NiO Grained-Flowers and Nanoparticles for Ethanol Sensing

The Addition of Co into CuO-ZnO Oxides Triggers High Antibacterial Activity and Low Cytotoxicity

In the present work, a simple two-step method is proposed for mixed oxide synthesis aimed at the achievement of antibacterial nanomaterials. In particular, Cu, Zn and Co have been selected to achieve single-, double- and triple-cation oxides. The synthesized samples are characterized by XRD, IR, SEM and EDX, indicating the formation of either crystalline or amorphous hydrocarbonate precursors. The oxides present one or two crystalline phases, depending on their composition; the triple-cation oxides form a solid solution of tenorite. Also, the morphology of the samples varies with the composition, yielding nanoparticles, filaments and hydrangea-like microaggregates. The antibacterial assays are conducted against E. coli and indicate an enhanced efficacy, especially displayed by the oxide containing 3% Co and 9% Zn incorporated into the CuO lattice. The oxides with the highest antibacterial properties are tested for their cytotoxicity, indicating a low toxicity impact, in line with literature data.

CuO Nanoparticles and Microaggregates: An Experimental and Computational Study of Structure and Electronic Properties

The link between morphology and properties is well-established in the nanoparticle literature. In this report, we show that different approaches in the synthesis of copper oxide can lead to nanoparticles (NPs) of different size and morphology. The structure and properties of the synthesized NPs are investigated with powder X-ray diffraction, scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS). Through detailed SEM analyses, we were able to correlate the synthetic pathways with the particles' shape and aggregation, pointing out that bare hydrothermal pathways yield mainly spheroidal dandelion-like aggregates, whereas, if surfactants are added, the growth of the nanostructures along a preferential direction is promoted. The effect of the morphology on the electronic properties was evaluated through DRS, which allowed us to obtain the electron bandgap in every system synthesized, and to find that the rearrangement of threaded particles into more compact structures leads to a reduction in the energy difference. The latter result was compared with Density Functional Theory (DFT) computational models of small centrosymmetric CuO clusters, cut from the tenorite crystal structure. The computed UV-Vis absorption spectra obtained from the clusters are in good agreement with experimental findings.

Nanomaterial Gas Sensors for Biosensing Applications: A Review

BACKGROUND

Nanomaterial is one of the most used materials for various gas sensing applications to detect toxic gases, human breath, and other specific gas sensing. One of the most important applications of nanomaterial based gas sensors is biosensing applications. In this review article, the gas sensors for biosensing are discussed on the basis of crystalline structure and different categories of nanomaterial.

METHODS

In this paper, firstly, rigorous efforts have been made to find out research questions by going through a structured and systematic survey of available peer reviewed high quality articles in this field. The papers related to nanomaterial based biosensors are then reviewed qualitatively to provide substantive findings from the recent developments in this field.

RESULTS

In this mini-review article, firstly, classifications of nanomaterial gas sensors have been presented on the basis of the crystalline structure of nanomaterial and different types of nanomaterial available for biosensing applications. Further, the gas sensors based on nanomaterial for biosensing applications are collected and reviewed in terms of their performance parameters such as sensing material used, target gas component, detection ranges (ppm-ppb), response time, operating temperature and method of detection, etc. The different nanomaterials possess slightly different sensing and morphological properties due to their structure; therefore, it can be said that a nanomaterial must be selected carefully for a particular application. The 1D nanomaterials show the best selectivity and sensitivity for gases available in low concentration ranges due to their miniaturised structure compared to 2D and 3D nanomaterials. However, these 2D and 3D nanomaterials also so good sensing properties compared to bulk semiconductor materials. The polymer and nanocomposites which are also discussed in this patent article have opened the door for future research and have great potential for new generation gas sensors for detecting biomolecules.

CONCLUSION

These nanomaterials extend great properties towards sensing the application of different gases for a lower concentration of particular gas particles. Nano polymer and nanocomposites have great potential to be used as gas sensors for the detection of biomolecules.

