Preparation of ZnO nanorod by solvothermal reaction of zinc acetate in various alcohols

Rapid synthesis of blue emitting ZnO nanoparticles forfluorescentapplicationsLeta T.Jule a,n,Francis B.Dejene a,Kittessa T.Roro b,Zelalem N.Urgessa c,Johannes R.Botha ca Physics Department,University of the Free State,Private Bag X13,Phuthaditjhaba9866,South Africab CSIR-Energy center,Council for Scientific and Industrial Research,PO Box395,Pretoria,South Africac Department of Physics,Nelson Mandela Metropolitan University,P.O.Box77000,Port Elizabeth6031,South Africaa r t i c l e i n f oArticle history:Received4May2016Received in revised form8June2016Accepted9June2016Available online11June2016Keywords:ZnOBlue emissionThermal decompositionZinc acetate dehydrateFluorescent applicationDonor–acceptor pair(DAP)a b s t r a c tZnO nanoparticles(NPs),with size∼16–20nm were produced using simple,cost effective and rapidsynthesis method.In this method zinc salt(typically zinc acetate dehydrate)is directly annealed in air ata temperature from°200C to°500C for2h to form ZnO(NPs).This synthesis method,only requires zincprecursor to produce NPs that can emit visible emission without external doping.X-ray diffraction(XRD)patterns confirm the prepared ZnO NPs is polycrystalline structure with wurtzite phase.The observedvariation in scanning electron microscopy(SEM)images showed spherical shape of the ZnO NPs.It wasfound that the NPs exhibited the estimated direct bandgap(E g)of3.28eV,3.29eV,3.33eV and3.39eVfor a decomposition temperature of500,400,300and°200C.Energy dispersive X-ray(EDX)analysisshowed that carbon is the only impurity at lower temperature which was most likely originated from theacetate group.The photoluminescence(PL)spectra of ZnO NPs showed the appearance of a blue emis-sion,attributed to Zn interstitials,whose intensity reduces with increase in decomposition temperatureand the underlying mechanism are discussed.For the samples prepared at°200C and300°C a tem-perature dependent PL was studied and found out that there are about three transition lines at∼3.01eV,∼3.21eV and∼3.33eV,which are ascribed to zinc vacancy(V zn),donor–acceptor pairs(DAP)and excitonsbound to structural defects respectively.It is hoped that ZnO NPs produced using this method would beideal for blue light emittingfluorescent application as it is catalyst free growth,uses simple equipment,less hazardous and easy to control particle size and morphologies by scalable temperature.&2016Elsevier B.V.All rights reserved.1.IntroductionSemiconductor nanostructures are promising candidates forfuture electronic and photonic devices.Nanostructures based onwide bandgap semiconductors such as GaN and ZnO are of parti-cular interest because of their applications in short wavelengthlight emitting devices andfield emission devices[1,2].ZnO is apotential competitor of GaN for blue and UV emission and char-acterized by direct band gap of3.37eV at room temperature withlarge exciton binding energy of60meV compared to GaN(28meV)[3–5].In addition to the UV emission ZnO is also known to emit in thevisible region[6].The photoluminescence spectrum of ZnO isnormally composed of two parts:excitonic near band edge emis-sion with energy around the band gap of ZnO and defect relateddeep level emission in the visible range.ZnO is n-type semi-conductor due to oxygen vacancies,impurities like Al,H and in-terstitial Zn ions which act as donors in ZnO lattice.These nativedefects are believed to be responsible for visible photo-luminescence.The UV emission is due to excitonic related re-combination[7,8].The exact mechanism for deep level emission isstill controversial although intrinsic defects such as oxygen va-cancies,oxygen interstitial,zinc vacancies and extrinsic impuritiesare all considered as a possible origin[9–12].However,under-standing the origin of photoluminescence in ZnO nanoparticlesand improving the emission efficiency is still a major challenge.Synthesis and characterization of zinc oxide(ZnO)nano-particles has found widespread interest during past few years dueto their unique electro optical properties,which can be employedin devices such as ultraviolet(UV)light-emitting diodes(LEDs)and blue luminescent devices[13].Searching of new methodology to synthesize ZnO NPs with auniform morphology,size and reproducibility is of greatContents lists available at ScienceDirectjournal homepage:/locate/physbPhysica