Exploring the potentialities of waste plant materials for the production of gold nanoparticles and multi-metallic composite particles and its application in wastewater treatment

Abagero, Wubshet Belay

http://hdl.handle.net/10400.1/10135

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Authors

Abagero, Wubshet Belay

Advisor(s)

Costa, Maria Clara

Dandlen, Anahi

Abstract(s)

Biosynthesis of metallic nanoparticles has been regarded as a green, environmentally friendly and efficient method for nanoparticles production that avoids the usage of toxic chemicals and generation of hazardous waste during the process. In this study we reported a green, facile and rapid biosynthesis method for the synthesis of gold nanoparticles (AuNPs) and multi-metallic composite particles using raspberry leave extract as both reductant and capping agent in a single-pot process. Various waste plant materials were collected from the Algarve region for extract preparation. The waste plant materials were selected based on the availability and the cost of the material. Reduction potential of each extract was determined using FRAP method. Optimization of the synthesis method (synthesis time and metal precursor concentration) was investigated to get the best synthesis conditions. Standard gold-(III) chloride solution for AuNPs and AMD wastewater from São Domingos mine site, southwest Portugal, for multi-metallic composite particles was used as source of the corresponding metal ions. The UV–Vis spectra showed a SPR peak at 560nm for the AuNPs that were synthesized using optimized synthesis conditions which were 15 min synthesis time, 100 mg/L gold-(III) solution concentration and 1:10 (v/v) extract to standard gold (III) solution ratio at room temperature. TEM images of the precipitates obtained from Au-(III) solution showed different shape and sizes which consist of spherical NPs (51–70 nm), along with few rods (71–80 nm), triangular (61-70 nm) and hexagonal (61-70 nm) particles. TEM images of multi-metallic composite particles revealed there were mostly composed of spherical particles with an approximate average size of 100 nm (range between 70-150 nm). In XRD pattern, the crystalline natures of the synthesized AuNPs showed sharp intense peaks of Bragg reflections corresponding to (111), (200), (220), (311) and (222) planes at 2θ values of 38.20, 44.50, 64.70, 77.70 and 81.20, respectively, displays the crystalline nature of AuNPs and no other peaks were observed due to impurities. These planes are assigned to cubic structure of the AuNPs according to the high-Score Plus software with the ICDD PDF-2 database. The AuNPs were further characterized by Energy dispersive X-ray spectra (EDS) analysis, which gives additional evidence for the reduction of Au-(III) solution to elemental gold thus confirming gold as the only element in the precipitate. The EDS analysis for multi-metallic composite particles suggested that the particles are mainly composed by iron, aluminum and copper, probably as oxides. The stability of AuNPs and multi-metallic composite particles were measured using zeta potential and both particles showed moderate to good stability at different pH range and lower stability at pH 1 and pH 2. The application of the synthesized multi-metallic particles as adsorbent was tested for the removal of phosphate from synthetic wastewater and it showed up to 70.0 ± 3.9 % removal efficiency. In conclusion, in this study suitable, eco-friendly, nontoxic, and single pot synthesis method was developed for the production of AuNPs and multi-metallic composite particles using raspberry leave extract. This study also revealed the potential utilization of acid mine drainage wastewater as a source of multi-metallic composite particles which has proven efficiency to remove phosphate from wastewater via adsorption.