Three-dimensional ZnO Research Articles

ZnO nanostructures with controlled morphological and optical properties for applications as efficient photocatalyst for malachite green degradation

This study aims to comparatively investigate the morphological and optical characteristics of zinc oxide nanoparticles as a function of the preparation conditions. A series of ZnO nanoparticles were synthesized by facile precipitation method at constant temperature, by varying the zinc sources (zinc acetate, zinc nitrate and zinc chloride) or the precipitant nature (hexamethylenetetramine, urea). The structural, morphological and optical attributes of the prepared ZnO samples were assessed by SEM, XRD, FTIR, UV–Vis and photoluminescence analyses. The morphology of the achieved samples varies from spiky sticks to hexagons or foils with irregular shapes, observing that urea favour the development of two- or three-dimensional ZnO nanostructures, while hexamethylenetetramine predominantly triggered the formation of highly organized one-dimensional structures. The XRD patterns of all ZnO samples matches zincite crystalline hexagonal phase and the evaluation of crystallite size revealed higher values for the samples prepared in the presence of hexamethylenetetramine (HMTA). The optical band gap of ZnO NPs, as estimated from the UV–Vis absorption spectra, varied slightly from 3.13 to 3.21 eV, while fluorescence investigation proves that samples prepared with urea precipitant have a lower rate of charge recombination. Tests on the photocatalytic degradation of malachite green dye under UV light irradiation demonstrated that the dynamics of photogenerated charge carriers play a significant role in the photocatalytic performance of ZnO samples.

Silver-decorated three-dimensional ZnO nanoflowers enhancing the electromagnetic coupling for ultrasensitive SERS detection of multi-pesticide residues

—The development of sensitive analytical methods is of prime importance for the detection of pesticide residues on the surfaces of fruits and vegetables at extremely low concentrations. Here, we synthesized Ag-decorated three-dimensional ZnO nanoflowers (ZnO@Ag) composed of ultrathin nanosheets as surface-enhanced Raman spectroscopy (SERS) substrates. Combined with the finite-difference time-domain (FDTD) method, it is proven that the ultrathin nanosheets greatly improve the electromagnetic coupling between the two metal nanoparticles due to the high refractive index of ZnO and generate new “hot spots”. The nanosheets also endow the incident light with multiple reflections to motivate the local electromagnetic field. The substrate presents high sensitivity and the enhancement factor was as high as 2.98 × 107 utilizing R6G as probe molecules. The detection concentration of thiram and malachite green (MG) solutions can reach 10−10 M and 10−9 M, respectively. For the real-life sample assays, the substrate can simultaneously detect the two pesticides on apple skin with high sensitivity. The research also reveals the importance of semiconductors toward the local electromagnetic field enhancement in noble metal-semiconductor substrates, benefiting the realization of highly sensitive SERS substrates and the wide application of the SERS technology in real-world scenarios.

High-performance photoelectrochemical (PEC) type self-powered ultraviolet photodetectors (PDs) based on three-dimensional ZnO film/carbon fiber paper

Novel photoelectrochemical ultraviolet detection technologies based on semiconductor/electrolyte heterojunctions have attracted significant attention due to their cost-effective fabrication and self-powered characteristic. In this study, ZnO films were deposited on three-dimensional carbon fiber paper (3D CFP) using a one-step sputtering method, resulting in the preparation of 3D ZnO/CFP composites as photoanodes for photoelectrochemical (PEC) type photodetectors (PDs). The fabricated device demonstrates outstanding photoelectrochemical performance, showcasing a remarkable responsivity of approximately 31.76 mA/W, a detectivity of 3.06 × 1012 jones, and a rapid photoresponse time of 76.51/48.51 ms. Furthermore, the device exhibits exceptional photoresponse stability during cycling tests. The unique structure of 3D CFP, composed of intertwined carbon fiber in three dimensions, offers an enlarged specific surface area and efficient carrier transport pathways for the photoanode in self-powered PEC-PDs. This characteristic facilitates effective electrolyte diffusion throughout the entire film, as well as efficient transport of photo-generated charge carriers, thereby significantly enhancing the overall performance of the PEC-PDs. This study affirms the effectiveness of the synergistic interaction between 3D CFP and ZnO film for advanced UV photodetectors, demonstrating both mass production viability and promise for the future of photoelectrochemical detection technology.

