Porous ZnO Nanorods Research Articles

Excellent NO2 sensor based on porous Pd-ZnO nanorods prepared by a facile hydrothermal method

Noble metal nanoparticles (NPs) decorated on the surface of semiconducting metal oxides to enhance the gas-sensitive properties of sensing materials have attracted considerable interest from numerous researchers worldwide. Here, we introduce an effective method to decorate Pd NPs on the surface of porous ZnO nanorods to improve NO2 gas-sensing performance. Porous ZnO nanorods were synthesized using a simple hydrothermal method without surfactant. Surface decoration of porous ZnO nanorods with Pd NPs was performed through in situ reduction of PdCl2 using Pluronic as the reducing agent. The gas-sensing properties of porous Pd-ZnO nanorods were evaluated toward NO2 toxic gas in a concentration range of 0.1–2 ppm at various operating temperatures of 25 °C–250 °C. Pd NPs decorated on the surface of porous ZnO nanorods not only improve the sensor response (3-folds) and reproducibility but also reduce the optimal operating temperature. The improvement in gas-sensing activity is attributed to the modulation of the depletion layer via oxygen adsorption and the formation of the Schottky potential barrier between Pd and ZnO through chemical and electronic mechanisms.

Highly Semiconducting One-Dimensional Porous ZnO Nanorod Array Nanogenerators for Mechanical Energy Harvesting Functions

The development of energy harvesters based on inexpensive inorganic materials has attracted considerable attention to envisage next-generation self-powered electronic devices. In this work, we presented surface modification of ZnO nanorods (NRs) by thermochemical reaction using photoresist (PR) as an etching source. The morphological and microstructural properties of surface-etched ZnO NRs (M: ZnO) were systematically studied in detail through SEM and HRTEM. The morphological results show that the surface-etched NRs possess nanofiber-like porous structures and are penetrated throughout the NRs with high surface area. We fabricated triboelectric nanogenerators (TENG) using M: ZnO NRs with poly (dimethylsiloxane) (PDMS) as negative triboelectric material and mica as positive triboelectric material. The prepared M: ZnO NR TENG successfully delivered an output voltage of up to 20 V and a current density of 3.2 μA cm−2, which is ∼1.5 times higher than those observed for smooth ZnO NRs, respectively. The prepared M: ZnO NR TENG device can be able to lit 24 red light-emitting diodes (LEDs) as the power source. Finally, to demonstrate the practical applications of M: ZnO NR TENG, it was attached to the human body (elbow, knee, wrist, and heel) and efficiently harvested the energy from daily human activities.

Research on pH-responsive antibacterial materials using citral-modified zinc oxide nanoparticles

Abstract Objectives With the increasing damage caused by foodborne pathogens to human health and the increasing attention given to healthy diets, novel food antimicrobial agents have been widely studied. Materials and Methods In this study, three different morphologies of citral-modified ZnO nanoparticle antimicrobial materials were prepared, and the citral-modified porous ZnO nanorod antimicrobial materials with the highest loading (60.35%) and the strongest inhibitory effect (MIC=0.2–0.1 mg/mL) were screened through a series of characterization and bacterial inhibition experiments. This novel antimicrobial material has excellent and long-lasting antimicrobial properties. It inhibited Escherichia coli by 100% when stowed at 25 °C and protected from light for 10 d and inhibited the growth of E. coli by 58.17% after being stowed under the same conditions for 60 d. Furthermore, we tested the pH change during 24 h of E. coli growth and the pH responsiveness of the materials. Results The results demonstrated that under the acid-producing condition of E. coli growth, the pH-sensitive imine bond (–CH=N–) formed by the condensation of the amino of functionalized ZnO nanoparticles and citral was hydrolyzed to release the citral, which indicated that the release mechanism of citral in the antibacterial material was pH-sensitive. Conclusions The antibacterial materials in this study have broad application prospects in the field of food production and packaging in the future. Moreover, this study provides a theoretical basis for guaranteeing food quality and safety.

Synergetic enhancement effect of two-dimensional MoS2 nanosheets and metal organic framework-derived porous ZnO nanorods for photodegradation performance.

