Photoexcited Electron Transfer Research Articles

Graphitic C3N4 and Ti3C2 nanocomposites for the enhanced photocatalytic degradation of organic compounds and the evolution of hydrogen under visible irradiation

Graphitic carbon nitride (g-C3N4) and Ti3C2 nanocomposites were formed in aqueous dispersions under ultrasound, by the calcination of the mixtures of solid dicyandiamide (DCDA) and Ti3C2, and of dissolved DCDA and Ti3C2 in an aqueous phase. A heterojunction between g-C3N4 and Ti3C2, based on mutual chemical bonds, was created in all the synthetized materials as observed by X-ray photoelectron spectroscopy and also indicated by the decrease of band bap energies from 2.71 eV to 2.59 eV. The transfer of photoexcited electrons from g–C3N4 to Ti3C2 was documented by photoluminescence spectroscopy.Molecular modelling confirmed an observation provided by scanning electron microscopy that Ti3C2 was not equally dispersed in g-C3N4 but formed separated agglomerates.It was calculated that the interactions of g-C3N4/g-C3N4 and Ti3C2/Ti3C2 layers were stronger than those of g-C3N4/Ti3C2, and the interactions of Ti3C2 functionalized with oxygen were stronger than those of Ti3C2 functionalized with fluorine.The g-C3N4/Ti3C2 nanocomposites were further tested for photocatalytic oxidation reactions, such as the degradation of phenol and ofloxacin, and for reduction reactions, such as the evolution of hydrogen. Ofloxacin was degraded more efficiently (max. 79.4 %) than phenol (max. 20.1 %) during 120 min. The highest hydrogen yield was 76.9 μmol after 4 h of irradiation. All the photocatalytic experiments were performed under visible irradiation and confirmed the electron transfer from g-C3N4 to Ti3C2 enhancing the photocatalytic activity of g-C3N4.

In-plane electric field induced by cyano groups and graphitic carbon structure for enhancing photocatalytic hydrogen production of carbon nitride

Inducing an intrinsic driving force into a two-dimensional semiconductor plane to boost the separation and transfer of photoexcited electrons and holes near the photoexcited sites is an effective way of suppressing the recombination of photogenerated carriers. In this work, a photocatalyst (CN-g-C3N4-C) with in-plane continuous π-conjugated bonds was developed by introducing cyano groups (abbreviated as CN) and graphitic carbon (abbreviated as C) in the in-plane structure of carbon nitride (g-C3N4). Different from traditional interface modulation approaches based on the van der Waals forces or hydrogen bonds, chemical bonds are formed between the cyano groups and graphitic carbon component in the CN-g-C3N4-C atomic junction, which facilitate the efficient migration of photogenerated carriers. The ultra-thin porous lamellar structure of CN-g-C3N4-C not only shortens the carrier transfer distance, but also effectively increases the specific surface area. In the CN-g-C3N4-C plane, the strong in-plane electric field can drive the orderly transfer of photoexcited electrons and holes to the graphitic carbon end and the cyano group end, respectively, resulting in enhanced separation and transfer of the electrons and holes near the photoexcited sites. Due to its high charge carrier separation efficiency, CN-g-C3N4-C possesses excellent photocatalytic activity, and its hydrogen production rate is 14.8 times higher than that of pristine g-C3N4. This work provides an atomic-level strategy for designing efficient and economical photocatalysts.

Engineering cotton fibers with zirconium metal-organic frameworks as a recyclable material for sensing and removing aflatoxins in water

