Hal Nanotubes Research Articles

Yield stress and microstructure of composite halloysite-LAPONITE® gels: Effects of mixing ratio, surface chemistry, and ageing time

The dependences of yield stress and microstructure of composite halloysite (Hal)-LAPONITE® (Lap) gels on the Lap/Hal mixing ratio, surface chemistry (pH and ionic strength), and ageing time were investigated in this study. The yield stress was measured using the vane technique and the microstructure was revealed by the cryogenic scanning electron microscopy (cryoSEM) images. At a fixed solid loading, the yield stress of composite Hal-Lap gels first quickly decreased to a lowest point and then kept increasing as Lap/Hal mixing ratio increased. The corresponding microstructure changed from Hal dominated network to Lap dominated network showing strong interactions between Hal and Lap particles through heterogeneous charge attractions. Six stages, each with distinct features, were identified during the transition. The maximum of yield stress displayed at around pH 11 for composite Hal-Lap gels and pure Hal gel. The attractive interactions between pure Hal-Hal and Lap-Lap particles and composite Lap-Hal particles were still present in a significant manner at pH 12 as reflected by the high yield stress. The microstructure of composite Hal-Lap gels and pure Hal gel displayed a high content of fibre end-face interactions even at high pH. However, “phase separation” occurred at low pH 4. Increasing ionic strength resulted in higher bond strength due to the van der Waals attraction and heterogeneous charge attraction, so it produced higher yield stress gels of pure Hal gel and composite Hal-Lap gels with low Lap content. At high ionic strength, small Hal particles formed aggregates with large Hal nanotubes while Lap particles formed large agglomerates. The H18L2 showed microstructure with circular agglomerates dispersed in a suspension of Hal rods. The agglomerates consisted of a mixture of tightly packed Hal rods and Lap particles. The microstructure of composite Hal-Lap gels was also strengthened during ageing due to the particle rearrangement. A water-gel phase separation due to the Hal particles sedimentation was observed for composite gels with low Lap/Hal mixing ratio as increasing ageing time.

Preparation and characterization of manganese oxides supported on functionalized halloysite nanotubes with enhanced catalytic oxidation for toluene

In this study, halloysite (Hal) nanotubes treated with an acid and intercalation, were designed as a functionalized nanotubular structure to load and improve the dispersion of the Mn oxide doping of CeO for the toluene oxidation. The prepared catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The average pore size and specific surface areas of Hal nanotubes treated with an acid and intercalation (AI-Hal) offered significant improvement. The XRD and TEM indicated that different types of MnO2 were successfully loaded on the external surface of AI-Hal nanotubes. The XPS data confirmed that the MnIII and MnIV dominated on the surface of MnO2 due to the reversible redox reaction between MnIII and MnIV. The evaluation of catalytic activities showed that the γ-MnO2/AI-Hal presented good TOC performance of toluene. The doped CeO particles with diameters of approximately 10 nm were adsorbed on the external surfaces and lumen of Hal nanotubes and displayed a homogeneous dispersion state, which significantly improved the catalytic performance of the γ-MnO2/AI-Hal catalyst system with the T90 of 265 °C. The study indicated that catalytic activity of AI-Hal nanotube-supported manganese oxides was dependent on the valence state, oxygen vacancy and dispersion of active sites, and Hal nanotubes are acceptable reactants for the synthesis of supported catalysts with suitable MnOx.

Influence of selective acid-etching on functionality of halloysite-chitosan nanocontainers for sustained drug release

