Metal Oxide Nanomaterials Research Articles

Effect of aspect ratio of c-axis oriented ZnO nanorods on photoelectrochemical performance and photoconversion efficiency

In recent times, the field of dye-sensitised solar cells (DSSC) has made great strides; but has yet to achieve high efficiency with existing photoanode material.To achieve this goal, materials are required that have structural superiority.Tuning the morphology of metal oxide nanomaterials has become one of the most emerging techniques to improve the performance of the photoanode for dye sensitised solar cells (DSSC) application. The diverse morphologies of ZnO based photoanode allow achieving superior photoconversion efficiency in DSSC. Thus, the present study reports the synthesis of ZnO nanorods using microwave technique with various aspect ratios and its utilisation as photoanode for DSSC by changing the microwave power alone. More importantly, the microwave synthesis route has advantages over the conventional synthesis methods in terms of duration of the reaction and uniformity of the nanostructures. The structural and morphological analysis of the samples confirms the formation of nanorods with a preferential growth along the c-axis, which is further assembled to form a flower like structure. Lower microwave irradiation favours the formation of nanorods with a higher aspect ratio due to the variation in axial and lateral growth of ZnO. Among all the samples, the ZnO nanorod with the highest aspect ratio exhibits improved photoconversion efficiency compared to the remaining samples. The photoconversion efficiency of the ZnO photoanode with the highest aspect ratio was found to be 2.5 times greater than that of the lowest aspect ratio. This is explained further based on detailed physicochemical and photoelectrochemical (PEC) analyses, which helps establish the correlation between the charge carrier dynamics and the dye adsorption capacity of the optimal photoanode.

Enhanced Electrocatalytic Detection of Choline Based on CNTs and Metal Oxide Nanomaterials

Choline is an officially established essential nutrient and precursor of the neurotransmitter acetylcholine. It is employed as a cholinergic activity marker in the early diagnosis of brain disorders such as Alzheimer’s and Parkinson’s disease. Low levels of choline in diets and biological fluids, such as blood plasma, urine, cerebrospinal and amniotic fluid, could be an indication of neurological disorder, fatty liver disease, neural tube defects and hemorrhagic kidney necrosis. Meanwhile, it is known that choline metabolism involves oxidation, which frees its methyl groups for entrance into single-C metabolism occurring in three phases: choline oxidase, betaine synthesis and transfer of methyl groups to homocysteine. Electrocatalytic detection of choline is of physiological and pathological significance because choline is involved in the physiological processes in the mammalian central and peripheral nervous systems and thus requires a more reliable assay for its determination in biological, food and pharmaceutical samples. Despite the use of several methods for choline determination, the superior sensitivity, high selectivity and fast analysis response time of bioanalytical-based sensors invariably have a comparative advantage over conventional analytical techniques. This review focuses on the electrocatalytic activity of nanomaterials, specifically carbon nanotubes (CNTs), CNT nanocomposites and metal/metal oxide-modified electrodes, towards choline detection using electrochemical sensors (enzyme and non-enzyme based), and various electrochemical techniques. From the survey, the electrochemical performance of the choline sensors investigated, in terms of sensitivity, selectivity and stability, is ascribed to the presence of these nanomaterials.

Biopolymer‐Templated Deposition of Ordered and Polymorph Titanium Dioxide Thin Films for Improved Surface‐Enhanced Raman Scattering Sensitivity

