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Hydrogen peroxide production by direct synthesis (H2 + O2 → H2O2) is a promising alternative to the commercialized indirect process involving sequential hydrogenation and oxidation of anthraquinone...

Detailed information on structural, chemical, and physical properties of natural cleaved (10.4) calcite surfaces was obtained by a combined atomic force microscopy (AFM) and infrared (IR) study using CO as a probe molecule under ultrahigh vacuum (UHV) conditions. The structural quality of the surfaces was determined using non-contact AFM (NC-AFM), which also allowed assigning the adsorption site of CO molecules. Vibrational frequencies of adsorbed CO species were determined by polarization-resolved infrared reflection absorption spectroscopy (IRRAS). At low exposures, adsorption of CO on the freshly cleaved (10.4) calcite surface at a temperature of 62 K led to the occurrence of a single C-O vibrational band located at 2175.8 cm-1, blue-shifted with respect to the gas phase value. For larger exposures, a slight, coverage-induced redshift was observed, leading to a frequency of 2173.4 cm-1 for a full monolayer. The width of the vibrational bands is extremely small, providing strong evidence that the cleaved calcite surface is well-defined with only one CO adsorption site. A quantitative analysis of the IRRA spectra recorded at different surface temperatures revealed a CO binding energy of -0.31 eV. NC-AFM data acquired at 5 K for sub-monolayer CO coverage reveal single molecules imaged as depressions at the position of the protruding surface features, in agreement with the IRRAS results. Since there are no previous experimental data of this type, the interpretation of the results was aided by employing density functional theory calculations to determine adsorption geometries, binding energies, and vibrational frequencies of carbon monoxide on the (10.4) calcite surface. It was found that the preferred geometry of CO on this surface is adsorption on top of calcium in a slightly tilted orientation. With increased coverage, the binding energy shows a small decrease, revealing the presence of repulsive adsorbate-adsorbate interactions.

Metal-nitrogen-carbon materials (M-N-C) are non-noble-metal-based alternatives to platinum-based catalysts and have attracted tremendous attention due to their low-cost, high abundance, and efficient catalytic performance towards the oxygen reduction reaction (ORR). Among them, Fe-based materials show remarkable ORR activity, but they are limited by low selectivity and low stability. To address these issues, herein, we have synthesized FeCu-based M-N-C catalysts, inspired by the bimetal center of cytochrome c oxidase (CcO). In acidic media, the selectivity was notably improved compared with Fe-based materials, with peroxide yields less than 1.2% (

The growth of ZnO clusters supported by ZnO‐bilayers on Ag(111) and the interaction of these oxide nanostructures with water have been studied by a multi‐technique approach combining temperature‐dependent infrared reflection absorption spectroscopy (IRRAS), grazing‐emission X‐ray photoelectron spectroscopy, and density functional theory calculations. Our results reveal that the ZnO bilayers exhibiting graphite‐like structure are chemically inactive for water dissociation, whereas small ZnO clusters formed on top of these well‐defined, yet chemically passive supports show extremely high reactivity ‐ water is dissociated without an apparent activation barrier. Systematic isotopic substitution experiments using H2 16O/D2 16O/D2 18O allow identification of various types of acidic hydroxyl groups. We demonstrate that a reliable characterization of these OH‐species is possible via co‐adsorption of CO, which leads to a red shift of the OD frequency due to the weak interaction via hydrogen bonding. The theoretical results provide atomic‐level insight into the surface structure and chemical activity of the supported ZnO clusters and allow identification of the presence of under‐coordinated Zn and O atoms at the edges and corners of the ZnO clusters as the active sites for H2O dissociation., Chemical nature of small ZnO clusters: The combined infrared reflection absorption spectroscopy (IRRAS) and theoretical results reveal that the Ag(111)‐supported graphitic ZnO bilayers are chemically inactive. Significant activity is observed when small ZnO clusters are supported by these bilayers. This apparently barrier‐free water dissociation takes place at under‐coordinated Zn and O atoms at the edges and corners of the ZnO nanostructures. Various acidic hydroxyl species are identified by isotopic substitution experiments and the formation of weak H bonds to coadsorbed CO molecules.

The applications of the most promising Fe-N-C catalysts are prohibited by their limited intrinsic activities. Manipulating the Fe energy level through anchoring electron-withdrawing ligands is found effective in boosting the catalytic performance. However, such regulation remains elusive as the ligands are only uncontrollably introduced oweing to their energetically unstable nature. Herein, we report a rational manipulation strategy for introducing axial bonded O to the Fe sites, attained through hexa-coordinating Fe with oxygen functional groups in the precursor. Moreover, the O modifier is stabilized by forming the Fe-O-Fe bridge bond, with the approximation of two FeN4 sites. The energy level modulation thus created confers the sites with an intrinsic activity that is over 10 times higher than that of the normal FeN4 site. Our finding opens a novel strategy to manage coordination environments at an atomic level for high activity ORR catalysts.

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal‐organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect‐free HKUST‐1 MOF thin films, we demonstrate that Cu+/Cu2+ dimer defects, created in a controlled fashion by reducing the pristine Cu2+/Cu2+ pairs of the intact framework, account for the high catalytic activity in low‐temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O2 species, weakly bound to Cu+/Cu2+. Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites., A complex interplay: A thorough study combining advanced spectroscopy and theory reveals that electronic and steric effects occur at reduced Cu+/Cu2+ single dimers in defect‐engineered HKUST‐1 SURMOF to yield high catalytic activity for low‐temperature CO oxidation. A new reaction mechanism is presented involving an uncharged O2 species as the key intermediate.

