Substitution Of Oxygen Research Articles

Enhanced mechanical properties of HfO2 film by nitrogen doping

The chemical composition, structure and mechanical properties of hafnium oxide films with different nitrogen constituents were investigated. X-ray photoelectron spectrum analysis showed that nitrogen atoms acted as oxygen substitution and interstitial atoms. The crystalline features exhibited no change during nitrogen doping. Nevertheless, the films with high compressive stress displayed significantly enhanced mechanical properties. The enhanced mechanism could mainly be attributed to the dislocation obstacle motion by inserting nitrogen atoms.

Structural features of the carbon-sulfur chemical bond: a semi-experimental perspective.

In this work semi-experimental and theoretical equilibrium geometries of 10 sulfur-containing organic molecules, as well as 4 oxygenated ones, are determined by means of a computational protocol based on density functional theory. The results collected in the present paper further enhance our online database of accurate semi-experimental equilibrium molecular geometries, adding 13 new molecules containing up to 8 atoms, for 12 of which the first semi-experimental equilibrium structure is reported, to the best of our knowledge. We focus in particular on sulfur-containing compounds, aiming both to provide new accurate data on some rather important chemical moieties, only marginally represented in the literature of the field, and to examine the structural features of carbon-sulfur bonds in the light of the previously presented linear regression approach. The structural changes issuing from substitution of oxygen by sulfur are discussed to get deeper insights on how modifications in electronic structure and nuclear potential can affect equilibrium geometries. With respect to our previous works, we perform non-linear constrained optimizations of equilibrium SE structures with a new general and user-friendly software under development in our group with updated definition of useful statistical indicators.

Recent Advances in Anti-inflammatory Potential of Pyridazinone Derivatives.

Pyridazinone and its derivatives have various ranges of biological and pharmacological activities including anti-inflammatory, antifeedant, anticonvulsant, antidiabetic, herbicidal, antihypertensive, antiplatelet, antifungal, antibacterial, anticancer and antiviral activities. Pyridazinone magic moiety has allowed the generation of a huge number of structurally different derivatives. Most of the pyridazinone derivatives are derived from substitution of the pyridazinone oxygen, nitrogen and C4/C5/C6 carbon positions. Pyridazinone can be used for the synthesis of a large variety of heterocyclic compounds and as intermediate for a broad spectrum of drug synthesis. Constant use of non-steroidal anti-inflammatory drugs is often accompanied by side effects such as bleeding, nephrotoxicity and gastrointestinal lesions. To minimise these side effects some of the pyridazinone derivatives are synthesised with an improved gastrointestinal tract and renal safety profile linked to other non-steroidal anti-inflammatory drugs. In this review, we have discussed the pyridazinone nucleus which serves as an important therapeutic agent in the field of nonsteroidal anti-inflammatory drugs. This nucleus has a wide spectrum in bioorganic and medicinal chemistry and application in drug discovery.

Purification and immobilization of lipoxygenase for production of anti-inflammatory and antibacterial agents

Three unsaturated fatty acids, namely 9-cis,12-cis-linoleic acid, 1,2,3-tri-cis, cis-9,12-octadecadienoyl (glycerol trilinolein) and 1,2,3-tri-cis-9-octadecenoyl (triolein) were selected as models of components of plant extractives to monitor the hydroperoxygenation induced by soybean lipoxygenase (LOX), which was applied as an oxidative catalyst at room temperature. The fatty acids were monitored in colloidal dispersions in relation to their molecular changes using 1H/13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and UV spectroscopies. The detection of the hydroperoxy group was limited due to its unstable nature. However, the reduction of protons associated with the diene groups and the substitution of hydroperoxy groups at the allylic positon in conjugated lipids were detected by the induced chemical shift of HOO-bearing 13C and 1H resonances and the oxygen absorption owing to changes in the molecule. Moreover, compared to the two other substrates, no oxygen substitution was observed in triolein, in accordance with its lower level of saturation and the absence of bis-allylic carbon. Our results are of relevance to plant fiber processing, since fatty acids are major constituents of hydrophobic deposits that cause a range of manufacturing challenges.

