Formation of aligned ZnO nanotube arrays by chemical etching and coupling with CdSe for photovoltaic application

High density aligned ZnO nanotube (NT) arrays were synthesized using a facile chemical etching of electrochemically deposited ZnO nanorods (NRs). The influence of etching time and solution concentration on the ZnO NT formation was investigated. Moreover, cadmium selenide (CdSe) nanoparticles as sensitizers were assembled onto the ZnO NT and NR arrays for solar cell application. A conversion efficiency (η) of 0.44% was achieved for CdSe/ZnO NT-based solar cell under the white light illumination intensity of 85 mW/cm². An 8% enhancement in η was observed between the CdSe/ZnO NT-based and NR-based solar cell due to the enhancement of the photocurrent density. ZnO NT arrays have been proved to have a superior ability as compared with ZnO NR arrays when employed as a semiconductor film.     

Enhanced performance of Al2O3 coated ZnO nanorods in CdS/CdSe quantum dot-sensitized solar cell

CdS/CdSe quantum dot-sensitized solar cells (QDSCs) based on ZnO nanorods, 4.55 μm in length, were studied. Many studies have shown that the performance of QDSCs is limited by a recombination process. Therefore, the interface layer was fabricated on the surface of the ZnO nanorods to retard recombination at the interface between the semiconductor and electrolyte. Overall, the performance of the QDSCs was improved by a surface coating of aluminum isopropoxide (Al₂O₃) on the ZnO nanorod, which facilitates a decrease in electron recombination and increased adsorption of CdS/CdSe QDs on the ZnO nanorods.     

Efficient removal of chromate and arsenate from individual and mixed system by malachite nanoparticles

Malachite nanoparticles of 100-150 nm have been efficiently and for the first time used as an adsorbent for the removal of toxic arsenate and chromate. We report a high adsorption capacity for chromate and arsenate on malachite nanoparticle from both individual and mixed solution in pH ～4-5. However, the adsorption efficiency decreases with the increase of solution pH. Batch studies revealed that initial pH, temperature, malachite nanoparticles dose and initial concentration of chromate and arsenate were important parameters for the adsorption process. Thermodynamic analysis showed that adsorption of chromate and arsenate on malachite nanoparticles is endothermic and spontaneous. The adsorption of these anions has also been investigated quantitatively with the help of adsorption kinetics, isotherm, and selectivity coefficient (K) analysis. The adsorption data for both chromate and arsenate were fitted well in Langmuir isotherm and preferentially followed the second order kinetics. The binding affinity of chromate is found to be slightly higher than arsenate in a competitive adsorption process which leads to the comparatively higher adsorption of chromate on malachite nanoparticles surface.     

Synergistic effects of SPR and FRET on the photoluminescence of ZnO nanorod heterostructures

Solution-grown ZnO nanorods (NRs) were successfully conjugated with CdSe/ZnS quantum dots (QDs) and Ag nanoparticles (NPs) to suppress intrinsic defect emission and to enhance band-edge emission at the same time. First, high-density and high-crystallinity ZnO NRs of diameter 80–90 nm and length 1.2–1.5 μm were grown on glass substrates using a low-temperature seed-assisted solution method. The as-synthesized ZnO NRs showed sharp photoluminescence (PL) band-edge emission centered at ～377 nm together with broad defect emission in the range of ～450–800 nm. The ZnO NRs were decorated with CdSe/ZnS QDs and Ag NPs, respectively, by sequential drop-coating. The PL of CdSe/ZnS QD||ZnO NR conjugates showed that ZnO band-edge emission decreased by 73.8% due to fluorescence resonance energy transfer (FRET) and charge separation between ZnO and CdSe/ZnS by type II energy band structure formation. On the other hand, Ag NP||CdSe/ZnS QD||ZnO NR conjugates showed increased band-edge emission (by 25.8%) and suppressed defect emission compared to bare ZnO NRs. A possible energy transfer mechanism to explain the improved PL properties of ZnO NRs was proposed based upon the combined effects of FRET and surface plasmon resonance (SPR).     

