Preparation of doping titania antibacterial powder by ultrasonic spray pyrolysis

Available online at www.sciencedirect.com●CIHNCE)DInEOT.Transactions ofNonferrous Metals骂PSociety of ChinaScienceTrans. Nonferrous Met. Soc. China 18(2008) 1145-1150Presswww.csu.edu.cn/ysxb/Preparation of doping titania antibacterial powder byultrasonic spray pyrolysisWEI Shun-wen(韦顺文)，PENG Bing(彭兵), CHAI Li-yuan(柴立元),LIU Yun-chao(刘云超)", LI Zhu-ying(李竹英}1. School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China;2. Yiwu Bureau of Quality and Technical Supervision, Yiwu 320000 ChinaReceived 29 October 2007; accepted 6 March 2008Abstract: Doping titania powders were synthesized by ultrasonic spray pyrolysis method from an aqueous solution containingH2TiF。and AgNO3. The effects of the processing parameters on particle size distribution, structure, and morphology of dopingparticles were investigated. The results show that aggregation-free spherical particles with average diameter of 200 -600 nm areobtained and the particle size of the powder can be controlled by adjusting the concentration of solution. The experimental approachindicates that the size and the value of standard deviation of particle size increase from 210 nm to 450 nm and from 0.46 to 0.73respectively with the increase of the fitanic ion concentration from 0.05 to 0.4 mol/L. Composite TiOF2 is obtained when thepyrolysis temperature is set to be 400 C. With increasing pyrolysis temperature from 400 C to 800 C, the crystal size of titaniapowders increases from 14.1 to 26.5 nm and TiOF2 content of powder decreases dramatically. The property of ion released frompowder is affected signifcantly by the pyrolysis temperature, and the amount of fluorine ion and silver ion released from powderdecrease with increasing pyrolysis temperature. The optical property of doping titania powders is not affected by pyrolysistemperature. Antibacterial test results show that composite powders containing more fluorine ions exhibit stronger antibacterialactivity against E.coli.Key words: doping; titania; spray pyrolysis; antibacterial powdertreatment. The color stability of silver ion in titania is1 Introductionaffected by many factors[8]， such as the ligand,dispersion of silver ion, particle size and structure ofTitanium dioxide is an attractive photocatalyst andtitania. These factors are related to the preparationhas been applied widely[1-2]. Due to its photosemi-method, so it is very important to choose a suitableconductor properties[3], titanium dioxide may find anpreparation route to obtain titania composite powdersapplication as an antibacterial agent[4] for thecontaining silver. UItrasonic spray pyrolysis is one of thedecomposition of organism. But its photocatalysis is onlybest methods to produce small and uniform particle,activated by UV light and only 5% of solar spectnum ismoreover, the preparation of silver-doped titania bused[5]. In order to enhance the quantum efficiency ofspray pyrolysis has not been reported. Therefore, in thisthe titanium dioxide catalyst, many efforts have beenwork, titania containing silver was prepared by spraymade to eliminate the fast geminate recombination ofpyrolysis method. The effects of process parameters, suchelectron-bole pairs produced by the photon excitation.as pyrolysis temperature and titanic ion concentration onhe addition of noble metal such as silver, gold andthe properties of doping titania particles were studied.platinum is one of the methods to improve thephotocatalytic activity[6 -7]. When titanium dioxide is2 Experimentaldoped by silver ion, composite has a good antibacterialactivity even without the presence of light. But silver ion2.1M中国煤化工is unstable and easily transformed to black metallic silverMYHCNMHGed by adding silveror brown silver oxide during illumination or thermalSonstat molar ratioFoundation ltem: Project(04GK2007) supported by the Key Project of Scientific and Technological Department of Hunan Province, ChinaCorresponding author: CHAI Li-yuan; Tel: +86. 731-8836840; Fax: +86-731-87101712; E-mail: lychai@mail.csu.edu.cn1146WEI Shun-wen, et a/Trans. Nonferrous Met. Soc. China 18(2008)0.0045 of Ag to Ti, the starting solution was diluted bywhere w is the mass fraction of rutile in the powder,water, and the titanic concentration of the startingwhile Is and Ik are the X-ray integrated intensities of thesolution was adjusted to 0.05, 0.1, 0.2 and 0.4 mol/L,(101) reflection of anatase and (110) reflection of rutile,respectively. Doping TiO2 powders were synthesized byrespectively.spray pyrolysis from the starting solution. The schematicThe silver release property of the particles wasdrawing of ultrasonic spray pyrolysis system for dopingexamined by leaching with ditlledl water. 