Electron-hole Research Articles

G-C3N4 Modified with Metal Sulfides for Visible-Light-Driven Photocatalytic Degradation of Organic Pollutants.

Graphitic carbon nitride (g-C3N4) proved to be a promising semiconductor for the photocatalytic degradation of various organic pollutants. However, its efficacy is limited by a fast electron hole recombination, a restricted quantity of active sites, and a modest absorption in the visible range. To overcome these limitations, g-C3N4-Bi2S3 and g-C3N4-ZnS composites were effectively produced utilizing a starch-assisted technique. The findings from FT-IR, XRD, EDX, XPS, BET, SEM, and TEM demonstrated that the enhanced photocatalytic activity of g-C3N4-Bi2S3 and g-C3N4-ZnS composites was primarily due to their improved photocarrier separation and transfer rates. The photocatalyst facilitated the aerobic photocatalytic degradation of colorless contaminants such as coumarin and para-nitrophenol (4-NP). For the decomposition of 4-NP, g-C3N4-Bi2S3 exhibited a maximum efficiency of 90.86% in UV light and 16.78% in visible light, with rate constants of 0.29 h-1 and 0.016 h-1, respectively. In contrast, g-C3N4-ZnS demonstrated a maximum efficiency of 100% in UV light and 15.1% in visible light, with rate constants of 0.57 h-1 and 0.018 h-1, respectively. The bioinspired synthesis combined with the modification with metal sulfides proved to considerably enhance the photocatalytic activity of g-C3N4, increasing its potential for practical applicability in environmentally friendly water treatment systems for the efficient removal of recalcitrant organic contaminants.

Coating MOF Layer on Fe3O4 Nanoparticles Towards Enhancing Photocatalysis Activation of Peroxydisulfate via Layer Thickness Control

ABSTRACTAs the photocatalytic layer, metal organic frameworks (MOFs) with thickness control were coated on the surface of Fe3O4 nanoparticles to investigate the influence of photocatalysis on the activation of peroxydisulfate to degrade antibiotic pollutants. A suitable thickness of MOF layer can not only enhance the adsorption of the substrate molecules on the composite catalyst but also provide optimized electron transfer distance and path, which is conducive to improving the efficiency of electron–hole separation, thereby enhancing the activation of peroxydisulfate and the degradation efficiency of pollutants.

A Versatile Ionic Liquid Additive for Perovskite Solar Cells: Surface Modification, Hole Transport Layer Doping, and Green Solvent Processing.

Hole-transport layers (HTL) in perovskite solar cells (PSCs) with an n-i-p structure are commonly doped by bis(trifluoromethane)sulfonimide (TFSI) salts to enhance hole conduction. While lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopant is a widely used and effective dopant, it has significant limitations, including the need for additional solvents and additives, environmental sensitivity, unintended oxidation, and dopant migration, which can lead to lower stability of PSCs. A novel ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (MMPyTFSI), is explored as an alternative dopant for 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD). MMPy ions act as a surface passivator, reducing defects on the perovskite surface, while TFSI ions facilitate p-type doping. MMPyTFSI functions as an efficient dopant, maintaining excellent performance even when tetrahydrofuran (THF) is utilized as a solvent in place of chlorobenzene (CB), while significantly reducing the environmental impact of the process. The optimized PSC achieves a power conversion efficiency (PCE) of 23.10% and demonstrates enhanced long-term stability in all aging tests for over 1000 h in a humid atmosphere, at high temperature, and under simulated sunlight illumination. These results demonstrate that MMPyTFSI is an effective and environmentally friendly dopant for producing stable and efficient PSCs.

