Internally Modified Halloysite Nanotubes as Inorganic Nanocontainers for a Flame Retardant

Abstract

We have selectively hydrophobized halloysite nanotube lumens for efficient loading with a flame retardant for controlled releasing composite materials. The inner lumen of octadecylphosphonic-acid-modified halloysite was loaded with hydrophobic bisphenol-A bis(diphenyl phosphate). This flame retardant was released from the clay nanotubes in linear fashion over 60 h demonstrating the system potential utility as effective nanocontainers for smart composite systems.There has been considerable interest in materials based on aluminum silicate nanotubes because of their unique features and applications. 13 Halloysite nanotubes (HNTs) are naturally occurring aluminum silicate hollow cylinders with a length of 0.51¯m, the outer and inner diameters of ca. 3050 and 10 30 nm, respectively.3 High loading efficiency of the halloysite nanotubes is related to efficient adsorption of drugs into positively charged HNTs' inner lumen, 4,5 using a variety of solvents 6 and polarity differences of the adsorbent and adsorbate. 7 Halloysite can be selectively modified to achieve the hydrophobicity of its inner surface.3,7 Bisphenol-A bis(diphenyl phosphate) (BDP) is known to be one of the most effective nonhalogenated, environmentally benign flame retardants. 8,9 However, due to the weak interaction between rather hydrophobic BDP and hydrophilic inner surface of the pristine halloysite tubes, it is difficult to achieve its high loading efficiency. Recently, we reported a novel selective modification for the inner lumen of halloysite with octadecylphosphonic acid (ODP), based on strong specific interaction between the phosphonic acid group and aluminol groups of the clay inner lumen.3 Here we report the high loading and controlled release of bisphenol-A bis(diphenyl phosphate) into the ODP-modified halloysite tubes (Scheme 1).The selective ODP grafting on the surface of inner lumens of halloysite was carried out by pulling and breaking vacuum. The BDP was sorbed in the ODP-modified halloysite nanotubes (HNTs-ODP) by adding a saturated ethanol solution of BDP to a suspension of HNTs-ODP and stirring the mixture for one week. The suspension was centrifuged, and the precipitate was dried at 393 K under ambient pressure for 10 h resulting in the final formulation: HNTs-ODP-BDP. Figure 1 shows the nitrogen adsorptiondesorption isotherm of HNTs, HNTs-ODP, HNTs-BDP, and HNTs-ODP-BDP at 77 K. Corresponding surface area (S BET ), pore volume (V pore ), and pore size (d peak ) are listed in Table 1. The samples were dried at 373 K for 30 min and outgassed under vacuum at 373 K flame retardant(BDP)

Carbon hybridized halloysite nanotubes for high-performance hydrogen storage capacities

“…All the isotherms exhibit type II with distinct type H3 hysteresis loop in the relative pressure ( p/p 0 ) range of 0.7–1.0 together with a H2 hysteresis loop in the relative pressure range of 0.4–0.729. According to the standard setup by International Union of Pure and Applied Chemistry (IUPAC)30, hysteresis loop is the representative of capillary condensation occurred among the ordered porous channels or interspaces of particles.…”

“…For instance, HNTs have a hydrogen adsorption capacity of 0.35 wt%, measured at room temperature and 2.65 MPa. Halloysite nanotubes have natural aluminosilicate characteristic with large surface area, high porosity, tunable surface chemistry, and plenty of hydroxyl, which could be considered as one of the best candidates for hydrogen storage2931. The interlayer spacing is a little larger than the molecular kinetic diameter of hydrogen molecular31, so it allows the hydrogen molecules to enter into the interlayer which leads to a considerable hydrogen adsorption capacity.…”

“…5e. The interlayer spacing of HNTs is a little larger than the molecular kinetic diameter of hydrogen molecular2931, which can ensure the Pd particles between carbon layer and HNTs to contact with hydrogen gas. Moreover, the special nano-scale hollow cylinders of HNTs could provide excellent channels to avoid hydrogen blocking9.…”

Halloysite nanotubes as support for metal-based catalysts

“…39,56,57 The increasing interest in these nanomaterials could involve, in the long term, the release and accumulation of the nanoclay in the environment and could therefore cause damage to human health or plants; therefore, it is important to study the toxicity of halloysite nanotubes towards living organisms.…”

Halloysite Nanotubes: Green Nanomaterial for Functional Organic‐Inorganic Nanohybrids

“…As mentioned in the introduction, HNT has shown plenty of valuable usages, such as drug loading and releasing,,,,, nanofiller for polymer composites,,, and environment remediation,,, because of the versatile features of nanotubular structure, high porosity, active surface chemistry, and large surface area. However, surface modification of the nanotube is required to improve the performances and selectivity.…”