Photoexcited Electron Transfer Research Articles

Photochromism in the periodic nanospace of zeolite LTA by the transfer of photoexcited electrons of adsorbed Na atoms.

Cationic sodium (Na) clusters incorporated into a dehydrated Na-form LTA (Na-LTA) zeolite by the adsorption of Na atoms exhibit diamagnetism regardless of their adsorption amount. These clusters preferentially form in β-cages under the condition of dilute adsorption. In this study, photochromism was observed on the dilute Na-adsorbed Na-LTA, which showed a color change from yellow-green to dark blue-green at room temperature. This phenomenon resulted in dissociation of the diamagnetic Na clusters in β-cages upon light irradiation and thereby in the formation of two metastable Na43+ clusters with C3v symmetry in α-cages from the photoabsorption and electron spin resonance spectra. We also observed photochromism in a sample of insufficiently dehydrated Na-LTA with dilute Na adsorption-i.e., the initial white color changed to blue, then blue-green and finally dark moss-green upon irradiation with UV light. This phenomenon consists of two steps. First, products in the β-cages, formed by the reaction of residual water molecules with adsorbed Na atoms, release electrons upon irradiation. The electrons transfer to the α-cages, forming the metastable Na43+ clusters. Next, the diamagnetic Na clusters are formed in vacant β-cages by the thermal transfer of electrons from the Na43+ clusters in the α-cages. Na clusters including multiple electrons were also formed in the α-cages by long exposure to UV light irradiation, which had a similar effect to increasing the adsorption amount of Na atoms onto the dehydrated Na-LTA. After termination of irradiation, the sample required a week to change its color to light yellow.

(Invited) All-Solid-State Z-Scheme Overall Water-Splitting Photocatalysts for Effective Utilization of Solar Energy

Since Fujishima and Honda reported photoelectrochemical water splitting using a TiO2 electrode in 1972 [1], solar hydrogen (H2) from water using a photocatalyst has attracted attention as a clean energy resource. Most recent research has been focusing on the visible-light sensitization of catalysts to effectively utilize solar energy. Our group has investigated water-splitting photocatalysts that are able to utilize the whole range of visible light and even infrared light on the basis of material designs and mechanistic approaches. We successfully created a solid-state hetero-junction photocatalyst, following a conventional well-known Z-scheme mechanism [2], but the present photocatalyst did not require any chemicals as a redox mediator. The solid-state hetero-junction photocatalyst is silver (Ag) inserted zinc rhodium oxide (ZnRh2O4 (ZRO), bandgap energy (E g) of 1.2 eV) and bismuth vanadate (Bi4V2O11 (BVO), E g of 1.7 eV), abbreviated to ZRO/Ag/BVO, where Ag, ZRO, and BVO act as an electron mediator, H2-evolution photocatalyst, and oxygen (O2)-evolution photocatalyst, respectively [3,4]. Overall water splitting, liberating H2 and O2 simultaneously from pure water at a stoichiometric ratio 2 to 1, was accomplished using ZRO/Ag/BVO irradiated with red light at wavelengths of up to 740 nm. This system functioned via the inserted Ag which could transfer photoexcited electrons from the conduction band (CB) of BVO to the valence band (VB) of ZRO. The photoexcited electrons in the CB of ZRO and photogenerated holes in the VB of BVO can effectively reduce and oxidize water, respectively, producing H2 and O2 at a molar ratio of 2 to 1.In place of BVO, silver vanadium oxide (Ag2V4O11 (AVO), E g of 1.4 eV) was utilized to directly connect to ZRO, forming ZRO/BVO. ZRO/BVO accomplished overall pure-water splitting under irradiation with near-infrared light at wavelengths of up to 910 nm. The key point without an electron mediator is that the CB potential of AVO is almost the same as the VB top potential of ZRO [5]. Thus, photoexcited electrons transfer smoothly from the CB of AVO to the VB of ZRO.Notably, both ZRO/Ag/BVO and ZRO/AVO systems did not include a cocatalyst, which is inevitably required for the water splitting reaction due to the increase in the lifetime of electron-and-hole pairs and storing either electrons or holes. Thus, to enhance the water splitting activity, we tried to load a cocatalyst, platinum (Pt), Ag or copper (Cu), selectively onto the H2-evolution photocatalyst, ZRO, in ZRO/Ag/BVO to enhance the photosensitivity of this system. The loading of Pt, Ag, or Cu was performed by a photo-deposition method under light irradiation at wavelength longer than 850 nm. Under the irradiated light condition, only ZRO was photo-excited because the energy of irradiated light was higher than the E g of ZRO (1.2 eV) but smaller than that of BVO (1.7 eV). Due to the specific photoexcitation of ZRO, Pt, Ag, or Cu was expected to be only photo-deposited onto this material, generating Pt/ZRO/Ag/BVO, Ag/ZRO/Ag/BVO, or Cu/ZRO/Ag/BVO. The deposition of Pt, Ag, or Cu 3-fold enhanced the H2 and O2 evolution rates compared to those of bare ZRO/Ag/BVO, demonstrating that Pt, Ag and Cu functioned as cocatalysts for the overall water-splitting reaction [6,7]. In addition, we discuss on the selective loading of a cocatalyst, cobalt oxide (CoOx), onto the O2-evolution photocatalyst, BVO, in ZRO/Ag/BVO and co-loading of Cu and CoOx on ZRO and BVO, respectively, at the conference.This work was performed by Assoc. Prof. T. Takashima, Mr. M Yoda, and Mr. J. Osaki. I am deeply grateful to JSPS KAKENHI (Grant-in-Aid for Scientific Research) (B), Grant Number JP21H02043 for its financial support.

