Electrochemically‐Induced Deposition of Amine‐Functionalized Silica Films on Gold Electrodes and Application to Cu(II) Detection in (Hydro)Alcoholic Medium

Well‐adherent amine‐functionalized porous silica films have been deposited on gold electrodes by combining the self‐assembly technology, the sol–gel process, and the electrochemical modulation of pH at the electrode/solution interface. A partial self‐assembled monolayer of mercaptopropyl‐trimethoxysilane (MPTMS) was first formed on disposable gold electrodes from recordable CDs (Au‐CDtrodes). The so pretreated MPTMS‐Au‐CDtrodes were immersed in a stable sol solution (pH 3) containing (3‐aminopropyl)‐triethoxysilane (APTES) and tetraethoxysilane (TEOS). Polycondensation of the APTES and TEOS precursors was then achieved by applying a negative potential for a given period of time to generate a local pH increase at the electrode/solution interface and promote the deposition of the amine functionalized silica film adhering well to the electrode surface owing to the MPTMS monolayer acting somewhat as a “molecular glue”. Various parameters affecting the electrodeposition process have been studied and the film permeability to redox probes in solution was characterized by cyclic voltammetry. The amine‐functionalized silica film electrodes were then applied to the preconcentration of copper(II) species prior to their electrochemical detection by anodic stripping differential pulse voltammetry. Getting high sensitivity has however required the application of an electrochemical pre‐activation step as the majority of the organo‐functional groups were in the form of ammonium moieties (because the film was prepared from an acidic sol). This was achieved by applying a sufficiently negative potential to the electrode surface to reduce protons and increase consequently the amine‐to‐ammonium ratio within the film and, thus, the efficiency of the precocentration process. The resulting device was then optimized for copper(II) determination in hydroalcoholic medium, giving rise to a linear response in the 0.1–10 μM concentration range.     

Development of Sulfonic-Acid-Functionalized Mesoporous Materials: Synthesis and Catalytic Applications

Sulfonic acid based mesostructures (SAMs) have been developed in recent years and have important catalytic applications. The primary applications of these materials are in various organic synthesis reactions, such as multicomponent reactions, carbon–carbon bond couplings, protection reactions, and Fries and Beckman rearrangements. This review aims to provide an overview of the recent developments in the field of SAMs with a particular emphasis on the reaction scope and advantages of heterogeneous solid acid catalysts.     

Mesoporous Materials‐Based Electrochemical Sensors

A review (350 references) is given to the interest of mesoporous materials for designing electrochemical sensors. After a brief summary of the implication of template‐based ordered mesoporous materials in electrochemical science, the various types of inorganic and organic‐inorganic hybrid mesostructures used to date in electroanalysis and the corresponding electrode configurations are described. The various sensor applications are then discussed on the basis of comprehensive tables and some representative illustrations. The main detection schemes developed in the field are (volt)amperometric sensing subsequent to preconcentration and electrocatalytic detection.     

Mesoporous Silica Particles as Topologically Crosslinking Fillers for Poly(N‐isopropylacrylamide) Hydrogels

Here it is demonstrated that mesoporous silicas (MPSs) can be used as effective “topological crosslinkers” for poly(N‐isopropylacrylamide) (PNIPA) hydrogels to improve the mechanical property. Three‐dimensional bicontinuous mesporous silica is found to effectively reinforce the PNIPA hydrogels, as compared to nonporous silica and two‐dimensional hexagonally ordered mesoporous silica.     

New Microporous and Mesoporous Materials: Elucidation of Their Structures by Electron Microscopy

We have recently published three papers (P. Wagner et al., Phys. Chem. 103 (1999) 8245; S. Inagaki et al., J. Am. Chem. Soc. 121 (1999) 9611; A. Carlsson et al., J. Electron Microscopy 48 (1999) 795) that herald a new approach to structural solutions in micro- and mesoporous solid state materials. Among these materials are the first hybrid inorganic–organic mesoporous materials, synthesized using the organosilane compound 1,2-bis(trimethoxysilyl) ethane (BTME). Both organic and inorganic fragments are distributed completely uniformly at the molecular scale in the mesoporous walls. Two distinct phases with two- and three-dimensional (2d- and 3d-) hexagonal periodic pore-arrangements have been detected. We have also recently reported another new cubic hybrid phase with a decaoctahedral crystal morphology. Two new approaches for solving the structures of porous materials from either electron diffraction (ED) or high-resolution electron microscope (HREM) observations have also been developed. The former was successfully applied by combining direct methods for structural analysis of the new microporous crystal SSZ-48, which crystallizes only in very small crystals. The latter technique was applied to 3d-structural analysis of the mesoporous material MCM-48. The structure solutions, in the latter case, are obtained uniquely without preassumed models or parameterization, unlike previous reports.     

