Chemically clean single-step oxido-reductive synthesis of green luminescent graphene quantum dots as impending electrocatalyst

Enhancing Light Absorption and Charge Transfer Efficiency in Carbon Dots through Graphitization and Core Nitrogen Doping

“…These observations suggest that photogenerated electrons absorbing near 500 nm are the more reactive excited state species,a nd that their formation is related to the high photocatalytic activity observed in g-N-CD and not g-CD.This result is in line with previous observations, and may reflect ahigher reactivity of p electrons from excited core states compared to surface states originating from OH groups. [30] In contrast to EDTA, addition of NiP as an electron scavenger to CD solutions had no observable effect on the TAS. This indicates that, for the concentration of NiP used, electron transfer to NiP only proceeds by ar eductive quenching mechanism following hole scavenging by EDTA ( Figure 4).…”

“…[30] Thek inetics at 505 nm are observed to decay slower than those at 665 nm ( Figure S25), also in line with previous studies and supports the presence of different types of excited states. [30,31] To simplify the comparison of complex decay traces (stretched exponentials on the fs-ns timescale ( Figure S26), biphasic behavior on the ms-s timescale), the decay kinetics were characterized by t 50 % .F rom fs-TAS measurements, t 50 % is on the order of af ew picoseconds (9 ps for g-N-CD, Figure 4) and does not show excitation fluence dependence ( Figure S27), indicating av ery fast geminate intrinsic relaxation process that outcompetes bimolecular reactions (100 ps assuming k diff = 1 10 10 m À1 s À1 and 1m of reactant). This is the primary restriction on the overall activity of the system.…”

Enhancing Light Absorption and Charge Transfer Efficiency in Carbon Dots through Graphitization and Core Nitrogen Doping

“…Interestingly,t his 500 nm spectral feature is more prominent for g-N-CD and a-CD,b oth by fs-and ms-TAS ( Figure S31). [30] In contrast to EDTA, addition of NiP as an electron scavenger to CD solutions had no observable effect on the TAS. These observations suggest that photogenerated electrons absorbing near 500 nm are the more reactive excited state species,a nd that their formation is related to the high photocatalytic activity observed in g-N-CD and not g-CD.This result is in line with previous observations, and may reflect ahigher reactivity of p electrons from excited core states compared to surface states originating from OH groups.…”

“…An unoptimized EQE of 5.20 AE 0.08 %, corresponding to an IQE of 5.25 AE 0.08 %, was obtained using 0.5 mg g-N-CD and 30 nmol NiP in 3mLo fEDTAs olution (0.1m)a tp H6.T his efficiency is high for anoble and toxic metal free system and significantly higher than that reported for a-CD/NiP (1.40 AE 0.08 %, IQE). [30] Thek inetics at 505 nm are observed to decay slower than those at 665 nm ( Figure S25), also in line with previous studies and supports the presence of different types of excited states. Features are centered near 505 nm and 650 nm, similar to previous observations.…”

“…[3] Thep hotophysical properties of the CD systems were investigated using transient absorption spectroscopy (TAS), [28] from femtosecond to second timescales in order to investigate intrinsic relaxation processes,t he nature of photogenerated species and charge transfer reactions.fs-TAS experiments revealed that photoexcitation of all CD types gave rise to atransient absorption signal spanning the visible range from 450-750 nm decaying on ap st imescale (Figure 3a,S23 and S24). [30,31] To simplify the comparison of complex decay traces (stretched exponentials on the fs-ns timescale ( Figure S26), biphasic behavior on the ms-s timescale), the decay kinetics were characterized by t 50 % .F rom fs-TAS measurements, t 50 % is on the order of af ew picoseconds (9 ps for g-N-CD, Figure 4) and does not show excitation fluence dependence ( Figure S27), indicating av ery fast geminate intrinsic relaxation process that outcompetes bimolecular reactions (100 ps assuming k diff = 1 10 10 m À1 s À1 and 1m of reactant). [9,29] It is possible that the shorter and longer wavelength features relate to core and surface states,r espectively,a sd etermined for graphene quantum dots.…”