Low‐Temperature Synthesis of Crystalline Inorganic/Metallic Nanocrystal‐Halloysite Composite Nanotubes

We have demonstrated a facile approach for the low‐temperature synthesis of crystalline inorganic/metallic nanocrystal‐halloysite composite nanotubes by employing the bulk controlled synthesis of inorganic/metallic nanocrystals on halloysite nanotubes. The halloysite clay nanotubes can adsorb the target precursor and induce inorganic/metallic nanocrystals to grow in situ. The crystalline phase and morphology of the composite clay nanotubes is tunable. By simply tuning the acidity of the titania sol, the crystalline titania‐clay nanotubes with tunable crystalline phases of anatase, a mixture of anatase and rutile or rutile are achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate)‐halloysite composite nanotubes. Metallic nickel nanocrystal can also be grown on the surface of halloysite nanotubes at low temperature. The traditional thermal treatment for crystallite transformation is not required, thus intact contour of halloysite nanotubes and the crystallinity structure of halloysite nanotubes can be guaranteed. The combined properties from inorganic/metallic nanocrystal (high refractive index, high dielectric constant and catalytic ability) and the halloysite clay nanotubes are promising for applications such as photonic crystals, high‐k‐gate dielectrics, photocatalysis and purification.     

Halloysite nanotubes/polystyrene (HNTs/PS) nanocomposites via in situ bulk polymerization

Serials of halloysite nanotubes/polystyrene (HNTs/PS) nanocomposites with different contents of organo-modified halloysite nanotubes (organo-HNTs) were successfully prepared by the in situ bulk polymerization of styrene with the organo-HNTs as macromonomers. The percentage of grafting (PG%) of more than 230% was achieved, calculated from the results of the thermogravimetric analysis (TG). The TG results also showed that the thermal stabilities of the HNTs/PS nanocomposites prepared via the bulk polymerization were better than the pure polystyrene. And the maximum thermal degradation temperature of the nanocomposites increased with the increasing of the amount of the HNTs fillers added.     

Structure-property relationships in polyamide 12/halloysite nanotube nanocomposites

Polyamide 12 (PA12) nanocomposites based on halloysite nanotubes (HNTs) were obtained using a batch internal mixer or a twin-screw mini-compounder. In order to analyze the influence of HNTs dispersion on nanocomposite properties, morphological analysis (SEM and TEM) was combined with rheological and thermo-mechanical experiments. The linear viscoelastic properties and the dynamic storage modulus were expectedly found to increase with increasing HNT loading. Higher enhancements were observed for PA12/HNTs nanocomposites obtained by twin-screw mini-compounding. This finding was related to the better degree of dispersion and alignment of the silicate nanotubes throughout the matrix. Thermal stability was also improved by the halloysite nanotubes presumably by an entrapment mechanism of the volatile products inside the hollow tubular structure. DSC measurements further highlighted a nucleation effect of HNTs on the nanocomposites. In view of these results, halloysite nanotubes are promising candidates in the field of PA nanocomposites for structural applications.     

Tubule Nanoclay‐Organic Heterostructures for Biomedical Applications

Natural halloysite nanotubes (HNTs) show unique hollow structure, high aspect ratio and adsorption ability, good biocompatibility, and low toxicity, which allow for various biomedical applications in the diagnosis and treatment of diseases. Here, advances in self‐assembly of halloysite for cell capturing and bacterial proliferation, coating on biological surfaces and related drug delivery, bone regeneration, bioscaffolds, and cell labeling are summarized. The in vivo toxicity of these clay nanotubes is discussed. Halloysite allows for 10–20% drug loading and can extend the delivery time to 10–100 h. These drug‐loaded nanotubes are doped into the polymer scaffolds to release the loaded drugs. The rough surfaces fabricated by self‐assembly of the clay nanotubes enhance the interactions with tumor cells, and the cell capture efficacy is significantly improved. Since halloysite has no toxicity toward microorganisms, the bacteria composed within these nanotubes can be explored in oil/water emulsion for petroleum spilling bioremediation. Coating of living cells with halloysite can control the cell growth and is not harmful to their viability. Quantum dots immobilized on halloysite were employed for cell labeling and imaging. The concluding academic results combined with the abundant availability of these natural nanotubes promise halloysite applications in personal healthcare and environmental remediation.     

