Reduced Recombination Rate Research Articles

High photogeneration and low recombination rate leading to high-performance non-fullerene organic solar cells

TPV/TPC, EQE/IQE measurements and simulation modeling reveal that the high-performance organic solar cells originate from both an increasing charge generation and a reducing recombination rate coefficient, with PCE potentially exceeding 21%.

Construction of Z-scheme heterojunction based on BiOBr-nanoflakes embedded sulfonic-acid-functionalized g-C3N4 for enhanced photocatalytic removal of hazardous pollutants in aqueous media

BackgroundEnvironmental remediation and energy production via semiconductor photocatalysis has attracted great interest in the research field because of their enormous physicochemical properties and ease of modification through forming various heterojunctions. MethodsIn this work, the nanoflakes-like bismuth oxybromide embedded sulfonic acid-functionalized graphitic carbon nitride (BiOBr-NFs/g-C3N4-SAF) were prepared by hydrothermal and wet-impregnation methods. The FT-IR, XPS, and TGA studies confirm the presence of surface sulfonic groups. Meanwhile, PL, EIS, M-S, and transient photocurrent analyses indicate the suppressed recombination rate, interfacial charge transfer, band-edge potentials, and photoexcitation phenomena. Significant findingsThe surface modification and the heterojunction formation of BiOBr-NFs/g-C3N4-SAF enable adequate band-edge potentials for photooxidation and photoreduction reactions. Among the as-synthesized photocatalysts, the 20 wt.% BiOBr-NFs/g-C3N4-SAF resulted in 98.39% of Cr(VI) photoreduction and 99.88% of RhB photooxidation within 15 min and 30 min, respectively. The rate constant (k’) for the photooxidation of RhB (0.6615 min–1) is about 11.7 and 11.4 folds than g-C3N4-SAF and BiOBr-NFs, respectively. Meanwhile, the k’ for the photoreduction of Cr(VI) (0.6243 min–1) is around 30.1 and 15.8 folds than g-C3N4-SAF and BiOBr-NFs, respectively. This enhanced photocatalytic activity is ascribed to the strongly associated BiOBr-NFs/g-C3N4-SAF Z-scheme heterojunction interface, assuring effective photogenerated charge transport and high redox band-edge potentials and reduced recombination rates.

Mesoporous LaVO4/MCM-48 nanocomposite with visible-light-driven photocatalytic degradation of phenol in wastewater

Dearomatization through photocatalytic oxidation is a swiftly rising phenolic compounds removal technology that works at trifling operations requirements with a special emphasis on the generation of nontoxic products. The study aims to develop a LaVO4/MCM-48 nanocomposite that was prepared via a hydrothermally approach assisting the employment of an MCM-48 matrix, which was then utilized for phenol degradation processes. Various techniques including UV–Vis DRS, FTIR, PL, Raman, TEM, and BET analyses are employed to characterize the developed photocatalyst. The developed photocatalyst presented remarkable characteristics, especially increased light photon utilization, and reduced recombination rate leading to enhanced visible-light-driven photodegradation performance owing to the improved specific surface area, specific porosities, and <2 eV narrow energy bandgap. The LaVO4/MCM-48 nanocomposite was experienced on aqueous phenol solution having 20 mg/L concentration under visible-light exposure, demonstrating exceptional performance in photodegradation up to 99.28%, comparatively higher than pure LaVO4. The conducted kinetic measurements revealed good accordance with pseudo first-order. A possible reaction mechanism for photocatalytic degradation was also predicted. The as-synthesized LaVO4/MCM-48 nanocomposite presented excellent stability and recyclability.

