Charge Separation Research Articles

Side-chain engineering for regulating structure and properties of a novel visible-light-driven perylene diimide-based supramolecular photocatalyst

Systematic and in-depth explorations of the effects of side-chain modulation on the molecular assembly, optoelectronic properties, and photocatalytic properties of supramolecular systems, as well as the kinetics of charge separation and migration in these systems, are rare. In this study, a novel supramolecular photocatalyst with an alkoxy side chain (S-EPDI) was successfully developed through subtle design of the short and linear alkoxyl side chains, affording a phenol degradation efficiency approximately four times that of the counterpart with an alkyl side chain (S-APDI). Notably, combined density functional theory (DFT) calculations, absorption spectroscopy, and other characterizations revealed that the perylene diimide (PDI) molecular units, through π-π stacking, formed a unique rotationally offset stacked supramolecular structure, exhibiting a significant dipole moment. This gave rise to the formation of a larger inherent electric field within S-EPDI compared to S-APDI. Moreover, the study quantitatively demonstrated that a stronger inherent electric field and lower rate of surface charge recombination facilitate efficient separation of the photogenerated carriers. Therefore, the side-chain molecular engineering method employed in this study offers an effective approach for modulating the kinetics of charge migration.

Anchoring Cu2O onto WO3 by adsorption-ascorbic acid reduction: A p-n junction with improved photocatalytic and photoelectrochemical properties

Tungsten trioxide is a promising photoelectric material owing to its abundant structures and unique properties, but the serious photogenerated charge recombination limits its photocatalytic and photoelectrochemical performance. Herein, 0D Cu2O was anchored onto 3D WO3 in-situ via a facile adsorption-ascorbic acid reduction method at room temperature. The coupling of WO3 with Cu2O produces improved charge separation efficiency, thereby the photocatalytic degradation rate and transient photocurrent of optimal WO3/Cu2O are 2.7 and 1.6 times higher than those of WO3, respectively. The enhanced performance is ascribed to the formation of a p-n heterojunction, which was demonstrated by experimental characterizations and theoretical calculation.

Improved peracetic acid activation under simulated solar-light irradiation by regulating shells of Cu2O: In-situ photothermal activation

Advanced oxidation processes based on light-mediated peracetic acid (PAA) activation are novel degradation systems for wastewater purification. In this work, different shells of Cu2O are controllably synthesized and used to activate PAA under simulative solar light. Interestingly, the kobs in the system without temperature control is 2.47 times that in the temperature-controlled system, implying the important role of the photothermal conversion effect in PAA activation. Reactive oxygen species identification demonstrates that photothermal promotes the decomposition of PAA into radical OH with higher redox potential instead of R–O, which together with non-radical 1O2 achieves a high mineralization rate (72.49%). The core–shell structure enhances light absorption and photogenerated charge separation of Cu2O, thereby improving photothermal conversion efficiency. Meantime, the in-situ photothermal conversion effect expedites the diffusion of ROS and the cycle of active Cu(Ⅱ)/Cu(Ⅰ) ultimately achieves the high-efficiency and long-lasting PAA activation. This work provides novel strategies for solar energy utilization and PAA activation processes in wastewater purification.

Precise design and construction of NiO-Ni heterostructures for active hydrogen evolution photocatalysis

The design of metal-oxide-metal heterostructure photocatalysts is an effective and widely used approach to solve global environmental problems. In this work, we designed and prepared a NiO-rich NiO-Ni heterostructure in an N-doped carbon matrix as a photocatalyst using a simple chemical method for hydrogen evolution reactions. It has an optimal photocatalytic hydrogen production rate of 1395 μmol. g−1. h−1, which is ~8 times higher than that of Ni rich NiO-Ni (178 μmol. g−1. h−1). Combined experimental results demonstrate that such a good performance benefits from the specific NiO-Ni interface, which could improve the utilization of sunlight and charge separation efficiency. Moreover, this interface contributes to improved structural stability during the photocatalytic reactions, ensuring superior catalytic performance. This work provides a new strategy for the design and synthesis of efficient precious-metal-free heterostructure catalysts for photocatalytic hydrogen evolution reactions.

