3D Flower-like ZnO Research Articles

Hydrothermal synthesis and characterization of Ag2O/CeO2 modified 3D flower-like ZnO as the N-butanol-sensing

In this work, Ag2O/CeO2 modified 3D flower-like ZnO have been synthesized by a novel SDBS−PEG assisted hydrothermal route and the gas sensor fabricated from this material has prominent performance to n-butanol vapor. The 3D microporous ZnO flower-like structures with excellent adsorption property have been indicated by the images of field-emission electron microscopy (FESEM) and the analysis results of Brunauer-Emmett-Teller method (BET). The uniformly dispersed pure phase with high crystallinity existed has been verified by the X-ray diffraction (XRD) patterns combined with the Energy Dispersive Spectrometer (EDS) analysis. The X-ray photoelectron spectroscopy (XPS) further confirmed the co-existence of Ce3+/Ce4+, Ag/Ag+. Meanwhile, the gas sensor of the Ag2O/CeO2 modified ZnO (3 at% Ce, 1 at% Ag) showed the highest response to n-butanol of 100 ppm is 254 at 160 °C. It also exhibits good repeatability and satisfactory selectivity to target gases at 160 °C during gas sensing test. Even more importantly, a particular synergistic enhancement mechanism of Ag2O/CeO2 modified ZnO as the n-butanol-sensing has been explained. Employing SDBS/PEG micelles as structure-directing agent, the process of assembling 2D nanosheets into the 3D microporous ZnO flower-like structures has been discussed.

NO2 sensing properties of 3D flower-like ZnO nanostructure decorated with thin porous petals synthesized using a simple sol–gel drop-casting method

A three-dimensional flower-like ZnO nanostructured film decorated with the thin porous ‘petals’ is synthesized using an inexpensive sol–gel drop-casting method, and the NO2 detection characteristics of the nanostructured film are studied. The gas-sensing study shows higher sensitivity with selectivity toward NO2 gas, exhibiting good reproducibility and stability. The as-synthesized nanostructured 3D flower-like ZnO film shows excellent NO2 sensing performance, with a maximum gas response of 23.3 for 100 ppm NO2 gas at an operating temperature of 180 °C. A detailed gas-sensing study reveals that the enormous porous petals with various inter-connected pores fused on the flower-like ZnO nanostructure improve the adsorption of gas molecules; consequently, the synthesized ZnO nanostructure exhibits a superior level of NO2 gas-sensing activity. This study provides a promising path towards the development of a highly sensitive NO2 gas sensor and an easy way to fabricate the 3D morphology decorated with exceedingly porous ‘petals’.

Microwave assisted facile synthesis of 3D flower-like ZnO nanostructures for enhanced photocatalytic degradation/removal of Eosin Y from water

Three-dimensional ZnO nanoflower has been synthesized via microwave irradiation technique using glycine as complexing/capping agent for the first time. TEM, SAED, XRD, FTIR, UV and PL spectra have been recorded to characterize the synthesized ZnO nanostructures. The TEM image indicates the formation of 3D flower-like ZnO nanostructures having diameter ~0.74-1.60 μm. The spacing between adjacent lattice fringes obtained from the HRTEM image is 0.145 nm which indicated the presence of (103) lattice plane of ZnO. The synthesized ZnO nanoflower show excellent luminescence properties. The photocatalytic properties of synthesized ZnO nanoflower is depicted by the degradation of Eosin Y dye under solar irradiation. It is found that 98.9% of Eosin Y dye is degraded within 50 min under solar irradiation. Henceforth, ZnO nanoflower acts as an effective photocatalyst for the degradation of Eosin Y dye.

3D porous flower-like ZnO microstructures loaded by large-size Ag and their ultrahigh sensitivity to ethanol

3D porous flower-like ZnO microstructures loaded by large-size Ag were successfully synthesized via a simple two-stage method. XRD and XPS results proved that the synthesized Ag/ZnO was a pure phase. SEM and TEM results showed that the Ag nanoparticles with large size (about 400 nm) were successfully loaded on the porous flower-like ZnO. The sensitivity of Ag/ZnO was 268 to 200 ppm ethanol at 300 °C, which was 6 times higher than that of pure ZnO. In addition, the sensor of Ag/ZnO exhibited a faster response/recovery behavior and a lower detection limit. The enhanced gas sensing performance of Ag/ZnO has been explained from three aspects: the “spillover effect” of Ag, the formation of metal-semiconductor heterojunction and the role of “electronic sensitization”.

