Enriching Photoelectrons via Three Transition Channels in Amino-Conjugated Carbon Quantum Dots to Boost Photocatalytic Hydrogen Generation

Abstract

Well-steered transport of photogenerated carriers in optoelectronic systems underlies many emerging solar conversion technologies, yet assessing the charge transition route in nanomaterials remains a challenge. Herein, we combine the photoinduced absorption, emission, and excitation properties in high luminescent carbon quantum dots (CQDs) with an amino-modified surface to identify the existence of three photoelectron transition channels, that is, near-band-edge transition, multiphoton active transition in CQDs, and transfer from amino groups to CQDs, and together they contribute to strong blue photoluminescence (PL) independent of the excitation wavelength. Moreover, the enriching electron reservoir via these three channels was demonstrated in a holes cleaning environment to efficiently trigger water splitting into hydrogen with excellent stability and recyclability.

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

“…Similarly,a na ctivity of 7950 mmol H2 (g CD ) À1 h À1 was achieved using 0.1 mg (4 nmol) g-N-CD and 100 nmol NiP.T his H 2 evolution rate is the highest reported specific activity for aC Dused in photocatalytic H 2 production and represents an order-of-magnitude improvement over undoped a-CD. [2,3,25,26] With decreased catalyst to CD ratio,higher per catalyst performance could be achieved. Optimized conditions resulted in at urnover frequency( TOF Ni )o f1 43 (mol H2 )(mol Ni ) À1 h À1 and at urnover number (TON Ni )of277 (mol H2 )(mol Ni ) À1 after 4hirradiation using 0.5 mg (23 nmol) g-N-CD and 10 nmol NiP (Figure S19).…”

“…Graphitized CDs (g-CD and g-N-CD) show improved light absorption compared to amorphous particles (a-CD), resulting in increased specific activity (per mass of CD) in photocatalytic H 2 evolution systems.H owever, g-N-CD also outperformed g-CD by af actor of 5, with ar ecord CD specific activity of 7950 mmol H2 (g CD ) À1 h À1 . [25,26] Thehigher photoactivity of g-N-CD stems from ac ombination of improved light harvesting Figure 4. Representative timescales of the relaxation and charge transfer steps and determined reaction mechanism under photocatalytic conditions.…”

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

“…[25,26] Thehigher photoactivity of g-N-CD stems from ac ombination of improved light harvesting ability without significantly compromising photogeneration of reactive electrons,c harge transfer activity or recombination kinetics.T AS investigations revealed fast geminate recombination as ak ey limiting factor in CD photocatalytic systems,w hich needs to be addressed in future CD development. Graphitized CDs (g-CD and g-N-CD) show improved light absorption compared to amorphous particles (a-CD), resulting in increased specific activity (per mass of CD) in photocatalytic H 2 evolution systems.H owever, g-N-CD also outperformed g-CD by af actor of 5, with ar ecord CD specific activity of 7950 mmol H2 (g CD ) À1 h À1 .…”

Functionalized carbon dots on TiO2 for perovskite photovoltaics and stable photoanodes for water splitting

“…Similarly to other carbon materials, nitrogen and sulfur doping in CDs has been related to the activity as co-catalyst in the cathode for electrochemical hydrogen evolution [35]. In addition, it has been reported that amino groups can active mechanisms of electron transfer to CDs during the photocatalytic hydrogen evolution [36]. In TiO 2 photoanodes, the role of the nitrogen doping level in hydrothermally synthesized CDs has been evidenced on both the photocatalytic hydrogen evolution and PEC water splitting [37].…”