Photoexcited Electrons Research Articles

Assembly of 2D/2D Bi2WO6/Boron-doped g-C3N4 Z-type heterojunction photocatalysts for efficient antibiotic adsorption and degradation

The photocatalytic heterojunction systems have shown remarkable development in improving the efficiency of visible-light absorption and photocarriers separation. Herein, we successfully engineered efficient 2D/2D Bi2WO6/Boron-doped g-C3N4 (BiWO/BCN) architectures as Z-type heterojunction photocatalysts with different BiWO to BCN ratios for degradation of antimicrobial drug sulfamethoxazole (SMX) under visible illumination. The SMX degradation using the optimized 40%BWO/BCN sample was obviously enhanced, and the degradation rate was 99.3 % after 120 min of irradiation. Its degradation efficiency was 6.5-, 3.2-, and 2.9-times better than that of BiWO, CN, BCN, and, respectively. The significantly boosted performance of the BiWO/BCN photocatalyst was credited to the effective separation of photo-excited electron and hole pairs. The SMX photodegradation pathways have been explained with a complete assessment of the active species, which showed the major role of •O2− and electrons. The reusability tests proved the high photostability of 40%BiWO/BCN sample throughout 5 sequential cycles (only 3.8 % reduction was witnessed). Therefore, this work presents an innovative photocatalyst combination for green degradation of SMX antibiotic.

Electron-transfer dynamics and photocatalytic H2-production activity of PbS@Cu2S nanocomposites

BackgroundLead citrate is a precursor that can be prepared by recycling the spent lead paste of lead-acid batteries. Lead citrate is used to synthesize lead oxide, which can be repeatedly utilized for the lead-acid battery application. MethodsWe report a new application of lead citrate precursor to synthesize PbS@Cu2S nanomaterials for photocatalytic H2 production. PbS@Cu2S was prepared by microwave-assisted hydrothermal and ion-exchange processes. The electron-transfer dynamics and H2-production activity of PbS@Cu2S photocatalysts were studied. Significant findingsA S-scheme heterojunction is proposed based on the results of Tauc plots, ultraviolet photoelectron spectroscopy, the electron paramagnetic resonance scavenger test, and in situ near-edge X-ray absorption fine structure (NEXAFS) analysis. Results of in situ NEXAFS reveal the transfer of photoexcited electrons from PbS to Cu2S. By loading an optimized amount of Cu2S, the carrier separation and photocatalytic activity of PbS@Cu2S photocatalysts are improved. This technology can transform the lead citrate precursor to the PbS@Cu2S photocatalyst with excellent high H2 production activity (3824 μmol g−1 h−1).

Step-by-step transfer of photoexcited electron in donor-acceptor-catalyst configuration covalent triazine framework for efficient photoreduction CO2 to formic acid

Covalent triazine frameworks (CTFs) have great potential for photocatalysis. However, the electron-hole recombination and the lack of efficient catalytic sites constrain the activity and selectivity. Herein, a novel design strategy of donor–acceptor-catalyst (D-A-C) configuration is proposed. This configuration enables the photoexcited electron undergoes stepwise transfer from donor unit to acceptor unit and ultimately reaches catalytic center, effectively inhibiting electron-hole recombination. The proof-of-concept model CTF-TT-Ir, in which thieno[3,2-b]thiophene (TT) serves as the donor unit, triazine as the acceptor unit, and Cp*Ir(bpy) (Ir) as the built-in catalytic site, was prepared for the photocatalytic reduction of CO2 to HCOOH. The stepwise transfer of photoexcited electrons in the ternary structure has been demonstrated through the in-situ XPS measurements and the theoretical calculations. Photoluminescence and photocurrent tests have indicated CTF-TT-Ir exhibits superior charge separation efficiency. Without additional photosensitizer and co-catalyst, the photocatalytic HCOOH yield rate of CTF-TT-Ir reached 245 μmol g−1h−1 (selectivity of 97 %).

Coating of Chlorophylls a and b Enhanced Photoelectrochemical Capacitor Reaction of TiO2/MnO2 Composite Electrode.

We prepared composite electrodes using TiO2 coated with chlorophylls a and b as photoelectric conversion material and MnO2 as energy storage material and investigated their photoelectrochemical capacitor properties. The coating with the combination of chlorophylls a and b improved the photoelectric conversion function of TiO2, compared with the coating with each alone. Na+ adsorption on MnO2 was enhanced with increasing the chlorophyll coating amount. The reason is that more chlorophylls a and b absorb visible light in different wavelengths to promote an easier photoexcited electron transfer to MnO2, just as they improve the efficiency of photosynthesis reactions in nature.