Solar‐Driven Methanogenesis through Microbial Ecosystem Engineering on Carbon Nitride

AbstractSemi‐biological photosynthesis combines synthetic photosensitizers with microbial catalysts to produce sustainable fuels and chemicals from CO2. However, the inefficient transfer of photoexcited electrons to microbes leads to limited CO2 utilization, restricting the catalytic performance of such biohybrid assemblies. Here, we introduce a biological engineering solution to address the inherently sluggish electron uptake mechanism of a methanogen, Methanosarcina barkeri (M. barkeri), by coculturing it with an electron transport specialist, Geobacter sulfurreducens KN400 (KN400), an adapted strain rich with multiheme c‐type cytochromes (c‐Cyts) and electrically conductive protein filaments (e‐PFs) made of polymerized c‐Cyts with enhanced capacity for extracellular electron transfer (EET). Integration of this M. barkeri‐KN400 co‐culture with a synthetic photosensitizer, carbon nitride, demonstrates that c‐Cyts and e‐PFs, emanating from live KN400, transport photoexcited electrons efficiently from the carbon nitride to M. barkeri for methanogenesis with remarkable long‐term stability and selectivity. The demonstrated cooperative interaction between two microbes via direct interspecies electron transfer (DIET) and the photosensitizer to assemble a semi‐biological photocatalyst introduces an ecosystem engineering strategy in solar chemistry to drive sustainable chemical reactions.

Highly efficient magnesium ferrite/graphene nano-heterostructure for visible-light photocatalytic applications: Experimental and first-principles DFT studies

In this research study, the electronic structure of magnesium ferrite/graphene (MFO/Gr) nano-heterostructure for photocatalytic application was studied. The MFO nanoparticles with a median size of 85 nm were composited with Gr sheets using a photo-assisted reduction process. The XRD and SAED results, respectively, showed the spinal crystalline structure of MFO and the hexagonal structure of Gr in MFO/Gr nanocomposite. The XPS results revealed that the orbitals of MFO and Gr atoms interacted with each other, implying a Van der Waals heterojunction nanocomposite. The optical characteristics using UV–Vis diffuse reflectance spectrophotometry (UV–Vis DRS) and photoluminescence (PL) spectra demonstrated a lowering of MFO band gap from 2.05 to 1.84 eV by incorporation of Gr. Furthermore, the photoelectrocatalytic and photocatalytic dye degradation examinations showed a substantial impact of Gr on the photocatalytic activity of MFO nanoparticles: a 28-fold increase in the photocurrent and an 8-fold increase in the dye-degradation rate. The density functional theory (DFT) studies on MFO/Gr heterojunction revealed a considerable hybridization between Gr atoms orbitals (2p orbitals) and MFO atoms orbitals (Mg 3 s and Fe 3d orbitals) in the conduction band, which facilitate the transfer of photo-excited electrons from MFO to Gr. Also, the charge density difference at the MFO/Gr interface led to a polarized field at the interface, which is desirable for hindering photogenerated electron-hole recombination in the MFO/Gr nanocomposite. Along with the experimental results, the DFT results also revealed that the MFO/Gr nano-heterostructure is an excellent candidate for photocatalytic applications such as water splitting using sunlight to produce green hydrogen fuel.

