Interfacial Electron Transfer Dynamics Research Articles

Hydrogen bond-assisted construction of MOF/semiconductor heterojunction photocatalysts for highly efficient electron transfer

It remains challenging for the fabrication of metal-organic framework (MOF)/semiconductor heterojunction photocatalysts with close contact interfaces. In this work, a novel MOF/semiconductor heterojunction photocatalyst consisting of H2O2-modified TiO2 nanotubes (H2O2-TNTs) and MIL-88B(Fe)-NH2 (labeled as H-T/M) was firstly constructed based on the hydrogen-bonded combination between the O atoms from –OOH groups resulting from H2O2 absorbed on the surface of TiO2 nanotubes and the H atoms of the –NH2 group in MOF. The significantly enhanced photocatalytic property of the H-T/M heterojunction for reducing Cr(VI) could be ascribed to the accelerated interfacial electron transfer dynamics by a channel of hydrogen bonds (N···H–O–O–Ti), which could be extracted from the femtosecond transient absorption spectroscopy (fs-TAS). Moreover, the built-in electric field and the differences in charge density based on density functional theory (DFT) calculations could provide the driving force for charge transfer.

Interfacial electron transfer of perylenes: Influence of the anchor binding mode.

Interfacial electron transfer (IET) through saturated single-linker and dual-linker groups from a perylene chromophore into nanostructured TiO2 films was studied by ultrafast spectroscopy. Perylene chromophores with one and two propanoic acid linker groups in the peri and ortho positions were investigated. In comparison to previously studied perylenes bound via unsaturated acrylic acid linkers, the chromophores with saturated linkers showed bi-exponential IET dynamics. Two distinct transfer times were observed that indicate the presence of two concurrent binding modes. A comparison between ortho- and peri-substituted sensitizers resulted in slower IET dynamics and weaker electronic coupling for ortho substitution. Finally, IET from sensitizers with saturated linker groups is neither promoted nor hindered by a second linker group. This indicates that only one of the two linkers binds covalently to the surface. This study reveals the importance of the anchor-binding mode and design considerations of the linker for regulating IET.

Anchor Group Effects in Ruthenium (II) Photosensitizers Bearing N-Heterocyclic Carbene and Polypyridyl Ligands for DSSCs: A Computational Evaluation

In this work, we evaluate the bonding characteristics and interfacial electron transfer dynamics of three heteroleptic ruthenium photosensitizers featuring different terpyridine (tpy) acceptor end configurations through quantum-chemical calculations. These photosensitizers...

Efficient Charge Transfer in the Perovskite Quantum Dot-Hemin Biocomposite: Is This Effective for Optoelectronic Applications?

Inorganic perovskite quantum dots (PQDs) have great potential for optoelectronic applications as a result of their tunable optical properties, significant absorption coefficient, and high mobility. Combining PQDs with molecular adsorbates offers exciting possibilities for future applications, making it important to study interfacial electron transfer in PQD-molecular composites. Here, we present a study of PQD and hemin composites (PQD-hemin) to understand how their interfacial electron transfer dynamics are affected by adsorbate and PQD properties. Our femtosecond ultrafast transient absorption and time-resolved photoluminescence (TRPL) studies reveal that hot carrier relaxation, charge separation, and charge recombination processes are significantly impacted in the PQD-hemin composite system under different excitations, both higher and lower energy. Additionally, our alternating current (AC)- and direct current (DC)-bias-driven electrical studies show that, despite efficient charge separation in the PQD-hemin composite system, the light-induced transient photocurrent drops. The findings on the PQD-molecular composite will give useful outlooks for designing a variety of optoelectronic devices.

Plasmonic Nanozyme of Graphdiyne Nanowalls Wrapped Hollow Copper Sulfide Nanocubes for Rapid Bacteria‐Killing