Ag and Cu2O modified 3D flower-like ZnO nanocomposites and evaluated by photocatalysis oxidation activity regulation

In this study, Ag and Cu2O nanoparticles modified flower-like ZnO nanostructures have been successfully synthesized by stepwise method, and the photocatalytic properties were investigated in detail. High-resolution transmission electron microscopy, X-ray diffractions analysis, X-ray photoelectron spectroscopy and scanning electron microscopy were used to analyze the samples. Meanwhile, the derived nanoparticles’ structured and morphologic characters were analyzed by Brunauer–Emmett–Teller. The results have shown that the 3D flower-like ZnO microspheres were composed of 2D ZnO nanosheets decorated Ag and Cu2O and exhibiting flower-like Ag@Cu2O/ZnO architectures. We studied the optical absorption (UV–vis) as well as emission (PL) characters of the specimen and the outcomes suggested more superior photocatalytic characteristics for cuprous oxide and silver co-doped zinc oxide sample compared to other samples. Electron Paramagnetic Resonance test results show that there are mainly ⋅O2−, h+ and OH• free radicals in the process of CR degradation. A Radical-trapping test indicated that of ⋅O2− and h+ was more effective than OH• in the degradation of CR.

Microwave-assisted solution synthesis and photocatalytic activity of Ag nanoparticles supported on ZnO nanostructure flowers

Ag nanoparticles supported on the surface of three-dimensional (3D) flower-like ZnO nanostructure were synthesized by a microwave-assisted solution method. The obtained products were characterized by X-ray diffraction analysis, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectrophotometry, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The analytical results confirmed homogeneously distributed Ag nanoparticles supported on the surface of flower-like ZnO nanostructure. The photocatalytic effect of the heterostructure Ag/ZnO nanocomposites was investigated using photodegradation under ultraviolet (UV) light of methylene blue as model dye. The heterostructure Ag/ZnO nanocomposites exhibited much higher photocatalytic activity than pure ZnO flowers. The improved photocatalytic properties are attributed to formation of a Schottky barrier at the metal–semiconductor interface of the Ag/ZnO nanocomposites.

PEG—assisted morphological transformation of 3D flower-like ZnO to 1D micro-/nanorods and nanoparticles for enhanced photocatalytic activity

A simple, non-toxic, cost-effective and environmentally benign hydrothermal method has been used to synthesize ZnO with different morphologies. The effects of polyethylene glycol (PEG) addition on the structural, morphological, optical properties and photocatalytic performance of the ZnO nano-/microstructures were studied. The synthesized ZnO products were of highly crystalline hexagonal phase. The reorientation of crystal planes took place without any alteration of the crystalline phase with the addition of PEG. The morphology of the ZnO products could be controlled using appropriate amounts of PEG in the reaction precursor. Compositional analyses revealed that the obtained products were phase pure with a 1:1 atomic ratio of Zn versus O. The band gap of ZnO without PEG additive was determined to be 3.36 eV and changed slightly with the addition of PEG. The photoluminescence (PL) study revealed defect-related emissions and the enhancement or decreases in PL intensity depended significantly on the amount of the PEG addition. The photocatalytic activity of the ZnO catalyst was evaluated for methylene blue dye, which shows 98% degradation within 60 min.

Flower-Like CuO/ZnO Hybrid Hierarchical Nanostructures Grown on Copper Substrate: Glycothermal Synthesis, Characterization, Hydrophobic and Anticorrosion Properties.

In this work we have demonstrated a facile formation of CuO nanostructures on copper substrates by the oxidation of copper foil in ethylene glycol (EG) at 80 °C. On immersing a prepared CuO film into a solution containing 0.1 g Zn(acac)2 in 20 mL EG for 8 h, ZnO flower-like microstructures composed of hierarchical three-dimensional (3D) aggregated nanoparticles and spherical architectures were spontaneously formed at 100 °C. The as-synthesized thin films and 3D microstructures were characterized using XRD, SEM, and EDS techniques. The effects of sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), and polyethylene glycol (PEG) 6000 as surfactants and stabilizers on the morphology of the CuO and ZnO structures were discussed. Possible growth mechanisms for the controlled organization of primary building units into CuO nanostructures and 3D flower-like ZnO architectures were proposed. The hydrophobic property of the products was characterized by means of water contact angle measurement. After simple surface modification with stearic acid and PDMS, the resulting films showed hydrophobic and even superhydrophobic characteristics due to their special surface energy and nano-microstructure morphology. Importantly, stable superhydrophobicity with a contact angle of 153.5° was successfully observed for CuO-ZnO microflowers after modification with PDMS. The electrochemical impedance measurements proved that the anticorrosion efficiency for the CuO/ZnO/PDMS sample was about 99%.

