Hal Nanotubes Research Articles

Radical guided selective loading of silver nanoparticles at interior lumen and out surface of halloysite nanotubes

Silver nanoparticles (nps) selectively loaded in the lumen cavity and outer surface of halloysite (Hal) nanotubes were realized through the simple impregnation strategy. The Hal mineral was pre-treated through leaching by sulfuric acid followed by calcinations. The silver nps have been loaded on both sides of the Hal nanotubes when nitrate was used as the raw source, while the nps were found only in the lumen cavity when acetate was used. The formation of Ag nps on both sides of the Hal tubes has partially destroyed the wall structures. Those Ag nps at outer surface showed the relatively higher efficiency to the HCOH oxidation, 6.9% of the organic molecular have been oxidized at 125°C, while Ag nps loaded in the lumen cavity only showed 1.0% in the same conditions. The physico-chemical properties of the two sides of the tubes determined the affordability of acid treatment, which induced the surface defects in the cavity; while the electron affinity, ionization energy and steric configuration of the ionic radical of the raw sources have showed differed coordination manner with outer surface of the Hal tubes, induced the selective adhesion of metal cations, and resulted in the selective formation of Ag nps.

Photodegradation of aniline in water in the presence of chemically activated halloysite

Photocatalytic degradation of aniline was investigated in aqueous solutions containing halloysite (Hal) nanotubes, chemically activated halloysite (AHal), and photocatalysts: TiO2 (anatase) and commercial titania P25, under UV illumination. Powder X-ray diffraction (XRD), UV–Vis/DR spectra and nitrogen adsorption isotherms were carried out to characterize the activated halloysite. The effects of the AHal and titania photocatalyst amount as well as aniline concentration were examined. It is observed that the photodegradation of aniline has a similar course in the presence of AHal and in the presence of P25 and TiO2, both with respect to the decomposition of aniline and in decreasing the amounts of photoproducts being formed during the irradiation of aniline. The photodegradation of aniline is clearly slower in presence of Hal nanotubes than for AHal and P25. The disappearance of aniline follows approximately according to the Langmuir–Hinshelwood kinetics. The values of rate photodegradation constant are decreasing in the following order: P25>TiO2>AHal>Hal nanotubes. These results have indicated that halloysite containing titanium dioxide could be employed during photocatalytic removal of aniline from the aqueous solution, similarly to commercial titania photocatalysts.

Halloysite/alginate nanocomposite beads: Kinetics, equilibrium and mechanism for lead adsorption

This study highlights the potential of Hal/alginate nanocomposite beads for the removal of Pb2+ in aqueous solutions. This is based on comprehensive physicochemical–mechanical characterizations involving adsorption equilibrium, adsorption kinetics, diffusion studies, FTIR, EDX, FESEM, zeta potential, and compression tests. Results show Langmuirian adsorption isotherms and reasonably rapid second order adsorption kinetics. The Hal/alginate nanocomposite beads have high adsorption capacity for Pb2+ (i.e. 325mg/g) compared to that of free Hal nanotubes (i.e. 84mg/g). The overall process was diffusion limited, well described by the shrinking core model. The Hal/alginate beads removed Pb2+ through ion exchange with Ca2+ followed by coordination with carboxylate groups of alginate, in addition to physisorption on Hal nanotubes. Vital for industrial applications, the Young's modulus of the nanocomposite beads was strengthened by Hal nanotubes loading as well as Pb2+ uptake. As such, this adsorbent incorporates distinctive merits of both Hal nanotubes and alginate, which include the high affinity towards Pb2+, strong mechanical properties, and easy separation from the treated solution.

Strengthening and stiffening carbon fiber epoxy composites by halloysite nanotubes, carbon nanotubes and silicon carbide whiskers

Low-cost natural halloysite (Hal) nanotubes (0.1μm diameter) were effective for strengthening and stiffening continuous fiber epoxy composites, as shown for cross-ply carbon fiber (5μm diameter, ~59vol.%) epoxy nanocomposites under flexure, giving 17% increase in strength, 11% increase in modulus and 21% decrease in ductility. They were less effective than expensive multiwalled carbon nanotubes (0.02μm diameter), which gave 25% increase in strength, 11% increase in modulus and 14% decrease in ductility. However, they were more effective than expensive silicon carbide whiskers (1μm diameter), which gave 15% increase in strength, 9% increase in modulus and 20% decrease in ductility. Each filler, at ~2vol.%, was incorporated in the composite at every interlaminar interface (interface between adjacent fiber laminae) by fiber prepreg surface modification. The flexural strength increase due to Hal nanotubes incorporation corroborated with the interlaminar shear strength increase. The measured values of the composite modulus agreed roughly with the calculated values based on the Rule of Mixtures. The interlaminar interface thickness was higher for the SiC whiskers case than the carbon nanotubes or Hal nanotubes case. The lamina thickness was not affected by the fillers. The composite density was 2% higher for the Hal nanotubes and SiC whiskers cases than the carbon nanotubes case.