Synthesis And Catalytic Properties Of Supported Silver Nanocomposites Catalysts

The treatment of water environmental pollution is an important part of ecological civilization construction,especially the advanced treatment of refractory organic pollutants,which is the core problem and technical bottleneck of the current global environmental pollution treatment.Fortunately,recent studies have found that catalytic reactions driven by silver nanoparticles（Ag NPs）are considered to be one of the most effective methods for the treatment of organic pollutants in water.However,a single Ag NPs is easily oxidized and agglomerated and loses its catalytic ability.In order to solve these problems,the most effective method is to doping silver into various carriers.Therefore,the preparation of such supported nano-silver catalyst and its application in the catalytic reduction of organic pollutants in water has important research value and scientific significance.In this paper,highly active silver nanoparticles were prepared on the support of artificial allomelanin nanoparticles（AMNPs）,natural sepia eumelanin（SE）and porous silica zeolite nanoparticles（PSZN）,respectively,which can reduce methylene blue（MB）and 4-nitrophenol（4-NP）efficiently.In addition,the effect of the porous structure and active group of the support on the supported small size Ag NPs was studied.The contents were summarized as follows:In this paper,AMNPs prepared by 1,8-dihydroxynaphthalene（1,8-DHN）oxidation and oligomerization were used as the support to prepare Ag/AMNPs nanocomposite catalyst.This catalyst was prepared by in situ self-reduction of silver ammonia solution with the effect of electrostatic attraction and the using electrons released by transforming the group of 1,8-DHN on carriers surface to the quinone structure,which were analyzed and characterized by FT-IR,XRD,UV-Vis,SEM and TEM.It was found that Ag NPs were uniformly distributed on the surface of AMNPs microspheres.With the increase of Ag loading,the particle size of Ag NPS gradually increased,and which distribution ranged from 3-30nm.The catalytic tests showed that the prepared Ag/AMNPs nanocomposite microspheres had high catalytic activity in catalytically reduced MB and 4-NP,with corresponding reaction rates of 0.91 min^-1and 0.32 min^-1,respectively.On this basis,SE,which was separated from cuttlefish ink sac,was used as a support to load Ag NPs with a mean particle size of 5.23 nm.Using polyvinylpyrrolidone（PVP）as the reducing agent,a series of Ag/SE nanocomposite microspheres with significant catalytic activity were obtained.The catalytic reduction experiments show that the Ag/SE catalyst has the best catalytic performance when the silver concentration of precursor is 1 M,the removal rates of MB and 4-NP were 0.24 min^-1and 9.08×10^-3s^-1,respectively,and the removal rates were above 98%.In addition,SE rich active groups and photothermal conversion effect can not only bind Ag NPs by electrostatic adsorption and coordination effect,but also accelerate the reaction under light conditions to play a catalytic role.Finally,porous PSZN were synthesized by hydrothermal method,and Ag/PSZN nano-composite catalyst was prepared using this powder as support.The morphology of PSZN shows that the porous structure of PSZN provides a large number of sites for small size Ag NPs loading and inhibits its agglomeration by spatial confinement.By changing the concentration of precursor silver,the loading of Ag NPs could be effectively regulated.With the increase of Ag content,the catalytic reduction of 4-NP and MB by Ag/PSZN would increase first and then decrease.The Ag NPS was only 3.97 nm in average size,and the catalytic reduction of MB(4 min,0.77 min^-1)and 4-NP(200 s,1.03 min^-1)was the first order reaction,after 10 cycles of reaction,the removal rate of both pollutants can be maintained above 90%,with good repeatability.In addition,adsorption experiments also confirmed that PSZN carrier also has a good ability to adsorb pollutants can assist catalysis.