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1.
The fast separation rate of photogenerated carriers and the high utilization of sunlight are still a major challenge that restricts the practical application of carbon nitride (g-C 3N 4) materials in the field of photocatalytic hydrogen (H 2) evolution. Here, ultrathin oxygen (O) engineered g-C 3N 4 (named UOCN) was successfully obtained by a facial gaseous template sacrificial agent-induced bottom-up strategy. The synergy of O doping and exfoliating bulk into an ultrathin structure is reported to simultaneously achieve high-efficiency separation of photogenerated carriers, enhance the utilization of sunlight, and improve the reduction ability of electrons to promote photocatalytic H 2 evolution of UOCN. As a proof of concept, UOCN affords enhanced photocatalytic H 2 evolution (93.78 μmol h ?1) under visible light illumination, which was significantly better than that of bulk carbon nitride (named CN) with the value of 9.23 μmol h ?1. Furthermore, the H 2 evolution rate of UOCN at a longer wavelength (λ = 450 nm) was up to 3.92 μmol h ?1 due to its extended light absorption range. This work presents a practicable strategy of coupling O dopants with ultrathin structures about g-C 3N 4 to achieve efficient photocatalytic H 2 evolution. This integrated engineering strategy can develop a unique example for the rational design of innovative photocatalysts for energy innovation. 相似文献
2.
Graphite carbon nitride (g‐C 3N 4) is a promising candidate for photocatalytic hydrogen production, but only shows moderate activity owing to sluggish photocarrier transfer and insufficient light absorption. Herein, carbon quantum dots (CQDs) implanted in the surface plane of g‐C 3N 4 nanotubes were synthesized by thermal polymerization of freeze‐dried urea and CQDs precursor. The CQD‐implanted g‐C 3N 4 nanotubes (CCTs) could simultaneously facilitate photoelectron transport and suppress charge recombination through their specially coupled heterogeneous interface. The electronic structure and morphology were optimized in the CCTs, contributing to greater visible light absorption and a weakened barrier of the photocarrier transfer. As a result, the CCTs exhibited efficient photocatalytic performance under light irradiation with a high H 2 production rate of 3538.3 μmol g ?1 h ?1 and a notable quantum yield of 10.94 % at 420 nm. 相似文献
3.
Regulating flow direction of photo-excited electrons from interior to active sites in surface is critical to enhance the photocatalytic performance. Herein, photoinduced chemical reduction process was utilized to pinpoint deposit CdS and NiS nanodots sequentially onto g-C 3N 4 nanosheets. The resulted hybrid composite NiS/CdS/g-C 3N 4 was much more active under visible light, and eventually boosted the hydrogen evolution rate of 3015 μmol g ?1 h ?1, to be 2.4 folds better than that of g-C 3N 4. Because of the relative low content of CdS (around 3.0 wt%), the enhanced activity is due to the favoring band overlapping and promoting charge separation rather than increasing light absorption. Femto-second time-resolved transient absorption spectroscopy (fs-TAS) clearly reveals that the photo-excited electrons are from g-C 3N 4, and then migrate unidirectionally to CdS and finally to NiS, which is caused by the precisely regulate the position of CdS and NiS on g-C 3N 4 surface. This study elucidates the electron transfer kinetics and processes in multi-component system and affords a new avenue to construct stable photocatalysts with high activity. 相似文献
4.
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/C 3N 4 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 Pt 0 species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum‐decorated C 3N 4 catalyst. As expected, H 2 production activity (14.7 mmol h ?1 g ?1) was enhanced significantly with the single‐atom Pt/C 3N 4 catalyst as compared to metallic Pt‐C 3N 4 (0.74 mmol h ?1 g ?1). 相似文献
5.
A rapid and highly efficient strategy for introducing C into g‐C 3N 4 involves copolymerizing π‐electron‐rich barbituric acid with melamine via a facile microwave‐assisted heating, thereby eliminating the issues in conventional electric furnace heating, such as the severe volatilization, owing to the mismatch of the sublimation temperatures of barbituric acid and melamine. The g‐C 3N 4 catalyst after optimizing the C‐doping content actively generates increased amounts of H 2 under visible light exposure with the highest H 2 generation rate of 25.0 μmol h ?1, which is nearly 20 times above that using g‐C 3N 4 produced by conventional electric furnace heating of two identical monomers (1.3 μmol h ?1). As such, the microwave‐assisted heating strategy may stand out as an extremely simple route to incorporating π‐electrons into g‐C 3N 4 with markedly improved photocatalytic performance. 相似文献
6.