Sensitization of ZnO nanorods with CdSe quantum dots

We have optimized the low-temperature growth of aligned arrays of zinc oxide nanorods of controlled length and diameter on conductive substrates. Varying the solution concentration and growth time, we were able to tune the nanorod diameter and length in the ranges 40–600 nm and 0.5–15 μm, respectively. The grown zinc oxide nanorods were photosensitized with CdSe quantum dots (QDs) in an oleic shell, which was replaced by pyridine. We studied the optical and transport properties of the ZnO nanorod arrays, with and without CdSe QDs on their surface. The current-voltage characteristics of the ZnO nanorod arrays with CdSe QDs are significantly influenced by illumination with light at a wavelength under the absorption band of the QDs, which points to effective interaction between the QDs and ZnO matrix.     

Semiconductor/metal nanocomposites formed by in situ reduction method in multilayer thin films

A layer-by-layer adsorption and in situ reduction method was adopted for synthesizing semiconductor/metal nanocomposites in multilayer ultra-thin films. Alternate adsorption of ZnO nanoparticles modified with poly(ethyleneimine), hydrogentetrachloroaurate and poly(styrenesulfonate) sodium results in the formation of ZnO/AuCl₄⁻-loaded multilayer films. In situ reduction of the incorporated metal ions by heating yields ZnO/Au nanocomposites in the films. UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy were used to characterize the components of the composite films. UV-vis spectra indicate regular growth of the films. The electrochemistry behavior of the multilayer films was studied in detail on indium tin oxide electrode. The combined results suggest that the layer-by-layer adsorption and subsequent reduction method used here provides an effective way to synthesize ZnO/Au nanocomposites in the polymer matrix.     

Microstructure and hemocompatibility of neodymium doped zinc oxide thin films

By the radio frequency magnetron sputtering, both un-doped and neodymium (Nd) doped ZnO thin films were grown on Si (100) substrates. The microstructure of the films has preferred c-axis growth orientation confirmed by the X-ray diffraction spectra. The crystallite size of ZnO crystallite decreases with the increasing of Nd concentration. We show that the hemocompatibility can be improved by a suitable Nd doping in the ZnO thin films. It is verified by both calculations on surface energy and interfacial tension of the sample, and experiments on the wettability, the proteins adsorption, and the platelets adhesion.     

Luminescence from single CdSe nanocrystals embedded in ZnO thin films using atomic layer deposition

We report the embedding of CdSe/ZnS core-shell nanocrystals into thin films of ZnO grown by atomic layer deposition. Fluorescence from ensembles and that from individual nanocrystals show that the nanocrystal luminescence intensity and stability are preserved through the embedding process. These results are encouraging for the fabrication of optoelectronic nanodevices based on colloidal nanoparticles.     

Improved photocatalytic activity of surface charge functionalized ZnO nanoparticles using aniline

Functionalization of aniline molecules on zinc oxide(ZnO)nanoparticles is reported using a simple impregnation technique.Functionalized ZnO samples were systematically characterized based on mor-phology,surface and optical properties,and photocatalytic performance towards methyl orange(MO).Aniline functionalization increased the surface charge of the modified ZnO.Compared to pristine ZnO,the aniline-functionalized ZnO yielded faster photodegradation of MO,degrading 98.29％ of MO in 60 min and superoxide radicals were the major species during the MO photodegradation reaction.These results indi-cate that the improvement of photocatalytic degradation could be attributed to opposite charge-induced surface adsorption.Hence,protonated amine as a positively charged molecule was expected to increase the surface adsorption of MO(as an anionic dye)on ZnO nanoparticles surfaces,thereby increasing their photocatalvtic degradation performance.     

