Separation Of Charge Carriers Research Articles

Oxygen vacancies mediated enhanced photocatalytic activity of band gap engineered BaSn1-x Cu x O3 towards methylene blue degradation under visible and sunlight.

Photocatalysis, an advanced oxidation process (AOP), has been well explored as a promising and sustainable technology for tackling environmental pollution. This method involves semiconductors which generate powerful reactive oxygen species, capable of breaking down organic pollutants, on excitation with appropriate light energy. Among the diverse range of oxide semiconductors explored, perovskite oxides are an important family. While BaSnO3 is a known perovskite photocatalyst, its intrinsic photocatalytic efficiency is limited by poor separation of charge carriers. To overcome this, a proven strategy is to create oxygen vacancies. These defects suppress electron-hole recombination leading to enhanced photocatalytic degradation. Hence, we have synthesized the system BaSn1-x Cu x O3 (x = 0.0 to 0.2) and characterized well. Synthesis of the BaSn1-x Cu x O3 series was successfully carried out via a facile solid-state reaction route. Powder X-ray diffraction (XRD) confirms the phase purity and cubic crystal structure. Fourier transform infrared spectroscopy (FT-IR) confirms the Ba-O, Sn-O, Cu-O vibrations. The surface morphology and particle size distribution examined using field emission scanning electron microscopy (FE-SEM) reveal that the particles are cubic in shape. The optical properties investigated using ultraviolet diffuse reflectance spectroscopy (UV-DRS) indicate the band gaps to be in the range of 3.15-2.42 eV. Photoluminescence study confirms the effective charge carrier separation on doping with Cu. Its photocatalytic activity under visible and sunlight using methylene blue (MB) as a model pollutant has been studied. Indeed, we could enhance the photocatalytic activity of BaSnO3 and Cu doping at the Sn site (x = 0.2) exhibits 8 times higher rate constant than the parent phase under visible light and 60 times higher under sunlight respectively. The degradation percentages of MB are more than 95% in the doped phase in 30 min in both visible & sunlight whereas the parent phase exhibits it in 3 h. The significantly enhanced activity can be attributed to the oxygen vacancies created due to the substitution of Sn4+ by Cu2+. We have also proposed a possible degradation pathway. This study constitutes the first documentation of the photocatalytic activity of BaSn1-x Cu x O3, thereby opening new avenues for its potential applications in environmental remediation.

Innovative non-toxic exfoliation of bulk g-C3N4 into ultra-thin 1D/2D nanosheets and nanotubes for accelerated sunlight-driven photocatalysis.

A relatively green and safer in situ H2O2-mediated solvothermal technique has been employed to significantly enhance the photocatalytic activity of bulk g-C3N4 (bulk CN). This novel approach generates free oxygen (O2), facilitating simultaneous exfoliation and heteroatom doping of bulk CN. As a result, the optoelectronic and physicochemical properties of g-C3N4 are synergistically improved. The morphological transformation of bulk CN from thick multilayered structures to 2D ultrathin nanosheets and 1D nanotubes improves its discrete band structure, enhances its pore network and specific surface area, and facilitates the separation of photoexcited charge carriers. The 48 h exfoliated CN (CN-48) exhibits a significantly enhanced photocurrent response (447%) compared to bulk CN, along with a longer lifetime of photogenerated charge carrier separation. Furthermore, electrochemical impedance spectroscopy (EIS) reveals that CN-48 has a lower charge transfer resistance (Rct) than bulk CN, confirming its superior charge transport efficiency. Accordingly, CN-48 exhibited 220% and 180% higher degradation rates for Congo red (CR) and tetracycline (TC), respectively, compared to bulk CN. Furthermore, CR and TC degradation efficiencies were enhanced by increasing the pH and decreasing pollutant concentrations. The total organic carbon/chemical oxygen demand (TOC/COD) was effectively reduced by 80% and 74% following the degradation of 50 mg L-1 of CR and TC, respectively. Additionally, CN-48 demonstrated sustained degradation efficiencies of 98% for CR and 93% for TC over five consecutive cycles. This innovative exfoliation method is both facile and eco-friendly, providing a practical and scalable approach to significantly enhance photocatalytic activity under sunlight compared to existing exfoliation techniques.

Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution and CO2 Reduction over Silver-Modified Tubular Carbon Nitride with Enriched Nitrogen Vacancies.

Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution and CO2 Reduction over Silver-Modified Tubular Carbon Nitride with Enriched Nitrogen Vacancies.

Efficient Crystallization of Conjugated Microporous Polymers to Boost Photocatalytic CO2 Reduction

ABSTRACTThe use of conjugated microporous polymers (CMPs) in photocatalytic CO2 reduction (CO2RR), leveraging solar energy and water to generate carbon‐based products, is attracting considerable attention. However, the amorphous nature of most CMPs poses challenges for effective charge carrier separation, limiting their application in CO2RR. In this study, we introduce an innovative approach utilizing donor π‐skeleton engineering to enhance skeleton coplanarity, thereby achieving highly crystalline CMPs. Advanced femtosecond transient absorption and temperature‐dependent photoluminescence analyses reveal efficient exciton dissociation into free charge carriers that actively engage in surface reactions. Complementary theoretical calculations demonstrate that our highly crystalline CMP (Py‐TDO) not only greatly improves the separation and transfer of photoexcited charge carriers but also introduces additional charge transport pathways via intermolecular π–π stacking. Py‐TDO exhibits outstanding photocatalytic CO2 reduction capabilities, achieving a remarkable CO generation rate of 223.97 μmol g−1 h−1 without the addition of chemical scavengers. This work lays pioneering groundwork for the development of novel highly crystalline materials, advancing the field of solar‐driven energy conversion.

Important features, applications and future perspective of zinc oxide based reduce graphene oxide nanocomposite

Abstract The Sustainable Development Goals (SDGs) play key role in propelling transformative changes, and highlighting burning issues to be addressed to achieve successful global developmental initiative. Zinc oxide (ZnO) and reduced graphene oxide (rGO) are helpful in achieving various SDGs. However, both materials have some limitations. To overcome the drawbacks of individual ZnO and rGO nanomaterials, ZnO/rGO nanocomposites are designed. This review aims to highlight issues being faced by ZnO and graphene oxide and their resolution through the development of ZnO/rGO nanocomposite. Various characterization techniques are discussed to explore physio-chemical properties. As the composite materials exhibit enhanced charge carrier separation, and extended lifetime of photoinduced charge carriers, making them a promising agent for improved photocatalytic degradation of pollutants, biosensors, and energy conversion and storage devices such as solar cells, and lithium batteries etc. Morphological relationship with various activities and potential applications in numerous fields, including controlling environmental pollution, biomedical, bio-sensing, energy etc., have also been discussed to explore their importance. Additionally, for further advancement to design next generation material several recommendations have been given. The knowledge gained from this review is the way for the development of next-generation nanomaterials, capable of addressing global challenges in energy and environmental sustainability etc.

Enhanced photocatalytic performance of 2D/3D g-C3N4/MoS2 heterojunction for water remediation of real-world pollutants

