Prepared ZnO Nanostructures Research Articles

Nanostructural Design of ZnO Using an Agro-Waste Extract for a Sustainable Process and Its Photocatalytic Activity.

The use of agro-waste extracts (AWEs) as a sustainable medium for developing cost-effective and ecologically friendly nanomaterials has piqued the interest of current researchers. Herein, waste extracts from papaya barks, banana peels, thumba plants, and snail shells were used for synthesizing ZnO nanostructures via a hydrothermal method, followed by calcination at 400 °C. The crystallinity and pure wurtzite phase formation of ZnO nanostructures were confirmed via X-ray diffraction. ZnO nanostructures with various morphologies such as tight sheet-like, spherical, porous sheet-like, and bracket-shaped, comprising small interconnected particles with a highly catalytically active exposed (0001) facet, were observed via field emission scanning electron microscopy and transmission electron microscopy. The formation mechanism of the various morphologies of the ZnO nanostructures was proposed. Ultraviolet-visible spectra showed different absorption band edges of ZnO nanostructures with a bandgap in the range of 3.17-3.27 eV. Photoluminescence studies showed the presence of various defect states such as oxygen and zinc vacancies and oxygen and zinc interstitials on ZnO nanostructures, which are usually observed in traditionally prepared ZnO. The photocatalytic activity of ZnO nanostructures was evaluated under direct sunlight using rhodamine B (RhB) and Congo red (CR) dyes as probe pollutants. Furthermore, prepared ZnO nanostructures could potentially adsorb anionic dyes (e.g., CR) in the absence of light. Superoxide and hydroxide radicals played a vital role in the photocatalytic activity of ZnO. The photocatalyst could be reused for up to three cycles, indicating its stability. Therefore, this study reports the diverse use of AWEs as cost-effective media for nanomaterial synthesis.

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.

Structural and Optical Properties of ZnO Nanostructures Synthesized by Hydrothermal Method at Different Conditions

ZnO nanostructures were synthesized by hydrothermal method at different temperatures and growth times. The effect of increasing the temperature on structural and optical properties of ZnO were analyzed and discussed. The prepared ZnO nanostructures were characterized by X-ray diffraction (XRD), UV–Vis. absorption spectroscopy (UV–Vis.), Photoluminescence (PL), and scanning electron microscopy (SEM). In this work, hexagonal crystal structure prepared ZnO nanostructures was observed using X-ray diffraction (XRD) and the average crystallite size equal 14.7 and 23.8 nm for samples synthesized at growth time 7 and 8 hours respectively. A nanotubes-shaped surface morphology was found using scanning electron microscopy (SEM). The optical properties showed that the samples had good absorbance in the UV-Vis. region and wide band gap. The PL spectrum displayed that the intensity of ultraviolet (UV), band gap and defect bands depend on the growth temperature of the ZnO nanostructure. The largest band gap was 3.351 eV for ZnO nanostructure synthesized at 100 °C and growth time 8h.

Transient photodetection studies on 2D ZnO nanostructures prepared by simple organic-solvent assisted route

Development of the highly responsive and cost-effective device for UV photodetection has been attracted a lot of attention from the global scientific community. A facile, easy processable and cost-effective synthesis method for the preparation of two dimensional ZnO nanomaterial is presented in this research work. A prepared sample was characterized by different characterization tools. XRD patterns reveal the crystalline nature of prepared ZnO nanostructures. The optical tenability of the material is further described by UV–vis and FTIR spectroscopic analysis. Scanning electron microscopy is used for the surface morphological studies and elemental analysis is done by electron diffraction spectroscopy (EDS). Photodetector performance parameters were analyzed under the illumination intensity of 50 μW/cm2. Various photodetector parameters such as responsivity, detectivity LDR, and EQE were found to be 60.34 mA/W, 4.09 × 1011 Jones, 14.71 dB and 20.45% respectively.

