Preparation Of Magnetic Chitosan Supported Silver Catalysts And Their Catalytic Application

Chitosan is a very abundant biopolymer containing a number of amino andhydroxyl, which allows it has a strong chelation for metals ions. Chitosan can be usedas a good support as it is able to reduce metal ions while stabilizing metalnanoparticles. In this thesis, magnetic chitosan supported silver catalysts weresuccessfully prepared and characterized by means of FT-IR, XRD, TG and TEM.Various factors influencing catalytic degradation of the azo dyes (methyl orange,Congo red and acid scarlet GR) and nitro dye (4-nitrophenol) over the synthesizedcatalysts in presence of sodium borohydride were investigated.Firstly, Fe3O4nanoparticles were synthesized using coprecipitation, magneticchitosan were fabricated by crosslinking, and magnetic chitosan supported silvercatalysts were prepared by reduction of silver nitrate solution under thermal treatment.The catalysts were characterized by means of FT-IR, XRD, TG and TEM and theresults indicated that silver nanoparticles on the synthesized catalysts were smallerthan10nm in diameter, and the size of Fe3O4nanoparticles was in the range of10-30nm.Secondly, effects of the process conditions of preparing magnetic chitosansupported silver catalysts and the evaluation condition on catalytic performance ofmethyl orange degradation were investigated. The optimum conditions for thecatalyst preparation are reaction temperature80℃, reaction time3h, pH9andconcentration of silver nitrate0.05mol/L. The catalyst prepared at this condition wasused for the degradation of10mg/L methyl orange in presence of sodiumborohydride and the degradation rate of methyl orange could reach more than90%within20minutes. In addition, the result shows that increasing the amount of catalyst,decreasing the initial methyl orange concentration is beneficial to the catalyticreaction. The rate constants evaluated in terms of pseudo-first-order kinetic modelincreased with increasing the amount of catalyst and decreasing the initial methylorange concentration. For other azo dyes, the catalyst also exhibited excellent catalytic activity to the reduction of Congo red and acid scarlet GR with sodiumborohydride. The degradation of20mg/L Congo red and acid scarlet GR only require42minutes.Lastly, magnetic chitosan supported silver catalysts were also used for thereduction of4-nitrophenol with sodium borohydride. The result shows that thecatalytic reaction was accelerated by increasing the temperature, decreasing the initial4-nitrophenol concentration, or increasing the amount of catalyst. The reductionreaction followed the pseudo-first-order kinetic and was diffusion controlled, theapparent activation energy was about31.64kJ/mol. The rate constant increased whilethe temperature increased, the initial4-nitrophenol concentration decreased, or theamount of catalyst increased.During the catalytic degradation of azo dyes and nitro dye in presence of sodiumborohydride, magnetic chitosan supported silver catalysts demonstrated high catalyticactivity and stability. Moreover, the results of catalysts reuse suggested that thesynthesized catalysts were not poisoned or deactivated during the catalytic reaction,and the catalysts could be easily recycled and reused. Hence the magnetic chitosansupported silver catalysts are environmental friendly.