Electron-hole Transfer Research Articles

Immobilization of Metal-Organic Framework MIL-100(Fe) on the Surface of BiVO4: A New Platform for Enhanced Visible-Light-Driven Water Oxidation.

The development of new dual functional photocatalysts is highly desirable for conversion and storage of solar energy. Herein, we first constructed hierarchical structure MIL-100(Fe)@BiVO4 in situ growing MIL-100(Fe) nanoparticles (NPs) on the surface of decahedron BiVO4 under mild hydrothermal conditions. The as-synthesized hybrid nanostructure is unambiguously determined using a series of characterization methods. These results demonstrate that the ultra-tiny MOF MIL-100(Fe) particles are immobilized on the surface of decahedron BiVO4 and the composite exhibits a strong interaction between BiVO4 and MIL-100(Fe). This hybrid material MIL-100(Fe)@BiVO4 is employed as a photocatalyst for water oxidation reaction and demonstrates higher O2 production activity in comparison with bare BiVO4. The best performance obtained at the optimal mass percentage of MIL-100(Fe) (8.0 wt %) reaches 333.3 μmol h-1 g-1 of the O2 evolution rate irradiated with visible light, which is almost 4.3 times higher than bare BiVO4 (77.3 μmol h-1 g-1). The enhanced water oxidation performance is due to the more efficient interfacial electron-hole transfer between MIL-100(Fe) and BiVO4, which is verified by the results of various photo-electrochemical characterizations. Moreover, the as-prepared composite MIL-100(Fe)@BiVO4 also displays excellent stability for visible-light-driven water oxidation. This study affords a rational strategy for the controllable construction by loading metal-organic frameworks on a semiconductor surface, which is a good reference for other artificial photosystems.

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation.

Herein, CuO/Bi2MoO6 hybrid nanosheets were prepared as a surface multifunctional photocatalyst for gas-phase toluene oxidation with high conversion (>99%). Aberration-corrected scanning transmission electron microscopy suggested that CuO species were highly dispersed on the nanosheets. X-ray absorption fine structure spectra indicated that the distorted and stretched Cu-O coordination structures in CuO/Bi2MoO6 nanosheets would provide open active sites. In situ Fourier transform infrared and density functional theory results showed that toluene molecules could be chemisorbed and activated on the active sites of CuO/Bi2MoO6 nanosheets by the C-H group forming CuO/Bi2MoO6···Ph-CH3 surface complex compounds. These would induce electron-hole transfer and initiate photocatalytic reactions under visible light irradiation. The corresponding intermediates of benzaldehyde and benzoic acid would be detected by in situ diffuse reflectance infrared Fourier transform spectroscopy. Furthermore, the synergistic effect of CuO and Bi2MoO6 nanosheets could monitor charge dynamics to facilitate their respective transmission from photoexcitation sites to active centers. This work provides new insights into the essence of visible-light-driven surface photocatalysis and is expected to promote the design of novel and more effective photocatalysts at the molecular level.

Advances in molecular engineering of organic-inorganic/inorganic halide perovskites: Photochemical properties behind the energy conversion ability

Here, molecular engineering of the organic-inorganic/inorganic halide perovskites indicates the role of cation, anion and halide components on the efficiency of the perovskite solar cells (PVSCs). The frontier molecular orbitals alignment of the ABX3 perovskites (A = Im; Imidazolium, Az; Azetidinium, Hy; Hydrazinium, Cs, Rb, Tl, B = Pb, Sn, Ge, X = Br, Cl, I) showed a balanced electron-hole transfer. The cation and halide ion are the main parts of the charge transfer from the dynamic viewpoint, while the exciton formation/dissociation rates, Rd/Ra, are mainly affected by BX3 anion. In addition to Cs+ and Rb+, Im+-based perovskites show an effective charge transfer distance and electron-hole (e-h) overlap, which makes them good excitation modes. I-based perovskites represent a higher response to the electric field, originated from their less electronic chemical harness. According to final efficiency, Cs+, Rb+, and Az+-based perovskites are introduced as the best photosensitizers.

