Photoexcited Charge Carriers Research Articles

One-pot in-situ hydrothermal synthesis of ternary In2S3/Nb2O5/Nb2C Schottky/S-scheme integrated heterojunction for efficient photocatalytic hydrogen production

MXene-derived photocatalysts continue to fascinate the research community in developing photo-driven green and sustainable fuel production. However, the efficiency of MXene-derived photocatalyst is still low due to the wide bandgap and high recombination rate of photo-excited charge carriers. Here, we have synthesized the Nb2C MXene-derived ternary photocatalyst via one-pot in-situ hydrothermal method for photocatalytic hydrogen (H2) evolution. The partial oxidation of Nb2C MXene into Nb2O5 nanorods and coupling with In2S3 nanoparticles via in-situ chemical anchoring were the key factors toward high efficiency and long-term stability during photocatalytic H2 evolution. The optimized ternary photocatalyst composite manifested the highest H2 evolution efficiency at 68.8 µmol g−1 h−1, which was 11 and 7.5 times higher than the Nb2O5/Nb2C (NNC) and pure In2S3 photocatalyst, respectively. Moreover, the photocatalytic stability of the optimized ternary photocatalyst composite was analyzed for five consecutive cycles, and above 87% activity retention was observed even after the fifth cycle without any obvious decline. The separation efficiency of photoexcited charge carriers could be attributed to the synergic effect of the In2S3/Nb2O5 heterojunction and the redox reactions at different sites of the composite. More importantly, the participation of Schottky junction and S-scheme heterojunction charge transfer for the obtained novel ternary photocatalyst was evaluated via ultraviolet photoelectron spectroscopy (UPS) and electron paramagnetic resonance (EPR). This research will provide additional insight into the extended potential of MXene-derived ternary photocatalysts towards efficient H2 production to meet future global energy demands.

Photothermal-Reagent-Triggered Visual Thermoresponsive and Quantized Photoelectrochemical Dual-Signal Assay.

In vitro biosensing chips are urgently needed for early-stage diagnosis and real-time surveillance of epidemic diseases. Herein, a versatile zone with photothermal effects is implanted in the miniature space of a collapsible lab-on-paper photoelectrochemical biosensor for on-site detection of microRNA-141 in body fluids, which can flexibly interconnect the traditional photocurrent signal with functional temperature response. The visualized thermoresponsive results are enhanced by the exciton energy conversion between Fe3O4 nanoparticles (Fe3O4 NPs) and formed Prussian blue nanoparticles under near-infrared irradiation, which not only presents heat energy gradient variations but also generates color changes. Significantly, the controlled release of Fe3O4 NPs is actuated by a target-triggered enzyme assist strand displacement cycle strategy to efficiently improve the accuracy of target temperature signal prediction, which can concurrently mediate photoelectric signal attenuation via promoting the rapid recombination of photoexcited charge carriers on the CuInS2/CoIn2S4 electrode surface, affording dependable ultrasensitive detection results. Benefitting from the ingenious design of the versatile thermoresponsive-photoelectric sensing platform, the preliminary screening and ultrasensitive quantitative analysis can be simultaneously achieved in a single-drop sample. As a consequence, speedy prediction results and satisfied monitoring data are acquired in the ranges of 0.5 pM to 2 nM and 0.001 pM to 5 nM by measuring the temperature change and photocurrent intensity. By right of these advantages, such research paves a prospective paradigm for the manufacture of a visual, rapid, broad-spectrum, and reliable real-time surveillance platform, which allows it to be a promising candidate for epidemic disease home diagnosis and intelligent diagnosis.

A system investigation on Ru-MOF-74 with efficient photocatalytic nitrogen fixation performance

Developing highly efficient photocatalysts for nitrogen fixation into ammonia is of great importance for solving the energy crisis and sustainable development. In this work, we report a simple synthesis of Ru3+ ions modified MOF-74 nanostructures. These Ru3+ ions are introduced into the internal channels of MOF-74 structure. The photocatalytic activity of nitrogen fixation was remarkably improved under visible irradiation (λ > 400 nm). After the introduction of Ru3+ ions, the visible response is enhanced and the photo-excited charge carriers are separated and transferred to the surface efficiently, leading to an improved photocatalytic performance. This work may offer a better understanding for designing and developing MOFs photocatalysts with high performance and low cost.