AbstractTitanium dioxide (TiO2) is an excellent candidate material for semiconductor metal oxide‐based substrates for surface‐enhanced Raman scattering (SERS). Biotemplated fabrication of TiO2 thin films with a 3D network is a promising route for effectively transferring the morphology and ordering of the template into the TiO2 layer. The control over the crystallinity of TiO2 remains a challenge due to the low thermal stability of biopolymers. Here is reported a novel strategy of the cellulose nanofibril (CNF)‐directed assembly of TiO2/CNF thin films with tailored morphology and crystallinity as SERS substrates. Polymorphous TiO2/CNF thin films with well‐defined morphology are obtained by combining atomic layer deposition and thermal annealing. A high enhancement factor of 1.79 × 106 in terms of semiconductor metal oxide nanomaterial (SMON)‐based SERS substrates is obtained from the annealed TiO2/CNF thin films with a TiO2 layer thickness of 10 nm fabricated on indium tin oxide (ITO), when probed by 4‐mercaptobenzoic acid molecules. Common SERS probes down to 10 nm can be detected on these TiO2/CNF substrates, indicating superior sensitivity of TiO2/CNF thin films among SMON SERS substrates. This improvement in SERS sensitivity is realized through a cooperative modulation of the template morphology of the CNF network and the crystalline state of TiO2.

Comparison of uptake and elimination kinetics of metallic oxide nanomaterials on the freshwater microcrustacean Daphnia magna

The widespread use and release of nanomaterials (NMs) in aquatic ecosystems is a concerning issue as well as the fate and behavior of the NMs in relation to the aquatic organisms. In this work, the freshwater microcrustacean Daphnia magna was exposed to 12 different and well-known NMs under the same conditions for 24 h and then placed in clean media for 120 h, in order to determine their different uptake and elimination behaviors. The results showed that most of the tested NMs displayed a fast uptake during the first hours arriving to a plateau by the end of the uptake phase. The elimination behavior was determined by a fast loss of NMs during the first hours in the clean media, mainly stimulated by the presence of food. Remaining NMs concentrations can still be found at the end of the elimination phase. Two NMs had a different profile (i) ZnO-NM110 exhibited increase and loss during the uptake phase, and (ii) SiO2-NM204 did not show any uptake. A toxicokinetic model was applied and the uptake and elimination rates were found along with the dynamic bioconcentration factors. These values allowed to compare the NMs, to cluster them by their similar rates, and to determine that the TiO2-NM102 is the one that has the fastest uptake and elimination behavior, SiO2-NM204 has the slowest uptake and CeO2 <10 nm has the slowest elimination. The present work represents a first attempt to compare different NMs based on their uptake and elimination behaviors from a perspective of the nano-bio interactions influence.

The use of soil enzymes activity, microbial biomass, and basal respiration to assess the effects of cobalt oxide nanomaterial in soil microbiota

Despite the high array of potential applications of cobalt oxide nanomaterial (nano-Co3O4), data regarding its toxicity to soil biota is limited, compromising the capability of predicting the risks of this metal oxide nanomaterial (MO-NM). In a previous study the predicted no effect concentration of nano-Co3O4 to soil (PNECsoil) was estimated to be 5.3 mg kg−1 soildw. Given limitations in available data, this threshold was obtained through the application of assessment factors, which are known to overestimate the risks, by being a deterministic and highly protective approach. Thus, this PNECsoil value could be refined if there were more ecotoxicological data. Aiming to contribute to fill this lack of data, this work intended to assess the impact of nano-Co3O4 on soil microorganisms, by measuring soil enzymes activity (dehydrogenase, acid phosphatases, arylsulphatase, CM-cellulase, urease), the nitrogen mineralization, the soil microbial biomass carbon and the soil basal respiration at a range of concentrations up to 1000 mg of nano-Co3O4 kg−1 soildw. The results showed that the arylsulphatase (87.8–296.3 mg kg−1soildw), the acid phosphatase (87.8–1000 mg kg−1soildw) and the soil basal respiration at the lowest concentration tested (87.8 mg kg−1) were significantly affected by the nano-Co3O4 exposure. Conversely, significant stimulatory effects were observed in enzymes activity related to carbon (296.3–666.7 mg kg−1soildw) and nitrogen cycling (87.8–296.3 and 1000 mg kg−1soildw) and basal respiration (131.7–197.5 and 666.7–1000 mg kg−1soildw). Microbial biomass carbon was not significantly affected in any test treatment but showed a tendency to increase with increasing nano-Co3O4 concentration. Multiple mechanisms may be involved in the interaction of this NM with soil enzymes and soil microbial cells. The data obtained did not allow any adjustment to the previous PNECsoil value by taking into account the soil microbial community, because the results obtained point for effects at concentrations lower than the range tested in this study (87.8 mg nano-Co3O4 kg−1soildw) in terrestrial environment.

