Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Graphene oxide membrane synthesis, structural characterization and permeation properties were studied in this thesis. Three types of precursor graphite oxide were tested for membrane preparation: For this thesis membranes out of “Single Layer Hummers Graphite Oxide” (SL-H-GO), Hummers Graphite Oxide (H-GO) and Brodies Graphite oxide (B-GO) were synthesized and analyzed.
Main results of our studies can be summarized as following:
• The membranes were grown using solutions of these pristine materials by controlled filtering according to procedures described in ref. , . Similar to these earlier studies, membranes were prepared using Hummers graphite oxide. A new type of membrane was prepared using Brodie graphite oxide dispersed in solution in slightly alkaline solution.
• SL-H-GO solution was found to be not suitable for preparation of homogenous membranes. The H-GO membranes are less transparent then the B-GO membranes.
• Growth time is shorter for H-GO then for B-GO membranes under same conditions of deposition.
• XRD characterization shows that GO membranes consist of planar sheets stacked in parallel orientation. The ordering of these sheets is qualitatively similar to the one in pristine graphite oxide powders.
• However the (001)-d-spacing of freshly prepared membranes is slightly higher and decreases slowly under ambient conditions. After prolonged storing of the membranes for several weeks the interlayer spacing decreases to the value of pristine powder.
• For water immersed H-GO membranes the interlayer spacing increases similar to the spacing of pristine powder.
• When the H-GO membrane dries up the interlayer spacing decreases to the value of freshly grown membranes within several hours.
• During the process of heating membranes the interlayer-distance decreases within the first hour stronger than in the hours after.
• For ethanol vapour the H-GO and B-GO membranes are not or very little permeable, but for water vapour they are permeable.
• Water vapour permeates much faster through the H-GO membrane (like through an open hole) and about 6 times slower through the B-GO membrane.
• After heating for one hour at 145°C the H-GO membrane is not permeable also for water vapour.
• Tests with ethanol-water mixtures with over 75%vol ethanol show: Liquid ethanol water mixtures can permeate through the membrane. Both water and ethanol are able to permeate trough the membrane of ethanol, but permeation rate of water is faster.
• The difference between permeation rates of water and ethanol exposed to binary liquid mixture decreases for compositions with higher fraction of ethanol. Therefore, efficiency of ethanol purification by passing through the membrane decreases as the concentration of ethanol goes over ~90-95%.
• Possible application of H-GO membrane for ethanol purification was successfully demonstrated by achieving 99% purity. However, the process of separation is rather slow and significant loss of ethanol on the later stages of purification were observed.
It can be concluded that graphene oxide membranes are, in principle, suitable for purification of ethanol from ethanol/water mixtures. However, set of problems needs to be addressed for practical applications. Most important problems are following:
• permeation rates of liquid ethanol and water for water/methanol mixtures are not sufficiently different.
• membranes are not sufficiently stable when in contact with liquid water/ethanol mixture