Novel Sodium Alginate/Polyvinylpyrrolidone/TiO2 Nanocomposite for Efficient Removal of Cationic Dye from Aqueous Solution  
[PERSON]  
1 Advanced Technology and New Materials Research Institute (ATNMRI), City of Scientific Research and Technological Applications (SRTA-City), New Borg El-Arab City, Alexandria P.O. Box 21934, Egypt; [EMAIL_ADDRESS] (M.H.G. ); [EMAIL_ADDRESS] (M.S.E. ); [EMAIL_ADDRESS] (A.H.); [EMAIL_ADDRESS] (M.A.A.E.-L)  
2 Environment and Natural Materials Research Institute, City of Scientific Research and Technological Applications (SRTA-City), New Borg El-Arab City, Alexandria P.O. Box 21934, Egypt; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (M.A.E.-L)  
3 Center of Physics and Engineering of Advanced Materials (CeFEMA), Instituto Superior Tecnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
available with a low cost price, has high transparency to visible light, and can be activated with sunlight or UV radiation [12; 13]. The problem regarding the application on an industrial scale of TiO\({}_{2}\) nanostructures is the low adsorption of organic pollutants, uniform distribution of nanoparticles, and the sluggish separation and recovery of nanosized particles during the process of wastewater treatment. Supporting TiO\({}_{2}\) nanostructures on a polymeric matrix can overcome this difficulty. TiO\({}_{2}\) incorporated into a calcium (Ca)-alginate film matrix was used as a photocatalyst to remove methyl orange with 82.2% effectiveness after 120 min of UV irradiation [14]. ZnO and TiO\({}_{2}\) nanoparticles embedded into Ca-alginate beads were also used as a photocatalyst to remove copper ions [10]. By using cross-linked sodium alginate (SA) with TiO\({}_{2}\), forming a SA-TiO\({}_{2}\) hydrogel, an adsorption efficiency for methyl violet dye of 99.6% was reported, whereas SA-based film only achieved 85%. This effect was attributed to the electrostatic attraction between the methyl violet dye and TiO\({}_{2}\), which behaves as an anionic center in the hybrid hydrogel [15]. On the other hand, after two cycles of reuse, the SA-TiO\({}_{2}\) hybrid film was still effective in degrading Congo red under UV light, with no appreciable loss of catalytic activity [16]. Generally, adsorption-photocatalytic degradation of dyes is favored using TiO\({}_{2}\); however, a high concentration of dye solution can hinder the photocatalytic activity of TiO\({}_{2}\) due to its surface saturation. Besides, the dye molecules are prone to absorb light energy. As a result, the production of reactive oxygen species and hydroxyl radicals is reduced. SA is a brown seaweed-derived natural polysaccharide polymer. It is a non-toxic, biocompatible, and biodegradable polymer composed of two acids, namely \(\alpha\)-L-guluronic and \(\beta\)-D-mannuronic acid. SA is suitable for chemical modification and can be shaped as hydrogel beads by cross-linking the \(\alpha\)-L-guluronic acid units with poly- or divalent cations [17; 18]. It is frequently employed as a polymeric matrix that can support catalysts [10]. To overcome the natural polymer's drawbacks, such as microbial breakdown and low mechanical strength, SA was blended with synthetic polymers, including polyvinyl alcohol (PVA) [19], polyethylene glycol (PEG), and polyethylene oxide (PEO) [20]. The inclusion of active functional groups on natural and synthetic polymers in the polymeric network allows the hydrogel beads to be used efficiently as adsorbents as a result of the blending [21]. In this study, to improve the porosity of the produced beads, polyvinylpyrrolidone (PVP) was combined with SA as a natural pore-forming polymer [22]. In addition, TiO\({}_{2}\) nanotubes were incorporated into SA/PVP polymer matrix to yield novel SA/PVP/TiO\({}_{2}\) nanocomposite beads using calcium chloride (CaCl\({}_{2}\)) as the cross-linker. The main objective was to obtain a novel hybrid nanocomposite material having adsorption-photocatalyst activity by a simple, cheap, and efficient method.