Charge Separation Rate Research Articles

Interface-engineered dual Z-scheme of BiVO4/NH2-MIL-125(Ti)/POF photoanode with enhanced photoelectrochemical performance

The key factors that restrain the decomposition activity of photoelectrocatalysis (PEC) are poor redox ability and low charge separation rate. In this work, the dual Z-scheme BiVO4/NH2-MIL-125(Ti)/POF (BiVO4/NM125(Ti)/POF) heterojunctions were successfully established for visible-light driven PEC degradation of phenol. As expected, the optimum BiVO4/NM125(Ti)/POF photoanode exhibited outstanding PEC performance with near-total degradation of phenol within 2 h of illumination. The evaluated activity was assigned to high charge transfer rate and dual Z-scheme heterostructures with double electron transport channels. The fabrication of dual Z-scheme heterojunctions improved a more efficient separation of photo-induced charge carriers while holding a higher redox ability to generate more reactive oxygen species (ROS) such as O2•− and •OH to decompose organic pollutants. In addition, excellent chemical stability and recyclability were also achieved after five times cycles, and the degradation pathway of phenol was also put forward. Finally, the quantitative structure-activity relationship (QSAR) was applied to forecast phenol and its degradation products toxicity. This research gives novel insights into establishing highly effective photoanode with promising applications for organic contaminants degradation, and offers in-depth understanding of charge separation and migration in PEC process.

Rational molecular engineering towards efficient heterojunction solar cells based on organic molecular acceptors

The selection of photoactive layer materials for organic solar cells (OSCs) is essential for the photoelectric conversion process. It is well known that chlorophyll is an abundant pigment in nature and is extremely valuable for photosynthesis. However, there is little research on how to improve the efficiency of chlorophyll-based OSCs by matching chlorophyll derivatives with excellent non-fullerene acceptors to form heterojunctions. Therefore in this study we utilize a chlorophyll derivative, Ce6Me3, as a donor material and investigate the performance of its heterojunction with acceptor materials. Through density functional theory, the photoelectric performances of acceptors, including the fullerene derivative PC71BM and the terminal halogenated non-fullerene DTBCIC series, are compared in detail. It is found that DTBCIC-Cl has better planarity, light absorption, electron affinity, charge reorganization energy and charge mobility than others. Ce6Me3 has good energy level matching and absorption spectral complementarity with the investigated acceptor molecules and also shows good electron donor properties. Furthermore, the designed Ce6Me3/DTBCIC interfaces have improved charge separation and reorganization rates (K CS/K CR) compared with the Ce6Me3/PC71BM interface. This research provides a theoretical basis for the design of photoactive layer materials for chlorophyll-based OSCs.

Engineering of Ultra-Thin Layer of MIL-125(Ti) Nanosheet\Zn-Tetracarboxy-Phthalocyanine S-Scheme Heterojunction as Photocatalytic CO2 Reduction Catalyst.

Metal-organic frameworks (MOFs) with ultrathin 2D structure have attracted remarkable attention in photocatalytic application owing to the accessibility of abundant active sites on the surface. But high charge recombination results in poor photocatalytic activity. Herein, the synthesis of ultrathin MIL-125(Ti) nanosheets is reported with a thickness of 1.3nm through a simple chemical reaction route of precursor solution aging and subsequent solvothermal process for photocatalytic CO2 production. The maximal CO evolution rate achieves 200.8µmol g-1 h-1, which is prominently higher than that (78.6µmol g-1 h-1) of the bulk MIL-125(Ti) counterpart. Furthermore, the structurally stable Zn (II) tetracarboxy phthalocyanine (ZnTcPc) molecules assembly on ultrathin MIL-125(Ti) nanosheet (NS) to form MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction through the strong interaction between the Ti3+ in MIL-125(Ti) and the COOH in ZnTcPc. The introduction of ZnTcPc greatly extends light absorption range and increases charge separation rate. The experimental and density functional theory calculation results validate that the MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction can favor CO2 adsorption and effectively depress the formation energy of the intermediates, achieving a high CO evolution rate of 450.8µmol g-1 h-1. This work provides a strategy of engineering 2D MOF-based heterostructure systems for photocatalytic application.