Biofabricated nanoscale ZnO and their prospective in disease suppression and crop growth of Brassica species: A review

Biofabricated zinc oxide nanoparticles (ZnO Np’s) are made by biological means for example microbes, plants, etc. by using nanotechnology. Nanotechnology is the technology that involves the manipulation of a matter up to a nanometre scale by various methods. The future of the industrial revolution is nanotechnology and almost all the industries developing or developed will be fundamentally renovated by this technology soon. Besides application in various fields nanotechnology have a promising role in agriculture which is the heart and soul of the Indian economy. As per the scientists, metal and metal oxide nanomaterials in agriculture can help in improving the poor agriculture conditions in India. Recent reports indicate that 80% of diseases in crop plants occur due to fungal pathogens and to cure these diseases, various chemical, as well as biological fungicides, have been used. Chemical fungicides are toxic to our environment whereas biofabricated metal and metal oxides nanoparticles for example ZnO Np’s are eco-friendly, non-toxic, cost-effective, have antimicrobial activity, and also have a role in crop growth. The mechanistic approach behind their antifungal activity and crop growth is not fully explored yet. Fungal pathogens like Alternaria species and Sclerotinia species infect Brassica species which is the second most economically important oilseed crop after groundnut. There is a need for new strategies to develop novel fungicides to control fungal infections. The present review will address the possible role of ZnO Np’s in disease suppression caused by the fungal pathogens of Brassica species and also their role in crop growth.

Review on Nanomaterial-based Electrochemical Aptasensors for Heavy Metal Detection in Food

Heavy metal ions are highly toxic contaminants in food and environment, which can easily cause foodborne diseases and irreversible damage to human being. There are several limitations in traditional detection methods for heavy metal ions such as time consuming and expensive, so it’s urgent to develop a rapid technology for heavy metal detection in food. Due to their rapid, high sensitivity and specificity, nanomaterial-based electrochemical aptasensors are perspective in real-time detection of heavy metal ions. This paper summarize the characters of metallic nanomaterials (such as gold nanoparticles), metal oxide nanomaterials (such as Fe3O4 nanoparticles), and carbon nanomaterials (such as carbon nanotubes and graphene) and then review the application of electrochemical aptasensors based on nanomaterials in heavy metal detection (mainly lead (II), mercury (II), arsenic (III) and cadmium (II)), in order to provide inspiration for the development of heavy metal detection methods.

Importance and Analytical Perspective of Green Synthetic Strategies of Copper, Zinc, and Titanium Oxide Nanoparticles and their Applications in Pathogens and Environmental Remediation

Background: Nanotechnology is a promising field of science which deals with the production and utilization of material under nanoscale dimensions. The nanoscale regime provides exceptional applications in various fields of science due to its large surface to volume ratio and many valuable properties. Hence, the production and use of nanomaterials are the prominent areas of modern research. Amongst the nanomaterials, metal oxide NPs have gained much attention due to their vast number of applications in different areas, including electrochemical applications, dye degradation, catalysis, and are known to be the exceptional entities in the battle against different pathogens. The metal oxides are viably synthesized through chemical methods that require the use of many noxious chemicals. Henceforth, it is the demand of the modern world to carry out research on the synthesis of metal oxide nanomaterials through eco-friendly, greener, and non-toxic routes. Thus, various green methods are employed to engineer the metal oxide NPs by using different greener, cheaper, and eco-friendly sources, employing the use of plant extracts, bacteria, fungi and other biological bodies. The present review covered the green synthesis of CuO, ZnO, TiO2 NPs and their applicability towards different pathogens and environmental remediation reported from the year 2015 to date. Objective: The exceptional catalytic properties, environmental, and anti-microbial applications of metal oxide, especially CuO, ZnO, TiO2, are the main highlights of this review articles. The most cost-effective and greener routes for the synthesis of CuO, ZnO, TiO2, are discussed in the present review. To date, various green synthetic methods for the preparation of mentioned nanoparticles and their applicability towards different pathogens and degradation of different hazardous dyes with some electrochemical applications has been thoroughly covered in this review. Conclusion: The biosynthesis of metal oxide NPs using greener and eco-friendly approaches have been the attentive area in the last decade. Green synthesis requires chemical-free active components from biological sources, which act as both the reducing and stabilizing agent for the size and shapecontrolled production of NPs. The future vision of bacterial, fungal, and plant-mediated production of NPs includes the postponement of laboratory-based work to a large industrial scale, exposition of different phytochemicals involved in the biosynthesis of NPs using bioinformatics techniques and stemming the real mechanism involved in preventing the growth of pathogenic bacteria, fungi, and algae. The plant-mediated NPs can have diverse applications in the arena of pharmaceutical, food, and cosmetic industries, and thus, became a vital area of modern research.

