ZnO Aggregates Research Articles

S-Schematic CuWO4/ZnO nanocomposite boosted photocatalytic degradation of organic dye pollutants

S-schematic CuWO4/ZnO nanocomposite photocatalyst was synthesized by an impregnation method. Synthesized CuWO4 and ZnO nanoparticles, and CuWO4/ZnO nanocomposites were thoroughly characterized. X-ray diffraction (XRD) analysis of the CuWO4/ZnO nanocomposite confirmed the respective triclinic and hexagonal wurtzite structures of CuWO4 and ZnO crystals. Raman and Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) revealed bond formations in CuWO4 and ZnO, and confirmed the synthesis of the CuWO4/ZnO nanocomposite. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed CuWO4 nanoparticles adhered to ZnO aggregates. Energy dispersive X-ray spectrometry (EDS) confirmed the distribution of CuWO4 on the ZnO aggregates. UV–Vis diffuse reflectance spectroscopy (DRS) showed optical bandgap energies of 2.36 eV for CuWO4 and 3.18 eV for ZnO nanoparticles. The photocatalytic performance of the CuWO4/ZnO nanocomposite was investigated through the degradation of the cationic dyes methylene blue (MB) and Rhodamine B (RhB) and the anionic dye methyl orange (MO). A 5.0%CuWO4/ZnO nanocomposite degraded 100% of MB within 120 min, 91.02% of RhB within 300 min, and 89.13% of MO within 300 min. The pseudo-first order kinetic rate constant fit well for the degradation of all the dyes on the CuWO4/ZnO nanocomposite. The CuWO4/ZnO nanocomposite could better degrade the cationic dyes than the anionic dye in an aqueous solution. The hole (h+), the hydroxyl radical (•OH), and the superoxide ion (•O2−) were the active species responsible for degrading MB, RhB and MO dyes. The proposed CuWO4/ZnO nanocomposite could be applied for environment friendly wastewater treatment.

Naphthalimide Molecular‐Doped Zinc Oxide Cathode Interfacial Layer Inhibits Charge Trapping in Organic Solar Cells

So far, the recombination center of photogenerated carriers caused by surface defects in ZnO results in poor thickness tolerance and inefficient charge extraction, severely limiting the performance and stability of inverted organic solar cells (OSCs). Therefore, hybrid cathode interfacial layers (CILs) are fabricated in devices by doping naphthalimide‐based molecules (NE and NDA) into ZnO, and significantly improved performance and stability are achieved for all tested devices. It is found that doping NE or NDA not only solves the problems of ZnO aggregation and surface defects, but also enhances the ability of charge transfer and lowers the work function of cathode. As a result, the OSCs based on PM6:Y6 with ZnO:NE 1% as a CIL exhibit the highest power conversion efficiency (16.72%), which is better than that of pristine ZnO. The research shows that N atoms in naphthalimide react with Zn ions, and −NH bonds form noncovalent interaction with heteroatoms in the blend, which is conducive to the formation of better chemical bond in hybrid materials and providing more transfer channels for carriers. This study highlights a promising strategy for enhancing the performance of inverted OSCs by the hybrid CIL strategy.

Activation of pine needles with zinc chloride: Evolution of functionalities and structures of activated carbon versus increasing temperature

Functionalities of activated carbon (AC) is one of the essential factors determining its performance for adsorption. In this study, the evolution of functionalities and structure of AC from activation of pine needles with ZnCl2 versus temperature was explored. The results indicated that the ZnCl2 activator could remarkably increase yields of solid product (AC) via catalyzing dehydration, condensation and aromatization of sugary structures, minimizing the formation of aliphatic and phenolic organics in bio-oil. The pore structures of AC generated by this process also exhibited high sensitivity to temperature. The specific surface area of resulting AC could increase from 699.2 m2g−1 at 400 °C to 2030.2 m2g−1 at 500 °C, which could also decrease to 907.9 m2g−1 at 700 °C. Migration and aggregation of ZnO at 700 °C resulted in the loss of capability for supporting carbon structures, leading to shrinkage or collapse of the pore structures. The characterization with in-situ IR technique showed that ZnCl2 catalyzed dehydration of hydroxyl group and conversion of carbonyls in aldehydes/ketones into larger π-conjugated structures but not worked on the C-O-C bonds for bridging benzene rings. However, the transformation of ZnCl2 to ZnO above 500 °C lost the catalytic activity, inducing little change of elemental composition but re-structuring of AC through merge of pores.