Syntheses of APTMS-Coated ZnO: An Investigation towards Penconazole Detection

Extrinsic chemiluminescence can be an efficient tool for determining pesticides and fungicides, which do not possess any intrinsic fluorescent signal. On this basis, (3-aminopropyl) trimethoxysilane (APTMS)-coated ZnO (APTMS@ZnO) was synthesized and tested as an extrinsic probe for the fungicide penconazole. Several synthetic routes were probed using either a one-pot or two-steps method, in order to ensure both a green synthetic pathway and a good signal variation for the penconazole concentration. The synthesized samples were characterized using X-ray diffraction (XRD), infrared (IR), Raman and ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM) imaging and associated energy-dispersive X-ray (EDX) analysis. The average size of the synthesized ZnO nanoparticles (NPs) is 54 ± 10 nm, in line with previous preparations. Of all the samples, those synthesized in two steps, at temperatures ranging from room temperature (RT) to a maximum of 40 °C, using water solvent (G-APTMG@ZnO), appeared to be composed of nanoparticles, homogeneously coated with APTMS. Chemiluminescence tests of G-APTMG@ZnO, in the penconazole concentration range 0.7-1.7 ppm resulted in a quenching of the native signal between 6% and 19% with a good linear response, thus indicating a green pathway for detecting the contaminant. The estimated detection limit (LOD) is 0.1 ± 0.01 ppm.

VOC Detections by p-Type Semiconducting Sensors Using Nano-Sized SmFeO3 Particles

Nano-sized SmFeO₃ particles are prepared by the pyrolysis of heteronuclear cyano-complex, Sm[Fe(CN)₆]·4H₂O at a temperature of 600 °C in ozone. The low temperature decomposition followed in ozone successfully yielded fine particles with a high specific surface area of 20.0 m³/g (sample A). The fine particles were classified into further smaller particles with a unimodal size distribution and this process yielded a high specific surface area of 26.0 m³/g (sample B). These semiconducting powders were deposited on a sensor electrode by electrophoretic deposition (EPD) and tested on their sensing properties to VOCs. The sensors consisting of samples A and B both showed good responses to ethanol at 285 and 320 °C. The sensor with sample B showed extraordinarily good selectivity of ethanol for toluene at 320 °C. This could be because the detection film of sample B with moderately grown particles selectively reduced the reaction activity of toluene. The sensor with sample B also exhibited good selectivity of ethanol for hexane and dichloromethane.

Recent Advances in the Synthesis of Inorganic Materials Using Environmentally Friendly Media

Deep Eutectic Solvents have gained a lot of attention in the last few years because of their vast applicability in a large number of technological processes, the simplicity of their preparation and their high biocompatibility and harmlessness. One of the fields where DES prove to be particularly valuable is the synthesis and modification of inorganic materials-in particular, nanoparticles. In this field, the inherent structural inhomogeneity of DES results in a marked templating effect, which has led to an increasing number of studies focusing on exploiting these new reaction media to prepare nanomaterials. This review aims to provide a summary of the numerous and most recent achievements made in this area, reporting several examples of the newest mixtures obtained by mixing molecules originating from natural feedstocks, as well as linking them to the more consolidated methods that use "classical" DES, such as reline.

NiO-Based Electronic Flexible Devices

Personal, portable, and wearable electronics have become items of extensive use in daily life. Their fabrication requires flexible electronic components with high storage capability or with continuous power supplies (such as solar cells). In addition, formerly rigid tools such as electrochromic windows find new utilizations if they are fabricated with flexible characteristics. Flexibility and performances are determined by the material composition and fabrication procedures. In this regard, low-cost, easy-to-handle materials and processes are an asset in the overall production processes and items fruition. In the present mini-review, the most recent approaches are described in the production of flexible electronic devices based on NiO as low-cost material enhancing the overall performances. In particular, flexible NiO-based all-solid-state supercapacitors, electrodes electrochromic devices, temperature devices, and ReRAM are discussed, thus showing the potential of NiO as material for future developments in opto-electronic devices.

