Floating TiO2-Cork Nano-Photocatalysts for Water Purification Using Sunlight

Abstract

In the present study, titanium dioxide (TiO2) nano-photocatalysts were synthesized through microwave irradiation. In a typical microwave synthesis, TiO2 nanomaterials were simultaneously produced in powder form and also directly covering cork substrates. The TiO2 nanopowder was analyzed by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM), revealing that the solvothermal microwave synthesis resulted only in the TiO2 anatase phase. From Fourier-transform infrared spectroscopy (FTIR), cork’s organic species, along with bands of TiO2, were detected. UV–VIS absorption spectrum revealed an absorption extension to the visible region, since a brown powdered TiO2 product was obtained. Very fine nanoparticles were observed displaying a nearly spherical shape that agglomerates in larger particles. These larger particles fully covered the surface of the honeycomb cork cells, originating TiO2 functionalized cork platforms. The TiO2 functionalized substrates were further tested as floating photocatalysts and their photocatalytic activity was assessed from rhodamine B degradation under solar simulating light and natural sunlight. Reusability tests were also performed under natural sunlight. The strategy applied in this research work allowed the production of green and low-cost cork platforms based on TiO2 photoactive materials with the ability to purify polluted water under natural sunlight.

Microwave Synthesis of Visible-Light-Activated g-C3N4/TiO2 Photocatalysts

“…In accordance with the SEM results, it can be observed that the g-C 3 N 4 sheets are covered with TiO 2 nanostructures—however, not forming a continuous film—and larger agglomerates are also detected ( Figure 4 a–f) but, as observed previously, are expressively smaller than those for the pure TiO 2 material. As reported in an analogous study [ 86 ], it can be seen that these agglomerates are formed by very fine TiO 2 nanoparticles with irregular shapes, where near spherical nanocrystals and more elongated ones can be observed ( Figure 4 g–i). The average TiO 2 particle size was found to be 5.17 ± 1.37 nm, and it can be seen from the particle size distribution (inset of Figure 4 d) that smaller particles in the range of 4–7 nm are more likely to be found.…”

“…After this time, a transparent solution could be observed ( Figure S3f ). The MO degradation ratio (%) was calculated based on Equation (2): where is the initial absorbance of the MO solution before irradiation, and is the absorbance of the MO solution after a certain exposure time (t) [ 23 , 78 , 86 , 113 , 114 ]. Based on Figure S3a–e , it is possible to calculate the ratio between the maximum value of each absorbance spectrum ( ) at each exposure time and the initial absorbance of the solution ( ), as depicted in Figure 10 a.…”

“…As shown in Figure 10 a, MO degradation without the catalyst was insignificant in the dark and under solar simulating light, which indicates that the MO solution is highly stable under light exposure cycles. In fact, a slight increase in MO intensity is observed over time, likely associated with the evaporation of the solvent [ 86 ].…”

“…Regarding the effect of particle size, large TiO 2 aggregates composed of nanocrystals were obtained (with an average size of ~543 nm, as confirmed by SEM). It is well known that larger particles possess lower specific surface area and surface-to-volume ratio [ 86 ]. In spite of that, some hollow spheres were also observed ( Figure 3 b), providing more active sites for photocatalytic reactions.…”

“…In Equation (3), is the photodegradation apparent rate constant (min −1 ), t is the time (min), is the initial concentration (mg/L), and C is the concentration at a certain time (mg/L) [ 86 , 114 ].…”