AbstractPlasmon stimulation represents an appealing way to modulate enzyme mimic functions, but utilization efficiency of plasmon excitation remains relatively low. To overcome this drawback, a heterojunction composite based on graphdiyne nanowalls wrapped hollow copper sulfide nanocubes (CuS@GDY) with strong localized surface plasmon resonance (LSPR) response in the near‐infrared (NIR) region is developed. This nanozyme can concurrently harvest LSPR induced hot carriers and produce photothermal effects, resulting in dramatically increased peroxidase‐like activity when exposed to 808 nm light. Both experimental results and theoretical calculations show that the remarkable catalytic performance of CuS@GDY is due to the unique hierarchical structure, narrow bandgap of GDY nanowalls, LSPR effect of CuS nanocages, fast interfacial electron transfer dynamics, and carbon vacancies on CuS@GDY. This plasmonic nanozyme exhibits rapid, efficient, broad‐spectrum antibacterial activity (>99.999%) against diverse pathogens (methicillin‐resistant Staphylococcus aureus, Staphylococcus aureus, and Escherichia coli). This study not only sheds light on the mechanism of the nanozyme‐/photocatalysis coupling process, but also opens up a new avenue for engineering plasmonic NIR light driven nanozymes for rapid synergistic photothermal and photo‐enhanced nanozyme therapy.

Tuning the Conduction Band for Interfacial Electron Transfer: Dye-Sensitized SnxTi1–xO2 Photoanodes for Water Splitting

Interfacial electron transfer (IET) dynamics in dye-sensitized SnxTi1–xO2 (x = 0, 0.25, 0.50, 0.75, and 1) were investigated using ultrafast transient absorption spectroscopy, linear absorption spe...

Superior surface electron energy level endows WP2 nanowire arrays with N2 fixation functions

Nitrogen reduction reaction (NRR) under ambient conditions is always a long-standing challenge in science, due to the extreme difficulty in breaking the strong NN triple bond. The key to resolving this issue undoubtedly lies in searching superior catalysts to efficiently activate and hydrogenate the stable nitrogen molecules. We herein evaluate the feasibility of WP2 for N2 activation and reduction, and first demonstrate WP2 with an impressive ammonia yield rate of 7.13 μg h−1 cm−2, representing a promising W-based catalyst for NRR. DFT analysis further reveals that the NRR catalysis on WP2 proceeds in a distal reaction pathway, and the exceptional NRR activity is originated from superior surface electron energy level matching between WP2 and NRR potential which facilitates the interfacial proton-coupled electron transfer dynamics. The successfully unraveling the intrinsic catalytic mechanism of WP2 for NRR could offer a powerful platform to manipulate the NRR activity by tuning the electron energy levels.

Molecular design of porphyrin dyes using different electron-withdrawing moieties for high performance dye-sensitized solar cells

In spite of having some favorable light harvesting properties, porphyrins are still inferior to ruthenium dyes in dye sensitized solar cells. Nevertheless, there are enormous scope for improving the efficacy of these dyes. To recognize the connection between the structure and light-harvesting properties, herein, we have made a systematic theoretical investigation on a series of Zn-porphyrin dyes. We have explored the effect of benzodithiazole based model acceptor groups on their photovoltaic properties, especially on the electron injection dynamics with TiO2 photoanode. The model dyes show enhance light absorption in the entire visible region of solar spectrum in comparison to the parent dye which has been synthesized recently. The interfacial electron transfer (IET) dynamics reveals that suitable heteroatom substitution in acceptor group offers faster (sub-picosecond) electron injection as compared to the parent dye.

Regulated surface potential impacts bioelectrogenic activity, interfacial electron transfer and microbial dynamics in microbial fuel cell

Influence of surface anode potential on the performance of microbial fuel cell (MFC) was evaluated by opting positive and negative poised anode potentials (+100/-100 mV) on two MFCs, and studied at two phases (during potential (DP) and post potential (PP)) along with a third MFC operated as control (no applied anode potential). Variation in physico-chemical factors as well as biocatalytic metabolic behavior was analyzed in terms of electron transfer, power density, electro-kinetics and microbial community. Post potential operation at −100 mV depicted rapid electron transfer, higher redox catalytic currents (−0.44/0.42 mA) and voltage (653 ± 28 mV) in comparison to other experimental conditions. Disparity in electron carriers is noticed at both the phases with +100 mV (dominantly direct electron transfer)/-100 mV (cytochrome components) potential as well as control (non-specific and multiple carriers) which signify alteration in electron transfer mechanism aligned with change in surface potential. Microbial community analysis depicted the enrichment of exo-electrogenic bacteria belonging to phylum Proteobacteria (Gram negative bacteria) dominant at −100 mV, while Firmicutes (Gram positive bacteria) at +100 mV and a mixed bacterial population at control. Electrochemical investigations correlated with biological efficiency of MFC, which discerns a way to comprehend the underlying electron transfer process triggered in response to change in anode potential.

