Surface Of Halloysite Nanotubes Research Articles

Surface grafting of fluorescent polymers on halloysite nanotubes through metal-free light-induced controlled polymerization: Preparation, characterization and biological imaging.

Halloysite nanotubes (HNTs) are a kind of aluminosilicate clay with a unique hollow tubular structure that has been intensively explored for various applications especially in biomedical fields owing to their excellent biocompatibility, biodegrading potential and low cost. Surface modification of HNTs with functional polymers will greatly improve their properties and endow new functions for biomedical applications. In this work, a light-induced reversible addition-fragmentation chain transfer (RAFT) polymerization was introduced to successfully prepare HNTs based fluorescent HNTs/poly(PEGMA-Fl) composites in the presence of oxygen using diacrylate-fluorescein and poly (ethylene glycol) methyl ether methacrylate (PEGMA) as the monomers. Without other catalysts, heating, and deoxygenation procedure, the polymerization process can take place under mild conditions. Besides, owing to the introduction of fluorescein and PEGMA on the surface of HNTs, the resultant HNTs/poly(PEGMA-Fl) composites display high water dispersibility and stable fluorescence. The results from cell viability examination and confocal laser scanning microscopy also demonstrated that HNTs/poly(PEGMA-Fl) composites could be internalized by L929 cells with bright fluorescence and low cytotoxicity. Taken together, we developed a novel photo-initiated RAFT polymerization method for the fabrication of HNTs based fluorescent polymeric composites with great potential for biomedical applications. More importantly, many other multifunctional HNTs based polymer composites could also be fabricated through a similar strategy owing to good designability of RAFT polymerization.

Convenient Cr(VI) Removal from Aqueous Samples: Executed by a Promising Clay‐Based Catalytic System, Magnetized by Fe3O4 Nanoparticles and Functionalized with Humic Acid

AbstractHere, a nanoscale efficient adsorbent for chromium(VI) ion is presented, which is constructed of halloysite nanotubes (HNTs) as a natural basis. On the other hand, to add magnetic property, iron oxide (Fe3O4) nanoparticles have been incorporated inside and leaded onto the surface of HNTs. As the main component of nanoabsorbent, humic acid (HA) is also loaded onto the surface of HNT/Fe3O4 nanocomposite. Cr(VI) removal process has been carefully monitored in the presence of the fabricated HNT/Fe3O4‐HA nanoabsorbent from aqueous solutions with different concentrations of K2CrO4. The adsorption isotherms are interpreted by Langmuir graphs, and 98% removal efficiency (RE) has been obtained at room temperature, in 15 min contact time. Additionally, all the analyses related to the structure of desired product have been done, and the recyclability of produced nanoabsorbent is precisely investigated, as well.

Facile production of HNTs\PDA\PF nanocomposites by unique and environment-friendly method for the removal of phenolic pollutants in water as an environmental adsorbent

Abstract A new kind of hybrid nanocomposites (NC)s consisted of phenol-formaldehyde (PF), polydopamine (PDA) and modified halloysite nanotubes (HNT)s had been prepared by sonochemical synthesis. The surface modifications of HNTs were achieved by mussel inspired sonochemistry using dopamine (DA) as an active intermediate. In this process bio-safe DA could self-polymerized to adhere to the surface of HNTs and formed an active PDA species. The PF/PDA/HNT NCs had been fabricated by the in-situ polymerization of phenol, formaldehyde in alkaline condition in the presence of PDA modified HNTs through polycondensation reaction. Characterizations with FT-IR, powder X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) confirmed the synthesis of NCs with well dispersion properties. In continuation of the research the possiblity of application of prepared nanomaterials for removal of phenolic compounds were inspected. Obtained results showed that the presence of nanotubular filler, existance of different polar functional units in PDA structures, H-bonding and hydrophobic interactions of PF matrix with phenols are the key factors for improving the adsorption capacity for phenol by PF/PDA/HNTs NCs.

