Presence Of Halloysite Nanotubes Research Articles

Enhanced OSL emission from α- Al2O3 produced in the presence of halloysite nanocrystals

Aluminum oxide (Al2O3) compounds are extensively used in ionizing radiation dosimetry due to their high sensitivity when doped with carbon. However, their production is difficult and expensive, leading to much research on alternative ways to increase its sensitivity. This paper proposes a seed-mediated synthesis of α-Al2O3 by the combustion method with halloysite nanocrystals as seeds, which also have the ability to scavenge heavy metal ions. The dosimetric features were studied by radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL). Scanning electron microscopy images and X-ray diffraction patterns pointed to the halloysite nanotubes (HNT) acting as heterogeneous nucleation seeds, and as adsorber centers for the chromium ions (Cr3+), as evidenced by the decreased crystallite size and Cr3+ RL emission. Decreased TL intensity upon increasing HNT content in addition to the RL data suggested that the Cr3+ ions strongly participate in the TL emission process as a luminescent center. Remarkable 6-fold enhanced OSL area intensity and 69-fold OSL initial intensity enhancement were registered from the samples seed-mediated by HNT, revealing that, by scavenging Cr3+, the HNT eliminated a luminescent center that competes with the OSL emission. Therefore, HNTs are promising nanomaterials to enhance the sensitivity of Al2O3 dosimeters with potential application in medical physics, where a decrease in the density of concurrent luminescent centers and an increase in OSL intensity were evidenced by the presence of HNT in Al2O3.

Comparison of Synthetic Pathways for Obtaining Fluorescent Nanomaterials Based on Halloysite and Carbon Dots for Potential Biological Sensing.

Recently, fluorescent sensors have gained considerable attention due to their high sensitivity, low cost and noninvasiveness. Among the different materials that can be used for this purpose, carbon dots (CDs) represent valuable candidates for applications in sensing. These, indeed, are easily synthesized, show high quantum yield and are highly biocompatible. However, it was pointed out that the photoluminescence properties of these nanomaterials are strictly dependent on the synthetic and purification methods adopted. The presence of halloysite nanotubes (HNTs), a natural, low cost and biocompatible clay mineral, has been found to be efficient in obtaining small and highly monodispersed CDs without long and tedious purification techniques. Herein, we report the comparison of synthetic pathways for obtaining halloysite-N-doped CDs (HNTs-NCDs) that could be used in biological sensing. One was based on the synthesis of N-doped CDs by a bottom-up approach on HNTs' surface by a MW pyrolysis process; the other one was based on the post-modification of pristine N-doped CDs with halloysite derivatives. The evaluation of the best synthetic route was performed by different physico-chemical techniques. It was found that the bottom-up approach led to the formation of N-doped CDs with different functional groups onto the HNTs' surface. This evidence was also translated in the different fluorescence quantum yields and the existence of several functional groups in the obtained materials was investigated by potentiometric titrations. Furthermore, the ability of the synthesized nanomaterials as sensors for Fe3+ ions detection was assessed by spectroscopic measurements, and the cellular uptake was verified by confocal/fluorescence microscopies as well.

Charge-Selective Photocatalytic Degradation of Organic Dyes Driven by Naturally Occurring Halloysite Nanotubes

This study explores the use of Halloysite NanoTubes (HNTs) as photocatalysts capable of decomposing organic dyes under exposure to visible or ultraviolet light. Through a systematic series of photocatalytic experiments, we unveil that the photodegradation of Rhodamine B, used as a model cationic dye, is significantly accelerated in the presence of HNTs. We observe that the extent of RhB photocatalytic degradation in 100 min in the presence of the HNTs is ~four times higher compared to that of bare RhB. Moreover, under optimized conditions, the as-extracted photodegradation rate of RhB (~0.0022 min−1) is comparable to that of the previously reported work on the photodegradation of RhB in the presence of tubular nanostructures. A parallel effect is observed for anionic Coumarin photodegradation, albeit less efficiently. Our analysis attributes this discrepancy to the distinct charge states of the two dyes, influencing their attachment sites on HNTs. Cationic Rhodamine B molecules preferentially attach to the outer surface of HNTs, while anionic Coumarin molecules tend to attach to the inner surface. By leveraging the unique properties of HNTs, a family of naturally occurring nanotube structures, this research offers valuable insights for optimizing photocatalytic systems in the pursuit of effective and eco-friendly solutions for environmental remediation.