Thermochemical CO2 Reduction Catalyzed by Homometallic and Heterometallic Nanoparticles Generated from the Thermolysis of Supramolecularly Assembled Porous Metal-Adenine Precursors.

A family of unprecedented supramolecularly assembled porous metal-organic compounds (SMOFs), based on [Cu6M(μ-adeninato)6(μ3-OH)6(μ-H2O)6]2+ cations (MII: Cu, Co, Ni, and Zn) and different dicarboxylate anions (fumarate, benzoate, and naphthalene-2,6-dicarboxylate), have been employed as precursors of catalysts for the thermocatalytic reduction of CO2. The selected metal-organic cation allows us to tune the composition of the SMOFs and, therefore, the features and performance of the final homometallic and bimetallic catalysts. These catalysts were obtained by thermolysis at 600 °C under a N2 atmosphere and consist of big metal particles (10-20 μm) placed on the surface of the carbonaceous matrix and very tiny metal aggregates (<10 nm) within this carbonaceous matrix. The latter are the most active catalytic sites for the CO2 thermocatalytic reduction. The amount of this carbonaceous matrix correlates with the organic content present in the metal-organic precursor. In this sense, CO2 thermocatalytic reduction experiments performed over the homometallic, copper only, catalysts with different carbon contents indicate that above a certain value, the increase of the carbonaceous matrix reduces the overall performance by encapsulating the nanoparticles within this matrix and isolating them from interacting with CO2. In fact, the best performing homometallic catalyst is that obtained from the precursor containing a small fumarate counterion. On the other hand, the structural features of these precursors also provide a facile route to work with a solid solution of nanoparticles as many of these metal-organic compounds can replace up to 1/7 of the copper atoms by zinc, cobalt, or nickel. Among these heterometallic catalysts, the best performing one is that of copper and zinc, which provides the higher conversion and selectivity toward CO. XPS spectroscopy and EDX mappings of the latter catalyst clearly indicate the presence of Cu1-xZnx nanoparticles covered by small ZnO aggregates that provide a better CO2 adsorption and easier CO release sites.

Hydrogen Bonds as Stability-Controlling Elements of Spherical Aggregates of ZnO Nanoparticles: A Joint Experimental and Theoretical Approach

The effects of various organic additives, such as diethanolamine (DEA) and ethanolamine (EA), and variations in aging times on the formation and stability mechanisms of spherical aggregates of ZnO nanoparticles (NPs) prepared by using solvothermal synthesis were studied. The experimental results of the structural, morphological and optical properties monitored by using X-ray diffraction, field-emission scanning electron microscopy (FE-SEM) and UV-Vis spectroscopy were supported by quantum chemical calculations at the level of density functional theory (DFT). Understanding the mechanism of spherical ZnO aggregate formation and its stability by mimicking the processes at the computer level was achieved through theoretical simulations of the ZnO surface/additive interactions using (ZnO)36–DEA and (ZnO)36–EA models. The fine-tuned spherical aggregation of ZnO nanoparticles was driven by various interactions, in particular, strong O–H∙∙∙O and weak N–H∙∙∙O hydrogen bonds as controlling interactions. The calculated negative free release energy, ∆G*INT, indicates that the ZnO surface/additive interaction in diethanolamine media is a spontaneous exergonic process (∆G*INT = −7.73 kcal mol−1), whereas, in ethanolamine media, it is an unfavorable, slightly endergonic process (∆G*INT &gt; 0). The presence of two strong O–H∙∙∙O hydrogen bonds and, at the same time, a weaker N–H∙∙∙O hydrogen bond is the key factor for the very good and long-term aggregate stability of ZnO NPs in DEA media. This integrated experimental–theoretical study highlights the stability and compactness of spherical ZnO aggregates of ZnO NPs, prepared in the presence of diethanolamine compared to ethanolamine media, and provides a promising method and flexible design of ZnO nanomaterials to improve their adsorptive and optical properties.