B/10.1016/j.physb.2016.06.0080921-4526/&2016Elsevier B.V.All rightsreserved.n Corresponding author.E-mail address:JuleLT@ufs.ac.za(L.T.Jule).Physica B497(2016)71–77importance both for fundamental studies and practicaltion.In the past,several crystal-growth technology, explored,among which are sol-gel,spray pyrolysis,por transport,vapor-phase growth,chemical bath (CBD),direct precipitation methods and hydrothermalwhich also had the additional motivation of dopingeffort to obtain p-type material[1,14,15].However,theseinvolve a strictly controlled synthesis environment, procedures,high-temperature synthesis processes and equipment.Despite extensive research over the pastsome fundamental properties of theluminescence in the ZnO synthesized by thermalare not fully understood and rarely reported.In this paper,we therefore report on ZnO NPs thatvisible region without the requirement of additional temperature-dependent PL for samples of ZnOtemperature of°200C and°300C were discussed withderlying mechanism.Moreover,the structural and optical prop-erties of ZnO NPs synthesized via thermal decomposition method has been studied.2.Experiment2.1.Sample preparationThe zinc acetate dihydrate(Zn(CH3COOH)2Á2H2O))>99%,purity purchased from Sigma Aldrich,were used as precursor without further purification to prepare ZnO NPs.In order to determine possible decomposition temperature of zinc acetate dihydrate into ZnO NPs,samples were annealed at various temperature for2h. Four sets of5g of Zn(CH3COOH)2Á2H2O was put into sample holders,the crucible and annealed at a temperature of200,300, 400and°500C for2h in muffle furnace in air to produce the ZnO NPs.2.2.CharacterizationsThe crystal structures of the samples were determined with a Bruker AXS D8ADVANCE Discover diffractometer(XRD),with Cu Ka(1.5418)radiation.Surface morphologies and elemental com-positions were studied using a scanning electron microscope(SEM) (Shimadzu model ZU SSX-550Superscan)equipped with EDX.The optical absorption measurements were carried out in the200–600nm wavelength range using a Perkin Elmer UV/Vis Lambda20 powder Spectrophotometer.Luminescence measurements were done using a photoluminescent(PL)laser system 5.0(Photon systems,USA),which uses a He–Cd laser with an excitation wa-velength of248.6nm.3.Results and discussion3.1.Structural analysisFig.1shows the XRD pattern of ZnO NPs synthesized by ther-mal decomposition method for various annealing temperatures. XRD pattern of ZnO NPs exhibits various peaks which could be indexed according to ZnO diffraction peak(JCPDS card no.36-1451).The presence of various diffraction peaks reveals hexagonal wurtzite phase of ZnO which suggests polycrystalline nature of ZnO.The diffraction peaks at scattering angleθ()2of31.74°,34.43°, 36.25°and47.5°belongs to100,002,101and102diffraction planes from ZnO,and the other peak marked with asterisks* corresponds to zinc acetate.It can be clearly seen that by increasing the growth temperature from°200C to°500C ZnO peaks became prominent and prevailed.No other impurities are observed except for zinc acetate related peaks in the samples prepared at lower temperature,but fully decomposes for the higher temperature.The estimated lattice constants slightly in-creased as the decomposition temperature increased from°200C to°500C as summarized in Table1.The increase of the lattice parameter of ZnO NPs with increase in temperature was calculated using the equation:=+()⎛⎝⎜⎜⎞⎠⎟⎟d a c143111 101222where d is the interplanar distance,a and c are the lattice parameters.Fig.2shows the variation of FWHM as measured from dif-fraction plane101and particle size of ZnO NPs synthesized at various decomposition temperatures for annealing time of2h.The FWHM,which is an indication of the crystalline quality of the prepared ZnO NPs,decreases significantly as the decomposition temperature increases.Fig.3depicts variation of lattice parameter, a and c with increasing annealing temperature respectively con-firming the increase in grain size at higher decomposition temperature.The average crystallite size of prepared ZnO NPs can be esti-mated from the FWHM of the101diffraction peak estimated using the Debye Scherrer's equation:λβθ=() D0.9cos2 where D is the crystallite size,λis the wavelength λ(=)0.15402nm of radiation used,θis the Bragg angle andβis the full-width at half-maximum measured in degrees.The estimated average particle sizes were16.3,17.8,19.6and19.7nm2degree))ΘFig.1.XRD pattern of ZnO nanoparticles synthesized at various temperatures for 2h.Table1Measured properties of ZnO nanoparticles at various temperature.Temp.