Photocatalytic activity of hyperbranched polyester/TiO2 nanocomposites

TiO2 nanowires (NWs) were prepared by hydrothermal treatment of TiO2 nanoparticles in alkaline medium, while hyperbranched polyester HPES-OH was prepared by polycondensation. Chemical structure of HPES-OH was confirmed by 1H and 13C NMR spectroscopy, FTIR and the molar mass was determined using gel permeation chromatography (GPC). Nanocomposites based on HPES-OH and TiO2 NWs are synthesized either by ex situ method or by in situ technique. Formation of the nanocomposites and investigation of their morphology were done using transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD). Photocatalytic activity of the synthesized nanocomposites compared to that of pure TiO2-NWs was studied. The chemical oxygen demand (COD) analysis confirmed the mineralization of wastewater via photocatalytic degradation. The results showed that not only photocatalytic activity of nanocomposites was much higher than that of the pure TiO2-NWs, but also the degradation time was reduced to large extent. This result can be attributed to reduction of the crystallite size produced due to the modification reaction. Durability of HPES-OH/TiO2 nanocomposites was investigated and the results confirmed that utilization of the modified TiO2-NWs in the second run was favorable, which suggests that strong adhesion between the NWs and HPES-OH was achieved through the formation of 2D structure.