CuO ZnO Research Articles

Microwave-Epoxide-Assisted Hydrothermal Synthesis of the CuO/ZnO Heterojunction: a Highly Versatile Route to Develop H2S Gas Sensors.

A robust synthesis approach to develop CuO/ZnO nanocomposites using microwave-epoxide-assisted hydrothermal synthesis and their proficiency toward H2S gas-sensing application are reported. The low-cost metal salts (Cu and Zn) as precursors in aqueous media and epoxide (propylene oxide) as a proton scavenger/gelation agent are used for the formation of mixed metal hydroxides. The obtained sol was treated using the microwave hydrothermal process to yield the high-surface area (34.71 m2/g) CuO/ZnO nanocomposite. The developed nanocomposites (1.25–10 mol % Cu doping) showcase hexagonal ZnO and monoclinic CuO structures, with an average crystallite size in the range of 18–29 nm wrt Cu doping in the ZnO matrix. The optimized nanocomposite (2.5 mol % Cu doping) showed a lowest crystallite size of 21.64 nm, which reduced further to 18.06 nm upon graphene oxide addition. Morphological analyses (scanning electron microscopy and transmission electron microscopy) exhibited rounded grains along with copious channels typical for sol–gel-based materials . Elemental mapping displayed the good dispersion of Cu in the ZnO matrix. When these materials are employed as a gas sensor, they demonstrated high sensitivity and selectivity toward H2S gas in comparison with the reducing gases and volatile organic compounds under investigation. The systematic doping of Cu in the ZnO matrix exhibited an improved response from 76.66 to 94.28%, with reduction in operating temperature from 300 to 250 °C. The 2.5 mol % doped Cu in ZnO was found to impart a response of 23 s for 25 ppm of H2S. Gas-sensing properties are described using an interplay of epoxide-assisted sol–gel chemistry and structural and morphological properties of the developed material.

WO3–ZnO and CuO–ZnO nanocomposites as highly efficient photoanodes under visible light illumination

We prepared ZnO nanocomposites with WO3 or CuO nanostructures to improve the photocatalytic performance of ZnO nanostructures. Characterization of the nanocomposites using scanning electron microscopy, x-ray diffraction, UV–vis spectrometry and photoluminescence revealed the morphologies and wide light absorption range of the materials. The highest current densities of WO3/ZnO and CuO/ZnO nanocomposites were 1.28 mA cm−2 and 2.49 mA cm−2 at 1.23 V (versus a reversible hydrogen electrode) under AM 1.5 100 mW cm−2, which are ~1.2- and 3.5-fold greater than those of bare ZnO nanostructures, respectively. The easy fabrication process suggests that nanocomposites with narrow bandgap materials, such as WO3 and CuO, will improve the performance of electrochemical and optoelectrical devices such as dye-sensitized solar cells and biosensors.

Nanocrystalline transition metal oxides and their composites with reduced graphene oxide and carbon nanotubes for photocatalytic applications

Transition metal oxide nanoparticles (CuO, ZnO & Fe2O3) and mixed metal oxides CuO. ZnO.Fe2O3 were fabricated by facile co-precipitation approach for photocatalytic treatment of organic dyes. The structural features, phase purity, crystallite size and morphology of individual and mixed metal oxides were analysed by X-rays diffraction patterns (XRD) and scanning electron microscopic (SEM) analysis. Electrical behaviour of CuO, ZnO, Fe2O3 and mixed metal oxides CuO. ZnO.Fe2O3 was explored by current-voltage (I-V) measurements. Functional groups present in the synthesized metal oxides were investigated by Fourier transform infrared spectroscopy (FTIR) which ensures the existence of M-O functional groups in the samples. The optical bandgap analysis was carried out by UV–visible spectroscopic technique which revealed that the blend of three different transition metal oxides reduced the bandgap energy of mixed metal oxides. The reason behind this reduced bandgap energy is formation of new electronic state which arises due to the metal-oxygen interactions. Moreover, the nanocomposites of CuO.ZnO.Fe2O3 with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) were prepared to study the effect of the carbonaceous materials on the rate of photodegradation. These carbonaceous nanomaterials have plethora properties which can bring advancement in sector of photocatalytic treatment of wastewater. The photocatalytic experiments were performed using methylene blue (MB) as standard dye for comparative study of metal oxides and their composites with rGO and CNTs. The percentage degradation of methylene blue (MB) by nanocomposite CuO.ZnO.Fe2O3/rGO is 87% which is prominent among all samples. This result ascribed the photocatalytic aspects of reduced graphene oxide along with mixed metal oxides.

