Supporting Information. Interfacial engineering of a carbon nitride-graphene oxidemolecular. Ni catalyst hybrid for enhanced photocatalytic activity

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1 Supporting Information Interfacial engineering of a carbon nitride-graphene oxidemolecular Ni catalyst hybrid for enhanced photocatalytic activity Hatice Kasap, 1 Robert Godin, 2 Chiara Jeay-Bizot, 2 Demetra S. Achilleos, 1 Xin Fang, 1 James R. Durrant, 2 Erwin Reisner 1,* 1 Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK 2 Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, UK Corresponding author: reisner@ch.cam.ac.uk Contents Tables S1 to S10 Figures S1 to S30 Supporting References page S1 page S11 page S41

2 Table S1. Solar light driven (AM 1.5G, 100 mw cm 2, 25 C) H2 production in the presence of NCN CNx (5 mg) and NiP (50 nmol) in aqueous ethylenediamine tetraacetic acid (EDTA, 0.1 M, ph 4.5) solution with different graphene oxide (GO) loadings. Control experiments in the absence of GO, NCN CNx and in the presence of reduced graphene oxide (RGO) were also conducted. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry GO loading/ wt% H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) GO loading ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.71 Control Experiments 8 GO, > 495 nm GO, (No NCN CNx) RGO, [a] ± ± ± ± RGO, (No NCN CNx) [a] GO replaced by RGO. S1

3 Table S2. Solar light driven (AM 1.5G, 100 mw cm 2, 25 C) H2 and aldehyde production in the presence of NCN CNx (5 mg) and NiP (50 nmol) in aqueous potassium phosphate buffer, KPi, (0.1 M, ph 4.5) containing 4-methyl benzyl alcohol, 4-MBA (30 µmol) with different GO loadings. Control experiments in the absence of GO, NCN CNx and in the presence of RGO were also conducted. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry GO loading/ wt% Aldehyde ± σ / µmol (after 4 h) Alcohol Conversion ± σ / (%) H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) GO screening ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 4.53 Control Experiments 8 GO, > 495 nm GO, (No NCN CNx) RGO, [a] ± ± ± ± ± ± RGO, (No NCN CNx) [a] GO replaced by RGO. S2

4 Table S3. Solar light driven (AM 1.5G, 100 mw cm 2, 25 C) H2 and aldehyde production in the presence of different amount of NCN CNx loadings and NiP (50 nmol) in KPi (0.1 M, ph 4.5) containing 4-MBA (30 µmol) with different GO loadings. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry CNx loading / mg GO loading / wt% Aldehyde ± σ / µmol (after 4 h) Alcohol Conversion ± σ / (%) H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) CNx loading ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.94 Table S4. Solar light driven (AM 1.5G, 100 mw cm 2, 25 C) H2 and aldehyde production in the presence of NCN CNx (5 mg) loadings and NiP (50 nmol) in KPi (0.1 M, ph 4.5) containing 4-MBA (30 µmol) in the presence of wt% GO loading (6.3 g) with different sizes of GO. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry GO size / µm Aldehyde ± σ / µmol (after 4 h) Alcohol Conversion ± σ / (%) H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) GO size screening 1 < ± ± ± ± ± ± < ± ± ± ± ± ± ± ± ± ± ± ± 2.92 S3

5 Table S5. Solar light driven (AM 1.5G, 100 mw cm 2, 25 C) H2 production in the presence of H2N CNx (5 mg) and NiP (50 nmol) in EDTA (0.1M, ph 4.5) with different GO loadings. Control experiments in the absence of GO, H2N CNx and in the presence of RGO were also conducted. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry GO loading/ wt% H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) GO loading ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.30 Control Experiments 5 GO, 1.00 (No NCN CNx) RGO, 1.00 [a] 5.22 ± ± ± ± RGO, 1.00 (No NCN CNx) [a] GO replaced by RGO. S4

