Fully recyclable gold-based nanocomposite catalysts with enhanced reusability for catalytic hydrogenation of p-nitrophenol

Abstract Nanocomposite (NC) materials, which demonstrate catalytic activity under mild conditions, have garnered considerable attention due to the environmental hazards associated with aromatic nitro compounds. Herein, a novel in-situ synthesis of NCs with zero-valent Au (Au°) is proposed. These materials are based on suspension copolymers with molecular reactors that enable the fabrication of Au° and the enhancement of both the catalytic activity and reusability. NCs were obtained using amino-based nanoreactors (3–14 mmol per gram of a polymer) derived from polyethyleneimine (PEI), 1-(2-hydroxyethyl)piperazine (HEP), 1,4-bis(3-aminopropyl)piperazine (APP). The resultant Au@PEI, Au@HEP, and Au@APP NCs were investigated using optical microscopy, SEM, and TEM. Additionally, the physiochemical structures of both the polymeric matrix and Au° were evaluated using, i.a., FT-IR and XRD. The so-obtained NCs were used as nanocatalysts (NCats) for the catalytic hydrogenation of 4-nitrophenol (4-NP) under mild conditions. The method developed for the synthesis of NCs produced gold-based NCats with 25–37 % Au° content. The synergism between the polymeric matrix and Au° enabled the hydrogenation of 4-NP within approx. 30―38 min with a rate constants of 0.071 min−1 (Au@HEP) and 0.028 min−1 (Au@APP) and, respectively. The spherical millimetric morphology of the polymeric support facilitated the facile recyclability of NCats that maintained their catalytic activity for more than 10 cycles of 4-NP reduction.