(°C)Particle diameterR070.5(nm)Lattice parameter,a(Å)Lattice parameter,c(Å)20016.3 3.245 5.29930017.8 3.247 5.30240019.6 3.249 5.30550019.7 3.250 5.307L.T.Jule et al./Physica B497(2016)71–77 72corresponding to the 200,300,400and °500C decomposition temperatures.The estimated particle sizes increases with anneal-ing temperature and it has highest value at of °500C due to nar-rowing of the diffraction peak.According to Ostwald ripening the increase in the particle size is due to the merging of the smaller particles into larger ones as suggested by Nanda et al.[16]and is a result of potential energy difference between small and large particles and can occur through solid state diffusion.The intensity ratio,()()I I 002101of the peaks presenting ()002and (101)at °500C is equalto 0.53which is higher than the corresponding standard value of 0.44of bulk hexagonal wurtzite ZnO [17]suggesting the prepared ZnO structure is preferred the (002)orientation.3.2.Morphological analysisFig.4A –C illustrates the SEM images of ZnO NPs prepared at a temperature of 300,400and °500C respectively.The SEM images clearly indicate that the surface morphology of the ZnO NPs de-pending on the synthesis temperatures.It is interesting to observe the formation of spherical ZnO NPs which is fully noted when the decomposition temperature was increased to °500C (see the inset in Fig.4C).It is observed that as decomposition temperature increases,the structural defects(dis-location)for the ZnO NPs prepared at a temperature of °200C reduces as compared to °500C causing uniform ZnO NPs which are purely spherical in shape.Fig.4D –F shows chemical stoichiometryof the ZnO nanoparticles prepared at a temperature of 300,400and °500C .The results presented shows that the prepared mate-rial contains C,O and Zn elements.The decrease in the C con-centration with increasing synthesis temperature is suggested to be as a result of ef ficient evaporation of the acetate-group.4.UV –visible spectrophotometer analysisFig.5shows room-temperature UV –visible absorption spec-trum of ZnO nanoparticles synthesized for various decomposition temperatures.The prepared ZnO NPs have band edge absorption peaks at 362.2nm,389.4nm,429.72nm and 455.32nm for sam-ples prepared at a temperature of 200,300,400and °500C re-spectively.These absorption peaks conform to the well-known intrinsic band gap absorption of ZnO.The absorption edge around 389.4nm was assigned to intrinsic band-gap absorption of ZnO due to the electron transitions from the valence band to the con-duction band →O Zn p d 23[18]and the other possible explanation are given in terms of structural defects associated with Zn inter-stitial as reported in Refs.[6,19].It is observed from the spectra that the absorbance of the samples reduces slightly with increase in decomposition temperature and the absorption edge slightly shifts to lower energy.Furthermore this red shift indicated the shrinkage effect in the band gap energy as a function of tem-perature.They obtained ZnO which exhibited a high absorption band in the UV region λ(<)380nm .Fig.6represents the relationship αν()h 2versus the photon en-ergy ν()h from which the optical band gap of the nanoparticle was determined by extrapolating the linear part of the spectrum.The characteristic's change of the band gap with increase in size of the ZnO nanostructure has been studied by the observation of the red shift in photoluminescence peak position.Thus photo-luminescence is useful for the study of quantum con finement of electrons.The direct bandgap energy of the synthesized ZnO na-noparticles was estimated using Tauc's plots relation [20].ZnO nanoparticles synthesized have estimated band gap values of 3.28eV,3.29eV,3.33eV and 3.39eV for samples prepared at a temperature of 500,400,300and °200C respectively.Thus,the estimated band gap energy of the ZnO nanoparticles was found to decrease with the increase in the decomposition temperature and similar results were obtained by Kathalingam et al.