Plant sources mediated green synthesis of bismuth nanoparticles and its applications towards wastewater treatment

As nanoscience and nanotechnology have started a new era in modern science, nanomaterials are vastly used in various advanced research works along with other convenient purposes such as food processing, medicinal, leather, textile, chemical, pharmaceutical, research, soil engineering, wastewater treatment, cosmetics, electronics, space industries, and environmental science. Among the nanomaterials, Metal nanoparticles are the most suitable ones because of their tunable size and shape, large surface area and volume ratio, and highly active surfaces. From very old age, Bismuth has been used as a green element because of its lower toxicity. It is also highly abundant. As a result, Bismuth nanoparticles (BiNPs) have established a flourishing huge interest in various fields of modern science due to their unique properties such as high X-ray attenuation coefficient, less toxicity, large surface-to-volume ratio, and compact size. To avoid the chemical synthetic route, and costly instrumentations, green synthesis could be an expectative alternative to chemical synthesis for its eco-friendly behavior. In this study, orange peel, a mostly common, widely accessible, and redundant plant source in Bangladesh was utilized to synthesize crystalline BiNPs. In a typical procedure, bismuth salt was mixed with peel extract, and employed optimum conditions to get the desired product. The phytochemicals present in orange peel extract acted as a reducing and capping agent that emphasized the development of stable BiNPs. The obtained products were characterized by UV-visible, XRD, SEM, EDX, TEM, FTIR, and TG analytical techniques. In the UV-visible spectroscopic analysis, the surface plasmon resonance band shows at 272 nm which indicates the preliminary synthesis of BiNPs. Then, the Fourier transform infrared analysis reveals the functionality of different phytochemicals capped on the surface of BiNPs. The X-ray diffraction (XRD) pattern indicates the obtained BiNPs are crystalline with a rhombohedral phase having an average crystallite size of 15 nm. The Scanning Electron Microscope (SEM) image indicates the surface morphology, shape, and size of the synthesized BiNPs. Electron dispersive X-ray analysis confirms the elemental composition of the BiNPs. The surface morphology, shape, and size are further confirmed by the Transmission Electron Microscope (TEM) image. Moreover, electron microscopy analysis reveals that BiNPs are spherical having an average size of 32 n,m and poly-dispersed. After that, the Thermogravimetric analysis confirms the thermal stability and the presence of phytochemicals capped on BiNPs. The nanoparticles are capped with phytochemicals which makes them stable. A great potency was marked by the synthesized BiNPs in the reduction of organic dyes. As a model reaction, the obtained BiNPs were used as a nanocatalyst to reduce 4-nitrophenol (4-NP) in the presence of NaBH4 and 4- aminophenol (4-AP) forms on the contrary which is less toxic and safe. This process was monitored by the UV-Visible spectroscopic analysis. In the time dependence UV-visible spectra, the characteristic peak of 4-NP decreases gradually with time, and a new set of peaks appeared and started to grow at 300 nm. After 30 minutes, the characteristic peak of 4-NP completely disappeared which confirms the obtained BiNPs as an excellent nano-catalytic for the degradation of the organic dyes. Besides, BiNPs show a strong zone of inhibition against various bacterial strains, namely, Escherichia coli (ATCC- 8739), Staphylococcus aureus (ATCC-6538), Vibrio cholerae (ATCC-51394), Salmonella typhi (ATCC-1408), indicating excellent effectiveness of obtained BiNPs as an antibacterial agent. Therefore, effective wastewater treatment becomes a logical consequence of the green way. According to these studies, the obtained BiNPs can be used in agriculture, food safety, and other usage addressing their good medicinal properties. Finally, this green synthesis route can be a great plausibility to achieve the pinnacle in the environmental scope and modern nanoscience for its affordability and wastewater treatment features.

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