Capped Mesoporous Silica Nanoparticles for the Selective and Sensitive Detection of Cyanide

The development of easy and affordable methods for the detection of cyanide is of great significance due to the high toxicity of this anion and the potential risks associated with its pollution. Herein, optical detection of cyanide in water has been achieved by using a hybrid organic–inorganic nanomaterial. Mesoporous silica nanoparticles were loaded with [Ru(bipy)₃]²⁺, functionalized with macrocyclic nickel(II) complex subunits, and capped with a sterically hindering anion (hexametaphosphate). Cyanide selectively induces demetallation of nickel(II) complexes and the removal of capping anions from the silica surface, allowing the release of the dye and the consequent increase in fluorescence intensity. The response of the capped nanoparticles in aqueous solution is highly selective and sensitive towards cyanide with a limit of detection of 2 μm .     

Mesoporous silicas by self-assembly of lipid molecules: ribbon, hollow sphere, and chiral materials

Using lipids (N-acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0 degrees C to 10, 15, or 20 degrees C. The structures were studied by electron microscopy. It was found that 1) the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2) these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid-solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3) the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L-form N-acyl amino acid was used as the lipid template; 4) the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries.     

Selective Electroanalysis of Ascorbic Acid Using a Nickel Hexacyanoferrate and Poly(3,4‐ethylenedioxythiophene) Hybrid Film Modified Electrode

The mixed‐valent nickel hexacyanoferrate (NiHCF) and poly(3,4‐ethylenedioxythiophene) (PEDOT) hybrid film (NiHCF‐PEDOT) was prepared on a glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. The films were characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and electrochemical impedance spectroscopy (AC impedance). The advantages of these films were demonstrated for the detection of ascorbic acid (AA) using cyclic voltammetry and amperometric techniques. The electrocatalytic oxidation of AA at different electrode surfaces, such as the bare GCE, the NiHCF/GCE, and the NiHCF‐PEDOT/GCE modified electrodes, was determined in phosphate buffer solution (pH 7). The AA electrochemical sensor exhibited a linear response from 5×10⁻⁶ to 1.5×10⁻⁴ M (R²=0.9973) and from 1.55×10⁻⁴ to 3×10⁻⁴ M (R²=0.9983), detection limit=1×10⁻⁶ M, with a fast response time (3 s) for AA determination. In addition, the NiHCF‐PEDOT/GCE was advantageous in terms of its simple preparation, specificity, stability and reproducibility.     

Preparation,Structure, and Second‐order Nonlinear Optical Properties of a Borate‐Carboxylic Acid Compound: NH4B[d‐(+)‐C4H4O5]2·H2O

The organic‐inorganic hybrid nonlinear optical (NLO) material NH₄B(d‐ (+)‐C₄H₄O₅)₂ · H₂O (NBC) was synthesized in a borate‐carboxylic acid system. Its structure was determined by single crystal X‐ray diffraction. It crystallizes in the orthorhombic system, space group Pna2₁ (No. 33), with cell parameters a = 11.484(6) Å, b = 5.354(3) Å, c = 21.079(12) Å, V = 1296.0(12), Z = 4. It exhibits a three‐dimensional pseudo tunnel structure consisting of fundamental building block [B(d‐ (+)‐C₄H₄O₅)₂]^– anions. The small cavities are occupied by the H₂O molecules and NH₄⁺ cations, which stabilize the whole structure by O–H ··· O and N–H ··· O hydrogen bonds. The powder X‐ray diffraction (PXRD) of the crystal was also recorded. Elemental analyses, FT‐IR and FT‐Raman spectra analyses, thermal analysis, and diffuse‐reflectance spectra for the compound are also presented, as are band structures and density of states calculation. Nonlinear optical measurements indicate that the material has second harmonic generation (SHG) properties and is phase‐matchable.     