Low-temperature and highly sensitivity H2S gas sensor based on ZnO/CuO composite derived from bimetal metal-organic frameworks

The bimetallic metal-organic frameworks (MOF) Zn/Cu-BTC were prepared by a facile solvothermal method in one step and used as a self-sacrificed template to obtain the ZnO/CuO composites. The composites with different Cu/Zn molar ratios were characterized by XRD, FESEM, and XPS. The ZnO/CuO composite exhibited an octahedral structure, and a p-n heterojunction may be formed between p-type CuO and n-type ZnO. To prove its functional characteristics, the ZnO/CuO composite was used as a sensing material to test its gas sensitivity. The effect of Cu/Zn molar ratios was examined, and the results showed that the optimized ZnO/CuO (1: 0.33) composite based gas sensor exhibited reasonable selectivity to 10 ppm H2S, operated at 40 °C. The sensitivities were improved by 17.1 times and 327.8 times compared with the pristine CuO and ZnO based gas sensors, respectively. Moreover, the detection limit to H2S of such sensors could be reduced as low as 300 ppb. The sensing mechanism has been thoroughly studied and such ZnO/CuO composite is an ideal candidate for highly sensitive detection for H2S with low power consumption in the real application.

Engineered ZnO and CuO Nanoparticles Ameliorate Morphological and Biochemical Response in Tissue Culture Regenerants of Candyleaf (Stevia rebaudiana).

Sustainable production of secondary metabolites in medicinal plants by artificial culturing on the industrial scale has gained worldwide importance. Engineered nanoparticles (ENPs) play a pivotal role in the elicitation of compounds of medicinal value. This investigation explores the influence of ZnO and CuO ENPs on in vitro roots formation, non-enzymatic antioxidant activities, and production of steviol glycosides (SGs) in regenerants of Candyleaf, Stevia rebaudiana. ENPs were applied in 0, 2, 20, 200, and 2000 mg/L of concentration in the MS medium containing plant shoots. The percentage of rooting induced was 91% and 94% by applying ZnO ENPs (2 mg/L) and CuO ENPs (20 mg/L), respectively. Moreover, at 2 mg/L of ZnO and 20 mg/L of CuO ENPs, the high performance liquid chromatography studies determined the significantly greatest content of SGs; rebaudioside A (4.42 and 4.44) and stevioside (1.28 and 1.96). Phytochemical studies including total flavonoid content, total phenolic content, and 2,2-diphenyl-1-picryl hydrazyl-free radical scavenging activity were calculated highest by the regenerants grown in 2 mg/L of ZnO and 20 mg/L of CuO ENPs dosage. Both ZnO and CuO ENPs at 200 mg/L and 2000 mg/L of concentration induced adverse effects on plant biomass, antioxidant activities, and SGs content up to 1.22 and 1.77 for rebaudioside A and 0.21 and 0.25 for stevioside. Hence, the biochemical and morphophysiological responses of Candyleaf were elicited as a defense against ZnO and CuO ENPs applied under threshold limit. This artificial biotechnological technique holds great promise for continued production of natural antioxidants on commercial scale and our study has further strengthened this impact.

