Natural Halloysite Nanotubes Research Articles

An efficient Ni-Mg/HNTs catalyst for CO2 methanation prepared by sol-gel method assisted with citric acid

Developing a stable and effective Ni-based catalyst for low-temperature CO2 methanation remains a significant challenge. This study presents the synthesis of a range of MgO-promoted Ni-based catalysts supported on natural halloysite nanotubes (HNTs) through a sol-gel method assisted by citric acid. At 275°C, Ni-Mg/HNTs-1.0 CA exhibits the highest CO2 conversion (88.5%) and CH4 selectivity (98.4%). The sufficient basic sites and Ni0 sites of Ni-Mg/HNTs-1.0CA are beneficial for CO2 activation and H2 dissociation, leading to high activity at low temperatures. Additionally, Ni-Mg/HNTs-1.0 CA exhibits better anti-sintering ability during 100 h reaction, attributed to the increased interaction between metal and support. The in-situ DRIFTS results show that Ni-Mg/HNTs-1.0 CA mainly follows both formate and CO pathways, and the rapid transformation of intermediates causes superior catalytic performance. This work offers a rational design of stable and active catalysts for low-temperature CO2 methanation.

Study on the effect of halloysite nanotubes on the mechanical properties and swelling resistance of ethylene-propylene diene monomer (EPDM)/nitrile butadiene rubber (NBR) blend nanocomposites

Abstract Research was undertaken to explore the alteration of natural halloysite nanotubes (HNTs) using a blend of resorcinol and hexamethylenetetramine (RH), (γ-aminopropyl) triethoxysilane (APTES), and diethoxydimethyl silane (DMS). This investigation delved into the impact of incorporating various proportions of RH-modified HNTs (RH-HNTs), APTES-modified HNTs (APTES-HNTs), DMS-modified HNTs (DMS-HNTs), and unmodified HNTs into ethylene propylene diene monomer (EPDM) and nitrile butadiene rubber (NBR) for their potential as seal materials. The study assessed key properties such as tensile strength, stress at 100% elongation, elongation at break, compression set, hardness, and swelling and abrasion resistance to gauge the influence of HNT additions. As nanofiller content increased, the crosslinking rate rose, while scorch time and optimum cure time decreased. Findings indicated that incorporating nanofillers at 6 phr compositions notably enhanced composite strength initially, with a subsequent slight reduction. However, rebound resilience diminished with increasing filler content, though composite hardness experienced a slight improvement. Mole percent uptake decreased, particularly at higher filler loadings. Notably, systems containing 6 phr RH-HNTs exhibited a 140% increase in tensile strength. FESEM micrographs depicted a rough fracture surface with well-dispersed nanofillers within EPDM/NBR. Additionally, compression set data illustrated enhanced composite performance under compression, crucial for seal applications.

Novel eco-friendly bio-nano flame retardant via the electrostatic-driven hybridization of natural halloysite nanotubes and phytic acid for superior fire safety of epoxy composites

Driven by increasingly stringent safety regulations and enhanced fire hazards awareness, rationally designing a highly flame-retardant and eco-friendly polymer composites has become critically significant, but remains challenging. Herein, to endow epoxy resin (EP) composites with exceptional fire safety while maintaining its desirable performances, a novel bio-nano flame retardant GPP@HNTs was successfully prepared via the electrostatic-driven hybridization of two natural-available green materials, halloysite nanotubes (HNTs) and phytic acid (PA). It was found that the GPP@HNTs can uniformly disperse in EP matrix due to its strong interfacial interaction with EP. In compassion with EP, the flame retardancy of GPP@HNTs/EP composites was effectively enhanced, reaching UL-94 V-0 rating and exhibiting a 42.55 % increase of LOI value, 32.76 % decrease in peak heat release rate (PHRR), 25.92 % reduction in total heat release (THR). Furthermore, the GPP@HNTs/EP composites also present excellent thermal stability and mechanical properties. Such a facile yet efficient hybridization design of bio-nano flame retardant paves the way for wide practical applications of the flame-retardant and mechanically robust EP composites in various industrial fields.

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.