Phonon signatures for polaron formation in an anharmonic semiconductor

Mechanistic studies on lead halide perovskites (LHPs) in recent years have suggested charge carrier screening as partially responsible for long carrier diffusion lengths and lifetimes that are key to superior optoelectronic properties. These findings have led to the ferroelectric large polaron proposal, which attributes efficient charge carrier screening to the extended ordering of dipoles from symmetry-breaking unit cells that undergo local structural distortion and break inversion symmetry. It remains an open question whether this proposal applies in general to semiconductors with LHP-like anharmonic and dynamically disordered phonons. Here, we study electron-phonon coupling in Bi2O2Se, a semiconductor which bears resemblance to LHPs in ionic bonding, spin-orbit coupling, band transport with long carrier diffusion lengths and lifetimes, and phonon disorder as revealed by temperature-dependent Raman spectroscopy. Using coherent phonon spectroscopy, we show the strong coupling of an anharmonic phonon mode at 1.50 THz to photo-excited charge carriers, while the Raman excitation of this mode is symmetry-forbidden in the ground-state. Density functional theory calculations show that this mode, originating from the A1g phonon of out-of-plane Bi/Se motion, gains oscillator strength from symmetry-lowering in polaron formation. Specifically, lattice distortion upon ultrafast charge localization results in extended ordering of symmetry-breaking unit cells and a planar polaron wavefunction, namely a two-dimensional polaron in a three-dimensional lattice. This study provides experimental and theoretical insights into charge interaction with anharmonic phonons in Bi2O2Se and suggests ferroelectric polaron formation may be a general principle for efficient charge carrier screening and for defect-tolerant semiconductors.

Codesigning Alloy Compositions of CdSeyTe1−y Absorbers and MgxZn1−xO Contacts to Increase Solar Cell Efficiency

Thin‐film solar cells such as CdTe are a major commercial photovoltaic technology, with more than 25 GW installed worldwide and levelized costs of electricity competitive with fossil fuels. Further progress may result from integrating CdSeyTe1−y absorbers with MgxZn1−xO contacts, but the device efficiency is difficult to maximize due to coupled dependence on chemical composition of both alloys. Herein, a high‐throughput approach is demonstrated to codesign chemical compositions in alloyed MgxZn1−xO/CdSeyTe1−y thin‐film solar cells, using combinatorial libraries of PV devices with orthogonal composition gradients in CdSeyTe1−y absorbers and MgxZn1−xO contacts. It is found that the solar cell performance is a strong and coupled function of both elemental compositions, with efficiency up to 17.7% (VOC = 836 mV, fill factor = 69%, JSC = 30.6 mA cm−2) at atomic compositions of Mg/(Mg + Zn) ≈18% and average Se/(Se + Te) ≈4%. These performance trends among >100 devices are explained by >100 ns lifetime of photoexcited charge carriers at the MgxZn1−xO/CdSeyTe1−y interface where strong Se accumulation is also observed. This study reports the optimal compositions of the commercially relevant MgxZn1−xO/CdSeyTe1−y solar cells and demonstrates a general approach to codesigning performance of alloyed thin‐film solar cells and other optoelectronic devices.

Carbon dots decorated cadmium sulphide heterojunction-nanospheres for the enhanced visible light driven photocatalytic dye degradation and hydrogen generation