Field emission enhancement of composite structure of ZnO quantum dots and CuO nanowires by Al2O3 transition layer optimization

In this paper, ZnO quantum dots (QDs)-CuO nanowires (NWs) heterostructure was synthesized by a mild solution method. The Al2O3 transition layer were deposited on CuO NWs by surface modification engineering using atomic layer deposition (ALD) to increase the nucleation probability of ZnO QDs. The field emission properties of the composites were investigated. The results reveal that the CuO@Al2O3/ZnO QDs ternary heterostructures have the turn-on field of 2.82 V/μm and the field emission enhancement factor of 5798, which are superior to that of ZnO QDs-CuO NWs and pure CuO NWs. The improvement of field emission performance is mainly attributed to the decrease of the electron transport barrier at the interface and the increase of the oxygen vacancies, making it easier to transport electrons to ZnO QDs. The use of amorphous Al2O3 in the transition layer also effectively alleviates the lattice mismatch between ZnO QDs and the substrate. This study provides an effective method for enhancing the field emission performance of the core-shell nanomaterial device.

Optical and electronic properties of chemical bath deposited p-CuO and n-ZnO nanowires on silicon substrates: p-CuO/n-ZnO nanowires solar cells with high open-circuit voltage and short-circuit current

P-type cupric oxide (p-CuO) and p-type cupric-oxide/n-type zinc oxide nanowires (p-CuO/n-ZnO NWs) heterojunction diodes were fabricated by employing chemical bath deposition technique on n-silicon (n-Si) substrate. The work demonstrates the potential of zinc oxide nanowires as window layer owing to its wide and direct band gap for metal oxide based solar cells. Optical and electronic properties of the CuO film and ZnO nanowires including refractive index, absorption coefficient and band gaps were investigated by using spectroscopic ellipsometric analysis. Impact of nanowire morphology, chemical composition and crystallite structures on optical and photovoltaic performance of p-CuO/n-Si and p-CuO/n-ZnO NWs were investigated. Absorption coefficient in the near UV–visible range was observed to improve significantly by incorporating n-ZnO nanowires which was desired for the solar cell applications. The comparative photovoltaic performance showed improvements of both the short-circuit current density (Jsc) and open circuit voltage (Voc), due to reduced interface recombination and enhanced absorption for the increased surface-to-volume ratio of ZnO nanowires in the p-CuO/n-ZnO NWs heterojunction. Photovoltaic performance with Jsc, Voc and power conversion efficiency of 11.1 mA/cm2, 1.1 V and 4.19% was obtained. Therefore, the work emphasizes importance of using the combination of n-ZnO nanowires and p-CuO film as the wide- and low- band gap materials for improving performance of the future low-cost solar cell with superior efficiency.

Simulation of single-step dimethyl ether synthesis from syngas

Dimethyl ether (DME) is an alternative energy that simplest ether. DME has 2 ways to synthesis from syngas. The single-step DME synthesis combined methanol synthesis and methanol dehydration in one reactor. This study is focusing on DME production from synthesis gas by used catalyst as CuO–ZnO–Al2O3/γ-Al2O3. For the simulation we simulated in Aspen Plus V8.8 and used Langmuir–Hinshelwood Hougen–Watson (LHHW) kinetic model for the reaction rate of DME synthesis in a plug flow reactor with catalyst. Simulation is varying the temperature range between 220 °C to 300 °C and pressure between 20 bar to 80 bar to find the suitable condition for the single-step DME synthesis with CuO–ZnO–Al2O3/γ-Al2O3 catalyst.

Structural, Microscopy Analysis and Compressive Strength of ZnO–CuO Nanocomposites

Currently, researches on nanocomposites become an active research area due its unique properties. Earlier, many researches are done for synthesizing the multidimensional structures for developing efficient and new Nano devices. In this present work, we synthesized ZnO–CuO nanocomposites using sol–gel method. The obtained nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) analysis and Compressive strength analysis using compressive testing machine (CTM). Herein, the structure and size of the ZnO–CuO nanocomposites were studied using XRD. And the average particle size was found to be 34 nm. The TEM analysis has the evidence of the XRD result. The enhancement in compressive strength of the ZnO–CuO nanocomposites was determined using CTM machine up to 4 wt.%.

