Preparation of sodium alginate and xanthan gum bionanocomposite films reinforced with hybrid halloysite nanotubes containing ZnO and licorice root extract for wound dressing applications

This study aims to fabricate bio-nanocomposite films using a solution-casting method based on sodium alginate (SA)1 and xanthan gum (XG).2 These films are reinforced with hybrid Halloysite nanotubes (Hal)3 containing zinc oxide nanoparticles (ZnO-Hal) and licorice root extract (ZnO-Hal-LRE) in various concentrations. These films were characterized using FT-IR, XRD, and scanning electron microscopy (SEM). The ZnO-Hal-LRE nanohybrids significantly enhanced the films' mechanical properties, thermal stability, and water vapor permeability (WVP) barrier. The tensile strength (TS) increased from 6 MPa to 13.204 MPa, and the WVP improved from 1.82 × 10-9 g·m·m-2·h-1·Pa-1 to 1.25 × 10-9 g·m·m-2·h-1·Pa-1. Furthermore, incorporating LRE4 into the nanohybrids enhanced antibacterial and antioxidant activities and increased the cell viability of NIH-3T3 fibroblast cells. The in vitro release study of licorice extract from the nanocomposite film demonstrated a controlled and sustained release, prolonging the half-life of the licorice extract. These findings indicate that the prepared bio-nanocomposite films have significant potential for biomedical applications, particularly wound dressing.

Preparation, acid modification and catalytic activity of kaolinite nanotubes in α-pinene oxide isomerization

In this work kaolinite nanotubes (KNT) were obtained from commercial kaolin AKF-78 (Uzbekistan) by starting material sequential intercalation by DMSO and methanol, followed by treatment with a cetyltrimethylammonium chloride solution. Acid functionalization of KNT for catalytic applications was successfully performed for the first time using a two-step treatment with piranha solution (H2SO4-H2O2), which resulted in the removal of organic impurities as synthetic artifacts and an increase in specific surface area by 3.9 times (up to 159 m2 g-1), pore volume by 1.5 times (0.23 cm3 g-1) and acidity by 4.1 times (49 μmol g-1). The values of the porous structure parameters and concentration of acid sites in processed kaolinite nanotubes practically corresponded to those for natural halloysite nanotubes (HNT) modified in the same way. Both types of materials demonstrated catalytic activity in the model reaction of α-pinene oxide isomerization in various solvents, including green ones, with selectivity to trans-carveol up to 55-57% and campholenic aldehyde of 50-51%, depending on the medium used. A satisfactory correlation between solvent polarity and selectivity was also observed. To the best of our knowledge, this is the first example of using modified kaolinite nanotubes per se as a catalyst. Overall, treatment of KNT with piranha solution provides not only catalytic activity but also the opportunity for further functionalization and application of these nanomaterials.

Development of Spiropyran Immobilization and Characterization Protocols for Reversible Photopatterning of SiO2 Surfaces

Spiropyran is a dynamic organic compound that is distinguished by its reversible conversion between two forms: the colorless closed spiropyran (SP) form and the purple open merocyanine (MC) form. Typically triggered by UV light and reversed by visible light, spiropyran-functionalized surfaces offer reversible conversion in properties including color, polarity, reactivity, and fluorescence, making them applicable to diverse applications in chemical sensors, biosensors, drug delivery, and heavy metal extraction. While spiropyran has been successfully incorporated into various material platforms with SiO2 surfaces, its application on flat surfaces has been limited due to surface area constraints and a lack of standardized evaluation methods, which largely depend on the integration approach and substrate type used. In this study, we systematically review the existing literature and categorize integration methods and substrate types first and then report on our experimental work, in which we developed a streamlined three-step immobilization protocol, which includes surface activation, amination with (3-aminopropyl) triethoxysilane (APTES), and subsequent functionalization with carboxylic spiropyran (SP-COOH). Using SiO2 surfaces as a demonstration, we have also established a robust characterization protocol, consisting of contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and fluorometric analysis. Our results evaluate the newly developed immobilization protocol, demonstrating effective activation and optimal amination using a 2% APTES solution, achieved in 5 min at room temperature. Fluorescence imaging provided clear contrast between the SP and the MC forms. Furthermore, we discuss limitations in the surface density of functional groups and steric hindrance and propose future improvements. Our work not only underscores the versatility of spiropyran in surface patterning but also provides optimized protocols for its immobilization and characterization on SiO2 surfaces, which may be adapted for use on other substrates. These advancements lay the groundwork for on-chip sensing technologies and other applications.

The Effect of Silanized Halloysite Nanotubes on the Structure of Polyethylene-Based Composite

Chemical modification of the surface of halloysite nanotubes (HNT) by alkalization (with sodium hydroxide (NaOH)) and grafting with silanes (bis(trimethylsilyl)amine (HMDS)) was carried out. The efficiency of the alkalization and grafting process was evaluated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and the nitrogen adsorption method were used. XRD and FTIR analysis confirmed the formation of bonds of trimethylsilyl groups to the HNT surface which changed the nature of the surface from hydrophilic to hydrophobic. In addition, it was noted that grafting with silanes decreases by 7.2% the specific surface area of the halloysite compared to the alkalized material. High-density polyethylene (HDPE) composites with halloysite (HNT), alkalized halloysite (alk-HNT), and HMDS-modified halloysite (m-HNT) were processed in the molten state in a Brabender mixer chamber. On SEM/EDS micrographs of HDPE composites with silanized HNT, a change in surface characteristics from smooth to ductile was observed. Higher melting point values based on differential scanning calorimetry (DSC) analysis of HDPE composites with 5%wt silanized halloysite in comparison with HNT and alk-HNT of, respectively, 2.2% and 1.4% were found, which indicates a slight beneficial influence of the filler on the quality of ordering of the crystalline phase of the matrix.