Carbon dots (C-dots) developed from beetroot is used for the rational design of cadmium sulphide based heterojunction photocatalysts (C-dots@CdS) using hydrothermal technique. The crystal structure, phase, morphology and optical characteristics of the synthesised materials are determined using X-ray diffraction (XRD), High resolution transmission electron microscopy (HR-TEM), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–Visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL spectroscopy), BET adsorption, X-ray photoelectron spectroscopy (XPS) and electrochemical studies. Using C-dots@CdS catalytic system, a superior photocatalytic activity relative to the undecorated CdS is observed. Among the C-dots@CdS samples, the CdS loaded with 6 wt% of C-dots exhibited enhanced hydrogen evolution rate compared with other samples considered for the study. CdS nanospheres modified with C-dots (6 wt%) resulted in the photocatalytic hydrogen evolution rate of 1582 µmolg−1 against 849 µmolg−1 evolution rate obtained for CdS nanospheres within 3 h. In spite of being 0D/0D type nano-heteroarchitecture, C-dots@CdS system obtained an apparent quantum yield of 6.37 % for the catalytic dosage of 20 mg under the irradiation of visible light. CdS in the C-dots@CdS system serves as the light harvester while C-dots with discernible edges can maintain the continuous supply of photo-excited charge carriers and hence can reduce the charge-carrier recombination. Further, the photodegradation of crystal violet dye using the optimised dosage of C-dots@CdS-6 exhibited an efficiency of 97.3 % in 120 min of visible light irradiation under neutral conditions. The detailed kinetic study reveals that the mechanism of photodegradation of crystal violet dye using C-dots@CdS system can be described using pseudo-second-order kinetics. The presence of oxygen rich hydrophilic surface functionalities of C-dots, the formation of near-surface heterojunction and the suitable band structure of C-dots@CdS system leading to the optimum charge carrier separation kinetics can be attributed to the enhanced photocatalytic performance. This work offers a promising strategy to develop bio-derived C-dots based heterojunction photocatalyst to address the burgeoning energy and environmental demands.

Synthesis of O-doped C3N4 decorated with C3N4 quantum dots: Construction of a homo junction photocatalyst for the enhanced photocatalytic degradation of tetracycline

BackgroundConstructing a homo junction was a promising approach to inhibit the recombination of photoexcited electrons&holes and improve the photocatalytic performance for pollutant removal. However, there were few reports on adjusting the internal electric field (IEF) intensity of a homo junction via energy band engineering. MethodsA homo junction photocatalyst (O-doped C3N4/C3N4 quantum dots) was prepared by facile chemical oxidation and hydrothermal treatment. Significant findingsThe results indicated that the quantum size effect of C3N4qds and O doping were the key factors for constructing the homo junction. This unique structure provided good inter-crystal compatibility and the feasibility to enhance the IEF intensity. Consequently, the separation of photoexcited charge carriers was promoted, and the photocatalytic performance was thus improved. As expected, the best degradation of tetracycline was obtained over O-doped C3N4/C3N4qds. The corresponding first-order kinetic constant was 2.43, 3.06 and 4.29 times that of C3N4/C3N4qds, C3N4/C3N4non-qds and the bulk phase C3N4, respectively. The reactive species capturing experiments verified that singlet oxygen was the major reactive species during the photocatalytic degradation of tetracycline. Additionally, the photocatalytic mechanism and the possible degradation pathways of tetracycline were proposed. This work offered a novel idea to prepare photocatalysts for wastewater treatment.

Band structure alignment transitioning strategy for the fabrication of efficient photocatalysts for solar fuel generation and environmental remediation applications

Indium hydroxide (In(OH)3) and indium oxide (In2O3) have proven to be efficient catalysts for photocatalytic water-splitting reactions to produce hydrogen (H2) and for organic pollutant degradation applications. However, the limited optical absorption features of indium-based nanostructures have restricted their practical applications. In this study, we have successfully designed indium hydroxide- and indium oxide-loaded metal sulfide (cadmium sulfide, CdS) heterostructures as excellent photocatalytic systems for photocatalytic hydrogen evolution and tetracycline hydrochloride pollutant degradation reactions. In this system, In(OH)3 and In2O3 established Type-I and S-scheme heterojunctions, respectively, with CdS, resulting in superior charge separation properties and outstanding photocatalytic activity. Specifically, the rational and appropriate design of the aforementioned indium-based heterostructures promoted the separation of photoexcited charge carriers via Type-I and S-scheme paths. Accordingly, enhanced photocatalytic H2 evolution activities of 9.58 and 14.98 mmol·g−1·h−1 were achieved for CdS–In(OH)3 and CdS–In2O3, respectively. Furthermore, the highest degradation efficiency of CdS–In2O3 was ∼ 90%, which was higher than those of CdS–In(OH)3 (72%) and bare CdS nanorods (51%). Therefore, the results of this study provide an opportunity to enhance the catalytic activities of heterostructured photocatalytic systems by utilizing the strategy of transitioning band structure alignment from the Type-I to the S-scheme.