Bioinspired carbon black deposited polyimide fabric for sustainable water energy harvesting

Water is the source of life and the largest energy carrier on Earth. Various excellent hydrovoltaic technologies have been proposed, but still suffer from issues such as intermittent output, material limitations, and poor flexibility. Here, we proposed a method for fabrication of a hydrovoltaic generator using the flexible polyimide fabric. Carbon black was deposited on the polyimide fabric surface using a simple method of candle flame burning. On the basis of water transport in the fabric and charge separation induced by negatively charged carbon black channels, sustainable hydrovoltaic power generation was achieved by the generator. A single carbon deposited polyimide fabric (CBP) could generate a continuous voltage output of nearly 260 mV by dripping a water drop on one side. Multiple CBP devices were connected in series and parallel to increase output power, which could be applied for the power and energy storage of small electronic devices. This work may provide a convenient strategy for fabricating sustainable flexible hydrovoltaic generators and offer insights for the development of clean power sources.

Construction of polarized 2D/2D g-C3N4/BiOCl nanosheet dual piezoelectric Z-scheme heterojunction and its efficient charge separation mechanism

A multi-electric field synergistic strategy based on heterojunction construction and polarization engineering enhances carrier separation and migration, achieving excellent piezoelectric photocatalytic performance of g-C3N4 based materials. Here, through the in-situ growth of BiOCl nanosheets (BOCs) on g-C3N4 nanosheets (GCNs), a 2D/2D Z-scheme GCNs/BOCs heterojunction was successfully fabricated, and its outstanding piezo-photocatalytic property was demonstrated. Compared to individual BOCs and GCNs, the high degradation rate (97.64%) of rhodamine B (RhB) can be achieved over the optimal composite (GCNs/BOCs-50) after 50min irradiation. Inspiringly, the polarized GCNs/BOCs-50 composite degraded RhB almost completely within 30min under the simultaneous light irradiation and ultrasound, which reduced the photocatalytic time by 40%, and its k reached 0.1410min-1 (12.59 and 2.48 times that of BOCs and GCNs). This work is of great significance for designing a novel heterojunction photocatalysts using polarized ferroelectric materials.

Cyanoacetamide co-sensitizers DY-1 and DY-2: Unveiling a promising path to highly efficient photovoltaic devices

This paper presents a novel approach for enhancing the efficiency of dye-sensitized solar cells (DSSCs) through the co-sensitization of cyanoacetamide-based dyes DY-1 and DY-2 with N3 dye. The synthesis and characterization of DY-1 and DY-2 co-sensitizers are described and their potential applications in photovoltaic devices are investigated. The absorption properties of DY-1 and DY-2 were analyzed, revealing their efficient light absorption in the visible range. The co-sensitization of DY-1-2 with N3 dye demonstrated a significant enhancement in photovoltaic efficiency, ranging from 7.40% to 7.92%. The reasons for this efficiency enhancement were thoroughly analyzed and attributed to several factors. First, the combination of DY-1-2 with the N3 dye led to a broader light absorption spectrum, enabling more efficient utilization of incident photons. Additionally, co-sensitization facilitates efficient charge separation and injection processes, contributing to improved photocurrent. The acid-base co-sensitization approach further enhances the overall efficiency by maximizing the charge transfer and coverage on the semiconductor surface. This study sheds light on the development of novel sensitizers to enhance the performance of DSSCs, and the findings contribute to the advancement of photovoltaic devices.

Investigation of a visible-light-driven molecularly imprinted photoelectrochemical sensing platform for ultrasensitive and selective detection of diflubenzuron utilizing an in-situ grown 3D hierarchical structure

An ultrasensitive molecularly imprinted polymer-photoelectrochemical (MIP-PEC) sensing platform has been successfully fabricated for the detection of diflubenzuron (DBZ) under visible-light irradiation. The noval photoactive material was a ternary Bi2S3/BiVO4/TiO2 nanotube arrays (BVT) heterojunction, grown in-situ on a Ti substrate. The distinct architecture of BVT featured BiVO4 nanoparticles anchored onto TiO2 nanotube arrays and wrapped by Bi2S3 nanofibers. This innovative design, coupled with the aligned energy bands of BVT, significantly boosted visible-light absorption, and photo-induced charge separation and transfer, leading to an enhanced photocurrent response surpassing that of binary and single-component systems. The sensing platform displayed remarkable sensitivity and a broad detection range for DBZ with a linear range of 0.01–1000 ng mL−1 and a limit of detection of 1.25 pg mL−1. Its selectivity was further validated by comparable photocurrent responses in the presence of interfering substances, highlighting its accuracy in detecting DBZ in complex matrices. Additionally, the sensing platform demonstrated excellent stability and reproducibility, ensuring reliable results over multiple measurements. Evaluation of the sensing platform in real samples, including tap water and apples, has confirmed its high accuracy with recovery rates between 94.4 % and 103.4 %. Therefore, this visible-light-driven MIP-PEC sensing platform exhibits considerable potential for application in ultrasensitive detection of DBZ. This work offers novel insights into the in-situ preparation of high-performance sensors for applications in food safety and environmental monitoring.

