Separation Of Charge Carriers Research Articles

Awakening n-π* electron transition in structurally distorted g-C3N4 nanosheets via hexamethylenetetramine-involved supercritical CO2 treatment towards efficient photocatalytic H2 production.

Graphitic carbon nitride (g-C3N4) has been regarded as highly potential photocatalyst for solar energy utilization. However, the restricted absorption of visible light for pristine g-C3N4 significantly limits the solar-light-driven chemical reaction efficiency. Herein, structurally distorted g-C3N4 nanosheets with awakened n-π* electron transition were successfully synthesized through hexamethylenetetramine (HMTA)-involved supercritical CO2 (scCO2) treatment and following pyrolysis of melamine precursor. ScCO2 treatment was conductive to homogeneously dissoving melamine precursor and HMTA, and then the modification by HMTA with three-dimensional structure changed the g-C3N4 photocatalyst from a symmetrical planar structure to an asymmetrical non-planar structure. The resulting awakened n-π* electron transition in structurally distorted g-C3N4 nanosheets greatly extended the photoresponse range of g-C3N4 and increased the amount of catalytically active π electrons. Moreover, the unique distorted structure of g-C3N4 enhanced photogenerated charge carriers separation and provided sufficient reactive sites for photocatalytic H2 production. Consequently, the structurally distorted g-C3N4 nanosheets exhibited enhanced photocatalytic H2 production performance, which was up to 6.4 times that of pristine g-C3N4. This work presents a promising scCO2 strategy towards precursor treatment to regulate the microstructure of g-C3N4, and provides valuable guidance to obtain efficient g-C3N4 photocatalyst by microstructure engineering.

From Anatase TiO2 Nano-Cuboids to Nano-Bipyramids: Influence of Particle Shape on the TiO2 Photocatalytic Degradation of Emerging Contaminants in Contrasted Water Matrices.

Water pollution, resulting from industrial effluents, agricultural runoff, and pharmaceutical residues, poses serious threats to ecosystems and human health, highlighting the need for innovative approaches to effective remediation, particularly for non-biodegradable emerging pollutants. This research work explores the influence of shape-controlled nanocrystalline titanium dioxide (TiO2 NC), synthesized by a simple hydrothermal method, on the photodegradation efficiency of three different classes of emerging environmental pollutants: phenol, pesticides (methomyl), and drugs (sodium diclofenac). Experiments were conducted to assess the influence of the water matrix on treatment efficiency by using ultrapure water and stormwater (basic) collected from an urban drainage system as matrices. The size and shape of the nano-cuboids were accurately controlled during synthesis to assess their impact on photoactivity and selectivity. Regarding total organic carbon removal using TiO2 nano-cuboids in basic environments, the results were particularly remarkable. TiO2 nano-cuboids and truncated bipyramids synthesized in the 200-250 °C temperature range showed an enhanced photocatalytic efficiency when compared to alternative formulations. Diclofenac, methomyl, and phenol were fully mineralized from ultrapure water and basic stormwater. The TiO2 nano-cuboids/nano-bipyramids demonstrated better selectivity and photoactivity in comparison to irregular TiO2 nanoparticles. The differences in photoactivity and selectivity are explained in terms of charge carrier separation and trapping on the different crystal facets. Their performance demonstrates their potential as sustainable materials for the photodegradation of emerging pollutants in various water matrices.

Multiple Exciton Generation on Doped Wide-Band Semiconductor Photoanode with Hierarchical Quantum Structure.

The multiple exciton generation (MEG) effect, which produces multiple photo-generated charge carriers from a single high-energy photon absorption by a semiconductor with a narrow bandgap, has the potential to revolutionize photovoltaic, photoelectric detection, and other technologies. Here, this work finds that the surface carbon-modified wide-bandgap photoanode with hierarchical quantum structure can drive a photoelectrochemical reaction with a quantum efficiency exceeding 145% by the first time. More studies reveal that the presence of the MEG effect in the MEG-CdS photoanode is attributed to the formation of high-quality surface C-modified CdS quantum nanosheets on CdS bulk film by in situ, this hierarchical quantum structure leads to quantum confinement effects that increase effective Coulomb interaction for driving MEG and decrease competition for thermal exciton cooling. The acceptor level introduced by carbon reduces the MEG threshold (approximately twice the energy level difference) and collaborates with the built-in electric field of the C-CdS/bulk-CdS homojunction to enable the effective generation and separation of photo-generated charge carriers. The internal quantum efficiency of the MEG-CdS photoanode reaches up to a recording value of 145%, providing a novel perspective on the contribution of surface-modified wide-band semiconductors and their quantum effects in the application of MEG.

