Direction Of Electron Flow Research Articles

Magnetite-mediating direct interspecies electron transfer is not pivotal role in directing electrons toward methane production from sulfate containing wastewater

Sulfate reduction can compete for electrons with methane production, thereby reducing methane production. Several factors, such as magnetite addition, carbon sources, and the chemical oxygen demand (COD)/SO42− ratio, can influence the direction of electron flow toward methanogenesis. However, their contributions to methane production remain unclear. In this study, the addition of magnetite significantly enhanced the maximum methane production rate (Rmax). The enrichment of Methanothrix and Methanobacterium in the conductive material groups indicated the establishment of a methanogenesis process through direct interspecies electron transfer (DIET). Although the DIET pathway enhanced Rmax in the conductive material groups, this increase did not translate into a higher methane yield in this study. The contribution of DIET pathway to methane yield was negligible compared with the effect of COD/SO42− ratio and carbon sources. The relative contribution of COD/SO42− ratio exceeded 40 % in directing electron flow.

Preventing Nitrite Desorption via Switching Hydrogenation Position: A Dual-Site Approach for Selective Nitrate Reduction to Ammonia.

The electrochemical nitrate reduction reaction (NO3RR), which converts harmful nitrates into valuable ammonia (NH3) with zero carbon emission, is one of the most promising alternatives to the Haber-Bosch process. However, the NO3RR process is complex and involves multiple proton-coupled electron transfers that generate intermediates or byproducts, such as NO2 -, resulting in low ammonia yields and faradaic efficiency (FE). Herein, by constructing a FeCu bimetallic catalyst (FeCu-NC), the hydrogenation position of *NO3 is switched at the FeCu dual-atom site, preventing the desorption of *NO2 intermediate. Furthermore, electron transfer from Cu to Fe sites mimics the electron flow direction in natural nitrite reductase enzymes and accelerates the reduction of *NO2 to NH3, achieving efficient conversion of NO3 - to NH3. A 24-hour electrocatalytic experiment with FeCu-NC demonstrates negligible NO2 - formation throughout the NO3RR process, with an ammonia production rate of 6.13mgh-1mgcat -1 and an impressive FE of 95%, which are remarkably superior in comparison to most of the NO3RR electrocatalysts. This work opens new avenues for the fundamental understanding of catalytic mechanisms and the development of next-generation catalysts for sustainable ammonia production.

Stepwise-Induced Synthesis and Excellent Corrosion Protection of Ce/Eu Codoped ZnO Solid Solution Materials.

Under purely inorganic conditions, a synthesis route was devised wherein elements were introduced stepwise via coprecipitation based on differences in compound solubility. This synthesis method can change the microscopic morphology of the material without relying on a templating agent, resulting in the formation of the multilayered lamellar Ce/Eu codoped zinc oxide solid solution (ZCEOSS) with a self-assembled nested imbrication structure. The study improves the critical matter of corrosion by focusing on the electron and energy transfer mechanisms. By introduction of the bandgap modulator cerium element and fluorescence enhancer europium element into the ZnO material, the anticorrosion material has been successfully endowed with both photocathodic protection and luminescent initiative/stress dual corrosion defense functions. Due to the energy level staircase protection mechanism synergistically generated by the 4f electron shell of rare-earth elements in concert with semiconductor zinc oxide, the energy band positions were modulated to progressively guide the direction of electron flow, thereby suppressing corrosion reactions. In particular, the ZCEOSS material synthesized by doping 1% cerium and 7% europium and adding rare-earth elements at pH 7 exhibited the best corrosion inhibition performance. After immersion in simulated seawater for 96 h, Tafel polarization test results showed that compared to epoxy resin and ZnO anticorrosion systems, the ZCEOSS anticorrosion system exhibited significantly improved corrosion inhibition efficiency with enhancements of 1028.3 and 402.9%, respectively. This study provides new insights into the development of highly efficient inorganic anticorrosion materials.

