Zinc Oxide Nanoflowers Research Articles

Controllable synthesis of ZnO nanoflowers with structure-dependent photocatalytic activity

Abstract Zinc oxide (ZnO) nanomaterials are functional photocatalysts that show excellent photocatalytic activity, among which diverse morphologies, such as nanospheres, nanorods, nanoleaves, nanodisks, or nanoflowers, often possess different photocatalytic activities. In this study, we employed a simple ultrasonic treatment to controllably synthesize three types of three-dimensional (3D) fluffy ZnO nanoflowers with different nanostructures. Specifically, one nanoflower with smooth edges was formed via direct hydrothermal reaction without ultrasonic treatment (denoted as ZnO-0), and the other two with different jagged margins were obtained by ultrasonic treatment at 250 W and 950 W, respectively, before the hydrothermal procedure (denoted as ZnO-250 and ZnO-950). The results showed that the size, specific surface area, crystallite dimension, intrinsic donor defects and the signals of reactive radicals of ZnO nanoflowers all decreased with increasing ultrasonic intensity. Furthermore, the photocatalytic performance of such ZnO nanoflowers with similar morphologies but different nanostructures was investigated using methyl orange (MO) as a model pollutant. As expected, ZnO-0 possessed the highest photocatalytic activity with a kinetic constant of 0.0478 min−1, while the value decreased to 0.0251 min−1 and 0.013 min−1 for ZnO-250 and ZnO-950 under simulated sunlight irradiation, respectively, suggesting that the photocatalytic efficiency of ZnO nanoflowers decreased due to the ultrasonic treatment. These findings provide structural insight into the photocatalytic activity of ZnO nanoflowers.

Fabrication of a thermal responsive hemoglobin (Hb) biosensor via Hb-catalyzed eATRP on the surface of ZnO nanoflowers

A new kind of thermal responsive protein imprinted polymers (TPIPs) was prepared for the electrochemical biosensor. The TPIPs were synthesized on the surface of zinc oxide (ZnO) nanoflowers via electrochemically mediated atom transfer radical polymerization (eATRP), with bovine hemoglobin (Hb) as both catalyst and template. N-isopropyl acrylamide (NIPAM) and methacrylic acid (MAA) were used as temperature sensitive and assistant functional monomer, respectively. The biosensor fabricated by TPIPs and ZnO was successfully used for detecting Hb by differential pulse voltammetry (DPV). Under suitable conditions, the detection range of Hb was from 1.0 × 10−13 to 1.0 × 10−1 mg·L−1 with a low detection limit of 3.1 × 10−14 mg·L−1 (S/N = 3). This biosensor was used for detecting bovine hemoglobin in real samples with the recoveries of 95–105%. The good temperature response, good selectivity and repeatability allowed the TPIPs to be a great importance for the polymer-modified electrodes and the sensitive detection of Hb.

Development and Optical Properties of ZnO Nanoflowers on Porous Silicon for Photovoltaic Applications

In the present work, a comparison between zinc oxide (ZnO) nanoflowers and nanorods for photovoltaic applications is presented. Using chemical bath deposition technique, ZnO nanoflowers were grown on porous silicon (PS) while ZnO nanorods were deposited on flat Si substrate. The morphology of ZnO/PS sample indicated the formation of nanoflowers by accumulation of ZnO nanorods on PS walls. The structural studies indicated that ZnO nanoflowers experienced a stress relief compared to ZnO nanorods which was due to the role of porous substrate for accommodating the lattice strain in order to obtain the subsequent ZnO nanoflowers with reduced strain. The optical results obtained from ZnO nanoflowers showed more intense photoluminescence and Raman peaks compared with nanorods. It was due to the higher specific surface area of nanoflowers which led to a higher absorption coefficient and increased the generation of electron–hole pairs in this sample. Due to their elevated specific surface area, ZnO nanoflowers can capture the incident light and reduce the reflection coefficient of silicon substrates. Thus, they can be considered as an effective antireflective layer to improve the efficiency of solar cells. The optoelectrical results showed an improvement in the efficiency of fabricated solar cells by use of ZnO nanoflowers on PS structures when compared to the conventional ones possessing ZnO nanorods on flat silicon substrates. Development of ZnO nanoflowers on PS substrates can further extend the applications of ZnO nanostructures in photovoltaic devices.

