Mesoporous ZnO Research Articles

Mesoporous Ag/ZnO multilayer films prepared by repeated spin-coating for enhancing its photonic efficiencies

The aim of the present work is to enhance the photonic efficiency of mesoporous ZnO films by photodeposition of Ag nanoparticles. Mesoporous ZnO multilayer films were synthesized by a sol–gel method in the presence of triblock co-polymer Pluronic (F-127) as a template agent, followed by spin coating on soda lime glass substrates. The as-prepared mesoporous ZnO films with different layers (1–10) were calcined at 450°C for 3h. Ag nanoparticles were photodeposited onto mesoporous ZnO multilayer films. XRD results of Ag/ZnO films indicated that ZnO nanoparticles had a hexagonal wurtzite structurewith a highly crystalline state. TEM images revealed that Ag nanoparticles are agglomerated and all pores can be regarded as irregular voids between ZnO particles and the prepared films have a large amount of voids. The prepared films have been evaluated by the determination of their photonic efficiencies during degradation of methylene blue (MB). The photonic efficiencies of mesoporous ZnO and Ag/ZnO films were found to improve with increasing number of layers from 1 to 5 and a further increase in film thickness (10 layers) doesn't lead to any enhancement in photoactivity. MB photodegradation was enhanced significantly when Ag was photodeposited onto ZnO using 5 layers with 1.165% photonic efficiency. The prepared Ag/ZnO with different layers demonstrates a highly stable nature of the designed photocatalyst with almost the same photocatalytic performance after 10 repeated cycles.

Experimental and DFT study of the degradation of 4-chlorophenol on hierarchical micro-/nanostructured oxide films

Hierarchical ZnO nanoporous/nanowire architectures immobilized on a substrate were prepared by a facile two-step electrochemical technique. The layer optical properties have been characterized by absorption spectroscopy and photoluminescence measurements. The structures strongly absorbed UV light and had a high structural quality. The porosity of the hierarchical layers could be tuned by changing the duration of the second growth step. The photocatalytic activity of ZnO films was higher than that of arrayed ZnO nanowire layers and mesoporous ZnO films. The photocatalytic activity for 4-chlorophenol degradation could be enhanced by developing hierarchical structures with a high percentage exposure of polar (0001) facets, high specific surface area and good accessibility of the pollutant to the oxide surface. The modeling by density functional theory (DFT) of the degradation of 4-chlorophenol molecules by OH radicals lead to several important results, namely that the hydroxylation of the aromatic ring and its opening can occur in parallel releasing hydroperoxyl radical and hydroxyl radical, respectively. The restored OH radical can either further oxidize the primary ring opening product or attack another molecule of 4-chlorophenol. These computational results are in good agreement with the photocatalytic degradation observations made using both ZnO and TiO2 photocatalysts.

Optical and gas sensing properties of mesoporous hollow ZnO microspheres fabricated via a solvothermal method

Mesoporous, hollow ZnO microspheres were synthesized via a hydrothermal method, using glycerol and zinc acetate as the starting materials. XRD and FESEM analysis showed that the surface morphology of the spheres with a Wurtzite structure could be reasonably adjusted by varying the weight ratio (Rw) of Zn(CH3COO)2·2H2O:H2O:C3H8O3. The responses of the gas sensor based on the spheres to 100 ppm ethanol and 100 ppm acetone are 18.9 and 10.4, respectively. The response and recovery times of the sensor to ethanol and acetone are 2 s and 3 s, 3 s and 5 s, respectively. The hollow spheres show an intense UV emission at ∼392 nm and a broad blue-green emission at ∼488 nm. Interestingly, a light trapping phenomenon is revealed by UV emission and scattering measurements on the microspheres, which can be attributed to the mesoporous shell and hollow structure of the microsphere.

ZnO Thin Film Prepared by Two-Step Electrodeposition Method for Dye-Sensitized Solar Cell

Mesoporous ZnO thin film is an important part of dye-sensitized solar cells (DSSCs) due to it determines the amount of adsorbed dyes. However, small specific surface area of ZnO thin film prepared by ordinary methods restricts the increase of conversion efficiency of DSSCs. In this work we adopted two-step electrodeposition method to fabricate ZnO thin film, which increase the roughness and dyes adsorption. ZnO nanosheets with many adsorbing nanoparticles were observed by scanning electron microscope (SEM). It is noteworthy that DSSC based on two-step electrodeposition method exhibit more outstanding photoelectric performance than those based on one-step electrodeposition method, which demonstrates that two-step electrodeposition method is in favor of increasing specific surface area and adding dyes adsorption, which eventually contributes to improvement the conversion efficiency of DSSCs.

