Structural and Photocatalytic Studies on Oxygen Hyperstoichiometric Titanium-Substituted Strontium Ferrite Nanoparticles
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abstract
Doping of ferrites is an important domain of research for their application as photocatalysts. In the present work, the effect of Ti4+ substitution on the structural and photocatalytic properties of strontium ferrite nanoparticles (NPs) is studied. Ternary doped Sr1xTixFe2O4+ ferrite NPs (x = 0.01.0) were synthesized by solgel methodology. Tetravalent Ti4+ ions caused oxygen hyperstoichiometry and enhancement in the surface area from 44.3 m2/g for SrFe2O4 NPs to 77.6 m2/g for Sr0.4Ti0.6Fe2O4+ NPs. The average diameter of NPs ranged between 2535 nm as revealed by TEM analysis. The presence of two sextets in the Mssbauer spectrum of pristine SrFe2O4 and Ti4+-substituted ferrite NPs and a paramagnetic doublet in the TiFe2O5 confirmed their phase purity. The photocatalytic potential of pure and Ti4+-substituted ferrite NPs was studied using nitroaromatic compounds, viz. pendimethalin, p-nitrophenol and Martius yellow, as model pollutants. Doped ferrite NPs with a composition of Sr0.4Ti0.6Fe2O4+ NPs showed the highest degradation efficiency ranging from 87.2% to 94.4%. The increased photocatalytic potential was ascribed to the lowering of band gap (Eg) from 2.45 eV to 2.18 eV, a fourfold decrease in photoluminescence intensity, increased charge carrier concentration (4.90 1015 cm3 to 6.96 1015 cm3), and decreased barrier height from 1.20 to 1.02 eV. O2 radicals appeared to be the main reactive oxygen species involved in photodegradation. The apparent rate constant values using the LangmuirHinshelwood kinetic model were 1.9 102 min1, 2.3 102 min1 and 1.3 102 min1 for p-nitrophenol, pendimethalin and Martius yellow, respectively. Thus, tuning the Ti4+ content in strontium ferrite NPs proved to be an effective strategy in improving their photocatalytic potential for the degradation of nitroaromatic pollutants.