Introducing HaNTr – Halloysite Nanotubes Targeting System for The Selective Delivery of Antibiotics

Antibiotics have been established to induce indiscriminate detrimental effects on the gut commensal bacteria which are vital for human health. This study unprecedently reports the mitigation of this challenge through the targeted delivery of antibiotics to a specific intestinal model pathogen using naturally occurring nanoclay. The designed Halloysite nanotubes targeting (HaNTr) system employs intrinsically mesoporous clay particles, functionalized with antibodies against Escherichia coli (E. coli). Loaded with the antibiotic ciprofloxacin (CIP), the HaNTr particles demonstrate enhanced selectivity of their payload in a human microbiome ex vivo system, preserving the composition of non‐target populations. Furthermore, the HaNTr system exhibits up to a 10‐fold increase in selectivity against E. coli, compared to neat CIP, in a heterogenous culture. This enhanced selectivity is attributed to the sustained and localized release of CIP from the HaNTr particles (≈0.8 ng CIP min−1 mg−1), following their specific binding to target bacteria, as quantitatively measured by high‐throughput imaging flow cytometry. Importantly, HaNTr particles are also shown to be biocompatible with Caco‐2 cells, mimicking the intestinal epithelium. This work highlights the prominent capability of the HaNTr system in alleviating antibiotic‐associated dysbiosis by the targeted delivery of antimicrobials to potentially any microorganism against which the immobilized capture probe can be customized.

Sustainable organosolv-lignin coated nanosilver-halloysites reinforced poly (vinyl alcohol) nanocomposites for wound healing application

This study involves the fabrication of innovative poly (vinyl alcohol) nanocomposite films by incorporating silver-embedded clay nanotubes with organosolv-lignin by the solution casting approach. The confirmation of this procedure was achieved through the utilisation of many techniques, including FTIR, PXRD, FE-SEM, and TGA. The aforementioned research have verified the adherence of silver nanoparticles to the surface of raw halloysites. The confirmation of lignin functionalization on these nanotubes has been established. This novel nanofiller was used to make a range of nanocomposite films with varying weight percentages ranging from 0 wt% to 5 wt%. With the increase in the wt% of nanofillers, These nanocomposite films exhibited greater thermal and mechanical stability compared to plain PVA. An investigation was conducted to examine the impact of the films on the cellular behaviour of murine fibroblast (NIH3T3) cell lines. Based on the findings from cell proliferation and scratch testing, it has been determined that these nanocomposite films are not harmful to cells, exhibit a greater rate of cell multiplication (116 ± 1.19), and demonstrate increased migratory capabilities (86.5 ± 0.50). Further investigations of human blood corroborate the evidence that these films are compatible with blood. Nanocomposite films have the potential to serve as wound healers following pre-clinical and clinical testing.

Augmentin loaded functionalized halloysite nanotubes: A sustainable emerging nanocarriers for biomedical applications

Clay minerals such as Halloysite nanotubes (HNTs), abundantly available green nanomaterial, exhibit a significant advantage in biomedical applications such as drug delivery, antibacterial and antimicrobials, tissue engineering or regeneration, etc. Because of the mesoporous structure and high absorbability, HNTs exhibit great potential as a nanocarrier in drug delivery applications. The sulfuric acid treatment enhances the surface area of the HNTs and thereby improves their drug-loading capacity by enlarging their lumen space/inner diameter. In the present investigation, based on the literature that supports the efficacy of drug loading after acid treatment, a dual treatment was performed to functionalize the HNTs surface. First, the HNTs were etched and functionalized using sulfuric acid. The acid-functionalized HNTs underwent another treatment using (3-aminopropyl) triethoxysilane (APTES) to better interact the drug molecules with the HNTs surfaces for efficient drug loading. Augmentin, a potential drug molecule of the penicillin group, was used for HNTs loading, and their antibacterial properties, cytotoxicity, and cumulative drug release (%) were evaluated. Different characterization techniques, such as X-ray diffractometer (XRD) and Fourier Transform Infra-Red (FT-IR), confirm the loading of Augmentin to the APTES@Acid HNTs. TEM images confirm the effective loading of the drug molecule with the HNTs. The drug encapsulation efficiency shows 40.89%, as confirmed by the Thermogravimetric Analysis (TGA). Also, the Augmentin-loaded APTES@Acid HNTs exhibited good antibacterial properties against E. coli and S. aureus and low cytotoxicity, as confirmed by the MTT assay. The drug release studies confirmed the sustainable release of Augmentin from the APTES@Acid HNTs. Hence, the treated HNTs can be considered as a potential nanocarrier for effectively delivering Augmentin and promoting enhanced therapeutic benefits.

Incorporation of sodium alginate functionalized halloysite nanofillers into poly (vinyl alcohol) to study mechanical, cyto/heme compatibility and wound healing application

In this study, the Halloysite nanotubes (HNTs) are surface-functionalized with sodium alginate (Sod.alg) and poly (vinyl alcohol) (PVA) were employed to generate nanocomposite films (Sod.alg-rHNT/PVA). These nanocomposite films were made via the solution casting technique. FE-SEM data verified sod.alg-rHNT dispersion into the PVA matrix. The modifications were confirmed from FTIR, TGA and PXRD techniques. In the mechanical studies of synthesized nanocomposite films, the films showed a considerable increase in the tensile strength and Young's modulus values. The nanocomposite film's ability to induce cell proliferation and migration was investigated using murine fibroblast (NIH3T3) cells. The films increased cellular proliferation (128 ± 1.07 %) compared to the neat PVA. Cell adhesion tests showed cytocompliant films. In the scratch assay, the 5 wt% film elicited wound closure at a faster rate (91.53 ± 1.04 %). Films were compatible with human blood cells. Therefore the prepared nanocomposite films can be used as promising wound healers after pre-clinical and clinical testing.