Ultrafast Charge Separation and Recombination across a Molecule/CsPbBr3 Quantum Dot Interface from First-Principles Nonadiabatic Molecular Dynamics Simulation

All-inorganic perovskite quantum dots (QDs) hold great promise in photovoltaic solar cells. However, the reduced dimensionality of QDs confines the photoexcited electron–hole pairs, suppresses charge separation, and accelerates charge recombination (CR), limiting the photon-to-electron conversion efficiency of a solar cell. Molecule passivation can overcome this shortcoming via efficiently extracting charge carriers from QDs. Using a combination of time-domain density functional theory and nonadiabatic (NA) molecular dynamics, we demonstrate that low-frequency vibrations promoted both charge separation and recombination. The photoexcited excitons on a CsPbBr3 QD can efficiently dissociate into free charge carriers via rapid interfacial electron transfer (ET) and hole transfer (HT) to a binding benzoquinone (BQ) and a phenothiazine (PTZ) molecule on similar sub-100 ps time scales, respectively. This is manifested by the fact that the QD-BQ system holds smaller energy gap and NA coupling between the donor a...

Synergistic adsorption and photocatalytic reduction of Cr(VI) using Zn-Al-layered double hydroxide and TiO2 composites

Abstract Three TiO2 and Zn-Al-layered double hydroxide composites, denoted LDH-TiO2 composites, were prepared using the sol–gel method and characterized utilizing scanning and transmission electron microscopy with energy dispersive spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, X-ray diffraction, N2 adsorption–desorption, X-ray photoelectron spectroscopy, photocurrent, photoluminescence and electrochemical impedance spectroscopy techniques. The characterization results illustrated that TiO2 was attached onto the surface of LDH and the sizes of both TiO2 and LDH particles were in the nanoscale range. The combination of LDH and TiO2 promoted the photogenerated electron–hole transfer and separation. The removal abilities of the LDH-TiO2 composites for Cr(VI) were evaluated using the synergistic adsorption and photocatalytic method. The adsorption percentages of the three LDH-TiO2 composites for 20.0 mg/L Cr(VI) solutions ranged between 26% and 75%, and upon ultraviolet irradiation, the total removal percentages rapidly increased to approximately 100%. The removal efficiency for Cr(VI) depended on the TiO2 contents of the LDH-TiO2 composites. Increasing the TiO2 percentage resulted in decrease in the adsorption capacities and increase in the photocatalytic removal ratios. The kinetic and isothermal data well fitted the pseudo-second-order and Langmuir equations, respectively. The high removal efficiencies suggested that the composites were suitable for the treatment of Cr(VI)-containing wastewater.

Effective Electron–Hole Separation Over Controllable Construction of CdS/Co-Ni-P Core/Shell Nanophotocatalyst for Improved Photocatalytic Hydrogen Evolution Under Visible-Light-Driven

In artificial photocatalysis, the slow kinetics of electron–hole transfer and high charge recombination rate have been the Achilles heel of photocatalytic conversion efficiency. Therefore, methods for promoting exciton splitting and charge separation have received sustained attention. Here, Co-Ni-P is used as a molecular cocatalyst, which is designed onto the surface of cadmium sulfide nanorods. CdS-Co-Ni-P constitutes a unique CdS/Co-Ni-P core/shell structure, which is a new type of efficient heterostructure photocatalysts used for photocatalytic decomposition of water to produce hydrogen. The modification strategy maximizes the contact area between the cocatalyst and the reactant, which effectively increases the light absorption capacity of the composite catalyst, reduces the overpotential of generating hydrogen, and accelerates the interface transfer rate of electron–hole pairs, thus achieving better photocatalytic decomposition of water. The reaction kinetics of the reduction is enhanced. Compared with pure CdS of the same quality, the optimal photocatalyst CdS-Co-Ni-P has a hydrogen evolution rate of 9.67 mmol g−1 h−1, which is about 5.3 times that of pure CdS. This work demonstrates that the new and efficient CdS/Co-Ni-P core/shell photocatalyst has great potential for photocatalytic production of H2.

Novel multilayer TiO2 heterojunction decorated by low g-C3N4 content and its enhanced photocatalytic activity under UV, visible and solar light irradiation

In this paper, we used a facile ball milling, microwave radiation and heating treatment method to achieve the surface modification of TiO2 with low g-C3N4 concentration, and a multilayer heterojunction composite with TiO2 as the main part and g-C3N4 as the modification agent was obtained. The obtained materials were analyzed by several characterizations to get information on their chemical composition, crystalline structure, vibrational features and optical properties. The photocatalytic performance was evaluated by degradation of rhodamine B (RhB) and methylene blue (MB) under UV, visible and direct solar light irradiation. Its photocatalytic activity was enhanced depended on the novel structure of g-C3N4/TiO2 hybrid and the special Z-scheme electron-hole transfer model of multilayer heterointerfaces. The material preparation and structural features could be useful for the design and development of other photocatalysts with high photocatalytic activity.

