Influence of Zn-substitution on structural,morphological, electrical,and gas sensing properties of ZnxAl2O4 (x = 0.1 to 0.5) synthesized by a sol-gel auto-combustion method

The nanosphere decorated needle-like morphology of zinc-substituted aluminate having general formula Zn_xAl₂O₄ (x = 0.1, 0.2, 0.3, 0.4, and 0.5) (ZAN) samples were synthesized by a sol-gel auto-combustion method. The phase formation and stability temperature were confirmed by TG-DTA analysis. XRD study confirmed the formation of a cubic spinel structure of ZAN samples. The effect of Zn-substitution on structural and morphological properties of aluminate were investigated using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM), and Energy dispersive X-ray analysis (EDAX). The D.C. electrical resistivity study of ZAN samples revealed that resistance decreased with increasing temperature confirmed semiconducting nature. Nanosphere existing on micro-needles of zinc-substituted aluminate gas sensor revealed sensing to several analyte gases such as H₂S, Cl₂, CH₃OH, SO₂, and NO₂ working at room temperature to 300 ^°C. The Zn_0·4Al₂O₄ compositional gas sensor produced the highest response at operating temperature 200 ^°C to 100 ppm H₂S. The results revealed that the prepared nanosphere decorated needles of the ZAN sensor was sensitive and selective to H₂S gas.     

MOF assisted synthesis of a Ho2O3/CNT nanocomposite photocatalyst for organic pollutants degradation

In this work, a holmium oxide (Ho₂O₃/CNT) photocatalysts were successfully synthesized through a MOF assisted route for the first time. The effects of the morphology and purity on the photocatalytic behavior of the products, were investigated by determining various physicochemical properties. The Ho₂O₃/CNT nanocomposite was systematically analyzed by powder X-ray diffraction (P-XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy studies. The Ho₂O₃ derived from a MOF assisted synthetic route using Ho(NO₃)₃·5H₂O and terephthalic acid with a 1:1 M ratio at a temperature of 750 °C for 3 h prove the most advantageous, 98% degradation of 20 mg/L aqueous tetracycline pollutant was observed within 60 min. The elevated photocatalytic activity was mainly attributable to the unique synthetic route, improved crystallinity, wide UV-light absorption rate and excellent adsorption capabilities of CNT, as well as enhanced oxygen deficiency. The photocatalytic results confirm that the Ho₂O₃/CNT nanocomposite is an efficient photocatalyst for the degradation of toxic tetracycline pollutant and is thus suitable for use in environmental remediation.     

In2O3 nanosheets array directly grown on Al2O3 ceramic tube and their gas sensing performance

Arrayed In₂O₃ nanosheets were synthesized directly via a two-step solution approach on an Al₂O₃ ceramic tube. Their morphology and structure were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy, and scanning electron microscopy (SEM). The results reveal that the length of each nanosheet is about 1 µm, the width of the bottom of nanosheet is about 200 nm. Importantly, the In₂O₃ nanosheets with large specific surface area possess highly sensing performance for ethanol detection. The response value to 100 ppm ethanol is about 45 at an operating temperature of 280 °C, and the response and recovery time are extremely short. It is expected that the directly grown In₂O₃ nanosheets with large specific surface area and excellent sensing properties will become a promising functional material in monitoring and detecting ethanol.     

Mn1-xCuxO2/ reduced graphene oxide nanocomposites: Synthesis,characterization, and evaluation of visible light mediated catalytic studies

The narrow optical band gap, higher electrical conductivity, and wider-absorption range are three key features that a good photocatalyst must possess. Herein, we have fabricated Cu-doped MnO₂ (Mn_1-xCu_xO₂) nanostructure by facile wet chemical approach and formed its nanocomposite with r-GO (Mn_1-xCu_xO₂/r-GO) via ultra-sonication approach. The successful replacement of host metal ions (Mn⁴⁺) with the dopant metal ions (Cu²⁺) was supported with the PXRD, FT-IR, and EDX characterizations. The effect of Cu-doping on the band gap and r-GO matrix on the conductivity of the fabricated nanocomposite was also evaluated via Tauc plots and I–V tests, respectively. The photocatalytic efficiency of the fabricated photocatalysts was tested and compared against the methylene blue (MB) under visible light irradiation. The photocatalytic experiments revealed that Mn_1-xCu_xO₂/r-GO photocatalyst exhibited superior photocatalytic aptitude than that of pristine MnO₂ and Mn_1-xCu_xO₂ photocatalysts. More precisely, the Mn_1-xCu_xO₂ photocatalysts degraded 86.89% MB dye at the rate of 0.021 min^?1 after a 90-min exposure to the visible light. Observed superior catalytic activity of the nanocomposite can be attributed to the synergistic effects between the Cu doped MnO₂ and r-GO nanosheets that resulted in its narrow band-gap (2.19 eV) and excellent conductivity (2.217 × 10^?2 Scm^?1).     

