Cu2O quantum dots modified by RGO nanosheets for ultrasensitive and selective NO2 gas detection

Real-time monitoring of trace NO₂ emission has been an emerging challenge in environment and health sectors lately. Aiming to overcome this challenge, NO₂ gas sensors based on cuprous oxide quantum dots (Cu₂O QDs) anchored onto reduced graphene oxide (RGO) nanosheets serving as a sensitive layer were prepared in this report. Apart from a series of purposive measurements, various characterization techniques such as XRD, Raman, XPS and TEM were employed as well to assist the exploration of sensors performance to NO₂ gas. The experimental results revealed a 580% response enhancement for prepared RGO/Cu₂O sensors compared with pure RGO counterparts, as well as an excellent selectivity. In a specific experiment, the sensing response attained 4.8% and 29.3% toward 20 ppb and 100 ppb NO₂ respectively at 60 °C, which was larger than most Cu₂O based resistive gas sensors. Moreover, further subtle modulation of this RGO/Cu₂O nanocomposites led to a preferable room-temperature response of 37.8% toward 100 ppb NO₂, which also offered a favorable stability of 98.1% response retention after four exposures within ten days. The obtained results imply that the prepared RGO/Cu₂O QDs sensors possess a competitive capability of trace NO₂ detection.     

Enhanced NO2 detection using hierarchical porous ZnO nanoflowers modified with graphene

Because of their potential applications in gas sensing and catalysis, reduced graphene oxide (RGO) and ZnO have been the focus of much recent attention. However, few reported materials have been produced via the combination of hierarchical ZnO structures with RGO to achieve high sensing performances. In this paper, a hydrothermal method was used to synthesize hierarchical porous ZnO nanoflowers, which were then combined with graphene to enhance their sensing performances. The rapid detection of 1 ppm NO₂ was achieved at 174 °C. The morphologies and structures of these materials were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Photoluminescence measurements and X-ray photoelectron spectroscopy were also used to investigate the mechanism of gas sensing by these materials.     

Sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets and their photocatalytic oxidation and Li-ion storage capabilities

Nanosized anatase TiO₂ particles anchored on nanocarbon substrates have great potential for practical applications in high-performance lithium ion batteries and efficient photocatalysts. The synthesis of this material usually utilizes calcination to crystallize amorphous titania, which normally causes the formation of aggregates and some side effects. In this work, we demonstrated that sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets in aqueous solution at a temperature of 90 °C and atmospheric pressure, without further calcination. The photocatalytic oxidation activity and electrochemical properties of graphene oxide/anatase TiO₂ (GO/A) and reduced graphene oxide/anatase TiO₂ (RGO/A) were comparatively investigated. We found that GO/A showed higher photocatalytic oxidation activity than RGO/A under UV light irradiation. Graphene oxide accepted electrons and suffered reduction, which finally decreased GO/A’s photocatalytic oxidation activity to an extent similar to RGO/A. We also found that, as anode material for Li-ion battery, the specific capacity of RGO/A was nearly three times that of GO/A at the same current rate. This study will inspire better design of metal oxide/nanocarbon nanocomposites for high performance lithium ion battery and photocatalysis applications.     

Facile synthesis of reduced graphene oxide/CeO2 nanocomposites and their application in supercapacitors

The combination of the attractive properties of graphene with excellent characteristics of other functional nanomaterials has become a popular pathway for achieving applications in multiple fields. Herein, reduced graphene oxide (RGO)/CeO₂ nanocomposites with enhanced capacitive performance were designed and synthesized by a facile two-step approach with a self-assembly method followed by thermal treatment. The structure, morphology and composition of the resulting RGO/CeO₂ nanocomposites were systematically investigated. The presence of RGO can prevent the aggregation and control the structures of the CeO₂ nanocrystals in the annealing process. The nanocomposites as electrode materials for supercapacitor exhibited an enhanced capacitive performance due to the synergic effect between RGO nanosheets and CeO₂ nanocrystals. The excellent capacitive performance of the RGO/CeO₂ nanocomposites offer great promise for supercapacitor applications.     