[21].It is clear that when the particle size increases,the electronic states are not discrete as a result the band gap energy reduces and the oscillator strength decreases [5,22].5.Photoluminescence analysisFig.7shows the PL spectra of ZnO NPs prepared at various annealing temperatures.In the PL spectrum,four emission bands,including band edge emission at 398.3nm (3.11eV),402.8nm (3.07eV),406.9nm (3.04eV)and 409.6nm (3.02eV)for ZnO prepared at a temperature of 500,400,300and °200C respectively were observed.The visible emission in ZnO is due to different intrinsic defects such as oxygen vacancies (V o ),zinc vacancies (V Zn ),oxygen interstitials (O i ),zinc interstitials (Zn i )and oxygen antisites (O Zn )[7,23].Band edge emission centered at around 398.3nm should be attributed to the recombination of excitons and V Zn [24,25].However the origin of violet emissions centered at 3.07eV(402.79nm),406.9nm (3.04eV)and 409.6nm (3.02eV)are ascribed to an electron transition from a shallow donor level of neutral Zn i to the top level of the valence band [26,27,9].The broad deep level emission that started from UV to the visible region 360–480nm with the maximum peak at 409.64nm for the sample prepared at °200C was observed.The decrease in PL intensity withTemperature (C )P a r t i c l e s i z e (n m )F W H M ()Fig.2.Variation of FWHM of (101)X-ray diffraction peaks and estimated particle sizes plotted against decompositiontemperature.Temperature (0C )L a t t i c e p a r a m e t e r a ,(A n g .)L a t t i c e p a r a m e t e r c ,(A )Fig.3.Variation of lattice parameter,a and c as a function of temperature.L.T.Jule et al./Physica B 497(2016)71–7773increase in decomposition temperature can be attributed to for-mation of better ZnO stoichiometry and near surface band bending caused by surface impurities [15,28,29].In samples of ZnO pre-pared at higher decomposition temperatures,the increase in grain size will reduce the relative contribution from recombination near the grains,resulting in strongly reduced violet emission.On the other hand,as the decomposition temperature increases more and more ZnO NPs with less deep defects form and as the result the transition line for the emission will decrease causing the PL in-tensity to decrease [25].The other possible explanation can be given as the existence of high dislocation density (defects)at the lower decomposition temperature.The dislocation density (δ),which represents the amount of defects in the sample is de fined as the length of dislocation lines per unit volume of the crystal andisFig.4.SEM micrograph and EDX spectrum of ZnO nanoparticles at:(A)°300C .(B)°400C .(C)°500C for 2h,and D,E and F are the corresponding EDX spectra.L.T.Jule et al./Physica B 497(2016)71–7774calculated using the equation [23]:δ=()D 132where D is the crystallite size.Calculating the dislocation density (δ)of ZnO NPs synthesized at °200C and °500C using Table 1and Eq.(3)it has value of ×−25.76104()−nm 2and ×−37.63104()−nm 2respectively,suggesting high dislocation density at °200C and the lattice imperfection decrease with increase in particle size.Moreover,defect density decreases with synthesis temperature in the present study.For samples synthesized at low temperature,a number of lattice defects which can act as radiative recombination centers are suggested.The reduction of these defect related ra-diative centers after annealing at °500C in air is likely related to formation better stoichiometric ZnO NPs.This hypothesis can be supported by the fact that surface defects strongly depend on morphology (SEM),with suppression of the emission as discussed under PL section.6.Temperature dependent PLRelative changes in state population with temperature provide evidence that PL peaks originate in the same part of the sample and that carriers are free to move between the available states.This feature can be useful because thermal quenching can hide sparse low-energy states and thermal broadening can obscure important details in the spectrum,low temperature PL experi-ments were conducted for samples prepared at 200and °300C .Fig.8and 9A depicts the temperature dependent PL spectra of synthesized ZnO NPs prepared at °200C and °300C respectively studied at a temperature of 300K,273K,173K,123K and 73K.The broadness and increase in PL emission intensity were ob-served with decreasing temperature as shown in Fig.8.It is well known that the donor –acceptor pair transition energy decreases along with the band gap energy when the temperature is in-creased causing the PL intensity to decrease.The experimental data for the temperature dependence of PL band intensity can be fitted by the following expression [14]:()=+()−βI T I Ae 14E 0a where I o is the peak intensity at temperature T ¼0K,A is assumed to be constant,E a is the activation energy of the thermal quenching process,and Kb is the Boltzmann's constant.Fig.9B is a plot of the integrated intensity of the 3.21eV transition versus reciprocal temperature for the ZnO NPs prepared at a temperature of °300C in the luminescence as one step quenching process andA b s o r b a n c e (a r b .u n i t s )Wavelength (nm)Fig.5.UV –vis absorbance spectra of ZnO nanoparticles synthesized at different annealing temperatures.