6 Table S6. Solar light driven (AM 1.5G, 100 mw cm 2, 25 C) H2 and aldehyde production in the presence of H2N CNx (5 mg) and NiP (50 nmol) in KPi (0.1 M, ph 4.5) containing 4-MBA (30 µmol) with different GO loadings. Control experiments in the absence of GO, H2N CNx and in the presence of RGO were also conducted. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry GO loading/ wt% Aldehyde ± σ / µmol (after 4 h) Alcohol Conversion ± σ / (%) H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) GO screening ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 1.09 Control Experiments 5 GO, 1.00 (No NCN CNx) RGO, 1.00 [a] 2.04 ± ± ± ± ± ± RGO, 1.00 (No NCN CNx) [a] GO replaced by RGO. S5

7 Table S7. Charging and discharging experiments were executed with a photoreactor containing NCN CNx (5 mg) and NCN CNx (5 mg) - GO/RGO (0.125 wt%; 6.3 g) hybrids in the presence of 4-MBA (30 μmol) in an aqueous KPi solution (0.1 M, ph 4.5) in the absence of NiP. Total solvent volume was 3 ml with a headspace volume of 4.74 ml. The samples were irradiated under 1 Sun (AM 1.5G, 100 mw cm 2, 25 C) for 30 min, 2 h and 4 h. The vials were then moved into dark, NiP (50 nmol in KPi solution) was injected and the amount of H2 and aldehyde production was monitored. Entry GO loading/ wt% Aldehyde ± σ / µmol (after 4 h) Alcohol Conversion ± σ / (%) H2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) 30 mins irradiation ± ± ± ± ± ± ± ± ± ± ± ± RGO, [a] 1.32 ± ± ± ± ± ± h irradiation ± ± ± ± ± ± , 2h in dark 1.00 ± ± ± ± ± ± ± ± ± ± ± ± RGO, [a] 1.60 ± ± ± ± ± ± h irradiation ± ± ± ± ± ± ± ± ± ± ± ± RGO, [a] 1.74 ± ± ± ± ± ± h irradiation ± ± ± ± ± ± 2.71 [a] GO replaced by RGO. S6

8 Table S8. Summary of selected photocatalytic systems for H2 production and CO2 reduction in the literature. Photosensitizer Catalyst Electron donor (ED) Light Source TOFcat/ h 1 TONcat Activity/ µmol g 1 h 1 Ref H2 Production Carbon Nitride Systems CNx-GO composite Pt 25% methanol 350 W Xe arc lamp (λ > 400 nm), 180 mw cm CNx-RGO Pt 10% lactic acid 3 W LED lamps (λ > 420 nm), 80 mw cm μmol h 1 2 CNx-GO Methyl blue solution 300 W Xe arc lamp (λ > 420 nm) C60-graphene-CNx Pt 10% TEOA 5W LED (λ > 420 nm),12.6 mw cm EY-CNx-GO Pt 20% TEOA 300 W Xe arc lamp (λ > 420 nm) NCN CNx-GO NiP 10mM 4-MBA 100 mw cm 2 (AM1.5G) This work TiO2 Systems TiO2-GO Pt 25% methanol 350 W Xe arc lamp, 20 mw cm 2 TiO2-GO MoS2 25% ethanol 350 W Xe arc lamp 20 mw cm μmol h 1 7 TiO2-RGO Pt 10%TEOA 100 mw cm 2 (AM1.5G) S7

9 BiVO4 systems FTO-BiVO4-RGO Pt H2O 0.75 µmol h 1 9 PRGO-BiVO4 and Ru:SrTiO3:Rh Z-scheme Cd quantum dots Ru Aq H2SO4 (ph 3.5) CdS-GO Pt Na2S (0.35 M) Na2SO3 (0.25 M) 350 W Xe arc lamp (λ > 420 nm) 350 W Xe arc lamp (λ > 420 nm) CdS-graphene Pt 10% lactic acid 350 W Xe arc lamp (λ > 420 nm) 180 mw cm 2 CdS-RGO NiCl2 Ethanol/water (1:1) 500 Hg lamp (λ > 400 nm) 120 mw cm 2 CO2 reduction CNx-GO H2O 15 W energy-saving daylight bulb CNx-RGO H2O 15 W energy-saving daylight bulb (N-TiO2)-graphene (coated on glass rods) Flow reactor. Mixture of CO2 and water vapor. 15 W energy-saving daylight bulb CdS nanorod-rgo H2O 300 W Xe arc lamp (λ > 420 nm) 150 mw cm Electrochemical water splitting cell. + Value estimated from published data. Amount of photocatalyst used is not reported. S8

