Sulfur‐Doped Graphene Oxide Quantum Dots as Photocatalysts for Hydrogen Generation in the Aqueous Phase

Abstract

Sulfur-doped graphene oxide quantum dots (S-GOQDs) were synthesized and investigated for efficient photocatalytic hydrogen generation application. The UV/Vis, FTIR, and photoluminescence spectra of the synthesized S-GOQDs exhibit three absorption bands at 333, 395, and 524 nm, characteristic of C=S and C-S stretching vibration signals at 1075 and 690 cm , and two excitation-wavelength-independent emission signals with maxima at 451 and 520 nm, respectively, confirming the successful doping of S atom into the GOQDs. Electronic structural analysis suggested that the S-GOQDs exhibit conduction band minimum (CBM) and valence band maximum (VBM) levels suitable for water splitting. Under direct sunlight irradiation, an initial rate of 18 166 μmol h g in pure water and 30 519 μmol h g in 80 % ethanol aqueous solution were obtained. Therefore, metal-free and inexpensive S-GOQDs hold great potential in the development of sustainable and environmentally friendly photocatalysts for efficient hydrogen generation from water splitting.

Recent Advances in Graphene Quantum Dots: Synthesis, Properties, and Applications

“…By refluxing carbon black in concentrated HNO 3 , Xie et al synthesized GQDs that were further reduced and self‐assembled onto hematite hybrid electrodes to increase the photocurrent eightfold compared with Fe 2 O 3 without GQDs at 1.23 V . Other GQD‐based, inexpensive electrocatalysts, such as sulfur‐doped GQDs, GQDs/CoP, GQDs/C 3 N 4 , and GQDs/H‐TiO 2 hybrid nanostructures have also shown promising performance in hydrogen generation …”

Graphene-Based Materials as Efficient Photocatalysts for Water Splitting

“…In a similar approach, S-doped GO QDs were prepared by a hydrothermal method using citric acid as GO QDs precursor and NaHS as dopant source [46]. The aim of the S doping was to enhance light harvesting of the GO QDs in the visible region.…”

“…However, when 20% (v/v) of ethanol was included in the reaction mixture at the same conditions 508 µmol/g·h were measured. Further increase in the alcohol concentration produced an improvement of the photocatalytic activity up to reaching 1471 µmol/g·h of H 2 when 80% (v/v) ethanol was used [46].…”

Challenges and future prospects of graphene-based hybrids for solar fuel generation: moving towards next generation photocatalysts

“…The surface transfer doping occurs primarily due to the additional functional groups over the graphene sheet and the natural tendency of these groups like donating and withdrawing electrons from the graphene, which leads to an n or p-type conductivity, respectively. 18,60,82,83 The substitutional doping can obtain by replacing the carbon atoms in the graphene lattice with heteroatoms with a different number of valance electrons like atoms having more valance electrons than the carbon leads to the n-type conductivity and atoms with fewer valance electrons than the carbon gives rise to p-type conductivity. Generally, doping in graphene introduces additional states in the density of the states due to the formation of additional free charge carriers.…”