Graphitic-carbon nitride quantum dots (g-C3N4QDs), as a rising star in the carbon nitride family, show great potential in many fields involving bioimaging, fuel cells, and photo(electro)catalysis, ...due to their fascinating optical and electronic properties. Especially, the efficient light capture, tunable photoluminescence and extraordinary up-conversion photoluminescence properties of g-C3N4QDs may offer promising potential for full utilization of the solar spectrum, thus promoting their applications in photocatalytic reactions. Some reviews on g-C3N4 have been presented; while most of them have concentrated on g-C3N4 in 3-dimensional (3D) or 2D structures, few focused on g-C3N4QDs. Therefore, this review aims to summarize the recent advances in g-C3N4QDs regarding their synthesis, optical and electronic properties and photocatalytic applications for degrading organic pollutants. Moreover, crucial issues in g-C3N4QD future application in these flourishing research areas are discussed, with prospects towards the final realization of efficient and long-term stable g-C3N4QD-based photocatalysts.
Recently, reactive iron species (RFeS) have shown great potential for the selective degradation of emerging organic contaminants (EOCs). However, the rapid generation of RFeS for the selective and ...efficient degradation of EOCs over a wide pH range is still challenging. Herein, we constructed FeN4 structures on a carbon nanotube (CNT) to obtain single-atom catalysts (FeSA-N-CNT) to generate RFeS in the presence of peroxymonosulfate (PMS). The obtained FeSA-N-CNT/PMS system exhibited outstanding and selective reactivity for oxidizing EOCs over a wide pH range (3.0–9.0). Several lines of evidences suggested that RFeS existing as an FeN4O intermediate was the predominant oxidant, while SO4 ·– and HO· were the secondary oxidants. Density functional theory calculation results revealed that a CNT played a key role in optimizing the distribution of bonding and antibonding states in the Fe 3d orbital, resulting in the outstanding ability of FeSA-N-CNT for PMS chemical adsorption and activation. Moreover, CNT could significantly enhance the reactivity of the FeN4O intermediate by increasing the overlap of electrons of the Fe 3d orbital, O 2p orbital, and bisphenol A near the Fermi level. The results of this study can advance the understanding of RFeS generation in a heterogeneous system over a wide pH range and the application of RFeS in real practice.
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IJS, KILJ, NUK, PNG, UL, UM
Innovation in transition-metal nitride (TMN) preparation is highly desired for realization of various functionalities. Herein, series of graphene-encapsulated TMNs (Fe x Mn6–x Co4–N@C) with ...well-controlled morphology have been synthesized through topotactic transformation of metal–organic frameworks in an N2 atmosphere. The as-synthesized Fe x Mn6–x Co4–N@C nanodices were systematically characterized and functionalized as Fenton-like catalysts for catalytic bisphenol A (BPA) oxidation by activation of peroxymonosulfate (PMS). The catalytic performance of Fe x Mn6–x Co4–N@C was found to be largely enhanced with increasing Mn content. Theoretical calculations illustrated that the dramatically reduced adsorption energy and facilitated electron transfer for PMS activation catalyzed by Mn4N are the main factors for the excellent activity. Both sulfate and hydroxyl radicals were identified during the PMS activation, and the BPA degradation pathway mainly through hydroxylation, oxidation, and decarboxylation was investigated. Based on the systematic characterization of the catalyst before and after the reaction, the overall PMS activation mechanism over Fe x Mn6–x Co4–N@C was proposed. This study details the insights into versatile TMNs for sustainable remediation by activation of PMS.
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Carbon and defects co-modified carbon nitride (CxCN) was synthesized by a novel and facile method, shows porous structure, a lower bandgap and longer life of photogenerated electron-hole pairs for ...more fully use of solar-energy, and thus its photocatalytic degradation activity is about 22 times higher than that of pristine g-C3N4.
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•Carbon and defects co-modified g-C3N4 (CxCN) was synthesized with a facile method.•Carbon and defects tune the band structure to promote utilization of solar energy.•CxCN structure is established by DFT calculation to explain related mechanism.•CxCN shows efficiently photocatalytic degradation of BPA under visible light.