Enhanced catalytic properties of cobaltosic oxide through constructing MXene-supported nanocomposites for ammonium perchlorate thermal decomposition

The novel Co3O4@MXene nanocomposites (CMNs) were fabricated by a facile, green and highly tunable strategy without using any chemical modifiers. Various characterization results proved that nano-size Co3O4 was loaded on MXene nanosheets and CMNs exhibited a large specific surface area, especially for CMNs-3 (76.9 m2·g−1). The catalytic properties of CMNs for ammonium perchlorate (AP) thermal decomposition were investigated by a series of catalytic experiments. The results showed that the high-temperature decomposition (HTD) temperature and decomposition heat of AP mixed with CMNs-3 (2 wt%) could significantly decrease to 316.3 °C and remarkably increase to 1457.9 J·g−1, respectively. Moreover, the CMNs-3 could significantly reduce the apparent activation energy of AP by 49.1% and increase the value of reaction rate constant of AP by 482.0%. As for the effects of mass content of CMNs-3 on AP decomposition, the HTD temperature could decrease by as high as 128.0 °C with ratios of 10.0 wt% CMNs-3. It could be predicted that CMNs-3 with excellent catalytic performance would be a potential catalyst to promote AP decomposition and the synthesis method of CMNs-3 could provide an idea for the preparation of other metal oxide nanomaterials with high catalytic activity.

NANOMATERIAL SENSORS FOR ENVIRONMENTAL POLLUTANTS

Nowadays, global environment of water, soil, and atmospheric systems has continuously been deteriorating due to the incessant release of toxic chemicals from various constructed sources. The existence of heavy metal ions in the environment poses serious threats to human health and the ecosystem. Therefore, this review focuses on the advent of nanotechnology that has given immense opportunities for developing advanced nanomaterials with unique functionalities. This review reports on the development of sensing techniques based on nanomaterials including metal and metal oxide nanomaterials, quantum dots, carbon nanomaterials and polymer nanocomposites. Nanomaterials well possess excellent electrical, optical, thermal, catalytic properties and strong mechanical strength, which offer great opportunities to construct nanomaterials-based sensors or devices for environmental pollutants. The nanosorbents themselves should be nontoxic, the sorbents present relatively high sorption capacities and selectivity to the low concentration of pollutants. The adsorbed pollutants can be removed from the surface of the nanoadsorbent easily and sorbents infinitely recycled.

MoO3 structures transition from nanoflowers to nanorods and their sensing performances

Morphology transformation and crystal growth strategies of metal oxide semiconductors are still extensively studied in material science recently, because the morphology and crystallinity significantly affect the physicochemical characteristics of metal oxide nanomaterials. However, understanding the morphology changes of α-MoO3 induced by annealing is still a challenge. Herein, the nanostructure transition of α-MoO3 induced by the annealing temperature is carefully investigated via the XRD and SEM methods. It can be found that crystallization is highly dependent on the annealing temperature. Interestingly, the MoO3 nanoflowers can change into nanosheets at 500 °C. Afterward, the nanosheets turned into microrods with the increase in annealing temperature due to the continuous growth of MoO3 crystal. On the other hand, the sensing performances of various MoO3 nanostructures are studied toward ethanol gas. Compared to the MoO3 nanoflowers and microrods, the MoO3 nanosheets-based sensor exhibits superior sensing performance to ethanol, and the maximum response value is 8.06.

