Efficient peroxydisulfate activation process not relying on sulfate radical generation for water pollutant degradation.

TLDR: It is reported that copper oxide (CuO) can efficiently activate PDS under mild conditions without producing sulfate radicals and shows significant advantages over sulfate radical oxidation by achieving much higher 2,4-DCP degradation capacity and avoiding the formation of highly chlorinated degradation products.

Abstract: Peroxydisulfate (PDS) is an appealing oxidant for contaminated groundwater and toxic industrial wastewaters. Activation of PDS is necessary for application because of its low reactivity. Present activation processes always generate sulfate radicals as actual oxidants which unselectively oxidize organics and halide anions reducing oxidation capacity of PDS and producing toxic halogenated products. Here we report that copper oxide (CuO) can efficiently activate PDS under mild conditions without producing sulfate radicals. The PDS/CuO coupled process is most efficient at neutral pH for decomposing a model compound, 2,4-dichlorophenol (2,4-DCP). In a continuous-flow reaction with an empty-bed contact time of 0.55 min, over 90% of 2,4-DCP (initially 20 μM) and 90% of adsorbable organic chlorine (AOCl) can be removed at the PDS/2,4-DCP molar ratio of 1 and 4, respectively. Based on kinetic study and surface characterization, PDS is proposed to be first activated by CuO through outer-sphere interaction, the rate-limiting step, followed by a rapid reaction with 2,4-DCP present in the solution. In the presence of ubiquitous chloride ions in groundwater/industrial wastewater, the PDS/CuO oxidation shows significant advantages over sulfate radical oxidation by achieving much higher 2,4-DCP degradation capacity and avoiding the formation of highly chlorinated degradation products. This work provides a new way of PDS activation for contaminant removal.

Figures

Figure 6. Comparison of PDS/CuO with Co2+/PMS for 2,4-DCP degradation. Conditions:

Figure 5. Influences of PDS dose on 2,4-DCP decomposition (A: [2,4-DCP]o = 5 µM, CuO dose = 400 mg L-1), 2,4-DCP dose on PDS decomposition (B: [PDS]o = 20 µM, CuO dose = 400 mg L-1), and CuO dose on PDS decomposition (C: [PDS]o = 20 µM, [2,4-DCP]o = 10 µM) during PDS/CuO oxidation. Conditions: pH = 5.8, T = 20 oC.

Figure 2. Influences of pH on the degradation rates of 2,4-DCP and 2,4,6-TCP in PDS/CuO oxidation and copper leaching in 2,4-DCP degradation. Conditions: [PDS]o = 20 µM, [2,4-DCP]o/ [2,4,6-TCP]o = 5 µM, CuO dose = 200 mg L -1, reaction time = 20 min, T = 20 oC, error bars representing the deviation of three replicates.

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Copyright
Ecient Peroxydisulfate Activation Process Not Relying
on Sulfate Radical Generation for Water Pollutant
Degradation
Tao Zhang, Yin Chen, Yuru Wang, Julien Le Roux, Yang Yang, Jean-Philippe
Croue
To cite this version:
Tao Zhang, Yin Chen, Yuru Wang, Julien Le Roux, Yang Yang, et al.. Ecient Peroxydisulfate
Activation Process Not Relying on Sulfate Radical Generation for Water Pollutant Degradation. En-
vironmental Science and Technology, American Chemical Society, 2014, 48 (10), �10.1021/es501218f�.
�hal-01211451�

1
Efficient peroxydisulfate activation process not relying on sulfate
radical generation for water pollutant degradation
Tao Zhang
a
, Yin Chen
b
, Yuru Wang
a
, Julien Le Roux
a
, Yang Yang
c
and Jean-Philippe Croué
a*
a. Water Desalination and Reuse Center, King Abdullah University of Science and Technology,
Thuwal 4700, Kingdom of Saudi Arabia
b. KAUST Catalysis Center, King Abdullah University of Science and Technology, Thuwal 4700,
Kingdom of Saudi Arabia
c. Advanced Nanofabrication Imaging and Characterization Lab, King Abdullah University of
Science and Technology, Thuwal 4700, Kingdom of Saudi Arabia
* Corresponding author: Tel.: + 966 (0) 2 808 2984.
E-mail address: jp.croue@kaust.edu.sa

2
TOC Art

3
ABSTRACT
Peroxydisulfate (PDS) is an appealing oxidant for contaminated groundwater and toxic industrial
wastewaters. Activation of PDS is necessary for application because of its low reactivity. Present
activation processes always sulfate radicals as actual oxidants which unselectively oxidize organics
and halide anions reducing oxidation capacity of PDS and producing toxic halogenated products.
Here we report that copper oxide (CuO) can efficiently activate PDS under mild conditions without
producing sulfate radicals. The PDS/CuO coupled process is most efficient at neutral pH for
decomposing a model compound, 2,4-dichlorophenol (2,4-DCP). In a continuous-flow reaction with
an empty-bed contact time of 0.55 min, over 90% 2,4-DCP (initially 20 µM) and 90% of adsorbable
organic chlorine (AOCl) can be removed at the PDS/2,4-DCP molar ratio of 1 and 4, respectively.
Based on kinetic study and surface characterization, PDS is proposed to be first activated by CuO
through outer-sphere interaction, the rate-limiting step, followed by a rapid reaction with 2,4-DCP
present in the solution. In the presence of ubiquitous chloride ions in groundwaters/industrial
wastewater, the PDS/CuO oxidation shows significant advantages over sulfate radical oxidation by
achieving much higher 2,4-DCP degradation capacity and avoiding the formation of highly
chlorinated degradation products. This work provides a new way of PDS activation for contaminant
removal.

4
INTRODUCTION
Persulfates, including peroxymonosulfate (PMS) and peroxydisulfate (PDS), have received
increasing interest in recent years in both research and application for the remediation of organic
pollutants in groundwater and wastewaters. They are relatively stable, thus favoring storage and
transportation. When activated by alkaline, UV, heat and transition metals, they can produce strong
sulfate radicals.
1−5
PDS ($0.74 per kg) is much cheaper than PMS (sold as Oxone
(KHSO
5
·1/2KHSO
4
·1/2K2SO
4
), $2.2 per kg) and even cheaper than H
2
O
2
($1.5 per kg), thus having
a better application potential.
6−8
Activated PDS is applied for in situ chemical oxidation (ISCO) for
contaminated groundwater.
9
It could also be an alternative to Fenton or Fenton-like oxidation for
the treatment of toxic wastewaters containing high concentrations of organic contaminants.
10,11
Since PDS itself has very low reactivity towards organic pollutants, activation processes are
necessary for its application.
9, 12
Heating and alkaline addition are usually recommended as feasible
PDS activation methods for ISCO.
3, 13
UV irradiation leading to homolytic cleavage of PDS is a
well-known wet oxidation technique applied in TOC analyzers. Electron donors such as low valent
metals (Fe
o
, Fe
2+
and Ag
+
) can also react with PDS to generate sulfate radicals.
1, 14, 15
All these
activation methods intensively consume energy or chemicals. It was recently reported that some
organic compounds (e.g. quinones and phenoxides) could also react with PDS to generate sulfate
radicals,
16, 17
but these organics cannot be artificially introduced into contaminated waters for
technical and environmental reasons (i.e., toxicity). Metal oxides or minerals (e.g., Fe
2
O
3
, α-FeOOH
and MnO
2
) received particular attention to heterogeneously activate PDS, because they are not
consumed during the activation and no additional energy is required.
18, 19
However, the low
efficiency of present heterogeneous activation processes in terms of long contact time (usually in