10 Table S9. Calculation of the number of radicals per heptazine unit generated during charging and discharging experiments of NCN CNx and NCN CNx-GO/RGO (same order as in Table S7). The calculations are based on the assumptions that 2 trapped radicals are used to produce one molecule of H2 and no other decay pathway is available for the radicals. 18 Each vial contains 5 mg of NCN CNx with a repeating heptazine unit of 249 g mol 1, which corresponds to 20 µmol of NCN-heptazine units. Entry GO loading/ wt% H2 ± σ / µmol (after 4 h) Calculated radicals / µmol [b] Charge accumulated per heptazine unit / % 30 mins irradiation ± ± ± ± RGO, [a] 0.94 ± ± h irradiation ± ± , 2 h in dark 1.06 ± ± ± ± RGO, [a] 1.28 ± ± h irradiation ± ± ± ± RGO, [a] 2.29 ± ± [a] GO replaced by RGO. [b] Radicals calculated from generated H2 in dark phase. S9

11 Table S10. Solar light driven alcohol oxidation and proton reduction in the presence of NiP and NCN CNx for mechanistic interpretation. Experiments were performed using NCN CNx (5 mg) in aqueous in an aqueous KPi solution (0.1 M, ph 4.5) containing 4-MBA (30 µmol), or benzyl alcohol, BA (30 µmol) and NiP (50 nmol). The samples were irradiated under 1 Sun (AM 1.5G, 100 mw cm 2, 25 C). Total solvent volume was 3 ml with a headspace volume of 4.74 ml. Entry Conditions Gas detected Aldehyde ± σ / µmol (after 4 h) Alcohol Conversion ± σ / (%) H2/ D2 ± σ / µmol (after 4 h) TON (4 h) ± σ / mol H2 NiP 1 Activity/ µmol H2 (g CNx) 1 h 1 (after 1h) TOF ± σ / h 1 (after 1h) Solvent Screening 1 H2O, 4-MBA H ± ± ± ± ± ± D2O, 4-MBA D ± ± ± ± ± ± 2.32 Substrate Screening 3 BA H ± ± ± ± ± ± D2-BA H ± ± ± ± ± ± 1.97 Electron Acceptors 5 N2, NiP H ± ± ± ± ± ± N2, No NiP H ± ± Air, No NiP H ± ± *All the experiments showed 100% selectivity towards aldehyde formation and no carboxylic acid was detected. S10

12 (a) (b) Figure S1. (a) ATR FT-IR and (b) Raman spectrum of bare NCN CNx and GO and that of NCN CNx GO and NCN CNx RGO hybrids at 10 wt% GO/RGO loading. Characterizations were also performed at wt %, but this loading was too low to observe significant differences. We therefore only present data with 10 wt% loading. S11

13 Figure S2. X-ray diffraction (XRD) patterns of bare NCN CNx and GO and that of the NCN CNx GO hybrid at 10.0 wt% GO loading. S12

14 Figure S3. SEM images of bare NCN CNx and NCN CNx GO hybrids with increasing GO loading, weight % (top to bottom). S13

15 Figure S4. TEM images of (a) bare NCN CNx, (b) bare GO and NCN CNx GO hybrids with (c) 0.125, (d) and (e) wt% GO loading. S14

16 (a) (b) Figure S5. (a) UV-vis absorption profile of NCN CNx (0.5 mg), GO, NCN CNx-GO and NCN CNx-RGO hybrid in the presence of wt% loading in an aqueous KPi solution (0.1 M, ph 4.5, 3 ml) recorded at 25 C. (b) Photoluminescence measurements for NCN CNx (0.5 mg), NCN CNx-GO and NCN CNx-RGO hybrids at wt% loading, recorded in an aqueous KPi solution (0.1 M, ph 4.5, 3 ml) with ex = 320 nm. S15

