ZnO Nanoclusters Research Articles

Strategy for sensitive and selective NO2 detection at low temperatures utilizing p-type TeO2 nanowire-based sensors by formation of discrete n-type ZnO nanoclusters

Heterostructured nanomaterials have been extensively studied for gas sensing applications because of their unique properties. In this study, we synthesized heterostructured nanomaterials consisting of p-type TeO2 (p-TeO2) NWs and discrete n-type ZnO (n-ZnO) nanoclusters (NCs) to detect NO2 gas molecules. These nanomaterials were synthesized via thermal evaporation and atomic layer deposition (ALD) techniques and then systematically investigated for NO2 sensing capabilities with regard to operating temperature, NO2 response, response/recovery times, and selectivity. The successful formation of discrete n-ZnO NCs depending on ALD conditions was observed via scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and these nanomaterials were characterized by energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The NO2 response of the p-TeO2 NW sensors was considerably enhanced through the formation of discrete n-ZnO NCs. In addition, the synthesized sensors showed good NO2 selectivity in comparison with interfering gases such as SO2, CO, and C2H5OH. Herein, the enhanced NO2 sensing mechanisms of p-TeO2 NWs by formation of discrete n-ZnO NCs will be discussed in detail. We also believe that the formation of discrete n-ZnO NCs is an effective way to enhance NO2 sensing capabilities of p-TeO2 NW-based gas sensors.

A DFT study for adsorption of CO and H2 on Pt-doped ZnO nanocluster

Using density functional theory calculations, we studied structural, electronic and adsorption properties of CO and H2 adsorption on the Pt-doped (ZnO)12 nanoclusters. The more suitable position for the Pt atom is its lateral doping on the nanocluster surface. The lower energy gap for the Pt-doped (ZnO)12 nanoclusters denotes that their conductivity is higher in comparison with the bare nanocluster. The results showed quite a reasonable increase in CO and H2 gas molecules adsorption energies on the nanoclusters compared with the pristine (ZnO)12 due to Pt doping. The sensitivity of the electronic and adsorption properties to the number of molecules was calculated as well. Upon CO adsorption on the Pt-doped (ZnO)12 nanoclusters energy, it is better when no more than two molecules can be attached to one Pt atom, while H2 adsorption provides at least three hydrogen molecules on Pt atom. Also, changes in electronic spectra of nanoclusters under the influence of adsorbed CO and H2 molecules imply a decline in conductivity in such systems. These investigations proved that the Pt-doped (ZnO)12 nanoclusters can be proposed as an approachable candidate in gas sensors for detecting CO and H2 gas. Also, the calculation results of H2 adsorption on Pt-doped (ZnO)12 nanoclusters can help in consideration of the possibility of hydrogen storage media creation.

Tuning of electronic energy levels of NH3 passivated ZnO nanoclusters: A first principle study

We have investigated the optical structural and electronic properties of NH3 capped (ZnO)21 and (ZnO)34 nanoclusters of varying sizes, and their complexes by using density functional theory (DFT. B3LYP functional with LANL2DZ basis set which are implemented in the Gaussian09 package. Structural study of bond length, bond angle and bond distortion increases slightly with increase in the surface passivation. From PDOS there is merely an equivalent contribution to the surface states from ZnO and NH3 molecules except for 3 NH3 capping where contribution of ZnO is very less. Surface of nanoclusters is capped upto five NH3 molecules for both nanoclusters have been examined. The band gap of ZnO clusters decreases with the increase in particle size, illuminating quantum confinement in nanoclusters. The band gap becomes reliable with increase in the surface passivation. Additionally, the uv–vis spectra delivers blue shift of the entire absorption spectra. The amount of spectral displacement from red to blue shift happens due to increase in NH3. Also the presence of amine group on Zn atom will extensively increases its nucleophilicity.