Unveiling the interfacial electrochemiluminescence behavior of lead halide perovskite nanocrystals.

In this study, a three-phase heterostructure interface including glassy carbon (conducting medium), CsPbBr3 perovskite nanocrystals (PNCs, emitter) and acetonitrile (electrolyte) is constructed for fully investigating the interfacial electrochemiluminescence (ECL) behavior of CsPbBr3 PNCs. We find that these interfaces serve as bridges for efficient electron–hole transfer during the ECL process. As a proof of concept, the increase of the heterostructure interface area will accordingly enhance the ECL intensity of CsPbBr3 PNCs. About seven-fold enhancement of the ECL intensity could be achieved when the interface area has triple-fold increase, which provides a new perspective to construct more efficient ECL systems via interface engineering.

High-Performance Fullerene-Free Polymer Solar Cells Featuring Efficient Photocurrent Generation from Dual Pathways and Low Nonradiative Recombination Loss

Efficient charge generation is a prerequisite to achieve high power conversion efficiency (PCE) in organic/polymer solar cells (OSCs/PSCs), which involves photoinduced electron transfer and/or hole transfer between the donor/acceptor interface upon photoexcitation. A high yield of charge from both processes usually requires sufficient energy offset between the donor and acceptor for charge separation, fast transport, and extraction for charge collection, as well as significant absorption complementation to maximize photon harvest. Here we demonstrate highly efficient PSCs with efficient dual photocurrent generation pathways from a blend of a polymer donor and two narrow-bandgap nonfullerene acceptors, with an outstanding certified PCE of 13.0% (verified as 12.5%) in PSCs with single-junction device architecture. The devices from these material systems show nonradiative recombination loss of ∼0.22–0.24 V, one of the smallest values for OSCs achieved so far and comparable to those of solar cells based on mo...

Isotype heterojunction g-C3N4/g-C3N4 nanosheets as 2D support to highly dispersed 0D metal oxide nanoparticles: Generalized self-assembly and its high photocatalytic activity

Graphitic carbon nitride (g-C3N4) has attracted increasing interest in recent years as a metal-free polymeric photocatalyst for water splitting and degradation of organic pollutants. However, the relatively low photocatalytic activity and serious aggregation of g-C3N4 nanosheets substantially limit its applications. Herein, we propose a generalized and facile bottom-up approach to self-assembly synthesis of isotype heterojunction g-C3N4/g-C3N4 nanosheets/0D metal oxide nanoparticles hierarchical architectures, in which the highly dispersed 0D metal oxide (CeO2 and ZnO as representatives) nanoparticles are anchored on 2D flexible g-C3N4/g-C3N4 heterojunction nanosheets, and the former can be spatially separated by the latter as well. The pyrolysis-induced gases play a critical role in the construction of unique 0D metal oxide/2D g-C3N4/g-C3N4 (metal oxide/CN-UT) hierarchical architectures, which possess improved light harvesting and pollutant adsorption capacity, as well as enhanced separation of photoinduced charge carriers via the three-level electron–hole transfer process owing to the intimate contact between constituents and band alignment among them. As a result, the obtained metal oxide/CN-UT exhibits extraordinary photocatalytic performance under natural sunlight and indoor light illumination. This work demonstrates a generalized bottom-up synthetic method to design efficient composite photocatalysts by adopting integrative nanostructure engineering and a cocatalyst strategy and highlights the promising applications in the field of energy and environment.

Interfacial engineering in colloidal “giant” quantum dots for high-performance photovoltaics

