Preparation and Analytical Application of Palladium Nanoparticles Protected by Organic-Ligands

Author:Zhang Lei

Supervisor:dong chuan li zhong ping


Degree Year:2019





Nanomaterials have been praised as “the most promising materials in the 21 st century”,and they have received more and more attention.Because of their special properties such as quantum size effect and macroscopic quantum tunneling,they show many excellent properties.Their characteristics make them have great scientific research potential and application prospects.Preparation of palladium nanomaterials with good stability,water solubility and dispersibility has become a research trend.In this thesis,small-sized water-soluble palladium nanoparticles(Pd NPs)with N-acetyl-L-cysteine(NAC)and N,N-dimethylformamide(DMF)as ligands were synthesized and then characterized by UV-visible absorption spectroscopy(UV-vis),infrared spectroscopy(IR),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA),Dynamic Light Scattering(DLS)and other techniques.In conjunction with reversed-phase high-performance liquid chromatography and mass spectrometry,palladium nanoparticles mixtures were analytically separated to capture more specific structures of various palladium nanoparticles.Finally,an electrochemical sensor was fabricated based on a water-soluble palladium nanoparticles modified electrode,with high sensitivity,good selectivity to copper(II)ions,excellent stability and low cost.the sensor could be applied to the detection of copper ions in the environment.Specifically,the content of the paper mainly includes the following:Chapter 1: Review of Palladium Nanaoparticles.The characteristics of nanomaterials,preparation methods,ligand,characterization methods and research progress of palladium nanoparticles were reviewed.Chapter 2: Preparation of NAC-protected Pd Nanoparticles.N-acetyl-L-cysteine(NAC)was used as a ligand,and water-soluble palladium nanoparticles were synthesized by reducing H2PdCl2 by Na BH4 under different NAC/Pd molar ratios under the condition of ice bath.The NAC-Pd NPs synthesized by different molar ratios were characterized by UV-Vis spectrophometry,X-ray photoelectron spectroscopy,infrared spectroscopy,thermogravimetric analysis and transmission electron microscopy.When the synthesized NAC/Pd molar ratio is greater than 2,the palladium nanoparticles are a mixture of PdII-NAC;however,when the NAC/Pd molar ratio is 1:1,the NAC-Pd NPs are Pd0 nanoparticles with a particle size of about 2.17±0.20 nm,and the dispersion and particle size distribution are uniform.It is concluded that the sulfhydryl group in the ligand NAC combines with the palladium atom to form a stable Pd-S bond during the reaction,and the H2 Pd Cl4 is reduced to a palladium atom by Na BH4,and NAC also rapidly reacts with the palladium atom to encapsulate it and prevent it from aggregation;thus,NAC acts as a ligand to stabilize and protect the palladium nanoparticles.Chapter 3: Analysis of NAC-protected Pd Nanoparticles.Using a column C18(250 x 4.6 mm,5 μm),the mobile phase is methanol and tetrabutylammonium fluoride(Bu4N +F-)aqueous solution,combined with gradient elution,using reversed-phase ion-pair high performance liquid chromatography The method separates water-soluble NAC-Pd NPs.The effects of Bu4 N +F-and methanol content on the separation of NAC-Pd NPs are studied.The fractions of 11 NAC-Pd NPs are separated by UV-Vis spectroscopy and matrix-assisted laser desorption tandem time-of-flight mass spectrometry(MALDI-TOF-MS)analyze.The results show that each of the separated components has a unique UV-Vis absorption spectrum that cannot be obtained by studying the NAC-palladium nanoparticle mixture.Eleven kinds of isolated NAC-Pd NPs are eluted in the order of the number of palladium atoms eluted from the C18 column.By studying the MALDI-TOF-MS of the separation components