Topics in Current Chemistry (2020) 378:3
1 3
is structurally well defined, fine control at a nanometer level can be achieved. This
is the case of previously reported work in which TiO 2 anatase nanocrystals with
exposed {001} facets were effectively prepared by recycling the waste anodic electrolyte containing ethylene glycol [58]. Figure 2 shows the extraction (h) and analysis (f, g) of the waste anodic electrolyte produced from the anodization process.
The electrolyte was later subjected to a calcination process from which the crystal size of the particles and the percentage of exposed {001} facets were relatively
easily adjusted over a wide range after cooling to room temperature. The anatase
TiO 2 and N-doped TiO 2 (TiO 2 –xNx) exhibited higher photocatalytic activity than
the P25 TiO 2 commercial sample for humic acid (HA) and bentazone degradation
(Fig. 2i–k). Recyclability tests also indicated potential reusability of the obtained
photocatalysts [58].
3 ZnO‑based Materials: Zn from Waste
ZnO has been proposed as an alternative photocatalyst to TiO 2 , as it possesses similar band gap energy but exhibits higher absorption efficiency under sunlight irradiation than TiO 2 [59]. Galvanizing plants produce a significant amount of Zn-containing waste, which constitutes an interesting opportunity to produce cheap ZnO-based
materials. In a representative work, ZnO nanoparticles obtained from Zn dust waste
from a hot-dip galvanizing plant were used as a photocatalytic material for MB. The
study analyzed the influence of precipitation pH level and amount of hydroxypropyl
cellulose added during the hydrothermal process on sample morphology and photocatalytic response. ZnO nanorods of different sizes were synthesized, obtaining
optimal activity at pH = 12 and 0.10% (w/v) of hydroxypropyl cellulose [60]. As
expected, agglomeration of the structure and reduced superficial area were generally found to lead to worse photocatalytic activity. In fact, the real illuminated area,
which was associated with the total superficial area, was shown to be one of the most
important parameters for obtaining outstanding quantum efficiency results [61]. A
Zn dust-derived material with very large surface area was recently reported [62].
The proposed synthetic approach includes the valorization of polyethylene terephthalate (PET) bottle waste to produce a 3D mesoporous carbon (graphite) nanocomposite using a simple thermal decomposition method. As presented in Fig. 3a, b, the
carbon structure exhibited a nanosheet appearance, while ZnO particles appeared
with relatively good dispersion on the carbonaceous surface. Figure 3c shows the
degradation efficiency of MB, with the C/C 0 ratio as a function of irradiation time
in the presence of samples PET 700, PETZ 0.1, PETZ 0.5, PETZ 0.75, and PETZ
1.0 (denoting the reference sample obtained in the absence of Zn dust and samples
obtained using 10 g of plastic and 0.1, 0.5, 0.75, and 1 g of Zn dust, respectively).
The waste-derived nanocomposites exhibited superior photocatalytic activity for
the degradation of organic dyes (MB and malachite green) under UV illumination.
Composites obtained by upcycling of plastic/metal mixed waste could represent an
attractive opportunity in photocatalysis since, as the authors noted, plastic and metal
waste exist together in several industries, for example in electronic waste, medical
waste, batteries, and accumulators [62]. Another interesting contribution that can be
6
Reprinted from the journal
1 3
is structurally well defined, fine control at a nanometer level can be achieved. This
is the case of previously reported work in which TiO 2 anatase nanocrystals with
exposed {001} facets were effectively prepared by recycling the waste anodic electrolyte containing ethylene glycol [58]. Figure 2 shows the extraction (h) and analysis (f, g) of the waste anodic electrolyte produced from the anodization process.
The electrolyte was later subjected to a calcination process from which the crystal size of the particles and the percentage of exposed {001} facets were relatively
easily adjusted over a wide range after cooling to room temperature. The anatase
TiO 2 and N-doped TiO 2 (TiO 2 –xNx) exhibited higher photocatalytic activity than
the P25 TiO 2 commercial sample for humic acid (HA) and bentazone degradation
(Fig. 2i–k). Recyclability tests also indicated potential reusability of the obtained
photocatalysts [58].
3 ZnO‑based Materials: Zn from Waste
ZnO has been proposed as an alternative photocatalyst to TiO 2 , as it possesses similar band gap energy but exhibits higher absorption efficiency under sunlight irradiation than TiO 2 [59]. Galvanizing plants produce a significant amount of Zn-containing waste, which constitutes an interesting opportunity to produce cheap ZnO-based
materials. In a representative work, ZnO nanoparticles obtained from Zn dust waste
from a hot-dip galvanizing plant were used as a photocatalytic material for MB. The
study analyzed the influence of precipitation pH level and amount of hydroxypropyl
cellulose added during the hydrothermal process on sample morphology and photocatalytic response. ZnO nanorods of different sizes were synthesized, obtaining
optimal activity at pH = 12 and 0.10% (w/v) of hydroxypropyl cellulose [60]. As
expected, agglomeration of the structure and reduced superficial area were generally found to lead to worse photocatalytic activity. In fact, the real illuminated area,
which was associated with the total superficial area, was shown to be one of the most
important parameters for obtaining outstanding quantum efficiency results [61]. A
Zn dust-derived material with very large surface area was recently reported [62].
The proposed synthetic approach includes the valorization of polyethylene terephthalate (PET) bottle waste to produce a 3D mesoporous carbon (graphite) nanocomposite using a simple thermal decomposition method. As presented in Fig. 3a, b, the
carbon structure exhibited a nanosheet appearance, while ZnO particles appeared
with relatively good dispersion on the carbonaceous surface. Figure 3c shows the
degradation efficiency of MB, with the C/C 0 ratio as a function of irradiation time
in the presence of samples PET 700, PETZ 0.1, PETZ 0.5, PETZ 0.75, and PETZ
1.0 (denoting the reference sample obtained in the absence of Zn dust and samples
obtained using 10 g of plastic and 0.1, 0.5, 0.75, and 1 g of Zn dust, respectively).
The waste-derived nanocomposites exhibited superior photocatalytic activity for
the degradation of organic dyes (MB and malachite green) under UV illumination.
Composites obtained by upcycling of plastic/metal mixed waste could represent an
attractive opportunity in photocatalysis since, as the authors noted, plastic and metal
waste exist together in several industries, for example in electronic waste, medical
waste, batteries, and accumulators [62]. Another interesting contribution that can be
6
Reprinted from the journal