Colloidal quantum dots (QDs) are semiconductor nanocrystals which exhibit discrete energy levels. They are promising building blocks for optoelectronic devices, thanks to their tunable band structure. Here, we explore a nanoengineering approach to highlight the influence of an alloyed interface on the optical and electronic properties of CdSe/(CdS)6 “giant” core/shell (CS) QDs by introducing CdSexS1-x interfacial layers between core and shell. By incorporating of CdSexS1-x interfacial layers, CdSe/(CdSexS1-x)4/(CdS)2 (x = 0.5) core/shell (CSA1) QDs exhibit a broader absorption response towards longer wavelength and higher electron-hole transfer rate due to favorable electronic band alignment with respect to CS QDs, as confirmed by optical absorption, photoluminescence (PL) and transient fluorescence spectroscopic measurements. In addition, simulations of spatial probability distributions show that the interface layer enhances electron-hole spatial overlap. As a result, CSA1 QDs sensitized solar cells (QDSCs) yield a maximum photoconversion efficiency (PCE) of 5.52%, which is 79% higher than QDSCs based on reference CS QDs. To fully demonstrate the structural interface engineering approach, the CdSexS1-x interfacial layers were further engineered by tailoring the selenium (Se) and sulfur (S) molar ratios during in situ growth of each interfacial layer. This graded alloyed CdSe/(CdSexS1-x)5/(CdS)1 (x = 0.9–0.1) core/shell (CSA2) QDs show a further broadening of the absorption spectrum, higher carrier transport rate and modified confinement potential with respect to CSA1 QDs as well as reference CS QDs, yielding a PCE of 7.14%. Our findings define a promising approach to improve the performance of QDSCs and other optoelectronic devices based on CS QDs.

Directing Charge Transfer in Quantum Dot Assemblies.

The optical and electronic properties of semiconductor quantum dots (QDs) make them attractive candidates for applications in photovoltaics, spintronics, photocatalysis, and optoelectronics. Understanding how to control the flow of charge in QD assemblies is essential for realizing novel applications. This Account explores some unique characteristics of charge transport in QD dyads, triads, and their assemblies. The emerging features of these assemblies that provide new opportunities to manipulate charge flow at the nanoscale are (1) cascading energy landscapes and band offsets to inhibit charge recombination, (2) electrostatic fields that direct charge flow through QD-QD and QD-conjugated polymer junctions, and (3) QD chirality and chiral imprinting that promotes vectorial electron and spin selective transport. Charge flow kinetics is determined by a combination of familiar electron transfer parameters (reaction free energy, reorganization energy, and electronic coupling), donor and acceptor electronic densities of states, and internal electric fields. Electron transfer and electronic structure theory, combined with kinetic modeling, place the measured kinetics of QD electron transfer donor-acceptor assemblies into a unified conceptual context. The experimental transfer rates measured in these systems depend upon structure and the internal electric fields that are present in the assemblies. A negatively charged donor and positively charged acceptor, for example, facilitates (inhibits) electron (hole) transfer, while an electric field of opposite orientation (reversal of charges) inhibits (promotes) electron (hole) transfer. These and other emerging rules that govern charge flow in NP assemblies provide a strategy to design the directionality and yield of interfacial charge transport. Chirality at the nanoscale can induce spin selective charge transport, providing new ways to direct charge (and spin) flow in QD assemblies. Magnetoresistance and magnetic conductive probe atomic force microscopy experiments show spin selective electron transport for chirally imprinted QD assemblies. Photoinduced electron transfer from achiral donor-QDs to chiral acceptor-QDs depends on the electron spin and chiroptical properties of the acceptor-QDs. These assemblies show transport characteristics that correlate with features of the QDs' circular dichroism spectra, presenting intriguing challenges to theory, and indicating that spectroscopic signatures may assist in the design and diagnosis of functional molecular assemblies. Theoretical and experimental studies of charge transport in well-defined QD assemblies are establishing design principles for vectorial charge transport and are also refining questions surrounding the mechanism and control of these processes. These intensified efforts are forging links between fundamental discoveries regarding mechanism and practical applications for these novel assembled nanostructures.

Ultrafast Electron Attachment and Hole Transfer Following Ionizing Radiation of Aqueous Uridine Monophosphate.

The primary localization process of radiation-induced charges (holes (cation radical sites) and excess electrons) remains poorly understood, even at the level of monomeric DNA/RNA models, in particular, in an aqueous environment. We report the first spectroscopic study of charge transfer occurring in radiolysis of aqueous uridine 5'-monophosphate (UMP) solutions and its components: uridine, uracil, ribose, and phosphate. Our results show that prehydrated electrons effectively attach to the base site of UMP; the holes in UMP formed by either direct ionization or reaction of UMP with the radiation-mediated water cation radical (H2O•+) facilely localize on the ribose site, despite the fact that a part of them were initially created on either the phosphate or uracil. The nature of phosphate-to-sugar hole transfer is characterized as a barrierless intramolecular electron transfer with a time constant of 2.5 ns, while the base-to-sugar hole transfer occurs much faster, within a 5 ps electron pulse.