Two-dimensional transition metal dichalcogenides and semiconductor metal oxides have shown great potential in photocatalysis. However, their stability and efficiency need to be further improved. In this paper, porous ZnO nanorods with high specific surface area were prepared from metal-organic framework ZIF-8 by a simple hydrothermal method. A MoS2/ZnO composite was constructed by loading MoS2 onto the surface of porous ZnO nanorods. Compared with ZnO materials prepared by other methods, MoS2/ZnO prepared in this paper exhibits superior photocatalytic performance. The enhanced photocatalytic activity of the MoS2/ZnO composite can be attributed to the formation of heterojunctions and strong interaction between them, which greatly facilitate the separation of electrons and holes at the contact interface. In addition, due to the wide absorption region of the visible spectrum, MoS2 can greatly broaden the light absorption range of the material after the formation of the composite material, increase the utilization rate of visible light, and reduce the combination of electrons and holes. This study provides a new way to prepare cheap and efficient photocatalysts.

Fabrication of porous and visible light active ZnO nanorods and ZnO@TiO2 core-shell photocatalysts for self-cleaning applications.

Highly transparent and self-cleaning ZnO nanorods (NRs) and ZnO@TiO2 core-shell (CS) nanoarrays were fabricated using the sol-gel dip-coating technique. TiO2 nanoparticles (NPs) were coated as a shell layer over the hydrothermally grown ZnO NRs. The number of shell layers on the ZnO NRs was varied by modulating the number of dipping cycles from 1 to 3 to optimize their transmittance. The optimized CS nanoarrays with two dipping cycles display a 2% enhancement of optical transmission compared to the ZnO NRs. In addition, superhydrophilicity (contact angle ∼of 12°) stimulates the self-cleaning nature of the thin films. A water contact angle of 12° was noted for the ZnO@TiO2: 2 cycle sample, indicating their superhydrophilic nature. Moreover, the photocatalytic activity of the pristine ZnO NRs and ZnO@TiO2 CS nanoarrays was tested under UV and direct sunlight through the dye degradation of methylene blue (MB). Based upon the TiO2 morphology and accessibility of the ZnO@TiO2 heterojunction interface, CS nanoarrays with two shell layers exhibit the highest degree of dye photodegradation efficiency of 68.72% and 91% under sunlight and UV light irradiation, respectively. The CS nanoarrays demonstrate medium sunlight and excellent UV-light-driven photocatalytic activity. Our findings suggest that the ZnO@TiO2 CS nanoarrays are potential photocatalysts for dye degradation and self-cleaning applications in solar cell coverings.

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.

ZIF-L-derived porous C-doped ZnO/CdS graded nanorods with Z-scheme heterojunctions for enhanced photocatalytic hydrogen evolution

This study presents a novel approach for synthesizing C–ZnO/CdS graded nanorods derived from metal–organic frameworks (MOFs) that can be applied as a catalyst for photocatalytic hydrogen evolution from pure water. Porous C-doped ZnO was prepared by a self-template method using imidazole-like metal–organic backbone (ZIF-L) as a precursor through a two-step calcination method. CdS nanoparticles were deposited on ZIF-L surface by chemical deposition. The two-step calcination method introduced elemental C, and the unique architecture of ZIF-L played an essential role in forming the hierarchical structure of the porous ZnO nanorods. Compared with other ZnO/CdS catalysts, the C-doped ZnO/CdS graded nanorods exhibited remarkable photocatalytic activity for hydrogen production. The highest hydrogen production rate of 20.25 mmol g−1 h−1 with an apparent quantum yield (AQY) of 24.7% at 365 nm obtained over C–ZnO/CdS with Pt as co-catalyst, which was 24.4 and 65.3 times higher than that over CdS (0.83 mmol g−1 h−1) and ZnO (0.31 mmol g−1 h−1), respectively. This outcome was attributed to (i) the formation of Z-scheme heterojunction that significantly promoted the separation and migration of photogenerated electron–hole pairs; (ii) C doping that reduced the bandgap of ZnO and broadened its spectral response range; and (iii) the ordered arrangement of porous nanorods that effectively reduced the recombination rate of the electron–hole pairs.

