Adsorption of diastase over natural halloysite nanotubes (HNTs)

Adsorption of diastase over natural halloysite nanotubes is studied in order to evaluate the adsorption capacity of diastase. The halloysite surface characteristics were assessed using nitrogen adsorption, x-ray diffraction (XRD), thermal gravimetric analysis (TGA) and Fourier transformed infrared (FTIR). The surface area of the natural halloysite is found to be 51 m²·g^-1, with total pore volume of 0.106 cm³·g^-1. The natural halloysite has a basal spacing (d001) of 10 Å confirming the structure of the natural halloysite material. TGA results indicated that halloysite loses its interlayer water in the range of 30 to 105 °C and the dehydration in the structural layer above 150 °C. The dehydroxylation of halloysite has occurred at approximately 460 °C. The FTIR result of the thermally treated halloysite sample indicated that the bands observed are assigned to Si-O and Al-O bonds. The effects of solution pH and temperature were studied on the adsorption capacity and percent removal of diastase from the solution. The adsorption kinetic found to fit well with both the Pseudo first-order and Pseudo second-order models, and the values of the kinetic constant were found to be 0.173 min^-1 and 0.00018 g·mg^-1·min^-1 respectively. The Langmuir isotherm model is found to fit well to the adsorption data and a kinetic value is found to be 0.00059 m³·g^-1. The maximum adsorption capacity was found to be 370 mg·g^-1, indicating the potential for applications of the natural nanostructured halloysite material as an effective adsorbent for diastase.