Effect of ZnO in various alcohols on photoelectric characteristics of OSC

The paper presents the results of a study of the effect of alcohols on the electron transport of the ETL layer of a ZnO polymer solar cell with an inverted structure. To obtain films, zinc acetate was dissolved under the same experimental conditions in isopropanol, butanol and ethanol. According to the SEM data, it was found that the use of various alcohol solvents in the synthesis of the film shows a change in the morphology of the surface. The observed changes in the interface of the surface of the films are associated with the formation of ZnO aggregates depending on the polarity used of the alcohols. It is shown that the optical width of the ZnO band gap also depends on alcohol solvents. It is shown that the aggregation of ZnO has an effect on the electron transport and efficiency of the polymer solar cell. The voltage characteristics of the solar cells FTO/ ZnO/P3HT: IC60MA/PEDOT: PSS/Ag were measured. It is shown that the smallest aggregation of ZnO is observed in Isopropanol, in which the organic cell showed the highest efficiency of converting solar energy into electrical energy. The polymer solar cell has been the efficiency 2.5 %. From the obtained ETL impedance measurement data, the ZnO based layer obtained in Ethanol has the lowest electron transport parameters. This is due to the high degree of aggregation of ZnO, as a result of which the resistance to increases of the interface ZnO/FTO. The solar cells based ZnO in Ethanol demonstrated an efficiency value of 0.9 % compared to ZnO in Butanol with an efficiency of 1.6 %.

ZnO@Carbon Dot Nanoparticles Stimulating the Antibacterial Activity of Polyvinylidene Fluoride-Hexafluoropropylene with a Higher Electroactive Phase for Multifunctional Devices.

To further advance the application of flexible piezoelectric materials in wearable/implantable devices and robot electronic skin, it is necessary to endow them with a new function of antibacterial properties and with higher piezoelectric performance. Introducing a specially designated nanomaterial based on the nanocomposite effect is a feasible strategy to improve material properties and achieve multifunctionalization of composites. In this paper, carbon dots (CDs) were sensitized onto the surface of ZnO to form ZnO@CDs nanoparticles, which were then incorporated into polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to obtain a multifunctional composite. On the one hand, the antibacterial property of ZnO was improved because CDs had good optical absorption of visible light and their surface functional groups were favorable for electrostatic adsorption with bacteria. Therefore, ZnO@CDs endowed the composite with an outstanding antibacterial rate of 69.1% for Staphylococcus aureus. On the other hand, CDs played a bridging role between ZnO and PVDF-HFP, reducing the negative effect of ZnO aggregation and interface incompatibility with PVDF-HFP. As a result, ZnO@CDs induced β-phase formation of 80.4% in PVDF-HFP with a d33 value of 33.8 pC N-1. The multifunctional device exhibited excellent piezoelectric and antibacterial performance in the application of energy harvesters and self-powered pressure sensors.