Scalable production of visible light photocatalysts with extended nanojunctions of WO3/g-C3N4 using zeta potential and phase control in sol-gel process

Semiconductor photocatalysis for water splitting is promising approach to the current energy and environmental crisis. Although heterostructure photocatalysts exhibit enhanced photoactivity, the construction of a continuous junction at the interfaces between heterogeneous substances. In this study, visible light responsive tungsten oxide/graphitic carbon nitride composite photocatalysts with extended nanojunctions (en-WO3/g-C3N4) were synthesized through a novel sol-gel process that controlled zeta potential and sol-gel phase. The rational design of porous sphere en-WO3/g-C3N4 composite photocatalyst was constructed micropores and intimate contact between WO3 nanoparticles (NPs) and 2-dimensional (2D) g-C3N4 platelet interface. The en-WO3/g-C3N4 composite photocatalyst exhibited improved UV–vis absorbance and reduced recombination rate of photogenerated electron-hole pairs. The photocatalytic activity of hydrogen production was significantly enhanced by facile mass transfer and efficient charge-carrier separation due to direct Z-scheme mechanism. As a result, the hydrogen (H2) production of optimal en-WO3/g-C3N4 photocatalyst was obtained as much as 1060 µmol h-1g-1 which is 3.8-folds higher than g-C3N4 photocatalyst (281 µmol h-1g-1). Also, the designed en-WO3/g-C3N4 showed good stability for H2 production for 12 h under visible light irradiation.

Enhanced photocatalytic organic dye degradation activities of pristine and Zn-doped V2O5 nanoparticles

This research work presents the photocatalytic activities of pristine and Zn-doped V2O5 nanoparticles for the degradation of Methylene Blue (MB), Methyl Violet (MV), and Malachite Green (MG) dyes. The nanoparticles of V2O5 pure and Zn with different atomic ratios (1–5 at%) were prepared by sol–gel method. X-ray diffraction (XRD) studies confirm the orthorhombic phase. X-ray Photoelectron spectroscopy (XPS) confirms the presence of V, O, and Zn elements along with their oxidation states. Further, decreased photoluminescence (PL) intensity spectra confirm the reduced recombination rate. Band structure analysis were studied with valance band XPS (VB-XPS), Mott-Schottky (M−S) curves, and Kubelka-Munk (K-M). The Time resolved photoluminescence (TRPL) and Electrochemical impedance spectroscopy (EIS) studies showed that the charge carrier life time was increased and charge transfer resistance was lowered with increasing Zn concentration. The photocatalytic studies show excellent degradation efficiencies against MB, MV, and MG dyes. The results from the present work show the degradation time decreases as the Zn concentration increases. The reusability test was performed and the dye degradation (DD) mechanism with their kinetics are discussed in detail with the radical test. The consistency of the samples were tested by taking XRD, FTIR and BET analysis after three trials of usage.

Linked selection, differential introgression and recombination rate variation promote heterogeneous divergence in a pair of yellow croakers.

Understanding the mechanisms underlying heterogeneous genomic divergence is of particular interest in evolutionary biology. Highly differentiated genomic regions, known as genomic islands, often evolve between diverging lineages. These genomic islands may be related to selection promoting adaptation or reproductive isolation. Based on whole genome assembly and genome-wide RAD sequencing in a pair of yellow croakers (genus: Larimichthys), we investigated the evolutionary processes shaping genomic landscapes of divergence. Demographic modelling indicated that the two species diverged following a secondary contact scenario, where differential introgression and linked selection were suggested to be involved in heterogeneous genomic divergence. We identified reduced recombination rate in genomic islands and a relatively good conservation of both genetic diversity and recombination landscapes between species, which highlight the roles of linked selection and recombination rate variation in promoting heterogeneous divergence in the common ancestral lineage of the two species. In addition, we found a positive correlation between differentiation (FST ) and absolute sequence divergence (Dxy ), and elevated Dxy in genomic islands, indicating that the genomic landscape of divergence was not shaped by linked selection alone. Restricted gene flow in highly differentiated regions has probably remodelled the landscape of heterogeneous genomic divergence. This study highlights that highly differentiated genomic regions can also arise from a combination of linked selection and differential gene flow in interaction with varying recombination rates.

Recent Innovations in Low Dimensional ZnO Nanostructures/Nanocomposites for Photocatalytic Degradation

The energy and environmental application of materials can be improved dramatically by efficiently consuming a large section of the solar spectrum. Scientists are exploring the wide band gap metal oxides and their nanocomposites as heterogeneous photocatalysts for effective performance in solar wavelengths. Increased surface area, efficient photon absorption, and reduced recombination rate can be achieved by structural engineering and developing efficient nanocomposites. A thorough review of recent innovations in ZnO nanostructures/nanocomposites exclusively for photocatalytic dye degradation has been conducted. The review provides insight into the effects of ZnO nanostructure and recent advancements in ZnO nanocomposites to improve the photocatalytic activity of organic pollutants under different radiations. The review concludes that structural and material engineering can boost the photocatalytic performance of ZnO structures.

