Iron/titanium oxide-biochar (FeTiO/BC): A versatile adsorbent/photocatalyst for aqueous Cr(VI), Pb, F and methylene blue.

This is the first report of the metal Fe-Ti oxide/biochar (FeTiO/BC) composite for simultaneous removal of aqueous Pb, Cr, F and methylene blue (MB). Primary FeTiO nano particles and aggregates were dispersed on a high surface area Douglas fir BC (∼700 m/g) by a simple chemical co-precipitation method using FeCl and TiO(acac) salts treated by base and heated to 80 °C. This was followed by calcination at 500 °C. This method previously was used without BC to make the neat mixed oxide FeTiO, exhibiting a lower energy band gap than TiO. Adsorption of Cr(VI), Pb(II), fluoride, and MB on FeTiO/BC was studied as a function of pH, equilibrium time, initial adsorbate concentration, and temperature. Adsorption isotherm studies were conducted at 5, 25, and 45 ℃ and kinetics for all four adsorbates followed the pseudo second order model. Maximum Langmuir adsorption capacities for Pb, Cr, F and MB at their initial pH values were 141 (pH 2), 200 (pH 5), 36 (pH 6) and 229 (pH 6) mg/g at 45 ℃ and 114, 180, 26 and 210 mg/g at 25 ℃, respectively. MB was removed from the water on FeTiO/BC by synergistic adsorption and photocatalytic degradation at pH 3 and 6 under UV (365 nm) light irradiation. Cr, Pb, F, and MB each exhibited excellent removal capacities in the presence of eight different competitive ions in simulated water samples. The removal mechanisms on FeTiO/BC and various competitive ion interactions were proposed. Some iron ion leaching at pH 3 catalyzed Photo-Fenton destruction of MB. FeTiO, BC, and FeTiO/BC bandgaps were studied to help understand photocatalysis of MB and to advance supported metal oxide photodegradation using smaller energy band gaps than the larger bandgap of TiO for water treatment. A long range goal is to photocatalytically destroy some sorbates with adsorbents to avoid the need for regeneration steps.