Search

It is critical to design bifunctional nonprecious electrocatalysts with low costs and high efficiency for hydrogen production. Conventional electrocatalysts, on the other hand, frequently exhibit s...

Low-cost and high-performance UV photodetector (PD) based on anatase titanium dioxide (TiO2) and nitrogen-doped graphene quantum dots (N-GQDs) bilayer heterojunction were fabricated on a commercial SiO2/Si substrate by drop-casting the N-GQDs solution on the surface of anatase TiO2 thin film, which was initially prepared by thermally oxidizing a DC-sputtered titanium (Ti) film in air. The anatase TiO2 and N-GQDs films were characterized with several techniques in order to study their structure and morphology properties. XRD, XPS, and AFM revealed that the phase of the as-sputtered Ti film transformed to a highly crystalline pure anatase TiO2 film when thermally oxidized at 600 °C in air. In addition, TEM, HRTEM, and FTIR revealed that the N-GQDs are highly crystalline and narrowly distributed in size. Furthermore, the optical and UV light harvesting properties of photodetectors based on pure anatase TiO2 film (without N-GQDs) and anatase TiO2 (with N-GQDs) were investigated. The photoresponsivity of the hybrid photodetector based on anatase TiO2/N-GQDs heterojunction has been enhanced by almost 2.5 times in magnitude than that of the photodetector based on pure anatase TiO2 film. This result was validated by elucidated energy band alignment between the anatase TiO2 and N-GQDs films, which resulted in a higher absorption rate, and an efficient transport mechanism in the hybrid junction-based photodetector than that of the pure TiO2-based photodetector.

This paper reports the photoluminescence and nonlinear optical (NLO) properties of Ce2O3–TiO2 nanocomposites synthesized via sol–gel process with different concentrations of cerium. The physical characterization studies by means of XRD indicated for the successful incorporation of Ce into the lattice of TiO2, while the UV-visible spectra for an absorption edge shift of TiO2 to the higher wavelength side following the Ce addition, and FESEM analysis for the morphology and particles sizes of the synthesized materials. On testing of the photoluminescence properties recorded through time-resolved fluorescence (TCSPC) technique, a decrease in the intensity of TiO2 with that of increased Ce concentration was observed and is due to an escalation in the number of oxygen vacancies. Further, the observation NLO properties for Ce2O3–TiO2 was done by a Z-scan technique of 5ns continuous wave (cw) laser at 532 nm, where the involvement of active mechanisms in the nonlinear refraction and nonlinear absorption are due to the saturable absorption (SA) and nonlinear thermal effects.

Herein, we report a facile hydrothermal synthesis of MnO2 nanoparticles anchored multi walled carbon nanotubes (MnO2@MWCNTs) as potential anode materials for lithium-ion (Li-ion) batteries. The prepared MnO2@MWCNTs were characterized by several techniques which confirmed the formation of MnO2 nanoparticles anchored MWCNTs. The X-ray diffraction and Raman-scattering analyses of the prepared material further revealed the effective synthesis of MnO2@MWCNTs. The fabricated Li-ion battery based on MnO2@MWCNTs exhibited a reversible capacity of ~823 mAhg−1 at a current density of 100 mAg−1 for the first cycle, and delivered a capacity of ~421 mAhg−1 for the 60 cycles. The coulombic efficiency was found to be ~100% which showed excellent reversible charge–discharge behavior. The outstanding performance of the MnO2@MWCNTs anode for the Li-ion battery can be attributed to the distinctive morphology of the MnO2 nanoparticles anchored MWCNTs that facilitated the fast transport of lithium ions and electrons and accommodated a broad volume change during the cycles of charge/discharge.

Herein, we report a successful synthesis of supramolecularly assembled polyaniline/silver oxide/graphene oxide composite (PANI/Ag2O/GO) for enhanced NO2 gas sensing application. The PANI/Ag2O/GO composite was synthesized by facile stirring followed by an ultrasonication process. The prepared material was characterized by different techniques such as x-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and Raman-scattering spectroscopy. The detailed analysis revealed that the average crystallite sizes of PANI/Ag2O and PANI/Ag2O/GO composites were found to be 37.37 nm and 41.55 nm, respectively. FESEM and TEM analysis showed coral-like rough-surfaced and extensively agglomerated morphology for PANI and ultrathin flexible sheet-like morphology for GO. Ag2O nanoparticles with diameters 20–30 nm were well incorporated in the GO sheets and PANI matrix in the case of PANI/Ag2O/GO composites. The synthesized materials were used to make resistive sensor devices that had a high response to NO2 gas. The fabricated sensors were examined at various temperatures to obtain the optimal sensing temperature. The fabricated NO2 gas sensor device based on PANI/Ag2O/GO composite exhibited a highest sensitivity of 5.85 for 25 ppm at an optimized temperature (100 °C) as compared to the pure PANI (2.5) and PANI/Ag2O composite (3.25). Further, the fabricated sensor device based on PANI/Ag2O/GO composite was also examined at different NO2 gas concentrations.

Herein, a heterostructure of MoS2/CdS/TiO2 nanotube arrays is constructed by successive ionic layer adsorption/reaction of CdS and dipping-assembly of MoS2 on the vertically oriented TiO2 nanotubes prepared by anodization method. The heterostructure is extensively investigated in terms of the composition, morphology, structural, and optical properties. It is observed that the co-modification of TiO2 nanotube arrays with CdS and MoS2 significantly enhances the visible light response and boosts the facile photo-generated electrons’ transfer and charge separation efficiencies. Therefore, the prepared heterostructure photo-anode exhibits significantly enhanced photoelectrochemical properties including photocurrent, open circuit potential, and photo-conversion efficiencies compared with that of pure TiO2 nanotube arrays and CdS/TiO2 nanotube systems. Interestingly, it is found that the MoS2 coatings on the surface of CdS/TiO2 nanotube arrays greatly enhance their photoelectrochemical stability. The presented work demonstrates that MoS2/CdS/TiO2 nanotube heterostructures are a promising material for improved photoelectrochemical properties. A heterostructure of MoS2/CdS/TiO2 nanotube arrays was constructed by successive ionic layer adsorption/reaction of CdS and dipping-assembly of MoS2 on the vertically oriented TiO2 nanotube arrays, and their improved photoelectrochemical properties were demonstrated

