A Tunable Template-Assisted Hydrothermal Synthesis of Hydroxysodalite Zeolite Nanoparticles Using Various Aliphatic Organic Acids for the Removal of Zinc(II) Ions from Aqueous Media

Hydroxysodalite zeolite nanoparticles with different crystallite sizes (37.61–64.88 nm) were synthesized using a hydrothermal method in the absence and presence of low-cost aliphatic organic acids as templates. The templates used were oxalic acid dihydrate, tartaric acid, citric acid monohydrate, succinic acid, maleic acid, and ethylenediaminetetraacetic acid (EDTA). The synthesized nanoparticles were characterized using HR-TEM, FE-SEM, FT-IR, and XRD techniques. The hydroxysodalite zeolite synthesized using ethylenediaminetetraacetic acid (EDTA) has the smallest crystallite size (37.61 nm) whereas the template free one has the largest crystallite size (64.88 nm). The synthesized nanoparticles could be effectively applied to purify polluted water from the zinc(II) ions, and the maximum adsorption capacity was 8.53 mg/g. Kinetic study displayed that the adsorption process of zinc(II) ions obeyed pseudo-second-order, intra-particle diffusion, liquid film diffusion, and pore diffusion models whereas the rate determining step of the adsorption is only controlled by the pore diffusion model. In addition, equilibrium study showed that the adsorption process fitted well with the Langmuir isotherm model compared to the Freundlich isotherm model. Besides, thermodynamic study showed that the adsorption process is exothermic, spontaneous, and chemisorption. Moreover, desorption and reusability study revealed that there is a slight decrease in both of the % removal and adsorption capacity of the hydroxysodalite adsorbent with progressing five cycles. Hence, we can infer that this new hydroxysodalite adsorbent can possibly be utilized repeatedly without sacrificing its adsorption capacity towards zinc(II) ions.