This study presents a highly efficient photocatalyst composed of hydrothermally synthesised g-C3N4/MoS2 heterostructures. Three-dimensional (3D) flower-like MoS2 nanostructures were combined with two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets. The synthesised g-C3N4/MoS2 heterostructures were utilised to evaluate their photocatalytic efficacy in degrading organic pollutants, including Rhodamine B (RhB), Methylene blue (MB), and the antibiotic Tetracycline (TC), under simulated solar light illumination. An optimized quantity of g-C3N4 in the g-C3N4/MoS2 heterostructures markedly improved the photocatalytic degradation efficiency, resulting in 99.9% degradation of RhB in 30 min, 99.9% degradation of MB in 10 min, and 94% degradation of TC in 40 min with a minimal catalyst dosage (0.20 mg/ml). The g-C3N4/MoS2 heterojunction showed remarkable efficacy in the concurrent degradation of RhB, MB, and TC in a mixed solution. The superior photocatalytic performance of the g-C3N4/MoS2 nanocomposites can be ascribed to multiple factors, such as enhanced light absorption, augmented specific surface area, and plentiful active sites for reactions. The establishment of a built-in potential at the g-C3N4/MoS2 interface, resulting from the heterostructure, enhances efficient charge carrier separation, encourages charge migration, and prolongs the lifespan of photoinduced electrons and holes. The photocatalytic mechanism is elucidated by the alignment of energy bands at the heterojunction interface, which improves electron-hole separation and transport. The results underscore the promise of the g-C3N4/MoS2 photocatalyst for wastewater treatment and environmental remediation applications.

Tailoring Multiscale Interfaces in Heterojunction Photocatalysis for NOx Removal.

Nitrogen oxides (NOx) severely threaten human health and ecosystems. Photocatalytic technology offers a promising solution for eliminating low-concentration yet highly toxic NO. However, it faces challenges in catalyst stability, control of intermediate and final products, reaction selectivity, and disclosure of interfacial mechanisms. The key to surmounting these hurdles is effective carrier separation, vital for distinct redox reactions in photocatalysts. Additionally, the charge carrier efficiency (formation, transfer, separation, and further dynamics) and catalyst photocorrosion upon light irradiation significantly influence the photocatalytic performance and long-term stability of metal oxide-based systems. Heterojunctions, with their superior charge carrier separation efficiency, can effectively regulate the reaction pathways during NO conversion. Moreover, heterojunction engineering has been proven to mitigate photocorrosion by optimizing interfacial charge transfer and reducing the level of charge accumulation on vulnerable active sites. Despite the proliferation of reviews on photocatalytic heterojunctions, a critical gap exists in works that systematically unify the classification, synthesis, and application of diverse heterojunctions specifically for NO removal, while explicitly linking multiscale interfacial engineering, e.g., atomic-level defects, nanoscale band alignment, molecular adsorption to the precise control of reaction pathways and selectivity. Addressing this gap, this review establishes an innovative, unified framework that integrates heterojunction principles, classifications, and construction methods with their operational performance in NO removal, with an emphasis on their latest advancements. Uniquely, it maps design strategies directly to overcome real-world bottlenecks, such as byproduct suppression, relative humidity resistance, and selectivity enhancement. It interprets the state-of-the-art applications, highlighting how interfacial engineering synergistically enhances carrier efficiency and product control. By emphasizing the significance of improving carrier efficiency and controlling intermediate/final product formation by reactive oxygen species generation, this review provides valuable insights to guide future research toward securing higher NO conversions and reaction selectivity. Additionally, it lays the groundwork for the development of more effective and eco-friendly environmental cleanup technologies.

N-doped carbon quantum dots-Bi4O5Br2 composites: A case of van der Waals heterojunctions for efficient photocatalytic removal of NO under visible light irradiation.

N-doped carbon quantum dots-Bi4O5Br2 composites: A case of van der Waals heterojunctions for efficient photocatalytic removal of NO under visible light irradiation.

Facilitating carrier kinetics in ultrathin porous carbon nitride through shear-repair strategy for peroxymonosulfate-assisted water purification