Design of ZnO nanostructured films: Characterization and ecotoxicological studies

The potential ecotoxicological impact of ZnO nanostructured films was investigated using common Anabaena flos-aquae, Calothrix pulvinata cyanobacteria and Euglena gracilis euglenoid microalgae. The pre-formed ZnO nanoparticles were synthesized in di(ethylene glycol) medium by forced hydrolysis of ionic Zn²⁺ salts. Particle size and shape were controlled by addition of protective agents such as tri-n-octylphosphine oxide and polyoxyethylene stearyl ether. ZnO nanostructured films were directly prepared by spray deposition of pre-formed polyol-based ZnO nanoparticles (ZnO, ZnO-TOPO and ZnO-Brij-76) at 250 °C heated glass substrate. Another sample was prepared from zinc acetate in di(ethylene glycol) diluted in ethanol medium without nanoparticles (ZnO-SOL). In this case, ZnO nanostructured film was formed directly on the glass substrate at the same temperature. Water contact angle on ZnO-based films showed that nanostructured ZnO films containing ZnO nanoparticles prepared without protective agent or with tri-n-octylphosphine oxide present a hydrophobic character while the ones containing nanoparticles prepared using polyoxyethylene stearyl ether or the control sample are hydrophilic. Here we showed that (i) the use of protective agents, (ii) the surface properties of the films and (iii) the nature of the biological system can strongly influence the ecotoxicological studies. Epifluorescence microscopy analyses and Live/Dead tests showed that all films are toxic for Euglena gracilis. In the case of Anabaena flos-aquae and Calothrix pulvinata, tri-n-octylphosphine oxide and polyoxyethylene stearyl ether molecules can prevent ZnO nanoparticle toxicity.     

纳米ZnO-γ-Al_2O_3复合粉体的制备及其光催化性能

以γ-Al2O3为载体,采用均相沉淀法制备不同ZnO负载量的纳米ZnO-γ-Al2O3复合粉体。通过X射线粉末衍射(XRD)、扫描电镜(SEM)和氮气吸附对复合粉体的结构、表面形貌和比表面积进行表征。以壬基酚聚氧乙烯醚(NPE-10)为模拟污染物,对复合粉体的光催化性能进行评价。结果表明:ZnO成功负载到了γ-Al2O3表面,且负载量随着ZnO比例的增加而增加,当ZnO与γ-Al2O3质量比为2:1时,ZnO在γ-Al2O3表面形成均匀的薄膜,且这时的复合粉体催化性能最好。煅烧温度、复合物用量对其光催化性能有显著影响,300℃下煅烧所得的复合粉体,当添加量为0.3 g时,在紫外光下照射4 h后降解率可达到96%以上,重复使用6次后降解率仍可达90%以上。     

Preparation,characterization, and photoluminescence study of PVA/ZnO nanocomposite films

ZnO nanoparticles with average diameter of 25 nm were synthesized by a modified sol–gel method and used in the preparation of (in wt.%) (100 − x) poly(vinyl alcohol) (PVA)/x ZnO nanocomposite films, with x = 0, 1, 2, 3, 4, and 5. The PVA/ZnO films were exposed to UV radiation for 96 h and their thermal, morphological, and spectroscopic properties were investigated. In inert atmosphere, the nanocomposite films showed lower thermal stability than the pure PVA film, and the calorimetric data suggest an interaction between PVA and ZnO in the nanocomposite films. Some crystalline phases could be seen in the films with ZnO, and a direct dependence on the ZnO concentration was also observed. The original structure of ZnO nanoparticles remained unaltered in the PVA matrix and they were uniformly distributed on the film surface. The roughness of the PVA film was not modified by the addition of ZnO; however, it increased after 96 h of UV irradiation, more significantly in the nanocomposite films. The films showed an absorption band centered at 370 nm and a broad emission band in the UV–vis region when excited at 325 nm.     