Exploring superconductivity in dynamically stable carbon-boron clathrates trapping molecular hydrogen

Abstract The recent discovery of type-VII boron–carbon clathrates with calculated superconducting transition temperatures approaching ~100 K has sparked interest in exploring new conventional superconductors that may be stabilized at ambient pressure. The electronic structure of the clathrate is highly tunable based on the ability to substitute different metal atoms within the cages, which may also be large enough to host small molecules. Here we introduce molecular hydrogen (H2) within the clathrate cages and investigate its impact on electron–phonon coupling interactions and the superconducting transition temperature (Tc). Our approach involves combining molecular hydrogen with the new diamond-like covalent framework, resulting in a hydrogen-encapsulated clathrate, (H2)B3C3. A notable characteristic of (H2)B3C3 is the dynamic behavior of the H2 molecules, which exhibit nearly free rotations within the B–C cages, resulting in a dynamic structure that remains cubic on average. The static structure of (H2)B3C3 (a snapshot in its dynamic trajectory) is calculated to be dynamically stable at ambient and low pressures. Topological analysis of the electron density reveals weak van der Waals interactions between molecular hydrogen and the B–C cages, marginally influencing the electronic structure of the material. The electron count and electronic structure calculations indicate that (H2)B3C3 is a hole conductor, in which H2 molecules donate a portion of their valence electron density to the metallic cage framework. Electron–phonon coupling calculation using the Migdal–Eliashberg theory predicts that (H2)B3C3 possesses a Tc of 46 K under ambient pressure. These results indicate potential for additional light-element substitutions within the type-VII clathrate framework and suggest the possibility of molecular hydrogen as a new approach to optimizing the electronic structures of this new class of superconducting materials.

Mechanistic Multiscale Simulations and Charge Transport Properties of Amorphous and Crystalline α‐NPD Molecular Conformations: Insights From Molecule to Material Level

ABSTRACTThe optoelectronic and charge transfer integral properties of N,N′‐di(1‐naphthyl)‐N,N′‐diphenyl‐4,4′‐diamine (α‐NPD) organic light‐emitting diode (OLED) in amorphous and crystalline structures is studied based on the Marcus–Levitch–Jortner theory and quantum chemistry calculations. The charge transfer integral simulations have been investigated through hole‐hopping regime from molecule‐to‐molecule in dimers molecules and are determined by frontier molecular orbitals (FMOs) for hole and electron transport. Quantum approaches with TD/DFT and DFT have been used to describe the most relevant electronic transitions of α‐NPD, which present character in harmony with the solvent states. Furthermore, the obtained results reveal that geometric deformations have been relied to naphthalene form and benzene rings in α‐NPD structures, and the charge transfer integral in amorphous state shows and , and in the crystalline state, it shows and . Comparing the transfer integrals average of hole/electron in the both amorphous and crystalline states, a higher value of hole transfer is explored in the amorphous form. The charge transfer transition obtained from FMO states and density of states (DOS), as well as reorganization energies values, indicates that α‐NPD would be an effective organic electronic hole transport material.

Nanostructured Fe2O3/Cu x O heterojunction for enhanced solar redox flow battery performance.

Solar redox flow batteries (SRFB) have received much attention as an alternative integrated technology for simultaneous conversion and storage of solar energy. Yet, the photocatalytic efficiency of semiconductor-based single photoelectrodes, such as hematite, remains low due to the trade-off between fast electron hole recombination and insufficient light utilization, as well as inferior reaction kinetics at the solid/liquid interface. Herein, we present an α-Fe2O3/Cu x O p-n junction, coupled with a readily scalable nanostructure, that increases the electrochemically active sites and improves charge separation. Thanks to light-assisted scanning electrochemical microscopy (photo-SECM), we elucidate the morphology-dependent carrier transfer process involved in the photo-oxidation reaction at an α-Fe2O3 photoanode. The optimized nanostructure is then exploited in the α-Fe2O3/Cu x O p-n junction, achieving an outstanding unbiased photocurrent density of 0.46 mA cm-2, solar-to-chemical (STC) efficiency over 0.35% and a stable photocharge-discharge cycling. The average solar-to-output energy efficiency (SOEE) for this unassisted α-Fe2O3-based SRFB system reaches 0.18%, comparable to previously reported DSSC-assisted hematite SRFBs. The use of earth-abundant materials and the compatibility with scalable nanostructuring and heterojunction preparation techniques offer promising opportunities for cost-effective device deployment in real-world applications.

