Porous Zinc Oxide Research Articles

ZnO hierarchical microsphere for enhanced photocatalytic activity

As an important semiconductor material for photocatalysis, zinc oxide (ZnO) has been prepared by various methods to enhance its photocatalytic activity. Herein, hierarchically porous ZnO microspheres were synthesized by hydrothermal treatment of precursor zinc salts and subsequent low-temperature (300 °C) calcination for 2 h, and the photocatalytic properties of the ZnO microspheres were examined by degrading Rhodamine B under simulated solar light. The type of the precursor zinc salts (nitrate, acetate, sulfate and chloride) had a great impact on the morphological, textural, optical and photoelectrochemical properties of the as-prepared ZnO microspheres, which collectively affected the photocatalytic performance. The as-prepared hexagonal wurtzite ZnO exhibits unique hierarchical porous microsphere morphology with diameters in the range of 3–6 μm. The photocatalytic activity of the ZnO microspheres also depended on the zinc precursor and followed the order: zinc sulfate > zinc nitrate > zinc acetate > zinc chloride. The high photocatalytic activity of ZnO microspheres prepared from zinc sulfate was due to its higher specific surface area (91 m2 g−1), better visible light absorption, more oxygen defects and higher charge separation and transfer efficiencies, as well as the hierarchical pore structure that promotes the diffusion of reactant molecules. Moreover, electron paramagnetic resonance spectroscopy identified hydroxyl radicals and superoxide radical anions as reaction intermediates, shedding light on the mechanism of the dye photodegradation reaction.

Controlled Electrodeposition of Zinc Oxide on Conductive Meshes and Foams Enabling Its Use as Secondary Anode

Both compact and porous zinc oxide (ZnO) films were electrochemically deposited out of aqueous zinc nitrate solutions under pulsed galvanostatic control onto different three-dimensional (3D) substrates. Gold and carbon meshes as well as copper and nickel foams were used as substrates, all having complex geometries in micrometer dimensions with high surface area. Electrodepositions of ZnO were controlled by regulating the most relevant parameters: the applied current density, the total deposition time, and the length of current pulses and pauses to avoid gas evolution interfering with film growth at the electrodes. Optimization of these parameters for each of the substrates allowed deposition of homogeneous ZnO films of the desired total film thickness. Potential-time curves measured during deposition helped to monitor film growth. Scanning electron microscopy (SEM) micrographs showed that pinhole-free ZnO films were deposited uniformly in a 3D manner on all substrates. X-ray diffraction (XRD) measurements confirmed the formation of highly crystalline ZnO films. Such electrodeposited ZnO films on electronic conductive substrates with high surface area are promising for application in energy storage and conversion systems – especially for secondary batteries with zinc anodes which was shown by cyclic voltammetry (CV).

Light-soaking tests of zinc oxide photoanodes sensitized with an indoline dye on different transparent conductive substrates

Dye-sensitized solar cells (DSCs) were prepared using porous zinc oxide (ZnO) films on aluminum-doped zinc oxide (AZO) and fluorine-doped tin oxide (FTO) transparent conductive glass substrates. X-ray diffraction measurements revealed that, the porous ZnO films were crystallographically oriented differently on the two transparent substrates. The two DSCs were prepared using metal-free indoline dye as the sensitizer and a liquid electrolyte as the hole conductor. Measurements of the power conversion efficiency of the two DSCs over a period of time showed deterioration in the conversion efficiency of the DSCs with the deterioration being faster in ZnO/FTO than ZnO/AZO. The deterioration is attributed mainly to the decrease in light-harvesting ability of the sensitizer and recombination of photo-excited electrons resulting in the decrease in the short-circuit photocurrent densities and the open-circuit voltages in both DSCs during the light-soaking process.

Fabrication of hierarchical porous ZnO/NiO hollow microspheres for adsorptive removal of Congo red

Hierarchical porous zinc oxide (ZnO)/nickel(II) oxide (NiO) hollow microspheres were fabricated by a facile hydrothermal approach and subsequent calcination process. The synthesized samples were used as adsorbent for removing Congo red (CR), a commercial azo dye. The synthesized hierarchical porous ZnO/NiO composites exhibit a superior adsorption capacity for CR (518 mg/g), compared with pure NiO (397 mg/g) and ZnO (304 mg/g). The high CR adsorption capacity of ZnO/NiO composites was associated with its hierarchical porous hollow structures and large specific surface area (130 m2/g), which provide a large quantity of active sites for CR molecules. The adsorption kinetics data were perfectly fitted to a pseudo-second-order model. The isotherms were accurately described by the Langmuir model. The results suggest that the as-prepared hierarchical porous ZnO/NiO composites are a highly efficient adsorbent for treating organic dye-impacted wastewater.

