Gradient nanoporous phenolics as substrates for high-flux nanofiltration membranes by layer-by-layer assembly of polyelectrolytes

Thin film composite(TFC) membranes represent a highly promising platform for efficient nanofiltration(NF)processes. However, the improvement in permeance is impeded by the substrates with low permeances. Herein,highly permeable gradient phenolic membranes with tight selectivity are used as substrates to prepare TFC membranes with high permeances by the layer-by-layer assembly method. The negatively charged phenolic substrates are alternately assembled with polycation polyethylenimine(PEI) and polyanion poly(acrylic acid)(PAA)as a result of electrostatic interactions, forming thin and compact PEI/PAA layers tightly attached to the substrate surface. Benefiting from the high permeances and tight surface pores of the gradient nanoporous structures of the substrates, the produced PEI/PAA membranes exhibit a permeance up to 506 L? m-2?h-1?MPa-1, which is ~2–10 times higher than that of other membranes with similar rejections. The PEI/PAA membranes are capable of retaining N 96.1% of negatively charged dyes following the mechanism of electrostatic repulsion. We demonstrate that the membranes can also separate positively and neutrally charged dyes from water via other mechanisms.This work opens a new avenue for the design and preparation of high-flux NF membranes, which is also applicable to enhance the permeance of other TFC membranes.

Novel layer-by-layer assembly of rGO-hybridised ZnO sandwich thin films for the improvement of photo-catalysed hydrogen production

Metal oxide semiconductor materials such as ZnO have tremendous potential as light absorbers for photocatalysed electrodes in the electrochemical reduction of water. Promoters such as rGO have been added to reduce the recombination losses of charge carriers and improve its photoelectrochemical activity. In this study, the effect of layer ordering on the charge transfer properties of rGO-hybridised ZnO sandwich thin films for the photo-catalysed electrochemical reduction of water was investigated. rGO-hybridised ZnO sandwich thin films were prepared via a facile electrode position technique using a layer-by-layer approach. The thin films were analysed using FESEM, XRD, Raman, PL, UV–vis, EIS and CV techniques to investigate its morphological, optical and electrochemical properties. The FESEM images show the formation of distinct layers of rGO and ZnO nanorods/flakes via the layer-by-layer method. XRD confirmed the wurtzite structure of ZnO. PL spectroscopy revealed a reduction of photoemission intensity in the visible region（580 nm） when rGO was incorporated into the ZnO thin film. Among the six thin films prepared, ZnO/rGO showed superior performance compared to the other thin films（0.964 m A/cm） due to the presence of graphene edges which participate as heterogenous electrocatalysts in the photocatalysed electrolysis of water. rGO also acts as electron acceptor, forming an n-p heterojunction which improves the activity of ZnO to oxidise water molecules to O2. EIS revealed that the application of rGO as back contact（rGO/ZnO, rGO/ZnO/rGO） reduces the charge transfer resistance of a semiconductor thin film. Alternatively, rGO as front contact（ZnO/rGO, rGO/ZnO/rGO） improves the photo-catalysed electrolysis of water through the participation of the rGO edges in the chemical activation of water. The findings from this study indicate that the layer ordering significantly affects the thin film＇s electrostatic properties and this understanding can be further advantageous for tunable applications.

In vitro corrosion resistance,antibacterial activity and cytocompatibility of a layer-by-layer assembled DNA coating on magnesium alloy

A chitosan/deoxyribonucleic acid(CHI/DNA)_(5)coating was constructed by layer-by-layer(LbL)assembly dip coating method with Mg(OH)_(2)coating as an inner protective layer on AZ31 alloy.X-ray diffractometry,X-ray photoelectron spectrometry,Fourier transform infrared spectroscopy and field-emission scanning electron microscopy were utilized to represent the chemical compositions and surface morphologies of the coatings.Electrochemical tests and hydrogen evolution measurements were implemented to confirm the good corrosion resistance of the composite coating in artificial body fluid.Antimicrobial activity of the composite coatings was tested via the plate-counting method,and the cytotoxicity of the samples was appraised by MTT assay and Live/dead staining.A double action was put into effect for the composite coating,which the inner Mg(OH)2 coating plays the part of physical barrier,and the outer(CHI/DNA)5 coating is employed as an inducer to fabricate a biocompatible Ca-P corrosion product coating during immersion,making up for its thin thickness.Otherwise,the composite coating is also beneficial for the growth of bone,resulting from the biomineralization effect of the outer polyelectrolyte multilayer.The good antibacterial property of the(CHI/DNA)5/Mg(OH)2 coating is ascribed to the contact-killing strength of CHI.Thus,the obtained(CHI/DNA)5/Mg(OH)2 coating has a wide application prospect in the field of Mg-based bone implantation.

