Photocatalytic Coatings For Environmental Applications

Abstract

A series of nano- and micronparticle-grade anatase and rutile titanium dioxide pigments have been prepared with various densities of surface treatments, particle size and surface area. Their photocatalytic activites have been determined in a series of paint films by FTIR, chalking, color, gloss change and weight loss after artifical weathering. The pigments have also been examined by rapid assessment methodologies using photodielectric microwave spectroscopy, 2-propanol oxidation and hydroxyl analysis. The microwave response under light and dark cycles provides an extended timescale probe of charge-carrier dynamics in the pigments. Pigment particle size, surface area and properties clearly play an important role in dispersion and any polymer-pigment interactions. Photooxidation studies on several types of paint films show a clear demarcation between nanoparticle- and pigmentary-grade titanium dioxide, with the former being more active because of their greater degree of catalytic surface activity. The photosensitivity of titanium dioxide is considered to arise from localized sites on the crystal surface (i.e. acidic OH), and occupation of these sites by surface treatments inhibits photoreduction of the pigment by ultraviolet radiation; hence, the destructive oxidation of the binder is inhibited. Coatings containing 2-5% by weight alumina or alumina and silica are satisfactory for general-purpose paints. If greater resistance to weathering is desired, the pigments are coated more heavily to about 7-10% weight. The coating can consist of a combination of several materials, e.g. alumina, silica, zirconia, aluminum phosphates of other metals. For example, the presence of hydrous alumina particles lowers van der Waals forces between pigments particles by several orders of magnitude, decreasing particle-particle attractions. Hydrous aluminum oxide phases appear to improve dispersibility more effectively than most of the other hydroxides and oxides. Coated nanoparticles are shown to exhibit effective light stabilization in various water- and oil-based paint media in comparison with conventional organic stabilizers. Hindered piperidine stabilizers are shown to provide no additional benefits in this regard, often exhibiting strong antagonism. The use of photocatalytic titania nanoparticles in the development of self-cleaning paints and microbiological surfaces is also demonstrated in this study. In the former case, surface erosion is shown to be controlled by varying the ratio of admixture of durable pigmentary-grade rutile (heavily coated) and a catalytic-grade anatase nanoparticle. For environmental applications in the development of coatings for destroying atmospheric pollutants such as nitrogen oxide gases (NO(X)), stable substrates are developed with photocatalytic nanoparticle-grade anatase. In this study, porosity of the coatings through calcium carbonate doping is shown to be crucial in the control of the effective destruction of atmospheric NO(X) gases. For the development of microbiological substrates for the des...

Photoactive self-cleaning polymer coatings by TiO2 nanoparticle Pickering miniemulsion polymerization

“…Photocatalytic materials have gained extraordinary relevance in the last years due to their potential applications in fields such as photo-induced removal of pollutants from air and water, and self-cleaning and antibacterial materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Titanium dioxide (TiO 2 ) is the most widely investigated photocatalyst due to its high photoactivity, low cost, low toxicity and good chemical and thermal stability [16,17].…”

Toxicity and cellular responses of intestinal cells exposed to titanium dioxide

“…Nanomaterials, such as titanium dioxide (TiO 2 ), are now in daily use including popular sunscreens, toothpastes, and cosmetics (Wolf et al 2003;Kaida et al 2004). Moreover TiO 2 is used at the nanoscale level in manufacturing (Fisher and Egerton 2001;Allen et al 2005) and to decontaminate water, air, and soil by destruction of a pesticide (Higarashi and Jardim 2002;Konstantinou and Albanis 2004;Esterkin et al 2005). However, the safety and risk of commercialized products has not been examined in detail.…”

In Vitro Toxicity Evaluation of 25-nm Anatase TiO2 Nanoparticles in Immortalized Keratinocyte Cells

“…[1][2][3][4]. The engineered nanoparticles are already being used in sporting goods, strain-resistant clothing, sunscreens, electronics, cosmetics, and will also be increasingly utilized in medicine for the purpose of imaging, drug delivery, and diagnosis [5][6][7]. Although impressive from the perspective of material science, the novel properties of nanoparticles could also lead to adverse effects on biological systems.…”

“…Titanium dioxide (TiO 2 ), one of the most popular nanoparticles, have been widely used in manufacturing [5], in the environment to decontaminate air, soil, and water, and more recently in consumer products, car materials, rubber, [6,7] etc. The impacts of TiO 2 NPs on biological systems at cellular level have been put forward recently by scientists and organization [2,[8][9][10][11][12].…”