Qualitative and quantitative analysis of electrons donated by pollutants in electron transfer-based oxidation system: Electrochemical measurement and theoretical calculations

In order to gain a profound understanding of the fate of pollutants in advanced oxidation processes (AOPs), this study analyzed the electron contribution of pollutants qualitatively and quantitatively which rarely reported before. The rich electron transfer system was constructed by mesoporous carbon nitride (MCN) coupling with persulfate (PS) driven by visible light and the sulfanilamide antibiotics (SULs) were used as target contaminants. Firstly, the qualitative analysis of electron transfer in the system was confirmed systematically. The electron flow direction tested by i-t curves indicated that PS absorbed electrons, while SULs released electrons. The flow rate of electrons was also accelerated after the addition of SULs. The fitting curve between the kinetics and the peak potential difference tested by CV curve showed that the larger potential difference, the slower rate of oxidative degradation. Secondly, the quantification of electron transfer was achieved through theoretical calculations to simulate the interactions of the ‘catalyst-oxidant-antibiotic’ system. After the addition of SULs, the adsorption energy of the ‘catalyst-oxidant-antibiotic’ system was enhanced and the bond length of the peroxide bond was stretched. Notably, the electron transfer analysis results showed that the charge of SULs was around 0.032–0.056e, indicating that SULs pollutants played the role of electron contributors in the system. The oxidative degradation pathway included the direct cracking of S-N bond, shedding of marginal groups, ring-opening and hydroxyl addition reaction. This study clarified the electronic contribution of SULs in the oxidation system, providing necessary theoretical supplement for the analysis of the transformation of pollutants in AOPs.

In2S3 nanoparticles modify the porous Fe2V4O13 nanostructure photoanode to enhance charge separation efficiency and photoelectrochemical water splitting performance

In this study, we demonstrate for the first time a promising photoanode of Fe2V4O13/In2S3 (FVO/IS) nanoparticles (NPs) for photoelectrochemical (PEC) water splitting. Most importantly, this work presents the first application of X-ray photoelectron spectroscopy in tracking electron flow direction within FVO/IS to reveal the formation of heterojunction having the electron flow from IS to FVO. Mott-Schottky measurement confirms that the modification of IS NPs establishes the type II heterojunction between FVO and IS, favorable for the transport and separation of carriers. Spectral measurements of electrochemical impedance spectroscopy, photoluminescence and Bode diagram confirm the effective separation of carriers and the prolongation of the charge lifetime in the FVO/IS heterojunction photoanode. Moreover, the electrochemical measurements evidently demonstrate the substantial enhancement in the charge separation efficiency (ηseparation) and charge transfer efficiency (ηtransfer) of the photoanode, leading to significantly enhanced PEC water splitting capability. As a result, in contrast with the pure FVO NPs photoanode, the photocurrent density of the constructed FVO/IS NPs photoanode is increased by 27 times without bias. This study paves a new approach for boosting the PEC water splitting activity of FVO photoanodes by constructing heterostructures through modification with other semiconductors.

A novel MXene-bridged Z-scheme ZnO@Nb2CTx MXene@carbon nitride nanosheets photocatalyst for efficient enrofloxacin degradation

A Z-scheme photocatalyst, ZnO@Nb2CTx MXene@carbon nitride nanosheets (ZNC), is synthesized by the hydrothermal and electrostatic self-assembly strategy. The degradation test shows that ZNC photocatalyst has an enhanced photocatalytic efficiency of Enrofloxacin (ENR) degradation under visible light irradiation. The ENR removing rate has reached 98.2 % after 40 min light irradiation and has a degradation rate of 0.0961 min−1, which is 4.78 times higher than pure ZnO and 3.987 times higher than CNNS. Besides, a possible ENR degradation pathway was studied via LC-MS method. Furthermore, in-situ high resolution XPS spectroscopy and DFT calculation confirmed the direction of electron flow in the ZNC photocatalyst, highlighting that its improved degradation efficiency primarily stems from the introduction of the MXene electron transport layer, which promotes efficient charge transfer and separation of electron-hole pair. This study provides a guidance to design highly efficient Z-scheme photocatalyst for ENR degradation.