Enhanced performance of a solar cell based on a layer-by-layer self-assembled luminescence down-shifting layer of core–shell quantum dots

In this paper, core–shell quantum dots（QDs） with two polar surface functional groups（ZnSe/ZnS–COOH QDs and ZnSe/ZnS–NH;QDs） are synthesized in an aqueous phase. Photoluminescence（PL） and absorption spectra clearly indicate luminescence down-shifting（LDS） properties. On the basis of QDs, surface functional group multilayer LDS films（MLDSs） are fabricated through an electrostatic layer-by-layer（LBL） self-assembly method. The PL intensity increases linearly with the number of bilayers, showing a regular and uniform film growth. When the M-LDS is placed on the surface of a Si-based solar cell as an optical conversion layer for the first time, the external quantum efficiency（EQE） and shortcircuit current density（Jsc） notably increases for the LDS process. The EQE response improves in a wavelength region extending from the UV region to the blue region, and its maximum increase reaches more than 15% between 350 nm and 460 nm.

Power-Dependent Luminescence of CdSe/ZnS Nanocrystal Assembled Layer-by-Layer on a Silver Nanorod Array

We investigate the power-dependent luminescence of CdSe/ZnS semiconductor quantum dots closely packed layer- by-layer in the proximity of a silver nanorod array cavity. It is found that the emission peak shifts significantly to the longer wavelengths as the excitation power increases, especially when the longitudinal surface plasmon resonance of the Ag nanorod array cavity is adjusted to be close to the emission wavelength. The equivalent gain varies with the coating layer of CdSe/ZnS semiconductor quantum dots and the excitation power is also studied to explain this interesting spectrum-shifting effect. These findings could find applications in the dynamic information processing of active plasmonic and photonic nanodevices.

Induction of Superhydrophobicity in a Cellulose Substrate by LbL Assembly of Covalently Linked Dual-Sized Silica Nanoparticles Layers

Micro/nano texturized oxidized cellulose membranes (MNOCM) were constructed by layer-by-layer (LbL) assembly in which a base cellulose film was modified by covalent linkages to amino-functionalized silica nanoparticles (amino-SiO2 NPs, 260 nm diameter) and epoxy-functionalized silica nanoparticles (epoxy-SiO2 NPs, 30 nm diameter). The amino-SiO2 NPs grafted onto the MNOCM surface through a standard amidation reaction between the amino groups of the SiO2 NPs and the carboxyl groups of the MNOCM surface in the presence of EDC and NHS consequently forming a first layer of large (260 nm) nanoparticles;subsequently, it was reacted with smaller (30 nm) epoxy-SiO2 NPs. Continuous repetitions of these alternating sized silica NPs through a standard LbL approach lead to a highly micro/nano-texturized MNOCM film as shown by SEM, which was ultimately sealed with a layer of hydrophobic PFOTES (1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane). Although the wettability of MNOCM was no longer hydrophilic, it was found that at five layers deep of NPs, it became superhydrophobic as evidenced by a water contact angle of 151° ± 2° and slide angle of 4°. The change in wettability was attributed to increases in final LbL layer surface roughness induced by the sufficient LbL layering of alternating sizes of NPs akin to what is observed in a lotus leaf surface. It was also noted that these superhydrophobic-MNOCM materials displayed good self-cleaning.

Assembly and Electrochemical Study of Transition Metal Substituted Polyoxometalates SiW_(11)NiO_(39)^(6-) and SiW_(11)MnO_(39)^(6-) on 4-Aminothio-phenol Modified Glassy Carbon Electrode

Via layer-by-layer assembly, the polyoxometalates of Keggin type, SiW_ 11O_ 39Ni(H_2O) 6-(SiNiW_ 11) and {SiW_ 11O_ 39Mn(H_2O) 6-}(SiMnW_ 11) were first immobilized on a 4-aminothiophenol(4-ATP) modified glassy carbon electrode surface. The electrochemical behavior of these polyoxometalates was investigated. They exhibited some special properties in the films, which are different from those in a homogeneous aqueous solution. Their reaction mechanism in a multilayer film is proposed. The electrocatalytic behavior of these multilayer film electrodes for the reduction of BrO-_3 and NO-_2 were comparatively studied.

