# Enhancing the Photocatalytic Activity of Immobilized TiO2 Using Laser-Micropatterned Surfaces
###### Abstract  
In the past, the application of TiO2 slurry reactors has faced difficulties concerning the recovery and reusability of the catalyst. In response to these challenges, immobilized photocatalyst systems have been investigated, wherein the catalyst is fixed onto a solid support, frequently with reduced photocatalytic performance. In the present study, thin TiO2 films were developed in the anatase phase by the sol-gel process and spin-cast on laser-microstructured silicon substrates, to form photocatalytic surfaces of increased activity. The TiO2 films were thoroughly characterized using SEM-EDX, XRD, UV-Vis spectroscopy, and Raman spectroscopy. The photocatalytic activity of these surfaces was evaluated by the degradation of atrazine in aqueous solution under UV irradiation. Their photocatalytic activity was found to be significantly enhanced (mean \(k_{\text{obs}}\) 24.1 \(\times\) 10\({}^{-3}\) min\({}^{-1}\)) when they are deposited on laser-microstructured silicon compared with flat silicon (mean \(k_{\text{obs}}\) 4.9 \(\times\) 10\({}^{-3}\) min\({}^{-1}\)), approaching the photocatalytic activity of sol-gel TiO2 fortified with Degussa P25, used as a reference material (mean \(k_{\text{obs}}\) 32.7 \(\times\) 10\({}^{-3}\) min\({}^{-1}\)). During the photocatalytic process, several transformation products (TPs) of atrazine, namely 2-chloro-4-(isopropyl-2)-amino-s-triazine (CIAT), 2-chloro-4-amino-6-(ethylamino)-s-triazine (CAET), and 2-chloro-4-6-diamino-s-triazine (CAAT), were identified with LC-MS/MS. The stability of the photocatalytic surfaces was also investigated and remained unchanged through multiple cycles of usage. The surfaces were further tested with two other pollutants, i.e., 2A,6-trichlorophenol and bisphenol-a, showing similar photocatalytic activity as with atrazine. immobilized TiO2 photocatalysis; laser patterned silicon; atrazine; 2A,6-trichlorophenol; bisphenol-a 202420202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202022020202020202022020202020202020202020 from one phase to another as in the case of membranes or activated carbon. The most commonly studied photocatalyst is titanium dioxide (TiO\({}_{2}\)) due to its excellent stability, non-toxicity, and enhanced photocatalytic activity [2; 3]. However, the implementation of TiO\({}_{2}\) slurry reactors has encountered challenges related to catalyst recovery and reusability. In traditional slurry systems, the photocatalyst is suspended in a liquid, rendering separation and filtration processes cumbersome and energy intensive. The use of TiO\({}_{2}\) slurry reactors often leads to difficulties in maintaining a stable catalyst concentration and poses challenges in recovering the catalyst from the reaction mixture. This may result in increased costs and environmental concerns associated with the disposal of the slurry [4]. To address these issues, immobilized photocatalyst systems have been explored, where the catalyst is immobilized onto a solid support [5; 6; 7; 8]. This approach not only simplifies catalyst recovery but also enhances the stability of the photocatalytic process [9; 10]. Using immobilized photocatalysts allows for easy separation of the catalyst from the reaction medium, enabling its reuse and reducing the overall environmental impact. Moreover, the immobilization process can be tailored to specific substrates or matrices, providing flexibility in the design and application of photocatalytic systems [10; 11]. Overall, the transition from TiO\({}_{2}\) slurry reactors to immobilized photocatalyst systems represents a significant advancement in the field, addressing the challenges associated with catalyst recovery and contributing to the sustainable development of photocatalytic technologies [4; 9].