Hierarchical flower-like ZnO microstructures: preparation, formation mechanism and application in gas sensor

Three-dimensional (3D) flower-like ZnO hierarchical microstructures with high uniformity were fabricated from the decomposition of Zn(OH)4 2− precursor, which were synthesized by a facile hydrothermal reaction. XRD, FESEM and TEM were employed to characterize the morphology and structure of the products. The as-prepared flower-like ZnO microstructures with an average diameter of about 2 μm are assembled by large amounts of nanosheets, which have a thickness of ~43 nm. The morphology of the ZnO architectures can be tailored by changing hydrothermal conditions, e.g., hydrothermal temperature, reaction time, and concentration of Zn2+. On the basis of experimental results, the possible formation mechanism of the flower-like ZnO microstructures was also proposed, and the Zn2+ concentration was found to be a vital role in the growth and crystallzation of the flower-like microstructures. The Brunauer–Emmett–Teller measurement shows that the 3D flower-like ZnO hierarchical microstructures possess a specific surface area of about 34.86 m2/g. Most significantly, the gas sensing test reveals that the sensor made from 3D flower-like ZnO hierarchical microstructures exhibits outstanding gas sensing performance.

Microfluidic paper-based analytical device for photoelectrochemical immunoassay with multiplex signal amplification using multibranched hybridization chain reaction and PdAu enzyme mimetics

Combining multibranched hybridization chain reaction (mHCR), the photoelectrochemical (PEC) immunosensor was fabricated with a microfluidic paper-based analytical devices using different sizes of CdTe quantum dots (QDs) sensitized flower-like 3D ZnO superstructures as photoactive materials. Firstly, 4-aminothiophenol (PATP) functioned ZnO was anchored on gold-paper working electrode. With the aid of PATP, large-sized CdTe-COOH QDs (QDs1) were conjugated onto the ZnO surface because of the formation of a strong bond (Zn-S) between the thiol of PATP molecule and the ZnO, and the remaining amino group formed an amide bond with carboxylic acid group capping CdTe. Then the small-sized CdTe-NH2 QDs (QDs2) were modified on the QDs1 by forming amide bond, which leaded to a very strong photocurrent response because of the formation of cosensitized structure. The designed mHCR produced long products with multiple branched arms, which could attached multiple PdAu nanoparticles and catalyze the oxidation of hydroquinone (HQ) using H2O2 as anoxidant. Double strands DNA with multiple branched arms (mdsDNA) was formed by mHCR. In the presence of carcinoembryonic antigen (CEA), PdAu-mdsDNA conjugates-labeled CEA antibody was captured. The concentrations of CEA were measured through the decrease in photocurrent intensity resulting from the increase in steric hindrance of the immunocomplex and the polymeric oxidation product of HQ. In addition, the oxidation product of HQ deposited on the as-obtained electrode, which could efficiently inhibit the photoinduced electron transfer. Under optimal conditions, the PEC immunosensor exhibited excellent analytical performance: the detection range of CEA was from 0.001 to 90ngmL−1 with low detection limit of 0.33pgmL−1. The as-obtained immunosensor exhibited excellent precision, prominent specificity, acceptable stability and reproducibility, and could be used for the detection of CEA in real samples. The proposed assay opens a promising platform of clinical immunoassay for other biomolecules.

Preparation of flower-like ZnO architectures assembled with nanosheets for enhanced photocatalytic activity

As an important semiconductor metal oxide, various methods have been developed for preparation of ZnO architectures owing to their excellent properties and extensive applications. In this paper, two kinds of 3D flower-like ZnO architectures assembled with numerous nanosheets were successfully synthesized by a simple hydrothermal route assisted by sodium dodecyl sulfate (SDS), origining from the different alkali environment created by urea and hexamine (HMT). SEM and TEM results revealed that the two products had hydrangea-like and rose-like nanostructures with uniform particle sizes, respectively. XRD results confirmed that the growth process of ZnO involved a phase transformation from intermediate compound basic zinc carbonate to ZnO. Base on the experimental results, the formation mechanisms of two kinds of flower-like ZnO undergoing nucleation, oriented growth and self-assembly processes were discussed. The photocatalytic results indicated that both samples exhibited high photocatalytic activities and good cycling stability for the degradation of rhodamine B (RhB), which was almost completely degraded within 25min, in comparison to those milled samples (above 45min). The excellent performances were mainly ascribed to their unique nanostructure, good stability, and uniform particle size.

