دانلود رایگان مقاله دوام پوشش نانوساختار TiO2 در سنگ آهک با توانایی خود تمیزشونده

Abstract

Coating with nanostructured Titanium dioxide is able to enhance natural stone surface with self-cleaning and depolluting abilities; nonetheless, the durability of the coatings is a crucial issue to be assessed in relation to their potential for use in the context of the building heritage. In this paper, the resistance of coatings applied on a compact and a soft limestone, which differ in roughness, porosity and cohesion features, has been investigated. A peeling and a water impact test were performed and their effect on the coated surface was evaluated as film loss by qualitative/quantitative ESEM-EDS analyses. Self-cleaning effectiveness was assessed by performing a photodegradation test of Rhodamine B. Crack-free and conformable films showed a good anchorage to both limestones; after the durability tests the coated surfaces exhibited almost unchanged Ti/Ca ratios and self-cleaning efficiencies. Large adhesion failures and decreased Ti amounts were recorded where coatings were fissured; they especially occurred on the surface of the compact limestone, along with a reduced self-cleaning ability. High surface roughness accounted for a better adhesion of both crack-free and fissured films to the soft limestone, but some erosion of the coated surface, which affected this friable stone under the water impact, compromised their preservation. Nonetheless, good self-cleaning performances were still provided due to the retention of nanoparticles under the surface. The overall results support that preservation of nanostructured TiO2 coatings on the stone surface depends on the inherent characteristics of both films and supports; durability of the stone itself can play an important role.

4. Conclusions

Durability of nanostructured stone coatings obtained by the application of colloidal suspensions of Titanium dioxide synthesized by sol-gel and hydrothermal process, was investigated on the surface of two limestones. Resistance of the coatings to peeling and water impact laboratory tests was evaluated. The study highlighted that stability of photocatalytic TiO2 coatings in relation to large-scale application to the stone surfaces in outdoor conditions deserves great attention, as different issues in terms of either film adhesion or long lasting photocatalytic effectiveness of the coated surface can be obtained, depending on the inherent characteristics of both coatings and substrates. A better resistance was found for conformable and crack-free films, showing a good anchorage to both the stone supports, compared to the films affected by fissuring. Almost unchanged Ti/Ca ratios and self-cleaning efficiencies, as measured on the coated surface by EDS analysis and by the rate of photodecomposition of Rhodamine B, respectively, proved a good preservation of these films. Large adhesion failures and noticeable decrease of the Ti amounts were recorded when coatings were affected by cracking coming from the accumulation of titania applied in high amounts. The fissured coating showed a very low adhesion to the surface of the compact limestone, where it was mostly lost under the slight action of the peeling. In that case a reduced self-cleaning ability was recorded after the durability tests, denoting a decrease of the overall extent of the photocatalytically active surface because of a complete removal of TiO2 NPs from some surface areas. Higher surface roughness of the soft limestone compared to the compact limestone accounts for the better adhesion of both fissured and crack free films to the substrate