光谱法研究埃洛石纳米管与溶菌酶间的相互作用

以溶菌酶作为模型蛋白,主要利用光谱法研究了埃洛石纳米管与溶菌酶之间的相互作用。荧光光谱结果表明向溶菌酶体系中加入埃洛石纳米管会出现荧光猝灭现象,猝灭机理符合静态猝灭规律。共振光散射强度的增加可能与埃洛石纳米管-溶菌酶复合物的形成而导致的分子尺寸的增加有关,这与紫外-可见吸收光谱的变化和静态猝灭机理相一致。同步荧光光谱分析表明两者之间的相互作用可能发生在色氨酸所处位置附近,作用过程使溶菌酶的二级结构发生变化,分子链错误折叠,加入浓度为100mg/L和200mg/L的埃洛石纳米管时,通过圆二色谱数据计算出分别导致α-螺旋的含量降低3.28%和6.89%。     

The suitability of halloysite nanotubes as a fire retardant for nylon 6

This work presents the first study on the fire behaviour of halloysite nanotubes-nylon 6 composites. The nylon 6-halloysite composites were prepared at 5-30 wt% of halloysite loadings by a simple melt extrusion process. A range of standard fire tests and characterization techniques were used to assess the efficacy and mechanism by which the halloysite nanotubes inhibited the burning of nylon. We found that for such systems, relatively high concentrations of additive (≥15 wt%) were required to achieve the levels of fire retardant property normally associated with nanoclay (or layered silicate) additives. We proposed that the primary mechanism of flame inhibition for halloysite nanotubes was similar to that of conventional nanoclays; however, the ease of composite preparation is an attractive consideration for further development or study of such systems.     

改性埃洛石材料的制备及其对亚甲基蓝吸附行为的研究

使用硅烷偶联剂KH550改性埃洛石纳米管获得改性材料HNTs-APTS,并对其吸附亚甲基蓝的行为进行研究。利用傅立叶变换红外光谱仪(FTIR)、X-衍射仪(XRD)对改性前后的埃洛石进行表征。考察了吸附时间和温度对吸附过程的影响,并采用Lagrange准二级动力学方程、Langmuir等温线方程及Freundlich等温线方程对实验数据进行拟合。结果表明,KH550成功负载到埃洛石表面;改性后材料的吸附能力大大提高。改性埃洛石对亚甲基蓝的吸附约在60 min达平衡,最大吸附容量为21.66 mg/g。其吸附过程符合准二级动力学方程,热力学较好地符合Langmuir等温线方程,且吸附过程为自发吸热,升高温度有利于吸附的进行。改性材料可重复再生6次,具有良好的再生性能,可在工业处理亚甲基蓝废水中使用。     

Effect of halloysite nanotubes on the thermal degradation behaviour of poly(ε-caprolactone)/poly(lactic acid) microfibrillar composites

This paper reports on the thermal degradation behaviour and kinetics of halloysite nanotubes containing microfibrillated poly(ε-caprolactone) (PCL)/poly(lactic acid) (PLA) blends. It was found that the nanotubes probably catalyzed the PLA degradation, and that the free radicals formed during the PLA degradation initiated PCL degradation at lower temperatures, maybe in combination with halloysite nanotubes (HNT) catalysis. Drawing to form microfibrillated nanocomposites had little influence on the degradation behaviour of these materials, but pre-mixing of the HNT with PLA or PCL prior to melt-mixing and extrusion-drawing of the blends did influence the degradation behaviour, but in different ways. No evidence could be found that the presence and amount of HNT, or the mode of preparation, had an influence on the degradation mechanism, as evidenced through a Fourier-transform infrared (FTIR) analysis of the degradation products.     

MORPHOLOGY,INTERFACIAL INTERACTION AND PROPERTIES OF STYRENE-BUTADIENE RUBBER/MODIFIED HALLOYSITE NANOTUBE NANOCOMPOSITES

 A natural nanotubular material, halloysite nanotubes (HNTs), was introduced to prepare styrene-butadiene rubber/modified halloysite nanotube (SBR/m-HNT) nanocomposites. Complex of resorcinol and hexamethylenetetramine (RH) was used as the interfacial modifier. The structure, morphology and mechanical properties of SBR/m-HNT nanocomposites, especially the interfacial interactions, were investigated. SEM and TEM observations showed that RH can not only facilitate the dispersion and orientation of HNTs in SBR matrix at nanometer scale, but also enhance the interfacial combination between HNTs and rubber matrix. FTIR and XPS investigations confirmed that a number of hydrogen bonds were formed between the phenol hydroxyl groups in resorcinol-formaldehyde resin derived from RH and the oxygen atoms in Si―O bonds or hydroxyl groups on HNTs surfaces. The m-HNTs modified with RH have significant reinforcing effect on SBR vulcanizates. RH as a good interfacial modifier can remarkably improve mechanical properties of SBR/HNT composites. The substantial improvement of comprehensive properties for SBR/m-HNT nanocomposites can be attributed to good dispersion and orientation of HNTs in SBR matrix at nanometer scale and the enhanced interfacial interaction between HNTs and rubber matrix.     

