Fabrication of n-type SnO2 nanofibers and improvement of their photocatalytic properties

Photocatalysis is considered to be one of the important technologies that can be utilized in the solution of environmental problems such as wastewaters and air pollution. n-type semiconductor tin dioxide (SnO2) is used in various photocatalysis-based applications like removal of toxic chemicals and organic pollutants from wastewater, thanks to its high oxidation capacity. In this thesis study, process optimization studies were carried out on SnO2 nanofiber production using electrospinning method, since nanofiber form exhibits high surface area, high interaction with light and high electrical charge mobility. Experimental results indicated that among the varying amount of Sn-source, the nanofiber samples with 1.2 g source had the optimum morphological characteristics. The photocatalytic behavior of SnO2 suffers from (i) its wide band gap, (ii) high recombination rate of electron-hole pairs, and (iii) lack of mechanisms for the migration of charge carriers toward the semiconductor surface. Elimination of these limitations, and as a result improving the photocatalytic activity of SnO2, is another aim of this study. For this purpose, SnO2 nanofiber surfaces were decorated with particles of oxides, exhibiting different electronic properties, in order to obtain heterostructured photocatalysts. These oxides were (i) semiconductor CuO with narrow band gap, (ii) delafossite CuCrO2 with p-type electrical conductivity and high optical transparency, and (iii) perovskite PMN-PT (Pb(Mg,Nb)O3-PbTiO3) with electrical polarization potential which in turn could effectively separate the charge carriers. Structural, morphological, optical, and electrical properties of pure SnO2 and heterostructured photocatalysts were characterized using XRD, SEM, TEM, XPS, UV-Vis, and Potentiostat/Galvanostat electrochemical system. Photocatalytic activity was evaluated by degrading methylene blue (MB) dye in wastewater samples. Effect of the amount of CuO, CuCrO2, and PMN-PT particles in heterostructured photocatalysts on the photocatalytic performance was studied systematically. Heterostructures with highest photocatalytic performance were obtained with compositions having 0.35 wt% CuO, 0.60 wt% CuCrO2, and 1.75 wt% PMN-PT. The degradation rate constants were 71%, 41%, and 82% higher for 0.35 wt% CuO, 0.60 wt% CuCrO2, and 1.75 wt% PMN-PT decorated nanofibers compared to the pure SnO2 nanofibers, respectively. Lastly, scavenger tests proved that the holes in both SnO2 nanofibers and heterostructured photocatalysts were the main active species in the photodegradation process, whereas the effect of superoxide and hydroxyl radicals were limited.