Porous Silica Microspheres with Immobilized Titania Nanoparticles for In‐Flow Solar‐Driven Purification of Wastewater

Abstract

In this paper, inorganic silica microspheres with interconnected macroporosity are tested as a platform for designing robust and efficient photocatalytic systems for a continuous flow reactor, enabling a low cost and straightforward purification of wastewater through solar‐driven photocatalysis. The photocatalytically active microspheres are prepared by wet impregnation of porous silica scaffolds with Trizma‐functionalized anatase titania (TiO 2 ) nanoparticles (NPs). NPs loading of 22 wt% is obtained in the form of a thin and well‐attached layer, covering the external surface of the microspheres as well as the internal surface of the pores. The TiO 2 loading leads to an increase of the specific surface area by 26%, without impacting the typically interconnected macroporosity ( ≈ 60%) of the microspheres, which is essential for an efficient flow of the pollutant solution during the photocatalytic tests. These are carried out in a liquid medium for the decomposition of methyl orange and paracetamol. In addition to photocatalytic activity under continuous flow, the microspheres offer the advantage that they can be easily removed from the reaction medium, which is an appealing aspect for industrial applications. In this work, the typical issues of TiO 2 NPs photocatalysts are circumvented, without the need for elaborate chemistries, and for low availability and expensive raw materials.

Macroporosity Control by Phase Separation in Sol-Gel Derived Monoliths and Microspheres

“…The resulting photocatalytic porous microspheres were inserted in a chamber of the continuous flow reactor set up and exposed to a solar simulator (1 Sun illumination). They were shown to allow a similar, or even better photocatalytic activity than other works in the literature ( k of the order of 10 −2 min −1 g −1 ), for methyl orange degradation, however with the advantage of the photocatalyst being easily removed from the reaction medium, since the NPs are grafted to a micron-size support material (MICROSCAFS), recyclable, and more appealing to a real, industrial application [ 3 ].…”

“…Reprinted from the open access paper by A.C. Marques, M. Vale, D. Vicente, M. Schreck, E. Tervoort, M. Niederberger, “Porous Silica Microspheres with Immobilized Titania Nanoparticles for In-Flow Solar-Driven Purification of Wastewater”, Glob. Challenges 5 (2021) [ 3 ]. (accessed on 19 March 2021).…”

“…This process resulted in the immobilization of TiO 2 NPs on the microspheres, promoted by solvent evaporation and electrostatic interactions, forming a well attached, thin layer of NPs along the pores surface, as shown in Figure 33, not affecting the characteristic macroporosity of the spheres. The mechanical robustness, chemical inertness and transparency in the UV, associated with their macro and mesoporosity, make these microspheres an emerging platform for generating new and efficient engineered photocatalytic systems, by acting as a support and synergic structure where photocatalytic NPs are immobilized [3]. The inorganic SiO2 microspheres loaded with TiO2 NPs were prepared by direct wet impregnation with an aqueous dispersion of TiO2 NPs, as shown in Figure 32.…”

“…The synthesis and development of porous microspheres for the photocatalytic purification of water (driven by the United Nations Sustainable Development Goals) is an example of the immense applications of porous support materials [ 3 ]. In this case, porosity directly influences the photocatalytic activity, since macropores (>50 nm) facilitate the mass transport of liquids and gases to the active sites, giving better performance in flow-through catalytic systems; mesopores (2–50 nm) are responsible for the high surface area of these materials, as well as for the size and shape selectivity.…”

Application of Spinel and Hexagonal Ferrites in Heterogeneous Photocatalysis

“…This review presents all the aspects, focusing on the newest trends, applied for the use of spinel and hexagonal ferrites (selected groups of ferromagnets) in heterogeneous photocatalysis, as an efficient method for semiconductor recycling. Of course, other types of separation/recycling have been proposed and investigated, such as sedimentation, coagulation, (ultra)filtration, immobilization of photocatalysts on elements of photoreactors (walls [16], quartz protecting tubes of lamps and LEDs [17,18], and optical fibers [19]) or additional supporters (glass beads [16], microspheres [20], balls [21], mesh [22], cloth [22], rings [23], membranes [24][25][26], and plates/films/foils [27][28][29][30]) [31].…”