Enhanced hydrophilicity and stability of carbon-based aerogel with assembling of halloysite nanotubes and silica fibers for efficient solar seawater evaporation and desalination

Solar vapor generation has emerged as a sustainable technique for seawater evaporation and desalination. Integrating high hydrophilicity, strong light absorbance, good salt resistance, fast water transfer and good structural stability simultaneously in one evaporator at low cost for achieving cost-effective evaporation and long-term utilization is highly desirable but still challenging. Herein, an eco-friendly and low-cost aerogel (CSH) with natural chitosan, halloysite nanotubes and silica fibers was prepared by freeze-casting, which was then carbonized to construct a robust aerogel (cCSH) as evaporator. The cellular structure of cCSH aerogel with microchannels enables fast water transfer and rapid salt dissolution, the carbonized chitosan favors enhanced light absorption, the halloysite assembled on the walls endows the aerogel with excellent hydrophilicity, and the silica fibers penetrating the multilayer guarantee good structural stability. As expected, the prepared evaporator (cCSH200) exhibits remarkable evaporation rates of 2.49/7.20 kg·m−2·h−1 under one/four sun, respectively, exceeding most biomacromolecule-derived aerogels. Besides, it displays outstanding salt resistance, wastewater purification ability and long-term cycle stability. Outdoor test further substantiates the admirable evaporation performance, long-term durability and enormous application prospect of the cCSH200. This work affords a low-cost tactic for the development of efficient evaporator for solar-driven seawater desalination and wastewater treatment.

Electrospun polylactic acid nanofibers membrane with copper ion-loaded clay nanotubes for fresh-keeping packaging

The plastics derived from fossil fuels for food packaging results in serious environmental problems. Developing environment-friendly materials for food packaging is urgent and essential. In this study, polylactic acid (PLA) composite nanofibers membranes were prepared with good biocompatibility and antibacterial property. Cu2+ loaded in the natural halloysite nanotubes (HNTs) was used for the antibacterial agent. Cu2+ was loaded in the HNTs and was confirmed by the X-ray photoelectron spectroscopy (XPS). PLA nanofibers with different HNTs-Cu content were continuous nanofibers with the nanoscale range. HNTs-Cu entered into the nanofiber successfully. Thermal analysis results showed composite nanofibers had good thermal stability. Composite nanofiber membranes had the good hydrophobic property. HNTs-Cu improved the mechanical property of composite nanofibers than pure PLA nanofibers. Tensile strength and elasticity modulus of composite nanofibers with 4 % HNTs-Cu content were the most outstanding. L929 cells were cultured on the nanofiber membranes for biocompatibility evaluation. Cell viability of nanofiber membranes was above the 90 %. Cell live/dead staining results showed L929 cells was seldom dead on the nanofiber membranes. PLA/HNTs-Cu nanofiber membranes exhibited excellent antibacterial effects on S. aureus and E. coli. The inhibitory rates against S. aureus and E. coli were 98.31 % and 97.80 % respectively. The fresh-keeping effects of nanofiber membranes were evaluated by the strawberry preservation. Strawberries covered by nanofiber membranes exhibited better appearance, lower weight loss and higher firmness than control, PLA and PLA/HNTs groups. It promised that PLA/HNTs-Cu composite nanofiber membranes have the significant potential application for active food packaging.

Germ must be found: The HNT@RhB@MOF-Tb polychromatic fluorescent nanoprobe is applied for the visual detection of 2,6-dipicolinic acid

A polychromatic fluorescent nanoprobe based on natural halloysite nanotubes with fluorescent dyes and porous metal–organic frameworks co-loaded on the surface and inner wall of the nanotubes was constructed for the highly sensitive visual identification of the Bacillus anthracis biomarker 2,6-dichlorophenolic acid (DPA). The limit of detection for DPA was 11.27 nM, which is significantly lower than the spore-borne dose for anthrax infection (60 uM). The multi-color fluorescent probe showed potential for rapid, accurate, and highly selective detection of Bacillus anthracis markers in actual samples. Besides, a portable fluorescence detection platform was developed in combination with a smartphone color scanning APP to simplify the detection process and realize real-time semi-quantitative analysis.

