Influence of ZIF‐8 polymorphism catalysts and nanosizes in p‐nitrophenyl ester hydrolysis

Abstract

Three ZIF‐8 polymorphism structures (ZIF‐L, n21ZIF‐8 and n35ZIF) were synthesised by varying molar ratios of 2‐methylimidazole and zinc nitrate hexahydrate (8:1, 21:1 and 35:1) in water at room temperature without any modulator. A high yield of up to 88% was produced for ZIF‐L. Based on their distinct physicochemical characteristics, all were tested as catalysts for the hydrolysis reaction of p‐nitrophenyl palmitate (p‐NPPal) into p‐nitrophenol (p‐NP). The polymorphisms exhibited varying catalytic performance, which was related to altering the imidazolate linker. ZIF‐L outperformed others up to 94 μmol/min/g of p‐NPPal hydrolysis at optimum conditions (1 w/v % of catalyst, incubated at 90°C, 300 rpm for 15 min). Meanwhile, n35ZIF‐8 with nanoscale particle (150 nm) demonstrated a good kinetics (R2 = 0.99921) and recovery rate up to 78% by maintaining 50% activity until the fifth cycle.