegradation [9,10]. For good adsorption, an affinity between the solid and the pollutant is first required such as performed is the case of grafted silica or modified titanium oxides [11].…”