Synthesis of halloysite nanotubes decorated with green silver nanoparticles to investigate cytotoxicity, lipid peroxidation and induction of apoptosis in acute leukemia cells

Leukemia is the 15th most common cancer in adults and the first most common cancer in children under the age of five, and unfortunately, it accounts for many deaths every year. Since leukemia chemotherapy usually fails due to chemotherapy resistance and disease relapse, many efforts are being made to develop new methods of leukemia treatment. Therefore, for the first time, we decorated halloysite nanotubes (HNTs) with green silver nanoparticles (Ag NPs) with the help of Moringa Peregrina leaves extract to increase the solubility of Ag NPs and to use the protective ability of HNTs against lipid peroxidation in erythrocytes. Cell survival assay by the MTT method showed that HNTs-Ag NPs can decrease the survival of Jurkat T-cells to about 10% compared to the control. The IC50 value was estimated as 0.00177 mg/mL after 96 h of treatment. Investigating the expression of genes involved in apoptosis by Real-time PCR proved that decorated HNTs with Ag NPs can increase the Bak1/Bclx ratio by 17.5 times the control group. Also, the expression of the caspase-3 gene has increased 10 times compared to the control. Finally, the reduction of malondialdehyde production after 24 h proved that the presence of HNTs can have a good protective effect on lipid peroxidation in erythrocytes. Therefore, on the one hand, we can hope for the ability of HNTs-Ag NPs to induce apoptosis in blood cancer cells and on the other hand for its protective effects on normal blood cells.

Combined Effect of Poly(lactic acid)-Grafted Maleic Anhydride Compatibilizer and Halloysite Nanotubes on Morphology and Properties of Polylactide/Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Blends.

Given the global challenge of plastic pollution, the development of new bioplastics to replace conventional polymers has become a priority. It is therefore essential to achieve a balance in the performances of biopolymers in order to improve their commercial availability. In this topic, this study aims to investigate the morphology and properties of poly(lactic acid) (PLA)/ poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) (at a ratio of 75/25 (w/w)) blends reinforced with halloysite nanotubes (HNTs) and compatibilized with poly(lactic acid)-grafted maleic anhydride (PLA-g-MA). HNTs and PLA-g-MA were added to the polymer blend at 5 and 10 wt.%, respectively, and everything was processed via melt compounding. A scanning electron microscopy (SEM) analysis shows that HNTs are preferentially localized in PHBHHx nodules rather than in the PLA matrix due to its higher wettability. When HNTs are combined with PLA-g-MA, a finer and a more homogeneous morphology is observed, resulting in a reduction in the size of PHBHHx nodules. The presence of HNTs in the polymer blend improves the impact strength from 12.7 to 20.9 kJ/mm2. Further, with the addition of PLA-g-MA to PLA/PHBHHX/HNT nanocomposites, the tensile strength, elongation at break, and impact strength all improve significantly, rising from roughly 42 MPa, 14.5%, and 20.9 kJ/mm2 to nearly 46 MPa, 18.2%, and 31.2 kJ/mm2, respectively. This is consistent with the data obtained via dynamic mechanical analysis (DMA). The thermal stability of the compatibilized blend reinforced with HNTs is also improved compared to the non-compatibilized one. Overall, this study highlights the effectiveness of combining HNTs and PLA-g-AM for the properties enhancement of PLA/PHBHHx blends.