ZnO decorated luminescent graphene as a potential gas sensor at room temperature

We present a simplistic single step synthesis and a detailed study of the remarkable room temperature gas sensing and photoluminescence (PL) properties of zinc oxide (ZnO) decorated graphene oxide sheets (GrO). Investigation of opto-electronic properties reveal near UV to blue PL and semiconducting behavior of ZnO–GrO sheets. ZnO nano-crystallites serve the dual purpose of acting as a nano-spacer between dried graphene sheets as well as a primary sensing transducer for the gas sensing applications. PL has been used as a tool to study the defects associated with the surface of the nanocrystallite’s trap levels and/or acceptor–donor recombinations. Time-resolved PL was used to determine free carrier or exciton lifetimes, a vital parameter related to quality of composite and device performance. Results are presented for the detection of common industrial toxins like CO, NH₃ and NO for concentrations as low as 1 ppm at room temperature. A large sensor response and quick recovery time was observed at room temperature with preferred selectivity towards electron donor gases like CO and NH₃.     

Numerical Study of NOx Abatement Using Ozone Injection Integrated with Wet Absorption

Nitrogen oxides emitted from power plants and the chemical industry are poisonous to humans and animals, contribute to ozone depletion, and cause acid rain. More than 90% of nitrogen oxides (NO_x) consist of nitric oxide (NO), which is insoluble in water. Among the various available techniques of NO_x abatement, ozone injection is a promising method in which NO is oxidized to higher-order nitrogen oxides (NO₃, N₂O₃, N₂O₄, and N₂O₅), which can easily be absorbed in a wet scrubber. In this article, the ozone injection process integrated with an absorber column is numerically modeled and simulated at various operating conditions. The predicted results of NO_x oxidation with ozone injection and absorption in water agree with the published experimental results. The ozone injection process is modeled using a plug flow reactor, while the wet absorption is based on a rigorous rate-based RateFrac model. Detailed kinetic mechanisms of O₃-NO_x oxidation and absorption of nitrogen oxides in water are incorporated in the model to simultaneously predict the performance efficiency of the ozone reactor and absorber column. Thermodynamic properties of the components are estimated using an Electrolyte NRTL model. The influence of performance parameters (such as feed gas flow rate, inlet gas temperature, reactor configurations, ozone concentration, and NO/NO₂ molar ratio) on the oxidation efficiency of NO_x in the reactor and absorber column is investigated to predict the optimal operating conditions.     

Ultra-high compression and wear resistant hybrid filled polyimide composite: Synergistic effect of Fe2O3 decorated RGO

Herein, the tribological performance, thermal and compression resistance behavior of polyimide (PI) reinforced by Fe₂O₃ decorated reduced graphene is systematically investigated. The remarkable synergistic effect of Fe₂O₃ decorated reduced graphene oxide (RGO) is demonstrated in its PI wear resistance, and PI/RGO/Fe₂O₃ composites show good thermal stability and much higher compression resistant ability than PI, PI/RGO, and PI/Fe₂O₃ composites when the filling contents are same. Additionally, the PI/RGO/Fe₂O₃ composites also exhibited ultra-wear-resistant properties under high load condition, and the lowest wear rate is 3.18 × 10⁻⁸ mm³N⁻¹ m⁻¹, which is an order of magnitude lower than that of pure PI. The investigation of its tribological mechanism also showed strong synergistic effect and interface force of Fe₂O₃ decorated RGO, which contribute to its high-performance friction-reducing behaviors. These findings give an inside view to Fe₂O₃ decorated RGO and its polyimide composites, and open an avenue for the graphene oxide (GO) based composite to act as compression wear-resisting solid fillers and lubricants when polymer composite with excellent compressive, thermal and tribological properties is required.     