Correction: Comparison of porous and nano zinc oxide for replacing high-dose dietary regular zinc oxide in weaning piglets.

[This corrects the article DOI: 10.1371/journal.pone.0182550.].

Electrical Behavior of Solar Cell based on ZnO/PS

Because of high loss of photovoltaic conversion due to reflection of incident photon by the silicon surface, we proposed in this work a single heterojunction solar cell model based on porous silicon (PS) and Zinc oxide to minimize this loss, which the ZnO could act like front n-layer as well as antireflection coating saving processing cost and complexity. In the experiment the ZnO layer was deposited by spray pyrolysis method on porous silicon (PS) using nitrate precursors with different molar concentration. The proposed treatment has also demonstrated a significant decrease in the reflectivity of ZnO/PS. To simulate a solar cell based on porous silicon and zinc oxide, we have used PC1D software. The variation of internal and external quantum efficiency, and I-V characteristics have been done by changing the reflectivity of ARC layer, The I-V results obtained by PC1D simulation was compared with the experiment results: Simulations anticipated conversion efficiency was 14,5% while by experiments was 12% for the device fabricated with 0.25 M.

Comparison of porous and nano zinc oxide for replacing high-dose dietary regular zinc oxide in weaning piglets

The aim of this study was to compare the effect of dietary supplementation with low dose of porous and nano zinc oxide (ZnO) on weaning piglets, and to evaluate the possibility of using them as an alternative to high dose of regular ZnO. Piglets were randomly allocated into four treatment groups fed with four diets: (1) basal diet (NC), (2) NC+ 3000 mg/kg ZnO (PC), (3) NC + 500 mg/kg porous ZnO (HiZ) and (4) NC + 500 mg/kg nano ZnO (ZNP). The result showed that piglets in HiZ group had less diarrhea than ZNP group (P < 0.05). Besides, there was no significant difference between PC, HiZ and ZNP groups in terms of serum malondialdeyhde (MDA) concentration and glutathione peroxidase (GSH-Px) activity (P > 0.05). Analysis of trace metal elements revealed that piglets fed with high dose of regular ZnO had the highest Zn level in kidney (P < 0.05), which may induce kidney stone formation. Additionally, a decrease in ileal crypt depth was observed in PC, HiZ and ZNP group, suggesting an effective protection against intestinal injury. Results of mRNA analysis in intestine showed that ZNP supplementation had better effects on up-regulated trefoil factor 3 (TFF3) and nuclear factor erythroid 2-related factor 2 (Nrf2) levels in duodenum and jejunum than HiZ did (P < 0.05), implying that nano ZnO may possess higher anti-inflammatory capacity than porous ZnO. In conclusion, dietary supplementation with low dose of porous and nano ZnO had similar (even better) effect on improving growth performance and intestinal morphology, reducing diarrhea and intestinal inflammatory as high dose of regular ZnO in weaning piglets. Compared with nano ZnO, porous ZnO had better performance on reducing diarrhea but less effect on up-regulation of intestinal TFF3 and Nrf2.

Template-free synthesis of porous ZnO/Ag microspheres as recyclable and ultra-sensitive SERS substrates

The porous structured zinc oxide (ZnO) microspheres decorated with silver nanoparticles (Ag NPs) have been fabricated as surface-enhanced Raman scattering (SERS) substrate for ultra-sensitive, highly reproducible and stable biological/chemical sensing of various organic molecules. The ZnO microspheres were hydrothermally synthesized without any template, and the Ag NPs decorated on microspheres via photochemical reaction in situ, which provided stable Ag/ZnO contact to achieve a sensitive SERS response. It demonstrates a higher enhancement factor (EF) of 2.44×1011 and a lower detection limit of 10−11M–10−12M. This porous SERS substrate could also be self-cleaned through a photocatalytic process and then further recycled for the detection of same or different molecules, such as phenol red (PhR), dopamine (DA) and glucose (GLU) with ultra-low concentration and it possessed a sensitive response. The excellent performances are attributed to morphology of porous microspheres, hybrid structure of semiconductor/metal and corresponding localized field enhancement of surface plasmons. Therefore, it is expected to design the recyclable ultra-sensitive SERS sensors for the detection of biological molecules and organic pollutant monitoring.

