Cellulose–Wool Keratin Composite Hydrogels as Selective Support Carriers for Gold Nanoparticles: Synthesis and Catalytic Applications in the Reduction of 4-Nitrophenol in Water

The continuous rise in global population and rapid economic growth have led to excessive consumption of nonrenewable resources and severe environmental pollution. Consequently, increasing efforts have been directed toward reducing the dependence on these resources and promoting the development of renewable alternatives. In this study, we proposed an effective strategy for utilizing keratin derived from waste textiles as a potential feedstock for producing value-added materials. The distinctive chemical structure of wool keratin, characterized by a high content of cysteine residues with thiol groups, enables its strong selective anchoring ability for gold nanoparticles (AuNPs). This property suggests that the wool keratin-based regenerated hydrogels can be applied as ideal supports for AuNPs immobilization. Accordingly, a series of cellulose/wool keratin composite hydrogels were synthesized and employed as supports for AuNPs, which were formed by reducing selectively absorbed Au³⁺ ions using sodium borohydride (NaBH₄). Structural and morphological analyses confirmed the uniform distribution of anchored AuNPs with an average diameter of approximately 3.74 nm. These composite hydrogels exhibited good catalytic activity in the reduction of 4-nitrophenol (4-NP) and demonstrated remarkable reusability, maintaining catalytic efficiency over 10 cycles. In the presence of C50W50@Au, the activation parameters for the 4-NP reduction were determined as <i>E</i>_a = 11.320 kJ mol^-1, Δ<i>H</i>^# = 8.729 kJ mol^-1, and Δ<i>S</i>^# = 50.106 kJ mol^-1 K^-1. Thus, this work focused on the high-value applications of wool keratin waste and presents a stable and efficient precious-metal nanoparticle catalyst for aqueous-phase catalysis.