Modification of halloysite nanotubes with xanthene dyes and their application in luminescent polymer nanocomposites

In this study, halloysite nanotubes (HNTs) were modified with three xanthene dyes and subsequently utilized for the fabrication of luminescent polymer nanocomposites. Two different sets of dyes (rhodamine B, rhodamine 6G, and fluorescein) were chosen because of their ability to interact differently with HNTs. Rhodamines B and 6G were adsorbed on the negatively charged external surface of HNTs due to their cationic nature, while fluorescein was infiltrated into the positively charged nano-size lumen of HNTs. The influence of the HNTs substrate on photoluminescence (PL) of the dyes in the polystyrene matrix was investigated. An enhancement in the PL intensity of fluorescein by a factor of 8 was observed upon its encapsulation into lumens of HNTs. On the other hand, the adsorption of rhodamines on HNTs led to a decrease in their PL intensity. A homogenous dispersion of the dye molecules achieved at nanoscale introduced luminescence properties in the polymer nanocomposites. The robust protocol for the modification of halloysites with organic chromophores provides a straightforward way to distribute the dye molecules in a polymer matrix and to incorporate luminescent properties into different polymer matrices.

Fabrication of biocompatible antibacterial nanowafers based on HNT/PVA nanocomposites loaded with minocycline for burn wound dressing.

Bacterial infections of burn wounds are a significant problem that usually slows or stops the process of burn wounds healing. The use of topical antibiotics based on a novel drug delivery system could overcome the limitations of burn wound healing. In this work, the development of new wound dressings based on nanocomposite film of polyvinyl alcohol (PVA) and halloysite nanotubes (HNT) for the delivery of minocycline was investigated. These elastomeric nanocomposites were prepared based on HNT surface modification by APTES and then PVA coating by LbL strategy. The resulting nanocomposites were characterized by FT-IR, XRD, zeta potential, Tg analysis, FESEM, and antibacterial studies. The biodegradability and water uptake of the film were evaluated, the results of which revealed the absorption of scarring and non-degradation of the nanocomposite during treatment. Because minocycline decomposes by light, increasing photostability was another goal that was achieved. The release profile of the drug from the nanocomposite was studied, and it was found to be consistent with the Korsmeyer-Peppas model. In-vitro studies showed the antibacterial effect of nanocomposite on exposure to Gram-positive and Gram-negative bacteria. Due to the properties of the resulting nanocomposite film, it can be considered as a promising candidate for wound healing. In-vivo studies, cell culture, neuroprotective and anti-inflammatory effects may be investigated to develop this wound dressing in the future.

Differential antimicrobial and cellular response of electrolytically metalized halloysite nanotubes having different amounts of surface metallization.

We demonstrate an electrolytic method to metalize the outer surface of halloysite nanotubes (HNTs). Different metal HNT (mHNT) combinations (copper, silver, zinc) were produced with metal content in the 5-30 wt% range. mHNTs were characterized using a Scanning Electron Microscope (SEM), energy-dispersive spectroscopy (EDS), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). Different amounts of surface/lumen metal content of a system can confer differing antimicrobial/cellular response; hence, it is essential to assess the antimicrobial/cellular response as a function of metal content. Cellular response after exposure to mHNTs was studied in Staphylococcus aureus and pre-osteoblasts, respectively. Coated mHNTs could easily be identified using the characterization methods, and contrasting bacterial and cellular responses were obtained, which we propose was due to the extent of metallization. These findings demonstrate the potential of this method for creating metal-coated HNTs and suggest they have potential as an implant coating solution.

Self-Assembly of Protamine Biomacromolecule on Halloysite Nanotubes for Immobilization of Superoxide Dismutase Enzyme.

An antioxidant material composed of halloysite nanotubes (HNTs), protamine sulfate polyelectrolyte (PSP), and superoxide dismutase (SOD) enzyme was prepared by self-assembly of the PSP and SOD biomacromolecules on the nanoparticulate support. The structural, colloidal and biocatalytic features were assessed. Adsorption of PSP on the oppositely charged HNT surface at appropriate loadings gave rise to charge neutralization and overcharging, which resulted in unstable and stable dispersions, respectively. The formation of a saturated PSP layer on the HNT led to the development of positive surface charge and to remarkable resistance against salt-induced aggregation making the obtained HNT-PSP hybrid suitable for immobilization of negatively charged SOD. No enzyme leakage was observed from the HNT-PSP-SOD composite indicating sufficient structural stability of this material due to electrostatic, hydrophobic, and hydrogen bonding interactions taking place between the particles and the biomacromolecules. Enzymatic assays revealed that SOD kept its functional integrity upon immobilization and showed high activity in superoxide radical dismutation. In this way, stable antioxidant bionanocomposite dispersions were obtained, which can be used as antioxidants in heterogeneous samples.

