ZnO Nanoflowers Research Articles

Synthesis of super-hydrophobic CuO/ZnO layered composite nano-photocatalyst

The introduction of super-hydrophobicity into the field of photocatalysis has attracted the attention of many researchers nowadays. Here, CuO nanowires were synthesized via thermal oxidation method. The flower-like ZnO nanostructures were self-assembled with CuO nanowires by hydrothermal growth method. The functionalized super-hydrophobic CuO/ZnO layered composite nano-photocatalyst was obtained though polydimethylsiloxane (PDMS) grafting. We analyzed the effects of zinc sources, hydrothermal reaction time, solution concentration and surfactant concentration on the properties of the composite nano-photocatalyst. FESEM micrographs revealed CuO/ZnO layered composite nanostructures, which were composed of CuO nanowires with uniform morphology and carnation-like ZnO nanoflowers. XRD spectrum showed CuO/ZnO layered composite nano-photocatalyst possessed pure CuO phase and the wurtzite structure of ZnO. UV–vis spectrum manifested that the composite nanostructures had desired light absorption for ultraviolet light band and the contact angle (CA) results confirmed the successful modification of super-hydrophobic functionalization. After the modification of PDMS, the CuO/ZnO layered composite nano-photocatalyst prepared with the optimal conditions shows desired photocatalytic properties and super-hydrophobicity. The stable super-hydrophobic property after photocatalytic degradation is expected to improve self-cleaning and broaden the application field of photocatalyst.

Annealing temperature-dependent morphology and structure of ZnO nanoflowers for high-sensitivity ultraviolet photodetectors

Annealing temperature-dependent morphology and structure of ZnO nanoflowers for high-sensitivity ultraviolet photodetectors

ZnO nanoflower based electrochemical sensor for the selective determination of venlafaxine

ZnO nanoflower based electrochemical sensor for the selective determination of venlafaxine

A new method for synthesis of ZnO flower-like nanostructures and their photocatalytic performance

ZnO flower-like nanostructures have been successfully synthesized by a new and facile hydrothermal method. Their crystal structures and photocatalytic performance were also investigated. The amount of surfactant cetyltrimethyl ammonium bromide (CTAB) added to the precursor had an important effect on the ultimate morphology of the ZnO flower-like nanostructures. As the CTAB amount increased, the petals of the ZnO nanoflowers architecture changed from nanorods to nanosheets. In addition, for the nanoflowers assembled by nanosheets, the thickness of nanosheet can be controlled by adjusting the CTAB amount. The plausible growth mechanisms of the ZnO flower-like nanostructures were proposed. Furthermore, the nanosheets-assembled nanoflowers exhibited better photocatalytic performance than the nanorods-assembled nanoflowers toward Rhodamine B owning to their larger specific area and more OH groups absorbed on the nanosheet surface.

Growth of ZnO Nanoflower Arrays on a Patterned Sapphire Substrate

In this study, we investigated a novel technology to grow the ZnO nanoflower arrays on a patterned sapphire substrate using hydrothermal method. The process to prepare the substrate and grow ZnO nanoflower arrays were that the patterned concave sapphire substrates were cleaned using acetone, isopropyl alcohol, and D.I. water in an ultrasonic cleaner. Al sacrificial layer with the thickness of 600 nm was deposited using a thermal evaporation technology. The sol-gel process was used to deposit the ZnO seed layer on the patterned concave sapphire substrates, and then the ZnO seed layer was annealed at 500°C in Ar ambient for 1 h. The optical grade silicone A-B glue was coated on the ZnO seed layer and then the mixed solution of K3Fe(CN)6 : KOH : H2O = 10 g : 1 g : 100 ml was used to etch the sacrificial Al layer. (f) A lift-off technology was used to move the ZnO seed layer/silicone A-B glue to silicon substrate. Finally, a hydrothermal method was used to grow the ZnO nanorods on the ZnO seed layer/silicone A-B glue/silicon substrate at 90oC with the different durations of 10 to 60 min. Focused ion beam system (FIB) was used to observe the cross sectional morphology of patterned ZnO seed layer. The crystal structural of the flower-like ZnO nanostructures was analyzed using X-ray diffraction (XRD) pattern, the morphological of the flower-like ZnO nanostructures was observed using FIB and field emission scanning electron microscope (FESEM). Also, the optical properties of the flower-like ZnO nanostructures were investigated.