Proton conduction in nanopores is important for applications in fuel cells, chemical sensors and information processing devices inspired by nature. Here, we present a nanoporous material, a metal–organic framework (MOF) thin film, allowing photomodulation of the aqueous and alcoholic proton conduction of the guests by almost two orders of magnitude. The MOF film possesses spiropyran groups which undergo reversible UV-light induced isomerization to the merocyanine form, a highly polar, zwitterionic molecule, where the strong binding of the guests to the merocyanine isomer efficiently suppresses the proton conduction. Such materials with photomodulated ionic conduction contribute to the development of advanced, remote-controllable chemical sensors and to switchable devices interfacing with biological systems.

Fluorescent molecular sensors offer a sensitive and straightforward approach to monitoring biologically or environmentally important targets. However, obtaining high-performance chemosensors are still challenging in terms of laborious synthesis and low success rate. Herein we report a general and efficient strategy for fabrication of complex fluorescent chemosensors. Noncovalent synthesis of supramolecular sensors was realized by self-assembly of structurally simple subunits bearing hydrogen-bonding linkers. Based on the selected use of three recognition subunits and three signalling subunits, an array of fluorescent sensory co-assemblies with different subunits combination patterns were fabricated for sensitive detection of bisulfite, saccharides, carbon dioxide or chemical warfare agents. The multiplicity and ratios of these subunits can be flexibly adjusted to obtain desirable functions such as signal amplification, ratiometric responses and simultaneous multitarget monitoring.

Previous investigation showed that intravenous injection of ginsenoside Rg1 had a therapeutic effect on Escherichia coli lipopolysaccharide-induced mastitis in lactating goats and it protected animals from lipopolysaccharide challenge via toll-like receptor 4 signaling pathway. The present study was to use proteomic approach to explore the anti-inflammatory mechanisms of Rg1. Nine dairy goats were randomly divided into three groups with 3 animals in each: groups 1 and 2 received intra-mammary infusion of lipopolysaccharide and then intravenously injected with saline or Rg1 solution; animals in group 3 were first intramammarily and then intravenously administered saline solution, and served as a control group. Milk whey at 6 h post lipopolysaccharide challenge was prepared for tandem mass tags based quantitative proteomic analysis. The results showed that 791 proteins were totally identified from the whey. Of them, 98 proteins between groups 1 (lipopolysaccharide + Saline) and 3 (Saline + Saline), and 34 proteins between groups 2 (lipopolysaccharide + Rg1) and 1 were significantly different. Group 1 than group 3 had significantly more inflammatory factors such as interleukin 6, acute phase proteins, blood coagulation factors, complement proteins, and oxidative stress markers while these factors were reduced in group 2 treated with Rg1. In addition, proteins in group 2 associated with peroxisome-proliferator-activated receptor γ activation and recovery of milk fat and production were upregulated compared to group 1. Therefore, Rg1 may exert its anti-inflammatory effect on lipopolysaccharide-induced mastitis in goats via modulating expression of proteins relating to peroxisome-proliferator-activated receptor γ and toll-like receptor 4 signaling pathway.

Metal oxide-supported bimetallic AuPd nanoparticles (NPs) are known to exhibit significantly enhanced activity and selectivity in numerous reactions compared to their monometallic counterparts. An ...

Purpose: In the present study, to achieve high paclitaxel (PTX) loading in a conjugated drug delivery system with minimal long-term side effects, we formulated a novel degradable stereocomplexed micelle-like particle with a core-shell structure. Materials and methods: In this system, methoxy polyethylene glycol (MPEG) acted as the hydrophilic shell, and the stereocomplex of polylactic acid with PTX (SCPLA-PTX) acted as the hydrophobic core. The MPEG-SCPLA-PTX micelle-like particles were synthesized via the self-assembly of a MPEG-poly L-lactic acid (PLLA) copolymer with a PTX-poly D-lactic acid-PTX copolymer. The resultant copolymers and their intermediates were characterized using 1H nuclear magnetic resonance and GPC. Micelle-like particles with different molecular weight ratios of MPEG and PLLA were synthesized to demonstrate the functions of both components. Results: PTX loading into MPEG2000Da-PLLA6000Da particles reached as high as 20.11%. At 216 h, the cumulative release from MPEG5000Da-PLLA6000Da, MPEG2000Da-PLLA6000Da, and MPEG5000Da-PLLA22000Da particles were 51.5%, 37.7%, and 52.0%, respectively. Conclusions: According to the cell uptake experiments, inhibition of tumor cell growth was satisfactory, indicating that the stereocomplexed particles developed in the present study can be employed as a promising nanocarrier for PTX delivery.

Selective C(sp3) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of an on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints, which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring., Direct transformation of n-alkanes and alkyl-substituted derivatives has been achieved under surface constraints to yield conjugated polyenes with programmed length and functionalities.

In ceria-based catalysis, the shape of the catalyst particle, which determines the exposed crystal facets, profoundly affects its reactivity. The vibrational frequency of adsorbed carbon monoxide (CO) can be used as a sensitive probe to identify the exposed surface facets, provided reference data on well-defined single crystal surfaces together with a definitive theoretical assignment exist. We investigate the adsorption of CO on the CeO2(110) and (111) surfaces and show that the commonly applied DFT(PBE)+U method does not provide reliable CO vibrational frequencies by comparing with state-of-the-art infrared spectroscopy experiments for monocrystalline CeO2 surfaces. Good agreement requires the hybrid DFT approach with the HSE06 functional. The failure of conventional density-functional theory (DFT) is explained in terms of its inability to accurately describe the facet- A nd configuration-specific donation and backdonation effects that control the changes in the Câ"O bond length upon CO adsorption and the CO force constant. Our findings thus provide a theoretical basis for the detailed interpretation of experiments and open up the path to characterize more complex scenarios, including oxygen vacancies and metal adatoms. Fil: Lustemberg, Pablo German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Consejo Superior de Investigaciones Científicas; España Fil: Plessow, Philipp N.. Karlsruher Institut fur Technologie; Alemania Fil: Wang, Yuemin. Karlsruher Institut fur Technologie; Alemania Fil: Yang, Chengwu. Karlsruher Institut fur Technologie; Alemania Fil: Nefedov, Alexei. Karlsruher Institut fur Technologie; Alemania Fil: Studt, Felix. Karlsruher Institut fur Technologie; Alemania Fil: Wöll, Christof. Karlsruher Institut fur Technologie; Alemania Fil: Ganduglia Pirovano, Maria Veronica. Karlsruher Institut fur Technologie; Alemania