Biomass Chitosan-Induced Fe3O4 Functionalized Halloysite Nanotube Composites: Preparation, Characterization and Flame-Retardant Performance

An inorganic–organic nanohybrid flame retardant, HNT@CS@Fe3O4, is prepared by Halloysite nanotubes (HNT) as nanotemplate, chitosan (CS) as char-forming agent and ferroferric oxide (Fe3O[Formula: see text] playing in a catalytic role, aiming to endow enhanced flame-retardant performance of its nanohybrid. Results show that HNT@CS@Fe3O4 nanohybrids have a corn-like structure and can significantly improve the flame retardancy and thermal stability of epoxy resin (EP). Especially, the initial thermal degradation temperature of EP/HNT@CS@Fe3O4 is significantly improved by [Formula: see text]C relative to pure EP, and the residual carbon yield under air atmosphere is 8.8[Formula: see text]wt.%, which is significantly higher than other EP composites, indicating a higher thermal stability is offered by the as-prepared nanohybrid. The limiting oxygen index of EP/10HNT@CS@Fe3O4 is 31.3%, which is 10.2% higher than that of pure EP. Meanwhile, the HNT@CS@Fe3O4 nanofiller reduces the peak heat release rate, CO production and peak smoke production release of EP nanocomposite by 32.0%, 44.0% and 33.0% in a cone calorimeter test, respectively. This is because the HNT-based composite can form a three-dimensional network structure into the EP matrix to inhibit heat release and diffusion of flammable moieties upon burning of EP. In the meantime, the incorporated Fe3O4 nanoparticle can in situ catalyze the charring of CS and EP matrix on the surface of HNT during the combustion process, which also contributes to the significantly increased fire safety of EP.

Controlled degradation of poly-ε-caprolactone for resorbable scaffolds

A lipase from Burkholderia cepacia was successfully adsorbed on the surface of halloysite nanotubes and the coated tubes were incorporated into poly-ε-caprolactone (PCL). The efficiency of the halloysite in the adsorption of the enzyme was characterized by the total protein content determined with the Bradford method. The activity of the adsorbed enzyme was estimated by the kinetic resolution of racemic 1-phenylethanol. The immobilized enzyme was mixed with the polymer and compression molded films were prepared at 70 °C. Activity measurements proved that the enzyme remains active even after adsorption; in fact, larger activities were measured for the immobilized enzyme than for the neat enzyme preparation. The supported enzyme degraded PCL efficiently, the rate of degradation depended on the amount of enzyme adsorbed. The kinetics of degradation was described quantitatively with an appropriate model accounting for two of the three steps of the process, i.e. degradation and the denaturation of the enzyme. The determination of time constants allows the adjustment of degradation rate. This is the first time that the enzyme, which catalyzes degradation, is incorporated into the polymer, and not into the degradation medium, thus allowing the preparation of resorbable scaffolds with controlled lifetime.

Multiscale Characterization of a Wood-Based Biocrude as a Green Compatibilizing Agent for High-Impact Polystyrene/Halloysite Nanotube Nanocomposites.

This paper investigates merits of using a wood-based biocrude (WB) from aspen wood to improve the compatibility of halloysite nanotubes (HNTs) with high-impact polystyrene to develop nanocomposites with desirable thermomechanical properties. Morphological, thermal, and rheological properties of the resulting nanocomposite are used as indicators of the compatibility and dispersion of the modified HNT within the polymer matrix. Computational modeling using density functional theory is used along with laboratory experiments to provide a multiscale characterization of the above biocrude and nanocomposites. Studies performed through dispersion-corrected density functional theory calculations show that the active functional groups of WB molecules including carbonyl, hydroxyl, and carboxylic interact with the HNT surface, while their aromatic tails interact with the phenyl groups of the polystyrene. Furthermore, the studies reveal how WB molecules act as bridges between the hydrophobic polymer and the hydrophilic clay improving the compatibility. The latter was confirmed by Hansen solubility parameters and was evidenced in improved dispersion of clay within the polystyrene matrix observed by microscopy. Rheological and thermal analyses of the modified HNT and nanocomposites showed physical interactions of WB with HNT surface as well as interactions between the WB-modified HNT and the high-impact polystyrene. The WB was found to be a strong candidate as a green compatibilizing agent for HNT in high-impact polystyrene. The study results can provide insights for formulators and manufacturers looking for green compatibilizing agents in conventional nanocomposites for construction and manufacturing applications.