Fabrication of hierarchical porous ZnO-Al2O3 microspheres with enhanced adsorption performance

Hierarchical porous ZnO–Al2O3 microspheres were fabricated through a simple hydrothermal route. The as-prepared hierarchical porous ZnO–Al2O3 composites were utilized as adsorbents to remove organic dye Congo red (CR) from water. The ZnO–Al2O3 composites had morphology of microspheres with diameters in the range of 12–16μm, which were assembled by nanosheets with thicknesses of approximately 60nm. The adsorption kinetics of CR onto the ZnO–Al2O3 composites was properly fitted by the pseudo-second-order kinetic model. The equilibrium adsorption data were perfectly described by the Langmuir isotherm and had a maximum adsorption capacity that reached 397mg/g, which was significantly higher than the value of the pure alumina (Al2O3) and zinc oxide (ZnO) samples. The superior CR removal efficiency of the ZnO–Al2O3 composites was attributed to its well-developed hierarchical porous structures and larger specific surface area (201m2/g), which were conducive to the diffusion and adsorption of CR molecules. Moreover, the regeneration study reveals that the ZnO–Al2O3 composites have suitable stability and reusability. The results also indicate that the as-prepared sample can act as a highly effective adsorbent in anionic dye removal from wastewater.

Porous zinc oxide nanocrystalline film deposition by atmospheric pressure plasma: Fabrication and energy band estimation

Porous ZnO nanocrystalline films have drawn research attention due to improvement in gas sensing, adsorption, photocatalytic, and photovoltaic applications. However, scalable synthesis of porous nanostructures has been a challenge. Here, This paper reports a very easy, fast, and scalable one‐step process for synthesis and deposition of porous ZnO nanocrystalline film by low‐temperature atmospheric pressure plasma. The plasma is generated with radio frequency power using a metallic zinc wire as a precursor. Nanostructures have been synthesized and agglomerate to form a porous film at the substrate. Energy band structure of the deposited film has been investigated to understand the corresponding band alignment, which is relevant to many applications. An in‐depth study of the grown nanostructured ZnO film has been included and characterized by X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, kelvin probe measurement, ultra‐violet/visible absorption, and photoluminescence.

Development of Composite Material Based on Porous Microfibrous Carbon and Zinc Oxide for Energy Storage Application

Development of Composite Material Based on Porous Microfibrous Carbon and Zinc Oxide for Energy Storage Application

Photoluminescence of Porous Silicon–Zinc Oxide Hybrid structures

Arrays of ZnO nanostructures, which are optically transparent in the visible range, were grown on the surface of porous silicon by electrochemical deposition. Photoluminescence excitation and emission spectra of the obtained hybrid structures were investigated in 220–450 and 400–800 nm regions, respectively. It is established that multicolor emission is formed by combining the luminescence bands of porous silicon and zinc oxide. The possibility of controlling the photoluminescence spectra by changing the excitation energy is demonstrated. It is revealed that thermal annealing has an effect on the luminescent properties of porous silicon/zinc oxide hybrid structures. Thermal processing at 500°С leads to a sharp decrease of long-wavelength luminescence associated with porous silicon and to an increase of short-wavelength luminescence intensity related to zinc oxide.

Controlled deposition of Li metal

Metallic lithium (Li°) is an attractive anode material for high-energy lithium batteries. However, its commercial applications in secondary batteries, such as the lithium-sulfur and lithium-oxygen batteries, are hindered with the uncontrolled growth of detrimental Li dendrites during Li plating and the random fracture of the dendrites during Li stripping. Herein, we show that the deposited Li prefers to stay in the pits on a micro-patterned titanium (Ti) foil. In light of this, micro-/nano-architectured porous silicon (Si) and zinc oxide (ZnO) electrodes were employed and proved equally effective in guiding the deposition of Li metal. These findings demonstrate that the electrochemical activity of the porous electrode becomes less important than the specially designed porous structure of the electrode in the position of lithium deposition. Therefore, designing electrodes with appropriate micro-/nano-architecture can be a promising strategy for controlling the deposition of the Li metal and strictly confining the Li dendrites (if there are) within the pits by constructing anodes with properly designed architectures.

Synthesis of hierarchical porous zinc oxide (ZnO) microspheres with highly efficient adsorption of Congo red

Hierarchical porous zinc oxide (ZnO) was successfully synthesized via a facile hydrothermal method followed by calcination, and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption, and Fourier transform infrared spectroscopy analyses. The as-prepared porous ZnO exhibits microsphere morphologies with diameters of 6–8μm, which are assembled from two-dimensional nanosheets. The as-prepared hierarchical porous ZnO microspheres possessed high specific surface areas (57m2/g), and were evaluated for adsorption of Congo red (CR) in aqueous solution. The adsorption kinetics data were described by the pseudo-second-order kinetics and intraparticle diffusion models, while the equilibrium adsorption data were well fitted to the Langmuir model, with a maximum adsorption amount of 334mg/g. The as-prepared hierarchical porous ZnO exhibited higher CR adsorption capacity than commercial ZnO and various other materials, and thus could be an effective adsorbent for removal of anionic organic dyes from wastewater.