Investigation of a visible-light-driven molecularly imprinted photoelectrochemical sensing platform for ultrasensitive and selective detection of diflubenzuron utilizing an in-situ grown 3D hierarchical structure

An ultrasensitive molecularly imprinted polymer-photoelectrochemical (MIP-PEC) sensing platform has been successfully fabricated for the detection of diflubenzuron (DBZ) under visible-light irradiation. The noval photoactive material was a ternary Bi2S3/BiVO4/TiO2 nanotube arrays (BVT) heterojunction, grown in-situ on a Ti substrate. The distinct architecture of BVT featured BiVO4 nanoparticles anchored onto TiO2 nanotube arrays and wrapped by Bi2S3 nanofibers. This innovative design, coupled with the aligned energy bands of BVT, significantly boosted visible-light absorption, and photo-induced charge separation and transfer, leading to an enhanced photocurrent response surpassing that of binary and single-component systems. The sensing platform displayed remarkable sensitivity and a broad detection range for DBZ with a linear range of 0.01–1000 ng mL−1 and a limit of detection of 1.25 pg mL−1. Its selectivity was further validated by comparable photocurrent responses in the presence of interfering substances, highlighting its accuracy in detecting DBZ in complex matrices. Additionally, the sensing platform demonstrated excellent stability and reproducibility, ensuring reliable results over multiple measurements. Evaluation of the sensing platform in real samples, including tap water and apples, has confirmed its high accuracy with recovery rates between 94.4 % and 103.4 %. Therefore, this visible-light-driven MIP-PEC sensing platform exhibits considerable potential for application in ultrasensitive detection of DBZ. This work offers novel insights into the in-situ preparation of high-performance sensors for applications in food safety and environmental monitoring.

Ultrasonic controllable synthesis of sulfur-functionalized metal–organic frameworks (S-MOFs) and their application in piezo-photocatalytic rapid reduction of hexavalent chromium (Cr)

The United Nations’ Sustainable Development Goals (SDGs) are significant in guiding modern scientific research. In recent years, scholars have paid much attention to MOFs materials as green materials. However, piezo catalysis of MOFs materials has not been widely studied. Piezoelectric materials can convert mechanical energy into electrical energy, while MOFs are effective photocatalysts for removing pollutants. Therefore, it is crucial to design MOFs with piezoelectric properties and photosensitivity. In this study, sulfur-functionalized metal–organic frameworks (S-MOFs) were prepared using organic sulfur-functionalized ligand (H2TDC) ultrasonic synthesis to enhance their piezoelectric properties and visible light absorption. The study demonstrated that the S-MOFs significantly enhanced the reduction of a 10 mg/L solution of hexavalent chromium to 99.4 % within 10 min, using only 15 mg of catalyst. The orbital energy level differences of the elements were analyzed using piezo response force microscopy (PFM) and X-ray photoelectron spectroscopy (XPS). The results showed that MOFs functionalized with sulfur atom ligands have a built-in electric field that facilitates charge separation and migration. This study presents a new approach to enhance the piezoelectric properties of MOFs, which broadens their potential applications in piezo catalysis and piezo-photocatalysis. Additionally, it provides a sustainable method for reducing hexavalent chromium, contributing to the achievement of sustainable development goals, specifically SDG-6, SDG-7, SDG-9, and SDG-12.