POLYANILINE, HALLOYSITE NANOTUBES AND THEIR NANOCOMPOSITE AS ADSORBENTS FOR ORGANIC DYES

This work is devoted to the study of the adsorption efficiency of methylene blue and methyl orange dyes by polyaniline base (PANI), halloysite nanotubes (HNTs), and their nanocomposite (HNTs/PANI). PANI and the nanocomposite were prepared by the chemical oxidative polymerization of aniline in the absence and presence of HNTs followed by subsequent dedoping by ammonia solution. The morphology and thermal stability of the adsorbents were explored. In particular, the TEM method showed that the nanocomposite consisted of practically non-agglomerated nanoparticles with a “core-shell” morphology. Particles of pure polymer are quite agglomerated and form massive aggregates. The kinetics of decreasing the concentration of dyes in solutions upon their contact with adsorbent powders was studied by the method of electron spectroscopy. The HNTs/PANI nanocomposite was found to absorb both dyes with slightly higher efficiency than the PANI base probably due to more developed surface of the former. Processing of the obtained results of adsorption of both dyes on the studied adsorbents according to different kinetic models (pseudo-first and pseudo-second order and intraparticle diffusion) showed that in all cases this process is best described by the pseudo-second order model, which indicates the chemical nature of adsorption. The calculated adsorption capacity of the adsorbents under study appeared be quite close to the experimental one. These materials can be used as effective adsorbents for cleaning wastewaters from organic dyes.

Sodium alginate/xanthan-based nanocomposite hydrogels containing 5-fluorouracil: Characterization and cancer cell death studies in presence of halloysite nanotube

This work was aimed to synthesize 5-fluorouracil (5-FU)-loaded sodium alginate (SA)/xanthan gum (Xan) hydrogels containing sulfuric acid-treated halloysite nanotube (tHNT) using free radical polymerization and evaluate their apoptosis against HeLa cells in cervical cancer therapy. The nanocomposite hydrogel including tHNT (SA/Xan: tHNT, 1:1) showed a rough surface with cross-linking density of 171.9 × 10-4 mol/cm3 compared to tHNT-free sample (62.5 × 10-4 mol/cm3). The 5-FU encapsulation efficiency of the samples in the presence and absence of tHNT was obtained approximately 60 % and 76 %, respectively. Moreover, the drug release of the samples with and without tHNT were measured 72 % and 93 % in acidic medium as well as 32 % and 57 % in basic environment after 72 h. Finally, the cytotoxicity results revealed the minimum cell viability (3.3 %) for tHNT-loaded hydrogel sample on the 4th day, and flow cytometry assessments also exhibited that the apoptosis rate of HeLa cells for this sample was 85.4 %, resulting in its remarkable potential for destroying this cancerous cell line.

PEO Coatings Modified with Halloysite Nanotubes: Composition, Properties, and Release Performance.

In this work, the properties of the coatings formed on the Mg-Mn-Ce alloy by plasma electrolytic oxidation (PEO) in electrolytes containing halloysite nanotubes (HNTs) were investigated. The incorporation of halloysite nanotubes into the PEO coatings improved their mechanical characteristics, increased thickness, and corrosion resistance. The studied layers reduced corrosion current density by more than two times in comparison with the base PEO layer without HNTs (from 1.1 × 10-7 A/cm2 to 4.9 × 10-8 A/cm2). The presence of halloysite nanotubes and products of their dihydroxylation that were formed under the PEO conditions had a positive impact on the microhardness of the obtained layers (this parameter increased from 4.5 ± 0.4 GPa to 7.3 ± 0.5 GPa). In comparison with the base PEO layer, coatings containing halloysite nanotubes exhibited sustained release and higher adsorption capacity regarding caffeine.

Aspects of halloysite nanotubes integration in epoxy nanocomposites: Curing kinetics and deformation mechanism