Self-assembled MXene-based Schottky-junction upon Transition metal oxide for regulated tumor microenvironment and enhanced CDT/PTT/MRI activated by NIR irradiation

Transition metal oxide nanomaterials (TMOs) have been adopted to produce reactive oxygen species (ROS) and adjust tumor microenvironment (TME) in cancer therapy. However, mono-modal treatment and the incompatibility of biological enzyme both hampered the therapeutic effect. Herein, we developed a multimodal TMO-based nanoplatform that the ultrathin Ti3C2 nanosheets were attached onto the MnFe2O4 nanoparticles self-assembled by applying chitosan as a chemical crosslinker to construct an interfacial Schottky junction, Ti3C2@Chitosan-MnFe2O4 (TC@Ch-MFO), achieving improved ROS generation as well as optimized biocompatibility. This heterojunction can controllably catalyze hydrogen peroxide (H2O2) to generate O2 and deplete the overexpressed glutathione (GSH) levels in hypoxic TME, which realizes the chemodynamic therapy (CDT) by cyclized Fenton reaction under NIR excitation. TC@Ch-MFO also constructs a multimodal treatment nanoplatform by introducing available high-efficiency photothermal agent (PTA), Ti3C2, for phtotheraml therapy (PTT). In addition, it simultaneously integrates the visualization with T1- and T2-weighting magnetic resonance imaging (MRI). The toxicity of TC@Ch-MFO to normal tissue cells is negligible. This platform could provide new insights into the development of multimoded synergistic nanoplatform for biological applications, especially breaking the shackles of MXenes merely used as a photo-thermal agent, adopting it to bioimaging sensor and drug loading.

Chemical bath deposition of h-MoO3 on optical fibre as room-temperature ammonia gas sensor

This study successfully developed a semiconductor metal oxide-based ammonia gas sensor that was powered by an Ultraviolet–Visible-near-IR optical light source. However, optical fibre gas sensors using single metal oxide nanomaterial are limited. To address this situation, a h-MoO3 nanorod was grown on a tapered region of optical fibre glass using a simple chemical bath deposition to form a unique sensing element. An additional annealing treatment was then performed to modify the oxidation state of h-MoO3. The property changes of the samples were characterised using different techniques, such as FESEM, TEM, XRD, XPS, TGA and UV–Vis. Overall, the annealing treatment improved the sensitivity performance, response and recovery time of the sensor towards NH3. h-MoO3 that was annealed at 150 °C in air showed stable room temperature absorbance responses of 0.05, 0.18, 0.22, 0.28 and 0.35, a fast response time of 210 s towards 500 ppm of NH3 and strong stability and repeatability. The optical NH3 gas-sensing behaviour was significantly correlated with the non-stoichiometric Mo5+ content. The chemisorbed oxygen species and physiosorbed NH3 altered the refractive index and its absorption coefficient on the nanorod, which manipulated the optical signal and acts as a sensing mechanism. These results verify that a chemical bath deposition growth of the h-MoO3 nanorod exhibits a promising optical sensing characteristic, which paves a path for emerging gas-sensing technology.

Manganese vanadium sulfate-oxide cylindrical core-shell heterostructures by electro-spray deposition on graphite foil for Li+ ion intercalation

Heterostructure based on metal sulfides and oxides nanomaterials can be relevant to the charge storage devices. Here, we show that Mn(CH3COO)2·4H2O and VOSO4·xH2O can react in ethanol/water droplets generated by an electric field assisted spray system, so that MnSx-VSx/MnzV2O5 heterostructures in the shape of nanometric cylindrical particles can be deposited on a graphite foil substrate. The composite material phases were detected by several microscopies and microscopic probes spectroscopies, i.e., micro-Raman and scanning X-ray photoemission microscopy. The nanometric cylindrical particles were relatively homogenously distributed throughout the film covering the graphite foil. Film thickness modulation on surface was calculated between 100 and 300 nm range. We show that the segregation of MnV-O and MnV-S relative abundance in the internal and external volume of the cylindrical nanoparticles respectively, can be exploited during faradaic and non-faradaic processes in charge/discharge.

