Biomimetic mineralization of nacre-inspired multiple crosslinked PVA/CaAlg/SiO2 membrane with simultaneously enhanced mechanical and separation properties.

Inspired by the natural nacre structure, we propose a new strategy to fabricate mineralized, multiple crosslinked hydrogel membranes with the "rigid silica in soft polymer" nacre-like structure. In-situ SiO2 nanoparticles (NPs) and polyvinyl alcohol/sodium alginate (PVA/NaAlg) are used to simulate the rigid "bricks" and soft "mortar" compositions of nacre, respectively. The nacre-like mineralized (PVA/CaAlg/SiO2) membrane showed a higher tensile strength of 4.1 ± 0.08 MPa, excellent pure water flux of 170 ± 3 L/m2h, and an oil/water rejection rate of 99 %. The interwoven hierarchal structure, similar to nacre, was determined by SEM analysis. In addition, incorporating SiO2 NPs increases the anti-swelling, roughness, and hydrophilicity of the membranes. PVA/CaAlg/SiO2 membrane exhibited excellent superhydrophilicity (WCA value was 0°) and superoleophobicity underwater (OCA value was 162°). PVA/CaAlg/SiO2 membrane also showed excellent separation performance for water-soluble organic pollutants and can be used for dye separation with rejection efficiencies of 99.5 %, 99.1 %, and 98.3 % for Congo red (CR), Alizarin red (AR), and Sunset yellow (SY), respectively. Moreover, PVA/CaAlg/SiO2 membrane had outstanding long-term filtration and antifouling performance. The biomineralization-inspired structure provides a promising technique that can be used to prepare high-performance organic-inorganic membranes with great promise for wastewater separation application.

Resettable fluorescence logic gate based on calcein/layered double hydroxide ultrathin films.

A fluorescent logic gate was fabricated based on calcein/layered double hydroxide ultrathin films (UTFs) via alternate assembly technique, which exhibits high stability, reversibility, and resettability. The logic gate was manipulated by utilizing pH value, Hg(2+) and Cl(-) ion as inputs, and the fluorescence emission of the (calcein/LDH)(16) UTF as output, serving as a three-input logic gate that combines the YES and INHIBIT operation.

Magnetic-field-assisted assembly of layered double hydroxide/metal porphyrin ultrathin films and their application for glucose sensors.

The ordered ultrathin films (UTFs) based on CoFe-LDH (layered double hydroxide) nanoplatelets and manganese porphyrin (Mn-TPPS) have been fabricated on ITO substrates via a magnetic-field-assisted (MFA) layer-by-layer (LBL) method and were demonstrated as an electrochemical sensor for glucose. The XRD pattern for the film indicates a long-range stacking order in the normal direction of the substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the MFA LDH/Mn-TPPS UTFs reveal a continuous and uniform surface morphology. Cyclic voltammetry, impedance spectroscopy, and chronoamperometry were used to evaluate the electrochemical performance of the film, and the results show that the MFA-0.5 (0.5 T magnetic field) CoFe-LDH/Mn-TPPS-modified electrode displays the strongest redox current peaks and fastest electron transfer process compared with those of MFA-0 (without magnetic-field) and MFA-0.15 (0.15 T magnetic field). Furthermore, the MFA-0.5 CoFe-LDH/Mn-TPPS exhibits remarkable electrocatalytic activity toward the oxidation of glucose with a linear response range (0.1-15 mM; R(2) = 0.999), low detection limit (0.79 µM) and high sensitivity (66.3 µA mM(-1) cm(-2)). In addition, the glucose sensor prepared by the MFA LBL method also shows good selectivity and reproducibility as well as resistance to poisoning in a chloride ion solution. Therefore, the novel strategy in this work creates new opportunities for the fabrication of nonenzyme sensors with prospective applications in practical detection.

Biodiesel production from soybean oil by quaternized polysulfone alkali-catalyzed membrane.

