Experimental study and modeling of photocatalytic reduction of Pb2+ by WO3/TiO2 nanoparticles

A pure nanocomposite photocatalyst was prepared from WO3/TiO2 using a modified sol-gel technique. The prepared material was characterized using XRD, SEM, BET and XPS. XRD results revealed the presence of anatase, rutile and tungsten oxide with a mass ratio of rutile to anatase of 58.1:41.9. SEM and XPS results demonstrated that the prepared nanocomposite particles have spherical shape with an average size of 7.6 nm when the percent loading of tungsten onto the surface of TiO2 nanoparticles was 2.7 wt%. BET isotherms showed a specific surface area and an average pore volume of 112 m(2)/g and 0.0248 cm(3)/g, respectively. Photocatalytic experiments for Pb2+ conversion into metallic atoms in synthetic aqueous solution revealed a reduction capacity of 52.2% when pure TiO2 was used in 50 mg/L of initial lead concentration. This percentage has increased to 74.7% when the catalyst was doped with 2.7 wt% WO3. This reduction capacity has increased with increasing the mass of the catalyst in the solution and with decreasing the initial lead concentration. Thermodynamic analysis showed that the interaction of Pb2+ onto the nanocomposite surface has an exothermic nature with an average Delta G of 14J/ mol K, Delta H of -4.5 J/mol K and Delta S of -65.3 J/mol K. A kinetic model was developed to simulate the experimental data. It was found that the reaction constant increases and reaches a maximum value of 3.95 x 10(-4) cm(2)/J with decreasing the kinetic parameters. However, the mass transfer coefficient showed an opposite trend, with an estimated maximum value of 8.24 x 10(-4) cm/s. (C) 2014 Elsevier B.V. All rights reserved.