An eco-friendly magnetic catalyst based on copper nanoparticles supported on lignin/iron oxide cores

Transforming renewable biomass into high-performance heterogeneous catalysts represents an attractive strategy for advancing sustainable chemical processes. This work reports a sustainable strategy for the development of highly efficient copper-based nanoparticles supported on lignosulfonate and magnetite or maghemite cores. Controlled thermal transformation of a copper-containing lignin matrix was shown to be a decisive factor in tailoring the textural properties and catalytic performance of the resulting materials. The catalysts were evaluated in the model reduction of 4-nitrophenol to 4-aminophenol using NaBH 4 as hydrogen donor, revealing a clear activity hierarchy in which the directly carbonized material exhibited markedly superior performance. The thermally treated catalyst combined a high specific surface area (519 m 2 g −1 ) with an outstanding turnover frequency (TOF 1 / 2 = 1382 h −1 ), positioning it among the most active copper-based systems reported so far for this transformation. In contrast, untreated materials, with lower porosity and surface area (65 m 2 g −1 ), displayed a substantially reduced activity, highlighting a strong structure–activity relationship governed by carbonization-induced pore development. Kinetic analysis indicated the formation of a reaction intermediate, consistent with a multi-step reduction mechanism. Overall, this investigation demonstrates the potential of lignin-derived magnetic carbon nanostructures as efficient, recyclable, and environmentally benign catalytic platforms, underscoring the importance of synthesis-driven control over porosity and surface chemistry in biomass-based heterogeneous catalysis.