Papers by Keyword: Charge Transfer

Abstract: The rapid recombination of carriers on plasmon metal nanoparticles leads to relatively low efficiency of traditional photocatalysts. The combination of a metal and a semiconductor allows to the separation of hot electrons and holes to improve photocatalytic efficiency. In this study, Au nanoparticles were integrated with semiconductor TiO₂ nanoparticles of different sizes to improve the photocatalytic activity. Various techniques have been developed to study the mechanism of catalytic activity, the significance of band bending in the space-charge region within metal–semiconductor nanocomposites, and the built-in electric field. The results provide theoretical and experimental evidence for the design of a high-performance surface plasmon resonance (SPR) photocatalyst. To reveal the interface band structure, surface-enhanced Raman spectroscopy (SERS) was employed to analyze the band structure of the TiO₂–metal composites. This approach was based on the electrochemical Stark effect and a molecular probe strategy, combined with X-ray photoelectron spectroscopy (XPS), Electrochemical impedance spectroscopy (EIS), and other techniques at the molecular level. The results demonstrated that charge transfer occurred spontaneously between the Au nanoparticles and TiO₂, and that the TiO₂–metal interface constitutes a Schottky barrier. Moreover, the size of the TiO₂ nanoparticles affects the degree of band bending. Optimal state matching was achieved with TiO₂ (60 nm)–Au, improving the photocatalytic activity of the nanocomposite. The photocatalytic coupling reaction of p-aminothiophenol (PATP) acted as a probe to study the catalytic performance of TiO₂–metal nanocomposites. The results revealed that the introduction of TiO₂ improves the SPR catalytic activity of Au, mainly through the efficient separation of electrons and holes at the TiO₂–metal interface.

Abstract: In this work, the effect of carbon on the electrochemical properties of multi-walled carbon nanotube (MWCNT) functionalized Lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials a systematic study based on a combination of structural and spectroscopic techniques. The phosphor-olivine LiFe_0.5Mn_0.5PO₄, was synthesized via a simple microwave synthesis using LiFePO₄ and LiMnPO₄ as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe_0.5Mn_0.5PO₄ redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn²⁺/Mn³⁺ (4.1 V vs Li/Li⁺) and Fe²⁺/Fe³⁺ (3.5 V vs Li/Li⁺) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe_0.5Mn_0.5PO₄-MWCNTs having high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulates faster electron transfer and stability for the LiFe_0.5Mn_0.5PO₄ framework, which demonstrates favorable as a host material for Li⁺ ions.

Abstract: A simple aqueous based synthesis technique at room temperature was performed for preparation manganese-doped zinc sulfide quantum dots. Under 4 eV excitation quantum dots show photoluminescence bands at 2.11 and 3.1 eV corresponded to Mn²⁺ and intrinsic ZnS emission respectively. ZnS quantum dots were used as the luminescent sensing element for methane detection in aqueous media. The luminescent sensor response occurs due to photoinduced electron transfer from QDs to methane molecule resulting in QD luminescence quenching.

Abstract: Fluorescent zinc blende structured pure and Mn²⁺ doped ZnS quantum dots were prepared by simple aqueous based technique at room temperature. Under UV-excitation the quantum dots show photoluminescence bands at 2.1 and 3.0 eV corresponded to Mn²⁺ and ZnS intrinsic defect emission, respectively. The photocatalytic activity was tested for the photodegradation of methylene blue in aqueous solution. The influence of the Mn²⁺ concentration on the dye decolorization efficiency was studied. The highest photocatalytic degradation rate of methylene blue was obtained for ZnS quantum dots in glutathione shell doped with 0.5 at.% of Mn²⁺. The mechanisms of photoluminescence and photocatalytic activity were discussed.

Abstract: Electrochemical reactions occurring at a SiC electrode were investigated to gain insight into the effects of lithium salts, such as LiPF₆, LiClO₄, LiCF₃SO₃, and LiBF₄, on the interfacial resistance. Lithium salts were found to exert little effect on the magnitude of the resistance of the solid-electrolyte interphase (SEI). In contrast, the charge-transfer reactions observed in the LiCF₃SO₃-containing solution exhibited the smallest resistance. Charge-discharge analysis revealed that the nature of the SEI was significantly different from that formed in ethylene carbonate-based solutions containing different lithium salts. The SiC electrode exhibited large discharge capacity and low coulombic efficiency in the LiCF₃SO₃-containing solution. This might be closely related to the smallest charge-transfer resistance.

