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Preparation Of Gold Nanoparticles In Functionalized Ionic Liquid And Periodic Mesoporous Organosilica

Posted on:2008-06-19Degree:MasterType:Thesis
Country:ChinaCandidate:P J WangFull Text:PDF
GTID:2121360215987492Subject:Physical chemistry
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Gold nanoparticles have been extensively investigated in recentyears because of their potential applications in optics, electronics, andcatalysis etc. The potentialities of nanoparticles are mainly due to thequantum size effect, which is derived from a dramatic reduction of thenumber of free electrons in nanoparticles smaller than 5 nm. Therefore,how to control carefully the particle size, distribution and stability of thenanoparticles becomes very important. On the one hand, alkanethiols arereported to be a kind of effective capping reagents for stabilizing thesmall size of gold nanoparticles (GNPs). However, the applications of theGNPs capped by such alkanethiol derivatives are limited due to lack ofwater solubility. Thiol-linked ionic liquids, known as "green solvent",with controllable miscibility with organic solvent and water determinedby their anionic and cationic structure, should be the potentially goodcandidates for the preparation of nanoparticles to satisfy variousapplications. Usually, sodium borohydride (NaBH4) is used as a reducingagent to obtain GNPs. However, it is not easy to control the stepwiseaddition of NaBH4, which may result in poor repetition of the GNPs withthe same properties. On the other hand, the catalytic and adsorptionproperties of GNPs are influenced by gold dispersion, structure andinteraction between GNPs with the support as well as the type of supports. For supported gold catalysts, the agglomeration of Au particles is a majorcause of catalyst deactivation. Usually, functional organic moietiescontaining polar head groups like -SH, -NH2, etc. are incorporated intomesoporous silicas to stabilize nanoparticles and to prevent particlesagglomeration. However, such organo-functionalized mesoporous silicaswith terminal organic groups possess an inhomogeneous distribution ofthe organic groups in the pore surface, which, ultimately, results in aninhomogeneous distribution of metal nanoparticles.In this dissertation, GNPs stabilized by either thiol-functionalizedionic liquid (TFIL) or a novel periodic mesoporous organosilica withionic liquid functional moieties containing disulfide groups weresynthesized. The main contents discussed were as follows:(1) A convenient sonochemical route to the preparation of goldnanoparticles capped by thiol-functionalized ionic liquid using hydrogenperoxide as a reducing agent was proposed. H2O2 instead of NaBH4 usedas a reducing agent not only avoids the troublesome stepwise additionprocedure but also simplifies the purification process in post-treatment.Ultrasound irradiation accelerates the formation of GNPs and helps thedispersion of nanoparticles in TFIL. It is found that the molar ratio ofgold atom in chloroauric acid to thiol group in TFIL (Au/S) has greateffects on the particles size and distribution of GNPs. Small goldnanoparticles size of 2.7±0.3 nm with narrow uniform distributions can be obtained at the molar ratio of Au/S=1:2 under ultrasound irradiationfor 12 h. It should be noted that the method presented here, which isperformed in ionic liquid and hydrogen peroxide solution underultrasound irradiation, is friendly to environment.(2) The stabilization of gold nanoparticles (GNPs) by disulfide groupslinked to imidazolium chloride units in periodic mesoporous organosilicaof SBA-15 and their catalytic performances in the epoxidation of styrenewere investigated. The mesoporous organosilica (PMO-SBA-15) wassynthesized via a one-pot condensation process involving the assembly ofionic liquid silsesquioxane organic precursor containing disulfide groupand tetraethoxysilane in the presence of P123. Aqueous chloroaurate ionswere in-situ reduced by the silanol groups presented on the channelsurface of the mesoporous organosilica to form GNPs that weresubsequently captured by disulfide group to obtain Au-containingmesoporous organosilica (Au-PMO-SBA-15). It was found that bothPMO-SBA-15 and Au-PMO-SBA-15 have the typical characteristics ofmesoporous SBA-15, and that the GNPs entrapped into the channels ofAu-PMO-SBA-15 possess mean size of ca. 1.8 nm. TheAu-PMO-SBA-15 was used as a catalyst in the epoxidation of styrene.95% of styrene conversion and 75% of selectivity to styrene epoxidewere obtained over the novel Au-PMO-SBA-15 catalyst. Furthermore, theAu-PMO-SBA-15 can be conveniently recovered for recycled use without significant loss of catalytic activity and selectivity.
Keywords/Search Tags:Gold nanoparticle, ionic liquid, ultrasound, periodic mesoporous organosilica, styrene epoxidation
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