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.

Effect of halloysite addition on the dynamic mechanical and tribological properties of carbon and glass fiber reinforced hybrid composites.

Composite materials have become prominent in the aerospace, automotive, wind energy, biomedical, and machine tool industries. This has demanded the evaluation of the dynamic mechanical and tribological behaviour of composites to understand their performance and ensure their reliability and safety in varied operating conditions. In this study, the effect of halloysite nano-clay addition on the dynamic mechanical and tribological properties of the carbon/glass hybrid composites was investigated. The composites were produced with the vacuum assisted resin infusion process. by varying the content of halloysite nano-clay (1, 3, and 5 wt%). The dynamic mechanical properties of the manufactured composites were examined at temperatures ranging from 30 °C to 180 °C. The tribological properties of the specimens were assessed by varying the applied load (10, 20, and 30 N), sliding speed (1.5, 3, and 4.5 m/s) and sliding distance (500, 1000, and 1500 m). Box-Behnken design was utilized to optimize the number of experiments. The results showed that the halloysite-added samples had better dynamic mechanical and tribological properties than the carbon/glass hybrid composites. Especially, hybrid composites containing 3 wt% halloysite outperformed the other composites investigated. A scanning electron microscope (SEM) was used to examine the worn surface and wreckage in the investigated composite specimens.

Nickel Oxide Decorated Halloysite Nanotubes as Sulfur Host Materials for Lithium-Sulfur Batteries.

Lithium-sulfur batteries with high energy density still confront many challenges, such as polysulfide dissolution, the large volume change of sulfur, and fast capacity fading in long-term cycling. Herein, a naturally abundant clay material, halloysite, is introduced as a sulfur host material in the cathode of Li-S batteries. Nickel oxide nanoparticles are embedded into the halloysite nanotubes (NiO@Halloysite) by hydrothermal and calcination treatment to improve the affinity of halloysite nanotubes to polysulfides. The NiO@Halloysite composite loaded with sulfur (S/NiO@Halloysite) is employed as the cathode of Li-S batteries, which combines the physical confinements of tubular halloysite particles and good chemical adsorption ability of NiO. The S/NiO@Halloysite electrode exhibits a high discharge capacity of 1205.47 mAh g-1 at 0.1 C. In addition, it demonstrates enhanced cycling stability, retaining ≈60% of initial capacity after 450 cycles at 0.5 C. The synthesized NiO@Halloysite can provide a promising prospect and valuable insight into applying natural clay materials in Li-S batteries.

Halloysite Nanotubes as Bimodal Lewis/Brønsted Acid Heterogeneous Catalysts for the Synthesis of Heterocyclic Compounds.

Halloysite nanotubes can be used for the preparation of solid catalysts. Owing to their natural availability at low-cost as well as to their large and easy-to-functionalize surface, they can be conveniently activated with mineral acids or derivatized with acidic groups. Nevertheless, the use of HNTs as catalysts in complex transformations is still limited. Herein, we report two strategies to utilize HNT-based materials as solid acidic catalysts for the Biginelli reaction. To this aim, two methods for increasing the number of acidic sites on the HNTs were explored: (i) the treatment with piranha solution (Pir-HNTs) and (ii) the functionalization with phenylboronic acid (in particular with benzene-1,4-diboronic acid: the sample is denoted as HNT-BOA). Interestingly, both strategies enhance the performance of the multicomponent reaction. Pir-HNTs and HNT-BOA show an increased reactivity (72% and 89% yield, respectively) in comparison with pristine HNTs (52%). Additionally, Pir-HNTs can be reused up to five times without significant performance loss. Moreover, the method also displays good reaction scope, as demonstrated by the preparation of 12 different 3,4-dihydropyrimidinones in up to 71% yield. Therefore, the described strategies are promising for enhancing the acidity of the HNTs as catalysts for the organic reaction.

Preparation of halloysite nanotubes-encapsulated magnetic microspheres for elemental mercury removal from coal-fired flue gas.

Halloysite nanotubes (HNTs) as a natural and inexpensive clay mineral with hollow nanotubular structures, good biocompatibility and active surfaces have been ubiquitously applied in many fields. In this work, a novel multifunctional core-shell sorbent based on HNTs, CuCl2-HNTs encapsulated magnetic microspheres (SiO2@Fe3O4), was successfully fabricated and applied for Hg0 removal from flue gas with good performance for the first time. The core-shell structure prevented the composites from aggregating but kept their magnetism, which enabled the adsorbents being easily separated for reuse by an external magnetic field. In addition, the special structure also significantly enhanced the adsorption capacity of the composites by dispersing the CuCl2 modified HNTs on the prepared magnetic microspheres. The adsorption performance was comprehensively investigated and fitted by dynamic models. The adsorption followed surface adsorption, particle diffusion and chemisorption with very good SO2 tolerance. The Cu+, Cl- and lattice oxygen were the crucial components for Hg0 removal. In order to further understand the possible mechanism, an online home-made coupling system of temperature-programmed decomposition (TPD) was used to investigate the mercury species on the spent adsorbent in addition to X-ray photoelectron spectroscopy analysis. The results confirmed the mercury species adsorbed were primarily Hg0, HgO and HgCl2.