Ultralong and Mesoporous ZnO and γ-Al2O3 Oriented Nanowires Obtained by Template-assisted Hydrothermal Approach

Highly mesoporous ZnO and γ-Al2O3 nanowires (NWs) are both synthesized by a hydrothermal method using commercially available porous anodic aluminium oxide (AAO) as template. AAO membrane acts as template for ZnO NWs and both as template and precursor for γ-Al2O3 NWs. The formation of intermediate phases of porous Zn6Al2(OH)16CO3 and boehmite (γ-AlOOH) were observed, both occurring during the hydrothermal synthesis of porous ZnO and γ-Al2O3 NWs, respectively, and disappearing after annealing at 600 °C. This novel template-assisted hydrothermal process leads to the formation of porous ZnO and γ-Al2O3 NWs (specific surface area of 192 m2 g−1 and 263 m2 g−1, respectively), showing pore sizes around 4 nm in diameter. The influence of the reaction parameters on the nanostructure morphology was also investigated. A ZnO seed layer, deposited on the AAO channels prior to the hydrothermal synthesis, leads to more compact ZnO nanowires (99 m2 g−1) protecting the AAO host from the chemical attack of the precursor solution.

Fabrication of gas sensor based on mesoporous rhombus-shaped ZnO rod arrays

Mesoporous rhombus-shaped ZnO rod arrays based gas sensors were successfully fabricated by a post-thermal conversion of rhombic Zn(OH)F precursors after a low temperature fluorine-mediated hydrothermal method. The gas sensors annealed at 350, 450, 550 and 650°C showed different responses for ethanol detection. Increasing of the annealing temperatures resulted in the decline of gas response, which is due to the effect of grain size distributions, specific surface area and defect concentration. At low temperature (less than 350°C), the incomplete decomposition of Zn(OH)F led to the instability of the sensors. The sensor annealed at 450°C showed the best performance, and the response to 100ppm ethanol reached ∼11.8 at 300°C. The sensor also exhibited good response/recovery speed (4s and 7s), excellent gas response and good stability. The fabrication of the high-performance gas sensors possesses the capability of constructing complex architectures with mesoporous rhombus-shaped ZnO rod arrays as the building block.

Synthesis of mesoporous Ag/ZnO nanocrystals with enhanced photocatalytic activity

Mesoporous Ag/ZnO nanocrystals have been successfully synthesized at different Ag contents (0–10wt%) through a single-step sol–gel method in presence of triblock copolymer as a structure directing agent. The as-prepared hybrid materials were calcined at 450°C in air for 4h, subsequently, Ag nanoparticles have been photo-reduced from AgNO3 onto mesopores ZnO nanocyrstals. The XRD and Raman analysis revealed that well crystalline ZnO hexagonal wurtzite phase and face-centered cubic metallic Ag nanoparticles were formed. TEM images of mesoporous ZnO nanocrystals showed that synthesized materials composed of discrete ZnO nanoparticles agglomerated with worm-like mesoporous structure. The lattice fringes exhibit the typical distances, i.e., Ag(111) and ZnO(100) and the average Ag and ZnO nanoparticle diameters are ∼5 and 10nm, respectively. The photocatalytic performance of different prepared photocatalysts was evaluated by degradation of methylene blue (MB) under visible light irradiation. The results indicate that the photocatalytic efficiencies of mesoporous ZnO photocatalysts were remarkably enhanced by adding 1% Ag nanoparticles which completely degrade the target MB dye within 150min. The photodegradation rate was found to increase linearly with increasing the Ag contents from 0 to 1% and it is faster 2.2 times than undoped ZnO. From economic point of view, 1% Ag/ZnO photocatalyst contains optimum Ag content as there is no significant increase in the photocalatytic performance at higher Ag content.

SnO2 Nanorods on ZnO Nanofibers: A New Class of Hierarchical Nanostructures Enabled by Electrospinning as Anode Material for High-Performance Lithium-Ion Batteries

The ZnO/SnO2 heterogeneous nanofibers (HNFs) have been prepared via an electrospinning method followed by calcination at 500°C in air. XRD, BET, SEM, TEM and electrochemical measurements were performed to characterize the new material, including structure, morphology and electrochemical properties. The spacing between adjacent SnO2 nanorods on mesoporous ZnO nanofibers is about twice the diameter of each SnO2 nanorod. The SnO2/ZnO11 (molar ratio of Sn: Zn=1:1) HNFs based electrodes exhibit excellent cycle performance and rate performance, which is attributed to the heterogeneous and mesoporous structure as well as the ultrafine ZnO NPs embedded in the HNFs matrix. Outstanding electrochemical performance as anode material for LIBs together with low cost, facile procedures and high reproducibility make the SnO2/ZnO HNFs have a prospect in the field of energy storage.