Construction of an interpenetrating manganese residue-derived FeC2O4/CuC2O4 composite with enhanced charge transfer in photo-Fenton reactions via mechanical activation pre-anchoring strategy

The low rates of charge separation and migration and the pronounced photo-corrosion of FeC2O4 significantly limit its environmental applications. Strengthening the charge transfer rate by constructing a tight bimetallic interface is an attractive method. Herein, a novel interpenetrating manganese residue (MR)-derived FeC2O4/CuC2O4 (MAMR-FeCuOx) composite with intimate interface was constructed via mechanical activation (MA) pre-anchoring and liquid-phase deposition-photo-reduction strategy, and was used as a photo-Fenton catalyst for efficient degradation of oxytetracycline (OTC) under visible light irradiation. The Cu2+ was uniformly dispersed and anchored on the surface of MR after MA pretreatment and an interpenetrating structure was formed through the liquid-phase deposition-photo-reduction process. MAMR-FeCuOx displayed excellent photo-Fenton catalytic performance and stability with a 99% OTC removal rate within 10 min, which is 20.87 times higher than that of FeC2O4, and maintained over 96% OTC removal rate even after ten consecutive cycles. These enhanced catalytic performances and stability can be attributed to the formation of an interpenetrating structure with the intimate interface between FeC2O4 and CuC2O4 induced by MA pretreatment, which promoted electronic interactions between Fe and Cu for effectively reducing the charge transfer barriers. This improved the utilization rate of visible light, the interface electron migration, and the separation efficiency of photogenerated charge carriers. This study provides new insights into the valorization of solid waste and the development of stable and efficient FeC2O4-based catalysts.

Ultrafast symmetry-breaking charge separation in Perylenemonoimide-embedded multichromophores: impact of regioisomerism.

Symmetry-breaking charge separation (SB-CS) has recently evolved as an emerging concept offering its potential to the latest generation of organic photovoltaics. However there are several concerns that need to be addressed to reach the state-of-the-art in SB-CS chemistry, for instance, the desirable molecular geometry, interchromophoric distance and extent of electronic coupling. To shed light on those features, it is reported herein, that ortho-functionalized perylene monoimide (PMI) constituted regioisomeric dimer and trimer derivatives with varied molecular twisting and electronic conjugation have been synthesized. In steady-state photophysical studies, all the dimers and trimer derivatives exhibit a larger bathochromic shift in the emission spectra and a significant reduction of fluorescence quantum yield in polar DMF. Among the series of multichromophores, ortho- and self-coupled dimers display the strikingly different optical feature of SB-CS with a very fast charge separation rate (τCS = 80.2 ps) upon photoexcitation in DMF, which is unveiled by femtosecond transient absorption (fs-TA) studies. The SB-CS for two dimers is well-supported by the formation of PMI˙+ and PMI˙- bands in the fs-TA spectra. Further analysis of fs-TA data revealed that, among the other multichromophores the trimer also exhibits a clear charge separation, whereas SB-CS signatures are less prominent, but can not be completely disregarded, for the meta- and para-dimers. Additionally, the charge separation dynamics of those above-mentioned PMI derivatives are devoid of a kinetically favorable excimer or triplet formation. The evidence of a profound charge transfer phenomenon in the ortho-dimer is characterized by density functional theory (DFT) calculations on excited state electronic structures. The excitonic communications in the excited state electronic arrangements unravel the key role of dihedral twisting in SB-CS. The thermodynamic feasibility of CS (ΔGCS) and activation barrier (ΔG≠) of the derivatives in DMF are established from the Rehm-Weller equation and Marcus's theory, respectively. This work is an in-depth study of the effect of mutual orientation of PMIs and regioisomerism in determining sustainable guidelines for using SB-CS.

LSPR-enhanced photocatalytic N2 fixation over Z-scheme POMOF-derived Cu/WO2 modified C-BiOBr with multiple active sites

The conception and production of nitrogen-fixing photocatalysts with efficient charge separation rates and multiple active sites have been the focus of research. In this paper, we prepared Cu/WO2 nanoparticles by...

