Contact Charge Transfer Research Articles

An S-Scheme CeO2/Bi2O2S heterojunction photoanode for the photoelectrocatalytic degradation of sulfamethoxazole in synthetic and real wastewater

We prepared an S- scheme heterojunction photoanode using cerium oxide (CeO2) and bismuth oxysulfide (Bi2O2S) for the photoelectrocatalytic degradation of sulfamethoxazole. The CeO2 /Bi2O2S photoanode was synthesised via an in-situ hydrothermal method, ensuring strong contact and efficient charge transfer between the CeO2 and Bi2O2S. The materials and photoanode were characterized with XRD, XPS, photoluminescence, and photoelectrochemistry. The S-scheme configuration observed in the formation of heterojunction in CeO2 /Bi2O2S photoanode was responsible for the improved photoelectrocatalytic performance for the visible light-assisted degradation of sulfamethoxazole. Operational parameters such as the effect of pH and current density were examined. The extent of sulfamethoxazole mineralisation was calculated to be 72 % using the total organic carbon (TOC) measurement. The LC-MS analysis was used to predict the degradation pathway and products. Furthermore, the photoelectrocatalytic efficiency of the CeO2/Bi2O2S photoanode was investigated in real wastewater matrices with TOC removal of 54 %. Therefore, the S scheme CeO2/Bi2O2S photoanodes lends itself to photoelectrochemical water treatment applications.

In-situ construction of Bi-MOF-derived S-scheme BiOBr/CdIn2S4 heterojunction with rich oxygen vacancy for selective photocatalytic CO2 reduction using water

In this study, a highly selective MOF-BiOBr/CdIn2S4 (MOF-BiOBr/CIS) heterostructure with CdIn2S4 nanosheets grown in situ on the tubular structure derived from Bi-MOF-based BiOBr was successfully constructed using a hydrothermal method. Under simulated solar light without sacrificial or photosensitizing agents, the 20-MOF-BiOBr/CIS composite exhibited excellent photocatalytic CO2 performance, achieving production rates of 30.18 μmol‧g−1‧h−1 for CO and 1.50 μmol‧g−1‧h−1 for CH4. Compared to pure MOF-BiOBr and CdIn2S4, the CO production rates were increased by approximately 9 and 116 times, respectively. It was revealed that the 20-MOF-BiOBr/CIS composite with rich oxygen vacancy exhibited close interfacial contact and efficient charge transfer. The formation of MOF-BiOBr/CdIn2S4 heterojunction thereby provided efficient CO2 photocatalytic reduction. The CO selectivity of 20-MOF-BiOBr/CIS reached 83.4 %, and the MOF-BiOBr/CIS heterojunction exhibited good stability over multiple cycles. Furthermore, a mechanism for enhanced photocatalytic CO2 reduction by the MOF-BiOBr/CIS heterojunction was also proposed.

Boosted antibiotic elimination over 2D/2D mesoporous CeO2/BiOCl S-scheme photocatalyst

Exploring efficient photocatalysts holds significant importance for the prevention and treatment of antibiotic pollution. This research reports a 2D/2D CeO2/BiOCl S-scheme photocatalyst constructed by mesoporous CeO2 and BiOCl nanosheets (NSs). Efficient charge separation and transfer was achieved by the synergistic effect of large-area contact and S-scheme charge transfer mechanism, which significantly enhanced the photocatalytic performance of CeO2/BiOCl. Experimental results demonstrated that the CeO2/BiOCl photocatalyst displayed superior photocatalytic activity to the individual components, which could efficiently eliminate four types of antibiotics, namely tetracycline (TC), chlortetracycline (CTC), doxycycline (DOC), and oxytetracycline (OTC) under UV light irradiation. Particularly, the sample of 0.4CeO2/BiOCl exhibited the highest catalytic efficiency, with a TC degradation rate constant of 0.01524 min−1, which was 1.85 and 22.74 times higher than that of single CeO2 and BiOCl, respectively. Moreover, liquid chromatograph-mass spectrometer (LC-MS) analysis is employed to reveal the degradation pathways of TC. This work offers an insightful idea for the fabrication of novel S-scheme photocatalysts applied in environmental purification.

