Effective Charge Separation Research Articles

Piezoelectric Applications of Low-Dimensional Composites and Porous Materials.

Low-dimensional (LD) materials, with atomically thin anisotropic structures, exhibit remarkable physical and chemical properties, prominently featuring piezoelectricity resulting from the absence of centrosymmetry. This characteristic has led to diverse applications, including sensors, actuators, and micro- and nanoelectromechanical systems. While piezoelectric effects are observed across zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) LD materials, challenges such as effective charge separation and crystal structure imperfections limit their full potential. Addressing these issues requires innovative solutions, with the integration of LD materials with polymers, ceramics, metals, and other porous materials proving a key strategy to significantly enhance piezoelectric properties. This review comprehensively covers recent advances in synthesizing and characterizing piezoelectric composites based on LD materials and porous materials. The synergistic combination of LD materials with other substances, especially porous materials, demonstrates notable performance improvements, addressing inherent challenges. The review also explores future directions and challenges in developing these composite materials, highlighting potential applications across various technological domains.

Flower-like 3D MoS2/Cu2O hybrids with enhanced photoelectrochemical performance

Molybdenum disulfide (MoS2) is widely employed as a photoanode in photoelectrochemical (PEC) tests due to its energy gap in the visible region and strong interaction with light. In this work, three-dimensional (3D) flower-like MoS2 heterostructures have been introduced by the CVD method and decorated with copper (I) oxide (Cu2O) nanoparticles synthesized by electrodeposition. SEM, XRD, Raman, UV-Visible, current-potential and EIS analyses have been performed to evaluate the heterostructure. The results show that the MoS2/Cu2O heterostructure is not only well-formed but associated with a 61% increase in photocurrent density compared to MoS2. This is due to the smaller charge transfer resistance and effective charge separation in the heterostructure compared to MoS2, based on the EIS analysis and corresponding band energy diagram. A cyclic test of the electrode also shows its excellent stability, making it suitable for practical applications.

Anthracene-based dual channel donor-acceptor triazine-containing covalent organic frameworks for superior photoelectrochemical sensing

Covalent organic frameworks (COFs) exhibit excellent photoelectrically active structures and serve as channels for photon capture and charge carrier transport. However, their relatively high charge-carrier recombination rates and lack of specific recognition sites limit their application in photoelectrochemical sensing. This paper reports a functionalized donor–acceptor (D-A) COF comprising electron-rich polycyclic aromatic moieties and electron-deficient triazines (Tz) incorporating boronic acid through ligand exchange. The number of aromatic rings in the polycyclic aromatic moiety is crucial for establishing an efficient D-A system within COF. In the absence of an external electron donor, the anthracene-based COF exhibited a five-fold enhancement in photocurrent compared to the naphthalene-based COF. The resulting anthracene-based D-A COF exhibited enhanced orbital overlap and electron push–pull interactions, facilitating more effective charge separation. Furthermore, introducing boronic acid enabled the selective enrichment of low-concentration external electron donors, such as dopamine, in the inner Helmholtz plane. This ingenious approach establishes a unique dual-channel D-A system that allows direct measurement of dopamine in serum. Under optimized conditions, the test platform achieves good correspondence for dopamine at 1 to 100 nM and 0.5 to 100 μM with a detecting limit of 0.36 nM (3σ/S, n = 11). This strategy introduces a novel dimension to photoelectrochemical sensing, focusing on the effect of spatial separation between the external electron donor and the photoelectrode interface that intricately shapes the behavior and enhances the performance of the photoelectric system.

Central core substitution optimized molecular aggregation and photovoltaic performance in A-DA′D-A type acceptors

With the development of A-DA′D-A (D: electron-donating unit; A: electron-withdrawing unit) type acceptors, the performances of organic solar cells (OSCs) have reached a new stage. The central core of A-DA′D-A molecules exhibits a significant impact on molecular planarity and stacking. In this research, the conjugated central core of A-DA′D-A type molecules was extended to the two-dimensional (2D) direction, and the influence of alkyl chains on the 2D-central cores on molecular structure and device performances was explored. Compared with TPTC6 containing alkyl chains, TPTC0 without alkyl chains showed stronger intermolecular interactions and crystallinity, which realized advantageous phase separation in the blend film, leading to more effective charge separation and transport. Therefore, devices based on TPTC0 exhibited an excellent power conversion efficiency (PCE) of 17.70%. In contrast, the blend film exhibited a high energetic disorder due to the poor miscibility between PM6 and TPTC0, resulting in decreased VOC compared with TPTC6. In this work, the influence of alkyl chains on molecular stacking and crystallinity in 2D-expanding conjugated materials was discussed in detail, which would promote the development of related research.