High-Sensitivity Enzymatic Glucose Sensor Based on ZnO Urchin-like Nanostructure Modified with Fe3O4 Magnetic Particles.

A novel and efficient enzymatic glucose sensor was fabricated based on Fe3O4 magnetic nanoparticles (Fe3O4MNPs)-modified urchin-like ZnO nanoflowers (ZnONFs). ZnONFs were hydrothermally synthesizing on a flexible PET substrate. Fe3O4MNPs were deposited on the surface of the ZnONFs by the drop-coating process. The results showed that the urchin-like ZnONFs provided strong support for enzyme adsorption. For Fe3O4MNPs, it significantly promoted the redox electron transfer from the active center of GOx to the ZnO nanoflowers beneath. More importantly, it promoted the hydrolysis of H2O2, the intermediate product of glucose catalytic reaction, and thus improved the electron yield. The sensitivity of the Nafion/GOx/Fe3O4MNPs/ZnONFs/Au/PET sensor was up to 4.52 μA·mM−1·cm−2, which was improved by 7.93 times more than the Nafion/GOx/ZnONFs/Au/PET sensors (0.57 μA·mM−1·cm−2). The detection limit and linear range were also improved. Additionally, the as-fabricated glucose sensors show strong anti-interference performance in the test environment containing organic compounds (such as urea, uric acid, and ascorbic acid) and inorganic salt (for instance, NaCl and KCl). The glucose sensor’s service life was evaluated, and it can still maintain about 80% detection performance when it was reused about 20 times. Compared with other existing sensors, the as-fabricated glucose sensor exhibits an ultrahigh sensitivity and wide detection range. In addition, the introduction of Fe3O4MNPs optimized the catalytic efficiency from the perspective of the reaction mechanism and provided potential ideas for improving the performance of other enzymatic biosensors.

Eliminating pesticide quinalphos from surface waters using synthesized GO-ZnO nanoflowers: Characterization, degradation pathways and kinetic study

The presence of highly toxic and persistent pesticides in water bodies causes serious problems to human beings as well as aquatic life. Quinalphos is one such widely used organophosphorus pesticide in agricultural fields. Herein, for degradation and mineralization of quinalphos, ZnO nanoflowers and their hybrid nanocomposite with graphene oxide have been synthesized. FESEM analysis confirmed the formation of ZnO nanoflowers over nanosheets of graphene oxide having a thickness of 20 ± 10 nm. GO-ZnO composite exhibited remarkable photocatalytic activity in comparison to pure ZnO. 98 % degradation of quinalphos was achieved using GO-ZnO nano-catalyst at 6 pH within 45 min of irradiations, whereas it was 80 % for bare ZnO nanoflowers. Higher degradation with hybrid nanocomposite was attributed to improved surface area (36 m2 g−1), a substantial reduction in bandgap energy from 3.10 to 2.90 eV and enhanced charge separation (e−/h+ pairs) after the addition of GO. Reaction kinetics study followed pseudo-first-order behaviour. Further, mineralization to the extent of 90 % in 90 min was confirmed by TOC analysis. Based on identified intermediates, using LCMS analysis, degradation pathways were proposed. The plausible pathways confirmed the presence of smaller and safer reaction intermediates supported by excitation of e− from nanocomposite followed by oxidation of quinalphos with huge free radicals. Overall, this study is significant in terms of using photocatalysis as a tertiary treatment of quinalphos pesticide wastewater at pH 6 in a short duration.

Highly Sensitive and Selective Eco-Toxic 4-Nitrophenol Chemical Sensor Based on Ag-Doped ZnO Nanoflowers Decorated with Nanosheets.

