Examination of the doping effects of samarium (Sm3+) and zirconium (Zr4+) on the photocatalytic activity of TiO2 nanofibers

Pure and samarium (Sm3+) - or zirconium (Zr4+)-doped TiO2 nanofibers were synthesized by electrospinning method followed by calcination at 500 °C for 1 h. As-spun fibers were smooth, straight and continuous, whilst EDS analysis confirmed the fiber composition and incorporation of dopants in the fibers. Doping with Sm3+ and Zr4+ greatly inhibited the phase transformation of anatase to rutile, by surrounding of Sm3+ ions through formation of Ti-O-Sm bonds and by replacement of Ti4+ ions with larger Zr4+ ions. This was confirmed by HRTEM and SAED analysis. The size of nanofibers was determined to be 133 nm, 175 nm and 155 nm for pure, (0.5%)Sm3+:TiO2 and (1%)Zr4+:TiO2, respectively. After calcination, TiO2 crystal lattice with interplanar spacing of 0.353 nm of (101) crystal plane was not significantly disturbed by Sm doping whilst crystal lattice spacing of 0.357 nm of (101) planes of anatase phase in case TiO2:1.0%Zr4+, significantly differs from the value of pure TiO2 (0.352 nm), thus implying that Zr was doped into substitutional sites of the TiO2 lattice. The indirect band gaps were calculated to be in the range 3.07–3.24 eV. TiO2:0.5%Sm3+ and TiO2:1.0%Zr4+ exhibited higher specific surface area, of 47.1 and 59.4 m2/g, respectively, than pure TiO2 fibers (19.7 m2/g). Effects of Sm3+ and Zr4+ dopant content on the photodegradation efficiency of methylene blue (MB) were studied. TiO2:0.5%Sm3+ and TiO2:1.0%Zr4+ nanofibers have shown the highest photocatalytic activity of 97% and 98% with constant rates 0.01768 min−1 and 0.01939 min−1, respectively, within180 min irradiation under visible light.