Construction of 1D/3D Co9S8/Mn0.3Cd0.7S Schottky heterojunction for dramatically boosted photocatalytic H2 evolution performance

One of the most crucial strategies for transforming solar energy into sustainable hydrogen energy is photocatalytic H2 evolution, and constructing an effective and durable photocatalyst remains a difficult task. Herein, a 1D/3D Co9S8/Mn0.3Cd0.7S Schottky heterojunctions were successfully fabricated by three-step hydrothermal procedure, in which 3D Mn0.3Cd0.7S solid solution particles were immobilized on the 1D tube-like Co9S8 surface, allowing for extremely effective charge separation and transfer. Through coupling Co9S8 with Mn0.3Cd0.7S, the photocatalytic H2 evolution activity and stability were significantly boosted. The 7 % Co9S8/Mn0.3Cd0.7S heterojunction possessed the highest photocatalytic activity with the H2 evolution rate of 1586.4 μmol⋅h−1, which was 3.73 times larger than that of pristine Mn0.3Cd0.7S, corresponding to 21.8 % apparent quantum efficiency (AQE) at 420 nm monochromatic light. The Schottky heterojunction mechanism between Co9S8 and Mn0.3Cd0.7S could plausibly explain the enhanced photocatalytic H2 evolution performance, according to density functional theory (DFT) calculations and ultraviolet photoelectron spectroscopy (UPS) measurements. This investigation would offer the useful insights to develop Co9S8 cocatalyst for application in photocatalytic H2 evolution.

A Simple Highly Efficient Catalyst with NiOX‐loaded Reed‐based SiC/CNOs for Hydrogen Production by Photocatalytic Water‐splitting

AbstractThe cocatalyst and the semiconductors are tightly coupled to achieve effective separation of charges, which is one of the effective ways to improve photocatalytic hydrogen production in recent years. In this report, natural reed as raw material was simple sintering to obtain silicon carbide (SiC) nanowires supported on carbon nano onions (CNOs), and NiOX as a cocatalyst was introduced and evenly distributed on the SiC and CNOs to form a NiOX/SiC/CNOs heterojunction composite, which can be used for photocatalytic hydrogen production under visible light. The structure and performance of the composite were investigated by XRD, XPS, TEM, SEM, FTIR, GC, etc. The results show that the NiOX/SiC/CNOs composite performed excellent photocatalytic activity, When the loaded NiOX is 1.0 wt %, the maximum hydrogenation rate can reach 3160.2 μmol ⋅ g−1 h−1 in the presence of Eosin Y (EY) as photosensitizer and triethanolamine (TEOA) as a sacrificial agent, which is 2.86 times that of SiC/CNOs. The improvement in photocatalytic performance was mainly attributed to synergistic effects of high light absorbing efficiency, effective charge separation, increasing the transfer rate of electrons, and NiOX high dispersion active sites in SiC/CNOs.

Synthesis of atomically precise Ag16 nanoclusters and investigating solvent-dependent ultrafast relaxation dynamics.

In this article, the main focus is to employ a new synthetic strategy to prepare atomically precise Ag nanoclusters (NCs) and unveil the critical role played by the solvents in the excited state dynamics of Ag NCs. The compositional analysis confirms the formula of the nanoclusters as Ag16(PDT)8(PPh3)4 (Ag-PDT NCs). These NCs showed a sharp absorption band at 525 nm and a comparatively broad absorption band at 633 nm. The emission maximum was 630 nm with a quantum yield (QY) of 0.23%. Three-component relaxation dynamics was retrieved from global analysis and described as core relaxation (664 fs), core-to-surface state relaxation (500 ps), and ground state relaxation (>1 ns) for Ag NCs in the DCM solvent. The time constants are slightly higher at 1.25 ps, 624.25 ps, and >1 ns for Ag NCs in the DMF solvent because of the less effective charge separation. The high QY in DMF follows this low charge separation (0.23% vs. 0.63%). The straight-chain dithiol capping agent (with lower electron density than an electron-rich aromatic ring) is mainly responsible for this less effective charge separation. Finding the pivotal role of the solvent in NC chemistry will help to characterize it thoroughly and produce a strategy for precise applications in various fields.