CoMo Sulfide Catalysts Supported on Natural Halloysite Nanotubes: Dealumination as an Effective Approach to Improve Catalytic Performance

CoMo Sulfide Catalysts Supported on Natural Halloysite Nanotubes: Dealumination as an Effective Approach to Improve Catalytic Performance

Robust and wear-durable coating based on halloysite nanotubes/polymer composite for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is an efficient strategy to achieve cooling through spectrally selective emission and high solar spectrum reflection. Current preparation strategies for PDRC materials mainly involve doping inorganic micro-nanoparticles into polymers, but their solar reflectance is usually insufficient. Here, we designed a super-white inorganic coating on different substrates based on natural halloysite nanotubes (HNTs) through the doctor blade method. Polyvinyl alcohol (PVA) and water-based acrylic resin (AR) were introduced to increase the adhesion for obtaining robust inorganic coating. HNTs/PVA/AR composite coating shows excellent water resistance, wear resistance, and environmental tolerance, which is mainly due to the strong interfacial interactions between HNTs, PVA, and AR. Compared with the uncoated transparent plastic, the coated plastic exhibits a super-white appearance (whiteness of ∼95%) and maximum solar reflectance of ∼97%. The maximum temperature difference of the HNTs/PVA/AR coated and pristine copper sheet is 15 °C under simulated sunlight. The PDRC property is related to the high surface roughness of the coating composed of disordered high-aspect ratio nanotubes and the high whiteness of the raw halloysite materials. The composite coating can tolerate pH from 1–13, temperature change (−60∼250 °C), and different salt environments. The composite coating increases thermal stability, flame retardancy, and giving protective effect of dye against UV degradation. In addition, the HNTs/PVA/AR coated plastic as packaging materials can maintain good freshness of different fruits under strong solar irradiation. The robust HNTs/PVA/AR composite coating with high PDRC properties shows promising application in food packaging, building energy conservation, metal anticorrosive coating, and sunscreen products.

Regulating the microenvironment of atomically dispersed cobalt to achieve the record-breaking mineralization and 100% removal of organic pollutant

Advanced-oxidation-process (AOPs) based on peroxymonosulfate (PMS) can provide strong reactive oxygen species (ROS) for the elimination of persistent-organic-pollutants (POPs), but the input of highly active environmentally friendly catalysts is the key. Here, confined cobalt was in-situ deposited on natural mineral halloysite nanotubes by Coulomb interaction, which further realizes the introduction of atomically-dispersed cobalt sites in nitrogen-doped hollow-carbon-nanotubes with large specific surface area. The constructed CoNC/NHCNTs-900 material can effectively activate PMS, resulting in the removal rate of tetracycline probe pollutants close to 100%, and the mineralization rate reached a record of 89.07%. Combined with density functional theory calculations, it was proved that the enrichment of graphite nitrogen is beneficial to regulate the microenvironment of Co and promote the adsorption and activation of PMS. In-depth tracking of the formation of ROS and the mechanism of tetracycline mineralization proved that CoNC/NHCNTs-900-driven AOPs degradation of POPs into a low-toxic species has reliability and practical significance.

A spectroscopic study on the effect of acid concentration on the physicochemical properties of calcined halloysite nanotubes

AbstractHalloysite nanotubes a naturally occurring type of clay with unique properties. This research intends to investigate of the effects of hydrochloric acid treatment on the physicochemical and pore properties of halloysite nanotubes. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, the nitrogen adsorption-desorption isotherm (BET), thermogravimetric analyses (TGA-DTA) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure of natural, calcined, and acid-treated calcined halloysite nanotubes. From the analysis of XRD, SEM, FT-IR, BET, and TGA-DTA, it was possible to infer that activation with HCl on the calcined nanotubes allowed for an increase in the specific surface area and the volume of pores while maintaining the tubular structure of these materials. Because the samples’ tubular structure was preserved, the study’s goal was to evaluate the effects of acid treatment on calcined halloysite nanotubes for use as potential adsorbents. The influence of treatment with hydrochloric acid on the structure of halloysite nanotubes calcinated at different temperatures was investigated using a surface sensitive XPS method.