Chemically functionalized manufactured sand as the novel additive for enhancing the properties of cement-based composites

The extensive applications of manufactured sand (AS) in cement-based composites were restricted because of its coarse surface texture, poor gradation and inevitable agglomeration. In this paper, a specifically designed polycarboxylate superplasticizer (PCE) decorated manufactured sand (AS-PCE) composite was synthesized via radical polymerization. The AS-PCE composite was characterized by FTIR, TGA, XPS and SEM. The load of PCE on the surface of AS was ∼12 wt%. Our results show that AS-PCE can promote cement hydration reaction and refine the microstructure of a cement-based material, thus, reinforcing its mechanical strength. Meanwhile, the fluidity of cement mortar with 1 wt% AS-PCE particles was increased by 35% after 1 h hydration, due to the steric hindrance effect provided by polycarboxylate superplasticizer affiliated with AS-PCE. The AS-PCE can also significantly enhance the mechanical strength (especially, the flexural strength was about 25% increased after curing for 28 days) of mortar. The excellent improvements result from the synergistic effects of AS-PCE including superb dispersibility, promotion of cement hydration reaction and the repair of interfacial defects between AS particles and the cementitious material. The research provides a promising method for the AS application in cement-based materials.

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.

Vertical Etching of Scandium Aluminum Nitride Thin Films Using TMAH Solution

A wide bandgap, an enhanced piezoelectric coefficient, and low dielectric permittivity are some of the outstanding properties that have made ScxAl1-xN a promising material in numerous MEMS and optoelectronics applications. One of the substantial challenges of fabricating ScxAl1-xN devices is its difficulty in etching, specifically with higher scandium concentration. In this work, we have developed an experimental approach with high temperature annealing followed by a wet etching process using tetramethyl ammonium hydroxide (TMAH), which maintains etching uniformity across various Sc compositions. The experimental results of etching approximately 730 nm of ScxAl1-xN (x = 0.125, 0.20, 0.40) thin films show that the etch rate decreases with increasing scandium content. Nevertheless, sidewall verticality of 85°~90° (±0.2°) was maintained for all Sc compositions. Based on these experimental outcomes, it is anticipated that this etching procedure will be advantageous in the fabrication of acoustic, photonic, and piezoelectric devices.

Gold Nanorod-Incorporated Halloysite Nanotubes Functionalized with Antibody for Superior Antibacterial Photothermal Treatment

The global spread of antibiotic-resistant strains, and the need to protect the microflora from non-specific antibiotics require more effective and selective alternatives. In this work, we demonstrate for the first time a superior antibacterial photothermal effect of plasmonic gold nanorods (AuNRs) via their incorporation onto natural clay halloysite nanotubes (HNTs), which were functionalized with anti-E. coli antibodies (Ab-HNTs). AuNRs were incorporated onto the Ab-HNTs through a facile freeze-thaw cycle, and antibody integrity following the incorporation was confirmed via infrared spectroscopy and fluorescence immunolabeling. The incorporation efficiency was studied using UV-Vis absorption and transmission electron microscopy (TEM). Mixtures of E. coli and AuNR-Ab-HNTs hybrids or free AuNRs were irradiated with an 808 nm laser at 3-4 W cm^-2, and the resulting photothermal antibacterial activity was measured via plate count. The irradiated AuNR-Ab-HNTs hybrids exerted an 8-fold higher antibacterial effect compared to free AuNR under 3.5 W cm^-2; whereas the latter induced a 6 °C-higher temperature elevation. No significant antibacterial activity was observed for the AuNR-Ab-HNTs hybrid against non-target bacteria species (Serratia marcescens and Staphylococcus epidermidis). These findings are ascribed to the localization of the photothermal ablation due to the binding of the antibody-functionalized clay to its target bacteria, as supported through TEM imaging. In the future, the HNTs-based selective carriers presented herein could be tailored with other antibacterial nanoparticles or against another microorganism via the facile adjustment of the immobilized antibody.

Nanoclays: Promising Materials for Vaccinology

Clay materials and nanoclays have gained recent popularity in the vaccinology field, with biocompatibility, simple functionalization, low toxicity, and low-cost as their main attributes. As elements of nanovaccines, halloysite nanotubes (natural), layered double hydroxides and hectorite (synthetic) are the nanoclays that have advanced into the vaccinology field. Until now, only physisorption has been used to modify the surface of nanoclays with antigens, adjuvants, and/or ligands to create nanovaccines. Protocols to covalently attach these molecules have not been developed with nanoclays, only procedures to develop adsorbents based on nanoclays that could be extended to develop nanovaccine conjugates. In this review, we describe the approaches evaluated on different nanovaccine candidates reported in articles, the immunological results obtained with them and the most advanced approaches in the preclinical field, while describing the nanomaterial itself. In addition, complex systems that use nanoclays were included and described. The safety of nanoclays as carriers is an important key fact to determine their true potential as nanovaccine candidates in humans. Here, we present the evaluations reported in this field. Finally, we point out the perspectives in the development of vaccine prototypes using nanoclays as antigen carriers.