A theoretical study on the pure and doped ZnO nanoclusters as effective nanobiosensors for 5‐fluorouracil anticancer drug adsorption

AbstractThe electronic sensitivity and effectiveness of the pristine, Fe,‐ Mg‐, Al‐ and Ga‐doped ZnO nanoclusters interacted with 5‐fluorouracil (5‐FU) anticancer drug are theoretically investigated in the gas phase using the B3LYP/wB97XD density functional theory calculations with LANL2DZ basis set. It is concluded that 5‐FU adsorption on the doped nanoclusters has relatively higher adsorption energy as compared with the pristine zinc oxide. A number of thermodynamic parameters, such as band gap energy (Eg), adsorption energy (Ead), molecular electrostatic potential, global hardness (η) and density of electronic states, are attained and compared. Also, calculated geometrical parameters and electronic properties for the studied systems indicate that Mg‐ and Ga‐doped Zn12O12 present higher sensitivity to 5‐FU compared with the pristine nanocluster. Theoretical results reveal that adsorption of 5‐FU on the doped nanoclusters is influenced by the electronic conductance of the nanocluster. Therefore, Mg‐ and Ga‐doped ZnO can be considered as promising nanobiosensors for detection of 5‐FU in medicine.

Photocatalytic, dye degradation, and bactericidal behavior of Cu-doped ZnO nanorods and their molecular docking analysis.

Nanostructures of Cu-doped ZnO (Cu:ZnO) were prepared with the chemical precipitation technique with an aim to enhance the photocatalytic and antibacterial properties of ZnO. Phase constitution, the presence of functional groups, optical properties, elemental composition, surface morphology and microstructure were evaluated using an X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometer, energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HR-TEM), respectively. Emission spectra were obtained with a photoluminescence (PL) spectroscope whereas interlayer d-spacing was estimated through HR-TEM. ZnO consisted of a hexagonal wurtzite structure. The crystallinity of the sample was observed to increase with increasing doping concentration. The addition of Cu to ZnO served to transform nanoclusters into nanorods as revealed during SEM analysis. Catalytic activity enhanced due to the formation of nanorods, and UV-Vis absorption spectra showed that methylene blue (MB) degraded more efficiently with ZnO nanoclusters compared to the NaBH4 reagent. In addition, the doped NPs showed enhanced bacterial efficiency for G +ve. Finally, a molecular docking study was undertaken to highlight the importance of the binding interactions of the Cu-doped ZnO nanorods with β-lactamase and beta-ketoacyl-acyl carrier protein synthase III (FabH) as possible enzyme targets. This research indicates that Cu-doped Zn nanorods are a highly efficient photocatalyst and can be aptly employed for wastewater treatment and antibacterial applications.

Obtaining, structure and gas sensor properties of nanopowder metal oxides

The theoretical and experimental researches of formation processes of the nanopowder metal oxides by means of pulsed laser ablation in chemically active environment and studied their properties were carried. Molecular dynamics simulations of the oxidation of zinc nanoclusters to investigate the process of the formation of ZnO nanocluster or Zn-ZnO “core–shell” nanostructures were performed. It established that the structure, shape and oxide layer thickness of the obtained particles directly depends on the initial oxygen density and initial temperature of the system. Density-functional theory studies of the structural and electronic properties of (ZnO)n (n = 34, 60) nanoclusters with native point defects were performed. It was determined that the most favorable defects of the clusters structure were Zn and O vacancies. The study of the features of photoluminescence in different gas environment (vacuum, air, H₂, CO) of nanopowder metal oxides obtained by pulsed laser reactive technology has been done. Correlation between chemical composition, microstructure and electronic properties of initial, laser-modified and doped metal oxides and structures on their basis and their gas sensitivity are established. The peculiarities of the influence of surface doping by impurities (Mg, Au, Pt, Cu, Ge, In, Si, Ni, Sn) on the sensitivity and selectivity of the signal response during adsorption of gases are established. The optimal luminescent gas-sensitive materials (initial and doped ZnO and also the complex metal oxides ZnSiO4:Mn, ZnSiO4:Ti, ZnTiO3, ZnGa2O4, KGa5O8:Mn, ZnGdO3:Eu) were selected to build a multielement gas sensory matrix, the color of its light is determined by the composition of the gas environment. Measurement of the signals of all cells of the gas sensory matrix at once and digital processing make it possible to detection of many gases simultaneously.