Natural halloysite nanotubes decorated with organophosphorous for highly flame‐resistant epoxy composites

AbstractHighly flame‐resistant epoxy composites have important application value in many industrial fields. Unfortunately, epoxy resins (EPs) are inherently flammable materials and exhibit great fire hazard. In this study, the commercially available 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was chemically immobilized on the surface of natural halloysite nanotubes (HNTs) via the linkage of vinyltrimethoxysilane to obtain a novel flame‐retardant VD@HNTs containing P/Si/Al elements. It was found that the flame‐retardant VD@HNTs can effectively improve the thermal stability and flame resistance of epoxy composites. Typically, when 10% of VD@HNTs is added in EP, the limiting oxygen index of as‐prepared VD@HNTs/EP composites reaches 30.3%, and it also successfully reaches V‐0 classification in the UL‐94 test. Besides, the ignition time of VD@HNTs/EP composites was enhanced from 42 s for pure EP to 60 s, and the maximum heat release rate was reduced from 1221 to 758 kW∙m−2. These great findings promise an innovative and efficient strategy for improving the fire safety of EP products and may also offer valuable insight toward fabricating various novel organic–inorganic flame retardants as well as highly flame‐resistant polymer composites.Highlights A novel flame‐retardant VD@HNTs containing P/Si/Al elements was prepared by the chemical decoration of HNTs with organophosphorous. The VD@HNT can effectively improve the thermal stability and flame resistance of epoxy composites. Synergistic flame‐retardant mechanism of phosphorus‐based flame retardants and natural HNTs was classified.

Nitric Acid-Pretreated Natural Halloysite Nanotubes as Ni Nanoparticle Catalyst Supports for CO2 Methanation

Nitric Acid-Pretreated Natural Halloysite Nanotubes as Ni Nanoparticle Catalyst Supports for CO₂ Methanation

Composite materials based on halloysite clay nanotubes and cellulose from Posidonia oceanica sea balls: from films to geopolymers

The combination of natural halloysite nanotubes and cellulose recovered from egagropili is effective to fabricate composite films and geopolymers promising for packaging and building applications, respectively.

CoPMoV Sulfide Catalysts Supported on Natural Halloysite Nanotubes in Hydrotreating of Dibenzothiophene and Naphthalene

Mixed sulfided CoMo catalysts supported on γ-Al2O3 and halloysite nanotubes (HNTs) were synthesized by incipient wetness impregnation with salt solutions of Keggin-type phosphorus- and vanadium-containing heteropolyacids. The synthesized materials were characterized by low-temperature nitrogen adsorption, energy dispersive X-ray fluorescence analysis, temperature-programmed reduction (both for the oxide and sulfide catalysts), and Raman spectroscopy, and were tested in hydrogenation of naphthalene and hydrodesulfurization of dibenzothiophene. The HNT-supported catalyst exhibited a greater activity in these reactions.

Dual modification of natural rubber/halloysite nanotubes composites by silane and maleated natural rubber

As the performance of natural rubber (NR) and halloysite nanotube (HNT) composites is uncertain due to low compatibility between the materials, malleated natural rubber (MNR) is then used as a compatibilizer to encourage filler–rubber compatibility. However, the properties of these composites remain unsatisfactory, and the treatment of HNT requires further improvement. Therefore, this study introduced acid treatment and silane coupling agents to increase the interactions between NR and HNT. Besides, this study also introduced the methods of compounding the rubber composites, either with single-stage or two-stage treatments. The application of a two-stage treatment to acid-treated HNT has given tensile strength a 26.5% improvement. Two-stage treatment enabled better silanization, while acid-treated HNT provided effective silanols for such interactions. The use of silane with acid-treated HNT was found to enhance the tensile strength, modulus, and tear strength of the composites, which was clearly due to better filler–rubber interactions. The Payne effect, which decreased up to 64.03% after applying a two-stage treatment, served as further confirmation of better filler–rrubber interactions. This conclusively proved that modifying both the rubber matrix and HNT enhances the performance of NR/HNT composites.

Experimental and compactional studies of interface toughening on GFRP by hierarchical distribution of halloysite nanotubes