Homologous recombination risk in baculovirus expression vector system

The baculovirus expression vector system (BEVS) is widely used for producing recombinant proteins. To achieve high expression level of recombinant proteins, baculoviral elements, such as enhancers, promoters, signal peptide coding sequences and 3′-UTR, have been extensively employed. There is a recombination risk derived from homologous sequences between viral genome and functional baculovirus-derived elements associated with foreign genes. Although homologous recombination have distinct biological functions, these potential adverse recombination may trigger a DNA fragment being inverted or looped out, resulting in the production of defective viruses and eventual yields declines of recombinant proteins. However, the risk of such homologous recombination has not been systematically assessed. Here, we measured the recombination rate using a promoter-less fluorescent reporter integrated with various lengths homologous of p10 coding region. Homologous fragments longer than 60 bp possess sufficient recombination probability and exerts effect on purity and integrity of virus. Shortening the length of homologous fragments and separating homologous fragments by point mutations can effectively reduce unfavorable recombination. These findings reveal a homologous recombination risk resulted from genome-homologous baculoviral elements and propose reliable strategies reducing recombination rate to facilitate viral stability and integrity in baculovirus expression vector system.

Controllable Phase Transformation and Enhanced Photocatalytic Performance of Nano-TiO2 by Using Oxalic Acid.

Degradation of organic pollutants, especially organic dyes and antibiotics, by semiconductor photocatalysts is an efficient strategy for wastewater treatment. TiO2 nanomaterials are considered to be promising photocatalysts due to their high chemical stability, high efficiency and availability. Anatase TiO2 generally has superior photocatalytic activity to the rutile phase. However, the anatase phase can be irreversibly transformed to rutile phase when calcined at an elevated temperature. Methods to improve the stability of anatase are especially important for the TiO2 gas sensors working at high temperatures. The addition of strong acids can effectively suppress this transformation process. However, these strong acids are relatively expensive, corrosive and environmentally unfriendly. Herein, oxalic acid (OA) as a natural acid was used to control the hydrolysis process of tetrabutyl titanate (TBOT), leading to controllable crystalline phase transformation and reduced crystalline size of TiO2 on the nanoscale. What is more, the photocatalytic degradation performances were enhanced continuously when the molar ratio of OA to TBOT increased. The degradation reaction rate constants of CT650-R25 were about 10 times that of CT650-R0. The mechanism study shows that the enhanced photocatalytic activity can be attributed to the improved dispersibility, increased specific surface area and reduced recombination rates of photo-induced charge carriers and decreased energy bands as the concentration of OA increased. Thus, this work provides a simple, mild and effective method for controlling the crystalline forms of nano-TiO2 with enhanced photocatalytic performance towards waste water treatment.

Novel Z-scheme LaVO4/Bi3O4Cl heterojunctions for highly efficient degradation of ofloxacin under visible light irradiation

The construction of a Z-scheme heterojunction favors the improvement of the photocatalytic activity of photocatalysts. Herein, the LaVO4/Bi3O4Cl Z-scheme heterojunction was designed reasonably by the method of in situ growth. The obtained heterojunction was further used as a photocatalyst for the degradation of ofloxacin (OFX), an antibiotic, in wastewater. The degradation efficiency of OFX by the optimal sample (LBC-2) was 94.3 % and the values of k were about 114.7 and 2.4 times those of LaVO4 and Bi3O4Cl, respectively. In addition, LBC-2 maintained high activity after 4 cycles. The significantly reduced recombination rate of carriers in LBC-2 was reflected by the results of the photoluminescence (PL), photocurrent (PC), and electrochemical impedance spectroscopy (EIS) studies. The degradation pathways of OFX were proposed accounting to the intermediates detected by liquid chromatography-mass spectroscopy (LC-MS). Toxicity estimations showed that the toxicity of some intermediates decreased. This work provides new insight into the development of Z-scheme photocatalysts for the removal of antibiotics as pollutants.