Facile synthesis and characterization of halloysite@W18O49 nanocomposite with enhanced photocatalytic properties

W18O49 nanocrystals grown on halloysite nanotube surfaces could be facilely prepared through a hydrothermal process coupled with a calcination treatment. The as-prepared halloysite@W18O49 nanocomposite shows a smaller bandgap, stronger light absorption, and higher photocatalytic activity than W18O49 nanocrystals. Due to the narrow gap and chemical passivation aroused by inherently negative charges on the surface of halloysite nanotube, halloysite@W18O49 nanocomposite was endowed with superior performance to halloysite nanotube and W18O49 nanocrystals.

Pt-Cu Bimetallic Nanoparticles Loaded in the Lumen of Halloysite Nanotubes.

In this study, we demonstrate that Pt-Cu bimetallic nanoparticles with different compositions (Pt3Cu, PtCu, PtCu3) can be loaded in the lumen of halloysite nanotube (HNT) via a simple one-pot reduction. Increasing the pH of metallic precursor (H2PtCl6 and CuCl2)/HNT solutions enhances the dissociation of H2PtCl6, advancing the association of [PtCl6]2- with the positively charged inner surface (Al-OH) of HNT. Moreover, the shrinkage of bond length from Pt-Cl in [PtCl6]2- to Pt-O in [PtCl4(OH)2]2- due to pH-modulated ligand exchange may also assist Pt(IV) being trapped inside the halloysite. In the meantime, Cu(II) cations may complex with Pt(IV) anions via electrostatic force that would help the formation of Pt-Cu bimetallic nanoparticles inside the halloysite. The obtained PtCu3@HNT system shows a significantly enhanced catalytic performance in the reduction of 4-nitrophenol by sodium borohydride, with a mass activity approximating 60 times higher than that of unloaded Pt nanoparticles. The high catalytic efficiency can be maintained after thermal treatment at 200 or 400 °C.

SILVER NANOPARTICLE SYNTHESIS USING ULTRASOUND AND HALLOYSITE TO CREATE A NANOCOMPOSITE WITH ANTIBACTERIAL PROPERTIES

Abstract—The antibacterial nanocomposites creation is a current trend against microbial contamination and microorganism’s biofilm formation. Existing methods for producing nanocomposites based on silver nanoparticles are difficult, expensive, and not environment friendly; therefore it has become necessary to develop a new method for their synthesis that didn’t have these minus. The paper discusses the possibility of silver nanoparticles synthesizing and obtains a new nanocomposite using halloysite nanotubes and ultrasound. Transmission electron microscopy revealed the silver nanoparticles presence on the inner and outer surface of halloysite nanotubes, and sample mapping showed a uniform distribution of silver nanoparticles in the nanocomposite. The antibacterial activity of the obtained nanocomposite against the strain Serratia marcescens (S. marcescens) was more than twice higher than that of the control. The swarming motility method showed that the diameter of migration of S. marcescens was 2.05 ± 0.05 cm, and in the presence of the nanocomposite, it was 1.63 ± 0.04 cm, indicating the ability of the nanocomposite to inhibit biofilm formation in these bacteria. In the future, the obtained nanocomposite can be used as an additive to various materials or as a coating protecting against bacterial contamination of various surfaces and materials.