17 (a) (b) Figure S6. (a) Photocatalytic H2 production in the presence of NCN CNx (5 mg) with different GO loadings, GOwt%, and NiP (50 nmol) in aqueous EDTA solution (0.1 M, ph 4.5, 3 ml), (b) in aqueous KPi solution (0.1 M, ph 4.5, 3 ml) containing 4-MBA (30 μmol), under 1 Sun irradiation (100 mw cm 2, AM1.5G, 25 C) for 4 h. S16

18 (a) (b) Figure S7. (a) Photocatalytic H2 production and 4-MBA oxidation in the presence of different amount of NCN CNx and GO loadings, 4-MBA (30 μmol) and NiP (50 nmol) in an aqueous KPi solution (0.1 M, ph 4.5, 3 ml) under 1 Sun irradiation (100 mw cm 2, AM1.5G, 25 C). The pair of hollow and filled symbols of the same shape and color corresponds to H2 and aldehyde production, respectively. Amount of aldehyde formed is detected after 4 h of irradiation. (b) Bar chart comparing specific activity of NCN CNx after 1 h of irradiation. S17

19 (a) (b) Figure S8. (a) Photocatalytic H2 production and 4-MBA oxidation in the presence of NCN CNx (5 mg) and different sizes of GO at wt% loading, 4-MBA (30 μmol), and NiP (50 nmol) in an aqueous KPi solution (0.1 M, ph 4.5, 3 ml) under 1 Sun irradiation (100 mw cm 2, AM1.5G, 25 C). The pair of hollow and filled symbols of the same shape and color corresponds to H2 and aldehyde production, respectively. Amount of aldehyde formed is detected after 4 h of irradiation. (b) Bar chart comparing total amount of H2 produced and TONNiP reached after 4h of irradiation. S18

20 (a) (b) Figure S9. (a) Photocatalytic H2 generation using H2N CNx (5 mg), different GO loadings and NiP (50 nmol) in aqueous EDTA solution (0.1 M, ph 4.5, 3 ml) under 1 Sun irradiation (100 mw cm 2, AM1.5G, 25 C). (b) Control experiments in the presence of 1 wt.% loading of GO and RGO as well as in the absence of H2N CNx are also presented. S19

21 (a) (b) Figure S10. (a) Photocatalytic H2 production and 4-MBA oxidation in the presence of H2N CNx (5 mg), different GO loadings, 4-MBA (30 μmol), and NiP (50 nmol) in an aqueous KPi solution (0.1 M, ph 4.5, 3 ml) under 1 Sun irradiation (100 mw cm 2, AM1.5G, 25 C). (b) Control experiments in the presence of 1 wt.% loading of GO and RGO as well as in the absence of H2N CNx are also presented. The pair of hollow and filled symbols of the same shape and color corresponds to H2 and aldehyde production, respectively. Amount of aldehyde formed is detected after 4 h of irradiation. S20

22 Figure S11. (a) Photocatalytic H2 and aldehyde production with NCN CNx (5 mg), NiP (50 nmol), 4-MBA (30 µmol) in KPi (0.1 M, ph 4.5, 3 ml) prepared in H2O or D2O under 1 Sun irradiation (100 mw cm 2, AM 1.5G, 25 C). Inset: MS monitoring the headspace gas produced overtime in suspension prepared with H2O and D2O. (b) Photocatalytic H2 production with NCN CNx (5 mg), NiP (50 nmol), BA or D2-BA (30 µmol) in KPi (0.1 M, ph 4.5, 3 ml) under 1 Sun irradiation (100 mw cm 2, AM 1.5G, 25 C) Inset: MS monitoring the headspace gas produced overtime in the presence of BA and D2-BA. The pair of hollow and filled symbols of the same shape and color corresponds to H2 and aldehyde production, respectively. Amount of aldehyde formed is detected after 4 h of irradiation. (c) Proposed mechanism for alcohol oxidation with NCN CNx, NiP and 4-MBA in KPi under inert atmosphere. S21

