ZnO Microflowers Research Articles

New electrocatalyst of Ni6MnO8@AB/PtNPs with efficient synergistic enhancement in electrochemical aptasensor for sensitive detection of neuron specific enolase

As one of the specific markers for small cell lung cancer (SCLC), the clinical value for serum neuron-specific enolase (NSE) detection in diagnosis, monitoring and therapy of SCLC is considerable. Herein, a sensitive amperometric aptasensor was developed for the detection of NSE based on nickel-manganese oxide@acetylene black/platinum nanoparticles (Ni6MnO8@AB/PtNPs) composite as signal amplifier. The combination of Ni6MnO8, AB and PtNPs not only showed synergistically catalytic activity to hydrogen peroxide (H2O2), but also possessed lots of binding sites for loading the thiol-terminated signal probes (TSPs) through Pt-S bonds. Additionally, nitrogen-doped carbon nanotubes/poly (diallyldimethylammonium chloride)/ZnO microflowers (N-CNTs/P/ZnO MFs) exhibited outstanding electric conductivity and was used as substrate material to load more biotin-terminated capture probes (BCPs). In the presence of the NSE, the TSPs and BCPs specifically recognized the NSE to form a sandwich-type electrochemical aptasensor, which exhibited a broad linear response range from 0.00001 ∼ 100 ng mL−1 and a low detection limit of 2.86 fg mL−1 (S/N = 3). In addition, the electrochemical aptasensor obtained favorable detection results in diluted human serum, indicating that it had potential application in clinical NSE detection.

Engineering PVDF omniphobic membranes with flower-like micro-nano structures for robust membrane distillation

Conventional PVDF membranes are easily wetted and contaminated in membrane distillation (MD) process, especially when used in separating high-salinity water and oil-contained saline water. To address these issues, an omniphobic membrane was fabricated in this work. ZnO micro-flowers with a rough structure were successfully deposited onto the PVDF membrane with the assistance of polydopamine assistance. After undergoing a fluorination process, the omniphobic membranes were prepared by the synergistic effect of surface microstructure and free energy. The effects of varying Zn(NO3)2 concentrations and deposition times on morphology, pore size and separation efficiency were comprehensively examined. It was demonstrated that at a Zn(NO3)2 concentration of 50 mM and a deposition time of 0.5 h, the resulting PVDF composite membrane exhibited high liquid repellency towards all the test liquids, such as water, ethanol solution, paraffin oil, and etc. Furthermore, the membrane consistently exhibited impressive salt rejection behavior (99.99%) and maintained an average flux (15.54 kg·m−2·h−1) when exposed to high-salinity solution (up to 20 wt%-NaCl). Meanwhile, during treating an oil-contained saline water emulsion with the oil content of 200 ppm, the membrane also displayed high resistance to wetting and fouling during the continuously 24 h tests. The membrane displayed a rejection rate of 99.99 % with an average vapor flux of 18.60 kg·m−2·h−1. In summary, this omniphobic membranes demonstrated a great potential in MD for practical challenging wastewater treatment.

Exploring the photocatalytic activity of surfactant-free ZnO micro-flowers synthesized by microwave-assisted method

In present study, surfactant-free synthesis of highly crystalline ZnO micro-flowers was carried out by using the microwave-assisted method with a 4 min reaction time. The effect of different microwave powers on crystal structure, morphology, and photocatalytic activity was studied. The ZnO synthesized at 450 W showed better physico-chemical and photocatalytic performance. XRD pattern showed the formation of the highly crystalline wurtzite/hexagonal crystal structure with an average crystallite size of 31 nm. The presence of Raman active bands validated the formation of wurtzite/hexagonal crystal structure of the ZnO. Moreover, the XPS analysis confirmed the presence of Zn and O elements while the highest specific area of 24.2 m2/g was observed from BET. The morphological studies showed the formation of the ZnO microflowers with an average size of 5 μm. Synthesized ZnO showed a band gap of 3.19 eV. To check the applicability, the photodegradation of methylene blue by ZnO micro-flowers was studied under solar light. For 450 W, due to the highly crystalline and sharp-edged microstructure, high photodegradation efficiency is obtained at about 90 % with recyclability of 72.8 % after 3 cycles. Based on the obtained results, a microwave with low power can be utilized to prepare highly crystalline microstructures of ZnO for better photocatalytic activity with very short reaction time.

