As an inactive electrode, PbO2-based electrode can produce abundant hydroxyl radicals which are beneficial to
the degradation of organic pollutants. In recent years, as a widely used material in electrochemical oxidation
technology, more and more PbO2-based electrodes have attracted much attention due to their high oxygen
evolution potential, high catalytic activity and good stability. Presently, most of the articles are devoted to the
modification of the electrode. To better understand electrochemical degradation of pollutants from waste water,
this review summarizes the research progress of wastewater treatment in recent years.
With the acceleration of population growth, industrialization and
urbanization, the problem of global water shortage has become increasingly
prominent, while water pollution has become increasingly
serious, and water quality has declined seriously, which threat human
life and health [1-5]. The goal of ecological civilization construction
and carbon neutrality have appeal human beings to protect the environment
[6]. Under the goal of double carbon, water treatment has received
widespread attention, which requires the synergy of pollution
reduction and carbon reduction in the field of water treatment [7-10].
For water resources management, many effects have been devoted to
improve the current situation [11-13]. In addition, in order to cope
with water shortage and pollution problems, some researchers have
been working to develop new water treatment technologies including
nanofiltration, ultrafiltration and reverse osmosis based on membrane
separation technology, photocatalytic water treatment, electrocatalytic
water treatment and water treatment technology based on
solar energy, which have the advantages of less energy consumption,
less pollution and higher purification rate, [5, 14]. Among them, electrocatalytic
technology has been welcomed due to its efficient energy
conversion, diversity of catalyst design, and environmental friendliness.
Recently, various electrocatalytic oxidation electrode materials
have been used for wastewater treatment. Electrocatalytic electrodes
are divided into two categories: active electrodes (Pt, IrO2, RuO2)
and inactive electrodes (SnO2, PbO2, BDD), which include noble metals
(such as Pt or Mn), carbon and graphite, metal oxide (MO) and
mixed metal oxide (MMO), boron doped diamond (BDD) and other
composite electrodes [15-17]. Among them, the most commonly used
electrodes are BDD, PbO2 and SnO2, because they have high oxygen
evolution overpotential (OER) and superior electrocatalytic performance
during the oxidation of organic pollutants. Previous studies
have shown that BDD has high chemical stability, strong anti-pollution
ability, and high oxygen evolution overpotential [18]. However,
its production cost is relatively high and complex, and its market supply
is limited. SnO2 is also an efficient anode material, but it is usually
prepared by thermal deposition method, which has poor stability
at high temperature and short service life [19, 20]. In contrast, PbO2
is considered to be the excellent anode material because of its easy
preparation, low cost, high corrosion resistance and hydroxyl radical
(•OH) generation ability [21, 22]. To further realize the treatment of
wastewater, this paper first discusses the research progress of PbO2-
based electrode on the degradation of different kinds of pollutants.
Then, the electrocatalytic oxidation was studied. Finally, some future
prospects were put on electrocatalytic water treatment.
The dyes used in the printing and dyeing process would be discharged
within wastewater, seriously causing water pollution. Dye
wastewater has the characteristics of high chroma, high alkalinity,
high content of organic pollutants and large changes in water quality.
Moreover, the dyes are chemically stable and difficult to be biodegraded,
posing a threat to the environment and human health
(Figure 1&2). In the published papers, most are composite electrocatalytic
materials used for dye degradation. Sanaa El Aggadi, et al.
[ 23] used iron (III)-doped PbO2 to decompose phthalocyanine dyes,
achieving a degradation effect of 92.7 % under the optimal experimental
conditions. Besides, Sanaa El Aggadi, et al. [24] prepared Fe/C
doped lead dioxide modified anode for electrocatalytic degradation
of reactive yellow 14 dye. Some azo dyes can not only produce aromatic
amines during decomposition, but also produce carcinogenic
aromatic amines after contact with the skin. Therefore, Yuan Zeng Jin,
et al. [25] designed Ti/SnO2-Sb/α -PbO2/Fe-β-PbO2-PTFE electrode
to degrade methyl orange. In addition, Ce modified Ti-PbO2 electrode
was also used for the degradation of reactive brilliant blue KN-R [26].
Basic dyes of rhodamine B and fuchsin were respectively degraded
by MXene (Ti3C2Tx) modified Ti/PbO2 as well as cerium and sodium
dodecyl benzene sulfonate co-modified Ti/PbO2 electrode [27, 28].
Moreover, the positive dye methylene blue was also degraded by rare
earth element doped PbO2 [29].