In this paper, pure SnO2 and Ce-doped SnO2 nanosheets were synthesized through a facile hydrothermal method. The synthesized materials were characterized by different techniques for their physico-chemical properties. The XRD data indicated the characteristic tetragonal rutile crystal phase for SnO2. Ce doping was ascertained by the presence of the diffraction peaks of CeO2 in all the doped samples of the SnO2 nanosheets. FESEM images revealed highly rough surfaces as well as the agglomeration of a large number of small nanoparticles of multiple shapes to form nanosheets like morphologies for pure SnO2 and Ce-doped SnO2. Electrochemical techniques like cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry were applied to demonstrate the electrochemical performances of the pure SnO2 and Ce-doped SnO2 nanosheets/Nafion-modified glassy carbon electrode (GCE). The 3% Ce-doped SnO2 nanosheet/Nafion-modified GCE showed a remarkable sensitivity of 0.9986 μA μM−1 cm−2 over a linear dynamic range of 0.5–20.3 µM. The corresponding linear regression equation was Ip (μA) = 0.0709 [2-nitroaniline (μM)] + 0.1385 with R2 = 0.99325. The LOD of the modified sensor was found to be 6.3 ± 0.1 nM at the signal-to-noise ratio of S/N = 3. The newly developed sensor electrode exhibited good selectivity toward 2-nitroaniline in the presence of common interfering species. Fabrication and characterization of highly sensitive and selective 2-nitroaniline chemical sensor based on cerium-doped tin oxide nanosheets/Nafion-modified glassy carbon electrode.

Ethanol is one of the volatile organic compounds as well as organic pollutants that is essentially to be monitored using high response sensors. Semiconducting metal oxide nanostructures can be the potential sensor material for high-performance ethanol sensing application. Herein, we present the fabrication and characterization of highly sensitive and selective ethanol gas sensor based on flower-shaped CuO composed of thin nanoplates synthesized by facile hydrothermal process. The prepared flower-shaped CuO was examined by various techniques viz FESEM, XRD, EDS, elemental mapping, HRTEM, SAED, UV-visible spectroscopy, FTIR spectroscopy, and Raman spectroscopy, which confirmed the high-density growth, monoclinic crystal structure, and optical band gap of ~2.5 eV. The fabricated resistive sensor device based on flower-shaped CuO, at optimum experimental conditions, i.e., 250 °C, 100 ppm ethanol concentration, exhibited a high sensing response of 241%, while, at 10 ppm of ethanol concentration, the response was observed to be 5%. The transient responses as well as the stability of the sensor were analyzed and reported here. The selectivity of CuO sensor device was studied for NO2, CO2, CO, and CH4 gases and remarkably it was seen that the developed gas sensor devices demonstrated outstanding selectivity toward ethanol gas. Finally, the gas response mechanism of the fabricated resistive ethanol gas sensor was explained on the basis of the ionosorption model.

For the construction of high-performance energy storage and conversion devices, the development of advanced electrode materials with specific nanostructural characteristics is a requirement of the ...

In this paper, star-fruit-shaped CuO microstructures were hydrothermally synthesized and subsequently characterized through different techniques to understand morphological, compositional, structural, crystal, optical and vibrational properties. The formation of star-fruit-shaped structures along with some polygonal and spherical nanostructures was confirmed by FESEM analysis. XRD data and Raman spectrum confirmed the monoclinic tenorite crystalline phase of the CuO with crystal size 17.61 nm. Star-fruit-shaped CuO microstructures were examined for ethanol gas sensing behavior at various operating temperatures and concentrations. The gas response of 135% was observed at the optimal temperature of 225 °C. Due to excellent selectivity, stability and re-usability, the as-fabricated sensor based on star-fruit-shaped CuO micro-structures may be explored for future toxic gas sensor applications.

In this study, the deposition parameters of the SU8 2000.5 negative photoresists have been investigated and optimized for the photolithographic technique. Then, applied the inductive coupled plasma reactive ion etching (ICP RIE) to produce V-shaped groove diffraction grating on a silicon substrate. Spin coater (speed: 1000 rpm) was used to coat the photoresist over the Si substrate. The observed photoresist film thickness was measured by ellipsometry and found to be 800 nm. Interestingly, the film exhibited some stability with increasing the spin speed. The thermogravimetric analysis was used to optimize the baking temperature which was found to be ~105 °C. Contrast curves were obtained experimentally and used to optimize the exposure energy along with the images obtained from the field emission scanning electron microscopy (FESEM). The optimized energy fluence was found to be 17 mJ/cm2. It was interesting to observe that the thickness of the photoresists film was increasing with the elevation of the exposure energy fluence. The FESEM images were used to optimize the ICP RIE etching process and the best etching conditions for the Si substrate were ICP power: 150 W, bias power: 100 W, and SF6 gas flow rate: 32 SCCM (standard cubic centimeters per minute), O2 gas flow: 8 SCCM, and Ar gas flow of 8 SCCM. It is worth to mention that well-defined V-shaped grooves were observed with a depth of 2 μm under the same experimental conditions.

Methylene blue intercalated layered MnO2 nanosheets (MB-MnO2) were synthesized through an ex-situ method at room temperature. Tetramethylammonium hydroxide (TMAOH) was used as a delaminating agent for the synthesis of nanosheet-like structures of MnO2. The prepared nanocomposites were analyzed by various instrumental techniques such as UV–visible, FTIR, XRD, FESEM, and EDX for the close examination of the morphology, structure, shape, crystallinity, and vibrational characterization. Typical two-dimensional layer sheet-like morphologies with multiple folds were observed for non-intercalated MnO2, whereas intercalated MnO2 showed more flattered and planar square-shaped and elongated ultrathin sheet-like structures with occasional folds and crinkles. MB intercalated MnO2nanosheets were used as an efficient electron mediator for the electrooxidation of the ascorbic acid to dehydroascorbic acid. Cyclic voltammetry and chronoamperometry confirmed the excellent electrocatalytic activity of the modified MB intercalated MnO2 nanosheets/GCE over a wide range of ascorbic acid concentrations in 0.1 M PBS. The detection limit was computed to be 0.05 μM. The effect of the scan rates and concentration of the ascorbic acid were also analyzed.