Fabrication of a high-efficiency hydrogen generation Pd/C3N5-K,I photocatalyst through synergistic effects of planar and spatial carrier separation

Non-metallic I heteroatoms and metal Pd nanoparticles construct the charge transfer pathways within and across the CN layers, enhancing electron–hole separation.

Rational design of a carbon nitride photocatalyst with in-plane electron delocalization for photocatalytic hydrogen evolution

Introducing B doping into the π-conjugated system of CN not only induces electron delocalization but enhances the separation and transfer of photoinduced electron–hole pairs. This leads to a 8.6-fold improvement in the photocatalytic H2 evolution.

Interfacial polarization charge engineering with co-designed LQB and EBL for enhanced EQE of AlGaN DUV LEDs

Abstract In this paper, we propose to modulate the polarization charges at the interface between the last quantum barrier (LQB) and the electron blocking layer (EBL) via strategically adjusting the Al composition in the LQB and EBL simultaneously. With appropriate design of the linear gradient profile in Al composition, the original positive polarization charges at the LQB/EBL interface can be diminished or converted into negative charges, which helps to reduce the positive electric field in EBL, thus adjusting the energy band near the LQB/EBL interface. Enhanced effective barrier height for electrons, decreased effective barrier height for holes, and accumulation of a large number of holes at the LQB/EBL interface are obtained, resulting in improved electron leakage and hole injection. In comparison with the reference deep ultraviolet light-emitting diode (DUV LED), an enhanced external quantum efficiency by 37.5% at an injection current density of 100 A cm−2 is achieved for the device with negative polarization charges. The modulation strategy of polarization charges at the LQB/EBL interface via co-designing the linear gradient of Al composition in LQB and EBL can be a feasible approach for obtaining high-performance DUV LEDs.

Exploring Intrinsic and Extrinsic p-Type Dopability of Atomically Thin β-TeO2 from First Principles.

Two-dimensional (2D) β-TeO2 has gained attention as a promising material for optoelectronic and power device applications, thanks to its transparency and high hole mobility. However, the mechanisms driving its p-type conductivity and dopability remain elusive. In this study, we investigate the intrinsic and extrinsic point defects in monolayer and bilayer β-TeO2, the latter of which has been experimentally synthesized, using the Heyd-Scuseria-Ernzerhof (HSE) + D3 hybrid functional. Our results reveal that most intrinsic defects are unlikely to contribute to p-type doping in 2D β-TeO2. Moreover, Si and H contamination could further impair p-type conductivity. Since the point defects do not contribute to p-type conductivity, we suggest two possible mechanisms for hole conduction: hopping conduction via localized impurity states, and substrate effects. We also explored substitutional p-type doping in 2D β-TeO2 with 10 trivalent elements. Among these, the Bi dopant is found to exhibit a relatively shallow acceptor transition level. However, all the dopants introduce deep localized states, where hole polarons are trapped by the lone pairs of Te atoms. Interestingly, monolayer β-TeO2 shows potential advantages over bilayers due to reduced self-compensation effects for p-type dopants. These findings provide valuable insights into defect engineering strategies for future electronic applications involving 2D β-TeO2.

Preparation and properties of high-efficiency lignin-carbon based photocatalytic composites for the degradation of dye wastewater under visible light

Lignin-based carbon/cadmium sulfide (LCS) composite photocatalytic materials with excellent porous structures were prepared by simple carbonization and in situ precipitation using lignin from a wide range of sources as a carbon source. The CdS nanoparticles were uniformly fixed in LC, which improved the sunlight absorption ability and good stability of the photocatalyst. The effect of different factors on the pore structure of composite photocatalytic materials was investigated. The results showed that the obtained LCS composites had the maximum specific surface area (334.841 m2·g−1) and porosity (0.4406 mL·g−1) when the mass ratio (the lignin: the templating agent) was 2:1 and the carbonization was carried out at 600 °C for 1.5 h (LCS-600-1.5-2). Compared with pure CdS, the photodegradation performance of the prepared LCS under simulated sunlight (500 W Xe lamp) irradiation was significantly improved. The degradation rate of methylene blue (MB) and methyl orange/methylene blue (MO/MB) by LCS reached 91.7% and 90.8% in 2 h, respectively. The material stability test of LCS showed that LCS has good acid–base stability, and the degradation rate of MB remained above 80% after 5 cycles. The LCS prepared from lignin biomass, improved the dispersion uniformity of cadmium sulfide, reduced the recombination of photogenic electron hole, enhanced the photocatalytic performance under visible light, which greatly expanded the application of photocatalytic material.