Room temperature CO sensing by polyaniline/Co3O4 nanocomposite

Polyaniline/cobalt oxide (PANI/Co₃O₄) nanocomposites have been investigated for their sensitivity towards carbon monoxide (CO) gas at room temperature. The Co₃O₄ nanoparticles were prepared by ultrasound assisted coprecipitation method and then incorporated into the PANI matrix. Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy, powder X‐ray diffraction, and field emission scanning electron microscopy have been used to characterize the nanomaterials. The PANI/Co₃O₄ nanocomposite sensors were found to be highly selective to CO gas at room temperature. A significantly high response of 0.81 has been obtained for 75 ppm CO concentration with a response time of 40 s. Based on the observations of the sensing study, a mechanism for CO sensing by the nanocomposite has been proposed. Influence of humidity on the sensor response towards CO has also been studied and the results presented. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44115.     

Investigation of g-C3N4/ZnAl2O4 and ZnO/ZnAl2O4 nanocomposites: From synthesis to photocatalytic activity of pollutant dye model

The fabrication of nanocomposite photocatalytsts with excellent photocatalytic activity is an important step in the improved degradation of organic dyes. A series of nanocomposite photocatalysts was synthesized with g-C₃N₄ and ZnO loading contents of 10, 20 and 30%. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The optical band gaps of g-C₃N₄, ZnO and ZnAl₂O₄ were about 2.79, 3.21 and 3.55 eV, respectively. Methylene blue (MB) was degraded over the prepared photocatalysts under UV irradiation. Photocatalytic activity was about 9.1 and 9.6 times higher, respectively, on 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts than on pure ZnAl₂O₄ spinel powders. Recycling experiments showed that 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts exhibited good stability after five cycles of use.     

Facile synthesis of In2O3 nanoparticles with high response to formaldehyde at low temperature

In₂O₃ nanoparticles with uniform particle size (10-25 nm) were obtained using the facile precipitation strategy at room temperature with following calcined treatment. The gas-sensing performance of In₂O₃ nanoparticles with different calcined temperatures was investigated. The results demonstrated that the In₂O₃ nanoparticles calcined at 500°C exhibited highest sensing response (R_a/R_g = 68.1) to 10 ppm HCHO at 100°C with good selectivity, stability, reproducibility, and ultra-low limit of detection (1 ppm). The results of XPS, UV, and other characterizations indicated that In₂O₃-500 possessed the most absorbed oxygen species, the highest carrier mobility, and lowest band gap energies. Our work offers new insights into the development of sensing materials to the detection of volatile organic compounds (VOCs).     

Low concentration CO gas sensor constructed from MoS2 nanosheets dispersed SnO2 nanoparticles at room temperature under UV light

In consideration of the different electron structure-associated physical properties and internal sensing merits of MoS₂ and SnO₂, this work reports a nanocomposite with unique structure of MoS₂ nanosheets dispersed SnO₂ nanoparticles. The sensing performance of MoS₂/SnO₂ sensor toward low concentration CO was investigated at room temperature under the UV light illumination. It was found that MoS₂/SnO₂ sensor shows improved CO gas response (R ~ 4.97 at 40 ppm CO) compared with pure SnO₂ (R ~ 3.27 at 40 ppm CO), which is due to the unique structure and the formation of heterostructure between MoS₂ and SnO₂. Moreover, the fabricated sensor also exhibits fast response and recovery time (43 s/36 s). The sensor provides a potential platform for monitoring CO gas at room temperature.     

Photocatalytic degradation of methyl tert-butyl ether (MTBE) by Fe-TiO2 nanoparticles

Nowadays, since the underground waters are known as the main source for supplying the drinking water, their pollution to the organic contaminants such as methyl tert-butyl ether (MTBE) is a very significant issue. Therefore, in this study, photocatalytic degradation of MTBE was investigated in the aqueous soloution of Fe-TiO₂ nanoparticale under UV irradiation (wavelenght 254 nm) in a batch reactor. The Fe-TiO₂ mixed oxides were prepared by sol–gel impregnation method. The samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and BET specfic surface area. Then, the effect of various operational parameters namely pH, catalyst loading, molar ratio of [H₂O₂]₀/[MTBE]₀ and UV light intensity on degradation of aqueous MTBE were evaluated in a batch reactor. The optimal condition to achieve the best degradation for the initial concentration of 75 ppm MTBE was found at pH 7, catalyst concentration 2 g/L, molar ratio of [H₂O₂]₀/[MTBE]₀ 4, and UV irradiation 24 W. Total degradation of MTBE with initial concentration of 75 ppm was reached in optimal condition after 70 min. In addition, investigations were also carried out to determine the appropriate kinetics of MTBE degradation using UV/Fe-TiO₂/H₂O₂ process in optimal condition.     