ZnO Nanocrystal-Based Chloroform Detection: Density Functional Theory (DFT) Study

We investigated the detection of chloroform (CHCl3) using ZnO nanoclusters via density functional theory calculations. The effects of various concentrations of CHCl3, as well as the deposition of O atoms, on the adsorption over ZnO nanoclusters were analyzed via geometric optimizations. The calculated difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for ZnO was 4.02 eV. The most stable adsorption characteristics were investigated with respect to the adsorption energy, frontier orbitals, elemental positions, and charge transfer. The results revealed that ZnO nanoclusters with a specific geometry and composition are promising candidates for chloroform-sensing applications.

A Density Functional Study on the Sensitivity of Small ZnO Nanoclusters to Sulfamethazine Considering Semilocal and Nonlocal Functionals

In this study, the possible application of small ZnO nanoclusters in the development of biosensors was investigated by density functional theory. Sulfamethazine is an antibiotic compound with an extensive range of prophylactic and therapeutic applications in animal husbandry. Because of the environmental risks associated with the overconsumption of antibiotics, the development of precise and selective detection methods is imperative. In this regard, the interaction of sulfamethazine and ZnO nanoclusters was investigated utilizing the semilocal functional of Perdew, Burke, and Ernzerhof and nonlocal functional developed by Vydrov and Voorhis. The results showed that the antibiotic can be adsorbed on ZnO nanoclusters. By considering van der Waals interactions, an increase was observed in adsorption energy when compared with the semilocal functional. Inclusion of van der Waals forces, however, did not alter the spatial configuration of the adsorbed molecule. The imaginary part of the dielectric function of ZnO nanoclusters was reduced upon antibiotic adsorption, which became more pronounced in the case of larger ZnO nanoclusters.

The Multisensor Array Based on Grown-On-Chip Zinc Oxide Nanorod Network for Selective Discrimination of Alcohol Vapors at Sub-ppm Range.

We discuss the fabrication of gas-analytical multisensor arrays based on ZnO nanorods grown via a hydrothermal route directly on a multielectrode chip. The protocol to deposit the nanorods over the chip includes the primary formation of ZnO nano-clusters over the surface and secondly the oxide hydrothermal growth in a solution that facilitates the appearance of ZnO nanorods in the high aspect ratio which comprise a network. We have tested the proof-of-concept prototype of the ZnO nanorod network-based chip heated up to 400 °C versus three alcohol vapors, ethanol, isopropanol and butanol, at approx. 0.2–5 ppm concentrations when mixed with dry air. The results indicate that the developed chip is highly sensitive to these analytes with a detection limit down to the sub-ppm range. Due to the pristine differences in ZnO nanorod network density the chip yields a vector signal which enables the discrimination of various alcohols at a reasonable degree via processing by linear discriminant analysis even at a sub-ppm concentration range suitable for practical applications.

Transition metals doped ZnO nanocluster for ethylene oxide detection: A DFT study

Abstract Density functional theory (DFT) studies at B3LYP/6-31G (d) (Becke, 3-parameter, Lee-Yang-Parr) level were performed to evaluate adsorption interactions between ethylene oxide (EO) molecule, and pristine and transition metals (TM) (i.e., Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped ZnO nanocluster (TM-doped Zn12O12). The adsorption energy (Ead), band gap energy (Eg), Mulliken charge transfer (QT) and molecular electrostatic potential (MEP) were calculated to examine the sensitivity of the Zn12O12 and its TM-doped forms toward EO detection. It was found that in contrast to the pristine Zn12O12, the electronic properties of TM-doped Zn12O12 were sharply sensitive to the presence of EO gas molecules. The results revealed that among the studied TM-doped Zn12O12, Cr- and V-doped Zn12O12 have great potential applicability as EO sensor, due to their highest Eg change (ΔEg) values, after the EO adsorption. Moreover, the density of state (DOS) calculations confirmed that strong electronic interaction between Cr- and V-doped Zn12O12 and EO molecules can makes them interesting empirical candidate for detection and adsorptive removal of EO gas molecules.