Effect of variation of average pore size and specific surface area of ZnO electrode (WE) on efficiency of dye-sensitized solar cells.

Mesoporous ZnO nanoparticles have been synthesized with tremendous increase in specific surface area of up to 578 m2/g which was 5.54 m2/g in previous reports (J. Phys. Chem. C 113:14676-14680, 2009). Different mesoporous ZnO nanoparticles with average pore sizes ranging from 7.22 to 13.43 nm and specific surface area ranging from 50.41 to 578 m2/g were prepared through the sol-gel method via a simple evaporation-induced self-assembly process. The hydrolysis rate of zinc acetate was varied using different concentrations of sodium hydroxide. Morphology, crystallinity, porosity, and J-V characteristics of the materials have been studied using transmission electron microscopy (TEM), X-ray diffraction (XRD), BET nitrogen adsorption/desorption, and Keithley instruments.

Simple and rapid synthesis of mesoporous nanosheet-based ZnO hierarchical structure loaded with metal nanoparticles

In this paper, mesoporous nanosheet-based ZnO hierarchical structures decorated with Ag nanoparticles were synthesized via a simple, rapid, environment-friendly and cost-effective one pot synthesis approach using NaOH as the precipitating agent. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy were performed in order to investigate the morphology, crystalline structure and molecular nature of the as-synthesized composite. Several rod shaped nanosheets assembled as petals were synthesized with metal particles well-dispersed on their surface. The photocatalytic performance of the nanocatalyst was tested using Rhodamine B (RhB) as the organic pollutant and results revealed that Ag/ZnO composites have higher photocatalytic efficiency as compared to pure ZnO. ZnO composites also showed enhanced antibacterial property in the zone of inhibition test using Escherichia coli (E.coli) as the bacterial strain.

Synthesis and properties of magnetic fluorescent bi-functional graphene oxide-based nanocomposites

A type of graphene oxide-based nanocomposite ((Fe3O4–ZnO QDs)@SiO2–GO nanocomposite) was synthesized via an amidation process by introducing mesoporous Fe3O4 nanoparticles and ZnO quantum dots onto the surface of GO. The structure characterization, optical properties, and magnetic properties of such nanocomposites were systematically studied by FT-IR and PL emission spectroscopy as well as AFM, VSM, TEM and SEM examination. The results show that the graphene oxide-based nanocomposite has high surface area, superparamagnetic properties and tunable fluorescence. Additionally, methylene blue was chosen as a model substance to investigate the loading capacity of this nanocomposite. The loading experiments indicate that such a nanocomposite has a loading capacity up to 1175.8 mg g−1, implying that this bi-functional graphene oxide-based nanocomposite is likely to find applications in some challenging fields such as drug carriers.

Study on the Performance of a Cobalt Complex as Redox Couple in DSSCs Based on ZnO Thin Films Obtained by Electrochemical Methods and Effect of Passivation of Recombination Paths at the Metal Oxide Surface on the Solar Cell Parameters

