Modified Z-scheme heterojunction of TiO2/polypyrrole recyclable photocatalyst

Abstract

A straightforward physical mixing method was used to prepare the highly efficient TiO₂/polypyrrole (PPy) photocatalysts of hydrothermally prepared TiO₂ and PPy, obtained by the chemical oxidative polymerization, with different amounts of PPy (0, 0.5, 1, 1.5, 3, and 5 wt.%). Synthesized composites were characterized by XRPD, FTIR, FESEM, EDS, BET, and UV–Vis methods, while their photocatalytic activity was estimated towards the degradation of toxic dye Reactive Orange 16 (RO16) based on UV–Vis and TOC. XRPD showed that the TiO₂ was obtained as nanoanatase with crystallites of 26 nm. Band gap energies of the nanocomposites decreased with the PPy content increase from 3.11(3) to 2.94(3) eV. The TiO₂/1%PPy demonstrated the highest photocatalytic activity by completely degrading RO16 for 120 min under simulated solar light with degradation described by the pseudo-first reaction order with the rate constant of 0.056(5) min⁻¹. It was established that 73% of the total reactive oxidative species were h⁺ and that the photodegradation mechanism followed a slightly modified direct Z-scheme in which PPy played an active and irreplaceable role by opening a new reaction path. Besides extremely high photocatalytic efficiency, the recyclability of TiO₂/1%PPy was confirmed since no decrease in efficiency was found after several runs of photocatalysis.