The presence of aflatoxins in natural water bodies has been discovered in more and more countries and regions. The simultaneous removal and detection of aflatoxins are urgently needed to prevent and control their contamination. In this research, water-stable and luminescent zirconium metal-organic frameworks (Zr-LMOFs) were in-situ grown on natural cotton fibers. Then, the as-prepared Zr-LMOFs@Cotton was utilized as a recyclable dual-functional material for removal and detection of aflatoxins in aqueous solutions. The removal efficiency towards different AFB1 concentrations (25–100 µg/L) in irrigation water and rice vinegar reached 92 % and 97 %, respectively. The possible mechanism for efficient removal was investigated and attributed to the synergistic effect of π-π interactions and hydrophobic effect. The Zr-LMOFs@Cotton maintained more than 95 % of its removal efficiency even after 10 cycles. Further, utilizing the Zr-LMOFs@Cotton for visual and semi-automatic removal of the most concerned AFB1 in water samples was verified. Also, the fluorescent Zr-LMOFs@Cotton has been combined with a microplate reader to explore a high throughput method for rapidly detecting aflatoxins. A low detection limit of 0.1 μg/L (0.32 nM) and a wide linear range from 0.05 to 20 mg/L was realized. The efficient quenching of Zr-LMOFs@Cotton by AFB1 resulted from both the inner filter effect and photoexcited electron transfer. The Zr-LMOFs@Cotton could accomplish the simultaneous removal and detection of aflatoxins in 5 min with simple and convenient operations. The excellent absorptivity, stable fluorescence, and easy renewability of the developed Zr-LMOFs@Cotton provides a cost-effective and environment-friendly material and strategy for simultaneously removing and monitoring aflatoxins in liquid samples.

Construction of ZnO@CDs@Co3O4 sandwich heterostructure with multi-interfacial electron-transfer toward enhanced photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into small-molecule chemical feedstocks can meet the growing demand for energy and alleviate the global warming. Herein, a p-n ZnO@CDs@Co3O4 heterojunction with sandwich structure was constructed by calcination method of self-assembled ZIF-8@CDs@ZIF-67. The ZnO@CDs@Co3O4 with well-defined interfacial structure exhibited the significantly enhanced photocatalytic CO2 reduction activity, and the optimal catalyst indicated the (CO + CH4) evolution rate of 214.53 µmol g−1 h−1 under simulated solar light, which was superior to ZnO, Co3O4 and binary ZnO@Co3O4. The internal cavity, exposed active sites, multiple interfaces and constructed p-n heterojunction can facilitate the light harvesting and photoexcited electron transfer. Besides, after introduction of CDs placed in the middle layer between ZnO and Co3O4, CDs with excellent photoelectric property further promoted charge separation and migration. This work represents an appealing strategy to construct well-defined photocatalysts for boosting CO2 photoreduction.

Position-selected cocatalyst modification on a Z-scheme Cd0.5Zn0.5S/NiTiO3 photocatalyst for boosted H2 evolution

Photocatalytic water splitting by semiconductors is a promising technology to produce clean H2 fuel, but the efficiency is restrained seriously by the high overpotential of the H2-evolution reaction together with the high recombination rate of photoinduced charges. To enhance H2 production, it is highly desirable yet challenging to explore an efficient reductive cocatalyst and place it precisely on the right sites of the photocatalyst surface to work the proton reduction reaction exclusively. Herein, the metalloid NixP cocatalyst is exactly positioned on the Z-scheme Cd0.5Zn0.5S/NiTiO3 (CZS/NTO) heterostructure through a facile photodeposition strategy, which renders the cocatalyst form solely at the electron-collecting locations. It is revealed that the directional transfer of photoexcited electrons from Cd0.5Zn0.5S to NixP suppresses the quenching of charge carriers. Under visible light, the CZS/NTO hybrid loaded with the NixP cocatalyst exhibits an optimal H2 yield rate of 1103 μmol h−1 (i.e., 27.57 mmol h−1 g−1), which is about twofold of pristine CZS/NTO and comparable to the counterpart deposited with the Pt cocatalyst. Besides, the high apparent quantum yield (AQY) of 56% is reached at 400 nm. Further, the mechanisms of the cocatalyst formation and the H2 generation reaction are discussed in detail.