Solar-Driven Methanogenesis through Microbial Ecosystem Engineering on Carbon Nitride.

Semi-biological photosynthesis combines synthetic photosensitizers with microbial catalysts to produce sustainable fuels and chemicals from CO2. However, the inefficient transfer of photoexcited electrons to microbes leads to limited CO2 utilization, restricting the catalytic performance of such biohybrid assemblies. Here, we introduce a biological engineering solution to address the inherently sluggish electron uptake mechanism of a methanogen, Methanosarcina barkeri (M. barkeri), by coculturing it with an electron transport specialist, Geobacter sulfurreducens KN400 (KN400), an adapted strain rich with multiheme c-type cytochromes (c-Cyts) and electrically conductive protein filaments (e-PFs) made of polymerized c-Cyts with enhanced capacity for extracellular electron transfer (EET). Integration of this M. barkeri-KN400 co-culture with a synthetic photosensitizer, carbon nitride, demonstrates that c-Cyts and e-PFs, emanating from live KN400, transport photoexcited electrons efficiently from the carbon nitride to M. barkeri for methanogenesis with remarkable long-term stability and selectivity. The demonstrated cooperative interaction between two microbes via direct interspecies electron transfer (DIET) and the photosensitizer to assemble a semi-biological photocatalyst introduces an ecosystem engineering strategy in solar chemistry to drive sustainable chemical reactions.

Sulfur-vacancy induced asymmetric active site for Bi19S27Br3 nanorods photocatalyzes CO2 conversion to ethylene

The photocatalytic conversion of CO2 into high value-added C2 products remains a significant challenge due to the limited active sites and high energy barrier of C-C coupling process. Herein, the sulfur-vacancy was established on the surface of Bi19S27Br3 nanorods, leading to the electron on residual S atoms become unstable and active. Under the light irradiation, the photoexcited electron transfer from S atoms to neighboring Bi atoms to generate in-situ charge-polarized Bi(3-x)+ asymmetric active sites, which can enhance CO2 adsorption-activation capacity and regulate C-C coupling process for the C1 intermediate. The experimental results and theoretical calculation confirm that more charges aggregate around the induced Bi atoms, reducing the energy barrier of the C-C coupling reaction and improving C2H4 formation. Consequently, the sulfur-vacancy Bi19S27Br3 nanorods achieve efficient C2H4 generation through photocatalytic CO2 reduction, which C2H4 formation rate is 17.80 µmol g−1 after 5-hour photocatalytic reaction, with the product selectivity and electron selectivity of 49 % and 85 %, respectively, outperforming the low sulfur-vacancy Bi19S27Br3 nanorods by four-folds. This research provides new insights into the design of photocatalysts.

Effect of ground-state charge transfer on photoexcited charge transfer in transition metal dichalcogenide heterostructures

We report an experimental investigation on the effect of ground-state charge transfer and its induced electric field on photoexcited charge transfer in van der Waals heterostructures. Two heterostructure samples were fabricated by stacking an undoped WSe2 monolayer with either a Nb-doped or undoped MoSe2 monolayer. While no ground-state charge transfer is expected in the MoSe2/WSe2 heterostructure, the doped holes in the MoSe2:Nb/WSe2 heterostructure can transfer to WSe2, creating a space-charge electric field. By comparing the photoluminescence and time-resolved differential reflectance of the two heterostructures, we find that photoexcited hole transfer from MoSe2 to WSe2 is largely blocked by this field, whereas photoexcited electron transfer from WSe2 to MoSe2 is less affected. These results provide insight into the impact of doping on the charge-transfer performance of van der Waals heterostructures.