BASE-INDUCED RELEASE OF MOLECULES FROM HYDROGEN BONDING DIRECTED LAYER-BY-LAYER FILM

On the basis of hydrogen bonding directed layer-by-layer (LbL) assembly we have fabricated two multilayersystems, poly(acrylic acid) bearng spironaphthoxazine (PAA-SO)/poly(4-vinylpyridine) and carboxyl-terminated polyetherdendrimer (dendrimer-COOH)/poly(4-vinylpyridine). UV-Vis spectroscopy indicates that either PAA-SO or dendrimer-COOH can be released from the corresponding multilayer assemblies upon immerssion in a basic aqueous solution.Furthermore, the rate of molecule release can be controlled either by changing the pH value or by adjusting the layerstructure.

Layer-By-Layer技术构建化学传感器酶电极检测水体中有机磷的研究

基于层层累积自组装法将胆碱氧化酶和胆碱酯酶逐层固定在电极表面，制备了电流型水质有机磷检测化学传感器。讨论了自组装膜层数、pH值、温度对传感器电流响应的影响。制备的化学传感器对有机磷在浓度10^-9～10^-5mol／L呈良好的线性响应，检出限为1×10^-10mol／L。传感器的稳定性好，30天时的响应值仍保持90％。

LbL层层纳米自组装法制备新型微胶囊

本文介绍了一种新颖、灵活的制备纳米或微米胶囊方法———层层纳米自组装法 (LbL)。LbL法制备微胶囊的显著优越性在于能够在纳米尺度上对胶囊的大小、组成、结构、形态和囊壁厚度进行精确的控制。这种新型的微胶囊在生化、制药、药物控释、化妆品和催化等领域具有潜在的应用前景。

LbL法制备磁性纳米复合纤维膜生物相容性的研究

目的将磁性纳米材料嫁接到静电纺丝纤维膜上以达到增强其生物相容性的目的。方法通过"层-层自组装"(Lb L)的方法将Fe3O4磁性纳米颗粒组装到聚乳酸-羟基乙酸共聚物(poly(lactic-co-glycolic acid),PLGA)、ε-聚己内酯(ε-caprolactone,PCL)、明胶(gelatin,Gel)共混静电纺丝纤维膜(PPG)上,使用接触角仪、电子万能试验机、扫描电镜和振动样品磁强计对其表面形貌、亲水性、拉伸性能及磁学性能进行测试。将MC3T3-E1细胞接种到复合膜上,通过CCK-8法测试其细胞增殖,并与对照组进行比较。结果扫描电镜显示Fe3O4组装到膜表面,膜仍然保持类似细胞外基质的疏松纳米纤维结构。振动样品磁强计结果显示PPG膜在修饰了Fe3O4磁性纳米颗粒后具备超顺磁性性能。接触角及吸水率测量表明PPG-F膜亲水性显著改善,CCK-8检测结果显示PPG-F膜细胞增殖活性显著高于对照组PPG膜(P<0.05)。结论本方法形成的PPG-F纳米纤维复合膜具有良好生物相容性。

Synthesis of montmorillonite-chitosan hollow and hierarchical mesoporous spheres with single-template layer-by-layer assembly

In order to develop a facile and precisely controlled approach to synthesize hierarchical mesoporous materials with tailored property, in this work, a novel study was carried out to fabricate montmorillonitechitosan hollow and hierarchical mesoporous spheres(MMTNS@CS-HMPHS) based on single-template layer-by-layer(Lb L) assembly. Scanning electron microscopy(SEM), transmission electron microscopy(TEM), specific surface area analysis and X-ray photoelectron spectroscopy(XPS) analyses were carried out to characterize the morphology and surface properties of MMTNS@CS-HMPHS. Benefitting from the unique lamellar structure of MMTNS, mesoporous channels are formed on the shell of MMTNS@CS hollow spheres, resulting in high surface area. Moreover, the surface functionalization and pore size of MMTNS@CS-HMPHS can be easily tuned, due to the tailored property through Lb L assembly method.Besides the unique microstructure, MMTNS@CS-HMPHS also possesses the active sites generated from both MMT and chitosan, which greatly promotes its performance in fields of adsorption, drug delivery and catalyst supports, etc.

Determination of carcinoembryonic antigen using a novel amperometric enzyme-electrode based on layer-by-layer assembly of gold nanoparticles and thionine

Electrochemical sensing of carcinoembryonic antigen(CEA)on a gold electrode modified by the se- quential incorporation of the mediator,thionine(Thi),and gold nanoparticles(nano-Au),through co- valent linkage and electrostatic interactions onto a self-assembled monolayer configuration is de- scribed in this paper.The enzyme,horseradish peroxidase(HRP),was employed to block the possible remaining active sites of the nano-Au monolayer,avoid the non-specific adsorption,instead of bovine serum albumin(BSA),and amplify the response of the antigen-antibody reaction.Electrochemical ex- periments indicated highly efficient electron transfer by the imbedded Thi mediator and adsorbed nano-Au.The HRP kept its activity after immobilization,and the studied electrode showed sensitive response to CEA and high stability during a long period of storage.The working range for the system was 2.5 to 80.0 ng/mL with a detection limit of 0.90 ng/mL.The model membrane system in this work is a potential biosensor for mimicking the other immunosensor and enzyme sensor.

