| With the rapid development of chemical industries,there are more and more water-soluble aromatic dyes and nitro compounds existing in water environment,which pose a serious threat to human life and health.Treating these water-soluble aromatic pollutants with the method of catalytic reduction has attracted extensive attention due to its advantages of simple operation,high efficiency,thorough treatment and low cost.Therefore,it is of increasing scientific significance to find an efficient,stable and recyclable catalyst.In this dissertation,Ni-Ag bimetallic nanoparticles and their graphene composites were prepared in response to the problems of easy agglomeration and difficulty in separation and recovery of nano-silver catalysts,and the effect of structure,morphology on catalytic properties were studied systematically.Furthermore,the xomposite catalysts were endowed with the magnetic response to the external magnetic field.The catalytic performance of the composites for catalytic reduction of 4-nitrophenol was also studied.The details are as follows:?1?Ni-Ag bimetallic catalysts with different molar ratios of Ni and Ag?2:1,1:1 and 1:2,respectively?were prepared by one-step method,and the effects of different molar ratios on the structure,morphology,dispersion and magnetism of Ni-Ag bimetallic particles were studied systematically.The XRD test indicated that Ni and Ag existed in the composites,both of which were plane-centered cubic structures,and no other phases were detected.The results of SEM showed that the microstructure of Ni-Ag bimetallic catalyst was granular and its dispersion decreased with the increase of Ag content.TEM showed that the prepared nanoparticles were Ni-Ag bimetals.The catalytic activity of the composites was studied using 4-nitrophenol as the pollutant model.The results showed that the Ni-Ag bimetallic catalyst had excellent catalytic activity for reduction of 4-nitrophenol,among which the[Ni]:[Ag]=1:1 catalyst had the best performance.10 mg of Ni-Ag bimetallic catalyst can completely catalyze the 4-nitrophenol of 0.1 mmol/L within 12 min,and its reaction rate constant?k?was 0.2568 min-1.The saturation magnetization intensity of[Ni]:[Ag]=2:1,1:1and 1:2 were 21.94,15.43 and 7.62 emu/g,respectively,showing the excellent magnetic response to the external magnetic field,and magnetic recovery can be achieved.The cyclic experiments showed that the performance of the catalyst had just a slight decline even after 5cycles,so it had excellent stability.?2?Ni-Ag/rGO composite catalysts with different weight fractions of GO?0.0 wt%,0.1wt%,0.5 wt%,1.0 wt%?were prepared by one-step coreduction method.The structure,morphology,element composition and magnetism of Ni-Ag/rGO composite were analyzed by XRD,XPS,SEM,TEM and SQUID.The results showed that the dispersion of Ni-Ag/rGO composite became better with the addition of GO but then got worse with the further increase of the GO,in which the GO weight fraction of 0.1wt%and 0.5wt%was the best,and the average particle size was the smallest?60 nm?,and Ni-Ag bimetallic particles were loaded uniformly on the rGO.XPS results showed that trace amounts of Ni atoms on the surface of Ni-Ag/rGO composites were oxidized,and the Ni2p peak occurs forward shift of 0.5 eV,indicating that some electrons were transferred from Ni-Ag to rGO,which enhanced the catalytic activity of Ni-Ag/rGO.The catalytic reduction of 4-nitrophenol showed that the catalytic performance was the best when the GO weight fraction was 0.5wt%,with a k value of 0.8585 min-1.10 mg of Ni-Ag/rGO could completely reduce4-nitrophenol within 4 min,and showed an excellent recycling performance.Its catalytic enhancement mechanism was that rGO introduced the graphene network of transferring electrons,which accelerated the electron conduction between Ni-Ag bimetals in the catalytic process,thus enhanced the catalytic activity of the material,and improved the catalytic activity for reduction of 4-nitrophenol. |
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