Regulation of photoinduced charge transfer in all-small-molecule organic solar cells through the synergistic effect of external electric field and solvent

The donor (BTR-Cl) and acceptor (BTP-FCl-FCl) have well-defined small molecule properties and excellent repeatability, and they can form charge transfer complexes with a wide spectral absorption range. Using density functional theory (DFT), we simulate the photoinduced charge transfer of bulk-heterojunction (BHJ) organic solar cell (OSC) materials modulated by the external electric field (Fext) at the microscopic level. The excited-state properties, reorganization energy (λ), Gibbs free energy (ΔG), electron coupling matrix elements (VDA) and intermolecular charge transfer (ICT) rate dependent on Fext are systematically analyzed. The results manifest that Fext has apparent positive regulation on the charge separation rate (KCS), and VDA is the main factor affecting KCS. The synergistic effect of solvent and Fext on charge transfer process is further investigated. It is found that the charge transfer rate in solvent is lower than that in solvent-free conditions, and the charge transfer rate in chlorobenzene (CB) solvent does not change significantly under the control of Fext. At the same time, Fext has a positive effect on the charge transfer rate in tetrahydrofuran (THF) solvent. Considering the charge transfer rate under different solvents and Fext intensities, it is found that the solvent and Fext play an essential role in determining the KCS and charge recombination rate (KCR).

Rational design of pyrene and thienyltriazine-based conjugated microporous polymers for high-performance energy storage and visible-light photocatalytic hydrogen evolution from water

Conjugated microporous polymers (CMPs) have found extensive applications in various fields such as optoelectronics, CO2 capture, and catalysis. However, their potential in electrochemical supercapacitors as energy storage and H2 production systems remains relatively unexplored. This limited exploration can be attributed to certain challenges, including issues related to structural and electrochemical stability, as well as the relatively modest specific capacitance. Additionally, many of the CMPs discovered thus far have exhibited lower energy densities, further contributing to this underexplored aspect of their utility. In this study, we prepared two different CMPs [TPET-TTh and PyT-TTh CMPs] containing thienyltriazine units (TTh) for the redox mechanism and constructed electrodes for supercapacitor applications. The synthesized TPET-TTh and PyT-TTh CMPs displayed exceptionally high specific surface areas of 545 and 528 m² g⁻¹, respectively. Furthermore, their pore sizes were very similar, centered at approximately 0.39 and 0.36 nm, respectively. To evaluate their electrochemical properties, the TTh-CMPs were examined using cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The resulting CV curves exhibited rectangular shapes, indicative of the characteristic behavior of electric double-layer capacitors, across a range of potential and scan rates. These TPET-TTh and PyT-TTh CMPs delivered nominal specific capacitances of 74 and 76 F g−1 at 0.5 A g−1, respectively. In addition, they exhibited outstanding capacity retentions of 95.2 and 97.30 % even after 2000 cycles [analyzed at 10 A g−1]. The TTh-CMPs also exhibited excellent light-capture capabilities. The PyT-TTh CMP has faster charge separation and lower charge recombination rates than TPET-TTh CMP. This results in a higher hydrogen evolution rate from the water decomposition reaction. The H2 production rate of PyT-TTh CMP could be as high as 18,533 μmol g−1 h−1, which is approximately 4-fold that of TPET-TTh CMP. This study offers a strategy for the design of TTh-containing CMPs that exhibit exceptional energy storage application and photocatalytic efficiency for H2 evolution.

Theoretical study of the effect of D-A type polymer donors on the performance of Y6-based organic solar cells

Non-fullerene organic solar cells (OSCs) based on Y6 molecule have developed rapidly in recent years, and the power conversion efficiency (PCE) varies greatly when the OSC device constructed by Y6 and donor molecules with small structural difference. In this work, the influence of six donor-acceptor (D-A) polymer donors on Y6-based OSCs were focused. The ground-state properties (planarity, frontier molecular orbital energy levels, driving force), excited-state properties of donors (primary indicators, Coulomb attraction) and donor/acceptor interfaces (Frenkel excitation (FE) and charge transfer (CT) states, electron coupling and charge separation rates) were discussed. The results show that symmetrical alkyl chains in the acceptor unit is favorable for maintaining planarity of molecule, while fluorination induces twisting in the thiophene bridge and acceptor unit. And the investigated high-performance molecules have desirable driving force, smaller Coulomb attraction and significant degree of holes and electrons delocalization. Also, the highest-performance system has multiple charge transfer pathways, which can improve charge separation efficiency. At the same time, high-performance systems often have better planarity and more favorable substituent positions. The high-performance donor/Y6 systems have more advantage in charge separation than the low-performance systems. This work provides a fundamental understanding of the impact of D-A type donor materials on the cell performance and theoretical guidance for further optimization of polymer donor materials in Y6-based OSCs.