Sulfur vacancies and heterogeneous interfaces promote high performance sodium storage of bimetallic chalcogenide hollow nanospheres

Transition metal sulfides have high theoretical capacities and are considered as potential anode materials for sodium-ion batteries. However, due to low inherent conductivity and significant volume expansion, the electrochemical performance is greatly limited. In this study, a nickel/manganese sulfide material (Ni0.96Sx/MnSy-NC) with adjustable sulfur vacancies and heterogeneous hollow spheres was prepared using a simple method. The introduction of a concentration-adjustable sulfur vacancy enables the generation of a heterogeneous interface between bimetallic sulfide and sulfur vacancies. This interface collectively creates an internal electric field, improving the mobility of electrons and ions, increasing the number of electrochemically active sites, and further optimizing the performance of Na+ storage. The direction of electron flow is confirmed by Density functional theory (DFT) calculations. The hollow nano-spherical material provides a buffer for expansion, facilitating rapid transfer kinetics. Our innovative discovery involves the interaction between the ether-based electrolyte and copper foil, leading to the formation of Cu9S5, which grafts the active material and copper current collector, reinforcing mechanical supporting. This results in a new heterostructure of Cu9S5 with Ni0.96Sx/MnSy, contributing to the stabilization of structural integrity for long-cycle performance. Therefore, Ni0.96Sx/MnSy-NC exhibits excellent electrochemical properties following our modification route. Regarding stability performance, Ni0.96Sx/MnSy-NC demonstrates an average decay rate of 0.00944% after 10,000 cycles at an extremely high current density of 10000 mA g−1. A full cell with a high capacity of 304.2 mA h g−1 was also successfully assembled by using Na3V2(PO4)3/C as the cathode. This study explores a novel strategy for interface/vacancy co-modification in the fabrication of high-performance sodium-ion batteries electrode.

S-scheme p-n junction Na0.6CoO2/g-C3N4 heterostructure as an efficient photocatalyst for green hydrogen production: fabrication, characterization and mechanisms

Probing the spatial separation and transport process of photogenerated charges at nanoscale interfaces is essential for understanding catalytic reaction mechanisms on heterostructure photocatalysts. Here, we developed a p-n junction Na0.6CoO2/g-C3N4 S-scheme photocatalyst via electrostatic self-assembly technology. A significant hydrogen production rate of ∼ 0.294 mmol g−1 h−1 was achieved on the optimal Na0.6CoO2/g-C3N4, which was ten times higher than that of pure g-C3N4. In-situ XPS shows that the electrons in Na0.6CoO2/g-C3N4 had different flow directions without and with illumination, demonstrating a built-in electric field being formed through Na0.6CoO2 and g-C3N4 interaction. DFT calculations and ultraviolet photoelectron spectroscopy verified that g-C3N4 and Na0.6CoO2 possess the energy band structures conforming to the heterostructure of S-scheme. In-situ Kelvin probe microscope studies show that Na0.6CoO2 and g-C3N4 both have a self-induced electric field effect, and their combination significantly strengthens the built-in electric field and improves the space separation of photogenerated electrons. Compared with the change of the surface photovoltage of g-C3N4 (60 mV) and Na0.6CoO2 (−30 mV), the average surface contact potential difference of Na0.6CoO2/g-C3N4 reached 320 mV, yielding a higher efficiency of photogenerated electron separation. This work also provides direct evidence on the existence of a built-in electric field and an electron flow direction for heterostructure photocatalyst materials.

Utilization of the through-space effect to design donor-acceptor systems of pyrrole, indole, isoindole, azulene and aniline.

