Oil-phase cyclic magnetic adsorption to synthesize Fe3O4@C@TiO2-nanotube composites for simultaneous removal of Pb(II) and Rhodamine B

In this work, to simultaneously remove organic dyes and Pb(II) from wastewater, a series of magnetic Fe3O4@C@TiO2-nanotube composites were designed and successfully synthesized via a new facile oil-phase cyclic magnetic adsorption (OCMA) method. The structural properties of the synthesized composites were investigated by different characterization methods systematically. It was found that Fe3O4 was uniformly deposited on the inner walls of TiO2 nanotubes. Although a Type III band alignment was formed in the catalysts, Fe3O4@C@TiO2-nanotube composites exhibited enhanced light absorbing ability and enlarged absorption edge due to efficient separation of h+ and e−, which was verified by UV–Vis (Ultraviolet–visible) and PL (Photoluminescence) spectra. Decontamination experiments of 1FeCTi showed that more than 98% of RhB and about 92% of Pb(II) ions could be removed through adsorptive removal in the dark equilibrium period and further elimination during the illuminating period. The pseudo-first-order model, L-H model and adsorption-reaction model were established to describe the adsorption of Pb(II) in the dark, photodegradation of RhB and further elimination of Pb(II), respectively. A four-step mechanism was proposed to describe the decontamination process of Pb(II) during the illuminating period according to the final forms of Pb (Pbδ1, Pbδ2, Pb0 and PbO). Finally, it was found that the photocatalytic activity would be maintained in the recycle experiments due to the existence of 1FeCTi@PbO heterostructure.