OH Sites Research Articles

Dynamics in hydrated inorganic nanotubes studied by neutron scattering: towards nanoreactors in water.

Water dynamics in inorganic nanotubes is studied by neutron scattering technique. Two types of aluminosilicate nanotubes are investigated: one is completely hydrophilic on the external and internal surfaces (IMO-OH) while the second possesses an internal cavity which is hydrophobic due to the replacement of Si–OH bonds by Si–CH3 ones (IMO-CH3), the external surface being still hydrophilic. The samples have internal radii equal to 7.5 and 9.8 Å, respectively. By working under well-defined relative humidity (RH) values, water dynamics in IMO-OH was revealed by quasi-elastic spectra as a function of the filling of the interior of the tubes. When one water monolayer is present on the inner surface of the tube, water molecules can jump between neighboring Si–OH sites on the circumference by 2.7 Å. A self-diffusion is then measured with a value (D = 1.4 × 10−5 cm2 s−1) around half of that in bulk water. When water molecules start filling also the interior of the tubes, a strong confinement effect is observed, with a confinement diameter (6 Å) of the same order of magnitude as the radius of the nanotube (7.5 Å). When IMO-OH is filled with water, the H-bond network is very rigid, and water molecules are immobile on the timescale of the experiment. For IMO-OH and IMO-CH3, motions of the hydroxyl groups are also evidenced. The associated relaxation time is of the order of 0.5 ps and is due to hindered rotations of these groups. In the case of IMO-CH3, quasi-elastic spectra and elastic scans are dominated by the motions of methyl groups, making the effect of the water content on the evolution of the signals negligible. It was however possible to describe torsions of methyl groups, with a corresponding rotational relaxation time of 2.6 ps. The understanding of the peculiar behavior of water inside inorganic nanotubes has implications in research areas such as nanoreactors. In particular, the locking of motions inside IMO-OH when it is filled with water prevents its use under these conditions as a nanoreactor, while the interior of the IMO-CH3 cavity is certainly a favorable place for confined chemical reactions to take place.

Phosphorus-doped h-boron nitride as an efficient metal-free catalyst for direct dehydrogenation of ethylbenzene

The N2PO and N3P–OH sites of PBN synergistically catalyzed the direct dehydrogenation reaction of ethylbenzene with a styrene production rate of 6.63 mmolST g−1 h−1 even after 100 h.

Evaluation of U(VI) adsorption from Ca2+ coexisted bicarbonate solution by synthetic inorganic and mineral materials

Abstract Part weakly alkaline natural uranium-containing water contains abundant Ca2+ and (bi)carbonate. Herein, two kinds of materials, namely mesoporous hydrous manganese dioxide (MHMO) and polyacrylonitrile (PAN)/dolomite composites were synthesized and characterized to evaluate their adsorption behaviors of U(VI) from Ca2+ coexisted bicarbonate solution. Characterization results showed that both samples exhibited good structural stability after U(VI) load. MHMO could coordinate U(VI) through the surface –OH sites, whereas an unfavorable U(VI) adsorption onto mineral composites was deduced. Adsorption tests indicated that increasing Ca2+ and (bi)carbonate amounts suppress U(VI) adsorption process, and ∼19.0 mg/g U adsorbed by MHMO could be obtained in solutions with 1 mmol/L [Ca2+], 5 mmol/L [CO3]T, 50 mg/L [U(VI)]initial at pH 8.0. Moreover, a heterogeneous surface chemical adsorption was verified through kinetics and isotherms study. Results from our study should be useful in exploring the adsorption behaviors and mechanisms of U(VI) on selected inorganic and mineral materials from natural uranium-containing water.

Effect of sulfate on Cu(II) sorption to polymer-supported nano-hydrated ferric oxides: Experimental and modeling studies

Incorporating of hydrous ferric oxide (HFO) inside porous supports with large sizes has become an effective way to decontaminate the water from heavy metals. Ubiquitous anions like sulfate are usually present in high concentrations in water, and might greatly affect adsorption behavior of hybrid HFO. Here, a polymer-based HFO-CPS was fabricated by encapsulating nano-HFO inside a chloromethylated polystyrene polymer (CPS) and the reactivity of HFO-CPS with Cu(II) was evaluated in the presence of sulfate ions. Surface complexation theory was firstly employed to describe the effect of sulfate on Cu(II) adsorption edges of hybrid HFO-CPS, where constant capacitance model (CCM) was adopted. The available weak adsorption site Fe (2) OH of hybrid HFO-CPS was found to decrease from 20% Fe to 5% Fe, which might be caused by the pore plugging effect after HFO encapsulation. With the assumption that a ternary complex was formed, the effect of sulfate on Cu(II) adsorption by HFO-CPS were successfully described by CCM using the optimized Fe (2) OH site under different sulfate concentrations (1 or 10 mmol·L −1 ) and Cu/Fe ratios (0.0042 or 0.0252). It is confirmed that the formation of FeOHCuSO 4 ternary surface complexes played an important role in enhancing Cu(II) adsorption on HFO-CPS in the presence of sulfate.