Study of Fabrication Process and Performance Analysis of the CDS/CDTE Based Photovoltaic Cell

Fabrication of CDS/CDTE based heterojunction photovoltaic cell has been undertaken to explore better light conversion efficiency. We have developed a photovoltaic cell using glass coated with Indium doped Tin Oxide (ITO) which works as transparent conducting oxide (TCO). ITO coated glass has promising prospects of enhancing the efficiency of the photovoltaic cell. ITO layers are known to be employed as anode terminal due to the negative polarity they possess compared to the whole PV cell; here, we have employed it for the same function as the front layer. During fabrication of the photovoltaic cell, the deposition of nanoparticles of CDS and CDTE layer is undertaken through doctor-blade method. We have employed pure CDS as window layer for its high band gap of 3.8 eV (particle size: 8 nm) and CDTE as absorber layer due to its high optical absorption coefficient with high mobility, good carrier lifetime and enhanced crystallographic properties. The CDS window layer and CDTE absorber layer together constitute a p-n junction where the CDS window layer captures high intensity photons and transmits the photo-excited electron to CDTE absorber layer, thereby leading to photo-current output, which serves as a base to explore and test its further applications. To obtain band gap of respective CDTE and CDS nanoparticles, optical characterization is used. Silver paste is used as rear contact to form anode terminal having good conductivity and providing better mechanical support to the photovoltaic cell.

Improved charge kinetics of BiVO4/MoS2 photoanode by an TiO2 electron transport layer for photocatalytic fuel cell photodegradation and electricity generation

The poor contact between the photocatalyst and the FTO substrate are the main factors lead to the low performance of photocatalytic fuel cell (PFC). Herein, a FTO pre-treated with a TiO2 electron transport layer was used as a substrate for the synthesis of the MoS2/BiVO4/pre-FTO photoanode. The proposed MBV-4/pre-FTO photoanode with its enhances the visible light absorption and effectively delays the recombination of the photoexcited charge. The MBV-4/pre-FTO composite photoanode (6.02 mA/cm2) exhibited a photocurrent density that was 2.2 times higher than that of the BiVO4 photoanode (2.78 mA/cm2). This is attributed to the short charge migration length of the thin MoS2 layer, the fast photoexcited electron transport effect of the TiO2 seed layer, and the heterojunction structure of the proposed photoanode. The DFT calculation result indicated that the TiO2 electron transport layer showed an outstanding photoelectron attractive and transporting effect. The MoS2/Ni foam was employed as the photocathode to establish a mismatched Fermi level for driving PFC. The short-circuit current, open-circuit voltage, and maximum power density of the PFC were 0.578 mA/cm2, 0.632 V, and 0.125 mW/cm2, respectively. The main photodegradation active species are the superoxide anion (∙O2–) and the photoexcited hole (h+), and the degradation efficiency is 61.97 %.

Spatially separated HOMO-LUMO sites in highly intra- and inter-plane crystalline g-C3N4 photocatalyst for exceptional H2 generation

Spatially separated HOMO-LUMO sites in the highly crystalline g-C3N4 can vastly facilitate the rapid transfer and separation of photogenerated charges to greatly improve its photocatalytic performance, which remains a great challenge to be achieved. In this study, the highly intra- and inter-plane crystalline g-C3N4 (c-CN) with the spatially separated HOMO-LUMO sites is explicitly produced through a moderate Na-modulated strategy to efficiently promote the directional transfer and separation of photoinduced charges. As a result, the optimized c-CN1.0 photocatalyst exhibits exceptional H2-evolution performance (313.5 μmol h−1, AQE = 13.38 %), which is ca. 14.3 times of the bulk g-C3N4. The excellent hydrogen-generation efficiency of c-CN photocatalyst is mainly ascribed to the synergism of high intra- and inter-layer crystallization of g-C3N4 and spatially separated HOMO-LUMO sites, which can vastly boost the directional transfer and effective separation of photoexcited electrons and holes. This research may open novel avenues to construct other photocatalysts with high efficiency.

Cocrystalline Matrices for Hyperpolarization at Room Temperature Using Photoexcited Electrons.