Characterization and property of bifunctional Zn-incorporated TiO2 micro-arc oxidation coatings: The influence of different Zn sources

Abstract In the present work, Zn-incorporated TiO2 coatings are prepared through a one-step micro-arc oxidation (MAO) method on a grade 4 pure titanium with the addition of either Na2Zn-EDTA solution or ZnO nanoparticles (NPs) as Zn sources. The microstructural features of both Zn-incorporated TiO2 coatings were systematically examined. It is revealed that different Zn sources result in significant difference of phase component, chemical state, composition and morphology between the resultant Zn-incorporated MAO coatings. Zn species could be present as ZnO and Zn(OH)2 in the coating when Na2Zn-EDTA was used as Zn source whereas the presence of ZnO nano-clusters is obvious on the coating surface with ZnO NPs as Zn source. The addition of ZnO NPs during the MAO process also leads to a lower Zn content of the resultant coating, which is more defective with increased thickness in comparison to that of Na2Zn-EDTA. Further, antibacterial property and osteogenic activity of both Zn-incorporated coatings were examined. Both Zn-incorporated coatings exhibit favourable bacterial inhibition ability and bone formability, suggesting the successful synthesis of bifunctional coatings through the facile one-step micro-arc oxidation method.

Structure, electrical properties and luminescence of ZnO nanocrystals deposited in SiO2/Si track templates

ZnO nanoclusters obtained by electrochemical deposition (ECD) of zinc in track template a-SiO2/Si-n have been studied. The structure SiO2/Si was irradiated at DC-60 cyclotron with 200 MeV Xe ions (Φ = 108 ions/cm2) with subsequent chemical etching in the diluted hydrofluoric acid (HF). Electrochemical deposition (ECD) of Zn in track template was carried out in the potentiostatic mode. The surface of samples was examined using a SEM JSM 7500F microscope. X-ray diffraction analysis was carried out using a D8 ADVANCE ECO X-ray diffractometer. According to XRD, the electrodeposition of zinc into the a-SiO2/Si-n track template resulted in a formation of zincblende (ZB) ZnO nanocrystals. Current-voltage characteristics and photoluminescence of SiO2/Si track template with ZnO ZB nanocrystals were investigated.

Low-Cost and High-Performance ZnO Nanoclusters Gas Sensor Based on New-Type FTO Electrode for the Low-Concentration H₂S Gas Detection.

A low-cost and high-performance gas sensor was fabricated by the in-situ growing of ZnO nanoclusters (NCs) arrays on the etched fluorine-doped tin dioxide (FTO) glass via a facile dip-coating and hydrothermal method. Etched FTO glass was used as a new-type gas-sensing electrode due to its advantages of being low cost and having excellent thermal and chemical stability. ZnO NCs are composed of multiple ZnO nanorods and can provide adequate lateral contacts to constitute the paths required for the gas-sensing tests simultaneously, which can provide many advantageous point junctions for the detection of low-concentration gases. The gas-sensing tests indicate that the ZnO NCs gas sensor has good selectivity and a high response for the low-concentration H2S gas. The sensing response has reached 3.3 for 500 ppb H2S at 330 °C. The excellent gas-sensing performances should be attributed to the large specific surface area of in-situ grown ZnO NCs, the perfect ohmic contact between ZnO NCs and FTO electrode and the variation of grain boundary barrier at the cross-linked junctions of multiple nanorods. In addition, the detailed effect of work temperature and gas concentration on gas-sensing, the stability of gas sensors and the corresponding response mechanism are also discussed in the present paper.