Halloysites modified polyethylene glycol diacrylate/thiolated chitosan double network hydrogel combined with BMP-2 for rat skull regeneration.

Hydrogel serve as bone tissue engineering have lately received great attention for their good biocompatibility and structures similar to natural extracellular matrices. However, a single component polymer hydrogel is generally detrimental to cell adhesion due to the weaker mechanical properties, which limits their application considerably. In an effort to overcome this disadvantage, we adopt an unconventional dual network hydrogels consisting of the polyethylene glycol diacrylate (PEGDA) covalent network, a thiolated chitosan (TCS) ion crosslinking network and thiolated halloysites (T-HNTs) as reinforcing filler. In addition, bone morphogenetic protein-2 (BMP-2) was loaded into the prepared dual network (DN) hydrogel to improve the bone regeneration function of the DN hydrogel. The resulting PEGDA/TCS/T-HNTs hydrogels showed favourable mechanical property, higher crosslinking density, the lower swelling degree, excellent biocompatibility and cell adhesion ability. The histomorphometric and immunohistochemical analyses revealed the excellent bone regeneration ability for composite hydrogel after implant into rat skull defect. Thus, our results indicated that composite scaffold can be applied as a new bone regeneration biomaterial to be applied as a local drug delivery system with good bone induction performance.

Performance evaluation of nanotubular halloysites from weathered pegmatites in removing heavy metals from water through novel artificial intelligence-based models and human-based optimization algorithm.

The efforts of this study aimed to evaluate the feasibility of the nanotubular halloysites in weathered pegmatites (NaHWP) for removing heavy metals (i.e., Cd2+, Pb2+) from water. Furthermore, two novel intelligent models, such as teaching-learning-based optimization (TLBO)-artificial neural network (ANN), and TLBO-support vector regression (SVR), named as TLBO-ANN and TLBO-SVR models, respectively, were proposed to predict the Cd2+ and Pb2+ absorption efficiencies from water using the NaHWP absorbent. Databases used, including 53 experiments for Pb2+ absorption and 56 experiments for Cd2+ absorption from water, under the catalysis of different conditions, such as initial concentration of Pb2+ and Cd2+, solution pH, adsorbent weight, and contact time. Subsequently, the TLBO-ANN and TLBO-SVR models were developed and applied to predict the efficiencies of Cd2+ and Pb2+ absorption from water, aiming to evaluate the role as well as the effects of different conditions on the absorption efficiencies using the NaHWP absorbent. The standalone ANN and SVM models were also taken into consideration and compared with the proposed hybrid models (i.e., TLBO-ANN and TLBO-SVR). The results showed that the NaHWP detected in a Kaolin mine (Vietnam) with 70% nanotubular halloysites is a potential adsorbent for water treatment to eliminate heavy metals from water. The two novel hybrid models proposed, i.e., TLBO-ANN and TLBO-SVR, also yielded the dominant performances and accuracies in predicting the Cd2+ and Pb2+ absorption efficiencies from water, i.e., RMSE = 1.190 and 1.102, R2 = 0.951 and 0.957, VAF = 94.436 and 95.028 for the TLBO-ANN and TLBO-SVR models, respectively, in predicting the Pb2+ absorption efficiency from water; RMSE = 3.084 and 3.442, R2 = 0.971 and 0.965, VAF = 96.499 and 96.415 for the TLBO-ANN and TLBO-SVR models, respectively, in predicting the Cd2+ absorption efficiency from water. Furthermore, the validation results also demonstrated these findings in practice through 23 experiments with the accuracies of 98.3% and 98.37% for the TLBO-ANN and TLBO-SVR models, respectively, in predicting the Pb2+ absorption efficiency from water; the accuracies of 98.3% and 97.46% for the TLBO-ANN and TLBO-SVR models, respectively, in predicting the Cd2+ absorption efficiency from water. Besides, solution pH was evaluated as the most critical parameter that can be adjusted to enhance the performance of the absorption of the heavy metals in this study. By using the NaHWP absorbent and the novel proposed intelligent models developed, heavy metals can be eliminated entirely from water, providing pure water/clean freshwater without any risk of adverse health effects for the short term or long term.

Selective recognition and enrichment of sterigmatocystin in wheat by thermo-responsive imprinted polymer based on magnetic halloysite nanotubes.