Herein, we have developed a novel sensing electrode to detect the eco-toxic 4-nitrophenol (4-NP). Ag-doped-ZnO nanoflowers were synthesized by facile hydrothermal method and examined by several characterization techniques in order to understand the morphology, crystal structure, composition, and surface properties. Morphological results were confirmed by the formation of Ag-doped ZnO nanoflowers decorated with nanosheets. Ag-doped ZnO/glassy carbon electrode (GCE) electrode-material-matrix was used for electrochemical sensing of toxic 4-NP. Under optimized conditions, Ag-doped ZnO/GCE modified electrode exhibits high-sensitivity and selectivity compared to the bare GCE electrode. The Ag-doped ZnO/GCE modified electrode exhibits high electrocatalytic oxidation towards 4-NP. Anodic peak current of 4-NP is increased linearly by increasing the concentration of nitrophenol. Additionally, Ag-doped ZnO/GCE shows a wide range of sensitivity from 10 µM to 500 µM, and a linear calibration plot with a good detection limit of 3 µM (S/N = 3). The proposed Ag-doped ZnO/GCE modified electrode showed high sensing stability. In addition, the oxidation mechanism was studied. The obtained results revealed that the Ag-ZnO/GCE electrode could be the promising sensing electrode for 4-NP sensing.

Metal‐organic frameworks derived ZnO@MOF@PZS flame retardant for reducing fire hazards of polyurea nanocomposites

Transition metal as flame retardant has attracted intense interests in recent years. In this work, ZnO@MOF@PZS was prepared via hydrothermal and polycondensation methods. ZnO nanoflowers played the role as a template for growth of MOF@PZS and zinc source for formation of MOF. Subsequently, the obtained ZnO@MOF@PZS was mixed into polyurea (PUA) to investigate its flame retardancy and toxicity suppression properties. The cone calorimeter test (CCT) showed that ZnO@MOF@PZS significantly improved the flame retardancy of PUA composites. The addition of 3 wt% ZnO@MOF@PZS into PUA could result in peak heat release rate (PHRR), total heat release (THR) and total CO production (TCO) of 28.30%, 19.59% and 36.65%, respectively. The result of universal testing machine showed that ZnO@MOF@PZS‐add PUA had better mechanical properties. It is notable that the improved flame retardant properties for PUA composites are mainly attributed to ZnO@MOF@PZS promoting the formation of dense char residue.

Self-assembled and highly faceted growth of Mo and V doped ZnO nanoflowers for high-performance supercapacitors

The rational design of metal ion-doped transition metal oxides has been considered as a novel electrode material for the development of high-performance asymmetric supercapacitors (ASCs). Herein, we facilely synthesized molybdenum and vanadium doped zinc oxide (Mo- and V-doped ZnO) lotus flower-like hierarchical structures using the co-precipitation method for use as a high capacity cathode material for ASCs. The formation mechanism during the self-assembly growth and highly faceted Mo- and V-doped ZnO lotus flowers were examined. Utilizing the beneficial properties of high electrochemical conductivity and excellent electroactive area, Mo- and V-doped ZnO lotus flowers demonstrated maximum specific capacities of 336 C g−1 and 362 C g−1 with good cycling stability. Furthermore, the ASC has been fabricated with V-doped ZnO as a cathode and activated carbon as a negative electrode, which shows a high specific capacitance of 111 F g−1, an energy density of 32.4 Wh kg−1, and a power density of 5.16 kW kg−1, respectively. The fabricated device also demonstrated excellent electrochemical capacitance retention of 85% and Coulombic efficiency of 98% after 2000 cycles. These superior characteristics indicate the promising potentiality of the new materials reporting for low-cost and high-performance supercapacitors.

