Photoluminescent multilayer film based on polyoxometalate and tris(2,2-bipyridine)ruthenium

A photoluminescent multilayer film based on Keggin-type polyoxometalate PMo₁₂O₄₀³⁻ (PMo₁₂) and transition metal complex tris(2,2-bipyridine) ruthenium [Ru(bpy)₃]²⁺ (Ru(bpy)) was prepared by using layer-by-layer assembly(LBL). The formation of multilayer film was monitored by ultraviolet absorption spectra. The absorption intensity of characteristic peaks increase with a four-layer cycle, indicating that the LBL assembly film grow linearly and reproducibly from layer to layer. The composition of the film was measured by X-ray photoelectron spectrum (XPS). The data of XPS confirmed the presence of the expected elements. The film exhibited photoluminescence arising from π^*−t_2g ligand-to-metal transition of Ru(bpy) and redox activity attributing to molybdenum-centered redox processes of PMo₁₂. The surface morphology of multilayer film was characterized by atomic force microscopy (AFM). The result shows that the film had a smooth surface with root-mean-square (rms) roughness ca. 1.363 nm for {PEI/(PSS/PEI/PMo₁₂/Ru(bpy))₃}. The grains are homogeneously dispersed in the substrate and have a rather narrow diameter size distribution.     

多金属氧酸盐-三(2,2′-联吡啶)钌层接层自组装纳米复合膜的制备及光致发光性质

层接层自组装技术作为制备均匀、超薄多层薄膜的有效方法已引起人们极大的关注 .利用这种方法可以将无机、有机组分有序地组合在薄膜中 ,在固体基底上构建功能性分子的超分子结构 ,并且可以在分子水平上调控每层膜的结构和厚度 ,从而实现薄膜的光、电、磁、非线性光学等功能化 [1～ 6 ] .多金属氧酸盐具有独特、优异的物理化学性能 ,在药物化学、电化学、催化化学及材料化学等方面具有十分广阔的应用前景 [7～ 9] ,将其组合在薄膜中 ,可赋予膜材料更优异的功能特性 .钌的联吡啶配合物在光化学、电化学及电子和能量转移等领域颇受关注 ,并已…     

Effects of film structure on electrochromic properties of the multilayer films containing polyoxometalates

Multilayer films of tungstophosphate anion (P₂W₁₈) and poly(allylamine hydrochloride) (PAH) were fabricated on quartz and ITO substrates by layer-by-layer self-assembly method. These films were characterized by UV–vis spectroscopy, cyclic voltammetry (CV), chronoamperometric (CA), chronocoulometry (CC) and atomic force microscopy (AFM). The effects of film structure on multilayer electrochromic properties were investigated. The electrochromic responses of the composite films were related to the surface coverage of anion and multilayer thickness. It was found that higher concentration of polycation and anion, or adding salt to the polycation solution used for multilayer film preparation led to thicker and denser film structure which improved optical contrast and coloration efficiency whereas prolonged response time.     

Electrochemical study of multilayer films built on glassy carbon electrode with polyoxometalate anions and two multi-charged molecular cationic species

Electrochemical results are reported on complex films built onto glassy carbon electrodes. Each film involves one polyoxometalate and one or two cations : methyl viologen and meso-tetra(4N-methylpyridyl porphyrin). In a given film, layers of polyoxometalate anions alternate with layers made of one of the two cations. Electrochemical studies indicate the effective building of films with polyoxometalate and both cations present. They also demonstrate that, in the film building process, the electrochemical response of every new layer is influenced by coulombic interactions and conducting properties with the immediately underlying layer.     

Self-assembled multilayer films of poor water-soluble copper(II) complexes constructed from dipyrido[3,2-d:2′,3′-f]quinoxaline (Dpq) ligand as well as their fluorescent properties

New multilayer films were prepared by alternating adsorption of poly(sodium 4-styrenesulfonate) (PSS) and a new complex of [Cu₂(Dpq)₂(Ac)₂(H₂O)₂] (ClO₄)₂·H₂O (1) (Dpq=dipyrido[3,2-d:2′,3′-f]quinoxaline, Ac=acetate) or a related complex [Cu(Dpq)₂(H₂O)] (ClO₄)₂·H₂O (1a) by electrostatic layer-by-layer self-assembly technique, respectively. Compounds 1 and 1a have been synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. Single-crystal X-ray analyses show that complexes 1 and 1a possess a dinuclear and a mononuclear structure, respectively, which are further extended into layered frameworks by π-π stacking and hydrogen-bonding interactions. The multilayer films were characterized by UV-vis spectroscopy, fluorescence spectroscopy, small-angle X-ray reflectivity measurements, and atomic force microscopy (AFM) imaging. UV spectroscopy shows that the deposition process is regular and highly reproducible from layer to layer. AFM image indicates that the film surface is uniform and smooth. The fluorescent properties of the films were studied and the results showed that the forming condition of the films had great influence on their properties.     

