| Summary: | 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 (FA<sub>mag</sub> 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 (FA<sub>mag</sub>@CS@CuFe) was prepared via a facile, environmentally friendly and cost-effective method based on three components: FA<sub>mag</sub> as the core, a biobased polymer chitosan (CS) as the linker and copper ferrite CuFe<sub>2</sub>O<sub>4</sub> nanoparticles (CuFe) as the active sites. The structure, morphology, composition and magnetic properties of the FA<sub>mag</sub>@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 FA<sub>mag</sub> and bare CuFe nanoparticles. The FA<sub>mag</sub>@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.
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