Catalytic Hydrodechlorination Of 4-Chlorophenol With Palldium Nanoparticle Supported On Magnetic Chitosan

Chlorophenols were widely used in printing and dyeing,pesticides,paper making and cosmetics industries.But the potential risk for the ecological environment and human were also worrying.In recent years,people have paid increasing attention to it.Chlorinated phenols were classified in list of priority control pollutants by many countries and organization.How to remove the chlorophenols in water environment efficiently has become the research focus of researchers at home and abroad.The catalytic hydrodechlorination is consider to be a promising method for the degradation of chlorophenols in water because of its mild reaction conditions,fast dechlorination rate and high atomic utilization.The catalytic hydrodechlorination mainly depends on the catalyst,but most of the catalysts have some disadvantages,such as difficult separation,easy deactivation,narrow pH range of application and poor recycling effect.In order to solve these problems,the catalyst material prepared in this paper is the magnetic chitosan supported palladium nanoparticles(Pd@MCTS),which is easy to separate and performing great recycling stability as well as high dechlorination rate.In this paper,sodium borohydride(NaBH4)is used as the hydrogen source,and the operation and storage are safer and more economical than that of conventional hydrogen source hydrogen(H2).The target pollutant is 4-chlorophenol(4-CP),which is widely used in dye,medicine and pesticide industry.Variety of characterization were applied to analyze the Pd@MCTS.In the meantime,catalytic hydrodechlorination tests of 4-CP were implemented,under different conditions.The stability of Pd@MCTS was investigated.The kinetic analyze and reaction mechanism were studied.The paper consists of three parts as follow:(1)The magnetic chitosan(MCTS)was prepared by co-precipitant method,then Pd2+was reduced to Pd0 by NaBH4 through impregnation to be supported on MCTS,and formed Pd@MCTS.Transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS),diffraction of x-rays(XRD),Brunauer、Emmett and Teller Testing method(BET)and Vibrating Sample Magnetometer(VSM)were applied to studied Pd@MCT thoroughly.TEM results show that,the average particle size of Pd@MCTS is 7-10 nm with good dispersion.XPS analysis testified the successful loading of Pd,meanwhile,the amino group contributed to support Pd.Each facet of diffraction peak of Fe3O4 was obtained by XRD,and VSM measurement indicated that the loading of Pd improved the magnetic properties of the supports.Through BET,the specific surface area was 57.60 m2·g-1.The results displayed that the supported Pd nanocatalyst with good dispersivity and easy separation has been successful prepared.(2)Several tests with diverse reaction condition were employed to investigate the performance of Pd@MCTS,including initial pH of solution,the dosage of NaBH4,Pd loading ratio,dosage of Pd@MCTS and reaction temperature,and evaluate this factor’s influence on catalytic effect.Experiments prove that the products of hydrodechlorination was only phenol and the selectivity was 100%.Meanwhile Pd@MCTS could adapt to different range of pH,which could complete 100%dechlorination at different pH range.Only 5 mM NaBH4 was needed to remove 1 mM 4-CP in 30 mins,furthermore,the reaction rate constant per unit was 57.07 min-1 g-1.Pd@MCTS could reach 96%removal rate of 4-CP after 4 times recycling tests displaying good stability.The results show that the excellent dechlorination performance of Pd@MCTS.(3)The catalytic hydrodechlorination kinetic model of Pd@MCTS was established.The apparent rate constants in different Pd loading,dosage of Pd@MCTS and different reaction temperature were calculated,and the reaction activation energy was figured as 50.15 kJ·mol-1.The reaction mechanism of HDC of 4-CP by Pd@MCTS was discussed.Pd@MCTS can both activate H2 to hydrogen radical(H*)attacking C-Cl bond and catalyzed the hydrolysis of NaBH4.NaBH4 plays a role in regulating pH and providing H2 at the same time.According to the different pH,the hydrolysis mechanism of NaBH4 includes acid catalytic hydrolysis and Pd catalytic hydrolysis.In this paper,the synthesis and preparation of Pd@MCTS Nano catalyst has good magnetic separation and stability,and has excellent dechlorination performance at different pH.It has practical significance for the treatment of chlorophenols in water.