A new visible‐light responsive metallic photocatalyst, nanostructured MoO2, has been discovered. The metallic nature of MoO2 is confirmed by valance X‐ray photoelectron spectroscopy spectrum and ...theoretical calculations. However, MoO2 itself shows only moderate activity due to the serious charge recombination, a general disadvantage of metallic photocatalysts. The findings suggest that its effective charge diffusion length Lp is smaller than 1.0 nm while the separation efficiency ηsep is less than 10%. Therefore, only the periphery of the metallic MoO2 can effectively contribute to photocatalysis. This limitation is overcome by integrating MoO2 in a hydrothermal carbonation carbon (HTCC) matrix (mainly contains semiconductive polyfuran). This simple chemical modification brings two advantages: (i) an internal electric field is formed at the interface between MoO2 and HTCC due to their appropriate band alignment; (ii) the nanostructured MoO2 and the HTCC matrix are intertwined with each other intimately. Their small size and large contact area promote charge transfer, especially under the internal electric field. Therefore, the separation rate of photoexcited charge carrier in MoO2 is greatly enhanced. The activity increases by 2.4, 16.8, and 4.0 times in photocatalytic oxygen evolution, dyes degradation, and photoelectrochemicl cell, respectively. The new approach is helpful for further development of metallic photocatalysts.
An effective solution to the problem of serious charge recombination in metallic photocatalysts is described. The concept is demonstrated by encapsulating individual metallic MoO2 particles in a hydrothermal carbonation carbon (HTCC) matrix. When integrating with HTCC, MoO2 exhibits enhanced charge separation efficiency and photocatalytic activity because of an internal electric field and appropriate band alignment.
•Porous Fe2O3 was prepared by heating Fe-MOF (FeFe(CN)6) templates.•Above method is effective to control the phase composition.•The phase composition significantly affects the gas sensing performance ...for VOCs.•Sensibility of α-Fe2O3 comes from the concentration change of free carriers.•Sensibility of γ-Fe2O3 is from transformation between γ-Fe2O3 and Fe3O4.
Recently, the phase composition of a certain metal oxide has been regarded as an important factor that can significantly influence the gas sensing performance. For a better comparison, an appropriate method is necessary to control the phase composition of metal oxides. Herein, three Fe2O3 samples with different phase compositions of α-Fe2O3, γ-Fe2O3 and a mixed phase of α-Fe2O3 and γ-Fe2O3 were prepared by calcining MOF (metal-organic framework) templates at different temperatures. As-prepared Fe2O3 samples have a similar morphologic structure but quite different gas sensing properties for VOCs (volatile organic compounds). Among them, α-Fe2O3 has the smallest specific surface area, but the highest response toward n-butanol. It is indicated that α-Fe2O3 and γ-Fe2O3 have different gas sensing mechanisms. The sensitivity of α-Fe2O3 comes from the concentration change of free carriers within the surface region. Differently, the transformation between γ-Fe2O3 and Fe3O4 determines the response of γ-Fe2O3. The findings can be used in the design of Fe2O3 gas sensing materials in the future.
Carbohydrates in biomass can be converted to semiconductive hydrothermal carbonation carbon (HTCC), a material that contains plenty of sp2-hybridization structures. Under solar light illumination, ...HTCC generates photoexcited electrons, holes, and hydroxyl radicals. These species can be used for photocatalytic treatment such as water disinfection and degradation of organic pollutants. The photocatalytic activity of HTCC can be significantly enhanced by iodine doping. The enhancement mechanism is investigated by density functional theoretical calculations and electrochemical measurements. The iodine dopants twist and optimize the structures of the sp2-hybridization in HTCC, thereby favoring photon-induced excitation. Moreover, the iodine dopants facilitate the charge transfer between different sp2-hybridization structures, thus increasing the conductivity and activity of the HTCC. An added benefit is that the I-doped HTCC exhibits lower cytotoxic effect than the pure HTCC. In addition to monosaccharides (glucose), disaccharides (sucrose), and polysaccharides (starch), we have also transformed crops (e.g., rice), plants (e.g., grass), and even agricultural waste (e.g., straw) and animal waste (e.g., cow dung). The conversion of carbohydrates to HTCC may be considered as a “Trash to Treasure” approach. We believe this discovery will attract a lot of attention from researchers involved in environmental catalysis, waste recycling, and pollution treatment.
