Recycle calcium silicate hydrate adsorbent waste for preparing CuNi bimetallic hydrogenation catalyst of p-nitrophenol

As a solid hazardous waste material, economical and environmental efficacy of spent adsorbent loaded by toxic heavy metals (HMs) are often neglected, which maybe bring serious secondary pollution. In this work, we report a green recycle route for spent HM-bearing calcium silicate hydrate (CSH) adsorbents to construct nanocrystal-loaded functional materials. Typically, bimetallic CuNi catalyst (Cu-Ni@deCa-CSH) is obtained by CO2 weathering decalcification of the exhausted CSH adsorbed by Cu2+ and Ni2+, and subsequently reducing at 550 ℃ for 6 h under 5 vol% H2/Ar. The universal precursor, HM loaded CSH spent adsorbents, could be ideal for implementing 'CO2 decalcification-H2 reduction' to obtain more metal or metal oxide nanoparticle loaded deCa-CSH samples (Cu-Fe@deCa-CSH, Cu-ZnO@deCa-CSH, Cu-CoO@deCa-CSH, Cu-CeO2@deCa-CSH, etc.), which can dramatically change the surface acidity of substrate owing to the phase transformation from basic CSH to inert silica (deCa-CSH), thus benefitting catalytic reactions. As a case study, the typical 100Cu-100Ni@deCa-CSH (The initial ion concentration is 100 mg/L) exhibits good catalytic activity and stability for p-nitrophenol (p-NP) hydrogenation into p-aminophenol (p-AP) with NaBH4 reducing agent. The conversion efficiency of 99.04% can be achieved within 18 min (initial p-NP: 60 mL, 20 mg/L, Catalyst: 20 mg, NaBH4: 40 mg, pH = 8). Ni addition facilitates electron transfer from Ni to Cu, and the resultant lower electron binding restraint in the heterostructure thus improves the conversion efficiency of p-NP. Important parameters (p-NP initial concentration, NaBH4 addition dosage, solution pH, etc.) are discussed extensively to understand how to prefer reaction conditions for p-NP hydrogenation. The developed surface chemistry strategy thus provides a realistic basis for the formation of functional materials via explore the potential value of solids post-use.