Sonication Assisted Hierarchical Decoration of Ag-NP on Zinc Oxide Nanoflower Impregnated Eggshell Membrane: Evaluation of Antibacterial Activity and in Vitro Cytocompatibility

Metal/metal oxide nanoparticles have long been used as an antibacterial substitute, but fabrication of an effective carrier or delivery matrix for achieving a sustain release profile with high bact...

A novel electrochemical sensor for determination of DNA damage biomarker (8-hydroxy-2'-deoxyguanosine) in urine using sonochemically derived graphene oxide sheets covered zinc oxide flower modified electrode.

To explore a novel and multi-layer based graphene oxide covered zinc oxide nanoflower (ZnO NFs@GOS) as a modified electrode materials by sonochemical technique (40 kHz, 300 W). Herein, novel nanocomposite is successfully characterized by various characterization analysis (FESEM, HRTEM, XRD, XPS and (EIS) electrochemical impedance spectroscopy) and employed as high sensitive modified electrode (ZnO NFs@GOS nanocomposite) for the electrochemical determination of biomarker. 8-hydroxy-2'-deoxyguanosine (8-HDG) is one of the important cancer and oxidative stress biomarker. The results demonstrated that the ZnO NFs@GOS modified SPCE reveal well-defined electro-oxidation peak at 0.36 V (vs. Ag/AgCl). The high sensitive properties of the optimized flower like modified electrode are because of the excellent synergistic effect of the ZnO flower and the graphene oxide nanosheets, as evidenced by a superior bio-sensing performance. The nanocomposite fabricated modified biosensor was facilitating the analysis of 8-HDG in the concentration ranges of 0.05-536.5 µM with a low detection limit is 8.67 nM. The ZnO NFs@GOS modified sensor can also employed for the determination of 8-HDG in human urine samples, promising its application towards the quantification of cancer biomarker in biological samples.

Layer by Layer Assembly of Zinc Oxide Nanotubes and Nanoflowers as Catalyst for Separate and Simultaneous Catalytic Degradation of Dyes and Fuel Additive

AbstractZinc oxide nanotubes and nanoflowers are synthesized using urea as template through hydrothermal technique. XRD confirmed that product is consists of zinc and oxygen atoms forming a hexagonal crystal system with ZnO chemical formula. SEM showed that tubes and flower like particles are formed. ATR‐IR confirmed the presence of Zn−O bond as a functional group. UV‐VIS spectroscopic analysis exhibits that product has a band gap energy of 3.49 eV. Synthesized product due to its outstanding properties such as wide band gap semiconductor and large surface area to volume ratio is used as a catalyst for individual and simultaneous catalytic degradation of methylene blue (MB) and Congo red (CR) dyes. The apparent rate constant (kapp) value of individual and simultaneous catalytic degradation of CR dye is decreased with increase in catalyst dosage while kapp value of individual and simultaneous catalytic degradation of MB dye is increased with increase in catalyst dosage. The synthesized product is found more active towards CR dye as compared to MB dye. Small size and high surface area to volume ratio of product also make it a desirable additive for enhancing the efficiency of diesel fuel. Results obtained from fuel additive activity show that as the concentration of nanoadditive is increased from 20, 40, 60, 80 and 100 ppm the calorific value is increased which indicates the enhanced efficiency of fuel due to additive.

Hierarchically porous Zr-MOFs labelled methylene blue as signal tags for electrochemical patulin aptasensor based on ZnO nano flower