Modeling Nucleation and Growth of ZnO Nanoparticles in a Low Temperature Plasma by Reactive Dynamics.

The very first stages of nucleation and growth of ZnO nanoparticles in a plasma reactor are studied by means of a multiscale computational paradigm where the DFT-GGA approach is used to evaluate structure and electronic energy of small (ZnO) N clusters ( N ≤ 24) that are employed as a training set (TS) for the optimization of a Reactive Force Field (ReaxFF). Reactive Molecular Dynamics (RMD) simulations based on this tuned ReaxFF are carried out to reproduce nucleation and growth in a realistic environment. Inside the reaction chamber the temperature is around 1200 K, and the zinc atoms are oxidized in an oxygen-rich atmosphere at high pressure (about 20 atm), whereas in the quenching chamber where the temperature is lower (about 800 K) the ZnO embryo-nanoclusters are grown. The main processes ruling gas-phase nucleation and growth of ZnO nanoclusters are identified and discussed together with the dependence of the inception time and average stoichiometry of nanoclusters of different size on the composition of precursor material and physical parameters.

ZnO Nanoclusters Supported on Dealuminated Zeolite β as a Novel Catalyst for Direct Dehydrogenation of Propane to Propylene

AbstractSmall ZnO nanoclusters supported on dealuminated β zeolite were prepared and evaluated for catalyzing direct dehydrogenation of propane to propylene (PDH), exhibiting high catalytic performance. N2 sorption, XRD, TEM, 27Al and 28Si MAS NMR, IR, XRF, DR UV‐vis, XPS, and NH3‐TPD techniques were employed to characterize the physicochemical properties of this novel catalyst system. It is found that the Zn species can be accommodated in the vacant T‐atom sites of dealuminated β zeolite due to the reaction of aqueous zinc acetate solution with silanol groups, and thus, producing massive small ZnO nanoclusters as active phases in PDH. Additionally, dealuminated β zeolite can greatly depress side reactions attributable to the absence of strong acid sites, thereby guaranteeing high catalytic activity, propylene selectivity and stability. As a result, the optimal catalyst of 10 wt% Zn loaded on dealuminated β zeolite exhibits a high initial propane conversion of around 53 % and a superior propylene selectivity of about 93 % at a space velocity of 4000 cm3 gcat−1 h−1, together with the high stability and satisfactory reusability. This study may open a new way to design and synthesize highly active PDH catalysts with high selectivity and stability.

One-step synthesis of reduced graphene oxide sheathed zinc oxide nanoclusters for the trace level detection of bisphenol A in tissue papers

After a long-term toxicity study on Bisphenol A (BPA), the European Union and U.S food and drug administration updating the rules regarding the usage of BPA by extending the prohibition of BPA to include in the production of papers, on February 2018. Therefore, it is essential to establish the trace level BPA detectors in paper samples. In this report, the synthesis of novel ZnO nanoclusters wrapped with reduced graphene oxide (ZnO NCs/rGO) and its application towards the selective electrocatalytic detection of BPA are described. Initially, ZnO NCs/rGO is synthesized by the one-step hydrothermal approach, and various characterizations explain the compound's compositions and structure. The significance of ZnO NCs/rGO together with good electrocatalytic properties leads this material to the platform for electrochemical sensor. Finally, ZnO NCs/rGO was fabricated and validated as an effective sensor for the sensitive detection of BPA. The demonstrated sensor revealed excellent detection of BPA with the very low detection limit (2.1 nM), and also it offered good analytical parameters with more extensive linear range and higher sensitivity. Likewise, the sensor annexes good durability, reproducibility, and selectivity towards the determination of BPA. Due to the nourishing capacity of the prepared ZnO NCs/rGO, it is employed for the detection of BPA in tissue paper samples.