MnxOy embedded within CNT supporting porous carbon for enhanced lithium storage

Achievement of improved structural stability and conductivity for Mn-based oxides is the crucial premise for them to be high-performance anodes of lithium-ion batteries due to their large volume effect and poor intrinsic conductivity. Herein, the lithium storage performance of the MnxOy nanoparticles containing dominant MnO and slight MnO2 and Mn3O4 has been significantly improved by embedding them into a CNT supporting porous carbon. This composite is therefore denoted as CNT/MnxOy/C. The comparison results of the electrochemical performance of thus CNT/MnxOy/C with CNT/Mn3O4 and pure Mn3O4 nanoparticles demonstrate that the well-designed synergistic effect of high conductive CNT support and flexible spongy porous carbon is responsible for its improved performance, which efficiently enhances not only the structural stability but also the electrochemical kinetics of the CNT/MnxOy/C. As a result, this CNT/MnxOy/C anode shows outstanding performance, obtaining high capacities of 936.5 and 410.5 mAh g-1 at 200 and 1000 mA g-1 after 260 and 800 cycles, respectively. Moreover, this strategy proposed here will be hopefully instructive in constructing other advanced metal oxide nanomaterials toward improved performance of lithium-ion battery anodes.

Defects rich nanostructured black zinc oxide formed by nanosecond pulsed laser irradiation in liquid

Zinc oxide (ZnO) is a wide bandgap semiconductor for energy applications while the spectral absorption only in UV region limits the use as a visible light absorber. Here, visible light absorbing modified ZnO (black) is prepared by creating surface defects and vacancies using pulsed laser irradiation in liquid. The modified ZnO nanoparticles have spherical morphology and they are free from impurity phases. The optical bandgap of this modified material is narrowed by increased irradiation time with a morphological transformation to mostly nanospheres. XPS analysis confirmed the oxygen vacancies contribution and the valance band study showed a reduction in the band edge. With the results of Raman and photoluminescence spectra, the oxygen defects and vacancies were confirmed. Thin films were fabricated using these materials via doctor blade method and their photocatalytic studies showed enhanced activity in organic dye decay under visible light. Results of this study show a facile method for fabrication of defects rich metal oxide nanomaterials by pulsed laser irradiation in liquid.

Metal oxides nanocomposite membrane for biofouling mitigation in wastewater treatment

These days our one of the major challenges is the treatment of polluted wastewater produced by the growing population and industrial activities. The conventional wastewater treatment methods are costly and need to be more advanced. For this reason, membrane technology has been used as an effective wastewater treatment method for many decades due to its high removal power, selectivity, and permeability properties. Biofouling causes a serious concern related to membrane permeability, shortens membrane life, and selectivity. Polymeric membranes are widely used in wastewater treatment due to their good pore-forming ability, higher flexibility, and relatively low costs but are limited to their hydrophobicity property and more susceptible to fouling. Metal oxides nanomaterials are widely used in the formation of polymer nanocomposite membranes because of their hydrophilicity, larger surface area, pore channels, and high toxicity towards pathogenic micro-organisms. In this review, we have discussed the factors affecting membrane biofouling and their conventional and current treatment methods with their limitations. We have also referred to the use of metal oxide nanomaterials, as an antibacterial agent, for the fabrication of polymer nanocomposite membranes and discuss their antibacterial activity with antibiofouling behavior.

