Modified Halloysite Nanotubes Research Articles

Bio-derived modified halloysite nanotubes as eco-friendly flame retardants to endow epoxy with high thermal stability, mechanical performance and flame retardancy

Bio-derived modified halloysite nanotubes as eco-friendly flame retardants to endow epoxy with high thermal stability, mechanical performance and flame retardancy

Optimization of nanofiller compositions for enhancing thermo-mechanical properties of epoxy-based composites through the application of response surface methodology with central composite design

An epoxy based composite of modified halloysite nanotubes (A) and modified fly ash (B) with improved thermo mechanical and morphological properties has been successfully fabricated. The primary objective of this study is to analyze the factors (composition of A and B) that significantly affect the properties of nanocomposites and to find out the best optimize values of these factors using Response Surface Methodology (RSM) with Central Composite Design(CCD). The enhancement of 80 percent in the tensile strength, nearly 240 percent of flexural strength, and nearly 166 percent in impact strength has been achieved at the optimal composition of A and B. The scanning electron microscopy (SEM) analysis in the present study highlight the importance of achieving proper dispersion and interaction with the polymer matrix in order to address issues like HNT aggregation. The efficient dispersion of A (3 wt%) and B (6 wt%) in the polymer is confirmed by SEM studies. In addition the TGA graph shows good thermal stability at 340 °C.

Designing a smart polyurethane anti-corrosion coating loaded with APTES/IMZ modified halloysite nanotubes

Protective coatings are efficient for preventing corrosion, but they may not be sufficient for applications in aggressive and extreme environments, such as in coastal areas that could be subjected to corrosion. Inhibitors can suppress the corrosion rate significantly, but direct addition to the coating is ineffective because the inhibitor is easily soluble in water and can reduce the effectiveness of the barrier properties of the coating. Encapsulating the inhibitor into a nanocontainer is a promising alternative that may lead to a self-healing coating technology. Halloysite nanotubes (HNT) have been successfully reported for their application in smart coatings, and they exhibit superior aerodynamic and hydrodynamic properties and better process ability than spherical capsules for the same amount of load. Therefore, nanotubes are appropriate candidates to be used as nanocontainers for inhibitors over smart coating applications. This research discusses the design of a polyurethane coating loaded with modified halloysite nanotubes for corrosion protection of steel. Halloysite nanotubes were first functionalized using aminopropyltriethoxysilane (APTES) to improve their dispersion in the polyurethane matrix. The modified halloysite nanotubes were then loaded with the corrosion inhibitor 2-mercaptobenzimidazole (IMZ). The loaded nanotubes were incorporated into polyurethane coatings. Various characterization techniques were used to confirm the successful modification and loading of the halloysite nanotubes. The distribution of particles in the matrix was investigated by Transmission Electron Microscopy (TEM) test. The modified nanotubes showed better dispersion in the polyurethane coating, which improved the coating's barrier properties and corrosion resistance. Electrochemical Impedance Spectroscopy (EIS) and salt spray tests showed that the polyurethane coating containing the loaded and modified halloysite nanotubes exhibited the highest resistance to corrosion. The adhesion strength of the coating was also improved after immersion in a saline solution, particularly for the coating with modified and loaded halloysite nanotubes. In summary, the functionalization and loading of halloysite nanotubes improved their dispersion in the polyurethane coating, which in turn enhanced the coating's barrier properties, corrosion resistance, and adhesion strength, making it a promising approach for designing smart corrosion protective coatings.

Polymer-incorporated modified halloysite nanotubes for efficient CO2/N2 separation

