Silica nanoparticles assisted photodegradation of acridine orange in aqueous suspensions

Silica nanostructured materials are often used as catalyst support but their catalytic role has not been deeply investigated yet. In the present study, the photocatalytic degradation of acridine orange zinc chloride double salt (AO) has been studied using silica nanoparticles (NPs) as catalysts. NPs of different size (55 and 146 nm) were prepared by a sol-gel procedure and their surface was modified with amino groups to investigate the role of the chemical groups linked to the silica surface on the dye degradation. The silica nanomaterials were fully characterized by use of transmission electron microscopy (TEM), zeta potential measurements and UV-vis spectrophotometric methods. The photodegradation experiments were carried out irradiating at 313 or 490 nm for 50 min the aqueous samples containing the dye and the silica NPs of 55 or 146 nm in diameter. The photocatalytic degradation of the dye was determined from the decrease of its fluorescence intensity. AO fluorescence intensity did not change when bare SiO2 beads were used as catalysts, whereas an efficient decoloration (up to 58%) was achieved with amino functionalized NPs, with a photodegradation rate constant value of 0.136 m(-1). The data collected from the degradation experiments demonstrated that the functional groups on the silica surface have a fundamental role in the efficiency of the degradation processes. (C) 2015 Elsevier B.V. All rights reserved.