The functionality of halloysite (Hal) nanotubes as drug carriers can be improved by lumen enlargement and polymer modification. This study investigates the influence of selective acid etching on Hal functionalization with cationic biopolymer chitosan. Hal was subjected to lumen etching under mild conditions, loaded under vacuum with nonsteroidal antiinflammatory drug aceclofenac, and incubated in an acidic solution of chitosan. The functionality of pristine and etched Hal before and upon polymer functionalization was assessed by ζ-potential measurements, structural characterization (FT-IR, DSC and XRPD analysis), cell viability assay, drug loading and drug release studies.Acid etching increased specific surface area, pore volume and pore size of Hal, decreased ζ-potential and facilitated binding of the cationic polymer. XRPD and DSC analysis revealed crystalline structure of etched Hal. Successful chitosan binding and drug entrapment were further confirmed by FT-IR and DSC studies. XRPD showed surface polymer binding. DSC and FT-IR analyses confirmed the presence of the entrapped drug in its crystalline form. Drug loading was increased for ≈81% by selective lumen etching. Slight decrease of drug content occurred during chitosan functionalization due to aceclofenac diffusion in the polymer solution. The drug release was more sustained from etched Hal nanocomposites (up to ≈87% for 12 h) than from pristine Hal (up to ≈97% for 12 h) due to more intensive chitosan binding. High human fibroblast survival rates upon exposure to pristine and etched Hal before and after chitosan functionalization (>90% in the concentration of 1000 μg/mL) confirmed that both lumen etching under mild conditions and polymer functionalization had no significant effect on cytocompatibility.Based on these findings, selective lumen etching in combination with polycation modification appears to be a promising approach for improvement of Hal nanotubes functionality by increasing payload, polymer binding capacity, and sustained release properties with no significant effect on their cytocompatibility.

Preparation of Ni, CoO-supported halloysite nanotube catalyst and its application in the hydrogenation of furfural to furfuryl alcohol

In this study, halloysite (Hal) nanotubes were designed as a carrier and stabilizer as well as a nanostructured matrix. A series of Ni, CoO-Hal catalysts were then synthesized through a deposition method. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The catalytic properties of the catalyst were evaluated using the hydrogenation of furfural to furfuryl alcohol. The average pore size of activated Hal ranged from 20 nm to 32 nm, and the specific surface areas of Hal increased up to 125.55 m2/g. The Ni or CoO particles were successfully loaded on the external surface of Hal nanotubes with diameters of approximately 10 nm. The XPS data confirmed zero-valent character for metal Ni at 852.6 eV and the oxide form for metal Co with type of CoO and Co3O4; meanwhile, a small amount of nickel protoxide was observed due to the weak oxidation on the surface of metal Ni. The evaluation of catalytic activities showed that the Ni-Hal catalyst presented favorable selectivity to furfural alcohol (approximately at 99.0%) and good furfural conversion. The successive catalytic cycles indicated that the furfural conversion and selectivity to furfural alcohol of the prepared catalyst maintained good stability (approximately at 96% and 65%, respectively).

Porous architectures based on halloysite nanotubes as photothermal materials for efficient solar steam generation

Solar steam generation assisted by photothermal materials has attracted extensive attention due to its advantages of excellent evaporation rate and high photothermal conversion efficiency. In this work, we report a simple method by employment of halloysite (Hal) nanotubes (HNT) and graphene oxide (GO) as raw materials to produce efficient solar photothermal materials (named as GO-HNT). The as-prepared GO-HNT has rich porosity, excellent 90% light absorption and good thermal insulation performance (thermal conductivity 0.162 W m−1 K−1). Based on these characteristics, GO-HNT can be used as a promising solar receiver. Correspondingly, the solar energy conversion efficiency of the GO-HNT solar receiver was measured to be 83.67%, 77.17% and 77.05% respectively under 1 sun, 2 sun and 3 sun irradiations. As a 1D nanocrystalline clay mineral, HNT have great advantages of environmentally friendly, cost-efficient and commercial availability with abundant reserves. In combination with its simple and scalable manufacture method, this GO-HNT-based solar receiver may hold great potentials for a broad range of applications, such as seawater desalination, distillation, sterilization, sewage treatment, etc.