Flexible Nano-TiO2 Sheets Exhibiting Excellent Photocatalytic and Photovoltaic Properties by Controlled Silane Functionalization-Exploring the New Prospects of Wastewater Treatment and Flexible DSSCs

TiO₂ nanoparticles surface-modified with silane moieties, which can be directly coated on a flexible substrate without the requirement of any binder materials and postsintering processes, are synthesized and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, time-correlated single-photon counting, and transmission electron microscopy. The viability of the prepared surface-modified TiO₂ (M-TiO₂) sheets as a catalyst for the photo-induced degradation of a model dye, methylene blue, was checked using UV-visible absorption spectroscopy. The data suggest that, compared to unmodified TiO₂, M-TiO₂ sheets facilitate better dye-degradation, which leads to a remarkable photocatalytic activity that results in more than 95% degradation of the dye in the first 10 min and more than 99% of the degradation in the first 50 min of the photocatalytic experiments. We also demonstrate that M-TiO₂ can be recycled with negligible reduction in photocatalytic activity. Further, the photovoltaic properties of the developed M-TiO₂ sheets were assessed using UV-visible absorption spectroscopy, electrochemical impedance spectroscopy (EIS), and photochronoamperometry. Dye-sensitized solar cells (DSSC) fabricated using M-TiO₂ as the photoanode exhibited a photoconversion efficiency of 4.1% under direct sunlight. These experiments suggested that M-TiO₂ sheets show enhanced photovoltaic properties compared to unmodified TiO₂ sheets, and that, when N-719 dye is incorporated, the dye-TiO₂ interaction is more favorable for M-TiO₂ than bare TiO₂. The simple solution processing method demonstrated in this paper rendered a highly flexible photoanode made of M-TiO₂ with superior charge-separation efficiency to an electrode made of bare TiO₂. We propose that our findings on the photovoltaic properties of M-TiO₂ open up arenas of further improvement and a wide scope for the large-scale production of flexible DSSCs on plastic substrates at room temperature in a cost-effective way.

Magnetic responsive mesoporous alginate/β-cyclodextrin polymer beads enhance selectivity and adsorption of heavy metal ions

Mesoporous (~7-8 nm) biopolymer hydrogel beads (HNTs-FeNPs@Alg/β-CD) were synthesised via ionic polymerisation route to separate heavy metal ions. The adsorption capacity of HNTs-FeNPs@Alg/β-CD was higher than that of raw halloysite nano tubes (HNTs), iron nanoparticles (FeNPs), and bare alginate beads. FeNPs induce the magnetic properties of adsorbent and metal-based functional groups in and around the hydrogel beads. The mesoporous surface of the adsorbent permits access of heavy metal ions onto the polymer beads to interact with internal active sites and the mesoporous polymer network. Maximum adsorption capacities of lead (Pb), copper (Cu), cadmium (Cd), and nickel (Ni) were 21.09 mg/g, 15.54 mg/g, 2.47 mg/g, and 2.68 mg/g, respectively. HNTs-FeNPs@Alg/β-CD was able to adsorb heavy metals efficiently (75-99%) under environment-relevant concentrations (200 μg/L) from mixed metal contaminants. The adsorption and selectivity trends of heavy metals were Pb > Cu > Cd > Ni, despite electrostatic binding strength of Cd > Cu > Pb > Ni and covalent binding strength of Pb > Ni > Cu > Cd. It demonstrated that not only chemosorption but also physisorption acts as the sorption mechanism. The reduction in surface area, porosity, and pore volume of the expended adsorbent, along with sorption study results, confirmed that pore filling and intra-particle diffusion played a considerable role in removing heavy metals.

Poly (caprolactone)/sodium-alginate-functionalized halloysite clay nanotube nanocomposites: Potent biocompatible materials for wound healing applications

In this study, halloysite nanotubes (HNTs) were subjected to surface functionalization using sodium alginate and incorporated into poly(caprolactone) (PCL) to fabricate nanocomposites for potential wound healing applications. The nanocomposite films were fabricated through the solution casting technique and characterized using various instrumental methods. The films exhibited enhanced thermal and mechanical properties. FE-SEM and AFM analyses confirmed the uniform dispersion of the HNTs and increased roughness of the films, respectively. The swelling properties, in-vitro enzymatic degradation, and anti-inflammatory activity of the films were also analyzed. The MTT assay performed using NIH3T3 cell lines revealed enhanced cell proliferation (126 ± 1.38) of 5 wt% film. Besides, the cell adhesion tests of the films revealed their cytocompatibility. The scratch assay tests conducted for observing the effectiveness of the films for wound closure showed that the 5 wt% film offered a higher rate of fibroblast cell migration (32.24 ± 0.49) than the pristine PCL film. The HRBCMS assay demonstrated the hemocompatibility of these films. The biological test results indicated the delayed enzymatic degradability and haemocompatiblity of nanocomposites with enhanced cell adhesion, cell proliferation, and cell migration capabilities with respect to fibroblast cells. In summary, the synthesized nanocomposite films can be effectively used in wound healing applications after further clinical trials.

Integrating Halloysite Nanostraws in Porous Catalyst Supports to Enhance Molecular Transport

In many porous catalyst supports, the accessibility of interior catalytic sites to reactant species could be restricted due to limitations of reactant transport through pores comparable to reactant dimensions. The interplay between reaction and diffusion in porous catalysts is defined through the Thiele modulus and the effectiveness factor, with diffusional restrictions leading to high Thiele moduli, reduced effectivess factors, and a reduction in the observed reaction rate. We demonstrate a method to integrate ceramic nanostraws into the interior of ordered mesoporous silica MCM-41 to mitigate diffusional restrictions. The nanostraws are the natural aluminosilicate tubular clay minerals known as halloysite. Such halloysite nanotubes (HNTs) have a lumen diameter of 15-30 nm, which is significantly larger than the 2-4 nm pores of MCM-41, thus facilitating entry and egress of larger molecules to the interior of the pellet. The method of integrating HNT nanostraws into MCM-41 is through a ship-in-a-bottle approach of synthesizing MCM-41 in the confined volume of an aerosol droplet that contains HNT nanotubes. The concept is applied to a system in which microcrystallites of Ni@ZSM-5 are incorporated into MCM-41. Using the liquid phase reduction of nitrophenol as a model reaction catalyzed by Ni@ZSM-5, we show that the insertion of HNT nanostraws into this composite leads to a 50% increase in the effectiveness factor. The process of integrating nanostraws into MCM-41 through the aerosol-assisted approach is a one-step facile method that complements traditional catalyst preparation techniques. The facile and scalable synthesis technique toward the mitigation of diffusional restrictions has implications to catalysis and separation technologies.