Root like structured Ni-doped zinc oxide [Zn(1-x)NixO (x = 0.09)] thin films were deposited on a non-conducting glass substrate by indigenously developed spray pyrolysis system at optimized substrate hotness of 573±5 K. Thus obtained Ni-doped ZnO thin films were characterized by UV-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM). XRD result revealed that Ni-doped ZnO has a polycrystalline nature with a hexagonal wurtzite structure. For pure ZnO and Ni-doped ZnO thin films, the particle sizes were 60.9 and 53.3 nm while lattice strain values were 1.56×10−3 and 1.14×10−3, respectively. The film surface showed characteristic root-like structure as observed by the SEM. It was observed that the Ni-doped ZnO thin films were grown in high density along with more extent of branching as compared to pure ZnO thin films but retained the root-like morphologies, however, the branches were more-thinner and of shorter lengths. AFM analysis showed that the surface grains of the Ni-doped samples are homogeneous with less RMS roughness values compared with the undoped ZnO samples. The photocatalytic activity of the prepared thin films was evaluated by the degradation of methyl orange (MO) dye under UV light irradiation. Pure ZnO and Ni-doped ZnO thin films took 150 min and 100 min to degrade about 60% MO dye, respectively.

ZnO–SnO2 nanocubes were used as promising material for efficient sensing of p-nitrophenol and faster photocatalytic degradations of dyes like methyl orange (MO), methylene Blue (MB) and acid orange 74 (AO74). ZnO–SnO2 nanocubes were prepared by the facile solution process at 50 °C using Zn(NO3)2·6H2O and SnCl2·2H2O as a precursor in the presence of ethylenediammine. The synthesized material was examined for its morphological, structural, crystalline, optical, vibrational, and compositional studies by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy. FESEM studies revealed the formation of well-defined ZnO–SnO2 nanocubes where the structural examinations revealed the formation of a crystalline tetragonal rutile phase for SnO2 with some crystal sites doped with Zn. The as-synthesized nanocubes were explored for their photocatalytic activities towards three different dye viz. MO, MB, and AO74. Practically, complete degradation of AO74 was seen within 4 minutes of photo-irradiation in the presence of 0.05 g ZnO–SnO2 nanocubes. However, 97.17% and 41.63% degradations were observed for MB and MO within 15 and 60 minutes, respectively. All the dye degradation processes followed the pseudo-first-order kinetic model. Moreover, the as-synthesized nanocubes were utilized to fabricate highly sensitive and selective fluorescent chemical sensor for the detection of p-nitrophenol (PNP). ZnO–SnO2 nanocubes showed a very low detection limit of 4.09 μM for the detection of PNP as calculated according to the 3σ IUPAC criteria. Further, the as-synthesized ZnO–SnO2 nanotubes were found to be highly selective for p-nitrophenol as compared to the other two isomers.

Nanostructured ZnO doped with different Ce precursor concentrations (1, 5 and 10 mol%) has been prepared via co-precipitation method and tested for their photocatalytic and chemical sensing performances toward methyl orange (MO) and picric acid (PA) chemicals, respectively. After addition of Ce dopant, the spherical morphology of ZnO particles changed to a cone-like structure and exhibited the single-phase wurtzite structure, except for the 10 mol % dopant concentration. Blue-shift was detected in 5 mol% Ce doping, and this was found to be the optimum concentration for achieving the maximum dye degradation and sensing performances. The 5 mol% Ce doped ZnO expressed the complete MO degradation under UV light illumination, but the decrease in MO degradation with 10 mol% Ce doped ZnO was suggested to suppress the Ce3+ character in the sample. Facile redox couple Ce3+/Ce4+ appeared to improve the charge separation of Ce-doped ZnO upon UV illumination, forming the basis for release of O2, leading to increased catalytic and PA sensing performances.

Implementing sensitive and fast ppb-level formaldehyde sensing at room temperature is still in extreme demand for practical indoor air quality monitoring. Herein, we developed a visible-light-sensitive and dipole-modified graphene-based nanocomposite ZnOx@ANS-rGO for ultrasensitive trace formaldehyde sensing. The rich oxygen vacancy zinc oxide (ZnOx) nanoparticles on graphene nanosheets provide OH-groups and edge sorption sites to facilitate the activation of adsorbed oxygen. Moreover, the supramolecular assembled 5-aminonaphthalene-1-sulfonic acid-modified graphene (ANS-rGO) nanosheets with donor–π–acceptor dipole served as an excellent conduction platform to transport and collect photo-generated electrons. Based on the collaboration of rich ZnOx and ANS-rGO, the obtained sensor ZnOx@ANS-rGO-0.1 showed the highest response (Ra/Rg = 1.58 to 1 ppm HCHO) among the MOS materials reported so far, and its limit of detection (LOD) can be as low as 5 ppb under 405 nm light illumination at RT. The outstanding efficiency and accuracy of the obtained gas sensor were confirmed by practical performance estimation in a 30 m3 chamber. The selectivity, long-term stability, repeatability and humidity resistance of the obtained sensors at RT were also revealed. The sensing mechanism based on the combination of visible-light activation and dipole modification was analyzed by the O-XPS, PL, in situ ATR-FTIR and charge density difference calculation.

Silicon substrate on-chip (SSOC) supercapacitors have recently attracted considerable attention in electronic devices because of their compatibility with the current silicon-based micro- and nanofa...

Herein, we report the facile solution phase precipitation synthesis of ZnO nanoparticles doped with various concentrations, i.e. 1, 5 and 10 mol% of lanthanum (La). The synthesized nanoparticles were characterized in detail by several techniques which confirmed the high-density growth and well-crystalline nature of La-doped ZnO nanoparticles. The XRD results revealed the successful incorporation of 1 mol% La ions in the hexagonal wurtzite structure of ZnO; however, small XRD peaks of La2O3 were detected in 5 and 10 mol% La-doped samples. All the La-doped nanoparticles were found to be UV responsive. For the application prospective, all the synthesized nanoparticles were used as photocatalyst for the photocatalytic degradation of three toxic dyes, i.e. methyl orange (MO), Rhodamine B (Rh B) dyes and picric acid (PA). By detailed photocatalytic investigations, interestingly, 1 mol% La-doped ZnO was found to be most efficient photocatalyst towards the degradation of all three organic dyes. Further, the synthesized nanoparticles were also used as fluorescent probe for the fluorescence sensing of picric acid (PA). Remarkably, the 1 mol% nanoparticles exhibited highest sensitivity, i.e. lowest limit of detection (LOD) value (1.05 µM L−1) towards PA compared to 5 and 10 mol% (1.38 µM L−1) La-doped ZnO nanoparticles.