(h v 101(e V /c m hv (eV))αFig.6.The optical absorption energy band gap estimated using Tauc's plot relationfor ZnO nanoparticles synthesized at different annealing temperatures.P L i n t e n s i t y (a r b .u n i t s )Wavelength (nm)Fig.7.PL emission of ZnO nanoparticles synthesized at various temperatures.P L I n t e n s i t y (a r b .u n i t s )Energy (eV)Fig.8.Temperature dependent PL emission of ZnO nanoparticles prepared at °200C .L.T.Jule et al./Physica B 497(2016)71–7775fitted by the Eq.(4).The best fit,demonstrated by the solid curve has been achieved with parameters =I 10200,=E 12.9meV a .A range of experimental values have been reported for the quench-ing of the dominant bound exciton for ZnO nanorods as 13.2meV and 13.1meV for bulk ZnO [11,25,26].Haynes'empirical rule E a ¼a þb E D can be used to calculate thedonor binding energy E D ,using the value obtained for =E 12.9meV a .Different values have been reported for the con-stants a and b in the above relation.In our opinion,the most ac-curate values have been reported by Meyer et al.[11],namely =−a 3.8meV and b ¼ing these values,E D was cal-culated to be 45.8meV.This agrees with the value reported in Ref.[25].In the prepared ZnO NPs,it seems entirely plausible that hydrogen (from precursor)is the dominant donor.Fig.8shows temperature-dependent PL for ZnO NPs prepared at a temperature of °200C ,for which five distinct deep-level emission peaks at 3.01eV,3.03eV,3.04eV,3.08eV and 3.16eV were observed which was ascribed to native defects.The tem-perature-dependent PL spectra shown in Fig.9A for sample of ZnO NPs prepared at °300C clearly depicts thermal redistribution among states compared to the ZnO sample prepared at °200C .The transition line at 3.01eV were attributed to native defect (V zn )and the near-band-edge (NBE)emission peak at 3.21eV were assigned to DAP.The peak labeled in 3.21eV gains strength with decreasing temperature,in contrast,peak labeled 3.01eV is strong at low temperature because carriers are trapped at these sites and do not have enough thermal energy to escape,but it disappears at room temperature(300K)because the states are sparse relative to the intrinsic bands.With increasing temperature,the DAP emission energy was shifted to the low energy side because carriers on DAP with small donor –acceptor distance are released into the band [14,18].The transition at 3.33eV is ascribed to excitons bound to structural defects.This transition line at 3.33eV was previously observed in various ZnO samples and tentatively ascribed to donor bound excitons (DX),acceptor bound excitons,transitions of in-trinsic point defects and excitons bound to extended structural defects.The most detail study of this transition was reported by Yalishev et al.[12]and Wagner et al.[3].In their work,the 3.33eV emission line was attributed to recombination of excitons bound to extended structural donor defect complexes which disappear at temperature of 10K.Study done by Urgessa et al.[26]on ZnO nanorods growth for temperature dependent PL also observe dominance of donor-bound exciton as possible reason for this emission.Fig.10illustrates the Commission Internationale de l'Eclairage (CIE)chromaticity diagram of ZnO NPs prepared at various growth temperatures calculated using photoluminescence data and color calculator software.The coordinates were shown deep blue region with the increase in annealing temperature indicating growth temperature play a major role in tuning the emission color of the ZnO NPs.7.ConclusionIn conclusion,the luminescent properties of ZnO NPs prepared from zinc precursor at various decomposition temperatures have been investigated.The samples of ZnO NPs synthesized at a tem-perature from 200–500°C exhibits broad visible emission.ZnO NPs with crystallite size of 16–20nm and hexagonal wurtzite structure was successfully produced.A linear