One-pot green synthesis of ZnO–CuO nanocomposite and their enhanced photocatalytic and antibacterial activity

This work focused on employing Calotropis gigantea leaf extract as reducing agent/fuel and (Zn(NO3)2.6H2O), (Cu(NO3)2.3H2O) as precursors to synthesise ZnO–CuO nanocomposite by solution combustion method. Prepared nanocomposites were characterised using x-ray powder diffraction (XRD), scanning electron microscope (SEM) with energy dispersive x-ray analysis (EDAX), high-resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared spectroscopy (FT-IR). XRD result revealed crystalline nature with average crystallite size of 35 nm. SEM images indicate that particles are agglomerated and EDAX confirms the composition of elements with pure phase. HR-TEM images indicated that average sizes of the prepared ZnO–CuO nanocomposite were 10–40 nm with spherical and hexagonal shapes. The presence of functional groups such as Zn−O, Cu−O, −OH, −C–O, and C–H was confirmed by FT-IR spectrum. The optical energy bandgap was estimated using Kubelka-Munk equation by the aid of diffuse reflectance spectroscopy (DRS). The synthesised nanocomposite showed superior photocatalytic activity of degradation efficiency 97.93% against methylene blue dye. Further, anti-bacterial activity was investigated by agar well diffusion procedure against two bacterial strains (Escherichia coli and Staphylococcus aureus) and significant zone of inhibition to the bacterial strains was observed.

Light and Shadow Effects in the Submerged Photolytic Synthesis of Micropatterned CuO Nanoflowers and ZnO Nanorods as Optoelectronic Surfaces

A facile surface patterning method using low temperature and atmospheric pressure is desirable for optoelectronic device fabrication. In this work, we demonstrate a fascinating dynamic fabrication ...

Bioavailability and translocation of metal oxide nanoparticles in the soil-rice plant system

To determine the bioavailability and translocation of metal oxide nanoparticles (MONPs) in the soil-rice plant system, we examined the accumulation and micro-distribution of ZnO nanoparticles (NPs), CuO NPs and CeO2 NPs (50, 100 and 500 mg/kg) in the paddy soil and rice plants under flooded condition for 30 days using single-step chemical extraction and diffusive gradients in thin films (DGT) technique combined with micro X-ray fluorescence spectroscopy (μ-XRF). The results show that various MONPs changed the soil properties, especially the redox potential was enhanced to −165.33 to −75.33 mV compared to the control. The extraction efficiency of Zn, Cu and Ce in the paddy soil from high to low was EDTA, DTPA, CaCl2 and DGT. Moreover, exposure to 500 mg/kg CuO NPs and CeO2 NPs induced the primary accumulation of Cu and Ce elements in rice roots as high as 235.48 mg Cu/kg and 164.84 mg Ce/kg, respectively, while the Zn concentration in shoots was up to 313.18 mg/kg under highest ZnO NPs with a 1.5 of translocation factor. The effect of MONPs on the plant growth was mainly related to the chemical species and solubility of MONPs. Micro-XRF analysis shows that Zn was mostly located in the root cortex while Cu was primarily accumulated in the root exodermis and few Ce distributed in the root. Pearson correlation coefficients indicate that only DTPA-extracted metals in soil were significantly and well correlated to the Zn, Cu and Ce accumulation in rice seedlings exposed to MONPs. This work is of great significance for evaluating the environmental risks of MONPs in soil and ensuring the safety of agricultural products.

Enhancement in the performance of nanostructured CuO-ZnO solar cells by band alignment.

