Architecting Nitrogen Functionalities on Graphene Oxide Photocatalysts for Boosting Hydrogen Production in Water Decomposition Process

Abstract

This study elucidates how nitrogen functionalities influence the transition and transfer of photogenerated electrons in graphene‐based materials. Graphene oxide dots (GODs) and Nitrogen‐doped GODs (NGODs) are synthesized by thermally treating graphene oxide (GO) sheets in argon and ammonia, respectively, and then ultrasonically exfoliating the sheets in nitric acid. The nitrogen functionalities of NGODs are mainly quaternary/pyridinic/pyrrolic, and the nitrogen atoms in these functionalities are planar to the GO sheets and repair the vacancy defects on the sheets. Hydrothermal treatment of NGODs in ammonia yields ammonia‐treated NGODs (A‐NGODs), with some pyridinic/pyrrolic groups being converted to amino/amide groups. The nitrogen atoms in the amino/amide groups are not planar to the GO sheets and are prone to donate their lone pair electrons to resonantly conjugate with the aromatic π electrons. The promoted conjugation facilitates the relaxation of photogenerated electrons to the triplet states and prolongs the electron lifetime. When deposited with Pt as the co‐catalyst, the samples catalyze H2 production from an aqueous triethanolamine solution under 420 nm monochromatic irradiation at quantum yields of 7.3% (GODs), 9.7% (NGODs), and 21% (A‐NGODs). The high activity of A‐NGODs demonstrates that architecting nitrogen functionalities effectively mediate charge motion in carbon‐based materials for application to photoenergy conversion.

Photoluminescence from amino functionalized graphene quantum dots prepared by electrochemical exfoliation method in the presence of ammonium ions

“…The transmittance bands at 1100 cm À1 can be assigned to C-N stretching vibrations. 24 It is worth noting that the O-H group at 3300-3500 cm À1 corresponds to physically adsorbed moisture onto carbon surface, while the band appears at 2900-3200 cm À1 for the vibration of N-H groups in sp 2 domain plane of GNs. 25 The NGQD-5 sample shows an emerging band in the range of 2900-3200 cm À1 as compared to the others, indicating presence of a large amount of amino or amide groups.…”

“…1 eV). 9,24 The later three oxygen functionalities, phenolic, carbonyl, and carboxylic group, are frequently attached to basal and edge sites of graphene layer. It should be noted that the emergence of p-p* satellite peak ($298 eV) of sp 2 carbon domain in all N-modied GN samples conrms the resonance in the aromatic orbitals of GNs.…”

A Benchmark Quantum Yield for Water Photoreduction on Amorphous Carbon Nitride

“…It is actually possible that there was hydrogen production at 600 nm, but that it was minute such that it could not be detected in the gas chromatograph. Aside from this limitation, the main reason behind the discrepancies might be the lower probability of excitation of valence electrons to the conduction band under the longer wavelength irradiation . We investigated this by computing the electronic bandgap using Kubelka–Munk (K–M) technique.…”

Effect of Nitrogen Doping Level on the Performance of N‐Doped Carbon Quantum Dot/TiO2 Composites for Photocatalytic Hydrogen Evolution

“…hybrids have been reported, some achieving high photocatalytic efficiencies . Recently, N‐doping‐induced charge transfer enhancement has been at the forefront of this field and is considered to be a useful tool for improving the photocatalytic performance of NCDs‐based materials . Although NCDs with different N/C atomic ratios have been synthesized through both top‐down and bottom‐up approaches, the contribution of N‐doping level to the structure and optical properties of NCDs is not well understood.…”