Solution processed,vertically aligned,AZO nanocolumn array for chemiresistive sensor application with UV-enhanced sensitivity

In this work, a wide and highly sensitive chemiresistive sensor has been developed based on the AZO nanocolumn array film. This is meant for the room detection of H₂O₂ under UV illumination. A cost-effective one step multi-layers growth process was adopted for the synthesis of the AZO nanocolumn array. The experimental studies were done by scanning electron microscopy (SEM), transmission and electron microscopy (TEM).Then X-ray diffraction confirmed that the AZO column array was closely packed, connected, vertically aligned, and polycrystalline, with a high surface area. This structure ensures better electrical conduction over random and separated nanostructures. The hall-effect measurement indicates that the AZO film was n-type, with high conductivity (3.60 × 10³ Ωcm), high carrier density (11.3 × 10²⁰cm⁻³) and with acceptable mobility (0.95 cm²/Vs). The x-ray photoemission spectroscopy suggests that the AZO film consists of a large amount of adsorbed oxygen-related species at the sheath layer of the thin-film, which is vital for sensors. By the UV light activation, sensors based on the AZO nanocolumn array exhibited enhanced H₂O₂ detection properties at room temperature. At a concentration from 15 μM to 30 mM, H₂O₂ sensitivity evaluated by relative response was remarkably increased from 15% to 36%. The operation under ambient conditions and wide range sensing shows that this chemiresistive AZO sensor is adequate for biomedical and environmental applications.     

V-doped In2O3 nanofibers for H2S detection at low temperature

Pristine and vanadium-doped In₂O₃ nanofibers were fabricated by electrospinning and their sensing properties to H₂S gas were studied. X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the inner structure and the surface morphology. The H₂S-sensing performances were characterized at different temperatures ranging from 50 to 170 °C. The sensor based on 6 mol% V-doped In₂O₃ nanofibers exhibit the highest response, i.e. 13.9–50 ppm H₂S at the relatively low temperature of 90 °C. In addition, the fast response (15 s) and recovery (18 s) time, and good selectivity were observed.     

One-pot synthesis of Ag-TiO2/reduced graphene oxide nanocomposite for high performance of adsorption and photocatalysis

The Ag-TiO₂/r-GO nanocomposite was synthesized via a facile one-pot solvothermal method. X-ray diffraction (XRD), Transmission electron microscopy (TEM),High resolution transmission electron microscopy(HRTEM), UV–vis diffuse reflectance spectroscopy (DRS), Fourier transformed infrared spectroscopy (FT-IR), Photoluminescence (PL) and N₂ adsorption-desorption were used for the characterization of prepared samples. The adsorbent and photocatalytic performance of prepared samples were evaluated by remove of Rh B dyes and reduction of CO₂. Both the adsorbent and photocatalytic ability of all the Ag-TiO₂/r-GO samples were much higher than pure hollow TiO₂. The excellent adsorbent capacity can be attributed to the large BET surface area and the enhanced photocatalytic activity can be assigned to the predominant properties of graphene and the localized surface plasmon(LSPR) effect of Ag nanoparticles.     

One-pot synthesis of zinc oxide - polyaniline nanocomposite for fabrication of efficient room temperature ammonia gas sensor

Development of efficient room temperature ammonia (NH₃) gas sensor from one pot synthesized zinc oxide (ZnO) – polyaniline (PANI) nanocomposite is reported in the present article. Prior to gas sensing study, the material is characterized to understand the structural, morphological, compositional, optical and thermal properties. Structural and morphological studies indicate good incorporation of ZnO particles in PANI matrix. The gas sensing efficiency of ZnO-PANI nanocomposite is examined at room temperature for ethanol (C₂H₅OH), methanol (CH₃OH) and NH₃ gas. The results confirm that ZnO-PANI nanocomposite to be highly selective for NH₃ with fast response time and better stability. The response and recovery times are observed to be significantly dependent on NH₃ concentration and the lowest detectivity limit of the sensor for NH₃ is found 10 ppm. ZnO-PANI nanocomposite shows better gas sensing efficiency as compared to the sensors developed from single phase PANI film.     