Molecular electrostatic potential (MESP) topology analysis reveals the underlying phenomenon of the through-space effect (TSE), which imparts electron donor-acceptor properties to a wide range of chemical systems, including derivatives of pyrrole, indole, isoindole, azulene, and aniline. The TSE is inherent in pyrrole owing to the strong polarization of electron density (PoED) from the formally positively charged N-center to the C3C4 bonding region. The N → C3C4 directional nature of the TSE has been effectively employed to design molecules with high electronic polarization, such as bipyrroles, polypyrroles, phenyl pyrroles, multi-pyrrolyl systems and N-doped nanographenes. In core-expanded structures, the direction of electron flow from pyrrole units towards the core leads to highly electron-rich systems, while the opposite arrangement results in highly electron-deficient systems. Similarly, the MESP analysis reveals the presence of the TSE in azulene, indole, isoindole, and aniline. Oligomeric chains of these systems are designed in such a way that the direction of electron flow is consistent across each monomer, leading to substantial electronic polarization between the first and last monomer units. Notably, these designed systems exhibit strong donor-acceptor characteristics despite the absence of explicit donor and acceptor moieties, which is supported by FMO analysis, APT charge analysis, NMR data and λmax data. Among the systems studied, the TSEs of many experimentally known systems (bipyrroles, phenyl pyrroles, hexapyrrolylbenzene, octapyrrolylnaphthalene, decapyrrolylcorannulene, polyindoles, polyazulenes, etc.) are unraveled for the first time, while numerous new systems (polypyrroles, polyisoindoles, and amino-substituted benzene polymers) are predicted to be promising materials for the creation of donor-acceptor systems. These findings demonstrate the potential of the TSE in molecular design and provide new avenues for creating functional materials.

Low-temperature plasma-induced porous Sb2WO6 microspheres with rich oxygen vacancies to promote high-performance photocatalytic activity

The escalating issue of water pollution has sparked significant attention among researchers in the field of photocatalysis. Consequently, it holds immense significance to develop photocatalysts that exhibit high charge separation efficiency and stability for effectively degrading pollutants in water. In this study, OV-Sb2WO6-X photocatalyst was synthesized by incorporating oxygen vacancies into pristine Sb2WO6. The introduction of oxygen vacancies significantly enhanced the charge separation efficiency, resulting in a substantial improvement in the photocatalytic activity. The content of oxygen vacancies was controlled by plasma treatment time, processed for 10, 20 and 30 min, and electron paramagnetic resonance (EPR) test demonstrated the introduction of oxygen vacancies successfully. Furthermore, X-ray photoelectron spectroscopy (XPS) characterized the internal electron flow direction of the photocatalyst. OV-Sb2WO6-20 showed the degradation rate of Rhodamine B (RhB) that nine times of the Sb2WO6, while the Tetracyclines (TC) degradation rate showed 3.5 times that of Sb2WO6. Moreover, OV-Sb2WO6-20 exhibited superior stability in terms of recycling activity and material structural integrity. Additionally, free radical trapping experiments and electron spin-resonance spectroscopy characterization demonstrated that h+ played a crucial role as the reactive species during the degradation process. This research presents a viable approach for the modification of Sb2WO6-based materials, enabling effective treatment of dye wastewater and achieving successful purification.

Redox-active polyphenol nanoparticles deprive endogenous glutathione of electrons for ROS generation and tumor chemodynamic therapy

Chemodynamic therapy (CDT) based on generating reactive oxygen species (ROS) is promising for cancer treatment. However, the intrinsic H2O2 is deficient for CDT, and glutathione (GSH) eliminates ROS to protect tumor cells from ROS cytotoxicity. Herein, we propose a strategy to switch the electron flow direction of GSH for O2 reduction and ROS generation rather than ROS clearance by using P(DA-Fc) nanoparticles, which are polymerized from ferrocenecarboxylic acid (Fc) coupled dopamine. P(DA-Fc) NPs with phenol-quinone conversion ability mimic NOX enzyme to deprive electrons from GSH to reduce O2 for H2O2 generation; the following •OH release can be triggered by Fc. Semiquinone radicals in P(DA-Fc) are significantly enhanced after GSH treatment, further demonstrated with strong single-electron reduction ability by calculation. In vitro and in vivo experiments indicate that P(DA-Fc) can consume intrinsic GSH to produce endogenous ROS; ROS generation strongly depends on GSH/pH level and eventually causes tumor cell death. Our work makes the first attempt to reverse the function of GSH from ROS scavenger to ROS producer, explores new roles of PDA-based nanomaterials in CDT beyond photothermal reagents and drug carriers, and provides a new strategy to improve the efficiency of CDT. Statement of SignificanceP(DA-Fc) nanoparticles performing tumor microenvironment response capacity and tumor reductive power utilize ability were fabricated for CDT tumor suppression. After endocytosis by tumor cells, P(DA-Fc) deprived GSH of electrons for H2O2 and •OH release, mimicking the intrinsic ROS production conducted by NADPH, further inducing tumor cell necrosis and apoptosis. Our work makes the first attempt to reverse the function of GSH from ROS scavenger to producer, explores new functions of PDA-based nanomaterials in CDT beyond photothermal reagents and drug carriers, and provides a new strategy to improve CDT efficiency.

