Photocatalytic behavior of TiO_2 and ZnO prepared with different methods under ultraviolet and visible light irradiation

IntroductionIn recent years photocatalytic oxidation hasreceived considerable attention as an alternativeremediation technology since the method offers anumber of advantages over conventionaltechnologies [1,2] Elimination o…     

Photocatalytic behavior of TiO2 and ZnO prepared with different methods

In recent years photocatalytic oxidation has received considerable attention as an alternative remediation technology since the method offers a number of advantages over conventionaltechnologies. Elimination of organic pollutants in water by oxidation with molecular oxygen and sunlight is the most environmentally friendly pollution-treatment method. Of the materials being developed for photocatalytic applications,titanium dioxide (TiO2） remains the most promising because of its high efficiency, low cost,chemical inertness, and photostability. However,     

Synthesis of three-dimensional hierarchically porous reduced graphene oxide–TiO2 nanocomposite for enhanced hydrogen storage

Three-dimensional hierarchically porous graphene-TiO₂ (3D-HPGT) nanocomposites were synthesized through electrostatic assembly method. The obtained 3D-HPGT nanocomposites exhibited hierarchically porous structure with multi-level pores (macro-, meso- and micropores), high specific surface area (705?m²/g), large pore volume (0.41?cm³/g) and higher hydrogen storage capacity. At the pressure of 5?bar, 3D-HPGT nanocomposite showed a maximum hydrogen capacity of 4.11 and 1.48?wt% at 77 and 298?K, respectively, which were much higher than those of previously reported graphene-based materials. The enhanced hydrogen storage capacities were attributed to the three-dimensional hierarchically porous structure, evenly distributed TiO₂ nanoparticles on the graphene nanosheets, strong attachment of TiO₂ nanoparticles to the underlying graphene nanosheets, and hydrogen spillover effect originated from TiO₂ nanoparticles.     

Reduced graphene oxide for Li–air batteries: The effect of oxidation time and reduction conditions for graphene oxide

Reduced graphene oxide (rGO) has shown great promise as an air-cathode for Li–air batteries with high capacity. In this article we demonstrate how the oxidation time of graphene oxide (GO) affects the ratio of different functional groups and how trends of these in GO are extended to chemically and thermally reduced GO. We investigate how differences in functional groups and synthesis may affect the performance of Li–O₂ batteries. The oxidation timescale of the GO was varied between 30 min and 3 days before reduction. Powder X-ray diffraction, micro-Raman, FE-SEM, BET analysis, and XPS were used to characterize the GO’s and rGO’s. Selected samples of GO and rGO were analyzed by solid state ¹³C MAS NMR. These methods highlighted the difference between the two types of rGO’s, and XPS indicated how the chemical trends in GO are extended to rGO. A comparison between XPS and ¹³C MAS NMR showed that both techniques can enhance the structural understanding of rGO. Different rGO cathodes were tested in Li–O₂ batteries which revealed a difference in overpotentials and discharge capacities for the different rGO’s. We report the highest Li–O₂ battery discharge capacity recorded of approximately 60,000 mAh/g_carbon achieved with a thermally reduced GO cathode.     

Dielectric and electromagnetic wave absorption properties of reduced graphene oxide/barium aluminosilicate glass–ceramic composites

BaAl₂Si₂O₈ (BAS) glass–ceramic powders were prepared by sol–gel method. Graphene oxide (GO)/BAS mixture powders were prepared by a simple mixing process of GO and BAS. Dense and uniform reduced graphene oxide (RGO)/BAS composites were fabricated by the hot-pressing of GO/BAS, which was accompanied by the in-situ thermal reduction of GO. Microstructure, phase composition, dielectric and electromagnetic wave (EM) absorption properties of RGO/BAS were investigated. The results reveal that RGO can promote the hexacelsian-to-celsian phase transformation of BAS. In the frequency range from 8 GHz to 12 GHz, the complex permittivity of RGO/BAS increases with increasing RGO content. The composite with 1.5 wt% of RGO shows good EM absorbing ability. When the sample thickness is 2.1 mm, the minimum reflection coefficient (RC) reaches −33 dB, and the effective absorption bandwidth is more than 3.1 GHz.     