Enhanced photocatalytic activity of ZnO microflowers by a trace amount of Ti3C2 MXene

As a novel metal compound with a narrow bandgap and excellent conductivity, two-dimensional (2D) layered Ti3C2 MXene has received growing attention from researchers. In this work, microflower-like ZnO/Ti3C2 composite photocatalysts were prepared by a one-pot method and characterized by XRD, SEM, TEM and XPS techniques. The photocatalytic performances of the ZnO/Ti3C2 photocatalysts were evaluated by the degradation of methyl orange (MO) under UV–visible light irradiation. The photocatalytic activity of ZnO was obviously enhanced with a trace amount of Ti3C2. The pseudo-first-order rate constants of the ZnO/Ti3C2-0.05 and ZnO/Ti3C2-0.5 with Ti3C2 mass percentages of 0.041% and 0.41%, respectively, were 2.9 and 4.2 times higher than that of the ZnO. The enhanced photocatalytic activity of ZnO/Ti3C2 composite was due to the increased transfer of photo-generated charge carriers. Furthermore, the ZnO/Ti3C2-0.5 composite also showed good stability, the degradation efficiency of MO was still maintained 99% even after 10-cycle of reutilization. ZnO/Ti3C2 and other Ti3C2-containing composites may have potiential application in wastewater treatment and environment remediation.

Charge transfer and ZnO defect state mediated FRET dependent luminescence in nanocomposites based on PPy nanowires and ZnO microflowers

The role of Forster resonance energy transfer (FRET) and charge transfer on controlling the overall luminescence of the nanocomposites based on PPy and ZnO is discussed here. Polypyrrole-ZnO (PPy-ZnO) nanocomposites have been synthesised with the variation of ZnO content (10 wt %, 30 wt % and 50 wt %) in the nanocomposite through chemical oxidative polymerization method. Nanowires of PPy and PPy-ZnO nanocomposites are observed from SEM and TEM images. The diameters of nanowires in PPy-ZnO nanocomposites are found to vary with ZnO content. Ordering in the polymer chain with the incorporation of ZnO is observed from XRD spectra. Red shift of the absorption peak of PPy in PPy-ZnO nanocomposites gives the evidence of increase in order of the polymer chain which in turn increases the singlet exciton diffusion through the polymer chain. Two photophysical phenomena i.e. FRET and charge transfer have significant impact on controlling the overall luminescence of the composites depending upon the ZnO content in the composite. At lower amount of ZnO (10 wt %), FRET occurs predominantly from defect states of ZnO to PPy and overall enhancement of luminescence is noticed. But no significant enhanced luminescence is observed when higher amount of ZnO is added to the composite. This happens due to dominant charge transfer between PPy and ZnO since they have type II band alignment. When the amount of ZnO is high in the composite, the interfacial area between PPy and ZnO get increased. XPS spectra reveals that ratio of polaron to neutral nitrogen in PPy chain also increases in the composite with higher amount of ZnO which results in the modification of band structure of PPy. Thus high interfacial area between PPy and ZnO as well as modification of band structure in PPy increases the rate of charge transfer between PPy and ZnO. Therefore, inspite of possibility of FRET, charge transfer occurs more efficiently in the nanocomposite when the ZnO content is high in the composite. This ultimately prohibits the radiative recombination of singlet exciton inside the composite with higher amount of ZnO. Hence the Photoluminescence (PL) intensity quenches considerably. Thus optimizing the amount of ZnO in the composite, the photophysical phenomena as well as luminescence of the composite can be controlled for the potential application of different optoelectronic devices like solar cell.

