Abstract
Nanocrystalline titania was synthesized by a simple, innovative and eco-friendly gelation method by using biopolymers (polysaccharides). The effect of the gelling agent, such as carboxymethylcellulose (CMC) or alginate (Alg), and the drying routes (conventional drying at room temperature, or freeze-drying) on the properties and photocatalytic performances of nanostructured TiO2 was examined. The crystallographic structures, and textural and morphological characteristics were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive spectrometry (ESEM-FEG-EDS), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and N2 adsorption/desorption isotherms. The as-synthesized samples were fully crystallized and appeared to be highly phase-pure anatase or mixed titania polymorphs, and have a quasi-spherical shape with a particle size ranging from 10.34 to 18.07 nm. Phase-pure anatase was obtained by using alginate as the gelling agent, whereas CMC's gelation promotes mixed structures. The presence of rutile phase results in a lower bandgap value of 3.04 eV corresponding to 408 nm. Thus, the material absorption wavelength shifts slightly from the UV (190–380 nm) to visible region (380–750 nm). The drying process also affects TiO2 properties. The lyophilization route improves the oxide's specific surface area, and also its photocatalytic properties verified during Orange G dye photodegradation study.
Highlights
The crystallographic structures, and textural and morphological characteristics were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive spectrometry (ESEM-FEG-EDS), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and N2 adsorption/desorption isotherms
We investigated the in uence of the gelling agent and the drying manner on the properties of titania
The lyophilization removes frozenwater via sublimation under vacuum. This can be achieved without the deformation of three-dimensional structure and synthesized via gelation of biopolymers: (a) CMC and (b) alginate
Summary
Titania (TiO2) stands out among the widely studied semiconductor materials.[1,2,3] In addition to its excellent physicochemical properties, chemical stability in a broad pH range and low cost, this oxide is environmentally benign.[2,3,4,5,6,7,8,9,10,11] TiO2 has many high-tech applications such as photocatalysis, batteries, super capacitors, sensors and drug formulations.[5,12,13,14,15,16,17,18] TiO2 occurs in four commonly known crystal forms: anatase, rutile, brookite and bronze.[19,20,21,22] Anatase and rutile both have tetragonal structures, whereas the brookite crystal system is orthorhombic, and bronze is monoclinic.[20,21,23] Anatase has a bandgap of 3.2 eV (385 nm), while the rutile phase has a smaller bandgap of 3.0 eV (410 nm).[3]. TiO2 performances closely related on the drying process used, which can directly impacted to oxide's porosity.[42] The possibility of preserving porosity and avoiding capillarity collapse, improves, amongst others, the material speci c surface area, and in some cases enhances its photoactivity.[42,43,44] To this end, exploring novel innovative technologies for well-controlled growth of titania, especially: its shape, its size, its morphology, its structure, and its speci c surface area, remains a challenge.[21,45,46] Eco-design and bioinspired methodologies for the nanostructured TiO2 preparation have of great importance due to the growing need for contemporary society to develop sustainable approaches.[46]. Mixed phases showed the highest activities, which is further improved by oxides obtained via the freeze-drying of hydrogel-beads
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