Thermal excitation of carriers at tail states and recombination rate in hydrogenated amorphous silicon

Measurements of low-energy photoluminescence (PL) in hydrogenated amorphous silicon (a-Si:H) have been performed by means of frequency-resolved spectroscopy. Temperature variation of radiative recombination rate of electron–hole pairs and thermal excitation of carriers at the tail states are discussed. The results suggest that the tail electrons do not contribute to the PL of the energy lower than 1.0 eV. Experimental results are quantitatively explained by considering a two-level system instead of the tail states.

Thermoelectric and electrical properties of triple-conducting multicomponent oxides based on substituted barium cerate-zirconate.

Multicomponent oxides often have exceptional thermal stability and interesting electronic properties. The present work presents the thermoelectric and electrical properties of the Ba(Zr0.2Hf0.2Sn0.2Ti0.2Fe0.2)O3-δ and Ba(Zr0.1Hf0.1Sn0.1Ti0.1Co0.1Ce0.1Bi0.1Fe0.1Y0.1Zn0.1)O3-δ multicomponent perovskites. Single-phase cubic perovskites were synthesized using the solid-state reaction method. They were characterized using X-ray diffraction, drop-solution calorimetry, and thermogravimetry methods. The total electrical conductivity and Seebeck coefficient measurements were performed in dry and wet air at temperatures between 600 and 1050 K. It was found that Ba(Zr0.1Hf0.1Sn0.1Ti0.1Co0.1Ce0.1Bi0.1Fe0.1Y0.1Zn0.1)O3-δ is thermodynamically less stable than Ba(Zr0.2Hf0.2Sn0.2Ti0.2Fe0.2)O3-δ. Moreover, this oxide incorporates a higher amount of water and exhibits higher conductivity and lower Seebeck coefficient. Charge transport in both perovskites can be assigned to the small-polaron hopping process via electron holes. An interesting temperature dependence of the Seebeck coefficient was found and, at temperatures above 750 K, related to hopping between energetically inequivalent states.

Learning Intermolecular Electronic Coupling with Molecular-Orbital-Based Descriptors.

Electronic coupling is the key parameter to determine the rate of intermolecular electron transfer and energy transfer at excited states. When excited states are involved, the couplings are state-specific, as they originate from the interactions between different molecular orbitals (MOs). Based on the MO overlap description of the electron transfer (ET) and excitation energy transfer (EET) couplings taken as the domain knowledge, here we propose a graphic molecular orbital (MO) based descriptor to predict intermolecular electronic couplings. As the MOs are characterized by the spatial distribution of their wave functions, namely, the size and sign of the lobes, we transform the grid points of a MO into two feature vectors containing the quantum and spatial information. Then, inspired by the MO overlap description of the electronic couplings, we build the descriptors by multiplying the vectors for paired MOs. Together with a deep neural network (DNN) model, we learn the couplings of hole transfer (HT), electron transfer (ET), and Dexter energy transfer (DET). For the couplings of naphthalene dimers, high accuracy of learning is achieved by our approach compared with the results from quantum chemical (QC) calculations with a small size of training data. Therefore, the MO-pair-based descriptor shows the ability to characterize MO interaction for the high performance learning of electronic couplings and implies the potential of this strategy for other state-specific properties of excited molecular systems.