Mixed-matrix membranes (MMMs) as one of solid sorbents for carbon dioxide (CO2) separation face the challenge of merging efficient separation with economical preparation process using scalable raw material. Halloysite nanotubes (Hal) with unique one-dimensional gas transmission channels have great prospect in MMMs for gas separation. However, the insufficient porosity of Hal has restricted further development of CO2 separation performances. Herein, a facile and efficient modification approach was carried out, involving successive treatments of calcination and selective leaching. The resulting nanotubes with continuous channel systems (CA-Hal) are embedded in poly(ether-block-amide) for the preparation of mixed-matrix membranes with enhanced gas transport. The performances of MMMs with modified nanotubes as inorganic fillers obtained by different modification methods (calcination, selective leaching, and a combination of calcination and selective leaching) were specifically discussed. CA-Hal with the highest specific surface area and certain surface energy has an excellent potential as inorganic fillers, which can be uniformly dispersed in the polymer matrix to form interfacial channels, preventing the particle agglomeration and producing non-selective interfacial defects. The hierarchical porous structure of CA-Hal can serve as fast gas transport channels in MMMs for efficient CO2 diffusion and enhanced separation. The MMMs containing 5 wt% CA-Hal have demonstrated excellent CO2 permeability (179.5 Barrer), CO2 diffusivity (17.56 10−7 cm2·S−1) and CO2/N2 selectivity (98.7). In addition, the prepared MMMs exhibits improved mechanical properties compared with the pure membrane without inorganic fillers.

Fabricating of Pd and Ni bimetal modified halloysite nanotube composite and its application for photocatalytic degradation of tetracycline

Tetracycline (TC) is extensively employed as a broad-spectrum antibacterial agent, and its byproducts have been identified in a variety of water bodies, posing a significant risk to both aquatic ecosystems and human health. Among the prevalent techniques for treating water contaminants, photodegradation stands out. In this research, we synthesized a novel nanocomposite material, embedding bimetallic nanoparticles onto halloysite nanotubes (HNT) (Pd@Ni/N-HNT), aimed at photocatalytically degrading TC. The Pd@Ni/N-HNT demonstrated the capability to enhance the TC degradation efficiency to 100 % under visible light for a duration of 120 min, effectively doubling the performance of pure H2O2 degradation. The influence of pH levels in aquatic environments on the TC degradation efficiency was explored. Through electron spin resonance (EPR) studies and free radical scavenging tests, it was verified that •O2− and h+ are pivotal in the degradation process. Furthermore, Pd@Ni/N-HNT showcased effective degradation capabilities in both tap and river water, achieving degradation rates exceeding 70 % in 120 min and 95 % in 180 min, respectively. This investigation not only sheds light on the potential of utilizing Pd@Ni/N-HNT as a potent catalyst for the photocatalytic degradation of TC but also offers a comprehensive framework for the future development of nanomaterials aimed at the environmental remediation of organic pollutants. The findings herein provide a pivotal reference and guide for advancing the application of nanotechnology in the purification of water, thereby contributing to the safeguarding of aquatic ecosystems and public health.

Design synthesis of melamine amino tris-methylene phosphonate modified halloysite nanotubes for epoxy resin with simultaneously improved flame retardancy, dielectric properties and mechanical performance

The development of epoxy resin (EP) with simultaneous enhancements in flame retardancy, mechanical performance, and low dielectric properties represents a significant and complex challenge. In this study, halloysite nanotubes (HNTs) were modified with melamine amino tris-methylene phosphonate (MA) to produce MA-modified HNTs (HMA), which were then integrated into EP to form EP/HMA composites. The incorporation of 1 wt% HMA significantly enhanced the flame retardancy (limit oxygen index up to 29.7%, UL-94 V-0 rating), reduced peak heat release rate by 23.4%, decreased total heat release by 11.9%, reduced total smoke production by 18.4%, and improved mechanical properties (tensile strength by 17.0%, impact strength by 61.0%) compared to pure EP. Additionally, EP/HMA showed a low dielectric constant (3.16) and a dielectric loss (0.019) at 1 GHz. This research presents a versatile strategy for creating multifunctional EP composites with high potential for applications in microelectronics, electronic packaging, and other relevant fields.

