Titanium Carbide (Ti3C2) MXene as a Promising Co-catalyst for Photocatalytic CO2 Conversion to Energy-Efficient Fuels: A Review
TL;DR: In this article, the authors proposed photocatalytic CO2 reduction to produce valuable chemicals and fuels using solar energy provides an appealing route to alleviate global energy and environmental problems.
Abstract: Photocatalytic CO2 reduction to produce valuable chemicals and fuels using solar energy provides an appealing route to alleviate global energy and environmental problems. However, available semicon...
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TL;DR: Z-scheme photocatalysts have recently received tremendous attention because of their strong light utilization and redox ability as mentioned in this paper , which is considered a promising strategy to solve the growing global energy demands and environmental problems.
Abstract: Solar-driven fuel production is considered a promising strategy to solve the growing global energy demands and environmental problems. Z-scheme heterojunctions have been reported to exhibit considerably improved photocatalytic fuel production due to enhanced light harvesting, spatially separated reductive and oxidative active sites, and strong redox capability. Understanding the fundamental principles of Z-scheme photocatalytic systems and mastering their improvement strategies will help greatly with the further development of highly efficient Z-scheme photocatalysts for solar-driven fuel production and other photocatalytic applications. Z-scheme photocatalysts have recently received tremendous attention because of their strong light utilization and redox ability. This cutting-edge photocatalytic platform allows photocatalysts to convert light into chemical energy with high activity, selectivity, and stability. In this review, we highlight some of the recent key contributions in the field, including fundamental principles, advanced characterization methods, and a series of photocatalytic applications (e.g., water splitting, CO2 reduction, N2 fixation, H2O2 production). Significant improvement strategies for Z-scheme photocatalysts are also discussed and summarized. With increasing achievements, Z-scheme photocatalytic systems (PSs) will make a historic breakthrough in activity, solar utilization, selectivity, and fabrication cost and move toward practical production in the near future. Z-scheme photocatalysts have recently received tremendous attention because of their strong light utilization and redox ability. This cutting-edge photocatalytic platform allows photocatalysts to convert light into chemical energy with high activity, selectivity, and stability. In this review, we highlight some of the recent key contributions in the field, including fundamental principles, advanced characterization methods, and a series of photocatalytic applications (e.g., water splitting, CO2 reduction, N2 fixation, H2O2 production). Significant improvement strategies for Z-scheme photocatalysts are also discussed and summarized. With increasing achievements, Z-scheme photocatalytic systems (PSs) will make a historic breakthrough in activity, solar utilization, selectivity, and fabrication cost and move toward practical production in the near future. a typical layered 2D material with puckered layers of phosphorus stacked together via van der Waals forces. the energy band formed by free electrons. a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. one of the most widely used theoretical calculation technologies. a Z-scheme photocatalyst that shows photocatalytic activity under all wavelengths of light. an emerging 2D layered transition-metal carbide/carbonitride/nitride. metal–semiconductor contact that has a negligible contact resistance relative to the bulk or series resistance of the semiconductor. the charge-transfer route in S-scheme mode resembles a macroscopic ‘step’ (from low CB to high VB; Figure 1D). MoS2 with unsaturated S atoms on exposed edges as reactive sites forms three stacked atomic layers. the energy band formed by valence electrons. the minimum energy required to move an electron from the interior of a solid to its surface. the photogenerated carrier transfer route looks like the letter Z.
70 citations
TL;DR: In this article , a review of 2D/2D interfaces with state-of-the-art 2D cocatalysts, spanning from carbon-containing to phosphorus-containing, metal dichalcogenide, and other cocatallysts, is presented.