The adsorption behaviors of Cl2 on TiC (100) surface: A density functional theory study

It is important to study the adsorption behavior of Cl2 molecules on the TiC surface and the formation and transfer of reaction products to understand and to regulate the low-temperature chlorination reaction process of carbonized titanium-bearing slag. Based on the first-principles ab initio calculation method of density functional theory (DFT), the adsorption models of Cl2 molecules on the TiC (100) intact surface and the surface with carbon vacancy are established, and the adsorption structures, electronic properties, differential charge density and partial density of states (PDOS) are calculated and analyzed. The formation process and the optimal formation path of the adsorption reaction product are explored. The investigated results indicate that the Cl atoms in the system bonded to the surface Ti atoms are more stable than the structure formed by bonding to the surface C atoms. The electron flow direction is Ti → C and Ti → Cl. In the reaction of TiC with Cl2 molecules, the TiCl3 intermediate is easier to form than the TiCl2 intermediate. The energy barrier to be overcome to form the TiCl3 intermediate is lower and the energy to be supplied is easily met by external conditions. TiCl3 is then further chlorinated to form TiCl4.

Highly efficient photoanode in visible light water splitting through development of Z-scheme structure between compositing TiO2 with GQDs and Ba doped VO2 (m) with smart selection of Ag nanoparticles sites

A highly efficient photoanode for water splitting under visible light is designed by placing Ag nanoparticles (NPs) at the interface of Ba doped VO2 (m) (BaV) and compositing hierarchical porous TiO2 NPs with a graphene quantum dots layer (TG). In fact, the electron flow direction in the photoanode is simply adjusted to develop the Z-scheme structure through solution processing assembly. A very high photocurrent of 2.15 mA cm−2 at 1.23 V vs. RHE is achieved for sequentially assembled reduced graphene oxide (RGO)/BaV/Ag/Ag@TG photoanode. This value is 30 times higher than that of pristine TiO2 photoanode (0.07 mA cm−2 at 1.23 V vs. RHE) and a 70 % increase over type-II heterojunction with RGO/Ag@TG/BaV assembly. Importantly, the stability of this Z-scheme photoanode is 10 times higher than its type-II heterojunction counterpart, making it a promising option for practical applications in water splitting under visible light.

3D porous carbon nitride composited oxygen vacancy‐induced indium oxide for high photocatalytic nitrogen fixation on the interfacial surface

Semiconductor photocatalysis can utilize solar energy for clean energy conversion, but the catalytic efficiency is often unsatisfactory due to limited photo response and efficient separation of photogenerated carriers. In this work, 3D porous carbon nitride (3DPCN) composited oxygen vacancy‐induced indium oxide (3DPCN/VO‐In2O3) was successfully prepared and analyzed by some characterization methods. Meanwhile, the performance of photocatalytic nitrogen fixation was further investigated. X‐ray photoelectron spectroscopy and X‐Ray diffraction (XRD) confirmed the successful preparation of the composites and revealed the electron flow direction; scanning electron microscopy (SEM) and transmission electron microscopy showed the surface structure of the composites; diffuse reflectance spectroscopy and temperature programmed desorption (TPD) revealed the energy band position and adsorption mechanism; electron paramagnetic resonance (EPR) characterization confirms the successful construction of oxygen vacancies; and electrochemical impedance spectroscopy, photoluminescence, and other photochemical characterization results showed that 3DPCN/VO‐In2O3 band gap is narrower and more effective in capturing light than other materials, improving the photocatalytic nitrogen fixation ability. The test results show that the nitrogen fixation capacity of 3DPCN/VO‐In2O3 can reach a maximum value of 156 within 2 h. This result demonstrates that the modification of carbon nitride improves its nitrogen fixation effect, and the introduction of oxygen vacancy‐induced In2O3 improves the light absorption performance and is advantageous to the separation of photogenerated charge carriers.