2D SnO2 disks with excellent purity and crystallinity were synthesized through a low cost, facile hydrothermal process and were characterized in terms of their morphological, structural, optical and electrochemical properties. The 2D disk-like morphology of synthesized SnO2 presented the average thickness of ∼1 μm and possessed the typical rutile tetragonal phase for the SnO2 with preferred growth along (100) plane. As-synthesized SnO2 disks were used for the fabrication of gas sensors for reducing gases like H2, CO, and C3H8. With the optimized temperature at 400 °C, the as-synthesized SnO2 electrode expressed the gas responses of 14.7, 9.3 and 8.1 for H2, CO, and C3H8, respectively. Contrary, the reasonable response times of 4 s, 3 s, and 8 s and the recovery times of 331 s, 201 s, and 252 s were recorded for H2, CO, and C3H8 gases, respectively. The DFT studies conducted herein suggest that the adsorbed oxygenated species act as a primary redox mediator for gas sensing reaction between reductive gases like H2, CO and C3H8, and SnO2 sensor. From DFT analysis, a very low heat of adsorption (≤0.2 eV) estimated which suggested the physisorption of the H2 molecules on the surface of the sensing material (i.e. SnO2). In contrast, the deposited oxygen atom forms strong chemical bonds with O2c and O3c sites. The oxygen atom bonded to O2c site control the conductivity of the sensor better than the O3c sites.

For gas sensing applications, most of the reported two-dimensional (2D) materials are suffering from relative low sensitivity and high limit of detection (LOD) at room temperature. In this work, we...

Photocatalysts provide excellent potential for the full removal of organic chemical pollutants as an environmentally friendly technology. It has been noted that under UV-visible light irradiation, nanostructured semiconductor metal oxides photocatalysts can degrade different organic pollutants. The Sn6SiO8/rGO nanocomposite was synthesized by a hydrothermal method. The Sn6SiO8 nanoparticles hexagonal phase was confirmed by XRD and functional groups were analyzed by FT-IR spectroscopy. The bandgap of Sn6SiO8 nanoparticles (NPs) and Sn6SiO8/GO composites were found to be 2.7 eV and 2.5 eV, respectively. SEM images of samples showed that the flakes like morphology. This Sn6SiO8/rGO nanocomposite was testing for photocatalytic dye degradation of MG under visible light illumination and excellent response for the catalysts. The enhancement of photocatalytic performance was mainly attributed to the increased light absorption, charge separation efficiency and specific surface area, proved by UV-vis DRS. Further, the radical trapping experiments revealed that holes (h+) and superoxide radicals (·O−2) were the main active species for the degradation of MG, and a possible photocatalytic mechanism was discussed.

Herein, we report the facile synthesis, characterization and visible-light-driven photocatalytic degradation of perforated curly Zn0.1Ni0.9O nanosheets synthesized by hydrothermal process. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies confirmed the cubic phase crystalline structure and growth of high density perforated curly Zn0.1Ni0.9O nanosheets, respectively. As a photocatalyst, using methylene blue (MB) as model pollutant, the synthesized nanosheets demonstrated a high degradation efficiency of ~76% in 60 min under visible light irradiation. The observed results suggest that the synthesized Zn0.1Ni0.9O nanosheets are attractive photocatalysts for the degradation of toxic organic waste in the water under visible light.

The synthesis, characterization, and photodetector application of pure and Ni doped CdS thin films prepared by the spray pyrolysis technique are presented in this paper. Various techniques were used to analyze the thin films that had been produced. The hexagonal phase of the produced thin films is confirmed by X-ray diffraction (XRD) and FT-Raman (FTR) measurements. Scanning electron microscopy (SEM) was used to investigate the morphology of the thin film surface, revealing the development of nanograins. The energy band gaps for all of the prepared thin films were calculated to be approximately 2.4 eV. When the films were stimulated at 450 nm wavelength, a strong photoluminescence emission was seen at ∼540 ± 6 nm. The dark/photo I-V electrical performance of the developed films was observed. The fabricated Au/CdS/Au and Au/Ni:CdS/Au photodetectors were studied for recombination behavior, dark and photo surface resistivity, and photosensitivity. Interestingly, the dark surface resistivity was found to be greater compared to the photo-resistivity. When the light intensity was increased to 1450 Lux, the photosensitivity improves from 10% to 35%. These findings indicate that the fabricated CdS/Ni:CdS films-based photodetectors are suitable for optoelectronic devices.

Herein, NOx, i.e., nitric oxide (NO) and nitrogen dioxide (NO2), gas sensors were fabricated using iron (Fe)-doped ZnO nanoparticles prepared via the facile hydrothermal process. The synthesized Fe-doped ZnO nanoparticles were analyzed through several techniques that revealed the well-crystallinity and dense growth of nanoparticles with the typical diameters of 25 ± 5 nm. The synthesized nanoparticles were utilized as a prospective material for the fabrication of NOx gas sensors operating at different temperatures, i.e., 350 °C, 400 °C, and 450 °C. The detailed sensing performances revealed that the optimum and most suitable sensing temperature for the fabricated sensors is 400 °C. In presence of 10 ppm NO gas, the fabricated sensor exhibited the highest gas response of 1.35 with a response (tresponse) and recovery (trecovery) time of 44 s and 402 s, respectively. Similarly, the fabricated NO2 gas sensor, in presence of 10 ppm gas shows the highest gas response of 1.33 with a response and recovery times of 50 s and 281 s, respectively. The presented results demonstrate that Fe-doped ZnO nanomaterials are capable to fabricate efficient NOx gas sensors.

Herein, we report the high-temperature electrical characteristics of heterojunction diode fabricated based on n-Ga-doped ZnO nanowires/p-Silicon substrate. Various electronic properties such as rectification ratio, the effective barrier height, the diode ideality factor, etc. of the fabricated heterojunction diode at high temperature were investigated. The electrical characteristics were examined in the high-temperature range of 293 K–433 K in both reverse and forward biased conditions, which exhibited good stability over the entire temperature range. The observed current–voltage (I–V) studies confirmed three different conduction mechanisms for the fabricated heterojunction diodes, i.e., either field emission or tunneling, recombination-tunneling mechanism and the transport mechanism dominated by space-charge-limited current at the different regions. The observed electrical results exhibited fluctuations in the sensitivity of the quality factor of the heterojunction diode and consequently corresponding fluctuations in the resistance. The linear dependence of effective barrier height on quality factor can be attributed to the presence of some lateral inhomogeneities in the barrier height. The analysis of C–V data was conducted to deduce the value of barrier height of Schottky barrier for the fabricated heterojunction diode. Interestingly, the observed results assert the mismatch that occurs between the interface states and resulting capacitance of the fabricated heterojunction diode.