Photo-Modulation of Atomically Thin Molybdenum Diselenides Functionalized with Photochromic Molecules

Two-dimensional (2D) transition metal dichalcogenide semiconductors have garnered significant attention due to their extraordinary electrical and optical properties. It has been increasingly important to develop strategies for modulating their properties. A number of methods have been introduced, including doping, electric and magnetic fields, mechanical strain, etc. Herein, we report a novel approach of using photochromic molecules to modulate optoelectronic properties of monolayer MoSe2 with light. We have synthesized photochromic diarylethene (DAE) molecules that can switch between two isomeric forms, referred to as open and closed, under UV and visible light, respectively. The DAE molecules formed a uniform layer with a thickness of approximately 2 nm on monolayer MoSe2. Our density functional theory (DFT) calculations suggest that the TMD and DAE will align their band energy levels such that UV irradiation moves the lowest unoccupied molecular orbital (LUMO) energy of DAE in between the conduction band minimum (CBM) and valence band minimum (VBM) of MoSe2. This will facilitate photoexcited electron transfer from MoSe2 to DAE LUMO. Experimentally, we have confirmed our predictions by observing a strong quenching of photoluminescence (PL) and an increase of electrical conductivity in MoSe2. In contrast, visible light induced isomerization to the open form of DAE and expanded its energy levels, moving the LUMO level above the MoSe2 CBM. Therefore, the PL was retained and there was no significant change in electrical conductivity. We showed that this photoswitching can dynamically modulate the optoelectronic properties by demonstrating multiple cycles of PL emission and quenching, by alternating UV and visible light repeatedly. Lastly, our Kelvin probe force microscopy (KPFM) revealed that the potential of MoSe2 monolayers can also be modulated with photochromic molecules and external light irradiation. Our work elucidates photo-processes and exciton mechanisms at the hybrid interfaces and lays the foundation for novel applications including new phototransistors and other 2D optoelectronic devices.

Bacteria-photocatalyst biohybrid system for sustainable ammonium production

Although the Haber–Bosch process supports the growth of modern agriculture with abundant ammonia and fertilizer production, substantial energy consumption and enormous greenhouse emissions demand an alternative and sustainable approach. Here, we report a novel approach that combines the non-photosynthetic bacterium Shewanella oneidensis MR-1 (S. oneidensis MR-1) with cadmium sulfide nanoparticles (CdS NPs) to enable the photosynthesis of ammonium (NH4+) from nitrate (NO3−) using photoexcited electrons as donors. The NO3− reduction efficiency reached almost 100%, with an NH4+ production selectivity of over 90%. The maximum instantaneous quantum efficiency was 3.01% under light irradiation. The reverse metal-reducing (Mtr) pathway is responsible for the transfer of photoexcited electrons to intracellular compartments. Parallel reaction monitoring analysis illustrated that NO3− to NH4+ was produced via the dissimilatory nitrate reduction to ammonium (DNRA) pathway in S. oneidensis MR-1. This study provides a facile strategy for light-driven ambient NH4+ synthesis and solar-to-chemical conversion.

Enhanced hydrogen production performance via noble-metal-free amorphous NiZnSx-CS co-catalyst with novel gradient coating structure

