Hole Pairs Research Articles

Photocatalytic Composites Based on Biochar for Antibiotic and Dye Removal in Water Treatment

Many semiconductor photocatalysts are characterized by high photostability and non-toxicity but suffer from the limited excitation in the UV part of the spectrum and the fast recombination of the photogenerated electron–hole pairs. To improve the above properties, biochar-supported composite photocatalysts have recently attracted much attention. Compared with the pure photocatalyst, the biochar-enriched catalyst has superior specific surface area and high porosity, catalytic efficiency, stability, and recoverability. Biochar can be obtained from various carbon-rich plant or animal wastes by different thermochemical processes such as pyrolysis, hydrothermal carbonization, torrefaction, and gasification. The main features of biochar are its low price, non-toxicity, and the large number of surface functional groups. This paper systematically presents the latest research results on the method of preparation of various composites in terms of the choice of photoactive species and the source of biomass, their physico-chemical properties, the mechanism of the photocatalytic activity, and degradation efficiency in the treatment of organic contaminants (dyes and antibiotics) in an aquatic environment. Particular emphasis is placed on understanding the role of biochar in improving the photocatalytic activity of photoactive species.

Effect of Hydrothermal Reaction Time and Etching on Nanorod TiO2 Thin Film

Titanium dioxide (TiO2) has the most potential function in numerous research domains because of its various advantages. Among the variety of ways, TiO2 nanorods (TNRs) are one of interest nanoparticle structures due to their superior delocalisation of the electron holes pair and lower charge recombination. However, TNRs inhibit solar spectrum absorption and have a high resistivity. In this study, etching treatment is introduced to increase the specific surface area and reduce resistivity. The effect of reaction time was investigated on TNRs thin film by using the hydrothermal method. From the findings, the 8-hour reaction time of TNRs thin film revealed the most striking characteristics. The preferred (101)-orientation of TNRs was observed and the diameter of rods increased along with reaction time. As the reaction time rises, the bandgap energy of TNRs approaches the value of 3.0 eV and presents a compact surface. After etching treatment, the peak intensity of (101)-orientation of TNRs increases indicating high crystallinity. The morphology of nanorods changed into smaller rods, apparently a nanowire with deeper depth. The surface roughness and band gap increased due to the surface area affected by etching. The electrical properties of etched-TNRs thin film after showed a reduction of resistivity aligning to thickness decrement. Thus, hydrothermal etching treatment showed effectiveness in enhancing TNRs properties in terms of crystallinity, surface morphology and reducing resistivity.

Enhanced degradation and mineralization of OFX in water: Triggering the shift of dominant role from •OH to O2•- in dielectric barrier discharge plasma system

Faced with the threat to water environment posed by non-standard antibiotic usage, enhanced removal and mineralization of ofloxacin (OFX) were achieved concurrently by adding MnFe2O4/MXene to trigger the dominant role of O2•- based on dielectric barrier discharge plasma (DBDP). The electron (e-)-hole (h+) pairs formed by the action of high-energy electrons or photons in DBDP on MnFe2O4/MXene created the majority of the O2•- through catalyzing H2O2 and O2. Besides, multiple advanced oxidation processes (AOPs), Fenton-like reaction and O3 catalysis for example, were also involved in the MnFe2O4/MXene-DBDP system. MXene effectively inhibited the recombination of e--h+ pairs, while also facilitating the charge transfer from Mn/Fe sites to the antibonding orbits of the adsorbed H2O2, O2 and O3. Notably, the predicted serial toxicities of potential intermediates confirmed the necessity of focusing on mineralization efficacy. This study provided a promising alternative for refractory organic pollutant removal and enriched the catalytic mechanism at the micro level.