Preparation of palladated porous nitrogen-doped carbon using halloysite as porogen: disclosing its utility as a hydrogenation catalyst

In this article, halloysite nanoclay (Hal) was used as porogen for the synthesis of nitrogen doped porous carbon material with high specific surface area and pore volume. To this purpose, polymerization of melamine and terephthalaldehyde (MT) was performed in the presence of amine-functionalized carbon coated Hal (Hal@Glu-2N) that was prepared from hydrothermal treatment of Hal and glucose. Then, the prepared nanocomposite was palladated and carbonized to afford Pd@Hal@C. To further improve the textural properties of the nanocomposite, and introduce more pores in its structure, Hal nanotubes were etched. The characterization of the resulting compound, Pd@C, and comparing it with Pd@Hal@C, showed that etching of Hal significantly increased the specific surface area and pore volume in Pd@C. Pd@C was successfully used as a heterogeneous catalyst for promoting hydrogenation of nitroarens in aqueous media using hydrogen with atmospheric pressure as a reducing agent. The comparison of the structural features and catalytic activity of the catalyst with some control catalysts, including, Pd@Hal, Pd@Hal@Glu, Pd@Hal@Glu-MT and Pd@Hal@C confirmed that nitrogen groups in C could improve the Pd anchoring and suppress its leaching, while etching of Hal and introduction of more pores could enhance the catalytic activity through facilitating the mass transfer.

A new durable pigment with hydrophobic surface based on natural nanotubes and indigo: Interactions and stability

Covering with polyorganosilane (POS) was proved as an effective way to enhance the chemical and thermal stability of clay/dye hybrid pigments. But the photostability and interactions with clay minerals, dyes and POS layer has never been reported. In order to investigate above issues, new organic-inorganic hybrid pigments based on halloysite (Hal) and indigo (In) were prepared by grinding method. X-ray diffraction, transmission electron microscopy, thermogravimetry, Fourier transform infrared spectroscopy were applied to characterize the structure of In-Hal (without POS layer) and In-Hal-POS (with POS layer) pigments. Solid state nuclear magnetic resonance (NMR) was employed to reveal the interactions between Hal, In and POS. Reflection spectra and CIE 1976 color space system were used to evaluate the color parameters and color changes of pigments. Thermal stability, chemical resistance to ethanol, 1 mol·L−1 HCl and 1 mol⋅L−1 NaOH, and light fastness to visible light were tested. Indigo molecules dispersed on the surface of Hal nanotubes. POS layer homogeneously covered on the surface of hybrid pigments, without changing the crystal structure and morphology of Hal. Covering with POS layer seldomly affect the color of hybrid pigments. However, In-Hal-POS exhibited better stability than In-Hal, due to hydrophobic surface which can prevent indigo molecules from chemical reactions and degradation. A new route was proposed to prepare organic-inorganic hybrid pigments, ignoring the interaction between dye molecules and substrates.

Toxic influence of pristine and surfactant modified halloysite nanotubes on phytopathogenic bacteria

Halloysite nanotube (Hal nanotube) – a clay mineral nanomaterial, was surface modified using cationic, anionic and non-ionic surfactants – cetyl trimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and Tween 80 respectively. The pristine Hal nanotube and the three surfactant modified Hal nanotubes (SM-Hal nanotubes) were tested against three phytopathogenic bacteria Xanthomonas oryzae, Agrobacterium tumifeciens and Ralstonia solanacearum. In the present study, by performing various bacterial toxicity assays, it has been established that SM-Hal nanotubes had a higher killing efficiency of phytopathogenic bacteria than pristine Hal nanotube. The surfactant modifications improved the dispersion of the Hal nanotube and altered the physico-chemical properties like grain size, particle diameter, surface charge and hydrophilicity, which consecutively enhanced the interaction and the toxic effects on phytopathogenic bacteria. SM-Hal nanotubes inhibited phytopathogenic bacteria at a lower minimum inhibitory concentration (MIC) as compared to the pristine Hal nanotube. Among the three SM-Hal nanotubes, CTAB-modified Hal nanotube effectively suppressed the growth, disrupted the cell membrane integrity, induced higher reactive oxygen species (ROS) production and inhibited the biofilm formation of all the three phytopathogenic bacteria followed by Tween 80-modified and SDS-modified Hal nanotubes. Hence, it is evident that these tailor made SM-Hal nanotubes, can be effectively used as potent clay mineral nanomaterials to control phytopathogenic bacteria.