Halloysite nanotubes-based hybrid silica monolithic spin tip for hydrophilic solid-phase extraction of sulbactam, cefoperazone, and cefuroxime in whole blood

In this study, we proposed a novel method utilizing polyethyleneimine (PEI)-modified halloysite nanotubes (HNTs)-based hybrid silica monolithic spin tip to analyze hydrophilic β-lactam antibiotics and β-lactamases inhibitors in whole blood samples for the first time. HNTs were incorporated directly into the hybrid silica monolith via a sol-gel method, which improved the hydrophilicity of the matrix. The as-prepared monolith was further modified with PEI by glutaraldehyde coupling reaction. It was found that the PEI-modified HNTs-based hybrid silica monolith enabled a large adsorption capacity of cefoperazone at 35.7 mg g−1. The monolithic spin tip-based purification method greatly reduced the matrix effect of whole blood samples and had a detection limit as low as 0.1 − 0.2 ng mL−1. In addition, the spiked recoveries of sulbactam, cefuroxime, and cefoperazone in blank whole blood were in the range of 89.3–105.4 % for intra-day and 90.6–103.5 % for inter-day, with low relative standard deviations of 1.3–7.2 % and 4.9–10.5 %, respectively. This study introduces a new strategy for preparing nanoparticles incorporated in a hybrid silica monolith with a high adsorption capacity. Moreover, it offers a valuable tool to monitor sulbactam, cefoperazone, and cefuroxime in whole blood from pregnant women with the final aim of guiding their administration.

Preparation of modified halloysite nanotubes@Ag3PO4/polyacrylonitrile electrospinning membranes for highly efficient air filtration and disinfection

Particulate matters (PMs) and airborne bacteria are among the most severe indoor air issues due to their substantial implications for human health. Therefore, it was imperative to conduct a comprehensive investigation on air filtration materials with superior filtration performance and antibacterial properties. Here, the m-Hal@Ag3PO4 composite particles were prepared by using modified halloysite nanotubes (m-Hal) as the support of Ag3PO4 nano-photocatalysts. These composite antibacterial particles were uniformly dispersed within a polyacrylonitrile (PAN) solution and were subsequently electrospun into m-Hal@Ag3PO4/PAN composite nanofiber membranes (CNMs) possessing excellent antibacterial properties. The incorporation of 30 wt% m-Hal@Ag3PO4 additionally enhanced the filtration efficiency of PM0.3 to 99.9%, at an airflow rate of 32 L/min, while concurrently reducing the pressure drop by 36.7%. The photocatalytic degradation efficiency of CNMs towards ciprofloxacin reached 99%. The antibacterial experiments demonstrated that CNMs exhibited potent antibacterial activity against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)under dark and light conditions. Under visible light irradiation, the average diameter of the inhibition zone for the composite membrane surpassed that observed under dark conditions, indicating a predominant enhancement in its antibacterial efficacy through photocatalysis. The enhanced photocatalytic performance and excellent stability can be attributed to the incorporation of Ag3PO4 with m-Hal, which enhanced the dispersibility and facilitated efficient carrier separation of Ag3PO4. The present type of CNMs exhibited the advantages of high efficiency and low resistance air filtration, photodegradation ability, and recyclability, thereby enhancing the efficacy and lifespan of PMs filtration, bacteria disinfection, and antibiotic degradation. This offered a novel concept and viable approach for indoor air and water purification based on electrospinning technology.

Bio-derived polyphosphazene modified halloysite nanotubes as eco-friendly flame retardants to significantly reduce smoke release and enhance the fire safety of epoxy resin

At present, designing efficient bio-based flame retardants for epoxy resin (EP) and exploring low-toxicity and sustainable flame retardant strategies is still a great challenge. In this work, a novel bio-based hybrid flame retardant was successfully prepared by constructing a resveratrol-based cyclic cross-linked polyphosphazene (PPZ) shell on the surface of halloysite nanotube (HNT). The enhancement effects of HNT@PPZ on the fire safety of EP composites were investigated by thermal degradation, simulated fire performance (cone calorimeter test), gas-phase product analysis, and condensed-phase char residue analysis. Compared to pure EP, he total heat release (THR), total smoke production (TSP) and the average yield of carbon monoxide (Av-COY) of EP/3HNT@PPZ were reduced by 47.8 %, 46.5 % and 48.8 % respectively. Furthermore, the EP composites containing HNT@PPZ had a stable flame retardancy even after 6 months of natural aging. It was found the barrier effect of HNT@PPZ in condensed phase was further strengthened by the formation of new product aluminum phosphate, which formed a multiple protective char layer. Additionally, PPZ shell improved compatibility and dispersion of HNT in EP matrix, the mechanical properties of the composite with HNT@PPZ were improved significantly. This work proposed a feasible solution for the preparation of highly efficient bio-based flame retardants with excellent heat reduction and smoke toxicity reduction ability, which could be expected to broaden the application of biomass resources in the development of highly efficient flame retardants.