Carbon dots incorporated in hierarchical macro/mesoporous g-C3N4/TiO2 as an all-solid-state Z-scheme heterojunction for enhancement of photocatalytic H2 evolution under visible light

In recent years, coupling TiO2 with other narrow bandgap semiconductors to improve photocatalytic hydrogen generation rate has attracted widespread attention. Herein, carbon dots (C dots) decorated g-C3N4/TiO2 all-solid-state Z-scheme heterojunction photocatalysts with hierarchical macro/mesoporous structure have been fabricated via a facile solvothermal and calcination method. The dosage of C dots greatly influences the microstructure and the visible-light photocatalytic H2 evolution rate (HER). Under the optimal condition, the ternary composites consisting of C dots, g-C3N4 and TiO2 exhibited the highest HER of 580 μmol g−1 h−1, exceed the pure TiO2, pure g-C3N4 and the binary g-C3N4/TiO2 hybrid photocatalyst by a fact of 6.6 times, 2.1 times and 1.6 times, respectively. The excellent photocatalytic performance for hydrogen evolution is ascribed to the stronger light absorption, higher specific surface area and faster charge transportation. An all-solid-state Z-scheme heterojunction mechanism was proposed in which C dots serve as a mediator to improve the separation and transportation of photo-excited charge carriers.

CdS Coated Mn Doped ZnO Nanospheres as Textile Catalyst: Fabrication, Physicochemical Techniques and Dye Removal Under Natural Light

ZnO as a promising photocatalyst has gained much attention for the removal of organic pollutants from water. However, the main drawbacks of the relatively low photocatalytic activity and high recombination rate of photo excited electronhole pairs, restrict its potential applications. Promoting the spatial separation of photo excited charge carriers is of paramount signi? cance for photocatalysis, because the dierence in the band positions make the potential gradient at the composite boundary. In this work, our aim is to enhance the photocatalytic efficiency of CdS coated Mn doped ZnO nanospheres under solar light irradiation. Objectives in this work are, to fabricate the CdS coated Mn doped ZnO nanospheres by a simple ethanolic dispersion method, and its applied for testing the photocatalytic activity of methylene blue (MB) dye. The fabricated binary composites were analyzed with different physicochemical techniques like PXRD, SEM with EDX, UV-DRS, PL and TEM. The photocatalytic degradation results have revealed that, the CdS coated Mn doped ZnO nanospheres exhibits admirable activity toward the photocatalytic degradation of the MB. The remarkably enhanced photocatalytic activity of CdS coated Mn doped ZnO nanospheres can be interpreted in terms of lots of active sites, which efficiently separate the photo generated electron and holes. A plausible mechanism is also elucidated via active species trapping experiments with various scavengers, which indicating that the photo generated O2 -and. OH radicals play a crucial role in photo degradation reactions under visible light irradiation. This work suggests that, the rational design and construction of heterostructures is powerful for developing highly efficient, and reusable visible-light photocatalysts for environmental purification and energy conversion. The enhanced photo degradation activity indicates the potential of the nanocomposite for the treatment of organic pollutants from the textile wastewater.

CdS Coated Mn Doped ZnO Nanospheres as Textile Catalyst: Fabrication, Physicochemical Techniques and Dye Removal Under Natural Light

ZnO as a promising photocatalyst has gained much attention for the removal of organic pollutants from water. However, the main drawbacks of the relatively low photocatalytic activity and high recombination rate of photo excited electronhole pairs, restrict its potential applications. Promoting the spatial separation of photo excited charge carriers is of paramount signi? cance for photocatalysis, because the dierence in the band positions make the potential gradient at the composite boundary. In this work, our aim is to enhance the photocatalytic efficiency of CdS coated Mn doped ZnO nanospheres under solar light irradiation. Objectives in this work are, to fabricate the CdS coated Mn doped ZnO nanospheres by a simple ethanolic dispersion method, and its applied for testing the photocatalytic activity of methylene blue (MB) dye. The fabricated binary composites were analyzed with different physicochemical techniques like PXRD, SEM with EDX, UV-DRS, PL and TEM. The photocatalytic degradation results have revealed that, the CdS coated Mn doped ZnO nanospheres exhibits admirable activity toward the photocatalytic degradation of the MB. The remarkably enhanced photocatalytic activity of CdS coated Mn doped ZnO nanospheres can be interpreted in terms of lots of active sites, which efficiently separate the photo generated electron and holes. A plausible mechanism is also elucidated via active species trapping experiments with various scavengers, which indicating that the photo generated O2 -and. OH radicals play a crucial role in photo degradation reactions under visible light irradiation. This work suggests that, the rational design and construction of heterostructures is powerful for developing highly efficient, and reusable visible-light photocatalysts for environmental purification and energy conversion. The enhanced photo degradation activity indicates the potential of the nanocomposite for the treatment of organic pollutants from the textile wastewater.

