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1.
《化学:亚洲杂志》2017,12(5):515-523
Carbonyl‐grafted g‐C3N4 porous nanosheets (COCNPNS) were fabricated by means of a two‐step thermal process using melamine and oxalic acid as starting reagents. The combination of melamine with oxalic acid to form a melamine–oxalic acid supramolecule as a precursor is key to synthesizing carbonyl‐grafted g‐C3N4. The bulk carbonyl‐grafted g‐C3N4 (COCN) was further thermally etched onto porous nanosheets by O2 under air. In such a process, the carbonyl groups were partly removed and the obtained sample showed remarkably enhanced visible‐light harvesting and promoted the separation and transfer of photogenerated electrons and holes. With its unique porous structure and enhanced light‐harvesting capability, under visible‐light illumination (λ >420 nm) the prepared COCNPNS exhibited a superior photocatalytic hydrogen evolution rate of 83.6 μmol h−1, which is 26 times that of the p‐CN obtained directly from thermal polycondensation of melamine.  相似文献   

2.
Hydrogen energy is an abundant, clean, sustainable and environmentally friendly renewable energy source. Therefore, the production of hydrogen by photocatalytically splitting water on semiconductors has been considered in recent years as a promising and sustainable strategy for converting solar energy into chemical energy to replace conventional energy sources and to solve the growing problem of environmental pollution and the global energy crisis. However, highly efficient solar-driven photocatalytic hydrogen production remains a huge challenge due to the poor visible light response of available photocatalytic materials and the low efficiency of separation and transfer of photogenerated electron-hole pairs. In the present work, organic heterojunction structures based on bacteriochlorophyll (BChl) and chlorophyll (Chl) molecules were introduced and used for solar-driven photocatalytic hydrogen production from water under visible light. Also, noble metal-free photocatalyst was successfully constructed on Ti3C2Tx nanosheets by simple successive deposition of Chl and BChl, which was used for the photocatalytic splitting water to hydrogen evolution reaction (HER). The results show that the optimal BChl@Chl@Ti3C2Tx composite has a high HER performance with 114 μmol/h/gcat, which is much higher than the BChl@Ti3C2Tx and Chl@Ti3C2Tx composites.  相似文献   

3.
Hydrogen, as a sustainable and clean energy, has been considered as a promising candidate to replace fossil fuels. And it is meaningful to fabricate the photocatalysts to drive photocatalytic water splitting leading to hydrogen production. Herein, a facile approach was developed by the means of the template effect of poly (ionic liquid) and self-assembly of cyanuric acid and melamine through hydrogen bonds, to obtain carbon nitride hollow microspheres with highly hierarchical porosity. The influence of poly (ionic liquid) concentration on the structure and photocatalytic activity of as-prepared carbon nitride was investigated. The optimized carbon nitride hollow microspheres possessed the multiple porous channels and improved surface area (71 m2/g) due to the decomposition of poly (ionic liquid) and cyanuric acid-melamine supramolecular aggregates. Moreover, the as-prepared carbon nitride hollow microspheres exhibited a remarkable catalytic activity in the photocatalytic hydrogen evolution reaction under visible light irradiation. Especially, the sample CN-0.02 exhibits the highest hydrogen evolution rate (90.1 μmol h−1). The outstanding photocatalytic activity is attributed to the high specific surface area, broad light absorption range and fast separation rate of photogenerated electron–hole pairs. This novel method opens up a new way toward the development of highly-active photocatalysts for water splitting.  相似文献   

4.
Efficient separation of photogenerated electrons and holes, and associated surface reactions, is a crucial aspect of efficient semiconductor photocatalytic systems employed for photocatalytic hydrogen production. A new CoOx/TiO2/Pt photocatalyst produced by template‐assisted atomic layer deposition is reported for photocatalytic hydrogen production on Pt and CoOx dual cocatalysts. Pt nanoclusters acting as electron collectors and active sites for the reduction reaction are deposited on the inner surface of porous TiO2 nanotubes, while CoOx nanoclusters acting as hole collectors and active sites for oxidation reaction are deposited on the outer surface of porous TiO2 nanotubes. A CoOx/TiO2/Pt photocatalyst, comprising ultra‐low concentrations of noble Pt (0.046 wt %) and CoOx (0.019 wt %) deposited simultaneously with one atomic layer deposition cycle, achieves remarkably high photocatalytic efficiency (275.9 μmol h−1), which is nearly five times as high as that of pristine TiO2 nanotubes (56.5 μmol h−1). The highly dispersed Pt and CoOx nanoclusters, porous structure of TiO2 nanotubes with large specific surface area, and the synergetic effect of the spatially separated Pt and CoOx dual cocatalysts contribute to the excellent photocatalytic activity.  相似文献   

