Enhancing the phase, thermal stability, band gap energy, and surface area of iron oxide nanoparticles by varying reducing agents and examining their efficacy in photocatalytic dye degradation

Iron oxide nanoparticles were synthesized using NaOH, NaBH 4 , and Calpurnia aurea leaf extract as reducing agents. XRD analysis confirmed the formation of hematite nanoparticles with rhombohedral structure when using NaOH and NaBH 4 as reducing agents, having the average crystallite size of 28.2287 and 21.86575 nm, respectively. The iron oxide nanoparticles synthesized using Calpurnia aurea leaf extract were maghemite with a cubic spinal structure having an average crystallite size of 21.69002, 21.09579, and 19.61541 nm with leaf extract to precursor ratios of 1:2, 1:1, and 2:1, respectively. The FT-IR analysis demonstrated the formation of Fe-O bonds between 460 and 550 cm -1 and around 570 cm -1 for hematite and maghemite nanoparticles, respectively. The optical band gap energy calculation from DRS analysis gave the indirect band gap energy of 1.32 and 1.14 eV and direct band gap energy of 1.62 and 1.55 eV for hematite nanoparticles synthesized using NaOH and NaBH 4 , respectively. For maghemite nanoparticles synthesized with the leaf extract, indirect band gap energies of 1.62, 1.57, and 1.66 eV and direct band gap energies of 2.09, 2.09, and 2.20 eV were calculated for leaf extract to precursor ratios of 1:2, 1:1, and 2:1, respectively. The TGA-DTA analysis confirmed the improved thermal stability of the maghemite nanoparticles synthesized using the leaf extract. The hematite nanoparticles synthesized with NaOH exhibited a total weight loss of 27.278% with three different endothermic peaks at 89.95, 31.79, and 650.79°C, while a weak endothermic peak was observed for hematite nanoparticles obtained using NaBH 4 at 94.25°C. For the maghemite nanoparticles synthesized using leaf extract, the maximum weight loss observed is 8.192% at a ratio of 1:1, while there are no endothermic or exothermic peaks observed for the three ratios. From the BET analysis, surface areas of 31.082 and 27.113 m 2 /g were calculated for hematite nanoparticles synthesized with NaOH and NaBH 4 , respectively, and 45.998, 52.743, and 56.243 m 2 /g were calculated for maghemite nanoparticles synthesized with leaf extract to precursor ratios of 1:2, 1:1, and 2:1, respectively. The photocatalytic malachite green degradation experiment indicates 98.944, 98.902, and 97.930% degradation efficiency at the optimized experimental parameters for maghemite nanoparticles synthesized with leaf extract and hematite nanoparticles synthesized with NaBH 4 and NaOH, respectively. The degradation of malachite green with the three photocatalysts fits first-order kinetics. • Leaf extract of Calpurnia aurea is found to be a good reducing and capping agent for the preparation iron oxide nanoparticles relative to NaOH and NaBH 4 • Thermal stability, surface area, and band gap energy enhanced when using the leaf extract • Two phases of iron oxide produced when the reducing agents varied • The synthesized nanoparticles were found to be good photocatalysts for dye degradation • The photocatalytic degradation of dye fits first-order kinetics • The leaf extract of Calpurnia aurea was found effective enough in equal or greater manner to the synthetic reducing agents