Abstract: It is necessary to develop NO₂ gas sensors as NO₂ is a pollutant. While, different from the reducing gases, oxidizing gas NO₂ will put up a complicated sensing process. Density functional theory (DFT) calculations are necessary to be performed to understand NO₂-sensing mechanisms at the atomic level. In this study we introduce NO₂ to SnO₂ (110) surface with oxygen species pre-adsorbed. The results show that NO₂ sensing mechanism of SnO₂ surface strongly depends on the concentration of oxygen in the ambient atmosphere (usually, no effects of temperature and pressure are considered). The direct interactions between NO₂ molecule and SnO₂ sub-reduced surface (with two rows of fold-coordinated bridging oxygens removed) for very low oxygen concentrations show that, NO₂ gas molecules interact directly with Sn instead of reacting with oxygen species, resulting in an increase in resistance of SnO₂. We investigate gas-sensing processes of interaction between NO₂ molecule and SnO₂ surface with pre-adsorbed oxygen species for the case of considerable high oxygen concentrations. Adsorbed molecular oxygen ions compete with adsorbing NO₂ molecules for available surface sites and electrons from the SnO₂. As the availability of oxygen ions on the SnO₂ surface increasing, the interaction between NO₂ and adsorbed oxygen species give rise to a reducing interaction, which brings a decrease in resistance of SnO₂.

Abstract: Due to its outstanding photo-catalysis properties, low-dimensional V₂O₅ has many important applications in lithium ion batteries, supercapacitors, electrochromic devices, photocatalysts, sensors, et al. As good photocatalysts for organic pollutants, some key issues of photocatalysts are charge generation, separation, transfer of nanocomposites under irradiation of visible light. To improve their important properties and pave the effective conductive channels for charge transfer and separation, low-dimensional V₂O₅/graphene nanoribbons nanocomposites were prepared_. The emphasis is put on adsorption response to VOC of nanocomposite based on the QCM (quartz crystal microbalance) device. In order to investigate the mechanism of charge-generated by visible light, the photoconductivity response to visible light and 808 nm laser with low-power were studied based on interdigital electrodes of Au on flexible PET (polyethylene terephthalate) film substrate. Some good results were obtained. This illustrates that this nanocomposite can easily produce the charge-generate with visible light and 808 nm laser with low-power, avoiding the recombination of charge-generate by light. It would be good applications in remove the organic pollutants with photocatalysis effects.

Abstract: Nano/Micro-structured CeO₂ and their nanocomposites have been received considerable attention in basic research and commercial applications, such as, new energy fields, photocatalysts, environmental fields, et al. To extend its visible light response and pave the effective conductive channels for charge transfer and separation in nanoscale is still facing great challenges. To explore these key issues of materials chemistry and physics, CeO₂ nanorods were prepared with aid of soft templates by wet chemical approach. Graphene nanoribbons were obtained with unzipping method of carbon nanotube (CNTs). Entanglement of CeO₂ nanorods and graphene nanoribbons oxides was realized based on the supermolecular interactions between surface active groups of CeO₂ nanorods and graphene nanoribbons oxides and excellent flexibility of graphene nanoribbons. A series of characterizations were examined by SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (X-ray diffraction), the Fourier-Transform Infrared (FTIR) spectra, ultraviolet-visible spectroscopy (UV-Vis) and so on. Photocatalytic efficiency was examined by selecting typical organic pollutants. The results indicated that the entanglement of a small amount of graphene nanoribbons on the surface of CeO₂ nanorods not only expanded the light response of nanocomposite to visible light, but also enhanced the adsorption properties to organic pollutants. Because of excellent charge transfer properties and high mobility of graphene nanoribbons, the nanocomposites of CeO₂/graphene nanoribbons are favor for electron-holes pairs generated by visible light, separation, and transfer, which would be important potential applications in photocatalysts, artificial photosynthesis system, nano/micro-devices, et al.

Abstract: CdSe semiconductor nano crystals (NCs) and Polyaniline (PAni) are mixed uniformly to prepare CdSe NCs/PAni complex. PAni can quench the fluorescent signal of CdSe NCs. The fluorescent intensity of CdSe NCs/PAni complex is related to the size of CdSe NCs and concentration of PAni. Ultraviolet visual (UV-Vis) absorption spectra and fluorescence spectra are employed to analysis the quenching phenomenon. The mechanism of fluorescence quench is dependent on two factors: on one hand, the FÖrster resonance energy transfer conducts from CdSe to PAni; on the other hand, PAni can intercept the electron charge of CdSe and lead to the interruption of radiative recombination.

Abstract: Adsorption mechanism of carbon monoxide (CO) on PtRu and PtRuMo alloy surfaces is investigated using density functional theory (DFT). It includes evaluation of binding configuration and the adsorption strength. The results show that CO preferentially adsorbs onto the 3 fold hollow site of the PtRu-surface, while on the PtRuMo surface we observe the shift from the fcc hollow site to near the bridge site. We also note that adsorption energy of CO on the PtRuMo is stronger than that of adsorption on the PtRu surface. From the charge transfer analysis, we conclude that the stronger binding energy is caused by the more charge transferred to the surface-adsorbate bonding region brought by alloying Mo to the PtRu.