23 Figure S12. Photocatalytic H2 production and 4-MBA oxidation in the presence of NCN CNx (5 mg), 4-MBA (30 μmol), with and without NiP (50 nmol) in an aqueous KPi solution (0.1 M, ph 4.5, 3 ml) under N2 with 1 Sun irradiation (100 mw cm 2, AM1.5G, 25 C). The photocatalytic activity was also monitored under air, in the absence of NiP. The pair of hollow and filled symbols of the same shape and color corresponds to H2 and aldehyde production, respectively. Amount of aldehyde formed is detected after 4 h of irradiation. S22

24 (a) (b) Figure S13. (a) PL spectra recorded with spectrofluorometer equipped with an integrating sphere for NCN CNx (5 mg) and terephthalic acid, THA (30 μmol) in KPi solution (0.1 M, ph 4.5, 3 ml) after 1 h of irradiation ( > 400 nm). The sample was centrifuged, and the emission spectrum was recorded for the supernatant with ex = 315 nm and em = nm. Control experiments in the absence of THA, light, NCN CNx and only THA are also shown. (b) PL spectra recorded for THA and 2- hydroxyterephthalic acid, THA-OH (0.05 μmol), as reference are also shown. Black trace in both plots corresponds to same conditions. Formation of < 0.02 µmol of THA-OH was detected. S23

25 Figure S14. (a) Absorption spectra (red) and emission spectra (black) of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) with ex = 404 nm, under Ar atmosphere. (b) tr-pl of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) with GO and RGO loadings in the absence and (c) presence of 4-MBA (0.01 M), under Ar atmosphere, with ex = 404 nm and em = 490 nm at 25 C. S24

26 (a) (b) Figure S15. tr-pl of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) with 50 wt.% GO loading in the (a) absence and (b) presence of 4-MBA (0.01 M), under Ar atmosphere, with ex = 404 nm and em = 490 nm at 25 C. S25

27 (a) (b) Figure S16. (a) μs-tas spectra from 470 nm to 1000 nm at several time delays after photoexcitation of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5). (b) Typical μs-tas decay of 1.67 mg ml 1 NCN CNx dispersed KPi solution (0.1 M, ph 4.5) monitored at = 610 nm under = 355 nm pulsed excitation at 25 C. The power law fitting is overlaid in red and is of the form y = y0 + t t0 b. t0 represents the time offset between the trigger signal and the arrival of the excitation pulse to the sample, typically t0 = 1x10-7 s. y0 is the absorbance offset at infinite times and the b value is S26

28 (a) (b) Figure S17. (a) Typical µs-tas decay kinetics of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) with and without 4-MBA (0.01 M) under Ar atmosphere monitored at = 610 nm under = 355 nm pulsed excitation at 25 C. (b) Photographs of NCN CNx dispersions in the presence of 4-MBA (0.01 M) before (yellow) and after laser irradiation (blue), under Ar atmosphere. S27

29 Figure S18. µs-tas decay kinetics normalized at 2 µs of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) with various GO and RGO loadings, monitored at = 610 nm under = 355 nm pulsed excitation. Data is the same as shown in Figure 4a in the main text. S28

30 Figure S19. μs-tas decay kinetics of (a) H2N CNx, H2N CNx and GO/RGO samples with wt% loading (6.3 g) at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) monitored at = 800 nm under = 355 nm pulsed excitation, (a) without 4-MBA, (b) with 4-MBA (0.01 M) and (c) with 4-MBA (0.01 M) and NiP (50 nmol) in KPi solution at 25 C. S29

31 Figure S20. µs-tas decay kinetics of NCN CNx at the concentration of 1.67 mg ml 1 with wt% GO loading dispersed in KPi solution (0.1 M, ph 4.5), monitored at = 800 nm under = 355 nm pulsed excitation. The repeat measurement was performed following the initial measurement (black trace). The trace for the repeated measurements is scaled by a factor of 1.2 in the right panel. S30

