Abstract
The use of clay minerals as catalyst is renowned since ancient times. Among the different clays used for catalytic purposes, halloysite nanotubes (HNTs) represent valuable resources for industrial applications. This special tubular clay possesses high stability and biocompatibility, resistance against organic solvents, and most importantly be available in large amounts at a low cost. Therefore, HNTs can be efficiently used as catalysts themselves or supports for metal nanoparticles in several catalytic processes. This review reports a comprehensive overview of the relevant advances in the use of halloysite in catalysis, focusing the attention on the last five years.
Highlights
Different studies dealing with the photodegradation of antibiotics or organic dyes from aqueous solution by means of valuable nanocatalysts based on metal nanoparticles supported on halloysite nanotubes (HNTs), both pristine and modified, have been reported (Table 3) [48,65,66,67,68,69,70]
Immobilized CdS quantum dots (QDs) on HNTs, developing a nanomaterial which showed good biosafety in vitro, and their results demonstrated that more than 80% of eukaryotic cells were viable after incubation with cadmium and mixed sulfides stabilized by HNTs [85]
The chemical treatment of HNTs by means different agents (such as H2SO4, heating treatment of the clay, followed by its interaction with cetyltrimethylammonium bromide allowed to Xiao, Jiang et al to force the synthesis of small Pd NPs inside HNTs lumen (Figure 15) [120]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The catalytic activity of clay minerals is related to their capacity to act as solid acids in either the Brønsted or Lewis sense as influenced by sample pretreatment and experimental conditions They possess the ability to displace some water molecules, physisorbed on their surfaces, with cations generating active centers which explain their catalytic ability towards chemical reactions. As catalystsInthemselves, papers started to deal with the application of kaolin group’s clay minerals in catalysis, ing their intrinsic acidity or their cation-exchange properties. In this period, more papers focusing their cracking of catalysts in petrochemical processing. A short paragraph will be devoted on the future perspectives about the use of the clay in the catalytic field
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