A series of alkalized polysulfones (APSF) were synthesized by several chemical reactions (chloromethylation, quaternization and alkalization). Among these reactions, chloromethylation and quaternization are two key reactions and have been studied in detail regarding the optimization of both chloromethylation and quaternization. FTIR and (1)H NMR spectrum confirmed the successful preparation of chloromethylated polysulfone. The best IEC of APSF was obtained for 1.68meqg(-1) under reaction time of 10h and reaction temperature of 45°C. The APSF membrane as a heterogeneous catalyst for the transesterification of soybean oil with methanol was prepared through the method of solvent evaporation phase inversion. The effects of co-solvent types, mass ratios of soybean oil/co-solvent, water content and free fatty acids (FFAs) content in soybean oil on the conversions using the APSF membrane during transesterification were studied. The reusability of the APSF membrane and the kinetics of the reaction catalyzed by the APSF membrane were also investigated.

Continuous esterification to produce biodiesel by SPES/PES/NWF composite catalytic membrane in flow-through membrane reactor: experimental and kinetic studies.

A novel composite catalytic membrane (CCM) was prepared from sulfonated polyethersulfone (SPES) and polyethersulfone (PES) blend supported by non-woven fabrics, as a heterogeneous catalyst to produce biodiesel from continuous esterification of oleic acid with methanol in a flow-through mode. A kinetic model of esterification was established based on a plug-flow assumption. The effects of the CCM structure (thickness, area, porosity, etc.), reaction temperature and the external and internal mass transfer resistances on esterification were investigated. The results showed that the CCM structure had a significant effect on the acid conversion. The external mass transfer resistance could be neglected when the flow rate was over 1.2 ml min(-1). The internal mass transfer resistance impacted on the conversion when membrane thickness was over 1.779 mm. An oleic acid conversion kept over 98.0% for 500 h of continuous running. The conversions obtained from the model are in good agreement with the experimental data.

Biodiesel production from waste chicken fat with low free fatty acids by an integrated catalytic process of composite membrane and sodium methoxide.

An integrated process of catalytic composite membranes (CCMs) and sodium methoxide was developed to produce biodiesel from waste chicken fat. The free fatty acids (FFAs) in the chicken oil were converted to methyl esters by esterification with methanol using a novel sulfonated polyethersulfone (SPES)/PES/non-woven fabric (NWF) CCMs in a flow-through catalytic membrane reactor. The CCM is that the NWF fibers were fully embedded in SPES/PES with a homogeneous and microporous structure. The oil obtained after esterification was carried out by transesterification of sodium methoxide. The results showed that the FFAs conversion obtained by CCMs with the acid capacity of 25.28 mmol (H(+)) was 92.8% at the residence time 258s. The CCMs present a good stability during the continuous running of 500 h. The conversion of transesterification was 98.1% under the optimum conditions. The quality of the biodiesel met the international standards.

Esterification of acidified oil with methanol by SPES/PES catalytic membrane.

A sulfonated polyethersulfone (SPES)/polyethersulfone (PES) blend catalytic membrane was prepared and used as a heterogeneous catalyst in the esterification of the acidified oil (acid value 153 mg KOH/g) with methanol for producing biodiesel. The results showed that the free fatty acids conversion reached 97.6% using SPES/PES catalytic membrane under the optimal esterification conditions. Meanwhile, the SPES/PES membrane with 20.3% degree of sulfonation showed a good catalytic stability. A pseudo-homogeneous kinetic model was established. The results indicated that the reaction rate constant increased with increasing methanol/acidified oil molar ratio, the loading of catalytic membrane and reaction temperature. The reaction order was 2 and the activation energy decreased from 74.65 to 21.07 kJ/mol with increasing catalytic membrane loading from 0 to 0.135 meq/g(oil). It implies that the esterification is not diffusively controlled but kinetically controlled. The predicted results were in good agreement with the experimental data.

Layer-by-layer assembly of electroactive dye/inorganic matrix film and its application as sensor for ascorbic acid.