Site-Specific for CO2 Photoreduction with Single-Atom Ni on Strained TiO2-x Derived from Bimetallic Metal-Organic Frameworks.

The photocatalytic reduction of CO2 in water to produce fuels and chemicals is promising while challenging. However, many photocatalysts for accomplishing such challenging task usually suffer from unspecific catalytic active sites and the inefficient charge carrier's separation. Here, a site-specific single-atom Ni/TiO2-x catalyst is reported by in situ topological transformation of Ni-Ti-EG bimetallic metal-organic frameworks. The loading of nickel nanoparticles or individual atoms, which act as specific active sites, can be precisely regulated by chelating agents through the partial removal of nickel and adjacent oxygen atoms. Furthermore, the degree of lattice strain in Ni/TiO2-x catalysts, which improves the separation efficiency of charge carriers, can be modulated by fine-tuning the transformation process. By leveraging the anchored nickel atoms and the strained TiO2, the optimized NiSA0.27/TiO2-x shows a CO generation rate of 86.3 µmol g-1 h-1 (288 times higher than that of NiNPs/TiO2-x) and CO selectivity of up to 92.5% for CO2 reduction in a pure-water system. This work underscores the importance of tailoring lattice strain and creating specific single-atom active sites to facilitate the efficient and selective reduction of CO2.

Oxygen-modulated photoresponse in nickel oxide thin films for wide band gap photodetector application

Metal oxides, due to their wide band gap, are well suited for use in photodetectors as the active light-absorbing layer. While there have been extensive studies on n-type oxides, such as tungsten oxide and zinc oxide, there is relatively little work on the use of p-type oxides, such as nickel oxide (NiO), for photodetectors. Using these p-type oxides along with n-type conducting oxides to form heterojunctions can improve the detection capabilities by efficient separation of charge carriers. In this work, the photoresponse of a p-type NiO thin film, grown by room temperature reactive magnetron sputtering from a pure nickel target onto a conducting n-type indium-doped tin oxide (ITO) substrate, is investigated. Different ratios of oxygen to argon (10/45, 15/45, and 20/45) during sputtering are investigated, and the effect of oxygen concentration on the optical properties of the NiO film is studied, which helps in modulating the photoresponse of the developed detector. The O2/Ar ratio, with a value of 15/45, is found to perform better among the three ratios. For the corresponding photodetector, the current under illumination, is found to be nearly three orders of magnitude higher than the dark current, even at a very low applied voltage of 0.1 V. The calculated responsivity (at 0.012 A/W) is found to be the best among all three values. The device also has an excellent transient current response with a rise time of 0.5 s and a decay time of 1.4 s, which is the fastest transient behavior among all three ratio-based devices. The work paves the way for using metal oxide-based heterojunctions as wide band gap photodetectors.

Photocatalytic NO Removal by Ternary Composites Bi12GeO20/BiOCl/W18O49 Using a Waste Reutilization Strategy

Heterojunction creation is demonstrated as an effective strategy to enhance the transfer and separation of charge carriers, which is beneficial for subsequent photocatalytic reactions. In this study, “sea urchin-like” W18O49 was in situ-grown on the surface of Bi12GeO20 through a hydrothermal process, and the released Cl− anions tended to produce BiOCl simultaneously. Systematical characterizations confirmed the construction of ternary composites Bi12GeO20/BiOCl/W18O49 (GBW), in which Type I and Z-scheme models were integrated to promote charge carrier migration and separation by combining the structural merits of both models. Under UV–visible light, the catalytic performance of the as-synthesized samples was tested in terms of NO oxidation removal. Compared to pure Bi12GeO20, the composite GBW5 showed the highest NO photocatalytic removal efficiency of 42%, which was nearly four times that of pure Bi12GeO20. These improvements were mainly due to enhanced light absorption, suitable morphological features, effective separation of charge carriers, and the boosted generation of reactive species in the GBW series. This study paves the way for the construction of Bi12GeO20-based ternary composites using a comprehensive utilization of waste method and the employment of the composites for the photocatalytic removal of low concentrations of NO at the ppb level.