A Low‐dimensional Viologen/Iodoargentate Hybrid [(BV)2­(Ag5I9)]n: Structure,Properties, and Theoretical Study

A new low‐dimensional benzyl viologen/iodoargentate hybrid, [(BV)₂(Ag₅I₉)]_n ( 1 ) (BV²⁺ = benzyl viologen) was prepared. In 1 , (Ag₆I₉)_n^2– chain exhibits a new type of one‐dimensional chain constructed from vertex‐sharing of Ag₅I₁₀ units, and its two‐dimensional layer structure was constructed from C–H ··· I hydrogen bonds. Strong luminescence at 404 nm can be detected in 1 . DFT calculation suggests that 1 displays a reduced bandgap, which is led by a more dispersed LUMO band of BV²⁺ compared with MV²⁺ in [MV(Ag₂I₄)]_n.     

Organic‐Inorganic Hybrid Materials: Syntheses,X‐ray Diffraction Study,and Characterisations of Manganese,Cobalt, and Copper Complexes of Modified Bis(phosphonates)

Four new cobalt, manganese, and copper bis(phosphonates), [Co₂{Cl₂C(PO₃)₂}(H₂O)₇ · 4H₂O] ( 1 ), [Co{Cl₂C(PO₂O(C(O)C₆H₅))₂(H₂O)₅} · 2H₂O{Cl₂C(PO₂O(C(O)C₆H₅))₂}{Co(H₂O)₆}] ( 2 ), [Mn{[Cl₂C(PO₂O(C(O)C₆H₅))₂](H₂O)₃}] ( 3 ), and [Cu{(CH₂C₅H₅N)C(OH)(PO₃H)₂}₂ · 4H₂O] ( 4 ), were prepared by gel, liquid, and evaporation crystallisation methods. Compounds 1 – 4 were characterised by X‐ray single‐crystal diffraction, elemental analysis, infrared spectroscopy, and thermogravimetric analysis. The effects of metal and various substituted groups in bis(phosphonate) ligands on the structure formation of bis(phosphonates) were studied. In the structure of 1 , the clodronic acid ligand ( L1 ) is in bischelating bonding mode, and the dinuclear units of 1 are surrounded by two‐dimensional water cluster patterns. The hydrogen bond network of compound 1 is extended to a three‐dimensional framework when the phosphonate oxygen atoms serve as hydrogen‐bond acceptors. In complex 2 , the CoO₆ octahedron shares a corner of one PCO₃ tetrahedron of the dibenzoyl derivative of clodronic acid ligand ( L2 ), and forms a two‐dimensional hydrogen bonding network, which consists of [Co(H₂O)₆}]²⁺ cations, lattice water molecules and L2 ligand molecules. Compound 3 , in turn, consists of dimeric building blocks built up of PCO₃ tetrahedra of the ligand L2 , which connect the corner‐sharing MnO₆ octahedra and form an overall 2D structure through hydrogen bonds of coordinated and crystal water molecules and phosphonate oxygen atoms. Complex 4 is among the first metal complexes of risedronic acid ( L3 ). In compound 4 , two L3 ligand molecules chelate tridentately the Cu^II atom at the center of symmetry, and the monomeric units of 4 are connected to a 3D structure through hydrogen bonding of coordinated and lattice water molecules to both protonated and deprotonated phosphonate oxygen atoms and protonated nitrogen atoms in the pyridine ring.     

Synthesis,Crystal Structures,and Thermal Properties of New Zinc(II) Thiocyanato Coordination Compounds

Reaction of zinc(II) thiocyanate with pyrazine, pyrimidine, pyridazine, and pyridine leads to the formation of new zinc(II) thiocyanato coordination compounds. In bis(isothiocyanato‐N)‐bis(μ₂‐pyrazine‐N,N) zinc(II) ( 1 ) and bis(isothiocyanato‐N)‐bis(μ₂‐pyrimidine‐N,N) zinc(II) ( 2 ) the zinc atoms are coordinated by four nitrogen atoms of the diazine ligands and two nitrogen atoms of the isothiocyanato anions within slightly distorted octahedra. The zinc atoms are connected by the diazine ligands into layers, which are further linked by weak intermolecular S ··· S interactions in 1 and by weak intermolecular C–H ··· S hydrogen bonding in 2 . In bis(isothiocyanato‐N)‐bis(pyridazine‐N) ( 3 ) discrete complexes are found, in which the zinc atoms are coordinated by two nitrogen atoms of the isothiocyanato ligands and two nitrogen atoms of the pyridazine ligands. The crystal structure of bis(isothiocyanato‐N)‐tetrakis(pyridine‐N) ( 4 ) is known and consists of discrete complexes, in which the zinc atoms are octahedrally coordinated by two thiocyanato anions and four pyridine molecules. Investigations using simultaneous differential thermoanalysis and thermogravimetry, X‐ray powder diffraction and IR spectroscopy prove that on heating, the ligand‐rich compounds 1 , 2 , and 3 decompose without the formation of ligand‐deficient intermediate phases. In contrast, compound 4 looses the pyridine ligands in two different steps, leading to the formation of the literature known ligand‐deficient compound bis(isothiocyanato‐N)‐bis(pyridine‐N) ( 5 ) as an intermediate. The crystal structure of compound 5 consists of tetrahedrally coordinated zinc atoms which are surrounded by two isothiocyanato anions and two pyridine ligands. The structures and the thermal reactivity are discussed and compared with this of related transition metal isothiocyanates with pyrazine, pyrimidine, pyridazine, and pyridine.     

