Impregnation and hydrothermal synthesis of zeolite doped Ni/Al₂O₃ nanocomposite for urea adsorption

Abstract

Urea removal from aqueous solution is important for wastewater treatment and for artificial kidney (dialysate regeneration) systems. In this study, a zeolite-doped Ni/Al₂O₃ nanocomposite was synthesized by a hydrothermal- wet impregnation route and compared with silica zeolite as an adsorbent for urea. To investigate the adsorbent surface properties, techniques such as XRD, surface area measuring BET, (FE-SEM, TESCAN MIRA3) coupled with energy-dispersive X-ray spectroscopy EDS and Fourier Transform Infrared FT-IR were utilised. The nanocomposite had a higher specific surface area (146.84 versus 47.657 m² g⁻¹) and a smaller average pore diameter (4.997 versus 9.849 nm), its surface was covered with fine nanoparticles, and EDS confirmed Ni incorporation at about 10 wt%. Batch experiments examined the effects of adsorbent dose, contact time, pH, and temperature. The nanocomposite removed about 85% of the urea, compared with about 70% for silica zeolite, at half the adsorbent dose (0.2 versus 0.4 g in 25 mL), with an optimum pH of 8 and an equilibrium time of about 60 min (about 30 min for silica zeolite). The equilibrium data were described better by the Freundlich model (R² = 0.9576 and 0.9475) than by the Langmuir model (R² = 0.799 and 0.8148), indicating adsorption on a heterogeneous surface, with a higher Freundlich constant for the nanocomposite (K_f = 1.99 versus 0.458). Uptake decreased as the temperature rose from 293 to 323 K. At 293 K, all thermodynamic parameters were negative for silica zeolite and the nanocomposite, showing that adsorption is spontaneous, exothermic, and mainly physical. The zeolite-doped Ni/Al₂O₃ nanocomposite is therefore a more effective adsorbent for urea than silica zeolite.