Increasing the hydrophilicity and antifouling properties of polyvinylidene fluoride membranes by doping novel nano-hybrid ZnO@ZIF-8 nanoparticles for 4-nitrophenol degradation

ZIF-8 modification can reduce aggregation of ZnO (a typical photocatalyst), and enhances antifouling property of PVDF membranes. In this study, we developed a novel membrane by adding ZnO@ZIF-8 nanoparticles into polyvinylidene fluoride (PVDF) substrates by using non-solvent induced phase separation (NIPS) method. Filtration test with bovine serum albumin (BSA) showed that the modified membrane has good pure water flux (395 L m−2 h−1, PWF) and high flux recovery rate (94%, FRR). Furthermore, the SiO2:ZnO@ZIF-8 membrane showed high separation effect in 4-NP degradation test under light condition, with the flux achieved about 321 L m−2 h−1 during filtration process. The degradation efficiency reached 81.5%, the apparent rate constant (Kapp/min−1) was 0.211 min−1. Besides, in prolonged 4-nitrophenol (4-NP) degradation test, the SiO2:ZnO@ZIF-8 membrane maintained higher flux and degradation rate. Thus, we reported a novel membrane with a prominent antifouling property.

Hierarchical ZnO/MXene (Nb2C and V2C) heterostructure with efficient electron transfer for enhanced photocatalytic activity

Recently, MXene has attracted much attention as photocatalysts for efficient pollutant degradation in the field of environmental remediation but a rapid recombination of photogenerated carriers usually leads to a decrease in the photocatalytic performance. Constructing a heterostructure is considered as an effective way to improve the catalytic performance of MXene-based photocatalysts due to the promoted interfacial electron transfer. In this work, the chimeric ZnO nanosheets with good carrier mobility were formed on the accordion-shaped MXene (Nb2C and V2C) surface to construct hierarchical ZnO/MXene heterostructure as a photocatalyst for dye degradation. The obtained ZnO/Nb2C and ZnO/V2C hierarchical structure exhibited excellent photocatalytic performance in the degradation of methylene blue (MB): the degradation rate reached 62.62% and 99.53%, respectively, after irradiation with ultraviolet light for 120 min. Also, the apparent degradation rate constants (k) were 0.00777 min−1 and 0.04317 min−1, respectively, which were 2.92 and 16.23 times higher than those of pure ZnO. This was probably attributed to the heterostructures between ZnO and MXene which could shorten the carrier transfer path, which could facilitate the transfer of photo-generated electrons from conduction band (CB) of ZnO to CB of MXene, thereby significantly improving the photocatalytic degradation efficiency. In addition, the ZnO/Nb2C and ZnO/V2C hierarchical structure showed good photocatalytic stability: the degradation rate remained at 58.6% and 97.3%, respectively, after 4 cycles while it only maintained at 22.0% for pure ZnO because the obtained ZnO/MXene hierarchical structure could provide uniform active sites on the surface and porous structure, preventing the aggregation of ZnO or MXene. Therefore, this work could provide a feasible design strategy to improve the catalytic performance of 2D photocatalysts and shed a light on the design of other photocatalysts.

Controllable band structure of ZnO/g-C3N4 aggregation to enhance gas sensing for the dimethylamine detection

Volatile organoamines exist widely in various industrial and commercial products. The chronic and prolonged exposure to amines can compromise human health and cause even the risk of serious illness. Herein, the aggregation of ZnO decorated with g-C3N4 (ZOCN) is synthesized and it can serve as enhanced sensitive sensor for the detection of dimethylamine (DMA). The structure, morphology, composition and band structure of the materials are characterized by various analytical techniques. The results show that, controllable additions of g-C3N4 affect self-assemble of nanoparticles and aggregation structure, even energy band, as confirmed by DFT calculation. Notably, the formed heterojunction is conductive to electron transfer and adsorption of more O2 molecules to form reactive oxygen species, thereby promoting the reaction between oxygen and DMA and leading to high sensitivity to DMA with a detection limit of 920 ppb and about 2.5 times higher sensitivity than pristine ZnO. ZOCN-based sensor shows a high selectivity to DMA, a fast response time (1 s) and a fast recovery time (40 s) to various concentrations of gas phase DMA at low temperatures. Additionally, the sensor exhibits a linear relationship between the response and concentration of DMA vapor in a wide concentration range, a characteristic that is desirable for quantitative analysis in gas sensors.