Calorimetric and Dielectric Investigations of Epoxy-Based Nanocomposites with Halloysite Nanotubes as Nanofillers

Epoxy nanocomposites are promising materials for industrial applications (i.e., aerospace, marine and automotive industry) due to their extraordinary mechanical and thermal properties. Here, the effect of hollow halloysite nanotubes (HNT) on an epoxy matrix (Ep) was the focus of the study. The structure and molecular mobility of the nanocomposites were investigated using a combination of X-ray scattering, calorimetry (differential (DSC) and fast scanning calorimetry (FSC)) and dielectric spectroscopy. Additionally, the effect of surface modification of HNT (polydopamine (PDA) and Fe(OH)₃ nanodots) was considered. For Ep/HNT, the glass transition temperature (T_g) was decreased due to a nanoparticle-related decrease of the crosslinking density. For the modified system, Ep/m-HNT, the surface modification resulted in enhanced filler–matrix interactions leading to higher T_g values than the pure epoxy in some cases. For Ep/m-HNT, the amount of interface formed between the nanoparticles and the matrix ranged from 5% to 15%. Through BDS measurements, localized fluctuations were detected as a β- and γ-relaxation, related to rotational fluctuations of phenyl rings and local reorientations of unreacted components. A combination of calorimetry and dielectric spectroscopy revealed a dynamic and structural heterogeneity of the matrix, as confirmed by two glassy dynamics in both systems, related to regions with different crosslinking densities.

Harmonic optical microfiber Bragg grating immunosensor for the accelerative test of cardiac biomarker (cTn-I)

Fiber-optic biosensor has shown tremendous promise in probing cardiac biomarkers label-free and in-operando. However, temperature cross-sensitivity is ubiquitously found and impedes further advances of the fiber-optic biosensors, especially for the scenario of rapid test at-body. In this study, we exploit a new regime that harnesses the harmonic resonances of a single microfiber Bragg grating to rule out the impact of the thermal noise. The reflections yielded by the harmonics can be engineered simultaneously at the two overriding optical wavebands, i.e., 1 μm and 1.55 μm, promising a remote acquisition of the sensing signals at patient by virtue of the Yb and/or Er-doped fiber amplifiers which are highly commercial. Furthermore, the functionality of the temperature-offset allows for the understanding of the biomolecular stimulating at the body temperature and thus facilitating the acceleration of the cardiac biomarker test. The proposed proof-of-concept enriches the arsenal of tools for fiber biosensors and enables a vista for the instant and in-vivo diagnosis of acute heart diseases.

Antibody-Functionalized Halloysite Nanotubes for Targeting Bacterial Cells

Halloysite nanotubes (HNTs) are naturally occurring tubular clay particles which have emerged in recent years as a promising nanomaterial for numerous applications. Specifically, HNTs’ large pore volume and high specific surface area in combination with their biocompatibility make them ideal nanocarriers for bioactive compounds. This research aims to design and synthesize functionalized HNTs, which could selectively bind to target bacterial cells in suspension. Such a system can allow us to treat target cells within a challenging heterogeneous population, such as contaminated ecosystems or gut flora. HNTs functionalization is achieved by immobilizing specific antibodies onto the nanotube surface. The synthetic route is realized by the following subsequent steps: acidic etching of the HNTs, silanization of reactive surface hydroxyls, conjugation of protein A, and oriented immobilization of the antibody. HNT functionalization is studied by a set of analytical techniques including attenuated total reflectance Fourier-transform infrared spectroscopy, zeta potential measurements, thermal gravimetric analysis, scanning and transmission electron microscopy, as well as fluorescence microscopy. The selective binding of the functionalized HNTs to their target bacteria is observed upon incubation with live homogenous and heterogeneous cultures using fluorescence microscopy and high-throughput flow cytometry. Plate count and live/dead staining experiments demonstrate the biocompatibility of the antibody-HNT hybrid with its target bacteria. The suggested HNT-based smart carrier constitutes a generic platform for targeted delivery that could be selectively tailored against any microorganism by facile antibody adjustment.

The recovery of sulfuric acid from spent piranha solution over a dimensionally stable anode (DSA) Ti-RuO2 electrode

Piranha solution is a highly acidic mixture of sulfuric acid and hydrogen peroxide. The present study aimed at developing a dimensionally stable anode (DSA), made of titanium metal foil coated with Ruthenium Dioxide (RuO₂), for the electrochemical oxidation of hydrogen peroxide in the presence of strong sulfuric acid under ambient conditions. Results showed that hydrogen peroxide in the piranha solution was fully degraded in 5 h under a constant current of 2 A (or current density of 0.32 A-cm^-2). The oxidation kinetics of hydrogen peroxide followed the Langmuir-Hinshelwood model. The observed rate constant was a function of applied current. The initial current efficiency was 17.5% at 0.5 A (or 0.08 A-cm^-2) and slightly decreased to about 13.5% at applied current between 1.3 and 1.5 A (or current density of 0.208 and 0.24 A-cm^-2). Results showed the capability and feasibility of the electrochemical oxidation process for the recovery of sulfuric acid from the spent piranha solution in semiconductor industrial installations or general laboratories.