Fabrication of α-Fe2O3/TiO2 heterojunction for photocatalytic degradation of doxycycline hydrochloride

In this work, flower-like TiO2 (TiO2-F) was first prepared by modulating the morphology of TiO2, and then, α-Fe2O3 was loaded onto TiO2-F to successfully prepare α-Fe2O3/TiO2-F heterojunction materials. The material showed excellent degradation properties of doxycycline hydrochloride under visible light. The photocatalytic degradation efficiency of α-Fe2O3/TiO2-F2 for doxycycline hydrochloride under visible light reached 95.76 % in 120 min, and its pseudo-first-order degradation rate constant was 0.02647 min−1, which was 3.68 and 2.01 times higher than those of α-Fe2O3 and TiO2 alone, respectively. This good photocatalytic performance is attributed mainly to the introduction of α-Fe2O3 to form a Type II heterojunction with floral TiO2 (TiO2-F), which is capable of promoting the separation of electron–hole pairs of photocatalysts and exhibiting a stronger redox capacity. The material exhibits notable stability and maintains high degradation efficiency even after undergoing multiple cycles. Furthermore, free radical trapping experiments and electron spin resonance (ESR) characterization revealed that hydroxyl radicals play a dominant role in this system. Finally, the degradation pathways were analyzed, and relevant toxicological analyses were performed, indicating that the toxicity of doxycycline hydrochloride gradually decreased during the photocatalytic degradation process.

Achieving pure-fluorescent color-tunable WOLED through long-range coupling of spatially separated electron–hole pairs

Abstract Color-tunable white organic light-emitting diode (CT-WOLED) with a wide correlated color temperature (CCT) offers numerous advantages in meeting human daily needs related to circadian rhythm. The study of CCT variation trends and the rules governing the expansion of the CCT range will help further improve the performance of such devices. This research proposes an effective strategy for achieving high-efficiency fluorescent CT-WOLEDs through long-range radiative coupling of spatially separated electron–hole pairs. After inserting a 5 nm thick DMAC-DPS layer between the donor (TAPC) and the acceptor (PO-T2T), the charge transfer excitons between TAPC and PO-T2T still exist. As the voltage increases, holes selectively undergo different photophysical processes, resulting in a wide CCT range. This demonstrates the extraordinary potential of spatially separated electron–hole pairs in regulating luminescent properties. By further introducing a bulk exciplex and the conventional red fluorescent dye DCJTB, the device’s efficiency, brightness, and CCT range have been further optimized. Additionally, significant highest occupied molecular orbital energy level difference between the hole transport layer TAPC and the spacer layer facilitates hole accumulation at the TAPC/spacer interface, thereby enhancing the long-range coupling effect. In device E, we achieved a wide CCT range of 2774 K along with a high external quantum efficiency of 9.2%. The results indicate that our proposed long-range coupling strategy not only enables a wide CCT range but also ensures broad spectral emission and high electroluminescence efficiency, providing new possibilities for the field of intelligent lighting.

Boosting piezocatalytic activity for hydrogen bonding self-assembled Ti3C2/BaTiO3 heterojunction via accumulated piezoelectric effect

Constructing heterojunctions has been proved to effectively improve the carrier transfer capability for enhanced catalytic activity. Herein, Ti3C2/BaTiO3 heterojunctions were fabricated through self-assembly driven by hydrogen bonding between piezoelectric barium titanate (BaTiO3) stabilized by oleic acid molecules and titanium carbide (Ti3C2) with surficial functional groups under continuous ultrasonic vibration. Owing to the formation of heterojunction, the separation of free charges can be promoted by the conductive Ti3C2. Additionally, the recombination of electrons and holes pairs in BaTiO3 can be hindered by built-in piezoelectric field. Hence, the piezocatalytic activity of Ti3C2/BaTiO3 was significantly enhanced by the accumulated piezoelectric effect, maintaining stability during the piezocatalytic degradation of bisphenol A and achieving rate constants that were 22.2 and 3.2 times higher than those of Ti3C2 and BaTiO3, respectively. This work thus presents a novel strategy for designing high-activity heterojunction piezocatalysts through hydrogen bonding self-assembly.

