Removal of Chromium (III) Heavy Metal Ions from Aqueous Solutions by Green Synthesized Calix[6]arene

In this study, p-tert-butylcalix[6]arene has been successfully synthesized using tert-butylphenol, formaldehyde, and KOH base catalyst. The synthesis process was carried out using a solvent-free grinding technique to minimize waste formation. The grinding technique was selected because the synthesis process was easy and environmentally friendly. With the synthesis yield of 62.58%, the product obtained was a yellow-brownish solid with a melting point >300°C, insoluble in water but soluble in methanol. The product was characterized using FTIR spectrophotometer, and resulted in spectra showing absorption band for methylene bridge (-CH2-) vibration at the wave number of 1473.62 cm-1. The results of the LC-MS chromatogram analysis showed that the molecular weight of the compound was 974.77 g/mol. The product was then tested for its ability to adsorb Cr(III) metal ions by batch method at pH 5 with variations in contact time and different initial concentrations of metal ions. Calix[6]arene was tested as a Cr(III) metal ion adsorbent because the size of the cavity diameter of calix[6]arene matches to the size of the lower period heavy metal cation. The results showed that the amount of adsorbed metal increased with the increasing of the contact time and reaches stability within 120 min. The adsorption capacity value was 7.414 μmol/g with a Gibbs adsorption energy value of -26.198 kJ/mol.