Enhanced visible-light photocatalysis in three-dimensional rose-like ZnO with oxygen vacancies and Ag nanoparticles

Ag/Ar-ZnO displays enhanced visible light photocatalytic performance due to a narrower bandgap of 2.79 eV, highly increased light absorption and improved charge separation and transfer efficiencies induced by oxygen vacancies and Ag nanoparticles.

Zn Single Atoms/Clusters/Nanoparticles Embedded in the Hybrid Carbon Aerogels for High-Performance ORR Electrocatalysis.

Carbon-supported zinc single-atom catalysts have received considerable attention in the electrocatalytic oxygen reduction reaction (ORR) owing to the strong reduction capacity of zinc atoms and the abundant reserves of zinc elements. The common preparation method has been limited to the high-temperature pyrolysis of nitrogen-rich organic molecules and zinc ions, which makes it difficult to further improve the ORR performance. Herein, we first prepared ZnO/PNT/rGO aerogels as precursors via a simple hydrothermal method combined with freeze-drying, in which reduced graphene oxides (rGO) and polypyrrole nanotubes (PNT) together assembled into three-dimensional frames and numerous ZnO nanoparticles were anchored in the three-dimensional skeletons. Then, ZnO/PNT/rGO aerogels were calcined at 800 °C in the argon atmosphere, in which PNT/rGO were derived carbon aerogels, ZnO nanoparticles were reduced to Zn0 by carbon, and generating zinc single atoms were captured by the surrounding nitrogen atoms or aggregated into Zn clusters/nanoparticles in the carbon substrates. The obtained products were Zn single atoms/clusters/nanoparticles embedded into PNT/rGO-derived carbon aerogels, named Zn/NC catalysts. Zn/NC catalysts display a much higher half-wave potential and a larger limiting current density than pure rGO aerogels, NC, and Zn/C catalysts, indicating the synergy of excellent electronic transportation, high mass efficiency from outstanding porosity, and several active centers. Tailoring the quantity of zinc acetate can provide the optimal ORR performance with the Eonset of 0.96 V, the E1/2 of 0.845 V, and remarkable durability. This work exploits a novel strategy of carbon thermal reduction to construct high-performance Zn-based low-dimensional ORR catalysts.

Self-assembled three-dimensional flower-like ZnO encased by carbon toward stable lithium metal anode

Self-assembled three-dimensional flower-like ZnO encased by carbon toward stable lithium metal anode

High sensitivity ammonia QCM sensor based on ZnO nanoflower assisted cellulose acetate-polyaniline composite nanofibers

A Quartz crystal microbalance (QCM) ammonia sensor with ZnO nanoflowers (NFs) doped with cellulose acetate nanofiber (CA) nanofibers and polyaniline-modified nanocomposites (CA/PANI/ZnO) is presented in this paper. The CA/PANI composite was firstly produced by electrostatic spinning and further oxidative polymerization, and then three-dimensional self-assembled ZnO NFs was synthesized by further solvothermal method, and the two were blended to obtain the ternary CA/PANI/ZnO composite with high specific surface area. The morphology and elemental composition of the fabricated composite nanomaterials were tested and analyzed by a series of characterization techniques. The experimental results showed that the QCM sensor based on CA/PANI/ZnO composite nanomaterials at room temperature exhibited good performances over a wide range of ammonia concentrations (1–70 ppm), such as high sensitivity (4.54 Hz/ppm), short response recovery time (15 s/10 s), high linearity and high selectivity. The electrical parameters of the sensor are obtained by the impedance analyzer, and the quality factor is further calculated. The potential synergistic interaction between the composites is the key for ammonia adsorption. The results show that the sensor is expected to be a potential candidate for ammonia detection.

Controllable Synthesis of Sheet-Flower ZnO for Low Temperature NO2 Sensor.