Excimer-Mediated Intermolecular Charge Transfer in Self-Assembled Donor-Acceptor Dyes on Metal Oxides.

When conjugate molecules are self-assembled on the surface of semiconductors, emergent properties resulting from the electronic coupling between the conjugate moieties are of importance in the interfacial electron-transfer dynamics for photoelectrochemical and optoelectronics devices. In this work, we investigate the self-assembly of triphenylamine-oligothiophene-perylenemonoimide (PMI) molecules, denoted as BH4, on metal oxide surfaces via UV-vis absorption, photoluminescence, and transient near-infrared absorption spectroscopies and molecular dynamics simulations, and we report the excimer formation due to the π-π interaction of the PMI units between the neighboring dye molecules. To our best knowledge, this is the first experimental observation of intermolecular excimer formation when conjugate donor-acceptor molecules form a self-assembled monolayer. In addition, a long-lived (4.3 μs) intermolecular charge separation is observed, and a new excimer-mediated intermolecular charger-transfer mechanism is proposed. This work demonstrates that, through the design of dye molecules, the excited complexes or aggregates can provide a pathway to slow down the recombination rate in photoelectrodes that utilize donor-acceptor dyad molecules.

Gold nanoparticles stabilized by modified halloysite nanotubes for catalytic applications

A highly sustainable prototype of a flow system based on gold nanoparticles (4.2 nm) supported on thiol‐functionalized halloysite nanotubes (HNTs) was developed for catalytic applications. The catalytic performances were evaluated using the reduction of 4‐nitrophenol to 4‐aminophenol as a model system. Under the best experimental conditions (0.0001 mol%, 1.97 × 10−8 mg of Au nanoparticles), an impressive apparent turnover frequency value up to 2 204 530 h−1 was achieved and the halloysite‐based catalyst showed full recyclability even after ten cycles. The high catalytic activity confirms the importance of the use of HNTs as support for Au nanoparticles that can exert a synergistic effect both as medium for transfer of electrons from borohydride ions to 4‐nitrophenol and by modulating interfacial electron transfer dynamics. With the application of flow technology, the obtained heterogeneous HNT@Au catalyst was fully recovered and reused for at least one month.

Influence of one-dimensional TiO2 nanotube on interfacial electron transfer in dye-sensitized solar cells: Insights from theoretical investigation

A theoretical study has been carried out on the composed systems of two different kinds of dye molecules (bearing the carboxylate and the hydroxamate anchors, respectively) and TiO2 nanotubes (TiO2 NTs). Our results show that the structure of (12,0) TiO2 NT is similar to that of anatase, while the (0,4) TiO2 NT shows obvious structural deformation along the direction that is vertical to the axis of nanotube. Compared with carboxylate anchor, the highly water-stable hydroxamate anchor exhibits better light-harvesting ability. In addition, the hydroxamate anchor group also exhibits a slightly stronger binding to the TiO2 NT surface than the carboxylate anchor group. The interfacial electron transfer (IET) dynamics reveal that both of the two TiO2 NTs can provide much faster and more complete IET as compared with bulk TiO2. The plots of electronic isosurfaces show different electron transfer mechanisms for (12,0) and (0,4) TiO2 NTs. In (12,0) TiO2 NT, the optical-excited electrons can transfer on the surface of the nanotube with directions both parallel and vertical to the nanotube axis. While for (0,4) TiO2 NT, the electrons can only transfer on the surface along the nanotube axis. Our study is expected to promote the further development of such one dimensional nanotube in enhancing performance of DSSCs and in other optical-excited related applications.

Deciphering the Modulation Essence of p Bands in Co-Based Compounds on Li-S Chemistry

Summary Despite the fact that metal-based compounds have been extensively used as sulfur cathode additives, large variations in electrochemical performance have been commonly observed from one material to another, which cannot be simply explained by the adsorption capability. Herein, we have systematically studied the kinetic behaviors of Li-S chemistry on Co-based compounds with fixed metal cation and varied non-metal anions, and deciphered the intrinsic modulation essence of the anions. Among the Co-based compounds, CoP exhibits the lowest overpotential for polysulfide transformation. Even at 40.0 C, S@CoP/rGO still delivers a high capacity of 417.3 mA hr g−1 and an unprecedented power density of 137.3 kW kg−1, representing the best rate performance. DFT analysis reveals that the performance variations mainly originate from the shift of p band centers, which modulate the interfacial electron transfer dynamics. This work could unlock the potential of band engineering for Li-S batteries and beyond.