Atom Rearrangement by Cyclic Electron “Shaking”

The arrangement of atoms comprising a material determines its properties. Thus, atom arrangement controllability can substantially facilitate the creation of new materials such as functional materials. Relevant materials science research has relied heavily on heat treatments. This study investigates the phenomenon of atom rearrangement by applying a high‐frequency alternating current without heating. The proposed method spontaneously rearranges atoms to produce a dense crystal plane oriented parallel to the electron flow. The atoms are “shaken” by generating mechanical interaction between electrons and atoms. Transmission electron microscopy reveals the enlarged crystal grains and an increase in close‐packed planes resulting from the self‐alignment of the atoms along the direction of electron flow. Conventional heat treatments cannot result in such phenomena because heat treatments induce random vibration of the atoms. In contrast, the current flow in the high‐frequency alternating current enables direction‐specific vibration of the atoms. This novel technique could be applied to develop new functional materials that are difficult to obtain via conventional heat treatment methods. Furthermore, this atom rearrangement technology can be applied to expand the field of materials science research.

Hollow sphere of heterojunction (NiCu)S/NC as advanced anode for sodium-ion battery

Metal sulfide is considered as a potential anode for sodium-ion batteries (SIBs), due to the high theoretical capacity, strong thermodynamic stability and low-cost. However, their cycle capacity and rate performance are limited by the excessive expansion rate and low intrinsic conductivity. Herein, heterogeneous hollow sphere NiS-Cu9S5/NC (labeled as (NiCu)S/NC) based on Oswald ripening mechanism was prepared through a simple and feasible methodology. From a structural perspective, the hollow structure provides an expansion buffer and raises the electrochemical active area. In terms of electron/ion during the cycles, Na+ storage mechanism is optimized by NiS/Cu9S5 heterogeneous interface, which increases the storage sites and shortens the migration path of Na+. The formation of built-in electric field strengthens the electron/ion mobility. Based on the first principle calculations, it is further proved the formation of heterogeneous interfaces and the direction of electron flow. As the anode for SIBs, the synthesized (NiCu)S/NC delivers high reverse capacity (559.2 mA h g−1 at 0.5 A g−1), outstanding rate performance (185.3 mA h g−1 at 15 A g−1), long-durable stability (342.6 mA h g−1 at 4 A g−1 after 1500 cycles, 150.0 mA h g−1 at 10 A g−1 after 20,000 cycles with 0.0025% average attenuation rate). The matching cathode electrode Na3V2(PO4)3/C is assembled with (NiCu)S/NC for the full-battery that achieves high energy density (253.7 W h kg−1) and reverse capacity (288.7 mA h g−1). The present work provides a distinctive strategy for constructing electrodes with excellent capacity and stability for SIBs.

SnS2-covalent organic framework Z-scheme van der Waals heterojunction for enhanced photocatalytic reduction of uranium (VI) in rare earth tailings wastewater

Uranium removal by photocatalytic reduction is one of the most promising methods to reduce radioactive contamination in wastewater. Herein, a Z-scheme van der Waals heterojunction photocatalyst (SnS2COF) was synthesized in situ by combining covalent organic frameworks (COF) with semiconductor (SnS2) for U (VI) reduction in rare earth tailings wastewater. The synthesis method of van der Waals heterojunction is simple and solves the problem of no hanging bond in composite components. In this heterojunction, large areas of van der Waals interaction form high-speed electron transport channels. In addition, it is deduced that SnS2COF fits the Z-scheme heterojunction electron transport mode through the theoretical calculation of the ground state and excited state electron density difference and the related band structure. Under the photoexcitation, the direction of electron flow is reversed, which further promotes the separation of the photogenerated electron (e−)-hole (h+) under the action of the built-in electric field, maintains the high reducibility of the conduction band, and avoids the photocorrosion of SnS2. Compared with inorganic-inorganic heterojunction, SnS2COF has a wider light absorption range, more active sites, and higher e−-h+ separation and transfer efficiency. Therefore, it had a higher U (VI) reduction removal capacity, up to 1123.3 mg g−1, far surpassing the SnS2 and COF counterparts under ultraviolet/visible light. And the U (VI) removal rate reached 98.5 % in rare earth tailings wastewater. The design concept of organic–inorganic heterojunction materials provides an alternative strategy for improving the photocatalytic performance.

