Photocatalysis is considered as one of the promising routes to solve the energy and environmental crises by utilizing solar energy. Graphitic carbon nitride (g‐C3N4) has attracted worldwide attention ...due to its visible‐light activity, facile synthesis from low‐cost materials, chemical stability, and unique layered structure. However, the pure g‐C3N4 photocatalyst still suffers from its low separation efficiency of photogenerated charge carriers, which results in unsatisfactory photocatalytic activity. Recently, g‐C3N4‐based heterostructures have become research hotspots for their greatly enhanced charge carrier separation efficiency and photocatalytic performance. According to the different transfer mechanisms of photogenerated charge carriers between g‐C3N4 and the coupled components, the g‐C3N4‐based heterostructured photocatalysts can be divided into the following categories: g‐C3N4‐based conventional type II heterojunction, g‐C3N4‐based Z‐scheme heterojunction, g‐C3N4‐based p–n heterojunction, g‐C3N4/metal heterostructure, and g‐C3N4/carbon heterostructure. This review summarizes the recent significant progress on the design of g‐C3N4‐based heterostructured photocatalysts and their special separation/transfer mechanisms of photogenerated charge carriers. Moreover, their applications in environmental and energy fields, e.g., water splitting, carbon dioxide reduction, and degradation of pollutants, are also reviewed. Finally, some concluding remarks and perspectives on the challenges and opportunities for exploring advanced g‐C3N4‐based heterostructured photocatalysts are presented.
g‐C3N4‐based heterostructured photocatalysts have become research hotspots for their greatly enhanced charge carrier separation efficiency and photocatalytic performance. g‐C3N4‐based conventional type II heterojunction, g‐C3N4‐based Z‐scheme heterojunction, g‐C3N4‐based p–n heterojunction, g‐C3N4/metal heterostructure, and g‐C3N4/carbon heterostructure have been widely reported in recent years. This review summarizes the design principles, preparation methods, charge transfer mechanism, and photocatalytic applications of these g‐C3N4‐based heterostructured photocatalysts.
Single-atom Fe-N-C catalysts has attracted widespread attentions in the oxygen reduction reaction (ORR). However, the origin of ORR activity on Fe-N-C catalysts is still unclear, which hinder the ...further improvement of Fe-N-C catalysts. Herein, we provide a model to understand the ORR activity of Fe-N
site from the spatial structure and energy level of the frontier orbitals by density functional theory calculations. Taking the regulation of divacancy defects on Fe-N
site ORR activity as examples, we demonstrate that the hybridization between Fe 3dz
, 3dyz (3dxz) and O
π* orbitals is the origin of Fe-N
ORR activity. We found that the Fe-O bond length, the d-band center gap of spin states, the magnetic moment of Fe site and *O
as descriptors can accurately predict the ORR activity of Fe-N
site. Furthermore, these descriptors and ORR activity of Fe-N
site are mainly distributed in two regions with obvious difference, which greatly relate to the height of Fe 3d projected orbital in the Z direction. This work provides a new insight into the ORR activity of single-atom M-N-C catalysts.
Exploring cheap and efficient cocatalysts for enhancing the performance of photocatalysts is a challenge in the energy conversion field. Herein, 2D ultrathin Ti3C2 nanosheets, a kind of MXenes, are ...prepared by etching Ti3AlC2 with subsequent ultrasonic exfoliation. A novel 2D/2D heterojunction of ultrathin Ti3C2/Bi2WO6 nanosheets is then successfully prepared by in situ growth of Bi2WO6 ultrathin nanosheets on the surface of these Ti3C2 ultrathin nanosheets. The resultant Ti3C2/Bi2WO6 hybrids exhibit a short charge transport distance and a large interface contact area, assuring excellent bulk‐to‐surface and interfacial charge transfer abilities. Meanwhile, the improved specific surface area and pore structure endow Ti3C2/Bi2WO6 hybrids with an enhanced CO2 adsorption capability. As a result, the 2D/2D heterojunction of ultrathin Ti3C2/Bi2WO6 nanosheets shows significant improvement on the performance of photocatalytic CO2 reduction under simulated solar irradiation. The total yield of CH4 and CH3OH obtained on the optimized Ti3C2/Bi2WO6 hybrid is 4.6 times that obtained on pristine Bi2WO6 ultrathin nanosheets. This work provides a new protocol for constructing 2D/2D photocatalytic systems and demonstrates Ti3C2 as a promising and cheap cocatalyst.
A 2D/2D heterojunction of ultrathin Ti3C2/Bi2WO6 nanosheets with several atomic layers is constructed, showing remarkably enhanced performance toward photocatalytic CO2 reduction. The Ti3C2/Bi2WO6 2D/2D heterojunction possesses a large interface contact area and a quite short charge transport distance, leading to efficient bulk‐to‐surface and interfacial electron transfer. Moreover, the 2D/2D heterojunction possesses a distinctly enhanced CO2 adsorption capability, which further boosts the photocatalytic reactions.
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Photocatalytic carbon dioxide (CO2) reduction to obtain hydrocarbon solar fuels is one of the promising strategies to solve energy crisis and complement carbon cycle. However, the low ...activity and poor product selectivity greatly limit its practical application. Tuning product selectivity is of great significance to improve the yield of target product and deepen the understanding of CO2 reduction reaction mechanism. In this review, we firstly summarize the widely accepted pathways of photocatalytic CO2 reduction reactions. Secondly, important factors affecting product selectivity are analyzed, mainly including light-excitation attributes, band structure of photocatalysts, separation of photogenerated charge carriers, adsorption/activation of reactants, surface active sites of catalytic reaction, and adsorption/desorption of intermediates. Finally, the challenges and perspectives in developing photocatalysts with high CO2 reduction efficiency and product selectivity are presented.
