Size controlled green synthesis of gold nanoparticles using Coffea arabica seed extract and their catalytic performance in 4-nitrophenol reduction

Abstract

Well crystalline gold nanoparticles (AuNPs) of different sizes were fabricated using sundried Coffea arabica seed (CAS) extract at room temperature by controlling the pH of the green extract. The size, shape and crystallinity of the nanoparticles have been studied using electron microscopy and X-ray diffraction. The presence of phenolic groups (revealed through FT-IR studies) from the CAS extract are responsible both for the reduction of Au ions and stabilization of the formed AuNPs. The efficiency of the CAS extract mediated green synthesis technique for the production of AuNPs has been compared to the conventional chemical Turkevich technique, which not only uses a toxic reductant such as NaBH 4 , but also operates around the boiling point of water. It has been observed that the CAS extract mediated synthesis process produces relatively bigger AuNPs at similar pH values of the reaction mixture in comparison to the AuNPs produced in the Turkevich process. Although the AuNPs synthesized using CAS extract are relatively larger and polydisperse in nature, their catalytic efficiencies for the degradation of an aromatic nitro compound (4-nitrophenol) are found to be comparable to the chemically fabricated AuNPs. Probable mechanisms associated with the formation of AuNPs and their size control in the CAS extract mediated green synthesis process have been discussed. Fig. 2 Typical SEM images of GAuNPs (left column) and CAuNPs (right column) synthesized at different pH values of the reaction mixture. Insets show histogram reflecting the size dispersion corresponding to each pH; average size of the NPs vs. number of particles. 24822 | RSC Adv., 2018, 8, 24819-24826 This journal is

Green biosynthesis of gold nanoparticles using Chenopodium formosanum shell extract and analysis of the particles' antibacterial properties

“…The peaks at 1388.62 and 1308.32 cm −1 were attributed to the in‐plane bending of the O–H groups, and the peak at 1046.69 cm −1 was attributed to C–O bond stretching vibrations . The –C=O stretching and –OH stretching bands corresponded to the phenolic compounds …”

“…The red color of the aqueous extract faded in the supernatant of the centrifuged Au NPs solution (Fig. (a)), indicating that the pigment contributed to reduction of Au 3+ ions and stabilization of the formed Au NPs . Djulis contains a large amount of betanin and can serve as a reducing and stabilizing agent for the synthesis of Au NPs .…”

“…29 The -C=O stretching and -OH stretching bands corresponded to the phenolic compounds. 30 As represented in Fig. 8(b) line 2, the spectrum of Au NPs exhibited weaker bands than did that of the freeze-dried Djulis shell extract.…”

“…2 The bacterial strains culture solution grown at 37 ∘ C for 24 h was adjusted to 1 × 10 6 CFU mL −1 in Luria-Bertani broth. Subsequently 4 mL bacterial broth solutions were mixed with 1 mL of 40 μg mL −1 streptomycin solution (positive control), 1 mL Au NPs solutions of various concentrations (10,20,30, and 90 μg mL −1 ), or no antimicrobial substance (negative control) and incubated at 37 ∘ C for 18 h. The resultant reactions were observed at an optical density of 600 nm using a microplate reader spectrophotometer (Power wave X340, Bio-Tek, Winooski, VT, USA) in a 96-well microtiter plate. 2 The inhibition ratio (%) of bacterial strains was calculated using Eqn (1) 22 :…”

“…8(a)), indicating that the pigment contributed to reduction of Au 3+ ions and stabilization of the formed Au NPs. 30 Djulis contains a large amount of betanin and can serve as a reducing and stabilizing agent for the synthesis of Au NPs. 21,31 The proposed mechanism of Au 3+ conversion into Au NPs is shown in Fig.…”