Terminal OH Groups Research Articles

Preparation of TiO2/Ag binary nanocomposite as high-activity visible-light-driven photocatalyst via graft polymerization

Abstract We report the synthesis of a TiO 2 /Ag binary nanocomposite with high activity for visible-light-driven photocatalysts using graft copolymerization: (1) conversion of terminal OH groups on the surface of TiO 2 nanoparticles to Cl groups, (2) graft polymerization from TiO 2 –Cl via ATRP with ionically charged poly(styrene sulfonic acid), (3) ion exchange process with an AgNO 3 solution following sintering. TiO2/Ag binary nanocomposite showed enhanced photocatalytic performance for the degradation of methyl orange under visible light illumination. The improved photocatalytic performance of the TiO 2 /Ag binary nanocomposite was due to the plasmonic effect, recombination rate of electron–hole pairs that was suppressed by Ag nanoparticles.

Controlled release from aspirin based linear biodegradable poly(anhydride esters) for anti-inflammatory activity

This work reports the synthesis of a novel, aspirin-loaded, linear poly (anhydride ester) and provides mechanistic insights into the release of aspirin from this polymer for anti-inflammatory activity. As compared to conventional drug delivery systems that rely on diffusion based release, incorporation of bioactives in the polymer backbone is challenging and high loading is difficult to achieve. In the present study, we exploit the pentafunctional sugar alcohol (xylitol) to provide sites for drug (aspirin) attachment at its non-terminal OH groups. The terminal OH groups are polymerized with a diacid anhydride. The hydrolysis of the anhydride and ester bonds under physiological conditions release aspirin from the matrix. The resulting poly(anhydride ester) has high drug loading (53%) and displays controlled release kinetics of aspirin. The polymer releases 8.5 % and 20%, of the loaded drug in one and four weeks, respectively and has a release rate constant of 0.0035h-0.61. The release rate is suitable for its use as an anti-inflammatory agent without being cytotoxic. The polymer exhibits good cytocompatibility and anti-inflammatory properties and may find applications as injectable or as an implantable bioactive material. The physical insights into the release mechanism can provide development of other drug loaded polymers.

Relationship between Acid–Base Properties and the Activity of ZrO2‐Based Catalysts for the Cannizzaro Reaction of Pyruvaldehyde to Lactic Acid

AbstractThe Cannizzaro reaction of pyruvaldehyde to lactic acid is investigated in a flow reactor with ZrO2 catalysts with different structures and acid–base properties. The results show that a difference in the crystalline structures of two ZrO2 polymorphs strongly affects the conversion of pyruvaldehyde. The monoclinic phase of zirconia is the most active for this reaction. A good correlation is observed between the reaction rate and the concentration of Lewis acid sites of sufficient strength, which shows that these sites play a major role in the reaction. A reaction mechanism is proposed involving coordinatively unsaturated Zr4+ cations as sites for activating pyruvaldehyde molecules, whereas Zr4+−O2− pairs generate terminal OH groups through water dissociation.

Glycidyl Azide‐butadiene Block Copolymers: 2 Synthesis from a Mesylated Precursor

AbstractGlycidyl azide‐butadiene block copolymers are potential binders for solid propellants. The azidic part contributes to the overall energy outputs, while the butadiene block improves the mechanical properties. Synthetic strategies proposed in literature are not appropriate for production of large‐scale quantities. The mesylation of one homopolymer, followed by reaction with the OH terminal groups of the second is proposed here. The reaction is simple and does not show the drawbacks of the previously suggested alternatives. The block copolymers can be used as “partially” energetic binders. Moreover, they work well as compatibilizer in mechanical blends of the two homopolymers, that otherwise rapidly segregate in two distinct phases.

Synthesis, thermal behavior and physicochemical characterization of ZrO2/PEG inorganic/organic hybrid materials via sol–gel technique