Mesoporous NiFe2O4@g-C3N4-Based p-n Heterostructures for Boosting Solar-Driven Photocatalytic Dye Degradation and Hydrogen Evolution.

Mass-fraction-optimized heterojunction composites featuring precisely engineered interfaces and mesoporous structures are crucial for improving light absorption, minimizing electron-hole recombination, and boosting overall catalytic efficiency. Herein, highly efficient mesoporous-NiFe2O4@g-C3N4 heterojunctions were developed by embedding p-type NiFe2O4 nanoparticles (NPs) within n-type porous ultrathin g-C3N4 (p-uCN) nanosheets. The optimized NiFe2O4@g-C3N4, loaded with 20 wt % magnetic counterparts, exhibits exceptional photocatalytic methylene blue (MB) degradation, achieving the highest performance in both photocatalytic and photo-Fenton processes with rate constants of 0.062 min-1 and 0.161 min-1, respectively. These performance metrics are 1.3 and 2.55 fold higher than p-uCN (0.048 min-1 and 0.063 min-1) and 51.6 and 17.4 fold higher than NiFO (0.0012 min-1 and 0.009 min-1). Notably, mp-NiF@uCN-20 % with 1.0 wt % of Pt loading achieves the highest H2 evolution rate of 2294 μmolg-1h-1, which is 3.72, 1.52, and 13.49 times higher than that of pure CN, p-uCN, and NiFO, respectively. The enhanced performance is corroborated by increased surface area, improved separation of charge carriers, and effective charge transfer, which enables simultaneous reduction and oxidation processes. Further, the magnetic nanocomposite exhibits remarkable stability even after multiple runs, indicating their reusability. The experimental findings emphasize the importance of p-n heterojunctions, interfacial band alignment, and mesoporous architecture in enhancing the photocatalytic efficiency of NiFe2O4@g-C3N4 nanocomposites.

Tuning surface hydrophilicity of a BiVO4 photoanode through interface engineering for efficient PEC water splitting.

This study presents a novel approach to enhance photoelectrochemical (PEC) water oxidation by integrating cobalt phthalocyanine (CoPc) with bismuth vanadate (BVO) via a direct solvothermal method. The as-prepared BVO@CoPc photoanode demonstrated a photocurrent density of 4.0 mA cm-2 at 1.23 V vs. RHE, which is approximately 3.1 times greater than that of the unmodified BVO, and has superior stability. The incident photon-to-current conversion efficiency (IPCE) of the BVO@CoPc photoanode reaches an impressive value of 81%, accompanied by significant enhancements in charge injection efficiency. This excellent performance can be ascribed to the enhanced hydrophilicity with the BVO/CoPc interface engineering, which facilitates interfacial interaction between the electrode and electrolyte, accelerates photogenerated charge carrier transfer and separation. Furthermore, compared to the immersion and drop-casting methods, the BVO@CoPc-S composite photoanode prepared via the solvothermal method exhibits a significant improvement in interfacial contact and surface hydrophilicity. These findings highlight the potential of the strategy based on interfacial hydrophilicity modification to overcome key limitations in PEC water splitting, providing a pathway to more efficient and durable photoanode design.

Strong Metal-Support Interaction Facilitates the Separation of Electron-Hole Pairs at Au13/BiOCl Interface: Insight from Quantum Dynamics.

Focusing on Au13/BiOCl, we investigated the effects of the metal-support interaction (MSI) on the photogenerated charge carrier separation using nonadiabatic molecular dynamic simulations combined with time-domain density functional theory. Our results show that the time scales of electron transfer from the Au13 cluster to BiOCl are distinct depending on the intensity of MSI. Oxygen vacancy (OV) can enhance the interaction between the Au13 cluster and BiOCl, leading to a stronger nonadiabatic (NA) coupling in Au13/BiOCl with an OV system compared to that in a pristine Au13/BiOCl system. The time scale of electron transfer in Au13/BiOCl with the OV system is reduced by a factor of 1.65 compared to that of the pristine Au13/BiOCl system. Our study suggests that the electron transfer can be facilitated by enhancing the MSI and provides valuable principles for the design of high-performance photocatalysts.