Construction of metal-free dual S-scheme heterojunction photocatalysts by rational band alignment for efficient hydrogen evolution

Designing ternary heterojunction photocatalysts is regarded as a compelling approach to attain exceptional photocatalytic activity. However, they always suffer from poor interfacial contact and unclear charge transfer pathways. Herein, a metal-free dual S-scheme heterojunction photocatalyst comprised of black phosphorus (BP), carbon nitride (CN), violet phosphorus (VP) was designed by electrostatic self-assembly. The non-metallic feature of the BPCNVP heterostructure facilitates to form strong interfacial contact by coordinating active P sites in VP and BP with N atoms in CN. Notably, a definite dual S-scheme heterojunction configuration is achieved by rational band alignment of VP and BP, respectively, which significantly boosts the driving force for charge separation. The BPCNVP heterostructure exhibited a hydrogen evolution rate of 1669μmol h-1g−1 with excellent stability, surpassing most reported metal-free photocatalysts. This work demonstrates that the design of dual S-scheme heterojunction by metal-free materials provides valuable insights into the intricate reaction mechanism of ternary heterojunction photocatalysts.

0D/2D heterojunction constructed by Ag2S quantum dots anchored on graphdiyne (g-CnH2n−2) nanosheets for wide spectrum photocatalytic H2 evolution

Precisely crafting heterojunctions for efficient charge separation is a major obstacle in the realm of photocatalytic hydrogen evolution. A 0D/2D heterojunction was successfully fabricated by anchoring Ag2S quantum dots (Ag2S QDs) onto graphdiyne (GDY) nanosheets (Ag2S QDs/GDY) using a straightforward physical mixing technique. This unique structure allows for excellent contact between GDY and Ag2S QDs, thereby enhancing the rate of charge transfer. The light absorption capabilities of Ag2S QDs/GDY extend up to 1200 nm, enabling strong absorption of light, including infrared. Through DFT calculations and in-situ XPS analysis, it was demonstrated that incorporating Ag2S QDs onto GDY effectively modulates the electronic structure, promotes an internal electric field, and facilitates directional electron transfer. This directed electron transfer enhances the utilization of electrons by GDY and Ag2S QDs, with the added benefit of Ag2S QDs serving as electron reservoirs for efficient photocatalytic hydrogen evolution. A 7 %Ag2S QDs/GDY composite exhibited impressive efficiency and stable performance in photocatalytic hydrogen evolution (2418 μmol g−1 h−1), which is much higher than that of GDY and Ag2S QDs. This study conclusively demonstrates that the 0D/2D heterojunction formed by GDY and Ag2S QDs can establish high-quality contact and efficient charge transfer, ultimately enhancing photocatalytic performance.

Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene.

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Improvement effect of Co and Ce oxides on the properties of CeO2-Co2O3-Fe2O3 anode materials

Lithium-ion batteries offer several advantages, including high specific energy, extended lifespan, portability, and environmental friendliness. Transition metal oxides are attractive candidates for negative electrode materials due to their higher theoretical specific capacity. To address issues related to poor stability and volume expansion, cobalt trioxide and cerium oxide were introduced as dopants in iron oxide. This study involved the preparation of Co2O3-Fe2O3 and CeO2-Co2O3-Fe2O3 composites, followed by structural characterization and investigation of their electrochemical properties. The doping of cobalt and cerium oxide proved advantageous in refining particle size. Notably, 1% Co2O3-Fe2O3 particles displayed uniform sizing and tight binding. Additionally, the sample containing 0.05% CeO2 exhibited the smallest particle size and a more homogeneous distribution. Furthermore, cobalt and cerium oxide doping significantly improved electrochemical stability. The discharge capacity of 1% Co2O3-Fe2O3 and 0.05% CeO2-1% Co2O3-Fe2O3 after undergoing 100 constant-current charge and discharge cycle respectively remained at 553.17 mAh/g, 698.57 mAh/g. As a negative electrode material in lithium-ion batteries, the composite oxide 0.05% CeO2-1% Co2O3-Fe2O3 demonstrated superior reversibility and stability during the process of lithium-ion insertion and removal, while also exhibiting low contact resistance and charge transfer resistance.

