Journal Article•
Synergistic effect of 2D Ti₂C and g-C₃N₄ for efficient photocatalytic hydrogen production
TL;DR: In this article, a photocatalyst consisting of two-dimensional (2D) titanium carbide (Ti₂C) and graphitic carbon nitride (g-C₃N₄) was proposed for hydrogen production.
Abstract: Photocatalytic water splitting is an environmentally friendly technique for hydrogen production. In this work, we report a novel photocatalyst consisting of two-dimensional (2D) titanium carbide (Ti₂C) and graphitic carbon nitride (g-C₃N₄). We observe substantially enhanced water splitting activities due to the efficient synergistic interaction between Ti₂C and g-C₃N₄. Optimal properties are achieved in the g-C₃N₄ with a loading of 0.4 wt% Ti₂C with a hydrogen production rate of 47.5 μmol h⁻¹, which is 14.4 times as much as that in the case using pure g-C₃N₄, and it even outperforms Pt-loaded g-C₃N₄. We further show that the Ti₂C/g-C₃N₄ has high stability and good reproducibility. We expect that the Ti₂C/g-C₃N₄ can be a photocatalyst for large scale applications because both Ti₂C and g-C₃N₄ are low-cost, abundant, and nontoxic.
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TL;DR: In this paper, a review of 2D transition metal transition metal carbides, nitrides, and carbonitrides (MXenes) is presented, highlighting the expeditious advances and achievements in design strategies, physico-chemical properties, and catalytic applications of two-dimensional layered MXenes and their nanocomposites.
513 citations
TL;DR: In this paper, an ultrathin 2D/2D Ti3C2/g-C3N4 heterojunction was synthesized by direct calcination the mixture of bulk Ti3c2 and urea.
Abstract: In this paper, an ultrathin 2D/2D Ti3C2/g-C3N4 heterojunction was synthesized by direct calcination the mixture of bulk Ti3C2 and urea, where urea not only acts as the gas template to exfoliate Ti3C2 into nanosheets, but also as the precursor of g-C3N4 to craft Ti3C2/g-C3N4 heterojunction. CO2 photoreduction activity tests reveal that pure g-C3N4 (UCN) exhibits very weak photoactivity. However, when Ti3C2 was coupled with g-C3N4, the photocatalytic performance is soaringly enhanced. The optimal sample (10TC) shows the yields of 5.19 and 0.044 μmol h−1 g−1 for CO and CH4, respectively, and the total CO2 conversion is 8.1 times higher than that of UCN. The enhanced CO2 photoreduction activity is mainly attributed to the combined effects of (1) improved CO2 adsorption and activation, and (2) the construction of ultrathin 2D/2D Ti3C2/g-C3N4 heterojunction, where the intimate contact stimulates an efficient spatial separation of photo-excited charge carriers.
348 citations
TL;DR: In this paper, a 2D-2D2D 2D structure of Ti3C2@TiOO2@MoS2 composite is achieved, which shows a remarkable enhancement in the photocatalytic H2 evolution reaction.
Abstract: Exposing the highly active facets and hybridizing the photocatalyst with appropriate cocatalysts with right placement have been regarded as a powerful approach to high performance photocatalysts. Herein, TiO2 nanosheets (NSs) are in situ grown on highly conductive Ti3C2 MXene and then MoS2 NSs are deposited on the (101) facets of TiO2 NSs with mainly exposed high-active (001) facets through a two-step hydrothermal method. And a unique 2D-2D-2D structure of Ti3C2@TiO2@MoS2 composite is achieved. With an optimized MoS2 loading amounts (15 wt%), the Ti3C2@TiO2@MoS2 composite shows a remarkable enhancement in the photocatalytic H2 evolution reaction compared with Ti3C2@TiO2 composite and TiO2 NS. It also shows good stability under the reaction condition. This arises from: (i) the in situ growth of TiO2 NSs construct strong interfacial contact with excellent electronic conductivity of Ti3C2, which facilitates the separation of carriers; (ii) the coexposed (101) and (001) facets can form a surface heterojunction within single TiO2 NS, which is beneficial for the transfer and separation of charge carriers; and (iii) the MoS2 NSs are deposited on the electrons-rich (101) facets of TiO2 NSs, which not only effectively reduces the charge carriers recombination rate by capturing photoelectrons, but also makes TiO2 NSs expose more highly active (001) facets to afford high-efficiency photogeneration of electron-hole pairs.
340 citations
TL;DR: The results presented herein show that transition-metal carbide are promising co-catalysts for photocatalytic hydrogen production.
Abstract: Hydrogen production through facile photocatalytic water splitting is regarded as a promising strategy to solve global energy problems. Transition-metal carbides (MXenes) have recently drawn attention as potential co-catalyst candidates for photocatalysts. Here, we report niobium pentoxide/carbon/niobium carbide (MXene) hybrid materials (Nb2 O5 /C/Nb2 C) as photocatalysts for hydrogen evolution from water splitting. The Nb2 O5 /C/Nb2 C composites were synthesized by one-step CO2 oxidation of Nb2 CTx . Nb2 O5 grew homogeneously on Nb2 C after mild oxidation, during which some amorphous carbon was also formed. With an optimized oxidation time of 1.0 h, Nb2 O5 /C/Nb2 C showed the highest hydrogen generation rate (7.81 μmol h-1 gcat-1 ), a value that was four times higher than that of pure Nb2 O5 . The enhanced performance of Nb2 O5 /C/Nb2 C was attributed to intimate contact between Nb2 O5 and conductive Nb2 C and the separation of photogenerated charge carriers at the Nb2 O5 /Nb2 C interface; the results presented herein show that transition-metal carbide are promising co-catalysts for photocatalytic hydrogen production.