Facile In Situ Synthesis of ZnO Flower-like Hierarchical Nanostructures by the Microwave Irradiation Method for Multifunctional Textile Coatings.

ZnO nanoparticle-based multifunctional coatings were prepared by a simple, time-saving microwave method. Arginine and ammonia were used as precipitation agents, and zinc acetate dehydrate was used as a zinc precursor. Under the optimized conditions, flower-like morphologies of ZnO aggregates were obtained. The prepared nanopowders were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and UV/Visible spectroscopy. The developed in situ synthesis with microwave irradiation enabled significant ZnO nanoparticle deposition on cotton fabrics, without additional steps. The functionalized textiles were tested as a photocatalyst in methylene blue (MB) photodegradation and showed good self-cleaning and UV-blocking properties. The coated cotton fabrics exhibited good antibacterial properties against common microbial trains (Staphylococcus aureus, Escherichia coli, and Candida albicans), together with self-cleaning and photocatalytic efficiency in organic dye degradation. The proposed microwave-assisted in situ synthesis of ZnO nanocoatings on textiles shows high potential as a rapid, efficient, environmentally friendly, and scalable method to fabricate functional fabrics.

Mechanochemical Alkali-Metal-Salt-mediated synthesis of ZnO nanocrystals with abundant oxygen Vacancies: An efficient support for Pd-based catalyst

Zinc oxide is a key material in catalysis. Designing of ZnO crystal aggregates with the surface defect has received significant attention. Herein, we synthesized ZnO aggregates with tiny primary nanoparticles through a mechanochemistry-assisted salt-templating (potassium chloride) method. Interestingly, this KCl-templating strategy could lead to significant increase in specific surface area (SSA) of ZnO (up to 91 m2/g), whereas commercial ZnO-COM has a SSA of 5 m2/g. Meanwhile, this strategy via ZnCl2-KCl solid solution has also created a number of oxygen vacancies into ZnO aggregates. With these attractive features, as-made Pd-ZnO catalyst showed outstanding performance in methanol steam reforming, especially at low temperature (20 % Conversion and 95 % CO2 Selectivity at 150 °C). Current strategy provides a gateway for the rational design of ZnO-based catalytic materials.

One-step conversion of syngas to hydrocarbons and ethers over ZIF-8 derived ZnO coupling HZSM-5

Zeolitic imidazolate frameworks (ZIF-8) were synthesized by solvothermal method. Used as precursor, ZIF-8 was decomposed into nanoparticles ZnO at different pyrolysis temperature in air atmosphere. The composition, structure and crystal size of ZnO were characterized by XRD, TEM, XPS, and Raman methods. The ZnO nanoparticles were coupled with HZSM-5 to form bifunctional catalysts. The catalytic performances of bifunctional catalysts in the syngas conversion were investigated in a fixed-bed tubular reactor. The results demonstrate that the pyrolysis temperature has an important influence on the particle size of ZnO. The temperature affects the rate of grain formation. High temperature promotes the aggregation of ZnO. The ZnO grain size by changing the temperature plays a role in changing the product distribution. When the pyrolysis temperature is near or below 450°C, carbon-coated ZnO nanoparticles are obtained, and the ZnO grain size is less than 20 nm. The carbon-coated ZnO coupled with HZSM-5 catalyzes syngas mainly into dimethyl ether (DME). When the temperature is higher than 450°C, pure phase ZnO nanoparticles are obtained, and the ZnO grain size is larger than 20 nm. The pure ZnO coupled with HZSM-5 catalyzes syngas mainly into hydrocarbons. Obviously, the coupling modes of ZnO and HZSM-5 have a significant effect on the product selectivity of bifunctional catalysts.

Hybrid TiO2-ZnO Nanomaterials Prepared Using Laser Ablation in Liquid.