ZnO is a wide band gap semiconductor metal oxide that not only has excellent electrical properties but also shows excellent gas-sensitive properties and is a promising material for the development of NO2 sensors. However, the current ZnO-based gas sensors usually operate at high temperatures, which greatly increases the energy consumption of the sensors and is not conducive to practical applications. Therefore, there is a need to improve the gas sensitivity and practicality of ZnO-based gas sensors. In this study, three-dimensional sheet-flower ZnO was successfully synthesized at 60 °C by a simple water bath method and modulated by different malic acid concentrations. The phase formation, surface morphology, and elemental composition of the prepared samples were studied by various characterization techniques. The gas sensor based on sheet-flower ZnO has a high response value to NO2 without any modification. The optimal operating temperature is 125 °C, and the response value to 1 ppm NO2 is 125. At the same time, the sensor also has a lower detection limit (100 ppb), good selectivity, and good stability, showing excellent sensing performance. In the future, water bath-based methods are expected to prepare other metal oxide materials with unique structures.

S,N-GQD sensitization effect on the improvement of ZnO nanopencil photoelectrochemical properties.

ZnO photoanodes in photoelectrochemical (PEC) water splitting for green-hydrogen production are limited due to the large bandgap that is only confined to UV light. One of the strategies for broadening the photo absorption range and improving light harvesting is to modify a one-dimensional (1D) nanostructure to a three-dimensional (3D) ZnO superstructure coupling with a narrow-bandgap material, in this case, a graphene quantum dot photosensitizer. Herein, we studied the effect of sulfur and nitrogen co-doped graphene quantum dot (S,N-GQD) sensitization on the surface of ZnO nanopencil (ZnO NPc) to give a photoanode in the visible light spectrum. In addition, the photo energy harvesting between the 3D-ZnO and 1D-ZnO, as represented by neat ZnO NPc and ZnO nanorods (ZnO NRs), was also compared. Several instruments, including SEM-EDS, FTIR, and XRD revealed the successful loading of S,N-GQDs on the ZnO NPc surfaces through the layer-by-layer assembly technique. The advantages are S,N-GQDs's band gap energy (2.92 eV) decreasing ZnO NPc's band gap value from 3.169 eV to 3.155 eV after being composited with S,N-GQDs and facilitating the generation of electron-hole pairs for PEC activity under visible light irradiation. Furthermore, the electronic properties of ZnO NPc/S,N-GQDs were improved significantly over those of bare ZnO NPc and ZnO NR. The PEC measurements revealed that the ZnO NPc/S,N-GQDs stood out with a maximum current density of 1.82 mA cm-2 at +1.2 V (vs. Ag/AgCl), representing a 153% and 357% improvement over the bare ZnO NPc (1.19 mA cm-2) and the ZnO NR (0.51 mA cm-2), respectively. These results suggest that ZnO NPc/S,N-GQDs could have potential for water splitting applications.

Fabrication of Three-Dimensional ZnO: Ga@ITO@Ag SERS-Active Substrate for Sensitive and Repeatable Detectability

Vertically aligned ZnO: Ga nanotowers can be directly synthesized on a glass substrate with a ZnO seed film via the chemical bath method. A novel heterostructure of ZnO: Ga@ITO@Ag nanotowers was subsequently deposited in the ITO layer and Ag nanoparticles via the facile two-step ion-sputtering processes on the ZnO: Ga nanotowers. The appropriate ion-sputtering times of the ITO layer and Ag nanoparticles can benefit the fabrication of ZnO: Ga@ITO@Ag nanotowers with higher surface-enhanced Raman scattering (SERS) enhancement in detecting rhodamine 6G (R6G) molecules. Compared with ZnO: Ga@Ag nanotowers, ZnO: Ga@ITO@Ag nanotowers exhibited a high SERS enhancement factor of 2.25 × 108 and a lower detection limit (10-14 M) for detecting R6G molecules. In addition, the ITO layer used as an intermediate layer between ZnO: Ga nanotowers and Ag nanoparticles can improve SERS enhancement, sensitivity, uniformity, reusability, detection limit, and stability for detecting amoxicillin molecules. This phenomenon shall be ascribed to the ITO layer exhibiting a synergistic Raman enhancement effect through interfacial charge transfer for enhancing SERS activity. As a result, ZnO: Ga@ITO@Ag nanotowers can construct a three-dimensional SERS substrate for potential applications in environmentally friendly and cost-effective chemical or drug detection.