We propose using cocrystals as effective polarization matrices for triplet dynamic nuclear polarization (DNP) at room temperature. The polarization source can be uniformly doped into cocrystals formed through acid-acid, amide-amide, and acid-amide synthons. The dense-packing crystal structures, facilitated by multiple hydrogen bonding and π-π interactions, result in extended T1 relaxation times, enabling efficient polarization diffusion within the crystals. Our study demonstrates the successful polarization of a DNP-magnetic resonance imaging molecular probe, such as urea, within a cocrystal matrix at room temperature using triplet-DNP.

Coordination Defect‐Induced Lewis Pairs in Metal−Organic Frameworks Boosted Sulfur Kinetics for Bifunctional Photo‐Assisted Li−S Batteries

AbstractThe photo‐assisted strategy is regarded as a crucial approach to enhance the conversion kinetics of polysulfides in lithium–sulfur (Li–S) batteries. However, the development of photo‐assisted Li–S batteries still faces important challenges, such as the rapid recombination of photogenerated electron−holes on cathode and more severe shuttle effect. Herein, a breakthrough in overcoming the challenges has been made by constructing a promising photo‐assisted Li−S battery based on semiconducted metal−organic frameworks. During the discharging progress, the photoexcited electrons generated by H2BPDC ligand based on ligand‐to‐metal charge transfer (LMCT) effect, are injected into the Ti‐oxo clusters in Ti‐MOF, thereby facilitating the sulfur reduction to Li2S. And photoexcited holes are capable of promoting the decomposition kinetics of Li2S during charging. More importantly, the stronger chemical interaction between Ti‐BPDC‐d and polysulfides under light inhibits the polysulfides dissolution and shuttling, which fundamentally addresses the issue of light‐accelerated shuttling. As a result, the photo‐assisted Li–S batteries deliver a reversible capability of 1090.21 mAh g−1 at 0.2 C with a capacity retention of 82.91% over 150 cycles, and a superior rate capability of 673.58 mAh g−1 at 5 C. The findings are promising in advancing the design principles for photo‐rechargeable Li−S batteries.

Enhanced Electron Transport and Mitigated Voltage Loss in Perovskite Photovoltaics Using Sb2O5@SnO2 Composite Electron Transport Layer.

The efficacy of electron transport layers (ETLs) is pivotal for optimizing the device performance of perovskite photovoltaic applications. However, colloidal dispersions of SnO2 are prone to aggregation and possess structural defects, such as terminal-hydroxyls (OHT) and oxygen vacancies (VOs), which can degrade the quality of ETLs, impede charge extraction and transport, and affect the nucleation and growth processes of the perovskite layer. In this study, the Sb(OH)4 - ions hydrolyzed from SbCl3 in colloidal dispersion can bind to defect sites and effectively stabilize the SnO2 nanocrystals are demonstrated. Upon oxidative annealing, a Sb2O5@SnO2 composite film is formed, in which the Sb2O5 not only mitigates the aforementioned defects but also broadens the energy range of unoccupied states through its dispersed conduction band. The increased electron affinity (EA) facilitates more efficient capture of photoexcited electrons from the perovskite layer, thus augmenting electron extraction and minimizing electron-hole recombination. As a result, a significant improvement in power conversion efficiency (PCE) from 22.60% to 24.54% is achieved, with an open circuit voltage (VOC) of up to 1.195V, along with excellent stability of unsealed devices under various conditions. This study provides valuable insights for the understanding and design of ETLs in perovskite photovoltaic applications.

Spin polarization in Fe-doped CsPbBr3 perovskite nanocrystals for enhancing photocatalytic CO2 reduction

Spin manipulation offers an effective strategy to enhance photocatalytic activity in metal halide perovskites by suppressing the recombination of photo-excited electrons. However, the scope of the magnetic dopant inducing spin polarization is still limited. Here, we introduce synergetic strategies to polarize the spin in photo-excited electrons and boost their photocatalytic activity for CO2 reduction. We dope iron cation (Fe2+) into CsPbBr3 perovskite nanocrystals (PNCs). Fe ions induce paramagnetism, fostering spin polarization within the Fe-doped CsPbBr3 PNCs (Fe-CsPbBr3 PNCs) under magnetic fields. The magnetic compositions in PNC tend to stabilize the spin polarized electrons within the PNC, mitigate the recombination of photo-excited electrons and enhance the redox reaction for photocatalytic CO2 reduction. The synergistic effects of magnetic element doping and the application of magnetic fields resulted in a photocatalytic CO2 reduction of 133.04 μmol g−1, which is 1.68-fold increase compared to the Fe-PNC without a magnetic field. This work provides a simple and environmentally friendly approach to CO2 reduction based on PNCs.