Abstract 3804: Structural changes to SN79 result in ligands that stimulate a metabolic function of sigma-2 receptors

Abstract Sigma-2 receptors have been of interest as targets for imaging, diagnosis, and treatment of cancer nearly since their discovery. These membrane-bound proteins are highly upregulated in cancer cells compared to healthy tissue, with further upregulation in rapidly proliferating cancer cells compared to quiescent cells. Activation of sigma-2 receptors by traditional agonists induces programmed cell death. However, this function of sigma-2 receptors is inconsistent with upregulation in cancer cells, which is typically associated with survival benefit. We have recently shown the ability of sigma-2 receptors to induce an independent, non-toxic, metabolically stimulative function that is consistent with survival benefit to both cancer cells and rapidly proliferating normal cells, indicated initially by an increase in MTT reduction. CM764, a novel analog of the sigma-2 antagonist SN79, increased total NADH/NAD+ and ATP levels, decreased basal ROS, and increased VEGF levels via induction of HIF1a expression in SK-N-SH neuroblastoma cells (Nicholson et al., JPET, 2015). We also previously described single-element structural changes to the core structure of SN79 and the effects of these changes on sigma receptor binding affinity and ability to induce cell death (Nicholson et al., Proc. Amer. Assoc. Cancer Res. 75: #2440, 2015). Here, we describe further characterization of the metabolic stimulatory effect induced by binding of members of this series to sigma-2 receptors in SK-N-SH neuroblastoma cells. Substitution of the oxazolone oxygen or methyl ketone moieties of the heterocyclic ring system of the SN79 core structure resulted in ligands that all retained significant binding affinity for sigma-2 receptors. Drastic changes in cell viability effects were observed in response to changes to the methyl ketone position. As previously reported, -NCS substitutions to the methyl ketone position resulted in cytotoxic ligands. By contrast, substitutions of the SN79 methyl ketone moiety with an -NH2, either alone (CM571) or combined with heterocyclic ring oxygen atom substitution for an -NMe group (WA403), resulted in ligands that stimulated reduction of MTT, consistent with the metabolically stimulative phenotype previously described. This phenotype was also observed with -NMe and -S- substitutions to the heterocyclic ring oxygen atom without combined substitution of the methyl ketone group (NF7 and WA504, respectively), and for the nitro-substituted methyl ketone group alone (CM458). All stimulative ligands demonstrated maximal increase in MTT reduction after 24 h incubation at 30 μM, with WA504 exhibiting the greatest stimulation of 161% of the amount of MTT reduced by cells that were not treated. These data further support a dual role for sigma-2 receptor activation, inducing both pro-survival and apoptotic pathways, and highlight the impact of single-element changes to the binding and action of SN79 analogs at sigma-2 receptors. Citation Format: Hilary Elaine Nicholson, Walid Alsharif, Christopher R. McCurdy, Wayne D. Bowen. Structural changes to SN79 result in ligands that stimulate a metabolic function of sigma-2 receptors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3804.

Effect of band gap engineering in anionic-doped TiO2 photocatalyst

A simple yet promising strategy to modify TiO2 band gap was achieved via dopants incorporation which influences the photo-responsiveness of the photocatalyst. The mesoporous TiO2 was successfully mono-doped and co-doped with nitrogen and fluorine dopants. The results indicate that band gap engineering does not necessarily requires oxygen substitution with nitrogen or/and fluorine, but from the formation of additional mid band and Ti3+ impurities states. The formation of oxygen vacancies as a result of modified color centres and Ti3+ ions facilitates solar light absorption and influences the transfer, migration and trapping of the photo-excited charge carriers. The synergy of dopants in co-doped TiO2 shows better optical properties relative to single N and F doped TiO2 with c.a 0.95eV band gap reduction. Evidenced from XPS, the synergy between N and F in the co-doped TiO2 uplifts the valence band towards the conduction band. However, the photoluminescence data reveals poorer electrons and holes separation as compared to F-doped TiO2. This observation suggests that efficient solar light harvesting was achievable via N and F co-doping, but excessive defects could act as charge carriers trapping sites.

