Nobel metal nanoparticle loaded carbon nanotube (CNT) composites have wide applications in heterogeneous catalysis, and the catalytic properties are largely controlled by the size, composition, and dispersion state of the noble metal nanoparticles. However, the chemically inert feature of CNTs makes it difficult to directly disperse noble metal nanoparticles in a uniform manner. In this work, by an in situ galvanic replacement reaction between Cu nanoparticles and noble metal ions, a simple and efficient strategy was developed to produce magnetic multiwalled (MW) CNTs–Fe₃O₄ supported noble metal nanoparticles. The MWCNTs–Fe₃O₄–Pd showed impressive activity in the carbonylative Sonogashira coupling reaction and in the catalytic hydrodegradation of methylene blue.

Two kinds of multifunctional nanocomposites, SBA-15-NH₂/Pd-p and SBA-15-NH₂/Pd-f, with platelet-like and fiber-like morphologies, respectively, were fabricated by immobilizing Pd NPs onto amine-functionalized SBA-15. Some of the amino groups acted as anchoring sites for Pd NPs, whilst the remaining groups acted as Brønsted basic sites. As a result, the composites served as excellent multifunctional heterogeneous catalysts for one-pot multistep cascade reaction sequences. Moreover, when diffusion was the rate-determine step, SBA-15-NH₂/Pd-p, with small mesopores, was superior to the fiber-like control sample, owing to its short diffusion length, a lower possibility of pore clogging, and better mass transportation for the reaction species during the catalysis.

Hierarchically structured metal oxides have two or more levels of structure. Their nanometer-sized building blocks provide a high surface area, a high surface-to-bulk ratio, and surface functional groups that can interact with, e.g., heavy metal ions. Their overall micrometer-sized structure provides desirable mechanical properties, such as robustness, facile species transportation, easy recovery, and regeneration. In combination these features are suitable for the removal of heavy metal ions from water. Several general synthesis routes for the fabrication of metal oxides with various morphologies and hierarchical structures are discussed including soft and hard template-assisted routes. These routes are general, reliable, and environmentally friendly methods to prepare transition and rare earth metal oxides, including cobalt oxide, iron oxide, and ceria. As-prepared hierarchically structured metal oxides show excellent adsorption capacities for As^V and Cr^VI ions in water.