Preparation of porous zinc oxide-nickel oxide nanocomposites by facile one-pot solution process

Porous zinc oxide (ZnO)-nickel oxide (NiO) nanocomposites were fabricated via a one-pot process using aqueous solutions of zinc nitrate hexahydrate (Zn(NO), 10mM), hexamethylenetetramine (HMT, 10mM), and nickel acetate tetrahydrate (Ni(Ac), 7mM (7NZO), 10mM (10NZO)). The structural and morphological properties of these nanocomposites were investigated and compared to those of pure ZnO nanostructures. Rod-type nanostructures were observed in the pure ZnO sample, while porous sphere-like structures and continuous nanolayered structures were observed in the 7NZO and 10NZO samples, respectively. This difference in morphology might be due to the growth of the non-polar plane instead of the polar plane of ZnO in the clusters. The nanocomposites were composed of Ni, Zn, and O, which were homogeneously distributed. Distinct morphologies of the ZnO-NiO nanocomposites were obtained via a facile one-pot solution process.

A statistical model for the wettability of surfaces with heterogeneous pore geometries

We describe a new approach to modeling the wetting behavior of micro- and nano-textured surfaces with varying degrees of geometrical heterogeneity. Surfaces are modeled as pore arrays with a Gaussian distribution of sidewall reentrant angles and a characteristic wall roughness. Unlike conventional wettability models, our model considers the fraction of a surface’s pores that are filled at any time, allowing us to capture more subtle dependences of a liquid’s apparent contact angle on its surface tension. The model has four fitting parameters and is calibrated for a particular surface by measuring the apparent contact angles between the surface and at least four probe liquids. We have calibrated the model for three heterogeneous nanoporous surfaces that we have fabricated: a hydrothermally grown zinc oxide, a film of polyvinylidene fluoride (PVDF) microspheres formed by spinodal decomposition, and a polytetrafluoroethylene (PTFE) film with pores defined by sacrificial polystyrene microspheres. These three surfaces show markedly different dependences of a liquid’s apparent contact angle on the liquid’s surface tension, and the results can be explained by considering geometric variability. The highly variable PTFE pores yield the most gradual variation of apparent contact angle with probe liquid surface tension. The PVDF microspheres are more regular in diameter and, although connected in an irregular manner, result in a much sharper transition from non-wetting to wetting behavior as surface tension reduces. We also demonstrate, by terminating porous zinc oxide with three alternative hydrophobic molecules, that a single geometrical model can capture a structure’s wetting behavior for multiple surface chemistries and liquids. Finally, we contrast our results with those from a highly regular, lithographically-produced structure which shows an extremely sharp dependence of wettability on surface tension. This new model could be valuable in designing and evaluating processes for manufacturing liquid-repellent surfaces on an industrial scale.

GAS SENSORS BASED ON ORGANIC-INORGANIC NANOCOMPOSITES

The use of nanocrystals with large specific surface in sensor structures provides their high sensitivity to molecules of adsorbed gases. The aim of the work was to create sensor elements based on composite films of poly-3,4-ethylenedioxythiophene (PEDOT) in combination with nanocrystals of porous silicon (PS) and zinc oxide (ZnO) and to study the effect of adsorption of ammonia, ethanol and acetone molecules on the electrical parameters of the PEDOT-PS-ZnO structure.To produce film of PEDOT-PS-ZnO hybrid composite, 1% suspension of PEDO-PSS, zinc oxide with a particle size of 100 nm (Sigma-Aldrich Co, USA) and PS nanocrystals, obtained by electrochemical etching of silicon wafer were used. Research of adsorption-desorption processes in the composite films was carried out by measuring their electrical parameters at different concentrations of the analyzed gases. To evaluate the sensor properties, the adsorption sensitivity of the composite films was calculated and their dynamic characteristics were studied.Increase of electrical resistance of nanocomposite due to adsorption of ammonia, ethanol and acetone molecules was registered. The almost linear dependence of the resistance on the concentration of ammonia and acetone was observed. It is a significant advantage in developing of the gas sensors. The maximum sensitivity of the sensor elements is in the range of 1-2% concentration of the analyzed gases and the response time is 60-80 s. The films with higher content of PS nanocrystals were more sensitive to molecules of ammonia and ethanol, and the films containing more nanoparticles of ZnO - to molecules of acetone. To control functional parameters of the sensor films, the content ratio of semiconductor nanoparticles in hybrid composite can be changed.The combination of nanoparticles of porous silicon and zinc oxide provides not only an increase in working surface area of sensors, but also high sensitivity and selectivity to the ammonia, ethanol and acetone molecules. The obtained results can be used to create effective analyzers of gases.