In this paper, Ag doped MnO2-CNT nanocomposite was fabricated by using simple co-precipitation route. The synthesized nanocomposite was employed as adsorbent for elimination of Acridine Orange dye. The structural analysis of as synthesized Ag doped MnO2-CNT nanocomposite confirms the presence of (111) plane of Ag, (104) of carbon and (110) plane of MnO2. Processing of operational variable parameters such as, pH, adsorbent dose, and initial dye concentration with respect to contact time on adsorption of Acridine Orange was optimized and evaluated using Response Surface Methodology. The fit of the predictive model for the removal of dye was in good agreement with the experimental value. Isotherm data was modelled by means of Langmuir, Freundlich, Temkin and Dubinin- Radushkevich isotherm. Langmuir isotherm offered the best fit to experimental data proposing homogeneous dispersion of adsorption sites. Furthermore, the suitability of the adsorbent was also investigated by fitting the adsorption data with pseudo-second-order kinetic model. The recuperation and reusability of the adsorbent and adsorbate has made this process inexpensive and appropriate for large scale applications.

In this paper, a film of n-ZnO nanowalls was deposited over p-silicon (Si) substrate by thermally evaporating metallic zinc powder in oxygen gas environment. Several techniques were used to examine various properties of prepared ZnO nanowalls. The morphological study confirmed that the grown ZnO film possesses nanowalls shaped morphologies containing three dimensional (3D) interconnected nanowalls forming large voids with irregular shapes. Interestingly, whole Si substrate was covered with nanowalls shaped morphologies. The structural characterizations examined by x-ray diffraction (XRD) confirmed that the deposited nanowalls possess wurtzite hexagonal crystal structure. The presence of a strong UV and suppressed green emissions at room-temperature photoluminescence (PL) spectrum exhibited good optical properties of the deposited nanowalls. The electrical properties of the deposited n-ZnO nanowalls over p-silicon substrate assembly was examined in both forward and reverse bias conditions at room-temperature. The fabricated heterojunction device exhibits a standard rectifying behavior which manifests itself in an exponential increase of the current with increase in voltage at forward bias condition. Also, it has a good quality factor similar to an ideal diode.

Herein, we report the effect of synthesis temperature on the morphologies, optical and electronic properties of magnesium oxide (MgO) nanostructures. The MgO nanostructures were synthesized at different temperatures, i.e., 100 °C, 300 °C, and 600 °C by simple chemical reaction process and their morphology, particle size, optical, and electrical properties were examined by different techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and UV-Vis. spectroscopy. The morphological investigations revealed that various morphologies of MgO nanostructures, i.e., nanoparticles, nanosheet networks, and nanoneedles were synthesized at 100 °C, 300 °C, and 600 °C. The XRD results confirmed that with increasing the synthesis temperature, the crystallinity of the synthesized nanostructures increases. Further, the dielectric properties and AC conductivity at various frequencies for MgO nanostructures were studied which revealed that the dielectric losses decrease with increase in frequency and temperature. In addition, the observed band gap decreases from 4.89 eV to 4.438 eV (100 °C to 600 °C) representing its increase in the conductivity.

Conductive polymer composites (CPCs) have attracted intensive attention for several decades because they can endow the materials with not only good processability but also various functionalities e...

Herein, we report the facile microwave-assisted synthesis, characterization and photocatalytic degradation applications of Bismuth ferrite heterostructures composed of interconnected nanosheets (BHNs). The synthesized materials were subjected to several analytical studies such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy in order to examine the morphological, structural, optical and photo catalytic properties. The structural and morphological characterizations confirmed the rhombohedral perovskite crystal structure and the formation of heterostructures composed of interconnected nanosheets for the synthesized material. The compositional characterization revealed that the synthesized material is bismuth ferrite with high purity. The BHNs were further used as efficient photocatalyst for the photocatalytic degradation of highly hazardous pollutant methyl orange under sunlight irradiation. The sunlight driven photocatalytic experiments revealed ~86% photodegradation of methyl orange dye in 150 min. The presented work revealed that the synthesized BHNs are excellent material for the photocatalytic degradation of various organic contaminants and hazardous pollutants.

Herein, we report the synthesis and analysis of fern shaped La2O3 nanostructures as potential scaffolds for efficient hydroquinone chemical sensing application. A facile, low-cost hydrothermal method was applied for the synthesis of 3D fern shaped La2O3 nanostructures. Several techniques were employed to characterize the synthesized La2O3 nanostructures. XRD analysis confirmed the hexagonal phase for the La2O3 nanostructures with an average crystallite size of 35.18 nm. FESEM and TEM analysis established the 3D fern shaped structures for La2O3 nanostructures with dendritic arms of different lengths alongside triangular-ovate outlines. Purity, composition and vibrational features were confirmed by EDS, FTIR and Raman spectroscopic studies. The fabricated 3D fern shaped La2O3 nanostructures modified glassy carbon electrode (GCE) showed remarkable electron mediating properties towards hydroquinone even at very low analyte concentrations. The linear dynamic range (LDR), experimental limit of detection (LOD) and sensitivity for 3D fern shaped La2O3 nanostructures modified GCE in phosphate buffer solution (PBS) were found to be 0.0781–0.625 mM, 0.0781 mM and 463.3 μA mM−1cm−2, respectively. Finally, a mechanism was also proposed for the electrochemical sensing of the hydroquinone. The presented work thus, confirms that the 3D fern shaped La2O3 nanostructures may be the future potential candidates for fabricating efficient and reproducible electrochemical sensors.

Herein, we report a simple synthesis, characterization and photocatalytic degradation application of composite NiO-WO₃ nanoparticles. The nanoparticles were synthesized by facile low-temperature method and characterized by several techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis diffuse reflectance spectra (DRS). The synthesized NiO-WO₃ nanoparticles were used as efficient photocatalyst for the photocatalytic degradation of Eosin yellow (EY) dye. Interestingly, the synthesized photocatalytic exhibited a significant visible-light driven photocatalytic degradation of Eosin yellow (EY) dye. Under optimized conditions (pH = 5, catalyst dosage = 3 μM and initial dye concentration= 1.0 g/L), the obtained photo degradation of EY dye was above 95% in 180 min under visible light irradiation. Remarkably, reusability of the prepared photocatalyst was also observed and the photo-degradation reactions follow the pseudo-first-order model.