A novel CoFe2O4/polyacrylate nanocomposite prepared via an in situ polymerization in emulsion system

A CoFe₂O₄/polyacrylate nanocomposite was synthesized by in situ emulsion polymerization of an acrylic acid monomer in the presence of CoFe₂O₄ magnetic fluid. X-ray diffraction and FT-IR spectra confirmed the formation of the CoFe₂O₄/polyacrylate nanocomposite. Transmission electron microscopy images showed that CoFe₂O₄ nanoparticles with the particle sizes of about 12 nm were well dispersed in the polymer matrix. The nanocomposite exhibited superparamagnetic behavior at room temperature under an applied magnetic field. The formation mechanism of the nanocomposite was investigated as well.     

Ag/αFe2O3-rGO novel ternary nanocomposites: Synthesis,characterization, and photocatalytic activity

In this research, novel ternary Ag/αFe₂O₃-rGO nanocomposites with various contents of GO were synthesized via a facile one-pot hydrothermal method. Ag/αFe₂O₃-rGO nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometer (EDX), photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR). The results showed that hematite nanoparticles and Ag nanoparticles were well decorated on the graphene surface. Photocatalytic activity of Ag/αFe₂O₃-rGO ternary nanocomposites and pure Ag/αFe₂O₃ was investigated for photodegradation of Congo red dye solution as a model pollutant under UV light irradiation. The ternary nanocomposite with 1.8?mg/ml GO aqueous solution concentration shows higher degradation efficiency under UV light irradiation than the pure Ag/αFe₂O₃ and the nanocomposites with other GO aqueous solution concentrations. It was observed that the adsorption of the dyes on the nanocomposites surface is dependent on the graphene content due to a decrease in the recombination rate, particles size, and increase charge carrier transfer. The results show that the Ag/αFe₂O₃-rGO nanocomposite can be used as an excellent photocatalytic material for degradation of Congo red dye in wastewater. A possible photocatalytic mechanism was proposed for degradation of Congo red dye.     

Hydrogen sulfide sensing properties of multi walled carbon nanotubes

This paper investigates the effect of functional groups on the hydrogen sulfide sensing properties of multi-walled carbon nanotubes using carboxyl and amide groups and Mo and Pt nanoparticles as decorated precursors in gaseous state at working temperature. Carbon nanotubes were synthesized by the CVD process and decorated with the nano particles; provide higher sensitivity for H₂S gas detection. The MWCNTs were characterized by scanning electron microscopy combined with energy dispersive X-ray (SEM/EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), ATR-IR absorption and Fourier transforms infrared (FT-IR) analyses. The MWCNTs were deposited as a thin film layer between prefabricated gold electrodes on alumina surfaces. The sensitivity of carbon nanotubes was measured for different H₂S gas concentrations and at working temperature. The results showed that the measured electrical conductance of the modified carbon nanotubes with functional groups is modulated by charge transfer with P-type semiconducting characteristics and metal decorated carbon nanotubes exhibit better performances compared to functional groups of carboxyl and amide for H₂S gas monitoring at room temperature.     

Controlled synthesis of Fe3O4@SnO2/RGO nanocomposite for microwave absorption enhancement

A ternary nanocomposite of Fe₃O₄@SnO₂/reduced graphene oxide (RGO) with different contents of SnO₂ nanoparticles was synthesized by a simple and efficient three-step method. The transmission electron microscopy and field emission scanning electron microscopy characterization display that plenty of Fe₃O₄@SnO₂ core–shell structure nanoparticles are well distributed on the surface of RGO sheets. The X-ray diffractograms show that the products consist of highly crystallized cubic Fe₃O₄, tetragonal SnO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the products at room temperature. The microwave absorption properties of paraffin containing 50 wt% products were investigated at room temperature in the frequency range of 2–18 GHz by a vector network analyzer. The electromagnetic data show that the maximum reflection loss is −45.5 dB and −29.5 dB for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. Meanwhile, the reflection loss less than −10 dB is up to 14.4 GHz and 13.8 GHz for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. It is believed that such nanocomposite could be used as promising microwave absorbers.     