AbstractThe curing kinetics of diglycidyl ether of bisphenol A epoxy resin using amine‐based hardener in the presence of halloysite nanotubes (HNTs) are investigated by performing isothermal and dynamic differential scanning calorimetry measurements, followed by a detailed analysis of the experimental data via the kinetic free method and three common model‐based analysis. Kamal and Sourour model gave the best fit for the experimental data and thus, was further modified by Williams–Landel–Ferry diffusion control equations to calculate the diffusion constants near the glass transition temperature (Tg). The optimized model is used to find the curing kinetics parameters of epoxy/HNTs nanocomposites, and those finding are further validated and explained by performing rheometric measurements. Noncatalytic and autocatalytic curing reactions and diffusion constants are all functions of the amount of HNTs. HNTs shift the curing reaction slightly toward higher temperatures and promote etherification reactions, leading to an increase in the curing enthalpy, as extra bonds will be formed between HNTs and epoxy resin during the polymerization. The combination of acceleration and inhibition mechanisms dictates the complex kinetics of the reactions at high concentrations of HNTs, while the produced local topology of the polymeric network depends highly on HNTs weight ratio. Furthermore, to investigate the mechanical performance of the prepared nanocomposites under flexural loads, three points bending tests are performed in both modes, dynamic and static, followed by a fractography analysis of the fractured surfaces. The mechanical properties have improved by the addition of pristine HNTs without compromising the Tg of the polymer. This study provides a set of observational relationships between various chemical interactions during polymerization and the final topology and performance of the polymer, which in turn aims to bridge the gap in the literature between the curing kinetics of epoxy/HNTs nanocomposites and the performance of these nanocomposites under various thermal and mechanical stresses.

Hydrophobic PVDF-HNT membrane for oxytetracycline removal via DCMD: The influence of fabrication parameters on permeability, selectivity and antifouling properties

Halloysite nanotube (HNT) was incorporated in poly(vinylidene fluoride) (PVDF) membrane to remove contaminants of emerging concern (CEC) known as oxytetracycline (OTC), which is extensively used in the aquaculture industry. The presence of HNT in the PVDF matrix has improved the characteristics and separation of the pristine membrane. This study evaluated the effectiveness of low concentration of HNT loading for treating OTC molecules via direct contact membrane distillation (DCMD), which produced high flux recovery after ethanol cleaning. The performance of PVDF-HNT (PHNT) membrane with 0.5 % HNT loading was compared using immersion time of 5 and 15 s. Further improvement was carried out by reducing 500 μm of the membrane thickness to 250 and 100 μm. The wetting characteristics were determined to achieve the desired properties of DCMD membrane and gain insights into the antifouling mechanism of PHNT membrane. The modified membrane using 5 s immersion time obtained a high liquid entry pressure and contact angle (CA) of 2.13 bar ±0.34 and 140° ± 3.10, respectively. This membrane had removed 95 % of OTC molecules with a permeate flux of 5.52 L/m2h. A 38.4 % increment in flux permeation with 98 % removal was obtained after reducing the membrane thickness to 250 μm (7.64 L/m2h). The total and irreversible flux decline of this membrane was significantly low; as a result, the flux recovery obtained above 90 % after ethanol cleaning including for membrane regeneration and long-term operation investigation. OTC removal from the feed solution improved from 98 % to 100 % after the regeneration and long-term operation.

Preparation of intelligent magnetic halloysite nanotubes/polyurethane nanocomposites: The role of nanotube modification on the shape recovery rate

This study aimed to investigate the effect of modification of halloysite nanotubes (HNTs) with iron oxide on the morphology and thermomechanical properties of polyurethane with shape memory behavior. Iron oxide-functionalized halloysite nanotubes (I-HNTs) were synthesized via co-precipitation method. Polyurethane nanocomposites containing 1 and 2 wt.% HNTs and I-HNTs were prepared in situ by prepolymer method. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirmed the successful synthesis of I-HNT. Dynamic mechanical thermal analysis (DMTA), FTIR equipped with reduced overall reflectance, atomic force microscope (AFM), and differential scanning calorimetry (DSC) showed that phase separation increased by the addition of HNTs or I-HNTs and their propensity to rigid sections. The maximum degree of micro-phase separation was 66.8% in the sample containing 2 wt.% I-HNT. In DMTA, an improvement in the shape's return speed in the shape memory behavior was observed by adding HNTs to neat polyurethane. This increase was significant in samples based on I-HNT and the highest recovery rate was 179.1 GPa. °C−1 in the sample containing 2 wt.% I-HNT. Examination of shape memory behavior showed that by adding 1 wt.% HNT, shape fixity parameter increased due to the increase in soft phase purity and shape recovery parameter decreased due to reduced mobility in the presence of HNTs. This effect was more significant in I-HNT-based samples, and the highest shape stability (96.7%) was observed in nanocomposites containing 2 wt.% I-HNT.

