Photocatalytic performance of alkali-activated materials functionalized with β-Bi2O3/Bi2O2CO3 heterostructures for environmental remediation

Abstract

Alkali-activated materials (AAMs) are environmentally friendly binders produced with industrial solid wastes of low cost. They have good mechanical and physical properties, and their manufacture is associated with a low environmental impact and reduced greenhouse emissions. Thus, recently, AAMs have received considerable attention for new applications, such as environmental remediation. Here, alkali-activated materials functionalized with Bi2O2CO3 and Bi2O3/Bi2O2CO3 heterostructures were designed, fabricated, and evaluated as photocatalysts for environmental remediation. To demonstrate the applicability of these composites (or materials system), three representative photocatalytic reactions: (i) self-cleaning, (ii) air purification, and (iii) antimicrobial activity, were investigated. The photocatalysts were synthesized by solvent-deficient and hydrothermal methods, which promoted the formation of particles with flake and flower morphologies. Bi2O3/Bi2O2CO3 heterostructures exhibited lower band gaps and a more efficient charge transfer, whereas the Bi2O2CO3 photocatalysts showed higher surface area (28 m2/g) and smaller crystallite size. The alkali-activated materials functionalized with the photocatalysts showed a rough surface (∼1 μm) with a compact microstructure composed of several rod-like particles related to alkaline silicates with a Vickers hardness around 30–50 MPa. AAMs showed activity to remove methylene blue (∼30%) from their surface, which evidenced their self-cleaning activity. In addition, the AAMs showed remarkable activity to remove formaldehyde from the air, reaching efficiencies up to 81% after 3 h of irradiation. Furthermore, the antimicrobial activity of the AAMs was studied by means of the growth inhibition of Escherichia coli, Salmonella sp. and Staphylococcus aureus, under irradiation. The study with bacteria showed that, after 24 h in the culture medium, the AAMs exhibited inhibition zones against these microorganisms (Escherichia coli, 2.14–3.00 cm; Salmonella sp., 3.01–3.31 cm; and Staphylococcus aureus, 2.67–3.31 cm). Accelerated weathering tests were performed in the AAMs to guarantee their efficiency over their lifetime. The results confirm the photocatalytic activity of the AAMs functionalized with the heterostructured photocatalysts after 300 h of aging treatment. These results demonstrated the possibility of generating self-cleaning, air-depolluting, and antimicrobial surfaces by applying the AAMs fabricated with industrial wastes and Bi2O3/Bi2O2CO3 photocatalysts.