ZnO nanorods assembled microflower-based gas sensor for detecting formaldehyde

Herein, we report the facile hydrothermal synthesis and characterizations of ZnO nanorods assembled microflowers and their efficient sensing application for the detection of formalydehyde gas. The synthesized ZnO microflowers were examined by several techniques. The scanning electron microscopy (SEM) was employed to evaluate the surface morphology, X-ray diffraction (XRD) analysis for the crystal structure while the Fourier transformation infrared (FTIR), and Raman-scattering spectroscopy were employed to understand the functional groups in the synthesized material. The optical properties were evaluated by UV-visible spectroscopy Furthermore, the synthesized ZnO microflowers were used as a functional material to fabricate formaldehyde gas sensor which exhibited a high gas response of 113.36 (Rg/Ra) towards 50 ppm formaldehyde gas at 200 °C. The observed response and recovery times for the fabricated sensor were ∼65 s and ∼117 s, respectively. Finally, the enhancement of gas-sensing performance and mechanism were thoroughly discussed. This work revealed that simply prepared ZnO nanostructures can be used to fabricate high-performance gas sensors.

Facile preparation of porous ZnO microflowers with large surface area

ZnO microflowers (MFs) assembled by many porous nanosheets were prepared through an initial hydrothermal reaction with an extra annealing treatment at 300 °C. The samples were characterized by XRD, SEM, and TEM techniques, as well as the N2 adsorption–desorption test. The results indicated that the ZnO MFs possessed a size of about 6 µm and exhibited a large surface area of 58.6 m2/g, an average pore size of 14.1 nm with size distribution at 15.1 nm. The hydrothermal temperature was found to play an important role in determining the shape and size of ZnO products. Such ZnO MFs with porous structure and huge surface area may have application potential in the fields of gas sensors, photo-catalysis, electrochemical energy storage, and so on. The present synthetic method is simple and cost-effective, and can be extended to the preparation of other metal oxides with controlled structures.

Surface defect-rich ZnO nanostructures with high yellow-orange luminescence

ZnO nanostructures such as nanoislands, nanosheets, microflowers and nanoparticles were obtained successfully using a facile and rapid solution route employing low temperatures and reduced molar concentrations from precursor without using any surfactant agent or additional procedures. In this route, we use ZnCl2 as precursor ranging from 0.05 to 0.4 M and two hydrothermal times (2 and 4 h) to obtain different ZnO morphologies. According to SEM micrographs, the morphology of ZnO nanostructures showed a strong dependence on the ZnCl2 concentration and hydrothermal synthesis time. ZnO microflowers were obtained at 0.05 M during 2 h, while ZnO nanoislands, nanoparticles and nanosheets were observed at 0.05, 0.2 and 0.4 M, respectively, in 4 h. X-Ray diffraction and Raman results showed the wurtzite-type ZnO structure and good crystallinity in all cases. In addition, both techniques confirmed the best crystalline quality in ZnO nanoparticles followed by ZnO nanosheets. Finally, according to photoluminescence measurements, all samples exhibit a high yellow-orange emission, associated to a large number of surface defect states, such as oxygen and zinc interstitials. The largest amount of zinc interstitials and zinc vacancies were observed in ZnO nanoislands, while ZnO microflowers have the highest visible emission (followed by ZnO nanoparticles) which in turn, offered the lowest excitonic recombination from the conduction band to the valence band, which may result in a higher photocatalytic efficiency.

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

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

Effect of calcination temperature on the morphology and catalytic properties of ZnO nanostructures fabricated from a chiral precursor for photodegradation of both cationic and anionic dyes

A chiral Zn MOF is fabricated into ZnO microflowers, polyhedrons and nanorods at three different temperatures and these are utilized for the photodegradation of methylene blue and Congo red.

