HALLOYSITE NANOTUBES FUNCTIONALIZED WITH A BIOCIDE AS ANTIMICROBIAL NANOFILLER FOR CONSTRUCTION MATERIALS

In recent applications, nanotubes (NTs), nanometer-scale hollow cylinders, are emerging as a favourable choice to other vehicles (microparticles, layered clays, zeolites, etc.) for the entrapment and/or the delivery of active molecules, thanks to the advantages that they can offer: (1) NTs have open mouths, which makes the inner surface accessible and incorporation of species within the tubes particularly easy; (2) NTs have no swelling or porosity changes with changes in pH, and they are not vulnerable to microbic attack, therefore they are able to effectively protect the entrapped molecules against deterioration phenomena induced by external environment; (3) NTs have larger inner volumes (relative to the dimension of the tube), which can be filled with any desired chemical or biochemical species ranging in size from small molecules to proteins, and allow for loading more than one active agent in the same nanocarrier so that multifunctional systems can be obtained1. Amongst the different types of existing NT, halloysite NT (HNT), a two-layered (1:1) aluminosilicate chemically similar to kaolin [Al2Si2O5(OH)4•nH2O], with the 1÷15 micron of length and 10-100 nm of inner diameter, is a nature material and an economical viable clay material that can be mined from deposits as a raw mineral. HNTs are available in thousands of tons, and remain sophisticated and novel natural nanomaterials which can be used for the loading of agents, i.e. anticorrosives for plastic and metals, biocides, pest repellent, drugs, etc.2. The aims of this work is the development of a novel HNTs-based nanofiller with antimicrobial activity, useful for control the biodeterioration process of construction materials. Thanks to the high chemical compatibility of the HNTs with the cementitious materials, this nanofiller is expected to have improved antimicrobial effectiveness and higher stability, compared to the neat biocide not anchored to the HNTs. At this regard, natural HNTs were functionalized with a commercial biocide and used as co-formulating agent in a mortar substrate. The obtained samples were tested in order to verify the success of the HNTs functionalization procedure and the effect of the functionalized nanofiller on the properties and the microbial resistance of the mortar.