Abstract
A colloidal route was exploited to synthesize TiO2 anisotropic nanocrystal rods in shape (TiO2 NRs) with a surface chemistry suited for their dispersibility and processability in apolar organic solvents. TiO2 NRs were dispersed in chloroform and n-heptane, respectively, and the two resulting formulations were investigated to identify the optimal conditions to achieve high-quality TiO2 NR-based coatings by the spray-coating application. In particular, the two types of TiO2 NR dispersions were first sprayed on silicon chips as a model substrate in order to preliminarily investigate the effect of the solvent and of the spraying time on the morphology and uniformity of the resulting coatings. The results of the SEM and AFM characterizations of the obtained coatings indicated n-heptane as the most suited solvent for TiO2 NR dispersion. Therefore, an n-heptane dispersion of TiO2 NRs was sprayed on a highly porous limestone—Lecce stone—very commonly used as building material in historic constructions and monuments present in Apulia Region (Italy). A comprehensive physical-chemical investigation of the TiO2 NR based treatment on the surface of the stone specimens, including measurements of colour variation, static contact angle, water transfer properties, and morphological characterization were performed. Finally, the photocatalytic properties of the coatings were assessed under solar irradiation by using Lecce stone specimens and Methyl Red as a model target compound. The obtained results demonstrated that TiO2 NRs based coatings can be successfully applied by spray-coating resulting in an effective photocatalytic and hydrophobic treatment, which holds great promise as a material for the environmental protection of architectural stone in the field of cultural heritage conservation.
Highlights
TiO2 nanoparticles (NPs) are widely employed as building blocks for functional materials to be used in a plethora of applications, and, in particular, in the fields of energy production and environmental remediation [1]
The anisotropic growth of TiO2 NRs is promoted by the hydrolysis of titanium isopropoxide (TTIP) catalysed by trimethylamino-N-oxidedehydrate (TMAO) in the presence of oleic acid (OLEA) as a coordinating solvent
This work investigated and optimized the experimental conditions suited to effectively applying rod-shaped TiO2 nanocrystals by spray coating, with the final goal to convey hydrophobic and photocatalytic properties to the surface of the Lecce stone
Summary
TiO2 nanoparticles (NPs) are widely employed as building blocks for functional materials to be used in a plethora of applications, and, in particular, in the fields of energy production and environmental remediation [1]. Such a large interest is driven by the intrinsic and deeply investigated features of the nanomaterial such as its high surface area, high photoactivity, chemical stability [2], Coatings 2018, 8, 356; doi:10.3390/coatings8100356 www.mdpi.com/journal/coatings. The use of TiO2 NPs as the functional material in coatings requires their direct immobilization on surfaces or, alternatively, their incorporation in a suitable polymer matrix in order to exploit their functionalities.
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