The interaction of water with the basal plane (0001) of α-Fe2O3 (hematite) is a fundamental and challenging topic in the fields of surface science and earth science. Despite intensive investigations, many issues remain unclear especially due to the lack of direct spectroscopic evidence. Here, water adsorption on the pristine Fe-terminated α-Fe2O3(0001) surface was investigated by polarization-dependent infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy in conjunction with calculations from density functional theory. The combined results provide solid evidence that the interaction of water with α-Fe2O3(0001) is dominated by the heterolytic dissociation yielding an OwD species coordinated in atop-configuration to surface Fe3+ and an OsD species resulting from the deuterium/hydrogen transfer to an adjacent substrate O2–. Both isolated hydroxyl groups do not feature any hydrogen bonding, while the intact water molecules were identified as minor species that are bound to surface F...

The functional composite of metal nanoparticles (NPs) and defect-engineered metal–organic frameworks (DE-MOFs), NPs@DE-MOFs, is an emerging field of MOF materials chemistry. Herein, we report on a series of novel Pd-NPs@DE-HKUST-1(Cu/Pd) catalysts containing both micro- and mesopores through the incorporation of the defect-generating linker 2,6-pyridyldicarboxylate (pydc). The Pd NPs are formed by partial reduction of the Pd2+ sites of the pristine mixed-metal DE-HKUST-1(Cu/Pd) with methanol. The size regime and the spatial distribution of the Pd NPs can be controlled by the amount of framework-incorporated pydc. The samples exhibit superior catalytic activity in the aerobic oxidation of cinnamyl alcohol as compared to the parent HKUST-1.

The hydrogen evolution reaction is a crucial step in electrochemical water splitting. The most efficient catalysts for this reaction in acidic media are Pt based, but the high cost of Pt limits its practical applications. We developed a novel matrix architecture in which a trace amount of Pt is alloyed in situ with Ru nanoparticles uniformly and partially embedded in porous carbon spheres. The synthetic procedure is simple and efficient. Surface enrichment of metallic Pt nanoclusters on PtRu alloy nanoparticles results in weak bonding with hydrogen and rapid hydrated proton dissociation. These effects significantly increase the electrocatalytic activity in the hydrogen evolution process. This robust catalyst, with a Pt loading 99.9% less than that of a commercial Pt-based catalyst, gave a high turnover frequency (4.03 H2 s−1), a small Tafel slope (27.2 mV dec−1), and comparable overpotentials (19.7 mV and 43.1 mV), as well as achieved current densities of 10 and 100 mA cm−2, i.e., better than those obtained with commercial Pt/C catalyst, in 0.5 M H2SO4. This structure prevents nanoparticles from dissolving, agglomerating, and detaching during long-term operation; therefore there was no obvious decrease in catalytic activity after continuous reaction.

An atomic-level understanding of dioxygen activation on metal oxides remains one of the major challenges in heterogeneous catalysis. By performing a thorough surface-science study of all three low-index single-crystal surfaces of ceria, probably the most important redox catalysts, we provide a direct spectroscopic characterization of reactive dioxygen species at defect sites on the reduced ceria (110) and (100) surfaces. Surprisingly, neither of these superoxo and peroxo species was found on ceria (111), the thermodynamically most stable surface of this oxide. Applying density functional theory, we could relate these apparently inconsistent findings to a sub-surface diffusion of O-vacancies on (111) substrates, but not on the less closely packed surfaces. These observations resolve a long standing debate concerning the location of O-vacancies on ceria surfaces and the activation of O2 on ceria powders.

Platinum-based materials are widely applied to catalyze cathodic oxygen reduction reaction in H2/O2 fuel cell. Due the high price and scarcity of Pt, developing novel non-noble metal catalysts is of great importance for wide application of H2/O2 fuel cell due to their low price and abundance compared to platinum-based materials. Non-noble metal carbon-based oxygen reduction reaction catalysts, including transition-metals-nitrogen co-doped carbon composites and heteroatom-doped carbon composites, are intensively studied. Recognizing the active sites for such catalysts is of great importance for further improving the catalytic performance and scaled up synthesis, thus it has attracted tremendous research efforts. For the M–N–C type catalysts, M-N x /C ( x =1,2,3,4), N x -C, as well as active graphene layers in iron encapsulated within carbon nanotubes or graphene layers have been regarded as active sites in varied research, respectively. For the heteroatoms-doped carbon catalysts, carbon atoms adjacent to pyridinic nitrogen are accepted as active sites. However, it is difficult to eliminate trace amount of metal that introduced from precursors and during the synthesis course, thus synthetizing absolute non-metal heteroatoms-doped carbon and identifying the active sites are almost impossible. Therefore, distinguishing active sites from several components and improving catalysts active sites density are issues that we must resolve. This short review focuses on our recent results acquired regarding the activity and active sites for ORR, and we expect that this effort will promote further research on this challenging and important topic.

