Autoclave and pulsed ultrasound cavitation based thermal activation of persulfate for regeneration of hydrogen titanate nanotubes as recyclable dye adsorbent.

Abstract

In the dye removal application, regeneration of hydrogen titanate nanotubes (HTN, H2Ti3O7) has been achieved via thermal activation of persulfate anion (PS, S2O82-) by using the conventional hot plate technique which has limitations from the commercial perspective since it does not provide any precise control over the thermal generation process typically during the scale-up operation. To overcome this drawback, HTN have been synthesized via hydrothermal process which exhibit the methylene blue (MB) adsorption of 93% at the initial dye concentration and solution pH of 90µM and 10 respectively. HTN have been regenerated via the thermal activation of PS by varying its initial concentration and regeneration temperature, within the range of 0.27-1 wt% and 40-80°C, under the thermal conditions set by the autoclave and pulsed ultrasound (US) cavitation process. The results of recycling experiments suggest that the optimum values of initial PS concentration and temperature, for the regeneration of HTN under the autoclave conditions, are 1 wt% and 70°C with the maximum MB adsorption of 92%, while, the corresponding values for the pulsed US cavitation process are 1 wt%, 80°C, and 91% respectively. Thus, the regeneration and recycling of HTN have been successfully demonstrated by using the autoclave and pulsed US cavitation process. Under the optimum conditions, MB degradation involves the generation and attack of SO4•- for both the thermal generation techniques. The regeneration techniques developed here may be utilized in future during the scale-up operation and also for the regeneration of adsorbents besides HTN.