Fabrication of hierarchical hybrid ZnO/Au micro-/nanostructures for efficient dye degradation: role of gold nanostructures in photophysical process

In this work, colloidal solutions of gold nanoparticles (AuNPs) with an average diameter of 16 nm and gold nanorods (AuNRs) with an average aspect ratio of 6.8 were synthesized. These gold nanostructures were decorated on nanosheets assembled 3D ZnO microflower (ZnO-MF) synthesized via facile and cost-effective co-precipitation method. Plasmonic gold nanostructures act as optical concentrators and a reservoir of electrons under LSPR excitation. They extend the light harvesting capability of ZnO from UV–VIS–NIR region, promotes interfacial charge transfer process and helps in electron-hole pair separation. We report the occurrence of FRET (Fluorescence Resonance Energy Transfer) between defect rich ZnO-MF and gold nanostructures under UV light excitation as evident from micro-PL spectra. This triggers surface plasmon resonance in gold nanostructures which causes direct transfer of hot electrons to ZnO-MF. Time-resolved Photoluminescence of the hybrid samples monitored at near band edge of ZnO shows elongated decay kinetics as compared to bare samples which could be attributed to direct transfer of hot electrons from gold to conduction band of ZnO-MF after LSPR excitation. Thereafter, the photocatalytic activity of the hybrids is evaluated by degradation of four different dyes under sunlight. ZnO-MF/AuNPs exhibited superior photocatalytic activity compared to ZnO-MF/AuNRs. This could be attributed to numerous reasons like better energy transfer efficiency, effective near-field enhancement, small size of AuNPs and enhanced electron-hole pair separation which makes ZnO-MF/AuNPs a promising photocatalyst.

Facile synthesis of MnO2/ZnO coated on cotton fabric for boosted antimicrobial, self-cleaning and photocatalytic activities under sunlight

MnO2 nanosheet/ZnO microflower (MnO2/ZnO) coated on cotton fabric was synthesized using a reflux-thermal deposition combined method. Myriad spectroscopic methods were utilized to scrutinize the catalyst as well as the created composite fabric. The composite fabric displayed a potent antimicrobial effect against Escherichia Coli bacteria and Aspergillus Niger fungi. Importantly, the fabric was proved to possess excellent self-cleaning activity and photodegradation of methyl green aqueous solution under direct sunlight. The high photoactivity of composite fabric was ascribed to not only the pronounced capability in harnessing photon energies from visible region, but also the accelerated charge separation boosted by the MnO2 nanosheet distributed on the ZnO microflower. The promising performance shown in this work enable the scalable production of composite fabric for multifarious applications.

ZnO hierarchical structures as sacrificial inclusions for enhanced performance under full sun and indoor light in bifacial dye sensitized solar cells

We have already demonstrated a facile strategy for improving light scattering in bifacial dye sensitized solar cells (DSSCs) through fugitive inclusions of ZnO micro-flowers leading to enhanced photovoltaic performance without adversely affecting the transparency (Sasidharan et al., 2020). In the present work, we were able to further ameliorate the light scattering properties by employing micron sized ZnO hierarchical structures (fibril and sheet like aggregates) as sacrificial inclusions. ZnO hierarchical structures being deposited over TiO2 active layer were selectively etched off, leaving behind imprints over the TiO2 layer, which act as scattering centers to enhance the photocurrent of DSSCs owing to the increased light absorption. The present strategy extends the possibility to improve the performance of DSSCs under both one sun (100 mW/cm2) as well as indoor/ambient light conditions without compromising transparency to larger extend. By employing this strategy on a 6 µm thick TiO2 photoanode and implementing it in a DSSC using N719 sensitizer and iodide/triiodie electrolyte, power conversion efficiency of 15.5% could be achieved under indoor illumination (1000 lx) from a compact fluorescent lamp. A detailed study of the charge transfer dynamics at various interfaces were carried out using a range of electrical and optical perturbation techniques.

