Charge Transfer Distance Research Articles

Preparation of Bi2WO6/MXene(Ti3C2Tx) Composite Material and Its Photothermal Catalytic Reduction of CO2 in Air

In response to growing concerns about the greenhouse effect, the direct conversion of atmospheric CO2 has become a pivotal research focus. This research utilizes hydrothermal synthesis to develop Bi2WO6/MXene(Ti3C2Tx), which efficiently reduces CO2 directly at the gas–solid interface through photothermal synergy, without requiring additional sacrificial agents or alkaline absorption solutions. The results indicate that the CO formation rate is about 216.9 μmol·g−1h−1. Notably, this system demonstrates exceptional selectivity for reducing CO2 to CO. The outstanding photothermal catalytic efficiency is attributed to the introduction of MXene, which serves as an efficient and economical co-catalyst. The integration of MXene improves the composite material’s specific surface area and pore structure, enhances its CO2 adsorption capacity, and results in the Bi2WO6/MXene hybrid having a shorter charge transfer distance and a larger interface contact area. This ensures superior charge transfer capabilities, ultimately leading to a significant enhancement in the catalytic efficiency of the composite. This study presents a straightforward and highly selective method for capturing and converting atmospheric CO2, offering fresh insights for developing efficient photothermal catalytic materials.

Regulation of Exciton Effects in Functionalized Conjugated Polymers by B-N Lewis Pairs for Visible-Light Photocatalysis.

Strong excitonic effects are common in organic conjugated polymer semiconductors, severely hindering the generation of free charge carriers for conducting photocatalysis. Therefore, exploring new channels to modulate exciton dissociation in polymers is far-reaching in facilitating photocatalysis. A series of B-N Lewis pair functionalized conjugated polymers have been developed to minimize exciton effects by modulating charge transfer pathways. Theoretical studies have shown that introducing B-N Lewis pairs can dramatically increase the distance of charge transfer (D index) and the amount of electron transfer and reduce the Coulomb attraction energy (EC), which contributes to breaking the equilibrium of the coexistence of excitons and charge carriers. Further experimental results show that the singlet excitons are efficiently dissociated into more free-charge carriers under photoexcitation to participate in surface reactions. The optimized polymer PyPBM shows an exponential increase in photocatalytic hydrogen and hydrogen peroxide production performance by visible light illumination.

Regulation of Exciton Effects in Functionalized Conjugated Polymers by B‐N Lewis Pairs for Visible‐Light Photocatalysis

Strong excitonic effects are common in organic conjugated polymer semiconductors, severely hindering the generation of free charge carriers for conducting photocatalysis. Therefore, exploring new channels to modulate exciton dissociation in polymers is far‐reaching in facilitating photocatalysis. A series of B‐N Lewis pair functionalized conjugated polymers have been developed to minimize exciton effects by modulating charge transfer pathways. Theoretical studies have shown that introducing B‐N Lewis pairs can dramatically increase the distance of charge transfer (D index) and the amount of electron transfer and reduce the Coulomb attraction energy (EC), which contributes to breaking the equilibrium of the coexistence of excitons and charge carriers. Further experimental results show that the singlet excitons are efficiently dissociated into more free‐charge carriers under photoexcitation to participate in surface reactions. The optimized polymer PyPBM shows an exponential increase in photocatalytic hydrogen and hydrogen peroxide production performance by visible light illumination.

Dual Additive‐Assisted Layer‐by‐Layer Processing for 19.59% Efficiency Quasi‐Bulk Heterojunction Organic Solar Cells