(Invited) Coupling Metal-Organic Framework with Oxide Photocatalyst for Selective Photoredox Reactions

Oxide photocatalyst is one of the major groups of photoactive semiconductors capable of facilitating useful photoredox reactions for a variety of energy and environmental-related applications. The intrinsic optical and electronic properties of oxide photocatalysts encounter a number of limitations. Often, the wide band gap and inferior photoexcited charge transportation within oxide semiconductors are highlighted. Wide band gap limits the light absorption while inadequate charge transport properties such as low charge mobility and short lifetime can only afford mild photoactivities. Strategies have been formulated to improve the performance of these semiconductors in order to bridge the gap for practical use. Among many existing strategies, coupling oxide photocatalysts with metal-organic framework (MOF) has gained attention in the community as one potential method to improve performance (e.g. higher light absorption, better product yield, prolonged stability and etc). Attaching photoactive MOFs onto or “doping” metallic element into oxide photocatalyst may extend the light absorption of the composite materials. Improved product yield is, more often, attributed to the adsorption capacity of MOFs towards reactant, which bring about the localised concentration of reactants adjacent to active sites of photocatalyst. Encapsulation of oxide photocatalyst by MOFs can suppress the undesirable side reactions (such as preventing Cu2O from direct contact with moisture) to prolong the stability of oxide photocatalyst.In this presentation, in addition to the above mentioned advantages of MOFs, the role of MOFs in tuning the selectivity of product formation will also be examined and discussed. Figure 1 shows an example of improved selective oxidation of ethanol to form acetaldehyde using ZIF-8 encapsulated ZnO. Selectivity towards acetaldehyde has been improved from ~79% to ~92% with stable photocatalytic activity.1 In another work, Cu2O covered by Cu-MOF has afforded selective CO2 photoreduction to CH4.2 We believe there is charge interaction between the oxide photocatalyst and the adjacent MOF structure. Transfer of photoexcited electrons from the conduction band of Cu2O to the LUMO level of non-excited wide band gap Cu-MOF has been indicated using time-resolved photoluminescence. Because photocatalytic reactions are the results of electron transfer between photocatalyst and reactants, the presence of photocharge interplay between oxide photocatalyst and MOFs may provide new room for exploration as it has demonstrated significant influence in the selectivity of product formation. Figure 1. Example of improved product selectivity by incorporating MOFs to oxide photocatalyst. The left figure indicates the improved formation of acetaldehyde from photocatalytic ethanol oxidation. The right figure shows the reasonable stability of the MOF-oxide photocatalyst under illumination. Reference: H. Wu, T. H. Tan, R. Liu, H. -Y. Hsu, Y. H. Ng, Selective Ethanol Oxidation to Acetaldehyde on Nanostructured Zeolitic Imidazolate Framework-8-wrapped ZnO Photothermocatalyst Thin Films, Solar RRL 2021, 5, 2000423.H. Wu, X. Y. Kong, X. Wen, S. –P. Chai, E. C. Lovell, J. Tang, Y. H. Ng, Metal-Organic Framework Decorated Cuprous Oxide Nanowires for Long-lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4. Angew. Chem. Int. Ed. 2021, 60, 8455-8459. Figure 1

Design of porphyrin-based frameworks for efficient visible light-promoted reduction of CO2 from dilute gas: Combined experimental and theoretical investigation

The photocatalytic carbon dioxide reduction (CO2R) coupled with hydrogen evolution reaction (HER) constitutes a promising step for a sustainable generation of syngas (CO + H2), an essential feedstock for the preparation of several commodity chemicals. Herein, visible light/sunlight-promoted catalytic reduction of CO2 and protons to syngas using rationally designed porphyrin-based 2D porous organic frameworks, POF(Co/Zn) is demonstrated. Indeed, POF(Co) showed superior catalytic performance over the Zn counterpart with CO and H2 generation rates of 1104 and 3981 μmol g−1h−1, respectively. The excellent catalytic performance of Co-based POF is aided by the favorable transfer of photo-excited electrons from Ru-sensitizer to the CoII catalytic site, which is not feasible in the case of POF(Zn), revealed from the theoretical investigation. More importantly, the POF(Co) catalyzes the reduction of CO2 even from dilute gas (13% CO2), surpassing most reported framework-based photocatalytic systems. Significantly, the catalytic performance of POF(Co) was increased under natural sunlight conditions suggesting sunlight-promoted enhancement in syngas generation. The in-depth theoretical investigation further unveiled the comprehensive mechanistic pathway of the light-promoted concurrent CO and H2 generation. This work showcases the advantages of porphyrin-based frameworks for visible light/sunlight-promoted syngas generation by utilizing greenhouse gas (CO2) and protons under mild eco-friendly conditions.