Preparation of rGO‐CNT/Ag3PO4/Nb2O5 composite with enhanced photoresponse properties as a highly effective visible light driven photocatalyst

AbstractIn this study a facile method to synthesize a new type of photocatalyst by coating Ag3PO4/Nb2O5 composite on rGO‐CNT network was reported. The composite of Silver orthophosphate/Niobium(V) oxide (Ag3PO4/Nb2O5) was prepared through depositing Ag3PO4 particles on the surface of Nb2O5 particles. The prepared Ag3PO4/Nb2O5 composite photocatalyst shows a much higher photocatalytic activity for the degradation of MB than pure Ag3PO4 and Nb2O5 under simulated sunlight. This can be related to the efficient separation of photoinduced electron/hole pairs derived from the Ag3PO4/Nb2O5 heterojunction. Moreover, the prepared reduced Graphene Oxide‐Carbon nanotube (rGO‐CNT) network inhibits the restacking of sheets of Graphene Oxide (GO) during the reduction process and can create fast electronic conducting channels, making this an effective strategy for improving the photocatalytic performance of the prepared composite of Ag3PO4/Nb2O5. The degradation rate constant (kapp) of the optimized rGO‐CNT/Ag3PO4/Nb2O5 photocatalyst was higher by a factor of 6.7 times than that of the corresponding Ag3PO4 nanoparticles. The synergistic interactions between Ag3PO4, Nb2O5, and the presence of rGO‐CNT network lead to an increased surface area, a decreased aggregation of the particles, a reduced recombination rate for the photogenerated electron/hole pairs, and an efficient charge carrier transfer. In addition, no loss of photocatalytic activity was observed after six recycles. © 2022 Society of Chemical Industry (SCI).

Synergistic effects of Bi and N doped on ZnO nanorods for efficient photocatalysis

The fast pace of industrial growth during the current decade has seen a large family of dyes employed copiously in the production of various products such as paper and ink. These dyes pollute earth's ecosystems. Researchers look at various ways to degrade these dyes including the use of suitable nanomaterials. ZnO is an important semiconductor material that can be employed for this purpose. In this research work, we optimized the photocatalytic capability of ZnO by co-doping it with 1–7 wt% of Bi and N. The synthesized Bi and N co-doped ZnO nanorod samples showed excellent photocatalytic behavior towards Rhodamine-B (RhB). It was confirmed using XRD and SEM that (5, 2.5) wt.% Bi/N co-doped ZnO nanorods exhibited unique morphology and structure. EDX successfully assessed the elemental composition of the synthesized samples. To provide further insight into its microstructure, the HRTEM and SAED analysis were performed. Optical properties were determined using PL and UV–Visible spectroscopy. The prepared nanorod material degraded almost 89% of RhB in 180 min. The superior degradation ability of co-doped ZnO material when exposed to visible portion of sunlight spectrum is credited to the decrease in the recombination rate of charges and an increase in the depth penetration of photons. The degradation efficiency of Bi/N co-doped ZnO material is enhanced due to reduced recombination rate and increased production of number of defects and oxygen vacancies.

High-Efficacy Hierarchical Dy2O3/TiO2 Nanoflower toward Wastewater Reclamation: A Combined Photoelectrochemical and Photocatalytic Strategy.

Developing a sustainable photocatalyst is crucial to mitigate the foreseeable energy shortage and environmental pollution caused by the rapid advancement of global industry. We developed Dy2O3/TiO2 nanoflower (TNF) with a hierarchical nanoflower structure and a near-ideal anatase crystallite morphology to degrade aqueous rhodamine B solution under simulated solar light irradiation. The prepared photocatalyst was well-characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, energy-dispersive spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, diffuse reflectance UV-vis spectra, and X-ray photoelectron spectroscopy. Further analysis was performed to highlight the photoelectrochemical activity of the prepared photocatalysts such as electrochemical impedance spectroscopy, linear sweep voltammetry, photocurrent response, and a Mott–Schottky study. The crystalline Dy2O3/TNF exhibits superb photocatalytic activity attributed to the improved charge transfer, reduced recombination rate of the electron–hole pairs, and a remarkable red-shift in light absorption.