Effects of reinforcement of sodium alginate functionalized halloysite clay nanotubes on thermo-mechanical properties and biocompatibility of poly (vinyl alcohol) nanocomposites

In the present work sodium alginate functionalized halloysite nanotubes (HNTs) reinforced poly (vinyl alcohol) nanocomposite films were prepared by solution casting technique. Sodium alginate surface functionalizing on the HNTs through hydrogen bonding was confirmed by spectroscopic and morphological analysis. The functionalized HNTs were successfully incorporated into the PVA matrix. Further, the films were characterized by using FTIR, TGA, XRD, SEM, AFM, UTM, WCA and swelling ratio analysis. The obtained results indicated improved physico-thermal properties, and uniform distribution of nanotubes in the matrix and roughness of the surface compared with the pristine PVA films. After inclusion of functionalized nanotubes causes enhancement of tensile strength as well as young's modulus of the nanocomposite films. Water contact angle measurement was carried out to know the hydrophilic or hydrophobic nature of the films and results were correlated with swelling ratio analysis. Furthermore, the films were analyzed for in-vitro biocompatibility studies. In -vitro enzymatic degradation was carried out in PBS media and cellular behaviour studies were analyzed using NIH3T3 cell lines. The results showed enhancement in the enzymatic degradation, proliferation, adhesion activity compared to that of pristine PVA films. In extension, nanocomposite films were subjected to hemocompatibility studies using human erythrocyte. The results revealed that nanocomposite films were biocompatible and hemocompatible. The fabricated films can be used in biomedical application.

Incorporation of iron (oxyhydr)oxide nanoparticles with expanded graphite for phosphorus removal and recovery from aqueous solutions

In this work, iron (oxyhydr)oxide nanoparticle-doped expanded graphite (IO/EG-1 and IO/EG-2) was prepared via a hydrothermal reaction and applied for the phosphorus adsorption in the aqueous solutions. The analysis of scanning electron microscopy (SEM) and X-ray diffraction (XRD) verified the successful fabrication of IO/EGs, and iron (oxyhydr)oxide nanoparticles became more crystalized according to the calcination at high temperature (IO/EG-2). The maximum adsorption capacity of IO/EG-1 was considerably higher (7.30 mg/g) than that of IO/EG-2 (0.70 mg/g) mainly due to the electrostatic interaction between the negatively charged phosphate ions with iron (oxyhydr)oxides. At the neutral pH, IO/EG-1 exhibited more positively charged than IO/EG-2, which the iso-electric points (IEP) were pH of 9.1 and 6.0, respectively. The thermodynamic study also suggested that the phosphorus adsorption energy of IO/EG-1was considerably favorable (-12.13 kJ/mol) than that of IO/EG-2 (-7.43 kJ/mol). The regeneration of IO/EG-1 were efficiently achieved by a simple extraction using an alkaline solution such as NaOH. Overall, our study suggested that the prepared IO/EGs could be used as good adsorbents for the phosphorus recovery from aqueous solutions.

Past, Present and Future Perspectives on Halloysite Clay Minerals

Halloysite nanotubes (HNTs), clay minerals belonging to the kaolin groups, are emerging nanomaterials which have attracted the attention of the scientific community due to their interesting features, such as low-cost, availability and biocompatibility. In addition, their large surface area and tubular structure have led to HNTs' application in different industrial purposes. This review reports a comprehensive overview of the historical background of HNT utilization in the last 20 years. In particular it will focus on the functionalization of the surfaces, both supramolecular and covalent, following applications in several fields, including biomedicine, environmental science and catalysis.

Interfacial Structure Control and Three-Dimensional X-ray Imaging of an Epoxy Monolith Bonding System with Surface Modification

A monolith bonding system has a high reliability for dissimilar material bonding. The epoxy monolith layer fabricated on a substrate guarantees bond strength by the anchor effect, regardless of the compatibility of the used materials. Designing a high-performance monolith bonding system requires the suppression of an interfacial failure between the monolith and the substrate. In this study, silane and phosphine coupling agents containing amino and epoxy groups were used to construct a robust interfacial structure between the monolith and the substrates such as glass and metals. The internal and interfacial monolith structures were characterized by three-dimensional X-ray imaging as a nondestructive observation method in addition to the scanning electron microscopy of the sample cross sections. The modification of the substrate-monolith interface using the coupling agents improved the strength of dissimilar material bonding of the glass and metal substrates in combination with thermoplastic resins such as poly(ethylene terephthalate) and polycarbonate bisphenol-A.

Nano-interfacial decoration of Halloysite Nanotubes for the development of antimicrobial nanocomposites

In recent times, incorporation of Halloysite Nanotubes (HNTs) with various antimicrobial agents as interfacial materials between these nanotubes and pathogenic microorganisms, for the development of antimicrobial nanocomposites with enhanced antimicrobial activities has gained researcher's interest. The main benefits given by HNT to these nanocomposites include enhanced thermal and mechanical stability of the antimicrobial nanocomposites and also prolong durability and release of the antimicrobial agents in a sustained manner. The exceptional structure of these aluminosilicate minerals based nanotubes (hollow tubular lumen with huge surface area) and oppositely charged surface molecules assist in attaching various molecules on both, the internal surface as well as on the outer surface of these nanotubes. Other advantages of these clay-based minerals are their biocompatibility, non-toxicity, eco-friendly nature and their natural availability with affordable price, which also contribute in selecting them as supporting material for biological applications. Therefore, these clay-based nanotubes have been recently used for developing various antimicrobial nanocomposites. In this review, various antimicrobial nanocomposites developed through incorporation of HNT with myriad antimicrobial agents such as nanoparticles, metal ions, antibiotics, essential oils, biopolymers, phenolic compounds, surfactants and food preservatives as an interface between these nanotubes and microorganisms have been discussed. These antimicrobial nanocomposites could be synthesized in different forms (powder, film, nanocapsule and adhesive) which can be applicable in various fields such as food packaging, water decontamination, waste water management, healing of wounds, antimicrobial agents for surfaces, orthopedics and for the treatment of microbial infections.

