Environmental Engineering Reference
In-Depth Information
3
Cu
2
O-Based NaNOCOmpOsites fOr eNvirONmeNtal
prOteCtiON: relatiONship BetweeN struCture
aNd phOtOCatalytiC aCtivity, appliCatiON,
aNd meChaNism
Liangbin Xiong
1
, Huaqing Yu
1
, Xin Ba
2
, Wenpei Zhang
2
, and Ying Yu
2
1
School of Physics and Electronic-Information Engineering, Hubei Engineering University, Xiaogan, China
2
Institute of Nanoscience and Nanotechnology, College of Physical Science and Technology, Central China Normal University, Wuhan, China
3.1
iNtrOduCtiON
Photocatalytic organics degradation and H
2
evolution by using semiconductor photocatalysts have attracted considerable
interest since the pioneering work of Fujishima and Honda [1], who proved that water can be photoelectrochemically decom-
posed into hydrogen and oxygen by using a semiconductor (TiO
2
) electrode under ultraviolet (UV) irradiation. Photocatalysis
for water purification and wastewater treatment was also extensively studied, and it was proven to be a cost-effective, safe, and
promising alternative since Matsunaga et al. [2] first reported the efficiency of photocatalytic oxidation of
Saccharomyces
cerevisiae
(yeast),
Lactobacillus acidophilus
,
Escherichia coli
, and
Chlorella vulgaris
(green algae) in water using a Pt-TiO
2
photocatalyst upon illumination with near-UV light in 1985. In the past few decades, improvements in photocatalytic efficiency
have focused on the following two aspects: (1) increasing the absorption range of the solar spectrum and enhancing quantum
efficiency by modifying TiO
2
, for example, with noble metals [3-10], by doping, [11-14] and by coating with other semicon-
ductors (Fe
2
O
3
[15, 16], WO
3
[17-19], V
2
O
5
[20], Cu
2
O [21], CdS [22]), which were done in the late 1980s to develop second-
generation TiO
2
photocatalysts that could absorb both UV (290-400 nm) and visible (400-700 nm) light and thereby enhance
the overall efficiency; (2) screening other substitute materials of photocatalytic semiconductors, for example, CdS [23], Cr
2
O
3
[24], BiOX (X = Cl, Br, and I) [25], SrTiO
3
[26], ZnS [27], Fe
2
O
3
[28], ZnO [29], and Cu
2
O [30].
Copper (I) oxide (Cu
2
O, cuprous oxide) was the first substance known to behave as a semiconductor, together with
selenium. In 1916, photoconductivity of cuprous oxide was observed. After that, its semiconductor properties were inves-
tigated. Historically, the first real solar cell with Cu
2
O was fabricated by the end of 1920 [31, 32]. Rectifier diodes based
on this material were used industrially as early as 1924, and most theories on semiconductors were developed using the data
on Cu
2
O-based devices. Before the application of silicon, the use of Cu
2
O in the transistor industry was reported. In the
early 1950s, doping of silicon and germanium was discovered; these elements became the standard, and the attention on
Cu
2
O declined.
As a matter of fact, during the oil crisis of the 1970s, significant research effort was devoted to the study of alternative energy
supplies, and Cu
2
O, a very potential candidate material for solar energy conversion, came back into the limelight after several
decades. In 1998, Hara et al. [30] reported that illuminated Cu
2
O particles acted as photocatalysts in the evolution of H
2
and O
2
from water and that the particles displayed long-term (up to 1900 h) stability. Since then, extensive investigations on the photocatalytic