Photocatalytic degradation of dye by Ag/ZnO prepared by reduction of Tollen’s reagent and the ecotoxicity of degraded products

A heterostructure of Ag/ZnO powder was prepared by a reduction of Ag(NH₃) ₂ ⁺ ions in a basic solution or Tollen’s reagent. From this method, the existence of a metallic Ag coating on the ZnO surface was confirmed by transmission electron microscope and x-ray photoelectron spectroscopy. The photocatalytic activity of the Ag/ZnO powders was investigated by analyzing the degradation of an aqueous methylene blue solution under a blacklight irradiation. Furthermore, the parameters, including Ag content, catalyst loading, initial dye concentration and pH, were also studied. After the methylene blue solution was irradiated for 30min under a blacklight illumination, total mineralization was not observed as the presence of some carbon compound species was indicated in a mass spectrum. Furthermore, the toxicity of the treated methylene blue solution produced by the Ag/ZnO powders was also investigated by a test for the inhibition of the growth of Chlorella vulgaris.     

Synthesis,mechanical property,and thermal stability of reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin composites

Reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin (RGO–ZnO/CE/BMI) composites were synthesized via a blending method. The RGO–ZnO composite was incorporated into the CE/BMI copolymer to improve the properties of RGO–ZnO/CE/BMI composites. The structure, elements, and morphology of the RGO–ZnO composite were studied with XPS, FTIR, XRD, and SEM analyses. It indicated that the ZnO micro-sphere was attached to RGO by electrostatic attraction and the RGO–ZnO composite was prepared successfully. The mechanical properties and thermal stability of RGO–ZnO/CE/BMI composites were investigated. When RGO–ZnO composite was 1 wt.%, the flexural and impact strengths of RGO–ZnO/CE/BMI composites were 1.07 and 1.35 times of the CE/BMI copolymer, respectively. However, the RGO–ZnO composite tended to aggregate in the CE/BMI matrix with high loading. According to the SEM analysis, appropriate RGO–ZnO composite was evenly dispersed in the CE/BMI copolymer. Compared to the CE/BMI copolymer, the thermal stability of the RGO–ZnO/CE/BMI composites was good. Thus, the RGO–ZnO composite was successfully filled in the CE/BMI matrix; the mechanical properties and thermal stability of the RGO–ZnO/CE/BMI composites were enhanced.     

Photocatalytic evolution of hydrogen over nanocrystalline mesoporous titania prepared by surfactant-assisted templating sol–gel process

Nanocrystalline mesoporous titania was synthesized via a combined sol–gel process with surfactant-assisted templating route and evaluated for photocatalytic activity of hydrogen evolution from an aqueous methanol solution. In this proposed method, applied surfactant template molecules advantageously behaved as both mesopore-forming and gel formation-assisting agent. The activity of the mesoporous titania thermally treated under appropriate conditions, i.e., at calcination temperature of 600 °C for 4 h, was considerably higher than that of commercial titania powders, Ishihara ST-01 and Degussa P-25. It is clearly revealed that introducing mesoporous framework into TiO₂ by this synthetic system provided much better photocatalytic performance.     

Low-temperature catalytic oxidation of chlorobenzene over MnOX/TiO2–CNTs nano-composites prepared by wet synthesis methods

Catalytic oxidation of chlorobenzene (CB) was studied over MnO_X/TiO₂–CNTs (carbon nanotube) nano-composites prepared by the solvothermal and sol–gel methods. Microstructures and redox properties of these composites were characterized by X-ray diffraction, electron microscopy, and temperature-programmed reduction. The catalytic activity for CB oxidation was promoted with the introduction of CNTs into MnO_X/TiO₂, and CB oxidation efficiencies of 90% and almost 100% could be obtained at 150 °C and 300 °C, respectively, under a gas hour space velocity of 36,000 h^− 1.The high catalytic performance could be attributed to the good dispersion of active component and the selective adsorption of CB by CNTs.     