H2S Generation from CS2 Hydrolysis at a Dinuclear Zinc(II) Site.

The controlled generation of hydrogen sulfide (H2S) under biologically relevant conditions is of paramount importance due to therapeutic interests. Via exploring the reactivity of a structurally characterized phenolate-bridged dinuclear zinc(II)-aqua complex {LZnII(OH2)}2(ClO4)2 (1a) as a hydrolase model, we illustrate in this report that complex 1a readily hydrolyses CS2 in the presence of Et3N to afford H2S. In contrast, penta-coordinated [ZnII] sites in dinuclear {(LZnII)2(μ-X)}(ClO4) complexes (7, X = OAc; 8, X = dimethylpyrazolyl) do not mediate CS2 hydrolysis in the presence of externally added water and Et3N presumably due to the unavailability of a coordination site for water at the [ZnII] centers. Moreover, [ZnII]-OH sites present in the isolated tetranuclear zinc(II) complex {(LZnII)2(μ-OH)}2(ClO4)2 (4) react with CS2, thereby suggesting that the [ZnII]-OH site serves as the active nucleophile. Furthermore, mass spectrometric analyses on the reaction mixture consisting of 1a/Et3N and CS2 suggest the involvement of zinc(II)-thiocarbonate (3a) and COS species, thereby providing mechanistic insights into CS2 hydrolysis mediated by the dinuclear [ZnII] hydrolase model complex 1a.

Enhancing N2 Fixation Activity by Converting Ti3 C2 MXenes Nanosheets to Nanoribbons.

Metal carbides M2 C (MXenes) with two-dimensional (2D) structure have been indicated as promising materials for N2 fixation, with the activity being related to edge planes. Here, it is instead demonstrated that the transformation from a 2D- (nanosheets) to a 3D-type nanostructure (nanoribbons) leads to a significant enhancement of the N2 fixation activity due to the formation of exposed Ti-OH sites. A linear relationship is observed between ammonia formation rate and amount of oxygen on the surface of Ti3 C2 MXene.

Anchoring BaII to Pd/Hy WO3-x Nanowires Promotes a Photocatalytic Reverse Water-Gas Shift Reaction.

Surface deposition of BaII on Pd/Hy WO3-x nanowires was developed by using a solution-phase atomic layer deposition process. The procedure involves the generation of Brønsted surface OH sites by H2 spillover on Pd/WO3 , which can then hydrolytically condense with Ba(OEt)2 to produce surface BaII . At just 0.2 at % Ba, CO production by the light-assisted activity of the reverse water-gas shift (RWGS) reaction was observed to increase by about 300 %. In situ DRIFTS studies suggested enhanced CO2 capturing capabilities of a Ba-decorated surface. This study further exemplifies the importance of surface chemistry in optimizing materials for catalysis.

Insights into CO2 methanation mechanism on cubic ZrO2 supported Ni catalyst via a combination of experiments and DFT calculations

The CO2 methanation mechanism was studied via combined in-situ FTIR and DFT calculations on the cubic ZrO2 supported Ni catalyst. The formation and evolution of CO2 initial adsorbed species were addressed. The bicarbonates produced from CO2 reacting with surface OH sites are transformed to the CO2* adsorbed state on the Ni/ZrO2 interface (CO2*-interface) that are hydrogenated to CH4. The CO2 adsorbed states (CO2*-Ni) generated from CO2 reacting with surface Ni sites are hydrogenated to CO* as a byproduct rather than an intermediate for methanation. The formate pathway is dominated for methanation on Ni/ZrO2, in which bidentate formates hydrogenation to H2COO* is the rate-determining step with the activation energy of 1.01 eV. The presence of ZrO2 support improves the electron mobility and reducibility of Ni, and induces H-spillover effect to promote H2O* formation. Y3+ doping into the support of Ni/ZrO2 stabilizes the c-ZrO2 phase and promote methanation activity of the catalyst.