Six zirconia–polyethylene glycol (ZrO2/PEG) inorganic/organic hybrid materials were synthesized by the sol–gel technique with different amount of polyethylene glycol (PEG) (corresponding to 6, 12, 24, 50, 60 and 70 mass%). Scanning electron microscopy and Fourier transform infrared spectroscopic (FT-IR) techniques were used in a recent study to characterize the materials with PEG content up to 50 mass%, while in the present one this characterization was extended to the more promising materials with higher PEG content (60 and 70 mass%). All the six materials confirmed their nanocomposite hybrid nature and the formation of hydrogen bonds between the inorganic zirconia matrix and the water-soluble organic component, which involve the Zr–OH groups and both the terminal OH groups and oxygen atoms in the ethereal units of the polymer chains. Moreover, the occurrence of interactions between PEG and acetylacetone, an inhibitor used during the sol–gel synthesis, was observed in the samples with high polymer content. The thermal behavior of all six hybrid materials was studied for the first time by thermogravimetry and differential thermal analysis from room temperature to 1023 K, aiming at identifying all physical and chemical processes occurring in these interesting materials, with particular reference to the decomposition of PEG to establish their thermal stabilities and the most suitable temperature condition for a further thermal treatment. The results revealed that PEG degradation occurs in the range temperature 473–873 K, and the degradation temperature decreases with increasing the PEG content. A probable explanation for PEG-rich materials is due to free PEG (not involved in the formation of H bonds) not affected by the stabilizing effect of the linkage with the inorganic matrix that causes a shift of degradation temperature toward lower values.

Two New Octaborates Constructed of Two Different Sub-clusters and Supported by Metal Complexes

Two inorganic–organic hybrid borates, [Zn(en)2{B8O11(OH)4}] (1, en = ethylenediamine) and [Cd(TREN){B8O11(OH)4}] (2, TREN = tris(2-aminoethyl)amine) have been made under hydro(solvo)thermal conditions and characterized by IR spectroscopy, elemental analysis, single crystal X-ray diffraction, diffuse-reflectance spectroscopy, thermogravimetric analyses, and powder X-ray diffraction. Crystal data for 1: triclinic, P−1, a = 8.7091(5) A, b = 8.8731(2) A, c = 12.7642(8) A, α = 87.042(4)°, β = 78.198(5)°, γ = 80.816(4)°, V = 952.96(9) A3. Crystal data for 2: monoclinic, P21/c, a = 11.5051(4) A, b = 8.7879(4) A, c = 19.9322(7) A, β = 91.433(3)°, V = 2014.63(14) A3. They both contain [B8O11(OH)4]2− cluster units, which linked each other to form 1-D chains. These 1-D chains are further joined together to produce 3-D supramolecular frameworks via H-bonding interactions. Interestingly, the [B8O11(OH)4]2− cluster in 1 is made of [B5O8(OH)2]3− and [B3O5(OH)2]2− sub-cluster units with two O atoms in common, while in 2 consists of [B5O7(OH)3]2− and [B3O6(OH)]4− sub-cluster units with two O atoms in common. The [B8O11(OH)4]2− ligands in 1 and 2 are coordinated to the supporting metal complexes in different ways. The anion in 1 is coordinated to the Zn(en)2 by a terminal OH group whereas the anion in 2 is coordinated by a bridging O atom. The in situ organic rearrangement reaction from triethylene tetramine (TETA) to tris(2-aminoethyl)amine (TREN) has been observed in the formation of 2.

Identify OH groups in TiOF2 and their impact on the lithium intercalation properties

A detailed investigation on the chemical composition of the cubic form of titanium oxyfluoride-based compound reveals the presence of OH groups substituting the oxide/ fluoride sublattice. The substitution of oxide by hydroxyl groups induces the presence of titanium vacancies (□) which were characterized by 1H and 19F solid-state NMR. 1H NMR shows that OH groups are present as bridging Ti-OH-Ti or terminal OH groups, i.e. sitting close to a titanium vacancy Ti-OH-□. The electrochemical properties vs. Li+/Li indicates that the presence of OH groups prevents the intercalation of lithium in the upper voltage region (1.2–3 V vs. Li+/Li). Indeed, a partial dehydroxylation of the framework enables to improve the reversibility of the lithium insertion/de-insertion processes. Since the presence of OH groups in this type of compounds is usual and depends on the synthesis method employed, this work enables to rationalize the different electrochemical behaviors reported in the literature and further highlights the importance of a good knowledge of the chemical composition with regard to the physico-chemical properties.

