Biofabrication of iron oxide nanoparticles using manglicolous fungus Aspergillus niger BSC-1 and removal of Cr(VI) from aqueous solution

Superparamagnetic iron oxide nanoparticles (IONPs) (Fe3O4) of 20-40 nm size were successfully fabricated by using manglicolous (mangrove) fungus Aspergillus niger BSC-1 and utilized for the removal of hexavalent chromium from aqueous solution. The mycosynthesized IONPs were characterized using by UV-Vis spectroscopy, ATR-FTIR spectroscopy, Raman spectroscopy, XRD, electron microscopy (TEM and FESEM), zeta sizer and VSM. Batch experiment revealed the significantly (P < 0.05; two-way ANOVA and Tukey's multiple comparisons test) high Cr(VI) removal was at 40 degrees C and pH 3 with 2.5 g/L of IONPs dose. However, a significant (P < 0.05; two-way ANOVA and Tukey's multiple comparisons test) loss of Cr adsorption per g of IONPs was observed with an increase in adsorption dose indicating non-equivalence between iron and Cr molecule. The adsorption isotherm and kinetic model using Langmuir and pseudo-second order reaction respectively suggested monolayer adsorption of Cr onto IONPs surface. Presence of coexisting cations and anions did not exhibit any competitive effect on Cr(VI) removal revealing selectivity of mycosynthesized IONPs towards Cr(VI). Regeneration study confirmed that IONPs conserved their Cr(VI) removal efficiency with minimal loss (19.3%) after five adsorption/desorption cycles. Further, X-ray photoelectron spectroscopy indicated that both adsorption and redox reaction were involved in Cr(VI) detoxification. Therefore, the mycosynthesized IONPs could be utilized for heavy metal remediation from contaminated wastewater.