Three-dimensional ZnO–TiO2/graphene aerogel for water remediation: The screening studies of adsorption and photodegradation

Zinc oxide−doped titanium dioxide/graphene aerogel (ZnO−TiO2/GA) nanocomposite was fabricated by the two-step solvothermal method for efficient removal of dyes and toxic metals in aqueous media. Based on the results, ZnO−TiO2/GA material with an optimal ZnO amount of 300 mg has a synergistic effect on exhibiting an excellent photocatalytic-adsorption capacity. The highest degradation efficiency for methylene blue, rhodamine B, and methyl orange was 99.7, 97.3, and 94.9%, respectively, with the optimum conditions: catalyst dose of 0.2 g L−1, 20 ppm dye concentration at 20 min under ultra-visible (UV−11 W) light irradiation. Moreover, the material also showed outstanding reusability with more than 90% dye removal efficiency after 8 cycles of testing. The proposed pathway and intermediate products of dye degradation were also investigated using liquid chromatography−mass spectrometry (LC−MS) analysis. Besides that, the maximum absorption capacity for the toxic metal ions Cd2+ and Co2+ are 380.6 and 230.1 mg g−1, respectively, which followed by the Langmuir isotherm adsorption model. The results exhibited the material's potential for the treatment of water containing toxic metals and waste from textile dyeing.

Quantitative modeling, optimization, and verification of 63Ni-powered betavoltaic cells based on three-dimensional ZnO nanorod arrays

Quantitative modeling, optimization, and verification of 63Ni-powered betavoltaic cells based on three-dimensional ZnO nanorod arrays

Diverse scenarios selective perception of H2S via cobalt sensitized MOF filter membrane coated Three-Dimensional metal oxide sensor

Using metal–organic frameworks (MOF) materials as a filter membrane is an innovative method to improve the selectivity of gas sensors by adjusting the size of the pores and cavities; however, the active surface and dynamic sensing processes are inevitably negatively affected. A facile but effective strategy was implemented in this work by integrating Co ions as catalysts into the inner three-dimensional ZnO skeleton and outer MOF filter membrane. The appropriate incorporation of Co cations was found to increase the surface area, facilitate the adsorption of oxygen species onto the zeolitic imidazolate framework (ZIF) surface, and promote the catalytic oxidation of H2S. In the optimised gas sensor, an enhanced response of H2S (260 to 5 ppm) and a low detection limit (70 ppb) at 180 °C were obtained because of the catalytic action of appropriate amounts of Co. In addition, beyond the molecular sieve effect to exclude interference from larger gas molecules, the incorporation of Co catalysts can adjust the number of base sites in the ZIF filter (from 1.592 to 3.325 mol/g), which further assists in avoiding basic-type interference from gas molecules with smaller kinetic diameters. As a result, a 130-fold increase in H2S selectivity (among various interfering gases) and a 54-fold increase (compared to the control sensor without Co) were obtained. Moreover, the sensor was demonstrated to be a powerful platform for assessing trace amounts of H2S in pesticide volatile gas identification and protein food quality evaluation.

Visible Light-Induced Room-Temperature Formaldehyde Gas Sensor Based on Porous Three-Dimensional ZnO Nanorod Clusters with Rich Oxygen Vacancies.

Oxygen vacancy (VO) is a kind of primary point defect that extensively exists in semiconductor metal oxides (SMOs). Owing to some of its inherent qualities, an artificial manipulation of VO content in one material has evolved into a hot research field, which is deemed to be capable of modulating band structures and surface characteristics of SMOs. Specific to the gas-sensing area, VO engineering of sensing materials has become an effective means in enhancing sensor response and inducing light-enhanced sensing. In this work, a high-efficiency microwave hydrothermal treatment was utilized to prepare a VO-rich ZnO sample without additional reagents. The X-ray photoelectron spectroscopy test revealed a significant increase in VO proportion, which was from 9.21% in commercial ZnO to 36.27% in synthesized VO-rich ZnO possessing three-dimensional and air-permeable microstructures. The subsequent UV–vis–NIR absorption and photoluminescence spectroscopy indicated an extension absorption in the visible region and band gap reduction of VO-rich ZnO. It turned out that the VO-rich ZnO-based sensor exhibited a considerable response of 63% toward 1 ppm HCHO at room temperature (RT, 25 °C) under visible light irradiation. Particularly, the response/recovery time was only 32/20 s for 1 ppm HCHO and further shortened to 10/5 s for 10 ppm HCHO, which was an excellent performance and comparable to most sensors working at high temperatures. The results in this work strongly suggested the availability of VO engineering and also provided a meaningful candidate for researchers to develop high-performance RT sensors detecting volatile organic compounds.

