Pb(II) Removal Using TiO2-Embedded Monolith Composite Cryogel as an Alternative Wastewater Treatment Method

Different from direct application of free nano-particles (NPs) in water treatment, a composite material is used to reduce the release and potential toxic effects of NPs with maintained adsorption capacity and kinetics. Novel monolithic composites with TiO2 NPs incorporated into the walls of macroporous cryogels were synthesized and evaluated for material characteristics and their efficiency for removal of Pb(II) from aqueous solution in batch test and continuous mode. The uniformly distributed 6% TiO2-cryogel is shown to be optimal for minimizing TiO2 NP losses while maximizing Pb(II) removal. Under (25.0 +/- 0.1) degrees C with the initial Pb(II) concentration of 10 mg/l, TiO2-cryogels exhibit excellent adsorption characteristic for Pb(II) removal with adsorption capacity up to 23.27 mg/g TiO2, which is even a little higher than that of TiO2 NPs (21.58 mg/g TiO2), and the results fit well with LangmuirFreundlich isotherm. Both adsorbents work well in higher pH range with the highest removal rate at pH 6 for TiO2- cryogel, and the adsorption mechanism might be strong chemical interaction. Pseudo-second-order process can better describe the adsorption process rather than pseudo-first-order for both adsorbents. The external mass transfer process of Pb(II) on TiO2 NPs is much faster than that on TiO2-cryogel, and the ultimate equilibrium time is about the same (3 h) on both adsorbents. The synthesized composites could also withstand a continuous treatment, and the effect of competing and coexisting constituents such as Cd2+, SO42- and dissolved organic matter (DOM) is almost negligible. The composite design with small particles embedded into cryogels is proved to successfully keep the adsorption activity of TiO2 NPs and prevent them from releasing into the environment in engineering practice.