Formation mechanism of a ternary nanohybrid based on magnetite-chitosan-graphene oxide according to HSAB theory

Magnetic nanohybrids containing chitosan (CS) and/or graphene have promising applications in environmental remediation. In this study, a ternary nanohybrid based on magnetite (M)-CS-graphene oxide (GO) (MCSGO) was prepared in a facile manner via simultaneous reduction–precipitation at room temperature. The as-prepared nanohybrid was characterized by field-emission scanning electron microscopy/energy dispersive X-ray spectroscopy, transmission electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller/Barrett–Joyner–Halenda analysis, thermogravimetric–differential thermal analysis, and vibrating sample magnetometry. Most importantly, the mechanism associated with the formation of MCSGO was determined using hard-soft acid-base (HSAB) theory and spectroscopic analyses. HSAB theory predicted the following dominant interactions in MCSGO based on electron transfer calculations and energy lowering between the couplet components: (1) CS-Fe3O4: NH2→Fe(III); (2) GO-Fe3O4: Ar-O-Ar→Fe(III); and (3) GO-CS: O(Ar-OH)→-OH (→ denotes the direction of electron flow and Ar denotes the aromatic ring). The CS-Fe3O4 and GO-Fe3O4 interactions were much stronger than that for GO-CS. The predictions obtained by HSAB theory were supported by X-ray photoelectron spectroscopy, Fourier transformation infrared spectroscopy, ultraviolet–visible spectra, and fluorescent spectra. According to HSAB theory and spectroscopic analyses, a mechanism was proposed for the formation of MCSGO based on electron transfer-induced energy lowering. In addition, MCSGO still adsorbed 199.41 mg g−1 and 193.96 mg g−1 of Hg(II) and Zn(II), respectively, after six consecutive cycles, thereby demonstrating its favorable removal efficiency. The results obtained in this study may facilitate the development of efficient adsorbents based on the MCSGO architecture for environmental remediation.

Demystifying the roles of single metal site and cluster in CO2 reduction via light and electric dual-responsive polyoxometalate-based metal-organic frameworks.

Photo- or electroreduction of carbon dioxide into highly valued products offers a promising strategy to achieve carbon neutrality. Here, a series of polyoxometalate-based metal-organic frameworks (M-POMOFs) were constructed by metalloporphyrins [tetrakis(4-carboxyphenyl)-porphyrin-M (M-TCPPs)] and reductive POM for photo- and electrocatalytic carbon dioxide reductions (PCR and ECR, respectively), and the mysteries between the roles of single metal site and cluster in catalysis were disclosed. Iron-POMOF exhibited an excellent selectivity (97.2%) with high methane production of 922micromoles per gram in PCR, together with superior Faradaic efficiency for carbon dioxide to carbon monoxide (92.1%) in ECR. The underlying mechanisms were further clarified. Photogenerated electrons transferred from iron-TCPP to the POM cluster for methane generation under irradiation, while the abundant electrons flowed to the center of iron-TCPP for carbon monoxide formation under the applied electric field. The specific multielectron products generated on iron-POMOF through switching driving forces to control electron flow direction between single metal site and cluster catalysis.

Resonantly Enhanced Electromigration Forces for Adsorbates on Graphene.

We investigate the electromigration forces for weakly bonded adsorbates on graphene by using density-functional based calculations. We find that the nature of electromigration forces on an adsorbate critically depends on the energy level alignment between the adsorbate state and the Fermi level of the graphene. For a resonant adsorbate, whose frontier orbitals lie close to the Fermi level, the electromigration force is dominated by the electron wind force that is strongly enhanced along the electron flow direction, irrespective of the sign of the adsorbate charge. For a nonresonant adsorbate, the electromigration force is essentially the direct force that depends on the adsorbate charge. We also show that the magnitude of electromigration forces can be continuously tunable through electrostatic gating for resonant adsorbates. Our results provide new insight for understanding and controlling how nanoscale objects behave in or on host materials.