In photocatalytic water splitting for hydrogen production, co-catalyst is a key factor in enhancing the efficiency of photocatalyst. Various inexpensive co-catalysts besides noble metal co-catalysts have been developed; however, the illumination of the relationship between the structure and performance remains a challenge. Here, we present a bimetallic sulfide co-catalyst denoted as NiZnSx-CS with amorphous and gradient coating structures to achieve highly efficient hydrogen production activity. Upon coupling the co-catalyst with CdS, the hydrogen production rate of CdS loaded with NiZnSx-CS reaches 38.0 mmol/g/h, 11.0, 40.0 and 161.0 times higher than that loaded with bulk NiZnSx, 1.0 %Pt and naked CdS, respectively. The co-catalyst with an amorphous and gradient coating structure shows large capacitance and thus facilitates efficient storage, transfer, and separation of photo-excited electrons of semiconductors, effectively reducing the over-potential of hydrogen production. The co-catalyst also has a large specific surface area and excellent hydrophilicity attributed to the abundant active sites and intimate contact with the reactant. Additionally, the coordination structure and chemical environment of NiZnSx-CS elucidated using X-ray absorption spectroscopy (XAS). The intermediates and the role of lactic acid and water on the surface of NiZnSx-CS after irradiation are determined by in situ Fourier transform infrared spectroscopy (in situ FT-IR). This work proposes a strategy to develop a highly efficient special structure co-catalyst with suitable capacitance, specific surface area and hydrophilicity.

Antibacterial Activity of Visible Light Responsive‐Silver‐Nanoparticle/Titania Composite Thin Films with Unprecedently Higher Amounts of Silver

AbstractTo study the antibacterial efficacy of metallic Ag nanoparticle/titania (Ag‐NP)/TiO2 composite thin films against Escherichia coli (ATCC 25922), COMP‐Agn with various amounts of Ag (10 mol% ≤ n ≤ 80 mol%) are fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. The films are characterized by X‐ray diffraction, X‐ray photoelectron, scanning electron microscopy, transmission electron microscopy, photoluminescence, and UVvis techniques. The analysis reveals that the films are composed of metallic Ag‐NPs embedded in a mixture of anatase and rutile matrix, with a volumetric fraction of Ag ranging from 0.18 to 0.68. The antibacterial activity of the TiO2 thin film and COMP‐Agn are determined by disk diffusion and viable cell count methods. Neither pure TiO2 nor pure Ag films exhibit any discernible antibacterial under dark and visible light. The antibacterial of Ag content in composite films is observed to persist for a maximum increase of 70%. The model is proposed on the basis of photoexcited electron transfer from Ag NPs to the TiO2 conduction band of COMP‐Agn, which clarifies the main factors affecting the photoresponse and the excellent response to visible light via surface plasmon resonance.

Visible-Light-Driven Germyl Radical Generation via EDA-Catalyzed ET-HAT Process.

We have established a facile and efficient protocol for the generation of germyl radicals by employing photo-excited electron transfer (ET) in an electron donor-acceptor (EDA) complex to drive hydrogen-atom transfer (HAT) from germyl hydride (R3GeH). Using a catalytic amount of EDA complex of commercially available thiol and benzophenone derivatives, the ET-HAT cycle smoothly proceeds simply upon blue-light irradiation without any transition metal or photocatalyst. This protocol also affords silyl radical from silyl hydride.

Interfacial Charge Transfer in Photoexcited QD-Molecule Composite of Tetrahedral CdSe Quantum Dot Coupled with Carbazole.

Photoexcited charge transfer dynamics in CdSe quantum dots (QDs) coupled with carbazole were explored to model QD-molecule systems for light-harvesting applications. The absorption spectra of QDs with different sizes, i.e., Cd35Se20X30L30 (T1), Cd56Se35X42L42 (T2), and Cd84Se56X56L56 (T3) were simulated with quantum dynamical methods, which qualitatively match the reported experimental spectra. The carbazole is attached with a 3-amino group at the apex position of T1 (namely T1-3A-Cz), establishing proper electronic communication between T1 and carbazole. The spectra of T1-3A-Cz is 0.22 eV red-shifted compared to T1. A time-dependent perturbation was applied in tune with the lowest energy peak (3.63 eV) of T1-3A-Cz to investigate the charge transfer dynamics, which revealed an ultrafast charge separation within the femtosecond time scale. The electronic structure showed a favorable energy alignment between T1 and carbazole in T1-3A-Cz. The LUMO of carbazole was situated below the conduction band of the QD, while the HOMO of carbazole mixed perfectly with the top of the valence band of the QD, developing the interfacial charge transfer states. These states promoted the photoexcited electron transfer directly from the CdSe core to carbazole. A rapid and enhanced charge separation occurred with the laser field strength increasing from 0.001 to 0.005 V/Å. However, T1 connected to the other positions of carbazole did not show charge separation effectively. The photoinduced charge transfer is negligible in the case of T2-carbazole systems due to poor electronic coupling, and it is not observed in T3-carbazole systems. So, the T1-3A-Cz model acts as a perfect donor-acceptor QD-molecule nanocomposite that can harvest photon energy efficiently. Further enhancement of charge transfer can be achieved by coupling more carbazoles to the T1 QD (e.g., T1-3A-Cz2) due to the extension of hole delocalization between T1 and the carbazoles.

