Laser-controlled Synthesis Of Noble Metal Nanocomposites And Their Excellent Properties

Due to the combination of noble metals(Au,Ag,Pt,Pd)and other components,noble metal nanocomposites with tunable electronic structure exhibit excellent photo-electric conversion/transmission performance,which has been widely used in biomedicine,environmental monitoring,renewable new energy/conversion and storage.Among them,noble metal Au、Ag nanomaterials due to their inherent located surface plasmon resonance(LSPR)can be efficiently adjusted in visible-near infrared region,resulting in strong electromagnetic field generated by the laser excitation,which can enhance the Raman signal of probe molecules.The surface-enhanced Raman scattering(SERS)substrates constructed in this way can be used in micro-analysis of biomedical molecules,early diagnosis of tumor cells,monitoring of organic pollutant molecules,and trace detection of organic pesticide residues on fruits and vegetables.In addition,noble metal Pt.Pd nanomaterials because of their special d-electron orbit exhibit superior electrocatalytic activity,playing an important role in the development of high-efficiency clean energy such as direct methanol fuel cells(DMFC),proton exchange membrane fuel cells(PEMFC)and rechargeable metal-air battery.A lot of studies show that ingeniously control the microstructure of noble metals can significantly improve the properties of functional materials,which has attracted extensive attention of researchers at home and abroad.In recent decades,researchers have been devoted to regulating and optimizing the microstructure of noble metal nanomaterials.At early stages,researchers maily focused on regulating the morphology(multi-branches,hollow cages,two-dimensional layers,etc.),particle size and crystal phase(high index crystal plane,surface defects)of monometallic nanostructures.Subsequently,researchers gradually realized that the simplification of components greatly restrict the multi-functional application.Compared with monometallic nanostructures,bimetallic or multimetallic noble metal nanocomposites composed of two or more components exhibit more excellent performance in many applications due to the synergistic effect between different metals.At the moment,the overgrowth of noble nanostructures on the surface of two-dimensional(2D)materials(graphene and its derivatives)has been a new trend.The obtained nanocomposites present significant advantages:make full use of the large specific surface area of 2D support materials;benefit for the efficient transmission of free electrons in 2D plane;overcome the aggloration of noble metal nanoparticles and reduce the cost of noble metals in the application field;improve the utilization of noble metals and efficiently promote the industrialization process;the sufficient coupling between the two materials makes the resulting products not only have their own excellent physical/chemical properties,but also the unique interface effects can further stimulate new functions.Therefore,the exploration and construction of the unique nanocomposites has become the latest research trend.The research on the optimization of 2D materials/noble metal nanocomposites still has some limitations,and needs to be further improved.Most of studies mainly focused on 2D materials such as graphene,graphene oxide(GO),reduced graphene oxide(rGO)or transition metal sulfides.However,the chemical property of these 2D structures is unstable and not suitable for long-term application under extremely harsh(high temperature environment or strong oxidation/reduction environment)conditions,which limits the SERS detection of these 2D/noble metal nanocomposites in high temperature and strong oxidation or electrocatalytic reaction in strong acid/alkaline solution.In order to solve the above problems,it is an effective way to grow noble metal nanomaterials on the surface of 2D materials with extremely stable chemical properties,the obtained nanocomposites served as a multifunctional device is expected to be applied in the complex and harsh environment.At present,conventional synthesis method(based on high temperature/pressure nucleation or strong oxidation/reduction reactions)is difficult to realize the optimal control of this nanocomposite.In the view of this,a novel and effective synthesis strategy for the overgrowth noble metal Au,Ag,Pt,Pd nanostructures on 2D materials with extremely stable chemical properties is a key issue that needs to be solved urgently.This paper mainly focuses on the synthesis strategy of UV laser-induced irradiation in the liquid.By laser exciting 2D h-BN semiconductors to generate electron-hole pairs,the induced excited electrons as reducing agent can effectively reduce metal ions in the surrounding solution,and grow noble metal nanoparticles on chemically stable h-BN.Based on the above strategy,h-BN/Au and h-BN/CuAg as well as h-BN/PtPd coral-like nanocomposites have been successfully constructed.The uniqueness of this research:electrons and holes generated by laser irradiation of h-BN are easy to recombine instantly,the introduction of little eathanol can consume the generated holes,which effectively reduce the recombination rate of electron-hole and prolong the life of excited elctrons.Therefore,the growth efficiency of noble metal is greatly improved,which is beneficial to the