Highly Robust and Selective System for Water Pollutants Removal: How to Transform a Traditional Photocatalyst into a Highly Robust and Selective System for Water Pollutants Removal

Abstract

Highly porous monolithic aerogels based on ZnO photocatalyst and syndiotactic polystyrene (s-PS) were obtained by supercritical CO2 treatment of ZnO/s-PS gels. The prepared aerogels were characterized and their photocatalytic activity was evaluated using phenol and toluene as water pollutant models. The s-PS nanoporous crystalline phase, able to absorb pollutant molecules, was proven to be necessary to ensure high photocatalytic efficiency as the aerogel acts not only as a support, but also as pollutant pre-concentrator. The reusability of ZnO/s-PS aerogels is also strong showing no decrease in photocatalytic activity after six consecutive degradation trials. Finally, the aerogel matrix prevents ZnO dissolution occurring under acidic conditions and promotes a selective removal of the pollutants. The synergy between the photocatalyst and the innovative polymeric support provides the composite system with robustness, chemical stability, easy recovery after treatment, high efficiency of pollutant removal with a marked selectivity which make these materials promising for large scale applications.

Main parameters influencing the design of photocatalytic reactors for wastewater treatment: a mini review

“…Starting from the discovery by Fujishima and Honda about the photocatalytic properties of TiO 2, 1 the research activity about heterogeneous photocatalysis aimed to remove different types of pollutants in liquid phase has notably increased 2–7 . Generally, the photocatalytic processes involve the generation and the subsequent reaction of hydroxyl radicals (•OH), thanks to the simultaneous action of a suitable catalyst and light source.…”

Catalytic Composite Systems Based on N-Doped TiO2/Polymeric Materials for Visible-Light-Driven Pollutant Degradation: A Mini Review

“…The methods for fixing N-doped TiO 2 particles on the chosen polymeric substrate can be developed starting from those studied for the immobilization of undoped TiO 2 . They may vary from simple, such as the solvent-casting method [46][47][48][49][50] or sol-gel techniques [58], to more complex, specialized and expensive methods, such as magnetron sputtering [59] and gelation of a catalyst in a polymeric substrate and subsequent extraction with supercritical CO 2 [55,56,60]. It is worth noting that the method for immobilizing N-doped TiO 2 on a polymeric support influences the photocatalytic activity, which also depends on the type of substrate and pollutant to be degraded.…”

“…As an alternative, crystalline powders of N-doped TiO 2 can be immobilized and dispersed within the structure of visible-light-transparent polymeric aerogels, starting from a gel obtained from a dispersion of photocatalyst particles in an organic solvent for the polymer and followed by extraction in supercritical CO 2 [55,56,60].…”

“…Therefore, the use of s-PS aerogels allows the preservation of the photocatalytic properties of N-doped TiO 2 in powder form, minimizing the aggregation phenomena between photocatalyst particles that typically occur in slurry photocatalytic reactors, as pointed out above. Moreover, the N-doped TiO 2 /s-PS monolithic structure can also avoid the expensive and time-consuming separation processes, necessary for powder photocatalysts separation, allowing a scale-up of a photocatalytic system activated by visible light to be realized [60].…”

Nanoporous Crystalline Composite Aerogels with Reduced Graphene Oxide

“…High-porosity polymeric aerogels are also especially appealing for supporting catalysts as they are chemically inert and mechanically stable with high durability and they offer many benefits, such as high surface area and high sorption. Many examples of aerogel catalysts have been reported in literature [ 37 , 38 , 39 , 40 , 41 ].…”