Effect of bassorin (derived from gum tragacanth) and halloysite nanotubes on physicochemical properties and the osteoconductivity of methylcellulose-based injectable hydrogels

Injectable hydrogels have been known as promising materials for the regeneration of irregular shape tissue defects. In this study, novel thermosensitive methylcellulose (MC) hydrogels containing bassorin (Ba) and halloysite nanotubes (HNTs) have been developed for application in bone tissue engineering. Bassorin isolated from gum tragacanth (GT) with the concentration of 0.25-1.5 w/v% was blended with MC. The best MC/Ba gel (containing 0.5% bassorin) was chosen based on the results of injectability and rheological tests. HNTs (1-7%) were added to this formulation and tested for the physicochemical, mechanical, rheological, degradation, swelling, and biological properties. In vitro biological evaluations including cell proliferation (by MTT assay), cell attachment (by SEM), osteogenic activity (by Alizarin Red staining and alkaline phosphatase assay), and osteogenic gene expression (by quantitative real-time polymerase chain reaction) were done using MG-63 cells. Results showed that bassorin led to the increased gel-forming ability (at a lower temperature) and mechanical properties of MC hydrogel. The presence of HNTs and bassorin affected the degradation rate and swelling degree of MC-based hydrogel. Results showed significant enhancement in cell proliferation, differentiation, and mineralization, as well as higher bone-specific gene expression of the cell on bassorin and HNTs incorporated MC compared to pure MC hydrogel.

Cementitious binders modified with halloysite nanotubes for enhanced lead immobilization

Heavy metal-containing wastes pose long-term environmental threats. In the present work, cementitious binders in the presence of halloysite nanotubes (HNTs) at 1 wt%, 3 wt%, and 5 wt% by mass were used to immobilize lead (Pb(II)). Semi-dynamic leaching tests were used to quantify the Pb(II) leaching up to 64 days. The results showed that the addition of 1 wt%, 3 wt%, and 5 wt% HNTs particles strongly reduced the Pb(II) release. The optimal dosage of HNTs was 3 wt%, which decreased the cumulative release of Pb(II) by around 40.5% after 64 days. Isothermal calorimetry, X-ray diffractometry (XRD), thermogravimetry (TG), mercury intrusion porosimetry (MIP) and compression tests were then used to investigate better immobilization effect with HNTs addition. The results showed that HNTs particles promoted cement hydration, refined the pore structure of the hardened cementitious binders, decreased permeability, and enhanced mechanical strength. Zeta potential measurements indicated that the negative surface charge of the HNTs particles could adsorb Ca2+ ions from the pore solution of cement hydration, then facilitating adsorption of Pb(OH)3−.

Halloysite Nanotubes and Silane-Treated Alumina Trihydrate Hybrid Flame Retardant System for High-Performance Cable Insulation

The effect of the presence of halloysite nanotubes (HNTs) and silane-treated alumina trihydrate (ATH-sil) nanofillers on the mechanical, thermal, and flame retardancy properties of ethylene-vinyl acetate (EVA) copolymer/low-density polyethylene (LDPE) blends was investigated. Different weight percentages of HNT and ATH-sil nanoparticles, as well as the hybrid system of those nanofillers, were melt mixed with the polymer blend (reference sample) using a twin-screw extruder. The morphology of the nanoparticles and polymer compositions was studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The mechanical properties, hardness, water absorption, and melt flow index (MFI) of the compositions were assessed. The tensile strength increases as a function of the amount of HNT nanofiller; however, the elongation at break decreases. In the case of the hybrid system of nanofillers, the compositions showed superior mechanical properties. The thermal properties of the reference sample and those of the corresponding sample with nanofiller blends were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Two peaks were observed in the melting and crystallization temperatures. This shows that the EVA/LDPE is an immiscible polymer blend. The thermal stability of the blends was improved by the presence of HNTs and ATH-sil nanoparticles. Thermal degradation temperatures were shifted to higher values by the presence of hybrid nanofillers. Finally, the flammability of the compositions was assessed. Flammability as reflected by the limiting oxygen index (OI) was increased by the presence of HNT and ATH-sil nanofiller and a hybrid system of the nanoparticles.