Photocatalytic Oxygen Evolution with Prussain Blue Coated ZnO Origami Core-Shell Nanostructures.

The design and development of particulate photocatalysts has been an attractive strategy to incorporate earth-abundant metal ions to water splitting devices. Herein, we synthesized CoFe-Prussian blue (PB) coated ZnO origami core-shell nanostructures (PB@ZnO) with different mass ratio of PB components and investigated their photocatalytic water oxidation activities in the presence of an electron scavenger. Photocatalytic experiments reveal that the integration of PB on ZnO boosts the oxygen evolution rate by a factor of ~2.4 compared to bare ZnO origami. We ascribe this increased photocatalytic rate to an improved charge carrier separation and transfer due to the formation of heterojunction at the interface between PB and ZnO. Long-term photocatalytic experiments indicate that the activity and stability of the catalyst was preserved up to 9 h. Our results indicate that the core-shell PB@ZnO particles possess a proper band energy alignment for the photocatalytic water oxidation process.

An innovative BiOI@AgBiS2@NaYF4:Yb, Tm ternary heterostructure for efficient solar energy harvesting towards tetracycline hydrochloride degradation.

This study developed a BiOI@AgBiS2@NaYF4:Yb,Tm heterostructure photocatalyst. This design significantly enhances the generation and separation of charge carriers, leading to a marked improvement in solar energy harvesting. This advancement was effectively applied for the degradation of tetracycline hydrochloride. This strategy provides inspiration for designing and developing full-spectrum responsive photocatalysts.

Photocatalytic activity of zinc oxide nanorods incorporated graphitic carbon nitride catalyst

Background: Photocatalysts are user-friendly and serve as compatible materials for degrading industrial dye pollutants. This study utilizes zinc oxide/graphitic carbon nitride (ZnO/g-C3N4) nanocomposites against degrading methylene blue (MB). Methods: The hydrothermal method assisted sonication technique was used to fabricate the ZnO/g-C3N4 composite with varying ratios of ZnO/g-C3N4 (1:0.25, 1:0.50, 1:1). The synthesized materials have undergone various sophisticated techniques for finding their physiochemical properties and have been utilized for photodegradation activities. Significant Findings: The characterized results exhibit that the nanoflakes of g-C3N4 were covered with nanorods of zinc oxide when observed through scanning electron microscopy (SEM). Furthermore, the X-ray diffraction (XRD) studies demonstrate that the ZnO/g-C3N4 material was successfully synthesized. The X-ray photoelectron spectra (XPS) and Fourier-transform infrared (FTIR) spectra revealed the present oxidation states and chemical bonding of the materials. The photocatalytic activity results demonstrated that the concentration of ZnO molar ratio in varying g-C3N4 significantly affected the decomposition performance. The ZnO/g-C3N4 (1:0.50) presented a higher rate of degradation, reaching 92% at 120 minutes under UV light and 65% at 240 minutes under visible light irradiation. This could be explained by the mechanism that follows the separation of charge carriers, thereby producing hydroxyl radicals for the effective degradation of MB pollutants.

Ag2S/TiO2 Z-scheme heterojunction under magnetic field: Enhanced photocatalytic degradation of tetracycline

Multi-field assisted photocatalytic technology is an effective way to improve the photocatalytic performance of photocatalysts. Herein, we synthesized the Ag2S/TiO2 Z-scheme heterojunction photocatalyst and demonstrated the impacts of internal electric field (EF) and external magnetic field (MF) on the degradation of tetracycline (TC). Their structural, optical and electrochemical properties were characterized in detail. Ag2S/TiO2 demonstrated conspicuously enhanced photocatalytic activity towards the degradation of TC owing to the photosensitization of Ag2S and effective separation of charge carriers by forming an internal EF at the interface of the composite. Further, a higher degradation of TC (degradation conversion: 95.7% and TOC removal: 75.7%) was achieved by imposing the 1400 Gauss of an external MF and 500rpm. This is due to the high-rate charge carrier separation and migration caused by MF induced spin polarization and Lorentz force acting on charge carriers, accelerating TC degradation with lower active energy (MF: 33.18 KJ·mol-1 and NMF: 49.01 KJ·mol-1). Furthermore, Ag2S/TiO2 also demonstrated exceptional stability and reusability. The photocatalytic mechanism of Ag2S/TiO2 Z-scheme heterojunction under MF was discussed in detail based on the identification of the main reactive species (·OH and ·O2−) by radical trapping experiments and EPR analysis.

