Supporting Information Making Graphene Holey. Gold Nanoparticle-Mediated Hydroxyl Radical Attack on Reduced Graphene Oxide James G. Radich, 1,3 Prashant V. Kamat *1,2,3 Radiation Laboratory Department of Chemical & Biomolecular Engineering Department of Chemistry & Biochemistry University of Notre Dame, Notre Dame, IN 46556 * Address correspondence to this author (pkamat@nd.edu) 1 Department of Chemical & Biomolecular Engineering 2 Department of Chemistry & Biochemistry 3 Notre Dame Radiation Laboratory 1
A B Figure S1. Control experiment consisting of AuNP and H 2 O 2 (Figure S1-A) shows that when RGO is not present as electron donor the AuNP undergo significant surface degradation by OH as evidenced by the significant changes in the plasmon resonance peak. The particles also aggregate and crash from solution. In Figure S1-B a reproduction of Figure 1A is shown only to include time 0 and time 120 minutes as a comparison to the spectra in (A). 2
Figure S2. Transmission electron micrograph of pre-irradiated RGO sheet on carbon grid. The slight folds and wrinkles associated with RGO are observed in the sheet with other noticeable defects. The small crystals evident on the surface are residual reaction products from chemical reduction of GO with NaBH 4. 3
Figure S3. Irradiation of GO in place of RGO in presence of AuNP and H 2 O 2. The absorption spectra indicate for initial 30 minutes of irradiation (Figure S3-A) the GO undergoes reduction to RGO. After sufficient C=C bonds are restored during this initial 30 minutes, oxidation of RGO begins and decreases in absorption are observed for the remainder of the experiment (Figure S3- B). 4
Figure S4. Changes in UV-visible absorption characteristics of (A) single- and (B) double-beam laser irradiation of A-H-R solutions. The 266 nm beam acts as photolysis source for H 2 O 2 while the 532 nm source serves Au surface plasmon excitation. A Nd:YAG laser was used with 2 nd and 4 th harmonics as depicted in the diagram. The plasmon excitation yields slightly greater decreases in absorbance showing that only after significant irradiation time do plasmon effects become apparent. 5
Laser Flash Photolysis of H 2 O 2 and Competition Kinetics Experiments and Calculations Competition kinetics were used to calculate the rate constants for OH attack on RGO. k 1 2 k 2 This second reaction involves two steps, but it is treated as one. (1) (2) The product,, is monitored at 475 nm. It is formed kinetically as (3) (4) Integrating gives the yield of thiocyanate radicals:, (5) If there is no RGO present, then (6) The concentration of thiocyanate radical in (6) is indicative of an experiment with no RGO present. Dividing (6) by (5) gives 6
1 (7), Multipling numerator and denominator on the left-hand side of this equation by, where is the pathlength and is the extinction of thiocyanate radical species at 475 nm gives 1 (8), Assuming second order kinetics applies, a linear relationship should be apparent by plotting Δ Δ, from which we can extract the rate constants from the slope, and the intercept should then be, In order to correct for the filtering effect of RGO at 266 nm and evaluate a molar rate constant for RGO, a molar extinction coefficient was calculated for the RGO at 266 nm (327712 M -1 cm - 1 ) by using a C:O ratio of 15 from previous measurements of chemically-reduced RGO. 1 From this value and the mass concentration of RGO in solution, a molar value for carbon atoms in the material can be extracted. Filtering of photons by RGO was corrected using equation 9 given as 0 1 10 (9) 7
where I A (x) is the transmitted intensity, I(0) is the incident intensity, A A is the absorbance of A (H 2 O 2 ) at 266 nm, and A B is the absorbance of B (RGO) at 266 nm. At the highest concentration of RGO in the experiments, approximately 7% of the 266 nm photons are absorbed by the RGO and are not used in generating hydroxyl radicals. Competition kinetics values measured with RGO in suspension for evaluation of rate constants were corrected using this relationship. 8
Figure S5. UV-visible absorption spectra of water and copper sulfate (0.003 M) used in the light filtering experiments. As can be seen from the figure, the CuSO 4 filters UV photons in the photolytic range of interest for H 2 O 2 photolysis. Additional filtering of visible and NIR photons also would lead to lower photon thermalization rates and less bulk heating of the solution. References 1. Dreyer, D. R.; Park, S.; Bielawski, C. W.; Ruoff, R. S., The Chemistry of Graphene Oxide. Chem. Soc. Rev. 2010, 39, (1), 228-240. 9