Surface sensitization of graphitic carbon nitride with well-defined, organized Pd(II)-directed multiporphyrin array multilayers as ternary photocatalysts for Cr(VI) reduction in aqueous solution

Surface sensitization to a semiconductor is one of the most important strategies to increase the visible light-harvesting ability, photo-induced carrier separation and transfer rate, thus improving the photocatalytic efficiency. Here, ternary nanocomposites are constructed by a Pd(II)-directed layer-by-layer (LBL) coordination bonding of tetrakis(4-aminophenyl)porphyrin (TAPP) on the oxidized graphitic carbon nitride (O-g-C3N4). The nanocomposites of O-g-C3N4@(Pd-TAPP)n as-produced present a porous and ultra-thin lamellar structure with an enhanced absorption ability in the visible light region. As the heterogeneous photocatalyst, O-g-C3N4@(Pd-TAPP)n can reduce the toxic hexavalent Cr(VI) species under visible light irradiation with no need for the sacrificial agent. Further, the photocatalytic activity is enhanced by orders of magnitude higher than that before the surface modification, attributed to the reasons of increased specific surface area, elevated light utilization, meliorative charge separation and transfer rate, as well as the synergistic effect by the multiporphyrin arrays and coordinated Pd(II)/(0) species. In addition to the features of without need of sacrificial agent and irradiation under visible light, the Pd-TAPP multilayer modified nanocomposites have well stability and reusability, resulting in a possibility for the practical application.

Interfacial engineering of Bi12O17Br2/g-C3N4-x S-scheme junction boosting charge transfer for cooperative tetracycline decomposition and CO2 reduction

To realize the double winning goal of environment and energy, a novel dual-functional photocatalytic reaction system is designed by using CO2 conversion and pollutant oxidation in one cooperative system. S-scheme heterojunctions exhibit huge potential for accomplishing such synergetic coupling reaction system due to their strong redox ability and speedy charge separation rate. Howbeit, how to effectively adjust the charge transfer rate at nanometric heterointerface remains pivotal and challenging. Herein, interfacial Bi-N bond and N vacancy co-modulate Bi12O17Br2/g-C3N4-x S-scheme junction is constructed, which not only presents superior separation and migration efficiency of charges, but also possesses high redox capacity. A series of theoretical and experimental results manifest that the synergistic effect of interfacial Bi-N bond and N vacancy availably expedite carrier transfer dynamics, achieving excellent photo-redox activity for cooperative CO2 reduction and tetracycline oxidization. Furthermore, compared to two half-reactions, such elaborate cooperative reaction system displays an obviously elevated photo-redox activity. This work provides a deep insight into regulating interfacial charge migration of heterojunction by chemical bonds and defects.

Construction of novel dual Z-scheme g-C3N4/ZnFe2O4/Ag2CO3 heterojunction with enhanced visible-light-driven performance for tetracycline degradation and bacterial inactivation

Dual Z-scheme heterojunction with highly separation efficiency of photoinduced carriers and outstanding redox capability has received considerable attention and hold great promise for environmental remediation. Herein, magnetic dual Z-scheme g-C3N4/ZnFe2O4/Ag2CO3 heterojunction was successfully constructed, and applied as a dual-function photocatalyst for tetracycline (TC) degradation and bacterial inactivation. The optimized g-C3N4/ZnFe2O4/Ag2CO3 heterojunction exhibited excellent photocatalytic capacity for TC degradation with a rate constant of 0.0154 min−1, which is 2.73, 3.08, and 2.92 times higher compared to that of the g-C3N4, ZnFe2O4, and g-C3N4/ZnFe2O4, respectively. Impressively, the g-C3N4/ZnFe2O4/Ag2CO3-1.25 heterojunction displayed satisfying activity within a wider range of pH (3.0–9.0), TC concentration (5–25 mg L−1), and with the addition of various anions including Cl-, HCO3-, SO42-, and NO3-. Meanwhile, 6.5-log of Escherichia coli cells could also be inactivated by g-C3N4/ZnFe2O4/Ag2CO3-1.25 heterojunction under visible light. Mechanism exploration based on trapping experiment, electron paramagnetic resonance (EPR) analysis, and liquid chromatography-mass spectrometer (LC-MS) indicated that the improved photocatalytic performance resulted from the synergetic effect of semiconductors and constructed dual Z-scheme heterojunction, which significantly promotes charge separation rate and endows strong redox capacity. As expected, the toxicity of TC degradation intermediates was reduced according to the Toxicity estimation analysis based on a quantitative structure activity relationships (QSAR) method. Further, the g-C3N4/ZnFe2O4/Ag2CO3 heterojunction also demonstrated magnetic separation property and satisfactory photocatalytic stability even after 4 cycles. This work offers a new perspective on constructing novel magnetic dual Z-scheme heterojunction with dual-function photocatalytic properties and is of significance for water remediation.

