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ABSTRACT
Azo dyes are highly toxic and difficult to degrade. Decolourization of acid red 18 (AR18) and reactive yellow 4 (RY4) dye wastewater by the NaClO/NiOx(OH)y catalytic system was studied. The influence of reaction conditions was investigated. Their degradation mechanism was discussed by free radical scavenging experiment, and the degradation pathways were proposed. The continuous flow experiment was conducted. The results showed that the catalytic oxidation has a good decolourization effect on AR18, but it is not ideal for RY4. The continuous flow experiment of 3000 min showed that the decolourization effect was stable. The concentration of Ni2+ in the effluent from the reactor was always up to the standard, and the catalyst was not deactivated. The decolourization mechanism of the two dyes is different: AR18 is mainly decolourized by atomic oxygen/singlet oxygen, while RY4 is mainly decolourized by NaClO. The catalysts were characterized by XPS and XRD. The surface contains the largest proportion of chemisorbed oxygen. With the extension of the catalyst service time, chemisorbed oxygen decreased slightly and was converted into atomic oxygen/singlet oxygen, which was consumed in the decolourization process. Compared with the used catalysts, the β-NiOOH crystallinity of the fresh catalyst is better. The quantitative structure–property relationship analysis based on the decolourization data shows that there is a good linear correlation between the decolourization rate of azo dyes and their molecular structure descriptors. The inorganic–organic properties balance (IOB) value was determined as the main molecular descriptor that affected the decolourization of dyes.
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Wenying Xu
Dr Wenying Xu's career can be characterized as balanced in two aspects. She has developed successful research in wastewater treatment and sewage sludge treatment and teaching career in environmental engineering and management. She has over 20 years of experience with the industrial wastewater technology, 3 years of experiences with pyrolysis of sewage sludge and 18 years of university teaching. During her career, she has authored or co–authored over 80 journal manuscripts, conference papers, and technical report publications (20 peer reviewed journal manuscripts published in the past 5 years, among which 12 were included by SCI and EI). Dr. Xu's primary research interest is industrial wastewater treatment (including printing and dying wastewater, chemical wastewater, heavy oil produced water, refinery wastewater and cocking wastewater), electrochemical disinfection of drinking water and wastewater and pyrolysis of sewage sludge. Haoyang Gao was Dr. Xu's graduate student and has graduated. He is now an engineer in a well–known design institute in Shanghai.
Haoyang Gao
Haoyang Gao graduated from Tongji University 2 years ago, and now works as a water treatment engineer in a state–owned environmental protection design institute, participating in the design and commissioning of several water treatment projects. During the two and a half years of the post–graduate study, he and Dr. Xu had 5 research papers published related to this study, of which 3 are references #10, #11 and #16 in the paper. His thesis title: Preparation of catalyst for catalytic oxidation of sodium hypochlorite and its application in degradation of simulated printing and dying wastewater.