Efficient capture of solar energy will be critical to meeting the energy needs of the future. Semiconductor photocatalysis is expected to make an important contribution in this regard, delivering ...both energy carriers (especially H2) and valuable chemical feedstocks under direct sunlight. Over the past few years, carbon dots (CDs) have emerged as a promising new class of metal‐free photocatalyst, displaying semiconductor‐like photoelectric properties and showing excellent performance in a wide variety of photoelectrochemical and photocatalytic applications owing to their ease of synthesis, unique structure, adjustable composition, ease of surface functionalization, outstanding electron‐transfer efficiency and tunable light‐harvesting range (from deep UV to the near‐infrared). Here, recent advances in the rational design of CDs‐based photocatalysts are highlighted and their applications in photocatalytic environmental remediation, water splitting into hydrogen, CO2 reduction, and organic synthesis are discussed.
Carbon dots (CDs) have emerged as promising materials for various photocatalytic reactions owing to their tunable light‐harvesting range and outstanding electron‐transfer efficiency stemming from their intrinsic nanostructures. Recent advances in the rational design of CD‐based photocatalysts and their applications in photocatalytic environmental remediation, hydrogen evolution by water splitting, CO2 reduction, and organic synthesis are highlighted.
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The future large‐scale deployment of rechargeable zinc–air batteries requires the development of cheap, stable, and efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and ...oxygen evolution reaction (OER). In this work, a highly efficient bifunctional electrocatalyst is prepared by depositing 3–5 nm NiFe layered double hydroxide (NiFe‐LDH) nanoparticles on Co,N‐codoped carbon nanoframes (Co,N‐CNF). The NiFe‐LDH/Co,N‐CNF electrocatalyst displayed an OER overpotential of 0.312 V at 10 mA cm−2 and an ORR half‐wave potential of 0.790 V. The outstanding performance of the electrocatalyst is attributable to the high electrical conductivity and excellent ORR activity of Co,N‐CNF, together with the strong anchoring of 3–5 nm NiFe‐LDH nanoparticles, which preserves active sites. Inspired by the excellent OER and ORR performance of NiFe‐LDH/Co,N‐CNF, a prototype rechargeable zinc–air battery is developed. The battery exhibited a low discharge–charge voltage gap (1.0 V at 25 mA cm−2) and long‐term cycling durability (over 80 h), and superior overall performance to a counterpart battery constructed using a mixture of IrO2 and Pt/C as the cathode. The strategy developed here can easily be adapted to synthesize other bifunctional CNF‐based hybrid electrodes for ORR and OER, providing a practical route to more efficient rechargeable zinc–air batteries.
A bifunctional NiFe‐layered double hydroxide (LDH)/Co,N‐carbon nanoframe (CNF) electrocatalyst, comprising 3–5 nm NiFe‐LDH particles immobilized on Co,N‐doped carbon nanoframes (Co,N‐CNF), demonstrates excellent activities for both oxygen evolution reaction and oxygen reduction reaction, and outstanding performance and stability as cathode catalysts in rechargeable zinc–air batteries. Intimate contact between NiFe‐LDH and Co,N‐CNF preventing NiFe‐LDH aggregation is the key to the higher electrocatalytic activity and stability of NiFe‐LDH/Co,N‐CNF compared to precious metal‐based catalysts.
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A series of novel CoFe‐based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered‐double‐hydroxide (LDH) nanosheets at 300–700 °C. The chemical composition and morphology of ...the reaction products (denoted herein as CoFe‐x) are highly dependent on the reduction temperature (x). CO2 hydrogenation experiments are conducted on the CoFe‐x catalysts under UV–vis excitation. With increasing LDH‐nanosheet reduction temperature, the CoFe‐x catalysts show a progressive selectivity shift from CO to CH4, and eventually to high‐value hydrocarbons (C2+). CoFe‐650 shows remarkable selectivity toward hydrocarbons (60% CH4, 35% C2+). X‐ray absorption fine structure, high‐resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina‐supported CoFe‐alloy nanoparticles are responsible for the high selectivity of CoFe‐650 for C2+ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar‐energy to produce valuable chemicals and fuels from CO2.