A comparative study of synthetic tubular kaolinite nanoscrolls and natural halloysite nanotubes

Kaolinite (Kaol) nanoscrolls with a diameter of ~20 to 100 nm and length of ~0.25 to 2 μm were prepared from the exfoliation of Kaol precursor. New interlayer space and lumens could be obtained by delamination and exfoliation of platy Kaol while forming nanoscrolls. The morphological and structural differences between synthetic Kaol nanoscrolls and natural halloysite (Hal) nanotubes were invesigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TG-DSC), nitrogen adsorption-desorption techniques. TEM showed that Kaol nanoscrolls are thinner and longer than Hal nanotubes. Kaol nanoscrolls exhibited nitrogen adsorption-desorption isotherms and pore size distribution curves similar to those of Hal but the specific surface area and pore volume of the Kaol nanoscrolls were found to be 2 times higher than those of natural tubular Hal. Both the TG and DTA curves of Kaol nanoscrolls and Hal nanotubes indicated that small amount of adsorbed water was lost below 140 °C. The dehydroxylation of Kaol nanoscrolls occurred at 463 °C, which is between the dehydroxylation temperature of Kaol and that of Hal. The current comparative study of Kaol nanoscrolls and Hal nanotubes suggests that the former could possibly be substituted for the latter for improving some applications because of the higher surface area and different types of pore space of the Kaol nanoscrolls.

Bifunctional monomer molecularly imprinted sol-gel polymers based on the surface of magnetic halloysite nanotubes as an effective extraction approach for norfloxacin

Abstract An effective magnetic surface imprinted polymer with high adsorption ability and selectivity has been designed. Three magnetic halloysite nanotubes combined with molecularly imprinted polymer (MMIP) composites were fabricated. Halloysite nanotubes (Hal nanotubes) were us as supporting matrix, norfloxacin (NOR) as template molecules, Aminopropyltriethoxysilane (3-APTES) and Methacryloxypropyltrimethoxysilane (MTEOS) used as monomers and tetramethyl orthosilicate (TEOS) as cross linker through a one-pot sol-gel polymerization. The resulting MMIP were characterized by various techniques. The adsorption isotherms, adsorption kinetics and selective recognition of MMIP were investigated in detail. The imprinted polymers with bifunctional monomer possess the highest adsorption capacity (312.08 μg·mg−1) and the best select factor (5.41). After optimization of solid phase extraction (SPE) condition, imprinted polymer with bifunctional monomer possess the best extraction ability and can be successfully applied into the extraction of norfloxacin in lake water. In addition, the SPE-ultraviolet method established possesses good accuracy and precision. Hydrochloric acid (9:1/v:v) could be used as the best elution and the magnetic imprinted polymer could be reused for at least seven times.

Polyethylenimine-assisted seed-mediated synthesis of gold nanoparticles for surface-enhanced Raman scattering studies

Large-sized gold nanoparticles (AuNPs) were synthesized with a new polyethylenimine − assisted seed − mediated method for surface-enhanced Raman scattering (SERS) studies. The size and polydispersity of gold nanoparticles are controlled in the growth step with the amounts of polyethylenimine (PEI) and seeds. Influence of three silicon oxide supports having different surface morphologies, namely halloysite (Hal) nanotubes, glass plates and inverse opal films of SiO2, on the performance of gold nanoparticles in Raman scattering of a 4-aminothiophenol (4-ATP) analyte was investigated. Electrostatic interaction between positively charged polyethylenimine-capped AuNPs and negatively charged surfaces of silicon oxide supports was utilized in fabrication of the SERS substrates using deposition and infiltration methods. The Au-photonic crystal of the three SERS substrate groups is the most active one as it showed the highest analytical enhancement factor (AEF) and the lowest detection limit of 1x10−8 M for 4-ATP. Coupling of the optical properties of photonic crystals with the plasmonic properties of AuNPs provided Au-photonic crystals with the high SERS activity. The AuNPs clusters formed both in the photonic crystal and on the glass plate are capable of forming more hot spots as compared to sparsely distributed AuNPs on Hal nanotubes and thereby increasing the SERS enhancement.