2 g compositetitania powder preparation is shown in Fig. 1. The staringpowder was added in 200 mL of distilled water in asolution was atomized by a nebulizer(the power of thepolypropylene bottle at 37 C and sired mechanicallynebulizer is about 80 W, 2.50 MHz); then the formnedat 120 r/min. The supematant liquor was collected afterdroplets carried by gas and passed through athe powder was soaked in water for 1 d and analyzed forhigh-temperature tube under the suction of an aspirator.silver ion concentration by atomic adsorption spectro-The furmace temperature was set to be 500, 600, 700 andphotometry (AAS) and F ion concentration by ion800 C, respectively. The pyrolysis reaction proceededselective electrode method.quickly as droplets passed through the high-temperaturetube. The pyrolysis reactions were as follows:2.3 Antibacterial testThe antibacterial activity of composite powders wasH2TiF6+2H2O-一6HF+TiO2(1)evaluated by measuring the minimum inhibitoryH2TiF6+H2O- + 4HF+TiOF2concentration(MIC). The MIC of samples was defined asTiOF2+H20- ~ TiO2+2HF(3)he lowest concentration of samples in which more than)0% bacteria could not grow. A series of brothFurancecontaining samples were prepared, and the concentrationof samples was adjusted to 1-10 mg/mL by dilutingStartingappropriate volume of BHI-broth. E. coli species wassolutionCollectorcultured in BHI-broth, and the concentration of E.coliUltrasonic1 L Aspiratorinoculum was adjusted to 0*cells/mL under microscope.nebulizerThen, 1 mL E.coli inoculum was added to 9 mL of aFig.1 Schematic drawing of ultrasonic spray pyrolysis systemseries of broth containing samples, and the bacteria werecultured in the box at37 C for 48 h with gentle stiringThe generated powder was collected with a ceramicto prevent samples from depositing. The MIC of samplesfilter at the end of the tube.was measured.2.2 Characterizations3 Results and discussionThe particle size distribution, specific surface area(SSA), optical property, morphology and structure of3.1 Particle size distributionsamples were measured with a laser particle sizeThe theoretical diameter of the droplets sprayed byanalyzer (MS- 2000)，low temperature gas (nitrogen)ultrasonic generator can be approximately calculatedadsorption apparatus and UV-vis spectrophotometer,using Lang's equation[8]:transmission ectronic microscope(TEM)， PhilipsPW1780 X-ray diffractometer(XRD), respectively. TheD。=0.34x10|(聘)(6)crystallite sizes of anatase titania were estimated byanalyzing the broadening of the (101) reflection. Thewhere Da is the droplet diameter (um), σ is the solutionaverage particle sizes can be calculated by Scherrer law assurface tension (N/m), P is the solution density (g/cm),follows:andfis the ultrasonic frequency of the nebulizer (2.5 Hz).d=.0.924)By considering that the nitrate salts have no influence onβcosθσ and p, the diameter of the droplet calculated usingEqn.(6) is 2.1 um.where h is the wavelength of X-ray source (Cu Ka, 1.054The relationship between the theoretical diameter ofA), and β is the full width at half-maximum of the X-raythe doping titania particle and the droplet diameter candiffraction peak at the diffraction angle 0. The fraction ofbe describe as[8]rutile in each sample was determined by measuring the中国煤化工relative XRD intensities of the anatase (101) and rutile.MYHCNMHG(7)(110) from the following equation:w=1/[1+0.8(In/Ik)]5) where d is theoretical diameter of the doping titaniaWEI Sbun-wen, et al/Trans. Nonferrous Met Soc. China 18(2008)particle (nm), c is the concentration of titanium dioxide3.2 Structure and morphologyin the solution (mol/L), M is the molar mass of titaniumThe XRD patterns in Fig.4 indicate that thedioxide (g/mol), and Pr is theoretical titanium dioxidepyrolysis temperature has a great effect on the phasedensity (g/cm'). The theoretical diameters d calculatedcomposition of doping titania powders. A pure anataseusing Eqn.