The incorporation of nano-inclusions into the fiber-matrix interfacial regions to create hierarchical structured fiber reinforced polymers (FRPs) is a novel approach aimed at enhancing mechanical properties. However, the specific toughening mechanism facilitated by the hierarchical structure has not been extensively explored or discussed in detail. This study investigates the mechanical properties of glass fiber reinforced polymers (GFRPs) that have been hierarchically incorporated with natural halloysite nanotubes (HNTs) using experimental, computational, and numerical approaches. The hierarchical distribution of HNTs is achieved through electrophoretic deposition (EPD). The stiffening effect of HNTs incorporation is computed using the random-averaged micromechanical Mori-Tanaka model. Subsequently, stiffness and stress concentration analyses are carried out on mesoscale representative volume elements (RVEs) of GFRPs with periodic boundary condition (PBC) assignments in ABAQUS. Overall, the experimental results are consistent with the numerical and computational results in terms of trend and magnitude. The amorphous HNTs (AHNTs) with larger cross-sectional aspect ratios demonstrate significant enhancement of 45 % in transverse modulus. The in-plane stiffness and strength of GFRPs with hierarchical distribution are slightly inferior to those of GFRPs with random distribution. Nevertheless, the hierarchical distribution of nano-inclusions leads to a substantial improvement in interlaminar strength and toughness, with enhancements exceeding 70 % and 100 % respectively. This can be attributed to the reinforcement and toughening effects on the fiber-matrix interface brought about by the hierarchical distribution.

Synthesis and application of Pt-containing catalysts based on mordenite zeolite and natural halloysite nanotubes in the gas-phase isomerization of C-8 aromatic fraction

The MOR-type zeolite was synthesized by a template-free method using natural aluminosilicate halloysite nanotubes (HNT) as a hard template and a source of aluminum and silicon. Samples were studied using a complex of physicochemical methods of analysis: XRD, TEM, N2 physisorption, NH3-TPD and XRF. Specific BET surface area of MOR prepared using HNT is 306 m2/g, mesopores in the MOR:HNT accounted for 30 % of the total pore volume. Based on the synthesized materials (MOR, MOR:HNT and MOR + HNT), Pt-containing catalysts were prepared. The catalysts were investigated in the gas-phase isomerization of C-8 aromatic fraction in a temperature range of 360–420 °C, varying LHSV from 2 to 6 h−1, at H2 pressure of 1 MPa and hydrogen/feedstock volume ratio of 900 nl/l. The prepared catalysts demonstrated strong activity in ethylbenzene transformation (more than 95 %), while providing a high yield of p-xylene (more than 95 % of thermodynamic value).

High performance iridium loaded on natural halloysite nanotubes for CO-SCR reaction

Iridium nanocatalysts are ideal candidates for the selective catalytic reduction of NOx by CO (CO-SCR) in excess oxygen. Here, a high-performance Ir nanocatalyst supported on natural halloysite nanotubes (HNTs) was applied for the CO-SCR. The HNTs loaded with only 0.5 wt% Ir achieved 78 % NOx conversion at 250 °C in the presence of 5 % O2, which was the highest among catalysts with varied Ir loadings or reduction temperatures. It also possessed an excellent SO2 and H2O tolerance during longevity tests. An interesting SO2-enhanced CO-SCR long-term stability was observed, which was ascribed to the inhibitory effects of SO2 on the side reaction between CO and O2. The loading amount and the reduction temperature could modulate the size of Ir nanoparticles and the percent of Ir0, which were two key factors determining the CO-SCR activity. DRIFTS characterizations and DFT calculations coherently revealed the favorable adsorption sites of CO (top) and NO (hcp) on Ir nanoparticles. The Ir atoms served as a charge transfer bridge from the C atom of CO to the N atom of NO, leading to the enhanced breakage of N-O bonds. This work provides Ir/HNT as a promising CO-SCR material with high performance and robustness to tackle NOx pollution.

Tubular nanoclay as effective ionic channels for hybrid conductive sodium metal anodes

Sodium metal battery is expected to be employed for extensive energy storage owing to its high energy density and affordability. Nevertheless, a significant volume change may cause uneven stress distribution in Na anodes, leading to electrode pulverization and severe side effects. Herein, natural clay halloysite nanotubes with ionic conductivity were introduced to prepare hybrid sodium metal anodes (noted as Na@HNTs) by the melt infusion method and subsequent calendaring process. In Na@HNTs anode, a fast and continuous channel for electron and Na+ transport was created due to the presence of HNTs's ionic conductive phases at grain boundaries. Moreover, as-prepared Na@HNTs not only permits constant anode-level volume, but also simultaneously improves electrode surface chemistry. Na3V2(PO4)3 cathodes demonstrate excellent electrochemical performance in full cells with Na@HNTs anodes, displaying 80 mA h g−1 at 5C after 5000 cycles with 81.5% capacity retention. This work highlights the immense potential of utilizing natural clay as an effective ion diffusion channel for the development of hybrid sodium anodes.