Herein, an example of Cu‐doped few‐layer ZnIn2S4 nanosheets is used to reveal the origin of optimum and excess doping for photocatalysts at atomic level. Results show that the metal‐S4 coordination ...maintains well with 0.5 wt% Cu substituted Zn atoms in the lattice. The introduced Cu atoms bring electronic acceptor states close to the valence band (VB) maximum and thus ensures higher charge density and efficient carrier transport, resulting in an optimum hydrogen evolution rate of 26.2 mmol h−1 g−1 and an apparent quantum efficiency of 4.76% at 420 nm. However, a distorted atomic structure and largely upshift of VB maximum with Cu‐S3.6 coordination are found with excess doping concentration (3.6 wt%). These bring the heavy charge recombination and consequentially dramatic reduced activity. This work provides a new insight into elemental doping study and takes an important step toward the development of ultrathin 2D photocatalysts.
Few‐layer ZnIn2S4 nanosheets with tunable copper doping are used to disclose the origin of optimum and excess doping for photocatalysis at atomic level. Experimental and theoretical evidence reveal that optimal and excess doping is derived from the different local coordination configuration of dopants, extent of distortion, and the change of electronic structure.
Suppression of surface states is one of the general issues for metal oxide photoanodes in water oxidation. For hematite (α-Fe2O3), the surface states are mainly attributed to Fe3+/Fe2+ redox couples ...in oxygen deficient regions (surface oxygen vacancies). To date, most of the passivation overlayers against surface states are metal oxides. However, oxygen vacancies are prevalent for most metal oxides. This is because their formation in metal oxides is often thermodynamically favorable. In contrast, the formation of oxygen vacancies is more energy-consuming when oxygen atoms are covalently bonded. On the basis of this understanding, we propose a new strategy to transform the surface of Fe2O3 into amorphous iron phosphate (denoted “Fe-Pi”), where the oxygen atoms are “covalently fixed” in phosphate (PO4 3–). As a result, the oxygen vacancies are decreased and the surface states are effectively suppressed. The onset potential of corresponding photoanode shifts negatively by 0.15 V and the photocurrent density increases by 4.2 (simulated sunlight) and 4.1 (visible light) times. The suppression of surface states by amorphous Fe-Pi overlayer is then confirmed by series of electrochemical analysis. This work is expected to create new opportunities for optimizing the performance of Fe2O3 and other metal oxide photoanodes.
Earth-abundant red phosphorus was found to exhibit remarkable efficiency to inactivate Escherichia coli K-12 under the full spectrum of visible light and even sunlight. The reactive oxygen species ...(•OH, •O2 –, H2O2), which were measured and identified to derive mainly from photogenerated electrons in the conduction band using fluorescent probes and scavengers, collectively contributed to the good performance of red phosphorus. Especially, the inactivated-membrane function enzymes were found to be associated with great loss of respiratory and ATP synthesis activity, the kinetics of which paralleled cell death and occurred much earlier than those of cytoplasmic proteins and chromosomal DNA. This indicated that the cell membrane was a vital first target for reactive oxygen species oxidation. The increased permeability of the cell membrane consequently accelerated intracellular protein carboxylation and DNA degradation to cause definite bacterial death. Microscopic analyses further confirmed the cell destruction process starting with the cell envelope and extending to the intracellular components. The red phosphorus still maintained good performance even after recycling through five reaction cycles. This work offers new insight into the exploration and use of an elemental photocatalyst for “green” environmental applications.
Molecular oxygen (O2) is activated to reactive oxygen species (ROS) by transferring energy and carriers in the photocatalytic process, which plays an important role in environmental remediation. ...Herein, Cs-doped carbon nitride (CN-xCs, x = 0.2, 0.8, 1) was prepared by CsCl directly inducing the structural reconstruction of carbon nitride (CN), which had obvious molecular oxygen activation ability to promote tetracycline (TC) degradation. Besides, we explored the influence of Cs doping concentration. As a consequence, the doping concentration of Cs was an important factor affecting the activation of O2, which could cause changes in the physical and chemical structure of CN, make O enter the CN structure, form N vacancy defects and cyano groups. In addition, a proper amount of Cs doping could reduce the band gap value, increase the light absorption range, have better charge separation and transfer performance, which could remarkably promote the activation of O2. Benefiting from these advantages, CN-0.8Cs could generate a higher concentration of superoxide radicals (•O2−, 179.30 µmol/L), which was much higher than CN (6.22 µmol/L). Therefore, it exhibited excellent TC degradation photocatalytic performance, and the rate constant k of TC degradation was 0.020 min−1, which was 6.7 times the degradation rate of CN (k = 0.0030 min−1). Furthermore, the possible degradation pathways of TC were proposed based on the results of HPLC-MS.
