An
efficient and an easily scalable photocatalyst with CdS nanoparticles
placed on the outer surface and inside halloysite clay nanotubes with
cadmium sulfide content of ca. 3 wt % was developed. The CdS/halloysite
core–shell tubule nanocomposites showed a superior catalytic
activity and a high stability in the release of hydrogen under visible
radiation without cocatalysts or noble metal doping. The specific
activity was of 20 mmol of hydrogen per hour per gram of CdS. The
suggested approach opens the way to an inexpensive production of highly
efficient mesoporous catalyst based on a natural, abundantly available
clay support.
Nanoparticles, being objects with high surface area are prone to agglomeration. Immobilization onto solid supports is a promising method to increase their stability and it allows for scalable industrial applications, such as metal nanoparticles adsorbed to mesoporous ceramic carriers. Tubular nanoclay - halloysite - can be an efficient solid support, enabling the fast and practical architectural (inside / outside) synthesis of stable metal nanoparticles. The obtained halloysite-nanoparticle composites can be employed as advanced catalysts, ion-conducting membrane modifiers, inorganic pigments, and optical markers for biomedical studies. Here, we discuss the possibilities to synthesize halloysite decorated with metal, metal chalcogenide, and carbon nanoparticles, and to use these materials in various fields, especially in catalysis and petroleum refinery.
Halloysite tubular nanoclay was applied as a template for synthesis of ruthenium core−shell composite catalysts for the first time; 50 nm diameter ceramic tubular systems with metal seeded interiors were produced. The procedure for the metal deposition and prior halloysite modification had a significant influence on properties of the catalyst and, as a consequence, on its activity in hydrogenation of phenol. Cyclohexanol was the main reaction product, but its yield depended on the substrate conversion and nanoarchitectural composition of the catalysts used. The maximum catalytic activity (turnover frequency, TOF) achieved was 17 282 h −1 in terms of hydrogen uptake per surface Ru atoms. The substrate selectivity of halloysite-based catalysts was also demonstrated at the comparative hydrogenation of phenol and various cresols.
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