In this paper, nano-graphene oxide (GO) particles are applied to modify the epoxy resin, and the surface charge characteristics of the prepared composites under various temperatures are investigated. Based on the surface potential decay behaviors, trap energy level distribution of the neat epoxy resin and graphene oxide/epoxy resin composite is calculated. Obtained results show that the introduction of GO increases the shallower trap density as well as decreases the deeper trap density at the same temperature. With the increase of temperature, the deep trap density is decreased while the shallow trap density is enhanced. The introduction of graphene oxide results in the increase of shallower trap density, and which makes the temperature coefficient of conductivity of epoxy/graphene oxide nanocomposite is reduced.
Promoting photogenerated carriers separation and adjusting the activation path of the CO2 molecule are two effective solutions for improving the activity and selectivity of photocatalytic CO2 reduction. In this study, simultaneous phosphorylation and Bi modification are successfully introduced into BiOBr hierarchical spheres via a solvothermal reaction using red phosphorus as the additive. Remarkably, the synchronous phosphorylation and Bi modification of BiOBr lead to an improvement of CO2 conversion efficiencies, especially for the yield of CH4. Different characterization techniques were performed to explore the existence form of P and Bi modification, and the essence behind such an enhancement. Attributed to this in situ strategy, the regular hierarchical spheres morphology of BiOBr is preserved, and the Bi nanoparticles are well distributed with the average size of ca. 5 nm. Besides, the phosphorus exists in the form of BiPO4. The reasons for the enhanced photocatalytic activity are that the metal Bi modification could enhance the light harvesting and the selectivity of CH4; furthermore, the synchronous BiPO4 and Bi modification could improve the separation efficiency of photogenerated carriers and increase the surface charge transfer efficiency during the photocatalytic reaction process. We hope this work will provide a new perspective for fabrication of multivariate modification photocatalysts with highly efficient and highly selective photocatalytic CO2 reduction.
Transition metal phosphides are considered to be promising cocatalysts that can be used to improve the photocatalytic hydrogen production performance. However, the relatively low conductivity, high overpotential, and limited interface driving force between the photocatalysts hamper their activity. In this study, we introduce work function engineering via MoO2 modification to modulate the Fermi energy level of Ni2P to obtain an enhanced Schottky effect in the photocatalytic hydrogen evolution reaction (HER). Moreover, heterojunction engineering of MoO2/Ni2P decreases the adsorption energy of hydrions and facilitates the electrical conductivity and kinetics of HERs. The trifecta of MoO2 in hybrid cocatalysts significantly promotes the neutral photocatalytic HER efficiency of g-C3N4. Therefore, the as-prepared MoO2/Ni2P@g-C3N4 composite shows excellent photocatalytic HER performance, which reaches up to 1.38 times that of Pt-modified g-C3N4. Hence, this study provides in-depth insights into the simultaneous utilization of the work function and heterojunction modulation of cocatalysts to improve the photocatalytic HER performance.
Abstract Constructing a powerful photocatalytic system that can achieve the carbon dioxide (CO 2 ) reduction half‐reaction and the water (H 2 O) oxidation half‐reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF‐bpy‐Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust −C=C− bond linkages. The charge‐separation ability of viCOF‐bpy‐Re is promoted by low polarized π‐bridges between rhenium complexes and triazine ring units, and the efficient charge‐separation enables the photogenerated electron–hole pairs, followed by an intramolecular charge‐transfer process, to form photogenerated electrons involved in CO 2 reduction and photogenerated holes that participate in H 2 O oxidation simultaneously. The viCOF‐bpy‐Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6 μmol g −1 h −1 with about 100 % selectivity) and oxygen (O 2 ) evolution (90.2 μmol g −1 h −1 ) among all the porous catalysts in CO 2 reduction with H 2 O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50 hours. The structure–function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.
Methane is a greenhouse gas that contributes to global warming. Hence, effectively removing the low concentration (<1000 ppm) of methane in the environment is an issue that deserves research in the field of catalysis. In this study, oxygen-magnesium bivacancies are simultaneously imbedded into MgO by designing an in situ reduction combustion atmosphere for oxygen release and substituting magnesium with carbon to induce the formation of magnesium vacancies. The DFT calculations reveal that the surface electron density of MgO is improved by the oxygen vacancy structure and the substitution of Mg by C in bulk; this accelerates migration of the charge from the material surface to the adsorbed oxygen species, which leads to abundant surface peroxide species that enable activation and oxidation of methane at a low temperature (below 200 °C). This work could provide a concept for developing non-noble or transition metal oxides for low-temperature activation and conversion of alkanes in the thermocatalytic field through reactive oxygen species.
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