(7) for concentration of 0.05, 0.1, 0.2 and 0.4phase of titania was observed when the pyrolysismol/L are 207, 260, 328 and 414 nm, respectively. Thetemperature was set between 500 and 700 C. Sometheoretical diameter of the doping titania particlepeaks assigned to TiOF2 were observed for powderincreases with increasing the concentration of titaniumprepared at 400 C. It can be explained that the iondioxide in the solution (c).radius of fluorine atom (0.133 nm) is virtually the sameThe particle size distribution of doping titaniaas the replaced oxygen atom (0.132 nm), and the fluorinepowder prepared at 800 C is presented in Fig.2. Theatom can displace oxygen atom in TiO2 matrix to formaverage size and standard deviation(D) of particle areTiOF2. The rutile phase appeared in composite when theshown in Fig.3. It can be seen from Fig.2 and Fig.3 thatpyrolysis temperature was set to be 800 C, but athe mean size of particles and the values of D, increaseconsiderable amount of anatase still remained in powder.with increasing the titanic concentration of solution.The diffraction peaks corresponding to silver were notWhen the titanic concentration is 0.05 molL, the particleobserved in XRD patterns for low content of silver inhas a narrow size distribution around 210 nm; when thesamples. The crystal sizes of titania calculated from thetitanic concentration is 0.4 mol/L, the particle has a(101) peak of the XRD pattern are presented in Fig.5 andbroad size distribution around 450 nm. The increasing ofrange fom 14.1 to 26.5 nm, monotonically increasingD3 from 0.46 to 0.73 indicates that the uniformity ofwith increasing pyrolysis temperature.particle decreases. The change in average particle size isconsistent with the theoretically calculated results.●一Antase TiO2-Rutile TiO22r▲一TIOF2-0.05 molL0-0.1 mol/L一0.2 mol/L4 -0.4 mol/L800 CIn言4l 700|600s S00g0.010.11100400 CParticle size/um2Fig.2 Particle size distibution of doping titania powders as20/<°)function of Ti concentration of solutionFig.4 X-ray diffraction patterns of powders prepared at).5.0different furmnace temperatures.4Fig.6 shows TEM images of the doping TiO20.8powder prepared fom solution with various titanic0.3-concentrations. It can be seen that the doping TiO20.6powder is aggregation-free spherical particle with au.2-average diameter about 200 -600 nm. The diameter ofparticle prepared from 0.05 mol/L titanic solution is1- Mean size 0.4smaller than that prepared from 0.4 mol/L titanic solution..11一UniformityThe change in particle size is also consistent with0.2theor中国煤化工.T0.0.3 0.4 0.CNMHG[i#*)](mol-L ')3.3MHFig.3 Mean size of particles and standard deviation as functionIt is known that the electron (e) and hole (h) areofTit concentration of solutiongenerated when TiO2 is exposed in UV light. With1148WEI Shun-wen, et al/Trans. Nonferrous Met. Soc. China 18(2008)UV-vis transmission spectrometry. Fig.7 shows the28UV-vis absorption spectra of the doping titania. It can beseen from Fig.7 that the pyrolysis temperature has a24small effect on the spectra of doping titania powders.The absorption edge of doping titania powder wasbetween 385 nm (3.22 eV) and 383 nm (3.24 eV). These20个values are very close to those of anatase TiO2(3.2 eV),indicating that silver doping did not cause any significant5shift on the fundamental absorption edge of titania.16|1.61- 400C124000008003、500 C一600CTemperature/C1.2700 CFig.5 Effeet of furmace temperature on silver-doped titania5- 800 Ccrystal sizes号0.8a)0.44.5200 300 400 500 600 700 800Wavelength/nmFig.7 UV-vis absorption spectra of doping powders prepared atdifferent pyrolysis temperaturesb)3.4 Property of ion releaseThe antibacterial activity of doping TiO2 is closelyrelated to the concentrations of silver ion or other ionaround the surface of the specimen[10]. It is known thatantibacterial material exhibits stronger antibacterialactivity as it releases more silver ion into water.However, the release of excessive ions may shorten thelife of antibacterial material and contaminate the200nm .environment, thus the rate of ion release of doping titaniapowders attracts many attention.Fig.6 TEM images of powders prepared from solution withFig.8 shows the concentration ofF and Ag" in thevarious concentrations (pyrolysis temperature: 800 C ):supernatants Collected from water containing composite.(a) 0.05 molL; (b) 0.4 molLIt can be seen that the pyrolysis temperature has asignificant effect on the ion release of doping titaniathe action of electron (e) and hole (h7)， TiO2powders. The amount of fluorine and silver ions releasedphotocatalysts can decompose many organic compounds.decreases dramatically with increasing the pyrolysisThe photocatalytic activity of TiO2 is related to thetemperature. The concentration of fluorine ion releasedgeneration capacity of ectrons and holes, the separationdecreases from 145.3 to 30.5 mg/L and the concentrationefficiency of the photogenerated charge pair, and theof silver ion released decreases from 58.2 to 33.8 mg/Ltransfer efficiency of holes and electrons to compoundsas the pyrolysis temperature increases from 400 C toabsorbed on TiO2[9]. The yield of the photogenerated500 C. A lot of fluorine ions released from compositeelectron-hole pair mainly depends on the intensity ofpowde中国煤化Truted to the TiOFzincident photons with energy exceeding