(Keynote) The Electrodeposition and Stripping of Lithium Peroxide for Applications in Lithium-Oxygen Battery

Thanks to a high theoretical energy density combined to a relatively high operation voltage around 3 Volt versus Li+/Li, the non-aqueous Li-Air battery is a good candidate for future electric cars with an increased driving range. In principle, this battery relies on the reversible electrochemical reaction between the metallic Li and the gaseous O2 in presence of a non-aqueous electrolyte where Li+ ions and dissolved O2 molecules diffuse and react to form the ideal discharge product lithium peroxide Li2O2. However this apparently simple reaction process appears to be more complicated when put into practice. Considering the Li-O2 discharge process, there are two main models proposed in the literature to explain the oxygen reduction reaction which were unified in a single mechanism process where Li2O2 formation goes through a surface reaction or/and a solution reaction1, depending on system parameters such as the applied potential or the solvent properties. Using an electrochemical quartz crystal microbalance (EQCM) we studied the products formed in discharge as well as the reversibility of the reactions from a mass point of view during cycling.2 Regarding the Li-O2 charge process, the Li2O2 decomposition occurring is a rather sluggish and incomplete process. A lot of efforts was made in this area by the research community including in the Toyota group, and several approaches were proposed to facilitate and fasten the Li2O2 decomposition: the use of solid state catalyst of several kind (doped carbon, non-precious materials…) or soluble catalysts also called redox mediators, such as for example TTF3 (tetrathiafulvalene), TEMPO4 (2,2,6,6-tetramethylpiperidinyloxyl), Cobalt Bis(terpyridine)5, lithium iodide6 (LiI). The mobile redox mediators, electron-hole transfer agents, aid the oxidation of Li2O2 as has been reported previously. In our EQCM study we activated in situ the TTF and confirms its usefulness on the mass reversibility of the deposition/dissolution of Li2O2 during cycling2. Later on, we performed a detailed study of the effect of LiI redox mediator on the formation and decomposition of Li2O2.7 We showed that the solvent could drastically change the mechanism of decomposition during charge8. Finally we will discuss the parameters able to influence the most the deposition and stripping of Li2O2 in a non-aqueous medium. 1 L. Johnson, C. Li, Z. Liu, Y. Chen, S. A. Freunberger, J. M. Tarascon, P. C. Ashok, B. B. Praveen, K. Dholakia, P. G. Bruce, Nature Chemistry, 6, 1091 – 1099 (2014). 2 S. Schaltin, G. Vanhoutte, M. Wu, F. Bardé, J. Fransaer, Phys. Chem. Chem. Phys. , 17, 12575 – 12586 (2015). 3 Y. Chen, S. A. Freunberger, Z. Peng, O. Fontaine, and P. G. Bruce, Nature Chemistry, 5, 489 – 494 (2013). 4 Y. Hase, J. Seki, T. Shiga, F. Mizuno, H. Nishikoori, H. Iba, K. Takechi, Chem. Commun., 52, 12151 – 12154 (2016). 5 Koffi P.C. Yao, J. T. Frith, S. Youssef Sayed, F. Bardé, J. R. Owen, Y. Shao-Horn, N. Garcia-Araez, J. Phys. Chem. C, 120 (30), 16290 – 16297 (2016). 6 Y. Qiao, S. Wu, Y. Sun, S. Guo, J. Yi, P. He, H. Zhou, ACS Energy Letters, 2, 8, 1869 – 1878 (2017). 7 M. Tulodziecki, G.M. Leverick, C.V; Amanchukwu, Y. Katayama, D.G. Kwabi, F. Bardé, P. Hammond, Y. Shao-Horn, Energy Environ. Sci., 10, 1828, (2017). 8 G. Leverick, M. Tułodziecki, R. Tatara, F. Bardé and Y. Shao-Horn, In Preparation

Preparation of CdS/BiOCl/Bi2O3 double composite system for visible light active photocatalytic applications

