Application of Fe-rich coal fly ashes to enhanced reduction of 4-nitrophenol

Abstract

The potential harmful of 4-Nitrophenol (4-NPh) extensively used in agriculture, pharmaceutics, amongst others industrial applications makes this compound an important organic contaminant. Its removal by heterogeneous catalytic reduction is framed within circular economy purpose the only reaction product, 4-aminophenol (4-APh), is a value-added product and the catalysts can be easily separated and re-used. The most common methods use expensive metals and the search for cheap and easily available material is one of a state of art challenges for the industrial application. Coal fly ash (CFA) are an excellent alternative since contains iron-rich morphotypes in the form of ferrospheresIn this study and, for the first time, the catalytic reduction of 4-nitrophenol (4-NPh) was performed using the original magnetic fraction of CFA or the treated fractions (using water, NaOH or NaBH4) avoiding the incorporation of any metals/oxides nanoparticles. The most promising results were obtained using: 1) the magnetic fraction treated with NaOH, where a complete reduction of 4-NPh was observed in 5 min which is a remarkable catalytic efficiency, comparable with noble metal nanocatalysts in the literature; 2) the magnetic CFA treated under NaBH4 with 100% of 4-NPh reduction in 30 min. These results highlight the potential of the magnetic fractions of CFA to be use as alternative to the precious metal catalysts to successfully convert 4-NPh to 4-APh. Furthermore, these CFA-based catalysts present very good stability with no loss of activity in consecutive 5 cycles showing the ability of these materials to be applied not only in 4-NPh but also in other nitroarenes reduction and potentially in water remediation.

Keywords

• Coal fly ash
• Ferrospheres
• Reduction
• Nitroarenes
• Heterogeneous catalysis
• Water treatment