The doping of Cs broadened the light absorption range of CN, promoted the separation and transfer of electrons, made it have obvious O2 activation ability, and promoted the degradation of TC
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Single‐atom catalysts (SACs) have garnered enormous interest due to their remarkable catalysis activity. However, the exploitation of universal synthesis strategy and regulation of coordination ...environment of SACs remain a great challenge. Herein, a versatile synthetic strategy is demonstrated to generate a series of transition metal SACs (M SAs/NC, M = Co, Cu, Mn; NC represents the nitrogen‐doped carbon) through defect engineering of metal‐organic frameworks (MOFs). The interatomic distance between metal sites can be increased by deliberately introducing structural defects within the MOF framework, which inhibits metal aggregation and consequently results in an approximately 70% increase in single metal atom yield. Additionally, the coordination structures of metal sites can also be facilely tuned. The optimized Co SAs/NC‐800 exhibits superior activity and excellent reusability for the selective hydrogenation of nitroarenes, surpassing several state‐of‐art non‐noble‐metal catalysts. This study provides a new avenue for the universal fabrication of transition metal SACs.
A general metal–organic framework defect engineering strategy is proposed to increase the yield of single‐atom catalysts. This strategy enlarges the distance between metal active sites, effectively hindering the aggregation of metal atoms and affording a 70% improved yield of metal single atoms. The optimized Co SAs/NC‐800 exhibits superior activity and reusability in nitroarene hydrogenation.
Herein, we have reported the CuO micro-polyhedrons with special exposed crystal facet, showing enhanced gas sensing performance based on improved catalytic activation of oxygen. The as-prepared CuO ...showed the uniform shapes of polyhedrons with the size of several micrometers and can be facilely controlled by simply adjusting the precipitants and heating steps. Then, the gas sensitive performance of CuO polyhedrons was evaluated toward typical alcohols at a working temperature of 235 °C. It showed a good sensitivity of n-butanol among several typical alcohols. Moreover, the response value of CuO-m3 (2.43) is significantly higher than that of CuO-m1 (1.92) and CuO-m2 (1.83), which is directly proportional to the exposure degree of (110) crystal facet of CuO. Analysis of mechanism showed that this crystal facet may have the best adsorption capacity of oxygen, thus more reactive oxygen can be generated via a catalytic oxidation process. Our work offered a kind of cheap oxide with exposed facet toward typical alcohols, which is very potential for the development of related industrial sensors.
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The oxygen content of the resulting SiOx ultrafine nanoparticles including two phases (SiO1.35 and SiO0.93) with a Si: O atom ratio of about 1: 1.3, for the first time, are prepared ...by IR laser ablation and used as anode materials for lithium ion battery. The synthesized SiOx ultrafine nanoparticles are utilized as anode material for lithium batteries (LIBs), and show excellent cycling stability and have a capacity is still comparable to that of the commercialized graphite.
•In this work, the oxygen content of the resulting SiOx ultrafine nanoparticles with a Si: O atom ratio of about 1: 1.3, for the first time, are prepared by IR laser ablation and used as anode materials for lithium ion battery.•The large yellow ultrafine SiOx nanoparticles including two phases (SiO1.35 and SiO0.93) are produced at the edge of the ablation area due to the strong heat interaction, when a silicon chip is irradiated by a flat-top high energy infrared laser.•When the synthesized SiOx ultrafine nanoparticles are utilized as anode material for lithium batteries (LIBs), the specific capacity of the electrode is maintained at 344mAhg−1 after 800 cycles. SiOx ultrafine nanoparticles show excellent cycling stability and have a capacity is still comparable to that of the commercialized graphite.
Silicon based materials have been suggested as promising alternative anode materials for their high higher theoretical capacity and lower working potential. As a novel method of preparing ultrafine oxide nanoparticles, laser ablation method provides an important way for the preparation of anode materials for lithium ion batteries. When a silicon chip was irradiated by a flat-top high energy infrared laser, large yellow ultrafine SiOx nanoparticles with high oxygen content were produced at the edge of the ablation area due to the strong heat interaction. The resulting sample had a Si: O atom ratio of 1: 1.3. The results suggested that the ultrafine nanoparticles were composed of two phases: SiO1.35 and SiO0.93. When the synthesized SiOx ultrafine nanoparticles were utilized as anode material for lithium batteries (LIBs), the specific capacity of the electrode gradually increased at a current density of 0.2Ag−1, and delivered a maximum of 438mAhg−1 at the 451th cycle before it stabilized. In the following cycles, there was only sight degradation for specific capacity, and the specific capacity of the electrode was maintained at 344mAhg−1 after 800 cycles.