Facile Synthesis of a Micro–Nano-Structured FeOOH/BiVO4/WO3 Photoanode with Enhanced Photoelectrochemical Performance

In the realm of photoelectrocatalytic (PEC) water splitting, the BiVO4/WO3 photoanode exhibits high electron–hole pair separation and transport capacity, rendering it a promising avenue for development. However, the charge transport and reaction kinetics at the heterojunction interface are suboptimal. This study uses the hydrothermal–electrodeposition–dip coating–calcination method to prepare a microcrystalline WO3 photoanode thin film as the substrate material and combines it with nanocrystalline BiVO4 to form a micro–nano-structured heterojunction photoanode to enhance the intrinsic and surface/interface charge transport properties of the photoanode. Under the condition of 1.23 V vs. RHE, the photoelectric current density reaches 1.09 mA cm−2, which is twice that of WO3. Furthermore, by using a simple impregnation–mineralization method to load the amorphous FeOOH catalyst, a noncrystalline–crystalline composite structure is formed to increase the number of active sites on the surface and reduce the overpotential of water oxidation, lowering the onset potential from 0.8 V to 0.6 V (vs. RHE). The photoelectric current density is further increased to 2.04 mA cm−2 (at 1.23 V vs. RHE). The micro–nano-structure and noncrystalline–crystalline composite structure proposed in this study will provide valuable insights for the design and synthesis of high-efficiency photoelectrocatalysts.

Antimony (Sb)-doped PbTe nanostructured alloys with improved optical and thermoelectrical characterizations for clean energy applications

The current work investigates the influence of antimony doping on the morphology, optical behavior, and thermoelectric performance of PbTe nanostructures fabricated using the hydrothermal method. Analyses employing X-ray diffraction (XRD) and Raman spectroscopy techniques asserted the existence of the cubic phase, a defining characteristic of PbTe compounds. The morphology and internal structure of the samples are examined by the scanning and high-resolution transmission electron microscopes. The photoluminescence spectra show a band gap energy around 3.0 eV which is higher than that of the bulk sample. Raman spectra show three peaks corresponding to longitudinal optical (LO) phonon mode and higher-harmonic multiphonon process of PbTe. The PL spectra exhibit a strong peak at the wavelength 401 nm which is ascribed to a recombination of excitons and/or shallowly trapped electron–hole pairs. The thermoelectric properties are studied in the temperature range of 300–500 K and confirm the domination of p-type conduction in the whole temperature range. The electrical conductivity (σ) versus temperature showed thermally activated behavior as the charge carrier mobility is activated and the average carrier kinetic energy increases with temperature. Activation energy was obtained from the plots of Ln σ as a function of 1000/T. The recorded values were found at 62, 50,73 and 34 meV for x = 0, 0.04, 0.06 and 0.08, respectively. The Seebeck coefficients (S) of the synthesized nanostructures revealed a dominance of p-type conduction due to consistently positive S values. The S-T plots exhibit an initial increase in S with temperature at lower values (T < Tₛ). However, a transition occurs at a specific temperature (Tₛ), marked by a step change in S from positive to negative values, followed by a decrease in S with further temperature rise (T > Tₛ). The highest Seebeck coefficient was observed around 196.2 μV/ K and recorded at 418 K for the sample of x=0.04 Sb content. The largest power factor was recorded at 13.6×10-5 W. m-1. K-2, obtained for pure PbTe at 438 K due to the high value of electrical conductivity.

Surface Plasmon Polariton Photoluminescence Enhancement of Single InP Nanowires with InAsP Quantum Wells

A significant (up to 4 times) photoluminescence enhancement of single InP/InAsP/InP nanowires transferred onto a silicon oxide‐covered silver layer on silicon substrate with a metal surface roughness level of less than 1 nm and a dielectric thickness of 5 nm has been demonstrated. This phenomenon is explained by the interaction of electron–hole pairs in the semiconductor with surface plasmon polaritons. The photoluminescence kinetics and results of modeling confirm the indicated enhancement mechanism.