Photocatalytic dual-functional reaction under visible light irradiation represents a sustainable development strategy. In detail, H 2 production coupled with benzylamine oxidation can remarkably lower the cost by replacing sacrificial agents. In this work, Cd S quantum dots(Cd S QDs) were successfully loaded onto the surface of a porphyrinic metal-organic framework(Pd-PCN-222) by the electrostatic selfassembly at room temperature. The consequent Pd-PCN-222/CdS heterojunction composites... 相似文献
7.
As a metal‐free nitrogen reduction reaction (NRR) photocatalyst, g‐C 3N 4 is available from a scalable synthesis at low cost. Importantly, it can be readily functionalized to enhance photocatalytic activities. However, the use of g‐C 3N 4‐based photocatalysts for the NRR has been questioned because of the elusive mechanism and the involvement of N defects. This work reports the synthesis of a g‐C 3N 4 photocatalyst modified with cyano groups and intercalated K + ( mCNN), possessing extended visible‐light harvesting capacity and superior photocatalytic NRR activity (NH 3 yield: 3.42 mmol g ?1 h ?1). Experimental and theoretical studies suggest that the ‐C≡N in mCNN can be regenerated through a pathway analogous to Mars van Krevelen process with the aid of the intercalated K +. The results confirm that the regeneration of the cyano group not only enhances photocatalytic activity and sustains the catalytic cycle, but also stabilizes the photocatalyst. 相似文献
8.
Zinc molybdate (ZnMoO4), a layer perovskite material, has the advantages of high stability, excellent optical and charge properties. However, its high band gap and high electron–hole recombination efficiency limit its application in the photocatalytic reduction field like hydrogen production. In this study, we used CdS as a co-catalyst and successfully prepared CdS/ZnMoO4 composite photocatalysts with different loadings. The hydrogen evolution rate of CdS/ZnMoO4 reached 530.2 µmol h?1 g?1, which was approximately 11 and 100 times more than rates of pure CdS and ZnMoO4 under the same conditions, respectively. It is the presence of CdS that contributed to this improved performance, which acted as an electron acceptor to separate electrons and holes. Besides, a reasonable mechanism was provided based on photoelectrochemical characterizations. CdS loading greatly improved the hydrogen evolution performance of ZnMoO4 under visible light, providing a direction to improving the performance of perovskite based photocatalysts. 相似文献
9.
A novel visible‐light‐driven g‐C 3N 4/MIL‐53(Al) composite photocatalyst was successfully prepared using a facile stirring method at room temperature. The g‐C 3N 4/MIL‐53(Al) composites were characterized and their effects on the photocatalytic activities for rhodamine B degradation were investigated. The g‐C 3N 4(20 wt%)/MIL‐53(Al) photocatalyst displayed optimal photocatalytic degradation efficiency, which was about five times higher than the photocatalytic activity of pure g‐C 3N 4. The improved photocatalytic performance of the g‐C 3N 4/MIL‐53(Al) photocatalyst was predominantly attributed to the efficient separation of electron–hole pairs and the low charge‐transfer resistance. g‐C 3N 4/MIL‐53(Al) also exhibited excellent stability and reusability. A proposed mechanism for the enhanced photocatalytic activity is also discussed based on the experimental results. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
In this work, graphitic C 3N 4 decorated with a CoP co‐catalyst (g‐C 3N 4/CoP) is reported for photocatalytic H 2 evolution reaction based on two‐step hydrothermal and phosphidation method. The structure of g‐C 3N 4/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‐C 3N 4/CoP‐3.4 %), the highest H 2 evolution amount of 8.4×10 2 μmol g −1 is obtained, which is 1.1×10 3 times than that over pure g‐C 3N 4. This value also is comparable with that of g‐C 3N 4 loaded by the same amount of Pt. In cycling experiments, g‐C 3N 4/CoP‐3.4 % shows a stable photocatalytic activity. In addition, g‐C 3N 4/CoP‐3.4 % is an efficient photocatalyst for H 2 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‐C 3N 4/CoP‐3.4 % and pure g‐C 3N 4, it is concluded that the presence of the CoP co‐catalyst accelerates the separation and transfer of photogenerated electrons of g‐C 3N 4, thus resulting in improved photocatalytic activity in the H 2 evolution reaction. 相似文献
11.
Herein, a novel broken case‐like carbon‐doped g‐C 3N 4 photocatalyst was obtained via a facile one‐pot pyrolysis and cost‐effective method using glyoxal‐modified melamine as a precursor. The obtained carbon/g‐C 3N 4 photocatalyst showed remarkable enhanced photocatalytic activity in the degradation of gaseous benzene compared with that of pristine g‐C 3N 4 under visible light. The pseudo‐first‐order rate constant for gaseous benzene degradation on carbon/g‐C 3N 4 was 0.186 hr ?1, 5.81 times as large as that of pristine g‐C 3N 4. Furthermore, a possible photocatalytic mechanism for the improved photocatalytic performance over carbon/g‐C 3N 4 nanocomposites was proposed. 相似文献
12.