RETRACTED: Rapid one-pot synthesis of Ag-decorated ZnO nanoflowers for photocatalytic degradation of tetracycline and product analysis by LC/APCI-MS and direct probe ESI-MS

A high potential nanostructure photocatalyst, Ag-decorated ZnO nanoflowers (Ag/ZnO NFs), was synthesized by a rapid one-pot surfactant-free microwave-assisted aqueous solution method. The morphology, structure, and optical property of Ag/ZnO were well-characterized. The method qualifies to be energy conserving and environment friendly. The size of the flower petals ranges from 200 to 250 nm and highly dispersed Ag nanoparticles (NPs) with dimensions ranging from 10 to 30 nm were anchored onto the surface of them. The as-prepared Ag/ZnO demonstrated enhanced photocatalytic performance in eliminating tetracycline (TC) aqueous solution under the illumination of visible light. The Ag/ZnO exhibited 100% degradation efficiency within 30 min. The effect of operating parameters such as pH, catalyst dose, and TC concentration was investigated. The reaction byproducts were identified by LC/APCI-MS (liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry) and ESI-MSn (electrospray ionization tandem mass spectrometry) analysis and a pathway was proposed as well. Kinetic studies indicated that the photodegradation process follows pseudo-first-order kinetics. The enhanced photocatalytic activity was due to the special architecture, the suppression of electron/hole (e–/h+) pair recombination, and the acceleration of surface charge transfer induced by the highly dispersive Ag NPs, which was further demonstrated by the cyclic voltammetry measurement.

Phyto-reflexive Zinc Oxide Nano-Flowers synthesis: An advanced photocatalytic degradation and infectious therapy

Combating the limitations of chemical approach, a Phyto-reflexive surface decorated ZnO nanoparticles were synthesis for enhanced activity against resistant infectious agent and toxic dyes. Flower-like ZnO nanostructure with average size of 30 nm and 25 nm using chemical method and Phyto-synthesised respectively. Prepared ZnO nano-flowers have been characterised by UV (UV–visible spectrometry), XRD (X-ray Diffraction), TEM (Transmission Electron Microscopy), HRTEM (High Resolution Transmission Electron Microscopy) and EDS (Energy Dispersive X-ray Spectroscopy). Anti-bacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa , exhibited 78%, 88% inhibition for chemical prepared ZnO NFs and Phyto-reflexive surface modified ZnO NFs exhibited 85%, 94% compared to Ciprofloxacin. MIC (Minimum Inhibitory Concentration) values against S. aureus and P. aeruginosa of biological ZnO NFs, were calculated as 62.5 and 125 ug/ml and 125 and 250 ug/ml for chemically synthesized ZnO NFs respectively. Anti-fungal activity against Aspergillus niger and Candida Albicans showed 78%, 80% activity with chemically ZnO NFs and 91%, 100% inhibition with biologically ZnO NFs. Anti-oxidant potential determination revealed 56.5% and 67.8% activity at 50 mg/mL with chemical and biological ZnO NF respectively. Furthermore, Degradation of methylene blue (MB) using ZnO NFs up to 78% using chemically prepared and 90% using Phyto-reflexive ZnO NFs. Thus, the comparative analysis concluded, Phyto-reflexive surface modified synthesis of ZnO NFs improved infections activity against pathogens and photocatalytic activity for hazardous chemicals.

Oriented ZnO nanoflowers obtained after calcination of electrospinning poly(vinyl alcohol)/zinc oxide/zinc acetate composite mats

Recently, nanofibers have attracted attention from researchers worldwide because they can be applied in various fields. The obtaining of oriented ZnO nanoflowers from polyvinyl alcohol (PVA) at a concentration of 10 wt% loaded with ZnO nanoparticles and zinc acetate (Zn(OAc)2) at various concentrations by electrospinning was investigated. The molecular weight of PVA was determined to be approximately 63,547 g/mol. The effects of the Zn(OAc)2 concentration on the electrical conductivity of the polymer suspension and the morphological properties of the composite nanofibers were also determined. The electrical conductivity increased with increasing Zn(OAc)2 concentration as a consequence of greater availability of charge. Also, this is likely because the accumulation of particles might increase the charge, which would result in an increase in the average fiber diameter of the obtained electrospun product. Finally, FT-IR spectra indicated that ZnO and Zn(OAc)2 were merely suspended in the aqueous PVA solution without any chemical bonding of ZnO and Zn(OAc)2 with the PVA chains. They also indicated that PVA could be composed entirely of nanofibers and, simultaneously, Zn(OAc)2 could be converted to ZnO after calcination at 600 °C.