AbstractThe ideal vertical phase separation active layer morphology is crucial for the photoelectric conversion of organic solar cells. In this work, a layer‐by‐layer sequential deposition method is used to prepare D18/L8‐BO‐based organic solar cells and a dual additives strategy is adopted to construct the ideal active layer. Additive DIM regulates the crystallization of the D18 layer, and additive DIO induces L8‐BO to diffuse into the interior of the D18 layer to form a vertical composition distribution with large donor/acceptor interpenetrated regions. The improvement of active layer induced by DIM and DIO dual additives promote exciton generation and dissociation, shorten charge transfer distance, and improve carrier dynamics. With improved charge transport performance and suppressed carrier recombination, the short‐circuit current density and fill factor of the D18/L8‐BO quasi‐bulk heterojunction organic solar cells are improved simultaneously, and the power conversion efficiency is boosted significantly from 18.21% to 19.59%. Moreover, the improved photovoltaic performance is further verified in D18/Y6 and PM6/L8‐BO‐based organic solar cells, which implies the generalizability of the dual additive‐assisted layer‐by‐layer ‐sequential deposition method.

Insights into the Structural Modification of Selenium-Doped Derivatives with Narrowband Emissions: A Theory Study.

The research on boron/nitrogen (B/N)-based multiresonance thermally activated delayed fluorescence (MR-TADF) emitters has been a prominent topic due to their narrowband emission and high luminous efficiency. However, devices derived from the common types of narrowband TADF materials often experience an efficiency roll-off, which could be ascribed to their relatively slow triplet-singlet exciton interconversion. Since inserting the heavy Se atom into the B/N scheme has been a proven strategy to address the abovementioned issues, herein, extensive density functional theory (DFT) and time-dependent DFT (TD-DFT) simulations have been employed to explore the effects of the structural modification on a series of structurally modified selenium-doped derivatives. Furthermore, the two-layered ONIOM (QM/MM) model has been employed to study the pressure effects on the crystal structure and photophysical properties of the pristine CzBSe. The theoretical results found that the introduced tert-butyl units in Cz-BSeN could result in a shorter charge transfer distance and smaller reorganization energy than the parent CzBSe. In contrast to directly incorporating the o-carborane (Cb) unit to CzBSe, incorporating the bridged phenyl units is important in order to achieve narrowband emissions and high luminous efficiency. The lowest three triplet excited states of CzBSe, Cz-BSeN and PhCb-BSeN all contribute to their triplet-singlet exciton conversions, resulting in a high utilization of triplet excitons. The pressure has an evident influence on the photophysical properties of the aggregated CzBSe and is favored for obtaining narrowband emissions. Our work is promised to provide a feasible strategy for designing selenium-doped derivatives with narrowband emissions and rapid triplet-singlet exciton interconversions.

Enhanced hydrogen evolution performance of twinned Mn0.65Cd0.35S with Zn-doped cadmium selenide under visible light irradiation

The cadmium manganese sulfide, despite being recognized as a highly efficient photocatalytic semiconductor for hydrogen evolution, faces significant challenges in terms of charge recombination when used solely as a catalyst for photocatalytic hydrogen production. The construction of heterojunction photocatalysts is regarded as one of the effective strategies to enhance the efficiency of photocatalytic hydrogen production. In this work, Zn-doped CdSe was adopted to enhance the photocatalytic active sites of the twinned Mn0.65Cd0.35S. As results, the photocatalytic hydrogen evolution of Zn–CdSe-1/T-MCS-40 can reach approximately 47447.15 μmol g−1 after 5 h, representing a 15 times increase compared to Mn0.65Cd0.35S. Besides, the hydrogen evolution rate shows almost no significant attenuation after four consecutive cycles (20 h). The significant achievement can be largely attributed to the successful construction of an S-scheme heterojunction of Zn–CdSe-1/T-MCS-40, which effectively minimized the charge transfer distance and suppressed the recombination of photo-generated electron-hole pairs. Additionally, the incorporation of Zn-doped CdSe significantly expands the response range to visible light, thereby providing a conceptual framework for advancing the design of solar-to-chemical energy conversion and effectively guiding the fabrication of metal sulfide-based photocatalytic heterojunctions.

