Biogenic iron oxide nanoparticles and activated sodium persulphate for hydrocarbon remediation in contaminated soil

Biogenic iron oxide nanoparticles synthesized from a locally sourced, readily available plant — Azadirachta indica, were used synergistically with sodium persulphate (PS) to degrade total petroleum hydrocarbons (TPHs) in contaminated soil. A chemometric approach to optimizing the conditions for the degradation of TPH was developed using central composite design (CCD). Characterization of iron oxide nanoparticles was carried out with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected electron area diffraction (SAED). Analysis of TPH was carried out with gas chromatography flame ionization detector (GC-FID). The optimum condition for the complete degradation of TPH was achieved at pH 6.0 and oxidant dosage of 0.74 M within 14 h and 5 days. Iron nanoparticles AZA FeNP (1:1) and AZA FeNP (2:1) were synthesized by varying the ratio of extract/precursor. The nanoparticles displayed heterogeneous, amorphous morphology with increased agglomeration in AZA FeNP (1:1). AZA FeNP (2:1) XRD spectra exhibited characteristic peaks at 27.0°, 35.4° and 44.5°, which are attributed to iron nanoparticles. TEM and HR-TEM images confirmed spherical nanoclusters’ presence with an average size of 9.3 and 10.0 nm for AZA FeNP (1:1) and AZA FeNP (2:1), respectively. The EDX spectra displayed intense peaks of oxygen, carbon, and iron at 0.4, 0.6 and 6.4 KeV confirming the presence of FeNP. Under optimized conditions, PS alone degraded 68% TPH while 0.07 and 0.15 g/L FeNP achieved ∼93 and 95% degradation, respectively. Additionally, 0.07 and 0.15 g/L FeNP-activated PS achieved ∼99 and 100% TPH degradation, respectively. The outcome of these findings suggests that FeNP synthesized using A. indica successfully catalyzed PS for complete degradation of TPH in crude oil-contaminated soil.