Environmental Engineering Reference
In-Depth Information
activity for dimethyl phthalate degradation than that of TiO
2
produced by a sol-gel process. The effectiveness of TiO
2
/uv/O
3
system was more than that of the TiO
2
/uv/O
2
(uv/O
3
) system, implying a synergistic effect between photocatalysis and
ozonation [45].
The efficiency of nano-ZnO particles has been studied for two different sizes: nano- and microsized particles, to study the
effect of catalyst size on catalytic ozonation of 4-nitrochlorobenzene (4NCB). The effect of pH was also examined. According
to the results, with increasing particle size from nanosize to microsize range and pH from 3.0 to 9.0, a higher degradation of
4NCB was obtained. Based on these results, it is suggested that the hydroxyl radical does not affect the degradation of 4NCB,
but the surface of the catalyst plays an important role [46]. in contrast, a high degree of degradation during catalytic ozonation
of dye and formaldehyde was achieved using mgO nanoparticles. in both cases, the catalyst has the ability to enhance the
decomposition of ozone and promotes the formation of OH
·
radicals [47].
Catalytic ozonation was carried out in the presence of nanosized magnetite and biogenic magnetite. Both of them were found
to enhance the degradation of
para
-chlorobenzoic acid. The surface functional groups are responsible for the catalytic activity.
despite having more surface functional groups, the catalytic efficiency of biogenic magnetite is less than that of nanosized
magnetite, as a result of the formation of bigger aggregates of biogenic magnetite than of nanosized magnetite [41].
To determine the effect of morphology on catalytic performance, CeO
2
nanoparticles with varying morphology (aggregates
of irregularly shaped particles, crystalline, irregular aggregate morphology) were prepared to study the catalytic ozonation of
phenol. The differences in the catalytic activity demonstrated by these three oxides were attributed to amounts of Ce
3+
on the
CeO
2
surface and, consequently, to the demand for oxygen to burn each precursor [48].
The combined use of ozone and AC has been identified as an interesting alternative to destroy toxic organic compounds.
However, AC is easily oxidized in the process of ozonation. Ozone attacks AC, leading to soluble organic matter production,
which increases the dissolved total organic carbon concentration in the absence of organic compounds [49]. CNTs may be more
suitable for catalyst support than AC in liquid phase reactions. liu et al. [50] showed that a higher catalytic activity was
obtained for Pt deposited on CNTs than for Pt deposited on AC. The mechanism assumes radical chain reactions. mWCNTs
with different surface chemical properties were prepared by gonçalves et al. The correlation between surface properties of the
mWCNTs and their performances as catalysts for the degradation of oxalic and oxamic acids through ozonation were evalu-
ated. generally, a low acid character of the catalysts enhances the efficiency of this process. mWCNTs present a higher
catalytic activity compared to AC, which was justified by the differences in their surface chemistry [51].
depositing noble metals (e.g., Au, Ag, and Pt) on the semiconductors is one of the best-known methods used to enhance
catalytic activity. it is reported that noble metals can act as electron sinks to enhance the interfacial charge transfer processes
[52]. However, it requires a solid support or stabilizing agent to interact with the various substrates. Some attempts have been
made recently to study the ozonation reactions in the presence of gold nanoparticles [9t, 53]. For example, the catalytic ozona-
tion of acid orange 10 in the presence of Au-Bi
2
O
3
/Bi
2
O
3
nanocatalysts was investigated by Pugazhenthiran et al. [2]. β-mnO
2
nanowires have potential utility as catalysts for catalytic ozonation of organic compounds. For example, dong et al. [54]
revealed high efficiency of β-mnO
2
nanowires as a catalyst of phenol ozonation. A free radical mechanism was proposed which
involves ozone decomposition and hydrogen peroxide formation. Furthermore, it was observed that mn ions dissolving into the
solution negatively impact the efficiency of the catalytic process [40].
membrane application in surface water treatment provides many advantages over conventional treatments. However, this
effort is hampered by the fouling issue. Ozone has been used to resolve the fouling issue; however, only ceramic membranes
can be used in combination with ozone, as they are resistant to ozone. Coating the ceramic membranes with catalytic materials
such as iron oxide [55] or manganese oxide has been shown to reduce their fouling [56] as they catalyze the oxidation of the
organic foulants that deposit on the membrane surface. Corneal et al. discussed the effect of the number of coating layers on
the structure of the resulting catalytic coating, and the filtration performance of the manganese oxide-coated membranes.
The results showed that intermittent catalytic ozonation effectively maintained high permeate fluxes and prevented membrane
fouling, as compared to that observed with the uncoated membrane [57].
24.4
catalytic electrochemical processes
electrochemical methods for environmental applications are not a new technology. Anodic oxidation of wastewater was first
mentioned as early as 1890. However, regarding cost-effectiveness, electrochemical techniques are still unfeasible in
comparison with traditional biological techniques. in recent years, many investigations have been especially focused on the
improvement of the electrocatalytic activity of electrode materials to facilitate the degradation efficiency of pollutants [58].
Attempts for an electrochemical oxidation treatment for organic pollutants can be divided into two categories: direct
oxidation at the anode and indirect oxidation using appropriate, anodically formed oxidants. The direct electro-oxidation