In this study, we investigated the effect of cobalt doping on band alignment and the performance of nanostructured ZnO/CuO heterojunction solar cells. ZnO nanorods and CuO nanostructures were fabricated by a low-temperature and cost-effective chemical bath deposition technique. The band offsets between Zn1−xCoxO (x = 0, 0.05, 0.10, 0.15, and 0.20) and CuO nanostructures were estimated using X-ray photoelectron spectroscopy and it was observed that the reduction of the conduction band offset with CuO. This also results in an enhancement in the open-circuit voltage. It was demonstrated that an optimal amount of cobalt doping could effectively passivate the ZnO related defects, resulting in a suitable conduction band offset, suppressing interface recombination, and enhancing conductivity and mobility. The capacitance–voltage analysis demonstrated the effectiveness of cobalt doping on enhancing the depletion width and built-in potential. Through impedance spectroscopy analysis, it was shown that recombination resistance increased up to 10% cobalt doping, thus decreased charge recombination at the interface. Further, it was demonstrated that the insertion of a thin layer of molybdenum oxide (MoO3) between the active layer (CuO) and the gold electrode hinders the formation of a Schottky junction and improved charge extraction at the interface. The ZnO/CuO solar cells with 10% cobalt doped ZnO and 20 nm thick MoO3 buffer layer achieved the best power conversion efficiency of 2.11%. Our results demonstrate the crucial role of the band alignment on the performance of the ZnO/CuO heterojunction solar cells and could pave the way for further progress on improving conversion efficiency in oxide-based heterojunction solar cells.

In situ approach to fabricate heterojunction p–n CuO–ZnO nanostructures for efficient photocatalytic reactions

Stable interfacial contact in p–n CuO–ZnO nanostructures with different morphologies synthesized via in situ addition of a controlled copper remarkably improved their photocatalytic properties in contrast to incorporation by an impregnation approach.

Tailoring the optical properties of zinc/copper–incorporated onto eggshell synthesized via electrochemical method

Zinc/copper–incorporated onto eggshell was prepared by electrochemical technique and catalysts was subjected UV–vis DRS analysis for optical properties evaluation. The reflectance band edge of ZnO was slightly shifted from 375 to 371 nm after coupling with CuO. Different ZnO and CuO ratio content influence the intensity of ZnO–CuO characteristic reflectance band. Increased CuO ratio content narrower the band energy with 1 wt% ZnO–5 wt% CuO/ES catalyst established lowest value 1.67 eV.

Connecting theory with experiment to understand the photocatalytic activity of CuO–ZnO heterostructure

Semiconductor based photocatalysis attracts wide attention because of its ability to directly utilize solar energy to degrade pollutants and convert energy, with heterojunction photocatalysts being good candidates for superior activity due to the spatial separation of photogenerated electron–hole pairs. Herein, CuO/ZnO heterostructures were successfully synthesized by a microwave-assisted hydrothermal method, with the structure, electronic and photocatalytic properties analyzed by means of experimental and theoretical methods. The X-ray diffraction patterns revealed that a CuO/ZnO heterostructure was formed, while FE-SEM analysis indicates the role of different morphologies for CuO, ZnO and CuO/ZnO heterostructures. The solar-driven photocatalytic measurements combined with DFT calculations indicate that CuO, as a p-type and narrow band-gap sensitizer, can make the n-type ZnO respond to visible light and promote the separation of photogenerated charge carriers by building a p-n heterogeneous structure. As a result, the CuO/ZnO heterostructure shows good promise for solar-driven photodegradation.

Efficient formaldehyde sensor development based on Cu-codoped ZnO nanomaterial by an electrochemical approach

An aggregated copper codoped zinc oxide (CZO; CuO.ZnO) nanomaterial was synthesized to detect formaldehyde (HCHO) from aqueous solution via electrochemical reactions. The as-grown CZO nanostructures have a typical diameter of 140 ± 15 nm in size. From the spectroscopic and electrochemical studies it was revealed that the CZO nanomaterials exhibit completely different electrochemical and electro-catalytic properties from the constituents. In terms of electro-catalytic oxidation reactions, the best reactivity was noticed at the 7.0 pH value. At the CZO surface, when HCHO molecules come in contact with the CZO surface, a coupled two electron two protons transfer reaction occur. This CZO/GCE sensor showed an excellent sensitivity (5.427 μAμM−1 cm-2), extremely low limit of detection (LOD: 4.1 ± 0.1 nM; S/N = 3), limit of quantification (LOQ: 13.67), long-term stability, and decent repeatability. In the investigative study, a linear calibration plot was found for a wide range of concentration of HCHO (0.002 μM–6000 μM; r2 = 0.9982). Compared to the bare ZnO NPs and CuO NPs, the response value at the CZO NPs toward 2.25 μM HCHO is more than ten-fold higher. This method could be an effective method of sensitive and selective electrochemical sensor development to detect hazardous and carcinogenic chemicals in aqueous medium for the safety of environmental and healthcare fields in broad scales.