Synthesis of three-dimensional flower-like hierarchical ZnO nanostructure and its enhanced acetone gas sensing properties

A three-dimensional (3D) flower-like hierarchical ZnO nanostructure was successfully synthesized via a facile and efficient hydrothermal method. The sample was characterized by XRD, FESEM, Raman, UV–vis DRS and Photoluminescence (PL) techniques. The XRD pattern revealed that the sample was well-crystallized in a hexagonal wurtzite structure. FESEM images showed that the as-prepared ZnO exhibited a nanosheet-assembled hierarchical flower-like ZnO nanostructure, which was self-assembled by thin and uniform nanosheets with a thickness of approximately 30 nm. Raman spectra exhibited that the sample kept the crystal structure of the bulk ZnO and possessed more surface defects. UV–vis spectra showed that a significant blue-shift in the absorption edge for the as-prepared ZnO as compared to the commercial ZnO. PL spectra indicated that the concentration of surface oxygen vacancies in the as-prepared ZnO was much higher than that of the commercial ZnO. Furthermore, the nanosheet-assembled flower-like ZnO nanostructure exhibited excellent gas sensing properties towards acetone, indicating that the as-prepared ZnO architecture is a promising material for gas sensors.

Preparation of graphene supported flower-like porous 3D ZnO–NiO ternary composites for high capacity anode materials for Li-ion batteries

Flower-like ZnO–NiO mesoporous architectures were synthesized through annealing the zinc hydroxide carbonate–nickel hydroxide carbonate composite precursor, which was prepared via a one-pot hydrothermal route. More importantly, we successfully prepared flower-like porous ZnO–NiO/graphene composites by introducing flexible graphene into the flower-like porous ZnO–NiO. In addition, we explore the application of the 3D flower-like ZnO–NiO composite mesoporous architectures and flower-like porous ZnO–NiO/graphene composites as anode materials for lithium ion battery. Electrochemical study presented that the as-prepared flower-like porous ZnO–NiO/graphene composites demonstrate excellent electrochemical performance and cycling stability. The first discharge capacity is 1205.7mAh/g at a high current density of 300mA/g. After 50 cycles, the reversible capacity is 452.7mAh/g at a current density of 300mA/g and the coulomb efficiency reaches at 99%.The improved electrochemical performances are mainly attributed to its morphological characteristics of mesoporous, nanosheet self-assembling architectures, as well as the addition of graphene. These results suggest that such 3D flower-like porous ZnO–NiO/graphene composites are promising materials for lithium ion battery.

Self-assembly and template-free synthesis of ZnO hierarchical nanostructures and their photocatalytic properties

Despite significant progress in the field of semiconductor photocatalysis has been made, it is still a great challenge to prepare low-cost photocatalysts with high activities. In our work, three dimensional (3D) flower-like ZnO hierarchical nanostructures assembled with numerous nanosheets were fabricated by a simple, template-free and one-step hydrothermal route. The products were characterized by XRD, UV–Vis, PL, SEM, TEM, HRTEM techniques. In the process, NH4F played a crucial role for the formation of ZnO hierarchical nanostructures, which was acted both as the alkali source and morphology director. Furthermore, the growth of ZnO involved a phase transformation from intermediate compound ZnF(OH) to ZnO. To further improve the photocatalytic activity, Ag-doped ZnO photocatalyst was also prepared. The photocatalytic results indicated that the Ag/ZnO exhibited higher photocatalytic activity than the pure ZnO. The great enhancement was mainly ascribed to their unique hierarchical nanostructures as well as the modification of Ag nanoparticles. Additionally, both ZnO and Ag/ZnO microspheres showed good recycling stabilities over several separation cycles in photodegradation.

Synthesis and enhanced photocatalytic activity of 3D flowerlike ZnO microstructures on activated carbon fiber

A hydrothermal method was utilized to attach 3D flowerlike ZnO microstructures to the surface of activated carbon fiber (ACF). The phase structure, morphology and optical property of the obtained sample were characterized. SEM demonstrated that the flowerlike structures consisted of multilayered petals, which were wholly comprised of ZnO rods. XRD analysis confirmed patterns for the wurtzite hexagonal phase of ZnO and ACF from the sample. The formation mechanism of the flowerlike ZnO grown on ACF was also discussed. The ZnO/ACF composite showed a superior photocatalytic activity in the degradation of methyl orange as compared with pure ZnO. The enhancement was attributed to a red shift, stronger UV light absorption ability and higher absorption behavior in ZnO/ACF, and the capture and transportation of photogenerated electrons by ACF.