Pectin wrapped halloysite nanotube reinforced Polycaprolactone films for potential wound healing application

The current research work focuses on preparing the polycaprolactone (PCL) based nanocomposite films embedded with surface modified Halloysite Nanotube (HNT). The avenue of the study is to unravel the applicability of polymer nanocomposites for wound healing. The flexible property of HNT was taken as the major force to accomplish the addition of biopolymer pectin onto its surface. Functionalization of HNT with pectin has certainly enhanced its binding nature with the polymer. The PCL nanocomposite films were characterized by several promising techniques such as FTIR, XRD, DSC-TGA, FESEM, TEM, AFM, and mechanical properties were too examined along. When compared to the plane PCL film, the nanocomposite films manifested favorable results in terms of mechanical and chemical properties. Additionally, biometric studies such as in-vitro swelling, enzymatic degradation, and hemolysis performed on the films gave extremely good results. The haemolytic percentage recorded for the films exhibited a steady decrease with increasing amount of nanofillers. The MTT assay showed cell proliferation and its increase as the embedded HNT is more in the matrix. Wound closure study performed on NIH3T3 cell line with 1, 3 and 5wt% of films has given a strong proof for the involvement of polymer and HNT in the healing procedure.

Modified halloysite nanotubes as GRAS nanocarrier for intelligent monitoring and food preservation

Conventional “all-in-one” methods for multi-component active packaging systems are not wholly adequate for fresh food. Given the need for multifunctional properties, introducing halloysite nanotubes (HNTs) could be a promising way to achieve controllable release of active ingredients while endowing with pH-sensitive performance. Here, we pioneered a GRAS composite with multifunctional properties, employing natural HNTs as a nanocarrier, citral (Cit) as an active antimicrobial agent, and myricetin (Myr) for monitoring freshness. The Cit-HNTs-Myr had excellent DPPH, ABTS and ·OH radical scavenging capacity, dual-model (contact and fumigant) antibacterial properties, and pH-sensitive performance. Subsequently, a smart tag prepared by dipping cellulose fibers into Cit-HNTs-Myr, which extended the shelf life of shrimp and blueberries, and provided freshness information for the shrimp. These results demonstrate the applicability of Cit-HNTs-Myr in the preservation of perishable goods and freshness monitoring.

Halloysite nanotubes (MHNTs) modified S-scheme g-C3N4/γ-Fe2O3 photocatalyst for enhancing charge separation and photocatalytic activity

Photocatalysis is a surface process and an increase in the adsorption of target molecules on the surface of a photocatalyst could be of prime necessity in the photodegradation efficiency enhancement of dyes. To attain such a purpose, this study equips g-C3N4 with pores-modified halloysite nanotubes (MHNTs), then gets it wrapped by γ-Fe2O3 nanoparticles with high specific surface area (SSA) and S-scheme mechanism through a one-pot synthesis and co-precipitation, respectively. Characterization of fabricated photocatalysts is conducted to detect physical, chemical, optical, magnetic, and electrical properties by XRD, FT-IR, XPS, FE-SEM, EDX+MAP, TEM, BET, DRS, PL, VSM, Photocurrent, and EIS analyses. This research introduces a novel, ternary nanocomposite (g-C3N4/MHNTs/γ-Fe2O3) with dual functionality towards adsorption of both anionic and cationic dyes. Modified halloysite nanotubes (MHNTs), due to predominant negative charges (Si-O) on their outer surface, perform a significant role in the separation of holes (h+) from the photocatalysts and higher adsorption in MB photodegradation. In contrast, the inner surface of MHNTs through positive charges of AL-OH is beneficial for the electron (e-) separation and MO treatment. MHNTs with mesopores structure (Mean pore diameter: 10.6 nm) and high specific surface area (76.25 m2/g) contribute to higher adsorption and rapid transfer of photoexcited charges to the surface of ternary photocatalyst (g-C3N4/MHNTs/γ-Fe2O3 – 59.06 m2/g). After adding γ-Fe2O3 to g-C3N4/MHNTs, band gap of g-C3N4/MHNTs/γ-Fe2O3 reduces to 2.70 eV from 2.85 eV of g-C3N4/MHNTs, indicating influential role of γ-Fe2O3 nanoparticles in shifting photocatalytic activity of the ternary photocatalyst towards larger wavelengths (≥ 900 nm), and real world’s application (under illumination of sunlight). Among fabricated photocatalysts, g-C3N4/MHNTs/γ-Fe2O3 excels at degrading both MB and MO with the efficiency of %99.99 in 60 min and %89.1 in 120 min, respectively. To recognize the photocatalytic mechanism of the ternary photocatalyst, a trapping experiment was utilized for detecting oxidizing radicals in the photocatalytic process and then a photocatalytic mechanism was proposed.

