Tóm tắt: Nghiên cứu sự hình thành tác nhân oxi hóa peroxymonocarbonate và ứng dụng xử lý một số hợp chất màu hữu cơ

MINISTRY OF EDUCATION OF TRAINING
HANOI NATIONAL UNIVERSITY OF EDUCATION

NGUYEN THI HANH

RESEARCH ON PEROXYMONOCARBONATE FORMATION
AND APPLICATION IN THE TREATMENT
OF SOME ORGANIC DYES

Major: Analytical Chemistry
Code: 9.44.01.18

PhD THESIS ABSTRACT

Hanoi – 2022


Place:
Hanoi National University of Education

Advisors:
1. PhD. Nguyen Bich Ngan
Hanoi National University of Education.
2. PhD. Vu Ngoc Duy
University of Science, Vietnam National University Ha Noi.

Reviewer 1: Assoc. Prof. PhD. Nguyen Tuan Dung
Institute of Tropical Technology

Reviewer 2: Assoc. Prof. PhD. Duong Thi Tu Anh
Thai Nguyen University of Education

Reviewer 3: Assoc. Prof. PhD. Pham Thi Ngoc Mai
University of Science, Vietnam National University Ha Noi.

The thesis is completed in Hanoi National University of Education
in 2022

The thesis can be found at:
- National Library of Vietnam
- Library of Hanoi National University of Education


LIST OF PUBLISHED PAPERS
1. Nguyen Thi Hanh, Nguyen Thi Bich Viet, Nguyen Bich Ngan, Vu
Ngoc Duy (2020), Research on the degaradation process of organic
colors by advance oxidative method. Journal HPU2, 69, 3 - 11.
2. Thi Bich Viet Nguyen, Ngan Nguyen Bich, Ngoc Duy Vu, Hien Ho
Phuong and Hanh Nguyen Thi (2021), Degradation of Reactive Blue
19 (RB19) by a Green Process Based on Peroxymonocarbonate
Oxidation System, Journal of Analytical Methods in Chemistry, Volume
2021,
Article
ID 6696600,
8
pages.
( />3. Nguyen Thi Bich Viet, Nguyen Bich Ngan, Nguyen Thi Hanh, Vu
Ngoc Duy (2021), Study on the formation and decomposition of
peroxymonocarbonate (HCO4-) in aqueous solution, Journal of
Analytical Sciences, 26 (3A), 117-120.
4. Nguyen Thi Bich Viet, Ho Phuong Hien, Nguyen Bich Ngan, Nguyen
Thuy Ha, Vu Ngoc Duy, Nguyen Thi Hanh (2021), Decolorization of

Reactive blue 21 textile dye by a peroxymonocarbonate – base oxidation
system, Journal of Analytical Sciences, 26 (Vol espcially),175 – 180.
5. Nguyen Thi Hanh, Pham Thi Huyen, Nguyen Hoai Thu, Nguyen Bich
Ngan, Vu Ngoc Duy, Nguyen Thi Bich Viet (2022), Study on catalytic
activity of Co(II) in Rhodamine B decolorization by
peroxymonocarbonate in aqueous solution, Vietnam Journal of
Chemistry,
60
(special
issue),
96
102
(DOI:
10.1002/vjch.202200089).



1
INTRODUCTION
1. Urgency of the thesis
Environmental pollution and environmental pollution treatment are
worldwide concerns, especially prioritizing effective wastewater treatment
(high efficiency, short treatment time, economy) but not generating secondary
waste are pollution sources. Untreated wastewater discharged into natural water
sources has resulted in environmental pollution by impurities, including organic
dyes, growth chemicals, aromatic compounds, and agrochemicals, organic
compounds containing sulfur and nitrogen... Among the types of production,
the textile industry generates a large amount of wastewater and causes serious
pollution, especially in the country where the textile industry is considered one
of the most important. major export industry like Vietnam. Increased