Large-scale synthesis of sub-micro sized halloysite-composed CZA with enhanced catalysis performances

Large scale synthesis of catalyst with intriguing performances is a hot issue in the fields of both chemical and material science. In this paper, sub-micro sized ceria-zirconia-alumina (CZA) oxide material and that composited with halloysite (Hal) were synthesized in multi-gram scale through a simple co-precipitation method. X-ray diffraction (XRD), N2 adsorption-desorption isotherms, transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy(XPS), and temperature-programmed H2 reduction (H2-TPR) were used to characterize the crystalline, textural, morphological characters, and reducibility of the products. Three-way catalytic performances of the supported products were tested in stoichiometric air/fuel condition. The samples were all composed of sub-mirco sized particles. Size of CZA was about 200nm, while the hybrid material introduced with Hal (CZAH) showed a rod-like and sheet-like morphology consisted of agglomerated nanoparticles with size of about 100nm. The adaption of PEG-4000 has guided the formation of nanoparticles and their self-assembly into nano-rods in the products. The Hal mineral in the composites retained their tubular morphology and penetrated into bulk of the CZA. The CZAH composite showed larger BET surface area, favorable pore structure, and better oxygen storage capacity than the CZA sample thanks to the introduction of Hal nanotubes. The supported Pd-Rh/CZAH showed the ignition temperature at about 210°C, and converting efficiency reached near 100% for NOx and CO before 230°C in TWC tests, which also showed the optimized catalytic performances than CZA matrix.

Halloysite-based hybrid bionanocomposite hydrogels as potential drug delivery systems

In this investigation, the preparation of novel Halloysite-based chitosan/oxidized starch (Hal/CTS/OSR) Hybrid bionanocomposite hydrogels is described. The obtained hybrid hydrogels were characterized by using FT-IR, SEM, XRD, TGA and DTG techniques. In addition, the efficiency of hydrogels as drug delivery systems was studied. The results demonstrated that depending on experimental parameters, such as the ratio of CTS/OSR, and the type of Hal nanotubes (modified or unmodified), the hydrogel properties can be affected and modulated significantly. 74.3%, 71.2% and 69.45% MTZ release were observed for CTS/OSR/mHal 10, CTS/OSR and CTS/OSR/Hal 10 respectively.

The piezoelectric response of electrospun PVDF nanofibers with graphene oxide, graphene, and halloysite nanofillers: a comparative study

Although, many efforts were performed to develop piezoelectric systems with high energy conversion rate, but they still show insufficient performance. In this study, the effect of three nanofillers with different morphology and their concentration on macro/micro structure and piezoelectric properties of polyvinylidene fluoride (PVDF) nanofibers were investigated and compared. Graphene oxide (GO) and graphene (Gr) as planner nanofillers, and halloysite (Hal) nanotube were introduced into a PVDF solution in different concentrations (0.05–3.2 wt/wt%). The prepared solutions were fabricated into nanofibers through electrospinning method. The electroactive phase (β-phase) of nanofibrous PVDF mat increased up to ~49% in comparison with PVDF powder. The presence of nanofiller in PVDF matrix also increased it more up to 10%. Gr nanofiller had least effect on piezoelectric properties attributed to its low interaction with PVDF chains. PVDF/Hal nanocomposite with low filler content concentration ( 0.4 wt/wt%) caused higher polar phase. Hal nanotubes with a rod like morphology caused more oriented and finer nanofibers than PVDF/GO and PVDF/Gr nanofibers. However, PVDF/0.8 Hal showed higher output voltage (0.1 V), despite of its lower β-phase in compared with PVDF/0.8GO nanocomposites. It was concluded that the piezoelectric response cannot be just evaluated with dielectric constant of nanofiller or β-phase percentage in an electrospun PVDF nanocomposite, but there are some other important factors like orientation and fineness of electrospun nanofibers.