Effect of Calcination-Induced Oxidation on the Photocatalytic H2 Production Performance of Cubic Cu2O/CuO Composite Photocatalysts

This study explores the H2 production performance of CuO/Cu2O with different morphology (nanocubes) synthesized by different methods using different sacrificial reagent (lactic acid), compared with the other three reported CuO/Cu2O photocatalysts used for H2 production. A cubic Cu2O photocatalyst was prepared using a hydrothermal method. It was then calcined at a certain temperature to form a cubic Cu2O/CuO composite photocatalyst. XRD, TEM, and XPS spectra confirmed the successful synthesis of cubic Cu2O/CuO composite photocatalysts by calcination-induced oxidation at a certain temperature. As the calcination temperature increases, the crystal phase of the photocatalyst changes from Cu2O to Cu2O/CuO and then to CuO. The effects of calcination-induced oxidation on morphology, light absorption, the separation of photoexcited carriers, and the H2 production activity of photocatalysts were studied. EPR spectra were monitored to analyze the oxygen vacancies in different samples. Mott–Schottky and Tauc plots were utilized to establish the band structure of the composite photocatalyst. Cu2O/CuO is a type II photocatalyst with a heterogeneous structure that helps to improve electron–hole separation efficiency. The H2 production efficiency of Cu2O/CuO composite photocatalyst reaches 11,888 μmol h−1g−1, 1.6 times that of Cu2O. The formation of the Cu2O/CuO heterojunction leads to enhanced light absorption, charge separation, and hydrogen production activity.

Sustainable Removal of Phenol Dye-Containing Wastewater by Composite Incorporating ZnFe2O4/Nanocellulose Photocatalysts

The escalating issue of phenol-containing wastewater necessitates the development of efficient and sustainable treatment methods. In this context, we present a novel composite photocatalyst comprising ZnFe2O4 (ZFO) nanoparticles supported on nanocellulose (NC), aimed at addressing this environmental challenge. The synthesis involved a facile hydrothermal method followed by the impregnation of ZFO nanoparticles onto the NC matrix. The morphology and structure of ZFO, NC, and ZFO/NC were investigated by TEM, SEM-EDX, UV–vis, FT-IR, XRD, and XPS analyses. ZFO, as a weakly magnetic semiconductor catalytic material, was utilized in photocatalytic experiments under magnetic field conditions. By controlling the electron spin states through the magnetic field, electron–hole recombination was suppressed, resulting in improved photocatalytic performance. The results demonstrated that 43% and 76% degradation was achieved after 120 min of irradiation due to ZFO and 0.5ZFO/NC treatment. Furthermore, the composite 0.5ZFO/NC demonstrated the highest photocatalytic efficiency, showing promising recyclability by maintaining its activity after three cycles of use. This study underscores the potential of the ZFO/NC composite for sustainable wastewater treatment, offering a promising avenue for environmental remediation.

Synthesis and Characterization of MgO-Fe₂O₃/γ-Al₂O₃ Nanocomposites: Enhanced Photocatalytic Efficiency and Selective Anticancer Properties

In the present work, we achieved the fabrication of MgO-Fe2O3/γ-Al2O3 NCs using a deposition–coprecipitation process. XRD, TEM, and SEM with EDX, XPS, FTIR, and PL spectroscopy were applied to examine the physicochemical properties of the samples. XRD analysis confirmed the successful incorporation of γ-Al2O3, MgO, and Fe2O3 phases. TEM and SEM images indicate that the nanocomposites exhibited an agglomerated morphology with spherical shapes and particle sizes in the range of 6–12 nm. EDX and XPS spectra revealed a composition of MgO-Fe2O3/γ-Al2O3 NCs. FTIR spectra identified characteristic vibrational bands corresponding to the chemical bonds present in the samples, confirming their successful synthesis. PL analysis showed the reduced recombination rate of electron–hole pairs and enhanced charge separation efficiency, which are important factors for improved photocatalytic activity. Photocatalysis results show that the MgO-Fe2O3/γ-Al2O3 NCs exhibited significantly higher photocatalysis efficiencies of 87.5% for Rh B and 90.4% for MB after 140 min, compared to γ-Al2O3 NPs and Fe2O3/γ-Al2O3 NPs. In addition, prepared MgO-Fe2O3/γ-Al2O3 NCs demonstrated superior stability after six runs. Biochemical data showed that the MgO-Fe2O3/γ-Al2O3 NCs exhibited significant toxicity toward A549 cancer cells while displaying low toxicity toward IMR90 normal cells. The IC50 values (µg/mL ± SD) for γ-Al2O3 NPs, Fe2O3/γ-Al2O3 NPs, and MgO-Fe2O3/γ-Al2O3 NCs were 16.54 ± 0.8 µg/mL, 14.75 ± 0.4 µg/mL, and 11.40 ± 0.6 µg/mL, respectively. These results suggest that the addition of Fe2O3 and MgO to γ-Al2O3 not only enhances photocatalytic activity but also improves biocompatibility and anticancer properties. This study highlights that the MgO-Fe2O3/γ-Al2O3 NCs warrant further exploration of their potential applications in environmental remediation and biomedicine.