Three unique CoFe‐based catalysts are successfully fabricated via direct H2 reduction of a CoFeAl layered‐double‐hydroxide (CoFeAl‐LDH) nanosheets precursor by varying the reduction temperature. LDH precursor reduction at temperatures above 600 °C results in the formation of CoFe‐alloy nanoparticles, thereby affording a remarkable CO2 hydrogenation selectivity toward high‐value (C2+) hydrocarbons under simulated solar excitation through photothermal effects.
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Photocatalytic hydrogen evolution is a promising technique for the direct conversion of solar energy into chemical fuels. Colloidal quantum dots with tunable band gap and versatile surface properties ...remain among the most prominent targets in photocatalysis despite their frequent toxicity, which is detrimental for environmentally friendly technological implementations. In the present work, all-inorganic sulfide-capped InP and InP/ZnS quantum dots are introduced as competitive and far less toxic alternatives for photocatalytic hydrogen evolution in aqueous solution, reaching turnover numbers up to 128,000 based on quantum dots with a maximum internal quantum yield of 31%. In addition to the favorable band gap of InP quantum dots, in-depth studies show that the high efficiency also arises from successful ligand engineering with sulfide ions. Due to their small size and outstanding hole capture properties, sulfide ions effectively extract holes from quantum dots for exciton separation and decrease the physical and electrical barriers for charge transfer.
Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber-Bosch process, a metallic iron catalyst and high ...temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave NN bonds, motivating the search for alternative catalysts that can transform N
to NH
under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO
nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper-doping strategy, is reported. These defect-rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N
to NH
in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N
and water, resulting in unusually high rates of NH
evolution under visible-light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N
using solar energy.
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Semiconductor photocatalysis attracts widespread interest in water splitting, CO2 reduction, and N2 fixation. N2 reduction to NH3 is essential to the chemical industry and to the Earth's nitrogen ...cycle. Industrially, NH3 is synthesized by the Haber–Bosch process under extreme conditions (400–500 °C, 200–250 bar), stimulating research into the development of sustainable technologies for NH3 production. Herein, this study demonstrates that ultrathin layered‐double‐hydroxide (LDH) photocatalysts, in particular CuCr‐LDH nanosheets, possess remarkable photocatalytic activity for the photoreduction of N2 to NH3 in water at 25 °C under visible‐light irradiation. The excellent activity can be attributed to the severely distorted structure and compressive strain in the LDH nanosheets, which significantly enhances N2 chemisorption and thereby promotes NH3 formation.
Layered‐double‐hydroxide (LDH) nanosheets are shown to exhibit outstanding visible‐light‐driven photocatalytic activity for the reduction of N2 to NH3 under ambient conditions. Irradiation of CuCr‐LDH nanosheets in N2‐saturated water with 500 nm monochromatic light produces NH3. The excellent activity can be attributed to the severely distorted structure and compressive strain of the LDH nanosheets, promoting NH3 formation.
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Plasmon‐mediated photocatalytic systems generally suffer from poor efficiency due to weak absorption overlap and thus limited energy transfer between the plasmonic metal and the semiconductor. ...Herein, a near‐ideal plasmon‐mediated photocatalyst system is developed. Au/CdSe nanocrystal clusters (NCs) are successfully fabricated through a facile emulsion‐based self‐assembly approach, containing Au nanoparticles (NPs) of size 2.8, 4.6, 7.2, or 9.0 nm and CdSe quantum dots (QDs) of size ≈3.3 nm. Under visible‐light irradiation, the Au/CdSe NCs with 7.2 nm Au NPs afford very stable operation and a remarkable H2‐evolution rate of 73 mmol gCdSe−1 h−1 (10× higher than bare CdSe NCs). Plasmon resonance energy transfer from the Au NPs to the CdSe QDs, which enhances charge‐carrier generation in the semiconductor and suppresses bulk recombination, is responsible for the outstanding photocatalytic performance. The approach used here to fabricate the Au/CdSe NCs is suitable for the construction of other plasmon‐mediated photocatalysts.