Characterization and reactivity of VMgO catalysts prepared by wet impregnation and sol–gel methods

This paper reports the study of physicochemical, surface, and catalytic properties of two series of VMgO catalysts prepared by two different methods: wet impregnation and sol–gel. The characterizations of the elaborated materials were performed using N₂-sorption (Brunauer, Emmett and Teller (BET)), X-ray diffraction, Raman, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analyses. The catalytic properties of the elaborated materials were investigated in the isopropanol decomposition reaction to determine their acid–base character and in the selective oxidation of n-butane to evaluate their dehydrogenation properties. The preparation method and vanadium content strongly affected the properties of our materials. The sol–gel method leads to smaller crystallite size, higher specific surface area, and uniform particle distribution compared to the impregnation one. Both impregnation and SG solids promote the formation of acetone, which is related to the presence of strong basic sites (O^2? species) on the catalytic exposed surface. The more pronounced basic character was obtained through the SG samples. The sol–gel samples exhibited the highest catalytic activity and C4-olefin selectivity in the partial oxidation of n-butane. Whatever the preparation procedure, the nature of surface oxygen species plays an important role in the orientation of catalytic performances.     

Synthesis of acrolein from partial oxidation of propane on Mo–V–Te–P–O catalysts prepared by different methods

The Mo–V–Te–P–O catalysts were prepared by different methods and used for selective oxidation of propane to acrolein. It was found that different preparation methods of the catalysts could greatly affect the elemental valence of the active component and substantially affect the catalytic activity. These catalysts were characterized by X-ray powder diffraction, H_2⁻temperature programmed reduction and O_2⁻derivative thermogravimetric analysis studies, which revealed that the existence of (V_0.07Mo_{0. 93})₅O₁₄ phase in the catalysts could be very important for the selective oxidation of propane to acrolein.     

Processing influence on dielectric,mechanical, and electrical properties of reduced graphene oxide–TPU nanocomposites

Two different reduced graphene oxides (rGOs) with similar concentration of oxygen and defects and differences in exfoliation were prepared to produce the rGO/thermoplastic polyurethane nanocomposites by solution blending (SB) and melt compounding (MC). Morphology, electrical, and dielectric properties were studied. Large agglomerates have been observed for the composites produced by SB and discrete and low agglomerated rGO particles in the case on the composites produced by MC. These morphological differences justify the observations in hardness, electrical conductivity, and even in the dielectric properties. The composites do not follow Jonscher's universal power law (UPL) and a linear trend between UPL factors (Log A vs n) has been observed for composites produced by SB, however, no trend is observed in the composites produced by MC, being the first time observed. Differences in the tunneling effect and breakage of H-bonds within the polymer can be suggested from the dielectric relaxation characterization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47220.     

Ultrasonic assisted synthesis of TiO2–reduced graphene oxide nanocomposites with superior photovoltaic and photocatalytic activities

In this work, TiO₂–reduced graphene oxide (RGO) nanocomposites were successfully produced by an ultrasonication-assisted reduction process. The reduction of graphene oxide (GO) and the formation TiO₂ crystals occurred simultaneously. The synthesized nanocomposite was characterized by SEM, EDX, Raman spectroscopy, FTIR, XRD, XPS, UV–vis spectroscopy, photoluminescence spectrometer and electrochemical impedance spectroscopy. As a result of the introduction of RGO, the light absorption of octahedral TiO₂ was markedly improved. The photocatalytic results revealed that weight percent of RGO has substantial influence on degradation of Rhodamine B under visible light irradiation. The enhancement of the photocatalytic activity can be attributed to the enhancement of the visible-light irradiation harvesting and efficiently separation of the photogenerated charge carriers. Meanwhile, upon the RGO loading, the photoelectric conversion efficiency of TiO₂–RGO nanocomposite modified electrode was also highly improved.     