Figure 1
Phenolic Wastewater
Phenol-containing wastewater mainly comes from coking, refining,
petrochemical, gas power plants, plastics, resins, insulation materials,
wood preservation, pesticides, chemical industry, papermaking,
synthetic fiber and other industries. The corresponding wastewater
contains phenols, chlorophenols, phenoxy acids, ammonia, sulfides,
cyanide, tar and other substances, showing high chemical oxygen demand
(COD), wide pollution range and great harm, which has brought
serious harm to human body, water body, fish and crops. It is mainly
manifested in toxic effects on humans, harming to water bodies and
aquatic organisms, as well as crops [30-35]. Nitrophenol as a toxic
and refractory organic matter largely affects the environment, which
is easy to be adsorbed and accumulated in soil and water. Importantly,
only a very small amount of nitrophenol exists in the atmosphere,
mainly through wet deposition into water and soil. C. Borrás
et al. studied the oxidation of p-chlorophenol and p-nitrophenol by
Bi-PbO2 [36]. In addition, 3DN-PbO2 [37] and Ti/Ti4O7-PbO2-Ce [38]
were respectively prepared to degrade p-nitrophenol. Besides, trinitrophenol
can be efficiently degraded by PbO2-ZrO2 anode solid. It has
been reported that ZnO/PEG-Co(II)-PbO2 composite electrode was
prepared by anodic electrodeposition [39], and used for electrocatalytic
degradation of phenol. Additionally, PbO2-ILs/Ti electrode has
been attempted to degrade Bisphenol A [40]. A composite electrode
of Ti/SnO2-Sb/PPy/PbO2 was also designed and prepared to degrade
m-cresol [41]. Polyethylene glycol assisted synthesis of praseodymium
doped PbO2 electrode shows a high catalytic performance for
chlorophenol degradation [42].
Elemental Compound Pollution
The treatment of wastewater containing mental elements is
an important task for water purification. If poured into water body,
wastewater containing mental elements would become serious threat
to the environment and human health [43, 44]. Some elements such
as arsenic, copper, chromium, cadmium, nickel, zinc, lead, mercury,
and manganese have been identified with toxic and non-biodegradable.
The mentioned elements easily accumulate in groundwater, surface
water, soil, and crops, thereby endangering the health of humans,
animals, and plants. Organic compounds containing one or more elements
such as fluorine (F), chlorine (Cl), bromine (Br) and iodine (I)
can also cause serious environmental pollution [45]. In order to remove
these dissolved elements within wastewater, many effects have
been devoted. Zhijie Chen, et al. [45] summarized the electrocatalytic
degradation of halogenated organic pollutants by PbO2-based anode.
The degradation efficiency of perfluorooctanoic acid (PFOA) on Ti/
SnO2-Sb/PbO2 anode reached 91.1%, while, Ti/SnO2-Sb2O5/PbO2-
PVDF anode showed a higher degradation efficiency for PFOA. The
multilayer TNAs/SnO2/PPy/β-PbO2 anode has an excellent ability for
the electrocatalytic degradation of As (II) [46].
There are many kinds of pollutants, whether it is classified according
to the source of pollutants, such as herbicides, insecticides,
dyes, antibiotics, etc., or the composition of pollutants. The degradation
mechanisms of the wastewater are mainly divided into direct
electro-oxidation and indirect electro-catalytic oxidation. To oxidizing
the organic matter adsorbed on the anode surface by directly losing
electrons is called direct oxidation. Due to the high oxygen evolution
overpotential of the anode, H2O and OH- would undergo oxidation reaction
on the surface of the anode, which loses electrons and generates
•OH [15,47,48]. There is also a process called indirect oxidation.
In this process, organic matter is not directly involved in the electron
transfer process to the anode. The electrolyte solution produces
substances with strong oxidizing ability within the electric field.
These substances serve as an intermediate medium to build a bridge
for electron exchange between pollutants and electrodes, and then
convert macromolecular organic pollutants into low-toxic or even
non-toxic small molecules (Scheme 1). According to the composition
of the electrolyte, the generated oxygen-containing active species are
also different (Eqs. (1) and Eqs(2)). When no other substances are
added to the electrolyte, •OH dominates the oxidative degradation of
pollutants, and •OH reacts with organic pollutants on the anode surface.
This paper comprehensively reviews the development of PbO2-
based electrodes in recent years. The composite electrodes have the
ability to degrade almost common pollutants such as azo dyes in
dyes, nitrophenol wastewater in phenolic wastewater, etc. Finally, the
mechanism of electrocatalytic oxidation is discussed in detail.
Pacheco-Sánchez JH, FJ Isidro-Ortega, IP Zaragoza (2023) Catching CO2 pollutant gas through nanocomposite formed by chitosan with non-circular C16 carbon double ring: VAMP study. Revista Mexicana de Física 690: 31003.
Zhang Z, et al. (2021) Recent progress in engineering approach towards the design of PbO2-based electrodes for the anodic oxidation of organic pollutants. Journal of Water Process Engineering 42: 102173.
Wang H, et al. (2021) Comparison of Ti/Ti4O7, Ti/Ti4O7-PbO2-Ce, and Ti/Ti4O7 nanotube array anodes for electro-oxidation of p-nitrophenol and real wastewater. Separation and Purification Technology, 266: 118600.
ISSN: 2574 -1241
Abstract
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