Binder-Free Porous 3D-ZnO Hexagonal-Cubes for Electrochemical Energy Storage Applications.

Considerable efforts are underway to rationally design and synthesize novel electrode materials for high-performance supercapacitors (SCs). However, the creation of suitable materials with high capacitance remains a big challenge for energy storage devices. Herein, unique three-dimensional (3D) ZnO hexagonal cubes on carbon cloth (ZnO@CC) were synthesized by invoking a facile and economical hydrothermal method. The mesoporous ZnO@CC electrode, by virtue of its high surface area, offers rich electroactive sites for the fast diffusion of electrolyte ions, resulting in the enhancement of the SC’s performance. The ZnO@CC electrode demonstrated a high specific capacitance of 352.5 and 250 F g−1 at 2 and 20 A g−1, respectively. The ZnO@CC electrode revealed a decent stability of 84% over 5000 cycles at 20 A g−1 and an outstanding rate-capability of 71% at a 10-fold high current density with respect to 2 A g−1. Thus, the ZnO@CC electrode demonstrated improved electrochemical performance, signifying that ZnO as is promising candidate for SCs applications.

Zn2+ induced self-assembled fabrication of marigold-like ZnO microflower@Ni(OH)2 three-dimensional nanosheets for nonenzymatic glucose sensing

Precise control over the structure and morphology of nano/microarchitectures is the topic of immense interest to tune their physical features and chemical aspects for desired applications. In this work, a novel and effective Ni(OH)2 three-dimensional nanosheet-coated marigold-like ZnO microflower (mg-ZnO@Ni(OH)2 NSs) hybrid is designed for the nonenzymatic electrochemical determination of glucose. The morphological evolution of mg-ZnO and mg-ZnO@Ni(OH)2 NSs was achieved by a one-pot solvothermal strategy through control over the reaction conditions without any assistance of an external shape-controlling surfactant. Furthermore, the as-fabricated mg-ZnO and mg-ZnO@Ni(OH)2 NSs were systematically evaluated by different spectroscopic, microscopic and electrochemical characterization tools. The results indicate that highly exposed homogeneous nanocorners of mg-ZnO and the synergetic effect of Ni(OH)2 coating, collectively improve the electrocatalytic efficiency of the designed catalyst. The mg-ZnO@Ni(OH)2 NS-based sensing electrode exhibits excellent amperometric performance for glucose monitoring, comprising satisfactory sensitivity (259.78 and 62.82 μA mM−1 cm−2), wide linear range (0.084–0.941 mM and 0.941–6.50 mM), low limit of detection (0.06 µM, S/N = 3), good stability and high detection selectivity. Moreover, the designed sensor is promising for the potential application in the real-time glucose detection of human serum samples.

ALD oxygen vacancy-rich amorphous Ga2O3 on three-dimensional urchin-like ZnO arrays for high-performance self-powered solar-blind photodetectors.

The exploration of efficient self-powered solar-blind photodetectors is essential for applications in future sustainable optoelectronic systems. Herein, we demonstrate a photoelectrochemical (PEC)-type heterojunction-driven solar-blind detector constructed by atomic layer deposition (ALD) of oxygen vacancy-rich amorphous Ga2O3 on three-dimensional urchin-like ZnO nanorod arrays (3D VO-Ga2O3/ZnO). The as-fabricated device achieves excellent solar-blind photodetection performance in terms of a high photoresponsivity of 7.97 mA W-1 at 0 V bias, an ultrahigh light to dark ratio of 6.93 × 104 under 266 nm light illumination as well as fast response and recovery times. The excellent performance originates from abundant oxygen vacancies in a-Ga2O3 as donors, high specific surface area and good interface contact enabled by the 3D ordered nanostructure, and high carrier separation rates benefited from the Ga2O3/ZnO heterojunction. Our research offers a feasible and cost-effective approach towards the realization of a high-performance self-powered photodetection system for various applications.