Highly efficient plasmon‐mediated photocatalysts based on Au/CdSe nanocrystal clusters (NCs) are successfully fabricated through an emulsion‐based self‐assembly approach. The Au/CdSe NCs synergistically harness the excellent visible‐light‐absorption properties of CdSe quantum dots and Au nanoparticles, affording a remarkable H2 evolution rate of 73 mmol gCdSe−1 h−1 in aqueous solution under visible‐light illumination and excellent operational stability.
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An enormous research effort is currently being directed towards the development of efficient visible‐light‐driven photocatalysts for renewable energy applications including water splitting, CO2 ...reduction and alcohol photoreforming. Layered double hydroxide (LDH)‐based photocatalysts have emerged as one of the most promising candidates to replace TiO2‐based photocatalysts for these reactions, owing to their unique layered structure, compositional flexibility, controllable particle size, low manufacturing cost and ease of synthesis. By introducing defects into LDH materials through the control of their size to the nanoscale, the atomic structure, surface defect concentration, and electronic and optical characteristics of LDH materials can be strategically engineered for particular applications. Furthermore, through the use of advanced characterization techniques such as X‐ray absorption fine structure, positron annihilation spectrometry, X‐ray photoelectron spectroscopy, electron spin resonance, density‐functional theory calculations, and photocatalytic tests, structure‐activity relationships can be established and used in the rational design of high‐performance LDH‐based photocatalysts for efficient solar energy capture. LDHs thus represent a versatile platform for semiconductor photocatalyst development with application potential across the energy sector.
Nanostructured layered double hydroxide (LDH) photocatalysts, owing to their unique layered structure, compositional flexibility, low cost and ease‐of‐synthesis represent one of the hottest new research directions in semiconductor photocatalysis and solar energy conversion. Structure‐activity relationships in nanostructured LDH compounds are explored, and the importance of using advanced characterization techniques in the future development of more efficient LDH‐based photocatalysts is emphasized.
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Graphdiyne (GDY), with a highly π‐conjugated structure of sp2‐ and sp‐hybridized carbon, has triggered a huge interest in water splitting. However, all of the systems perform with no consideration of ...the surface wettability of GDY. Herein, for the first time, the fabrication of superhydrophilic GDY electrode via air‐plasma for oxygen evolution is described. As a representative catalyst, ultrathin CoAl‐LDH (CO32−) nanosheets have been successfully assembled onto the superhydrophilic GDY electrostatically. The resulting superhydrophilic CoAl‐LDH/GDY electrode exhibites superior activity with an overpotential of ≈258 mV to reach 10 mA cm−2. The turnover frequency (TOF) is calculated to be ≈0.60 s−1 at η = 300 mV, which is the best record in both CoAl‐based and GDY‐based layered double hydroxides (LDH) electrocatalysts for oxygen evolution. Density functional theory (DFT) calculations reveal that superhydrophilic GDY has stronger interactions with catalysts and attracts H2O molecules around catalysts, thus facilitating interfacial mass/electron transportation. Further, the fabrication is capable of improving the photoelectrochemical oxygen evolution activity remarkably. The results show the great potential of superhydrophilic GDY to boost water oxidation activity by promoting interfacial mass/electron transportation.
The first superhydrophilic graphdiyne (GDY) electrode is fabricated via air plasma for water oxidation. Experimental studies and density functional theory calculations reveal that superhydrophilic GDY is responsible for facilitating interfacial mass/electron transfer, thus resulting in superior oxygen evolution performance with an overpotential of ≈258 mV to reach 10 mA cm−2 and a TOF of ≈0.60 s−1 at overpotential of 300 mV, respectively.
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The authors provide at a look at the biological applications of supramolecular assemblies that have been designed for excitation energy transfer. The topics discussed include biosensors and ...bioimaging.
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