Anticorrosion reinforcement of waterborne polyacrylate coating with nano-TiO2 loaded graphene

Photocathodic protection coatings have been widely applied in various areas such as ship and architectural protection, or chemical industry. In this work, a composite of titanium dioxide loaded with reduced graphene oxide (RGO/TiO₂) was prepared and used as filler on waterborne polyacrylate (PA) coating to reinforce the metal protection against corrosion. Compared with the current filler of zinc phosphate used for anticorrosive coating, the photoelectrochemical properties of RGO/TiO₂-PA coating exhibit improved photocathodic protection under visible light illumination since RGO/TiO₂ composite has significant superiority in enhancing metal protection due to its dispersion, micropore blocking ability, and photoelectrochemical conversion performance. The mechanism of anticorrosion reinforcement of RGO/TiO₂-PA coating was hypothesized that graphene provides an extrabarrier layer to obstruct corrosive in dark condition and photocathodic protection under lighting. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48733.     

Investigation of flue-gas treatment with O3 injection using NO and NO2 planar laser-induced fluorescence

Direct ozone (O₃) injection is a promising flue-gas treatment technology based on oxidation of NO and Hg into soluble species like NO₂, NO₃, N₂O₅, oxidized mercury, etc. These product gases are then effectively removed from the flue gases with the wet flue gas desulfurization system for SO₂. The kinetics and mixing behaviors of the oxidation process are important phenomena in development of practical applications. In this work, planar laser-induced fluorescence (PLIF) of NO and NO₂ was utilized to investigate the reaction structures between a turbulent O₃ jet (dry air with 2000 ppm O₃) and a laminar co-flow of simulated flue gas (containing 200 ppm NO), prepared in co-axial tubes. The shape of the reaction zone and the NO conversion rate along with the downstream length were determined from the NO-PLIF measurements. About 62% of NO was oxidized at 15d (d, jet orifice diameter) by a 30 m/s O₃ jet with an influence width of about 6d in radius. The NO₂ PLIF results support the conclusions deduced from the NO-PLIF measurements.     

One-step hydrothermal synthesis of Sb2S3/reduced graphene oxide nanocomposites for high-performance sodium ion batteries anode materials

Sb₂S₃/reduced graphene oxide (SSR) nanocomposites were successfully synthesized through a facile one-step hydrothermal process, as used as anode materials for sodium ion batteries (SIBs). The characterization and electrochemical performance of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of reduced graphene oxide (RGO) can improve the electrochemical performances of SSR nanocomposites. SSR nanocomposites with 10 wt% RGO exhibits the highest reversible capacity of 581.2 mAh g⁻¹ at the current density of 50 mA g⁻¹ after 50 cycles, and excellent rate performance for SIBs. The improved electrochemical performance is attributed to the smaller Sb₂S₃ nanoparticles dispersed on RGO crumpled structure and synergetic effects between Sb₂S₃ and RGO matrix, which can increase specific surface area and improve electrical conductivity, reduce sodium ion diffusion distance, and effectively buffer volume changes during cycling process.     

Effect of Ozone Injection on the Catalytic Reduction of Nitrogen Oxides

The improvement in the catalytic reduction of nitrogen oxides (NO_x) by means of the ozone injection into the exhaust gas was investigated. Nitric oxide (NO) in the exhaust gas was first oxidized to nitrogen dioxide (NO₂) by ozone, and then the exhaust gas containing the mixture of NO and NO₂ was directed to the catalytic reactor where both NO and NO₂ were reduced to nitrogen. The ozone injection method was very efficient for the oxidation of NO to NO₂ in a wide range of temperatures, and the increase in the content of NO₂ by the ozone injection remarkably improved the performance of the catalytic reactor.     