increase in lattice parameters and grain size with temperature was observed.It was demonstrated that the morphology and band gap energy of ZnO NPs can be tuned with annealing temperature.The temperature dependent PL spectra of ZnO NPs prepared at a temperature of °300C shows three transition lines at 3.01eV,3.21eV and 3.33eV which are ascribed to zinc vacancy (V zn ),donor –acceptor pairs (DAP)and excitons bound to structural defects respectively.The activation and binding energy for the transition at 3.21eV were calculated to be about 12.9meV and 45.8meV respectively.De-pending on the hydrogen concentration in the precursor and these energy values,hydrogen was suggested to be the possible impurityP L I n t e n s i t y (a r b .un i t s )Energy (eV)AL o g i n t e g r a t e d i n t e n s i t y (a r b .u n i t s )100/T (K -1)Fig.9.(A).Temperature dependent PL emission of ZnO nanoparticles prepared at °300C and (B).shows thermally activated luminescence quenching of the 3.21eV emission for the ZnO NPs prepared at a temperature of °300C .Fig.10.CIE diagram for temperature dependent PL sample and ZnO prepared at various measuring temperature.L.T.Jule et al./Physica B 497(2016)71–7776acting as donor in our material.It is believed that ZnO NPs pro-duced using this method would be quick and cost effective synthesis method for blue light emittingfluorescent applications. 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物 理 化 学 学 报Acta Phys. -Chim. Sin. 2023, 39 (12), 2212039 (1 of 13)Received: December 23, 2022; Revised: February 6, 2023; Accepted: February 8, 2023; Published online: February 17, 2023. *Correspondingauthors.Emails:****************.cn(M.S.);************.cn(J.X.).†These authors contributed equally to this work.The project was supported by the National Natural Science Foundation of China (21673201), the Yangzhou Guangling District Science and Technology Plan Industry Foresight and Key Common Technology Key Project (GL202206), the Top-notch Academic Programs Project of Jiangsu Higher Education Institutions, China (TAPP), and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.国家自然科学基金(21673201), 扬州市广陵区科技计划产业前瞻性与共性关键技术重点项目(GL202206), 江苏高校品牌专业建设工程项目和江苏高校优势学科建设工程项目资助© Editorial office of Acta Physico-Chimica Sinica[Article]doi: 10.3866/PKU.WHXB202212039Performance Improvement and Antibacterial Mechanism of BiOI/ZnO Nanocomposites as Antibacterial Agent under Visible LightJing Kong 1,2,†, Jingui Zhang 3,†, Sufen Zhang 2, Juqun Xi 1,*, Ming Shen 2,3,*1 Medical College, Yangzhou University, Yangzhou 225009, Jiangsu Province, China.2 College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, Jiangsu Province, China.3 Jiangsu Huicheng Medical Technology Co., Ltd., Yangzhou 225108, Jiangsu Province, China.Abstract: Bacterial infections cause various serious diseases including tuberculosis, meningitis, and cellulitis. Moreover, there is an increase in the number of drug-resistant bacterial strains, which has caused a global health issue. Thus, it is highly essential to develop more effective antibacterial agents. Currently, zinc oxide (ZnO) is commonly used as an inorganic antibacterial agent, but with a notable limit in efficiency. In this work, to improve ZnO antibacterial activity under visible light, bismuth oxyiodide (BiOI) with a narrow bandgap of 1.8 eV was used as a suitable refinement to ZnO. Four different BiOI/ZnO nanocomposites were designed and synthesized via a simple mechanical stirring method in an atmospheric environment;these were denoted as BiOI/ZnO-2.5%, BiOI/ZnO-5%, BiOI/ZnO-10%, and BiOI/ZnO-20%. The successful synthesis of the BiOI/ZnO nanocomposites was verified through X-ray powder diffraction, energy-dispersive X-ray analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). A unique BiOI/ZnO heterojunction was also observed for the nanocomposites through high-resolution TEM, XPS, and selected area electron diffraction. Ultraviolet-visible diffuse reflectance spectroscopy revealed that all four BiOI/ZnO nanocomposites exhibited improved visible light absorption and possessed narrower bandgaps than the ZnO nanoparticles (nano-ZnO). Furthermore, the antibacterial activities of all BiOI/ZnO nanocomposites were investigated under visible light against both gram-positive and gram-negative bacteria strains. The results indicated a significant improvement in the antibacterial activities of BiOI/ZnO-10% and BiOI/ZnO-20% against both