or equaling theformecsiver ions releasedTiO2 band gap energy. In order to check the effect ofare duiY片CNM H Grss are capable ofprocess parameters on titania band gap energy, thedissolving composite released in water. When thoptical property of doping titania was investigated bypyrolysis temperature is above 500 C, there is slightWEI Shun-wen, et al/Trans. Noferrous Met. Soc. China 18(2008)1149difference between the concentration of fluorine ions andantibacterialmechanism of the fluorine ions[13]. One issilver ions released from the powders in spite of thethat fluorine ions can affect bacterial metabolism as anchange of heating temperature.enzyme inhibitor, and the other is that metal-fluoridecomplexes are responsible for fluoride inhibition of150proton- translocating F-AT-Pases anmimickingphosphate to form complexes with ADP at the reactioncenters of the enzymes[14].管100-Table 1 MIC of doping TiO2 powders against E.coliPyrolysis temperauerC__ MIC of powder/(mgL)4002.0营50-|5006.07.57008.5dd」600800300.0Temperature/CFig.8 Effect of pyrolysis termperature on ion release property ofThe antibacterial activity of titania has also beendoping TiO2 powersreported in the biomedical fields. The antibacterialmechanism of titania is that the reactive oxygen species3.5 Antibacterial activitygenerated by titania photocatalytic reactions promotedThe minimum inhibitory concentration of dopingperoxidation of the polyunsaturated phospholipidsTiO2 powder prepared at various temperatures is listed incomponent of the lipid membrane, induced majorTable 1. The MIC of doping TiO2 powder is smaller thandisorder in the bacteria and caused various damages tothe standard MIC value of Japanese antibacterial materialliving organism when TiO2 was iluminated in UV light(800 mg/L), which indicates that the composite powder[15-16]. Then, organic compounds were decomposedhas stronger antibacterial activity against E.coli. Theand mineralized by participating in a series of oxidationMIC of doping TiO2 powder increases with increasingreactions leading to carbon dioxide.the pyrolysis temperature, which means that theantibacterial activity decreases with increasing th4 Conclusionspyrolysis temperature. The decrease of antibacterialactivity is contributed to the decrease of ion release of1) Spherical doping titania composite powders werecomposite. lonic silver has the highest and broad-synthesized by spray pyrolysis from an aqueous solutionspectrum antibacterial activity among metal ions. Itcontaining H2TiF6 and AgNO3. The particle size ofadsorbs the protein on the surface of the bacterialmembrane, influencing membrane synthesis withS- Agpowder can be controlled by adjusting the concentrationbonds[11]，inhibits the DNA synthesis with directof solution. Both the particle size and the value ofbinding on the bacterial DNA and finally results in thestandard deviation of particle size increase with thedeath of bacteria[12]. So the amount of silver ionsincrease of the titanic concentration.released from materials is considered as one of the most2) The pyrolysis temperature has a significant effetimportant factors in evaluating its antibacterial activity.on the properties of composite powder. TiOF2 is obtainedIt can be seen from Table 1 that the MICs of doping TiO2in composite when the pyrolysis temperature is 400 C.powder prepared at 400, 500, 600, 700 and 800 C areWith increasing the pyrolysis temperature from 400 to2.0, 6.0, 7.5, 8.5 and 9.0 mg/L, respectively, from which800 C, the crystal size of titania increases from 14.1 tothe concentrations of silver ion calculated are 11.6, 20.3,26.5 nm. The amount of ion released from powder19.8, 21.3 and 22.8 mgL, respectively. The amount ofdecreases with increasing the pyrolysis temperature. Butsilver ions released ftom powders prepared at400 c isthe optical property of doping titania powders is notless than that prepared above 500 C. This indicates thataffected by the pyrolysis temperature.fluorine ions released from powder show antibacterial3) Antibacterial test results show that both silver ionactivity against E.coli as well. Fluorine ions withand.中国煤化工powder play anantibacterial effect against oral bacteria have beenantibMHCNMHG_nd the antibacterialreported in previous researches and fluoride-releasingactivagainst E.coli iscomposite is used as a highly elective anticaries agent instrengthened with the increase of the content of silver iondental fields. There are two possible explanations forand fluorine ion.1150WEI Shun-wen, et al/Trans. Nofrrous Met. Soc. China 18(2008)3018);: 2295 2303.References9] CHEN ShiFu, LIU Yun-Zhang. 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