Synthesis and properties of core–shell halloysite–polyaniline nanocomposites

We consider physico-chemical specificity (open circuit potential and pH changes) of the chemical oxidative aniline polymerization in the presence of halloysite nanotubes (HNTs) and morphology, structure and properties of the new nanocomposites of HNTs with polyaniline (PANI) doped by p-toluenesulfonic acid. We find that specificity of the PANI properties in such nanocomposites appears obviously due to adsorption on the HNTs surface and specific interactions of all participants of the polymerization process. The study of the open circuit potential and pH changes in the polymerization system and properties of the synthesized HNT/PANI nanocomposites revealed the strong dependence of their morphology, molecular structure, conductivity, thermostability and sensor behavior on the contents of the doped PANI. These findings indicate existence of specific interactions between the PANI component and the HNT surface, which significantly improved properties of the PANI component in the synthesized HNT/PANI nanocomposites as compared with that of the pure PANI. The best thermostability and sensing behavior were found for the synthesized HNT/PANI nanocomposites with the lowest contents of the doped PANI. In particular, the strongest sensor responses to gaseous ammonia are observed in the case of HNT/PANI nanocomposite with lowering the doped PANI content. This work shows for the first time applicability of HNT/PANI nanocomposites for gas sensing.

Multifunctional filtration membrane with anti-viscous-oils-fouling capacity and selective dyes adsorption ability for complex wastewater remediation

Multifunctional filtration membranes (MFMs), which can both effectively separate oil and selectively remove dyes from polluted aquatic system with robust anti-viscous-oil-fouling capacity, strong chemical/physical resistance, and long cycled stability, are highly required but still a challenge to be realized. Herein, a simple route has been demonstrated to address this challenge aforementioned by decorating both halloysite nanotubes (HNTs) and zwitterionic poly (sulfobetaine methyl methacrylate) (PSBMA) on the microporous polyvinylidene fluoride (PVDF) membrane surface via modified polydopamine (PDA) coating route. The as-prepared membrane exhibits super-hydrophilic/underwater super-oleophobic performance and high water permeation flux (32529 ± 278 L m−2 h−1 at 0.85 bar) to purify the diverse viscous oil-in-water emulsions from oily wastewater accompanying with good cycled stability (the recovery rate of permeate flux is close to 100% after 5 cycles). Moreover, the as-prepared MFM possesses not only strong chemical resistance under wide range of pH value (from 1 to 12) and high saline (NaCl: 10 wt%) environment, but also physical resistance against ultrasound bath for 30 min. Given the presence of HNTs, PDA, and PSBMA, our MFM shows enough active sites to adsorb the soluble dyes and metallic ions in wastewater. These excellent properties endow our MFM with great potential for the remediation of complex wastewater.

One-Shot Preparation of Polybasic Ternary Hybrid Cryogels Consisting of Halloysite Nanotubes and Tertiary Amine Functional Groups: An Efficient and Convenient Way by Freezing-Induced Gelation.

A convenient method for the preparation of polybasic ternary hybrid cryogels consisting of Halloysite nanotubes (HNTs) and tertiary amine functional groups by freezing-induced gelation is proposed. Ternary hybrid gels were produced via one-shot radical terpolymerization of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and DEAEMA in the presence of HNTs. The equilibrium swelling in various swelling media and the mechanical properties of the produced ternary hybrid gels were analyzed to investigate their network structure and determine their final performance. The swelling ratio of HNT-free gels was significantly higher than the ternary hybrid gels composed of high amount of HNTs. The addition of HNTs to terpolymer network did not suppress pH- and temperature-sensitive behavior. While DEAEMA groups were effective for pH-sensitive swelling, it was determined that both HEMA and DEAEMA groups were effective in temperature-sensitive swelling. Ternary hybrid gels simultaneously demonstrated both negative and positive temperature-responsive swelling behavior. The swelling ratio changed considerably according to swelling temperature. Both DEAEMA and HEMA monomers in terpolymer structure were dominant in temperature-sensitive swelling. Mechanical tests in compression of both as-prepared and swollen-state demonstrated that strength and modulus of hybrid cryogels significantly increased with addition of HNTs without significant loss of mechanical strength. Ultimately, the results of the current system can benefit characterization with analysis tools for the application of innovative materials.