A comprehensive model to describe the water stability of prototypical metal–organic frameworks (MOFs) is derived by combining different types of theoretical and experimental approaches. The results provide an insight into the early stages of water-triggered destabilization of MOFs and allow detailed pathways to be proposed for the degradation of different MOFs under aqueous conditions. The essential elements of the approach are computing the pKa values of coordinated water molecules and geometry relaxations. Variable-temperature and pH infrared spectroscopy techniques are used to corroborate the main findings. The model developed herein helps to explain stability limits observed for several prototypical MOFs, including MOF-5, HKUST-1, UiO-66, and MIL-101-Cr, in aqueous solutions, and thus, provides an insight into the possible degradation pathways in acidic and basic environments. The formation of a metal hydroxide through the autoprotolysis of metal-coordinated water molecules and the strength of carboxylate–metal interactions are suggested to be two key players that govern stability in basic and acidic media, respectively. The methodology presented herein can effectively guide future efforts, which are especially significant for in silico screening, for developing novel MOFs with enhanced aqueous stability.

Platinum single sites are highly attractive due to their high atom economy and can be generated on CeO2 by an oxidative high-temperature treatment. However, their location and activity are strongly debated. Furthermore, reaction-driven structural dynamics have not been addressed so far. In this study, we were able to evidence platinum-induced CeO2 surface restructuring, locate platinum single sites on CeO2 and track the variation of the active state under reaction conditions using a complementary approach of density functional theory calculations, in situ infrared spectroscopy, operando high-energy-resolution fluorescence detected X-ray absorption spectroscopy and catalytic CO (as well as C3H6 and CH4) oxidation. We found that the onset of CO oxidation is linked to the migration of platinum single sites from four-fold hollow sites to form small clusters containing a few platinum atoms. This demonstrates that operando studies on single sites are essential to assess their fate and the resulting catalytic properties. Single-atom catalysts hold great promise for process optimization by reducing metal utilization. However, their structure–activity properties remain elusive. Here, a combination of operando techniques and density functional theory analysis is used to capture the evolution of single platinum atoms on CeO2 during CO, C3H6 and CH4 oxidation.

A series of new defect-engineered metal-organic frameworks (DEMOFs) were synthesized by framework doping with truncated linkers employing the mixed-linker approach. Two tritopic defective (truncated) linkers, biphenyl-3,3',5-tricarboxylates (LH) lacking a ligating group and 5-(5-carboxypyridin-3-yl)isophthalates (LPy) bearing a weaker interacting ligator site, were integrated into the framework of Cu2(BPTC) (NOTT-100, BPTC = biphenyl-3,3',5,5'-tetracarboxylates). Incorporating LH into the framework mainly generates missing metal node defects, thereby obtaining dangling COOH groups in the framework. However, introducing LPy forms more modified metal nodes featuring reduced and more accessible Cu sites. In comparison with the pristine NOTT-100, the defect-engineered NOTT-100 (DE-NOTT-100) samples show two unique features: (i) functional groups (the protonated carboxylate groups as the Bronsted acid sites or the pyridyl N atoms as the Lewis basic sites), which can act as second active sites, are incorporated into the MOF frameworks, and (ii) more modified paddlewheels, which provided extra coordinatively unsaturated sites, are generated. The cooperative functioning of the above characteristics enhances the catalytic performance of certain types of reactions. For a proof of concept, two exemplary reactions, namely, the cycloaddition of CO2 with propylene oxide to propylene carbonate and the cyclopropanation of styrene, were carried out to evaluate the catalytic activities of those DE-NOTT-100 materials depending on the defect structure.

The adsorption and reactions of CH3OH on nonpolar mixed-terminated ZnO(100), polar O–ZnO(000) and Zn–ZnO(0001) surfaces have been studied systematically using high-resolution electron energy loss spectroscopy (HREELS) in conjunction with temperature programmed desorption (TPD). For all three ZnO surfaces, exposure to methanol at room temperature leads to (partially) dissociative adsorption resulting in the formation of hydroxyl and methoxy species. Upon heating to higher temperatures, the dissociated and intact methanol species on ZnO(100) predominantly undergo molecular desorption releasing CH3OH at 370 and 440 K. The Zn–O dimer vacancies are responsible for the decomposition of a small fraction of methanol yielding H2, CH2O and CO at 540 and 565 K. The interaction of methanol with polar O–ZnO and Zn–ZnO surfaces is dominated by thermal decomposition of CH3OH to produce CH2O, H2, CO, CO2 and H2O at elevated temperatures. The high chemical reactivity of both polar surfaces is related to the high abundance of different types of surface defects formed via massive restructuring. Importantly, the reconstructed Zn–ZnO surface exhibits high selectivity for hydrogen production at 520 K, which was not observed for the polar O–ZnO surface. The HREELS data revealed that this low-temperature hydrogen evolution on Zn–ZnO results from methoxy oxidation to a formate species occurring at O-terminated step-edge sites.

In this review, we highlight recent progress (2008–2016) in infrared reflection absorption spectroscopy (IRRAS) studies on oxide powders achieved by using different types of metal oxide single crystals as reference systems. Precise polarization- and azimuth-dependent IRRAS data recorded for single crystal substrates has allowed for fundamental insights into the surface chemistry and photochemistry of numerous probe molecules on various surfaces exposed by three very important metal oxides (ZnO, TiO2, and CeO2). When using carbon monoxide (CO) as a probe molecule, deep insight into the role of defects in the surface chemistry of oxides can be gained, as will be demonstrated by the characterization of different imperfections (e.g., O vacancies, nanofacets) present at oxidic samples. In addition, photostimulated excitations, e.g., electron or hole polaronic trap states, can be studied using IR-spectroscopy. Reliable and comprehensive reference data acquired for different oxide monocrystal model systems enables atomic-level insights into the structural, electronic, and reactive properties of the substantially more complex nanostructured oxide particles. We foresee that future application of IR spectroscopy to other challenging systems, including polar oxide surfaces with their often complex reconstruction patterns and oxide-supported highly dispersed metal particles, will provide a major advancement in the understanding of heterogeneous catalysts (539 references).