Selective modification of halloysite lumen with octadecylphosphonic acid: new inorganic tubular micelle

Selective fatty acid hydrophobization of the inner surface of tubule halloysite clay is demonstrated. Aqueous phosphonic acid was found to bind to alumina sites at the tube lumen and did not bind the tube's outer siloxane surface. The bonding was characterized with solid-state nuclear magnetic resonance ((29)Si, (13)C, (31)P NMR), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy. NMR and FTIR spectroscopy of selectively modified tubes proved binding of octadecylphosphonic acid within the halloysite lumen through bidentate and tridentate P-O-Al linkage. Selective modification of the halloysite clay lumen creates an inorganic micelle-like architecture with a hydrophobic aliphatic chain core and a hydrophilic silicate shell. An enhanced capacity for adsorption of the modified halloysite toward hydrophobic derivatives of ferrocene was shown. This demonstrates that the different inner and outer surface chemistry of clay nanotubes can be used for selective modification, enabling different applications from water purification to drug immobilization and controlled release.     

The crystallization of polypropylene/halloysite fibers

Journal of Thermal Analysis and Calorimetry - The halloysite (HNT) in the form of nanotubes was used as an agent for the improved mechanical, thermo-mechanical as well as surface properties of...     

Ru/CdS Quantum Dots Templated on Clay Nanotubes as Visible-Light-Active Photocatalysts: Optimization of S/Cd Ratio and Ru Content

A nanoarchitectural approach based on in situ formation of quantum dots (QDs) within/outside clay nanotubes was developed. Efficient and stable photocatalysts active under visible light were achieved with ruthenium-doped cadmium sulfide QDs templated on the surface of azine-modified halloysite nanotubes. The catalytic activity was tested in the hydrogen evolution reaction in aqueous electrolyte solutions under visible light. Ru doping enhanced the photocatalytic activity of CdS QDs thanks to better light absorption and electron–hole pair separation due to formation of a metal/semiconductor heterojunction. The S/Cd ratio was the major factor for the formation of stable nanoparticles on the surface of the azine-modified clay. A quantum yield of 9.3 % was reached by using Ru/CdS/halloysite containing 5.2 wt % of Cd doped with 0.1 wt % of Ru and an S/Cd ratio of unity. In vivo and in vitro studies on the CdS/halloysite hybrid demonstrated the absence of toxic effects in eukaryotic cells and nematodes in short-term tests, and thus they are promising photosensitive materials for multiple applications.     

Halloysite nanotubes as sustainable nanofiller for paper consolidation and protection

We investigated the filling process of cellulose-based paper with natural clay nanotubes and their mixtures with hydroxypropyl cellulose (HPC) that is commonly used as glue and consolidant for degraded paper. A comprehensive characterization of the materials was carried out through morphology, wettability, thermal degradation, and tensile properties. The treatment with halloysite nanotubes generated a decrease of the paper mechanical performance and did not alter the thermal properties. The co-presence of HPC and nanoparticles generated a more uniform nanotubes distribution in the paper fibrous structure and a significant enhancement of both the mechanical properties and the surface hydrophobicity with respect to the HPC treatment. This work proposes the use of halloysite/HPC mixture in a new protocol for paper consolidation and represents a starting point to develop, with a biocompatible approach, smart composite material in which the nanotube cavity is filled with active species for paper protection or active response to external stimuli.     

聚环氧乙烷/埃洛石纳米管复合材料的热稳定性和燃烧性质

采用熔融共混法制备了聚环氧乙烷(PEO)/埃洛石纳米管(HNTs)复合材料,重点研究了HNTs含量对PEO/HNTs复合材料的微观结构、热稳定性及燃烧性质的影响。结果表明,在熔融共混条件下,不同含量的表面未经任何处理的HNTs以纳米尺度均匀分散于PEO基体中;随着HNTs含量的增加,复合材料的热稳定性显著增加。氧指数和水平燃烧测试结果均表明随着HNTs含量的增加,复合材料的阻燃能力有较大提高。     