Graphite carbon nitride (g-C3N4, CN) is considered as a promising semiconductor for environmental catalysis. However, pure CN can not meet the requirements for actual applications due to its high recombination rate of photogenerated electron-hole pairs and a relatively large band gap preventing full utilization of solar energy. In this work, we report synthesis of a novel carbon and defects co-modified g-C3N4 (CxCN) by calcination of melamine activated by oxalic. This new catalyst CxCN has porous structure with much higher surface areas compared with pristine CN. UV–vis analysis and DFT calculations show that CxCN has a lower bandgap for enhancing visible light adsorption compared with CN. Photoluminescence (PL) and photoelectrochemical analyses show that CxCN has a low recombination rate of photogenerated electron-hole pairs, which improves the utilization of solar energy. As a result, CxCN samples show high efficiency for the degradation of bisphenol A (BPA) under visible light irradiation, where the best catalyst of CxCN (C1.0CN) samples shows about 22 times higher photocatalytic degradation rate than that of CN. Moreover, C1.0CN shows high mineralization rate and can degrade BPA into CO2 and H2O by the generated active species, like superoxide radicals (O2−) and holes (h+).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Synthesis of mesoporous graphene materials by soft-template methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene ...nanosheets. Herein, a micelle-template strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
CO oxidation is considered to be a model reaction to explore the relationships between structure and catalytic performance. In this work, several double-atom catalysts (DACs) M/UiO-66 (M = Pd, Pt, ...Cu, Ag, Au, Zn, or Cd, UiO-66 is a classical metal–organic framework) for CO oxidation have been investigated by density functional theory (DFT) calculations. DACs were obtained by doping metal atoms into the defect sites at the zirconium oxide clusters of UiO-66. All possible mechanisms (Eley–Rideal (ER), Langmuir–Hinshelwood (LH), and termolecular ER (TER) mechanisms) for CO oxidation were considered in detail. Compared with pristine UiO-66, M/UiO-66 remarkably promoted the CO oxidation performance. Among them, the superior catalysts were Zn and Ag-DACs, whose rate-limiting energy barriers ( E bar ) are as low as 0.14 and 0.22 eV, respectively. More importantly, three general rules affecting CO oxidation E bar were proposed: (i) from the aspect of geometric structure, the corresponding E bar is negatively correlated with the OC–O distance of the transition structure within a certain range; (ii) from the aspect of electronic structure, when the d-band center difference ratio of DACs is in the range of −15% to 15%, the corresponding E bar is less than 1.08 eV for most cases; (iii) if the E ads of individual O 2 and CO molecules are similar, or the E ads of an individual O 2 molecule is extremely large, the catalytic performance is expected to be satisfactory. Therefore, this work provides unique insights into the design of excellent DACs for CO oxidation, and the proposed rules can be extended to other complex reactions.
The 2D materials borophenes are able to selective chemical adsorption for C2H4 and H2CO from typical VOCs.
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In the field of volatile organic compounds (VOCs) pollution control, ...adsorption is one of the major control methods, and effective adsorbents are desired in this technology. In this work, the density functional theory (DFT) calculations are employed to investigate the adsorption of typical VOCs molecules on the two-dimensional material borophenes. The results demonstrate that both structure of χ3 and β12 borophene can chemically adsorb ethylene and formaldehyde with forming chemical bonds and releasing large energy. However, other VOCs, including ethane, methanol, formic acid, methyl chloride, benzene and toluene, are physically adsorbed with weak interaction. The analysis of density of states (DOS) reveals that the chemical adsorption changes the conductivity of borophenes, while the physical adsorption has no distinct effect on the conductivity. Therefore, both χ3 and β12 borophene are appropriate adsorbents for selective adsorption of ethylene and formaldehyde, and they also have potential in gas sensor applications due to the obvious conductivity change during the adsorption.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Single-atom catalysts have recently attracted considerable attention because of their highly efficient metal utilization and unique properties. Finding a green, facile method to synthesize them is ...key to their widespread commercialization. Here we show that single-atom catalysts (including iron, cobalt, nickel and copper) can be prepared via a top-down abrasion method, in which the bulk metal is directly atomized onto different supports, such as carbon frameworks, oxides and nitrides. The level of metal loading can be easily tuned by changing the abrasion rate. No synthetic chemicals, solvents or even water were used in the process and no by-products or waste were generated. The underlying reaction mechanism involves the mechanochemical force in situ generating defects on the supports, then trapping and stably sequestering atomized metals.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Explore the photo-piezoelectric synergistic micro-mechanism by density functional theory (DFT) calculations at the electronic and atomic level is important. In this work, to understand the ...synergistic mechanism, atomic and electronic properties of typical piezoelectric and photocatalytic material BaTiO3 were initially investigated with different strains. Subsequently, the adsorption of volatile organic compounds (VOCs) on the BaTiO3 (001) surface was determined during the piezoelectric process. In addition, the relationship between deformation ratio, the electronic structure and adsorption energy was understood in the deformation ratio range of 7%-12% for the optimal catalytic effect. The results of charge density differences and Born effective charge reveal the synergistic mechanism of piezoelectric photocatalysis. The built-in electric field formed by polarization results in the enhanced separation of charges, which makes the surface charges aggregation, enhancing the adsorption of VOCs, and benefiting the subsequent photocatalytic degradation. This work can provide significant theoretical guidance for the piezoelectric photocatalytic degradation of pollutants with the optimal strain range.
The distribution of atoms and charges in BaTiO3 structural unit is illustrated, where F and Ps represent the applied stress and the induced polarization, respectively. Schematic diagram of adsorption and charge transfer in the process of piezoelectric catalysis is shown. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Porous graphene and Al modified graphene have been reported to be promising hydrogen storage materials owing to their possible high hydrogen storage capacity. In this work, Al-decorated porous ...graphene is considered as hydrogen storage material, based on density functional calculations. It is found that the hydrogen storage capacity of the Al-decorated porous graphene is 10.5 wt%, with modest hydrogen adsorption energy from −1.11 to −0.41 eV/H2 to achieve efficient hydrogen storage/release at ambient conditions. In addition, hydrogen can be released gradually in three stages owing to different adsorption energy at different adsorption sites, which is desirable in actual hydrogen storage application. The mechanism for improving the hydrogen storage behavior by the decorated Al atom and its porosity is understood through analyzing the atomic charges, electronic distribution, and density of states of the system.
•A new hydrogen storage material–Al-decorated porous graphene is proposed.•It has high hydrogen storage capacity of 10.5 wt%.•The hydrogen adsorption energy is modest, from −1.11 to −0.41 eV/H2.•Hydrogen can be released gradually in three stages.•The hydrogen adsorption enhancement mechanism is analyzed through electronic distribution and density of states.
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