Catalytic Degradation Of Nitrobenzene In Aqueous Solution Using Titania-containing Slag

Nitrobenzene (NB) is a typical and environmental persistent organic pollutant (POP). Purification of wastewater contaminated with this pollutant is very difficult using general biological and chemical methods, since it is usually stable and disinfectant. In this work, concentrated titania ore, high-titania slag and titania-bearing furnace slag were used as the raw material for catalysts, aiming at an integrated utilization of resources and low-cost fabrication of semiconductor material. The removal efficiency of nitrobenzene catalyzed by titania-containing Slag under light, electricity, ultrasound thermal oxidation was investigated. The kinetics and mechanism of NB degradation under the conditions of light, electricity, ultrasound and thermal oxidation were analyzed. The conditions of reaction for nitrobenzene degradation were optimized, and BOD, COD, TOC of nitrobenzene wastewater were evaluated after the treatment.(1) Removal efficiency of nitrobenzene catalyzed by titania-containing slag under 365 nm high pressure mercury lamp,365 nm low pressure mercury lamp,254 nm low pressure mercury lamp and solar light in room was investigated. The products were also analyzed by high performance liquid chromatography (HPLC). The results showed that the effect of light source on the degradation of nitrobenzene is 365 nm high-pressure mercury lamp> 254 nm low pressure mercury lamp> 365 nm low pressure mercury lamp. However there is no degradation of nitrobenzene under solar light in room.100% of NB removal could be reached after 90 min under 365 nm high pressure mercury lamp. Total organic carbon removal rate was 78.52%. NB was ultimately oxidized to CO2 and H2O without other by-products by the action of free radicals provided by the ultrasound-catalysis. There is a by-product—m-nitrophenol produced. Titania-containing slag can remove nitrobenzene catalytically in the presence of light. The order is high-titania slag> concentrated titania ore> pangang slag> chenggang slag. Changes in acidity of the degradation rates of nitrobenzene were not significant in the range of pH from 3 to 11. Slightly acidic condition was conductive to reaction.(2) Electrochemical measurements of nitrobenzene aqueous solution under carbon paste electrode (containing 1% catalyst powder) as the working electrode was investigated. The results showed that the reaction of nitrobenzene which was reduced to aniline on the electrode was irreversible direct electrode reaction. Nitrobenzene electrode reactions were controlled by the diffusion steps. In acidic medium, the apparent activation energy of reduction of nitrobenzene to aniline is 14.11 kJ·mol-1 at room temperature. Its activation energy is lower, indicating NB reduction was easy on carbon paste electrode. In the inactive electrode system, the reaction factor of NB reduction to aniline was first-order. The observed rate constant k’ was 0.01895 min-1. BOD5/COD values increased from 0.07 to 0.57 after 40 min under experimental conditions, which made it possible that NB wastewater was treated by biodegradation(3) Removal efficiency of nitrobenzene was investigated by electrochemical advanced oxidization using dimensionally stable anode (DSA) basis Ti as electro-catalytic electrode and titania-containing slag. The products in anode and cathode were also analyzed by HPLC. The removal mechanism of nitrobenzene can be postulated from the results that nitrobenzene degradation follows the steps as nitrobenzeneâ†'p-nitrophenolâ†'phenolâ†'CO2 and H2O on the action of free radical.100% of NB removal could be reached after 25 min under 30 V when high-titania slag was used as catalyst. The products in anode were completely removed after 30 min on the analysis of COD value which showed no discharge of contaminants. With the extension of reaction time, the BOD5/COD value of product in cathode increased gradually and NB aqueous solution obtained biotransformation capability after 20 min.(4) Removal efficiency of nitrobenzene catalyzed by titania-containing slag under ultrasound was investigated, and the products were also analyzed by HPLC. The results showed that titania-containing slag can remove nitrobenzene catalytically in the presence of ultrasound. When 18.0 g·L-1 high-titania slag was used as catalyst, the removal efficiency of NB could reach 100%after 140 min under 45 kHz ultrasonic frequency. NB was ultimately oxidized to CO2 and H2O without other by-products by the action of free radicals provided by the ultrasound-catalysis. The reaction factor of NB degradation by ultrasound action was first-order. The observed rate constant kus was 0.00407 min-1. The corresponding reaction equation by ultrasound in the presence of high-titania slag is-d[NB]/dt=kUS[NB]+kseckpt[NB].Biotransformation increased after treatment of ultrasound. BOD5/COD value of NB wastewater treatmented 180 min under 45 kHz ultrasonic frequency increased nearly 10 times than original solution. NB aqueous solution obtained biotransformation capability.(5) Removal of nitrobenzene (NB) was investigated by using H2O2 as oxidizer and the reaction products were analyzed by HPLC. The effects of catalysts, initial concentration of NB, reaction temperature and time on NB degradation were studied by orthogonal layout experimental design. The results showed that free radical formed by H2O2 in thermal oxidized condition could attack the NB molecule, and NB degradation follows the steps as nitrobenzeneâ†'nitrophenolâ†'carbon dioxide and water. There was no accumulation of the trace intermediate products of o-, m-, p- nitrophenol. The products were in accordance with radical characteristics of degradation products. However, in NaClO medium system, oxidation product is catechol, in accordance with oxidation product. The nitrobenzene degradation kinetics was first-order and the observed reaction rate constant k’ was 0.0073 min-1...