Biomimetic Dual‐Driven Heterojunction Nanomotors for Targeted Catalytic Immunotherapy of Glioblastoma

AbstractThe existence of the blood–brain barrier (BBB) and the characteristics of the immunosuppressive microenvironment in glioblastoma (GBM) present significant challenges for targeted GBM therapy. To address this, a biomimetic hybrid cell membrane‐modified dual‐driven heterojunction nanomotor (HM@MnO2‐AuNR‐SiO2) is proposed for targeted GBM treatment. These nanomotors are designed to bypass the BBB and target glioma regions by mimicking the surface characteristics of GBM and macrophage membranes. More importantly, the MnO2‐AuNR‐SiO2 heterojunction structure enables dual‐driven propulsion through near‐infrared‐II (NIR‐II) light and oxygen bubbles, allowing effective treatment at deep tumor sites. Meanwhile, the plasmonic AuNR‐MnO2 heterostructure facilitates the separation of electron–hole pairs and generates reactive oxygen species (ROS), inducing immunogenic tumor cell death under NIR‐II laser irradiation. Furthermore, MnO2 in the tumor microenvironment reacts to release Mn2+ ions, activating the cGAS‐STING pathway and enhancing antitumor immunity. In vitro and in vivo experiments demonstrate that these dual‐driven biomimetic nanomotors achieve active targeting and deep tumor infiltration, promoting M1 macrophage polarization, dendritic cell maturation, and effector T‐cell activation, thereby enhancing GBM catalysis and immunotherapy through ROS production and STING pathway activation.

Enhanced photocatalytic degradation of organic pollutants by randomly oriented 2D SnS2 nanostructures

Abstract In this study, we present a bottom-up solvothermal technique using tin tetrachloride pentahydrate (SnCl4.5H2O) and thioacetamide as precursors to synthesize SnS2 nanostructures. Different solvents including isopropyl alcohol, ethanol (EN), and ethylene glycol were used in the reaction to enhance the photodegradation efficiency of organic pollutants, Methylene Blue (MB), and Tetracycline (TC) in an aqueous medium under simulated solar light irradiation. The SnS2 nanostructures synthesized with these solvents were characterized using various structural, morphological, and optical techniques, including x-ray diffraction, RAMAN, field emission scanning electron microscope, x-ray photoelectron spectroscopy, UV–Vis, and Brunauer–Emmett–Teller analysis. The choice of solvent was found to significantly affect the structural, morphological, and optical properties of the SnS2 nanostructures. Notably, the sample synthesized with EN as the solvent displayed a unique morphology, enhanced light-harvesting ability, efficient charge carrier separation, and a larger specific surface area, all of which contributed to its superior photocatalytic activity. This sample achieved 99.9% degradation of MB and 95% degradation of TC within 20 and 40 min, respectively. The kinetic analysis revealed maximum rate constant (k) values of 0.15242 min−1 for MB and 0.060 95 min−1 for TC, as determined by the pseudo-first-order kinetic model. We also discuss the plausible mechanism involving visible light-induced electron–hole pairs that generate reactive species, leading to the mineralization of dyes into H2O, CO2, and other gaseous products. The synthesized SnS2 nanostructures demonstrate significant potential for enhanced photocatalytic activity in organic pollutant degradation, underscoring their promise in addressing water pollution challenges.

A straightforward strategy to modulate ROS generation of AIE photosensitizers for type-I PDT

Type-I photodynamic therapy (PDT), valued for its reduced oxygen requirement, generates highly cytotoxic •OH radicals. However, conventional strategies for developing type-I photosensitizers (PSs) are complex and involve intricate organic synthesis. Herein, we present a novel strategy to alter the generation of reactive oxygen species (ROS) by simply manipulating the twisting degree of donor–acceptor (D−A) type aggregation-induced emission (AIE) PSs. Specifically, natural saturated fatty acids are employed to modulate the twisting state of AIE PSs, with higher doping ratios yielding more twisted structures and increased type-I ROS generation. In contrast, fatty acids with higher crystallinity promote planar structures and type-II ROS generation. Theoretical calculations suggest that AIE PSs with highly twisted structures lead to a prominent reduction in ΔEST and effective separation of electron−hole pairs, thereby favoring efficient intersystem crossing and charge transfer. The PDT system primarily driven by type-I ROS exhibits efficient bactericidal activity against clinically drug-resistant bacteria, which remarkably accelerates the recovery of bacteria-infected wounds in mice. This study demonstrates the first example of modulating ROS generation type by manipulating the twisting degree of D−A type AIE PSs, eliminating the need for intricate molecular design and organic synthesis. The proposed strategy opens up new avenues for advancing PDT applications.