Growth of tunable Au-BaO@TiO2/CdS heterostructures: Acceleration of hydrogen evolution from water splitting

The need for efficient and sustainable catalysts to generate clean energy through water splitting is a requirement of the current era. In this study, TiO2/CdS heterostructures were synthesized using hydrothermal reaction. To enhance the photocatalytic performances of TiO2/CdS, BaO and Au were in-situ deposited via chemical reduction and hydrothermal treatment at 165 °C for 6 h. Finally Au-BaO@TiO2/CdS catalysts were synthesized for photocatalytic hydrogen generation from water splitting. The optical and structural properties of catalysts were examined with FT-IR, XRD, Raman and UV–Vis-DRS techniques. The morphology and chemical properties of catalysts were obtained using EDX, AFM, XPS and SEM techniques. Photoreaction and H2 production activities were monitored at Pyrex reactor (150 mL) and GC-TCD (Shimadzu-2014). The tunable fabrication approach provides a novel strategy for tailoring the properties of TiO2/CdS heterostructures, allowing for optimization of their photocatalytic performance. The enhanced surface plasmon impact achieved through Au-NPs incorporation opens up new possibilities for improving the efficiency. The results demonstrate that Au-BaO@TiO2/CdS catalysts exhibit significantly higher H2 generation activity (13.54 mmol g−1h−1). This H2 evolution activity was found higher than other catalysts i.e. TiO2/CdS, BaO@TiO2/CdS and Au@TiO2/CdS. Higher catalytic activity in case of Au-BaO@TiO2/CdS was attributed to the co-existence of BaO and Au-NPs. The Au-NPs provide hot electrons (via SPR effect) that increase the electron pool over the surfaces of TiO2/CdS heterostructures. During photoreaction, BaO assists the transfer of photoexcited electrons from TiO2/CdS system to the active centers (i.e. Au cocatalysts). In addition, various factors that affect the H2 production rates (i.e. pH, temperature, catalyst dose and effect of light intensity) were evaluated and discussed.

Multiple Heteroatom‐Hydrogen Bonds Bridging Electron Transport in Covalent Organic Framework‐Based Supramolecular System for Photoreduction of CO2

AbstractSupramolecular systems consisting of covalent organic frameworks (COFs) and Ni complex are designed for robust photocatalytic reduction of CO2. Multiple heteroatom‐hydrogen bonding between the COF and Ni complex is identified to play a decisive role in the photoexcited electron transfer across the liquid‐solid interface. The diminution of steric groups on COF or metal complex can optimize catalytic performance, which is more attributable to the enhanced hydrogen‐bond interaction rather than their intrinsic activity. The photosystem with relatively strong strength of hydrogen bonds exhibits remarkable photocatalytic CO2‐to‐CO conversion, far superior to photosystems with supported atomic Ni or metal complex alone in the absence of hydrogen‐bond effect. Such heteroatom‐hydrogen bonds bridging electron transport pathway confers supramolecular system with high photocatalytic performance, providing an avenue to rationally design efficient and steadily available photosystems.

Multiple Heteroatom-Hydrogen Bonds Bridging Electron Transport in Covalent Organic Framework-Based Supramolecular System for Photoreduction of CO2.

Supramolecular systems consisting of covalent organic frameworks (COFs) and Ni complex are designed for robust photocatalytic reduction of CO2 . Multiple heteroatom-hydrogen bonding between the COF and Ni complex is identified to play a decisive role in the photoexcited electron transfer across the liquid-solid interface. The diminution of steric groups on COF or metal complex can optimize catalytic performance, which is more attributable to the enhanced hydrogen-bond interaction rather than their intrinsic activity. The photosystem with relatively strong strength of hydrogen bonds exhibits remarkable photocatalytic CO2 -to-CO conversion, far superior to photosystems with supported atomic Ni or metal complex alone in the absence of hydrogen-bond effect. Such heteroatom-hydrogen bonds bridging electron transport pathway confers supramolecular system with high photocatalytic performance, providing an avenue to rationally design efficient and steadily available photosystems.