Rapid methyl orange degradation using porous ZnO spheres photocatalyst

Porous zinc oxide (ZnO) spheres were synthesized by facile low temperature solution route. The as-synthesized porous ZnO spheres were characterized in detail in terms of their morphological, structural, optical and photocatalytic properties using field-emission scanning electron microscopy (FESEM, equipped with energy dispersive spectroscopy (EDS)), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffractometer (XRD), UV–visible spectroscopy and Raman-scattering measurements. Nitrogen adsorption-desorption analysis was performed to determine pore size distribution from the adsorption isotherm curves using the Barrett-Joyner-Halenda (BJH) method. Morphological and structural characterizations showed porous nature of ZnO spheres with high surface area, good crystallinity, wurtzite hexagonal phase and good optical features. Next, ZnO spheres were studied as photocatalyst for photodegradation of harmful dye, methyl orange (MO). Under ultraviolet light irradiation, the decrease in MO dye concentration was monitored by UV–visible spectroscopy at different time intervals until the dye was completely degraded to colorless end product. Rapid MO dye decomposition was observed with a degradation rate of ~96.3% within the initial 120min, which is attributed to the porous nature, large specific surface area (114.6m2g−1), narrow pore size distribution (~2.5 to 25nm) evaluated from N2 adsorption-desorption isotherms analysis and excellent electron accepting features of the engineered porous ZnO spheres.

Hierarchical triple-shelled porous hollow zinc oxide spheres wrapped in graphene oxide as efficient sensor material for simultaneous electrochemical determination of synthetic antioxidants in vegetable oil

Hierarchical triple-shelled porous hollow zinc oxide spheres (ZnO TPHS) were conveniently synthesized via a hard template method. And the ZnO TPHS were then wrapped into graphene oxide (GO) nanosheets though electrostatic attraction after being amino-functionalized. The composition of ZnO TPHS@GO hybrid was determined using energy dispersive X-ray spectroscopic analysis, X-ray diffraction and Raman spectra. The morphology of ZnO TPHS@GO hybrid was comprised of ZnO nanoparticles and ultrathin GO nanosheets that were characterized with scanning electron microscopy and transmission electron microscopy. The porous hollow structure and intimate contact between ZnO TPHS and GO interfaces provided a large surface area and high electron transfer activity for synthetic antioxidants in an acidic electrolyte. Based on this, a novel electrochemical sensor for the simultaneous determination of tert-butylhydroquinone (TBHQ) and butylated hydroxyanisole (BHA) has been constructed using ZnO TPHS@GO as sensing material. Under optimal conditions, the developed sensor exhibited excellent electrochemical responses in the co-detection of TBHQ and BHA, with limits of detection of 0.137 and 0.0488μM (S/N=3), respectively. Besides, the selectivity, reproducibility and application in edible vegetable oil samples were also investigated. This study proposed a novel method of fabrication of metal oxide-decorated GO-based materials for the fabrication of sensitive electrochemical sensors that met the needs of food safety control.

Porous nanosheet-based hierarchical zinc oxide aggregations grown on compacted stainless steel meshes: Enhanced flexible dye-sensitized solar cells and photocatalytic activity

Porous nanosheet-based hierarchical ZnO aggregations are prepared on compacted stainless steel meshes (CSSMs) using a facile precursor template method. The coverage density and morphology of the film are controlled by the concentration of alkaline in the precursor solution. Relative to the traditional planar substrate, CSSMs with multi-layered structure have larger surface area and higher porosity to capture more light from all directions. The three-dimensional (3D) hierarchical ZnO aggregations assembled by porous nanosheets could take both the advantages of nanosheets and micrometer-sized assemblies. As expected, combining the virtues of ZnO aggregations and CSSMs, the ZnO aggregations/CSSMs structure exhibit the significantly improved conversion efficiency as photoelectrode of flexible dye-sensitized solar cells and photocatalytic performance in the photodegradation of pollutants with a better recyclability. Furthermore, our work would offer idea for the growth of complex 3D hierarchical micro-/nanoarchitecture on the high curvature surface of the substrates.