Abstract: Sparked by natural photosynthesis, solar photocatalysis using metal‐free graphitic carbon nitride (g‐C3N4) with appealing electronic structure has turned up as the most captivating technique to the quest for sustainable energy generation and pollution‐free environment. Nonetheless, low‐dimensional g‐C3N4 is thwarted from sluggish kinetics and rapid recombination of photogenerated carriers upon light irradiation. Among multifarious modification strategies, engineering 2D cocatalysts is anticipated to accelerate redox kinetics, augment active sites and ameliorate electron–hole separation of 2D g‐C3N4 for boosted activity thanks to its face‐to‐face contact surface. It is of timely and technological significance to review the 2D/2D interfaces with state‐of‐the‐art 2D cocatalysts, spanning from carbon‐containing to phosphorus‐containing, metal dichalcogenide, and other cocatalysts. Fundamental principles for each photocatalytic application will be introduced. Thereafter, the recent advances of 2D/2D cocatalyst‐mediated g‐C3N4 systems will be critically evaluated based on their interfacial engineering, emerging roles, and impacts toward stability and catalytic efficiency. Importantly, mechanistic insights into the charge dynamics and structure–performance relationship will be deciphered. Last, noteworthy research directions are prospected to deliver insightful ideas for future development of g‐C3N4. Overall, this review is anticipated to serve as a scaffold and cornerstone in designing dimensionality‐dependent 2D cocatalyst‐assisted g‐C3N4 toward renewable energy and ecologically green environment.
67 citations
TL;DR: A new family of two-dimensional transition metal carbides, carbonitrides, and nitrides were discovered and developed at Drexel University in 2011, which is called MXene and is applicable for several critical applications as discussed by the authors .
49 citations
TL;DR: In this paper , the authors focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of the MXenes, and MXene-based photocatalysts for H2 evolution, CO2 reduction, and pollutant degradation.
Abstract: Photocatalytic water splitting, CO2 reduction, and pollutant degradation have emerged as promising strategies to remedy the existing environmental and energy crises. However, grafting of expensive and less abundant noble-metal cocatalysts on photocatalyst materials is a mandatory practice to achieve enhanced photocatalytic performance owing to the ability of the cocatalysts to extract electrons efficiently from the photocatalyst and enable rapid/enhanced catalytic reaction. Hence, developing highly efficient, inexpensive, and noble-metal-free cocatalysts composed of earth-abundant elements is considered as a noteworthy step toward considering photocatalysis as a more economical strategy. Recently, MXenes (two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides) have shown huge potential as alternatives for noble-metal cocatalysts. MXenes have several excellent properties, including atomically thin 2D morphology, metallic electrical conductivity, hydrophilic surface, and high specific surface area. In addition, they exhibit Gibbs free energy of intermediate H atom adsorption as close to zero and less than that of a commercial Pt-based cocatalyst, a Fermi level position above the H2 generation potential, and an excellent ability to capture and activate CO2 molecules. Therefore, there is a growing interest in MXene-based photocatalyst materials for various photocatalytic events. In this review, we focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of MXenes, and MXene-based photocatalysts for H2 evolution, CO2 reduction, and pollutant degradation. The existing challenges and the possible future directions to enhance the photocatalytic performance of MXene-based photocatalysts are also discussed.
48 citations
TL;DR: In this article , a comprehensive review is conducted on various approaches to enhance activity of pristine Co-MOFs for CO2 photo-reduction, which includes photosensitization, MOF templating, heterojunction formation and surface sensitization, and critical evaluation is carried out in view of band engineering, energy harvesting, stability and productivity to further boost the photo-conversion of CO2.
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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: More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist.
Abstract: The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.
4,745 citations
TL;DR: Evidence is presented for the exfoliation of the following MAX phases by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication.
Abstract: Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti2AlC, Ta4AlC3, (Ti0.5,Nb0.5)2AlC, (V0.5,Cr0.5)3AlC2, and Ti3AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the “A” group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.
3,080 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
TL;DR: Two-dimensional transition metal carbides, carbonitrides, and nitrides (MXenes) were discovered in 2011 and more than 20 different compositions have been synthesized by the selective etching of MAX phase and other precursors and many more theoretically predicted as mentioned in this paper.
Abstract: Two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides (MXenes) were discovered in 2011. Since the original discovery, more than 20 different compositions have been synthesized by the selective etching of MAX phase and other precursors and many more theoretically predicted. They offer a variety of different properties, making the family promising candidates in a wide range of applications, such as energy storage, electromagnetic interference shielding, water purification, electrocatalysis, and medicine. These solution-processable materials have the potential to be highly scalable, deposited by spin, spray, or dip coating, painted or printed, or fabricated in a variety of ways. Due to this promise, the amount of research on MXenes has been increasing, and methods of synthesis and processing are expanding quickly. The fast evolution of the material can also be noticed in the wide range of synthesis and processing protocols that determine the yield of delamination, as well as the quality...
2,559 citations