An efficient visible-light-harvesting (λ ≥ 420 nm) three component system heterojunction photocatalyst, CdS/BiOCl/Bi2O3 was prepared by anchoring of CdS nanoparticles on the surface of BiOCl/Bi2O3 composite. The effect of CdS nanoparticles on the surface of BiOCl/Bi2O3 composite photocatalyst had been justified in enhancing photocatalytic activity towards the degradation of organic pollutants in gas as well as aqueous phase. With the loading of CdS on to the BiOCl/Bi2O3 heterojunction composite photocatalyst, the photocatalytic activity of the CdS/BiOCl/Bi2O3 composite structure has been appreciably improved for the decomposition of 2-propanol (IPA) in gas phase and salicylic acid (SA) in aqueous phase under visible light irradiation (λ ≥ 420 nm). The amount of loading of CdS nanoparticles was optimized to 2 mol% CdS/BiOCl/Bi2O3. Compare to bare BiOCl/Bi2O3 photocatalyst, CdS/BiOCl/Bi2O3 heterojunction demonstrated 2 times decomposition of IPA in gas phase and 1.8 times of SA in aqueous phase after 120 min. of visible light irradiation. At the same time, with this composition the evolution of CO2 from degradation of IPA was 1.9 times higher than that of BiOCl/Bi2O3 composite. The enhanced photocatalytic efficiency is deduced from the electron (eˉ) and hole (h+) transfer among the component semiconductor nanoparticles Bi2O3, BiOCl and CdS due to their relative energy band positions. Several experimental evidences were also provided to confirm the electron-hole transfer among the semiconductors and a mechanistic way has been proposed.

Amide Neighbouring‐Group Effects in Peptides: Phenylalanine as Relay Amino Acid in Long‐Distance Electron Transfer

In nature, proteins serve as media for long-distance electron transfer (ET) to carry out redox reactions in distant compartments. This ET occurs either by a single-step superexchange or through a multi-step charge hopping process, which uses side chains of amino acids as stepping stones. In this study we demonstrate that Phe can act as a relay amino acid for long-distance electron hole transfer through peptides. The considerably increased susceptibility of the aromatic ring to oxidation is caused by the lone pairs of neighbouring amide carbonyl groups, which stabilise the Phe radical cation. This neighbouring-amide-group effect helps improve understanding of the mechanism of extracellular electron transfer through conductive protein filaments (pili) of anaerobic bacteria during mineral respiration.

Stable All Solid State Z-Scheme Based TiO2/M/CdxZn1-Xs Photo-Catalysts for Efficient Hydrogen Generation

Water splitting to hydrogen and oxygen molecules suing semiconductors as photocatalysts to store solar energy, is one of the “Holy Grails” in solar energy conversion1. The performance of a photocatalyst is largely limited by four requirements: 1) long term stability with respect to photo corrosion, 2) a narrow band gap materials to absorb a large fraction of solar light, 3) suitable band edges that match the redox potential of water, and 4) slow charge carrier recombination systems. In particular, with respect to point 4, many artificial Z-scheme based photocatalytic systems have been widely investigated2. Recently, Rao et al.,3 reported an all-solid state Z-scheme anisotropic ZnO/Pt/Cd0.8Zn0.2S heterojunction system which exhibited a high photocatalytic activity owing to an efficient electron-hole transfer between the ZnO conduction band and the CdS valence band through Pt nanoparticles (using benzyl alcohol and acetic acid as sacrificial reagents). However, this system is not stable over the long term mainly because ZnO is stable in a very narrow pH range (6-8)4, whereas the ideal pH for hydrogen production, either by sacrificial or direct water splitting, is often outside this range. As a consequence, the original Z-scheme structure is gradually destroyed following the dissolution of the ZnO which subsequently causes the decomposition of Cd0.8Zn0.2S. In this work, we have developed a novel TiO2/Ag-Pd/Cd(Zn)S based Z-scheme photocatalytic system. This system was found to be stable in the presence of aqueous solution containing benzyl alcohol/acetic acid (the role of both has been investigated). Catalysts were prepared and characterized by XRD, XPS, TEM and UV-Vis and the catalytic tests were conducted over the complete series of the Z-Scheme system and its individual components such as Ag-Pd/TiO2 and Cd0.8Zn0.2S. The hydrogen generation rate of the best system and that of its components were 3.3 mmol/h.gcatal. (TiO2/Ag-Pd/Cd0.8Zn0.2S), 1.1 mmol/h.gcatal. (Ag-Pd/TiO2) and 0.5 mmol/h.g catal. (Cd0.8Zn0.2S) respectively under identical conditions as described below. Figure 1

A facile and scalable route for synthesizing ultrathin carbon nitride nanosheets with efficient solar hydrogen evolution

