Visible light induced photodegradation of bio-polymeric waste using boron-enhanced titania nanotubes

Visible light-activated photocatalytic degradation allows renewable solar energy harvesting for sustainable waste remediation. The incorporation of dopant into the structure of photocatalysts enables photoactivation using visible light. In this work, titania nanotube (TNT) was doped with boric acid of different molarities (0.25, 0.5, 1.0 M) under alkaline hydrothermal condition to produce TNT doped boron (TNT-B) photocatalyst. The formation of microcrystalline structure on the surface of TNT evidenced the attachment of boron nanoparticle on the surface of TNT. The nanotube diameter and surface negativity increased with increasing dopant molarity. The doping did not incur significant changes on the crystallinity of TNT but resulted in an extension of light absorption to visible light range. Pristine TNT and TNT-B were tested for their photocatalytic activity under visible light irradiation for the photodegradation of bio-based polymeric colour pigments, namely lignin and tannic acid (TA). The doping significantly improved photoactivity of TNT under visible light conditions. Optimal doping was achieved with 0.5 M of boric acid, where TNT-B degraded 96.47% of lignin and 96.91% of TA within 240 min of irradiation. Radical scavenging experiments also revealed that both OH− and •O2− radicals were the major reactive species responsible for the degradation.