Nonequilibrium Hot-Carrier Transport in Type-II Multiple Quantum Wells for Solar-Cell Applications

Prototypes for hot-carrier solar cells based on type-II $\mathrm{InAs}/{\mathrm{AlAs}}_{0.16}{\mathrm{Sb}}_{0.84}$ multiple quantum wells are examined with ac photoconductivity as a function of lattice temperature and photoexcitation energy to determine the photoexcited charge-carrier transport. These samples previously exhibited an excitation energy onset of a metastable regime in their short-time charge-carrier dynamics that potentially improves their applicability for hot-carrier photovoltaic cells. The transport results illustrate that the ac photoconductivity is larger in the regime corresponding to the metastability as a result of higher excitation photocarrier densities. In this excitation regime, the ac photoconductivity is accompanied by slightly lower carrier mobility, arising from the plasmalike nature of carriers scattered by Auger recombination. Outside of this regime, higher mobility is observed as a result of a lower excitation density that is more readily achievable by solar concentration. Additionally, at ambient temperatures, more scattering events are accompanied by slightly lower mobility, but the excitation dependence indicates that this is accompanied by an ambipolar diffusion length that is greater than half a micron. These transport properties are consistent with good quality in-organic elemental and III-V semiconductor solar cells and far exceed those of organic and perovskite materials. The transport results complement the dynamics observed in type-II $\mathrm{InAs}/{\mathrm{AlAs}}_{0.16}{\mathrm{Sb}}_{0.84}$ and can guide the design of hot-carrier solar cells based on these and related materials.

0D/2D Ag3PO4/biotite nanocomposites for efficient visible-light-driven tetracycline hydrochloride degradation

Environmental problems caused by wastewater that contains antibiotics have attracted wide attention. Photocatalysis is a green and environmental friendliness method for dealing with environmental pollution. In this work, Ag3PO4/biotite composite photocatalysts were constructed by a room-temperature precipitation route. The two-dimensional biotite was used as a supporting matrix and dispersant for depositing size-tunable Ag3PO4 nanoparticles. The intrinsic physical and photoelectrochemical properties of the as-prepared Ag3PO4/biotite heterostructures were systematically characterized. The photocatalytic activity of the constructed catalysts was assessed by photocatalytic degradation of tetracycline hydrochloride (TCH). Compared with pure Ag3PO4, the synthesized Ag3PO4/biotite nanocomposites exhibited improved catalytic activity. The apparent kinetics constant of the optimized sample is about 2.28 times as high as the Ag3PO4, the improved photocatalytic activity can be attributed to the enlarged specific surface area as well as the efficient separation and transfer of the photoexcited charge carriers. Based on the XPS, active species trapping experiments and band edge position measurements, the possible Z-scheme photocatalytic mechanism was proposed.

Rational design of 3D carbon nitrides assemblies with tunable nano-building blocks for efficient visible-light photocatalytic CO2 conversion