High Catalytic Activity of Palladium(II)‐Exchanged Mesoporous Sodalite and NaA Zeolite for Bulky Aryl Coupling Reactions: Reusability under Aerobic Conditions

Exchange for the better : Mesoporous sodalite and NaA zeolite exchanged with Pd²⁺ exhibit remarkably high activity and reusability in C? C coupling reactions under aerobic atmosphere. It is proposed that the catalytic reactions are mediated by a molecular Pd⁰ species generated in situ within the pores (see picture), which is oxidized back to Pd²⁺ by O₂, preventing the formation of catalytically inactive Pd⁰ agglomerates.

     

Design of Interpenetrated Networks of Mesostructured Hybrid Silica and Nonconductive Poly(vinylidene fluoride)–Cohexafluoropropylene (PVdF–HFP) Polymer for Proton Exchange Membrane Fuel Cell Applications

Organic–inorganic hybrid membranes of poly(vinylidene fluoride)–cohexafluoropropylene (PVdF–HFP) and mesostructured silica containing sulfonic acid groups were synthesized by using the sol‐gel process. These hybrid membranes were prepared by in situ co‐condensation of tetraethoxysilane and an organically modified silane (ormosil) by a self‐assembly route using organic surfactants as templates for tuning the architecture of the hybrid organosilica component. In this paper, we describe the elaboration and characterization of hybrid membranes all the way from the precursor solution to the evaluation of the fuel cell performances. These hybrid materials were extensively characterized by using NMR and IR spectroscopy, electron microscopy, or impedance spectroscopy so as to determinate their physicochemical and electrochemical properties. Even though the ion‐exchange capacity (IEC) was quite weak, the first fuel cell tests performed with these hybrid membranes show promising results relative to optimized Nafion 112 thanks to great water management of the silica inside the hydrophobic polymer.     

Synthesis,Crystal Structure,and Optical Properties of (CH3NH3)2CoX4 (X = Cl,Br, I,Cl0.5Br0.5, Cl0.5I0.5, Br0.5I0.5)

The reaction of methylammonium halides and cobalt halides yielded the organic‐inorganic hybrid compounds of general formula (CH₃NH₃)₂CoX₄. By varying the different halides, we were able to synthesize the whole row from Cl to I as well as some mixed halides compounds and to determinate the crystal structures. (CH₃NH₃)₂CoX₄ (X = Cl, Br, Cl_0.5Br_0.5, Br_0.5I_0.5) crystallize isotypic to (CH₃NH₃)₂HgCl₄ in space group P2₁/c with Z = 4 [X = Cl: a = 7.6483(9), b = 12.6885(18), c = 10.8752(12) Å, β = 96.639(9)°; X = Cl_0.5Br_0.5: a = 7.8271(9), b = 12.9543(9), c = 11.1007(11) Å, β = 96.320(8)°; X = Br: a = 7.9782(2), b = 13.1673(2), c = 11.2602(2) Å, β = 96.3260(10)° and X = Br_0.5I_0.5: a = 8.2435(12), b = 13.645(2), c = 11.5856(18) Å, β = 95.54(2)°]. The mixed halides show a statistic distribution in both cases. In (CH₃NH₃)₂CoCl₂I₂ an ordered variant is realized representing a new structure type [C2/m, Z = 4, a = 18.808(4), b = 7.3604(7), c = 10.4109(17) Å, β = 120.364(13)°]. (CH₃NH₃)₂CoI₄ crystallizes again isotypic to the respective mercury compound [(CH₃NH₃)₂HgCl₄] [Pbca, Z = 8, a = 10.9265(5), b = 12.1552(5), c = 20.9588(9) Å]. All structures are build up by inorganic tetrahedral [CoX₄]^2– anions and organic (CH₃NH₄)⁺ cations. Additionally the Raman spectra as well as the optical reflectance spectra are discussed.