Hybrids of semiconductor nanomaterials often demonstrate properties that are superior to those of their components. In this study, we prepared hybrid nanomaterials of TiO2 and ZnO, which are among the most actively studied semiconductors, by means of millisecond-pulsed laser and analyzed how their morphology, particle size, and surface composition depend on preparation conditions. A series of nanomaterials were obtained via sequentially ablating Zn and Ti metal plates (in different sequences) in water, while laser pulses of lower (2.0 J/pulse) and higher (5.0 J/pulse) energy were applied. The properties of laser-produced hybrid TiO2-ZnO nanomaterials were shown to be governed by experimental conditions such as laser pulse width, pulse peak power, and reaction media (either pure water or colloid with nanoparticles). The morphology revealed nanospheres of TiO2 that decorate nanorods of ZnO or flower-like aggregates of zinc oxide. Intriguingly, after extended ablation time, titania was found to be self-doped with Ti3+ and Ti2+ ions, and the contribution of lower oxidation states of titanium could be controlled by the applied laser pulse energy. The physicochemical characteristics of hybrid nanomaterials were compared with pure ZnO and TiO2 prepared under the same laser conditions.

Molecular Structures of ZnO by Aggregates of Atoms and Interaction of Two Monolayers

The first-principles calculations are useful for determining electronic and structural properties for a model that simulates a material composed of atomic clusters of ZnO through the analysis of interaction energies and charge distribution. The two-dimensional structural form of ZnO aggregates shows regularly flat hexagons obtained in models of 6, 27 and 54 atoms of Zinc and Oxygen. The structure of a three-dimensional system was determined by dynamics calculations by using the interaction of a pair of monolayers consisting of 108 atoms and as a result, a cage structure was formed from a cluster of Zn54 and O54 identifying only bond atoms at the ends that promote the union of monolayers. The stable structure shows modifications of the atomic bonds in whose centers hexagonal rings prevailed and at the arrangements of the end of triangles, squares, pentagons and even rings of 10 and 11 atoms were obtained. Atomic positions and charge distribution were analyzed based on the methodology used Density Functional Theory (DFT), with the becke88-LYP exchange and correlation functional.

Molecular Structures of ZnO by Aggregates of Atoms and Interaction of Two Monolayers

The first-principles calculations are useful for determining electronic and structural properties for a model that simulates a material composed of atomic clusters of ZnO through the analysis of interaction energies and charge distribution. The two-dimensional structural form of ZnO aggregates shows regularly flat hexagons obtained in models of 6, 27 and 54 atoms of Zinc and Oxygen. The structure of a three-dimensional system was determined by dynamics calculations by using the interaction of a pair of monolayers consisting of 108 atoms and as a result, a cage structure was formed from a cluster of Zn54 and O54 identifying only bond atoms at the ends that promote the union of monolayers. The stable structure shows modifications of the atomic bonds in whose centers hexagonal rings prevailed and at the arrangements of the end of triangles, squares, pentagons and even rings of 10 and 11 atoms were obtained. Atomic positions and charge distribution were analyzed based on the methodology used Density Functional Theory (DFT), with the becke88-LYP exchange and correlation functional.

Effect of ethanolamine passivation of ZnO nanoparticles in quantum dot light emitting diode structure

The aging of ZnO nanoparticles in quantum dot light-emitting diode (QD-LED) structures was studied. Coarsening of as-synthesized ZnO nanoparticles is observed in both solution and thin film structures, which potentially deteriorates the performance of QD-LED devices over time. First, the temperature effect on ZnO coarsening was investigated, and it was revealed that aging of ZnO nanoparticles is faster at higher temperature due to a diffusion-controlled mechanism of nanoparticle coarsening. To observe aggregation of ZnO in the film state, the electron transporting part (ZnO/Al) of the QD-LED structure was prepared. The current density of a ZnO film and an electron-only device (QD/ZnO between two electrodes) was also measured. Resistance of the film increased as a function of aging time, which corresponded with observations of the ZnO film by optical microscopy. Aggregation of ZnO nanoparticles was directly measured by the root-mean-square value using atomic force microscopy. Ethanolamine (EA) stabilizer was added to the ZnO solution to disperse the ZnO nanoparticles without aggregation. The effect of EA on the surface passivation of the ZnO found to suppress pinhole formation, as revealed by scanning electron microscopy observations. Finally, the device lifetime was measured for QD-LEDs with EA-stabilized ZnO to understand the effect of ZnO aging on long-term QD-LED device operation.