5.
以单分散SiO2为模板,通过简单的一步煅烧法制备具有分级孔结构的g-C3N4。与体相g-C3N4相比,分级孔结构的g-C3N4不仅可见光吸收性能和比表面积得到提高,而且更有利于光生电子-空穴的分离。此外,具有分级孔结构的g-C3N4具有明显增强的可见光驱动的光催化产氢活性,当SiO2和二氰二胺质量比为1∶1时,制备所得g-C3N4(C3N4-2)产氢速率几乎是体相g-C3N4的18倍。  相似文献   

6.
Electrochemical water splitting is a promising approach for producing sustainable and clean hydrogen. Typically, high valence state sites are favorable for oxidation evolution reaction (OER), while low valence states can facilitate hydrogen evolution reaction (HER). However, here we proposed a high valence state of Co3+ in Ni9.5Co0.5−S−FeOx hybrid as the favorable center for efficient and stable HER, while structural analogues with low chemical states showed much worse performance. As a result, the Ni9.5Co0.5−S−FeOx catalyst could drive alkaline HER with an ultra-low overpotential of 22 mV for 10 mA cm−2, and 175 mV for 1000 mA cm−2 at the industrial temperature of 60 °C, with an excellent stability over 300 h. Moreover, this material could work for both OER and HER, with a low cell voltage being 1.730 V to achieve 1000 mA cm−2 for overall water splitting at 60 °C. X-ray absorption spectroscopy (XAS) clearly identified the high valence Co3+ sites, while in situ XAS during HER and theoretical calculations revealed the favorable electron capture at Co3+ and suitable H adsorption/desorption energy around Co3+, which could accelerate the HER. The understanding of high valence states to drive reductive reactions may pave the way for the rational design of energy-related catalysts.  相似文献   

7.
From previous reports, graphitic carbon nitride (g‐C3N4) can be used as a photocatalyst, although the low efficiency of solar energy utilization, small specific surface area and high recombination rate of photogenerated electron–hole pairs limit its practical application. For the purpose of increasing photocatalytic activity, especially under irradiation of visible light, we successfully synthesized a new composite, namely porous g‐C3N4/Ag/Cu2O, through chemical adsorption of Ag‐doped Cu2O on porous g‐C3N4, which has not been investigated carefully worldwide. The composition, morphology and optical properties of the composite were investigated through methods including X‐ray diffraction, energy‐dispersive X‐ray, Fourier transform infrared, UV–visible and photoluminescence spectroscopies and transmission electron microscopy. Using rhodamine B as organic pollutant to be degraded under the irradiation of visible light, different mass ratios of Ag/Cu2O doped on porous g‐C3N4 led to enhanced photocatalytic performance of the composite compared to pure porous g‐C3N4. When the mass ratio of Ag/Cu2O is 15%, porous g‐C3N4/Ag/Cu2O exhibits a degradation rate 2.015 times higher than that of pure porous g‐C3N4. The reasons for this phenomenon may be attributed to the increased utilization efficiency of visible light, high‐speed separation of photogenerated electron–hole pairs, accelerated interfacial transfer process of electrons and increased surface area of the composite. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