Self-Assembled Co3O4/GO Composites for Excellent Electrochemical Detection of Heavy-Metal Ions

Recently, electrochemical sensors have been applied for the detection of heavy metal ions. The modifier on the electrochemical electrode is the key factor for enhanced performance. Modification by combining metal oxide nanomaterials with good adsorption property and graphene oxide (GO) with good conductivity can construct a useful sensing interface to detect heavy metal ions. Here, the effects of structures and morphologies of Co3O4/GO composite modifiers on the electrochemical detection performance were studied. The results show that Co3O4/GO composite with holey nano-sheets of pure Co3O4 on lamella GO substrate had the best electrochemical performance for their large active sites and enhanced ion and charge transports. The limits of detection of the electrochemical sensors based on developed Co3O4/GO composite to Cd2+ and Pb2+ were calculated as 57 and 29.4 nM, respectively, which are lower than the guideline values recommended by the World Health Organization for drinking water. Furthermore, the designed sensor also showed excellent stability, selectivity, and acceptable reproducibility and reliablity. The results indicate that Co3O4/GO composite with holey layer structures as a promising electrode modifier could be potentially applied in the electrochemical detection of heavy metal ions on-site.

Evaluation of antibacterial behavior of in situ grown CuO-GO nanocomposites

The growth of harmful microorganisms is a severe threat to human life. Nowadays, it is necessary to prepare antimicrobials materials with high biocompatibility properties. Hence, the use of nanomaterials and their nanocomposites has been proposed as a suitable way to obtain safe and potent antibacterial materials. Recently, several studies have been conducted on the antibacterial properties of metal oxide and graphene oxide (GO) nanomaterials individually. This study investigated the synergistic effect of GO and copper oxide (CuO) as a nanocomposite. CuO-GO nanocomposite containing 5%, 15%, 25%, 50%, and 75% of GO were synthesized to study antibacterial properties. X-ray diffraction (XRD) results showed that CuO and GO synthesized were free of impurities and unwanted phases. Fourier Transform Infrared Spectroscopy (FTIR) spectrum of the prepared sample has revealed the presence of vibrational modes related to Cu-O, alkoxy group (O-H), epoxy group (C-O-C), and carboxyl group (C-O). In Raman spectroscopy, the CuO nanostructure has a redshift, and in the CuO-GO nanocomposite, D band and G band have blueshift and redshift by increasing the amount of GO, respectively. The results of UV-Vis spectra showed that synthesized CuO and GO have a higher band gap (4.54 eV and 3.03 eV, respectively) than previous studies. Also, the highest amount of band gap of nanocomposites is related to the 50%wt GO nanocomposite (3.40 eV). Field emission scanning electron microscope (FESEM) images showed that CuO nanosheets bonded with GO plates and decorated the GO plates. Antibacterial activity of synthesized nanocomposite investigated using Escherichia coli (E.coli) bacteria. The antibacterial test results showed that CuO nanoparticles have inadequate antibacterial activity (15%), while by composting with GO, the antibacterial activity against E. coli significantly increased (for 50% GO about 76%). However, the antibacterial activity reduced to 68% for the nanocomposite sample with 75% GO concentration; thus, 50% GO nanocomposite is the optimal concentration.

Self-Assembled 2D Networks of Metal Oxide Nanomaterials Enabling Sub-ppm Level Breathalyzers.

For extremely sensitive acetone sensors, here, we introduced an alcohol-assisted surfactant-free Langmuir-Blodgett process to rapidly assemble a single-layered two-dimensional (2D) network as a suitable percolation strategy of metal oxide semiconductor nanomaterials. The single-layered 2D network formation mechanism was investigated using zinc oxide (ZnO) nanobeads (NBs). Furthermore, the correlation between the response of the gas sensor and the average percolation number of the ZnO NBs, controlled by multi-stacking the 2D network, was investigated. It was inferred that a reduction in the number of percolations led to maximization of the response. Additionally, the versatility of the optimal percolation strategy was experimentally verified by confirming similar results to that achieved with ZnO NBs when utilizing different sizes, shapes, and compositions of metal oxides. Finally, the practical effectiveness of our extremely sensitive strategy was solidified by illustrating the response enhancement in a commercial exhalation diagnostic system that measures the amount of acetone in only 1 mL of exhalation.