Rationally engineering magadiite heavy metal adsorbent for p-nitrophenol hydrogenation reduction

The reutilization of spent heavy metal adsorbents as efficient heterogeneous catalysts is of great interests but remains a great challenge. In this work, cetyltrimethyl ammonium bromide intercalated magadiite (Mag) is facilely synthesized via cation exchange reaction, which possesses good uptake capacity towards metal ions and high structural stability. As a case study, these spent adsorbents loaded by Ag ⁺, Zn ²⁺, and Cu ²⁺ species are recycled to construct nanohybrids MeO _x-Mag and Me ⁰-Mag (Me = Ag, Cu, and Zn) by calcining the exhausted solids under air and H ₂/Ar (5 vol% H ₂ ), respectively. The resultant imperfect pillared solids still inherit the interlayer space and nanosheet morphology from their Mag precursors, which is verified by abundant microscopic and spectroscopic characterizations. Importantly, Cu ⁰ nanoparticle modified Mag (CuM) exhibits remarkable catalytic activity for a p-nitrophenol ( p-NP) hydrogenation reduction. 100% p-NP (60 mL, 20 mg/L) can be converted into p-aminophenol ( p-AP) within 30 min when 2 mg CuM is used with the assistance of 10 mg NaBH ₄. Discrete Cu ⁰ nanoparticles promote the generation of active H ^⁎ and thus the heterogeneous catalysis for p-AP products. The catalytic performance with important parameters (Cu ⁰ loading amount, p-NP initial concentration, NaBH ₄ addition dosage, etc.) is discussed extensively to understand how to prefer reaction conditions for optimum nitro hydrogenation performance. The present study provides a rational design of spent Mag-based adsorbents for advanced environmental and catalysis applications via exploring the potential value of solids post-use.