8.
《化学:亚洲杂志》2017,12(3):361-365
In this work, graphitic C3N4 decorated with a CoP co‐catalyst (g‐C3N4/CoP) is reported for photocatalytic H2 evolution reaction based on two‐step hydrothermal and phosphidation method. The structure of g‐C3N4/CoP is well confirmed by XRD, FTIR, TEM, XPS, and UV/Vis diffuse reflection spectra techniques. When the weight percentage of CoP loading is 3.4 wt % (g‐C3N4/CoP‐3.4 %), the highest H2 evolution amount of 8.4×102 μmol g−1 is obtained, which is 1.1×103 times than that over pure g‐C3N4. This value also is comparable with that of g‐C3N4 loaded by the same amount of Pt. In cycling experiments, g‐C3N4/CoP‐3.4 % shows a stable photocatalytic activity. In addition, g‐C3N4/CoP‐3.4 % is an efficient photocatalyst for H2 evolution under irradiation with natural solar light. Based on comparative photoluminescence emission spectra, photoelectrochemical I –t curves, EIS Nyquist plots, and polarization curves between g‐C3N4/CoP‐3.4 % and pure g‐C3N4, it is concluded that the presence of the CoP co‐catalyst accelerates the separation and transfer of photogenerated electrons of g‐C3N4, thus resulting in improved photocatalytic activity in the H2 evolution reaction.  相似文献   

9.
Activation of N2 on anionic trimetallic V3−xTaxC4 (x=0–3) clusters was theoretically studied employing density functional theory. For all studied clusters, initial adsorption of N2 (end-on) on one of the metal atoms (denoted as Site 1) is transferred to an of end-on: side-on: side-on coordination on three metal atoms, prior to N2 dissociation. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N2 is facile under mild conditions. The reaction process can be divided into two processes: N2 transfer (TRF) and N−N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has energy barriers similar to those of DIS. The overall energy barriers for heteronuclear V2TaC4 and VTa2C4 clusters are lower than those for homonuclear V3C4 and Ta3C4, showing that the doping effect is beneficial for the activation and dissociation of N2. In particular, V−Ta2C4 has low energy barriers in both TRF and DIS, and it has the highest N2 adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V−Ta2C4, is suggested to have high reactivity to N2 activation, and may serve as a prototype for designing related catalysts at a molecular level.  相似文献   

10.
采用原位溶剂热反应制备多级 Ag/Bi/Nv-g-C3N4(氮空位-g-C3N4)/Ti3C2Tx肖特基结, 并对其物相组成和晶体结构、微观形貌和孔结构、表面元素组成和化学态、光学和光电化学性质进行了表征。由于 Ag、Bi和 Ti3C2Tx协同的表面等离激元共振效应,Ag/Bi/Nv-g-C3N4/Ti3C2Tx表现出全光谱吸收特性。由载流子浓度差驱动的界面极化电荷转移诱导形成的肖特基结, 显著提高了光生载流子(包括热电子和热空穴)的分离效率和利用率。因此, 与 Nv-g-C3N4、Ti3C2Tx、Ag/Nv-g-C3N4、Bi/Nv-g-C3N4和 Ag/Bi/Nv-g-C3N4相比, Ag/Bi/Nv-g-C3N4/Ti3C2Tx表现出显著增强的全光谱催化活性, 其在可见光和近红外光照射下光催化降解四环素的反应速率常数分别为 0.033和 0.008 6 min-1, 为对比样品的 10~2.1倍和 8.6~1.8倍。  相似文献   

11.
Single-atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single-atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single-atom Pt/C3N4 catalyst in photocatalytic water splitting by synchronous illumination X-ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt−N bond cleavage to form a Pt0 species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum-decorated C3N4 catalyst. As expected, H2 production activity (14.7 mmol h−1 g−1) was enhanced significantly with the single-atom Pt/C3N4 catalyst as compared to metallic Pt-C3N4 (0.74 mmol h−1 g−1).  相似文献   

12.
Photocatalytic synthesis of hydrogen peroxide (H2O2) is a potential clean method, but the long distance between the oxidation and reduction sites in photocatalysts hinders the rapid transfer of photogenerated charges, limiting the improvement of its performance. Here, a metal-organic cage photocatalyst, Co14(L−CH3)24 , is constructed by directly coordinating metal sites (Co sites) used for the O2 reduction reaction (ORR) with non-metallic sites (imidazole sites of ligands) used for the H2O oxidation reaction (WOR), which shortens the transport path of photogenerated electrons and holes, and improves the transport efficiency of charges and activity of the photocatalyst. Therefore, it can be used as an efficient photocatalyst with a rate of as high as 146.6 μmol g−1 h−1 for H2O2 production under O2-saturated pure water without sacrificial agents. Significantly, the combination of photocatalytic experiments and theoretical calculations proves that the functionalized modification of ligands is more conducive to adsorbing key intermediates (*OH for WOR and *HOOH for ORR), resulting in better performance. This work proposed a new catalytic strategy for the first time; i.e., to build a synergistic metal-nonmetal active site in the crystalline catalyst and use the host–guest chemistry inherent in the metal-organic cage (MOC)to increase the contact between the substrate and the catalytically active site, and finally achieve efficient photocatalytic H2O2 synthesis.  相似文献   

