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.

Antimicrobial materials are tools used to reduce the transmission of infectious microorganisms. Photo-illuminated titania (TiO2) is a known antimicrobial material. Used as a coating on door handles and similar surfaces, it may reduce viability and colonization by pathogens and limit their spread. We tested the survival of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Saccharomyces cerevisiae on a nano-structured TiO2-based thin film, called ‘NsARC’, and on stainless steel under a variety of light wavelengths and intensities. There was significantly less survival (P<0.001) of all the organisms tested on NsARC compared to inert uncoated stainless steel under all conditions. NsARC was active in the dark and possible mechanisms for this are suggested. NsARC inhibited biofilm formation as confirmed by scanning electron microscopy. These results suggest that NsARC can be used as a self-cleaning and self-sterilizing antimicrobial surface coating for the prevention and reduction in the spread of potentially infectious microbes.

The crisis of hospital‐acquired infections is driving intense interest in surface coatings that can inhibit colonization and reduce spread of pathogens to vulnerable patients. Widespread use of antibiotics and antimicrobial silver and copper has been demonstrated to trigger evolution of resistant strains of bacteria. The self‐cleaning properties of TiO2 could be a breakthrough for fighting HAI outbreaks if the photocatalytic activity (PCA) can be shifted to the spectrum of indoor light, and if a robust coating could be manufactured on hospital touch surfaces. MOCVD using titanium tetraisopropoxide (TTIP) is currently the standard method for applying self‐cleaning TiO2 to industrial glass. In this study, pulsed‐pressure MOCVD (pp‐MOCVD) was used to produce a solid coating composed of columnar microstructure anatase phase TiO2 with 200 nm diameter. This microstructure has enhanced active surface area and co‐deposited amorphous carbon on the crystal surfaces. The microstructure and carbon content were studied as a function of deposition temperature, and the new TiO2 coating was demonstrated to exhibit significant PCA under standard indoor lighting.

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Titania‐carbon solid thin films are synthetized by pulsed pressure metal organic chemical vapor deposition. Increasing substrate temperature results in significant changes in both structure and composition of the film. The high temperature coatings are a remarkable black color, and exhibit significant visible light photocatalytic activity. The proposed mechanisms for PCA‐Vis are a thin pyrolytic carbon coating on crystal surfaces in the porous microstructure which has enhanced active surface area. This is reported by Susan Krumdieck and co‐workers in aritcle http://doi.wiley.com/10.1002/pssa.201700578.