Achieving high specific surface area (HSSA) in graphitic carbon nitride (g-C3N4) severely depolymerizes the molecular chain structure, resulting in sluggish carrier kinetic behaviors and thus moderated water purification performance in photocatalytic peroxymonosulfate (PMS) activation system. Herein, we report a versatile shear-repair strategy for fabricating ultrathin porous g-C3N4 nanosheets with a thickness of 1.5 nm, HSSA (138.5 m2 g−1), and highly polymerized molecular chains. This strategy accelerates exciton dissociation and charge carrier separation, with the exciton binding energy decreasing from 65.7 to 47.5 meV. Crucially, the electron-donating pollutant and electron-withdrawing PMS generate a microelectric field at the g-C3N4 surface that activates PMS to generate 1O2 sustainably. Consequently, our catalyst exhibits an exceptional imidacloprid (IMD) removal performance with a rate constant of 0.405 min−1 and remarkable PMS utilization efficiency (90% within 15 min). Moreover, under real conditions of sunlight irradiation, we observe an outstanding pollutants’ removal efficiency with a near-100% degradation rate over 20 days of continuous operation. Our work emphasizes the feasibility of synergistic molecular-level structural engineering for refining carrier kinetic behaviors in high-performance photocatalyst design.

One-pot synthesis of transition-metal-sulfides decorated CdS by low-temperature KSCN flux: An effective route to strengthen the interface for enhanced photocatalytic H2 evolution.

One-pot synthesis of transition-metal-sulfides decorated CdS by low-temperature KSCN flux: An effective route to strengthen the interface for enhanced photocatalytic H2 evolution.

Photocatalytic CO2 Conversion with H2O to CO and CH4 Over V2C/TiO2 Composite

Photocatalytic reduction of CO2 to valuable chemicals and fuels requires highly efficient semiconductor materials, and most available photocatalysts are less efficient. Due to their unique electrical properties, the new family of two-dimensional materials known as MXenes has drawn much interest in photocatalytic applications. The vanadium carbide (V2C) is one of the significant MXenes being considered because of its many advantages over other materials. In this work, V2C-loaded TiO2 composites were synthesized and tested for photocatalytic reduction of CO2 with H2O to produce value-added CO and CH4 fuels in a continuous flow photoreactor system. The optimized 10 % V2C-TiO2 was responsible for CO and CH4 formation of 1233.8 and 85.2 µmol g-1 h-1, respectively, which were many-fold higher than using pure TiO2. This enhanced photoactivity of the composite was due to increased conductivity, many active sites, and higher light absorbance, which allowed for the efficient separation of charge carriers and light absorbance. Thus, MXenes, particularly 2D V2C MXene, would be a promising cocatalyst to combine with a semiconductor to maximize photocatalytic activity during CO2 reduction application.

Recent Advances of COFs-based Materials for Photocatalytic U(VI) Separation: Structural Modulation and Mechanistic Exploration.

The development of efficient and selective U(VI) extraction from seawater and U(VI)-containing wastewater through photocatalytic technology holds significant importance for nuclear energy advancement and mitigation of radionuclide-related environmental and health risks. Covalent organic frameworks (COFs) have emerged as ideal photocatalytic materials for U(VI) separation due to their inherent porosity, robust frameworks, chemical stability, and exceptional structural regularity. This comprehensive review examines molecular-level structural optimization of COFs to enhance charge carrier separation and transfer, thereby improving photocatalytic U(VI) extraction efficiency. We systematically evaluate multiple design strategies, including: Donor-Acceptor (D-A) structure regulation, covalent linkage engineering, COF-based heterojunction construction, Metal-covalent organic frameworks (MCOFs) development, and piezo-photocatalytic synergy. Furthermore, we have discussed the fundamental principles of U(VI) separation mediated by COFs and carefully analyzed the mechanisms of U(VI) separation through photocatalysis by COFs. Finally, we analyzed the challenges faced in the photocatalytic separation of U(VI) based on COFs and prospected their development prospects. This review systematically summarizes the latest progress in the field of photocatalytic separation of U(VI) based on COFs, as well as the deficiencies in the catalytic mechanism. It can provide useful references for the rational design of efficient COF-based photocatalysts and in-depth exploration of the U(VI) separation mechanisms.

