Preparation And Application Of Carbon Encapsulated Metal Nanoparticles

Carbon encapsulated metal nano-particles (CEMNPs)are types of carbon/metalcomposite materials with core/shell structure in nanoscale. The different combination ofvarious metal nanometer materials as core and carbon as shell rewards the composite withmany peculiar physical and chemical properties.Therefore, CEMNPs have huge potentialapplications in many fields, such as s MRI contrast agent, bio-analysis, drug carrier, mediumhigh heat therapy, catalyst, magnetic record, magnetic separation and so on. The preparation,properties and applied basic research of carbon encapsulated metal nano-particles as a newkind of carbon based nanocomposite have become a research hotspot.A lot of methods have been developed for preparing carbon encapsulated metalnanoparticles. Currently, main preparation methods include high energy growing approach(such as electric arc, ion beam, laser and explosion), chemical vapor deposition and carbontransition. These methods have the features with high energy assumption, complex technicsand expensive prices. Moreover, the production rate is low for CEMNPs, especially forCEMNPs with magnetic cores, which limits the application and research interests ofCEMNPs.In this study, different types of carbon encapsulated metal nanoparticles, includingcarbon encapsulated cobalt nanoparticles (assigned as Co@C), carbon encapsulated coppernickel nanoparticles (assigned as CuNi@C), were prepared using pyrolysis the precursorunder N2atmosphere which obtained by evaporating the mixture solution of sucrose andmetal nitrate to dryness, and the preparation scale was dozens of grams at a time. A newpreparation method for synthesis of the monodispersed CEMNPs samples, which was namedas liquid reduction-high temperature carbonization method, has been put forward bycombination of soft chemistry method and pyrolysis method.Some CEMNPs samples,including carbon encapsulated copper nickel nanoparticles (assigned as Cu@C), carbonencapsulated iron nanoparticles (assigned as Fe@C), carbon encapsulated cobaltnanoparticles [assigned as Co@C(LR)] and carbon encapsulated iron-copper nanoparticles(assigned as FeCu4@C), have been prepared by the developed method. The preparation amontis dozens of grams once. The chemical composition, phase, micro-structure and some majorphysical, chemical properties of as prepared CEMNPs samples were systematicallycharacterized by various modern analysis methods. The friction and wear properties of somekinds of the as-prepared CEMNPs samples were then studied by adding them into the atoleine as an additive of lubricating oil. The electrochemical catalytic performance was measuredthrough modifying a glassy carbon electrode in the electrochemical reaction of p-Nitrophenol.The following research results are obtained in this study.The core of Co@C is fcc-Co while the shells are homocentrically hexagonal multi-layercarbon nets which are connected with some group, such as=O,-OH and so on. The dispersionparticle size is much bigger than that of observation under the transmission electronmicroscope (TEM) because there are some amorphous carbons being around of the Co@Cnanoparticles. Tthe average value of the former is equal to162.8nm and that of the latter isequal to35.3nm. The saturation magnetization, M_s, is equal to24.7emu/g under ambienttemperature measured using a vibrating specimen magnetometer (VSM), and the residualmagnetization, Mr=3.71emu/g, the magnetic coercive force, Hc=275.2Oe. The results ofTG-DSC test revealed that the metallic core of Co@C had been obviously oxygenated until1000℃for the protection of carbon shells. The sample of Co@C is an electrical conductorwhich resistivity is equal to9.46·cm under ambient temperature and there is absorbingcapacity for the microwave with the frequency of8～18GHz, the maximum is equal to6.36dB at the frequency of14.7GHz.The shells of Co@C(LR) are composed of amorphous carbons, and the cores arepolycrystal of fcc-Co. The nanoparticles are monodispersion with an average particle size of49.6nm. Only less than1/5of the carbons in the as-prepared sample are connected withanother carbon atom, and all of the else are connected with other groups. The cobalt atoms arein two states too. That is, the vast majority of the cobalt atoms are the metallic state, and theothers are oxidation state. The sample of Co@C(LR) showed a quasi-superparamagnetismunder room temperature, and M_s=130.7emu/g, Mr=13.0emu/g, Hc=56Oe. The