Superhydrophilic carbon@halloysite nanotube decorated sponge composites for high efficiency solar steam generation and cleanup of crude oil

Three dimensional composite evaporators have now widely been used for solar driven steam generation. However, some issues such as weak interfacial interaction, moderate water transport ability and salt precipitation should be addressed for high efficiency solar driven interface evaporation. Here, carbon modified halloysite nanotubes (CHTs) are firmly anchored onto the skeleton of Polyvinyl alcohol (PVA) sponges for preparation of compressible and superhydrophilic CHTs/PVA evaporators (CPEs). CHTs endow the evaporator with outstanding light absorption and photothermal conversion performance. In addition, the hierarchically porous and hollow structures inside CPEs ensure the evaporator powerful water transport capability and hence excellent salt rejection behavior. Benefiting from the strong interfacial interaction between CHTs and the PVA sponge, CPEs possess superior surface stability and durability. The synergy of the solar driven interface evaporation and natural evaporation from the side walls contributes to a high evaporation rate (up to 3.49 kg m−2 h−1). The evaporation rate is maintained when CPE is mechanically compressed. Also, the sponge composite can be used for cleanup of crude oil, based on the photothermally induced decrease of oil viscosity. This study can provide inspiration to develop solar evaporators for high performance desalination and water purification.

Preparation of HNTs‐e‐POSS hybrid nanoparticles and modification of gallic acid epoxy resin

AbstractGallic acid is a renewable plant phenolic resource, and the polyphenolic bio‐based epoxy resin prepared from it can be used as a substitute for bisphenol A epoxy resin in certain fields. However, bio‐based epoxy resins used in the field of high‐performance composite material matrices often require modification. In this paper, firstly, γ‐(2,3‐epoxypropoxy)propyl trimethoxysilane (KH560) was used as the raw material to prepare epoxy‐based cage silsesquioxanes (E‐POSS). Then, E‐POSS was grafted onto γ‐aminopropyltriethoxysilane (KH550) modified halloysite nanotubes (m‐HNTs) to prepare a novel hybrid nanoparticle HNTs‐e‐POSS. Experimental analysis shows that ring opening reactions of amino and epoxy groups can occur between m‐HNTs and E‐POSS, forming a hybrid nanoparticle system of POSS aggregates on the surface of HNTs. Bio‐based nanocomposites were prepared by adding different mass fractions of hybrid nanoparticles HNTs‐e‐POSS into polyphenol type gallic acid epoxy resin matrix (GAER) and using methyltetrahydrophthalic anhydride as curing agent. The properties and micromorphology of the composite were analyzed and characterized. The research showed that with the addition of HNTs‐e‐POSS nanoparticles, the strength and toughness of the composite resin system show a pattern of first increasing and then decreasing, while the storage modulus(E′), glass transition temperature (Tg), and thermal stability of the composite material increased. Mechanical performance analysis shows that the introduction of 0.5 wt% HNTs‐e‐POSS would increase the tensile strength of the composite by 25.46%, while adding 0.75 wt% HNTs‐e‐POSS can increase the impact strength by 15%. The E′(30°C) increased by 24.2% and Tg increased by 7.7°C when the HNTs‐e‐POSS addition was 0.25 wt%.Highlights Prepared hybrid nanoparticle HNTs‐e‐POSS by grafting POSS onto the HNTs surface. Application of HNTs‐e‐POSS in modification of bio‐based gallic acid epoxy resin. HNTs‐e‐POSS can co‐cured with epoxy matrix to increase the crosslinking degree. The strength, toughness, and modulus of gallic acid epoxy resin are improved. Tg and thermal stability of gallic acid epoxy resin are enhanced.