In this study, the photocatalytic activity of graphitic carbon nitride (g‐C 3N 4) synthesized via different precursors (urea, thiourea, and dicyandiamide) is investigated in the degradation process of tetracycline. Owing to the efficient charge separation and transfer, prolonged radiative lifetime of charge, large surface area, and nanosheet morphology, the urea‐derived g‐C 3N 4 exhibits superior photocatalytic activity for tetracycline degradation under visible‐light irradiation. This performance can compare with that of most reported g‐C 3N 4‐based composite photocatalysts. Through the time‐circle degradation experiment, the urea‐derived g‐C 3N 4 is found to have an excellent photocatalytic stability. The presence of NO 3?, CH 3COO ?, Cl ? and SO 42? ions with the concentration of 10 mm inhibits the photocatalytic activity of urea‐derived g‐C 3N 4, where this inhibitory effect is more obvious for Cl ? and SO 42? ions. For the coexisting Cu 2+, Ca 2+, and Zn 2+ ions, the Cu 2+ ion exhibits a significantly higher inhibitory effect than Ca 2+ and Zn 2+ ions for tetracycline degradation. However, both the inhibitory and facilitating effects are observed in the presence of Fe 3+ ion with different concentration. The h +, .OH and .O 2? radicals are confirmed as major oxidation species and a possible photocatalytic mechanism is proposed in a urea‐derived g‐C 3N 4 reaction system. This study is of important significance to promote the large‐scale application of g‐C 3N 4 photocatalysts in antibiotic wastewater purification. 相似文献
13.
A new set of Cr(III) complexes, {L}CrCl 3(THF), based on thiophene–imine ( 2a , L = PhOC 6H 4(N═CH)‐2‐SC 4H 3; 2b , L = PhOC 2H 4(N═CH)‐2‐SC 4H 3; 2c , L = Ph(NH)C 2H 4(N═CH)‐2‐SC 4H 3; 2d , L = PhOC 6H 4(N═CH)‐2‐SC 4H 2‐5‐Ph; 2e , L = Ph(NH)C 2H 4(N═CH)‐2‐SC 4H 2‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr) ?1 h ?1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined. 相似文献
14.
The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low‐cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g‐C 3N 4) from a low‐cost precursor, urea, is reported. The g‐C 3N 4 exhibits an extraordinary hydrogen‐evolution rate (ca. 20 000 μmol h ?1 g ?1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g‐C 3N 4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen‐evolution rate is significantly enhanced. 相似文献
15.
CdS nanoparticles were deposited on a highly stable, two‐dimensional (2D) covalent organic framework (COF) matrix and the hybrid was tested for photocatalytic hydrogen production. The efficiency of CdS‐COF hybrid was investigated by varying the COF content. On the introduction of just 1 wt % of COF, a dramatic tenfold increase in the overall photocatalytic activity of the hybrid was observed. Among the various hybrids synthesized, that with 10 wt % COF, named CdS‐COF (90:10), was found to exhibit a steep H 2 production amounting to 3678 μmol h ?1 g ?1, which is significantly higher than that of bulk CdS particles (124 μmol h ?1 g ?1). The presence of a π‐conjugated backbone, high surface area, and occurrence of abundant 2D hetero‐interface highlight the usage of COF as an effective support for stabilizing the generated photoelectrons, thereby resulting in an efficient and high photocatalytic activity. 相似文献
16.
Five examples of unsymmetrical 1,2‐bis (arylimino) acenaphthene ( L1 – L5 ), each containing one N‐2,4‐bis (dibenzocycloheptyl)‐6‐methylphenyl group and one sterically and electronically variable N‐aryl group, have been used to prepare the N,N′‐nickel (II) halide complexes, [1‐[2,4‐{(C 15H 13} 2–6‐MeC 6H 2N]‐2‐(ArN)C 2C 10H 6]NiX 2 (X = Br: Ar = 2,6‐Me 2C 6H 3 Ni1 , 2,6‐Et 2C 6H 3 Ni2 , 2,6‐ i‐Pr 2C 6H 3 Ni3 , 2,4,6‐Me 3C 6H 2 Ni4 , 2,6‐Et 2–4‐MeC 6H 2 Ni5 ) and (X = Cl: Ar = 2,6‐Me 2C 6H 3 Ni6 , 2,6‐Et 2C 6H 3 Ni7 , 2,6‐ i‐Pr 2C 6H 3 Ni8 , 2,4,6‐Me 3C 6H 2 Ni9 , 2,6‐Et 2–4‐MeC 6H 2 Ni10 ), in high yield. The molecular structures Ni3 and Ni7 highlight the extensive steric protection imparted by the ortho‐dibenzocycloheptyl group and the distorted tetrahedral geometry conferred to the nickel center. On activation with either Et 2AlCl or MAO, Ni1 – Ni10 exhibited very high activities for ethylene polymerization with the least bulky Ni1 the most active (up to 1.06 × 10 7 g PE mol ?1(Ni) h ?1 with MAO). Notably, these sterically bulky catalysts have a propensity towards generating very high molecular weight polyethylene with moderate levels of branching and narrow dispersities with the most hindered Ni3 and Ni8 affording ultra‐high molecular weight material (up to 1.5 × 10 6 g mol ?1). Indeed, both the activity and molecular weights of the resulting polyethylene are among the highest to be reported for this class of unsymmetrical 1,2‐bis (imino)acenaphthene‐nickel catalyst. 相似文献
17.