Nanostructured electroless Ni deposited SnO2 for solar hydrogen production.

Herein, Ni-decorated SnO2 (Ni@SnO2) nanostructures have been synthesized using SnO2 as a matrix via a simple electroless deposition method for the generation of hydrogen, a potent near-future fuel. XRD analysis confirmed the generation of rutile SnO2 in Ni@SnO2. FESEM and FETEM imaging exhibited the formation of SnO2 nanoparticles with a size of 10-50 nm, which are deposited with Ni nanoparticles (5-7 nm) and intermittent films (thickness 1-2 nm). The associated EDS elemental mapping validated Ni deposition on the surface of the SnO2 nanoparticles, further supplemented by FTIR, Raman and XPS analysis. Slight red shifts in the band gaps of the Ni@SnO2 nanostructures (in the range of 3.53-3.65 eV) compared to the pristine SnO2 nanoparticles (3.72 eV) were observed. Also, intensity quenching of the band gap and associated defect peaks were observed in PL analysis. The Ni@SnO2 nanostructures were used as photocatalysts and exhibited proficient hydrogen evolution. Among the samples, the 0.3 wt% Ni@SnO2 nanostructures showed the greatest hydrogen evolution, i.e., ∼50 μmol g-1 h-1 under visible light irradiation versus pristine SnO2 (8.5 μmol g-1 h-1) owing to the enhanced density of active sites and effective charge separation. It is noteworthy that the hydrogen evolution is much better as compared to earlier reports of Pt-doped-SnO2 based materials.

Effective charge separation in photoelectrochemical water splitting: a review from advanced evaluation methods to materials design

The total efficiency of PEC water splitting can be divided into light absorption, charge separation, and surface injection efficiencies. Charge separation process in ns–μs is valuable to modulate but is challenging to clarify the working mechanism.

Construction of oxygen-rich vacancies and heterojunctions coupled with different morphologies of CeO2/mesoporous TiO2 framework structures for efficient photocatalytic CO2 reduction performance.

The coupling of efficient adsorption and effective charge separation with photocatalysts enables the use of sunlight for photocatalytic reduction of carbon dioxide (CO2) into high-value-added products. In this work, we used a straightforward solid-phase hydrothermal technique to build an oxygen-vacancy-rich, heterogeneous interface-coupled CeO2/mesoporous TiO2 framework structural system. The heterogeneous structure was constructed by introducing oxygen-vacancy-rich CeO2 into mesoporous TiO2, which may encourage the transfer of charges and increase the number of active sites and CO2 adsorption by utilizing the coupled synergistic effect of oxygen vacancies and heterogeneous interfaces, and it can also regulate the pathway of the photocatalytic reaction and the selectivity of the products. The composite of CeO2 with different morphologies and oxygen-rich vacancies regulated the system's active sites and degree of exposure and enhanced photocatalytic CO2 reduction. The highest CO yield of 6.25 mmol gcat-1 was obtained by use of the rod CeO2/mesoporous TiO2 composite photocatalyst (R-CeO2/TiO2), and this yield was 1.6 times higher than that of pure mesoporous TiO2 and 1.84 times higher than that of pure R-CeO2. Also, the product selectivity increased by 4.3% compared to a single sample. Combining the Mott-Schottky plot results and the energy-barrier perspective to further explore the photocatalytic reduction of the CO2 reaction mechanism as well as the product selectivity, it appears that the construction of the composite system of oxygen-rich vacancies and heterogeneous boundary-coupled photocatalysis provides a practical pathway for the photocatalytic reaction, which may contribute to the photocatalytic reaction's high efficiency and yield selectivity.