Various amine functionalized halloysite nanotube as efficient metal free catalysts for H2 generation from sodium borohydride methanolysis

In this work, naturally available clay, halloysite (Hal) nanotube was modified systematically with various types and number of amine groups containing modifying agents and used as catalyst in the methanolysis of sodium borohydride (NaBH4) for hydrogen (H2) production. The modifying agents such as ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), and tris(2-aminoethyl)amine (TAEA), and polyethyleneimine (PEI) were used in Hal nanotube modification followed by protonation with HCl treatments. Various parameters affecting the H2 production rate such as the types of modification agents and/or catalyst types, NaBH4 amount, and the reaction temperature were investigated. The methanolysis of NaBH4 catalyzed by PEI modified and protonated Hal nanotube (H-PEI(750.000)-Hal nanotube) was found to follow first order reaction kinetic with respect to NaBH4 concentration. Interestingly, superior catalytic performances in comparison to the literature for the similar studies were obtained with 16.44kJ/mol, 14.05kJ/mol, and 196.46J/mol·K of activation energy, enthalpy and entropy, respectively for NaBH4 methanolysis catalyzed by H-PEI(750.000)-Hal nanotubes. The hydrogen generation rate of 2218mL/min·g that is comparable to the most of metal nanoparticle catalysts for H-PEI(750.000)-Hal nanotube catalyst was obtained.

Gold nanoparticle-decorated halloysite nanotubes – Selective catalysts for benzyl alcohol oxidation

Preparation of gold nanoparticle-decorated halloysite nanotubes (Au-Hal) by a deposition method and evaluation of their catalytic activity in an oxidation of benzyl alcohol are reported. An electrostatic attraction between positively charged polyethylenimine (PEI)-capped gold nanoparticles and the negatively charged external surfaces of halloysite nanotubes (Hal nanotubes) was the key factor in fabrication of Au-Hal nanotubes. Au-Hal catalysts showed good conversions and surprisingly high benzaldehyde selectivities (above 90%) in the benzyl alcohol oxidation. Influence of the amount of PEI used as a capping agent, the gold content and calcination of Au-Hal catalysts on the conversion and selectivity was investigated. A notable increase in the benzaldehyde selectivity at higher PEI contents and a significant drop in the benzaldehyde selectivity on calcination clearly indicate the central role of PEI in the selective formation of benzaldehyde. The high benzaldehyde selectivity of uncalcined catalysts are probably due to PEI donor molecules coordinating to certain surface sites on Au nanoparticles and thus blocking the catalytic sites required for further oxidation of benzaldehyde to benzoic acid. The high combined selectivity of benzoic acid and benzyl benzoate obtained with the calcined catalysts indicates that naked gold nanoparticles have the catalytic sites available for the benzoic acid formation.

Halloysite-carboxymethyl cellulose cryogel composite from natural sources

In this work, novel superporous composite cryogel using natural source such as carboxymethyl cellulose (CMC) and halloysite nanotubes (Hal nanotubes) was prepared. The composite was prepared via cryogelation method including the Hal nanotubes within polymeric matrices before cryogelation. A series of the Hal nanotubes/carboxymethyl cellulose composite were prepared by varying the used amounts of crosslinker, and Hal nanotubes amounts. Additionally, Hal nanotubes were modified with different modifying agent such as (3-aminopropyl)triethoxysilane (APTES), (3-chloro-2-hydroxypropyl)trimethylammonium chloride (CHPTACI), polyethylenimine (PEI), epichlorohydrin (ECH), diethylenetriamine (DETA), taurine (TA), and tris(2-aminoethyl)amine (TAEA), these modified Hal nanotubes were used in CMC cryogel composite preparation. Characterization of the synthesized materials was performed by Scanning and Transmission Electron Microscopy (SEM and TEM), Zeta Potential (ZP) measurement, Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR) spectroscopic measurement and Surface area and Porosity Analyzer.

Halloysite nanotubes - An efficient ‘nano-support’ for the immobilization of α-amylase

Amylases are a class of hydrolytic enzymes which help in the conversion of starch into reduced sugars. Several solid carriers have been utilized for the immobilization of amylase. The current study focused on the utilization of halloysite nanotubes (Hal nanotubes) for the immobilization of α-amylase post their surface functionalization with APTES. The immobilized enzyme was characterized for its ultrastructure and morphology using TEM which revealed the hollow tubular structure of nanotubes. Chemical characterization of Amylase-Hal nanotubes powder was done by FTIR in which the characteristic reflections of pristine Hal nanotubes and amylase were detected in the spectra for Amylase-Hal nanotubes powder. The thermal and crystalline behavior of the immobilized enzyme was studied using DSC and XRD analysis respectively. Further, the effect of time, pH, temperature and metal ions on the enzymatic activity of immobilized enzyme had also been probed into. The optimum pH and temperature for the immobilized amylase was found to be 7.4 and 40°C respectively. Slight increase in the enzymatic activity was also found for immobilized amylase as compared to free enzyme in the presence of Cu2+ and Mn2+ ions.