A label-free electrochemistry biosensor based flower-like 3-dimensional ZnO superstructures for detection of DNA arrays

A highly sensitive electrochemical DNA sensor was constructed by homogenously distributing Au nanoparticles (AuNPs) on a flower-like 3D ZnO superstructure–chitosan (CS) matrix.

Sol−gel-based hydrothermal method for the synthesis of 3D flower-like ZnO microstructures composed of nanosheets for photocatalytic applications

Self-assembled 3D flower-like ZnO microstructures composed of nanosheets have been prepared on a large scale through a sol−gel-assisted hydrothermal method using Zn(NO3)2·6H2O, citric acid, and NaOH as raw materials. The product has been characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The optical properties of the product have been examined by room temperature photoluminescence (PL) measurements. A possible growth mechanism of the 3D flower-like ZnO is proposed based on the results of experiments carried out for different hydrothermal treatment times. Experiments at different hydrothermal treatment temperatures have also been carried out to investigate their effect on the final morphology of the ZnO. The photocatalytic activities of the as-prepared ZnO have been evaluated by photodegradation of Reactive Blue 14 (KGL) under ultraviolet (UV) irradiation. The experimental results demonstrated that self-assembled 3D flower-like ZnO composed of nanosheets could be obtained over a relatively broad temperature range (90−150°C) after 17h of hydrothermal treatment. All of the products showed good photocatalytic performance, with the degree of degradation of KGL exceeding 82% after 120min. In particular, the sample prepared at 120°C for 17h exhibited superior photocatalytic activity to other ZnO samples and commercial ZnO, and it almost completely degraded a KGL solution within 40min. The relationship between photocatalytic activity and the structure, surface defects, and surface areas of the samples is also discussed.

A high activity photocatalyst of hierarchical 3D flowerlike ZnO microspheres: Synthesis, characterization and catalytic activity

In this study, three-dimensional (3D) hierarchical flowerlike ZnO microspheres have been hydrothermally synthesized by means of two surfactants at 100°C and characterized by XRD, SEM, TEM, TG, FT-IR and UV–Vis spectroscopies. The results show that the 3D flowerlike ZnO microspheres are composed of 2D nanosheets. A possible formation mechanism is proposed: 0D Zn5(CO3)2(OH)6 colloids tend to form 2D nanosheets with the aid of sodium dodecyl sulfonic, and then, these nanosheets can assemble to 3D flowerlike microspheres by means of two surfactants of sodium dodecyl sulfonic and PEG 600. The flowerlike ZnO has low bandgap energy and exhibits high catalytic activity for photocatalytic degradation of Rhodamin B, which is attributed to its unique morphology and uniform hierarchical structure that significantly facilitates the diffusion and mass transportation of organic molecules and oxygen species in the degradation reaction.

Facile synthesis of flower-like 3D ZnO superstructures via solution route

A novel flower-like 3D ZnO superstructure with high uniformity was fabricated on a large scale through a facile aqueous solution route at room temperature. The as-prepared ZnO superstructures with a diameter of about 3 μm are assembled by large amounts of interleaving nanosheets, which have a uniform thickness of about 15 nm and a well-crystalline structure with {100} planes as basal facets. The hierarchical microstructures, which were formed via a two-stage nucleation–growth process, highly depend on the concentration of NaOH and trisodium citrate dihydrate. The photoluminescence result indicates that the ZnO superstructures possess a relatively strong UV emission. The photodecomposition of methyl orange indicates that such ZnO superstructures possess excellent photocatalytic activity.

Self-assembly fabrication of 3D flower-like ZnO hierarchical nanostructures and their gas sensing properties

In this paper, three-dimensional flower-like ZnO hierarchical nanostructures were fabricated from the thermal-decomposition of 3D zinc hydroxide carbonate precursor, which was synthesized by a urea hydrothermal method with block copolymer F127 (EO106-PO70-EO106) as the morphology director. XRD, IR, UV-vis, SEM, TEM, TG and N2 adsorption–desorption isotherms have been employed to characterize the products. The influences of synthesis parameters such as reaction time, the type of zinc sources, and species concentration on the morphologies of the products were systematically studied. It was found that the reaction time played a key role in determining the final morphology of porous ZnO. On the basis of experimental results, a possible formation mechanism of the 3D flower-like ZnO hierarchical nanostructures was discussed. More importantly, the gas sensing tests indicated that the sensor made from porous ZnO hierarchical nanostructures exhibited better gas sensing properties to n-butanol compared with the sensor based on the commercial ZnO nanoparticles. The enhancement in gas sensing properties was attributed to their unique 3D hierarchical nanostructures, high surface areas, and greater number of surface active sites.