Herein, we report the facile synthesis of Iron oxide@Pt core-shell nanoparticles (NPs) by facile two step synthesis process. The first step follows the growth of iron oxide nanoparticle by thermal decomposition process while the second step deals with the formation of iron oxide@Pt core-shell nanoparticles by the chemical reduction method. The synthesized core-shell nanoparticles were characterized by several techniques and used for the catalytic reductive translation of Cr(VI) to Cr(III) in the presence of formic acid by a UV-vis spectrophotometer. The UV photo-spectrometer analysis confirmed the conversion efficiency from 12% to as high as 98.8% at the end of 30 minutes. Thus, the presence of Iron oxide @Pt core-shell nanoparticles (NPs) can be effectively used as a catalyst for the reducion of Cr(VI) to Cr(III) ions. Additionally, antibacterial studies were performed for the prepared core-shell nanoparticles against two bacterial strains, i.e., gram (+ve) Staphylococcus Aureus (S. Aureus) and gram (-ve) Escherichia Coli (E. Coli).

Herein, we report, for the first time, the facile synthesis of VO2(paramontroseite) by doping of Ge4+ ions into VO2 via simple hydrothermal route. The synthesized materials were characterized by different techniques in terms of their structural, morphological, and thermal properties using X-ray diffraction, transmission electron microscopy, and thermogravimetric analysis and differential scanning calorimetry, respectively. It was observed that the formation of a tunnel by the octahedral arrangement of VO6 in VO2(P) allows intercalations of ions from ionic electrolytes, making it useful for electrochemical applications. The detailed cyclic voltammetric studies, at different scan rates, and electrochemical impedance spectroscopic results showed that the VO2(P) is a potential material for electrochemical applications.

We demonstrate the preparation of nanostructures cobalt oxide/reduced graphene oxide (Co3O4/rGO) nanocomposites by a simple one-step cost-effective hydrothermal technique for possible electrode materials in supercapacitor application. The X-ray diffraction patterns were employed to confirm the nanocomposite crystal system of Co3O4/rGO by demonstrating the existence of normal cubic spinel structure of Co3O4 in the matrix of Co3O4/rGO nanocomposite. FTIR and FT-Raman studies manifested the structural behaviour and quality of prepared Co3O4/rGO nanocomposite. The optical properties of the nanocomposite Co3O4/rGO have been investigated by UV absorption spectra. The SEM/TEM images showed that the Co3O4 nanoparticles in the Co3O4/rGO nanocomposites were covered over the surface of the rGO sheets. The electrical properties were analyzed in terms of real and imaginary permittivity, dielectric loss and AC conductivity. The electrocatalytic activities of synthesized Co3O4/rGO nanocomposites were determined by cyclic voltammetry and charge-discharge cycle to evaluate the supercapacitive performance. The specific capacitance of 754 Fg-1 was recorded for Co3O4/rGO nanocomposite based electrode in three electrode cell system. The electrode material exhibited an acceptable capability and excellent long-term cyclic stability by maintaining 96% after 1000 continuous cycles. These results showed that the prepared sample could be an ideal candidate for high-energy application as electrode materials. The synthesized Co3O4/rGO nanocomposite is a versatile material and can be used in various application such as fuel cells, electrochemical sensors, gas sensors, solar cells, and photocatalysis.

Herein, α-Fe2O3 nanocubes were synthesized, characterized and employed as functional and promising material for the development of ethanol gas sensor. Facile hydrothermal process was used to synthesized the nanocubes and characterized by several techniques which confirmed the large-quantity synthesis, wellcrystallinity with rhombohedral structure of α-Fe2O3. The Raman-scattering spectrum of the synthesized nanocubes exhibited several Raman-active modes which further confirmed the formation of pure α-Fe2O3. As a functional material, the synthesized α-Fe2O3 nanocubes were used as electrode material to fabricate ethanol gas sensor which was tested at various working temperatures, i.e., 300 °C, 400 °C and 450 °C which revealed that the 400 °C was the optimal working temperature. Thus, at 400 °C working temperature, in presence of 100 ppm ethanol gas, the fabricated sensor exhibited highest gas response of 1.69 with response time < 1 s and recovery time of 1485 s.

Vanadium dioxide (VO2(M)) is a first order reversible thermochromic material which changes its phase at particular temperature and thus can be used as a thermochromic smart material for window coating. Similarly, the cerium dioxide (CeO2) is a well-known photo catalyst which can be applied on vanadium dioxide for self-cleaning. This paper reports a successful direct synthesis and detailed characterizations of core-shell VO2(M)@CeO2 spherical nanoparticles. In the core-shell nanoparticles, the vanadium dioxide core exhibits a solar light modulation property while cerium dioxide shell shows dye degradation through a facile photocatalytic process. Addition of ceria facilitates the VO2 (B) to VO2 (M) transformation and also improves its optical properties. With reduced transition temperature, the thermal stability was enhanced due to core –shell structure. To the extent of our knowledge, the synthesis of core-shell VO2@CeO2 nanoparticles is reported for the first time. The synthesized nanoparticles exhibited improved thermochromic and photocatalytic properties.

In this paper, the heterojunction diode based on n-Ga doped ZnO nanowires interconnected with disks/p-Si assembly was fabricated and their low-temperature electrical properties were examined. The Ga-doped ZnO nanowires interconnected with disks were grown over p-Si substrate and studied by numerous techniques to understand the structural, compositional and morphological characteristics. Electrical properties, at lowtemperatures ranging from 77 K–295 K, were examined for the fabricated heterojunction diode assembly both in reverse and forward biased conditions which exhibited an excellent stability over all the temperature range. The detailed electrical characterizations revealed that the current decreases gradually from 1.9 μA, to 0.87 μA to 0.84 μA when temperature increases from 77 K, 100 K to 150 K and then increases gradually from 1.86 μA–3.36 μA and to 9.95 μA when temperature increases from 200 K–250 K and to 295 K, respectively. Both the highest rectifying ratio at 100 K and the lowest one at 295 K occur in the voltage range of 2–5 V.

Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and reported here. Horizontal quartz tube thermal evaporation technique was used for the growth of ZnO nanorods on Si substrate. The nanorods were characterized by several techniques to examine the structural, morphological, scattering and electrical properties. Wurtzite hexagonal phase of the grown aligned nanorods was observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The appearance of a sharp Raman peak at 438 cm–1 was observed and it is related to the E2(high) mode of the wurtzite hexagonal phase of ZnO. The electrical properties of the fabricated heterojunction assembly were examined at different temperatures (298∼398 K) in both reverse and forward biased conditions, and a good stability was observed over the entire temperature range. A reduction in the turn-on and breakdown voltage was observed with increasing temperature. By increasing the temperature, the effective potential barrier height was increased, while quality factor was decreased. The observed activation energy was found to be ∼93.4 meV, higher than the exciton binding energy of ZnO.

Herein, we report the enhanced solar light-mediated photocatalytic degradation of brilliant green dye using BiPO4 nanospindles and MoS2/BiPO4 nanorods synthesized by facile hydrothermal process. The synthesized nanomaterials were examined by various techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM) attached with energy dispersive X-ray spectroscopy, Brunauer–Emmett–Teller, and pore size distribution analysis. The detailed characterizations revealed that after the introduction of MoS2, the crystalline phase transformation from hexagonal to monoclinic was observed for BiPO4. The TEM images clearly confirmed that BiPO4 possessed nanospindles and MoS2/BiPO4 exhibited nanorod-shaped morphologies. The photocatalytic activity of synthesized MoS2/BiPO4 nanorod heterojunction was explored for the degradation of brilliant green (BG) dye under solar light irradiation. Interestingly, approximate 80% degradation of BG was observed under solar light in 70 min using MoS2/BiPO4 nanorods as photocatalyst. As an efficient photocatalyst, the synthesized MoS2/BiPO4 nanorod heterojunction exhibited enhanced photocatalytic efficiency as compared to pure BiPO4 nanospindles, commercially available TiO2PC-50 and TiO2 PC-500 under solar light. The high photocatalytic activity of MoS2/BiPO4 nanorod heterojunction could be related to the amended visible light-harvesting tendency, effective charge separation, and facile transportation of photogenerated e−/h+ pairs at the heterojunction interface.

Well crystalline Ag/CeO2 nano-structured material being utilized for its photocatalytic and antibacterial activities was synthesized via simple solution combustion synthesis (SCS) approach using tartaric acid as a fuel. Interconnection of Ag with CeO2 was investigated to determine its morphological, structural, crystalline, surface and optical properties using common characterization tools. The synthesized Ag–CeO2 materials are of high purity and well-crystalline, having a porous nature with an average pore size of ∼5–7 nm. As-synthesized Ag–CeO2 materials were utilized as photocatalyst for catalytic Rhodamine B (RhB) dye degradation under UV irradiation, showing the almost full degradation of RhB dye molecules in 150 min. As-synthesized Ag/CeO2 nanostructured materials were also investigated for their antibacterial activity toward gram positive (S. aureus) and gram negative (P. aeruginosa) strains of bacteria. The minimum inhibitory concentration for inhibiting the growth of S. aureus (gram positive) and P. Aureginosa (gram negative) were found to be 3.125 μg/ml and 6.25 μg/ml in the presence of Ag/CeO2 materials. The results obtained for Ag/CeO2 materials clearly displayed the significantly improved catalytic and antibacterial properties in comparison with pure CeO2.

Herein, we report the successful synthesis of different phases of VO2 nanomaterials via a facile hydrothermal method by simply varying the molar ratio of the reducing agent (citric acid monohydrate) to vanadium precursor (vanadium (V) oxide). Six samples were synthesized with corresponding variation in molar ratio of vanadium (V) oxide to citric acid monohydrate as 1:1, 1:1.5, 1:2, 1:3, 1:4 and 1:5, respectively. The synthesized nanomaterials were characterized by phase identification, morphologies, compositional, optical, thermal, and electrical properties. The detailed characterizations confirmed the formation of single phase VO2 (B), VO2 (M) and amorphous VO2 by the mere variation of relative concentrations of reducing agent. Even though the synthesis of single phase VO2 is challenging and interestingly, a simple, one-step hydrothermal process procedure was used to produce pure phaseVO2 without the use of inert environment or post-synthesis heat treatments.

Carbon dioxide (CO2), an important gas molecule metabolite produced by the tricarboxylic acid cycle, is a direct signal for identifying cancers in cells and tissues. Herein, design and synthesis of a novel "breathable" block polymer supramolecular assembly probe consisting of a hydrophilic block, an amidine-containing CO2-responsive block, and an aggregation-induced emission (AIE) luminescence block to detect CO2 metabolized by cancer cells is reported. The triblock copolymer poly-(4-undecoxy tetraphenyl ethylene methacrylate)-b-poly-((N-amidino)-(2,3-dihydro-1H-1, 4-methyl-1, 2,3-triazole)-(ethenylbenzene))-b-poly(ethylene oxide) (PTPE-b-PAD-b-PEO) was successfully synthesized and characterized. This triblock copolymer could be self-assembled into "breathable" aqueous solution vesicles. In the presence of CO2, the amidine-containing CO2-responsive block (PAD block) of the vesicle "inhales" an amount of CO2, which causes the volume of the vesicle to expand. The expansion of the vesicle induces the aggregation of the AIE luminescence block (PTPE block), which resulted in the fluorescence intensity enhancement. The supramolecular vesicles "exhale" CO2, and the volume and AIE phenomenon of the vesicles decrease when N2 is passed into the solution. On the basis of this reversible change of fluorescence intensity, HeLa cervical cancer cells, CNE1 nasopharynx cancer cells, 5-8F nasopharynx cancer cells, 16HBE human bronchial epithelial cells, and GES-1 human gastric mucosa epithelial cells have all been successfully detected and identified.

Special functional groups to modify the surface of graphene have received much attention since they enable the charge transfer enhancement, thus realizing gas-sensing at room temperature. In this work, three typical redox dye molecules, methylene blue (MB), indigo carmine (IC) and anthraquinone-2-sulfonate (AQS), were selected to be supramolecularly assembled with reduced graphene oxide (rGO), respectively. Remarkably, three graphene-based materials AQS-rGO (response = 3.2, response time = 400 s), IC-rGO (response = 4.3, response time = 300 s) and MB-rGO (response = 7.1, response time = 100 s) exhibited excellent sensitivity and short response time toward 10 ppm NO2 at room temperature. The corresponding NO2 sensing mechanism of the obtained materials was further investigated by cyclic voltammetry (CV) measurements. CV was conducted to measure the anodic peak potential (Epa) of three redox dyes. Interestingly, it is obvious that the Epa values were positively correlated with the gas sensitivity and response time of the three materials. To explore the mechanism, UV–vis spectroscopy was adopted to analyze the lowest unoccupied molecular orbitals (LUMOs) of three redox dye molecules. The results show that the oxidation abilities of three redox dyes were also positively correlated with the gas sensitivity and response time of three corresponding graphene-based materials.