Halloysite nanotubes-loaded conductive polymer as substrate and label material for sensitive detection of amyloid-β protein by electrochemical immunosensor

Amyloid-beta protein (Aβ) is a unique biomarker for Alzheimer's disease (AD). The sandwich-type electrochemical immunosensor, one of the key tools for detecting biomarkers, relies on a high-performance signal amplification approach to enhance its sensitivity. Ni/PdH nanodendrites (Ni/PdH NDs) have increased catalytic activity due to their unique interaction with palladium hydride and their nickel-rich surface, tunable shape and high specific surface area. Modified halloysite nanotubes (mHNT)-loaded with polypyrrole (PPy@mHNT) possess excellent dispersion and a large surface area. This enables the formation of a conductive network to prevent the accumulation of Ni/PdH NDs. Additionally, it exposes more electrocatalytic active centers, effectively amplifying electrical signals. By utilizing Ni/PdH@PPy@mHNT as the labeling material, it shows a consistent and remarkable electrocatalytic activity in H2O2 reduction, leading to signal amplification. The acid-etched HNT coated with polyaniline (PANI@eHNT) exhibits an exceptionally low background signal and outstanding conductivity. This not only accelerates electron transfer on the electrode surface, but also ensures the stable incubation of biomolecules post-amino grafting. Utilizing NH2-PANI@eHNT as a substrate material can guarantee stable biomolecule incubation, offer a stable sensing platform and enhance immunosensor performance. The signal can be amplified and the immunosensor's sensitivity can be raised through the efficient cooperation of the aforementioned nanomaterials. Under optimum circumstances, the electrochemical immunosensor had the lowest detection limit of 5.53 fg mL−1 and a linear range of 50 fg mL−1 to 100 ng mL−1. Based on the outstanding performance previously mentioned, this immunosensor is anticipated to aid in the early detection of AD.

Effect of complex of resorcinol and hexamethylenetetramine modified halloysite nanotubes (RH-HNTs) on the mechanical and swelling characteristics of NR/EPDM nanocomposites

Effect of complex of resorcinol and hexamethylenetetramine modified halloysite nanotubes (RH-HNTs) on the mechanical and swelling characteristics of NR/EPDM nanocomposites

Development of chitosan-based antibacterial and antioxidant bioactive film incorporated with carvacrol-loaded modified halloysite nanotube

The chitosan (CS)-based bioactive packaging film with good antibacterial and antioxidant activities was developed using AHNT (modified halloysite nanotube) loaded with carvacrol (AHNT-Car) as the nanofiller. The zeta potential, Fourier transform infrared, and rheology analysis indicated that hydrogen bonding and electrostatic interactions were formed between AHNT-Car and CS film substrate, and scanning electron microscope images exhibited that the cross-sections of the bioactive film were denser. The mechanical and barrier properties (water vapor, oxygen, and light barrier properties) of the bioactive film were enhanced by adding AHNT-Car due to the hydrogen bonding, electrostatic interactions, and compact structure. Specifically, when the additional amount of AHNT-Car was 10 wt%, the film's tensile, oxygen barrier, and water vapor barrier properties were improved by 49.7%, 36.78%, and 11.92%, respectively. Moreover, compared to CS-Car film (adding Car into the CS film directly), the CS-10% film (AHNT-Car added at 10 wt%) had a slow-release effect on Car and could effectively protect the Car from external high temperature and UV light. In addition, the prepared bioactive film had sustained antioxidant and antibacterial properties and could significantly slow down the spoilage of pork during storage, proving the promising application of the bioactive film as food packaging.