New hybrid materials based on double‐functionalized linseed oil and halloysite

A series of hybrid systems which combine double‐functionalized linseed oil (methacrylated epoxidized linseed oil) and 2 types of functionalized halloysite (methacrylated halloysite and epoxidized halloysite) was designed in the current study. The curing of the new formulated oil‐clay mixtures was performed via 2 different mechanisms under the influence of the temperature: free‐radical and anionic polymerization. The effect of the functionalized clay tubes against the oil‐based macromonomer reactivity, representing the focus of this study, was monitored by differential scanning calorimetry and Fourier transform infrared spectrometry, concluding that both types of halloysite nanotubes (HNTs) exhibit significant influence on the building of methacrylate/epoxy networks. The effect of the HNTs on the methacrylated epoxidized linseed oil network properties was studied by dynamic mechanical analysis and thermogravimetric analysis, and the morphology of the synthesized hybrids was investigated by scanning electron microscopy. The results suggested that the designed oil‐based hybrid performance is determined by the presence of the both HNT molecules.     

Effect of the ruthenium deposition method on the nanostructured catalyst activity in the deep hydrogenation of benzene

Russian Chemical Bulletin - Ru-containing catalysts supported on halloysite aluminosilicate nanotubes (HNTs) were prepared by incipient wetness impregnation, vacuum impregnation, and impregnation...     

Theoretical Study of Retinol,Niacinamide and Glycolic Acid with Halloysite Clay Mineral as Active Ingredients for Topical Skin Care Formulations

The adsorption of retinol, niacinamide and glycolic acid active ingredients on the internal surface of halloysite in an aqueous environment was explored at the molecular level by means of calculations based on quantum mechanics and force fields from empirical interatomic potentials. These active ingredients are stably adsorbed on the internal surface of halloysite forming hydrogen bonds between the hydrogen, oxygen and nitrogen atoms with the hydroxyl groups of the inner surface of the halloysite. In addition, electrostatic interaction between these active ingredients with the water molecules was observed. Therefore, the theoretical results indicate that the adsorption of these active principles is favourable in the halloysite nanotube, which allows directing future experimental investigations for the development and design of retinol, niacinamide and glycolic acid with halloysite nanotubes systems, which may be topical formulations for skincare.     

Water‐compatible halloysite‐imprinted polymer by Pickering emulsion polymerization for the selective recognition of herbicides

A water‐compatible molecularly imprinted polymer was prepared by Pickering emulsion polymerization using halloysite nanotubes as stabilized solid particles. During polymerization, we used 4‐vinylpyridine as monomer, divinylbenzene as cross‐linking agent, toluene as porogen, 2,2‐azobisisobutyronitrile as initiator, 2,4‐dichlorophenoxyacetic acid as template to form the oil phase, and Triton X‐100 aqueous solution to form the water phase. The halloysite nanotubes molecularly imprinted polymer was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Kinetic and equilibrium bindings were also employed to evaluate the adsorption properties of the imprinted polymer. The imprinted polymer showed better selectivity, more rapid kinetic binding (60 min) for 2,4‐dichlorophenoxyacetic acid in pure water compared with rebinding in toluene. The imprinted polymer was used as a sorbent to enrich and separate 2,4‐dichlorophenoxyacetic acid from water, and was detected by high‐performance liquid chromatography with UV detection.     

Low-Temperature Combustion Synthesis of Halloysite-Based Catalysts for the Deep Oxidation of Hydrocarbons and Carbon Monoxide and the Methanation of Carbon Dioxide

Kinetics and Catalysis - Supported mono- and bimetallic catalysts containing 10 wt % Ni(I), 10 wt % Co(II), and 5 wt % Co + 5 wt % Ni(III) on halloysite nanotubes have been synthesized by...     

Halloysite‐based dopamine‐imprinted polymer for selective protein capture

We describe a facile, general, and highly efficient approach to obtain polydopamine‐coated molecularly imprinted polymer based on halloysite nanotubes for bovine serum albumin. The method combined surface molecular imprinting and one‐step immobilized template technique. Hierarchically structured polymer was prepared in physiological conditions adopting dopamine as functional monomer. A thin layer of polydopamine can be coated on the surface of amino‐modified halloysite nanotubes by self‐polymerization, and the thickness of the imprinted shells can be controlled by the mass ratio of matrix and dopamine. The polymer was characterized by Fourier transform infrared spectrometry, transmission electron microscopy, and thermogravimetric analysis. The prepared material showed high binding capacity (45.4 mg/g) and specific recognition behavior toward the template protein. In addition, stability and regeneration analyses indicated that the imprinted polymer exhibited excellent reusability (relative standard deviation < 9% for batch‐to‐batch evaluation). Therefore, the developed polymer is effective for protein recognition and separation.