Novel in-situ synthesis of nano-silica (SiO2) embedded into polyvinyl alcohol for dye removal: Adsorption and photo-degradation under visible light

Water pollution (especially from dye stuffs) has been considered one of the most dangerous issues that threaten human health. Therefore, the polyvinyl alcohol/silica (PVA/SiO2) nanocomposite films have been manufactured by the in-situ chemical reduction approach assisted with the casting technique for eliminating the dyes under the visible light. The in-situ reduction has been invited to reduce the tetraethyl orthosilicate (TEOS) to SiO2 through the interaction between the TEOS and the activated (-OH group) of PVA at 65 +/- 2 degrees C. The benefit of the in-situ method is reflected in the well distribution of silica (SiO2 similar to 27.58 +/- 2 nm) inside the PVA matrix. The X-ray results reveal the reduction in the crystallinity of the films as a result of reduction in the hydrogen bonding due to the consumption of (OH groups) of PVA during the reduction reaction to produce SiO2. Tensile strength and Young's modulus as mechanical functions of the PVA/SiO2 have shown a tendency to increase with increasing the SiO2 amount. A significant change in the absorption spectra is observed due to the formation of the silica nanoparticles which is reflected in decreasing the energy gaps by increasing the SiO2 amount. The refractive index has been evaluated by the becke line method, showing an increase in its value with SiO2 amount. The applicability of the PVA/SiO2 for removing the methylene blue (MB) and methyl orange (MO) dyes from the wastewater has been studied under the visible light (VL) irradiation. Importantly, the experiments show that the high adsorption of MB and MO on the PVA/SiO2 with removal efficiency similar to 84.97% and similar to 39.94%, respectively, in a dark (Light OFF) in 30 min. Interestingly, the photodegradation efficiency has been found to be (98.87% for MB) and (82.66% for MO) under a visible light (light ON) in 50 min. The PVA/SiO2 reusability test shows that high stable and reusable films for the 5(th) cycle with reducing by 4% of its efficiency at the 6(th) cycle. As a result, these PVA/SiO2 films can be functionalized in the purposes of water purification, dye removal and in environmental cleaning.