SnS2 and Ho-doped SnS2 thin films: Synergistic, DFT, photocatalytic, and antibacterial studies

This study investigates Ho-doped tin disulfide (Ho-SnS2) thin films prepared via spray coating, focusing on varying Ho doping levels (0 at. %, 2 at. %, and 4 at. %). Structural analysis through XRD and SEM showcased enhanced crystallinity and morphology in Ho-SnS2 films. Raman and XPS studies provided insight into the film's composition and chemical states. The antibacterial properties of the films were investigated using a bacterial growth inhibition assay. The results showed significant antibacterial activity against Gram-positive and Gram-negative bacteria, highlighting the potential applications of Ho-SnS2 thin films in antibacterial coatings. Ho-SnS2 films exhibited superior photocatalytic activity and antibacterial properties compared to SnS2 films, attributed to efficient charge separation. DFT analysis proposed a mechanism for the antibacterial activity. These findings highlight the efficacy of the spray coating technique in producing Ho-SnS2 films and the potential of Ho-SnS2 films for diverse applications like photocatalysis and antibacterial coatings.

Effects of heating rate and deposition cycle on the structural, optical, and photoelectrocatalytic properties of electrodeposited hematite films

In this research, electrodeposited hematite films were prepared at voltammetry deposition cycles of 60 and calcined at 550oC in a furnace after ramping the temperature at the rates of 2°C/min, 10°C/min, 35°C/min, and rapid heating of about 100°C/min. Additional samples were fabricated at deposition cycles of 15, 30, and 80, and also calcined at 550⁰C at a heating rate of 10⁰C/min. The impact of heating rate and deposition cycle number variations on the structural, optical, and photoelectrocatalytic (PEC) properties of the hematite films were assessed. All the films' X-ray diffraction (XRD) measurements showed strong peaks at the lattice planes (104) and (110), verifying hematite's rhombohedral crystal structure. The films prepared at the heating rate of 10⁰C/min boosted the crystallization of the films by 47.2% relative to the ones prepared at 2⁰C/min. An increase in the deposition cycle number resulted in increasing film thickness and the sample’s crystallization. An indirect bandgap of 1.94-2.1eV was estimated for the samples, with the least value obtained for the films treated at the heating rate of 10⁰/min and deposition cycles of 60. The same samples also yielded the largest photocurrent density of 26.2 μA/cm2 at 1.23V vs. reversible hydrogen electrode (RHE), while the photoanodes fabricated at 2°C/min exhibited the lowest photo-activity. The enhanced photocurrent observed for the films has been associated with high crystallinity, improved photon absorption, reduced flatband potential, and increased charge separation at the film’s surface. This research underscores the importance of optimizing both the heating rate and deposition cycle numbers in the fabrication of electrodeposited photoelectrodes for PEC applications.

Bio-based Epoxy Resin Demonstrating High Breakdown Strength and Low Dielectric Loss via Intrinsic Molecular Charge Traps Construction

In the ultra-high voltage, ultra-high capacity and high frequency energy systems, epoxy-based dielectric materials demonstrating high breakdown strength and low dielectric loss are urgently needed. This work reports a strategy to modulate the charge trap depth in bio-based epoxy dielectric materials by tailoring the local molecular chain structures, ultimately leading to the significant suppression of high-field conductivity and dielectric loss. With the introduction of octa(dimethylsiloxy)octasilsiloxane (POSS) as the intrinsic molecular charge traps, our synthesized epoxy dielectric material exhibits a high breakdown strength of Eb-DC=81.5 kV/mm, 37% higher than the traditional bisphenol A epoxy resin (DGEBA), and low dielectric loss of tan δ=0.0022, 45% lower than that DGEBA. Furthermore, simulation results give the structure-property relationships, guiding the molecular design. Specifically, the dielectric properties are positively correlated with the LUMO energy difference and charge separation index of the polymer molecular chains. This work provides a promising pathway to enhance the dielectric properties of polymers by building intrinsic molecular charge traps, which is prospective for practical electronics and electrical power systems.

