Change in lumen pore structure of halloysite nanotube membrane coating under varying pressure, time and temperature

In this article, the suitability of utilization of porous lumen structure of Halloysite (Hal) nanoclay has been studied elaborately. To utilize the lumen structure for membrane development, the effect of temperature, pressure and time on the porous lumen feature and subsequent use of the clay in pristine form as a membrane coating material for separation purposes at specified temperatures shows the importance of this study. The present study investigates structural changes in Halloysite nanoclay's inherent porous tubular morphology. Membranes are prepared by coating clay-alumina porous support tube with Halloysite sol under pressure and temperature of 100 and 160 °C for 24, 48 and 64 h, respectively. XRD and FTIR reveal that the tubular structure remains intact under experimental conditions. In contrast, the morphology of pristine Hal powder treated at the specified temperature and under in situ developed autogenous pressure shows a significant textural change in the nanotubular morphology observed from FESEM. At 100 °C, lumen porosity remains intact, but at 160 °C, under higher pressure, lumen mouth sealing, conjoining and coalescence of the halloysite nanotubes (HNT) result. In addition, for both temperatures under existing operating pressure, the effect of 24 h time duration on morphology is less. For practical viability, a preliminary study for dye removal is carried out with H1 membrane coating, which shows promising %rejection values. This study on powders and membrane coatings might thus help to assign new application fields, such as membrane-based separation utilizing the porous nature of HNT by controlling different process parameters.