Application of Mechanochemically Synthesised ZnS Nanoaprticles in Photo-Catalytic Oxidation of Phenol

作者：Tolia J^*; Murthy Z V P; Chakraborty M

来源：Research Journal of Chemistry and Environment, 2011, 15(2): 223-228.

• Mechanochemical method
• Semiconductor
• Advanced oxidation process
• Photo-degradation
• ZnS
• Mn doped ZnS

The main objective of this work is to study the possibility of using the advanced oxidation process (AOP's) based on photo-catalytic oxidation for the treatment of nonbiodegradable and toxic phenolic compounds which cannot be treated by conventional biological treatment. Light-induced electron/hole pair formation in semiconductor particles, accompanied by subsequent interfacial electron (hole) transfer, has always been considered as the first step of the photocatalytic action of semiconductor nanoparticles. The high oxidative potential of holes can lead to direct and indirect oxidation. In the indirect oxidation process, hydroxide radicals (OH.) are formed from combination of holes with water molecules. Primary photoproducts resulting from interfacial electron hole transfer, i.e. radical ions undergo further transformations leading to the formation of final photoproducts. Thus, semiconductors with wide band gap can be used for photocatalysts.
Most commonly used photo catalyst is semiconductors like TiO(2) and ZnO. However, TiO(2) photocatalysis has some limitation due to significant radiation loss during electron-hole recombination process. Recently, transition-metal sulfides, in particular ZnS and CdS, have been intensively studied because of their unique catalytic functions compared to those of TiO(2). Mechanochemical route is the easiest way to produce nanoparticles on large scale.
In this study, ZnS nanoparticle has been mechanochemically synthesized using zinc acetate and sodium sulphide in Pulverzitte-6 mill at 350 rpm with powder to ball ratio 1:10 and with 10h milling time. Mn dopped ZnS nanoparticles at different ratio (1:1, 1:2) are also synthesized mechanochemically. Zns and dopped ZnS nanoparticles were characterized by UV-VIS, particle size analyzer, TEM and XRD. The particle size obtained from Debye Scherer's formula (XRD) was found to be exactly matching with TEM data i.e. around 5.12nm. Result shows some aggregation of the nanoparticles in aqueous solution in absence of any stabilizer. ZnS nanoparticle has been used for photo-catalytic degradation of phenolic wastewater and % degradation was compared with TiO(2) (anatase). Degradation of phenol was influenced by the pH, the input concentration of H(2)O(2) and the dosing amount of the photocatalyst. The degradation reaction was found to follow the first order kinetics upto 45 mm whereas from 45-90 minutes degradation follows second order kinetics. Second kinetics indicates the formation of some intermediate compounds, identified by GC-MS spectra during degradation. The photo degradation of phenol in presence of TiO(2) and ZnS was found to be 95% and 92% respectively within 90 minutes of radiation time. Mn doping did not show any significant change in degradation kinetics.

• 出版日期2011-6