Inserting Bi atoms on the [WO6] framework: Photochromic WO3/Bi2WO6 nanoparticles enable visual sunlight UV sensing

Photochromic tungsten oxide (WO3) offers incredible prospects for protecting human health by visually sensing ultraviolet (UV) radiation exposure from sunlight. Heterojunction engineering can improve the charge carrier separation efficiency in the photochromic procedure to implement this possibility, but it suffers from the finiteness of crystal phase interfacial contact and/or the complexity of synthetic protocols. Here, the construction of an atomic-scale crystal/amorphous WO3/Bi2WO6 nanoparticle results from introducing Bi atoms on the [WO6] framework to form [Bi2O2] components for in-situs incorporating Bi2WO6 into the WO3 matrix. The absence of well-defined interfaces in WO3/Bi2WO6 type II heterostructures ensures an efficient photoexcited electrons transfer from Bi2WO6 to WO3; abundant WO6 units serve as the sites for rapid capture and consumption of photogenerated electrons to facilitate electron-hole separation. Complexing the efficient photochromic products with hydroxyethyl cellulose, the WO3/Bi2WO6-based photochromic films (PCFs) and a colorimetric card indicating different UV intensities are developed. The invisible UV rays are converted into visible color changes; thus, the UV radiation intensity can be estimated from the dark change in the colored PCFs. This work presents a way to elevate the carrier utilization efficiency in WO3 and delivers candidates for exploring efficient and cost-effective UV radiation sensors.

Atomic Cobalt-Silver Dual-Metal Sites Confined on Carbon Nitride with Synergistic Ag Nanoparticles for Enhanced CO2 Photoreduction.

Photocatalytic reduction of CO2 to value-added solar fuels is of great significance to alleviate the severe environmental and energy crisis. Herein, we report the construction of a synergistic silver nanoparticle catalyst with adjacent atomic cobalt-silver dual-metal sites on P-doped carbon nitride (Co1Ag(1+n)-PCN) for photocatalytic CO2 reduction. The optimized photocatalyst achieves a high CO formation rate of 46.82 μmol gcat-1 with 70.1% selectivity in solid-liquid mode without sacrificial agents, which is 2.68 and 2.18-fold compared to that of exclusive silver single-atom (Ag1-CN) and cobalt-silver dual-metal site (Co1Ag1-PCN) photocatalysts, respectively. The closely integrated in situ experiments and density functional theory calculations unravel that the electronic metal-support interactions (EMSIs) of Ag nanoparticles with adjacent Ag-N2C2 and Co-N6-P single-atom sites promote the adsorption of CO2* and COOH* intermediates to form CO and CH4, as well as boost the enrichment and transfer of photoexcited electrons. Moreover, the atomically dispersed dual-metal Co-Ag SA sites serve as the fast-electron-transfer channel while Ag nanoparticles act as the electron acceptor to enrich and separate more photogenerated electrons. This work provides a general platform to delicately design high-performance synergistic catalysts for highly efficient solar energy conversion.

Photocatalytic performance of pyrochar and hydrochar in heterojunction photocatalyst for organic pollutants degradation: Activity comparison and mechanism insight

Biochar-based photocatalysts have attracted widespread attention for the remediation of organic pollutants in water. Herein, we have successfully prepared Bi2WO6/TiO2 heterojunction photocatalysts modified by pyrochar (HC) and hydrochar (PC) to illustrate the role of two different biochar in the system. HC had a higher O elemental content and a larger specific surface area compared to PC. Under the visible light irradiation, PC with persistent radicals could facilitate the production of ·OH during the photocatalytic reaction, while the HC promoted the production of ·O2– due to the presence of oxygen-containing functional groups, which made the Bi2WO6/TiO2/HC exhibit superior photocatalytic property for sulfathiazole (STZ) degradation. The results of characterization revealed that PC could act as an electron shuttle to facilitate photo-excited electron transfer. For HC, the oxygen-containing functional groups (OFGs) could act as photosensitizers while the particles with rod structure function as an electron carrier, which could synergistically promote the photocatalytic degradation of sulfathiazole with Bi2WO6/TiO2 heterojunction. Surprisingly, the real water experiments, luminescent bacterial test, and Toxicity Estimation Software Tool program indicated that Bi2WO6/TiO2/HC and Bi2WO6/TiO2/PC exhibited excellent practicality and reduced toxicity, which could provide a prospering strategy and insight into the design of efficient biochar-based photocatalysts for environmental remediation.

