TiO2 nanoparticles grafted with 2,4-dinitrophenylhydrazine as a new adsorbent in efficient removal of formaldehyde from aqueous solution

A novel adsorbent prepared by the immobilization of 2,4-dinitrophenylhydrazine (DNPH) on TiO2 nanoparticles has been investigated for the removal of formaldehyde from aqueous solutions. Sodium dodecyl sulfate (SDS) surfactant was used to improve the DNPH grafting to the TiO2 surface. Isotherm modeling revealed that the Langmuir equation could better describe the adsorption of formaldehyde onto the TiO2/SDS/DNPH and the maximum adsorption capacity obtained was 51.282 mg/g. The equilibrium parameter (RL) indicated that TiO2/SDS/DNPH nanocomposites are useful for the removal of formaldehyde from aqueous solutions. Kinetic studies showed the best applicability of the pseudo-first-order model. It was found that the adsorption rate is rapid at the initial stages and reaches equilibrium after 245 min. According to the adsorption thermodynamics, & UDelta;H & DEG;, & UDelta;G & DEG;, and & UDelta;S & DEG; were calculated as -26.1, -5.6, and -63.2 (kJ/mol), respectively. Negative values obtained for thermodynamic parameters show that the reaction is exothermic and spontaneous at room temperature. Adsorption-desorption studies indicated that the prepared adsorbent kept its adsorption efficiencies constant over 5 cycles. The best conditions for TiO2/SDS/DNPH nanocomposites to remove 96.2% formaldehyde were an adsorbent dosage of 1.1 g/L, a pH of 7.424 and a contact time of 183.290 min.