Flexible CuO–ZnO nano-bulk junction with photovoltaic response

Nano-Bulk junction grown over flexible Cu substrate demonstrating photovoltaic response has been developed. The structure of the device fabricated by us is Cu/CuO/CuO-ZnO/ZnO/Ag with the entire device fabrication sequence taking place at a temperature lower than 330 K. A nano-crystalline p-type CuO layer was deposited on Cu substrate using chemical bath deposition at 300 K. The n-type ZnO was solution grown and spin coated over the blend of CuO-ZnO deposited as a buffer between p-type CuO an n-type ZnO layer. The optimized device exhibited an open circuit voltage of 0.25 V, a short circuit current density of 2 × 10–6 A cm−2, a fill factor of 8% and efficiency of 0.11%. A space charge limited conduction mechanism was identified for the best device structure. The optimized cell structure had a diode ideality factor of 2.11 and work function of 3.28 eV.

CuO–ZnO heterojunction derived from Cu2+-doped ZIF-8: A new photoelectric material for ultrasensitive PEC immunoassay of CA125 with near-zero background noise

By direct calcination of Cu2+-doped ZIF-8 in oxygen atmosphere, a new photoelectric material, CuO–ZnO heterojunction, was prepared. The morphology and structure were investigated in detail by several methods, such as scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption method and X-ray diffraction. Under visible light irradiation, CuO–ZnO heterojunction exhibits excellent PEC behavior in aqueous media with the presence of ascorbic acid (AA) and dissolved oxygen at −0.3 V. Taking the CA125-antibody functionalized CuO–ZnO heterojunction (CuO–ZnO-Ab2) as a signal source, a novel photoelectrochemical (PEC) immunosensing platform was developed for ultrasensitive assay of CA125. Because of the target-induced introduction of photoelectric material to the sensing platform, the proposed PEC immunosensor has excellent performance for CA125 assay: near-zero background noise, wide linear response range (1 × 10−5 U/mL to 100 U/mL) and low detection limit (3.16 × 10−6 U/mL). The developed CuO–ZnO heterojunction and the related PEC sensing platform may have promising applications in ultrasensitive and highly accurate monitoring of various proteins in bioanalysis and disease diagnosis.

Heterostructural CuO-ZnO Nanocomposites: A Highly Selective Chemical and Electrochemical NO2 Sensor.

A simple one-step chemical method is employed for the successful synthesis of CuO(50%)–ZnO(50%) nanocomposites (NCs) and investigation of their gas sensing properties. The X-ray diffraction studies revealed that these CuO–ZnO NCs display a hexagonal wurtzite-type crystal structure. The average width of 50–100 nm and length of 200–600 nm of the NCs were confirmed by transmission electron microscopic images, and the 1:1 proportion of Cu and Zn composition was confirmed by energy-dispersive spectra, i.e., CuO(50%)–ZnO(50%) NC studies. The CuO(50%)–ZnO(50%) NCs exhibit superior gas sensing performance with outstanding selectivity toward NO2 gas at a working temperature of 200 °C. Moreover, these NCs were used for the indirect evaluation of NO2 via electrochemical detection of NO2– (as NO2 converts into NO2– once it reacts with moisture, resulting into acid rain, i.e., indirect evaluation of NO2). As compared with other known modified electrodes, CuO(50%)–ZnO(50%) NCs show an apparent oxidation of NO2– with a larger peak current for a wider linear range of nitrite concentration from 20 to 100 mM. We thus demonstrate that the as-synthesized CuO(50%)–ZnO(50%) NCs act as a promising low-cost NO2 sensor and further confirm their potential toward tunable gas sensors (electrochemical and solid state) (Scheme 1).