A New Life for Tionite Industrial Waste: Regeneration Strategy towards Photocatalytic Applications

Industrial waste management is an urgent problem to solve possibly by recycling, reuse and recovery of resources. In this framework, the sludge of the TiO₂ manufacturing, called tionite, is of certain interest because it contains metallic oxide-bearing impurities, dangerous to the environment. Hence, we propose a strategy to recover TiO₂ from tionite, towards its effective re-use as a photocatalyst. In detail, tionite was treated under acidic or alkaline conditions to remove impurities and improve the TiO₂ accessibility, and each single purification step was monitored by a thorough multi-technique characterization. The photocatalytic activity of the modified tionite materials was tested for the partial oxidation of ferulic acid to vanillin, a relevant sustainable green reaction, being vanillin an industrially relevant high added value compound and ferulic acid an abundant component of lignin present in industrial waste. All the tionite catalysts have shown significant efficiency in terms of vanillin selectivity respect to the benchmark TiO₂ P25. In particular, the sample treated under acidic conditions showed the best performances, due to specific interaction between the organic substrates and the catalyst. Results demonstrated that an industrial waste such as tionite can be valorized by proposing a tailored regeneration strategy.