Single-junction organic solar cells with over 19% efficiency enabled by a refined double-fibril network morphology.

In organic photovoltaics, morphological control of donor and acceptor domains on the nanoscale is the key for enabling efficient exciton diffusion and dissociation, carrier transport and suppression of recombination losses. To realize this, here, we demonstrated a double-fibril network based on a ternary donor-acceptor morphology with multi-length scales constructed by combining ancillary conjugated polymer crystallizers and a non-fullerene acceptor filament assembly. Using this approach, we achieved an average power conversion efficiency of 19.3% (certified 19.2%). The success lies in the good match between the photoelectric parameters and the morphological characteristic lengths, which utilizes the excitons and free charges efficiently. This strategy leads to an enhanced exciton diffusion length and a reduced recombination rate, hence minimizing photon-to-electron losses in the ternary devices as compared to their binary counterparts. The double-fibril network morphology strategy minimizes losses and maximizes the power output, offering the possibility of 20% power conversion efficiencies in single-junction organic photovoltaics.

Si/SiO2/Al2O3 Supported Growth of CNT Forest for the Production of La/ZnO/CNT Photocatalyst for Hydrogen Production

The use of ZnO as a photocatalyst with a reduced recombination rate of charge carriers and maximum visible light harvesting remains a challenge for researchers. Herein, we designed and synthesized a unique La/ZnO/CNTs heterojunction system via a sol–gel method to evaluate its photocatalytic performance for hydrogen evolution. A ferrocene powder catalyst was tested for the production of CNT forests over Si/SiO2/Al2O3 substrate. A chemical vapor deposition (CVD) route was followed for the forest growth of CNTs. The La/ZnO/CNTs composite showed improved photocatalytic efficiency towards hydrogen evolution (184.8 mmol/h) in contrast to 10.2 mmol/h of pristine ZnO. The characterization results show that promoted photocatalytic activity over La/ZnO/NTs is attributed to the spatial separation of the charge carriers and extended optical absorption towards the visible light spectrum. The optimum photocatalyst shows a 16 h cycle performance for hydrogen evolution. The H2 evolution rate under visible light illumination reached 10.2 mmol/h, 145.9 mmol/h and 184.8 mmol/h over ZnO, La/ZnO and La/ZnO/CNTs, respectively. Among the prepared photocatalysts, ZnO showed the lowest H2 evolution rate due to the fast recombination of electron–hole pairs than heterojunction photocatalysts. This research paves the way for the development of ZnO and CNT-based photocatalysts with a wide optical response and reduced charge carrier recombinations.

Unraveling the Role of Energy Band Alignment and Mobile Ions on Interfacial Recombination in Perovskite Solar Cells

A key limitation in perovskite solar cell (PSC) performance is suboptimal electronic properties at the perovskite–transport layer (TL) interfaces, which result in parasitic nonradiative recombination. Interface recombination depends on the concentration of recombination‐active defects, but as a recombination event requires both an electron and a hole, the magnitude and sign of charge accumulation at the perovskite–TL heterojunctions are also critical. Here, we employ a well‐established numerical ion‐electron drift‐diffusion model of PSCs to illustrate how the work function of the transport layer is an important factor in determining the total recombination activity at the perovskite interfaces. We show that the equilibrium electrostatics of the perovskite–TL heterojunctions, which are determined by the work function difference between the two materials, can result in increased recombination rates for any given concentration of interface defects. As a case study, we compare PSCs incorporating a NiOX hole transport layer with those with a spiro‐OMeTAD. We show that the work function of NiOX can induce greater electron accumulation at the perovskite–NiOX interface, which leads to increased interface recombination. Finally, a higher ion concentration is found to be beneficial to overall device performance by displacing accumulated electrons or holes at the TL interfaces and thus reducing recombination rates.

