Preparation and characterization of novel TiO2/lignin and TiO2-SiO2/lignin hybrids and their use as functional biosorbents for Pb(II)

A new method of synthesis of advanced, functional hybrid materials obtained from TiO2 or TiO2-SiO2 and lignin has been proposed. The resulting hybrids exhibited specific physicochemical and structural properties, which were determined by a number of methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), nitrogen sorption and thermogravimetric analysis (TGA). Then, removal of lead(II) ions from aqueous solutions was studied by the batch technique on titania and titania-silica oxides system modified by lignin (TiO2/L and TiO2-SiO2/L). It was found that with the increasing initial lead(II) ions concentration from 25 to 100 mg/L at the phase contact time from 1 to 180 min, the maximum adsorption capacities increased gradually. The equilibrium was achieved after 20 min and 30 min for novel TiO2/lignin and TiO2-SiO2/lignin adsorbents, respectively. Kinetic analysis showed that the pseudo second order mechanism (PSO) was the most suitable. For the adsorption studies the experimental data were well fitted by the Langmuir isotherm model. The experimental adsorption capacities for TiO2/lignin and TiO2-SiO2/lignin were found to be 35.70 mg/g and 59.93 mg/g, respectively which incicates that the last is the best sorbet for lead(II) removal from the aqueous solutions. It was observed that lead(II) adsorption was reduced with the increasing temperature from 293 to 333 K for both TiO2/lignin and TiO2-SiO2/lignin system. The values of the thermodynamic parameters, ΔH°, ΔS° and ΔG°, indicated the process thermodynamically favourable.