Highly efficient charge carrier separation in ZnO-NiFe2O4@biochar Z-scheme heterojunction mediated by persistent free radicals for metronidazole degradation

Highly efficient charge carrier separation in ZnO-NiFe2O4@biochar Z-scheme heterojunction mediated by persistent free radicals for metronidazole degradation

A Novel S-scheme Heterojunction based on BiPO4/CdPSe3 for Effective Photocatalytic Degradation of Organic Pollutants

As a sustainable technology that can be utilized for degrading organic pollutants, photocatalysis becomes more and more important in the environment pollution control. One crucial factor that influences the degradation process is the design of photocatalyst. In this study, we utilized a simple hydrothermal method, liquid exfoliation and mechanical mixture to synthesize a novel S-scheme heterojunction based on BiPO4/CdPSe3. It was found that the optimal molar ratio BiPO4: CdPSe3= 2: 1 (noted as B2C) gave rise to an efficient removal of rhodamine B up to 97.5% after 30min dark reaction and 60min light exposure. This composite also possesses the degradation capacity for other antibiotics and inorganic pollutant. The capture experiments showed that superoxide radicals played the dominant role in the degradation process. Besides, hydroxyl radicals and holes were also important active species. The high photocatalytic degradation performance of B2C could be attributed to the increased specific surface area with more active sites, enhanced light absorption in the visible region, and, more importantly, the special S-scheme heterostructure for high photogenerated charge carrier separation, synergistically improved the photocatalyst degradation efficiency. This work provides a new perspective for designing high-efficient photocatalysts applicable in multiple organic and inorganic pollutants degradation.

Correlating photochemical H2 production and excited state lifetimes of heterostructured and doped ZnCdS nanoparticles.

A variety of ZnCdS-based semiconductor nanoparticle heterostructures with extended exciton lifetimes were synthesized to enhance the efficacy of photocatalytic hydrogen production in water. Specifically, doped nanoparticles (NPs), as well as core/shell NPs with and without palladium and platinum co-catalysts, were solubilized into water using various methods to assess their efficacy for solar H2 fuel synthesis. The best results were obtained with low bandgap ZnCdS cores and ZnCdS/ZnS core/shell NPs with palladium co-catalysts. The results, augmented with DFT and tight binding electronic structure calculations, revealed the importance of exciton charge carrier separation via tunneling. While the systems studied here were photocatalytically active, they nonetheless lagged behind the quantum efficiency observed from "gold standard" CdSe/CdS·Pt dot-in-rod nanoparticles as evident from quantum efficiencies that were estimated to be 0.5 → 2%.

Constructing a nickel complex/crystalline carbon nitride hybrid with a built-in electric field for boosting CO2 photoreduction.

Sluggish charge separation dynamics resulting from the amorphous structure and the lack of driving force for graphitic carbon nitride (GCN) limits its highly effective CO2 photoreduction performance. Herein, a built-in electric field (BEF) was constructed for a well-designed CCN/Ni hybrid composed of crystalline carbon nitride (CCN) and a metal complex, 2,2'-bipyridine-4,4'-dicarboxylic acid NiBr2 (dcabpyNiBr2), to steer charge carrier separation and migration. The CCN/Ni hybrid was synthesized via a solution-dispersion and molten-salt two-step approach, displaying an improved CO2 photoreduction to CO rate of 8.64 μmol g-1 h-1. In situ experimental results and theoretical simulations further investigated the relationships between BEF and photocatalytic activity. This work demonstrates an effective strategy to obtain high-efficiency photocatalytic systems by engineering the crystal structure and constructing a BEF.

Strategic design of emerging (K,Na)NbO3-based perovskites for high-performance piezocatalysis and photo-piezocatalysis.