Synthesis of graphene oxide-intercalated α-hydroxides by metathesis and their decomposition to graphene/metal oxide composites

Graphene oxide-intercalated α-metal hydroxides were prepared using layers from the delaminated colloidal dispersions of cetyltrimethylammonium-intercalated graphene oxide and dodecylsulfate-intercalated α-hydroxide of nickel/cobalt as precursors. The reaction of the two dispersions leads to de-intercalation of the interlayer ions from both the layered solids and the intercalation of the negatively charged graphene oxide sheets between the positively charged layers of the α-hydroxide. Thermal decomposition of the intercalated solids yields graphene/nanocrystalline metal oxide composites. Electron microscopy analysis of the composites indicates that the nanoparticles are intercalated between graphene layers.     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

Photocatalytic degradation of methanol on titania and titania–silica aerogels prepared by non-alkoxide sol–gel route

Titania and titania–silica aerogels were prepared by alkoxide or non-alkoxide sol–gel route and subsequent supercritical drying with carbon dioxide at low temperature. The resulting aerogels having high surface area and mesoporosity were used as photocatalysts for gas phase methanol degradation reaction. Photocatalytic degradation reactions were carried out on titania and titania–silica aerogels, and commercial Degussa P-25 titania. The photocatalytic activities of titania and titania–silica aerogels were higher than that of the P-25. While the conversion of methanol degradation over the P-25 catalyst was only 50–60%, that for the titania aerogel was observed to be above 98% due to the higher specific surface area and the well developed mesoporous structure. In spite of lower titania contents, much higher surface area and high dispersion of titania of titania–silica aerogel gave rise to the high photocatalytic activity in comparison to those of titania aerogels. Moreover, titania–silica aerogel was also used for the photodegradation and adsorption hybrid system. It was observed that the high removal efficiency for methanol was caused by the combination of higher catalytic activity and adsorption capacity.     

Exploring the filler–polymer interaction and solvent transport behavior of nanocomposites derived from reduced graphene oxide and polychloroprene rubber

Aliphatic solvent resistance of polychloroprene rubber (CR) reinforced reduced graphene oxide (RGO) nanocomposites were explored in the temperature range of 30–50 °C using hexane, heptane, and octane. Microstructure-assisted solvent resistant property is evident from transmission electron microscopy images of fabricated composites. Different transport parameters such as diffusion, permeation, and sorption constants were moderate while increasing RGO content. Diffusion mechanism was explained based on the permeating molecule and is found to be close to Fickian mechanism except for heptane. Evaluation of kinetic and thermodynamic parameters shows the ability of nanoreinforcement to alter thermodynamic characteristics and rate constant values. The extent of reinforcement was also evaluated by Kraus equation. From swelling studies, molecular mass between crosslinks was evaluated using Flory–Rehner equation and compared these values with theoretical predictions such as phantom and affine models to analyze the deformation and mobility of the network during swelling. Temperature plays a significant role in the transport of organic solvent through CR/RGO nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48168.     

UV light exposure of aqueous graphene oxide suspensions to promote their direct reduction,formation of graphene–metal nanoparticle hybrids and dye degradation

The use of UV light to trigger different processes involving graphene oxide sheets suspended in aqueous medium at room temperature has been investigated. These processes include (1) deoxygenation of the sheets in the absence of photocatalysts, reducing agents and stabilizers, (2) selective nucleation and growth of metal nanoparticles on the sheets to yield graphene-based hybrids and (3) decomposition of the dye molecule rhodamine B in the presence of only graphene oxide. Photoinduced heating of the suspended graphene oxide sheets by intense UV irradiation (～1 W cm^?2 delivered at the surface of the dispersion) was interpreted to generate at high temperature and reactive environment strictly localized at the sheets and their immediate aqueous medium, which in turn brings about the mentioned processes. In addition to providing a simple route toward reduction of graphene oxide dispersions, the present results suggest that intense UV light can be used to promote reactions at ambient conditions with this material that would otherwise require high temperatures, chemical reactants and/or catalysts.