Abstract The use of organic-based photocatalytic coatings is a promising technology for improving air quality by eliminating inorganic and organic pollutants and for creating self-cleaning and antibacterial surfaces. The most common photocatalyst is titanium dioxide, in nanoparticulate form, which is embedded in a film-forming agent. In the present work, we investigate the performance of different photocatalytic coatings containing TiO2 nanoparticles (Aeroxide® P25 TiO2), towards the photo-degradation of a dye (methylene blue) as model reaction in a lab-scale UV photo-reactor. The TiO2 nanoparticles (∼21 nm) are tested as aqueous slurry and further used for preparation of photocatalytic coatings following two approaches: i) dispersion of P25 in a commercial acrylic paint aimed at outdoor use as a proof-of-concept, and ii) full formulation of acrylic-based photocatalytic coatings from raw materials, engineered with different pigmentation degrees defined by the λ parameter (pigment volume concentration relative to critical pigment volume concentration). The TiO2-acrylic coatings prepared with both methods show activity towards dye degradation in UV-irradiation tests. After the first 50−60 min of UV exposure a significant increase (up to 70−100%) in the apparent rate constant for methylene blue photo-degradation sets in for the photocatalytic coatings suggesting that the coatings are activated in the early stages of UV exposure. Scanning-electron-microscopy analysis confirms that the activation mechanism involves the creation of a porous surface at the outermost layer of the coating, gradually exposing TiO2 photocatalyst, as result of partial binder photo-degradation. Water contact angle (WCA) measurements, performed with a digital microscope, reveal that the kinetic transition is accompanied by a sudden drop of the WCA, indicating an enhanced wettability that is attributable to the hydrophilicity OH-rich TiO2 surface becoming accessible with the increased porosity. Use of a high λ can induce initial porosity that lowers the relative magnitude of this initial activation.

中文翻译：

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光催化涂层性能的基准测试及其对污染物降解的活化

摘要 有机基光催化涂层的使用是一项有前景的技术，可通过消除无机和有机污染物来改善空气质量，并创造自清洁和抗菌表面。最常见的光催化剂是纳米颗粒形式的二氧化钛，其嵌入成膜剂中。在目前的工作中，我们研究了含有 TiO2 纳米粒子 (Aeroxide® P25 TiO2) 的不同光催化涂层的性能，在实验室规模的紫外线光反应器中，作为模型反应的染料（亚甲蓝）的光降解。TiO2 纳米粒子（~21 nm）作为水性浆料进行测试，并通过以下两种方法进一步用于制备光催化涂层：i）将 P25 分散在旨在户外使用的商用丙烯酸涂料中作为概念验证，ii) 由原材料制成的丙烯酸基光催化涂料的完整配方，设计具有由 λ 参数（颜料体积浓度相对于临界颜料体积浓度）定义的不同着色度。用这两种方法制备的 TiO2-丙烯酸涂层在紫外线照射测试中显示出对染料降解的活性。在紫外线照射的前 50-60 分钟后，光催化涂层的亚甲蓝光降解的表观速率常数显着增加（高达 70-100%），表明涂层在紫外线的早期阶段被激活接触。扫描电子显微镜分析证实，活化机制涉及在涂层最外层形成多孔表面，逐渐暴露 TiO2 光催化剂，由于部分粘合剂光降解。用数字显微镜进行的水接触角 (WCA) 测量表明，动力学转变伴随着 WCA 的突然下降，表明润湿性增强，这是由于亲水性富含 OH 的 TiO2 表面随着孔隙率的增加而变得容易接近. 使用高 λ 可以诱导初始孔隙率，从而降低该初始激活的相对幅度。