Environmental Engineering Reference
In-Depth Information
(a)
(b)
[001]
[011]
[02-11]
[010]
[11-1]
[-100]
O
2-
Cu
+
figure 3.15
The atomic arrangement in (100) (a) and (111) (b) planes of the Cu
2
O structure, respectively. Reproduced by permission
from Ref. [131]. © 2011, American Chemical Society.
different atomic arrangement of the exposed surfaces, Cu
2
O octahedral crystals bounded by {111} facets exhibited
higher activity in killing
E. coli
than cubic ones bounded by {100} facets. There is a difference in the inactivation activ-
ities between Cu
2
O cubic crystals and octahedral crystals because of the atomic arrangement of the exposed crystallo-
graphic facets. Cu
2
O has a cuprite crystal structure, which is composed of a body-centered cubic packing of oxygen
atoms with copper atoms occupying half of the tetrahedral sites. As shown in Figure 3.15, the structural arrangement
perpendicular to the [100] direction alternates between copper- and oxygen-containing planes. The two layers repeat
alternatively to maintain stoichiometry and charge neutrality. An ideal {100} plane should be either copper- or oxygen-
terminated. However, considering that the synthesis process was carried out in an aqueous medium, a copper-terminated
plane would be rather unstable due to the active interaction with the hydroxyl group. Here, the oxygen-terminated {100}
plane is expected for Cu
2
O cubic crystals. As regards the [111] direction, an ideal {111} plane possesses hexagonal sym-
metry. every Cu-containing plane is sandwiched between two O-containing planes. The three-plane unit repeats to sat-
isfy stoichiometry and charge neutrality. Thus, the ideal {111} plane should be terminated by an outer layer of oxygen
anions, with a second atomic layer of Cu
+
cations and a third atomic layer of oxygen anions. every two Cu atoms have
a dangling bond perpendicular to the {111} planes. Thus, the {111} plane is expected to possess a higher energy status
than the {100} plane that is 100% oxygen terminated. On the basis of the analysis of the relationship between the mor-
phology of different exposed surfaces and chemical activities, it is predicted that the octahedral crystals bounded by the
{111} facet are more active than the cubic crystals exposed with the {100} plane. experimental results agree well with
this analysis.
Though antibacterial activities of Cu
2
O were extensively investigated, very little attention has been paid to photocata-
lytic antibacterial activities of Cu
2
O. To the best of our knowledge, the photocatalytic activity of disinfection for pristine
Cu
2
O has been reported only by our group [182] until now. We prepared different morphologies of Cu
2
O films by copper
anode oxidation by controlling the reaction conditions (current density, temperature, and the reaction time). With the
increase in current density, nanonet, nanosheet, and nanorod arrays of Cu
2
O can be obtained. The Cu
2
O nanorod shows the
best photocatalytic activity for disinfection, and the disinfection efficiency can reach 90.85% in 1 h and 100% in 2 h. As we
know, Cu
2
O is unstable in aqueous solution under irradiation, and the oxidation product Cu
2+
ion or CuO and the reduction
product Cu can inactivate bacterium directly. Thus, compared with traditional TiO
2
photocatalysts for water disinfection,
Cu
2
O can not only harvest solar light due to its narrow band gap and inactivate bacteria under irradiation, but also kill
bacterium in the dark.
Cu
2
O-based NPs were extensively investigated for photocatalytic water disinfection. Wang et al. [183] prepared Cu
2
O
NPs-sensitized ZnO nanorod arrays on the indium tin oxide coated glass substrate via a facile electrodeposition process. Under
simulated sunlight illumination, the Cu
2
O NPs-sensitized ZnO nanorod arrays show a significant photocatalytic antibacterial
performance. Wong P.K.'s group [184] synthesized a VL-driven photocatalyst Cu
2
O-CuO/Sr
3
BiO
5.4
by the precipitation
method; 5.4 log of
E. coli
can be inactivated within 3 h in a Cu
2
O-CuO/Sr
3
BiO
5.4
suspension under VL irradiation provided
by the fluorescent lamps. Compared with Cu
2
O-CuO/Sr
3
BiO
5.4
suspension, a Cu
2
O/TiO
2
nanotube (TNT) [185] film
