不同水环境对纳米银颗粒聚集体粒径大小及界面电势的影响_英文_.pdf

收稿日期：2011-10-22。收修改稿日期：2011-12-10。广西省教育厅(No.2010101X536)资助项目。通讯联系人。E-mail：不同水环境对纳米银颗粒聚集体粒径大小及界面电势的影响张红印1陈少峰,2林庆宇3(1罗德岛大学土木与环境工程系，金士顿02881，美国)(2茂名职业技术学院化学工程系，茂名525000)(3贺州学院化学与生物工程系，贺州542800)摘要：研究了不同水环境对无稳定剂与PVP为稳定剂的纳米银颗粒的物化性能的影响。结果表明：随着电解质浓度的增加，纳米银颗粒的粒径与界面电势逐步增大；二价阳离子比一价阳离子更能有效地使纳米银粒径与界面电势增加；稳定剂PVP，腐植酸及其他天然有机物能够增加纳米银溶胶的稳定性；在天然水体中，纳米银在海水中的粒径颗粒与界面电势比湖水中更大。关键词：纳米银；稳定剂；粒径；界面电势中图分类号：614.122文献标识码：A文章编号：1001-4861(2012)04-0833-06Effect of Water Condition on Particle Size and-Potential of Silver NanoparticlesZHANG Hong-Yin1CHEN Shao-Feng2,LIN Qing-Yu3(1Department of Civil and Environmental Engineering,University of Rhode Island,Kingston,02881,USA)(2Department of Chemical Engineering,Maoming Vocational Technical College,Maoming,Guangdong 525000,China)(3Department of Chemical and Biological Engineering,Hezhou University,Hezhou,Guangxi 542800,China)Abstract:This study evaluates the effect of water condition on the physicochemical properties of silvernanoparticles(AgNPs)with/without capping agent.The results show that the average particle size of AgNPsincreases with increasing in electrolyte concentration.Divalent cation(Ca2+)can more effectively increase the sizeand-potential of AgNP aggregates than monovalent cation(Na+).This study also indicates that PVP,humic acidor natural organic matters can increase the stability of AgNP suspension.Larger AgNPs aggregates are formed inseawater than in lake water.Key words:silver nanoparticles;capping agents;particle size;-potential0IntroductionSilver nanoparticles(AgNPs)are widely usedbecause of their antimicrobial properties.Consumerproducts containing AgNPs accounted for more than25%ofthetotal1,317nanotechnology-basedconsumerproductsavailableonthemarketin20091.AgNPscanbesynthesizedbyphysicalorchemical method.Sharma et al.2introduced theTollens method which involves the reduction of Ag(NH3)2in aqueous Tollens reagent by an aldehydesuch as saccharides.During the synthesis process,capping agents are usually used to create a stableAgNP suspension2-4.Amongallthecappingagents,polyvinyl第28卷第4期2012年4月Vol28 No4833-838无机化学学报CHINESE JOURNAL OF INORGANIC CHEMISTRY第28卷无机化学学报pyrrolidone(PVP)is frequently used due to its goodstabilizing effect and low toxicity2-3.Previous studiesindicatethatthestabilityofAgNPsuspensionstabilized with PVP is better than that stabilized withsodium citrate5.Recent studies show that waterchemistrycaninfluencethephysicochemicalproperties of AgNPs.For instance,Gao et al.6suggested that water conditions of high ionic strengthform large aggregates.It is also reported that the sizeof AgNPs aggregates can influence their toxicity.Forexample,largerAgNPsaggregatesexhibitlowertoxicity on bacteria and human cells compared tosmaller AgNPs aggregates7-8.However,few researchstudies have compared the stability of AgNPs with/without capping agents in terms of particles size and-potential in different electrolyte solutions.In this work,AgNPs without cappingagent(“naked”AgNPs)and with PVP as capping agentwere synthesized via Tollens method.PVP stabilizedAgNPswereselectedbecausePVPisanenvironmentallyfriendlypolymericcoatingandfrequentlyusedbyotherresearchersforAgNPscharacterization and antimicrobial activity tests2,9.Particle sizes of AgNPs in monovalent and divalentcationic electrolyte solutions were measured using adynamic light scattering(DLS)technique.-potentialsof AgNPs were recorded to study their stability indifferent electrolyte solutions.The result obtained inthis study may serve as a reference for the riskassessment of the release of AgNPs into natural waterbodies since the availability and mobility of AgNPs ishighly dependent on their sizes of aggregates.1 Experimental1.1Electrolytesolutionsandnaturalwatersample preparationSynthetic water solutions containing CaCl2andNaClwerepreparedbyadjustingthecationsconcentrations from 10 to 1105mgL-1.Humic acid(HA)was added to the synthetic water solutions tomimic natural organic matter(NOM).Natural watersamples were collected