g-C3N4 is an appealing non-metal photocatalyst for CO2 reduction, while it shows unsatisfactory performance due to poor CO2 adsorption ability and deficient collection of photo-excited charges, but its efficiency greatly relies on the effective bulk and surface separation of photoexcited charge carriers. To address the challenges, we elaborately design Ag nanoparticles decorated 3D ordered g-C3N4 assemblies based on a synergistic route of Ag-induced supramolecular tailoring and assembling followed by thermal polymerization. The 3D structural topology of the nano-units for g-C3N4 can be altered from 2D orderly stacked nanosheets to 1D twisty g-C3N4 nanotubes by varying the amount of Ag(I). Moreover, the band structures and nitrogen vacancies can also be well-regulated. As supported by experimental and DFT calculation results, ACNNT-2 demonstrates excellent CO2 adsorption capacity, superior light harvesting ability, efficient charge separation and more localized charge density distribution, which can effectively decrease the energy barrier for COOH* intermediate and boost the CO* desorption, resulting in a superior photocatalytic selectivity. Consequently, in sharp contrast to BCN, the ACNNT-2 manifests a markedly improved CO generation rate of 145.5 μmol g−1h−1 under visible-light irradiation, reflecting an 18-fold enhancement together with a CO selectivity of 89%. This strategy provides a profound insight into the multiscale modulation of g-C3N4 photocatalysts with enhanced efficiency.

Flow cell for operando X-ray photon-in-photon-out studies on photo-electrochemical thin film devices

Background: Photo-electro-chemical (PEC) water splitting represents a promising technology towards an artificial photosynthetic device but many fundamental electronic processes, which govern long-term stability and energetics, are not yet fully understood. X-ray absorption spectroscopy (XAS), and particularly its high energy resolution fluorescence-detected (HERFD) mode, emerges as a powerful tool to study photo-excited charge carrier behavior under operating conditions. The established thin film device architecture of PEC cells provides a well-defined measurement geometry, but it puts many constraints on conducting operando XAS experiments. It remains a challenge to establish a standardized thin film exchange procedure and concurrently record high-quality photoelectrochemical and X‑ray absorption spectroscopy data that is unperturbed by bubble formation. Here we address and overcome these instrumental limitations for photoelectrochemical operando HERFD-XAS. Methods: We constructed a novel operando photo-electro-chemical cell by computer numerical control milling, guided by the materials’ X‑ray and visible light absorption properties to optimize signal detection. To test the cell’s functionality, semiconducting thin film photoelectrodes have been fabricated via solution deposition and their photoelectrochemical responses under simulated solar light were studied using a commercial potentiostat in a three-electrode configuration during HERFD-XAS experiments at a synchrotron. Results: We demonstrate the cell’s capabilities to measure and control potentiostatically and in open‑circuit, to detect X‑ray signals unperturbed by bubbles and to fluently exchange different thin film samples by collecting high-resolution Fe K-edge spectra of hematite (α -Fe2O3) and ferrite thin film (MFe2O4, M= Zn, Ni) photoelectrodes during water oxidation. Conclusions: Our cell establishes a measurement routine that will provide experimental access of photo-electro-chemical operando HERFD-XAS experiments to a broader scientific community, particularly due to the ease of sample exchange. We believe to enable a broad range of experiments which acquired fundamental insights will spur further photoelectrochemical research and commercialization of water splitting technologies

Interface Engineering of a 2D/2D BiVO4/Bi4V2O10 Heterostructure with Improved Photocatalytic Photoredox Activity.

Bismuth vanadate (BiVO4) is a promising photocatalyst for water pollution degradation and photocatalytic oxygen evolution. In this work, we prepared 2D/2D BiVO4-Bi4V2O10 heterostructure with tight interfacial contact via a facile one-step hydrothermal process. The crystal structure and morphology of the samples could be easily regulated by changing the pH values of the solution. The BiVO4-Bi4V2O10 heterostructure exhibited an enhanced photodegradation rate of Cr(VI) and oxygen evolution that of bare BiVO4, indicating that the synergistic effect and the interfacial fusions between BiVO4 and Bi4V2O10 can effectively promote the migration and separation rate of photoexcited charge carriers.

Directly Visualizing Photoinduced Renormalized Momentum-Forbidden Electronic Quantum States in an Atomically Thin Semiconductor.