Effects of Al2O3 atomic layer deposition on interfacial structure and electron transfer dynamics at Re-bipyridyl complex/TiO2 interfaces

Atomic layer deposition (ALD) of oxide layers on sensitizer- and/or catalyst-functionalized semiconductor surfaces have been used to improve the stability of dye-sensitized solar cells and photoelectrosynthesis cells. However, how the ALD layer affects the interfacial structure of adsorbed molecules and interfacial electron transfer dynamics is still unclear. Herein, we investigated the effects of ALD of Al2O3 on adsorption structure of Re bipyridyl complex on TiO2 nanocrystalline films and rutile (0 0 1) single crystals by IR absorption and sum frequency generation spectroscopy. Further, the electron transfer dynamics between the Re complex and TiO2 film was also examined by ultrafast infrared transient absorption spectroscopy. Our results show that the electron injection yield decreases with the increase of ALD layer thickness.

Evidence that ΔS‡ Controls Interfacial Electron Transfer Dynamics from Anatase TiO2 to Molecular Acceptors.

Recombination of electrons injected into TiO2 with molecular acceptors present at the interface represents an important loss mechanism in dye-sensitized water oxidation and electrical power generation. Herein, the kinetics for this interfacial electron transfer reaction to oxidized triphenylamine (TPA) acceptors was quantified over a 70° temperature range for para-methyl-TPA (Me-TPA) dissolved in acetonitrile solution, 4-[N,N-di(p-tolyl)amino]benzylphosphonic acid (a-TPA) anchored to the TiO2, and a TPA covalently bound to a ruthenium sensitizer, [Ru(tpy-C6H4-PO3H2)(tpy-TPA)]2+ "RuTPA", where tpy is 2,2':6',2''-terpyridine. Activation energies extracted from an Arrhenius analysis were found to be 11 ± 1 kJ mol-1 for Me-TPA and 22 ± 1 kJ mol-1 for a-TPA, values that were insensitive to the identity of different sensitizers. Recombination to RuTPA+ proceeded with Ea = 27 ± 1 kJ mol-1 that decreased to 19 ± 1 kJ mol-1 when recombination occurred to an oxidized para-methoxy TPA (MeO-TPA) dissolved in CH3CN. Eyring analysis revealed a smaller entropy of activation |ΔS‡| when the a-TPA was anchored to the surface or covalently linked to the sensitizer, compared to that when Me-TPA was dissolved in CH3CN. In all cases, Eyring analysis provided large and negative ΔS‡ values that point toward unfavorable entropic factors as the key contributor to the barrier that underlies the slow recombination kinetics that are generally observed at dye-sensitized TiO2 interfaces.

Direct Interfacial Electron Transfer from High-Potential Porphyrins into Semiconductor Surfaces: A Comparison of Linkers and Anchoring Groups

This study probes a series of linkers and anchoring groups for direct interfacial electron transfer (IET) from high-potential porphyrins into semiconductor surfaces. Eight different linker–anchor combinations of CF3-substituted, high-potential porphyrins were designed, synthesized, and characterized. Specifically, a series of four anchors was examined (carboxylate, hydroxamate, phosphonate, and silatrane), along with two different linkers (phenylene and benzanilidylene), which differ in terms of their electronic conjugation and overall length. The electrochemical and photophysical properties of the porphyrins were evaluated by steady-state and transient spectroscopies in solution and on mesoporous SnO2 substrates for use as dye photosensitizers in aqueous photoelectrochemical cells. IET dynamics were measured using time-resolved terahertz (TRTS) and transient absorption spectroscopies. From TRTS measurements, injection yields were determined relative to a commonly used phosphonated ruthenium(II) polypyrid...