The surface atomic arrangement of metal oxides determines their physical and chemical properties, and the ability to control and optimize structural parameters is of crucial importance for many applications, in particular in heterogeneous catalysis and photocatalysis. Whereas the structures of macroscopic single crystals can be determined with established methods, for nanoparticles (NPs), this is a challenging task. Herein, we describe the use of CO as a probe molecule to determine the structure of the surfaces exposed by rod-shaped ceria NPs. After calibrating the CO stretching frequencies using results obtained for different ceria single-crystal surfaces, we found that the rod-shaped NPs actually restructure and expose {111} nanofacets. This finding has important consequences for understanding the controversial surface chemistry of these catalytically highly active ceria NPs and paves the way for the predictive, rational design of catalytic materials at the nanoscale.

This study aims to establish the relative importance of sediment organic phosphorus (Po) to the total P and the major classes of organic molecules that contribute to sediment Po, determined by measuring their susceptibility to enzymatic hydrolysis, across a suite of lakes ranging from oligotrophic to eutrophic status. The results showed that Po accounted for 21–60% of total P, and bioavailable Po accounted for 9–34% of Po in the sediments. The bioavailable Po includes mainly labile (H2O-Po) and moderately labile (NaOH-Po) P forms. For H2O-Po (accounting for only1.4% of Po), 53% (average) was labile monoester P, 28% was diester P and 17% was phytate-like P. For NaOH-Po (accounting for 9–33% of Po), 32% was labile monoester P, 33% was phytate-like P and 18% was diester P. The composition of bioavailable Po, determined by enzyme assays, was related to the lake nutrient levels, which implies that sediment bioavailable Po could act as an effective indicator for lake eutrophic status. With the increase of lake nutrient levels, bioavailable Po content and alkaline phosphatase activity in the sediment all increased, indicating that Po represents an important and bioavailable source of P that increases with eutrophication, and could contribute to internal loading and resistance of eutrophic lakes to remediation. This implies that eutrophic lakes would maintain long-term eutrophic status and algal bloom phenomena even after the external input of P was controlled and the total P concentration of water has declined. Thus, in order to reduce the release risk of sediment P more efficiently and effectively, sediment P control technique should focus not only on reducing the total P and inorganic P, but should also pay close attention to the removal of bioavailable Po.

The adsorption of CO on two different mixed-terminated, single-crystal surfaces of zinc oxide, ZnO(10 1 − 0) and ZnO(11 2 − 0), was investigated by employing infrared reflection absorption spectroscopy (IRRAS) using p- and s-polarized light. For both surfaces, one negative CO band was observed only for p-polarized light, indicating that CO is bound to the surface Zn 2 + sites in a nearly upright geometry. In addition, we observed a substantial coverage-induced frequency shift for CO adsorption on both ZnO surfaces. For ZnO(10 1 − 0), the ν (C-O) band shows a red shift of 16 cm − 1 when increasing the CO coverage from 0.5 ML (2185 cm − 1 ) to 1 ML (2169 cm − 1 ). On the ZnO(11 2 − 0) surface, for isolated CO molecules, a frequency of 2192 cm − 1 was detected. The CO band shifts to 2170 cm − 1 at full monolayer. On both surfaces, the coverage-dependent frequency shift is attributed to a combination of dynamic and substrate-mediated static adsorbate–adsorbate interactions.

The adsorption and reaction of formaldehyde (CH2O) on the oxidized rutile TiO2(110) surface were studied by temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), infrared reflection–absorption spectroscopy (IRRAS), and density functional theory (DFT) calculations. The experimental and theoretical data reveal the presence of various species depending on the temperature and coverage. Exposure to formaldehyde at 65 K leads to the formation of CH2O multilayers, which desorb completely upon heating to 120 K. After smaller exposures at low temperatures (45–65 K), STM allowed us to identify individual, isolated CH2O monomers. The theoretical results indicate that these monomers are bound to the surface Ti5c sites via σ-donation and adopt a tilted geometry. Upon heating, the CH2O monomers polymerize to form paraformaldehyde (polyoxymethylene, POM) chains, oriented primarily along the Ti5c rows ([001] direction). Upon further heating, POM is found to decompose around 250 K, releasing CH2O i...

Polymyxin E (PME) plays an important role in fighting against Gram-negative bacterial infections; however, it causes nephrotoxicity, which limits its clinical use. The aim of this study was to investigate the protective effects of a plant extract Panax notoginseng saponins (PNS) on PME-induced nephrotoxicity in mice. In vivo studies showed that PNS significantly reduced blood urea nitrogen (BUN), serum creatinine (CRE) and number of apoptotic cells in kidney, as well as renal histopathological damage which increased in the presence of PME, and suppressed PME-induced oxidative stress in kidney, as shown by the up-regulation of superoxide dismutase (SOD) and the down-regulation of malondialdehyde (MDA) levels. Furthermore, PNS inhibited the expression of Bax, while increased the expression of Bcl-2 compared to the PME-treated group. In vitro studies showed that PNS decreased intracellular reactive oxygen species (ROS) and MDA levels, increased glutathione (GSH) levels, and enhanced the activity of SOD and glutathione peroxidase (GSH-Px) in murine renal tubular epithelial cells (TCMK-1 cells). In addition, PNS enhanced cell viability and the expression of Bcl-2, restored the mitochondrial membrane potential, inhibited the expression of Bax, inhibited the activity of caspase-3 and caspase-9, and reduce apoptotic rate in PME-treated TCMK-1 cells. PNS could reduce PME-induced nephrotoxicity. The protective effects could result from inhibition of oxidative stress, and prevention of cell apoptosis via the mitochondrial pathway. These findings highlight the potential of PNS as a safe adjunct for ameliorating the nephrotoxicity.