Zinc Tetrapyrrole Coordinated to Imidazole Functionalized Tetracyanobutadiene or Cyclohexa-2,5-diene-1,4-diylidene-expanded-tetracyanobutadiene Conjugates: Dark vs. Light-Induced Electron Transfer.

Using the popular metal-ligand axial coordination self-assembly approach, donor-acceptor conjugates have been constructed using zinc tetrapyrroles (porphyrin (ZnP), phthalocyanine (ZnPc), and naphthalocyanine (ZnNc)) as electron donors and imidazole functionalized tetracyanobutadiene (Im-TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded-tetracyanobutadiene (Im-DCNQ) as electron acceptors. The newly formed donor-acceptor conjugates were fully characterized by a suite of physicochemical methods, including absorption and emission, electrochemistry, and computational methods. The measured binding constants for the 1 : 1 complexes were in the order of 104 -105 M-1 in o-dichlorobenzene. Free-energy calculations and the energy level diagrams revealed the high exergonicity for the excited state electron transfer reactions. However, in the case of the ZnNc:Im-DCNQ complex, owing to the facile oxidation of ZnNc and facile reduction of Im-DCNQ, slow electron transfer was witnessed in the dark without the aid of light. Systematic transient pump-probe studies were performed to secure evidence of excited state charge separation and gather their kinetic parameters. The rate of charge separation was as high as 1011 s-1 suggesting efficient processes. These findings show that the present self-assembly approach could be utilized to build donor-acceptor constructs with powerful electron acceptors, TCBD and DCNQ, to witness ground and excited state charge transfer, fundamental events required in energy harvesting, and building optoelectronic devices.

Interfacial oxygen vacancy modulated ZIF-8-derived ZnO/CuS for the photocatalytic degradation of antibiotic and organic pollutants: DFT calculation and degradation pathways

Fabricating oxygen vacancies (Vo) is an effective approach to enhance photocatalytic performance, but its effect on the interfacial charge transfer pathway remains unelucidated to date. In this study, we used the simple aqueous solution method to create an oxygen-defected ZIF-8-derived CuS/ZnO (CZ) heterostructure, and various characterization techniques were used to investigate the prepared catalysts. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were used to determine the surface defects caused by the CuS nanoparticles in the ZnO matrix generated from ZIF-8. The optimized CuS/ZnO (CZ-2) catalyst exhibited efficient photocatalytic performance by effectively increasing the charge separation rate of the photogenerated electrons. The photocatalytic performances of methylene orange (MO) and ciprofloxacin (CIP) using the CZ heterostructure were 99.76 % and 94.59 %, respectively, with the corresponding rate constants of 0.0695 and 0.0312 min−1 at 40 min. The electron spin resonance and scavenger tests have established that •O2− is the primary oxidative radical species involved in photocatalytic activity. In addition, the density functional theory calculations were performed to determine the degradation mechanism of CIP, and the possible pathways of CIP degradation were investigated using liquid chromatography–mass spectroscopy. This study provides new insights into the development of metal–organic frameworks and metal sulfide-based heterostructures for environmental degradation applications.