Microwave absorption parameters over 2–18 GHz frequency range for the MXene composite – Ti3C2Tx @MnCo2O4

The great potential for electromagnetic wave (EMW) absorption is revealed in two-dimensional (2D) Ti3C2Tx (MXene) thin sheets that have numerous surface flaws and an extensive spectrum of functional groups. In this study, Ti3AlC2 (MAX Phase) is etched, and then ultrasonic exfoliation is used to create 2D ultrathin Ti3C2Tx nanosheets; a type of MXene. The MnCo2O4 spherical particles were grown on the layered structure of Ti3C2Tx via a one-pot hydrothermal process. The synthesized Ti3C2Tx/MnCo2O4 composite provides superior bulk-to-surface and interfacial charge transfer capabilities due to their short charge transfer distance and extensive interface contact area to the EMW. This article thoroughly evaluates the loss impact in Ti3C2Tx/MnCo2O4 absorbers as -44.4dB of reflection loss at 16.04GHz with a thickness of 5.114mm for the first time, which is essential for fabricating an effective microwave absorber.

3D visualization microscope of TENG contact interface based on astigmatic imaging

The triboelectric nanogenerator (TENG) is a mechanical device that can collect mechanical energy from the contact and separation of different materials. Due to the short distance of charge transfer, the characterization of the micro-contact state under localized stress has become an urgent issue in the study of TENG’s contact electrification mechanism. Most of the contact surfaces of TENG are curved surfaces, and there is a lack of effective means to characterize the contact state of curved surfaces. In this article, a technique based on astigmatic imaging principle is provided to visualize the three-dimensional contact interface of TENG, using polydimethylsiloxane (PDMS) and butyronitrile film with rough surface as TENG. Through this technique, the three-dimensional deformation of its contact interface was observed and the three-dimensional effective contact area was calculated. The comparison of current density generated at different pressing pressures verified that larger contact area leads to higher current density, which applies to the law in 3D contact interfaces as well. Visualizing conformal contact interfaces for TENG provide a powerful tool for analyzing the charge transfer-contact separation phase coordination mechanism, providing a new route approaching larger output efficiency. In addition, this technology offers possibility for characterization of TENG with both-side deformable, which abandons the requirements of the rigid contact surface in the total reflection scheme and is much more applicable for organic TENG.

A two-dimensional Aurivillius oxide for enhanced solar energy driven hydrogen evolution and waste water treatment

Bi2WO6 has attracted extensive attention in photocatalysts in recent years as a typical Aurivillius oxide. However, it suffers from severe electron-hole recombination due to the large charge transfer distance from bulk to surface. Unfortunately, strong chemical bonds between the neighboring layers in Aurivillius oxides lead to difficulties in the construction of 2D materials. Here, a facile NaBH4-assisted hydrothermal method is developed to construct 2D Bi2WO6 nanosheets with adjustable thickness from 4.03 to 1.51 nm and O vacancies density (named as BWO-x, x = 15, 30, 45, 60). By balancing the thickness and the O vacancy density in the nanosheets, the charge separation efficiency can be tuned and consequently, the photocatalytic activity can be optimized, leading to over 11 times enhancement in photocatalytic hydrogen evolution. Furthermore, the best performed nanosheets demonstrate universality in dye polluted water treatment. Nearly 100% degradation can be reached after only 5, 50, and 30 min with degradation rate constant of 29.73, 3.21, and 6.62 min−1g−1 for Rhodamine B, methyl orange, and methylene blue, respectively. This work provides a comprehensive approach to produce ultrathin 2D nanosheets of Aurivillius photocatalysts for enhanced charge separation and photocatalytic activity.

Decorating ZnIn2S4 with earth-abundant Co9S8 and Ni2P dual cocatalysts for boosting photocatalytic hydrogen evolution