In situ fabrication of a plasmonic Bi@Bi2O2CO3 core-shell heterostructure for photocatalytic CO2 reduction: structural insights into selectivity modulation.

The precise design of active sites and light absorbers is essential for developing highly efficient photocatalysts for CO2 reduction. Core-shell heterostructures constructed based on large-sized plasmonic Bi metals are ideal candidates because of the utilization of full-spectrum light and effective charge separation. However, the mechanism of selectivity modulation of large-sized Bi@semiconductor photocatalysts has yet to be explored in depth. Herein, a plasmonic Bi@Bi2O2CO3 core-shell heterostructure was successfully synthesized via a facile solvothermal treatment in deep eutectic solvents, demonstrating highly efficient photocatalytic CO2 reduction. This structure features a sizeable Bi sphere with a thin, epitaxially grown Bi2O2CO3 shell, which allows for the utilization of the entire light spectrum. Additionally, the oxygen vacancies in the Bi2O2CO3 shell can rapidly trap electrons transferred from the Bi core via Bi-O-Bi bonds, thereby forming abundant electron-rich interfaces that serve as the active sites for activating reactant molecules and facilitating the reaction.

High photopiezocatalytic energy conversion via effective charge separation and deformability in the asymmetric ternary heterojunction Bi4Ti3O12/PPy/TiO2

Boosted electric field via enhanced dipoles, increased charge transmission towards the catalyst surface and promoted electron energy via piezoelectric field resulted in the highly efficient photopiezocatalytic activity of ternary structures.

Design and development of symmetric aromatic bischalcogenide-based photocatalysts for water treatment application: a concise study of diphenyl diselenide polypyrrole nanocatalysis.

Dopant engineering can be a very selective approach in designing hybrid materials. Incorporating the required functionality in a dopant effectively modulates its properties towards aimed applications. Consequently, this work through a comparative study envisaged the incorporation of chalcogenides (S, Se, and Te) in a biphenyl motif based on the analysis of major photocatalytic descriptors. Bischalcogenides as tuned dopants have been impressive in enhancing the surface area, increasing crystallinity and facilitating band gap shifts towards better light harvesting. In addition, the chalcogen effect was observed to induce preferential ion migration, leading to effective charge separation and attenuated recombination rates. Photocatalytic descriptors evaluated from electrochemical impedance spectroscopy and photoluminescence data corroborated the chalcogen effect in the observed trend (Ph)2 < (PhS)2 < (PhSe)2 < (PhTe)2. The diphenyl diselenide polypyrrole nanocomposite emerged to be better among the studied systems. (PhSe)2/PPY was characterized and comprehensively evaluated for its photocatalytic activity towards varied dye classes and the colorless isoniazid antibiotic under environmentally viable conditions. Its calculated band potential values and scavenger experiments indicate OH˙ and O2 ˙- as dominant species in its photocatalytic activity. Control experiments confirmed photocatalytic degradation over photolysis as the dye decolouration mechanism. Taken together, (PhSe)2/PPY emerges as a good propensity photocatalyst worthy of real time customization for wastewater treatment on a pilot scale.

Fabrication of NiWO4/g-C3N4 S-scheme heterojunction photocatalyst for enhanced H2 evolution

Photocatalytic H2 production is a desired route to obtain green H2 for its cleanness and sustainability properties. It is still essential to explore the highly active photocatalysts in this field. Herein, a facile solvent evaporation strategy to fabricate a NiWO4/g-C3N4 heterojunction photocatalyst was employed. The research demonstrates that NiWO4/g-C3N4 hybrids can achieve an obviously enhanced H2 evolution actively, although they have poor activity individually. The H2-releasing rate of 10 % NiWO4/g-C3N4 can reach 2546 μmol·h−1·g−1 under 300 W artificial light source illumination in 20 vol.% TEOA. Further investigations indicate that NiWO4 and g-C3N4 can form S-scheme heterojunction according to band structure analysis and photoelectrochemical tests, which leads to an effective charge separation for the energy band bending, coulomb force and interfacial electric field between g-C3N4 and NiWO4, making reserved charges with higher redox activity. In addition, NiWO4 can reduce the H2 evolution overpotential, favoring fast surface H2-releasing kinetics.

