Effect of ZIF-90 Crystallite Size on the Confinement of Ag Nanoparticles and Their Catalytic Performance in p -Nitrophenol Reduction

High Resolution Image Download MS PowerPoint Slide In this study, three different kinds of zeolitic imidazolate frameworks ZIF-90, denoted as Z90-H 2 O, Z90-Et, and Z90-TB, were synthesized using Zn(NO 3 ) 2 ·6H 2 O as the metal precursor, with water (H 2 O), ethanol (EtOH), and tert -butanol ( t -BuOH) serving as solvents, respectively. The resulting ZIF-90 crystallites exhibited sizes of approximately 2.5 μm for Z90-H 2 O, 600 nm for Z90-Et, and 275 nm for Z90-TB, indicating that the use of tert -butanol as a solvent yielded the smallest crystallite size of ZIF-90. These ZIF-90 supports were subsequently employed to immobilize silver nanoparticles (Ag NPs) for use as catalysts in the liquid-phase reduction of p -nitrophenol ( p -NP) to p -aminophenol ( p -AP). In addition to their high specific surface area, the presence of aldehyde groups on the pore surface of ZIF-90 enhanced the metal–support interaction, restricted the mobility of Ag(I) ions, and facilitated the formation of homogeneously dispersed Ag NPs with sizes down to ∼4 nm. The concentration of the Ag precursor in the synthesis mixture was systematically varied to explore the influence of Ag loading on catalytic performance. The catalyst with the smallest size of Ag NPs exhibited an apparent reaction rate of 4.64 × 10 –2 s –1 and a high specific activity of 77.33 s –1 g –1 . Furthermore, the catalyst demonstrated high stability and durability, with strong metal–support interactions effectively preventing Ag NP aggregation and leaching.