Due to the synergistic effect of the rapid transfer of photo-generated electrons and enrichment of reactive active sites, reasonably assembling dual cocatalysts with semiconductor is considered as an excellent method to enhance the photocatalytic properties of semiconductors. Herein, earth-abundant Co9S8 and Ni2P dual cocatalysts modified-ZnIn2S4 (ZIS/CS/NP) composite photocatalyst has been constructed by the low-temperature solvothermal and in-situ photodeposition methods. A series of characterizations indicate the hollow structure of Co9S8 can reduce the charge transfer distance and enhance the migration of photo-generated electrons, while Ni2P acts as an electron collector and provides sufficient active sites for H2 release in this dual cocatalysts system. Because of the synergistic effect of dual cocatalysts, ZIS/CS/NP composites exhibit superior activity in the photocatalytic H2 production compared to blank ZIS, ZIS/CS and ZIS/NP. Notably, the optimal photocatalytic H2 production rate of ZIS/CS/NP reaches 6823.64 μmol g−1 h−1, which is approximately 86 times higher that of blank ZIS. This work is expected to provide useful reference for the construction of high-performance dual-cocatalyst modified semiconductor composite for photocatalytic H2 evolution.

Ni3S2@NiMo-LDH Composite for Flexible Hybrid Capacitors

Ni3S2 is a kind of transition metal sulfide (TMD) with excellent electrical conductivity and electrochemical activity. To further enhance the specific capacity of Ni3S2-based supercapacitors, we synthesize several nanosheet-decorated Ni3S2@NiMo-LDH nanostructures by a combination of hydrothermal and electrodeposition processes. The mesoporous structure provides a large number of electroactive sites, which shortens the charge transfer distance and increases the specific surface area of electrode materials. The assembled asymmetric supercapacitor shows an energy density of 62.8 W h kg−1 at 2701.6 W kg−1 and long-term cycling stability.

Chemically bonded CdS/Bi2MoO6 Z-scheme heterojunction synergises with strong internal electric field for photocatalytic CO2 reduction

Constructing strong interfacial electric fields to enhance the surface charge transport kinetics is an effective strategy for promoting CO2 conversion. Herein, we present the fabrication of CdS-Bi2MoO6 Z-scheme heterojunctions with a robust internal electric field (IEF) using an in situ growth technique, establishing chemical bonding between the components. The IEF at the interface can offer an impetus for the segregation and transportation of photogenerated carriers, while the Cd-O chemical bonding mode acts as a rapid conduit for these carriers, thereby reducing the charge transfer distance. As a result, the Z-scheme charge transfer is accelerated due to the synergistic influence of these two factors. Therefore, the optimized CdS/Bi2MoO6 Z-scheme heterojunction possesses significantly enhanced dynamic carrier mobility, thus promoting the conversion of CO2 to CO without the need for additional co-catalysts or sacrificial agents. This optimization yields a remarkable CO selectivity of up to 97%. Meanwhile, the expedited Z-scheme charge transfer mechanism is validated through X-ray photoelectron spectroscopy, Kelvin probe force microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy.

Tandem Four-Component Reaction to Access Fused Polycycles Exhibiting Aggregation-Enhanced Through-Space Charge Transfer Emission.

Rapid construction of new fluorescence emitters is essential in advancing synthetic luminescent materials. This study illustrated a piperidine-promoted reaction of chiral dialdehyde with benzoylacetonitrile and malonitrile, leading to the formation of the 6/6/7 fused cyclic product in good yield. The proposed reaction mechanism involves a dual condensation/cyclization process, achieving the formation of up to six bonds for fused polycycles. The single crystal structure analysis revealed that the fused cyclic skeleton contains face-to-face naphthyl and cyanoalkenyl motifs, which act as the electronic donor and acceptor, respectively, potentially resulting in through-space charge transfer (TSCT) emission. While the TSCT emissions were weak in solution, a notable increase in luminescence intensity was observed upon aggregation, indicating bright fluorescent light. A series of theoretical analyses further supported the possibility of spatial electronic communication based on frontier molecular orbitals, the distance of charge transfer, and reduced density gradient analysis. This work not only provides guidance for the one-step synthesis of complex polycycles, but also offers valuable insights into the design of aggregation-enhanced TSCT emission materials.

