  Achieving versatile routes to generate crystalline carbon-based
nanostructures has become a fervent pursuit in photocatalysis-related fields.
We demonstrate that the direct electrooxidation of ethanol, performed on Ni
foam, yields ultra-small and highly crystalline graphene-like structures named
carbon quantum dots (CQDs). We perform simulations of various sp2 and sp3
domains in order to understand the optical properties of CQDs by accounting
their contribution as absorbance/luminescent centers in the overall optical
response. Experiments and simulations reveal that absorbance bands for
as-synthesized CQDs are dominated by small sp2 domains comprised of r7
aromatic-rings. After 48 h synthesis, the dispersion transition from yellow to
red, exhibiting new and red shifted absorbance bands. Furthermore, fluorescence
emission is governed by medium-sized sp 2 domains (with aromatic ring counts
r12) and oxygen-containing groups. These oxygen-rich groups within the CQDs,
confirmed by FT-IR and XPS, are responsible for the fast photodegradation of
organic dyes, with B90% of methylene blue (MB) being degraded within the first
5 min of light exposure. Our work provides crucial insights about the
electrochemical synthesis and overall optical properties of carbon
nanostructures, while being effective and reliable toward the degradation of
contaminants in water.
