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Enhanced Sensing Performance to Toluene and Xylene by Constructing NiGa2O4-NiO Heterostructures
摘要： The selective detection of methyl benzene (e.g. toluene and xylene) using oxide semiconductor-based gas/vapor sensors is highly desirable but limited by the low chemical reactivity of the benzene compounds. Exploiting p-type semiconductor oxides (e.g., NiO) which provide distinctive catalytic activities for methyl benzene detection is an essential approach. However, the intrinsic responses of p-type semiconductor oxides are often low. In this paper, high-performance toluene and xylene detection has been realized by a sensor based on novel p-p heterojunction NiGa2O4-NiO nanospheres. Construction of optimized p-p heterojunctions, which resulting from the rationally controlling of the NiGa2O4 content in NiGa2O4-NiO, leads to significantly promoted sensing properties for toluene and xylene detection. It is found that the sensor based on 50% NiGa2O4-NiO exhibits the best sensing performances. Its highest response (Rg/Ra = 12.7 to toluene; Rg/Ra = 16.3 to xylene) is almost 10 times higher than that of the pure NiO (Rg/Ra < 2) to 100 ppm toluene and xylene at 230 oC. More importantly, the sensor exhibits superior selectively for detection of the methyl benzene even against more reactive interfering gases/vapors, such as formaldehyde and ethanol. The p-p oxide heterojunction suggests a promising sensing material for toluene and xylene detection with high response, excellent selectivity, good stability and rapid response/recover time.
关键词： Composite semiconductor,NiO,NiGa2O4,Heterojunction,Xylene,Toluene
更新于2025-09-10 09:29:36
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Light-Assisted Room-Temperature NO2 Sensors Based on Black Sheet-Like NiO
摘要： In this study, we use two-dimensional black flake nickel oxide as the sensitive material which was synthesized by a facile hydrothermal route. The as-synthesized sheet-like NiO possessed a large specific surface area, as verified by BET characterization. The as-prepared NiO nanosheets had strong absorption in the range of 250–800 nm including UV and visible light. Upon exposure to ppb-level NO2, the presented sensors showed significant responses under light illumination at room temperature. In addition, the light wavelength also had a remarkable effect on the sensing performance in terms of sensitivity, response and recovery kinetics. Furthermore, the sensor showed a low humidity dependence.
关键词： NiO,light illumination,room temperature,NO2
更新于2025-09-09 09:28:46
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Visible light enhanced black NiO sensors for ppb-level NO2 detection at room temperature
摘要： Although extensive studies have been carried out on n-type semiconductors for room-temperature gas sensor applications, some intrinsic problems remain. Therefore, other interesting attempts should be adopted to solve these issues, like p-type semiconductors. Previous studies have demonstrated that p-type semiconductor gas sensors exhibit better selectivity and less humidity dependence due to the distinctive oxygen adsorption and surface reactivity. Visible light is used as the external activation source to accelerate the sensing kinetics instead of heating. Stoichiometric NiO cannot absorb visible lights. Inspired by the works of black TiO2, we adopted three methods to prepare black NiO. XPS characterizations reveal that the presence of Ni3+ ions leads to the formation of black NiO. However, not all black NiO samples show good responses to NO2 at room temperature. Three main routes: synthesizing specific morphology with large specific surface area and porosity, introduction of Ni3+ ions and oxygen vacancies, are needed to get the enhanced sensing performance. The black NiO samples with large specific surface area and oxygen vacancies and Ni3+ ions show obvious response towards ppb-level NO2 with visible light irradiation at room temperature. Furthermore, light wavelength is found to play a vital role in the sensing characteristics, and blue light is the optimal choice. Different from traditional NiO sensors operated at high temperatures exhibiting superior response to reducing gases, the black NiO show excellent selectivity towards oxidizing gas, ppb-level NO2, at room temperature illuminated by blue light. In contrast with n-type semiconductors, the black NiO samples also exhibit less humidity dependence.
关键词： Room temperature,NO2 sensor,NiO,Visible light irradiation
更新于2025-09-09 09:28:46
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Facial construction of defected NiO/TiO2 with Z-scheme charge transfer for enhanced photocatalytic performance
摘要： Here we report a defected NiO/TiO2 composite (NiO/TiO2-OV) fabricated by a two-step hydrothermal method with the followed one-step calcination, which induced the in situ generation of Ti3+ and oxygen vacancies, coupled with the construction of a direct Z-scheme band structure. The NiO/TiO2-OV catalyst exhibited a substantially improved performance in the photodegradation of organic pollutant and photocatalytic hydrogen evolution reaction (HER). The sensitization by narrow bandgap semiconductor of NiO enhanced the light response of catalysts. More importantly, the intrinsic defects, the Ti3+ and oxygen vacancies, acted as the mid-gap state in TiO2, and resulted in the direct Z-scheme charge transfer between the Ti3+/oxygen vacancies state and the valance band (VB) of NiO to suppress the recombination of photogenerated electrons and holes. Meanwhile, the realignment of band structure caused by constructing NiO/TiO2 heterojunction made the photogenerated carries more active in the photocatalytic reduction and oxidation reactions.