Ti O2纳米管阵列基底退火温度对CdSe/Ti O2异质结薄膜光电化学性能的影响

通过电化学沉积法以TiO2纳米管阵列(TNTs)为基底制备CdSe/TiO2异质结薄膜。研究TiO2纳米管阵列基底不同退火温度(200,350,450,600℃)对CdSe/TiO2异质结薄膜光电化学性能的影响。采用SEM,XRD,UV-Vis,电化学测试等方法对样品的微观形貌、晶体结构、光电化学性能等进行表征。结果表明:立方晶型的CdSe纳米颗粒均匀沉积在TiO2纳米管阵列管口及管壁上。TiO2纳米管阵列未经退火及退火温度为200℃时,为无定型态,在TiO2纳米管阵列上沉积的CdSe纳米颗粒数量少,尺寸小,异质结薄膜光电性能较差,光电流几乎为零。随着退火温度升高到350℃,TiO2纳米管阵列基底开始向锐钛矿转变;且沉积在TiO2纳米管上的CdSe颗粒增多,尺寸增大,光电化学性能提高。退火温度为450℃时光电流值达到最大,为4.05mA/cm^2。当退火温度达到600℃时,TiO2纳米管有金红石相出现,CdSe颗粒变小,数量减少,光电化学性能下降。     

Effect of solid surface charge on the binding behaviour of a metal-binding peptide

Over the last decade, solid-binding peptides have been increasingly used as molecular building blocks coupling bio- and nanotechnology. Despite considerable research being invested in this field, the effects of many surface-related parameters that define the binding of peptide to solids are still unknown. In the quest to control biological molecules at solid interfaces and, thereby, tailoring the binding characteristics of the peptides, the use of surface charge of the solid surface may probably play an important role, which then can be used as a potential tuning parameter of peptide adsorption. Here, we report quantitative investigation on the viscoelastic properties and binding kinetics of an engineered gold-binding peptide, 3RGBP_1, adsorbed onto the gold surface at different surface charge densities. The experiments were performed in aqueous solutions using an electrochemical dissipative quartz crystal microbalance system. Hydrodynamic mass, hydration state and surface coverage of the adsorbed peptide films were determined as a function of surface charge density of the gold metal substrate. Under each charged condition, binding of 3rGBP₁ displayed quantitative differences in terms of adsorbed peptide amount, surface coverage ratio and hydration state. Based on the intrinsically disordered structure of the peptide, we propose a possible mechanism for binding of the peptide that can be used for tuning surface adsorption in further studies. Controlled alteration of peptide binding on solid surfaces, as shown here, may provide novel methods for surface functionalization used for bioenabled processing and fabrication of future micro- and nanodevices.     

Facile synthesis of highly uniform ZnO multipods as the supports of Au and Ag nanoparticles

Through the direct reaction of the aqueous solutions of zinc salts and KOH, highly uniform ZnO multipods consisted of rod-shaped branches are synthesized in an extremely high yield. The synthesis is conducted at low temperature, does not require any organic capping agents to affect the crystal habit, and is independent on the species of zinc sources. Moreover, by changing the reaction temperature from 25 to 70 °C, the tips of the multipods can be adjusted from taper to regular hexagon. The mechanism responsible for the formation of ZnO multipods is the self-regulation growth guided by the inherently asymmetric structure of hexagonal ZnO along the c-axis. After the surface modification with amino groups, ZnO multipods show good affinity to Ag and Au nanoparticles, which results in the spontaneous migration of Au and Ag nanoparticles to the surface of ZnO to form well-defined Au/ZnO and Ag/ZnO heterostructures. The fabricated hybrids are found to be effective surface-enhanced Raman scattering (SERS) substrates because of their distinct geometrical shape, large surface area, and the ability to create a strong local electromagnetic field by the metal–semiconductor heterojunction.     

Synthesis and characterisation of starch/agar nanocomposite films for food packaging application