Nonfluoride-modified halloysite nanotube-based hybrid: potential for acquiring super-hydrophobicity and improving flame retardancy of epoxy resin

With the development of modern engineering technology, the development of high-performance and multifunctional polymer materials has been promoted. In this work, a novel nanohybrid based on chitosan engraved zinc and iron mixed oxyhydroxide at the presence of halloysite nanotubes (HNTs) as the carrier, followed by surface capping with stearic acid to obtain super-hydrophobic HNT@CSZFMOH nanofiller. The as-obtained HNT@CSZFMOH nanofiller was incorporated into epoxy resin (EP) matrix. With the addition of 3 wt.% HNT@CSZFMOH, the peak heat release rate and peak smoke production of the EP nanocomposite decreased by 35% and 32%, respectively. This excellent flame retardancy is attributed to that the enhanced physical barrier derived from HNT@CSZFMOH, and the dense, highly graphitized char layer formed by catalytic charring of ultrafine FeOOH and ZnOOH nanoparticles. Meanwhile, the nanohybrid imparted outstanding hydrophobicity to the hydrophilic substrate EP with the water contact angle (CA) of 159°. EP-matrix nanocomposite exhibited desired self-cleaning performance as well as good resistance against corrosive liquids (acid and alkaline solutions) and ultraviolet irradiation. The present approach, with simple procedures and desired environmental acceptance, could provide feasible pathway to fabricating multifunctional polymer–matrix composites.

Fabrication of a water-retaining, slow-release fertilizer based on nanocomposite double-network hydrogels via ion-crosslinking and free radical polymerization

A new type of water-retaining, slow-release fertilizer (WSF) based on double-network hydrogels was fabricated via the ion-crosslinking of sodium carboxymethyl cellulose and the free radical polymerization of polymerizable β-cyclodextrin (MAH-CD), polyethylene glycol dimethacrylate (PEGDA), acrylamide (AM), and acrylic acid (AA) with urea-loaded halloysite as an additive. The effects of the AM to AA monomer ratio, the halloysite content, the AlCl3 content and the MAH-CD content on the swelling ratio were studied. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were applied to characterize the structure and properties of the WSF. The swelling behavior and water retention capacity of the fertilizer were investigated using a classic gravimetric method. The experimental results indicated that the presence of halloysite nanotubes clearly adjusted the swelling and release properties of the WSF. Kinetic modeling indicated that the swelling mechanism and slow release behavior were consistent with a Fickian diffusion mechanism. Form the considerations of its properties and raw materials, the fertilizer developed here has a good prospect of application and extension.

Bionanocomposite Films Containing Halloysite Nanotubes and Natural Antioxidants with Enhanced Performance and Durability as Promising Materials for Cultural Heritage Protection.

In the last decade, the interest toward the formulation of polymer films for cultural heritage protection continuously grew, and these films must be imperatively transparent, removable, and should not react/interact with surface of the artworks. In this research, bionanocomposite films, based on chitosan (Ch) and pectin (P) and containing naturally occurring fillers and antioxidants, were formulated by solvent casting methods and were accurately characterized. The natural halloysite nanotubes (HNT) have a two-fold role, specifically, physical compatibilizer and antioxidant carrier. Therefore, the theoretical solubility between Ch and P was estimated considering Hoy’s method for solubility of polymers, while the optimum ratio between biopolymer constituents was assessed by ζ-potential measurements. The transparency, wettability, and mechanical behavior of Ch:P films, also in presence of HNT without and with antioxidants, were investigated. The beneficial effects of natural antioxidants, such as vanillic acid (VA) and quercetin (Q), on Ch:P/HNT durability were found.