Preparation And Application Of Chitosan-based Green Fenton-like Catalyst

Our life is beauty and colorfulness due to the use of organic dyes,but the direct discharge of dye wastewater into the water system will cause great harm to the ecosystem and human health.Fenton-like oxidation technology is an effective measure to treat dye wastewater.Transition metal oxides(e.g.,manganese oxide,iron oxide)are a kind of common Fenton-like catalyst.When nano-metal catalyzer is directly used for degradation reaction,there are the following technological defects:(1)Nano-particles tend to agg·Lomerate,which leads to lower catalytic efficiency;(2)Metal loss leads to the decrease of active components and secondary pollution of water;(3)The nanoparticles are hydrophilic and difficult to be separated from the water system after the reaction.Therefore,it is necessary to develop efficient,stable and easily separable Fenton-like catalysts.In this study,natural polymer chitosan(CH)attribute to abundant source,low cost and good adsorption capacity was used as the substrate,which can be treated with physical or chemical modification to prepare chitosan based carrier.Under mild in-situ conditions,the MnO2 and Fe3O4 were be immobilized in the chitosan-based carrier by the strong affinity of amino and hydroxyl functional groups in the CH structure for transition metal ions.Finally,the green 1D/2D/3D Fenton-like composite catalyst was prepared and methylene blue(MB)as model target,was used to investigate the catalytic activity of 1D/2D/3D Fenton-like composite catalyst.The detail content of this study includes three parts:(1)Design and synthesis of 1D carbon microsphere catalyst MnO2/CS.Nanoscale MnO2 was in-situ synthesized on the chitosan-based carbon microspheres by two-step hydrothermal-oxidation method.Chitosan-based carbon microspheres have large specific surface area and rich amino groups on the surface,which can be used to firmly fix a large number of metal active components through chelation to prevent loss.The concentration of precursor Mn(NO3)2 solution directly affects the particle size,specific surface area and catalytic activity of MnO2/CS.Under the conditions of pH 7,the optimal dosage of MnO2/CS0.16 was 1000 mg·L-1,and the addition amount of H2O2 is 25 g·L-1,the degradation efficiency of 50 mg·L-1 MB was 83.5%.The degradation efficiency of MnO2/CS0.16 remained at 75.2%after 6 times of recycling,which indicated that the prepared MnO2/CS was a Fenton-like catalyst with high activity and stability.(2)Design and synthesis of 2D paper-based catalyst(MnO2/CH-FP).In this method,nanometer MnO2 was uniformly embedded into the filter paper pretreated with chitosan through the process of "manganese salt impregnation in-situ redox at room temperature.The introduction of chitosan enhanced the interaction between ordinary filter paper and Mn2+,and further improved the activity and stability of nano-MnO2.The concentration of Mn(NO3)2 directly affected the physical structure and catalytic performance of MnO2/CH-FP composite catalyst.The optimal catalyst 1.0MnO2/CH-FP could degrade 95.6%of MB within 90 min(50 mg·L-1 MB,1 g·L-1 catalyst,30 mg·L-1 H2O2,pH=7).After 6 cycles,catalytic activity of 1.0MnO2/CH-FP could still maintain 83.3%.This paper based catalyst overcomes the shortcomings of traditional MnO2 nanoparticles which are easy to agg·Lomerate and difficult to recycle.Due to a crowd of exposed metal active sites,the catalytic performance of MnO2/CH-FP composite catalyst is nearly 50%higher than that of pure MnO2,and the reaction can be turned on/off instantaneously by insertion/removal.(3)Design and synthesis of the 3D magnetic gel sphere catalyst(MnO2-Fe3O4/CH).The synthesis mechanism of the 3D magnetic gel sphere catalyst is that Fe and Mn ions co-precipitation oxidation reaction under alkaline environment could form metal oxides and crosslinking polymerization of chitosan magnetic gel sphere.Within 60 min,the optimal degradation efficiency of MnO2-Fe3O4/CH for MB was up to 96.8%(50 mg·L-1 MB,30m mg·L-1H2O2,4.0 g·L-1 catalyst,pH=7).After 6 cycles,the degradation efficiency of MB was nearly 87%.The excellent catalytic activity and stability of MnO2-Fe3O4/CH was attributed to its stable porous structure,more active sites and the synergistic effect between two components.At the end of the reaction,the macroscopic magnetic gel spheres can be easily separated from the reaction system magnetically.