In-situ growth of C-F@CCS@ZIF8/67–1/1 photocatalysts with internal electric field and interfacial enhancement on cobalt-copper foam surface for simultaneous removal of ciprofloxacin and Cr(VI)

ZIF8/67–1/1 and CuCo2S4 were grown on the surface of cobalt-copper foam by in-situ growth method, and p-n heterostructures were formed by induction of internal electric field. The DFT calculation reveals that the energy levels near the Fermi level are gradually distributed continuously after ZIF8/67–1/1 and CuCo2S4 recombination, which accelerates electron conduction. Furthermore, the electron orbitals in the composite structure are reallocated and the electrical conductivity of the interface is improved. This strong interfacial enhancement promotes the transfer of photoexcited electrons and promotes the photoinduced separation of electron-hole pairs. Thanks to the surface oxygen vacancy and unique structure, C-F@CCS@ZIF8/67–1/1 composites can simultaneously achieve 97.2% ciprofloxacin (CIP) degradation and 96.5% Cr(VI) reduction. This catalyst does not require any recycling process and remains structurally stable during use with only a minimal amount of metal leaching. This work also reveals the mechanism of heterojunction formation between metal-organic frameworks and sulfides, broadening their application potential.

Single-atom cobalt-incorporating carbon nitride for photocatalytic solar hydrogen conversion: An X-ray spectromicroscopy study

The use of carbon nitride-based materials and light to drive catalytic water splitting has enormous potential for the production of hydrogen. Revealing the processes of molecular conjugation, nucleation, and crystallization in crystalline carbon nitride is expected to enhance the photocatalytic activity through the creation of isotype heterojunctions and active sites. In this work, the addition of cobalt salts in ionothermal synthesis was found to promote the phase transition of heptazine-based crystalline carbon nitride (CCN) to triazine-based poly (triazine imide) (PTI), resulting in the formation of a single-atom cobalt-doped coordinated isotype CCN/PTI heterojunction. The new hybrid orbital modulates the atomic/electronic structure and the band gap of the CCN/PTI heterojunction, and synergistically increases the absorption of visible light, accelerating the separation and transfer of photoexcited electrons and holes. Synchrotron-based X-ray spectroscopy and microscopy are used to identify the origin of the improved performance of the single-atom cobalt-doped CCN/PTI heterojunction in the photocatalytic hydrogen evolution reaction. This work demonstrates that synchrotron X-ray spectroscopy is a promising tool for designing materials aimed at enhancing photocatalytic activity in solar energy conversion applications.

Highly sensitive photodetector based on two-dimensional ferroelectric semiconducting β-InSe/graphene heterostructure

A 2D ferroelectric β-InSe/graphene heterostructure was fabricated by mechanical exfoliation, and the carrier dynamics crossing the heterostructure interface has been systematically investigated by Raman, photoluminescence, and transient absorption measurements. Due to the efficient interfacial photo excited electron transfer and photogating effect from trapped holes, the heterostructure devices demonstrate superior performance with a maximum responsivity of 2.12 × 104 A W−1, detectivity of 1.73 × 1014 Jones, and fast response time (241 μs) under λ = 532 nm laser illumination. Furthermore, the photo responses influenced by the ferroelectric polarization field are investigated. Our work confirms a ferroelectric β-InSe/graphene heterostructure as an outstanding material platform for sensitive optoelectronic applications.