Organic frameworks induce synthesis and growth mechanism of well-ordered dumbbell-shaped ZnO particles

Coordination bonds of ligands and metal ions are generally considered for improving agglomeration during the synthesis of metal oxides. However, the strong interactions always limit the performance due to the requirement of additional energy and calcination. A new strategy of synthesizing ZnO particles is proposed through a hydrothermal inducing redox method by using 2-methyl imidazole and Zn(NO3)2. In situ direct redox between this organic ligand and NO3− in a hydrothermal condition is confirmed radical change instead of the simple coordination between organic ligands with Zn2+ in traditional method. The directly acquired ZnO particles possessing uniform dumbbell-like morphology have no obvious agglomeration. The yield reaches >95%. In particular, the synthesis mechanism and morphology evolution during the ZnO aggregates growth were carefully explored and proposed. Density functional theory (DFT) and surface energy calculations demonstrated the effects of activity variation of reactive groups and preferred growth surface of ZnO crystals. This work gives new insights into new synthesis strategy of ZnO particles via hydrothermal condition.

Linkage modification of a zinc oxide photoelectrode prepared with polyethylene glycol for electron transport improvement in dye-sensitized solar cells

The purpose of this study is to synthesize ZnO aggregate films using simple precipitation with polymer modification for linkage improvement of the ZnO photoelectrode. The starting materials of zinc acetate solution and ammonia solution were mixed under violent stirring conditions. A portion of the polymer (polyethylene glycol) was slowly added into the mixed solution to obtain the viscous ZnO precursor. The precursor was then coated onto a fluorine-doped tin oxide substrate and annealed to form ZnO films. The scanning electron microscopy results revealed the formation of ZnO aggregates with flower-like microstructures. The appearance of Zn and O elements indicated a fair ZnO formation. The X-ray diffraction patterns and Raman shift confirmed the hexagonal wurtzite crystal structure of the ZnO aggregates. For dye-sensitized solar cell (DSSC) application, power conversion efficiency was enhanced because of the improved photovoltaic characteristics including the open-circuit voltage, fill factor, series resistance, shunt resistances and recombination resistance, perhaps, due to the large particle size of the ZnO aggregates and their flower-like microstructures. The flower-like microstructure likely acts as a bridge to link each ZnO particle. The flower-like microstructure plays the role of an express pathway in electron transport in the DSSC. Therefore, the ZnO aggregation with a flower-like microstructure has the potential to improve the electron transport for efficiency enhancement of a DSSC.

A Facile Approach of Fabricating Various ZnO Microstructures via Electrochemical Deposition

A facile electrochemical route was proposed for the shape-selective synthesis of ZnO structures on conductive substrates. Our strategy for designing ZnO structures was based on a double-electrodes electrochemical deposition approach, in which the well-oriented ZnO structures with variable morphology on different conductive substrates could be adjusted by monitoring electrochemical parameters (e.g., zinc chloride concentration, deposition potential, and deposition temperature). The variation in deposition parameters led to the ZnO formation of different structures, such as ZnO flowers, sheets and aggregates. In addition, the analysis of I-V characteristics illustrated that the ZnO flowers were composed of sheets clustered on the graphite substrate and exhibited higher dark current than other structures. Furthermore, the remarkable Schottky contact behaviour was found for ZnO flowers deposited on carbon paper and copper foil substrates. This work demonstrates a simple method for tuning the growth of desired ZnO structures and exploring its application in functional optoelectronic devices.