Face-to-face interfacial assembly of a hybrid NiAl-LDH@BiOIO3 photocatalyst for the effective solar-induced abatement of antibiotic and dye pollutants: Insights into surface engineering and S-scheme charge transfer

The development of hybrid catalysts with 2D/2D interfacial contact and step-scheme (S-scheme) charge transfer is crucial for photocatalysis because these catalysts potentially offer more efficient photoexcited charge separation and separated charge carriers with a stronger redox capability. In this study, we strategically developed a novel hybrid NiAl layered double hydroxide (LDH)@BiOIO3 (BOI) photocatalyst with effective S-scheme charge transfer for the efficient solar-induced abatement of aqueous antibiotic and dye pollutants. The in-situ growth of LDH sheets on BOI sheets yielded a hybrid 2D/2D LDH@BOI photocatalyst with favorable face-to-face interfacial contact, which provided a broader platform for photoinduced charge migration and minimizes charge recombination. Furthermore, the S-scheme charge transfer mechanism within the hybrid photocatalyst effectively promoted the separation of the photoinduced charge carriers and preserved their strong redox capability. These beneficial features, in combination with the large specific surface area and enhanced light-harvesting capability, were responsible for the exceptional photocatalytic performance of the optimized hybrid LDH@BOI photocatalyst in terms of the degradation and mineralization of sulfamethoxazole and Congo red dye. Notably, the proposed hybrid photocatalyst outperformed BOI and LDH individually and previously reported state-of-the-art photocatalysts while maintaining its stability over consecutive test cycles, highlighting it as a promising candidate for photocatalytic applications.

Facile construction of 0D/2D In2O3/Bi2WO6 Z-scheme heterojunction with enhanced photocatalytic activity for antibiotics removal

Proper interfacial contact and efficient interfacial charge transfer play a predominant role in improving the photocatalytic performance. In this work, the 0D/2D In2O3/Bi2WO6 Z-scheme heterojunction was constructed successfully. The In2O3 nanoparticles were immobilized on the surface of the Bi2WO6 nanosheets via a facile hydrothermal-calcination method. The crystal structure and photoelectrochemical properties of samples were further characterized. 15% In2O3/Bi2WO6 (IB-15) exhibited optimal photocatalytic properties in degradation of tetracycline (TC) and oxytetracycline (OTC) under visible-light irradiation, and the possible degradation pathways of TC were acknowledged derived from LC-MS. According to the results of radical trapping experiments, superoxide radicals (•O2-) and photogenerated holes (h+) were predominant active species for TC degradation and a possible photocatalytic mechanism was proposed. The significant improvement of photocatalytic property was attributed to the unique Z-scheme heterojunction with 0D/2D architecture which facilitates the rapid separation of photo-excited carriers and expands the range of absorption spectrum.

Well‐dispersed FeOCl Nanosheets as High‐performance Chloride Ion Battery Cathode Material

AbstractThermal decomposition method has been widely used to synthesize FeOCl materials with simple process and low requirements for devices. However, the FeOCl particles show nonuniform size and are easy to grow up together with the rapid reaction. The formed aggregates contribute to the poor cyclic stability for chloride ion battery. Herein, NaCl template was developed to fabricate FeOCl nanosheets with uniform size of thermal decomposition method. When the Fe: Na molar ratio reached 1 : 10, the FeOCl nanosheets showed good dispersity and high chlorine content. The FeOCl‐1‐10‐NaCl cathode delivered a maximum discharge capacity of 145 mAh g−1 and an excellent capacity retention (80 %) over 50 cycles, due to the high particle dispersion in electrode slurry. With the amount of NaCl template increasing, the FeOCl‐1‐40‐NaCl cathode delivered a high initial discharge capacity of 173 mAh g−1, as a result of the low contact resistance and charge transfer resistance.