Preparation and Properties of Nano ZnO Dye Sensitized Solar Cells on (Titanium) Substrates

Nowadays, the development of science and technology has been increasing demand for energy. Energy problem has become a bottleneck to restrict the development of international social economy. People pay more and more attention to the development and research of renewable resources. Solar energy is a kind of renewable resource with great potential and no pollution. The commercialized solar cells are mainly silicon solar cells, among which the conversion efficiency of single silicon solar cells is the highest, but the cost of silicon solar cells is high. Therefore, people have been exploring new materials, among which titanium based nano ZnO dye sensitized solar cells have been paid more and more attention by scientists at home and abroad. Based on this, the preparation and performance of nano ZnO dye sensitized solar cells based on titanium are studied. In this paper, the optical anode materials of DSSC are used as the research objects. Three-dimensional ZnO nanoband, one-dimensional graded ZnO nanotube array and one-dimensional sub grade ZnO nanowire array are prepared by anodizing and hydrothermal synthesis. The photovoltaic properties of the three materials are studied. One dimensional graded ZnO, nanotube array films were prepared by two-step hydrothermal synthesis. One dimensional hierarchical ZnO nanowire array is obtained by two-step hydrothermal synthesis. The results show that DSSC is assembled by one-dimensional graded ZnO nanotube array film, and the photoelectric conversion efficiency is 5.1%. Compared with one-dimensional ZnO nanowire array, the efficiency is improved by nearly 90%. The ZnO nanowire of the sub grade is used instead of DSSC The efficiency of photoelectric conversion is only 4% in the photoanode, which is higher than that of the smooth ZnO nanowire photocell.

A multi-platform sensor for selective and sensitive H2S monitoring: Three-dimensional macroporous ZnO encapsulated by MOFs with small Pt nanoparticles

The high-selectivity and high-sensitivity determination of trace concentrations of toxic gases is a major challenge when using semiconductor metal oxide (SMO) gas sensors in complicated real-world environments. In this study, by strategically combining a three-dimensional inverse opal (3DIO) macroporous ZnO substrate and a ZIF-8 outer filter membrane, two series of sensors with Pt NPs loaded at different locations are developed. In the optimal 3DIO ZnO@ZIF-8/Pt sensor, the existence of small Pt NPs in ZIF-8 cavities can effectively accelerate the absorption of H2S, capture electrons from the N site of ZIF-8, and donate the electron to the S site of H2S, as indicated by density functional theory simulations, leading to a significantly increased response to H2S. Together with the molecular-sieving effect that ZIF-8 exerts on gas molecules with larger kinetic diameters, the 3DIO ZnO@ZIF-8/Pt sensor exhibits a high response to H2S (118–5.5 ppm), a detection limit of 40 ppb, and importantly, a 59-fold higher selectivity to H2S against typical interference gases. In addition, the 3DIO ZnO@ZIF-8/Pt sensor is developed as a multi-platform sensor to evaluate trace concentrations of H2S in meat quality assessment, halitosis diagnosis, and automobile exhaust assessment.

Nanoarchitectonics of three-dimensional ZnO–BiVO4 for trace nitrogen dioxide gas detection

In the present study, several novel three-dimensional (3D) ZnO–BiVO4 composites were prepared using the hydrothermal method, and their ability to detect nitrogen dioxide (NO2) gas was assessed. The fabricated sensing materials were examined using X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry, scanning electron microscopy, ultraviolet–visible spectrophotometry, X-ray photoelectron spectroscopy, and surface-area and porosity analysis. The sensing material assessments verified that 3D ZnO–BiVO4 was successfully prepared; the sensing data revealed that 3D ZnO–BiVO4 exhibited excellent sensing response (24.6) to 1-ppm NO2 at room temperature. The composites exhibited a fast response (28 s) and short recovery time (75 s) when detecting 1-ppm NO2; they also exhibited long-term stability (decline of approximately 7% after 30 days) and selectivity to 10-ppm NO2 gas. A reasonable NO2 gas sensing mechanism for 3D ZnO–BiVO4 heterojunction was also proposed in this paper.