Eur. Phys. J. Plus (2019) 134: 539
https://doi.org/10.1140/epjp/i2019-12981-6

Regular Article

Photocatalytic N-doped TiO₂ for self-cleaning of limestones

¹ Department of Mathematical, Physical and Computer Sciences, University of Parma, Parco Area delle Scienze 7/a, 43124, Parma, Italy
² Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/a, 43124, Parma, Italy
³ Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129, Torino, Italia
⁴ IMEM-CNR, Parco Area delle Scienze 37/A, 43124, Parma, Italy
⁵ Department of Chemical Engineering, Technion-Israel Institute of Technology, 32000, Haifa, Israel

^* e-mail: laura.fornasini@studenti.unipr.it

Received: 27 September 2018
Accepted: 5 September 2019
Published online: 31 October 2019

Abstract

Nanocrystalline nitrogen-doped TiO₂ photocatalysts were applied as surface coatings to three typical Israeli limestones, Maccabim, Halila and Hebron, widely used for historic buildings. Two different N-doped TiO₂ sols were synthesised by sol-gel method starting from titanium oxysulfate ( TiOSO₄ as Ti precursor: a new N-doped TiO₂ coating (N-TiF), obtained in neutral conditions, was developed and compared to a N-doped TiO₂ (N-TiA), obtained in acidic medium. XRD and Raman spectroscopy confirm the nanocrystalline nature of N-doped TiO₂, mainly in anatase phase, with size ∼ 4 nm as revealed by TEM analysis. Diffuse Reflectance Spectroscopy indicates a red-shift in the absorption spectra for both nanopowders, even if the X-ray Photoelectron spectroscopy results are not conclusive on the state and location of the N doping ions. The self-cleaning efficiency of the two TiO₂ coatings was assessed on the three Israeli carbonate stones and compared to commercial TiO₂ (Evonik P25) by the photoinduced degradation of two organic dyes (Methyl orange and Rhodamine B) and by following hydrophilicity changes, through static contact angle measurements. The harmlessness of these coatings was confirmed by colorimetric and water capillary absorption measurements.