Tuning the Surface Chemistry of Metal Organic Framework Nodes: Proton Topology of the Metal-Oxide-Like Zr6 Nodes of UiO-66 and NU-1000

Some metal organic frameworks (MOFs) incorporate nodes that are nanoscale metal oxides, and the hydroxy-containing functional groups on them provide opportunities for introducing catalytic sites with precisely defined structures. Investigations have been done to understand the structures of these groups on nodes and node vacancies, because, in prospect, atomic-scale modulation of the composition, areal density, and/or siting of the groups would open up possibilities for exquisite tuning of the siting and performance of subsequently anchored catalytic units (e.g., single metal ions, pairs of metal ions, or well-defined metal-ion-containing clusters). We have combined infrared (IR) spectroscopy and density functional theory (DFT) to demonstrate tuning of these sites, namely, hydrogen-bonded OH/OH2 groups on the Zr6 nodes of the MOFs UiO-66 and NU-1000 via the intermediacy of node methoxy (or ethoxy) groups formed from methanol (or ethanol). Methoxy (or ethoxy) groups on node vacancy sites are converted to a structure incorporating one vacant Zr site and one terminal OH group per face by reaction with water. Our results highlight how the combination of DFT and IR spectroscopy facilitates the determination of the identity and chemistry of the functional groups on MOF node vacancies and defect sites.

Surface Hydroxyl OH Defects of η-Al2O3 and χ-Al2O3 by Solid State NMR, XRD, and DFT Calculations

Abstract For the first time, the detailed structure of χ-Al2O3 and η-Al2O3 surface has been established by implementing the NMR crystallography approach. The surface of η-Al2O3 has been demonstrated to be formed primarily by the (111) facets, while the χ-Al2O3 surface is a combination of (111) and (110) facets. This observation supports the block model of aluminum oxides previously proposed by Tsybulya and Kryukova [S. V. Tsybulya, G. N. Kryukova, Phys. Rev. B 77 (2008) 024112.]. The additional terminal OH groups, observed experimentally and not contributing to (111) and (110) theoretical calculations, are considered to be bonded to the tetrahedral aluminum sites. Their origin is related to the junctions of crystallographic faces of spinel building blocks, being a part of discussed model. Higher content of these terminal OH groups in χ-Al2O3 is a result of more junctions in the case of its more mosaic structure compared to η-Al2O3.

Following the Reduction of Oxygen on TiO2 Anatase (101) Step by Step.

We have investigated the reaction between O2 and H2O, coadsorbed on the (101) surface of a reduced TiO2 anatase single crystal by scanning tunneling microscopy, density functional theory, temperature-programmed desorption, and X-ray photoelectron spectroscopy. While water adsorbs molecularly on the anatase (101) surface, the reaction with O2 results in water dissociation and formation of terminal OH groups. We show that these terminal OHs are the final and stable reaction product on reduced anatase. We identify OOH as a metastable intermediate in the reaction. The water dissociation reaction runs as long as the surface can transfer enough electrons to the adsorbed species; the energy balance and activation barriers for the individual reaction steps are discussed, depending on the number of electrons available. Our results indicate that the presence of donor dopants can significantly reduce activation barriers for oxygen reduction on anatase.

Molecular deposition of a macrocyclic cobalt catalyst on TiO2 nanoparticles

Hybrid photocatalysts consisting of molecular catalysts and solid-state surfaces have demonstrated great potential as robust and efficient systems in solar fuel production. Based on our prior work, we synthesized hybrid photocatalysts by depositing a macrocyclic Co(III) complex on three different TiO2 nanomaterials via a microwave method. The hybrid photocatalysts were tested in CO2 reduction and were thoroughly characterized with spectroscopic (UV–vis, FTIR and EPR) and microscopic (TEM) techniques. The presence of terminal OH groups on TiO2 surfaces was essential for the molecular deposition of catalytically active Co(III) sites. On a TiO2 material without such terminal OH groups, the Co(III) complex formed amorphous aggregates, which hindered interfacial electron transfer from photoactivated TiO2 to the surface molecular complex. EPR studies further revealed important information regarding the coordination geometry and interaction with CO2 of surface cobalt sites in the hybrid photocatalysts.

Effect of Introduction of B3+ OR Al3+ Ions in the Structure of Ti-, Sn-, AND Zr-Containing Heirarchical Zeolites on the Concentration of Lewis and Brønsted Acid Centers

It was established that Ti-, Sn-, and Zr-containing hierarchical zeolites of the BEA and MTW structural types contain two types of Lewis acid centers, the strength of which increases in the order Ti-MTW < Zr-MTW ≤ Sn-MTW, and also weak Bronsted acid centers formed by defect Sn—OH and Zr—OH terminal groups. The introduction of boron or aluminum ions into the structure of Ti-, Sn-, and Zr-silicate BEA and MTW zeolites leads to the appearance of additional Lewis and Bronsted acid centers.