Studying adsorption and detoxification of sulfur mustard chemical warfare onto ZnO nanostructures

Sulfur mustard is a strong vesicant, leading to severe skin damages as well as eye blistering and may lead to death if inhaled. Unfortunately, there are no effective treatments for mustard-induced injury. Hence, there is considerable attention in the development of materials that can absorb or detoxify mustard gas. In the first part of this report, detoxification of sulfur mustard is performed on the synthetic ZnO nanosheets. The intended ZnO nanostructure is prepared via a simple and efficient method and characterized by means of FT-IR, XRD, FESEM, and XPS to confirm formation of the desired nanosheets. Then, detoxification and degradation of sulfur mustard is carried out on the prepared ZnO nanostructures at room temperature and a good rate for sulfur mustard detoxification was attained at the initial stages of the reaction (1−12 h) with a rate constant of 0.081 h−1 and a half-life of 8.4 h. At the second part of the present study, the density functional calculations including B3LYP and wB97XD are used to monitor the adsorption of this toxic material on the surface of various ZnO nanoclusters (ZnONCs). The values of adsorption energy of mustard gas are determined in the range of about −16 to −54 kcal/mol with enthalpies in the range of about −15 to-51 kcal/mol and the Gibbs free energies in the range of −3 to −28 kcal/mol at 298 K based on B3LYP level of theory. The geometry parameters are calculated for all geometries by consideration of the charge analysis and frontier molecular orbitals. Findings revealed that these systems are useful chemical sensors for sulfur mustard. Moreover, it is found that the CCL-ZnONS can effectively interact with this material and modifies the sensitivity of zinc oxide towards this agent.

Characterization of zinc oxide nanocrystals with different morphology for application in ultraviolet‐light photocatalytic performances on rhodamine B

ZnO nanostructures of different morphology (nanorods, nano-leaf, nanotubes) were favourably grown using a chemical precipitation process. The prepared ZnO nanostructures were characterized systematically using absorption spectroscopy, emission spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared studies. XRD results showed the hexagonal wurtzite phase of the synthesized ZnO nanostructures. Structural properties such as average crystallite size, lattice constants, volume of the unit cell, atomic fraction, and structural bonds were also studied. The optical band gap of the synthesized ZnO nanocrystals varied from 3.52 eV to 3.69 eV with high quantum yield of the blue emission (~420 nm). Urbach energy for ZnO nanocrystals was calculated to be 0.702 eV, 0.901 eV, and 0.993 eV for nanorods, nano-leaf, and tube like ZnO crystals, respectively. Morphology of the fabricated nanostructures was investigated using SEM. Photocatalytic degradation of rhodamine B (Rh B) in solution under UV irradiation was explored with different ZnO morphology. Photocatalytic experiments showed that ZnO nano-leaf had a higher degradation rate of photocatalytic activity of photodegrading Rh B compared with the other tube shape and rods shape nanostructures. The Rh B dye degraded considerably by ∼79.05%, 74.41%, and 69.8% within 120 min in the presence of the as-fabricated fern nano-leaf, nanotubes, and nanorods of the ZnO nanocrystals at room temperature.

Effects of substrates on the crystalline growth and UV photosensitivity of glancing angle deposited porous ZnO nanostructures

We prepared ZnO nanostructures on three different substrates such as quartz, sapphire (Al2O3) (001) and MgO (100) by glancing angle deposition (GLAD) technique using KrF excimer pulsed laser and investigated the effects of various substrates on the growth and optical properties. The GLAD technique promotes a vertical growth of the nanostructures and hence creates necessary porosity for penetration of light through the top of the surface. Although these nanostructures are porous, they are highly crystalline and oriented along c-axis of the wurtzite structure. Notably, despite the amorphous nature of the quartz substrate, nanostructures on quartz are preferentially oriented towards the c-axis. All three samples show intense ultraviolet (UV) emission with a highly suppressed visible emission, where the suppression depends on the growth and porous morphology of nanostructures. The variation in morphology and the porosity strongly influenced the electrical properties and UV photo-detection of these nanostructures when exposed under UV (254 nm) light. Although we used the same technique of the growth, the lowest dark current (0.14 nA) with the highest UV photosensitivity (182 %) is achieved for the highly porous and yet crystalline nanostructures grown on the sapphire substrate. Generally, it is extremely difficult to maintain crystalline structure with porosity; however, here we demonstrate a promising approach in designing visible-blind photodetectors by combining these two opposites, porosity and crystallinity, in ZnO nanostructures using the GLAD-assisted pulsed laser deposition method.