13.
From the perspective of tailoring the reaction pathways of photogenerated charge carriers and intermediates to remarkably enhance the solar-to-hydrogen energy conversion efficiency, we synthesized the three low-cost semiconducting nickel phosphides Ni2P, Ni12P5 and Ni3P, which singly catalyzed the hydrogen evolution from ammonia borane (NH3BH3) in the alkaline aqueous solution under visible light irradiation at 298 K. The systematic investigations showed that all the catalysts had higher activities under visible light irradiation than in the dark and Ni2P had the highest photocatalytic activity with the initial turnover frequency (TOF) value of 82.7 min−1, which exceeded the values of reported metal phosphides at 298 K. The enhanced activities of nickel phosphides were attributed to the visible-light-driven synergistic effect of photogenerated electrons (e) and hydroxyl radicals (.OH), which came from the oxidation of hydroxide anions by photogenerated holes. This was verified by the fluorescent spectra and the capture experiments of photogenerated electrons and holes as well as hydroxyl radicals in the catalytic hydrogen evolution process.  相似文献   

14.
Visible‐light‐responsive hierarchical Co9S8/ZnIn2S4 tubular heterostructures are fabricated by growing 2D ZnIn2S4 nanosheets on 1D hollow Co9S8 nanotubes. This design combines two photoresponsive sulfide semiconductors in a stable heterojunction with a hierarchical hollow tubular structure, improving visible‐light absorption, yielding a large surface area, exposing sufficient catalytically active sites, and promoting the separation and migration of photogenerated charges. The hierarchical nanotubes exhibit excellent photocatalytic H2 evolution and CrVI reduction efficiency. Under visible‐light illumination, the optimized Co9S8/ZnIn2S4 heterostructure provides a remarkable H2 generation rate of 9039 μmol h?1 g?1 without the use of any co‐catalysts and CrVI is completely reduced in 45 min. The Co9S8/ZnIn2S4 heterostructure is stable after multiple photocatalytic cycles.  相似文献   

15.
Improving the insufficient carrier separation dynamics is still of significance in carbon nitride (C3N4) research. Extensive research has been devoted to improving the carrier separation efficiency through a single strategy, while ignoring the synergistic enhancement effect produced by coupling two or more conventional strategies. Herein, we reported the fabrication of cyano group-containing Fe-doped C3N4 porous materials via direct co-calcination of iron acetylacetonate and melamine for synergistically improving the photocatalytic performance. Iron acetylacetonate can promote the generation of cyano groups and form Fe-doping in C3N4, thereby increasing the visible-light absorption and reactive sites. Further, the internal donor-acceptor system formed by cyano groups and Fe-doped sites promoted charge carrier separation and inhibited the radiation recombination of e-h+ pairs. The optimized photocatalytic activity of Fe−CN-2 sample was 4.5 times of bulk C3N4 (BCN).  相似文献   

16.
Photodeposition has been widely used as a mild and efficient synthetic method to deposit co‐catalysts. It is also worth studying how to synthesize non‐noble metal photocatalysts with uniform dispersion. Different synthetic conditions in photodeposition have a certain influence on particle size distribution and photocatalytic activity. Therefore, we designed experiments to prepare the inexpensive composite photocatalyst Ni(OH)2/g‐C3N4 by photodeposition. The Ni(OH)2 co‐catalysts disperse uniformly with particle sizes of about 10 nm. The photocatalytic hydrogen production rate of Ni(OH)2/g‐C3N4 reached about 19 mmol g?1 h?1, with the Ni(OH)2 deposition amount about 1.57 %. During 16 h stability testing, the rate of hydrogen production did not decrease significantly. The composite catalyst also revealed a good hydrogen production performance under sunlight. The Ni(OH)2 co‐catalyst enhanced the separation ability of photogenerated carriers, which was proved by surface photovoltage and fluorescence analysis.  相似文献   