A Ag-La heterometallic 2D layer based on mono-lacunary Keggin polyoxometalate: Synthesis,structure, and photocatalytic property

A new two-dimensional (2D) purely inorganic 4d-4f heterometallic compound [La(H₂O)₈][Ag{La(H₂O)₆}₂{SiW₁₁La(H₂O)₄O₃₉}₂]·13H₂O (1), based on mono-lacunary Keggin-type {α-SiW₁₁O₃₉} cluster (abbreviated to SiW₁₁), was conventional synthesized and characterized by elemental analysis, IR, TG, and single crystal X-ray diffraction. In compound 1, two mono-substituted {SiW₁₁La(H₂O)₄O₃₉}₂ clusters (abbreviated to SiW₁₁La) polymerize together to form a dimer. And the dimers are linked by Ag⁺ and La³⁺ heterometallic cations displaying a 2D network. Furthermore, the photocatalytic experiment indicates that the title compound presents excellent photocatalytic activity towards degradation of rhodamine B (RhB) dye.     

Preparation and characterization of the nanoporous ultrathin multilayer films based on molybdenum polyoxometalate (Mo38)n

Ultrathin multilayer films of the wheel-shaped molybdenum polyoxometalate cluster (Mo₃₈)_n and poly(allylamine hydrochloride)(PAH) have been prepared by the layer-by-layer (LbL) self-assembly method. The ((Mo₃₈)_n/PAH)_m multilayer films have been characterized by X-ray photoelectron spectra (XPS) and atomic force microscopy (AFM). UV-VIS measurements reveal regular film growth with each (Mo₃₈)_n adsorption. The electrochemistry behavior of the film at room temperature was investigated.     

Rapid and selective oxidation of benzyl alcohols to aldehydes and ketones with novel vanadium polyoxometalate under solvent-free conditions

A novel vanadium polyoxometalate [(C₆H₅CH₂)(CH₃)₃N]₃[H₃V₁₀O₂₈]3H₂O works as a useful oxidant for selective and rapid oxidation of benzylic alcohols to the corresponding carbonyl compounds in the presence of PTSA under solvent-free, room temperature in excellent yield.     

A novel amperometric biosensor based on single walled carbon nanotubes with acetylcholine esterase for the detection of carbaryl pesticide in water

Amperometric biosensor is fabricated for the detection of carbaryl based on single walled carbon nanotubes (SWCNTs) and acetylcholine esterase (AchE). The dispersion of SWCNTs in positively charged polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), possibly takes place due to weak supramolecular interaction between them, which then binds electrostatically to the negatively charged AchE at pH 7.4 using layer-by-layer (LbL) self-assembly technique. The optical intensity of UV/vis spectra increased with the number of layers, indicating the build up of a multilayer coating on the electrode. The activity of acetylcholine esterase on modified electrode of 3 mm in diameter was found to be 0.2 U. The biosensor showed good sensitivity and stability towards the monitoring of carbaryl pesticides in water with the detection limit of 10⁻¹² g L⁻¹ and recovery of 99.8 ± 2.7% to 10⁻¹⁰ g L⁻¹. This protocol can be used for the immobilization of other enzymes to fabricate a range of biosensors.     