In situ assembly of halloysite nanotubes@cerium oxide nanohybrid for highly UV-shielding and superhydrophobic coating

CeO2 nanoparticles were successfully anchored on the surface of halloysite nanotubes (HNTs) by in situ assembly approach to fabricate a novel nanohybrid (HNTs@CeO2). The structure and composition of HNTs@CeO2 were systematically investigated by SEM, TEM, XRD, XPS and TGA. It suggested that the severe aggregation of CeO2 nanoparticles got efficiently suppressed with the aid of HNTs nanocarrier. And the unique hybrid architecture of HNTs@CeO2 endows the silicone coating with excellent UV-blocking effect. Specially, the polydimethylsiloxane (PDMS)/HNTs@CeO2 coating with a mass ratio of 15:1 (HNTs@CeO2: PDMS) could shield 93% ultraviolet B (UVB) and 84% ultraviolet A (UVA). Furthermore, the PDMS/HNTs@CeO2 coating also exhibited synergic feature of outstanding superhydrophobicity and excellent self-cleaning function. In summary, this work has proposed a practical method to resolve the severe aggregation of CeO2 nanoparticles and fabricated a highly UV-shielding and superhydrophobic silicone coating, which may offer a valuable inspiration for the fabrications of nanohybrid and multifunctional coating.

Modification of halloysite nanotubes with supramolecular self-assembly aggregates for reducing smoke release and fire hazard of polypropylene

A novel nano-clay flame retardant (HNTs@MEL-PA) is prepared by modifying halloysite nanotubes (HNTs) with supramolecular self-assembly technology using melamine (MEL) and bio-based phytic acid (PA) as the building blocks. Transmission electron microscopy images and Fourier transform infrared spectra show that the surface of HNTs is successfully decorated with MEL-PA supramolecular aggregates by hydrogen bonding. The feasibility of using HNTs@MEL-PA as a flame retardant for polypropylene (PP) is explored. Compared with PP/HNTs composites, the dispersion of HNTs@MEL-PA and its interfacial interactions with PP matrix are greatly improved. Heat release of PP is decreased in a certain degree and its smoke release is greatly reduced by HNTs@MEL-PA. With the addition of 15 wt% HNTs@MEL-PA, total smoke production of PP is decreased from 15.7 to 10.2 m2, indicating the greatly improved fire safety. Flame retardant and smoke suppression mechanisms of HNTs@MEL-PA are proposed based on thermal decomposition results and the analysis on char residue.

Halloysite nanotube-based H2O2-responsive drug delivery system with a turn on effect on fluorescence for real-time monitoring

In this paper, a novel halloysite-based hydrogel with a “turn-on” fluorescence character upon H2O2 was facilely prepared and used to construct the H2O2-responsive drug delivery system, in which a coprecipitation method was proposed to afford the drug-loaded halloysite nanotubes (DHNTs). DHNTs were carefully characterized by FTIR, TGA, XPS, XRD and TEM to demonstrate that the drugs were mainly loaded into the cavity rather than attached on the external surface of halloysite nanotubes (HNTs). The B-C linkage in the as-prepared hydrogel was broken in the presence of H2O2, resulting in the degradation and thereby a responsive release. The drug release was almost not occurred under the physiological concentration ([H2O2] = 0.02 μM), while a complete release (>90%) can be achieved under pathological concentration ([H2O2] = 200 μM). Moreover, the broken of B-C linkage triggered a transformation from arylboronates to phenols, in which the formed fluorescein gave rise to the change from non-fluorescent to fluorescent of the hydrogels. The fluorescence intensity enhanced with the increase of release rate, in which a good linear relationship can be achieved. The attractive properties make the halloysite-based hydrogels a promising application in the field of biomedicine.

Fabrication and Characterization of Biodegradable pH-Responsive Halloysite Poly(lactic-co-glycolic acid) Micro-sphere for Controlled Released of Phenytoin Sodium

In this paper, new porous pH-responsive microspheres based on functionalized halloysite nanotubes (HNTs) with poly-lactic-co-glycolic acid (PLGA) are investigated as the phenytoin sodium (PHT-Na) carrier. For this purpose, the surfaces of HNTs were modified by a silane coupling agent, (3-aminopropyl)triethoxysilane (APTES) and then the desired microsphere was synthesized through PLGA coating on modified HNTs. Formation of these hybrid particles are confirmed using various characterization methods like Fourier transform infrared (FT-IR), transmission electron microscope (TEM), scanning electron microscope (SEM), EDX, zeta-potential, and X-ray diffraction. The results of the FT-IR spectrum show the presence of APTES, PHT-Na and PLGA peaks, which supported the modification of HNTs and drug capsulation. TEM images confirm the presence of APTES on HNTs, due to the increase in outer diameter. SEM images displayed that by grafting PLGA polymer to modified HNTs, the shape of nanotubes has changed from rod-like to microsphere. Hence, the prospering connection of APTES and PLGA on HNTs was emphasized by zeta-potential results. Moreover, the profile of drug release is recorded via HPLC. In vitro drug release tests show that both the presence of polymer chains around drug containers and the pH value of the release medium play an important role in controlled release. Eventually, the kinetics of drug release was evaluated based on Korsmeyer–Peppas kinetic model.

