Preparation of novel porous carbon from hydrothermal pretreated textile wastes: Effects of textile type and activation agent on structural and adsorptive properties

High performance activated carbons from textile wastes were successfully developed for the removal of oxytetracycline (OTC) from aqueous solution. For this purpose, textile wastes consist of cotton (Co), polyester (PE) and cotton/polyester (Co/PE) were subjected to hydrothermal carbonization (HTC) as a pretreatment, followed by chemical (ZnCl2 and KOH) and physical (CO2) activation to obtain activated carbon. Results showed that both activation agents and textile waste types had considerable effects on activated carbon properties and OTC removal. The highest surface area was achieved by ZnCl2 activation of Co (1906 m2/g) and Co/PE hydrochars (1795 m2/g), which exhibited the best oxytetracycline (OTC) adsorption performance with -a capacity of 621.2 mg/g and 482.8 mg/g, respectively. Activated carbon fitted best to three parameter isotherm models namely Sips or Redlich-Peterson isotherms, indicating that adsorption can proceed on both homogenous and heterogeneous surface depending on the concentration of OTC molecules. The three-parameter Sips isotherm model provided the best fit for Co-KOH and Co/PE-KOH whereas adsorption of ZnCl2 and CO2 activated carbons followed both Redlich-Peterson isotherm model. Kinetic data of both activated carbons was best described by pseudo second order model, also revealing that Co-ZnCl2 had faster adsorption rate than that of Co/PE-ZnCl2. For Co and Co/PE hydrochars, the surface areas of KOH and CO2 activated carbons were relatively lower than ZnCl2 activated carbons. Nevertheless, KOH activation was rich in acidic surface groups while CO2 activation led to form activated carbons with high -carbon content (>90%. In the light of these findings, hydrothermal carbonization can be considered as a pretreatment, which allows conversion of textile wastes into promising precursor for porous carbon production, while the process was not appropriate to produce solid fuel.