Two thermo-responsive molecularly imprinted polymers (MHNTs@MIP and MCNTs@MIP) for the selective extraction of sterigmatocystin have been prepared on the surface of the magnetic halloysite nanotubes (MHNTs) and magnetic carbon nanotubes (MCNTs), respectively. 1, 8-dihydroxyanthraquinone, n-isopropyl acrylamide, methacrylic acid, ethylene dimethacrylate and dimethyl sulfoxide were used as the dummy template, thermo-sensitive functional monomer, co-monomer, cross-linker and porogen, respectively. The magnetic properties, adsorption properties as well as the temperature responsive behaviors of MHNTs@MIP and MCNTs@MIP were systematically studied and compared for the first time. Enough saturation magnetizations of MHNTs@MIP (9.42 emu/g) and MCNTs@MIP (10.54 emu/g) were obtained. MHNTs@MIP and MCNTs@MIP also showed controllable adsorption and release behaviors to sterigmatocystin in response to the temperature change (35 °C and 20 °C). Compared with MCNTs@MIP, MHNTs@MIP had higher adsorption affinity (KL = 0.120 L/mg), higher adsorption kinetic (K2 = 0.0100 g/(mg•min)) and higher imprinting factor (5.22) to sterigmatocystin. These results indicated that MHNTs@MIP was favorable adsorbent for the selective separation of sterigmatocystin. Furthermore, the elution conditions of MHNTs@MIP were optimized by response surface methodology. Under the optimal conditions, MHNTs@MIP coupled with high performance liquid chromatography were successfully applied to the selective recognition, purification, enrichment and detection of sterigmatocystin in wheat samples. The recoveries were calculated from 88.62% to 102.9% with RSDs less than 3.5 % and limit of detection of 1.1 µg/kg. This work provided a suitable carrier for the preparation of imprinted polymers and a practical approach for highly selective recognition and determination of analytes in real samples.

Alginate-based nanocomposite films reinforced with halloysite nanotubes functionalized by alkali treatment and zinc oxide nanoparticles.

Functionalized halloysite nanotubes were prepared by surface activation of halloysite (Hal) with sodium hydroxide and deposition of zinc oxide nanoparticles (ZnONP). The surface charge of Hal was changed from 0.18 ±â€¯0.6 mV to -35.2 ±â€¯2.8 mV after alkali treatment. The functionalized Hal (AT-Hal/ZnONP) was incorporated into alginate biopolymer as a reinforcing filler with different concentration of AT-Hal/ZnONP (1, 3, 5, and 7 wt% of alginate). Alginate films with AT-Hal/ZnONP exhibited a significant increase in the mechanical, water vapor barrier, and UV light barrier properties. The thermal stability of composite films has not changed after AT-Hal/ZnONP incorporation. The AT-Hal/ZnONP incorporated alginate films demonstrated strong antibacterial activity against food-borne pathogenic bacteria, Escherichia coli and Listeria monocytogenes. The nanocomposite film with 7 wt% of AT-Hal/ZnONP exhibited complete sterilization of E. coli and L. monocytogenes after 3 and 9 h of treatment, respectively.

Evaluation of polymethyl methacrylate resin mechanical properties with incorporated halloysite nanotubes.

PURPOSE: This study inspects the effect of incorporating halloysite nanotubes (HNTs) into polymethyl methacrylate (PMMA) resin on its flexural strength, hardness, and Young's modulus. MATERIALS AND METHODS: Four groups of acrylic resin powder were prepared. One group without HNTs was used as a control group and the other three groups contained 0.3, 0.6 and 0.9 wt% HNTs. For each one, flexural strength, Young's modulus and hardness values were measured. One-way ANOVA and Tukey's test were used for comparison (P<.05). RESULTS: At lower concentration (0.3 wt%) of HNT, there was a significant increase of hardness values but no significant increase in both flexural strength and Young's modulus values of PMMA resin. In contrast, at higher concentration (0.6 and 0.9 wt%), there was a significant decrease in hardness values but no significant decrease in flexural strength and Young's modulus values compared to those of the control group. CONCLUSION: Addition of lower concentration of halloysite nanotubes to denture base materials could improve some of their mechanical properties. Improving the mechanical properties of acrylic resin base material could increase the patient satisfaction.

Development of regenerated cellulose/halloysites nanocomposites via ionic liquids.

In this study, regenerated cellulose/halloysites (RC/HNT) nanocomposites with different nanofillers loading were fabricated by dissolving the cellulose in 1-ethyl-3-methylimidazolium chloride (EMIMCl) ionic liquid. The films were prepared via solution casting method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical properties were investigated by tensile testing. It clearly displayed a good enhancement of both tensile strength and Young's modulus with HNT loading up to 5 wt%. As the HNT loadings increased to 5 wt%, the thermal behaviour and water resistance rate was also increased. The TEM and SEM images also depicted even dispersion of the HNT and a good intertubular interaction between the HNT and the cellulose matrix.