Enhanced Photocatalytic Activity using Layer-by-Layer Electrospun Constructs for Water Remediation

Endocrine disruptors such as bisphenol A (BPA) are environmental pollutants that interfere with the body's endocrine system because of their structural similarity to natural and synthetic hormones. Due to their strong oxidizing potential to decompose such organic pollutants, colloidal metal oxide photocatalysts have attracted increasing attention for water detoxification. However, achieving both long-term physical stability and high efficiency simultaneously with such photocatalytic systems poses many challenges. Here a layer-by-layer (LbL) deposition approach is reported for immobilizing TiO2 nanoparticles (NPs) on a porous support while maintaining a high catalytic efficiency for photochemical decomposition of BPA. Anatase TiO2 NPs approximate to 7 nm in diameter self-assemble in consecutive layers with positively charged polyhedral oligomeric silsesquioxanes on a high surface area, porous electrospun polymer fiber mesh. The TiO2 LbL nanofibers decompose approximately 2.2 mg BPA per mg of TiO2 in 40 h of illumination (AM 1.5G illumination), maintaining first-order kinetics with a rate constant (k) of 0.15 h(-1) for over 40 h. Although the colloidal TiO2 NPs initially show significantly higher photocatalytic activity (k approximate to 0.84 h(-1)), the rate constant drops to k approximate to 0.07 h(-1) after 4 h of operation, seemingly due to particle agglomeration. In the BPA solution treated with the multilayered TiO2 nanofibers for 40 h, the estrogenic activity, based on human breast cancer cell proliferation, is significantly lower than that in the BPA solution treated with colloidal TiO2 NPs under the same conditions. This study demonstrates that water-based, electrostatic LbL deposition effectively immobilizes and stabilizes TiO2 NPs on electrospun polymer nanofibers for efficient extended photochemical water remediation.