Ecotoxicity of TiO2, cerium and zirconium doped TiO2 photocatalysts prepared by different preparation methods and using different titanium precursors

Ecotoxicological effects of manufactured TiO2, cerium doped TiO2 and zirconium doped TiO2 prepared by different chemical methods and using different chemical precursors were evaluated, since these nanomaterials are keenly investigated semiconductor photocatalysts for waste and drinking water and waste gas purification in last three decades. Acute biological toxicity of manufactured photocatalysts was evaluated based on Sinapis alba seeds germination and Lemna minor fronds growth tests, and was compared to commercial photocatalyst TiO2 Degussa P25. Toxicity tests exhibited good sensitivity for monitoring of the toxicity of investigated nanomaterials. TiO2 toxicity results demonstrate that TiO2 prepared using titanyl sulphate as a Ti precursor are toxic to both plant species contrary to TiO2 prepared using titanium (IV) isopropoxide. Cerium doped TiO2 with Ce amount <5.5 wt.% proved to be non-toxic to both plant species and zirconium doped TiO2 even stimulates both plant species growth. Small crystallite-size and high surface area are not the toxicity-determining factors. In case of TiO2 prepared by using titanyl sulphate (TiO2-TH-C, TiO2-TH-PW), the chemical issues, i.e. the huge release of Ti4+ ions to nutrient aqueous solutions from TiO2 photocatalysts and the presence of SO42− onto TiO2 photocatalyst surfaces were identified. The presence of SO42− was identified as the chemical cause of TiO2 toxicity to both Lemna minor fronds and Sinapis alba seeds. High toxicity of Ce0.05Ti0.95On photocatalyst to Sinapis alba seeds was attributed to high content of cerium (∼9 wt.%) in TiO2 which led to formation of CeO2 of nuclei-size.