Optical Bandgap Tuning and Solar Cell Efficiency Enhancement in Green‐Synthesized Transition Metal‐Doped TiO2 Solar Cells

The present study investigates the optical bandgap tuning and solar cell performance of pollution‐free, green‐synthesized titanium dioxide (TiO2) nanoparticles. Transition metal doping with copper, silver, gold, and platinum is explored to enhance TiO2‐based solar cells. Plant extracts of coriander, spearmint, and fenugreek are used for synthesizing the doped TiO2 nanopowders. X‐ray diffraction confirms successful incorporation of transition metals into the TiO2 lattice, while scanning electron microscopy shows uniform particle distribution. The optical bandgap decreases upon metal doping, with Cu‐doped TiO2 showing the maximum reduction to 2.21 eV. Solar cell performance is evaluated through J–V measurements. Among all dopants, Au‐doped TiO2 exhibits the best results, with a short‐circuit current density (Jsc) of 18.47 mA cm−2 and an efficiency of 13.65%. In comparison, Cu‐, Ag‐, and Pt‐doped TiO2 samples showed efficiencies of 6.87%, 8.42%, and 12.23%, respectively. The enhanced performance is attributed to improved charge carrier separation due to doping, and in the case of Au‐doped TiO2, plasmonic effects that boost light absorption and charge transport. This study highlights the importance of selecting appropriate transition metal dopants to optimize TiO2 for next‐generation photovoltaic applications.

Enhanced near-infrared photodetection via exciton–plasmon coupling in Ag nanoparticle decorated MoS2/Si-nanowire hybrid

This study focuses on developing high-performance near-infrared photodetectors using an MoS2/Si nanowire array (NWA) heterostructure decorated with plasmonic silver nanoparticles (AgNPs). Three-dimensional MoS2 stacked on vertical Si NWAs forming the heterostructure shows a broad spectral response from 400 to 1100 nm with a peak response at around 900 nm. The surface-plasmonic AgNPs significantly enhanced the detectivity of the photodetector. The AgNPs distributed on the MoS2 surface triggered plasmon–exciton coupling, resulting in higher light absorption and improved charge carrier separation. AgNPs/MoS2/Si NWAs had shown a high responsivity of 110 A/W and detectivity of 9 × 1010 Jones, which were threefold higher than that obtained heterostructure without plasmonic nanoparticles. The photodetector also shows a responsivity of 1.0 mA/W in the self-powered mode.

Co-doping and N defect synergistically boosting 2e- oxygen reduction reaction on carbon nitride for full-day degradation of nitenpyram.

Co-doping and N defect synergistically boosting 2e- oxygen reduction reaction on carbon nitride for full-day degradation of nitenpyram.

An asymmetrically tipped MoS2/CdS heterostructure for high-performance photocatalytic plastic reforming.

Photoreforming plastic waste into valuable chemicals while simultaneously splitting water to produce hydrogen (H2) under mild conditions presents a sustainable strategy to address environmental issues and generate solar fuels. Herein, we report a MoS2/CdS heterojunction photocatalyst synthesized via a one-pot solvothermal method for plastic reforming and H2 production. The strong Mo-S-Cd interaction at the interface creates a robust internal electric field (IEF), which promotes efficient charge carrier separation. The macroscopic asymmetry of tipping growth of MoS2 on one end of CdS nanorods further promotes imbalanced charge carriers' distribution and increased charge population. As a result, the IEF and structural asymmetry ensure electron migration from MoS2 to CdS for proton reduction to yield H2, leaving oxidative holes in MoS2 to drive poly(lactic) acid (PLA) reforming. Under visible light irradiation, the catalyst achieved a high H2 production rate of 97.7 mmol g-1 h-1 without using cocatalysts or sacrificial agents. Concurrently, MoS2/CdS converted PLA into lactate and pyruvate. This dual-function catalyst demonstrates exceptional promise for sustainable H2 production and plastic waste upcycling.

Enhanced piezo-photocatalytic performance of W18O49/BaTiO3 heterojunctions under synergistic broad-spectrum light and ultrasound excitation.

Enhanced piezo-photocatalytic performance of W18O49/BaTiO3 heterojunctions under synergistic broad-spectrum light and ultrasound excitation.