Effects of annealing pressure and Ar+ sputtering cleaning on Al-doped ZnO films

Post-treatments of Al-doped ZnO films fabricated by sol-gel method were studied in condition of annealing in air, vacuum and protective ambient, as well as the follow-up Ar+ sputtering cleaning. The effect of annealing pressure on resistivity of AZO films was investigated from 105 to 10−4Pa, where the resistivity decreased four orders of magnitude as the pressure decreased and approached to its minimum at 10Pa. It was observed that the main decreasing of resistivity occurred in a very narrow range of middle vacuum (between 100 and 10Pa) and high vacuum was dispensable. The XRD and XPS characterizations demonstrated that the radical increasing of oxygen vacancy, Zn interstitial and substitution of Al3+ for Zn2+ under middle vacuum were responsible for the significant enhancement of conductivity. The follow-up Ar+ sputtering cleaning can further decrease the resistivity through removing the chemisorbed oxygen on film surface and grain boundaries, meanwhile fulfil the surface texture process, and thus improve both electrical and optical performances for applications.

Recent Achievements on High Voltage Olivine-Type Cathode Materials

The development of high power and high energy density cathode materials for rechargeable Li-ion batteries suitable with high operation voltage is a challenge. In this regard, the fundamental understanding of the thermodynamic stability and performance limits of high voltage cathode materials is essential, since one allows us to predict/determine the intrinsic voltage limit of the cathode material [1, 2] and tailor the components of the battery cell to provide a high Li+ diffusion rate in the bulk material and across the interface. The main reasons which limit to use high voltage LiMPO4 (LMPO, M=Co, Ni) cathode materials for electric vehicle applications are low electronic conductivity, which results from the olivine structure where the valence electrons of the transition metal are isolated from each other by the polyanion (PO3- 4), and an instability of the electronic structure of LMPO at the electrode-electrolyte interface caused by the decomposition of liquid electrolytes at high voltage potential. Low electronic conductivity of the Co- and Ni based olivine-type cathode materials makes it difficult to use electronic spectroscopy techniques which give unambiguous information on the density of the occupied and unoccupied states near the Fermi level (E F), on the oxidation and spin states of the transition metals, as well as on the chemical composition at the electrode-electrolyte interface [3-5]. In this presentation, we demonstrate our latest achievements on the study of the electronic structure of the layered- and olivine- type film cathode materials and its correlation with the electrochemical performance, Fig. 1. We demonstrate that the electronic structure of the bulk cathode material and the cathode-electrolyte interface is a key parameter which governs the thermodynamic stability of the whole battery cell. By plotting the experimentally obtained energy diagrams of the LiCoO2 (LCO) layered structure and LCPO-olivine structure cathode materials, we demonstrate the role of the inductive effect [7] which leads to the increase of the voltage window by the substitution of oxygen (O2-) by the polyanion. We discuss the role of morphology of the LiMPO4 film cathode materials on the Li-ion rate and demonstrate that high electronic conductivity can be achieved without using the carbon additives to the active material, Figs. 1(b). On the example of a LCPO film with different lithium content, x, we demonstrates the gradual shift of E F to the valence band maximum due to the increase of the work function of the cathode material in accordance with the rigid band model. By the analysis of the evolution of the core-levels and valence band structure as a function of lithium content in LCPO, we demonstrate that the charge compensation caused by Li+ removal takes place at the Co site resulting in the change of Co2+ ions (x=1.0) with the high spin (HS) state to the Co3+state in the accordance with DFT calculations [8]. The possible physicochemical mechanisms contributed to the degradation of the LMPO batteries are also discussed. [1] J. B. Goodenough, Y. Kim, Challenges for Rechargeable Li Batteries. Chem. Mat. (2010) 22, 587. [2] D. Ensling, G. Cherkashinin, S. Schmid, S. Bhuvaneswari, A. Thissen, W. Jaegermann, Nonrigid Band Behavior of the Electronic Structure of LiCoO2 Thin Film during Electrochemical Li Deintercalation. Chem. Mater. (2014) 26, 3948. [3] G. Cherkashinin, D. Ensling, W. Jaegermann, LiMO2 (M=Ni, Co) Thin Film Cathode Materials: a Correlation Between the Valence State of Transition Metals and the Electrochemical Properties. J. Mater. Chem. A (2014) 2, 3571. [5] D. Becker, G. Cherkashinin, R. Hausbrand, W. Jaegermann, Adsorption of Diethyl Carbonate on LiCoO2 Thin Films: Formation of the Electrochemical Interface. J. Phys. Chem. C (2014) 118,962. [6] G. Cherkashinin, M. Motzko, N. Schulz, T. Späth, W. Jaegermann, Electron Spectroscopy Study of Li[Ni,Co,Mn]O2/Electrolyte Interface: Electronic Structure, Interface Composition, and Device Implications. Chem. Mater. (2015) 27, 2875. [7] A. K. Padhi, K. S. Nanjundaswami, J. B. Goodenough, Phospho- Olivines as Positive- Electrode Materials for Rechargeable Lithium Batteries, J. Electrochem. Soc. (1997) 144, 1188. [8] F. Zhou, M. Cococcioni, C. A. Marianetti, D. Morgan, G. Ceder, First- Principles Prediction of Redox Potentials in Transition-Metal Compounds with LDA+U. Phys. Rev. B (2004) 70, 235121. Figure 1