Simulation Approaches for the Study of the Oil Flow Rate Distribution in Lubricating Systems with Rotating Shafts

This study addresses the issue of predicting the distribution of lubricant flow through the outlets of a rotating shaft used in vehicle power transmission. A typical geometry with closely spaced rows of holes, suitable for the lubrication of multi-disk clutches, was considered. Both lumped parameter and computational fluid dynamics approaches were applied and compared. The test rig for model validation was designed with a variable speed shaft featuring an axial oil inlet and three equally spaced pairs of radial outlet holes. The main characteristic of the experimental facility is the possibility to selectively measure the flow rates through each outlet. It was found that the three-dimensional model based on the multiple reference frame approach provides a reliable prediction of how the flow rate is distributed. Generally, the flow rate is lower through the outlet closest to the inlet and is maximum at the farthest exit. The flow distribution is minimally affected by the shaft speed. The influence of geometric parameters on making the flow distribution more uniform was studied. It was found that a better flow balance is obtained with a low ratio between the diameter of the radial holes and that of the axial channel. The results obtained offer best-practice guidelines for accurately simulating comparable systems, in order to optimize reliability of the mechanical transmission and energy efficiency of the flow generation unit.

Hydroxylated SiO2-modified {0 0 1}-TiO2 nanosheets as a surface multifunctional photocatalyst for enhanced degradation of gaseous toluene

The relatively weak activity and serious deactivation of anatase TiO2 nanosheet catalysts with highly exposed {001} facets ({001}-TiO2) limits its wide application in photocatalytic degradation of gaseous pollutants. Herein, we propose a hybrid photocatalyst composed of {001}-TiO2 and SiO2 with numerous hydroxyl groups (denoted as {001}-TiO2/HO-SiO2). The catalyst showed excellent performance for gaseous toluene degradation under UV illumination, with 99.2 % removal efficiency and 204.7 μmol L−1 CO2 yield (about 85.9 % mineralization efficiency) within 120 min. It also demonstrated superior durability over five consecutive cycles of toluene photodegradation. The modification of HO–SiO2 on {001}-TiO2 facilitate the selective adsorption of toluene on the catalyst surface by H-bonding interaction, and make the major poisoning species, benzoic acid, easily desorb from the surface, reducing the catalyst inactivation. Most importantly, we found that the formed TiOSi bond promotes the separation of photogenerated electron–hole pairs, and provides abundant available electrons for the formation of reactive oxygen radicals and the left holes for the conversion of toluene to benzyl radicals or oxidation of H2O to hydroxyl radicals, which results in the improved activity. This study highlights the importance of the introduction of secondary components with special functions on TiO2, which is helpful for the design of photocatalysts with high performance and anti-deactivation ability for treatment of volatile organic compounds.

Core/Shell ZnO/TiO2, SiO2/TiO2, Al2O3/TiO2, and Al1.9Co0.1O3/TiO2 Nanoparticles for the Photodecomposition of Brilliant Blue E-4BA