Molecular assemblies based on the template-directing effect of anionic polyoxometalate clusters and organic cationic flexibility

Molecular assembly processes by utilizing the template-directing effect of anionic polyoxometalate clusters and the flexible organic cation have achieved three hybrids: (H₂bpp)(Hbpp)[PMo₁₂O₄₀]·3DMF (1), (H₂bpp)(Hbpp)(bpp)₂ [PMo₉V₃O₄₀(VO)₂]₂ (2), and (H₂bpp)₂[β-Mo₈O₂₆] (3) (bpp = 1,3-bis(4-pyridyl)propane). Three compounds were characterized using single crystal X-ray crystallography, elemental analysis, IR, XPS, EPR, voltammetric behavior and TGA. Crystal structural analyses revealed that compounds 1–3 were all constructed from protonated organic bpp cations with different POM clusters: isolated α-Keggin P–Mo cluster in 1; dimer of bi-capped α-Keggin P–Mo–V anions linked through a {V₂O₂} unit in 2; β-octamolybdate isopolyanion in 3, respectively. All three assemblies demonstrated a higher thermal stability. The protonated bpp cations lost at temperature higher than 300 °C that the strong intermolecular interactions may account for the high initial temperature of weight loss. The electrochemistry property of compound 2 modified carbon paste electrode was also studied in 1 M H₂SO₄ aqueous.     

Novel estradiol sensors based on carbon nanotube multilayer modified gold hair microelectrodes

Multi-walled carbon nanotube multilayers were modified onto a newly proposed gold hair microelectrode via a simple layer-by-layer assembling method.The resulting electrode showed a sensitive oxidation response to estradiol with detection limit as low as 1.0×10~(-8) mol/L,foreseeing a promising approach to the fabrication of high-sensitive microsensors.     

A novel detection of hydrogen peroxide based on a luminescent polyoxometalate

In this paper, we attempt to construct a simple and sensitive detection method for hydrogen peroxide based on reversible colour change and luminescence switching modulated by the electrochemical stimulation and redox reaction of H(2)O(2) with electroreduced polyoxometalate. This method successfully combines the electrochromic and luminescent properties of the polyoxometalate to develop a novel detection method for H(2)O(2) with good reversibility, which displays high sensitivity, a wide linear range and a low detection limit to H(2)O(2).     

Phosphorous-filled nanobrick wall multilayer thin film eliminates polyurethane melt dripping and reduces heat release associated with fire

Unique trilayer (TL) thin films of sodium montmorillonite (MMT), poly(allylamine hydrochloride) (PAH) and poly(sodium phosphate) (PSP) are prepared via layer-by-layer (LbL) assembly. This three-component nanocoating completely shuts down melt dripping and reduces heat release of open-celled flexible polyurethane (PU) foam when exposed to direct flame due to a synergistic interaction between PSP and the thermally shielding clay platelets in the condensed phase. Post burn scanning electron microscopy reveals the nanocoating's swollen morphology is able to maintain foam shape, cellular structure, and porosity. Cone calorimetry reveals that 4 TL coated foams (<3 wt% addition) have a peak heat release rate that is reduced by 54% relative to the uncoated control. Using LbL assembly, this work combines two common flame-retarding mechanisms (thermal shielding clay and intumescing PAH/PSP) in a single coating system and provides a foundational platform for new environmentally-benign flame retardant strategies for various substrates (e.g., foam found in home furnishings).     

Study of enzyme biosensor based on carbon nanotubes modified electrode for detection of pesticides residue

The paper describes a controllable layer-by-layer （LBL） self-assembly modification technique of multi-walled carbon nanotubes （MWNTs） and poly（diallyldimethylammonium chloride） （PDDA） towards glassy carbon electrode （GCE）, Acetylcholinesterase （ACHE） was immobilized directly to the modified GCE by LBL self-assembly method, the activity value of AChE was detected by using i-t technique based on the modified Ellman method. Then the composition of carbaryl were detected by the enzyme electrode with 0.01U activity value and the detection limit of carbaryl is 10^- 12 g L ^-1 so the enzyme biosensor showed good properties for pesticides residue detection.     

基于层层组装钴铝水滑石/聚电解质包裹碳纳米管的无酶葡萄糖传感器

采用共沉淀法合成了钴铝水滑石(CoAl-LDH),将CoAl-LDH与PSS包裹的CNTs(CNTs@PSS)通过层层自组装法构筑CNTs@PSS/CoAl-LDH多层膜电极,并将其应用于葡萄糖的分析测定。X射线衍射光谱、红外光谱和SEM表明:共沉淀法合成的CoAl-LDH具有典型的水滑石特征峰及形貌。电化学阻抗谱表明:CoAl-LDH可与CNTs@PSS均匀有效地组装构筑多层膜。电化学研究表明:CNTs的引入很好地提高了CoAl-LDH修饰电极的灵敏度。研究结果表明该传感器对葡萄糖在3.0×10-6～4.98×10-4mol/L范围内呈良好的线性响应,灵敏度为1.03×10-3A.L/mol。     