Staphylococcus aureus (S. aureus ) and Escherichia coli (E. coli ). Strong light exposure was found to be attributable to an increase in the antibacterial activity against S. aureus . In addition, the antibacterial mechanistic investigation was conducted upon visible light activation. The SEM images showed completely broken bacterial cell walls for both bacteria strains after treatment with the BiOI/ZnO nanocomposites. Hydroxyl radicals (•OH), which are strong reactive oxygen species, generated by the BiOI/ZnO nanocomposites under visible light, were also trapped by 5,5-dimethyl-1-pyrroline-N -oxide. Furthermore, zeta potential analysis revealed the presence of more positively charged BiOI/ZnO nanocomposite surfaces than the surfaces of nano-ZnO. The metal ions released from the BiOI/ZnO nanocomposites under visible light were also studied through inductively coupled plasma mass spectrometry. Based on the above results, BiOI/ZnO nanocomposites were found to exhibit antibacterial mechanism similar to that of nano-ZnO. In the dark, E. coli growth was only inhibited by Zn 2+ released from both BiOI/ZnO nanocomposites and pure nano-ZnO. After visible light activation, •OH generated from theBiOI/ZnOnanocomposites mainly contributed to the bacterial cell death of both E. coli and S. aureus. This study proposes an effective strategy to enhance the antibacterial activity of nano-ZnO under visible light upon the formation of nanocomposites with BiOI. Besides, this study indicates that the ZnO-based nanocomposites can be used as a more effective antibacterial agent in clinical applications.Key Words: BiOI/ZnO nanocomposites; Photocatalysis; Antibacterial activity; Visible light activation;Reactive oxygen species可见光激发的BiOI/ZnO纳米复合抗菌剂制备及其抗菌活性与机制孔菁1,2,†，张金贵3,†，张素芬2，奚菊群1,*，沈明2,3,*1扬州大学医学院，江苏扬州 2250092扬州大学化学化工学院，江苏扬州 2250023江苏汇诚医疗科技有限公司，江苏扬州 225108摘要：细菌感染可引发各种严重疾病，在细菌耐药性日益严重的今天开发无机抗菌药物具有重要意义。

学士学位论文题目：直接沉淀法制备纳米氧化锌直接沉淀法制备纳米氧化锌摘要：以硝酸锌和碳酸铵为原料,通过直接沉淀法制备了纳米ZnO.采用DSC、FT-IR、XRD、TEM等对前驱物和纳米ZnO粉体结构和形貌进行了表征,结果表明:前驱物是[Zn5(OH)6(CO3)2]；前驱物在550℃焙烧2h得到六方晶系的ZnO粉体；该粉体的形貌为长条形，平均宽度约为50nm, 长度为200nm，分布较均匀、纯度高。

关键词：氧化锌、纳米材料、直接沉淀法、XRDSynthesis of nano-sized ZnO powders by direct precipitation method Abstract Using Zinc nitrate and ammonium carbonate as raw materials, nanocrystalline ZnO was prepared by direct precipitation method. The structure and Morphology of nano-sized ZnO powders and the precursors were characterized by DSC、FT-IR、XRD、TEM. The result showed that the precursor was [Zn5(OH)6(CO3)2]; ZnO crystal powders obtained was six-party crystal when precursor was calcined at550℃ for 2h; The morphology of the powders is a long strip, with an average width of about 50nm, a length of 200nm, a more even distribution, high purity. Keyword ZnO;Nanoparticles; Direct precipitation method; XRD目录1 前言 (1)1.1 纳米氧化锌的制备方法 (1)1.2 纳米氧化锌的表征 (4)1.3 纳米氧化锌应用及前景 (5)2实验部分 (6)2.1 实验药品及仪器 (6)2.2样品的制备 (7)2.3 样品表征 (7)3 实验结果与讨论 (8)3.1 前驱体的热分析 (8)3.2前驱体及样品的XRD分析 (8)3.3前驱体及样品的红外光谱分析 (10)3.4 样品的透射电镜(TEM)分析 (11)4结论 (12)参考文献 (13)1 前言氧化锌是Ⅱ—Ⅵ族具有六方纤锌矿晶体结构的宽禁带直接带隙的半导体，室温禁带宽度约为3.37 eV，激子束缚能为60 meV [1]；它具有优良的物性，在声表面波、透明电极、蓝光器件等方面都有较大的应用潜力，目前倍受人们重视[2]。

[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.鄄Chim.Sin .,2008,24(7)：1165-1168July Received:February 25,2008;Revised:March 28,2008;Published on Web:May 26,2008.∗Corresponding authors.Email:wbqpaper@,yudp@;Tel:+8610⁃62759474.国家自然科学基金(90606023)、973项目(2002CB613505,MOST)、黑龙江省自然科学基金(D2007⁃113)和黑龙江省教育厅(1055G066)项目资助ⒸEditorial office of Acta Physico ⁃Chimica SinicaCo 掺杂ZnO 纳米棒的水热法制备及其光致发光性能王百齐1,2,∗夏春辉3富强2王朋伟2单旭东2俞大鹏2,∗(1天津医科大学公共卫生学院,天津300070;2北京大学物理学院,介观物理国家重点实验室电子显微实验室,北京100871;3齐齐哈尔医学院化学教研室,黑龙江齐齐哈尔161042)摘要：以Zn(NO 3)2·6H 2O 和Co(NO 3)2·6H 2O 为原料,通过水热法在较低温度下制备了纯ZnO 和Co 掺杂的ZnO(ZnO:Co)纳米棒.利用XRD 、EDS 、TEM 和HRTEM 对样品进行了表征,结合光致发光(PL)谱研究了样品的PL 性能.结果表明,水热法制备纯ZnO 和ZnO ∶Co 纳米棒均具有较好的结晶度.Co 2+是以替代的形式进入ZnO 晶格,掺入量为2%(原子分数)左右.纯的ZnO 纳米棒平均直径约为20nm,平均长度约为180nm;掺杂样品的平均直径值约为15nm,平均长度约为200nm 左右;Co 掺杂轻微地影响ZnO 纳米棒的生长.另外,Co 掺杂能够调整ZnO 纳米棒的能带结构、提高表面态含量,进而使得ZnO:Co 纳米棒的紫外发光峰位红移,可见光发光能力增强.