In-Depth Structural and Optical Analysis of Ce-modified ZnO Nanopowders with Enhanced Photocatalytic Activity Prepared by Microwave-Assisted Hydrothermal Method

Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization study of these materials using a battery of complementary techniques was performed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS), photoluminescence spectroscopy (PL) and UV–Visible absorption spectroscopy were used to evaluate the effect of Ce ions on the structural, morphological, optical and photocatalytic properties of the prepared ZnO nanostructures. The XRD results showed that the obtained photocatalysts were composed of hexagonal, wurtzite type crystallites in the 34–44 nm size range. The SEM and TEM showed nanosheet-shaped crystallites, a significant fraction of them in contact with bundles of randomly oriented and much smaller nanoparticles of a mixed cerium–zinc phase with a composition close to Ce0.68Zn0.32Ox. Importantly, in clear contrast to the prevailing proposals regarding this type of materials, the STEM-XEDS characterization of the photocatalyst samples revealed that Ce did not incorporate into the ZnO crystal lattice as a dopant but that a heterojunction formed between the ZnO nanosheets and the Ce–Zn mixed oxide phase nanoparticles instead. These two relevant compositional features could in fact be established thanks to the particular morphology obtained by the use of the microwave-assisted hydrothermal synthesis. The optical study revealed that in the ZnO:Ce samples optical band gap was found to decrease to 3.17 eV in the samples with the highest Ce content. It was also found that the ZnO:Ce (2 at.%) sample exhibited the highest photocatalytic activity for the degradation of methylene blue (MB), when compared to both the pure ZnO and commercial TiO2-P25 under simulated sunlight irradiation. The kinetics of MB photodegradation in the presence of the different photocatalysts could be properly described using a Langmuir–Hinshelwood (LH) model, for which the ZnO:Ce (2 at.%) sample exhibited the highest value of effective kinetic constant.

Growth and influence of Gd doping on ZnO nanostructures for enhanced optical, structural properties and gas sensing applications

Undoped and Gd-doped ZnO nanorods and nanoflowers were successfully prepared by one step hydrothermal method. The effect of Gd concentration on the formation of different morphology has been investigated. The X-Ray Diffraction analysis showed that the prepared ZnO nanostructures exhibits hexagonal wurtzite phase. The morphology of the nanostructures of ZnO was analyzed by FE-SEM and TEM. ZnO nanoparticles were transformed into nanorods and nanoflowers with increasing the wt% of Gd. UV-Visible spectroscopic studies showed that the presence of Gd in the ZnO matrix leads to tuning of bandgap. Where 6 wt% of Gd incorporation in ZnO matrix showed decrease in bandgap compared to undoped ZnO. The significant peak shift was observed in the electronic state of Zn at the higher concentration of Gd, which confirms the presence of Gd in ZnO matrix. Significant enhancement of xylene sensitivity was achieved by Gd doping in ZnO. These findings indicate that Gd-doped ZnO (GZ4) can be considered as good xylene sensing element at room temperature.

Grown of highly porous ZnO-nanoparticles by pulsed laser ablation in liquid technique for sensing applications

Pulsed laser ablation technique in deionized water with low laser fluency has been explored to prepare uniform dispersed porous ZnO nanoparticles for sensing applications. Surface morphology, particle size, porous structure, roughness, elemental distribution, and chemical bonding of the synthesized ZnO are analyzed by TEM, FESEM, AFM, EDX, and FTIR spectroscopy, respectively. Sensing behavior is observed by UV–Vis absorption measurements. TEM and FESEM analysis show that the prepared ZnO-coated film has homogeneous, dispersed, highly porous, and crack-free surface; the average particle size are observed ~ 24.72 ± 2.97 nm. The porous structure is responsible for appropriate sensing behavior. Low roughness value ~ 1.52 nm which is analyzed by AFM is advantageous for sensing behavior. EDX spectrum and elements mapping clearly show the uniform Zn and O distribution. XRD analysis confirms the hexagonal wurtzite structure of ZnO. FTIR reveals the Zn and O chemical bonding successfully. UV-Visible analysis exhibits that the prepared ZnO matrix has good incorporation with multi-dyes solutions at pH values 10–12 with significant changes in color behavior. The highest pKa value ~ 9.77 at a wavelength of 598.28 nm was calculated for multi-dyes immobilized ZnO matrix. So, it can be concluded that prepared ZnO nanostructures are potential candidates for sensing application.

Acetone gas sensors based on ZnO nanostructures decorated with Pt and Nb

In this study, the highly selective acetone gas sensors based on ZnO nanostructures with sputtered Pt and Nb were presented. The ZnO nanostructures were systematically prepared onto alumina substrates by a thermal oxidation technique at a working temperature of 500 °C. Pt and Nb were then coated on the prepared ZnO nanostructures by a DC pulse sputtering technique. Their surface morphologies and chemical compositions were analyzed via field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The ZnO nanostructures exhibited the wire-like structures while the ZnO nanostructures with Pt and Nb decoration (ZnO:Pt and ZnO:Nb) showed the fine particles attaching onto their surfaces. The gas sensing characteristics were evaluated toward acetone, ethanol and ethylene vapor at the operating temperatures of 275–450 °C. The maximum sensor response of sensors based on ZnO:Pt and ZnO:Nb were found upon exposure toward acetone vapor at 1000 ppm concentration with the value of 188.0 and 224.0, respectively. The observed sensor response enhancement in ZnO:Pt sensor is clearly explained by the catalytic effect in the oxygen and acetone adsorption reaction, while the sensor response enhancement in ZnO:Nb sensor is clarified by an adjustment of the depletion layer width to larger at the n-n nanoheterojunction of two semiconductors (ZnO:Nb2O5) leading to the sensor response enhancement with a higher resistance in air.

