Two luminescent hybrids, Znqb- and Znqp-montmorillonites (q = 8-hydroxyquinoline, b = 2,2'-bipyridine, p = 1,10-phenanthroline), were prepared by solid-solid reactions between Zn(II)-montmorillonite and two ligands (8-hydroxyquinoline and 2,2'-bipyridine or 1,10-phenanthroline) at room temperature. The intercalation and in situ complex formation of the two ligands into an interlayer space of Zn(II)-montmorillonite were confirmed by powder XRD, TG-DTA, as well as FT-IR, UV-vis and photoluminescence spectroscopies. The emission band of Znqb-montmorillonite was red-shifted compared to that of the mixture of Znq-montmorillonite and Znb-montmorillonite, confirming the formation of Znqb complex in montmorillonite. The photoluminescence intensity of Znqb-montmorillonite was higher than that of Znqp-montmorillonite, indicating that 2,2'-bipyridine enhanced the emission intensity of zinc(8-hydroxyquinoline) complex in montmorillonite, while the coordination of 1,10-phenanthroline quenched the intensity of the immobilized chelate.
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.
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