Self‐templated fabrication of 2-D dual nanoarchitecture Zn1-xCdxS porous nanosheet and ZnO nanorod for photoelectrochemical hydrogen production

Herein, dual nanostructured ZnO nanorod (NR)-Zn1-xCdxS porous nanosheet (PNS) photoanodes were produced on a zinc foil through cation exchange reaction of inorganic–organic hybrid ZnS(en)0.5 nanosheets. ZnS(en)0.5 NS’s photoanodes have been synthesized via a facile solvothermal method followed by a series of cadmium (Cd2+) ion-exchange using various ion-exchange reaction times and temperatures. During Cd2+ ion-exchange, the Zn1-xCdxS PNS and a new type of vertically aligned ZnO NR were subsequently grown on the zinc foil substrate. The different exposed surfaces of the vertically aligned hexagonal ZnO NR and Zn1-xCdxS PNS photoanodes contribute to appropriate morphology, effective light harvesting, and efficient charge separation in ZnO-NR-Zn1-xCdxS PNS160C. The optimum ZnO NR-Zn1-xCdxS PNS160C photoanode contributed the highest photocurrent density of 6.60 mA·cm−2 and hydrogen production of 250.65 μmol·cm−2 at 0 V vs. Ag/AgCl. Finally, the charge transfer mechanism in the optimum photoanode is discussed in detail.

Facile Synthesis of a Porous ZnO Nanorod Array with Enhanced Photocatalysis for Photoelectrochemical Water Splitting Application.

Highly efficient and effective porous ZnO nanorod arrays were fabricated by annealing ZnO nanorod arrays grown on a substrate using a simple hydrothermal method. The annealing had a positive effect on the nanorod morphology, structure and optical properties. The porosity was closely related to the annealing temperature. After heating at 450 °C, pores appeared on the nanorods. It was demonstrated that the porosity could be exploited to improve the visible light absorption of ZnO and reduce the bandgap from 3.11 eV to 2.99 eV. A combination of improved charge separation and transport of the heat-treated ZnO thus led to an increase in the photoelectrochemical properties. At an irradiation intensity of 100 mW/cm-2, the photocurrent density of the porous nanorod array was approximately 1.3 mA cm-2 at 1.2 V versus Ag/AgCl, which was five times higher than that of the ZnO nanorods. These results revealed the synthesis of promising porous ZnO nanorods for photoelectrochemical applications.

Structural and optical properties of porous ZnO nanorods synthesized by a simple two-step method

The porous ZnO nanorods were successfully synthesized by a two-step template free method consisting of a modified hydrothermal approach and subsequent annealing treatment. Additive formaldehyde was adopted in the initial hydrothermal approach. Numerous mesopores with orderly distribution along the c axis apparently appeared in the annealed products. It is suggested that formaldehyde might adsorb in ZnO nanorods during the hydrothermal process and decompose under elevated temperature. The release of the generated gas prompted the formation of the pores. A schematic model was proposed to describe the forming of pores in ZnO nanorods. Further investigation demonstrated that the emission behavior and crystallographic quality may highly depend on the annealing temperature. The intensity ratio of the ultraviolet emission peak and visible emission peak as well as the crystallographic quality fluctuates due to the competition of the forming of pores and annealed temperature. The samples annealed at 450 °C possess high crystallographic quality and large surface area, which may be the suitable candidate for highly effective photocatalyst and ZnO based photoelectric devices.

Enhancement of local surface plasmon resonance (LSPR) effect by biocompatible metal clustering based on ZnO nanorods in Raman measurements

The development of size-selective and non-destructive detection techniques for nanosized biomarkers has many reasons, including the study of living cells and diagnostic applications. We present an approach for Raman signal enhancement on biocompatible sensing chips based on surface enhancement Raman spectroscopy (SERS). A sensing chip was fabricated by forming a ZnO-based nanorod structure so that the Raman enhancement occurred at a gap of several tens to several hundred nanometers. The effect of coffee-ring formation was eliminated by introducing the porous ZnO nanorods for the bio-liquid sample. A peculiarity of this approach is that the gold sputtered on the ZnO nanorods initially grows at their heads forming clusters, as confirmed by secondary electron microscopy. This clustering was verified by finite element analysis to be the main factor for enhancement of local surface plasmon resonance (LSPR). This clustering property and the ability to adjust the size of the nanorods enabled the signal acquisition points to be refined using confocal based Raman spectroscopy, which could be applied directly to the sensor chip based on the optimization process in this experiment. It was demonstrated by using common cancer cell lines that cell growth was high on these gold-clad ZnO nanorod-based surface-enhanced Raman substrates. The porosity of the sensing chip, the improved structure for signal enhancement, and the cell assay make these gold-coated ZnO nanorods substrates promising biosensing chips with excellent potential for detecting nanometric biomarkers secreted by cells.