Natural pozzolana as standalone photocatalyst for water treatment

This study focuses on natural pozzolana (volcanic ash) as standalone photocatalyst for removal of organic water pollutants under solar irradiation. Natural pozzolana has been modified and investigated using various techniques (XRD, EDS, FTIR, TGA, and BET surface area). The investigated pozzolana material has worked as metal oxide heterojunctions with SiO2 (35.45 %), Al2O3 (12.56 %), Fe2O3 (14.15 %) and CaO (7.89 %) in a majority, besides other oxides (MgO (5.75 %), TiO2 (3.25 %), Na2O (2.15 %), K2O (1.23 %), and MnO (0.34 %)). The XRD results showed that pozzolana materials contains different crystalline forms such as Albite, Quartz, Biotite, Hematite and Magnesio hornblende. The performance of the prepared pozzolan material has been evaluated for photocatalytic degradation of BPB dye as model water pollutant and the photocatalytic activity was related to the characterization results. It was shown that the sieved pozzolana material (Ps) has the highest photocatalytic degradation rate (0.0175 min−1) compared to raw (P0) and calcined (Pc) samples. The photocatalytic activity of Ps was also higher than that of TiO2 anatase (0.0121 min−1) used under the same experimental conditions, which was attributed to the diversity of pozzolana compositions from various oxides, with a cascade transference of charge carriers leading to effective charge separation and transfer, hence enhancing the photocatalytic activity. Based on this, natural pozzolan could be used as cost effective and green material for sustainable photocatalytic applications.

Core-Shell and Yolk-Shell Nanocrystals for Hydrogen Production

With the inherently high degree of complexity, heterostructures composed of two or more materials joined in unique architectures may exhibit superior synergetic properties that are difficult or impossible to acquire from their individual constituents.[1-3] For semiconductor heterostructures, the relative band alignment of the constituents promotes effective charge separation to bring them desirable properties for photocatalysis applications. Among the different types of heterostructures, core-shell and yolk-shell nanocrystals have received particular interest due to their fascinating properties. Several representative works from our lab will be introduced to demonstrate the promising potentials of core-shell and yolk-shell nanocrystals for hydrogen production applications.

Bilayered graded phase homojunction FA0.15MA0.85PbI3-based organic-inorganic hybrid perovskite solar cells crossing 22 % efficiency

Making highly efficient and stable perovskite solar cells (PSCs) are often based on the processing techniques, band gap of the material and effective interface charge separation. The efficiency of PSCs can be enhanced through several methods including the utilization of a solar-friendly absorber, interface passivation and the implementation of multi-junction spectrally matched absorbers or bilayered phase homojunction (BPHJ) consisting of identical absorbers. Here, we demonstrated BPHJ concept by stacking identical compositions of highly efficient and stable FA0.15MA0.85PbI3 perovskite absorbers adopting solution process (SP) and thermal evaporation (TEV) techniques. We successfully achieved FA0.15MA0.85PbI3 (SP)/FA0.15MA0.85PbI3-(TEV) based BPHJ normal n-i-p devices, which significantly crossing 22.% PCE. These improvement stems from effective deposition method for achieving high-quality FA0.15MA0.85PbI3-based BPHJ enabling smooth charge transfer at the interfaces. The resulting BPHJ-based champion device achieve a 22.13 % PCE and retain >95 % its original efficiency over 1000 hours.

Small is Beautiful: Electronic Origin and Synthetic Evolution of Single-Benzene Fluorophores.