Oxygen substitution effects in Li10GeP2S12 solid electrolyte

For the lithium super-ionic conductor Li10GeP2S12, the partial substitution of sulfur by oxygen is achieved via a solid-state reaction. The solid-solution range of oxygen is found to be 0 ≤ x < 0.9 in Li10GeP2S12−xOx. Structure refinements using synchrotron X-ray diffraction data confirm the preference for oxygen substitution in the PS4 tetrahedra. The local structural change in the P(S/O)4 tetrahedra upon substitution is also indicated by Raman spectroscopy. Ionic conduction properties are maintained even after the oxygen substitution in Li10GeP2S12; the ionic conductivity of Li10GeP2S12−xOx (0.3 ≤ x ≤ 0.6) ranges from 1.03 × 10−2 to 8.43 × 10−3 S cm−1 at 298 K. No redox current is observed by cyclic voltammetry from nearly 0 to 10 V versus Li/Li+ except for that due to the lithium deposition/dissolution reactions. All-solid-state batteries using Li10GeP2S12−xOx (x = 0.3 and 0.6) as solid electrolytes with Li metal anodes show discharge capacities exceeding 100 mAh g−1 and better cycling performance compared to batteries using the original Li10GeP2S12. The partial substitution of oxygen for sulfur in Li10GeP2S12 affords a novel solid electrolyte, Li10GeP2S12−xOx, with high conductive properties and electrochemical stability.

New Insights in Advanced Fluorinated Phosphates As Electrode Materials for Li and Na-Ion Batteries