Effectively enhanced photocatalytic degradation performance of the Ag-modified porous ZnO nanorod photocatalyst

In the present work, the ZnO nanorods (NRs) and the Ag-modified ZnO NRs (ZnO NRs/Ag) photocatalysts were prepared using hydrothermal method and calcination treatment. Based on the experimental results, some Ag2O/Ag0 nanoparticles (NPs) formed and distributed onto the surface of the ZnO NRs after modification. Ag modification can significantly accelerate the photocatalytic degradation reactions and the ZnO NRs/Ag photocatalyst shows high photocatalytic stability. The Ag2O/Ag0 NPs can realize the effective separation of the photoinduced electrons and holes generated by ZnO NRs, and thus play important roles on the photocatalytic phenol degradation. Because of the mutual conversion of Ag0 and Ag+, the active groups can be generated promptly to accelerate the photocatalytic process.

Synthesis and Photocatalytic Characterization of Porous Cu-Doped ZnO Nanorods

Synthesis and Photocatalytic Characterization of Porous Cu-Doped ZnO Nanorods

Polyaniline nano-wrinkles array on three-dimensional graphene film for high performance supercapacitors

A facile approach has been developed to fabricate polyaniline nano-wrinkles arrays on three-dimensional graphene film (3rGN/PANI-NW) by electropolymerization, which using polystyrene microsphere (PS) as sacrificial templates to form porous structure and ZnO nanorods as scaffolds to form PANI nano-wrinkles. The novel structure can greatly reduce the diffusion length of ion and improve the utilization of electrode materials. When the composite film is used as a supercapacitor electrode, 3rGN/PANI-NW film displays a specific capacitance of 630.0Fg−1 at 0.5Ag−1 with excellent rate capability (remains 80% even at 10Ag−1), much higher than that of 3rGN/PANI film without using ZnO nanorod as a scaffold (358.0Fg−1 at 0.5Ag−1, 74% retention at 10Ag−1) in 1M H2SO4 aqueous solution. More importantly, the 3rGN/PANI-NW can maintain 90.5% of its initial capacitance after constant charge–discharge 5000 cycles at current density of 10Ag−1, suggesting a superior electrochemical cyclic stability and it is promising candidate for use in energy storage device applications.

Fabrication of Carbon Dots Modified Porous ZnO Nanorods with Enhanced Photocatalytic Activity

Porous ZnO nanorods that displayed excellent photocatalytic degradation of organic pollutants(RhB and phenol) were prepared via a solvent thermal method followed by surface modification with carbon dots(C-dots) using a deposition method.The photocatalysts were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),and ultraviolet-visible(UV-Vis) spectroscopy.The degradation of the organic pollutants using the nanorods was tested under Xe-light illumination and was enhanced following C-dot modification.Nanorods that were modified by the C-dots at a mass fraction of 1.2%(CZn1.2) exhibited the highest photocatalytic activity for the degradation of RhB,which was 2.5 times of the pure porous ZnO nanorods.Additionally,the modified nanorods with strangely oxidation ability could catalyze the degradation of phenol by open-rings reaction under Xe-light illumination.The improved photocatalytic activity was attributed to the effective separation of the photogenerated electrons and holes,in which the C-dots served as the receptor of the photogenerated electrons.

3D graphene/ZnO nanorods composite networks as supercapacitor electrodes

In this letter, we report a facile strategy to synthesize 3D graphene (3DG)/ZnO nanorods composite networks by chemical vapor deposition (CVD) and hydrothermal method. Integration of porous graphene networks and ZnO nanorods as supercapacitor electrode leads to a high specific capacitance (554.23F/g at 5mV/s). We have optimized the performance of 3DG/ZnO composite with respect to the contents of ZnO and achieved optimal preparation condition. From practical point of view, we have also evaluated electrochemical stability of present supercapacitor, which retained 94.4% of the initial capacitance after 2300 cycles, demonstrating excellent cycle stability with a high degree of reversibility in the repetitive charge/discharge. Present work might open a new strategy to fabricate functional 3DG and metal oxides composite materials as electrodes for the application in supercapacitors.