In situ fabrication of 2D Ti3C2/1T&2H-MoS2/TiO2 photocatalyst for sulfamethazine degradation

Sunlight-driven photocatalysis is a very appealing approach for solving the current energy crisis because it will not cause secondary pollution. Titanium dioxide (TiO2) has attracted much attention in the field of photocatalysis due to its simple preparation, environmental friendliness and easy modification. However, reducing the band gap and expanding the light absorption range to reduce the carrier recombination rate of TiO2 is still a huge challenge. Herein, we report a two-dimensional (2D) Ti3C2/1 T&2 H-MoS2/TiO2 photocatalyst obtained by in situ growth of a 1 T&2 H-MoS2/TiO2 Z-scheme heterojunction on a highly conductive Ti3C2 MXene surface. The spectral response range of the resulting Ti3C2/1 T&2 H-MoS2/TiO2 (Ti3C2:1 T&2 H-MoS2:TiO2= 1:10:10) photocatalyst was broadened to 696 nm and the band gap was reduced to 1.83 eV, which was responsible for the strong light-harvesting capacity and improved charge separation. The activity of the Ti3C2/1 T&2 H-MoS2/TiO2 photocatalyst was evaluated by photocatalytic degradation of sulfamethazine (SMZ). The degradation rate of SMZ reached 99.8 % after 90 min of illumination. These results demonstrate that the combination of Ti3C2 MXene and heterojunction is a feasible strategy to enhance the light-harvesting capacity and charge transport in photocatalytic reaction.

0D/2D Schottky heterojunction of CsPbBr3 nanocrystals on MoN nanosheets for enhancing charge transfer and CO2 photoreduction

Solar-driven conversion of CO2 to value-added chemical fuels has been regarded as a promising strategy for solving the climate problem and energy crisis. To realize this goal, it is vital to design photocatalysts with abundant catalytic active sites and excellent charge separation efficiency. Here, perovskite nanocrystals (CsPbBr3) were anchored on two-dimensional molybdenum nitride (MoN) using an in-situ growth method, forming a new and effective 0D/2D CsPbBr3@MoN (CPB@MoN) nanoheterosturcture with close contact interface for CO2 photoreduction. The introduction of MoN, acting as a charge transfer channel, could quickly trap the photoinduced charge from CsPbBr3 and provide abundant catalytic sites for CO2 photocatalytic reactions. For optimized CsPbBr3@MoN composites, the CO yield was 13.86μmol/gh−1 without any sacrificial reagent, which was a 4.5-fold enhancement of the pure CsPbBr3. Further, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the catalytic mechanism for the CO2 photoreduction process. This work provides a new platform for constructing superior perovskite/MoN-based photocatalysts for photocatalytic CO2 reduction.

Visible-light driven efficient cleavage of Cα–Cβ bond in lignin models and lignin over porous tubular carbon nitride

The photocatalytic selective breaking of recalcitrant Cα–Cβ bond in real lignin to product value-added chemicals under mild conditions is intriguing but remains challenging. Herein, a sustainable strategy for the efficient and selective breakage of Cα–Cβ bond in lignin β-O-4 model compounds and lignin over porous tubular g-C3N4 (PTCN) photocatalyst was designed under ambient conditions. Compared with bulk g-C3N4, the construction of PTCN not only facilitates photogenerated charge separation and transfer, but also provides more exposed interior active sites, which is conductive to reactant adsorption on the surface of PTCN, thereby resulting in the higher photocatalytic efficiency. With this strategy, 2-phenoxy-1-phenylethanol as the typical model substrate was completely converted into aromatic monomers with Cα–Cβ bond cleavage selectivity of 97.2 %. Both mechanistic studies and theoretical calculations revealed that the photogenerated holes, electrons and O2− respectively played an essential role in the Cβ–H dehydrogenation and Cα–Cβ bond breakage. Native lignin samples (alkaline, pine and wheat straw) were applied to these photocatalytic systems and successfully depolymerized with Cα–Cβ bond cleavage under optimal reaction conditions. This work could provide an in-depth insight into photocatalyst design for the economical and efficient valorization of lignin.

Advanced ion-selective wood membranes: Leveraging aligned cellulose nanofibers for enhanced osmotic energy conversion