Investigating particle-particle electrostatic effects on charged lunar dust transport via discrete element modeling

NASA surface exploration missions have always seen negative effects of dust including the Apollo missions. The astronaut-witnessed unusual behavior of the dust particles that surround the vehicle after engine cutoff has the potential to have more of an influence on surface systems dust loading than the high velocity lunar rocket plume ejecta in the landing process. The levitation and transport of the fine components of regolith on lunar surface has been linked to electrostatic effects and electric field, but so far there is no accurate model considering the inter-particle electrostatic interactions, especially when the particles are charged by rocket plume or other mechanical interactions due to exploration activities. This study is proposed to investigate the dynamics of charged lunar regolith with a discrete element method (DEM) approach focusing on the inter-particle interactions and contact charge transfer. The grain dynamics is coupled with mechanical and electrical particle interactions, and both short- and long-range interactions between spherical particles are incorporated. A tribo-charging model based on instantaneous collisions between particles is adopted and validated by comparing the simulation results to existing experimental data. Sensitivity analysis is conducted to quantify the effects of initial charge, tribo-charging, and E-field on transport of lunar dust based on JSC-1 simulants with a radius of 50 μm. DEM simulations are also conducted in a near realistic lunar environment with the estimations of initial conditions that shows the difference in position and velocity distributions between charged particles and uncharged particles. The results indicate that the charged dust particles have higher dispersion of position and velocity by several orders of magnitude due to electrostatic effects. This provides a potential explanation for the phenomena of the approximately 30 s dust lofting following Apollo Lunar Module landing.

In Situ Construction of a Liquid Film Interface with Fast Ion Transport for Solid Sodium-Ion Batteries

Solid sodium-ion batteries (SSIBs) are considered as one of the promising energy storage systems because of their high safety and high energy density. However, the sodium metal anode presents poor wettability with a solid electrolyte, resulting in high interface impedance and dendrite growth, which severely limits their application in practice. Herein, a novel liquid film (Na-BP) interface is constructed between sodium and solid electrolyte (Na3Hf2Si2PO12) with an excellent kinetic mass transfer ability and good fluidity, which could guarantee a close contact and fast charge transfer at interface. The symmetric cells with the designed interface show a high-rate and long-cycle performance and could cycle stably more than 1000 and 700 h at 0.2 and 0.5 mA cm-2, respectively. The critical current density of the cells can reach 3.6 mA cm-2 at room temperature, which is the highest value in similar works.

Z-scheme Cu2(OH)3F nanosheets-decorated 3D Bi2WO6 heterojunction with an intimate hetero-surface contact through a hydrogen bond for enhanced photoinduced charge separation and transfer

Enhancing the effective contact between heterogeneous interfaces and accelerating photo-generated charge separation is the focus of current photocatalysis research. Herein, a novel Z-scheme Cu2(OH)3F/Bi2WO6(CFO/BWO) heterojunctions with intimate hetero-surface contact were successfully synthesized via electronic coupling of the surface hydrogen bonds. The optimal proportion of 25%CFO/BWO displayed outstanding photocatalytic performance among the removal of tetracycline hydrochloride (TC-HCl). The excellent catalytic effect comes from the construction of the Z-Scheme heterojunction, which accelerates the separation of photogenerated carriers, and the linking of hydrogen bonds between different planes providing more charge transfer channels. Moreover, explored the main active substances in the reaction process and tested the stability of the as-prepared samples, and the charge transfer law and degradation mechanism in the Z-scheme heterojunction are discussed in detail. This work provides a new way to construct heterojunctions with more adequate hetero-surface contact and faster charge transfer capabilities.