DFT calculations at the B3LYP/LanL2DZ level of theory were utilized to investigate the adsorption of H2S and SO2 gases on the electronic properties of CuO-ZnO heterojunction structures. The results were demonstrated from the standpoint of adsorption energies (Eads), the density of states (DOS), and NBO atomic charges. The obtained values of the adsorption energies indicated the chemisorption of the investigated gases on CuO-ZnO heterojunction. The adsorption of H2S and SO2 gases reduced the HOMO-LUMO gap in the Cu2Zn10O12 cluster by 4.98% and 43.02%, respectively. This reveals that the Cu2Zn10O12 cluster is more sensitive to the H2S gas than the SO2 gas. The Eads values for SO2 and H2S were −2.64 and −1.58 eV, respectively. Therefore, the Cu2Zn10O12 cluster exhibits a higher and faster response-recovery time to H2S than SO2. Accordingly, our results revealed that CuO-ZnO heterojunction structures are promising candidates for H2S- and SO2-sensing applications.

Herein, a simple, economical and low temperature synthesis of leaf-shaped CuO nanosheets is reported. As-synthesized CuO was examined through different techniques including field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), fourier transform infrared spectroscopic (FTIR) and Raman spectroscopy to ascertain the purity, crystal phase, morphology, vibrational, optical and diffraction features. FESEM and TEM images revealed a thin leaf-like morphology for CuO nanosheets. An interplanar distance of ~0.25 nm corresponding to the (110) diffraction plane of the monoclinic phase of the CuO was revealed from the HRTEM images XRD analysis indicated a monoclinic tenorite crystalline phase of the synthesized CuO nanosheets. The average crystallite size for leaf-shaped CuO nanosheets was found to be 14.28 nm. Furthermore, a chemo-resistive-type gas sensor based on leaf-shaped CuO nanosheets was fabricated to effectively and selectively detect H2S gas. The fabricated sensor showed maximum gas response at an optimized temperature of 300 °C towards 200 ppm H2S gas. The corresponding response and recovery times were 97 s and 100 s, respectively. The leaf-shaped CuO nanosheets-based gas sensor also exhibited excellent selectivity towards H2S gas as compared to other analyte gases including NH3, CH3OH, CH3CH2OH, CO and H2. Finally, we have proposed a gas sensing mechanism based upon the formation of chemo-resistive CuO nanosheets.

Herein, we have developed a novel sensing electrode to detect the eco-toxic 4-nitrophenol (4-NP). Ag-doped-ZnO nanoflowers were synthesized by facile hydrothermal method and examined by several characterization techniques in order to understand the morphology, crystal structure, composition, and surface properties. Morphological results were confirmed by the formation of Ag-doped ZnO nanoflowers decorated with nanosheets. Ag-doped ZnO/glassy carbon electrode (GCE) electrode-material-matrix was used for electrochemical sensing of toxic 4-NP. Under optimized conditions, Ag-doped ZnO/GCE modified electrode exhibits high-sensitivity and selectivity compared to the bare GCE electrode. The Ag-doped ZnO/GCE modified electrode exhibits high electrocatalytic oxidation towards 4-NP. Anodic peak current of 4-NP is increased linearly by increasing the concentration of nitrophenol. Additionally, Ag-doped ZnO/GCE shows a wide range of sensitivity from 10 µM to 500 µM, and a linear calibration plot with a good detection limit of 3 µM (S/N = 3). The proposed Ag-doped ZnO/GCE modified electrode showed high sensing stability. In addition, the oxidation mechanism was studied. The obtained results revealed that the Ag-ZnO/GCE electrode could be the promising sensing electrode for 4-NP sensing.

Herein, we report a chemi-resistive sensing method for the detection of formaldehyde (HCHO) gas. For this, α-MnO2 nanowires were synthesized hydrothermally and examined for ascertaining their chemical composition, crystal phase, morphology, purity, and vibrational properties. The XRD pattern confirmed the high crystallinity and purity of the α-MnO2 nanowires. FESEM images confirmed a random orientation and smooth-surfaced wire-shaped morphologies for as-synthesized α-MnO2 nanowires. Further, the synthesized nanowires with rounded tips had a uniform diameter throughout the length of the nanowires. The average diameter of the α-MnO2 nanowires was found to be 62.18 nm and the average length was ~2.0 μm. Further, at an optimized temperature of 300 °C, the fabricated HCHO sensor based on α-MnO2 nanowires demonstrated gas response, response, and recovery times of 19.37, 18, and 30 s, respectively.

A low-cost and simple drop-casting method was used to fabricate a carbon nanodot (C-dot)/all-inorganic perovskite (CsPbBr3) nanosheet bilayer heterojunction photodetector on a SiO2/Si substrate. The C-dot/perovskite bilayer heterojunction photodetector shows a high performance with a responsivity (R) of 1.09 A/W, almost five times higher than that of a CsPbBr3-based photodetector (0.21 A/W). In addition, the hybrid photodetector exhibits a fast response speed of 1.318/1.342 µs and a highly stable photocurrent of 6.97 µA at 10 V bias voltage. These figures of merits are comparable with, or much better than, most reported perovskite heterojunction photodetectors. UV–Vis absorption and photoluminescent spectra measurements reveal that the C-dot/perovskite bilayer heterojunction has a band gap similar to the pure perovskite layer, confirming that the absorption and emission in the bilayer heterojunction is dominated by the top layer of the perovskite. Moreover, the emission intensity of the C-dot/perovskite bilayer heterojunction is less than that of the pure perovskite layer, indicating that a significant number of charges were extracted by the C-dot layer. The studied band alignment of the C-dots and perovskites in the dark and under emission reveals that the photodetector has a highly efficient charge separation mechanism at the C-dot/perovskite interface, where the recombination rate between photogenerated electrons and holes is significantly reduced. This highly efficient charge separation mechanism is the main reason behind the enhanced performance of the C-dot/perovskite bilayer heterojunction photodetector.