Development of silane grafted halloysite nanotube reinforced polylactide nanocomposites for the enhancement of mechanical, thermal and dynamic-mechanical properties

In this investigation, halloysite (Hal) nanotubes were surface modified with 3-aminopropyltriethoxysilane (APTES) to enhance the surface interaction of Hal nanotubes with polylactide or poly (lactic acid) (PLA) and to achieve good dispersion of Hal nanotubes across the PLA matrix. Unmodified and silane modified Hal nanotubes were characterized by Fourier transform infrared spectroscopy (FTIR), Nitrogen adsorption-desorption analysis, Thermogravimetric analysis (TGA) and Field emission scanning electron microscopy (FE-SEM) with Energy-dispersive x-ray spectroscopy (EDX) analysis. Nitrogen adsorption-desorption, FTIR and TGA analysis results were confirmed the successful modification of Hal nanotubes surface with APTES. The different wt% of unmodified and APTES modified Hal nanotubes reinforced PLA polymer composites were prepared by using a laboratory scale melt mixer. The resultant Hal-PLA nanocomposites were characterized for their morphology, thermal, mechanical and dynamic-mechanical properties. Tensile strength increased to 62.6MPa with the addition of 4wt% of APTES modified Hal-PLA nanocomposites which is 26.5% higher than pure PLA and 15% higher than unmodified (4wt%) Hal-PLA nanocomposites. Impact strength of 4wt% APTES modified Hal-PLA nanocomposites was 29.8MPa, which is 20% higher than the unmodified Hal-PLA nanocomposites and 40% higher than pure PLA. Thermal stability also increased by 17°C with the addition of 4wt% of APTES modified Hal nanotubes and 10°C for the unmodified Hal nanotubes onto PLA. Storage modulus increased >10% with the addition of 4wt% of APTES modified Hal nanotubes as compared to pure PLA and tan delta values were decreased for the modified Hal nanotubes due to an increase in the compatibilisation between filler and matrix phase. Based on these results, APTES is one of the best choices for the functionalisation of inorganic surface such as Hal nanotubes. The mechanical and thermal properties significantly improved with the addition of a small quantity (4wt%) of APTES modified Hal nanotubes.

Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglass-hydroxyapatite-halloysite nanotube nanocomposites films in surface engineering

This study investigated the effect of halloysite (Hal) concentration on electrophoretically deposited chitosan (CS)-bioglass (BG)-hydroxyapatite (HA)-halloysite nanotube and chitosan-halloysite nanotube films. The distribution of Hal nanotubes and morphological structure of the clay polymer nancomposite (CPN) were examined using TEM, FE/SEM, FT-IR, EDX, and XRD analysis. The stability of dispersion and pH of deposition were studied. The optimum pH chosen for the deposition of CS-BG-HA-Hal film was 2.5<pH<3 in 30% water-ethanol solvent. SEM and FT-IR analysis illustrated more nanotubes deposition in CS-based film by augmenting concentration of Hal nanotubes from 0.3gL−1 to 0.6gL−1. The CS-BG-HA-Hal deposition mechanisms were considered and discussed. Corrosion resistance analysis revealed that CS-BG-HA/Hal coated samples exhibit improved corrosion resistance than uncoated Ti. The increasing of Hal concentration in CPN film reduced corrosion current density (icorr), and increased corrosion potential (Ecorr) in corrected simulated body fluid (C-SBF) at 37°C. Furthermore, EIS analysis would be more reliable than electrochemical polarization to evaluate corrosion resistance of CS-based coatings containing Hal nanotubes.