Non‐Radical Mediated Photocatalytic H2O2 Synthesis in Conjugate‐Enhanced Phenolic Resins with Ultrafast Charge Separation

It is essential for the development of highly efficient polymeric photocatalysts for hydrogen peroxide (H2O2) production. Nevertheless, the non‐uniform molecular structures and sluggish reaction pathway of polymeric photocatalysts lead to low conversion efficiency. In this work, we report sulfur‐contained phenolic resins with regulated conjugation for photocatalytic H2O2 production. Due to the substitution of sulfur for methylene in the phenolic resin structure, the conjugation degree of the material is adjusted, resulting in the formation of a built‐in electric field. This effectively enhances the charge separation capability, enabling charge carriers to react faster with substrates. Through in‐situ characterization and theoretical calculations, we have unveiled that the introduction of sulfur can modulate the reaction pathway of phenolic resin materials, enabling a dual‐pathway photocatalytic H2O2 production mediated by non‐radical species. Impressively, the sulfur‐contained resin photocatalyst showcases exceptional H2O2 production activity with a solar‐to‐chemical conversion efficiency of 1.4% exceeding most reported systems, and generates 25 mmol m‐2 of H2O2 under natural sunlight through large‐scale equipment. This work provides a facile strategy to separate the photogenerated electron–hole pairs of polymer photocatalysts to achieve efficient artificial photosynthesis.

POM-Mediated Synthesis of Ag/PW12/g-C3N4 Nanocomposite Exhibiting Enhanced Photocatalytic Performance Under Visible Light

The photoreduction method was utilized to synthesize the Ag/PW12/g-C3N4 nanocomposite. The polyanion PW12O403− served as the photoreductant, and as a stabilizer and protectant for Ag nanoparticles. TEM images reveals that Ag nanoparticles with a size of approximately 5 nm were modified on the surface of g-C3N4. Photocatalytic experiments confirm that Ag/PW12/g-C3N4, with the mass ratio of Ag3PW12O40 to g-C3N4 nanosheets at 30%, exhibits high efficiency and durability in the photodegradation of Rhodamine B. Research on the photocatalytic mechanism indicates that decorating PW12O403− and Ag nanoparticles on the surface of g-C3N4 nanosheets is beneficial for improving the separation of electron–hole pairs and enhancing the capability for visible light absorption.

Exciton Thermodynamics in Pure Diamond

AbstractLow‐temperature condensation thermodynamics is a fundamental research in the field of condensed matter physics. Prior studies have extensively explored the exciton condensation of indirect‐bandgap semiconductors like silicon (Si) and germanium (Ge), which predominantly focus on temperature effects but neglect the relationship between the initial condensed state and the external excitation power density. Here, based on pure diamond, the impact of excitation power density on condensed‐state thermodynamics is analyzed. With power density as a key variable, an inter‐dependency among exciton, electron–hole plasma, and electron–hole droplets can be observed in diamond. For instance, as the average excitation power density increases (6.15 to 246 mW cm−2), the exciton emission quenching temperature rises from 60 to 120 K. This is because the variation in initial states of the excitonic condensed phase under different excitation power densities leads to the changes in quenching energy, which subsequently affects the temperature dependence of the exciton quenching. This study pioneers a novel approach to explore luminescent thermodynamics in indirect‐bandgap semiconductors with both excitation power density and temperature considered as dimensions simultaneously.