Nanofluidic reverse electrodialysis (RED) is widely recognized as an exceptionally effective method for harvesting osmotic energy. Nevertheless, its progress has been impeded by the high costs and intricate fabrication processes associated with the required ion exchange membranes. The ion-selective wood membranes (ISWM) are derived directly from natural wood through a meticulously designed two-step chemical modification and densification process. The obtained ISWM with a highly charged surface effectively preserves the alignment of nanochannels from the cellulose fibers sourced in natural wood. Moreover, the laminated structure consisting of oriented nanofibers enhances ion conductivity by a factor of 4 compared to natural wood birch under low KCl concentrations. The charged and aligned nanochannels serve as nanofluidic conduits, facilitating selective ion transport. This, in turn, engenders efficient charge separation and the generation of an electrochemical potential difference. In energy harvesting systems such as ISWM-RED, the synergistic interplay between the electrochemical potential difference and ionic flux manifests in a remarkable output power density, reaching up to 658 mW m−2 to a salinity gradient of KCl at a magnitude of 50-fold. ISWM is an outstanding nanofluidic material that provides a cost-effective and easy-to-prepare solution for producing natural nanofluidic materials. Our investigation delineates a promising trajectory for developing high-performance nanofluidic RED devices tailored for efficient osmotic energy harvesting from renewable and abundant natural resources.

Fabrication of two-dimensional FePS3 nanosheets for promising photo/electrocatalytic applications

Transition metal phosphorus trisulfides, namely sulfides composed of three elements, stand out within 2D nanomaterials due to the unique layered structure, distinctive bonding, and electronic configurations. However, the preparation of ultrathin nanosheets encounters significant challenges due to the inherent properties of the material itself and the complexity of the synthetic process. In this work, we successfully fabricated ultrathin FePS3 nanoflakes with lateral dimensions of 500-800 nm and an average thickness of 5 nm utilizing mechanically assisted liquid-phase exfoliation in N-Methyl-2-pyrrolidone solution. The unique few-layer structure of FePS3 may increase the number of active sites, facilitating the rapid separation and migration of photo-induced charge carriers. Consequently, this enhancement leads to an increase in photogenerated current and a substantial reduction in resistance. This study presents an effective approach for optimizing light absorption and charge separation processes of 2D nanostructure, thereby providing valuable insights for the rational design of efficient photocatalysts based on ultrathin FePS3 nanosheet as a co-catalyst.

Engineering single-atom rhodium-C3N sites on covalent organic frameworks for boosting photocatalytic hydrogen evolution

Developing efficient and stable photocatalysts for solar hydrogen (H2) energy conversion is meaningful but challenging. Herein, a novel photocatalyst with Rh single atoms (Rh SAs) anchoring in β-ketoimine-linked covalent organic frameworks (TpPa-1) via RhC3N sites is proposed for achieving highly efficient H2 production in phosphate buffer saline (PBS) solution with sodium ascorbate (SA) as sacrificial agent under visible light. TpPa-1 with abundant N and C-chelate sites provides a reliable basis for anchoring Rh single atoms. The optimized Rh SAs/TpPa-1 exhibits an outstanding hydrogen evolution activity (1836.81μmol h−1 g−1), 9.34 and 2.27 folds enhancement than that of pristine TpPa-1 and Rh NPs/TpPa-1. X-ray absorption fine structure (XAFS) combined with density functional theory (DFT) calculations reveal that the significant improvement in H2 evolution performance on Rh SAs/TpPa-1 originates from the unique RhC3N coordination environment, promoting the charge separation and migration at the atomic interface, and thus decreasing the energy barrier for H* formation. Notably, in situ Raman technique confirmed Rh SAs was the main active sites (RhH) for proton reduction.

Porous titanium foam-supported dual-sided nitrogen doped Bis-Rare-Earth MOFs/TiO2 nanoflowers photoelectrocatalyst

Rational implementation of auxiliary voltage in heterojunction structures to improve charge separation efficiency is an effective method to enhance photoelectrode performances. This work reported a novel p-n type heterojunction structure photoelectrode, constructed with nitrogen-doped bis-rare-earth metal–organic frameworks (NH2-La/Ce MOFs) and titanium dioxide nanoflowers (NTFs) on porous titanium foams (Ds-NH2-La/Ce MOFs/NTFs/Ti).The application in treating water pollution demonstrated that the Photoelectrocatalytic degradation of ibuprofen (IBP) at an auxiliary bias voltage of 1.5 V for 120 min reached 98.3 %. The density Functional Theory (DFT) calculations revealed that nitrogen-doped bis-rare-earth MOFs effectively reduce the bandgap and establish an internal electric field, which facilitated carrier separation and transport. The double-coupled n-n heterojunction structure designed herein share a good tactic to develop MOFs-based new photoelectrodes for future.