Self-Cleaning Coatings for the Protection of Cementitious Materials: The Effect of Carbon Dot Content on the Enhancement of Catalytic Activity of TiO2

Abstract

The urgent demand for pollution protection of monuments and buildings forced the interest towards specific preservation methods, such as the application of photocatalytic coatings with self-cleaning and protective activity. TiO2 photocatalysts without and with a variety of carbon dots loading (TC0, TC25–75) were synthesized via a green, simple, low cost and large-scale hydrothermal method using citric acid, hydroxylamine and titanium isopropoxide (TTIP) and resulted in uniform anatase phase structures. In photocatalysis experiments, TC25 and TC50 composites with 1:3 and 1:1 mass ratio of C-dots solution to TTIP, respectively, showed the best degradation efficiency for methyl orange (MO) under UV-A light, simulated solar light and sunlight compared to TiO2, commercial Au/TiO2 (TAu) and catalysts with higher C-dot loading (TC62.5 and TC75). Treatment of cement mortars with a mixture of photocatalyst and a consolidant (FX-C) provided self-cleaning activity under UV-A and visible light. This study produced a variety of new, durable, heavy metal-free C-dots/TiO2 photocatalysts that operate well under outdoor weather conditions, evidencing the C-dot dosage-dependent performance. For the building protection against pollution, nanostructured photocatalytic films were proposed with consolidation and self-cleaning ability under solar irradiation, deriving from combined protective silica-based agents and TiO2 photocatalysts free or with low C-dot content.

Hydrophobic and Photocatalytic Treatment for the Conservation of Painted Lecce stone in Outdoor Conditions: A New Cleaning Approach

“…The first part of the experiments was performed on raw Lecce stone, on which we evaluated the harmlessness of the TiO 2 /OrMoSil treatment through colorimetric tests, measurements of water absorption through capillarity and of permeability to water vapor and its durability by means of artificial ageing and salt crystallization. Then we tested, with colorimetric methods, the self-cleaning efficacy of the coating in the photodegradation of methyl orange (MeO) and methylene blue (MB) dyes, commonly used as model pollutants, under artificial solar irradiation [71][72][73][74].…”

Evaluation of the Performance and Durability of Self-Cleaning Treatments Based on TiO2 Nanoparticles Applied to Cement-Based Renders and Boards

“…In fact, the photocatalytic behavior of TiO 2 under light radiation (mostly UV) has been shown to degrade several pollutants (such as nitrogen oxides) and biological contaminants (such as bacteria), also providing super-hydrophilic properties that enhance the removal of dust and soiling by rain [3]. Of the two main polymorphs of titanium dioxide, namely anatase and rutile, anatase is generally accepted as the one with greater photocatalytic activity, but it was shown that a mixture of both phases is required for efficient photocatalysis [4,5] and that doping can significantly increase the photocatalytic activity of materials [6][7][8][9]. Many studies in the literature have also highlighted that, although the photocatalytic behavior of TiO 2 was demonstrated a long time ago, many parameters influence the actual photocatalytic effectiveness and self-cleaning performance of titania, such as the size and size distribution of nanoparticles [10], and the strategies aimed at resolving the agglomeration problem of TiO 2 [11].…”

“…Coatings 2023, 13, 990 2 of 11 began towards the end of the 1980s, aiming at the enhancement of the aesthetic durability of buildings and a reduction in environmental pollution [3,12,13]. Cementitious materials are widely used in outdoor applications, such as building façades, structures, roads and tunnels; hence, any improvement in their performance and/or the introduction of new and unique functionalities have potentially a very high impact on everyday life [8,14].…”