Nanostructured TiO2 anatase-rutile-carbon solid coating with visible light antimicrobial activity

Abstract

TiO2 photocatalyst is of interest for antimicrobial coatings on hospital touch-surfaces. Recent research has focused on visible spectrum enhancement of photocatalytic activity. Here, we report TiO2 with a high degree of nanostructure, deposited on stainless steel as a solid layer more than 10 μm thick by pulsed-pressure-MOCVD. The TiO2 coating exhibits a rarely-reported microstructure comprising anatase and rutile in a composite with amorphous carbon. Columnar anatase single crystals are segmented into 15–20 nm thick plates, resulting in a mille-feuilles nanostructure. Polycrystalline rutile columns exhibit dendrite generation resembling pine tree strobili. We propose that high growth rate and co-deposition of carbon contribute to formation of the unique nanostructures. High vapor flux produces step-edge instabilities in the TiO2, and solid carbon preferentially co-deposits on certain high energy facets. The equivalent effective surface area of the nanostructured coating is estimated to be 100 times higher than standard TiO2 coatings and powders. The coatings prepared on stainless steel showed greater than 3-log reduction in viable E coli after 4 hours visible light exposure. The pp-MOCVD approach could represent an up-scalable manufacturing route for supported catalysts of functional nanostructured materials without having to make nanoparticles.

Process-Induced Nanostructures on Anatase Single Crystals via Pulsed-Pressure MOCVD

“…Anatase columns appear pyramidal at the top and the rough dendritic structures are polycrystalline rutile ( Figure 2). The thick robust coatings produced on stainless steel substrates exhibited high antimicrobial activity under visible light [14]. Thinner films on fused silica substrates have formal quantum efficiency 59 times higher than the commercial photocatalyst Pilkington Activ TM [17], measured with stearic acid degradation in UV light [18].…”

“…Nano rods and other 2-D structures grown on substrates have not yet been demonstrated for practical coatings. The nanostructured, multiphase, thick solid coating grown by pulsed-pressure metalorganic chemical vapor deposition (pp-MOCVD) has been demonstrated to be adherent and durable [14]. Figure 1.…”

“…Figure 1. Illustration of (a) TiO2 nanoparticles; (b) rutile nanorods with secondary structures grown on a substrate [15]; (c) nanostructured TiO2 in a solid coating adhered to a substrate [14].…”

“…The properties of photocatalytic materials depend on the crystallography and morphology, but there has been no research reporting a study of nanoscale feature size in TiO2 bulk or coating materials to date. [15]; (c) nanostructured TiO 2 in a solid coating adhered to a substrate [14].…”

“…Thinner films on fused silica substrates have formal quantum efficiency 59 times higher than the commercial photocatalyst Pilkington Activ TM [17], measured with stearic acid degradation in UV light [18]. In previous work, we used ASTAR TM analysis of TEM samples of TiO 2 films grown on stainless steel to determine that the anatase columns were single crystals, even though they are made up of nano-plates, with A[220] columnar growth direction [14]. The properties of photocatalytic materials depend on the crystallography and morphology, but there has been no research reporting a study of nanoscale feature size in TiO 2 bulk or coating materials to date.…”