Synthesis, characterization, and application of polypyrrole/TiO ₂ composites in photocatalytic processes: A review

Hybrid materials composed of semiconductor oxide metals and conducting polymers have been highlighted as a new class of materials, with superior properties compared to their pure constituents. Among the studied composites to photocatalytic applications, the hybrids of titanium dioxide (TiO ₂ ) and polypyrrole (PPy) are promising due to several advantages over the pure TiO ₂ nanoparticles. The PPy/TiO ₂ composite has been effectively synthetized by chemical polymerization methods as in situ polymerization, photopolymerization, electrochemical polymerization, and molecular imprinting polymerization (MIP). All the cited methods appear to be effective in reducing the band gap energy, which suggests an increase in the formation of photoexcited electron-hole pairs and, consequently, an improvement of the light absorption in the visible region (400–700 nm). In addition, the doping of PPy/TiO ₂ with noble metals improves the separation of charges in the semiconductor particle, inhibiting the recombination of photogenerated electron-hole pairs. All advantages are evidenced by the characterization results of SEM, TEM, HRTEM, UV-vis DRS, FTIR, XRD, PL, TGA and electrical properties. Finally, results from literature present that PPy/TiO ₂ composites have better photocatalytic activity than the pure TiO ₂ , being an alternative photocatalyst promising for visible light applications. Thus, this work presents a review of the synthesis, characterization, and application of PPy/TiO ₂ composites in the photocatalytic processes.