Green approach: Ionic liquid assisted synthesis of nanocrystalline ZnO in phyto medium and their antibacterial investigation

In this paper reveals a novel greener strategy of zinc oxide nanocrystals (ZnO NCs) synthesis, which was developed via Punica granatum extract in the presence of ionic liquid (IL). Depending on the organization of IL network, the prepared ZnO nanostructures exhibit good hexagonal and sheet-like morphologies. The crystallization, morphology and chemical composition of synthesized ZnO NCs were characterized by XRD, FTIR, UV–Visible, DLS, SEM and EDS analyses. The morphologically improved ZnO NCs are exhibit very good antibacterial activity against the gram-negative (E. coli) bacterium.

Morphology dependent thermal conductivity of ZnO nanostructures prepared via a green approach

In this study, a green synthesis route for the preparation of ZnO nanostructures with different morphologies was demonstrated. The morphological, structural, elemental composition and thermal properties of the synthesized ZnO nanostructures are characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and thermal conductivity. The prepared ZnO nanostructures are well crystalline nature with a wurtzite structure. The FE-SEM results demonstrated that the ZnO nanostructures with different morphologies such as clusters of coral particles, flower-like particles, ovoid-like particles and spherical particles were obtained via changing the experimental conditions. The flower-like ZnO nanostructures revealed a better thermal conductivity of about 0.34 to 0.22 Wm−1K−1 measured in the temperature range of 298–673 K by coupling of thermal diffusivity and heat capacity.

40% Efficiency enhancement in solar cells using ZnO nanorods as shell prepared via novel hydrothermal synthesis

Herein, rod-like ZnO nanostructures were synthesized via a novel hydrothermal route using Zn(OAc)2, ethylenediamine and hydrazine as a new set of starting reagents. The as-synthesized products were characterized by techniques including XRD, EDS, SEM, XPS, Pl and FTIR. The prepared ZnO nanostructures were utilized as shell on TiO2 film in DSSCs. Effect of precursor type, morphology and thickness of ZnO shell (number of electrophoresis cycle) on solar cells efficiency were well studied. Our results showed that ethylenediamine has crucial effect on morphology of synthesized ZnO nanostructures and using ZnO nanostructures leads to an increase in DSSCs efficiency compared to bare TiO2 from 4.66 to 7.13% (~40% improvement). Moreover, highest amount of solar cell efficiency (7.13%) was obtained by using ZnO nanorods with two cycle of electrophoresis for deposition.

Organometallic synthesis of ZnO nanoparticles for gas sensing: towards selectivity through nanoparticles morphology

ZnO nanoparticles (NP) with different morphologies such as nanorods (NR), isotropic NP, and cloud-like (CL) structures have been synthesized by an organometallic route. The prepared ZnO nanostructures have been deposited on miniaturized silicon gas sensor substrates by an inkjet method, and their responses to CO, C3H8, and NH3 gases have been studied at different operating temperatures (340–500 °C) and relative humidity of 50 %. It is noteworthy that the morphology of the nanostructure of the sensitive layer is maintained after thermal treatment. The morphology of ZnO NP significantly influences the sensor response level and their selectivity properties to reducing gases. Among the three different ZnO types, sensors prepared with NR show the highest response to both CO and C3H8. Sensors made of isotropic NP and CL structures show a lower but similar response to CO. From all investigated nanostructures, sensors made of CL structures show the weakest response to C3H8. With NH3 gas, no effect of the morphology of the ZnO sensitive layer has been evidenced. These different responses highlight the important role of the nanostructure of the ZnO sensitive layer and the nature of the target gas on the detection properties of the sensors. Three different ZnO nanoparticles morphologies (cloud-like, dots, rods) have been employed as sensitive layers in chemoresistive sensors for the selective detection of CO, C3H8 and NH3.

