Synthesis of visible light-responsive cobalt-doped TiO2 nanoparticles with tunable optical band gap

Abstract

Visible light-responsive photocatalysts are the most promising candidates for green bioremediation processes that will degrade toxic organic industrial waste into harmless compounds. Among the photocatalysts, TiO 2 is best suited for large-scale photo-induced bioremediation processes mainly because of low cost and abundance. The major obstacle in its utilization as photocatalyst is its poor response to sunlight due to its wide energy band gap. This article reports sol-gel synthesis of pristine and cobaltdoped TiO 2 nanoparticles (TNPs). Titanium (IV) isopropoxide is hydrolyzed and condensed into amorphous titanium dioxide gel by water/ethanol under acidic conditions. Irrespective of the Co concentration, TNPs always crystallize into anatase phase when calcine at 500°C. No signature of other isomorphous phases, i.e., rutile or brookite, is detected. The optical band gap of pristine (0 % Co doped) TNPs is 3.03 eV (k = 409 nm), which decreases up to 1.93 eV (k = 642 nm) when Co concentration in TiO 2 matrix increases from 0 to 2 %. Co(?2) substitution at Ti(?4) site generates additional oxygen vacancies in the TiO 2 unit cell, which introduces extra energy levels in the forbidden band that reduces the indirect energy band gap of TNPs. Co doping in TNPs makes them sensitive to visible radiation, and hence, their photoresponse is expected to be better under sunlight than pristine bulk titania, which is active only in the UV region of the electromagnetic spectrum. Graphical Abstract

UV/Vis Light Induced Degradation of Oxytetracycline Hydrochloride Mediated by Co-TiO2 Nanoparticles

“…As could be seen, Co-TiO 2 -R exhibited band gap energy, which apparently decreased up to 2.93 eV, possibly because of the generation of Co-3d defect states near the valence band maximum of TiO 2 -R, as shown in the inset of Figure 3b, whereas the cobalt doping using hydrothermal synthesis does not affect significantly the band gap of TiO 2 -HT with a value of 3.03 eV for Co-TiO 2 -HT. This narrowing of the energy band gap of Co-TiO 2 has been also observed by the authors of [59], Choudhury [48], and Khurana, et al [49], and was explained by the introduction of new impurity states near the valence band edge of TiO 2 . It can be concluded from these results that Co 2+ -doping employing reflux synthesis results in a remarkable decrease in the band gap of TiO 2 and a red shift of the absorption onset within the visible spectrum, leading to much greater electrons and holes generation, which could migrate to the surface to drive redox reactions with the adsorbed pharmaceutical.…”

“…Among various transition metals (i.e., Pt, Ag, Au, Ru, and Pd) [28][29][30][31] and transition metal oxides (i.e., Cu 2 O, α-Fe 2 O 3 ) [32][33][34], cobalt [35,36] and cobalt oxides [37][38][39][40] as an interesting low-cost and earth-abundant mineral have attracted tremendous attention for the development of visible light active TiO 2 materials. Cobalt-doped TiO 2 photocatalysts have been synthesized by various methods, such as the sol/gel technique [36,[41][42][43][44][45][46][47][48][49][50], hydrothermal treatment [51][52][53][54], impregnation method [55,56], precipitation process [57] for the photocatalytic degradation of methylene blue [57,58], rhodamine B [58], methylene orange [57], phenol [41], 2-chlorophenol [41], and so on.…”

Shaped Co2+ doped TiO2 nanocrystals synthesized from nanotubular precursor: Structure and ferromagnetic behavior

“…Upon substitution of Ti 4+ ions by Co 2+ , the electrons in the d orbital of Co 2+ will undergo repulsion by the electrons of the six surrounding oxygen atoms which results in the splitting of d orbital of Co 2+ . Appearance of these transitions in the spectra of doped TiO 2 nanoparticles is an indication of incorporation of Co 2+ ions in TiO 2 lattice [43,47,48].…”

MOFs based on the application and challenges of perovskite solar cells

“…Due to Co doping, the charge transport resistance (RTRANS) and charge recombination resistance (RREC) is significantly reduced, and the dopant promotes electron transport and eases electron-hole recombination. These results are attributable to the internal and surface morphological rearrangement obtained by the thermal decomposition of the MOF template, and the improvement of electron transport caused by Co doping (Biswajit and Amarjyoti, 2012;Khurana et al, 2015).…”