Atomic-level understanding of interface interactions in a halloysite nanotubes-PLA nanocomposite

To understand the nature of the bonding mechanism between poly(lactic acid) (PLA) and halloysite nanotubes (HNT), a first-principles DFT study was performed on the adsorption behavior of the PLA monomer, lactic acid (LA), on the outer, inner, and edge surfaces of the HNT. The role of LA functional groups, and its orientation behavior in the formation of bonds with HNT are systematically studied. Analysis of the adsorption energy, total and partial electron density of states (DOS), electric charge transfer between LA atoms and HNT mineral surfaces shows that van der Waals attraction governs their interaction. The calculations of the most stable adsorption configurations of LA show that the predominant number of hydrogen bonds is determined by the activity of the carboxyl functional group of LA on the hydroxylated surfaces of HNT. The important role of the –OH surface groups in the mechanism of lactic acid binding has been established; their absence on the external siloxane surface significantly reduces the LA affinity for HNT. The binding energy of lactic acid on the hydroxylated internal and edge surfaces of the HNT is much higher (by about 275%) than on the external siloxane surface. Mulliken population analysis showed that the formation of a hydrogen bond with the LA atomic groups leads to a more significant redistribution of charge on the inner and edge surfaces of the HNT in comparison with its outer surface. Van der Waals attraction between the LA and HNTs, as well as hydrogen bonds, is responsible for the formation of the bonding mechanism in halloysite nanotubes-PLA nanocomposite. Our results are in accord with available literature.

The mechanism of bond formation between PLA and outer, inner and edge surfaces of HNT was established.

Study on the modification of hexamethylenediamine-phenol-based polybenzoxazine resins by halloysite nanotubes

In this study, hexamethylenediamine-phenol-based benzoxazine monomer (Ba-h) was synthesized using 1,6-hexamethylenediamine, phenol, and paraformaldehyde. Halloysite nanotubes (HNTs) were treated with silane coupling agent and succinic anhydride, respectively. Then the pristine and grafted HNTs were used as nano-fillers to modify Ba-h at different mass ratios ranging between 0 and 2.5 wt% via solution processing. Nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy confirmed the molecular structure of the monomer. The curing behaviors of the nanocomposites were examined by differential scanning calorimetry (DSC). The results of DSC, thermogravimetric analysis, and dynamic mechanical analysis displayed the obvious improvement in the thermal stability of the nanocomposites modified by the grafted HNTs. The results of impact and flexural tests revealed the improvement in the mechanical property of the nanocomposites modified by the pristine HNTs. These enhancements are related to the homogeneous dispersion of HNTs based on the scanning electron microscopy and transmission electron microscopy results.

Clay Nanotubes Aligned with Shear Forces for Mesenchymal Stem Cell Patterning

Aligned halloysite nanotubes on solid substrates are fabricated by a shearing method with brush assistance. These clay nanotubes are aligned by shear force in strip-like patterns accomplished with drying ordering at elevated temperatures. The nanotubes' orientation is governed by "coffee-ring" formation mechanisms depending on the dispersion concentration, nanotube charge, and speed of thermos-evaporation. Polarized light irradiated through the patterns demonstrates birefringence and confirms the orientation. Scanning electron microscopy and atomic force microscopy show that the nanotubes are aligned along the direction of the wetting lines above 4 wt%, while they are not oriented at lower concentrations. Halloysite concentration, drying temperature, and type of brush fibers affect the pattern ordering. The aligned halloysite systems on glass, tissue culture plates, and polymer films, provide a promising platform for biocell guiding. Human foreskin fibroblasts proliferated well on the aligned clay patterns and the cell orientation agrees with the nanotube direction. Human bone mesenchymal stem cells (HBMSCs) are also cultured on the organized halloysite coating. The clay patterns support HBMSC proliferation with alignment, and such nanostructured substrates promote osteogenesis differentiation without growth factors. This facile method for preparing aligned halloysite patterns on solid substrates is very promising for surface modification in biotissue engineering.

Novel Cellulose-Halloysite Hemostatic Nanocomposite Fibers with a Dramatic Reduction in Human Plasma Coagulation Time

High-performance cellulose-halloysite hemostatic nanocomposite fibers (CHNFs) are fabricated using a one-step wet-wet electrospinning process and evaluated for human plasma coagulation by activated partial thromboplastin time. These novel biocompatible CHNFs exhibit 2.4 times faster plasma coagulation time compared with the industry gold standard QuikClot Combat Gauze (QCG). The CHNFs have superior antileaching property of clay with 3 times higher post-wetting clotting activity compared to QCG. The CHNFs also coagulate whole blood 1.3 times faster than the QCG and retain twice the clotting performance after washing. Halloysite clay is also more effective in plasma coagulation than commercial kaolin clay. The physical and thermal properties of the CHNFs were evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, and thermogravimetric analysis. CHNFs show a 7-fold greater clay loading than QCG and their small average diameter of 450 ± 260 nm affords a greater specific surface area (33.6 m² g^-1) compared with the larger average diameter of 12.6 ± 0.9 μm for QCG with a specific surface area of 1.6 m² g^-1. The CHNFs were shown to be noncytotoxic and human primary fibroblasts proliferated on the composite material. The drastic reduction in coagulation time makes this novel nanocomposite a potential lifesaving material for victims of rapid blood loss such as military personnel and patients undergoing major surgical procedures or to aid in the treatment of unexpected bleeding episodes of patients suffering from hereditary blood clotting disorders. Since a person can die within minutes of heavy bleeding, every second counts for stopping traumatic hemorrhaging.