a ICMCB-CNRS, Université de Bordeaux, Bordeaux INP, F-33608 Pessac cedex, France b LRCS, Université de Picardie Jules Verne, F-80039 Amiens Cedex 1, France c ILL, Institut Laue Langevin, F-38000 Grenoble, France d CEMHTI, Université d’Orléans, F-45071 Orléans, France e CELLS - ALBA Synchrotron, Cerdanyola del Vallès, E-08290 Barcelona, Spain Contact: Laurence.Croguennec@icmcb.cnrs.fr Vanadium-rich fluorinated-phosphates are attractive positive electrode materials for Li-ion and Na-ion batteries due to their high capacity, rate capability and long-term cycling stability.1,2 We already reported on a complex phase diagram as a function of the charge state for Na3V2(PO4)2F3.3 From structural determination based on high resolution X-ray powder synchrotron data and bond valence sum analysis we proposed two vanadium environments in NaV2(PO4)2F3, V3+ and V5+, instead of a single one (i.e. V4+). We will report on the operando investigation of the redox processes involved during sodium deintercalation and on the charge compensation mechanism on the V site, from X-ray absorption near edge structure measurements collected at the V k-edge. We will compare that mechanism to those observed for other vanadium-rich phosphates such as LiVPO4(F, O, OH). We will also show how challenging is the control of oxygen over fluorine stoichiometry in these fluorinated phosphates. Existence of characteristic lithium defect environments has been for instance recently revealed using solid-state 7Li nuclear magnetic resonance in well-crystallized Tavorite LiVPO4F,4 despite they were not detected by high resolution X-ray and neutron diffraction as well as scanning transmission electron microscopy. Several studies performed on Na3V2(PO4)2F3 have revealed significant discrepancies in its structural description as well as in the electrochemical properties.5 Unit cell volumes ranging between 871 and 878 Å3 were for instance reported, whereas the phase diagram observed upon cycling was described either as complex with a series of two phase reactions or as a solid solution. Subtle differences in compositions exist. We will especially discuss in details the effect of a partial substitution of oxygen for fluorine and thus of a mixed valence state for vanadium (V3+,4+) on the structure and electrochemical properties of these materials. Acknowledgements CEA-Liten (Grenoble, France) and especially Loïc Simonin are acknowledged for their collaboration. This research is performed in the frame of the French network RS2E (http://www.energie-rs2e.com) and of the European network ALISTORE-ERI (http://www.alistore.eu). This project is partly funded by the French National Research Agency ANR (Descartes project SODIUM and Progelec project HIPOLITE) and by the H2020 European Program (Project NAIADES).

Atomistic Mechanism of Pt Extraction at Oxidized Surfaces: Insights from DFT

In this article, we propose a novel mechanism for the atomic-level processes that lead to oxide formation and eventually Pt dissolution at an oxidized Pt(111) surface. The mechanism involves a Pt extraction step followed by the substitution of chemisorbed oxygen to the subsurface. The energy diagrams of these processes have been generated using density functional theory and were analyzed to determine the critical coverages of chemisorbed oxygen for the Pt extraction and Oads substitution steps. The Pt extraction process depends on two essential conditions: (1) the local coordination of a Pt surface atom by three chemisorbed oxygen atoms at nearest-neighboring fcc adsorption sites; (2) the interaction of the buckled Pt atom with surface water molecules. Results are discussed in terms of surface charging effects caused by oxygen coverage, surface strain effects, as well the contribution from electronic interaction effects. The utility of the proposed mechanism for the understanding of Pt stability at bimetallic surfaces will be demonstrated by evaluating the energy diagram of a CuML/Pt(111) near-surface alloy.

Formation of nanostructure in magnesium diboride based materials with high superconducting characteristics

The paper presents an analysis of the properties of bulk superconducting magnesium diboride-based materials obtained by heating at high quasi-hydrostatic pressures (1–2 GPa), hot pressing (30 MPa), spark plasma sintering (16–96 MPa) and loose powder sintering. It is shown that the optimization of impurity distribution in MgB2 can be achieved by varying the synthesis conditions and introducing dopants. In particular, polycrystalline MgB2 materials synthesized at 2 GPa and containing a high amount of impurity oxygen demonstrates high critical current densities (106 and 103 A/cm2 at 20 K in magnetic fields of 1 and 8.5 T, respectively). It is found that the oxygen impurities are mainly localized in nanolayers or nanoinclusions, homogeneously distributed in the matrix. They act as pinning centers, while the MgB2 matrix also contains small amounts of dissolved oxygen. Impurity or intentionally added carbon entering the magnesium diboride structure leads to an increase in the critical magnetic fields up to Bc2 (22 K) = 15 T and Birr (18.5 K) = 15 T. The results of ab initio calculations of the electronic structure and stability of the magnesium diboride compounds with partial oxygen or carbon substitution for boron show that it is energetically favorable for carbon to distribute homogeneously in MgB2 structure, while oxygen atoms replace boron pairwise in neighboring positions or form zigzag chains.