Preparation and characterization of boronic acid- functionalized halloysite nanotube/poly(vinyl alcohol) nanocomposites

Organic-inorganic nanocomposite films consisting of surface functionalized halloysite nanotube (HNT) and poly (vinyl alcohol) (PVA) with improved mechanical and thermal properties were prepared. The surface of HNT was modified with boronic acid by two different methods. In the first method, a boronic acid group bearing a triethoxysilane was synthesized and used to modify HNT directly. In the second method, HNT was modified by 3-aminopropyltriethoxysilane (APTES) and 4-formylphenylboronic acid sequentially. The surface-modified HNT was characterized by ζ-potential, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The nanocomposite films were prepared by solvent casting, followed by compression molding. The molecular aggregation structure and physicochemical properties were investigated by UV–Vis spectrophotometry, differential scanning calorimetry, wide-angle X-ray diffraction, tensile test, and dynamic mechanical analysis.

Direct Assembly of Silica Nanospheres on Halloysite Nanotubes for “Green” Ultrahydrophobic Cotton Fabrics

AbstractThis paper presents a sustainable biomimetic approach to create ultrahydrophobic cotton fabrics. Cotton fabrics are modified using biobased raw materials to create multiple scale roughness and low surface energy on their surfaces. Naturally occurring halloysite nanotubes (HNT) are modified by silanization and direct assembly of silica (SiO2) nanospheres on the surface of HNTs. HNTs “decorated” with SiO2 nanospheres are covalently bonded onto the surface of cotton fabrics, creating a durable multiple scale surface roughness. Surface modified cotton fabrics are further grafted with fatty acid without using any solvent, via esterification. The combination of the hierarchical roughness pattern created on the surface through modified HNT, and fatty acid treatment results in ultrahydrophobic fabrics with water contact angles (WCAs) above 150°. Surface topographies of modified HNT particles and chemical changes are fully characterized. Attenuated total reflectance Fourier‐transform infrared and WCA studies are used to confirm the grafting of modified HNT particles and aliphatic fatty chains on surface of fabrics. The ultrahydrophobic cotton fabrics washed for five standard laundry cycles (25 home washings) show that the ultrahydrophobicity is durable. Moreover, the ultrahydrophobic fabrics are oleophilic, making them suitable for use in oil–water separation, anti‐biofouling and packaging, and other applications apart from water repellent clothing.

Functionalized Halloysite Nanotubes⁻Silica Hybrid for Enhanced Curing and Mechanical Properties of Elastomers.

Vulcanization and reinforcement are critical factors in governing the ultimate practical applications of elastomer composites. Here we achieved a simultaneous improvement of curing and mechanical properties of elastomer composites by the incorporation of a functionalized halloysite nanotubes–silica hybrid (HS-s-M). Typically, HS-s-M was synthesized by 2-mercapto benzothiazole (M) immobilized on the surface of halloysite nanotubes–silica hybrid (HS). It was found that the HS-s-M uniformly dispersed in the styrene-butadiene rubber (SBR) matrix, offering more opportunity for M molecules to communicate with rubber. In addition, the physical loss of accelerator M from migration and volatilization was efficiently suspended. Therefore, SBR/HS-s-M composites showed a lower curing activation energy and a higher crosslinking density than SBR/HS composites. Moreover, a stronger interfacial interaction between HS-s-M and SBR was formed by the cross-linking reaction, giving a positive contribution to the eventual mechanical properties. The possible vulcanization and reinforcement mechanisms of SBR/HS-s-M composites were also analyzed in detail.