PDF Publication Title:
Text from PDF Page: 006
478 D. PATRA AND R. EL KURDI Yet, it was found that the stability of the Au NPs increases, and the inhibition of aggregation is achieved where surfactants are added. For this reason, several researchers tend to prepare Au NPs using curcumin as a reducing agent and specific surfactant as a stabilizing agent. El Kurdi et al. were able to prepare gold nanoparticles with different shapes and sizes using curcumin as a redu- cing agent and several surfactants, under different reac- tion parameters. First of all, El Kurdi et al. (62,63) have prepared gold nanoparticles solution using curcumin and cucurbit[7]uril as a stabilizing agent in neutral media. They were able to form Au NPs solution contain- ing two different shapes: spheres and rods in the size range of 10–20 nm. The effect of curcumin as a reducing agent was obvious when preparing Au NPs without curcumin, where in the absence of curcumin the solution color changed from orange to pale gray after 24 h. However, in the presence of curcumin after 24 h, the color solution changed to dark gray. In the absence of curcumin, after centrifugation, the precipitation yield was almost 10% indicating that Au3+ was totally reduced to Au0. Yet, in the presence of curcumin, the yield of the reaction was increased remarkably, where after centrifuging the pre- cipitate was obtained in high yield (see Figure 4). Cucur- bit[7]uril in this case acted as a host molecule to protect the formed Au NPs from aggregation. Later on, El Kurdi et al. (54,64) have established new gold nanoparticles using curcumin and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethyl- ene glycol) as stabilizing agent (F-108) in neutral media. El Kurdi et al. in their work have summarized the preparation of gold nanoparticles in six steps (see Figure 5): The authors have demonstrated the role of curcumin as a reducing agent to reduce Au3+ to Au0 in this way. The reduction began with the formation of Cur3- when the hydrogen atom from the hydroxyl group of the enolic curcumin is dissociated. When Cur3- is formed, the electron on the O- ion enhanced the reduction of Au3+ to Au0. Therefore, Au0 atoms will form clusters that undergo cleavage and form small fragments pro- tected with F108 polymer. Moreover, the authors were interested in studying the effect of curcumin concen- tration during Au NPs synthesis. According to their analy- sis, the results showed that the size of the nanoparticles depends strongly on the amount of curcumin added during the synthesis. For example, when adding 1 and 5 mM of curcumin, Au NPs were obtained in different shapes with diameters between 120–140 nm and 100– 120 nm, respectively. In addition, at 50 mM of curcumin, Au NPs in spheres shape were formed with a size range between 30 and 40 nm. However, when adding 10 mM of curcumin, smaller spheres were obtained with a size range between 10 and 20 nm. Hence, in all cases, curcu- min has reduced Au3+ to Au0. Thus, different sizes were obtained. This difference is due to the fact that at low con- centration, the density of the functional groups of curcu- min molecule is low; therefore, the clusters formed did not undergo the cleavage phase, and thereby, the par- ticles remain big. Although at a high concentration of cur- cumin, the solubility of curcumin decreased, this leads to the precipitation of curcumin in the solution, inhibiting the formation of smaller nanoparticles. Thus, a medium concentration of curcumin (10 mM) induced the for- mation of small and stable Au NPs. Another type of polymer was used by Al Shehab et al. in order to produce Au NPs in the presence of curcumin (21). Al Shehab et al. have used poly(ethylene glycol) methyl ether thiol polymer (mPEG thiol). As mentioned before, curcumin in solution depends strongly on the pH of the media. Meaning that, in acidic and neutral media, curcumin is present in bis-keto form. Therefore, curcumin is considered a proton donor. Yet, in basic media, curcumin acts as an electron donor since it exists as an enolate form where the heptadienone chains predominate (38). For this reason, the authors were interested in studying the effect of pH on the Au NPs synthesis using curcumin as a reducing agent. Therefore, four different pHs (4, 7, 10, and 13) were studied by Al Shehab et al. to investigate their effect Figure 4. Synthesis of Au NPs with and without curcumin.PDF Image | Curcumin as a novel agent for metallic nanoparticles
PDF Search Title:
Curcumin as a novel agent for metallic nanoparticlesOriginal File Name Searched:
Curcumin-nanoparticles.pdfDIY PDF Search: Google It | Yahoo | Bing
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
Heat Pumps CO2 ORC Heat Pump System Platform More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)