A novel inorganic-organic composite ultrathin film was fabricated by layer-by-layer assembly of naphthol green B (NGB) and layered double hydroxides (LDHs) nanoplatelets, which shows remarkable electrocatalytic behavior for oxidation of ascorbic acid. LDHs nanoplatelets were prepared using a method involving separate nucleation and aging steps (particle size: 25±5 nm; aspect ratio: 2-4) and used as building blocks for alternate deposition with NGB on indium tin oxide (ITO) substrates. UV-vis absorption spectroscopy and XRD display regular and uniform growth of the NGB/LDHs ultrathin film with extremely c-orientation of LDHs nanoplatelets (ab plane of microcrystals parallel to substrates). A continuous and uniform surface morphology was observed by SEM and AFM image. The film modified electrode displays a couple of well-defined reversible redox peaks attributed to Fe(2+)/Fe(3+) in NGB (ΔE(p)=68 mV and I(a)/I(c)=1.1). Moreover, the modified electrode shows a high electrocatalytic activity towards ascorbic acid in the range 1.2-55.2 µM with a detection limit of 0.51 µM (S/N=3). The Michaelis-Menten constant was calculated to be K(M)(app)=67.5 µM.

Preparation and characterization of the organic-inorganic hybrid membrane for biodiesel production.

A novel organic-inorganic hybrid membrane as heterogeneous acid catalyst for biodiesel production was prepared from zirconium sulfate (Zr(SO4)2) and sulfonated poly(vinyl alcohol) (SPVA). The structure and properties of the hybrid catalytic membrane were investigated by means of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), thermogravimetry (TG), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of the hybrid membranes was tested by the esterification of the acidified oil with methanol. It was found that the Zr(SO4)2 particles were better dispersed in SPVA matrix as a result of the stronger interaction between Zr(SO4)2 and SPVA compared with Zr(SO4)2/poly(vinyl alcohol) (PVA) hybrid membrane. Esterification results showed that the conversions of free fatty acid (FFA) in acidified oil were 94.5% and 81.2% for Zr(SO4)2/SPVA and Zr(SO4)2/PVA catalytic membranes, respectively. The stability of Zr(SO4)2/SPVA catalytic membrane is superior to Zr(SO4)2/PVA catalytic membrane.

Layer-by-layer ultrathin films of azobenzene-containing polymer/layered double hydroxides with reversible photoresponsive behavior.

We report the preparation of a reversible photoresponsive ultrathin film containing a photoactive azobenzene polymer poly{1-4[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl sodium salt} (PAZO) and exfoliated layered double hydroxide (LDH) nanosheets using a layer-by-layer (LBL) self-assembly technique. Alternate irradiation with UV and visible light (lambda > 450 nm) results in a reversible switching between the trans isomer and the cis-rich photostationary state of the azobenzene group with concomitant significant changes in film color. Fluorescence polarization measurements indicated that the orientation of the azobenzene chromophores in the LDH matrix undergoes a reversible realignment during the photoisomerization processes. Photoisomerization induced by alternate UV and visible light irradiation was accompanied by reversible morphological changes of the LBL film, observable by atomic force microscopy (AFM). Molecular dynamics (MD) studies demonstrated that the LDH monolayers allow sufficient free space for the PAZO to undergo isomerization of its azobenzene chromophores. The reversible photoalignment of PAZO was also followed by MD simulations, and the results are in reasonable agreement with the experimental findings, further validating the configurational and orientational changes proposed for PAZO during the reversible photoprocess. It has been demonstrated that the host (LDH nanosheet)-guest (PAZO) interactions are key factors in determining the reversible photoresponsive performances of the film, since the comparative pristine PAZO film shows no such properties. Therefore, the incorporation of a photoactive moiety within the inorganic nanosheets of LDH by the LBL technique provides an attractive and feasible methodology for creating novel light-sensitive materials and devices with potential read-write capabilities.