Organic phosphorus (Po) constitutes the most important fraction of P in lake sediments, and the compositional properties of Po affect its behavior in lake ecosystems. In this study, 31P NMR, FT-IR spectroscopy, and UV–visible absorbance spectroscopy were combined to identify the dynamic composition of sediment Po across two sets of lakes in China ranging from oligotrophic to eutrophic, and their possible effects on lake eutrophication were evaluated. The results showed that sediment Po content (accounting for 24–75% of TP) was positively correlated with trophic status in both Eastern Plain and Yun-Gui Plateau lakes of China, and the linear relationship was more stable compared to total P (TP), implying that sediment Po may be a superior indicator of trophic status than TP. The Po component, phosphonate accounted for only 0.4% or less of Po, while the monoester P and diester P, accounted for 2–24% and 0.5–5% of Po, respectively, and were the main factors causing Po to increase with the increasing trophic status. The factors were closely related to the enhanced organic sewage load and intensification of contemporary sedimentation of phytoplankton. As trophic status increased, sediment Po might integrate into larger amounts of aromatic substances and functional groups, which could enhance the stability of Po in sediments. Furthermore, sediments from lakes with higher trophic status exhibited a higher degree of humification and molecular weights, which impart resistance to biodegradation, and therefore, reduced the risk of sediment Po release. However, the massive accumulation of bioavailable Po (monoester and diester P) allows possible degradation, supporting algal growth and maintains eutrophic status because there is abundant alkaline phosphatase in eutrophic lakes. Thus, to control lake eutrophication more effectively, targeted actions are urgently required to reduce the accumulation and degradation of Po in lake sediment.

Certain endophytic fungi belonging to the Hypoxylon genus have recently been found to produce volatile organic compounds (VOCs) that have potential relevance as hydrocarbon fuels. Here, a recently discovered Hypoxylon sp. (BS15) was demonstrated to also produce VOCs, but with diminished VOC production after an extended period of in vitro growth. Restoring VOC production was partially achieved by growing BS15 in growth media containing finely ground woody tissue from the original host plant (Taxodium distichum). In an effort to isolate VOC production modulators, extracts from this woody tissue were made by sequentially extracting with dichloromethane, methanol, and water. Both the dichloromethane and water extracts were found to modulate VOC production, while the methanol extract had no effect. Surprisingly, the woody tissue remaining after exhaustive extraction was also shown to act as a VOC production modulator when included in the growth media, with changes observed in the production of four compounds. This woody tissue also induced production of two compounds not observed in the original BS15 extract. Filter paper had the same modulating effect as exhaustively extracted woody tissue, suggesting the modulation was perhaps due to cellulose degradation products. Overall, this study demonstrated that VOC production in BS15 can be influenced by multiple compounds in the woody tissue rather than a single modulator.

The adsorption of two carboxylic acids, benzoic acid (BA) and terephthalic acid (TPA), on a single crystal rutile TiO$_{2}$(110) substrate was studied using infrared reflection–absorption spectroscopy (IRRAS) in conjunction with DFT calculations. On the basis of the high-quality IR data (in particular for the OH bands), various adsorbate species with different geometries could be identified. The adsorption of both, BA and TPA, on TiO$_{2}$(110) leads to deprotonation of carboxylic acids and protonation of substrate O-atoms. At low coverage, the deprotonated BA molecule adsorbs on TiO$_{2}$(110) in an upright, bidentate configuration, while the TPA molecule adopts a flat-lying geometry with both carboxylates bound to the surface in a monodentate geometry. At higher coverages, a transition from flat-lying to upright-oriented TPA molecules occurs. At saturation coverage, both BA and TPA molecules undergo dimerization indicating the presence of pronounced attractive intermolecular interactions. We propose that the BA dimers are stabilized by the interaction between adjacent phenyl rings, while the TPA dimerization is attributed to the formation of double hydrogen bonds between adjacent apical carboxylic groups.

Simultaneous incorporation of palladium within Pd-Pd and/or Pd-Cu paddlewheels as framework-nodes and Pd nanoparticle (NP) dispersion into MOF have been achieved for the first time via one-pot synthesis. In particular, the framework substitution of Cu(2+) by Pd(2+) as well as the pore loading with PdNPs have been confirmed and characterized by XPS. The obtained solids featuring such multiple Pd-sites show enhanced catalytic activity in the aqueous-phase hydrogenation of p-nitrophenol (PNP) with NaBH4 to p-aminophenol (PAP).

The adsorption of carbon monoxide on the anatase TiO2 (101) surface was studied with infrared reflection absorption spectroscopy (IRRAS), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT). The IRRAS data reveal only one CO band at ∼2181 cm–1 for both stoichiometric and reduced TiO2 (101) surfaces. From TPD, an adsorption energy of 0.37 ± 0.03 eV is estimated for the isolated molecule, which shifts to slightly smaller values at higher coverages. Combining STM imaging and controlled annealing of the sample confirms the adsorption energies estimated from TPD and the slight repulsive intermolecular interaction. CO molecules desorb from electron-rich, extrinsic donor defect sites at somewhat higher temperatures. Confronting the experimental results with DFT calculations indicates that the anatase (101) surface does not contain any significant concentration of subsurface oxygen vacancies in the near-surface r...

Isolated, coordinatively unsaturated metal sites within metal–organic framework (MOF) materials feature interesting chemical properties and offer applications as single-site catalysts. Here, we report on the recent progress in providing fundamental insight into chemical reactions occurring inside MOFs. In addition to the common form, powders, we discuss the potential of MOF thin films (SURMOFs). The combined spectroscopic and modeling approach applied to selected systems demonstrated that the catalytic activity of MOFs can be precisely tuned. A particular interesting case is the so-called defect-engineering, where structural imperfections are created in a controlled fashion. The chemical properties of MOF materials can be further modified by integration and decoration of linkers or loading with guest species, such as metal or metal–oxide nanoparticles or nanoclusters. A particularly interesting aspect of layer-by-layer approaches for the fabrication of MOF thin films is the prospect to realize tandem catalysts.