The synthesis and characterization of ZnO/TiO2, SiO2/TiO2, Al2O3/TiO2, and Al1.9Co0.1O3/TiO2 core/shell nanoparticles (NPs) is reported. The NPs were used for photocatalytic degradation of brilliant blue E-4BA under UV and visible light irradiation, monitored by high-performance liquid chromatography and UV-vis absorption spectroscopy. The size of the NPs ranged from 10 to 30 nm for the core and an additional 3 nm for the TiO2 shell. Al2O3/TiO2 and Al1.9Co0.1O3/TiO2 showed superior degradation under UV and visible light compared to ZnO/TiO2 and SiO2/TiO2 with complete photodecomposition of 20 ppm dye in 20 min using a 10 mg/100 mL photocatalyst. The “Co-doped” Al1.9Co0.1O3/TiO2 NPs show the best performance under visible light irradiation, which is due to increased absorption in the visible range. DFT-calculated band structure calculations confirm the generation of additional electronic levels in the band gap of γ-Al2O3 through Co3+ ions. This indicates that Co-doping enhances the generation of electron–hole pairs after visible light irradiation.

Theoretical and experimental investigation on electronic and photocatalytic properties of n-p BiOBr/FeWO4 heterojunction for dyes degradation

The present work reports novel n–p BiOBr/FeWO4 heterojunctions designed for proficient photodegradation of methyl orange and rhodamine B dyes. The structural and microstructural features confirm the realization of soft interface between BiOBr/FeWO4 phase with large number of singly ionized oxygen vacancies (VO•) as validated through electron paramagnetic resonance spectroscopy, which spectacle a significant role in the formation of electron (e-) ↔ hole(h+) pairs in the heterojunction. Photocatalytic tests exhibit outstanding improvement in the photocatalytic activity for heterojunctions in relation to pristine BiOBr and FeWO4 phases. Moreover, we have performed scavengers experiments viz., benzoquinone, isopropyl alcohol, and sodium ethylenediaminetetraacetate, where the superoxide and hydroxyl radicals were mainly responsible for the degradation of the methyl orange and rhodamine B dye. Finally, the theoretical calculations at the density functional theory level confirmed the presence of surface defects related to VO• at BiOBr/FeWO4 heterojunctions, responsible to control the electronic structure and adsorption features of the interface. We establish that the VO• on the surface play a significant role in reducing the e-↔h+ recombination rates, and the captured e- can be used to form radical oxygen’s species, which also contributing to improve the overall photocatalytic performance.

The Effect of Heat Treatment on the Sol–Gel Preparation of TiO2/ZnO Catalysts and Their Testing in the Photodegradation of Tartrazine

This study aims to synthesize TiO2/ZnO powders and to study the effect of heat treatment on their photocatalytic ability against the Tartrazine anionic dye. The as-obtained powders with the following compositions—90TiO2/10ZnO and 10TiO2/90ZnO (mol%)—were obtained by the sol–gel technique. The prepared gels were annealed at 500 °C and 700 °C and subsequently characterized by XRD, UV–Vis, and SEM methods. The single crystalline phase of TiO2, which has been detected at up to 500 °C is anatase, while for ZnO, it is the hexagonal wurtzite structure. Further increases in the temperature (700 °C) led to the appearance of rutile in the samples. The SEM analysis demonstrated that the binary oxide materials had irregular shaped particles with a tendency to agglomerate. The UV–Vis spectra of the gels exhibited a red shift in the cut-off of the 90TiO2/10ZnO sample compared with pure Ti(IV) butoxide. Photocatalytic tests showed that the investigated samples possessed photocatalytic activity toward Tartrazine. Compared with TiO2, the prepared TiO2/ZnO photocatalysts showed superior properties in the photodegradation of a Tartrazine water solution. The target photocatalysts’ enhanced photocatalytic activities can be explained by their reduced band gap energy, improved surface physicochemical characteristics, separation of photo-induced electron–hole pairs, and lowered recombination rate. Higher photocatalytic activity was observed for powders annealed at 500 °C, with the 10TiO2/90ZnO (mol%) sample exhibiting the highest photocatalytic degradation of the used organic dye.