In this work, the feasibility of a novel sensitive electrochemistry aptasensor for the detection of patulin (PAT) using hierarchically porous metal organic framework@methylene blue connection aptamer as signal tags was demonstrated. The substrate electrode of the aptasensor was prepared by electrodeposited gold nanoparticles (AuNPs) on chitosan-zinc oxide nano flower-modified electrode. Subsequently, the complementary single-stranded DNA was attached to the surface of the modified electrode by Au-S bond. Signal tags self-assemble on the surface of modified electrodes by aptamer-cDNA binding, while methylene blue as mediator for electrochemical detection. Thanks to the large specific surface area provided by zinc oxide nano flower, the electrode can load more signal tags and AuNPs to achieve signal amplification. In presence of PAT, Apt preferentially binds to PAT, causing dissociation of some Apt-cDNA and releasing some signal tags leading, resulting in decreased electrical signals. Under optimal conditions, the change in electrochemical signal was proportional to the logarithm of PAT concentration, from 5 × 10−8-5 × 10-1 μg mL−1, and the detection limit was estimated to be 1.46 × 10-8 μg mL-1. The aptasensor exhibited aceptable reproducibility, renewability, long-term stability and specificity. Moreover, aptasensor was reliable in determination of PAT in spiked apple juice samples.

Zinc oxide/vanadium pentoxide heterostructures with enhanced day-night antibacterial activities

Low photocatalytic efficiency of visible light and fast recombination of photo-generated carriers are two challenges facing the applications of photocatalyst sterilant zinc oxide (ZnO). Meanwhile, both light and dark photocatalytic activities are important. It is of great theoretical and practical significance to construct a day-night photocatalytic antibacterial material, which is beneficial to the effective use of energy and to tackle the limitation of using photocatalytic bacteriostat. ZnO nanoflowers decorated vanadium pentoxide (V2O5) nanowires heterojunction (ZVH) was firstly fabricated using a facile water-bathing method. The designed ZVH structure efficiently produced abundant reactive oxygen species (ROS) in both light and darkness. It yielded 99.8% and 99.0% of antibacterial rate against S. aureus due to oxidative stress induced by ROS in light and darkness, respectively. The generation of ROS played a major role in the antibacterial activities against S. aureus under both light and dark conditions. The prepared ZVH with improved antibacterial properties provides an alternative for day-night antibacterial agents.

Graphene oxide decorated with zinc oxide nanoflower, silver and titanium dioxide nanoparticles: fabrication, characterization, DNA interaction, and antibacterial activity.

The fabrication, characterization, and antibacterial activity of novel nanocomposites based on graphene oxide (GO) nanosheets decorated with silver, titanium dioxide nanoparticles, and zinc oxide nanoflowers were examined. The fabricated nanocomposites were characterized by various techniques including X-ray diffraction, ultraviolet-visible light absorption and fluorescence spectroscopy, Brunauer–Emmett–Teller theory analysis, Fourier transform infrared, and scanning electron microscopy. The antibacterial activity of the GO–metal oxide nanocomposites against two Gram-positive and two Gram-negative bacteria was examined by using the standard counting plate methodology. The results showed that the fabricated nanocomposites on the surface of GO could inhibit the growth of microbial adhered cells, and consequently prevent the process of biofilm formation in food packaging and medical devices. To confirm the antibacterial activity of the examined GO-nanocomposites, we examined their interactions with bovine serum albumin (BSA) and circulating tumor DNA (ctDNA) by steady-state fluorescence spectroscopy. Upon addition of different amounts of fabricated GO-nanocomposites, the fluorescence intensities of the singlet states of BSA and ctDNA were considerably quenched. The higher quenching was observed in the case of GO–Ag–TiO2@ZnO nanocomposite compared with other control composites.

Sunlight driven highly efficient degradation of methylene blue by CuO-ZnO nanoflowers

Highly efficient photocatalysis of methylene blue dye has been demonstrated using hierarchical copper oxide and zinc oxide (CuO-ZnO) nanoflower like structure. The flower like nanostructures are obtained using polyethylene glycol and sodium citrate with facile single step hydrothermal method. The effect of different operating parameters viz. effect of OH− ion concentration, metal ion precursor and synthesis method on typical morphology of the CuO-ZnO product has been studied in detail. The synthesized samples were characterized by various techniques and were then used in sunlight driven degradation of methylene blue dye. The photocatalytic performance of selected CuO-ZnO product (sample CZ-01) demonstrated the best photocatalytic activity under sunlight irradiation with rate constant of approximately 0.099 min-1. The superior photocatalytic performance of CuO-ZnO was attributed to suppressed charge-carrier recombination. Methylene blue dye (100 mL of 100 ppm) was observed to be completely degraded in 30 min with CuO-ZnO (sample CZ-01) hierarchical nanostructure as catalyst.