Progress in wastewater treatment via organic supramolecular photocatalysts under sunlight irradiation

Semiconductor photocatalysis offers a promising and sustainable avenue for wastewater treatment due to its ease of separation and recyclability. However, their practical application is currently hampered by limited energy utilization, insufficient mineralization, and low treatment capacity under sunlight. This account summarizes our progress in developing broad-spectrum responsive (extended to 950 nm) supramolecular organic photocatalysts capable of sunlight-driven over 95% pollutant mineralization. Through modulation of molecular dipole and crystallinity, we enhance the built-in electric field, thereby improving charge separation and photodegradation rates. Furthermore, to overcome the low-flux constraints of traditional photocatalysis, we integrated the Fenton catalyst to construct photo-self-Fenton systems, realizing a 29.63 L m2 h1 high-flux mineralization under sunlight. Finally, a brief conclusion and outlook on organic photocatalysts have also been presented.

Type-I CdS/ZnS Core/Shell Quantum Dot-Gold Heterostructural Nanocrystals for Enhanced Photocatalytic Hydrogen Generation.

Developing Type-I core/shell quantum dots is of great importance toward fabricating stable and sustainable photocatalysts. However, the application of Type-I systems has been limited due to the strongly confined photogenerated charges by the energy barrier originating from the wide-bandgap shell material. In this project, we found that through the decoration of Au satellite-type domains on the surface of Type-I CdS/ZnS core/shell quantum dots, such an energy barrier can be effectively overcome and an over 400-fold enhancement of photocatalytic H2 evolution rate was achieved compared to bare CdS/ZnS quantum dots. Transient absorption spectroscopic studies indicated that the charges can be effectively extracted and subsequently transferred to surrounding molecular substrates in a subpicosecond time scale in such hybrid nanocrystals. Based on density functional theory calculations, the ultrafast charge separation rates were ascribed to the formation of intermediate Au2S layer at the semiconductor-metal interface, which can successfully offset the energy confinement introduced by the ZnS shell. Our findings not only provide insightful understandings on charge carrier dynamics in semiconductor-metal heterostructural materials but also pave the way for the future design of quantum dot-based hybrid photocatalytic systems.

S-scheme MOF-on-MOF heterojunctions for enhanced photo-Fenton Cr(VI) reduction and antibacterial effects

The photocatalytic efficiency is commonly restrained by inferior charge separation rate. Herein, the S-scheme MIL-100(Fe)/NH2-MIL-125(Ti) (MN) photo-Fenton catalyst with the built-in electric field (BEF) was successfully constructed by a simple ball-milling technique. As a result, the MN-3 (the mass ratio of MIL-100(Fe) to NH2-MIL-125(Ti) was 3) composite presented the best visible-light-induced photocatalytic ability, in contrast to pure MIL-100(Fe) and NH2-MIL-125(Ti). The reduction efficiency of Cr(VI) almost reached 100% within 35 min of illumination. Moreover, the MN-3 heterojunction also exhibited the highest antibacterial activity, and about 100% E. coli and more than 90% S. aureus were killed within 60 min of illumination. In photo-Fenton system, In the photo-Fenton system, e−, O2•- and Fe2+ played vital roles for Cr(VI) reduction, and •OH, h+ and O2•- and 1O2 were responsible for sterilization. Additionally, 5 cyclic tests and relevant characterizations confirmed the excellent repeatability and stability of the composite. Also, the S-scheme charge transfer process was put forward. This work offers a novel idea for establishing the MOF-on-MOF photo-Fenton catalyst for high-efficiency environmental mitigation.

Effective Hydrogen Production from Alkaline and Natural Seawater using WO3-x@CdS1-x Nanocomposite-Based Electrocatalysts.