Two-dimensional (2D) graphene-like carbon nitride nanosheets (CN-S) with unique photoelectronic properties have received much attention in advanced photocatalysis applications. The challenge for the synthesis of this promising 2D metal-free nanomaterials is to develop a facile but scalable strategy. Herein we for the first time reported a feasible approach to prepare the few-layered CN-S by introduction urea as “bubble template” in the thermal polymerization process. Compared to the bulk carbon nitride (CN-B), the thin-layered CN-S with a thickness of around 4 nm possessed the large specific surface area, enlarge electronic-band structure, fast photogenerated electron-hole transfer capability, and increased charge lifetime. Eventually, the resulting CN-S not only had a relatively high yield of 44.5%, but also exhibited a superior photocatalytic hydrogen evolution activity (1400 μmol g-1 h-1) from water under visible-light irradiation (λ > 420 nm). This work highlights a cost-effective and strategy towards the one-step and large-scale production of high-performance CN-S photocatalysts for efficient solar-to-fuel conversion.

Ultrasonic assisted synthesis with enhanced visible-light photocatalytic activity of NiO/Ag3VO4 nanocomposite and its antibacterial activity

The NiO/Ag3VO4 nanocomposite photocatalysts were developed by ultrasonic assisted preparation method to study the photocatalytic activity under visible light irradiation. The samples were characterized by UV-DRS, XRD, FT-IR, XPS, SEM, EDX, TEM, EIS and BET analysis. The photocatalytic activity of NiO/Ag3VO4 nanocomposite for the photodegradation of 4-Nitro Phenol (4-NP) and Rose Bengal (RB) under visible light irradiation was studied and it is observed that the activity has been much higher than that of the pure Ag3VO4. DRS spectrum shows the absorption edge of NiO-Ag3VO4 in visible region of spectrum. The formation of cubic structured NiO and orthorhombic structured Ag3VO4 was confirmed by powder X-ray diffraction analysis. The results of XPS analysis confirmed the coexistence of NiO and Ag3VO4 in the NiO/Ag3VO4 composite. The specific surface area and pore structure of the prepared samples were measured by BET. Enhanced charge separation efficiency was confirmed by electrochemical impedance spectroscopy (EIS) measurements. The kinetics of the NiO/Ag3VO4 nanocomposite was proposed to investigate the intervened effects of NiO to Ag3VO4 on the promotion of photocatalytic property. NiO/Ag3VO4 was found to be stable and reusable without appreciable loss of catalytic activity up to four consecutive cycles. A possible electron-hole transfer mechanism at the NiO/Ag3VO4 interface is proposed. It also showed effective and efficient bactericidal activities against Staphylococcus aureus, Streptococcus, Proteus and Escherichia coli bacteria. Our results provide some new insights on the performance of visible light photocatalysts on environmental remediation.

Collision induced charge separation in ground-state water splitting dynamics.

In one type of photocatalytic dynamics of water splitting formally summarized as2H2O + 4hν + MH → 2H2O + M*H → 4H+ + 4e- + O2 + MHthe catalytic center M mainly composed of Mn oxides (clusters) along with supporting molecules like proteins is directly photoexcited and discharges electrons and protons. The mechanism can be comprehended in terms of the coupled proton electron-wavepacket transfer (CPEWT). In another type proposed in the literature, M is not directly photoexcited, and instead, lights are absorbed somewhere other than M, thereby creating complicated sequential steps (a ladder) of oxidation-reduction potential, thus sucking electrons successively from one molecular site to the next, and the final place providing electrons and protons is the catalytic center M. During charge separation dynamics, M is assumed to remain in the electronic ground state, and this type can be schematically summarized asM-H+ + Ω+ → M + H+ + Ω+e-where Ω indicates a cation species (a hole carrier) at the site of photon absorption. It is widely believed that the latter mechanism is responsible for water splitting in plants and cynobacteria, and M in photosystem II (PSII) is known to include Mn4CaO5. However, difficult questions about this mechanism of ground-state charge separation in the latter reaction arise as to whether it is quantum mechanically possible and what is it, if indeed possible? Besides, the time-constant for this reaction reported in the literature is so long, actually far longer than the time-scale for energy dissipation for inter- and intra-molecular vibrational energy redistribution, that the quantum mechanical coherence of the reaction should not be able to be maintained. More seriously, we wonder how protons and electrons can be isolated in the ground state, if any, and how they can be transferred unidirectionally (with no return)? We address these fundamental questions affirmatively by proposing a general chemical principle; collision induced charge separation dynamics in the ground state.