Ultrafast Electron Transfer in Au–Cyanobacteria Hybrid for Solar to Chemical Production

The rise of inorganic–biohybrid organisms for solar-to-chemical production has spurred mechanistic investigations into the dynamics of the biotic–abiotic interface to drive the development of next-generation hybrid systems. The model system, cyanobacteria–gold nanoparticle hybrids, combines a light harvester with a photosynthetic bacterium to drive the reduction of CO2 to glycerol with improved efficiency and increased glycerol production by 14.6%, in comparison to cyanobacteria only. In this work, we report insights into this unique photochemical behavior and propose a charge-transfer pathway from Au nanoparticle to cyanobacteria. Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates are on the order of a few ps to the potential electron acceptor in photosystem II. This work represents a promising platform to utilize a conventional spectroscopic methodology to extract insights from more complex biotic–abiotic hybrid systems.

Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer.

Photoinduced charge transfer in van der Waals heterostructures occurs on the 100 fs timescale despite weak interlayer coupling and momentum mismatch. However, little is understood about the microscopic mechanism behind this ultrafast process and the role of the lattice in mediating it. Here, using femtosecond electron diffraction, we directly visualize lattice dynamics in photoexcited heterostructures of WSe2/WS2 monolayers. Following the selective excitation of WSe2, we measure the concurrent heating of both WSe2 and WS2 on a picosecond timescale-an observation that is not explained by phonon transport across the interface. Using first-principles calculations, we identify a fast channel involving an electronic state hybridized across the heterostructure, enabling phonon-assisted interlayer transfer of photoexcited electrons. Phonons are emitted in both layers on the femtosecond timescale via this channel, consistent with the simultaneous lattice heating observed experimentally. Taken together, our work indicates strong electron-phonon coupling via layer-hybridized electronic states-a novel route to control energy transport across atomic junctions.

The photoexcited electron transfer and photocatalytic mechanism of g-C3N4/TiO2 heterojunctions: Time-domain ab initio analysis

The control of the carrier migration in the semiconductor heterojunctions is still one of the biggest challenges for the performance improvement of photocatalysts. In this paper, we systematically studied the carrier transfer of g-C3N4/A-TiO2 (anatase) and g-C3N4/R-TiO2 (rutile) by using non-adiabatic molecular dynamics. It has been shown that the g-C3N4 could form stable interfaces with A-TiO2(101) or R-TiO2(110). Electrons migrated from the CB of TiO2 to the VB of g-C3N4 in the g-C3N4/A-TiO2 and formed a typical S-scheme heterojunction, which benefited the electron-hole recombination on the VB of g-C3N4 to relieve hole accumulation and increased the photocatalytic efficiency. In contrast, the g-C3N4/R-TiO2, a typical Type-II heterojunction, had no such notable feature. By comparing with the VB and CB edge potentials of the normal hydrogen electrode (NHE), it was found that the photoexcited electrons and holes of the g-C3N4/A-TiO2 could reduce H+ to H2 and product O2, respectively, while g-C3N4/R-TiO2 only had a better ability to produce O2. The effective tuning of the charge transfer and bandgap of the g-C3N4/TiO2 by applying electric field was also explored. We believed that these findings not only demonstrated the advantages of S- scheme heterojunctions over Type-II heterojunctions, but also facilitated the rational design of better photocatalysts.

Efficient adsorption-photodegradation activity of MoS2 coupling with S,N-codoped porous biochar derived from chitosan

To extend the adsorption-photocatalytic application of biochar in wastewater purification, S-defected MoS2 coupling with S,N-codoped porous biochar (MoS2/SN-BC) was prepared from chitosan via the in-situ sulfurization. Compared with S-doped biochar (S-BC) and S,N-codoped biochar (SN-BC), MoS2/SN-BC has better adsorption and photocatalytic activities for tetracycline hydrochloride (TCH). The removal efficiency of TCH over optimal 3-MoS2/SN-BC with a Mo content of 12.69 % is 97.99 % for 180 mg L−1 within 120 min, and the tested adsorption capacity is 382.43 mg g−1. The adsorption-photocatalytic activity of 3-MoS2/SN-BC slightly declines after five cycles. The adsorption isotherm and kinetics of 3-MoS2/SN-BC follow the Langmuir and second order models, respectively. The abundant edge-sites favor TCH molecules adsorption and photons capture, and the tight junction interface between S-defected MoS2 and S,N-codoped porous biochar promotes the photo-excited electrons transfer and mobility.