Biosynthesis of ZnO Nanosheets Decorated with Pd Nanoparticles and Their Application for Electrochemical Investigation of Ethanol

Hierarchical ZnO microflowers with sheet thickness of ≈ 23 nm were prepared in the presence of Cystoceira baccata algae extract. Pd nanoparticles with an average size of 4.9 nm were embedded on the surface of these nanosheets in the presence of Cystoceira baccata algae extract. The structure of ZnO@Pd was characterized by XRD, FESEM, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy methods. To investigate the possible application of the synthesized nanoparticles, the electrooxidation of ethanol on the surface of ZnO@Pd modified carbon paste electrode in alkaline media was studied using cyclic voltammetry. The electrode showed high catalytic activity for ethanol oxidation. It also showed high selectivity toward ethanol in comparison to other alcohols. Chronoamperometric measurements showed that this electrode could be used as a probe for determination of ethanol in a relatively wide linear range (180–500 mM) with a low detection limit (60 μM).

Enabling high-performance sodium metal anode via a presodiated alloy-induced interphase

Irreversible plating/stripping process induces the dendritic/mossy Na growth and cracks propagation, which hinder the practical utilization of sodium metal anode. Herein, a heterogeneous interfacial layer, which composed of the carbon-coated ZnO microflowers and the encapsulated Sb nanocrystals ([email protected]/C), is employed to optimize the cycling stability. Upon the voltage-induced presodiation process, the sodiophilic species in-situ transform into the Na-Zn and Na-Sb intermediates and preferentially induce the metallic plating process, mitigating the nucleation overpotential without sacrificing the energy density; while the microflower substrate spatially accommodates the deposit propagation over the repetitive plating/stripping cycling. Consequently, the [email protected]/C dramatically reduces the nucleation barrier to one-third that of the bare Cu foil (4 mV vs. 12 mV at 0.5 mA cm−2) and obtains satisfactory coulombic efficiency values (>99.5%) even at the high rates. Besides, the in-situ presodiation of the [email protected]/C composite allows the stable Na plating/stripping cycling in energy-dense full-cell evaluations (paired with the NASICON type NaVPO4F cathode). The impressive energy/power densities (251.5 W h kg−1 at 1257.5 W kg−1) realized in the prototype construction, coupled with a facile voltage-induced presodiation process, suggest a feasible strategy to extend the performance limits of metal battery systems.

Nanorods-assembled ZnO microflower as a powerful channel for n-butanol sensing

Assembly of one-dimensional (1D) nanorods into organized three-dimensional (3D) architectures, coupled with open interspaces, is favorable for gas-interface interaction and diffusion. In this paper, a single-crystalline nanorods-built ZnO microflower has been successfully prepared through a facile hydrothermal route. The surface morphology, crystal structure, element composition and pore characteristic of this ZnO product were also conducted using diverse technical methods. In addition, the morphology evolution process was further clarified through a time-dependent reaction. The ZnO microflower-based gas sensor declared a remarkable response towards n-butanol in terms of outstanding selectivity, low detection limit (~ 0.1 ppm), and rapid response rate (≤ 12 s for 1–100 ppm n-butanol). Moreover, this ZnO sensor still maintained a powerful response (Ra/Rg = 46.53) towards 100 ppm n-butanol when exposed to high-level relative humidity (RH = 80%). The improvement of gas-sensing response was discussed in detail. This work demonstrates that integration of 1D nanorods into rational 3D structure is an efficient strategy for fabricating high-performance gas sensor.

P.714 Brain correlates of speech perception in schizophrenia patients with and without auditory verbal hallucinations

We demonstrate a general strategy to design step by step the Ag nanoparticle-functionalized ZnO micro-flowers (Ag/ZnO composites). XRD patterns confirmed the presence of Ag nanoparticles in ZnO/Ag composites, and the SEM and TEM results further demonstrated that Ag nanoparticles were highly dispersed and anchored onto the surface of each ZnO nanosheets. By using the ZnO/Ag composites, the photodegradation of two herbicide derivatives, metamitron and metribuzin, were studied. The enhanced photocatalytic performance was ascribed to the fact that the Ag deposition could reduce the recombination probability of electron-hole pairs, and the photocatalytic mechanism were also investigated in this paper.