optimization design the microstructure of noble metals.On the basis of this,the surface-enhanced Raman scattering(SERS)activity of h-BN/Au and h-BN/CuAg as well as the excellent electrocatalytic performance of h-BN/PtPd have been deeply investigated.In addition,by extending the strategy of laser ablation in liquid,we also synthesize hollow Ag@Au nanostructures,Pt/Ag nanourchins and Ag2S@Ag nanocomposites The main research contents and important research results obtained in this thesis are as follows:(1)Exploration of UV laser(405 um)irradiation-induced synthesis strategy,and overgrowth of Au nanoparticles on 2D h-BN.The content of Au nanoparticles(0-1.85%)can be regulated by changing the laser irradiation parameters,realizing the controlled synthesis of h-BN/Au nanocomposites.Based on the obtained h-BN/Au nanocomposites,using crystal violet(CV)as probe molecule,the SERS characteristics were systematically analyzed.Results show that h-BN/Au nanocomposites with 1.68%Au content perform excellent SERS activity,and the detection limit for CV molecules can reach femtomole(fM,10-15 M,which is better than many previous reports.The optimized h-BN/Au nanocomposites have been further applied to the SERS detection of biomolecule creatinine,which provides new ideas for accurate assessment of renal function damage in clinical medicine.(2)Based on the strategy of UV laser(405 nm)irradiation-induced in liquid,we successfully synthesized h-BN/CuAg nanocomposites.Compared with monometallic h-BN/Au and h-BN/Ag,the obtained h-BN/CuAg nanocomposites exhibit higher SERS activity due to the bimetallic synergy effect.The detection limit for CV molecules can be as low as 10-16 M,which is beneficial to ultra-low molecular diagnostic analysis.On the basis of this,we also obtained h-BN/CuAg/PET flexible substrates by directly combining the synthesized h-BN/CuAg nanocomposites with poly-terephthalic acid plastic(PET).Using this flexible material as SERS substrate and applying it back to the surface of tomatoes,we successfully realized the detection of pesticide residuals(tricylazole molecules)on the curved surface of tomatoes.The h-BN/CuAg/PET composites can not only reduce the cost of Au-based SERS substrates,but also can provide a basis for ultra-sensitive food safety and environmental pollution detection.(3)Fluffy coral-like h-BN/PtPd nanocomposites have been successfully synthesized by UV laser(405 nm)irradiation-induced in liquid.The content of noble metal component in h-BN/PtPd nanocomposites can be effectively adjusted by regulating the concentration of Pt2+and Pd2+ions.On the basis of this,the elctrocatalytic performance of tunable h-BN/PtPd nanocomposites was explored with the electrocatalytic alcohol reaction as the analysis object.The study found that h-BN/PtPd(Pt:Pd～l:1)has the most excellent electrocatalytic activity and long-term stability.For the methanol oxidation reaction(MOR)in alkaline solution,the peak of oxidation current reached 1462.8 mA mgPtPd-1,which is 5.4 and 13.4 times that of the commercial Pt/C(271.7 mA mgPt-1)and Pd/C(108.9 mA mgPd-1)catalysts,respectively.And after 50000 s cycle test,the current density can be maintained at 274.9 mA mgPtPd-1,which is about 200 times that of commercial Pt/C and Pd/C catalysts.The excellent elctrocatalytic performance of h-BN/PtPd nanocomposites is mainly due to the novel catalyst with a high-density surface nanoporous configuration,considerable specific surface area of two-dimensional h-BN,synergistic effect of PtPd and hydroxyl functional groups formed on the surface of the materials.The study based on laser-induced the optimization of h-BN/PtPd nanocatalysts can provide new opportunities for designing high-performance electrocatalytic fuel cells.(4)Extended exploration of laser ablation in liqud,based on the rapid quenching and cooling crystallization characteristics of the hot Ag plasma generated in the ablation,the obtained Ag nanoparticles have a unique structure with stable shell and internal lattice defects.Ag@Au nanocomposites with hollow interiors and dendritic shells can be controlled synthesis by subsequent galvanic replacement reaction.The efficient SERS activity of hollow Ag@Au multidentritic nanocomposites was explored,and it was found that this structure has good long-term stability in different liquid phases(ionic and strongly oxidizing solutions).In addition,we also fabricated Ag2S@Ag nanocomposites based on this synthesis,and studies shown that subsequent laser irradiation can also excite,disturb and reconstruct metal atoms on the surface of the material to achieve the optimization of the micro-defect structure.This novel nanocomposite structures have a significant electrostatic adsorption effect on methyl blue molecules(MB).After adsorption,these two materials will agglomerate together and naturally deposit to the bottom of the solution,overcoming the tedious separation of traditional nanoadsorbents after adsorbing pollutants,which provide a new idea for water pollution treatment.Based on the as-prepared Ag2S@Ag nanoparticles,we further synthesized Pt/Ag nanourchins using galvanic replacement reaction and explored excellent electrocatalytic performance.The series of research is beneficial to promoting the application and exploration of laser micro-processing and modification technology in many cutting-edge cross-disciplines.