of NAC-Pd NPs,the particle characteristics of the components can be displayed,and the chemical composition of each of the separated components is obtained,which are Pd10(NAC)7,Pd11(NAC)7,Pd11(NAC)8,Pd12(NAC)9,Pd13(NAC)6,Pd13(NAC)9,Pd14(NAC)5,Pd14(NAC)9,Pd15(NAC)9,Pd17(NAC)11 and Pd20(NAC)11,respectively.Chapter 4: Synthesis of DMF-protected Pd Nanoparticles.N,N-dimethylformamide (DMF) as ligand-protected water-soluble palladium nanoparticles(DMF-Pd NPs)are synthesized and characterized by UV-Vis spectrophometry,fluorescence spectroscopy,and infrared spectroscopy,The as-synthesized DMF-Pd NPs are further characterized by thermogravimetric analysis and transmission electron microscopy.The results show that during the synthesis reaction,DMF plays a triple role namely solvent,ligand and reducing agent at the same time.When the heating temperature is higher than 100 °C,DMF firstly was decomposed into dimethylamine and carbon monoxide(CO),and palladium ions was reduced to zero-valent palladium atoms by CO,and then DMF acts as a ligand to coordinate with palladium ions to form a complex,which is wrapped around the periphery of palladium nanoparticles to prevent the aggregation of palladium nanoparticles,forming DMF-Pd NPs.The DMF-Pd NPs synthesized by this method display the characteristics of fluorescence luminescence,good dispersibility,uniform particle size distribution,an average particle size of about 2.20±0.70 nm,and are easily soluble in organic reagents such as water and methanol,which are beneficial to living organisms and applications in the field of sensors.Chapter 5: Analytical Separation of DMF-Pd NPs.Water-soluble DMF-Pd NPs are separated by reversed-phase high performance liquid chromatography using a C18 column(250 x 4.6 mm,5 μm)with mobile phase of methanol and water in combination with gradient elution.The effects of different methanol contents in mobile phase on the separation of DMF-Pd NPs are studied.The 13 kinds of DMF-Pd are characterized by UV-Vis spectroscopy,fluorescence spectroscopy and matrix-assisted laser desorption time-of-flight mass spectrometry(MALDI-TOF-MS).The results show that each of the separated components has its own characteristic UV-visible absorption spectrum and fluorescence spectrum,which are not known when only studying the mixture of DMF-Pd NPs.The chemical compositions of the separated components are obtained as: Pd14(DMF)8,Pd10(DMF)8,Pd12(DMF)11,Pd14(DMF)8,Pd14(DMF)10,Pd14(DMF)12,Pd15(DMF)12,Pd16(DMF)15,Pd16(DMF)15,Pd16(DMF)15,Pd20(DMF)9,Pd17(DMF)13 and Pd20(DMF)9.Wherein components 8-10 have the same molecular formula Pd16(DMF)15,and components 11,13 have the same molecular formula Pd20(DMF)9,but the order of elution from the C18 column is different due to the DMF ligand and the coordination difference of Pd NPs.Chapter 6: Fabrication of DMF-Pd NPs Modified Electrode(DMF-Pd NPs/GC).DMF-Pd NPs are modified on the surface of glassy carbon electrode by a drop-coating method,and the modified electrode are electrochemically characterized.The electrochemical response of DMF-Pd NPs/GC modified electrode to Cu2+ are studied and optimized.A method based on DMF-Pd NPs/GC modified electrode for Cu2+ is thus established,achieving stable,rapid and sensitive detection of Cu2+.This method has potential application for determination of Cu2+ in environmental water samples.The electrochemical sensor exhibits a good linear relationship in the range of 4×10-7-5×10-5 mol/L.The linear equation is: Ip(μA)= 5.5727×10-6 + 2.2444×10-4C(μmol/L),R2 = 0.970,and the detection limit is 5×10-7 mol/L(S/N=3).DMF-Pd NPs/GC modified electrode has almost no electrochemical response to common heavy metal ions pollutants such as Cd2+、Mn2+、Co2+、Mg2+、Fe2+、Hg2+、Pb2+、Zn2+,but only shows a good response to Cu2+.These results show that the prepared DMF-Pd NPs/GC modified electrode has good selectivity to Cu2+.