Catalytic Degradation of an Organophosphorus Agent at Zn–OH Sites in a Metal–Organic Framework

Chemical warfare agents (CWAs), and in particular organophosphorus nerve agents, still pose a significant threat to society due to their continued use despite international bans. While nature has c...

Synthesis of glucoside-based imidazolium salts for Pd-catalyzed cross-coupling reaction in water

Sugar-based imidazolium salts (IMSs) represent an outstanding type of material making them eye-catching for a wide variety of applications. Herein, a series of glucoside-based IMSs (Glu-IMSs) combining glucoside and imidazolium head groups with different substituents were synthesized. The catalytic activities of these Glu-IMSs were evaluated by Pd-catalyzed Heck–Mizoroki and Suzuki–Miyaura reactions in water. Among them, the Glu-IMSs contain both –OH and NHCs coordination sites was found to be the most efficient ancillary ligand in comparison with other Glu-IMSs with just single NHCs coordination site. The HR-TEM analysis showed that the palladium nanoparticles stabilized by the Glu-IMSs with an average size of ~4.0 nm was formed in the reaction system, which may be act as an efficient real catalytic species. Under the optimized reaction conditions, a series of novel fluorine-cored organic small molecule functional materials were synthesized with favorable yields.

Quantitative Analysis of Linker Composition and Spatial Arrangement of Multivariate Metal–Organic Framework UiO-66 through 1H Fast MAS NMR

Fast 1H magic-angle spinning (MAS) solid-state NMR spectroscopy was utilized for quantitative analysis of the linker composition and spatial arrangement of functional groups of MTV-UiO-66–(BDC–CH3)x–(BDC–OH)y–(BDC–NH2)1–x−y. 2D 1H–1H DQ–SQ MAS NMR experiments facilitate the 1H NMR chemical shift assignments. It was demonstrated that the fast 1H MAS technique could improve the resolution of 1H NMR spectra and allow the quantitative determination of the relative content of functional linkers without acid-digested treatment of MTV-UiO-66. The spatial proximities of various components including BDC–CH3 and BDC–OH were verified from the 2D 1H–1H spin diffusion homonuclear correlation experiments. The relative intensities of the 1H–1H spin-diffusion buildup curves via OH → CH3 and CH3 → OH pathways were closely related to the linker composition of MTV-UiO-66. Additionally, the extracted slices along with the CH3 site and OH site from the 2D 1H–1H spin diffusion NMR spectra are nearly the same as the corresponding 1D 1H MAS NMR spectra, indicating that the three functional linkers are in approximately random distribution in MTV-UiO-66-A and MTV-UiO-66-B. This work provides an efficient approach to examine the spatial arrangement of MTV-MOFs containing three distinct linkers.

Removal of arsenic in groundwater using Slag based calcined layered double hydroxides (CLDHs) with dual functions of adsorption and photo-catalysis

We employed Ti-bearing blast furnace slag (Ti-BFS) as raw material to prepare calcined TiO2-loaded layered double hydroxides (TiO2-CLDHs) through acidolysis-alkali precipitation coupled with pyrolysis strategy. During the pyrolysis process, the involvement of TiO2 and LDHs made the TiO2-CLDHs composites have superior photocatalytic ability and abundant porosities, resulting in highly-efficient removal of arsenic (As) from groundwater. Meanwhile, OH played crucial role in the As(III) oxidation process through the results of Electron-spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS) measurements. In addition, the co-existing of humic acid in groundwater was found to compete for OH and adsorption sites of TiO2-CLDHs, leading to a decrease in As removal. This study not only provided a novel strategy for Ti-BFS disposal, but also evaluated the application of TiO2-CLDHs in the treatment of As contaminants in groundwater environment.

Utilization of industrial waste lithium-silicon-powder for the fabrication of novel nap zeolite for aqueous Cu(II) removal

An industrial waste, lithium-silicon-powder, was used as a raw material to produce NaP zeolite (PZ) via a one-step-hydrothermal method. The as-synthesized PZ was used for Cu(II) removal from aqueous solution. High adsorption capacity was obtained on PZ. Besides, the PZ could be recycled and reused after desorption and with a stable capacity of approximately 62.3 mg/g (298 K). Batch experiments including the influences of PZ dosages, solution pH, adsorption temperature, and initial concentration, as well as the results of N2 physisorption, XRD, FTIR, SEM, and XPS, indicated that the mechanism responsible for Cu(II) removal was Na+ ion on the PZ surface exchanged with Cu2+ in solution, and the Cu2+ was mainly adsorbed on the Si–OH sites on PZ. Overall, the findings presented in this work suggested that PZ has a considerable potential application in low-cost and eco-friendly heavy metal removal from water.