Dual‐functional UiO‐66/g‐C3N4 composites for photocatalytic pesticide removal and in situ adsorption of phosphate byproducts in water

AbstractBACKGROUNDWith the increasing global demand for food, a significant amount of organophosphorus pesticides is applied to farmland, leading to pollution as they are discharged into natural water bodies with agricultural runoff. This study employed a coupling approach, utilizing a 6:4 mass ratio of zirconium‐based metal–organic framework UiO‐66 and g‐C3N4 through a grinding and annealing method to construct a Z‐type heterojunction composite material named UG 6:4.RESULTSThis material is employed for photocatalytic removal of the representative organophosphorus pesticide, dichlorvos (DDVP), from water and simultaneous in situ adsorption of its inorganic phosphorus byproducts. Results demonstrate that for initial DDVP concentrations below 5 mg L−1 (calculated as total phosphorus), both the mineralization rate under ultraviolet light irradiation with a wavelength of 365 nm and a power of 125 W and the adsorption rate of phosphorus were 100% when the pH was 6 and the UG 6:4 dosage was 0.2 g L−1. The sheet‐like g‐C3N4 tightly envelops the surface of UiO‐66, forming a Z‐scheme heterojunction. This structure imparts UG 6:4 with enhanced light absorption, faster generation and separation of photogenerated electron–hole pairs compared to individual UiO‐66 or g‐C3N4, and the establishment of an internal electric field suppresses the recombination of photogenerated charge carriers.CONCLUSIONConsequently, UG 6:4 exhibits outstanding photocatalytic pesticide removal capabilities. Furthermore, UG 6:4 demonstrates specific adsorption of inorganic phosphorus through electrostatic attraction and ligand exchange. This study indicates that UG 6:4 is a promising dual‐functional photocatalytic adsorbent with excellent application prospects. © 2024 Society of Chemical Industry (SCI).

Effect of Vacancy Defects on the Electronic Structure and Optical Properties of Bi4O5Br2: First-Principles Calculations

First-principles calculations based on density functional theory are employed to investigate the impact of vacancy defects on the optoelectronic properties of Bi4O5Br2. The results indicate that vacancy defects induce minimal lattice distortion in Bi4O5Br2 without compromising its structural stability. Oxygen or bromine vacancies are more likely to occur than bismuth vacancies. The introduction of a bismuth vacancy leads to n-type semiconductor behavior in the Bi4O5Br2 system, while the creation of an oxygen vacancy reduces the bandgap and enhances the light absorption capacity. Bi4O5Br2 with three coordinated oxygen vacancies exhibits a higher effective electron–hole pair mass ratio, which is advantageous for the efficient separation of electron–hole pairs. Bi4O5Br2 with three coordinated oxygen vacancies exhibits enhanced absorption and reflection coefficients in the visible-light region compared to other systems, indicating that oxygen vacancy defects significantly promote visible-light absorption and electron–hole separation. This research provides new theoretical insights for understanding and optimizing the performance of photocatalysts based on Bi4O5Br2.

Incoherence-to-coherence crossover observed in charge-density-wave material 1T-TiSe2

Analogous to the condensation of Cooper pairs in superconductors, the Bose–Einstein condensation (BEC) of electron–hole pairs in semiconductors and semimetals leads to an emergence of an exotic ground state — the excitonic insulator state. In this paper, we study the electronic structure of 1T-TiSe2 utilizing angle-resolved photoemission spectroscopy and alkali-metal deposition. Alkali-metal adatoms are deposited in-situ on the sample surface, doping the system with electrons. The conduction bands of 1T-TiSe2 are thereby pushed down below the Fermi energy, which enables us to characterize its temperature dependence with precision. We found that the formation of the charge density wave (CDW) in 1T-TiSe2 at ~ 205 K is accompanied by a significant increase of the band gap, supporting the existence of excitonic pairing in the CDW state of 1T-TiSe2. More importantly, by analyzing the linewidth of the single-particle excitation spectrum, we unveiled an incoherence-to-coherence crossover at 165 K, which could be attributed to a possible exciton condensation that occurs beneath the CDW transition in 1T-TiSe2. Our results not only explain the exotic transport properties of 1T-TiSe2, but also highlight the possible existence of an excitonic condensate in this semiconducting material.