In the present work cassava starch/agar Ag and ZnO nanocomposite films were prepared by the solution casting method. The structural, physical and antimicrobial properties of the nanocomposite films were studied as a function of the concentration of Ag and ZnO nanoparticles. The results of the thermogravimetric analysis showed 8–15% degradation of both the nanocomposite films at 150°C endorsing the thermal stability of the films. Scanning electron microscopic analysis reveals the uniform blending of Ag and ZnO nanoparticles with a starch/agar matrix with tiny waves like appearance on the surface. The incorporation of Ag and ZnO nanoparticles in the film was found to reduce the moisture content, water solubility and water vapour permeability with increase in the concentration of Ag and ZnO nanoparticles. The growth kinetics study of Pseudomonas aeruginosa and Staphylococcus aureus in the presence of Ag and ZnO blended nanocomposite films showed promising results especially against Gram‐negative P. aeruginosa. Thus, the film synthesised in the present study bears the potential to be used as active packaging material to prevent food from bacterial contamination and spoilage.Inspec keywords: casting, microorganisms, scanning electron microscopy, nanoparticles, food preservation, solubility, thermal analysis, zinc compounds, food processing industry, food products, thermal stability, permeability, antibacterial activity, food packaging, contaminationOther keywords: water vapour permeability, food packaging, solution casting method, structural properties, physical properties, antimicrobial properties, water solubility, agar nanocomposite film, starch nanocomposite film, Pseudomonas aeruginosa, Staphylococcus aureus, bacterial contamination prevention, spoilage prevention, scanning electron microscopic analysis, thermogravimetric analysis, temperature 150.0 degC, Ag, ZnO     

Structural and optical properties of ZnO films grown on the AAO templates

Structural and optical properties of ZnO films grown on Al substrate and anodic alumina oxide (AAO) templates by rf magnetron reactive sputtering deposition were investigated using X-ray diffraction (XRD), atomic-force microscope (AFM) and photoluminescence (PL). We found that ZnO thin films on Al substrate show good C-axis orientation, while the orientation of ZnO film on AAO templates is disordered, this due to the fact that the crystalline of ZnO is greatly influenced by surface morphology of substrates. PL measurements show a blue band in the wavelength range of 400–500 nm caused by the interstitial Zn in the ZnO films. The intensity of emission peak of ZnO films deposited on AAO templates increases compared with that on the Al substrate. Combining electrical resistivity and carrier concentration measurements, we found that that the blue emission intensity is consistent with the concentration for the interstitial zinc in the ZnO films.     

The incorporation of preformed metal nanoparticles in zinc oxide thin films using aerosol assisted chemical vapour deposition

The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 °C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400-450 °C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented.     

Influence of the shape of nanostructured metal surfaces on adsorption of single peptide molecules in aqueous solution

Self-assembly and function of biologically modified metal nanostructures depend on surface-selective adsorption; however, the influence of the shape of metal surfaces on peptide adsorption mechanisms has been poorly understood. The adsorption of single peptide molecules in aqueous solution (Tyr(12) , Ser(12) , A3, Flg-Na(3) ) is investigated on even {111} surfaces, stepped surfaces, and a 2 nm cuboctahedral nanoparticle of gold using molecular dynamics simulation with the CHARMM-METAL force field. Strong and selective adsorption is found on even surfaces and the inner edges of stepped surfaces (-20 to -60 kcal/mol peptide) in contrast to weaker and less selective adsorption on small nanoparticles (-15 to -25 kcal/mol peptide). Binding and selectivity appear to be controlled by the size of surface features and the extent of co-ordination of epitaxial sites by polarizable atoms (N, O, C) along the peptide chain. The adsorption energy of a single peptide equals a fraction of the sum of the adsorption energies of individual amino acids that is characteristic of surface shape, epitaxial pattern, and conformation constraints (often β-strand and random coil). The proposed adsorption mechanism is supported and critically evaluated by earlier sequence data from phage display, dissociation constants of small proteins as a function of nanoparticle size, and observed shapes of peptide-stabilized nanoparticles. Understanding the interaction of single peptides with shaped metal surfaces is a key step towards control over self-organization of multiple peptides on shaped metal surfaces and the assembly of superstructures from nanostructures.     

多层气敏薄膜表面吸附及界面扩散的研究

制备了ＳｎＯ３／ＺｎＯ及ＺｎＯ／ＳｎＯ３多层结构的气敏薄膜，用能谱结合氩离子刻蚀的方法及Ｘ射线衍射法，对薄膜的表面吸附。膜间的相互与组成等进行了研究，结果表明：薄膜表面存在少量的吸附多层膜中锌的扩散远比锡一个模型，对吸附现象作了初步的解释，讨论了造成锌锡扩散的原因。