Integration of functional modules in a unified photoelectrochemical device for highly efficient solar-driven cathodic metal protection

The ever-increasing energy consumption stimulated the development of various solar energy conversion systems. Photocathodic protection (PCP), emerges as a promising photoelectrochemical technology to alleviate metal corrosion, but the centralization of all core reaction steps on one photoelectric-conversion-unit induces extremely low energy conversion efficiencies. Herein, a proof-of-concept modular PCP device incorporating electron transport layer (ETL), photoelectric conversion layer (PCL), hole transport layer (HTL) and hole consumption layer (HCL) is fabricated to delocalize the key reaction steps for the first time. Such a unified ETL/PCL/HTL/HCL architecture facilitates the efficient extraction of photoexcited electrons from the small-gap PCL to the protected metal through ETL, and holes to HCL for water oxidization through HTL. The directional “macroscopic” charge migration, prolonged charge lifetime and accelerated water oxidation lead to significantly improved PCP effectiveness in simulated seawater. Our findings provide a groundbreaking PCP design, allowing fine-tuning individual functional modules and inter-modular interfaces to vastly elevate performance.

Efficient photocatalytic molecular oxygen activation by TTF-based heterojunction for water purification

Tetrathiafulvalene (TTF), one of the well-known organic photoelectric materials, was served as active sites to accelerate the activation of molecular oxygen to degrade organic pollutants. Herein, a kind of Z-scheme heterojunction photocatalysis was constructed based on g-C3N4 and TTF. According to the experimental results, the mechanism of Z-scheme heterojunction was supported, in which photogenerated electrons transferred from g-C3N4 to TTF. More importantly, TTF on the catalyst surface could serve not only as electron donor, but also as the terminal active site to transfer photoexcited electrons to adsorbed oxygen molecules, producing mass of ⋅O2–. Meanwhile, the activation rate constant of TCN-5 for RhB was 0.0624 min−1, which was 10 and 5 times of g-C3N4 and TTF, respectively. In addition, the results of EPR spectra, rotating disk electrode measurement and molecular oxygen activation measurement also demonstrated that this catalyst was energetically favorable to generate ⋅O2– through the single-electron reduction pathway of molecular oxygen. Finally, four possible photodegradation routes for RhB were proposed based on the results of HPLC-MS. This work provides a new insight on the application of organic photoelectric materials in the purification of wastewater by the molecular oxygen activation.

Inverted nucleation for photoinduced nonequilibrium melting.

Ultrafast photoinduced melting provides an essential platform for studying nonequilibrium phase transitions by linking the kinetics of electron dynamics to ionic motions. Knowledge of dynamic balance in their energetics is essential to understanding how the ionic reaction is influenced by femtosecond photoexcited electrons with notable time lag depending on reaction mechanisms. Here, by directly imaging fluctuating density distributions and evaluating the ionic pressure and Gibbs free energy from two-temperature molecular dynamics that verified experimental results, we uncovered that transient ionic pressure, triggered by photoexcited electrons, controls the overall melting kinetics. In particular, ultrafast nonequilibrium melting can be described by the reverse nucleation process with voids as nucleation seeds. The strongly driven solid-to-liquid transition of metallic gold is successfully explained by void nucleation facilitated by photoexcited electron-initiated ionic pressure, establishing a solid knowledge base for understanding ultrafast nonequilibrium kinetics.

Photonic time-crystalline behaviour mediated by phonon squeezing in Ta2NiSe5.

Photonic time crystals refer to materials whose dielectric properties are periodic in time, analogous to a photonic crystal whose dielectric properties is periodic in space. Here, we theoretically investigate photonic time-crystalline behaviour initiated by optical excitation above the electronic gap of the excitonic insulator candidate Ta2NiSe5. We show that after electron photoexcitation, electron-phonon coupling leads to an unconventional squeezed phonon state, characterised by periodic oscillations of phonon fluctuations. Squeezing oscillations lead to photonic time crystalline behaviour. The key signature of the photonic time crystalline behaviour is terahertz (THz) amplification of reflectivity in a narrow frequency band. The theory is supported by experimental results on Ta2NiSe5 where photoexcitation with short pulses leads to enhanced THz reflectivity with the predicted features. We explain the key mechanism leading to THz amplification in terms of a simplified electron-phonon Hamiltonian motivated by ab-initio DFT calculations. Our theory suggests that the pumped Ta2NiSe5 is a gain medium, demonstrating that squeezed phonon noise may be used to create THz amplifiers in THz communication applications.