One-step microwave-assisted synthesis of Sb2O3/reduced graphene oxide composites as advanced anode materials for sodium-ion batteries

Sb₂O₃/reduced graphene oxide (RGO) composites were prepared through a facile microwave-assisted reduction of graphite oxide in SbCl₃ precursor solution, and investigated as anode material for sodium-ion batteries (SIBs). The experimental results show that a maximum specific capacity of 503 mA h g⁻¹ is achieved after 50 galvanostatic charge/discharge cycles at a current density of 100 mA g⁻¹ by optimizing the RGO content in the composites and an excellent rate performance is also obtained due to the synergistic effect between Sb₂O₃ and RGO. The high capacity, superior rate capability and excellent cycling performance of Sb₂O₃/RGO composites demonstrate their excellent sodium-ion storage ability and show their great potential as electrode materials for SIBs.     

The Effect of a Changing Lean Gas Composition on the Ability of NO2 Formation and NOx Reduction over Supported Pt Catalysts

Three model catalysts (Pt/Al₂O₃, Pt/TiO₂, Pt/V₂O₅/TiO₂) were examined in regard to their NO₂ formation ability under a changing lean gas composition. The results show that the NO to NO₂ oxidation function as well as the NO _x reduction under lean gas conditions is affected by a change in the lean gas atmosphere. The NO oxidation activity also decreased with time, for Pt/Al₂O₃ and Pt/TiO₂, and a possible explanation may be platinum oxide formation. This deactivation was not observed for Pt/V₂O₅/TiO₂.     

Formation of N2O and (NO)2 During NO Adsorption on Au 3D Crystals

The adsorption of NO on Au 3D hemispherical crystals (field emitter tips) has been studied by means of pulsed field desorption mass spectrometry (PFDMS) under dynamic gas flow conditions and at 300 K. Local chemical probing of ~200 Au sites in the stepped surface region between the central (111) pole and the peripheral (001) plane leads to the detection of NO⁺, N₂O⁺ and (NO) species. Obviously, molecular NO adsorption on stepped Au surfaces can lead to dimerization. Nitrous oxide formation probably occurs via the dimer, (NO)₂.     

Apparatus for steady-state kinetic measurements of the catalytic reduction of nitric oxide by ammonia on iron oxide

The reduction of nitric oxide with ammonia on an unsupported iron oxide catalyst has been studied in a continuous-flow recycle reactor using simulated flue gas. The responses of the employed reactor system to step and pulse inputs of tracer indicate that the system could be regarded as a continuous stirred tank reactor (CSTR). Preliminary tests were carried out to determine the effect of temperature and particle size on the measured reaction rates. Additional experiments were performed in order to study the influence of oxygen and water concentration on these rates. A gas chromatographic system has been developed to analyze the gas components NO, N₂O, NO₂, NH₃, H₂O, O₂, CO₂ and N₂. In addition, the concentrations of NO and NO₂ were measured with a nondisperse infrared (NDUV/NDIR) analyzer.     

Modification of polypropylene filter with metal oxide and reduced graphene oxide for water treatment

A hydrothermal method for the synthesis of reduced graphene oxide/titanium dioxide filter (RGO/TiO₂) and reduced graphene oxide/zinc oxide filter (RGO/ZnO) by using polypropylene (PP) porous filter is reported. Field emission scanning electron microscopy illustrated that the nanoparticles were uniformly distributed on the reduced graphene oxide nanosheets. Flexural tests showed that the physical properties of the modified filters have greater strength than the original filter. Thermogravimetric analysis revealed that the thermal property of the modified filters is the same as that of the original filter. Under a halogen lamp, the modified filter exhibited excellent photocatalytic degradation of methylene blue. The RGO/TiO₂ filter maintained its ability to degrade MB efficiently, even after five cycles of photocatalysis.     