from the Thirty-acre Pond(lake water)and Narragansett State Beach(seawater).The water samples collected were first filtered(0.45m)and then autoclaved to remove microorganisms inthe water.The major ionic component was analyzedusing ion chromatography techniques(IC)(DX-120,Dionex).Concentrations of HA and NOM in thesenatural water samples and were measured as totalorganic carbon(TOC)using a TOC analyzer(Apollo9000,Tekmar Dohrman).1.2 Preparation and characterization of silvernanoparticles“Naked”AgNPs and AgNPs stabilized with PVP(average molecular weight:29 000,Sigma-Aldrich)were prepared via a Tollens method.In brief,theinitial concentrations of the reactants were 1 10-3molL-1and 110-2molL-1for AgNO3and maltose,respectively.The concentration of ammonia was 5 10-3molL-1.pH value of the reaction system wasadjusted to about 11.5 using sodium hydroxide.Theobtained nano-suspension is the“naked”AgNPs.AgNP-PVP(PVP coated AgNPs)was simply preparedby adding 0.35wt%PVP into the reaction system.AgNPs solutions were cleaned with deionized(DI)water using a 10 kDa nominal molecular weight cut-off(NMWCO)ultrafiltration membrane(Millipore,Model 8200;NMWCO:10,000).UV-Vis absorptionspectrawererecordedusingaspectrophotometer(ThermoUnicam).ConcentrationofAgNPswasmeasured by ICP-MS(X series,Thermo Elemental).Cryo-transmissionelectronmicroscope(Cryo-TEM)was used to observe the morphologyofAgNPs.Surface charge and average hydrodynamic size ofAgNPs in different water conditions were determinedin triplicate by dynamic light scattering(DLS)using aZetasizer(Nano ZS,ZEN 3600,Malvern)at 25.2Results and discussion2.1Characterization of silver nanoparticles“Naked”AgNPs and AgNP-PVP exhibit similarshape(Fig.1).Fig.1(c)shows that both AgNPs presentsurface plasmon resonance band located approximatelyat 400 nm.This observation agrees with previousstudies showing similar surface plasmon resonanceband3,10-11.834第4期张红印等：不同水环境对纳米银颗粒聚集体粒径大小及界面电势的影响2.2Particle sizes of“naked”AgNPs and AgNP-PVP in electrolyte solutions and naturalwater samplesFig.2 and 3 present the size and shape of AgNPswhen they are suspended in different water conditions.It can be seen that the average size of“naked”AgNPsincreaseswithincreasingconcentrationofbothmonovalent cation(Na+)and divalent cation(Ca2+)in theelectrolyte solutions.The shape and size of theindividual AgNPs shown in Fig.3 are similar to that inFig.1.However,“naked”AgNPs form large aggregatesin electrolyte solutions.On the contrary,AgNP-PVPsolution is more dispersed.This can be attributed to thelow stability of both AgNPs due to an increase in chargescreening of cations in solutions.It is also noteworthythat lower concentration of Ca2+cation is needed to formAgNP aggregates in comparison with Na+12,16-21.Thisobservation agrees with the Schulze-Hardy rule,whichindicates that the critical coagulation concentration of atypical colloidal system is extremely sensitive to thevalence of the counter-ions.Similarly,Jin et al.1alsoobserved this phenomenon,which shows that AgNPs indivalent cationic solutions can form larger aggregates.On the contrary,AgNP-PVP demonstrates a relativelystable average particle size,showing that PVP is a goodcappingagentforhelpingstabilizationofthenanosuspension.When PVP is coated on the surface ofnanoparticles,long polymer chains may form complexsteric configurations which can increase the repulsionforce between nanoparticles13-14.In addition,nitrogenatom in PVP polymer can be strongly bonded on thesurface of nanoparticles.Stronger binding forces canensure a stronger attachment of the stabilizers on theAgNPs surface instead of being substituted by otherions such as Ca2+and Na+14,16-21.HA can mitigate the formation of AgNP aggregates(Fig.2).Greater mitigating effect was observed withincreasing addition of HA.This mitigating effect of HAis due to its adsorption on the surface of nanoparticles,which creates steric repulsion forces against aggregationof nanoparticles15,19-21.