Role of Ionics Surfactant in Synthesizing Cerate-Zirconate Ceramic Powder

BaCe0.54Zr0.36Y0.1O2.95 (denoted as BCZY10) ceramic powder was synthesized by a modified sol-gel method using metal nitrate salts as precursors. The samples were prepared using two different types of surfactants which are cationic surfactant of hexadecyldimethylammonium bromide (HTAB), nonionic surfactant of polyoxyethylene (10) oleyl ether (Brij 97), and sample without surfactant as a control. All samples were labeled as S1, S2, and S3 respectively. They were dried and calcined at T=325 °C and T=1100 °C accordingly. Chemicals bonding of the compound were analyzed using Fourier transform infrared (FTIR) spectrometry and their phase formation was identified by X-Ray Diffractometer (XRD). All the dried samples showed the adsorption peak at 3200-3700 cm-1 that related to the overlapping of OH stretching originated from –OH terminal group and N-H stretching vibrations. The peaks appeared at 1620-1640 cm-1 can be assigned to C=O stretching and at 1380-1450 cm-1 can be attributed for N-H bending vibration. The adsorption peak ≈500 cm-1 of metal-oxygen bond for all the calcined samples became pronounces indicating that the metal complexes were transformed to metal oxides. XRD results confirmed that S2 and S3 formed a single-phase of Ba (Ce,Zr)O3 perovskite type-oxide and S1 consists of multi-phases compound which are dominated by BaCeO3, and BaZrO3. Therefore, the used of different type of surfactant was found to give a significant effect on the synthesizing single-phase of BCZY10 ceramics compound.

Bis-tert-Alcohol-Functionalized Crown-6-Calix[4]arene: An Organic Promoter for Nucleophilic Fluorination.

A bis-tert-alcohol-functionalized crown-6-calix[4]arene (BACCA) was designed and prepared as a multifunctional organic promoter for nucleophilic fluorinations with CsF. By formation of a CsF/BACCA complex, BACCA could release a significantly active and selective fluoride source for SN2 fluorination reactions. The origin of the promoting effects of BACCA was studied by quantum chemical methods. The role of BACCA was revealed to be separation of the metal fluoride to a large distance (>8 Å), thereby producing an essentially "free" F(-). The synergistic actions of the crown-6-calix[4]arene subunit (whose O atoms coordinate the counter-cation Cs(+)) and the terminal tert-alcohol OH groups (forming controlled hydrogen bonds with F(-)) of BACCA led to tremendous efficiency in SN2 fluorination of base-sensitive substrates.

End-functionalized block copolymer electrolytes: effect of segregation strength on ion transport efficiency

We report the synthesis, morphology and ion transport properties of poly(styrene-b-ethylene oxide) (PS-b-PEO) block copolymers with various end-functional groups. The PS-b-PEO having an –OH terminal group showed poorly defined morphology, while the inclusion of a terminal acid unit (–SO3H or –COOH) in PS-b-PEO caused the development of an ordered lamellar structure. The terminal acid moieties in PEO were found to increase the segregation strength of PS-b-PEO and reduce the degree of crystallinity of PEO. This observation is intriguing given that the end group concentration of PEO in PS-b-PEO employed in this study is as small as 0.4 mol%. Decreased conductivity was observed for PS-b-PEO tethered with acid groups when doped with lithium salts, which we ascribe to the slow segmental motion of acid group-terminated PEO chains. However, organization of the PEO domains of PS-b-PEO with terminal acid units into self-assembled nanostructures having sharp interfaces proved beneficial for increasing ion transport efficiency by creating less tortuous ion conduction pathways. At high levels of salt loading, the thermodynamic effects of the terminal group on ion transport properties of PS-b-PEO were attenuated. Our results suggest a unique methodology for controlling the morphology and ion transport properties of block copolymer electrolytes via attachment of a single end functional unit. A unique methodology to control the morphology and ion transport properties of block copolymer electrolytes by the inclusion of functional terminal groups.

Solution-processed titanium carbide MXene films examined as highly transparent conductors.

MXenes, a new family of two-dimensional structures, have recently gained significant attention due to their unique physical properties suitable for a wide range of potential applications. Here we introduce Ti3C2Tx delaminated monolayers as ultrathin transparent conductors with properties exceeding comparable reduced graphene oxide films. Solution processed Ti3C2Tx films exhibit sheet resistances as low as 437 Ω sq-1 with 77% transmittance at 550 nm. Field effect transistor measurements confirm that these films have a metallic nature, which makes them suitable as electrodes. We show using Kelvin Probe Atomic Force Microscopy that the work function of delaminated Ti3C2Tx flakes (with OH terminal groups) is 5.28 ± 0.03 eV. These results demonstrate that solution-processed Ti3C2Tx conducting films could open up a new direction for the next generation of transparent conductive electrodes.