Electron-transfer dynamics and photocatalytic H2-production activity of PbS@Cu2S nanocomposites

BackgroundLead citrate is a precursor that can be prepared by recycling the spent lead paste of lead-acid batteries. Lead citrate is used to synthesize lead oxide, which can be repeatedly utilized for the lead-acid battery application. MethodsWe report a new application of lead citrate precursor to synthesize PbS@Cu2S nanomaterials for photocatalytic H2 production. PbS@Cu2S was prepared by microwave-assisted hydrothermal and ion-exchange processes. The electron-transfer dynamics and H2-production activity of PbS@Cu2S photocatalysts were studied. Significant findingsA S-scheme heterojunction is proposed based on the results of Tauc plots, ultraviolet photoelectron spectroscopy, the electron paramagnetic resonance scavenger test, and in situ near-edge X-ray absorption fine structure (NEXAFS) analysis. Results of in situ NEXAFS reveal the transfer of photoexcited electrons from PbS to Cu2S. By loading an optimized amount of Cu2S, the carrier separation and photocatalytic activity of PbS@Cu2S photocatalysts are improved. This technology can transform the lead citrate precursor to the PbS@Cu2S photocatalyst with excellent high H2 production activity (3824 μmol g−1 h−1).

Step-by-step transfer of photoexcited electron in donor-acceptor-catalyst configuration covalent triazine framework for efficient photoreduction CO2 to formic acid

Covalent triazine frameworks (CTFs) have great potential for photocatalysis. However, the electron-hole recombination and the lack of efficient catalytic sites constrain the activity and selectivity. Herein, a novel design strategy of donor–acceptor-catalyst (D-A-C) configuration is proposed. This configuration enables the photoexcited electron undergoes stepwise transfer from donor unit to acceptor unit and ultimately reaches catalytic center, effectively inhibiting electron-hole recombination. The proof-of-concept model CTF-TT-Ir, in which thieno[3,2-b]thiophene (TT) serves as the donor unit, triazine as the acceptor unit, and Cp*Ir(bpy) (Ir) as the built-in catalytic site, was prepared for the photocatalytic reduction of CO2 to HCOOH. The stepwise transfer of photoexcited electrons in the ternary structure has been demonstrated through the in-situ XPS measurements and the theoretical calculations. Photoluminescence and photocurrent tests have indicated CTF-TT-Ir exhibits superior charge separation efficiency. Without additional photosensitizer and co-catalyst, the photocatalytic HCOOH yield rate of CTF-TT-Ir reached 245 μmol g−1h−1 (selectivity of 97 %).

Coating of Chlorophylls a and b Enhanced Photoelectrochemical Capacitor Reaction of TiO2/MnO2 Composite Electrode.

We prepared composite electrodes using TiO2 coated with chlorophylls a and b as photoelectric conversion material and MnO2 as energy storage material and investigated their photoelectrochemical capacitor properties. The coating with the combination of chlorophylls a and b improved the photoelectric conversion function of TiO2, compared with the coating with each alone. Na+ adsorption on MnO2 was enhanced with increasing the chlorophyll coating amount. The reason is that more chlorophylls a and b absorb visible light in different wavelengths to promote an easier photoexcited electron transfer to MnO2, just as they improve the efficiency of photosynthesis reactions in nature.