Microstructure, corrosion behavior and evolution of hot-rolled high-carbon–chromium bearing steel were investigated using scanning electron microscopy and energy dispersive spectrometer (EDS). The ...results show that corrosion initiates adjacent to the network carbide, which is the initial austenite grain boundary. With the further increase in corrosion time, corrosion fraction is increased and extended into the grains. Finally, the whole grain near the network carbide is etched off and the grain boundary is detached from the sample, which forms the corroded holes. Based on the EDS analyses, it is confirmed that this corrosion behavior is resulted from the depletion of Cr as solid solute at the grain boundary. The depletion of Cr is the result of the formation of Cr carbide near the grain boundary.
In the present work, a general and simple approach to determine texture patterns using pole figure was developed. For the rolled materials, the rolling plane can be determined by the ratio of OP/R in ...the given pole figure. Here, OP is the length from the center to an arbitrary pole in the pole figure, and R is the radius of the projection circle in the pole figure. Rolling direction for the rolled materials or the extrusion direction for the extruded materials can be directly calculated using the coordinate values of the poles in the given pole figure. For cubic and hexagonal materials, the calculated results using the developed approach are in agreement with the standard stereographic projection pole figures. The textures in the rolled and annealed Fe–17Cr ferritic stainless steel and extruded Mg–2Mn alloy were examined by electron backscatter diffraction and X-ray diffraction. The proposed approach was applied to determine texture patterns in the above two materials. It was found that {111} type of γ-fiber texture develops for the as-annealed Fe–17Cr ferritic stainless steel and + <10−10> double fiber texture develops for the extruded Mg–2Mn alloy.
Abstract
Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN
4
site usually exhibits an ...unsatisfactory ORR activity due to its poor O
2
adsorption and activation. Here, we report an axial Fe–O coordination induced electronic localization strategy to improve its O
2
adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe–O coordination evokes the electronic localization among the axial direction of O–FeN
4
sites to enhance O
2
adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mössbauer spectra validate Fe–O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O
2
adsorption and activation with an ultralow Tafel slope of 27.5 mV dec
−1
and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance.
Carbon neutral becomes one of the most important environmental goals due to the excessive emission of CO
2
. The reduction of CO
2
into valuable chemicals or fuels is one of the important strategies ...to solve the carbon cycle and achieve carbon neutral. Atomic site catalysts show high activity and selectivity in CO
2
reduction reactions. However, due to the complexity of the multistep CO
2
reduction reaction, it is difficult for an isolated atomic site to achieve multi-functional requirements. Bimetallic atomic site catalysts can take advantage of the high activity and selectivity of atomic sites, and the synergies between bimetallic atomic sites can fully optimize the CO
2
reduction reactions. In this review, firstly, we summarize the design considerations of catalysts for CO
2
reduction reactions. Secondly, the preparation and characterization of bimetallic atomic site catalysts are reviewed. Thirdly, the role of bimetallic atomic sites in CO
2
reduction reactions was analyzed in detail.
Microstructure and mechanical properties of the as-annealed Ti-stabilized Fe-17Cr ferritic stainless steel were investigated by scanning electron microscopy (SEM), electron backscatter diffraction ...(EBSD) and tensile tests. Experimental results show that the size of the ferrite grain in the Fe-17Cr stainless steel is about 40 µm after rolling and annealing. Orientation distribution function (ODF) by EBSD indicates that nearly homogeneous {111} annealing texture is produced in the annealed sheets. Pole figures (PF) by EBSD show that Kurdjumov–Sachs orientation relationship between the TiN particles and ferrite grains is established in the as-annealed microstructure. Tensile tests demonstrate that the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the as-annealed Ti-stabilized Fe-17Cr ferritic stainless steel are 319 MPa, 626 MPa, and 36.5%, respectively. In the SEM micrograph of the fracture, deep dimples can be observed and TiN particles can be found in the core of the dimples, which indicates that the samples undergo large deformation before fracture.
Abstract
Atomically dispersed transition metals on carbon-based aromatic substrates are an emerging class of electrocatalysts for the electroreduction of CO
2
. However, electron delocalization of ...the metal site with the carbon support via d-π conjugation strongly hinders CO
2
activation at the active metal centers. Herein, we introduce a strategy to attenuate the d-π conjugation at single Ni atomic sites by functionalizing the support with cyano moieties. In situ attenuated total reflection infrared spectroscopy and theoretical calculations demonstrate that this strategy increases the electron density around the metal centers and facilitates CO
2
activation. As a result, for the electroreduction of CO
2
to CO in aqueous KHCO
3
electrolyte, the cyano-modified catalyst exhibits a turnover frequency of ~22,000 per hour at −1.178 V versus the reversible hydrogen electrode (RHE) and maintains a Faradaic efficiency (FE) above 90% even with a CO
2
concentration of only 30% in an H-type cell. In a flow cell under pure CO
2
at −0.93 V versus RHE the cyano-modified catalyst enables a current density of −300 mA/cm
2
with a FE above 90%.
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