High Sensitivity of NO Gas Sensors Based on Novel Ag-Doped ZnO Nanoflowers Enhanced with a UV Light-Emitting Diode.

An ultraviolet-enhanced (UV-enhanced) nitric oxide (NO) sensor based on silver-doped zinc oxide (ZnO) nanoflowers is developed using a low-cost hydrothermal method. The results indicate that silver (Ag) ions were doped into the ZnO nanostructure successfully, thus changing the morphology. In the high-resolution transmission electron microscopy images, we also found that some Ag ions were separated out onto the surface of the ZnO nanoflowers and that the Ag-doped and Ag nanoparticles improved the sensing property. The NO sensing property increased from 73.91 to 89.04% through the use of a UV light-emitting diode (UV-LED). The response time was approximately 120 s without the UV-LED, and the UV-enhanced Ag-doped ZnO nanoflower sensor exhibited a reduced response time (60 s). The best working temperature could be reduced from 200 to 150 °C using UV light illumination, and it was found that the NO response increased by 15.13% at 150 °C. The UV photoresponse of the Ag-doped ZnO nanoflowers and the mechanisms by which the improvement of NO sensing property occurred through the use of UV light illumination are discussed. The property of the gas sensor can be calibrated using a self-photoelectric effect under UV light illumination. These interesting UV-enhanced Ag-doped ZnO nanoflowers are viable candidates for practical applications.

Fabrication of three-dimensional zinc oxide nanoflowers for high-sensitivity fiber-optic ammonia gas sensors

ZnO is identified as one of the promising coating materials in optical fiber for ammonia gas sensors. In this work, three-dimensional ZnO nanoflowers are fabricated via a facile hydrothermal method and used as sensitive coating materials for optical fiber ammonia gas sensors. Results show that the sensor with ZnO nanoflowers exhibits a high sensitivity of 5.75 pm/(μg·L-1) for ammonia concentration ranging from 0 to 5460 μg·L-1, which is more than 2.6 times higher than that of the sensor with a coating of ZnO microspheres [2.2 pm/(μg·L-1)].

Reusable zinc oxide nanoflowers for the synthesis of α-aminophosphonates under solvent-free ultrasonication

A simple wet chemical method is used to prepare zinc oxide nanoflowers (ZnO NFs) which were subjected to various characterization techniques such as XRD, FTIR, UV–Vis, FE-SEM, and XPS. XRD pattern indicates pure, crystalline, and monodispersed form with hexagonal wurtzite phase. The 3-D flower shape morphology with hexagonal ZnO nanorods was confirmed in FE-SEM. The synthesized ZnO NFs was used to study catalytic behavior in Kabachnik–Fields reaction under controlled ultrasound cavitation technique. High surface-to-volume ratio of ZnO NFs and the effect of ultrasonication enhances the yield of α-aminophosphonate. The catalyst was recycled and reused four times without any significant loss of its catalytic activity. Moreover, existing method becomes attractive and practical due to its easy, clean, fast, cost-effective, and eco-friendly procedure.

Development and imaging of zinc oxide nanorods as a photosensitizer for the diagnosis and treatment of cancer using lasers11Web: www.nilop.edu.pk/faculty.html