Sequential fungal fermentation-biotransformation process to produce a red pigment from sclerotiorin

The fungus Penicillium sclerotiorum produces sclerotiorin, an orange compound closely related to the useful food coloring pigments produced by Monascus species. The high productivity, together with several biological activities reported for sclerotiorin highlights its potential application in food industry. In this work, sclerotiorin was obtained as the major metabolite produced in liquid fermentation by P. sclerotiorum standing for 30% of the fungal dry extract. Modulation of sclerotiorin color was accomplished by biotransformation using Beauveria bassiana generating a red derivative with 13.8% yield. Color modification was caused by fungal-mediated substitution of oxygen by nitrogen in the pyrone ring changing the molecule’s chromophore. A derivative, 1-methyl sclerotiorin was synthesized from sclerotiorin using diazomethane and fed to B. bassiana. In this case, substituent at C-1 avoided heteroatom substitution. Sclerotiorin derivatives obtained in the present show the great potential of sclerotiorin derivatives as food colorants.

Thin‐Film Solar Cells: Atomic‐Scale Observation of Oxygen Substitution and Its Correlation with Hole‐Transport Barriers in Cu2ZnSnSe4 Thin‐Film Solar Cells (Adv. Energy Mater. 6/2016)

Atomic-scale analyses represent oxygen-containing layers near grain boundaries in Cu2ZnSnSe4 films. In article number 1501902, Sung-Yoon Chung and co-workers identify the presence of nanoscale layers in which oxygen is substantially substituted for Se. Theoretical calculations demonstrate that oxygen substitution lowers the valence band maximum and thus makes a key contribution to the formation of a barrier blocking the holes from bulk grains.

Synthesis, structure, and electrochemical properties of crystalline Li–P–S–O solid electrolytes: Novel lithium-conducting oxysulfides of Li10GeP2S12 family

Novel lithium-ion (Li+)-conducting oxysulfides of the Li10GeP2S12 family were found in the ternary Li2S–P2S5–P2O5 system; Li10GeP2S12-type solid solutions with compositions Li3+5xP1−xS4−zOz (x=0.03–0.08, z=0.4–0.8) were confirmed. The solid solutions showed ionic conductivities from 4.14×10−5 to 2.64×10−4Scm−1 at 298K and a wide electrochemical window of 0–5.0V (vs. Li/Li+). Among the solid solutions synthesized, the purest phase had the composition Li3.35P0.93S3.5O0.5 (x=0.07, z=0.5). Structural analysis revealed that the novel oxysulfides are isostructural to the original Li10GeP2S12 structure and the (P/□)(S/O)4 tetrahedra, which indicates the presence of cation defects with oxygen substitution in the crystal structure. Electrochemical stability of the oxysulfides was confirmed in the voltage range of 0–5.0V. The solid-electrolyte interphase (SEI) resistivity and its cycle-dependence evaluation for new materials demonstrated that the oxysulfides had lower resistivities and furnished well-contacted SEI layers during the charge–discharge process.

Atomic‐Scale Observation of Oxygen Substitution and Its Correlation with Hole‐Transport Barriers in Cu2ZnSnSe4 Thin‐Film Solar Cells

Kesterite‐type Cu2ZnSn(S,Se)4 has been extensively studied over the past several years, with researchers searching for promising candidates for indium‐ and gallium‐free inexpensive absorbers in high‐efficiency thin‐film solar cells. Many notable experimental and theoretical studies have dealt with the effects of intrinsic point defects, Cu/Zn/Sn nonstoichiometry, and cation impurities on cell performance. However, there have been few systematic investigations elucidating the distribution of oxygen at an atomic scale and the correlation between oxygen substitution and charge transport despite unavoidable incorporation of oxygen from the ambient atmosphere during thin‐film fabrication. Using energy‐dispersive X‐ray spectroscopy, scanning transmission electron microscopy, and electron energy‐loss spectroscopy, the presence of nanoscale layers is directly demonstrated in which oxygen is substantially substituted for Se, near grain boundaries in polycrystalline Cu2ZnSnSe4 films. Density‐functional theory calculations also show that oxygen substitution remarkably lowers the valence band maximum and subsequently widens the overall bandgap. Consequently, anion modification by oxygen can make a major contribution to the formation of a robust barrier blocking the holes from bulk grains into grain boundaries, thereby efficiently attaining electron−hole separation. The findings provide crucial insights into achieving better energy conversion efficiency in kesterite‐based thin‐film solar cells through optimum control of oxidation during the fabrication process.