Fabrication of porous Cd-doped ZnO nanorods with enhanced photocatalytic activity and stability

Porous Cd-doped ZnO nanorods have been successfully synthesized on a large scale by a precursor thermal decomposition route. Rod-like Zn1−xCdxC2O4 precursors with 1 μm in average length were firstly fabricated via a solvothermal process. After calcining the Zn1−xCdxC2O4 precursors, the porous Cd-doped ZnO nanorods were obtained. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared Cd-doped ZnO nanorods for degradation of organic compounds and the printing and dyeing sewage under the 365 nm of UV light illumination were investigated. The results show that Cd-doped ZnO nanorods have a higher photocatalytic activity than pure ZnO and P25. This enhanced photocatalytic activity is attributed to the Cd doping, which increases the defects in the ZnO nanoparticles and reduces the bandgap width of ZnO. Furthermore, the photodegradation rate does not show an obvious decrease during ten successive cycles, indicating that our Cd-doped ZnO nanorods are very stable.

CuO nanoparticle decorated ZnO nanorod sensor for low-temperature H2S detection

CuO nanoparticle decorated porous ZnO nanorods were synthesized via a two-stage solution process. First, porous ZnO nanorods were fabricated by a low-temperature hydrothermal method. Afterward, the porous ZnO nanorods were used as supports to load CuO nanoparticles by a non-aqueous solution method. The morphology and structure of the prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). To demonstrate the practical application of the synthesized heterostructured porous CuO/ZnO nanorod hybrid, the sensing properties for H2S at low operating temperatures were investigated. The high sensitivity, reversible response and good selectivity indicated its potential application as a chemical sensor.

Porous ZnO nanorod for targeted delivery of doxorubicin: in vitro and in vivo response for therapeutic applications

Cancer cell specific targeted delivery (TDD) by porous nanocarrier is on a high role. Here in a simple route for the synthesis of porous ZnO nanorods (ZnO) has been demonstrated. ZnO expressed very high surface area of 305.14 m2 g−1 (SBET) and uniformly distributed pores of 5 nm. In continuation ZnO has been fabricated with 3-aminophosphonic acid followed by folic acid to yield folate conjugated porous ZnO nanorod (ZnO-FA). High surface area, uniformly distributed pores on its surface make the nanocarrier suitable for high drug loading (88%) of the anticancer drug doxorubicin (DOX). A pH triggered drug release was observed with minimum release in pathophysical conditions. In vitro efficacy of DOX loaded ZnO-FA (ZnO-FA-DOX) has been evaluated against breast cancer cells MDA-MB-231, which is not possible alone by DOX or ZnO-FA. Targeted scaffold with pendant –NH2 group has been covalently bonded with fluorescent dye (RITC) for cellular uptake and imaging studies in MDA-MB-231 cells; the possible pathway for cancer regression has also been evaluated. Even in vivo acute and intravenous toxicological evaluation on murine model system complemented biocompatibility of ZnO-FA in TDD. All together we have collaged a template free synthesis of porous ZnO nanorod, successful targeting on to cancer cells, high drug loading, pH triggered drug release, in vitro efficacy of ZnO-FA-DOX against MDA-MB-231 cells and in vivo compatibility as well. We envisioned the future prospect of porous ZnO nanostructures in TDD.

Extremely thin absorber solar cells based on nanostructured semiconductors

Extremely thin absorber (eta) solar cells aim to combine the advantages of using very thin, easily and cheaply produced absorber layers on nanostructured substrates with the stability of all-solid-state solar cells using inorganic absorber layers. The concept of using nanostructured substrates originated from the dye-sensitised solar cell, where having a very high surface area allows the use of very thin layers of dye while still absorbing sufficient sunlight. However, both the dye and liquid electrolyte used in these devices demonstrated poor stability, and efforts were made to replace them with very thin inorganic absorber layers and solid state hole collectors respectively. The combination of these concepts – a nanostructured substrate coated with a very thin inorganic absorber and completed with a solid state hole collector – is known as an eta solar cell. This review summarises the development of both the inorganic absorbers and solid state hole collectors in porous TiO2 and ZnO nanorod based cells, focusing on the material properties and growth/deposition methods. Future possibilities for eta solar cells are discussed, including utilisation of a wider range of materials, synthesis methods and novel materials such as quantum dots to produce tuned band gap and multijunction solar cells.