Halloysite-TiO2 Nanocomposites for Water Treatment: A Review

Abstract

Halloysite nanotubes (HNTs) are clay minerals with a tubular structure that can be used for many different applications in place of carbon nanotubes. Indeed, HNTs display low/non-toxicity, are biocompatible, and can be easily prepared. Moreover, the aluminum and silica groups present on HNTs’ inner and outer surfaces facilitate the interaction with various functional agents, such as alkalis, organosilanes, polymers, surfactants, and nanomaterials. This allows the deposition of different materials, for instance, metal and non-metal oxides, on different substrate types. This review article first briefly presents HNTs’ general structure and the various applications described in the last 20 years (e.g., drug delivery, medical implants, and energy storage). Then, it discusses in detail HNT applications for water purification (inorganic and organic pollutants). It focuses particularly on HNT-TiO2 composites that are considered very promising photocatalysts due to their high specific surface area and adsorption capacity, large pore volume, good stability, and mechanical features.

Charge-Selective Photocatalytic Degradation of Organic Dyes Driven by Naturally Occurring Halloysite Nanotubes

“…When HNT-dye mixtures are illuminated by UV radiation, their photocatalytic mechanism can be tentatively explained similarly to traditional semiconductor photocatalysts [40], as in Figure 5. The optical band gap of the photocatalysts (HNTs) has been estimated to be ~3.7 eV by diffuse reflectance studies presented in Figure S6 (Supporting Information).…”

“…lysts [40], as in Figure 5. The optical band gap of the photocatalysts (HNTs) ha mated to be ~3.7 eV by diffuse reflectance studies presented in Figure S6 (Sup formation).…”

CaCu3Ti4O12 Perovskite Materials for Advanced Oxidation Processes for Water Treatment

“…However, TiO 2 has limitations, such as low sunlight absorption and limited recovery and fast recombination of photogenerated charges. The use of TiO 2 perovskites, which can be modified by doping, is a promising method for reducing these limitations [ 67 ]. Dong et al demonstrate the ability of F-doped MnTiO 3 perovskite materials to degrade rhodamine B under visible light [ 68 ].…”

Preparation and Upscaling of Zeolite@TiO2 Core‐shell for the Removal of Pb(II) and Methylene Blue Dye from Wastewater

“…Filtration using nanofibrous membranes of polyacrylonirtrile/halloysite, nanosized TiO 2 supported on CNTs also remove dyes from water. [13] CeO 2 nanowires, mesoporous Fe 3 O 4 nanospheres, polyacrylonitrile and fly ash incorporated TiO 2 nanofibers removes organic dyes and heavy metal ions with high capacities. [14][15] Extensive use of nanomaterial in purification, is, however, still challengeable due to their hazardous nature and problem in recovering from water.…”

“…Nanocomposites materials like CNTs/Fe 3 O 4 , [7] functionalized graphene oxide, [8–9] TiO 2 /SiO 2 , [10] Cu−chitosan/alumina, [11] Polysulfone/nano−TiO 2 based ultrafiltration membranes [12] have been found to remove dyes and other contaminations from water solutions. Filtration using nanofibrous membranes of polyacrylonirtrile/halloysite, nano‐sized TiO 2 supported on CNTs also remove dyes from water [13] . CeO 2 nanowires, mesoporous Fe 3 O 4 nanospheres, polyacrylonitrile and fly ash incorporated TiO 2 nanofibers removes organic dyes and heavy metal ions with high capacities [14–15] .…”