Topics in Current Chemistry (2020) 378:3
1 3
outstanding morphological features, with the presence of assemblies of highly
porous flat carbon blocks (surface area: 1213 m
2
g
−1
). In addition, the p-Cof surface exhibited graphitic and pyridone-type nitrogen coordination, resulting in a
multifunctional and versatile catalyst for photocatalytic hydrogen production
(PHP) and electrocatalytic oxygen reduction reactions. The photocatalytic performance of p-Cof gave rise to 334 μmol h
−1
g
−1
and 575 μmol h
−1
g
−1
of hydrogen
from water splitting under visible light and solar light irradiation, respectively
(Fig. 12b).
In addition to the previously described example of egg valorization toward
the formation of CQDs, egg white from expired eggs was employed as a template in the synthesis of titania with enhanced morphological properties (Fig. 13)
[93]. The use of egg white as template led to an increase in surface area from
10 to 139 m
2
g
−1
as compared with the material prepared in the absence of the
residue. Remarkably, the synthetic process was carried out using a solvent-free
mechanochemical-assisted strategy. Such composite material could be potentially
employed for photocatalysis.
7 Other Examples: Waste‑derived Materials
Graphite-like carbon nitride (g-C 3 N 4 ) has recently emerged as one of the most
widely studied materials, both as a single phase and as part of a photocatalyst.
g-C 3 N 4 can be obtained by thermal treatment of nitrogen-rich precursors. Urea,
thiourea, melamine, cyanamide, and dicyandiamide are some of the common
starting materials. The production of g-C 3 N 4 from urea is a good opportunity for
waste (e.g. agricultural waste) valorization to move toward a circular economy
[94]. Nevertheless, in many examples, the photocatalytic efficiency of the pure
g-C 3 N 4 is limited by the high recombination rate of its photo-generated electron–hole pairs [49, 51]. Combination with metal-containing materials provides
a feasible route toward improving the photocatalytic response of g-C 3 N 4 . Along
these lines, a very recent report describes the valorization of waste toner powder
enriched with organic residues and magnetic Fe 3 O 4 to produce a g-C 3 N 4 –Fe 2 O 3
photocatalyst through a facile one-step calcination process [95]. The toner powder was first calcinated at 600 °C to produce the Fe 2 O 3 structure and then subjected to a second calcination treatment in the presence of thiourea (450 °C in
a muffle furnace for 2 h). Figure 14a shows a high-resolution transmission electron microcopy (HR-TEM) image of the pure Fe 2 O 3 toner-derived material in
which the (110) plane of α-Fe 2 O 3 can be identified. A similar result was derived
from microscopy analysis of the g-C 3 N 4 –Fe 2 O 3 composite samples, as shown in
Fig. 14b, demonstrating the successful formation of a heterojunction and close
contact between g-C 3 N 4 and Fe 2 O 3 . As expected, the introduction of iron oxide in
the structure led to enhanced visible light absorption as demonstrated by UV–Vis
spectroscopy (Fig. 14c). Such enhancement, in addition to a drastic reduction
in electron–hole pair recombination as demonstrated by photoluminescence,
yielded an outstanding material for MO and textile effluent degradation (Fig. 14d)
under sunlight-type illumination conditions. Last but not least, the composite
18
Reprinted from the journal
1 3
outstanding morphological features, with the presence of assemblies of highly
porous flat carbon blocks (surface area: 1213 m
2
g
−1
). In addition, the p-Cof surface exhibited graphitic and pyridone-type nitrogen coordination, resulting in a
multifunctional and versatile catalyst for photocatalytic hydrogen production
(PHP) and electrocatalytic oxygen reduction reactions. The photocatalytic performance of p-Cof gave rise to 334 μmol h
−1
g
−1
and 575 μmol h
−1
g
−1
of hydrogen
from water splitting under visible light and solar light irradiation, respectively
(Fig. 12b).
In addition to the previously described example of egg valorization toward
the formation of CQDs, egg white from expired eggs was employed as a template in the synthesis of titania with enhanced morphological properties (Fig. 13)
[93]. The use of egg white as template led to an increase in surface area from
10 to 139 m
2
g
−1
as compared with the material prepared in the absence of the
residue. Remarkably, the synthetic process was carried out using a solvent-free
mechanochemical-assisted strategy. Such composite material could be potentially
employed for photocatalysis.
7 Other Examples: Waste‑derived Materials
Graphite-like carbon nitride (g-C 3 N 4 ) has recently emerged as one of the most
widely studied materials, both as a single phase and as part of a photocatalyst.
g-C 3 N 4 can be obtained by thermal treatment of nitrogen-rich precursors. Urea,
thiourea, melamine, cyanamide, and dicyandiamide are some of the common
starting materials. The production of g-C 3 N 4 from urea is a good opportunity for
waste (e.g. agricultural waste) valorization to move toward a circular economy
[94]. Nevertheless, in many examples, the photocatalytic efficiency of the pure
g-C 3 N 4 is limited by the high recombination rate of its photo-generated electron–hole pairs [49, 51]. Combination with metal-containing materials provides
a feasible route toward improving the photocatalytic response of g-C 3 N 4 . Along
these lines, a very recent report describes the valorization of waste toner powder
enriched with organic residues and magnetic Fe 3 O 4 to produce a g-C 3 N 4 –Fe 2 O 3
photocatalyst through a facile one-step calcination process [95]. The toner powder was first calcinated at 600 °C to produce the Fe 2 O 3 structure and then subjected to a second calcination treatment in the presence of thiourea (450 °C in
a muffle furnace for 2 h). Figure 14a shows a high-resolution transmission electron microcopy (HR-TEM) image of the pure Fe 2 O 3 toner-derived material in
which the (110) plane of α-Fe 2 O 3 can be identified. A similar result was derived
from microscopy analysis of the g-C 3 N 4 –Fe 2 O 3 composite samples, as shown in
Fig. 14b, demonstrating the successful formation of a heterojunction and close
contact between g-C 3 N 4 and Fe 2 O 3 . As expected, the introduction of iron oxide in
the structure led to enhanced visible light absorption as demonstrated by UV–Vis
spectroscopy (Fig. 14c). Such enhancement, in addition to a drastic reduction
in electron–hole pair recombination as demonstrated by photoluminescence,
yielded an outstanding material for MO and textile effluent degradation (Fig. 14d)
under sunlight-type illumination conditions. Last but not least, the composite
18
Reprinted from the journal