As a leading Pb-free perovskite material (ABO3-type), potassium sodium niobate (K,Na)NbO3 (KNN)-based ferroelectrics/piezoelectrics have been widely used in electronics, energy conversion, and storage due to their exceptional ability to interconvert mechanical and electrical energies. Beyond traditional applications, the piezoelectric potential generated by mechanical strain or stress modifies their energy band structures and facilitates charge carrier separation and transport, drawing increasing attention in emerging fields such as piezocatalysis and photo-piezocatalysis. With excellent piezoelectric properties, chemical/thermal stability, and strain-tuning capability, KNN-based materials show great promise for high-performance piezocatalytic applications. Coupling KNN with semiconductors exhibiting strong optical absorption to form heterojunctions further boosts performance by suppressing electron-hole recombination and promoting directed charge transfer, which is crucial for photo-piezocatalysis. The flexibility of KNN's perovskite structures also allows for modifications in chemical composition and crystal structure, enabling diverse design strategies such as defect engineering, phase boundary engineering, morphology control, and heterojunction formation. This review comprehensively explores the recent advancements in KNN-based piezocatalysis and photo-piezocatalysis, starting with an overview of their crystal structures and intrinsic properties. It then explores the role of piezoelectric potential in charge carrier dynamics and catalytic activity, followed by strategic design approaches to optimize efficiency in environmental remediation and energy conversion. Finally, the review addresses current challenges and future research directions aimed at advancing sustainable solutions using KNN-based materials in these applications.

Perovskite‐Inspired Cs₂AgBi₂I₉: A Promising Photovoltaic Absorber for Diverse Indoor Environments

AbstractIndoor photovoltaics (IPVs) using low‐toxicity bismuth‐based perovskite‐inspired materials (PIMs) can potentially power the growing number of Internet of Things devices sustainably. However, modest indoor power conversion efficiency (PCE) values are reported due to intrinsic limitations of PIMs, particularly regarding charge carrier separation and transport. Herein, polycrystalline Cs₂AgBi₂I₉ thin films are developed with high phase purity and study their fundamental structural and photophysical properties. The comprehensive experimental and computational study reveals unique optoelectronic properties of Cs₂AgBi₂I₉ compared to other bismuth‐containing PIMs, including weak electron‐phonon coupling and low exciton binding energy (40 meV). This study also demonstrates the feasibility of large and highly mobile polaron formation in Cs₂AgBi₂I₉, supported by the observation of a phonon bottleneck and a delayed hot carrier lifetime of over 200 ps, which suggests enhanced defect tolerance and transport properties. Motivated by the suitable bandgap of this absorber (1.78 eV), the first Cs₂AgBi₂I₉‐based IPVs are developed, achieving a PCE of ≈8% at 1000 lux. Notably, the devices maintain high performance across various indoor environments with white LED color temperatures ranging from 2700 to 6500 K. The calculated theoretical PCE limit of >40% and the promising operational stability position Cs₂AgBi₂I₉ as one of the most intriguing candidates for sustainable IPVs.

Investigation of Mg-Doped SnO\(_2\) Nanoparticles as an Efficient Photocatalyst for the Degradation of Crystal Violet Dye

This study is an attempt to investigate the photocatalytic performance of magnesium (Mg) doped SnO2 nanoparticles (NPs) for the degradation of Crystal Violet (CV) dye under sunlight irradiation. Mg doped SnO2 NPs with varying concentrations of Mg were synthesized through coprecipitation method. The synthesized NPs were characterized using X-ray diffraction (XRD), UV-Vis spectroscopy and Fourier transform infrared (FTIR) spectroscopy to confirm their structural and optical properties. The photocatalytic efficiency of Mg-doped SnO2 NPs was evaluated by examining the degradation rate of CV dye. The results demonstrated that Mg doping significantly improved the photocatalytic activity of SnO2 NPs, with a 15wt% Mg doping concentration leading to the highest degradation rate of CV dye. The enhanced photocatalytic performance is attributed to the increased charge carrier separation due to Mg doping. This study highlights the potential of Mg-doped SnO2 NPs as effective photocatalysts for the degradation of organic pollutants, offering a promising approach for wastewater treatment applications.