Room Temperature Syntheses of ZnO and Their Structures

ZnO has many technological applications which largely depend on its properties, which can be tuned by controlled synthesis. Ideally, the most convenient ZnO synthesis is carried out at room temperature in an aqueous solvent. However, the correct temperature values are often loosely defined. In the current paper, we performed the synthesis of ZnO in an aqueous solvent by varying the reaction and drying temperatures by 10 °C steps, and we monitored the synthesis products primarily by XRD). We found out that a simple direct synthesis of ZnO, without additional surfactant, pumping, or freezing, required both a reaction (TP) and a drying (TD) temperature of 40 °C. Higher temperatures also afforded ZnO, but lowering any of the TP or TD below the threshold value resulted either in the achievement of Zn(OH)2 or a mixture of Zn(OH)2/ZnO. A more detailed Rietveld analysis of the ZnO samples revealed a density variation of about 4% (5.44 to 5.68 gcm−3) with the synthesis temperature, and an increase of the nanoparticles’ average size, which was also verified by SEM images. The average size of the ZnO synthesized at TP = TD = 40 °C was 42 nm, as estimated by XRD, and 53 ± 10 nm, as estimated by SEM. For higher synthesis temperatures, they vary between 76 nm and 71 nm (XRD estimate) or 65 ± 12 nm and 69 ± 11 nm (SEM estimate) for TP = 50 °C, TD = 40 °C, or TP = TD = 60 °C, respectively. At TP = TD = 30 °C, micrometric structures aggregated in foils are obtained, which segregate nanoparticles of ZnO if TD is raised to 40 °C. The optical properties of ZnO obtained by UV-Vis reflectance spectroscopy indicate a red shift of the band gap by ~0.1 eV.

Inorganic-Diverse Nanostructured Materials for Volatile Organic Compound Sensing

Environmental pollution related to volatile organic compounds (VOCs) has become a global issue which attracts intensive work towards their controlling and monitoring. To this direction various regulations and research towards VOCs detection have been laid down and conducted by many countries. Distinct devices are proposed to monitor the VOCs pollution. Among them, chemiresistor devices comprised of inorganic-semiconducting materials with diverse nanostructures are most attractive because they are cost-effective and eco-friendly. These diverse nanostructured materials-based devices are usually made up of nanoparticles, nanowires/rods, nanocrystals, nanotubes, nanocages, nanocubes, nanocomposites, etc. They can be employed in monitoring the VOCs present in the reliable sources. This review outlines the device-based VOC detection using diverse semiconducting-nanostructured materials and covers more than 340 references that have been published since 2016.

CQDs@NiO: An Efficient Tool for CH4 Sensing

A composite material based on carbon quantum dots (CQDs) and NiO was prepared and tested for methane sensing. The synthesis procedure is simple and foresees the preparation of the CQDs by citric acid pyrolysis and NiO by hydrothermal synthesis. A phase sonication and stirring procedure yielded the composite CQDs@NiO at different loads. The composites were characterized by X-ray diffraction, ultraviolet–visible light (UV–Vis) spectroscopy, SEM microscopy, energy-dispersive spectroscopy (EDS) mapping, and surface area, porosity, and impedance measurements. A gas sensor was built in-house and used to probe the response of the synthesized samples to CH4 detection, at constant environmental humidity. The CQDs@NiO at 1% weight load displayed excellent performances in terms of gas response both vs. temperature and vs. concentration, whereas higher loads resulted in CQD aggregation and diminished output. Response/recovery times of the 1%CQDs@NiO sample were good, as well as the selectivity and the stability over time and for variable environmental humidity. The estimated limit of detection was 0.1 ppm.