NBEXP0011

=NBEXP0011 — Spin-coat synthesis of 'graphene grass'=

=Objective=

To try and reproduce the 'graphene grass' structure using UV irradiation and applied bias on films made with spin-coating.

=Procedure=


 * 1) Prepare 3 G/TiO2 solutions: 0.3, 0.5 & 0.7mg G per 4mg TiO2. Make solution up to 5ml total vol. with ethanol.
 * 2) Irradiate each solution under Xenon lamp for 1 hour with Ar bubbling and stirring.
 * 3) After irradiation top up the solutions again w' ethanol to 5ml total vol (to account for vol. lost to evaporation during irradiation.)
 * 4) Cut up FTO glass into 1.5cm x 4cm slides. Cover ~0.5cm at one end of each slide with tape.
 * 5) Deposit as-made solutions on slides using program described in ..., dispensing 250ul at a time until all the solution is dispensed
 * 6) Between each coating cycle, warm each slide on a heater at ~50° for ~30 sec to evaporate off any remaining solvent.
 * 7) Calcince samples at 300° for one hour with a 3°/min ramp rate
 * 8) Perform photocurrent measurements in 0.5M NaOH solution
 * 9) Image samples using SEM

=Solutions & samples=


 * Sample 1** 0.3ml 1mg/ml GO, 1ml 4mg/ml TiO2, 4.7ml ethanol
 * Sample 2** 0.5ml 1mg/ml GO, 1ml 4mg/ml TiO2, 4.5ml ethanol
 * Sample 3** 0.7ml 1mg/ml GO, 1ml 4mg/ml TiO2, 4.3ml ethanol

=Results=



Sample 3


=Discussion=

Reduction
Images show colour change from brown to black, indicating that graphene oxide reduction was successful. No quantitative data was taken (XPS, Raman etc.)

Spin-coating
The solutions were deposited onto slides 100ul at a time. Sample 1 had 44 depositions, sample 2 had 46 and Sample 3 had 43. The differences are probably attributable to a slight difference in solvent evaporation rate and/or time of UV irradiation (the solutions were not topped up to a designated level after illumination). The slides were obviously darker than a clean FTO slide, and Sample 3 was noticeably darker than Sample 1, and Sample 2 was somewhere in between.

The films were not uniform however — there was some accumulation of material along the long edges of the slides. It seems the liquid beads at the edges of the slide, which probably means that either the spin speed or acceleration should be higher.

By depositing only 100ul at a time the amount of liquid waste was minimised, however it also took longer to make the slides — making the three samples took almost 2 hours.

UV-Vis measurements
2 points on each slide were measured for the transmission data and 4 points were measured and averaged for the absorbance values (the values were very similar).

Both the transmission and absorption measurements show the film absorbs substantially more light than FTO alone. According to the transmission data the film absorbs about 1/3 of the light passing through the FTO over all wavelengths. Even though the transmittance values of samples 2 and 3 are very similar, Sample 3 generates significantly higher photocurrent (about 1/3 to 1/2 more). So Sample 3 generates more current for each unit of light that passes through it.

Photocurrent measurements Again, higher concentrations of graphene lead to greater photocurrent values. The maximum photocurrent is about 5uA, which is significantly smaller than values from dropcast slides (~25uA). The electrolyte was 0.5M NaOH.

IV measurements
Both dark and light measurements are almost the same. I am not sure how to interpret this at this stage.

SEM
No graphene grass was identified. Large portions of the FTO were covered in material that looks like particle-coated graphene sheets. There were also frequent clusters of large particles which EDS showed to contain high amounts of titanium. Areas of FTO remained bare however, so complete coverage is not achieved with spin-coating.

=Conclusion=

No graphene grass was observed. The most significant difference between this synthesis procedure and the one that gave rise to the graphene grass structure was 1) spin-coating rather than drop-casting, and 2) no calcining step was used. The next attempt should probably involve a calcining step.

=Log=

2009-09-29

 * 14:53** Made up 1mg/ml GO in ethanol solution. 0.0998g GO was added to 100ml volumetric flask & filled with ethanol (absolute). Issued label **NBEXP0011-1** . Put soln in sonicator bath for 10 min
 * 15:06** Made up 4mg/ml TiO2 (ST-01) in ethanol soln. Added 0.3999g TiO2 to 100ml volumetric flask & filled w' ethanol (absolute). Issued label **NBEXP0011-2** and put in sonicator bath for 10 min
 * 15:29** Made up 0.3mg G:4mg TiO2 soln. Added 0.3ml NBEXP0011-1 & 1ml NBEXP0011-2 & 4.7ml ethanol (should have been 3.7ml). Issed label **NBEXP0011-3**
 * 15:36** Put solution under UV with Ar bubbling at 350kPa and stirring.
 * 15:47** Made up 0.5 and 0.7 mg GO in 1mg TiO2 solutions & made up to 6ml total vol. with ethanol (absolute). Issued labels **NBEXP0011-4** and **NBEXP0011-5** respectively.
 * 16:46** Removed **NBEXP0011-3** from UV.
 * 16:56** Put **NBEXP0011-4** under UV
 * 17:57** Removed **NBEXP0011-4** from UV.

2009-10-21
10:00 Sonicated 4mg/ml TiO2 solution at amplitude 20 (microtip), 4-5W, for 2 min. 562J delivered. 10:03 Somicated 1mg/ml GO solution at amplitude 20 (microtip), 4-5W, for 2 min. 601J delivered. 10:10 Made up samples 1, 2 and 3 10:30 Sonicated Solution 1 for 2 min with microtip for 2 min at amplitude 20 (496J) 10:40 Put solution 1 under UV with Ar bubbling 10:50 Put 3 fto slides in milliQ water in sonicator to clean 11:10 Drained FTO slides and put in oven to dry (110°) 11:14 Checked on Solution 1 — Ar had stopped flowing. Restarted flow 11:51 Sonicated sample 2 for 2 min, microtip amplitude 20, 492J 11:52 Removed sample 1 from UV 11:59 Put Sample 2 under UV 12:56 Sonicated sample 3. Microtip, amplitude 20, 2 min. 498J 12:58 Removed Sample 2 from UV. No interruption to Ar flow this time. 13:04 Put sample 3 under UV. 14:08 Removed Sample 3 from UV 14:15 Took photos of samples 1-3. Reduction was successful. 16:45 Begin spin-coating sample solutions onto cleaned FTO slides (cooled to room temp). Deposition volume was 100ul. Hot plate temp was ~80°; samples were placed on hot plate for ~10 seconds after each spin cycle & then allowed to cool.

2009-10-22
11:00 Performed UV-Vis measurements. Measured at 2 or 4 different points on each slide. 13:00 Photocurrent measurements with 0.5M NaOH electrolyte (10.06g NaOH in 500ml MilliQ). Performed photocurrent measurement, then dark IV, then light IV. For sample 2, a bias was applied (beginning at -1V) without current being recorded — measurement was aborted after a few seconds. This happened twice (cause was a software bug).

=Tags=