Enhanced H2 Generation via Piezoelectric Reforming of Waste Sugars and Fruits Using Au-Decorated g-C3N4

The food industry is responsible for generating considerable amounts of waste, such as excess fruits and leftover sugars, which contribute to resource depletion and pose environmental challenges. This research delves into the application of gold-modified graphitic carbon nitride nanosheets (Au/CN) as a potent catalyst for the transformation of these food wastes into H2 via piezoelectric reforming during sonication. Au/CN demonstrated a superior rate of H2 evolution compared to pristine g-C3N4 (i.e., 1533.3 vs. 364.9 µmol/g/h) and it maintained its efficiency through multiple cycles of use. The catalytic activity was found to be optimal at a neutral pH level and with increased sugar concentrations. The enhanced catalytic performance of Au/CN was ascribed to the efficient segregation of charge carriers as well as the reduced charge transfer distance. This study underscores the viability of using Au/CN as a means for converting food wastes into a sustainable source of H2 energy.

Enhanced charge separation of Cu-BTC@CuSe@TiO2 hollow octahedrons for efficient CO2 photoreduction with superior CO selectivity

Solar-driven photocatalytic conversion of CO2 into high-value-added fuels has attracted widespread attention. However, the relatively low conversion efficiency and product yield severely limited photocatalytic applications. In this work, binary Cu-BTC@TiO2 catalysts with adjustable inner cavity were prepared using copper-based metal organic framework (Cu-BTC) octahedrons as substrate via a solvothermal reaction. In this process, the inner Cu-BTC octahedrons can be controllably etched into a hollow octahedral structure in the presence of HF. Subsequently, the Cu-BTC@CuSe@TiO2 hollow octahedrons (HOs) were fabricated by selenization reaction and exhibited various properties such as abundant active sites for CO2 adsorption and reduction reactions, shortened charge transfer distance to prevent electron-hole recombination, and internal reflection/scattering effects to improve solar light utilization. Moreover, the formed dual p-n heterostructures between p-type CuSe and n-type semiconductors (Cu-BTC and TiO2) effectively promote spatial separation and migration of charge carriers. The synergistic effect of these advantages makes the optimized Cu-BTC@CuSe@TiO2 HO catalyst exhibit remarkable CO2 photoreduction performance with a CO production rate of 72.3 μmol h−1 g−1 and near 100 % selectivity. This work opens a new pathway for designing highly active photocatalysts with excellent product selectivity.

Orbital-Optimized Versus Time-Dependent Density Functional Calculations of Intramolecular Charge Transfer Excited States.

The performance of time-independent, orbital-optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital-optimized calculations, even when including orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. -2 eV for TD-DFT, no correlation is observed for the orbital-optimized approach. The orbital-optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with a long-range charge transfer character. Orbital-optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best-performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.

Impact of Diimine Ligand on Singlet-to-Triplet Charge Transfer Electroabsorption in Iron and Ruthenium Complexes.

The electroabsorption and absorption spectra of eight homoleptic complexes of the general form [M(LL)3]2+ where M = Ru, Fe, and LL = 1,10-phenanthroline (phen), 2,2'-bipyridine (bpy), and 4,4',-(R)2-bpy where R = -OCH3, -CF3, were quantified at 77 K in a butyronitrile glass. Intense metal-to-ligand charge transfer (MLCT) absorption bands were evident in the visible region. Electroabsorption spectra measured with applied electric fields >0.2 MV/cm were analyzed by the two-state Liptay model. Significant light-induced dipole moment changes of = 4-13 D were found consistent with a metal-to-ligand charge transfer (MLCT) excited state comprised an electron localized on a single diimine ligand, [MIII(LL-)(LL)2]*2+, in the initially formed Franck-Condon excited state. A low energy feature evident in the electroabsorption spectra was assigned to a direct singlet-to-triplet MLCT excited state. The identity of the diimine ligand had an unexpected and large impact on these transitions. Analysis relative to the higher energy absorption provides a comparison of spin-allowed and disallowed transitions for first- and second-row transition metal complexes. With the notable exception of [Fe(CF3bpy)3]2+, the change in dipole moment for the 3MLCT excited states was less than or equal to that of the 1MLCT excited states. The charge transfer distances for the iron complexes were generally larger than those for the Ru complexes, a behavior attributed to a smaller degree of iron-diimine coupling in the ground state. A striking result was the sensitivity of the extinction coefficient and spectral profile of the low energy electroabsorption assigned to the identity of the diimine ligand; data that suggests electronic coupling with ligand localized triplet states and high spin metal centered states must be considered when modeling the Franck-Condon excited state.