Study on interfacial interactions and optoelectronic properties of MEH-PPV/SnO2 hetero-structure

The exciton dynamics in nanocomposites of tin oxide (SnO2) nanoparticles with a conjugated polymer (poly (2-methoxy-5-(2'-ethylhexyloxy) 1,4-phenylenevinylene) (MEH-PPV) have been investigated by steady-state, time-resolved photoluminescence (PL) spectroscopy and cyclic voltammetry (CV) analysis. SnO2 is an air-stable, optically transparent, electrically conductive deep valance band metal oxide which is suitable as an electron-accepting material in organic photovoltaics (PVs). Results reveals that SnO2 is an efficient electron-accepting material in comparison with titanium dioxide (TiO2) nanoparticles. Efficient charge separation takes places at SnO2/MEH-PPV interfaces when the polymer is excited, leading to enhancement in quenching of PL efficiency (10%) and shortening of the measured PL lifetime. In addition, the reduction in recombination rate of MEH-PPV/SnO2 nanocomposite show that the incorporation of nanoparticles in the polymer chain reduce disorders in the polymer chains. The blue-shift in the absorbance and emission maxima denotes that the process of in situ polymerization resulted in shortening of polymer chain conjugation. The electrochemical analysis for MEH-PPV/SnO2 nanocomposite shows increase in current density compared to MEH-PPV/TiO2 and pristine MEH-PPV. Moreover, the PL degradation experiments showed that MEH-PPV/SnO2 exhibited enhanced stability. MEH-PPV/SnO2 film attained 50% of the original intensity in ∼10 d, while pristine MEH-PPV and MEH-PPV/TiO2 exhibited half-life of ∼5 d when exposed to an ambient environment. The effect of TiO2 nanoparticles to stabilize MEH-PPV is though less important than that of SnO2. Thus MEH-PPV/SnO2 nanocomposite with enhanced absorbance, conductivity, stability and lowered bandgap formed an effective type-II band structure suitable for the PV active layer.

Construction of highly efficient separable p-n junction based light driven composite (NiFe2O4/MnWO4) for improved solar light utilisation

Magnetic separable p-NiFe2O4/n-MnWO4(NFMW) composites were synthesised by combined co-precipitation and hydrothermal process with varied stoichiometry ratio of p-NiFe2O4. The best composite having 20 mg of p-NiFe2O4(NFMW-2) demonstrated excellent band gap, work function, durability, photo stability, ferromagnetism properties etc. XRD shows wolframite MnWO4 and spinel structure of NiFe2O4. Elemental mapping confirms the uniform dispersion of composites. The optimized loading of p-NiFe2O4 results in enhanced Light-harvesting capability. Photoluminescence analysis shows the prolonged decay time of the composite (8.769 µs) with reduced recombination rate. Transient photocurrent and Nyquist plot reveals the excellent separation efficiency and mobility of the charge carriers. Although NFMW-2 has shown ~56% reduction in the coercivity but withstands its ferromagnetic nature. Further, its edge potentials were evaluated through MS plot suggests Z-scheme mode of electron transfer. The solar photocatalysis process was dominated by superoxide and hydroxyl radicals and thus resulted in complete removal of Congo red and 92% for phenol within 240 min and 360 min.

The quiet evolutionary response to cellular challenges.

The quiet evolutionary response to cellular challenges.

Facile synthesis of ZnS/WO3 coupled photocatalyst and its application on sulfamethoxazole degradation

In this study, the coupled photocatalysts ZnS/WO3 were synthesized by a simple co-precipitation method, varying the content of ZnS (1, 5, and 10 wt%). The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS), N2 physisorption, UV–Vis with diffuse reflectance spectroscopy (DRS), atomic absorption (AAS), infrared (IR), and photoluminescence (PL) spectroscopies. Furthermore, the synthesized photocatalysts were evaluated on the photocatalytic degradation of sulfamethoxazole (SMX) under simulated sunlight. The activity of the different coupled photocatalysts ZnS/WO3 was significantly improved compared to the individual semiconductors (ZnS and WO3). This enhancement was attributed to the reduced recombination rate determined through PL analysis. The ZnS5%/WO3 photocatalyst exhibited the highest performance in comparison with the other coupled materials, achieving complete SMX degradation in 60 min. In combination, the enhanced specific surface area, high particle dispersion, and reduced recombination rate define the ZnS5%/WO3 photocatalyst as a suitable candidate for photocatalytic environmental applications.