TiO2 decorated functionalized halloysite nanotubes (TiO2@HNTs) and photocatalytic PVC membranes synthesis, characterization and its application in water treatment

In this study photocatalyst, TiO₂@HNTs were prepared by  synthesizing TiO₂ nanoparticles in situ on the  functionalized halloysite nanotubes (HNTs) surface. Photocatalytic PVC membrane TiO₂@HNTs M2 (2 wt.%) and TiO₂@HNTs M3 (3 wt.%) were also prepared. Photocatalyst TiO₂@HNTs and photocatalytic PVC membranes were used to study the photocatalytic activity against the methylene blue (MB) and rhodamine B (RB) dyes in UV batch reactor. The structure and morphology of photocatalyst and photocatalytic PVC membrane were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), UV-Vis spectrophotometer and photoluminescence (PL). The PL study showed that the oxygen vacancies and surface hydroxyl groups present on the surface of TiO₂@HNTs act as excellent traps for charge carrier, reducing the electron-hole recombination rate.TiO₂@HNTs 2 (2 wt.%) and TiO₂@HNTs 3 (3 wt.%) degraded MB dye up to 83.21%, 87.47% and RB dye up to 96.84% and 96.87%, respectively. TiO₂@HNT photocatalyst proved to be stable during the three consecutive cycle of photocatalytic degradation of the RB dye. TiO₂@HNTs M2 and TiO₂@HNTs M3 degraded MB dye up to 27.19%, 42.37% and RB dye up to 30.78%, 32.76%, respectively. Photocatalytic degradation of both the dyes followed the first-order kinetic model. Degradation product analysis was done using the liquid chromatography–mass spectrometry (LC-MS) and the results showed that the dye degradation was initiated by demethylation of the molecule. MB and RB dye degradation reaction were tested by TBA and IPA as OH^* and H⁺ scavengers respectively. Mechanism of photocatalytic activity of TiO₂@HNTs and photocatalytic PVC membrane were also explained.

Adsorption of phosphate on iron oxide doped halloysite nanotubes

Excess phosphate in water is known to cause eutrophication, and its removal is imperative. Nanoclay minerals are widely used in environmental remediation due to their low-cost, adequate availability, environmental compatibility, and adsorption efficiency. However, the removal of anions with nanoclays is not very effective because of electrostatic repulsion from clay surfaces with a net negative charge. Among clay minerals, halloysite nanotubes (HNTs) possess a negatively charged exterior and a positively charged inner lumen. This provides an increased affinity for anion removal. In this study, HNTs are modified with nano-scale iron oxide (Fe₂O₃) to enhance the adsorption capacity of the nanosorbent. This modification allowed for effective distribution of these oxide surfaces, which are known to sorb phosphate via ligand exchange and by forming inner-sphere complexes. A detailed characterization of the raw and (Fe₂O₃) modified HNTs (Fe-HNT) is conducted. Influences of Fe₂O₃ loading, adsorbent dosage, contact time, pH, initial phosphate concentration, and coexisting ions on the phosphate adsorption capacity are studied. Results demonstrate that adsorption on Fe-HNT is pH-dependent with fast initial adsorption kinetics. The underlying mechanism is identified as a combination of electrostatic attraction, ligand exchange, and Lewis acid-base interactions. The nanomaterial provides promising results for its application in water/wastewater treatment.

Surface modified halloysite nanotubes: A flexible interface for biological, environmental and catalytic applications

Halloysite Nanotubes (HNTs) are clay minerals that possess unique chemical composition and a tubular structure due to which, they have recently emerged as a potential nanomaterial for umpteen applications. Over the years, the myriad applications of HNT have been realized through the surface modification of HNT, which involves the modification of nanotube's inner lumen and the outer surface with different functional compounds. The presence of aluminum and silica groups on the inner and outer surface of HNT enhance the interfacial relationship of the nanotube with different functional agents. Compounds such as alkalis, organosilanes, polymers, compounds of biological origin, surfactants and nanomaterials have been used for the modification of the inner lumen and the outer surface of HNT. The strategies change the constitution of HNT's surface either through micro-disintegration of the surface or by introducing additional functional groups on the surface, which further enhances their potential to be used as a flexible interface for different applications. In this review, the different surface modification strategies of the outer surface and the inner lumen that have been employed over the years have been discussed. The biological, environmental and catalytic applications of these surface modified HNTs with such versatile interface in the past two years have been elaborately discussed as well.

Modified halloysite nanotube filled polyimide composites for film capacitors: high dielectric constant, low dielectric loss and excellent heat resistance

In this work, halloysite nanotubes (HNTs) were chosen as the fillers and high performance polyimide (PI) as the matrix to form a series of dielectric composite materials with high dielectric constant, low dielectric loss and excellent heat resistance. Firstly, KH550 was used to modify the surface of HNTs to make sure of a good dispersion of HNTs into the polymer. The results showed that the addition of KH550 modified HNTs (K-HNTs) can improve the dielectric constant of the composite films while maintaining their excellent dielectric loss properties. To further increase the dielectric constant of the HNTs/PI composites, conductive polyaniline (PANI) was used to coat the surface of HNTs to obtain PANI modified HNTs (PANI-HNTs). Compared with the K-HNTs filled systems, the dielectric constant of the PANI-HNTs/PI nanocomposite films is greatly enhanced. The highest dielectric constant of the PANI-HNTs/PI films can achieve 17.3 (100 Hz) with a low dielectric loss of 0.2 (100 Hz). More importantly, the as-prepared composite films have high breakdown strengths (>110.4 kV mm-1) and low coefficients of thermal expansion, as low as 7 ppm per °C, and a maximum discharge energy density of 0.93 J cm-3. Also, such properties are maintained stably up to 300 °C, which is critical for manufacturing heat-resisting film capacitors.