In recent years increased attention has been placed on the development of more efficient and lower cost devices for the conversion of solar energy into electricity, which is where the dye-sensitized solar cells (DSSCs) has shown promising results [1]. A DSSC is a photoelectrochemical device consisting of a nanostructured and mesoporous film of a metal oxide semiconductor sensitized to sunlight via dye molecules adsorbed to the surface. The dye absorbs visible light, injects an electron from its excited state into the conduction band of the metal oxide, and the oxidized dye is subsequently reduced by an electron donor in the electrolyte solution, which is then regenerated at the counter electrode. However, the process of recombination of photogenerated electrons with electron acceptor species in the electrolyte solution is one of the limiting factors to consider, in order to improve the performance of these cells.Great efforts have been made with the purpose of suppressing this loss process by slowing down the kinetics, and in the recent literature several strategies have been reported. For example, the use of organic dyes with high extinction coefficients, electrolyte solutions with redox couples based on cobalt complexes [2], passivation or shielding of recombination paths at the metal oxide surface by coadsorption of certain organic molecules, or deposition of a semiconductor interlayer, and combinations of these methods have been explored [3].On the other hand, efficient DSSCs with lower production costs involves the optimization of processing steps and components used, such as obtaining the semiconductor thin film, which has been used traditionally TiO2. ZnO is an attractive alternate material for use in these devices having a band gap similar to that of TiO2, but with a higher electron mobility. In addition, ZnO can be synthesized and deposited by electrochemical methods such as electrodeposition, with a good control over the morphology of the material and at low temperatures, which makes the use of plastic substrates viable.The work presented here is focused on the study of DSSCs based on nanostructured and mesoporous ZnO films prepared by electrodeposition. We report on the influence of the electrodeposition parameters on the morphology and crystallinity of the ZnO films: it is shown that at low current density, a crystalline film can be deposited, which would allow to avoid a high temperature sintering process. We have also used pulse plating conditions to prepare ZnO film, and we have applied these films as substrates in the DSSC.For the fabrication of the solar cells, we have used an organic dye, OD-8, as sensitizer and an electrolyte solution prepared with the redox couple [Co(III/II) tris(2,2'-bipyridine)]. Since this redox couple undergoes a one-electron reduction process, recombination through electron transfer from the metal oxide to the oxidized species in generally fast. However, the redox couple is bulky, and the recombination pathway may be blocked in several ways, using co-adsorbing additives or interfacial blocking layers. In this work, we explore several options to slow down recombination, and we show the influence on solar cell parameters, such as as the open circuit potential (VOC), short circuit current (ISC) and fill factor (FF). Electrochemical impedance spectroscopy (EIS) measurements, and chronopotentiometric experiments at open circuit conditions and under intermittent illumination were performed to support our conclusions.[1] Prog. Photovolt. : Res. Appl. 2013; 21: 1-11.[2] A. Yella, H.-W. Lee, H.N. Tsao, C. Yi, A. K. Chandiran, Md. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S.M. Zakeeruddin, M. Grätzel, SCIENCE 334(2011) 629-633.[3] N. R. Neale, N. Kopidakis, J. van de Lagemant, M. Grätzel and A. J. Frank, J. Phys. Chem. B 109(2005) 23183-23189.

Influence of structural and chemical properties on electron transport in mesoporous ZnO-based dye-sensitized solar cell

Two chemical bath deposition (CBD) solutions were prepared at two different temperatures of 60 and 80 °C for dye-sensitized solar cell (DSSC) application. The deposition time was varied from 12, 18, and 24 h. The X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis confirmed a transformation of hydrozincite into ZnO after calcined at 300 °C. The flower-like structure was observed by scanning electron microscopy (SEM) analysis. The ZnO photoanode deposited at 80 °C for 24 h showed the highest incident photon to charge carrier efficiency (IPCE) value of 5.25 %. The power conversion efficiency, η increased from 1.81 to 2.45 % for the photoanode deposited at 60 and 80 °C, respectively. The effective electron lifetimes, τeff of 6.36 ms was measured as much shorter than the TiO2-based DSSC (τeff of 25 to 160 ms). The effective electron diffusion coefficient, Deff, increased from 1.7 × 10−3 to 4.7 × 10−3 cm2.s−1 when the deposition temperature increases from 60 to 80 °C. Effective rate constant for recombination, keff of 157 s−1 was calculated for both samples. The results and analysis of the film’s surface structure, morphology, electron diffusion, and recombination inside the mesoporous ZnO photoanode proved the applicability of ZnO for the DSSC’s application.

Thermo-catalytic decomposition of formaldehyde: a novel approach to produce mesoporous ZnO for enhanced photocatalytic activities

A novel method, thermo-catalytic decomposition of formaldehyde, is used to synthesize mesoporous ZnO crystals with enhanced photocatalytic activities. The mechanism of the mesoporous formation is investigated by synthesizing a series of samples at various systems and characterizing them with FT-IR, EDS, XRD, SEM, and TEM. The results show that formaldehyde can be adsorbed on the crystal planes of ZnO during the crystal growth and can then be catalytically decomposed into CO, CO2 and H2 during a sintering process. Because of the formation and the escape of these gases, which act as templates, the crystalline particles of ZnO are forced to rearrange consistently, and pores are formed in the internal crystal. Also, porous TiO2 crystals have been obtained via the same approach. Photocatalytic tests indicate that a porous ZnO crystal has higher activity than that of a nonporous one.

Synthesize of Mesoporous ZnO Thin Films and Gas Sensing Property

In this work, ordered mesoporous ZnO thin films was synthesized and gas sensor properties were introduced. Mesoporous ZnO thin films were successfully formed by sol-gel process. In ZnO structure, complex agent (MEA) was used for the hydration and condensation reaction. According to the change of MEA concentration, porosity and pore arrangement, specific surface area could be changed. As complex agent concentration decreased, pore ordering was increased and gas sensitivity has the high value (8.01).