关键词：ZnO 纳米棒;Co 掺杂;水热法制备;光致发光(PL)中图分类号：O649Hydrothermal Preparation and Photoluminescence Property of Co 鄄Doped ZnO NanorodsWANG Bai ⁃Qi 1,2,∗XIA Chun ⁃Hui 3FU Qiang 2WANG Peng ⁃Wei 2SHAN Xu ⁃Dong 2YU Da ⁃Peng 2,∗(1School of Public Health,Tianjin Medical University,Tianjin 300070,P.R.China ;2Electron Microscopy Laboratory,State Key Laboratory for Mesoscopic Physics,School of Physics,Peking University,Beijing 100871,P.R.China ;3Chemistry Department,Qiqihaer Medical College,Qiqihaer 161042,Heilongjiang Province,P.R.China )Abstract ：Pure and Co ⁃doped ZnO nanorods were synthesized by hydrothermal method at low temperature using Zn(NO 3)2·6H 2O and Co(NO 3)2·6H 2O as raw materials.The as ⁃prepared samples were studied by XRD,EDS,TEM,and HRTEM,the photoluminescence (PL)property of the samples was principally investigated by PL spectroscopy.The results showed that the crystallinities of pure and ZnO ∶Co nanorods were rather well.Co atoms substituted Zn atoms positions to incorporate into nanocrystal,the dopant content was about 2%(atomic fraction).The average diameter and length of pure ZnO nanorods were about 20and 180nm,whereas the corresponding parameters of doped nanorods were respectively about 15and 200nm.This indicated that Co doping could influence the growth of ZnO nanorods.In addition,the Co doping could tune the energy level structure and enrich the surface states of ZnO nanorods,which led to emission peak redshift in UV region and luminescence enhancement in visible light region.Key Words ：ZnO nanorods;Co doping;Hydrothermal method;Photoluminescence (PL)ZnO 是一种重要的氧化物半导体,它具有较宽的带隙(E g =3.4eV)和较大的激子缚束能(60meV).因此,ZnO 在高密度信息存贮以及光转换等领域具有广阔的应用前景[1-4].一维ZnO 纳米材料由于具有奇异的电学、磁学及光学特性使其成为纳米光电器件等领域的研究热点.人们希望能够通过简单、经济的方法制备出结晶程度好、尺寸分布均匀、性能可调的一维ZnO 纳米材料.过渡金属掺杂能够有效地调1165Acta Phys.鄄Chim.Sin.,2008Vol.24节一维ZnO纳米材料的电子能态结构,改变表面状态,进而起到调控其性能的作用[5-8].Co是一种典型过渡金属元素,具有非常丰富的电子壳层结构.目前,国内外对于ZnO:Co的研究主要集中在薄膜材料的磁学方面,而对于Co掺杂低维ZnO纳米材料光学性能研究则刚刚起步[9,10].水热法具有反应条件温和、产品纯度高、实验过程可控等优点被广泛用于一维纳米材料的制备[11-14].近来,对于水热法制备过渡金属掺杂一维ZnO纳米材料逐渐引起科研人员的注意[15].本文在较温和的条件下,通过水热法制备出了ZnO:Co纳米棒,深入探讨了Co掺杂对于一维ZnO纳米材料结晶、形貌以及光学性能等的影响,得到了有意义的结果.1实验部分1.1试剂及样品的制备过程实验中所用到的试剂均为分析纯,未经进一步提纯.实验用水为二次去离子水.样品制备是结合文献[16]的水热过程,将0.005mol·L-1的NaOH乙醇溶液缓慢滴加到含有0.005mol·L-1的Zn(NO3)2·6H2O 乙醇溶液中.将混合溶液转移至高压反应釜中,在130℃下反应12h,将反应产物经二次去离子水、乙醇等洗涤后,在130℃下干燥,即可获得纯ZnO纳米棒.为了得到ZnO:Co纳米棒,将一定量的Co(NO3)2·6H2O加入到Zn(NO3)2·6H2O乙醇溶液中分散均匀,其余制备过程与纯ZnO纳米棒制备过程相同.1.2样品的表征利用日本Rigaku的D/MAX⁃2400型X射线衍射仪对样品的晶型结构进行分析(Cu K琢=0.15418nm,石墨单色器);采用PHILIPS的FECNAI F30型TEM 和HRTEM对样品的形貌及微观结构进行观察,工作电压300kV;Co元素掺杂量检测是在FECNAI F30型EDS谱仪上进行的;光致发光谱在Renishaw 的inVia光谱仪上采集得到,以He⁃Cd激光器325 nm紫外光作为激发源.2结果与讨论2.1XRD分析图1为纯ZnO及ZnO∶Co纳米棒的XRD图.由图可见,纯的及掺杂样品均与标准卡片(PDF Card No. 36⁃1451)符合很好,属于六方纤锌矿结构,空间群P63mc(186),晶胞参数为a=0.3249nm,c=0.5206nm.对照标准图可以看出,纯ZnO及掺杂样品的(100)、(002)和(101)晶面衍射峰的强度顺序发生了改变. (002)衍射峰由第三强峰转变为最强峰,表明ZnO纳米材料沿c轴具有明显择优生长趋势.对照纯ZnO 与Co掺杂样品的衍射图可见,ZnO∶Co纳米棒的衍射峰略微宽化,这意味着Co掺杂能够轻微地影响ZnO结晶;同时,掺杂样品的衍射峰向高角度方向移动了0.05°.众所周知,Co2+的半径(0.058nm)略小于Zn2+的半径(0.060nm)[17,18].因此,当Co2+替代ZnO 晶格中Zn2+的位置,晶面间距减小,则衍射角向高角度方向移动.也就是说,Co是以替代的形式进入到ZnO晶格中.另外,在纯的及掺杂样品中均未发现Co 的物相及杂质物相,这表明制备的样品纯度很高. 2.2EDS检测利用EDS对Co元素含量进行分析,图2为ZnO:Co纳米棒的EDS谱.图中在0.25keV位置处出现了C的特征峰,在8.05keV处出现了Cu的特征峰,它们主要来源于测试过程中的Cu网及其表面C膜;同时,在0.5keV处出现了O的特征峰.在图1纯ZnO及ZnO∶Co纳米棒的XRD图Fig.1XRD patterns of pure ZnO and Co⁃doped ZnOnanorods图2ZnO:Co纳米棒的EDS谱Fig.2EDS of Co⁃doped ZnO nanorods1166No.7王百齐等：Co 掺杂ZnO 纳米棒的水热法制备及其光致发光性能1.00、8.63、9.60keV 处出现的EDS 峰为Zn 元素的特征峰[19].值得注意的是,大约在6.91keV 处出现了Co 的特征峰[20],通过专业软件拟合计算可得其含量约为2%(原子分数).为了精确分析Co 的掺杂情况,利用EDS 对多根掺杂ZnO 纳米棒进行分析,发现每根Co 含量变化不大.这说明Co 2+在ZnO 纳米晶中均匀地替代Zn 2+的位置.这与前面的XRD 表征分析结果是相符合的.2.3TEM 与HRTEM图3为纯ZnO 及ZnO ∶Co 纳米棒的TEM 及HRTEM 照片.由图可见,纯的和掺杂样品均呈棒状.纯的ZnO 纳米棒直径平均约为20nm 左右,平均长度约在180nm 左右.掺杂样品平均直径约在15nm,平均长度为200nm 左右.通过TEM 检测可以看出,Co 掺杂能够轻微地影响ZnO 的生长,这与前面表征所得到的结论相符合.由HRTEM 照片3(b 、d)可以看出,掺杂前后样品的晶面间距均为0.52nm,对应[001]晶面间距.同时也进一步证实样品均沿c 轴生长.这与XRD 表征分析结果是一致的.由前面的分析可知,由于Co 2+与Zn 2+半径相差不大,当Co 2+以替代的形式占据了ZnO 纳米晶中Zn 2+的位置,HRTEM 中不会出现明显变化.2.4PL 检测图4为纯ZnO 和ZnO:Co 纳米棒的PL 谱图.由图可见,纯的及掺杂的ZnO 纳米棒均有两个较明显的发光区域.一是带边激子复合引起的紫外发光峰[21-23];另一个是与缺陷和氧空位有关的可见光发光带[24-26].通过对比可以看出,纯ZnO 纳米棒的紫外发光峰位于姿为380nm 左右,而Co 掺杂样品的峰位移至388nm 左右.这表明Co 掺杂能够有效地调整ZnO纳米晶的能带结构,减小其禁带宽度,从而使得它在紫外区的发光行为有所变化.此外,掺杂以后样品可见光发光强度显著增强,意味着掺杂样品具有较丰富的表面态,也就是说Co 掺杂能够明显地提高ZnO 纳米棒表面缺陷及氧空位的含量,从而提高其在可见光区的发光能力.这与前面的表征所得到的结果也是相符合的.3结论采用水热法在较低温度下制备了纯ZnO 和ZnO:Co 纳米棒.掺杂前后的样品均具有较好的结晶度,且沿c 轴生长.Co 离子是以替代的形式进入ZnO 晶格,掺入量约为2%(原子分数).纯ZnO 纳米棒平均直径约为20nm,平均长度约为180nm;掺杂样品的平均直径约为15nm,平均长度约为200nm 左右,Co 掺杂轻微地改变ZnO 纳米棒的生长.另外,Co 掺杂能够调整ZnO 纳米棒的能态结构,丰富其表面态,进而赋予ZnO:Co 纳米棒以新奇的发光特性.本研究为Co 掺杂低维ZnO 纳米材料在纳图3纯ZnO 和ZnO ∶Co 纳米棒的TEM 及HRTEM 照片Fig.3TEM and HRTEM images of pure and Co ⁃doped ZnO nanorods(a),(b)pure ZnO nanorods;(c),(d)Co ⁃doped ZnOnanorods图4纯ZnO 及ZnO ∶Co 纳米棒的PL 光谱Fig.4PL spectra of pure and Co ⁃doped ZnOnanorods1167Acta Phys.⁃Chim.Sin.,2008Vol.24米光电器件等方面应用提供了有力的实验基础. 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