Enhancement of active anti-corrosion properties of waterborne epoxy resin by mussel bionic modified halloysite nanotube

Halloysite nanotube (HNT) is often used as a microcapsule loaded with corrosion inhibitors due to its cavity structure. However, the strong van der Waals forces between halloysite nanotubes can cause aggregation in organic coatings. Therefore, in this study, a new type of modified halloysite nano-filler (PDA@T-AHNT) was synthesized by a step-by-step method using the characteristics of self-polymerization of dopamine under an alkaline environment to achieve surface coating of halloysite nanotubes by polydopamine (PDA) to improve the dispersion of halloysite nanotubes in waterborne epoxy resin. UV-Vis was used to characterize the pH-responsive release properties of the modified nanofillers. Composite coatings were formed by adding PDA@T-AHNT into the water-based epoxy resin. FE-SEM was used to observe the morphology of the coatings, and EIS was used to test the electrochemical behavior of the coatings soaked in 3.5 wt% NaCl for 60 days to characterize the corrosion resistance of the coatings. The final results show that the 3 wt% PDA@T-AHNT composite coating (EPP-3) has the best corrosion resistance with a low-frequency impedance of 2.81 * 106 Ohm.cm2 after 60 days of immersion, which is much higher than the 1.45 * 106 Ohm.cm2of the pure epoxy resin coating (WEP). In conclusion, the results of this study demonstrated the application potential of PDA@T-AHNT nano-filler in corrosion protection of steel, especially in metal corrosion protection under acidic environment.

Polyvinyl alcohol flame retardant film based on halloysite nanotubes, chitosan and phytic acid with strong mechanical and anti-ultraviolet properties

The research of additive biomass flame retardants is becoming more and more popular. In this work, amino modified halloysite nanotubes (A-HNTs), chitosan (CS) and phytic acid (PA) were introduced into polyvinyl alcohol (PVA) matrix to construct PA/A-HNT/CS/PVA organic-inorganic composite film with hydrogen bond and covalent bond cross-linking network structure. Adding PA/A-HNT/CS can remarkably improve the mechanical strength, UV resistance and thermal stability of PVA film. Compared with control PVA film, the transmittance of composite film in ultraviolet region decreases from 90 % to <15 %, and the tensile strength raises from 19.8 MPa to 31.0 MPa. The thermal decomposition temperature of the composite film increases, the weight loss rate decreases obviously, and the carbon residue can reach 26 wt% at 700 °C. The limiting oxygen index increases from 18.5 % to 32.2 %. Furthermore, the addition of this flame-retardant system can obviously reduce the combustion intensity of PVA, and its flame-retardant grade can reach V-0. It is of great significance to expand the application of PVA and the development of biomass flame retardant.

An enhanced MEMS-based polyimide capacitive-type relative-humidity sensor with halloysite nanotube as a modifier

Polymers have been widely used in the fabrication of humidity sensing materials, although, issues including sensitivity and hysteresis still exist, limiting its potential. Herein, we aim to enhance the humidity sensing performances of a polyimide (PI) capacitive-type relative-humidity sensor via a simple and efficient approach. Specifically, modified halloysite nanotubes (HNTs) were doped in the polyimide sensing layer to optimize the humidity sensing capabilities of the MEMS (Micro-electromechanical Systems)-based sensor. The configurational and morphological characteristic of the sensing membrane with different content of the nanofiller were characterized. The humidity sensing capabilities of the enhanced sensors were investigated under the relative humidity (RH) range of 10–90%. Owing to the rational structure design of the sensing layer, the modified sensor exhibited enhanced sensitivity, low humidity hysteresis and good linearity. The highest sensitivity of the device with the best overall performance reached 0.87 pF/%RH, which is 1.81 times that of the pure PI based humidity sensor. Meanwhile, the sensor maintained moderate humidity hysteresis (2.18%) as well as good linearity (R2 = 0.9813) within the humidity boundary from 10 to 90% RH. The aforementioned advantages of the PI-HNTs-NH2 based humidity sensor demonstrate its promising application in humidity measurement. As a low-cost and effective additive, HNTs own great application potential in the preparation of polymer sensing devices. This work provides valuable guidance for fabricating humidity sensors with outstanding sensing performances.