Tuning Zr6 Metal–Organic Framework (MOF) Nodes as Catalyst Supports: Site Densities and Electron-Donor Properties Influence Molecular Iridium Complexes as Ethylene Conversion Catalysts

The Zr6 nodes of the metal–organic frameworks (MOFs) UiO-66 and UiO-67 are metal oxide clusters of atomic precision and can be used as catalyst supports. The bonding sites on these nodes—that is, hydrogen-bonded H2O/OH groups on UiO-67 and non-hydrogen-bonded terminal OH groups on UiO-66—were regulated by modulation of the MOF syntheses. Ir(C2H4)2(C5H7O2) complexes reacted with these sites to give site-isolated Ir(C2H4)2 complexes, each anchored to the node by two Ir–Onode bonds. The supported iridium complexes on these sites have been characterized by infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies and density functional theory calculations. The ethylene ligands on iridium are readily replaced by CO, and the νCO frequencies of the resultant complexes and those of comparable complexes reported elsewhere show that the support electron-donor tendencies increase in the order HY zeolite ≪ UiO-66 < UiO-67 (= NU-1000) < ZrO2 < MgO. The sharpness of the IR νCO bands shows that t...

Effect of GO phase in Zn(OH)2/GO composite on the extent of photocatalytic reactive adsorption of mustard gas surrogate

Abstract Composites of zinc hydroxide with various contents of graphite oxide (GO) were synthesized with a controlled precipitation rate. They were used at ambient conditions as adsorbents of a mustard gas surrogate, 2-chloroethyl ethyl sulfide (CEES). The samples’ surface features were characterized by various physical and chemical methods. The materials acted as photocatalysts upon light irradiation, degrading CEES to less- or no-toxic compounds. Exposure to visible light and the presence of GO in the composites improved the performance. The results indicated a paramount role of terminal OH groups as well as the porosity in the reactive adsorption process. The enhanced performance is linked to an increase in the degree of chemical and structural heterogeneity upon addition of GO. The surface characteristics strongly depend on the amount of the carbonaceous phase and 10 wt% was found as an optimal content. The CEES degraded mainly to ethyl vinyl sulfide by dehydrohalogenation and to hydroxyethyl ethyl sulfide via a hydrolysis pathway. The irradiation under visible light led to further transformation to vinyl vinyl sulfide and methyl vinyl sulfide through radical's reaction. The presence of GO promotes the electrons transfer and oxygen activation.

Mitsunobu Reaction: A Versatile Tool for PEG End Functionalization.

The Mitsunobu reaction can be efficiently used for the transformation of poly(ethylene glycol) (PEG) terminal OH group(s) into a variety of functions. In comparison to more classical approaches of PEG functionalization, the main advantage of the Mitsunobu reaction attains to the fact that in one step, with no detrimental effect on PEG integrity (e.g., chain cleavage). Here, its quantitative conversion is demonstrated into derivatives that, either directly or after deprotection, are amenable to (bio)conjugation reactions: azides (Huisgen cycloaddition), aldehydes, primary amines (Schiff base formation and reduction), thiols, and N-oxymaleimide (Michael-type addition). Therefore this reaction is proposed as a general tool for the preparation of functionalities for the purpose of PEGylation, and more generally for (bio)conjugation purposes.

Water Dynamics in Nanoporous Alteration Layer Coming from Glass Alteration: An Experimental Approach

Protons dynamics in borosilicate glasses of various compositions (SiO2/B2O3/NaO/CaO/X, with X = Al2O3 or ZrO2) at various stages of alteration have been characterized at a picosecond scale using quasielastic neutron scattering (QENS). The results obtained were compared to the one from porous silica-based material (MCM41) having pore wall surfaces with Si–OH, Al–OH, or Zr–OH terminal groups and pore sizes around 2.3 nm. The composition and the nanoporosity of the alteration layers were characterized using solution analysis, small angle X-ray scattering and transmission electron microscopy. The strength hydrogen bonds of confined water were studied using thermogravimetric analysis and differential thermal analysis. The results showed that the free water bonding and the mobility of protons depend on the altered glass composition and that the residence time of water obtained from QENS analysis is apparently correlated to the alteration rate of the glass. Moreover, whereas the composition of the alteration lay...