Resolving the momentum degree of freedom of photoexcited charge carriers and exploring the excited-state physics in the hexagonal Brillouin zone of atomically thin semiconductors have recently attracted great interest for optoelectronic technologies. We demonstrate a combination of light-modulated scanning tunneling microscopy and the quasiparticle interference (QPI) technique to offer a directly accessible approach to reveal and quantify the unexplored momentum-forbidden electronic quantum states in transition metal dichalcogenide (TMD) monolayers. Our QPI results affirm the large spin-splitting energy at the spin-valley-coupled Q valleys in the conduction band (CB) of a tungsten disulfide monolayer. Furthermore, we also quantify the photoexcited carrier density-dependent band renormalization at the Q valleys. Our findings directly highlight the importance of the excited-state distribution at the Q valley in the band renormalization in TMDs and support the critical role of the CB Q valley in engineering the quantum electronic valley degree of freedom in TMD devices.

A highly sensitive photoelectrochemical biosensor for CEA analysis based on hollow NiS@NiO/TiO2 composite with typal p-n heterostructure

Heterostructured construction is regarded as a valuable approach to improve photoelectrochemical (PEC) performances. Herein, porous hollow NiS@NiO spheres were prepared derived from the Ni(TCY) MOFs precursor. Photoactive TiO2 was coupled with as-prepared NiS@NiO to form a close heterojunction interface of NiS@NiO/TiO2. NiS@NiO/TiO2 modified ITO electrode (NiS@NiO/TiO2/ITO) displayed fiercely enhanced photocurrent response, which was 4687-fold than that of NiS@NiO/ITO (0.008 μA) and 8.5-fold than that of TiO2/ITO (4.41 μA), respectively. Remarkable PEC property could be ascribed to the hollow NiS@NiO spheres with thin-shell structure provided there is a larger active surface area for harvesting the visible light. Most importantly, the p-n type NiS@NiO/TiO2 heterojunction could lead to generating more photo-excited charge carriers (e−/h+) and efficiently hinder the recombination of carriers, resulting in significantly augmented photocurrent output. Based on this outstanding PEC property, NiS@NiO/TiO2/ITO electrode fabricated sensing platform (BSA/anti-CEA/NiS@NiO/TiO2/ITO, BSA=Bovine serum albumin) exhibited high sensitivity for monitoring CEA (Carcinoembryonic antigen). Wide linear detection range was from 0.001 to 45 ng mL-1 and with a low detection limit of 1.67 × 10-4 ng mL-1 (S/N = 3). Prepared biosensors also showed good reproducibility, stability and had satisfying specificity. Thus, the proposed NiS@NiO/TiO2 heterostructured composite afforded well-design and synthesis strategy for constructing high-performance photoactive materials from MOFs-derivate.

Hetero-phase dendritic elemental phosphorus for visible light photocatalytic hydrogen generation

We demonstrate a carefully tailored elemental red phosphorus (red P) for a record-high photocatalytic hydrogen evolution rate of 1280 μmol g−1 h−1. This performance has even surpassed some of the established compound photocatalysts. Systematic studies reveal that the bismuth-catalyzed selective growth of the preferential crystal phases of red P leads to the formation of fibrous and Hittorf’s phases at distinctive sites within the same photocatalyst particle of dendritic morphology: nanobranches of fibrous phase and main stems of Hittorf’s phase. As each crystal phase possesses unique band energy potential, the intimate heterojunction between the two phases affords an effective built-in driving force for the efficient transportation of photoexcited charge carriers with suppressed charge trapping and recombination. The strategy in crystal phase engineering of red P as well as the understanding of its charge transportation properties in this work provides new insights into developing favorable elemental P-based materials for various photocatalytic applications.

Porous Cd3(C3N3S3)2/CdS composites with outstanding Cr(VI) photoreduction performance under visible light irradiation

As an efficient and sustainable technology, photocatalysis driven by visible light has made great contributions to the removal of heavy metals from environment. In this work, a series of Cd3(TMT)2/CdS heterojunction composite photocatalysts were prepared by self-formation of CdS nanoparticles using an octahedral coordination polymer Cd3(C3N3S3)2 (denoted as Cd3(TMT)2) as a precursor. The photocatalytic performance of Cd3(TMT)2/CdS heterojunction composites for Cr(VI) has been significantly improved under visible light irradiation owing to effective separation and migration of photoexcited charge carriers. Moreover, Cd3(TMT)2/CdS composites exhibited remarkable photocatalytic reduction performance of Cr(VI) solution with high concentration. This photocatalyst provides a novel route in the photoreduction of Cr(VI).