Band gap opening and optical absorption enhancement in graphene using ZnO nanocluster

Electronic, optical and transport properties of the graphene/ZnO heterostructure have been explored using first-principles density functional theory. The results show that Zn12O12 can open a band gap of 14.5 meV in graphene, increase its optical absorption by 1.67 times covering the visible spectrum which extends to the infra-red (IR) range, and exhibits a slight non-linear I–V characteristic depending on the applied bias. These findings envisage that a graphene/Zn12O12 heterostructure can be appropriate for energy harvesting, photodetection, and photochemical devices.

Influence of annealing on the optoelectronic properties of the GLAD synthesized SiO x –ZnO heterostructure nanoclusters

We utilized Glancing angle deposition (GLAD) technique to synthesize SiO x –ZnO heterostructure nanoclusters. The as deposited heterostructure nanoclusters were annealed at 550 °C for 1 h in an open air using heating and cooling ramp of 5°C min−1. The FEG-SEM image represents the uneven growth of SiO x –ZnO heterostructure nanoclusters. Due to the agglomeration of smaller nanocluster, SiO x –ZnO heterostructure nanoclusters become more prominent after annealing. EDX indicates the presence of O, Si and Zn. The increase in the concentration of oxygen in annealed SiO x –ZnO heterostructure nanoclusters is attributed to the absorption of O2 molecules during an open air annealing. The formation of heterostructure is shown by the TEM image. The nanoclusters consist of SiO x and ZnO indicating the length of ~ 126 and ~ 97 nm, respectively. The SAED pattern depicts the crystalline nature of ZnO nanoclusters. The XRD pattern revealed that ZnO nanoclusters had wurtzite structure with (100), (002) and (101) orientations. The PL emission at 420 nm is ascribed to the radiative recombination of photoexcited electrons in the conduction band (CB) of ZnO and acceptor such as traps present in SiO x . The band gap significantly increases to 3.45 eV after annealing and it corresponds to main band gap of ZnO. The FTIR result shows the bonding of SiO x –ZnO heterostructure nanoclusters. In addition to the above measurement, we determined the I–V characteristics of the as deposited and annealed SiO x –ZnO heterostructure nanoclusters. The as deposited sample shows schottky behavior which is applicable for nanoscale optoelectronic devices whereas the ohmic nature obtained after open air annealing is suitable for the application of solar cells.

A theoretical investigation on the adsorption of platinol drug on a ZnO nanocluster: Solvent and density functional effect

The reactivity, and electronic sensitivity of the synthesized Zn12O12 nanocluster were investigated toward anticancer platinol drug using density functional theory calculations at gas phase and aqueous solution. It was predicted that platinol lies on a hexagonal ring of the ZnO nanocluster so that its two H atoms and the Cl atoms simultaneously interact with O and Zn atoms of a ZnO bond. The adsorption energy and change of Gibbs free energy (298K and 1atm) are predicted to be about −31.7 and −20.8kcal/mol, respectively. The electronic properties of Zn12O12 nanocluster are significantly sensitive to the presence of platinol and the cluster may be promising candidate for detection of this drug. After the adsorption of the drug, the valence level of ZnO nanocluster implicitly shifts to higher energies. Thus, the electrical conductivity largely increases because of a decrease in the gap of semiconductor. As a result, the ZnO nanocluster can produce an electrical signal at the presence of the platinol drug which helps to detect it. Also, we found that the ZnO nanocluster benefits from a short recovery time about 1.7s at room temperature as a sensor for platinol. It was predicted that at water solvent, the adsorption energy and sensitivity of the ZnO are somewhat decreased.

Electrical and gas sensing properties of ZnO nanoclusters by microwaves and carbon assisted

ZnO nanoclusters were prepared by heating ZnO powder with carbon charcoal in a 1000 W microwave oven for 10, 20 and 30 min. The morphology of the prepared samples were studied by scanning electron microscopy (SEM(and X-ray diffraction techniques. SEM images revealed the agglomeration of the particles-clusters with 10-50 µm in diameter. The XRD patterns showed hexagonal crystal structure. The I-V characteristic curves of the synthesized products showed diode material behaviour. The gas sensing properties of the materials exhibit high sensitivity towards CO2 detection.