Ferrocene as an efficient and recyclable heterogeneous catalyst for catalytic ozonation in water

Heterogeneous catalytic ozonation is a promising technique to improve ozonation for degrading organic contaminants. Preparation of heterogeneous catalysts (e.g., substrate-supported metals and metal oxides) for ozonation typically involves multiple steps and reagents. Because iron (Fe) is an abundant and non-noble metal, Fe-based heterogeneous catalysts are attractive for ozonation. Therefore, it is critical to develop a readily-available, stable and non-toxic Fe-based heterogeneous catalyst. To this end, we propose ferrocene (Fc), consisting of two cyclopentadienyl rings bound on opposite sides of a central Fe2 + atom, as a catalyst for ozonation. Degradation of the toxic dye amaranth was employed as a model test. The presence of Fc significantly improved amaranth degradation extent and kinetics, and Fc did not adsorb amaranth in water. Factors influencing amaranth degradation were investigated including Fc and ozone dosages, temperature, pH, and addition of NaCl and humic acid. Effects of radical inhibitors were also examined to provide insights into the occurrence of radical species during Fc-catalyzed ozonation. Degradation of amaranth was primarily attributed to derivative reactive oxygen species, as well as direct degradation by ozone to a lesser extent. A pathway of amaranth degradation is proposed based on degradation intermediates detected using LC/MS/MS. Fc was also re-used over multiple cycles for catalyzing ozonation to degrade amaranth without a loss of efficiency. These results indicate that Fc is a promising commercially available nanoscale heterogeneous catalyst for catalytic ozonation.