Study On Preparation And Catalytic Performance Of Graphene-loaded Ag-Ni Composites

As a large country in the textile industry,the treatment and recycling of printing and dyeing wastewater have an important impact on the coordinated and sustainable development of industry,economy and people's livelihood.At present,photocatalytic technology that can decompose azo dyes in printing and dyeing wastewater by catalytic reduction method,and has many advantages,such as simple operation,high degradation efficiency and thorough treatment.It has become one of the most potential technologies for printing and dyeing wastewater treatment.For photocatalytic technology,the photocatalyst is the main factor about catalytic efficiency.Meanwhile,the precious metals have an unshakable position in the field of catalysis because it is easy to absorb energy and stimulate electrons to participate in the reduction reaction,however,it also has the problems of easy agglomeration and low efficiency.Due to the unique structure and properties of two-dimensional materials,combining with precious metals,the catalytic efficiency can be improved and play a synergistic role.Therefore,aiming at the problems of easy agglomeration and low efficiency using nano metallic silver(Ag NPs)catalyst,the reduced graphene oxide(rGO)was selects as the carrier,Ag-loaded rGO(Ag/rGO)composite powder and Ag-Ni-loaded rGO(Ag-Ni/rGO)composite powder are prepared by reduction method.The phase structure,surface morphology and surface chemical state of the composite powder were systematically characterized by XRD,SEM,TEM,XPS,FT-IR and Raman,and so on.Taking methylene blue as the target pollutant,the catalytic performance of the prepared composite powder is tested,and the influence law of Ag/rGO and Ag-Ni/rGO composite powder on the catalytic performance of methylene blue is studied.Finally,the catalytic mechanism is discussed in detailed.The specific results are as follows:(1)Through the chemical reduction method,the rGO(graphene oxide(GO)50 mg)was selected as the carrier,and Ag/rGO composite powders with different silver loading were prepared by using Ag NO₃ of different mass(0,10,20,40,80 and 160 mg).The results show that the diffraction peaks of Ag/rGO composite powder are:(111),(200),(220)and(311),which mainly come from Ag NPs with face centered cubic structure.Meanwhile,granular Ag NPs are loaded on the interlayer and surface of rGO,and the most dimension of the Ag NPs particles are distributed in the range of 30–60 nm;With the increasing of silver loading,Ag NPs particles presents a certain agglomeration phenomenon;Combined with XPS test,it was found that some oxygen-containing functional groups(C-OH,C=O,O-C=O,etc.)remained in the rGO structure;the MB with the concentration 10 mg·L^-1 of 50 was catalytically degraded by 5 mg of Ag/rGO composite powder under different silver loading.The results showed that the maximum adsorption rate of Ag₁₀/rGO composite powder was 70%in 30 min and the maximum photodegradation rate of MB was 97.02%in 60 min.The degradation rate of Ag/rGO composite powder was characterized by first-order kinetic model,and Ag₂₀/rGO composite powder had the best degradation rate(k=0.05976 min^-1),which is 2.12 times of the degradation rate of Ag NPs(k=0.02817 min^-1).It is indicated that the rGO as carrier can effectively prevent the agglomeration of Ag NPs and improve the catalytic rate.(2)Bimetallic Ag-Ni/rGO composite powders with different nickel loading were prepared by chemical reduction method,using Ni(NO₃)₂·6H₂O(7.5,15,30,60 and 120 mg),GO 50 mg and Ag NO₃ 20 mg.The results show that the Ag-Ni/rGO composite powder has the same Ag NPs diffraction peak compared with Ag/rGO composite powder.When the load of nano nickel is less,it is difficult to measure the phase of Ni NPs due to the influence of metal electronegativity during the loading process.But with the increasing of loading,the peak intensity of the phase diffraction increases.The TEM test showed that the Ni NPs had smaller particle size than Ag NPs,and are filled the surface and interlayer of rGO.The SEM showed that the Ag NPs on the surface of rGO decreases with the increasing of Ni NPs load.In XPS spectra,there are still peaks with oxygen-containing functional groups in rGO,and the binding energy shift of Ni NPs is+0.6 e V,indicating that some Ni NPs have been oxidized.The catalytic MB experiment showed that the adsorption efficiency of Ag-Ni/rGO composite powder was lower than Ag/rGO composite powder.But it has higher photodegradation rate(98.27%)and degradation rate(0.6905 min^-1).It shows that the existence of a certain amount of Ni NPs can change the chemical environment of Ag NPs particles with the rGO as carrier.The electron migration efficiency is enhanced and the catalytic effect can be further improved.