Investigation Of Catalytic Ozonation Of P-chloronitrobenzene By Pumice And Its Support Zinc Hydroxide

Industrial development and the improvement of living conditions have resulted in the extensive pollution of the water environment. Despite having low concentrations in water, some refractory organic pollutantshave serious harmful effects.However, conventional processes have beenshown to achieve very limited mineralization of organic micropollutants indrinking water treatment. Heterogeneous catalytic ozonation, asa promising advanced oxidation process, has recently receivedconsiderable attention in the field of water treatment for its high oxidationpotential.To provide active sites on catalystsand to improve ozone decomposition, pumice and ZnOOH/pumice were prepared in a laboratory and used as catalysts in this paper. Catalysts were applied in the catalytic oxidation of race concentrationsof p-chloronitrobenzene (pCNB). The relationshipamong the catalyst structure,surface hydroxyl, and catalytic activity in catalytic ozonationwas then determined. The catalysts, whichwere readily available, inexpensive, and easy to prepare, exhibit promising application potential for drinking water treatment.The use of pumice for heterogeneous catalytic ozonation significantly enhancesthe degradation efficiency and total organic carbon(TOC) removal of pCNB in an aqueous solution compared with ozonation alone because of the synergistic effect between ozone and the catalyst. The pCNB adsorption was insufficient to contribute significantly to the pCNB degradation during pumice-catalyzed ozonation.The catalyst prepared in the laboratory was pumice-supportedzinchydroxide(ZnOOH-pumice). Materials havea certain capability for the adsorption of gas.Experimental results show that the main functional group on the catalyst surface was hydroxyl.All hydroxidespossess abundant surface hydroxyl groups. At a reactiontime of20min during the catalytic removal of pCNB by ozonation alone, pumice/ozonation and ZnOOH-pumice/ozonation in distilled water increase from55.7%to72%and93%, respectively. In contrast to the experimental results of ozonation aloneand of catalytic ozonation processes, the adsorption of pCNB ontoZnOOH-pumice is insufficient to make a significant contribution to degradation efficiency and can therefore be neglected.The affecting factors of the catalytic ozonation of pCNB by ZnOOH-pumice were investigated. Results show that the removal of pCNB increased with the reaction temperature, ozone concentration,and initial concentration ofthe pCNB and catalyst, along with decreasing water purity. The effects of NO-3, Na+, and K+on the catalytic ozonation of pCNB can be ignored. Degradationefficiencywas slightly promoted in the presence of Ca2+and Mg2+. The ozonation of pCNBwas slightly inhibited by the high concentration of Cl-. Theremoval efficiency of pCNBdecreased in the presence of SO2-4, given that the hydroxyl inhibitors PO3-4and HCO-3can significantlyinhibit the catalytic degradation ofpCNB.The removal of pCNB decreased with increasing humic acidconcentration.The catalytic capability of the catalyst weakened with increasing calcinationtemperature. After10successive recycles, the catalyst remainedstable during the catalytic ozonation of pCNB.Ion dissolution was observed after catalyzed ozonation. How ver, the concentration of the residual ions was negligible. The concentrationof residual ionswas lower than the drinkingwater criterion in China.Pumice and ZnOOH-pumice significantly accelerate the decomposition of ozone in water.The rate constant of ozone decomposition increased by1.19times and2.84times when using pumice and ZnOOH-pumice, respectively.When pumiceand ZnOOH-pumice catalyzed ozone, higher·OH concentrations were generated under the same experimental conditions compared with those obtained from ozonealone. Tert-butanol significantly inhibited the degradation of pCNB in these three catalytic reaction systems.Enhancements of hydroxyl free radicals were achieved during catalyzed ozone decompositionusing pumice and ZnOOH-pumice. Thus,the catalytic oxidation of pCNB can be divided into two parts: main reaction withhydroxyl radicals and accessorial oxidation by ozone molecules. High pH also positively affected pumice-catalyzed ozonation,given that nearly uncharged surfaces (solution pH was close to the point of zero charge) are favorable for catalytic pCNB ozonation.The results of this study indicatethat hydrous oxide sites present on catalyst surface (S-OH) serve a key function in the catalytic ozonation mechanism.Surface hydroxyl groups were revealed to be important ctive sites onthe catalyst. Hydroxides, which show high catalytic activityduring ozone decomposition, possess abundant surface hydroxyl groups. Structuralhydroxyls or hydroxylsformed through the adsorption of hydrogen ions in waterare capable of catalyzing ozone decomposition. Ozone molecules in water can be adsorbed on these active hydroxyls, consequently promoting ozone decomposition with the production of·OH.