Theoretical investigation on the structure and antioxidant activity of (+) catechin and (−) epicatechin – a comparative study

The monomeric flavan-3-ols, namely (+) catechin (CT) and (−) epicatechin (ECT), are two important antioxidants available in nature. Density functional theory method has been used to study the homolytic, heterolytic bond cleavages and the associated radical scavenging activities at B3LYP/6-311G(2d,2p) level of theory. The radical scavenging mechanism of CT and ECT was studied by considering three scavenging mechanisms, namely hydrogen atom transfer (HAT), single-electron transfer-proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET). Parameters related to the above mechanisms, such as bond dissociation enthalpy (BDE), ionisation potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy in gas and solvent medium (benzene, methanol and water) were studied. The results suggest that 4’-OH site from B-ring would play a crucial role in the scavenging activity of both the compounds. We observed that HAT is a thermodynamically favoured mechanism in the gas phase, whereas SPLET mechanism is more preferential in the polar medium for both the compounds. The global descriptors, such as ionisation potential (IPv), electron affinity (EAv), chemical hardness (η), softness (S), electronegativity (χ) and electrophilic index (ω) also confirm the high antioxidant activity of CT and ECT. Reactive site of the electrophilic and nucleophilic attack is confirmed and visualised by molecular electrostatic potential (MEP) map. Highlights The optimised geometrical parameters of (+) catechin (CT) and (−) epicatechin (ECT) have been calculated using B3LYP with 6-311G(2d,2p) level of theory. The antioxidant properties of CT and ECT are compared using three mechanisms, namely hydrogen atom transfer (HAT), single-electron transfer-proton transfer (SET-PT), and sequential proton loss Electron transfer (SPLET) by homolytic and heterolytic bond cleavages. The hydroxyl group present at 4’ site from B-ring is the most preferential site for hydrogen donation in both the compounds. The HAT mechanism is thermodynamically preferred in the gas phase, while SPLET mechanism is more favourable in polar solvents. Identification of reactive site by MEP and global descriptors is also confirming the high antioxidant activity in both compounds at the gas phase

A competent bidrug loaded water soluble chitosan derivative for the effective inhibition of breast cancer

Drug resistance and damage caused to the normal cells are the drawbacks which have limited the use of the existing effective anticancer drugs. Attainment of a steady and extended release by encapsulating dual drugs into biocompatible and biodegradable vehicles is the key to enable the use of these drugs for effective inhibition of cancer. In this study, carboxymethyl chitosan (CMCS), a proficient water-soluble derivative of chitosan has been synthesized using chemical route and used for the delivery of 5-Fluorouracil and doxorubicin individually as well as in combination. Carboxymethylation occuring at –NH2 and OH sites of chitosan, has been confirmed using FTIR. EDX and Fluorescence studies elucidate the encapsulation of 5-Fluorouracil and doxorubicin into CMCS. The capability of CMCS to release the drugs in a more sustained and prolonged manner is evident from the obtained release profiles. About 14.9 µg/ml is enough to cause 50% cell death by creating oxidative stress and effectuating DNA fragmentation. Amidst the existing reports, the uniqueness of this work lies in using this rare coalition of drugs for the suppression of breast cancer and in reducing the side effects of drugs by encapsulating them into CMCS, which is evidenced by the high hemocompatibilty of the samples.

TPD characterization of Al-OD-Si sites at the interface of bilayer Al0.42Si0.58O2/Ru(0001) thin-films.

Temperature programmed desorption (TPD) has been used to isolate and investigate water interactions unique to bilayer Al0.42Si0.58O2/Ru(0001) via comparison with identical water TPD experiments on a polymorphically equivalent bilayer SiO2/Ru(0001) sample. Relative to SiO2, the aluminosilicate shows evidence of additional desorption processes leading to TPD peaks near 400, 500, and 600 K, with the highest temperature feature exhibiting excellent agreement to previous results documenting infrared monitored loss of Al-OD-Si sites from nominally identical samples. The second order desorption energy estimated from this peak is ~1.6 eV, which is considerably lower than that reported for conventional zeolites, but potentially on par with desorption features reported from other minerals within the feldspar family. Quantification of the peak intensity suggests a ~5% likelihood for formation during water condensation and subsequent desorption. The lower temperature features have been assigned to desorption of molecular water bound at the excess hydroxyl sites. Each hydroxyl appears to bind 2 additional water molecules, which then desorb in a stepwise sequential process. The same low temperature TPD features are also apparent after creating silanol groups on (Al-free) SiO2/Ru(0001) via electron bombardment of supported ice layers, indicating similar water-OH-film interactions independent of specific OH site type.