Offshore hydrogen production through water electrolysis presents significant technical and economic challenges. Achieving an efficient hydrogen evolution reaction (HER) in alkaline and natural seawater environments remains daunting due to the sluggish kinetics of water dissociation. To address this issue, we synthesized electrocatalytic WO3-x@CdS1-x nanocomposites (WCSNCs) using ultrasonic-assisted laser irradiation. The synthesized WCSNCs with varying CdS contents were thoroughly characterized to investigate their structural, morphological, and electrochemical properties. Among the samples tested, the WCSNCs with 20 wt % CdS1-x in WO3-x (Wx@Sx-20%) exhibited superior electrocatalytic performance for hydrogen evolution in a 1 M KOH solution. Specifically, the Wx@Sx-20% catalyst demonstrated an overpotential of 0.191 V at a current density of -10 mA/cm2 and a Tafel slope of 61.9 mV/dec. The Wx@Sx-20% catalysts demonstrated outstanding stability and durability, maintaining their performance after 24 h and up to 1000 CV cycles. Notably, when subjected to natural seawater electrolysis, the Wx@Sx-20% catalysts outperformed in terms of electrocatalytic HER activity and stability. The remarkable performance enhancement of the prepared electrocatalyst can be attributed to the combined effect of sulfur vacancies in CdS1-x and oxygen vacancies in WO3-x. These vacancies promote the electrochemically active surface area, enhance the rate of charge separation and transfer, increase the number of electrocatalytic active sites, and accelerate the HER process in alkaline and natural seawater environments.

Modified silver phosphate nanocomposite as an effective visible-light-driven photocatalyst in the reduction of aqueous Cr(VI)

A simple precipitation technique was used to synthesize novel modified Ag3PO4 (AP) with Ag2S (AS) and reduced graphene oxide (G). XRD, FT-IR, Raman spectra, HR-TEM, XPS, UV-Vis, and PL, were used to investigate the physicochemical and optical properties of the as-prepared materials. The produced AS/G/AP nanocomposites exhibited a more visible-light response, diminished bandgap energy, and enhanced the charge separation rate. For the first time, the photocatalytic efficiency of modified Ag3PO4 nanocomposites was tested in aqueous Cr(VI) reduction under visible light illumination. After 45 min of irradiation and adapting the dose to 0.05 g/L, the optimized composite with 20 wt%AS (20-AS/G/AP) attained the maximum photo-reduction efficiency of 98.7% for Cr(VI) with a rate constant of 0.0734 min−1, which is almost 49 times higher than pure AP. The XPS analysis of the spent catalyst confirmed the distinctive Cr(III) peaks. Moreover, the photocatalyst showed notable reusability for four cycles without substantial activity loss. Finally, the photo-reduction mechanism of the catalyst was suggested.

Synthesis and Excited State Charge Separation Involving Coordinated C60 of π-Extended Pyrazinepyrene Fused Zinc Phthalocyanines

Polycyclic aromatic hydrocarbons (PAHs) play an important role in organic electronics.[1] To increase the stability and the conjugation, pyrene units could be further attached through heteroatoms to improve the photo/chemical stability to oxygen or light.[2] In terms of the synthesis of these types of large acenes through pyrene, many routes have been studied and one of the best protocols is to synthesize the quinoxaline derivative from the dione and the corresponding diamino subunit.[3] Herein, we will present a series of pyrazinepyrene fused zinc phthalocyanines (ZnPc-Pyrn) as a new class of π-extended phthalocyanine systems. Bathochromically shifted absorption as a function of the number of pyrazinepyrene entities due to extended π-conjugation, and quenched fluorescence due to the presence of fused pyrazinepyrene were witnessed. The electronic structures of these phthalocyanines were probed by systematic computational and electrochemical studies while the excited state properties were examined by pump-probe spectroscopies operating at the femto- and nanosecond time scales. Like the excited singlet lifetimes, the excited triplet states also revealed diminished lifetimes with an increased number of pyrazinepyrene entities. Further, the coordinatively unsaturated zinc in these molecules was coordinated with phenyl imidazole functionalized fullerene, ImC60 to form a new series of donor-acceptor conjugates. Upon full characterization of these conjugates, the occurrence of excited-state charge separation was established by transient pump-probe spectroscopy covering wide temporal and spatial regions. With an increase in pyrazinepyrene entities, an increased rate of forward charge separation was witnessed while rate constants for charge recombination were slower resulting in the final lifetime of charge-separated states of about 40-50 ns, better than that reported earlier for a similar pristine zinc phthalocyanine derived dyad. [4]AcknowledgmentsAuthors acknowledge the support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER, PID2020-117855RB-I00 to ASS) and Generalitat Valenciana (CIPROM/2021/059 and MFA/2022/028 to ASS) and US-National Science Foundation (2000988 to FD). The computational work was completed at the Holland Computing Center of the University of Nebraska, which receives support from the Nebraska Research Initiative.