Positional assembly of multi-enzyme cascade reaction in polyelectrolyte doped microcapsule through electrospray and layer-by-layer assembly

Polyelectrolyte-doped microcapsules(PDM)was fabricated by coaxial electrospray of a mixture of glycerol and water containing 10 mg/mL cationic polyelectrolyte poly(allylamine hydrochloride)(PAH)fed as the core phase solution,and a N,N-dimethylacetylamide solution of 10 wt%polyurethane fed as the shell phase solution.Multienzyme system involving Candida Antarctica lipase B(CALB),glucose oxidase(GOD),and horseradish peroxidase(HRP)for cascade reaction was assembled in the PDM at three different places,namely,surface,shell,and lumen.Placing of enzyme inside aqueous lumen of the PDM was realized by in situ encapsulation through adding the enzyme in the core-phase solution for coaxial electrospray.By ion-pairing of enzyme with cationic surfactant CTAB,an organic soluble enzyme-CTAB complex was prepared,so that in situ embedding of enzyme in the shell of the PDM was realized by adding it into the shell phase solution.Surface attachment of enzymes was achieved by layer-by-layer(LbL)technology,which is based on the ion-exchange interactions between oppositely charged enzymes and PAH that was doped in PDM.The enzyme-decorated microcapsule was then studied as a microbioreactor,in which 1-Oxododecyla-α-glucopyranoside was converted by CALB to glucose,which was oxidised by GOD to gluconolactone in a second step.The hydrogen peroxide produced was then used by HRP to oxidize ABTS to form coloured radical cation ABTS•+for activity analysis.The successful fabrication of the PDM and precise localization of enzymes in the PDM by different strategies were fully characterized.By varying the immobilization strategy,totally six PDM bioreactors with three enzymes precisely positional assembled in different strategies were constructed and their activities for the cascade reaction were investigated and compared.The PDM micro-bioreactor prepared by novel electrospray technologies provide a smart platform for positional assembly of multi-enzyme cascade reaction in a precise and well-controlled manner.

Surface modification of polypropylene non-woven fibers with TiO_2 nanoparticles via layer-by-layer self assembly method:Preparation and photocatalytic activity

Polypropylene（PP） meltblown fibers were coated with titanium dioxide（Ti O2） nanoparticles using layer-by-layer（Lb L） deposition technique. The fibers were first modified with 3layers of poly（4-styrenesulfonic acid）（PSS） and poly（diallyl-dimethylammonium chloride）（PDADMAC） to improve the anchoring of the Ti O2 nanoparticle clusters. PDADMAC, which is positively charged, was then used as counter polyelectrolyte in tandem with anionic Ti O2 nanoparticles to construct Ti O2/PDADMAC bilayer in the Lb L fashion. The number of deposited Ti O2/PDADMAC layers was varied from 1 to 7 bilayer, and could be used to adjust Ti O2 loading. The Lb L technique showed higher Ti O2 loading efficiency than the impregnation approach. The modified fibers were tested for their photocatalytic activity against a model dye, Methylene Blue（MB）. Results showed that the Ti O2 modified fibers exhibited excellent photocatalytic activity efficiency similar to that of Ti O2 powder dispersed in solution. The deposition of Ti O23 bilayer on the PP substrate was sufficient to produce nanocomposite fibers that could bleach the MB solution in less than 4 hr.Ti O2-Lb L constructions also preserved Ti O2 adhesion on substrate surface after 1 cycle of photocatalytic test. Successive photocatalytic test showed decline in MB reduction rate with loss of Ti O2 particles from the substrate outer surface. However, even in the third cycle, the Ti O2 modified fibers are still moderately effective as it could remove more than 95% of MB after 8 hr of treatment.