New-type Hf-based NASICON electrolyte for solid-state Na-ion batteries with superior long-cycling stability and rate capability

The NASICON electrolyte with good chemical stability, suitable three-dimensional ion channel, high mechanical strength and wide electrochemical window, has been considered to be the one of most promising electrolytes for solid-state Na-ion batteries. However, the unsatisfactory ionic conductivity and large interface resistance severely limit its practical application. Herein, a new-type Hf-based NASICON electrolyte Na3.2Hf1.9Ca0.1Si2PO12 is synthesized, the conductivity of which can reach 1.07 × 10−3 S cm−1 at room temperature and the stability electrochemical window can reach 8.80 V. In addition, a mixed-ion-electron interphase was constructed on the surface of Na3.2Hf1.9Ca0.1Si2PO12 which can guarantee a close contact and fast charge transfer between sodium and the electrolyte. The batteries with this new-type electrolyte can cycle stably more than 2400 h at room temperature and the critical current density can reach 1.9 mA cm−2. Even the current density reaches 2.0 mA cm−2, there was still no obvious short circuit, which was the highest value in similar works. The full cell of Na/Na3V2(PO4)3 with this electrolyte can maintain a capacity of 103.1 mAh g−1 at 0.5 C without capacity decaying even after more than 300 cycles.

Contact Charge Transfer between Nominally Identical Materials

AbstractDifferences in concentrations of excited electrons arising from geometry‐dependent differences in de‐excitation paths lead to differences in Fermi energies, which enable contact charge transfer between otherwise identical solids of different size. This model is used with a quasi‐equilibrium description of the Fermi energy to estimate a lower bound of the magnitude of charging of pairs of like particles and the charge distribution in groups of interacting like particles. The predictions agree with observed charge transfer directions between large and small particles and with the broad particle size range over which charging is observed. Estimates of charging are compared to available measurements, the breakdown limits of air, and the relative strengths of interparticle electrostatic and gravitational forces. The influence of particle size distribution on the charge distribution in groups of particles is examined.

Redox-active nanostructure electrode of Mn/Ni bimetal organic frameworks anchoring on multi-walled carbon nanotubes for advanced supercapacitor

The metal-organic frameworks (MOF) is a promising electrode material for supercapacitor, but the traditional monometallic metal-organic frameworks are limited by poor conductivity and structural stability. In this work, a novel manganese (Mn) and nickel (Ni) bimetallic metal-organic frameworks anchored on multi-walled carbon nanotubes (Mn/Ni-MOF@MWCNTs) were fabricated via a one-step solvothermal method. The morphologies, micro-structures and electrochemical properties of Mn/Ni-MOF@MWCNTs with different mass ratios of Mn and Ni were compared. The results indicated that multi-walled carbon nanotubes (MWCNTs) provides numerous active anchoring sites which is introduced into the architecture of the optimal Mn/Ni-MOF; these sites are responsible for enhancing the electrons transfer and structural integrity, with the small contact resistance and charge transfer resistance. As a result, a specific capacitance of 793.6 F g −1 at 1 A g −1 in 1 M LiOH aqueous solution was achieved, and the capacitance retention was retained at 74.92% after 1000 cycles at 1 A g −1 . The crystal structures and valence band information of the anchored Mn/Ni-MOF were obtained by DFT calculation. Besides, Mn/Ni-MOF@MWCNTs//Mn/Ni-MOF@MWCNTs symmetry supercapacitor showed an excellent energy density of 33.2 Wh kg −1 at a power density of 1198 W kg −1 and stabilizing capacity retention of 78.3% over 2000 cycles. These results provide a promising strategy for high-performance electrochemical energy storage. • Mn/Ni-MOF@MWCNTs is an effective electrode material for supercapacitors. • The structure is well tailored at the optimal mass ratio of Mn to Ni of 1: 3. • Mn/Ni-MOF@MWCNTs shows excellent specific capacitance of 793.6 F g −1 at 1 A g −1 . • Mn/Ni-MOF@MWCNTs//Mn/Ni-MOF@MWCNTs SSC device shows an excellent energy density of 33.2 Wh kg −1 at a power density of 1198 W kg −1 . • Excellent cycling durability with 78.3% retention after 2000 cycles was observed.