A diversity of strategies is utilized for the diagnosis and treatment of cancer with limitations and side effects. Light-activated phototherapy with a suitable photosensitizer can provide a cancer cure at high specificity and tumor selectivity. The recent exposure of nanotechnology and nanoparticles in the field of medical science could assist cancer patients with light control in the presence of a suitable chemical. The cell death and tumor marker are directly related to the nanoparticles’ physiochemical composition, size, shape, self-fluorescence and activation upon suitable light excitation.In our experimental study, we demonstrated zinc oxide nanorods (ZnO NRs) as a photosensitizer and biomarker for cervical carcinoma cell line photodynamic therapy (PDT). The zinc oxide (ZnO) nanoparticles, nanoflowers and nanorods among other expensive nanoparticles have great potential in cancer therapy without toxicity and side effects. ZnO NRs have strong surface plasma resonance light absorption compared to nanoparticles and are a source of near-infrared light for deep tissue penetration. The ZnO NRs are synthesized with a hydrothermal method and characterized for their structural, physical, chemical, mechanical and optical properties. The x-ray diffraction pattern of the ZnO nanorods indicates sharp and strong diffraction peaks due to the crystalline structure with the diameter in the range of 80–120 nm and the mean diameter of 100 nm calculated through the Scherrer equation and confirmed by scanning electron microscopy using the ImageJ technique and Fourier transform infrared spectroscopy. The fluorescence and light activation of ZnO nanorods in cancer cells were determined through laser scanning confocal microscopy (LSCM) and fluorescence spectroscopy with excitation of 488 and 514 nm wavelength Ar + and He–Ne lasers. The surface profile at a fluorescence of 500–635 nm and 635–750 nm, a differential contrast image and combined LSCM image indicate fluorescence conformation, surface morphology and a diameter of 100–150 nm. The fluorescence of the ZnO NRs conjugated with the well-known PDT photosensitizer aminolevulinic acid was monitored for effective necrosis of the cancerous cells. The results indicate that ZnO NRs are active candidates for tumor narcosis under suitable light activation and are a biomarker in the diagnosis of malignant diseases.

Facile synthesis of Al-doping 1D ZnO nanoneedles by co-precipitation method for efficient removal of methylene blue

High quality and uniform Aluminum-doped zinc oxide (AZO) nanoflowers were successfully fabricated by co-precipitation method and de-ionized water was used as solvent in the whole fabrication process, which was in agreement with the development of green chemistry. The obtained one dimensional (1D) ZnO nanoneedles and AZO nanoflowers were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS), Photocurrent tests, which were conducive to know fully about crystal quality, the structure, surface composition and optical property of 1D ZnO nanoneedles and AZO nanoflowers. We not only synthesized 1D ZnO nanoneedles by adjusting the ratios of Zn 2+ and OH −, but also explored the effect of Al-doping and calcination temperature on the morphologies and performance of ZnO. The facile synthesis and environmentally-friendly method introduced by us is easy to control and industrialize. Moreover, there were no organic solvents, complexes and surfactants in the whole fabrication process, so it will exert a significant influence on the use of ZnO in the field of cosmetics and medical polymer materials. We investigated the photocurrent responses of ZnO and Al-doped ZnO and the photocatalytic activities of ZnO by degrading methylene blue (MB) solution. High quality 1D ZnO nanoneedles not only possess excellent photocatalytic activities, but also exhibit high photocatalytic stability and outstanding cycling stability.

High-Performance Flexible Piezoelectric-Assisted Triboelectric Hybrid Nanogenerator via Polydimethylsiloxane-Encapsulated Nanoflower-like ZnO Composite Films for Scavenging Energy from Daily Human Activities

We successfully synthesized flower-like zinc oxide (ZnO) nanoarchitectures by a chemical precipitation method which is a facile, cost-effective, low-temperature, and quick-synthesis process. Furthermore, these nanoarchitectures were used to design an MWCNT (multiwalled carbon nanotube)/ZnO/PDMS (polydimethylsiloxane) composite film-based hybrid nanogenerator (HNG). Here, the ZnO nanoflowers play an important role in enhancing the piezoelectric and triboelectric potentials of HNG, termed as piezoelectric-assisted triboelectric (PAT)-HNG. The ZnO nanoflowers were employed as the piezoelectric material as well as to enhance the surface roughness of PDMS, which can increase the triboelectric performance. Besides, the MWCNTs were also utilized to evenly distribute the ZnO nanoflowers and also to reduce the internal resistance of PAT-HNG. To maximize the electrical output power of the device, the concentration of ZnO and the amount of MWCNTs were changed and the electrical output performance of PAT-HNG was inve...