G-C3N4/Porphyrin-based graphdiyne (PDY) 2D/2D heterojunction for the ultrasensitive photoelectrochemical detection of microRNA-21

As an n-type semiconductor material with a wide band gap, g-C3N4 has been applied in the photoelectrochemical (PEC) sensing field, while the narrow absorption light range and tendency of electron-hole recombination significantly limit its practical applications. In this study, we developed a new g-C3N4/porphyrin-based graphdiyne (PDY) 2D/2D heterojunction photoelectric nanocomposites via in-situ growth of PDY on the g-C3N4 nanosheets. The introduction of PDY significantly enhances the light capture ability of g-C3N4 in terms of absorbance and the absorption range throughout the entire UV-Vis region. More importantly, the well-matched band structure between PDY and g-C3N4 inhibits the electron-hole recombination to improve the charge separation efficiency. In addition, such 2D/2D heterojunction has a short charge transfer distance and a large contact area, further promoting the interfacial charge transfer. As a result, the PEC response of g-C3N4/PDY is 2.54 times higher compared with that of g-C3N4, enabling the ‘turn on’ PEC determination of miRNA-21 according to the sandwich-type sensing strategy, and the linear range of 0.01 fM-100 pM with a limit of detection (LOD) of 0.005 fM was achieved. Due to the diversity of graphdiyne monomers, we envision that the g-C3N4/PDY 2D/2D heterojunction carrying different graphdiyne-based materials may exhibit great potential in PEC sensing, photocatalysis, and solar cells.

Earth Mover's Charge Transfer Distance: A General and Robust Approach for Describing Excited State Locality.

A novel approach for assessing the extent of electron displacement in optical transitions is proposed by implementing the Earth Mover's Distance (EMD) method, which quantifies the spatial dissimilarity between ground and excited state electron density distributions. In contrast to previous descriptors, this index provides a representative and intuitively understandable distance under a robust and computationally efficient scheme for all possible forms of locality, even in the most difficult to dissect topological cases. The theoretical differences among the existing indices and our method are first illustrated with the help of a simplified model system, followed by a benchmarking of several partial atomic charge models using experimentally relevant push-pull compounds with diverse symmetries. These same molecules are finally employed to further demonstrate the principal advantages of the EMD index and its capabilities in rationalizing charge transfer phenomena.

Interface Chemical Bond Enhanced Ions Intercalated Carbon Nitride/CdSe‐Diethylenetriamine S‐Scheme Heterojunction for Photocatalytic H2O2 Synthesis in Pure Water

AbstractPhotosynthesis of hydrogen peroxide (H2O2) is regarded as an economically efficient and environmentally friendly synthesis method. However, the scalability of photocatalytic H2O2 production (PHP) is hindered by the sluggish reaction kinetics and rapid recombination of photogenerated charge carriers. In this study, an organic amine‐constrained ions intercalated carbon nitride/CdSe‐diethylenetriamine (K+/I−‐CN/CdSe‐D) S‐scheme heterojunction is synthesized using an organic–inorganic hybrid approach and employed for PHP for the first time. The optimization of the heterojunction interface by I− and K+ ions contributed to enhanced light absorption capabilities and reduced interlayer charge transfer distance. Concurrently, the synergy of C─Se bonds at interface effectively modulated the electron transfer pathways. The coordination environment and charge transfer mechanism are thoroughly investigated by extended X‐ray absorption fine structure and in situ irradiated X‐ray photoelectron spectroscopy. The H2O2 production rate of 40%K+/I−‐CN/CdSe‐D reached 2240.23 µmol h−1 g−1 in pure water. This study highlights the significance of dual tuning of interface chemical bonds and ionic intercalation as an effective strategy for enhancing the photocatalytic H2O2 , paving the way for further advancements in PHP technology.