Olefin epoxidation with tert-BuOOH catalyzed by vanadium polyoxometalate immobilized on ionic liquid-modified MCM-41

Preparation and characterization of vanadium-containing polyphosphomolybdates supported on ionic liquid-modified MCM-41, MCM-41-Im, are reported. The catalyst, [PVMo@MCM-41-Im], was characterized by elemental analysis, X-ray diffraction, scanning electron microscopy and also FT-IR, and UV-Vis spectroscopic methods. This heterogeneous catalytic system was applied for efficient epoxidation of various olefins in the presence of tert-BuOOH in 1,2-dichloroethane under reflux. The catalyst can be reused several times without apparent loss of its catalytic performance.     

基于聚多巴胺/铜微粒自组装多层膜的无酶葡萄糖传感器

利用多巴胺易于在电极表面发生自聚反应,且聚多巴胺膜中富含邻苯二酚等反应性基团,可通过二次反应实现电极表面的进一步功能化修饰的特点,在玻碳电极(GCE)表面,将多巴胺自聚膜(PDA)与铜微粒(Cu)进行层-层自组装,构建了无酶葡萄糖电化学传感器(GCE/(PDA/ Cu) n )。传感器的灵敏度可通过控制多层膜的组装层数进行调控。采用紫外-可见光谱跟踪表征了多层膜的组装过程,结果表明,多层膜的生长是逐步且均匀的过程。采用循环伏安法和电流-时间曲线法研究了修饰电极对葡萄糖的电催化氧化性能。对于GCE/(PDA/ Cu)4,检测葡萄糖的线性范围为0.5~9.0 mmol/ L,检出限为5.8μmol/ L(S/ N=3)。本传感器具有良好的重现性、稳定性和较强的抗干扰能力。将本传感器用于血清中葡萄糖的测定,结果令人满意。     

A novel organic-inorganic hybrid based on a dinuclear copper complex supported on a keggin polyoxometalate

The autoassembly process of copper-oxalate dimers and Keggin type polyoxometalates leads to the first example of a new family of organic-inorganic hybrids, K(14)[(Cu(2)(bpy)(2)(mu-ox))(SiW(11)O(39)Cu(H(2)O))](2)[SiW(11)O(39)Cu(H(2)O)]. approximately 55H(2)O. This compound crystallizes in the monoclinic space group C2/m, a = 37.932(6) A, b = 21.303(3) A, c = 12.546(2) A, beta = 106.16(1) degrees, Z = 2. The crystal structure reveals the presence of a polymeric hybrid built up of alternating dimer and polyoxometalate entities.     

基于静电自组装牛血清白蛋白复合膜的研究

利用静电层层自组装技术制备了聚乙烯亚胺-牛血清白蛋白复合膜,通过紫外-可见分光光度法监测该组装过程。牛血清白蛋白溶液的质量浓度为0.1g·L-1,聚乙烯亚胺溶液的浓度为10mmol·L-1,石英片基底在两种溶液中的浸泡时间为均为5min,每次浸泡后用水清洗3次,每次1min。多层膜在特征吸收处的吸光度随膜层数递增均匀增加,且吸光度与膜层数间呈线性关系,这表明该复合膜是均匀组装的。该组装过程具有良好的重现性。该复合膜的组装方法有望用于制备酶生物传感器。     

Sonochemical preparation of photochromic nanocomposite thin film based on polyoxometalates well dispersed in polyacrylamide

Novel photochromic nanocomposite thin film containing phosphotungstic acid entrapped in polyacrylamide was prepared using ultrasound technique. TEM image revealed that the polyoxometalates nanoparticles with narrow size distribution were finely dispersed in polymer matrix. IR spectra showed that the Keggin geometry of polyoxometalates was still preserved inside the composite film and strong Coulombic interaction was built between heteropolyoxometalates and polyacrylamide via hydrogen bond. It was found that the thermal stability of the hybrid film was lower than that of pure polymer but the film was stable enough for photochromic application from the TG-DTA curves. The transparent film changed from colorless to blue under UV irradiation and showed reversible photochromism. The bleaching process occurred when the film was in contact with air or O₂ in the dark. The photoreduced process was in accordance with radical mechanism.