A copper(I) 3,5-diphenyltriazolate metal-organic framework (CuTz-1) was synthesized and extensively characterized by using a multi-technique approach. The combined results provided solid evidence that CuTz-1 features an unprecedented Cu5 tz6 cluster as the secondary building unit (SBU) with channels approximately 8.3 A in diameter. This metal-organic framework (MOF) material, which is both thermally and chemically (basic and acidic) stable, exhibited semiconductivity and high photocatalytic activity towards the degradation of dyes in the presence of H2 O2 . Its catalytic performance was superior to that of reported MOFs and comparable to some composites, which has been attributed to its high efficiency in generating . OH, the most active species for the degradation of dyes. It is suggested that the photogenerated holes are trapped by CuI , which yields CuII , the latter of which behaves as a catalyst for a Fenton-like reaction to produce an excess amount of . OH in addition to that formed through the scavenging of photogenerated electrons by H2 O2 . Furthermore, it was shown that a dye mixture (methyl orange, methyl blue, methylene blue, and rhodamine B) could be totally decolorized by using CuTz-1 as a photocatalyst in the presence of H2 O2 under the irradiation of a Xe lamp or natural sunlight.

We present azimuth- and polarization-dependent infrared spectroscopy results obtained under ultra-high vacuum conditions on surface species formed by the interaction of formic acid with the mixed-terminated ZnO(10\(\bar{1}\)0) surface. Since there are no previous IRRAS data for formic-acid derived species on any ZnO single crystal surfaces, we have carried out calculations using density function theory to aid the interpretation of the results. From our combined experimental and theoretical data we conclude that two different formate species are formed. The more strongly bound species is a bidentate with the formate molecular plane oriented along the [1\(\bar{2}\)10] direction. The less strongly bound species is a quasi-bidentate with its molecular plane oriented along the [0001] direction. This second species is characterized by a strong hydrogen bond between a surface OH species and the formate. In addition, IR data were recorded for the same molecule adsorbed on commercial ZnO nanoparticles. The different bands of the powder IR-data are assigned on the basis of the experimental and theoretical results obtained for the single crystal surface. This study demonstrates the importance of the Surface Science approach to heterogeneous catalysis also for ZnO, an important catalyst for the conversion of syngas to methanol.

Small Cu particles supported on and most likely activated by a ZnO substrate are the active component in the industrial catalyst used to convert syngas (H2, CO, CO2) into methanol, the third most important chemical product worldwide. Although a topic of intense research, the nature of the active site is still under debate. Recently, it has been pointed out that Zn atoms present at the surfaces of the Cu particles exhibit pronounced chemical activity and could explain some of the experimental findings. Another interesting suggestion is the presence of a thin layer of ZnOx species which forms on the surface of the Cu particles under reaction conditions. The importance of such thin oxide layers on the surface of metals under reaction conditions has already been pointed out in other contexts, where it was found that their chemical properties may differ substantially from those of the corresponding bulk oxides. In the case of ZnO this question is particularly interesting, since strong interactions between ZnO and the supporting metal have been reported for ZnO/ Cu and in recent work thin layers of ZnO have been shown to adopt a depolarized, graphitic structure, ZnO(gr), different from the wurtzite-type bulk. The properties of oxide thin films supported on metal substrates have been successfully studied in a number of cases, for example, for thin aluminum oxide films grown by oxidation of Ni/Al alloys. In contrast, the chemical activity of ZnO thin films supported on Cu single crystals has been investigated in a few cases only. Maroie et al. have investigated the adsorption and oxidation processes for single-crystal brass(110), brass(100), and brass(111) surfaces by X-ray photoelectron spectroscopy (XPS). Brass(110) and brass(111) show the same behavior with regard to the interaction with oxygen: the dissociative adsorption of oxygen on the surface is followed by the growth of thin ZnO layers. Wiame et al. reported that after oxidation of (111)-oriented Cu0.7Zn0.3 samples at room temperature the surface is covered by ZnO islands; it was suggested that these islands have (0001) and (0001) surface terminations. A more detailed characterization of the chemical properties of the thin ZnO layers was not carried out in this early work. In the present paper we report a detailed multitechnique investigation of a brass(111) single-crystal substrate (Cu/Zn ratio 9:1) subjected to different oxidation procedures using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) under ultrahigh vacuum (UHV) conditions. The experimental findings are then interpreted by comparison with the results of a rather extensive set of density functional theory (DFT) calculations. Our results reveal the growth of thin ZnO adlayers with chemical properties that are markedly different from those of normal, wurtzite-type ZnO substrates. XPS data recorded for the brass(111) surface before and after different oxidation procedures for two different exit angles of the photoelectrons are shown in Figure 1. Since it is difficult to discriminate between Cu and Cu on the basis of XPS data, also the corresponding results from Auger electron spectroscopy (AES) are shown. For the clean brass(111) substrate the data indicate a Zn atom concentration of 5%, clearly lower than the 10% expected based on the bulk Cu/Zn ratio. Upon oxidation, the XPS data reveal an increase of the surface Zn concentration. Since it is a crucial question whether, in addition to Zn, also Cu or Cu is present, we have carefully analyzed the XPS and AES data. Neither in the Cu2p XPS data nor in the Cu L3M45M45 Auger data were the characteristic signatures of Cu or Cu species resulting from an oxidation of copper atoms detected. Cu exhibits a L3M45M45 peak at electron kinetic energies of 915 eV– 917 eV, which is clearly absent in the present data (see Figure 1). This observation, which agrees with the conclusions presented in a previous study by Rameshan et al., is expected, since in the presence of the less noble Zn one would expect the formation of ZnO to precede that of CuxO. Oxidation at elevated temperatures results in a substantial increase of the Zn signal, revealing the formation of thicker ZnO adlayers. The thickness of these thin ZnO layers was determined from the intensity of the Zn2p3/2 and Cu2p3/2 XPS signals. Exposure of the samples to 500 L of O2 at room temperature yields a ZnO adlayer with an average thickness of about 1.7 , consistent with the presence of a monolayer. More extended exposures to oxygen at room temperature did not result in a significant further increase of the thickness of the ZnO layer. Even the oxidation of the brass substrate at [*] Dr. V. Schott, Dr. A. Birkner, Dr. M. Xu, Dr. Y. Wang Chair of Physical Chemistry Ruhr-University Bochum (Germany)

