Photocatalytic degradation of Rhodamine-B by phytosynthesized gold nanoparticles

Solving environmental problems by nanoparticles synthesized from plant derivatives has been a prime focus of nanotechnology research. The objective of the present study was to synthesize biogenic gold nanoparticles (AuNP) with dye degradation properties. The influence of mixing ratio of flower extract to metal salt, metal salt concentration and reaction time on nanoparticle size were also explored and optimized for the AuNP formation. For synthesis, flower extract of Wedelia urticifolia was added to yellow-coloured gold solutions, and the appearance of cherry red colour in 2 h of contact time demonstrated the fabrication of AuNPs. The synthesized nanoparticles were characterized by UV–Vis spectroscopy, dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Consequently, the nanoparticles were also tested for dye degradation property against Rhodamine-B as a model dye. The strong UV–Visible spectrum peaks at 530–540 nm confirmed the gold nanoparticle synthesis. The DLS results showed the synthesis of the smallest-sized nanoparticles at a 1:1 volume ratio of 1 mM metal solution to flower extract. The FTIR results revealed that proteins and polyphenols help in the reduction and stabilization of synthesized nanoparticles. The XRD analysis indicated that the nanoparticles synthesized were pure and crystalline. Besides, the TEM images displayed spherical particles of size less than 20 nm. The sunlight-driven Rhodamine-B degradation experiments reveal that the dye degradation is dependent on nanoparticle dosage, contact time, as well as pH of dye solution, and more than 90% of dye degradation can be achieved with an AuNP dosage of 20 mg/10 ml of dye solution, pH 3, and a contact time of 15 min. Further, the synthesized nanoparticles can be reused for up to 4 cycles for dye degradation. Hence, the current study quantifies a sustainable and eco-friendly technology for producing AuNPs with fast Rhodamine-B degradation ability.