Highly Efficient and Magnetically Recyclable Non-Noble Metal Fly Ash-Based Catalysts for 4-Nitrophenol Reduction

Abstract

4-nitrophenol (4-NPh) is a harmful compound produced in large amounts in the chemical industry, and its reduction to aminophenol (4-APh) using noble metals as catalysts is one of the most studied processes. The development of noble metal-free catalysts represents an economic advantage in large-scale applications and contributes to the sustainability of raw materials. Coal fly ash (FA), a major waste stream from coal combustion, contains an easily recoverable magnetic fraction (FAmag sample) composed of Fe-rich particles that could substitute noble metal catalysts in 4-NPh reduction, with the concomitant advantage of being easily recovered via magnetic separation. For this purpose, a new composite material containing copper ferrite nanoparticles (FAmag@CS@CuFe) was prepared via a facile, environmentally friendly and cost-effective method based on three components: FAmag as the core, a biobased polymer chitosan (CS) as the linker and copper ferrite CuFe2O4 nanoparticles (CuFe) as the active sites. The structure, morphology, composition and magnetic properties of the FAmag@CS@CuFe material were studied to assess the efficiency of the preparation. It was found that the biopolymer prevented the aggregation of CuFe nanoparticles and enabled a synergistically outstanding activity towards the reduction of 4-NPh in comparison to the pristine FAmag and bare CuFe nanoparticles. The FAmag@CS@CuFe catalyst showed efficiency and stability in the conversion of 4-NPh of up to 95% in 3 min over four consecutive cycles. Such remarkable catalytic results demonstrate the potential of this catalyst as a substitute for expensive noble metals.