Grinding-assisted heterogeneous nucleation of BiOAc on MoS2 nanoflowers to heterojunction with good visible-light photocatalytic performance

Bismuth oxide subacetate (CH3COO(BiO); BiOAc) with a large band gap energy (Eg) was first applied as an ultraviolet-light-driven photocatalyst in our group. MoS2 nanoflowers have been used to improve the visible-light photocatalytic activity of bismuth-based semiconductors with wide Eg because of their good visible-light response. Herein, the grinding-assisted solid-state reaction method was used to prepare a MoS2/BiOAc composite to improve the visible-light photoreactivity of BiOAc. As compared with commonly used wet chemical and hydrothermal routes, the grinding-assisted synthesis facilitated heterogeneous nucleation, which was beneficial to achieving close contact and subsequent charge transfer and separation at the interfaces, resulting in enhanced photocatalytic activity for malachite green, methylene blue, and antibiotic tetracycline degradation under visible-light irradiation. Notably, the dispersion in the mixing solution of ethanol and water (v/v=1) of MoS2 nanosheets induced self-assembly into flower-like nanostructures, thus enhancing the photocatalytic activity of MoS2/BiOAc. A possible mechanism for visible-light photocatalysis of MoS2/BiOAc was proposed.

Layered WS2/WO3 Z-scheme photocatalyst constructed via an in situ sulfurization of hydrous WO3 nanoplates for efficient H2 generation

Solar-driven H2 production over Z-scheme photocatalysts to mimic the natural photosynthesis represents a promising approach to the production of clean hydrogen energy. However, fabrication of Z-scheme heterostructures with intimate interfacial contact and smooth charge transfer for efficient H2 generation is still challenging. Herein, a series of layered WS2/WO3 heterostructures containing monoclinic WO3 (m-WO3) nanoplates and few-layer hexagonal WS2 with 2H structure (2H-WS2) is constructed via an in situ sulfurization process of hydrous WO3 nanoplates. The electronic interaction between the two moieties (2H-WS2 and m-WO3) follows a direct Z-scheme mechanism to retard the charge recombination without weakening the redox ability of the photoexcited charge carriers of the WS2/WO3 heterostructures. Moreover, the few-layer 2H-WS2 with thickness of ~4.2 nm and intimate interfacial contact between 2H-WS2 and m-WO3 due to the “S-W-O” transition layer can further provide shortened charge migration path and smooth interfacial charge transfer, which in turn enables the effective operation of the Z-scheme mechanism. Therefore, the WS2/WO3 Z-scheme photocatalyst with an optimal component ratio delivers ca. 5 times higher H2 generation activity than the few-layer 2H-WS2 alone. The present work offers a promising strategy to construct integrated nanostructured heterostructures with intimate interfacial contact, smooth charge transfer and improved photocatalytic performance.

Study of the mechanisms of contact electrification and charge transfer between polytetrafluoroethylene and metals

The contact electrification between polytetrafluoroethylene (PTFE) and metals (Al and Cu) is investigated, revealing that much more surface charge is generated in the Al/PTFE system than in the Cu/PTFE system, which is further demonstrated and systematically explained by density functional theory calculations. The charge is believed to firstly transfer to the C atoms and then partof it migrates to nearest F atoms. And the charge transfer at the interface is found to be closely related to the difference in the electronic attraction of the two surfaces in contact, rather than the potential barrier at the interface. Further investigation indicates that electrons transfer from the high energy state of the Al surface to the highest occupied molecular orbit (HOMO) of PTFE and then reach an equilibrium state in the PTFE/Al system, while in the PTFE/Cu system, the electrons of the Cu may transfer to both the HOMO and the lowest unoccupied molecular orbit of PTFE, which indicates a different mechanism of charge transfer. The findings advance our understanding of the contact electrification and charge transfer mechanism between metals and polymers, and sheds light on the material design and modification of contact- or tribo-electrification and other applications.

Contact charge transfer between inorganic dielectric solids of different surface roughness

We measured contact charge transfer between chemically identical, dielectric solids with different surface roughness. Glass of four different roughness levels had its own charge transfer series with the rougher glass negative with respect to the smoother in all combinations. Unpolished N-type silicon wafers became negative to polished N-type wafers; P-type wafers showed the opposite behavior. Rougher glass was more negative than smoother glass after contact with chemically non-identical samples. The results are consistent with modeling studies that show that the concentration of excited electrons is lower in solids in which there is greater access to surface de-excitation.