Spatially separated HOMO-LUMO sites in highly intra- and inter-plane crystalline g-C3N4 photocatalyst for exceptional H2 generation

Spatially separated HOMO-LUMO sites in the highly crystalline g-C3N4 can vastly facilitate the rapid transfer and separation of photogenerated charges to greatly improve its photocatalytic performance, which remains a great challenge to be achieved. In this study, the highly intra- and inter-plane crystalline g-C3N4 (c-CN) with the spatially separated HOMO-LUMO sites is explicitly produced through a moderate Na-modulated strategy to efficiently promote the directional transfer and separation of photoinduced charges. As a result, the optimized c-CN1.0 photocatalyst exhibits exceptional H2-evolution performance (313.5 μmol h−1, AQE = 13.38 %), which is ca. 14.3 times of the bulk g-C3N4. The excellent hydrogen-generation efficiency of c-CN photocatalyst is mainly ascribed to the synergism of high intra- and inter-layer crystallization of g-C3N4 and spatially separated HOMO-LUMO sites, which can vastly boost the directional transfer and effective separation of photoexcited electrons and holes. This research may open novel avenues to construct other photocatalysts with high efficiency.

Defective Cd0.3Zn0.7S / 1 T-2 H MoS2 Z-scheme heterojunctions: Rational design with efficient charge transfer for enhanced photocatalytic H2 generation

CdxZn1-xS photocatalysts have received increasing attention due to their better Photocatalytic hydrogen evolution. In this paper, Cd0.3Zn0.7S nanoparticles decorated by a small amount of 1 T-2 H mixed-phase MoS2 nanosheets ((X%) MoS2/Cd0.3Zn0.7S) were prepared by a secondary hydrothermal-hydrothermal precipitation method. The Z-scheme heterojunction between 2 H-MoS2 and Cd0.3Zn0.7S can effectively inhibit the recombination of photogenerated carriers in the photocatalysts, and 1 T-MoS2 with metallic properties in the mixed phase mainly acts as a bridge for the transfer of photoexcited electrons. Therefore, under UV–visible irradiation, when Na2S/Na2SO3 is used as the sacrificial agent, the photocatalytic hydrogen evolution reaction (HER) activity of 0.75% MoS2/Cd0.3Zn0.7S reaches 11172 umol.g−1.h−1, which is 1.8 fold higher than that of Cd0.3Zn0.7S. The apparent quantum yields of 0.75% MoS2/C3Z7S at 370 nm and 420 nm wavelength are 50.6% and 7.2%, respectively. There are no significant changes in the hydrogen production after three cycles, indicating that the 0.75% MoS2/C3Z7S sample has excellent stability. This study provides a facile and low-cost strategy for constructing composite photocatalysts with highly efficient steady hydrogen production activity.

Photoswitchable optoelectronic properties of 2D MoSe2/diarylethene hybrid structures

The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe2 with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe2, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe2, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe2 to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe2. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe2/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices.

Mediation of Interfacial Mo2C Bridging Effect in MoS2@Carbon Colloid Dots Featuring Improved Photovoltaic Performances of Si‐Based Hybrid Solar Cells

AbstractAdvances in silicon‐based hybrid solar cells with high photovoltaic performance, low synthetic cost, and sound environmental resistance are emerged as potential candidate for solar conversion. Solution‐processed few‐layer MoS2 sheets are regarded as compelling constitutes that paves ways for tailoring the solar harvesting capability; yet the improvement on charge separation of photoexcited carriers remains demanded, and the lack of environmental stability due to intentionally grabbing electrons from adsorbed moistures constrains the scope of practical assessment. In this work, the employment of MoS2/Mo2C/carbon colloid dots (CCDs) heterostructures within PEDOT:PSS matrix is invoked, where the transfer of photoexcited electrons from MoS2 is mediated with Mo2C electron‐transport channels, which further couple out the creation of positive trions by combining with defect‐bound excitons at CCD surfaces. These features dynamically involve with slow recombination probability and further improve the photovoltaic gain. Thus, the noticeable improvement of conversion efficiency of 16.1% with 1.6 times of efficiency enhancement outperforming the bare conventional hybrid solar cells is accomplished, and further exhibits a sound long‐term stability, which opens new avenues for exploiting the photophysical bound‐carrier transition on advanced photovoltaic applications.