Removal of NOx with radical injection caused by corona discharge

Removal of NO_x (namely DeNO_x) from simulated flue gas with direct current (d.c.) corona radical shower system was investigated. Steady streamer coronas occur when the flow rates of the fed gases are adjusted properly. The experimental results show that both the composition and the flow rate of the gas fed into the nozzles influence the V-I characteristic of corona discharge. The vapor in the flue gas restrains the discharge, reduces the discharge current, but enhances the DeNO_x efficiency. Furthermore, removal of NO_x from flue gas by radical injection associated with alkali solution (26% by weight of NaOH in water) scrubbing was carried out. Oxygen together with water vapor is fed into the nozzle electrode and the oxygen and water molecules are decomposed in the corona zone. It is found that NO and NO₂ can be converted into HNO₂ and HNO₃, respectively, by radicals formed during the discharge process and the conversion efficiency of NO_x in the plasma reactor is more than 60%. The overall DeNO_x efficiency of the system reaches 81.7% after the flue gas was scrubbed by the NaOH solution.     

The impact of carrier gas on room-temperature trace nitrogen dioxide sensing of ZnO nanowire-integrated film under UV illumination

Chemiresistive gas sensors have been extensively explored for hazardous gas detection. Currently, an overwheming majority of previous attention was focused on the parameter improvement of sensor performance while the impact of carrier gas species on the performance was severely ignored. Aiming to a deep insight into this issue, in this work we prepared zinc oxide (ZnO) nanowire-network sensor and explored its UV-activated sensing performance toward trace nitrogen dioxide gas (NO₂) at room temperature (25 °C) under two carrier gases, i.e., dry nitrogen (N₂) and air. Within N₂, the sensor exhibited a reversible response of 157 toward 50 ppb NO₂ and a sensitivity of 7.8/ppb, which was not only among the best showcases of the existing work, but much larger than those within air (11 and 0.091/ppb, respectively). Moreover, decent selectivity and long-term stability were demonstrated. Far more UV irradiation-induced electrons which reacted with adsorbed NO₂ molecules on ZnO surface as well as smaller baseline resistance under N₂ than those under air jointly led to the superior response and sensitivity. After long-time UV exposure prior to gas-sensing tests within both carrier gas cases, the remaining oxygen ions (O₂⁻) were weakly bonded on ZnO surface, contributing to the reversible behaviors at room temperature. The interconversion between physisorbed O₂ molecules and ionic O₂⁻ on ZnO surface was proposed to rationalize the sensing phenomena especially when no continuous oxygen was supplied under N₂ atmosphere, which enriched the current transduction mechanisms.     

Catalytic properties of oxide nanoparticles applied in gas sensors

A series of gas sensing layers based on indium oxide doped with gold were prepared by using the aerosol technology for deposition as the active contact layer in a metal oxide semiconductor capacitive device. The interaction between the measured species and the insulator surface was quantified as the voltage changes at a constant capacitance of the device. The sensor properties were investigated in the presence of H₂, CO, NH₃, NO, NO₂ and C₃H₆ at temperatures between 100–400 °C. Significant differences in the morphology of the layer and its sensitivity were noted for different preparation methods and different gas environments.     

Facile synthesis of a novel flower-like BiFeO3 microspheres/graphene with superior electromagnetic wave absorption performances

In recent years, porous or layered magnetic materials have received increasing attention due to their low density and lightweight. In this work, porous BiFeO₃ microspheres and three-dimensional porous BiFeO₃ microsphere-reduced graphene oxide (RGO) composite (3D porous BiFeO₃/RGO) were prepared by one-step etching processing using pure BiFeO₃ particles as precursors. The precursor undergoes dissolution-recrystallization/reduction process, resulting in large amount of BiFeO₃ fragments and graphene hybrid product, which forms 3D porous BiFeO₃/RGO composite. Electromagnetic (EM) absorption performance measurements exhibit that at low thickness of 1.8?mm, porous BiFeO₃/RGO composite can achieve reflection loss (R_L) value up to ?46.7?dB and absorption bandwidth (defined by R_L <?10?dB) exceeding 4.7?GHz (from 12.0 to 16.7?GHz), testifying outstanding microwave absorbing performance. Compared with pure porous BiFeO₃, improved EM wave absorption ability of as-prepared porous BiFeO₃/RGO composite is attributed to interfacial polarization, multiple reflections, scattering, and appropriate impedance matching.