17.
Uniform‐sized silica nanospheres (SNSs) assembled into close‐packed structures were used as a primary template for ordered porous graphitic carbon nitride (g‐C3N4), which was subsequently used as a hard template to generate regularly arranged Ta3N5 nanoparticles of well‐controlled size. Inverse opal g‐C3N4 structures with the uniform pore size of 20–80 nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back‐filling of the C3N4 pores with tantalum precursors, followed by nitridation in an NH3 flow gave regularly arranged, crystalline Ta3N5 nanoparticles that are connected with each other. The surface areas of the Ta3N5 samples were as high as 60 m2 g−1, and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g‐C3N4. Polycrystalline hollow nanoparticles of Ta3N5 were also obtained by infiltration of a reduced amount of the tantalum source into the g‐C3N4 template. An improved photocatalytic activity for H2 evolution on the assembly of the Ta3N5 nanoparticles under visible‐light irradiation was attained as compared with that on a conventional Ta3N5 bulk material with low surface area.  相似文献   

18.
The Z-scheme process is a photoinduced electron-transfer pathway in natural oxygenic photosynthesis involving electron transport from photosystem II (PSII) to photosystem I (PSI). Inspired by the interesting Z-scheme process, herein a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll (Chl) derivatives, Chl-1 and Chl-2, on the surface of Ti3C2Tx MXene with two-dimensional accordion-like morphology, forming Chl-1@Chl-2@Ti3C2Tx composite, is demonstrated. Due to the frontier molecular orbital energy alignments of Chl-1 and Chl-2, sublayer Chl-1 is a simulation of PSI, whereas upper layer Chl-2 is equivalent to PSII, and the resultant electron transport can take place from Chl-2 to Chl-1. Under the illumination of visible light (>420 nm), the HER performance of Chl-1@Chl-2@Ti3C2Tx photocatalyst was found to be as high as 143 μmol h−1 gcat−1, which was substantially higher than that of photocatalysts of either Chl-1@Ti3C2Tx (20 μmol h−1 g−1) or Chl-2@Ti3C2Tx (15 μmol h−1 g−1).  相似文献   

19.
In this work, hybrid porous Co3O4–CeO2 hollow polyhedrons have been successfully obtained via a simple cation‐exchange route followed by heat treatment. In the synthesis process, ZIF‐67 polyhedron frameworks are firstly prepared, which not only serve as a host for the exchanged Ce3+ ions but also act as the template for the synthesis of hybrid porous Co3O4–CeO2 hollow polyhedrons. When utilized as electrode materials for supercapacitors, the hybrid porous Co3O4–CeO2 hollow polyhedrons delivered a large specific capacitance of 1288.3 F g?1 at 2.5 A g?1 and a remarkable long lifespan cycling stability (<3.3 % loss after 6000 cycles). Furthermore, an asymmetric supercapacitor (ASC) device based on hybrid porous Co3O4–CeO2 hollow polyhedrons was assembled. The ASC device possesses an energy density of 54.9 W h kg?1, which can be retained to 44.2 W h kg?1 even at a power density of 5100 W kg?1, indicating its promising application in electrochemical energy storage. More importantly, we believe that the present route is a simple and versatile strategy for the preparation of other hybrid metal oxides with desired structures, chemical compositions and applications.  相似文献   

20.
The propulsion of photocatalytic hydrogen (H2) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS3]2− unit is introduced into the CuI clusters to form a series of atomically-precise MoVI−CuI bimetallic clusters of [Cu6(MoOS3)2(C6H5(CH2)S)2(P(C6H4R)3)4] ⋅ xCH3CN (R=H, CH3, or F), which show high photocatalytic H2 evolution activities and excellent stability. By electron push-pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these MoVI−CuI clusters can be finely tuned, promoting the resultant visible-light-driven H2 evolution performance. Furthermore, MoVI−CuI clusters loaded onto the surface of magnetic Fe3O4 carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster-based catalyst. This work not only highlights a competitively universal approach on the design of high-efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy.  相似文献   

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