Doping effect on photoabsorption and charge-separation dynamics in light-harvesting organic molecule

Using ab-initio theoretical methods, we demonstrate possible enhancement of photo-conversion efficiency of an organic solar cell via intentional doping in molecular graphene-fullerene heterojunction [the hexabenzocoronene (HBC)-triethylene glycol (TEG)–C60 molecule]. Photoabsorption analysis indicates oxygen substitution into HBC leads to an extension of the spectra up to an infrared regime. A quantum-mechanical molecular dynamics simulation incorporating nonadiabatic electronic transitions reveals that a dissociated charge state (D+ and A-) in the O-doped system is more stable than the pristine case due to the presence of an effective barrier by the TEG HOMO/LUMO level. We also find that oxygen doping in HBC enhances the intermolecular carrier mobility after charge separation. On the other hand, the pristine molecule undergoes rapid recombination between donor and acceptor charges at the interface. These analyses suggest that the graphene oxidation opens a new window in the application of organic super-molecules to solar cells.

Sulfur to oxygen substitution in BiOCuSe and its effect on the thermoelectric properties

The effects of S doping at the oxygen site on the thermoelectric properties of BiOCuSe have been investigated.

Synthesis of carbon doped WO3·0.33H2O hierarchical photocatalyst with improved photocatalytic activity

A carbon doping method is developed to overcome the drawback of conventional carbon doping method. The carbon dopant is synthesized by treating carbon with dilute nitric acid through hydrothermal process. Carbon-doped WO3·0.33H2O (CWO3·0.33H2O) is obtained by adding the carbon dopant solution, and then through an additional hydrothermal process. Based on XRD, Raman and XPS, carbon have been incorporated into the interstitial position of WO3·0.33H2O unit cell rather than substitution of oxygen in lattice of WO3·0.33H2O, which induces distortion of WO6 octahedron and lattice defect. In addition, carbon doping also induces the emergence of new level above the valence band. The new level increases the migration pathway of photo-generated carriers, which reduces the recombination rate of photo-generated carriers. The changes of band structure, distortion of WO6 octahedron and lattice defect are beneficial to improve the photocatalytic performance of WO3·0.33H2O. Compared with pristine WO3·0.33H2O, CWO3·0.33H2O display better photocatalytic performance on degradation of rhodamine B (RhB), which include the faster de-ethylation process and cycloreversion process. Moreover, the experiments of radical quenchers confirmed that the h+ display the main influence on degradation of RhB. This study implies that carbon can be doped into some metal oxide hydrates through a mild preparation process, which provides a possible way for the synthesis of carbon doped thermal unstable materials.

Remarkable suppression of thermal conductivity by point defects in MoS2 nanoribbons

By applying non-equilibrium molecular dynamics simulation, we investigate the effect of point defects on thermal conductivity of MoS2 nanoribbons, such as sulfur vacancies (VS) and oxygen substitutions to sulfur (SO). It is found that both VS and SO can significantly reduce thermal conductivity of monolayer MoS2 nanoribbons, but the suppression of thermal conductivity by vacancies is stronger than that by substitutions. For armchair MoS2 nanoribbon of 41.1nm length and 4.4nm width, when defect density is only 1.5%, the reduction of thermal conductivity at room temperature by VS defects and SO defects is 42.3% and 35.1%, respectively. We perform the vibrational eigenmodes analysis and find that the strong localization of phonons of all modes by defects results in the severe reduction of thermal conductivity of MoS2 nanoribbons. Further spectra analysis reveals that the localized modes are located in the sites of defects and the sites around defects, due to the change of force constant at these sites. Our findings are helpful for understanding and tuning the thermal conductivity of MoS2 nanoribbons by defect engineering.