Transient drift velocity of photoexcited electrons in CdTe

Transient drift velocity of photoexcited electrons in CdTe

Visible-Light-Induced C-H Cyanoalkylation of Azauracils with Cycloketone Oxime Esters via Catalytic EDA Complex.

Photoexcitation electron donor-acceptor (EDA) complexes provide an effective approach to produce radicals under mild conditions, while the catalytic version of EDA complex photoactivation remains scarce. Herein, we report a visible-light-induced organophotocatalytic pathway for the cyanoalkylation of azauracils using inexpensive and readily available 1,4-diazabicyclo[2.2.2]octane (DABCO) as a catalytic electron donor. This synthetic method exhibits exceptional compatibility with various functional groups and presents 34 examples in high yields. The efficient cyanoalkylation offers an environmentally friendly and sustainable route toward enhancing the structural and functional diversity of azauracils.

Argon nonthermal plasma etching of poly(L-lactic acid) films: Tunning the local surface degradation and hydrolytic degradation rate

Plasma technology is widely used in the industry for the surface modification of polymeric materials, improving the adhesion of paints in polymeric packaging and cellular adhesion on polymers' surfaces without using hazardous chemicals. Plasma etching is a fast way to modify polymers, creating new nanostructure surfaces and adding chemical groups for new applications like antimicrobial surfaces. Poly(L-lactic acid) (PLLA) is a biodegradable polymer with exciting properties for biomedical, tissue engineering, food packaging, and other applications. In many cases, these products must undergo plasma surface treatments to meet the technical requirements of their function. Herein, we evaluated the effects of surface modification of PLLA using Argon nonthermal plasma etching. The results from Gel Permeation Chromatography (GPC), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Excited Photoelectron Spectroscopy (XPS), and Matrix-assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF-MS) show that increasing the plasma exposure time causes an enhancement in bulk and local surface degradation, crystallization kinetics and susceptibility to hydrolytic degradation for PLLA. Atomic Force Microscopy (AFM) show that the PLLA films present the highest surface roughness after 60 s of plasma etching times. Our findings suggest that plasma etching can be a suitable tool to adjust the polymer degradation rate to design intracorporeal devices with controlled degradation kinetics.

Precise Regulation in Chain-Edge Structural Microenvironments of 1D Covalent Organic Frameworks for Photocatalysis.

Covalent organic frameworks (COFs) constitute a promising research topic for photocatalytic reactions, but the rules and conformational relationships of 1D COFs are poorly defined. Herein, the chain edge structure is designed by precise modulation at the atomic level, and the 1D COFs bonded by C, O, and S elements is directionally prepared for oxygen-tolerant photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) reactions. It is demonstrated that heteroatom-type chain edge structures (─O─, ─S─) lead to a decrease in intra-plane conjugation, which restricts the effective transport of photogenerated electrons along the direction of the 1D strip. In contrast, the all-carbon type chain edge structure (─C─) with higher intra-plane conjugation not only reduces the energy loss of photoexcited electrons but also enhances the carrier density, which exhibits the optimal photopolymerization performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance.

Exploring the structural, optical, and dielectric characteristics of polyacrylamide gel synthesized CeMnO3 nanoparticles with Co & Ni ion doping

Nanostructured perovskite materials doped with transition metal ions have attracted significant attention due to their unique electronic and dielectric properties. In this study, we present the synthesis and thorough characterization of cobalt (Co) and nickel (Ni) ion-doped CeMnO3 (CMO) perovskite nanoparticles using a modified polyacrylamide gel method. Our structural analysis suggests that the perovskite phase stabilizes with an orthorhombic phase (Pbnm space group). Morphological analysis conducted via field emission scanning electron microscopy (FESEM) unveils the formation of clustered nanospherical particles. X-ray photoelectron spectroscopy (XPS) reveals mixed oxidation states of Ce, Mn, and Ni ions. Furthermore, UV–Vis and photoluminescence spectra analyses demonstrate a distinctive reduction in band gap and suppressed charge carrier recombination upon doping. The substitution of Ni and Co ions also enhances the screening effect, reducing Coulombic interaction between photoexcited electrons and holes and subsequently increasing the dielectric constant. Analysis of the Cole-Cole plot demonstrates the augmentation of capacitance with Ni substitution. These findings collectively suggest that the decreased dielectric loss and enhanced dielectric constant support the feasibility of these materials for application in storage devices.