32 Figure S21. μs-tas decay kinetics normalized at 2 µs for H2N CNx, H2N CNx and GO/RGO samples with wt% loading at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) monitored at = 800 nm under = 355 nm pulsed excitation. Data is the same as shown in Figure S19a. S31

33 Figure S22. Typical µs-tas decay kinetics of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) containing 4-MBA (0.01M) and in EDTA (0.1M, ph 4.5) in Ar atmosphere at = 610 nm under = 355 nm pulsed excitation at 25 C. S32

34 a) (b) Figure S23. μs-tas decay kinetics monitored at the concentration of 1.67 mg ml 1 for a) H2N CNx and b) NCN CNx suspensions, and in NaDC (13.8 mg ml 1 ) hydrogel, in KPi solution (0.1 M, ph 4.5) under Ar, monitored at = 1000 nm ( H2N CNx) or 610 nm ( NCN CNx) with laser pulse excitation at = 355 nm at 25 C. S33

35 a) (b) Figure S24. (a) Photograph of hydrogel (50 mg ml 1 ) made from NaDC and NCN CNx powder. (b) Monitoring of μs-tas at = 610 nm without any laser pulse excitation for NCN CNx suspension (1.67 mg ml 1 ) and NCN CNx in NaDC (13.8 mg ml 1 ) hydrogel, with 4-MBA (0.01 M) in KPi (0.1 M, ph 4.5) under Ar at 25 C. S34

36 Figure S25. PIAS of (a) NCN CNx, (b) NCN CNx-GO, (c) NCN CNx-RGO samples with wt% GO and RGO loading (6.3 g) in NaDC (13.8 mg ml 1 ) hydrogel monitored at 610 nm with LED excitation at = 365 nm (0.5 mw cm 2 ), in KPi solution (0.1 M, ph 4.5) with 4-MBA (0.01 M) and different concentrations of NiP, under Ar at 25 C. The samples were only irradiated for 2 s and the absorbance was monitored during irradiation and for the next 58 s. S35

37 Figure S26. Normalized PIAS traces for NCN CNx, NCN CNx-GO/RGO samples (0.125 wt% loading of GO or RGO) in NaDC (13.8 mg ml 1 ) hydrogel monitored at = 610 nm with LED excitation at = 365 nm (0.5 mw cm 2 ), in KPi solution (0.1 M, ph 4.5) with 4- MBA (0.01 M) under Ar. The concentration of NiP is varied as indicated. The samples were irradiated for 2 s and then the light was switched off. S36

38 Figure S27. PIAS of NCN CNx, NCN CNx-GO and NCN CNx-RGO samples with wt% loading (6.3 g) in NaDC (13.8 mg ml 1 ) hydrogel monitored at 610 nm with LED excitation at = 365 nm (0.5 mw cm 2 ), in KPi solution (0.1 M, ph 4.5) with 4-MBA (0.01 M) and NiP (24 µm), under Ar at 25 C. The samples were only irradiated for 2 s and the absorbance was monitored during irradiation and for the next 58 s. S37

39 Figure S28. Decay kinetics of NCN CNx at the concentration of 1.67 mg ml 1 dispersed in KPi solution (0.1 M, ph 4.5) in the presence of 4-MBA (0.01 M) under air and Ar atmosphere monitored at = 610 nm under = 355 nm pulsed excitation at 25 C. S38

40 Figure S29. PIAS of H2N CNx and GO/RGO hybrid samples with wt% loading (6.3 g) recorded in KPi solution (a) without 4- MBA (b) with 4-MBA and (c) with 4-MBA (0.01 M) and NiP (50 nmol) monitored at 800 nm at LED excitation of = 365 nm (0.5 mw cm 2 ), under Ar at 25 C. The samples were only irradiated for 2 s and the absorbance was monitored during irradiation and for the next 5 s. S39

41 Figure S30. UV-visible absorption spectra of NiP (40 nmol) in KPi solution (0.1 M, 3 ml), before and after the addition different amounts of GO ( mg). GO was separated by centrifugation prior recording the electronic absorption spectra of NiP in the supernatant. Similar experiments were also attempted with bare NCN CNx and RGO, but these were hampered by their strong scattering. S40

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