Well-Coupled Nanohybrids Obtained by Component-Controlled Synthesis and in Situ Integration of MnxPdy Nanocrystals on Vulcan Carbon for Electrocatalytic Oxygen Reduction

Development of cheap, highly active, and robust bimetallic nanocrystal (NC)-based nanohybrid (NH) electrocatalysts for oxygen reduction reaction (ORR) is helpful for advancing fuel cells or other renewable energy technologies. Here, four kinds of well-coupled Mn xPd y(MnPd3, MnPd-Pd, Mn2Pd3, Mn2Pd3-Mn11Pd21)/C NHs have been synthesized by in situ integration of Mn xPd y NCs with variable component ratios on pretreated Vulcan XC-72 C using the solvothermal method accompanied with annealing under Ar/H2 atmosphere and used as electrocatalysts for ORR. Among them, the MnPd3/C NHs possess the unique "half-embedded and half-encapsulated" interfaces and exhibit the highest catalytic activity, which can compete with some currently reported non-Pt catalysts (e.g., Ag-Co nanoalloys, Pd2NiAg NCs, PdCo/N-doped porous C, G-Cu3Pd nanocomposites, etc.), and close to commercial Pt/C. Electrocatalytic dynamic measurements disclose that their ORR mechanism abides by the direct 4e- pathway. Moreover, their durability and methanol-tolerant capability are much higher than that of Pt/C. As revealed by spectroscopic and electrochemical analyses, the excellent catalytic performance of MnPd3/C NHs results from the proper component ratio of Mn and Pd and the strong interplay of their constituents, which not only facilitate to optimize the d-band center or the electronic structure of Pd but also induce the phase transformation of MnPd3 active components and enhance their conductivity or interfacial electron transfer dynamics. This work demonstrates that MnPd3/C NHs are promising methanol-tolerant cathode electrocatalysts that may be employed in fuel cells or other renewable energy option.

Au–Cd1−xZnxS core–alloyed shell nanocrystals: boosting the interfacial charge dynamics by adjusting the shell composition

Modulating the interfacial electron transfer dynamics of Au–Cd1−xZnxS core–shell nanocrystals by means of shell composition adjustment has been proposed and realized.

Dependences of the Optical Absorption, Ground State Energy Level, and Interfacial Electron Transfer Dynamics on the Size of CdSe Quantum Dots Adsorbed on the (001), (110), and (111) Surfaces of Single Crystal Rutile TiO2

Quantum dots (QDs) provide an attractive alternative sensitizer to organic dyes. However, there have been few reports on QD-sensitized solar cells (QDSCs) that have photovoltaic conversion efficiencies exceeding those of dye-sensitized solar cells. This is because of the lack of fundamental studies of QDs on conventional nanocrystalline metal oxide electrodes which possess much amount of heterogeneity. An important first step is an investigation of the dependences of the optical absorption, the ground state energy level, and the interfacial electron transfer (IET) on the size of QDs deposited on well characterized single crystal oxides. The present study focuses on a system of CdSe QDs adsorbed on the (001), (110), and (111) surfaces of single crystal rutile-TiO2. The optical absorption spectra, characterized using photoacoustic spectroscopy, were found to be independent of the surface orientation concerning the optical absorption edge. The exponential optical absorption tail (Urbach tail) suggests that t...

Electron Transfer from Bi-Isonicotinic Acid Emerges upon Photodegradation of N3-Sensitized TiO2 Electrodes.

The long-term stability of dye-sensitized solar cells (DSSCs) is determined to a large extent by the photodegradation of their sensitizers. Understanding the mechanism of light-induced decomposition of dyes sensitizing a mesoporous oxide matrix may therefore contribute to solutions to increase the life span of DSSCs. Here, we investigate, using ultrafast terahertz photoconductivity measurements, the evolution of interfacial electron-transfer (ET) dynamics in Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 (N3) dye-sensitized mesoporous TiO2 electrodes upon dye photodegradation. Under inert environment, interfacial ET dynamics do not change over time, indicating that the dye is stable and photodegradation is absent; the associated ET dynamics are characterized by a sub-100 fs rise of the photoconductivity, followed by long-lived (≫1 ns) electrons in the oxide electrode. When the N3-TiO2 sample is exposed to air under identical illumination conditions, dye photodegradation is evident from the disappearance of the optical absorption associated with the dye. Remarkably, approximately half of the sub-100 fs ET is observed to still occur but is followed by very rapid (∼10 ps) electron-hole recombination. Laser desorption/ionization mass spectrometry, attenuated total reflection-Fourier transform infrared, and terahertz photoconductivity analyses reveal that the photodegraded ET signal originates from the N3 dye photodegradation product as bi-isonicotinic acid (4,4'-dicarboxylic acid-2,2'-bipyridine), which remains bonded to the TiO2 surface via either bidentate chelation or bridging-type geometry.