Sensing Escherichia coli O157:H7 via frequency shift through a self-assembled monolayer based QCM immunosensor

By means of the specific immuno-recognition and ultra-sensitive mass detection, a quartz crystal microbalance (QCM) biosensor for Escherichia coli O157:H7 detection was developed in this work. As a suitable surfactant, 16-mercaptohexadecanoic acid (MHDA) was introduced onto the Au surface of QCM, and then self-assembled with N-hydroxysuccinimide (NHS) raster as a reactive intermediate to provide an active interface for the specific antibody immobilization. The binding of target bacteria with the immobilized antibodies decreased the sensor’s resonant frequency, and the frequency shift was correlated to the bacterial concentration. The stepwise assembly of the immunosensor was characterized by means of the electrochemical techniques. Using the immersion-dry-immersion procedure, this QCM biosensor could detect 2.0×102 colony forming units (CFU)/ml E. coli O157:H7. In order to reduce the fabrication time, a polyelectrolyte layer-by-layer self-assembly (LBL-SA) method was adopted for fast construction. Finally, the reproducibility of this biosensor was discussed.

NEAR INFRARED ELECTROCHROMIC VARIABLE OPTICAL ATTENUATOR FABRICATED BY LAYER-BY-LAYER ASSEMBLY

An eleetrochromic variable optical attenuator （ECVOA） was fabricated by layer-by-layer （LBL） assembly of disodium N,N-bis（p-sulfonatophenyl）naphthalenedicarboximide （Naph-SO3Na） and common cationic polymer poly（diallyldimethylammonium） chloride （PDDA）. The UV-Vis absorption spectra of the multilayer films revealed that approximately an equal amount of Naph-SO3Na was assembled in each deposition cycle. Upon one-electron reduction, multilayer films exhibited intense absorption around 452 nm and also a broad absorption band from 1200 nm to 1900 nm. Owing to the improved ionic conductivity, the optical attenuation at 1550 nm of the films showed rapid response time and reached 1.3 dB/μm within 5 s. These results indicate that layer-by-layer assembly could be an effective method for the preparation of ECVOA operating in near infrared region.

Strengthened graphene oxide/diazoresin multilayer composites from layer-by-layer assembly and cross-linking

The layer-by-layer assembly of graphene oxide and diazoresin is carried out via the electrostatic and hydrogen bond interactions on planar substrates and colloidal templates.The successful planar and spherical growth of multilayer could be investigated by UV-vis spectrophotometry and scanning electron microscopy,respectively.Subsequent UV irradiation or heating would convert the ionic bonds and hydrogen bonds to covalent bands,which significantly improves the stability of the multilayer composite against solvent etching.For the cross-linked core-shell composites,the template cores could be removed by dissolution and hollow microspheres are obtained.

In vitro corrosion resistance of layer-by-layer assembled polyacrylic acid multilayers induced Ca–P coating on magnesium alloy AZ31

Biodegradable magnesium(Mg)-based alloys have aroused great concern owing to their promising characteristics as temporary implants for orthopedic application.But their undesirably rapid corrosion rate under physiological conditions has limited the actual clinical application.This study reports the use of a novel biomimetic polyelectrolyte multilayer template,based on polyvinylpyrrolidone(PVP)and polyacrylic acid(PAA)via layerby-layer(LbL)assembly,to improve the corrosion resistance of the alloy.Surface characterization techniques(field-emission scanning electron microscopy,Fourier transform infrared(FTIR)spectrophotometer and X-ray diffractometer)confirmed the formation of biomineralized Ca–P coating on AZ31 alloy.Both hydrogen evolution and electrochemical corrosion tests demonstrated that the corrosion protection of the polyelectrolyte-induced Ca–P coating on AZ31 alloy.The formation mechanism of biomineralized Ca–P coating was proposed.

Fabrication of Covalently Linked PAH/PVS Layer-by-layer Assembled Multilayers via a Post-photochemical Cross-linking Strategy

A post-photochemical cross-linking strategy was successfully demonstrated to enhance the stability of polyelectrolyte poly（allylamine hydrochloride）（PAH）/poly（vinylsulfonic acid sodium salt）（PVS） multilayers. Con- ventional polyelectrolyte multilayers of PAH/PVS are usually fabricated through electrostatic layer-by-layer（LbL） assembly, resulting in poor stability, especially in basic solutions, which leads to the urgent demand for converting weak electrostatic interactions into covalent bonds to enhance the stability of the multilayers. This stability problem has been ultimately addressed by post-infiltrating a photosensitive cross-linking agent, 4,4＇-diazostilbene-2,2＇- disulfonie acid disodium salt（DAS）, into the LbL assembled films to initiate the photochemical reaction to cross-link the multilayers. The obviously improved stability of the photo-cross-linked multilayers was demonstrated through experiments with basic solution treatments. Compared to the complete decomposition of uncross-linked multilayers in basic solution, over 74.4% of the covalently cross-linked multilayers were retained under the same conditions, even after a longer duration of basic solution treatment.