Synthesis, Characterization, and Photodegradation Activity of Fe3O4@ZnO Nanoflowers

Technological advancement nowadays is detrimental to the environment. To deal with such a problem, waste decomposition should be carried out to produce a clean and healthy environment. In this study, the photodegradation method was used because it has advantages in efficiency and stability. The material used as a photodegradation catalyst was Fe3O4@ZnO nanoflowers. The synthesis of Fe3O4@ZnO nanoflowers was carried out using coprecipitation method for Fe3O4 and precipitation for composites. The variations in the mass of the catalyst used in this study were 50, 100, and 150 mg. The samples were characterized using an X-Ray Diffractometer (XRD) to analyze the phase, size, and crystal structure, Scanning Electron Microscopy (SEM) to determine morphology, and a photodegradation test to measure the photodegradation activity. The grain sizes of Fe3O4 and ZnO nanoflowers based on the Scherrer equation were 12.12 nm and 32.29 nm, respectively. Based on SEM characterization, the morphology of Fe3O4@ZnO nanoflowers showed a flower-like structure with an average diameter of 3.2 µm. The best performance of phenol photodegradation activity is 54.3 % obtained in the first cycle of 150 mg Fe3O4@ZnO nanoflowers under solar irradiation.

CdO–ZnO nanorices for enhanced and selective formaldehyde gas sensing applications

This paper reports synthesis, properties and gas sensing applications of ZnO nanoflowers and CdO–ZnO nanorices prepared by hydrothermal process. The morphological characterizations confirmed the formation of well-defined nanoflowers and nanorices structures for ZnO and CdO–ZnO nanomaterials, respectively. The structural properties revealed the wurtzite hexagonal phase of the synthesized materials. The sensor devices based on ZnO nanoflowers and CdO–ZnO nanorices were fabricated and tested towards various gases including ethanol, methanol, ammonia, carbon monoxide, methane and formaldehyde. The fabricated gas sensor based on CdO–ZnO nanorices exhibited a high response (34.5) towards 300 ppm formaldehyde gas at 350 °C compared to ZnO nanoflowers (14.5) under the same experimental conditions. The response and recovery times for ZnO nanoflowers-based sensor were~9.8 s and ~6 s while for CdO–ZnO based sensor, these were ~10s and ~6s, respectively. A rapid response (34.5) for CdO–ZnO nanorices based formaldehyde gas sensor was observed as compared to other gases such as ammonia (12.3), methanol (16.5), ethanol (20), carbon monoxide (16.3) and methane (12.4), which confirm the high-selectivity towards formaldehyde gas. Finally, a plausible formaldehyde gas sensing mechanism is proposed.

Novel Platycladus orientalis–shaped Fe-doped ZnO hierarchical nanoflower decorated with Ag nanoparticles for photocatalytic application

The Ag/Fe-doped ZnO composites were designed by controllable intergration of the three strategies of hierarchical assembly, Fe doping, and Ag loading. The 3D Fe-doped ZnO hierarchical nanoflowers were firstly constructed with Platycladus orientalis–shaped petals via a hydrothermal method, and then Ag nanoparticles were anchored on the surface of Fe-doped ZnO nanoflowers through impregnation/reduction of silver nitrate solution. The samples were characterized by using XRD, SEM, TEM, HRTEM, XPS, Raman spectra, BET, UV–vis DRS, PL, EIS, Mott-Schottky plots, and photocurrent response. The results showed that Fe doping increased BET surface area and oxygen vacancies of ZnO, Ag loading produced the LSP absorption at ~530 nm, Fe doping and Ag loading together extended the visible light absorption and facilitated the separation of photogenerated carriers, which favors photocatalytic activity of ZnO. The maximum degradation efficiency of 92.3% for MO was achieved after visible light irradiation for 80 min when the feed atom ratio of Fe to Zn was 1.2% and Ag loading was 4 wt% of Fe-doped ZnO. Four cycle tests had little effect on the morphology and structure of Ag/Fe-doped ZnO, suggesting good cycling stability. The photocatalytic mechanism was elucidated based on the scavenger experiments and energy bands alignment.