Annealing Temperature Dependence of ZnO Nanostructures Grown by Facile Chemical Bath Deposition for EGFET pH Sensors

Zinc Oxide (ZnO) nanostructures were deposited using chemical bath deposition (CBD) technique in water bath at 95 °C for 4 h. Post-deposition heat treatment in air ambient at various temperature ranging from 200-600 °C for 30 min was applied in order to enhance the electrical properties of ZnO nanostructures as the sensing membrane of extended-gate field effect transistor (EGFET) pH sensor. The as-deposited sample was prepared for comparison. The samples were characterized in terms of physical and sensing properties. FESEM images showed that scattered ZnO nanorods were formed for the as-deposited sample, and the morphology of the ZnO nanorods changed to ZnO nanoflowers when the heat treatment was applied from 200-600 °C. For sensing properties, the samples heated at 300 °C showed the higher sensitivity which was 39.9 mV/pH with the linearity of 0.9792. The sensing properties was increased with the increasing annealing treatment temperature up to 300 °C before decreased drastically.

Shape-controlled synthesis of three-dimensional zinc oxide nanoflowers for disinfection of food pathogens

The antibacterial activity of zinc oxide (ZnO) nanoflowers has been investigated and presented in this article. Classic three-dimensional nanoflowers have been prepared by hydrothermal method using zinc acetate dihydrate Zn(CH3COO)2·2H2O as the sole precursor. The X-ray diffraction and Fourier transform infrared spectra confirm the formation of ZnO crystals. Consequently, on the basis of morphological and chemical observations, the chemical reaction mechanism of ZnO nanoflowers was also proposed. Antibacterial activity was carried out against food-borne pathogen, Escherichia coli, which is ubiquitous in distribution among food-laden wastes. The experimental procedures for the antibacterial test included a spectroscopic method with different concentrations (5-20 μg/mL) of ZnO nanoflowers to unearth the minimum inhibitory concentration. Our investigation suggests that the lowest concentration of ZnO nanoflower solution that can hamper the growth of this microbial strain was 5 μg/mL.

Micropatternable Double-Faced ZnO Nanoflowers for Flexible Gas Sensor.

Micropatternable double-faced (DF) zinc oxide (ZnO) nanoflowers (NFs) for flexible gas sensors have been successfully fabricated on a polyimide (PI) substrate with single-walled carbon nanotubes (SWCNTs) as electrode. The fabricated sensor comprises ZnO nanoshells laid out on a PI substrate at regular intervals, on which ZnO nanorods (NRs) were grown in- and outside the shells to maximize the surface area and form a connected network. This three-dimensional network structure possesses multiple gas diffusion channels and the micropatterned island structure allows the stability of the flexible devices to be enhanced by dispersing the strain into the empty spaces of the substrate. Moreover, the micropatterning technique on a flexible substrate enables highly integrated nanodevices to be fabricated. The SWCNTs were chosen as the electrode for their flexibility and the Schottky barrier they form with ZnO, improving the sensing performance. The devices exhibited high selectivity toward NO2 as well as outstanding sensing characteristics with a stable response of 218.1, fast rising and decay times of 25.0 and 14.1 s, respectively, and percent recovery greater than 98% upon NO2 exposure. The superior sensing properties arose from a combination of high surface area, numerous active junction points, donor point defects in the ZnO NRs, and the use of the SWCNT electrode. Furthermore, the DF-ZnO NF gas sensor showed sustainable mechanical stability. Despite the physical degradation observed, the devices still demonstrated outstanding sensing characteristics after 10 000 bending cycles at a curvature radius of 5 mm.

Growth of Zinc Oxide Nanorod and Nanoflower Structures by Facile Treatment of Zinc Thin Films in Boiling De-Ionized Water

In this work, zinc oxide nanostructured films were developed by a facile treatment of the sputter deposited zinc thin films in boiling de-ionized water. Arrays of zinc oxide nanostructures with rod and flower-like shapes were obtained by changing the boiling water treatment time and manipulating the thickness of zinc film. Results of the scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, ultraviolet-visible-near infrared spectroscopy, and photoluminescence techniques indicate that the obtained nanostructures are crystallized stoichiometric zinc oxide. Zinc oxide nanorods and nanoflowers start to form on the surface and progress across the zinc film’s thickness as a function of treatment time in boiling de-ionized water, which allow a controllable method of fabricating semiconducting/metal multilayer coatings. The obtained nanostructured films showed different optical properties depending on starting zinc film’s thickness and boiling water treatment time. In addition, photoluminescence analysis showed that the nanostructured films possess a major energy band gap of 3.28 eV along with two other secondary defects-related energy band gaps of 2.27 and 1.67 eV.