Application of dithiocarbamate-modified starch for dyes removal from aqueous solutions

The present study shows that the dithiocarbamate-modified starch (DTCS) is a commercially promising sorbent for the removal of anionic dyes from aqueous solutions. It is more effective than activated carbon for this purpose. At the appropriate solution pH of 4, kinetic studies indicate that the sorption of the dyes tends to follow pseudo-first-order equation. The sorption equilibrium is best described by the Langmuir-Freundlich isotherm model at 298 K. The capacities for individual dyes follow the sequence acid orange 7 > acid orange 10 > acid red 18 > acid black 1 > acid green 25, which is consistent with the inverse order of molecular size. The negative enthalpy change for the adsorption process confirms the exothermic nature of adsorption, and a free energy change confirms the spontaneity of the process. The FT-IR spectra and thermogravimetric analyses verify the sorption based on starch-NH2+CSSH⋯−O3S-dye electrostatic attraction. The DTCS can be regenerated from the dye loaded DTCS in a weak basic solution containing sodium sulfate.