An Environmentally Benign Green Approach for the Reduction of Graphene …
375
2 Experimental
2.1 Materials
All chemicals were of analytical grade and were used without further purification.
Natural graphite flakes (LobaChemie) were used as the precursor for GO. Sulfuric
acid (about 98%), hydrochloric acid (about 37%), and hydrogen peroxide (about
35%) were purchased from Merck. Potassium permanganate (KMnO 4 ) (Merck) was
used as an oxidizing agent during the preparation of GO. Apples were purchased
from a local market in Jadavpur, India.
2.2 Synthesis of GO
In the synthesis of GO the modified Hummers’ method (Hummers and Offeman
1958), a weighed amount of natural graphite flakes was dissolved in concentrated
H 2 SO 4 in a round bottom flask placed in an ice bath at 0–5 °C (ice bath). Measured
quantity of KMnO 4 was added slowly to the magnetically stirred mixture to avoid
chances of explosion. The flask containing the reaction mixture was then put in an
oil bath at 50 °C and stirred for 8 h, followed by the addition of deionized and stirring
for further 2 h. 35% H 2 O 2 was added dropwise to the mixture turning it brown to
bright yellow. The excess of manganese salts was neutralized using a dilute solution
of hydrochloric acid (5% v/v). A brown colored dispersion of GO was obtained in
water. Finally, the GO dispersion was repeatedly washed using double distilled water
till the pH of the mixture became neutral.
2.3 Reduction of GO by Apple Juice
To remove impurities, the apples were first washed with double distilled water a
juicer (Bajaj Majesty 400-W Juice Extractor) was used to extract the juice. The juice
was twice filtered using 0.2 μm Whatman Filter paper. Finally, in order to remove
any heavy particles that may have still remained in the filtrate and centrifuged (Remi
R-8C plus) at room temperature at 6000 rpm for 7 min to use the supernatant as the
reducing agent. In a typical experiment, weighed amount of GO was dispersed in
double-distilled water and exfoliated using an ultrasonic bath (Labman Instruments)
which exhibited stability over a long time period. For reduction, fixed volumes of the
exfoliated GO dispersion and apple extract taken in a round bottom flask were placed
in an oil bath and refluxed at 90 °C while being continuously stirred at 350 rpm for
48 h. Visible changes in the color from the brown color of GO dispersed in water
to black marked the end of the reaction. The product was washed copiously using
375
2 Experimental
2.1 Materials
All chemicals were of analytical grade and were used without further purification.
Natural graphite flakes (LobaChemie) were used as the precursor for GO. Sulfuric
acid (about 98%), hydrochloric acid (about 37%), and hydrogen peroxide (about
35%) were purchased from Merck. Potassium permanganate (KMnO 4 ) (Merck) was
used as an oxidizing agent during the preparation of GO. Apples were purchased
from a local market in Jadavpur, India.
2.2 Synthesis of GO
In the synthesis of GO the modified Hummers’ method (Hummers and Offeman
1958), a weighed amount of natural graphite flakes was dissolved in concentrated
H 2 SO 4 in a round bottom flask placed in an ice bath at 0–5 °C (ice bath). Measured
quantity of KMnO 4 was added slowly to the magnetically stirred mixture to avoid
chances of explosion. The flask containing the reaction mixture was then put in an
oil bath at 50 °C and stirred for 8 h, followed by the addition of deionized and stirring
for further 2 h. 35% H 2 O 2 was added dropwise to the mixture turning it brown to
bright yellow. The excess of manganese salts was neutralized using a dilute solution
of hydrochloric acid (5% v/v). A brown colored dispersion of GO was obtained in
water. Finally, the GO dispersion was repeatedly washed using double distilled water
till the pH of the mixture became neutral.
2.3 Reduction of GO by Apple Juice
To remove impurities, the apples were first washed with double distilled water a
juicer (Bajaj Majesty 400-W Juice Extractor) was used to extract the juice. The juice
was twice filtered using 0.2 μm Whatman Filter paper. Finally, in order to remove
any heavy particles that may have still remained in the filtrate and centrifuged (Remi
R-8C plus) at room temperature at 6000 rpm for 7 min to use the supernatant as the
reducing agent. In a typical experiment, weighed amount of GO was dispersed in
double-distilled water and exfoliated using an ultrasonic bath (Labman Instruments)
which exhibited stability over a long time period. For reduction, fixed volumes of the
exfoliated GO dispersion and apple extract taken in a round bottom flask were placed
in an oil bath and refluxed at 90 °C while being continuously stirred at 350 rpm for
48 h. Visible changes in the color from the brown color of GO dispersed in water
to black marked the end of the reaction. The product was washed copiously using