Hollow Zinc Oxide Microflowers for Selective Preconcentration of Selenium Ions in Natural Water

Background: Selenium’s popularity in a wide variety of products and industries means that it has, unfortunately, become a common environmental pollutant, particularly from sources such as industrial wastewater discharge and agricultural runoff. Objective: Quantification of the selenium (IV) ion content of natural water sources via atomic fluorescence spectrophotometry (AFS) was performed using hollow ZnO microflowers as the enriched materials. The hollow ZnO microflowers were prepared via a hydrothermal method with polystyrene (PS) microspheres as the template. Methods: Since the pH of the selenium (IV) solution is known to influence the degree of adsorption onto the sorbent, both the acidity of adsorption and elution were studied at various pH values to obtain the adsorption isotherm and adsorption capacity of the sorbent. AFS was used to quantify the amount of selenium ion that was present in the samples. The structure of the hollow ZnO microflowers was characterized using XRD, SEM, and TEM characterization methodologies. Results: When the pH was between 6.0 and 7.0, the percentage of Se (IV) adsorption was as high as 93%. It was found that the amount of Se (IV) that was eluted from the sorbent exceeded 96% with 5.0 mL of a 0.01 mol L−1 NaOH solution over the course of 10 minutes. The maximum adsorption capacity was 31.5, 31.8, and 32.0 mg·g−1 at 273, 333, and 353 K, respectively. Conclusion: The LOD for Se (IV) detection via enrichment was achieved at 0.006 μg L−1 with a linear range between 0.1 and 200 μg L−1. Thus, this method is applicable to the analysis of natural water samples and GBW(E)080394.

Magnetic ZnO@Fe3O4 composite for self-generated H2O2 toward photo-Fenton-like oxidation of nitrophenol

The present work focuses on the synthesis of a magnetically separable and stable catalyst for self-supplying H2O2 in photo-Fenton degradation of p-nitrophenol. Different from the most popular Fe3O4@ZnO core-shell structure, ZnO microflower cores were partially wrapped with Fe3O4 nanoparticles via a layer-by-layer self-assembly process. Several characterisation techniques were employed to investigate the crystal structure, morphology, surface chemistry and optical properties of the produced composites. The band gaps of the ZnO and Fe3O4 were considerably decreased from 3.05 to 2.60 to 2.35 eV after the assembly. The optimum Fe3O4 deposition layer number was found to be 5 for achieving 100% p-nitrophenol removal in 60 min. The degradation was triggered with in-situ photocatalytic formation of hydrogen peroxide over Fe3O4@ZnO. The exposed Fe3O4 nanoparticles provided Fe2+ and Fe3+ Fenton-active species for stable operation. We explored possible mechanisms of the enhanced photocatalysis by quenching and radical trapping experiments. The magnetic separation was also performed to recover and reuse the spent catalyst.

Single-step fabrication of ZnO microflower thin films for highly efficient and reusable photocatalytic activity

Zinc oxide microflower thin films were deposited in a single-step process using cost-effective ultrasonic spray pyrolysis technique. Different molarity of precursor solution was used to grow the films. X-ray diffraction and Raman spectroscopy reveal the wurtzite structure of ZnO. Scanning electron microscope images showed the microflower morphology which has a better surface to volume ratio. Defects such as O interstitial and Zn vacancy were identified in these thin films with the help of photoluminescence (PL) spectroscopy. The contact angle of the films was found to decrease with increase in molarity of the precursor. Photocatalytic activity of three different molar samples (0.05, 0.1 and 0.15 M) of ZnO were studied for methylene blue (MB) degradation and 0.15 M film demonstrated better degradation efficiency under UV–Vis light. Further degradation studies were performed on this film under exposure to natural sunlight. 90% degradation of the dye was observed in both the conditions upon exposure of 3.5 h. Effect of defects, molarity, bandgap and contact angle of ZnO on the photocatalytic performance is discussed. Repeatability studies performed under both UV–Vis and natural sunlight exposures showed only a minor deviation of 1% from the initial degradation efficiency.