Structure and Properties of Hybrid Film Fabricated by Spin-Assisted Layer-by-Layer Assembly of Sacran and Imogolite Nanotubes

A free-standing (biomacomolecule/synthetic inorganic nanotubes) hybrid film was fabricated through an alternative layer-by-layer (LBL) assembly of sacran and imogolite nanotubes. Sacran is a natural polysaccharide extracted from the cyanobacterium Aphanothece sacrum, while imogolite is a natural tubular aluminosilicate clay found in volcano ash. The hybrid film thickness increased linearly with the number of the bilayers, because of the interaction between the negatively charged surface of sacran and the positively charged surface of imogolite. UV-vis spectroscopy indicated that the LBL film exhibited good transparency. The surface morphology of the LBL film was smooth in the micrometer scale; many imogolite nanotubes were adsorbed onto the sacran layer, while no imogolite clusters were observed. Furthermore, the structure, stability, gas permeability, and mechanical properties of the LBL films were investigated.

Photoactive nanoarchitectures based on clays incorporating TiO2 and ZnO nanoparticles

Thought as raw materials clay minerals are often disregarded in the development of advanced materials. However, clays of natural and synthetic origin constitute excellent platforms for developing nanostructured functional materials for numerous applications. They can be easily assembled to diverse types of nanoparticles provided with magnetic, electronic, photoactive or bioactive properties, allowing to overcome drawbacks of other types of substrates in the design of functional nanoarchitectures. Within this scope, clays can be of special relevance in the production of photoactive materials as they offer an advantageous way for the stabilization and immobilization of diverse metal-oxide nanoparticles. The controlled assembly under mild conditions of titanium dioxide and zinc oxide nanoparticles with clay minerals to give diverse clay-semiconductor nanoarchitectures are summarized and critically discussed in this review article. The possibility to use clay minerals as starting components showing different morphologies, such as layered, fibrous, or tubular morphologies, to immobilize these types of nanoparticles mainly plays a role in i) the control of their size and size distribution on the solid surface, ii) the mitigation or suppression of the nanoparticle aggregation, and iii) the hierarchical design for selectivity enhancements in the catalytic transformation and for improved overall reaction efficiency. This article tries also to present new steps towards more sophisticated but efficient and highly selective functional nanoarchitectures incorporating photosensitizer elements for tuning the semiconductor-clay photoactivity.