Characterizing Interlayer Excitons by Spectral Signature in Scattering Visible Near-Field Microscopy.

Interlayer excitons (IXs) in van der Waals heterostructures exhibit unique optical properties due to their spatially separated charge carriers. However, the weak oscillator strength and radiative broadening of IXs make them difficult to detect with conventional absorption spectroscopy. Here, we use scattering-type scanning near-field optical microscopy (s-SNOM) to directly probe the dielectric response at the nanoscale. We first validate this approach by measuring the B-exciton in a four-layer MoS2 sample, where ion irradiation introduced defect-induced broadening. Extending this method to a MoSe2/WSe2 heterostructure, we observe a Lorentzian resonance at 1.35 eV, characteristic of interlayer excitons, with broadening dominated by nonradiative decay. These results demonstrate the capability of s-SNOM to image and characterize weak excitonic resonances at the nanoscale, overcoming the limitations of conventional techniques and providing new insights into localized exciton dynamics in 2D heterostructures.

Core-Shell Engineering of One-Dimensional Cadmium Sulfide for Solar Energy Conversion.

Fabricating efficient photocatalysts that can be used in solar-to-fuel conversion and to enhance the photochemical reaction rate is essential to the current energy crisis and climate changes due to the excessive usage of nonrenewable fossil fuels. To attain high photo-to-chemical conversion efficiency, it is important to fabricate cost-effective and durable catalysts with high activity. One-dimensional cadmium sulfides (1D CdS), with higher surface area, charge carrier separation along the linear direction, and visible light harvesting properties, are promising candidates for converting solar energy to H2, reducing CO2 to commodity chemicals, and remediating environmental pollutants. The main disadvantage of CdS is photocorrosion due to the leaching of S2- ions during the photochemical reactions, and further charge recombination rate leads to low quantum efficiency. Therefore, the implementation of core-shell heterostructured morphology, i.e., the growth of the shell on the surface of the 1D CdS, which offers unique features such as protection of CdS from photocorrosion, a tunable interface between the core CdS and shell, and photogenerated charge carrier separation via heterojunctions, provides additional active sites and enhanced visible light harvesting. Therefore, the viability of the core-shell synthesis strategy and synergetic effects offer a new way of designing photocatalysts with enhanced stability and improved charge separation in solar energy conversion systems. This review highlights some critical aspects of synthesizing 1D CdS core-shell heterostructures, underlying reaction mechanisms, and their performance in photoredox reactions. Finally, some challenges and considerations in the fabrication of 1D CdS-based core-shell nanostructures that can overcome the current barriers in industrial applications are discussed.

Synergistic Integration of g-C3N4 with SnS: Unlocking Enhanced Photocatalytic Efficiency and Electrochemical Stability for Dual-Functional Applications

The synthesis of graphitic carbon nitride (g-C3N4) coupled with tin sulfide (SnS) has been identified as an effective method for improving the photocatalytic and electrochemical performance of SnS, a promising material for environmental and energy-related applications. In this study, we focused on how g-C3N4 influences the structural, optical, electrochemical, and functional properties of SnS. XRD and FTIR confirmed the formation of SnS/g-C3N4 heterostructure, while surface morphology analysis by SEM showed proper dispersion of SnS particles over g-C3N4 with a good interface contact. The SnS/g-C3N4 composite itself demonstrated improved photocatalytic performance, with the degradation rate of methylene blue reaching approximately 94% under visible light irradiation compared to the moderate activity of SnS. This enhancement can be credited to the successful charge carrier separation enabled by the type II heterojunction created between SnS and g-C3N4. Moreover, the composite presented improved electrochemical activity with a specific capacitance of 1340 F·g−1 at a scan rate of 10 A·g−1 and good cycling stability, where the capacitance was 92% after 5000 cycles. As such, these SnS/g-C3N4 composites suggest the specific application of this class of material in photocatalytic degradation as well as energy storage, putting forward new effective resolutions to environmental and energy issues.