Solvent free synthesis of ZnO nanostructures and evaluation of their capability for water treatment

ZnO hexagonal disks were successfully synthesized using mechanochemical reaction followed by heating treatment. Urea was used as a complexing and directing agent to produce precursor, namely, [Zn(CO(NH2)2)·(NO3)2]·3(H2O). The as-synthesized product indicated a pure and uniform morphology of hexagonal-based disks with the average thickness of 52nm and high aspect ratio of 96. The change of some reaction conditions was led to generate timber-like and particulate structures. The structural and morphological characteristics of all samples were also discussed in detail. In addition, the batch studies were carried out to evaluate the capability of the prepared products for the removal of toxic dyes like Brilliant green and Malachite green, the industry wastes, using adsorption process with a post-photocatalytic treatment. The results showed the hexagonal disks and timber-like nanostructures are the efficient decolorizing adsorbents for water treatment by both of adsorption and photocatalytic pathways. Although the value of maximum adsorption capacity was good, the photocatalytic degradation indicated a superior removal efficiency of dye pollutants on the prepared ZnO nanostructures.

Facile synthesis of ZnO nanoglobules and its photocatalytic activity in the degradation of methyl orange dye under UV irradiation

ZnO nanoglobules were synthesized by a facile hydrothermal process. The detailed structural characterizations revealed that the prepared ZnO nanostructures were uniform, crystalline and with the controlled morphology of nanoglobule-like structures. The photocatalytic activity of the nanoglobules was evaluated on degrading methyl orange dye under UV irradiation. A fast decomposition of the MO dye was observed with a degradation rate of ~94.3% within 150min, which was attributed to the high crystalline quality of ZnO nanostructures that produced reactive sites over the catalyst surface to decompose the MO dye.

Solvothermal Synthesis of One Dimensional ZnO Nanostructures and its Photocatalytic Applications

Here in, we have synthesized ZnO nanostructures using solvothermal reaction method at 200°C for 48h. The synthesized product was systematically characterized with various spectroscopic techniques. XRD analysis revealed the formation of crystalline hexagonal ZnO structure. ZnO indicate the UV-Visible absorbance peak at 379nm and photoluminescence spectra exhibited two peaks one at 391nm attributed to band edge emission and second at 500nm corresponds to certain defects. FE-SEM analysis showed formation of hexagonal shaped rod like morphology. Photocatalytic activity of the prepared ZnO nanostructures was evaluated using methylene blue degradation. The observed rate constant for photocatalytic MB degradation was (Kaap) 6.93 x 10-2 min-1.

Hydrothermal Synthesis of Flower-Like ZnO Nanostructures and their Optical Properties

Flower-like ZnO nanostructures have been synthesized using zinc nitrate hexahydrate and hexamethylenetetramine (HMT) by a low-temperature hydrothermal technique. The prepared ZnO nanostructures exhibit hexagonal wurtzite structure, well-defined flower-like morphology, and a strong blue emission photoluminescence. Flower-like ZnO nanostructures consisting of multilayered petals are formed with the length of about 1 μm. All the flower petals exhibit the tapering feature with the root size of 300-500 nm and tip size of 50-100 nm. The prepared ZnO sample has been studied using x-ray diffraction technique, energy dispersive x-ray analysis, scanning electron microscope and FTIR spectroscopy. The photoluminescence spectrum demonstrated two emission bands, a near band edge (NBE) emission in the UV region centering at 386 nm and a high intensity deep band emission (DBE) in the visible region centering at 483 nm.

Potential barrier modulation in ZnO nanostructures and their CO sensing properties

Colloidal ZnO nanostructures were synthesized by using a high-temperature solution-phase hydrolysis approach. ZnO nanoparticles (NPs) with ∼25 nm particle size were synthesized in ethylene glycol (EG), whereas ZnO nanospheres with an average diameter of ∼500 nm (composed of 10–15 nm ZnO NPs) were formed in polyethylene glycol (PEG). The effect of solvents on the morphology of ZnO nanocrystal clusters was investigated. UV-visible absorption band of both samples was blue-shifted as compared to bulk ZnO. ZnO NPs showed strong UV emission and weak green emission, whereas ZnO nanospheres displayed strong green emission, along with UV emission, in the photoluminescence (PL) spectrum. As prepared ZnO nanostructures were applied for CO sensing, where ZnO NPs exhibited higher response than ZnO nanospheres, although the grain size of ZnO NPs was almost double that of ZnO nanospheres. A relationship between sensing layer microstructure and inter-electrode gap was established. It was demonstrated that the arrangement of grains in the sensing layer between the electrodes plays an important role in gas sensing.