279 citations
TL;DR: In this paper, a step-scheme photocatalytic mechanism based on S/Cl-CN/CdSe-D heterostructure was proposed, where the S atom is appropriate to be incorporated into the CN framework to replace N atom, which is beneficial to adjust the band gap.
Abstract: The poor utilization of visible light and the speedy recombination of photoexcited carriers limit the further development of carbon nitride polymer (CN) photocatalysts. It is a valid means for enhancing the photocatalytic ability to ameliorate the electronic and physicochemical properties via modifying the structure of CN. The sulfur- and chlorine-codoped graphite CN (S/Cl-CN) was successfully fabricated with low-cost ammonium chloride and thiourea as precursors. The introduction of Cl atoms will establish interlayer channels to promote interlayer charge migration and up-shifted conduction-band level. S atom is appropriate to be incorporated into the CN framework to replace N atom, which is beneficial to adjust the band gap. Then, inorganic-organic CdSe-diethylenetriamine (D) grown in situ are employed to fabricate a S/Cl-CN/CdSe-D heterojunction. S/Cl-CN/CdSe-D heterojunction exhibits greater hydrogen evolution activity compared to CN, S-CN, Cl-CN, S/Cl-CN, CdSe-D and CN/CdSe-D. Finally, Step-scheme (S-scheme) photocatalytic mechanism based on S/Cl-CN/CdSe-D heterostructure was proposed.
277 citations
References
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TL;DR: Water photolysis is investigated by exploiting the fact that water is transparent to visible light and cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm.
Abstract: ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).
27,819 citations
TL;DR: It is shown that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor.
Abstract: The production of hydrogen from water using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. For an economical use of water and solar energy, catalysts that are sufficiently efficient, stable, inexpensive and capable of harvesting light are required. Here, we show that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. Contrary to other conducting polymer semiconductors, carbon nitride is chemically and thermally stable and does not rely on complicated device manufacturing. The results represent an important first step towards photosynthesis in general where artificial conjugated polymer semiconductors can be used as energy transducers.
9,751 citations
TL;DR: 2D nanosheets, composed of a few Ti 3 C 2 layers and conical scrolls, produced by the room temperature exfoliation of Ti 3 AlC 2 in hydrofl uoric acid are reported, which opens a door to the synthesis of a large number of other 2D crystals.
Abstract: Currently, however, there are relatively few such atomically layered solids. [ 2–5 ] Here, we report on 2D nanosheets, composed of a few Ti 3 C 2 layers and conical scrolls, produced by the room temperature exfoliation of Ti 3 AlC 2 in hydrofl uoric acid. The large elastic moduli predicted by ab initio simulation, and the possibility of varying their surface chemistries (herein they are terminated by hydroxyl and/or fl uorine groups) render these nanosheets attractive as polymer composite fi llers. Theory also predicts that their bandgap can be tuned by varying their surface terminations. The good conductivity and ductility of the treated powders suggest uses in Li-ion batteries, pseudocapacitors, and other electronic applications. Since Ti 3 AlC 2 is a member of a 60 + group of layered ternary carbides and nitrides known as the MAX phases, this discovery opens a door to the synthesis of a large number of other 2D crystals. Arguably the most studied freestanding 2D material is graphene, which was produced by mechanical exfoliation into single-layers in 2004. [ 1 ] Some other layered materials, such as hexagonal BN, [ 2 ] transition metal oxides, and hydroxides, [ 4 ] as well as clays, [ 3 ] have also been exfoliated into 2D sheets. Interestingly, exfoliated MoS 2 single layers were reported as early as in 1986. [ 5 ] Graphene is fi nding its way to applications ranging from supercapacitor electrodes [ 6 ] to reinforcement in composites. [ 7 ] Although graphene has attracted more attention than all other 2D materials combined, its simple chemistry and the weak van der Waals bonding between layers in multilayer structures limit its use. Complex, layered structures that contain more than one element may offer new properties because they
6,846 citations
TL;DR: Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting and its Applications d0 Metal Oxide Photocatalysts 6518 4.4.1.
Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519
6,332 citations
TL;DR: This study demonstrates the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers, and provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions.
Abstract: The intercalation of ions into layered compounds has long been exploited in energy storage devices such as batteries and electrochemical capacitors However, few host materials are known for ions much larger than lithium We demonstrate the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers MXenes combine 2D conductive carbide layers with a hydrophilic, primarily hydroxyl-terminated surface A variety of cations, including Na+, K+, NH4+, Mg2+, and Al3+, can also be intercalated electrochemically, offering capacitance in excess of 300 farads per cubic centimeter (much higher than that of porous carbons) This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions
3,018 citations