The photoreactivity of ceria, a photochemically inert, large band-gap oxide, can be increased to competitive values by introducing defects. We have investigated this previously unexplained phenomenon by monitoring UV-induced N2O decomposition on well-defined single crystals of this material using polarization-dependent infrared reflection-absorption spectroscopy (IRRAS). The IRRAS data, in conjunction with theory, provide direct evidence that reducing the ceria (110) surface yields high photoreactivity. On the (111) surface no such effects are seen. The low-temperature N2O photo¬decomposition occurs at surface O-vacancy sites on the (110) surface, where the electron-rich cerium cations with significantly lowered coordination number cause a local lowering of the huge band gap (~6 eV). The quantum efficiency of strongly reduced ceria (110) surfaces in N2O photodecomposition amounts to 0.03%, and is thus comparable to that reported for CO photooxidation on rutile TiO2(110).

CeO2 nanoparticles were synthesized via a one-step ultrasound synthesis in different kinds of ionic liquids based on bis(trifluoromethanesulfonylamide, [Tf2N]−, in combination with various cations including 1-butyl-3-methylimidazolium ([C4mim]+), 1-ethyl-2,3-dimethylimidazolium ([Edimim]+), butyl-pyridinium([Py4]+), 1-butyl-1-methyl-pyrrolidinium ([Pyrr14]+), and 2-hydroxyethyl-trimethylammonium ([N1112OH]+). Depending on synthetic parameters, such as ionic liquid, Ce(IV) precursor, heating method, and precipitator, formed ceria exhibits different morphologies, varying from nanospheres, nanorods, nanoribbons, and nanoflowers. The morphology, crystallinity, and chemical composition of the obtained materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and N2 adsorption. The structural and electronic properties of the as-prepared CeO2 samples were probed by CO adsorpt...

Active species of Cu-Cr catalysts, prepared by an epoxide-assisted sol–gel route, were investigated for the hydrogenolysis of glycerol to 1,2-propanediol. Structural characterization of the catalysts was performed by means of N2 physisorption, X-ray diffraction, H2-temperature programmed reduction, high-resolution X-ray photoelectron spectroscopy, NH3-temperature programmed desorption, and N2O titration. On the basis of the characterizations, the copper species on the calcined Cu-Cr catalysts and the reduced Cu-Cr catalysts were assigned. Combined with reaction results, it was found that there was not similar trend in copper metal surface area and glycerol conversion, indicating that a two-site (Cu0 and Cu+) mechanism existed in the hydrogenolysis of glycerol over Cu-Cr catalysts. Besides, the maximum conversion of glycerol was obtained when the surface Cu0/Cu+ ratio increased from 3.1 to 6.6, whereas decreased with increasing sequentially to 15.7, demonstrating that the appropriate surface Cu0/Cu+ ratio was required for optimum hydrogenation activity. Thus, the synergetic effect between the Cu0 and Cu+ was considered to be responsible for the high catalytic activity in the hydrogenolysis of glycerol, and that CuCr2O4 played a critical role in the glycerol hydrogenolysis reaction since it could function as a “hydrogen delivery bridge”.

A Nodulisporium species (designated Ti-13) was isolated as an endophyte from Cassia fistula. The fungus produces a spectrum of volatile organic compounds (VOCs) that includes ethanol, acetaldehyde and 1,8-cineole as major components. Initial observations of the fungal isolate suggested that reversible attenuation of the organism via removal from the host and successive transfers in pure culture resulted in a 50 % decrease in cineole production unrelated to an overall alteration in fungal growth. A compound (CPM1) was obtained from Betula pendula (silver birch) that increases the production of 1,8-cineole by an attenuated Ti-13 strain to its original level, as measured by a novel bioassay method employing a 1,8-cineole-sensitive fungus (Sclerotinia sclerotiorum). The host plant produces similar compounds possessing this activity. Bioactivity assays with structurally similar compounds such as ferulic acid and gallic acid suggested that the CPM1 does not act as a simple precursor to the biosynthesis of 1,8-cineole. NMR spectroscopy and HPLC-ES-MS indicated that the CPM1 is a para-substituted benzene with alkyl and carboxyl substituents. The VOCs of Ti-13, especially 1,8-cineole, have potential applications in the industrial, fuel and medical fields.

A mixed-linker solid-solution approach was employed to modify the metal sites and introduce structural defects into the mixed-valence Ru-II/III structural analogue of the well-known MOF family [M-3(II,II)(btc)(2)] (M= Cu, Mo, Cr, Ni, Zn; btc= benzene-1,3,5-tricarboxylate), with partly missing carboxylate ligators at the Ru-2 paddle-wheels. Incorporation of pyridine-3,5-dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed-linker isoreticular derivatives of Ru-MOF, which display characteristics unlike those of the defect-free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the "defective" variants in the dissociative chemisorption of CO2, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins., O.K. acknowledges Ruhr-University Research School (http://www.research-school.rub.de) for admission and additional support of her PhD project. I. L. and F. X. L. X. acknowledge support by Consolider-Ingenio 2010 (project MULTICAT) and the "Severo Ochoa" program.