Investigating the Influence of Temperature on Kaolinite- Base Synthesis of Zeolite and Urease Immobilization For Potential Fabrication of Electrochemical Urea Biosensor

Abstract

Temperature-dependent zeolite synthesis revealed unique surface morphology, surface area and pore size that influence morphology of zeolite synthesised from kaolin in the immobilization of urease on gold electrode support for biosensor fabrication. XRD characterization identified Zeolite X (Na) at all crystallization temperatures tested. However, Nitrogen adsorption and desorption results showed pore size and pore volume of Zeolite X (Na) 60 °C, Zeolite X (Na) 70 °C and Zeolite X (Na) 90 °C range from 1.92 nm – 2.45 nm and 0.012 cm3/g – 0.061 cm3/g respectively, with no significant differences. The specific surface area of Zeolite X (Na) at 60, 70 and 90 °C was 64 m2/g, 67 m2/g, and 113 m2/g respectively. The pore size, specific surface area and pore volumes of Zeolite X (Na) 80 °C and Zeolite X (Na) 100 °C were dramatically increased to 4.21 nm, 295 m2/g, 0.762 cm3/g and 4.92 nm, 389 m2/g, 0.837 cm3/g in that order. The analytical performance of the embedded urease in Zeolite X (Na) was also investigated using cyclic voltammetry measurements and the results showed distinct cathodic and anodic peaks by Zeolite X (Na) 80 °C and Zeolite X (Na) 100 °C. The molar conductance of the modified zeolite biosensors was measured as a function of urea concentration and gave an average exponential decay regression fit of 0.98. The findings in this study suggest crystallization temperature is a critical parameter for electrochemical analysis of zeolites synthesized from natural sources for various biomedical applications.