关键词： Z-scheme charge transfer,NiO/TiO2 hybrid,Photocatalysis,Surface defects,Self-doping of Ti3+
更新于2025-09-09 09:28:46
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Significant Enhancement of Hydrogen-Sensing Properties of ZnO Nanofibers through NiO Loading
摘要： Metal oxide p-n heterojunction nano?bers (NFs) are among the most promising approaches to enhancing the ef?ciency of gas sensors. In this paper, we report the preparation of a series of p-NiO-loaded n-ZnO NFs, namely (1?x)ZnO-xNiO (x = 0.03, 0.05, 0.7, 0.1, and 0.15 wt%), for hydrogen gas sensing experiments. Samples were prepared through the electrospinning technique followed by a calcination process. The sensing experiments showed that the sample with 0.05 wt% NiO loading resulted in the highest sensing performance at an optimal sensing temperature of 200 ?C. The sensing mechanism is discussed in detail and contributions of the p-n heterojunctions, metallization of ZnO and catalytic effect of NiO on the sensing enhancements of an optimized gas sensor are analyzed. This study demonstrates the possibility of fabricating high-performance H2 sensors through the optimization of p-type metal oxide loading on the surfaces of n-type metal oxides.
关键词： ZnO,NiO loading,sensing mechanism,gas sensor,nano?ber,p-n heterojunction
更新于2025-09-09 09:28:46
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Investigation of half-metallic ferromagnetism in hafnium and tantallum doped NiO for spintronic applications: A DFT study
摘要： Full Potential Linearised Augmented Plane Wave (FP-LAPW) method was used to investigate the electronic and magnetic properties of NiO doped with Hf and Ta within the frame work of density functional theory(DFT). NiO is found to be stable in rock salt structure. NiO shows metallic character for the lattice constant of 4.155?. Doping Hf and Ta in the metallic super cell of NiO separately in the doping concentration of 12.5%, the compounds Hf0.125Ni0.875O and Ta0.125Ni0.875O are formed. These compounds of Hf0.125Ni0.875O and Ta0.125Ni0.875O are found to be stable in the ferromagnetic phase. The density of states and band structure plots predict that these compounds exhibit half metallic character with formation of energy gap in one of the spins at the Fermi level. The total spin magnetic moments found in these compounds are 12.00689 μB and 10.97628 μ B.
关键词： DFT,Hf and Ta doping,spintronics,Half-metallic ferromagnetism,NiO
更新于2025-09-09 09:28:46
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Solar-charged pseudocapacitors: Simultaneous conversion and storage of solar energy in ZnO@NiO nanorod arrays
摘要： In this paper, bias-free solar-driven pseudocapacitors based on ZnO@NiO nanorod arrays had been reported, which enable the synergistic coupling of light harvesting and electrochemical storage within one single electrode. When solar-charging, ZnO/NiO PN junction served as a driving force to separate the excitons and induce electron-injection through the interface to counter electrode forming charging bias. At this bias, the OH- trapped by photoexcited holes can make redox reaction with NiO and produce electrons. As expected, under a 1-sun illumination and no external electric bias, this ZnO/NiO composite exhibits a good specific capacitance of 44.5 F g?1 at current densities of 0.5 A g?1 as well as a good cycling performance (99% capacity retention after 50 cycles). Additionally, the capacitance equation was derived to account for the boosted capacitance as the increased solar-charging time. These findings here suggest the potential of further developing light-induced electrical energy storage and release on demand by a one-component light-charged capacitors.
关键词： solar energy conversion,ZnO@NiO nanorod arrays,photo-capacitor,pseudocapacitance
更新于2025-09-04 15:30:14
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Visible light induced H2 evolution on the hetero-junction Ag/NiO prepared by nitrate route
摘要： The photo-electrochemical study of the hetero-junction Ag/NiO (5/95 wt%) prepared in situ by nitrate route was investigated to assess its photoactivity for the hydrogen production upon visible light. The X-ray diffraction pattern shows narrow peaks of Ag and NiO. The direct optical gap of the sensitizer NiO (1.51 eV) is well matched to the solar spectrum. It acts as n-type semiconductor and the potential of its conduction band (?0.35 VSCE), determined from the capacitance measurement, is more negative than the H2O/H2 level (～?0.3 VSCE), yielding water reduction under visible light; the photoactivity peaks at pH ～ 13. The excited electrons are transferred to Ag clusters, to reduce water into gaseous hydrogen owing to the low H2-over-voltage (～160 μmol). A quantum conversion efficiency of 0.11% is reported under visible light (3.42 × 1018 photons s?1) within ～10 min with an evolution rate of 96 μmol h?1 mg?1. The catalyst was tested for several successive photocatalytic cycles, a de-activation effect of ～7% per cycle is observed, thus proving its stability and repeatability. The heating of the catalyst under dynamic vacuum at 250 °C restores the initial photoactivity.
关键词： Hetero-junction Ag/NiO,Hydrogen,Semiconductor,Photo-electrochemical
更新于2025-09-04 15:30:14