Selective pulsed chemical vapor deposition of water-free HfOx on Si in preference to SiCOH and passivated SiO2

HfOx was selectively deposited on Si in preference to SiCOH using an oxygen-containing precursor, Hf(OtBu)4, via a pulsed chemical vapor deposition. The water-free process avoids nucleation by water on passivated oxide surfaces. The uniform HfOx film was deposited on Si by the thermal decomposition of the precursor, and the inherent selectivity of HfOx was retained over SiCOH until ~ 2 nm of HfOx was deposited on Si at 250 °C. Additional selectivity enhancement was demonstrated by employing molecular surface passivation and reversible adsorption/desorption of the precursor via control of the purge time. 1,1,3,3-tetramethyldisilazane (TMDS) and Bis(dimethylamino)dimethylsilane (DMADMS) were employed to passivate reactive –OH sites on SiO2 and SiCOH to increase the selectivity to ~ 7 nm HfOx deposition on Si before any significant nucleation occurred on TMDS passivated SiCOH. It is expected that the selective water-free HfOx deposition can be used for patterning nanoscale structures in MOSFET devices.

Disentangling different modes of mobility for triphenylphosphine oxide adsorbed on alumina.

Triphenylphosphine oxide (TPPO, 1) has been adsorbed on neutral alumina by dry grinding of the components in the absence of a solvent. The adsorption proves translational mobility of 1 on the surface of alumina. Different surface coverages from a densely packed monolayer (99% coverage) to a dilute sub-monolayer (25%) have been produced. The samples have been studied by diverse multinuclear 1H, 13C, and 31P variable temperature solid-state nuclear magnetic resonance (NMR) techniques. The interactions of 1 with the surface are determined by hydrogen bonding of the P=O group to OH groups on the surface. The 31P solid-state NMR spectra prove that even at low temperatures, the molecules of 1 are highly mobile on the surface. Using T1 and T2 relaxation time analyses of the 31P resonance in the solid state at variable temperatures allowed the identification and quantification of two different modes of mobility. Besides the translational mobility that consists of jumps from one hydrogen-bonding OH site on the surface to an adjacent one, a rotational movement around the axis defined by the P=O group of 1 occurs.

Oxidative desulfurization catalyzed by a novel ZrP/MCM-41 catalyst with high performance

The excellent catalytic performance of the ZrP/MCM-41 catalyst in oxidative desulfurization was attributed to the Zr–OH sites.

Nanostructure of CaO-(Na2O)-Al2O3-SiO2-H2O Gels Revealed by Multinuclear Solid-State Magic Angle Spinning and Multiple Quantum Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

(Calcium,alkali)-aluminosilicate gel frameworks are the basis of modern cements and alkali-activated materials for sustainable infrastructure and radioactive waste immobilization and also find application in glass alteration, mineral weathering, and zeolite synthesis. Here, we resolve the nanostructure of these gels that dictates mass transport, solubility, and mechanical properties. The key structural motifs comprising hydrous (calcium,alkali)-aluminosilicate gels are identified via 17O, 23Na, and 27Al triple-quantum magic angle spinning and 29Si magic angle spinning nuclear magnetic resonance spectroscopy of a novel class of stoichiometrically controlled 17O-enriched multiphase gels. Increased Ca content promotes low-Al, high-Ca chain-structured “C-S-H-type” products exhibiting significant nanostructural ordering, low levels of chain cross-linking, predominant Ca coordination of nonbridging oxygen atoms, and an increase in proton association with CaO layers to form Ca–OH sites. Al substitution is identified in multiple sites in the silicate chains, including cross-linking, bridging, and pairing tetrahedra. Increased Al content increases the proportion of cross-linking sites and gel disorder. The large increase in SiIV–O–AlIV sites increases the relative amounts of Na+ and AlV species charge-balancing AlO4– tetrahedra and results in the formation of an additional disordered low-calcium, framework-structured alkali aluminosilicate (“N-A-S-H-type”) gel, with high Al and Na contents. Changes in bulk composition significantly alter the nanostructures of the C-S-H-type and N-A-S-H-type gels. Mean SiIV–O–AlIV bond angles for each type of AlIV site environment are highly consistent, with compositional changes dictating the relative proportions of individual AlIV species but not altering the local structure of each AlIV site. These findings reveal the molecular interactions governing the (calcium,alkali)-aluminosilicate gel nanostructure, which are crucial in controlling material properties and durability.