NBEXP0014

=NBEXP0014 — High-resolution AFM imaging of graphene/TiO2=

=Objective=


 * 1) To obtain AFM images of TiO2 particles adhered to individual, single-layer graphene flakes.
 * 2) To determine the concentration of TiO2 particles on the graphene surface
 * 3) To determine the average size of the graphene flakes
 * 4) To determine the average height of the graphene flakes (1 layer, 2 layers, 3 layerss etc.)

=Procedure=


 * 1) Irradiate 0.7mg/mL and 4mg/mL solution under UV for 1 hr
 * 2) Take 1mL of irradiated solution and add to small sample tube, make up to 10mL with ethanol
 * 3) Sonicate solution for 10 min
 * 4) Take 1mL of sonicated solution and add to new small sample tube, make up to 10mL with ethanol
 * 5) Sonicate solution with horn probe for 2 min at amplitude 20
 * 6) Prepare fresh mica substrate by peeling off top layer with scotch tape
 * 7) Deposit 1 drop of horn-sonicated solution on mica
 * 8) Heat a hot plate to ~250 deg. Place sample on hot plate for 10 mim.
 * 9) After 10 min, remove sample & place in glass petri dish. Immediately transfer petri dish to vacuum chamber & leave overnight
 * 10) Remove sample from vacuum just prior to AFM imaging

=Results=

Almost all the material had agglomerated into small particles, ranging from 50 - 600nm in height and of various diameters. These particles were made up of smaller particles of about 40-50nm diameter. It was very difficult to individually identify individual graphene flakes; only one image was taken in which a graphene sheet was clearly visible. The rest are likely bound up within the large agglomerates.

The image of the graphene sheet shows the TiO2 particles to be bound to the outside of the sheet; few are embedded within the sheet. It is impossible to say whether the TiO2 is directly bound to the flake or has merely adsorbed there as the solvent evaporated.



=Discussion=

Graphene/TiO2 suspended in ethanol seems to agglomerate substantially, making it difficult to image Graphene/TiO2 flakes individually. Of the single image that was captured, the TiO2 was bound to the edges of the flake and not within the interior of the sheet.

The procedure must be modified to prevent graphene/TiO2 from agglomerating in solution. This may mean irradiating samples just before imaging, rather than using pre-irradiated solutions that have been standing around for some time. Stabilisers may need to be added to the solution.

=Conclusion=

Sample solutions of both concentrations showed extensive agglomeration; it was very difficult to find individual graphene/TiO2 flakes. Of the one that was identified, TiO2 was bound to the edges and not in the middle of the flake. The G/TiO2 flakes should be evenly dispersed for optimal sunlight conversion, so the synthesis requires modification.

=Log=

16:10 Used the G/Tio2 solution made up for previous G/TiO2 AFM experiment. From memory, 0.7ml of 1mg/mL GO soln & 1ml of 4mg/mL TiO2 solution was made up to 10ml with ethanol & irradiated with UV for 1 hour. 16:14 Sonicated G/TiO2 soln w' microtip for 3 min @ amplitude 20. Power was 4W & total energy of 723J was delivered. Solution was slightly warm. 16:34 Put 1 drop of soln on freshly-cleaved mica & put on foil-wrapped hot plate @ ~250 deg. Ethanol evaporated v' quickly leaving lines of black solid. Labelled Sample 1 16:44 Put 1 drop of soln on new mica substrate. Put foil covering over it & left to dry in ambient conditions on benchtop. 16:44 Removed sample 1 from hot plate & placed in vacuum 16:55 Took 1ml of G/TiO2 soln & made up to 10 mL w' ethanol. Labelled soln. 2. 17:00 Sonicated soln 2 for 3 min w' microtip @ amplitude 20. Power was 4W & 742J of power was delivered. Solution was warm. 17:11 Put 1 drop of soln. 2 on freshly-cleaved mica substrate. Left to dry in ambient conditions under foil cover. Labelled as sample 3. 17:15 Put sample 2 on hot plate @ 280 deg (soon cooled to 250 deg). 17:27 Removed sample 2 from hot plate & added sample 3. Put sample 2 in vacuum. Sample 2 mica adhesive had discoloured & partially decomposed. (This also happened to sample 1) 17:38 Removed sample 3 from hot plate and put in vacuum. Adhesive had also discoloured/decomposed.

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