Catalytic effect of nickel oxide nanoparticles from Lupinus Albus extract on green synthesis and photocatalytic reduction of methylene blue: kinetics and mechanism

Abstract

Green synthesis of nanomaterials is advancing due to their ease of synthesis, cheapness, nontoxicity, and renewability. An environmentally friendly biogenic method has been developed for the green synthesis of nickel oxide nanoparticles (NiO NPs) using phytochemical-rich bioextract. They are rich in bioextract phenolics, flavonoids, and berberine. These phytochemicals successfully reduce and stabilize NiNO₃ into NiO NPs. In this study, NiO NPs were synthesized by the green synthesis method from Lupinus Albus. Characterization of NiO NPs was carried out by TEM, XRD, SEM, UV, XRF, BET, and EDX analyses. According to XRD analysis, TEM results also support this, where the NiO NPs particle size diameter is 5 nm. It was determined by the Tauc equation that the band energy gap of NiO NPs is 1.69 eV. It was determined that the BET surface area of NiO NPs was 49.6 m²/g. NiO nanoparticles synthesized from Lupinus Albus extract by the green synthesis method were used as catalysts in the photocatalytic reduction of methylene blue with NaBH₄. In the photocatalytic reduction of methylene blue with NaBH₄, it was determined that there was no color change in 48 h without a catalyst, and in the presence of NiO nanoparticle catalyst, methylene blue was reduced by 97% in 8 min. The kinetics of the photocatalytic reduction of methylene blue with NaBH₄ is a pseudo-first-order kinetic model and the kinetic rate constant is determined as 0.66 min⁻¹, indicating that the catalytic effect of NiO NPs is very high at this value. NiO NPs were used five times in the photocatalytic reduction of methylene blue with NaBH₄ and it was determined that the reduction of methylene blue was over 90% in each use.

Novelty statement

NiO nanoparticles were synthesized from Lupinus Albus extract by green synthesis, which is an easily applied, cost-effective, and environmentally friendly method. The synthesized NiO nanoparticles were characterized using various characterization techniques. NiO nanoparticles have a high catalytic effect in the photocatalytic reduction of methylene blue with NaBH₄. Photocatalytic reduction of methylene blue with uncatalyzed NaBH₄ could not be achieved, and 97% reduction of methylene blue was completed in 8 min in the presence of NiO nanoparticle catalyst.

Keywords:

• Kinetics
• methylene blue
• nickel oxide
• reduction
• sodium borohydride