Mesoporous ZnO nanosheets for lithium ion batteries

Mesoporous ZnO nanosheets are prepared by a simple homogeneous precipitation method followed by a calcination process. The nanosheets have micron-sized length/width and nanosized thickness. They are constructed by many interconnected nanostrips and form a mesoporous net-like structure. As anode materials of lithium ion batteries, the electrochemical performance is investigated by galvanostatic discharge–charge cycle and cyclic voltammetry tests. The results show that mesoporous ZnO nanosheets exhibit an initial charge capacity of 640mAhg−1 and a 50th charge capacity of 420mAhg−1. Both the capacity and cycling performance are enhanced compared with those of common solid ZnO particles. It is believed that the mesoporous structure of ZnO plays important roles in the improved electrochemical performance.

Synergistic antimicrobial efficacy of mesoporous ZnO loaded with 4-(α-L-rhamnosyloxy)-benzyl isothiocyanate isolated from the Moringa oleifera seed.

The antimicrobial activities of isolated compounds from seed extracts of Moringa oleifera and synergistic antimicrobial efficacy through hybridized complex of organic-inorganic composite materials were studied. The two main components of the Moringa oleifera seed were isolated and determined to be niazimicin and 4-(α-L-rhamnosyloxy)-benzyl isothiocyanate (RBI). The antimicrobial activity of the separated compounds of the Moringa oleifera seed were tested in vitro against 3 bacterial species and 2 fungal species by the paper disc diffusion assay and broth dilution methods. Both compounds showed antimicrobial activity against tested species and RBI was more effective than niazimicin. The MIC of RBI on S. aureus, E. coli, P. aeruginosa, C. albicans, and A. niger was 0.005%, 0.1%, 0.5%, 0.5%, and 0.5%, respectively, while the MIC of niazimicin on S. aureus was 0.1%. Next, we investigated the combined antimicrobial action of mesoporous ZnO and RBI by incorporating the compound within the pore of mesoporous ZnO. The MIC of mesoporous ZnO with RBI on S. aureus, E. coli, P. aeruginosa, C. albicans, and A. niger was 0.001%, 0.01%, 0.5%, 0.1%, and 0.1%, respectively. A synergistic effect of RBI with mesoporous ZnO was shown. From these results, the mesoporous ZnO could act as a reservoir for RBI and mesoporous ZnO with RBI could be used for cosmetic preservatives.

Enhanced photovoltaic performance utilizing effective charge transfers and light scattering effects by the combination of mesoporous, hollow 3D-ZnO along with 1D-ZnO in CdS quantum dot sensitized solar cells

A combination of 3-dimensional (3D) hollow mesoporous ZnO microspheres (ZnO HMSP) and vertically grown one-dimensional ZnO nanowires (1D ZnO NWs) on a fluorine doped tin oxide (FTO) coated glass substrate has been investigated as a photoanode for a CdS quantum dot-sensitized solar cell (QSSC). A comparative study of the photovoltaic performance of the solar cell with devices fabricated with pristine ZnO HMSPs and ZnO NWs was carried out. The proposed photovoltaic device exhibits an enhancement in power conversion efficiency (PCE) upto ∼74% and ∼35%, as compared to the 1D ZnO NW and ZnO HMSP based solar cells. The maximum incident photon-to-current conversion efficiency (IPCE) for the solar cell was observed to be ∼40%, whereas for the devices fabricated with bare ZnO HMSP and ZnO NW the IPCE were only ∼32% and ∼19%, respectively. The enhanced photovoltaic performance of the solar cell is attributed to the high Brunauer-Emmett-Teller (BET) surface area, efficient light-scattering effects and facilitated diffusion of the electrolyte for better functioning of the redox couple (S(2-)/Sn(2-)) in the hybrid photoanode. Moreover, a faster electron transport through 1D ZnO NWs provides better charge collection from the photoactive layer, which leads to an increase in the short circuit current density of the device. The present study highlights the design and development of a new hybrid photoanode for solar harvesting.

One-pot synthesis of monodisperse Zn coordination polymer micro/nanostructures and their transformation to mesoporous ZnO photocatalysts

By a one-pot method, monodisperse micro/nanoscale Zn-based coordination polymers (CPs) were synthesized. The morphologies of products could be feasibly modulated with the change of the synthesis medium. These CPs were used as precursors to prepare ZnO architectures, which are mesoporous, inherit the morphology of CP precursors and exhibit high photoactivity.

Multiple drug-loaded electrospun PLGA/gelatin composite nanofibers encapsulated with mesoporous ZnO nanospheres for potential postsurgical cancer treatment

The novel PLGA/GE fibers encapsulated with DOX@mZnO were successfully fabricated, which enabled the delivery of two drugs with distinct rates.