Ultrabroad spectral absorption is required for semiconductor photocatalysts utilized for solar-to-chemical energy conversion. The light response range can be extended by element doping, but the photocatalytic performance is generally not enhanced correspondingly. Here we present a solid alkali activation strategy to synthesize near-infrared (NIR) light-activated carbon-doped polymeric carbon nitride (A-cPCN) by combining the copolymerization of melamine and 1,3,5-trimesic acid. The prepared A-cPCN is highly crystalline with a narrowed bandgap and enhanced efficiency in the separation of photogenerated electrons and holes. Under irradiation with NIR light (780 nm ≥ λ ≥ 700 nm), A-cPCN shows an excellent photocatalytic activity for H 2 generation from water with rate of 165 µmol g −1 h −1, and the photo-redox activity for H 2O 2 production (109 µmol g −1 h −1) from H 2O and O 2, whereas no observed photocatalytic activity over pure PCN. The NIR photocatalytic activity is due to carbon doping, which leads to the formation of an interband level, and the alkali activation that achieved shrinking the transfer distance of photocarriers. The current synergistic strategy may open insights to fabricate other carbon-nitrogen-based photocatalysts for enhanced solar energy capture and conversion. 相似文献
18.
PtPd bimetallic alloy nanoparticle (NP)-modified graphitic carbon nitride (g-C 3N 4) nanosheet photocatalysts were synthesized via chemical deposition precipitation. Characterization of the photocatalytic H 2 evolution of the g-C 3N 4 nanosheets shows that it was significantly enhanced when PtPd alloy NPs were introduced as a co-catalyst. The 0.2 wt% PtPd/g-C 3N 4 composite photocatalyst gave a maximum H 2 production rate of 1600.8 μmol g –1 h –1. Furthermore, when K 2HPO 4 was added to the reaction system, the H 2 production rate increased to 2885.0 μmol g –1 h –1. The PtPd/g-C 3N 4 photocatalyst showed satisfactory photocatalytic stability and was able to maintain most of its photocatalytic activity after four experimental photocatalytic cycles. In addition, a possible mechanism for the enhanced photocatalytic activity was proposed and verified by various photoelectric techniques. These results demonstrate that the synergistic effect between PtPd and g-C 3N 4 helps to greatly improve the photocatalytic activity of the composite photocatalyst. 相似文献
19.
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‐C 3N 4 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‐C 3N 4 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
20.
Exploring noble‐metal‐free, highly active and durable catalysts is vital to get to grips with the energy and environmental issues. Herein, we first dexterously design and synthesize a class of ternary Nb 6/CZS/g‐CN photocatalysts for the removal of hexavalent chromium Cr (VI) and organic dye pollutant (MO) from wastewater under visible‐light irradiation. A heterojunction Nb 6–1/CZS/g‐CN loaded with 0.01 g K 7HNb 6O 19 showed excellent photocatalytic performance, with the MO photodegradation efficiency of 94% in 1 h and the Cr (VI) (150 mg/l) photoreduction efficiency as high as 91% in 2 hr. The main active species were deemed to be O 2.‐. Additionally, the as‐prepared ternary heterojunction exhibits superior hydrogen evolution reaction (HER) rate. A heterojunction Nb 6–4/CZS/g‐CN loaded with 0.5 g K 7HNb 6O 19 exhibited the highest H 2 evolution rate as high as 1777.86 μmol h ?1 g ?1 under visible‐light illumination, which is increased to 5.7 and 2.7 times that of bare CZS and biphase heterojunction CZS/g‐CN . These findings afford a new class of promising low‐cost photocatalyst bodying for its huge potential value in sustainable energy development and wastewater treatment. 相似文献
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