Olibanum Lab Report

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3.7 Homogeneous Catalytic reduction of 4-nitrophenol
To investigate the redox catalytic activities of the synthesized AuNPs using the olibanum gum, we selected a well-known catalytic reaction the transformation of 4-NP to 4-AP by sodium borohydride (NaBH4) as a model reaction and the reaction was monitored using UV–visible spectroscopy. The absorption peak of 4-NP undergo red shift from 317 nm to 400 nm immediately after addition of NaBH4, corresponding change in the colour of the solution from yellow to intense yellow was observed due to the formation of 4-nitrophenolate ions under alkaline conditions. This peak at 400nm remained unaltered for many days in the absence of AuNPs. This indicates the inability of NaBH4 itself to reduce directly
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The activation energy was calculated from the slope (Ea/RT) by linear plot of ln k on l/T, using the Arrhenius equation k = ln A- Ea/RT, where k is rate constant of the reaction at temperature T (in Kelvin), A is a constant and R is the universal gas constant. The catalytic reduction of 4-NP was studied at six different temperatures (25, 30, 35, 45, 55, 65 and 70oC) using olibanum gum capped AuNPs as catalyst. A linear relationship was found between ln k and the reciprocal temperature from which the activation energy was measured. A plot of ln k versus 1/T, shown in Figure. 10, is a linear curve for 4-NP reduction using AuNPs. It was observed that the increase in temperature helps the rate of reaction to increase. The activation energy was calculated from the slope of the straight line and was found to be 7.4 ± 1.34 k Cal/mol. The above results are of clear indication that catalysis usually takes place on the surface of the nanoparticles.
3.8 Catalytic reduction of potassium hexacyanoferrate (III)
The electron transfer reaction between hexacyanoferrate (III) and sodium borohydride results in the formation of hexacyanoferrate (II) ion and dihydrogen borate ion and this reaction is strongly catalyzed by AuNPs. The redox reaction is described as BH4- + 8 [Fe (CN)6]3-
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The synthesis was carried out in an aqueous medium by microwaves using olibanum gum (Boswellia serrate) as a reducing and stabilizing agent without using any harsh, synthetic reducing agents. The greener synthesis of olibanum gum capped AuNPs was found to be eco-friendly due to the utilization of renewable plant material. The amount of gum and irradiation time effect the formation of NPs. Microwave irradiation can accelerate the formation of NPs and as the concentration of gum increases, the particle size decrease. The designed olibanum gum capped AuNPs are highly stable, and have shown effective catalyst in the reduction of 4-NP to 4-AP and electron transfer reaction between K3[Fe(CN)6] and NaBH4. The detailed kinetic features of catalytic reaction was evaluated by changing the reaction conditions. It is also observed that as the catalyst amount increases the reaction temperature, the rate of the reaction increases and reaction time

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