The Construction And Performance Of Magnetic Alloy/Graphene Supported Noble Metal Composite

With the advances in science and technology,and the development of industrial technology,the massive discharges of various organic pollutants cause the severe environmental pollution,which has the adverse effects on our production and life of human beings.Therefore,it is important to develop an efficient method to remove the organic pollutions.The catalytic reduction is an efficient,energy-saving and simple method,which is suitable for the effective removals of organic pollution in wastewater without secondary pollution.As the most important part of the catalytic reduction,the efficient,stable and recyclable catalysts are vital for the catalytic reduction reaction.The traditional catalysts consist largely of noble metal nanoparticle materials.However,the shortcomings of noble metal catalysts restrict their wide application in the field of catalysis,including the easy agglomeration,difficult recovery and high cost.The reduced graphene oxide（rGO）materials have large specific surface area and strong adsorption properties.The cobalt platinum（CoPt）alloy materials have good magnetic properties and catalytic performance.Therefore,it is significant to construct the composite catalysts with high catalytic performance and good cycle stability,which are consisted of rGO,CoPt alloy materials and noble metal nanoparticles.In this thesis,the composite catalyst composed of rGO,CoPt alloy nanoparticles and noble metal nanoparticles were constructed,which showed the excellent catalysis properties with the significant recycling property.In the presence of sodium borohydride（Na BH₄）,the catalytic performance of the composite catalyst for the catalytic reduction of organic pollution was studied.The catalytic reduction mechanism was explored.The main contents and conclusions of this work are as following:The composite catalysts of rGO/Ag,rGO/Au and rGO/Pt were synthesized by employing a simple co-reduction process,in which the GO and noble metal salts acted as precursors.The rGO worked as the supporting of the nanoparticles,which did not change the structure of the noble metal nanoparticles.As for the rGO/Ag composite catalysts,the rGO/5×10^-4mol Ag composite catalyst showed the best reduction property for4-nitrophenol（4-NP）reduction,and the rate constant k was 0.531 min^-1.The rGO/5×10^-4mol Ag composite catalyst was reused 4 times with the conversion of 4-NP was still as high as 86.9%.At room temperature,the catalytic reaction of Rh B and MB were completed by rGO/5×10^-4mol Ag in 7 and 5 min,respectively.When the rGO was loaded with Au,Ag,Pt respectively,the rGO/5×10^-4mol Au and rGO/5×10^-4mol Ag completed the catalytic reaction in 8 and 9 min.However,rGO/5×10^-4mol Pt did not finished the reduction over 60min.The rate constant k(0.618 min^-1)of rGO/5×10^-4mol Au was similar to that(0.55 min^-1)of rGO/5×10^-4mol Ag.Therefore,in view of the cost of the catalyst,noble metal Ag was a better choice for the wide application in the field of catalysis.The superparamagnetic Co_xPt_100-x（x=25,35,50,65,75）alloy nanoparticle catalysts with a small size were prepared.Combined with the co-reduction,CoPt alloy nanoparticles with different atomic ratios were prepared by adjusting the atomic ratio of Co to Pt.When the contents of the Co were 25,50,75 at%,the structures of the nanoparticles were face-centered cubic and face-centered tetragonal,respectively.In addition,the superparamagnetic nanoparticles showed the good magnetic response to the external magnetic field.The Co_xPt_100-x（x=25,50,75）alloy NPs with small sizes exhibited high catalytic performance for the 4-NP reduction with Na BH₄.The k of Co_xPt_100-x（x=25,50,75）alloy nanoparticle catalysts was determined to be 1.464,0.857,and 1.75 min^-1,respectively.After 4 times catalytic cycle reaction,the alloy nanoparticle catalysts still displayed high catalytic efficiency for 4-NP.In the view of cost and stability,Co₅₀Pt₅₀alloy nanoparticle catalyst was suitable for the catalytic reduction of 4-NP.In addition,Co₅₀Pt₅₀showed the good catalytic activity for Rh B and MB,and the catalytic reaction was completed in 4 and3 min in the presence of Na BH₄.The CoPt/Ag composite catalysts were prepared by a simple reduction and self-assembly methods.The surfaces of Ag nanoparticles were decorated by PEI,and CoPt alloy nanoparticles were linked to Ag surface.The catalysis properties were tuned by adjusting the Ag content.When Ag content was 3×10^-4mol,the k value for CoPt/Ag was determined to be 2.212 min^-1,which was higher than other samples.The result suggested the CoPt/3×10^-4mol Ag composite catalyst exhibited the best catalytic reduction performance.After 4 catalytic reduction recycles,the conversion of 4-NP was around 83%,and the superparamagnetic CoPt/Ag composite catalyst maintained its structure,confirming its good cycle stability during the catalytic reaction.In addition,CoPt/3×10^-4mol Ag showed the great catalytic activity for Rh B and MB,indicating its suitability.Combined with co-reduction and deposition method,the rGO/CoPt/Ag composite catalyst was prepared with high catalytic activity,rapid magnetic recovery and stable recycle.The rGO/CoPt/Ag composite catalyst showed the excellent catalytic performance for the catalytic reduction of 4-NP.The catalytic reduction of 4-NP by rGO/CoPt/Ag was completed in 1 min in the presence of Na BH₄,and the value of rate constant k was determined to be 5.306 min^-1and the normalized rate constant(k_nor)was up to 56.76min^-1mg^-1.The excellent catalytic property of rGO/CoPt/Ag catalyst was due to the good adsorption of rGO,the dual catalytic properties of CoPt and Ag,and the synergistic effects from the different compositions in the composite catalyst.After 4 catalytic cycle reactions,the conversion of 4-NP was still over 85%,and the structure of catalyst was unchanged,confirming the good cycling stability of rGO/CoPt/Ag during the catalytic reduction reaction.In addition,when the Rh B and MB acted as target pollutants,rGO/CoPt/Ag showed the excellent catalytic activity for Rh B and MB,indicating its suitability.In brief,the rGO/CoPt/Ag composite catalyst had high catalytic performance,good cycle stability and general applicability.