Characterization and photocatalytic activity of ZnO nanoflowers synthesized using Bridelia retusa leaf extract

In the current work, the leaf extract of Bridelia retusa was used for the first time to synthesize zinc oxide nanoparticles (ZnONPs). A zinc nanoparticle-specific 364-nm peak was discerned via UV–Vis studies with a typical bandgap energy of 3.41 eV. FE-SEM micrographs revealed flower-shaped structure of the ZnONPs. EDS analysis corroborated the presence of zinc and oxygen. XRD spectrum established the wurtzite structure, sized at 11.06 nm. The mesoporous texture (4.89 nm) of the nanoparticles was deduced from BET analysis, proving a higher specific surface area than commercial ZnONPs. FTIR spectroscopy resulted in absorption bands typical for ZnONPs. Within a span of 165 min, under solar irradiation, the ZnONPs facilitated the photocatalytic degradation of Rhodamine B dye upto 94.74%. Exhibiting pseudo-first-order kinetics, the process had a degradation constant of 0.0109 min−1. It was concluded that numerous factors led to the high degradation efficiency. High values of bandgap energy and specific surface area, along with the mesoporous and crystalline nature of the ZnONPs led to the observed effect. The ZnONPs were also stabilized by the phytochemicals in the B. retusa leaves. The study is thus able to successfully demonstrate the huge potential in the field of environmental nanoremediation. The viability of using ZnONPs as solar photocatalysts for treating dye-laden industrial wastewater was thus attested.

Solvent assisted evolution and growth mechanism of zero to three dimensional ZnO nanostructures for dye sensitized solar cell applications

We report the structural engineering of ZnO nanostructures by a consistent solution method using distinct solvents such as ethylene glycol, 1-butanol, acetic acid and water. The growth kinetics are found to depend strongly on the physicochemical properties of the solvent and zeta potential of the colloidal solution. Furthermore, the resulting nanostructures as a photoanode material, displayed a prominent structure dependent property in determining the efficiency of dye-sensitized solar cells (DSSCs). The fabricated solar cell with ZnO nanostructures based photoanode exhibited improved conversion efficiency. Moreover, the nanoflower based DSSCs showed a higher conversion efficiency of 4.1% compared to the other structures. The excellent performance of ZnO nanoflower is attributed to its better light-harvesting ability and increased resistance to charge-recombination. Therefore ZnO nanostructures can be a promising alternative for TiO2 in DSSCs. These findings provide new insight into the simple, low cost and consistent synthetic strategies for ZnO nanostructures and its outstanding performance as a photoanode material in DSSCs.

Enhancing the Ultraviolet Photocurrent and Response Speed of Zinc Oxide Nanoflowers using Surface Plasmons of Gold Nanoparticles and a Graphene Membrane

The enhancement effect of the plasmonic resonance of AuNPs and a graphene membrane on the optoelectronic properties of ZnO nanoflowers is investigated. A layered structure is fabricated, consisting of ZnO nanoflowers grown on a conductive fluorine‐doped tin oxide (FTO) glass substrate, decorated with gold nanoparticles, and covered by a multilayer graphene membrane. An excellent photocurrent response as high as 1650 A W−1 and a millisecond level response time are achieved. Compared with the pristine ZnO device, which has a responsivity of 2.98 A W−1 and a response time of tens of seconds, the photocurrent response is dramatically increased by 500‐fold and the response time is decreased by over 1000‐fold. The significant enhancement of the photocurrent can be attributed to the coupling of plasmonic resonance modes of AuNPs and the graphene membrane, according to finite‐difference time‐domain simulation results; whereas the tremendous improvement on response time can be attributed to the high electron mobility of graphene. The work is essential for further study of the plasmonic enhancement of ZnO optoelectronic performance and provides a new path for the fabrication of ZnO‐based high‐responsivity, high‐speed, and low‐cost ultraviolet emission and detection devices.

Electrochemical non-enzymatic biosensor for tyramine detection in food based on silver-substituted ZnO nano-flower modified glassy carbon electrode

Electrochemical non-enzymatic biosensor for tyramine detection in food based on silver-substituted ZnO nano-flower modified glassy carbon electrode