(a)TEM image of“naked”AgNPs;(b)TEM image of AgNP-PVP,black line:200 nm;(c)UV-Vis absorption spectra of“naked”AgNPs and AgNP-PVPFig.1TEM images and UV-Vis absorption spectra of AgNPsFig.2Particle size of AgNPs in CaCl2(a)and NaCl(b)solutions in presence and absence of HA835第28卷无机化学学报The shape of the individual AgNPs is similar toAgNPs in DI water as shown in Fig.1.However,theparticle size of AgNP aggregates in seawater is largerthan that in lake water(Fig.4 and 5).This is becausethe concentration of the major cations in lake water ismuch lower than that in seawater as shown in Table 1.In addition,NOM content(measured as TOC in Table 1)in lake water is much higher than that in seawater,resulting in a higher stabilizing effect.Fig.5TEM image of“naked”AgNPs(a)“Naked”AgNPs in CaCl2solution(Ca2+:400 mgL-1);(b)“Naked”AgNPs in NaCl solution(Na+:10 000 mgL-1);(c)AgNP-PVP in CaCl2solution(Ca2+:400 mgL-1),(d)AgNP-PVP in NaCl solution(Na+:10 000 mgL-1),black line:200 nmFig.3TEM images of AgNP aggregates in different water conditions.Fig.4Particle size of AgNPs in lake water and seawaterand AgNP-PVP(b)in seawater(black line:200 nm)Table 1Water chemistries of the collected water samplesWater sampleTOC/(mgL-1)Major ions/(mgL-1)Na+Mg2+Ca2+Cl-Lake water7.4193936Seawater1.912 2001 20032019 0002.3-potentials of silver nanoparticles in theelectrolyte solutions-potential refers to the stability of the colloidalsystems.Its value(negative or positive)indicates thedegree of repulsion between adjacent or chargedparticles in a colloidal system.As Table 2 shows,bothAgNPs in CaCl2and NaCl solutions exhibit negative-potential,attributed to the adsorption of various anions836第4期Table 3-potentials of“naked”AgNPs and AgNP-PVP in lake water and seawater samplesonto the AgNP surface.The data also suggest that the-potential of AgNPs solutions becomes less negative asthe salt concentration increases due to the screening ofthe negative charges on the surface of AgNPs by thecations.Similar to what has been discussed above,theadsorption of HA increases the steric repulsion betweenAgNPs,which contributes to the stability of the nano-suspension.For natural waters,the stability of AgNPs inlake water is higher than in seawater(Table 3),which ismainly due to the low concentration of cations and highconcentration of NOM.-potentials/mV(“Naked”AgNPs)-potentials/mV(AgNP-PVP)Na+conc./(mgL-1)100-17.7-25.2500-16.8-24.71000-14.7-16.85000-4.8-14.510000-1.9-6.9Na+conc./(mgL-1)(HA conc.:2 mgL-1as TOC)100-19.6-28.0500-18.2-27.31000-16.9-20.55 000-5.2-19.410 000-2.5-7.0Ca2+conc./(mgL-1)10-8.5-24.750-7.9-20.5100-7.8-19.2200-5.6-12.3400-2.6-10.5Ca2+conc./(mgL-1)(HA conc.:2 mgL-1as TOC)10-11.2-26.850-10.5-23.1100-8.2-21.3200-7.0-13.9Table 2-potentials of“naked”AgNPs and AgNP-PVP in NaCl and CaCl2solutions in presence and absence of HA3ConclusionsWe have comparedthe particle sizes and-potentials of“naked”AgNPs and AgNP-PVP in CaCl2and NaCl solutions in the presence and absence of HA.It can be concluded that 1.AgNP-PVP shows greaterstability than“naked”AgNPs.2.Particle size and-potential of both AgNPs increase with increasingconcentration of cations.Meanwhile,particle size and-potential are more sensitive to Ca2+than Na+.HA orNOM can mitigate AgNPs aggregation by adsorbing ontheir surface and creating a physical barrier,whichinhibits their aggregation.3.Both AgNPs exhibit largerparticle size and-potential in seawater than in lakewater attributed to the high concentration of cations andlow NOM content in seawater.References:1 Jin X,Li M,Wang J,et al.Environ.Sci.Technol.,2010,44(19):7321-73282 Sharma V K,Yngard R A,Lin Y,et al.Adv.ColloidInterface Sci.,2009,145:83-963 Kvitek L,Vanickova M,Panacek A,et al.J.Phys.Chem.,-potentials/mV(Naked AgNPs)-potentials/mV(AgNP-PVP)Lake water-24.8-25.1Seawater-0.8-2.2张红印等：不同水环境对纳米银颗粒聚集体粒径大小及界面电势的影响837第28卷无机化学学报2009,113:4296-43004 Rai M,Yadav A,Gade A.Biotechnol.Adv.,2009,27:76-835 Huynh K A,Chen K L.Environ.Sci.Technol.,DOI:10.1021/es200157h6 Gao J,Youn S,Hovsepyan 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