ConspectusSingle-benzene fluorophores (SBFs) are small molecules that produce visible light by using only one benzene ring as the sole aromatic core. This Account centers around the chemistry of a new class of SBF that we accidentally discovered but rationally developed and refined afterward. In a failed experiment that took an unintended reaction pathway, we encountered the bright green fluorescence of ortho-diacetylphenylenediamine (o-DAPA). Despite its uninspiring look, reminiscent of textbook examples of simple benzene derivatives, this molecule had neither been synthesized nor isolated before. This discovery led to our studies on the larger DAPA family, including isomeric m-DAPA and p-DAPA. Remarkably, p-DAPA is the lightest red fluorophore, with a molecular weight of only 192. While o- and p-DAPA are emissive, m-DAPA rapidly undergoes internal conversion, facilitated by sequential proton transfer reactions in the excited state.Leveraging the synthetic utility of the amine group, we carried out straightforward single-step modifications to create a full-color SBF library from p-DAPA as the common precursor. During the course of the investigation, we made another fortuitous discovery. With increasing acidity of the N-H group, the excited-state intramolecular proton transfer reaction is promoted, opening up additional pathways for emission to occur at even longer wavelengths. Tipping the balance between the two excited-state tautomers enabled the first example of a single-benzene white-light emitter. We demonstrated the practical utility of these molecules in white light-emitting devices and live cell imaging.According to the particle-in-a-box model, it is difficult to expect a molecule with only one small aromatic ring to produce long-wavelength emission. SBFs rise to this challenge by exploiting electron donor-acceptor pairs around the benzene core, which lowers the energy of light absorption. However, this answers only half of the question. Where do the exceptionally large spectral shifts in the light emission of SBFs originate from? Chemists have long been curious about the molecular mechanisms underlying the dramatic spectral shifts observed in SBFs. Prevailing paradigms invoke the charge transfer (CT) between electron donor and acceptor groups in the excited state. However, without a large π-skeleton for effective charge separation, how could benzene support a CT-type excited state? Our experimental and theoretical studies have revealed that large excited-state antiaromaticity (ESAA) of the benzene core itself is responsible for this remarkable phenomenon. The core matters, not the periphery. With appropriate molecular design, large and extended π-conjugation is no longer a prerequisite for long-wavelength light emission.

“One stone four birds” design atom co-sharing BiOBr/Bi2S3 S-scheme heterojunction photothermal synergistic enhanced full-spectrum photocatalytic activity

The rational design of heterostructure photocatalysts holds significant scientific and technical importance for maximizing the utilization of solar energy. In this study, a full spectrum-responsive S-scheme BiOBr/Bi2S3 heterojunction with co-sharing Bi atoms had been successfully constructed using an ion exchange approach accompanied by an in-situ growth process. Theoretical calculations and advanced techniques analysis demonstrate that the interfacial co-sharing of Bi atoms and the internal electric field (IEF) between BiOBr and Bi2S3 can greatly enhance S-scheme charge transfer, leading to effective spatial charge separation and the maintenance of maximum redox capacity. Additionally, the incorporation of Bi2S3 and the formation of oxygen vacancies (OVs) significantly increased NIR absorption and enhanced the photothermal property, further improving charge separation and utilization. As a result, the optimal photoreduction of Cr(VI) performance in BiOBr/Bi2S3 reached 100% within 10 min of full-spectrum light irradiation, and the CO yield was 20.32 µmol∙g–1 after 5 h of irradiation, which were 31.97 and 3.07 times higher than those of BiOBr, respectively. Furthermore, we elucidated the mechanism of Cr(VI) removal using DFT. This work provides valuable guidance for the rational design and construction of Bi-based S-scheme heterojunction photocatalysts with high-efficiency photocatalytic performance and effective solar light utilization.

Solar light driven photocatalytic degradation of methylene blue dye over Cu doped α-MnO2 nanoparticles

Cu-α-MnO2 nanoparticles were synthesized by hydrothermal method and their potential application in the aqueous-based degradation of organic contaminants was examined under solar light. Cu doping increases the particle size and affects the morphology of MnO2. The Cu-doped α-MnO2 XRD pattern showed a tetragonal crystalline structure with a crystal size of ∼30nm. When compared to α-MnO2, which has a band gap energy of 1.58eV, the 6% Cu-doped α-MnO2 photocatalyst has a lower band gap energy (1.23eV). As a result, the light absorption was increased towards the visible spectrum. The considerable change in PL intensity of MnO2 observed after Cu doping. The findings show that a 6% Cu- α-MnO2 sample degrades methylene blue dye completely within 2 h. The improvement of the photocatalytic activity of the Cu-α-MnO2 nanoparticles was significantly influenced by the expanded light absorption range and effective charge separation. A variety of scavengers were employed to identify the active species by capturing the radicals and holes generated upon the photocatalytic degradation process.