Hole concentration modulated gas sensor for selective detection of 2-methoxy ethanol

The inhaling rate of toxic gases in daily life is increasing alarmingly; in turn, human health is in question. To resolve this dilemma, the possible remedy is the early detection and adequate regulation of VOCs in the atmosphere via sensors. Therefore, the investigation focused on developing a gas sensor for sensing several VOCs and flourished with a highly selective C₃H₈O₂ gas sensor at room temperature. In-depth structural, elemental, and morphological analysis followed by the sensing test affirmed the enhanced C₃H₈O₂ detection performance of Ag–NiO over pure NiO. The nanosized sphere formation was confirmed via XRD and TEM characterizations alongside the effect of sintered temperature on the shape and crystallite size. Moreover, the XPS examined the combined effect of sintering temperature and doping on the synthesized nanostructures and optimized the exact temperature as 500 °C because of the improved hole concentration. The Ag–NiO(500 °C) exhibited appealing sensing characteristics, specifically, a high response of 6491.57 for 100 ppm C₃H₈O₂ at room temperature. The sensor displayed a quick response and recovery (10 s,10 s) C₃H₈O₂ alongside long-term repeatability and stability; it showed practical implementation in real-time scenarios.     

Synthesis and Characterization of Magnetically Retrievable Fe3O4/Polyvinylpyrrolidone/Polystyrene Nanocomposite Catalyst for Efficient Catalytic Oxidation Degradation of Dyes Pollutants

Recently, the application of metal oxides such as Fe₃O₄ nanoparticles have wide interest for environmental remediation and treatment of wastewater especially contaminated with azo dyes owing to its high degradation efficacy and low toxicity. The recovery of magnetic catalysts without losing their efficiency is an essential feature in the catalytic applications. The aim of this article is to investigate and synthesis of magnetically retrievable Fe₃O₄/polyvinylpyrrolidone/polystyrene (Fe₃O₄/PVP/PS) nanocomposite for the catalytic degradation of azo dye acid red 18 (AR18). Fe₃O₄/PVP/PS nanocomposite was prepared in two steps. Firstly, PVP/PS microsphere was synthesized by γ-irradiation polymerization of styrene in presence of PVP solution. Secondly, deposition of Fe₃O₄ nanoparticles on PVP/PS microsphere was achieved by the alkaline co-precipitation of Fe³⁺/Fe²⁺ ions. The chemical structural and morphological properties of PVP/PS microsphere and Fe₃O₄/PVP/PS nanocomposite were examined by XRD, TEM, DLS, FTIR, EDX and VSM techniques. TEM results showed homogeneous morphology, spherical shaped and well-dispersed Fe₃O₄ nanoparticles with average particle size of 26 nm around PVP/PS microspheres. The VSM measurements of Fe₃O₄/PVP/PS nanocomposite exhibit excellent magnetic response of saturation magnetization 26.38 emu/g which is suitable in magnetic separation. The effect of the synthesized Fe₃O₄/PVP/PS nanocomposite on the catalytic degradation of AR18 in presence of hydrogen peroxide (H₂O₂) as a heterogeneous Fenton-like catalyst was examined. The catalyst Fe₃O₄/PVP/PS/H₂O₂ played basic role in promoting the oxidation degradation efficiency of AR18 of initial concentration 50 mg/L to 94.4% in 45 min with excellent recyclability till the sixth cycles under the best conditions of pH 3, 2% v/v H₂O₂ and 0.3 g catalyst amount. Furthermore, the Fe₃O₄/PVP/PS/H₂O₂ hybrid catalyst system supports high capability for oxidation degradation of mixture of different dyes. The Fe₃O₄/PVP/PS nanocomposite catalyst had high magnetic and recyclability characters which are acceptable for the treatment of wastewater contaminated by various dyes pollutants.

     

Photo-assisted fenton mineralization of an azo-dye acid black 1 using a modified laponite clay-based Fe nanocomposite as a heterogeneous catalyst

Photo-assisted Fenton mineralization of an azo-dye Acid Black 1 (AB1) was studied in detail using a modified laponite clay-based Fe nanocomposite (Fe-Lap-RD) as a heterogeneous catalyst in the presence of H₂O₂ and UV light. The Fe-Lap-RD was characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption. The effects of reaction parameters such as initial AB1 concentration, H₂O₂ concentration, Fe-Lap-RD catalyst loading, initial solution pH, UV light wavelength and power, and reaction temperature on the mineralization of AB1 were investigated. Under the optimal reaction conditions (6.4 mM H₂O₂, 1.0 g Fe-Lap-RD/L, 8 W UVC, initial solution pH=3.0), complete discoloration and over 90% total organic carbon (TOC) removal of 0.1 mM AB1 were achieved after 90 min reaction. Discoloration kinetics of AB1 was also studied to obtain apparent reaction rate constants and reaction activation energy.