One Step Synthesis of Porous Polyurea and Its Application to Dye Adsorption in Water

A novel one-step protocol for facile preparation of porous polyurea material(PPU) through precipitation step polymerization of toluene diisocynate(TDI) as the sole monomer with water in water-acetone mixed solvent was presented, in which neither any porogen during the polymerization, nor chemical modification on the outcome polymer was need. The surface morphology and pore parameters of PPU as prepared were characterized by scanning electron microscope(SEM) and Brunauer-Emmett-Teller (BET) nitrogen adsorption, respectively. Presence of abundant amine groups on PPU surface was confirmed by infrared measurement. Using acid fuchsine(AF) in aqueous solution as an example for dyes in wastewaters, the effects of AF adsorption pH, adsorption time, AF concentration and amount of PPU on the adsorption process were studied. AF adsorption was more effective with pH located between 2-4; adsorption equilibrium was usually reached with 4 h. AF was nearly full adsorbed at low concentration or with high PPU loading. The maximum adsorption capacity of AF on PPU was 44.60 mg/g under optimized conditions. Analysis of the adsorption results demonstrated that the adsorption was better fit by Langmuir adsorption equation compared to Freundlich adsorption. In addition, Congo red(CR) was also used and its adsorption on PPU also studied. The maximal adsorption of CR on PPU was of 90.48 mg/g. Desorption test demonstrated that over 92% of the adsorbed dye molecules on PPU were desorbed when PPU with adsorbed dyes was immersed into NaOH solution (1 mol/L) or H2O/ethanol mixture(1 : 1, volume ratio) for 2 h. The following reuse of PPU demonstrated that dye adsorption was higher than 90% of the initial adsorption in the re-adsorption, and it was higher than 80% of the initial adsorption in the third adsorption. The results indicate that PPU is an effective absorbent to remove AF and CR in aqueous medium, and an attractive candidate for removal of anionic dyes from the wastewaters.