Jaspreet Kaur Grewal

The journal retracts the article titled “Structural and Photocatalytic Studies on Oxygen Hyperstoichiometric Titanium-Substituted Strontium Ferrite Nanoparticles”

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 Sr_1−xTi_xFe₂O_4+δ ferrite NPs (x = 0.0–1.0) were synthesized by sol–gel 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 Sr_0.4Ti_0.6Fe₂O_4+δ NPs. The average diameter of NPs ranged between 25–35 nm as revealed by TEM analysis. The presence of two sextets in the Mössbauer 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 Sr_0.4Ti_0.6Fe₂O_4+δ 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 (E_g) from 2.45 eV to 2.18 eV, a fourfold decrease in photoluminescence intensity, increased charge carrier concentration (4.90 × 10¹⁵ cm⁻³ to 6.96 × 10¹⁵ cm⁻³), 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 Langmuir–Hinshelwood kinetic model were 1.9 × 10⁻² min⁻¹, 2.3 × 10⁻² min⁻¹ and 1.3 × 10⁻² min⁻¹ 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.

The synthesis of carbon quantum dots (CQDs) from agricultural waste is a promising approach for waste valorization. In the present work, CQDs were synthesized using sugarcane bagasse as a carbon precursor. The nanocomposite of CQDs with trimetallic strontium–titanium ferrite was synthesized with an ultrasonication approach. The structural, magnetic and optical features of the synthesized nanocomposite and pristine NPs were studied using different analytical techniques. The TEM micrograph of the nanocomposite reveals the distribution of CQDs (8–10 nm) along with the agglomerated ferrite NPs. To validate the results, the photocatalytic efficiency of the nanocomposite, NPs and CQDs was comparatively studied for the photodegradation of nitroaromatic pollutants viz. p-nitrophenol, martius yellow and pendimethalin under visible-light irradiation. A nanocomposite having a 2:1 w:w ratio of CQDs and Sr_0.4Ti_0.6Fe₂O_4.6 displays an excellent photocatalytic performance, with the degradation efficiency ranging from 91.2 to 97.4%, as compared with 65.0–88.3% for pristine NPs and CQDs. These results were supported by band gap and photoluminescence analyses. The promising photocatalytic potential of the nanocomposite over the pristine CQDs and ferrite NPs could be ascribed to the increased specific-surface area (101.3 m²/g), lowering in band gap coupled with fluorescence-quenching which facilitated the transfer of photoinduced charge carriers. The impact of parameters affecting the photocatalytic process viz. pH, catalyst dose and contact time was also investigated. On the basis of quenching and gas chromatography-mass spectrometry (GC-MS) studies, plausible degradation pathways were proposed. The results highlight the broad potential of designing substituted ferrite-CQDs-based nanocomposites as reusable and visible-light-driven photocatalysts.