special surfacearea (SSA) measured using BET method is equal to167.0m2/g. The friction and wear testresults of adding the sample into the atoleine as an additive of lubricating oil showed that theCo@C(LR) had better performance of friction-reduction and anti-wear. The bearing capacityof the test oil has significantly increased when the additive amount of Co@C(LR) is0.6wt%,and the friction coefficient (μ) and wear rate (W) decrease to minimum when the additiveamount is0.4wt%, which are lower than that of the matched oil. The Co@C(LR) haspresented good catalytic activity in the electrochemical reaction of p-Nitrophenol (PNP) bycomparing the CV curves measured using a glassy carbon electrode (GCE) modified by theCo@C(LR) with that of measured using a bare GCE.The core of CuNi@C is composed of the polycrystal of fcc-CuNi alloy and the shells are carbon of which the lattice fringes can be observed but no longer continuous and perfect. Thedispersion particle size is much bigger than that of observation under TEM because there aresome amorphous carbons being around of the CuNi@C nanoparticles. The average value ofthe former is equal to134.1nm and that of the latter is equal to55.0nm. The quantity ofcarbon atoms connected with another carbon atom is about one third and the else areconnected with other groups. All of the cobalt and nickel are in two states: metallic state andoxidation state. The CuNi@C is apoor electrical conductor whose resistivity is equal to100.56·cm under ambient temperature and there is absorbing capacity for the microwavewith the frequency of8～18GHz, the maximum is equal to8.1dB at the frequency of14.9GHz. The friction and wear test results of adding the sample into the atoleine as anadditive of lubricating oil showed that the CuNi@C had better performance offriction-reduction and antiwear. The friction coefficient and wear rate decrease to minimumwhen the additive amount of CuNi@C is0.6wt%, which are much lower than that of thematched oil.The core of Fe@C is mainly composed of the polycrystal of bcc-Fe and the shells areamorphous carbons. The nanoparticles are monodispersion with an average particle size of48nm. The quantity of carbon atoms of the samples which are connected with another carbonatom is about43%and the others are connected with–OH=N and so on. The ratio of iron formetallic state is about76%, the valence state of other iron is Fe3+. The magnetic properties ofthe Fe@C measured by VSM are: M_s=54.56emu/g, Mr=5.35emu/g, Hc=205Oe. The specialsurface area measured by BET method is equal to522.7m2/g. The Fe@C has present goodcatalytic activity in the electrochemical reaction of p-Nitrophenol (PNP) and the bestconcentration of NaOH solution is1mol/L.The core of Cu@C is mainly composed of the polycrystal of fcc-Cu and the shells areamorphous carbons, but the lattice fringe can be observed on local area. The nanoparticles aremonodispersion with an average particle size of49.5nm. The quantity of carbon atoms of thesamples which are connected with another carbon atom is about1/2and the else areconnected with other groups. The atoms of copper are in two states: metal and CuO. Thespecial surface area measured by BET method is equal to94.1m2/g. The friction and wear testresults of adding the sample into the atoleine as an additive of lubricating oil showed that theCu@C had better performance of friction-reduction and anti-wear. Compared with thematched oil, the friction coefficient decreased21.6%, the wear rate reduced30.0%when theadding amount was0.6wt%. The Cu@C has present good catalytic activity in theelectrochemical reaction of p-Nitrophenol (PNP) and the best concentration of NaOH solution is0.5mol/L.The core of FeCu4@C is mainly composed of the polycrystal of fcc-FeCu4and the shellsare amorphous carbons. The nanoparticles are monodispersion with an average particle size of62.8nm. The ratio of carbon atoms of the samples which are connected with another carbonatom is about36%and the else are connected with other groups. The atoms of copper are intwo states: metal and Cu(OH)2. The content of iron is very lower so only the metallic state hasbeen detected. The magnetic properties of the Fe Cu4@C measured by VSM are:M_s=13.01emu/g, Mr=0.37emu/g, Hc=54.43Oe. The special surface area measured by BETmethod is equal to269.9m2/g.The knowledge for the preparation, characterization and tribology of carbonencapsulated metal nanoparticles gained in this study would enrichthe basic theory ofCEMNPs and promote the application of CEMNPs.