concentrations of hazardous substances require efficient, cost-effective
techniques for wastewater treatment. Traditional treatment systems such as
physicochemical methods (flocculation, adsorption, ion exchange), chemical
methods (chlorination, ozonation, flocculation) are effective not yet so need
enhanced treatment measures to effectively treat pollutants. Some methods
produce even more toxic compounds.
Advanced oxidation processes are very suitable for removing pollutants
in wastewater, especially persistent organic dyes that are difficult to degrade
biologically. Advanced oxidation processes generate reactive oxygen species
such as hydroxyl radicals •OH, oxygen singlet (1O2) and superoxide (•O2-)…
which can completely remove harmful pollutants. The use of ozone or oxygen
as an oxidizing agent often faces the problem of low gas solubility in solution
leading to high energy consumption, while treatment with H2O2 overcomes this
drawback, so it is more feasible. In previous studies, Fe 2+ agent has been widely
applied as a homogeneous catalyst in the decomposition of organic pollutants.
However, pH range for the Fenton process is quite low (pH 2 ÷ 4) while textile
dyeing wastewater is often highly alkaline (pH 9 ÷ 12) and generates a large
amount of sludge after treatment, leads to high treatment costs and secondary
pollution in practical applications. Therefore, it is necessary to find an advanced
oxidation system that uses environmentally friendly chemicals, does not create
secondary waste, has high efficiency, low cost and has potential for large-scale
application to protect the environment, successfully implement the sustainable
development of the economy.
In recent years, publications on advanced oxidation systems involving
bicarbonate - activated hydrogen peroxide yield a highly active substance called
peroxymonocarbonate (PMC), which is capable of degrading many stable
organic dyes. These studies only mention the rate constants of the forward
reaction and the rate constant of the reverse reaction forming PMC. Meanwhile,
the kinetics of the reaction of formation and decomposition of PMC in aqueous

2
solvent have not been studied. In addition, only 13C NMR nuclear magnetic
resonance method is used to analyze PMC content, so it is necessary to study
more methods to analyze PMC content which are simpler and still give accurate
results. In addition, the works on applying PMC to process pigments focus a lot
on processing efficiency, there is not enough information on the influencing
factors as well as the kinetics of the decolorization process.Therefore, this thesis
chooses the topic: "Research on peroxymonocarbonate formation and
application in the treatment of some organic dyes".
2. Goals of research
The purpose of the thesis is to determine the optimal conditions for the
formation of PMC in solution and evaluate the decolorization activity by
advanced oxidation method based on H2O2 - HCO3- system, thereby developing
the technology, treatment of organic colorants in particular and nonbiodegradable organic substances in general in wastewater in Vietnam.
3. Main research objects and contents
The main research objects of the thesis includes the decolorizing agent
peroxymonocarbonate (PMC) and the treated objects are some organic color
compounds as industrial dyes. PMC is a highly active and unstable substance
and should be prepared in situ from a solution of hydrogen peroxide and
sodium bicarbonate. Information of the formation and decomposition of PMC is
essential. Therefore, this thesis focuses on researching the following main
contents:
(1) Studying the kinetics of formation and decomposition of PMC from
the reaction between hydrogen peroxide and sodium bicarbonate under different
conditions: molar ratio H2O2 : HCO3-, pH, catalyst; building a kinetic model
(determining reaction order, reaction rate constant) to help predict the
concentration of PMC formed and decomposed over time.
(2) Investigation of the ability to handle the dyes: Reactive Blue 19
(RB19), Reactive Yellow 145 (RY145), Reactive Blue 21 (RB21), Rhodamine

B (RhB), Methylene Blue (MB) by PMC when changing conditions such as
oxidant concentration, pH, metal ion catalysts, catalyst concentration, UV
radiation; building a kinetic model of the decolorization process.
4. Scientific significance, practice and new contributions of the thesis
The results of the thesis contribute to adding more scientific basis to the
research base on oxidizing agent PMC and the oxidizing ability of some organic
dyes, in detail:
- Determined the suitable temperature for the quantitative analysis of
PMC in solution in the presence of H2O2 by standard iodine-thiosulfate method.
- Determined the optimized conditions for the fomation of PMC in
solution. From there, built a kinetic model of the fomation and decomposition
of PMC.


3
- Determined the rule of effect of molar ratio H2O2: NaHCO3, metal ion
catalysts, pH, UVC light to the ability to decolorize and mineralize organic
dyes.
- PMC when combined with UVC light has the effect of decolorization,
mineralization organic dyes, reducing COD and TOC values.
These results are the basis for the application of oxidizing agent PMC to
degrade organic dyes in the treatment environment.
5. Structure of thesis
The thesis consists of 115 pages, introduction 4 pages, overview 35
pages, experimental and research methods 18 pages, results and discussion 57
pages, conclusion 1 pages. The thesis consists of 49 figures and 25 tables. 15
pages of references with 138 documents. There is also an appendix with a
length of 17 pages.

4
CHAPTER 1. OVERVIEW
Chapter 1 introduces information about the issues under the research scope of
the thesis, including:
1.1. Textile dyeing wastewater pollution in Vietnam: an introduction to the
status of water pollution and textile dyeing wastewater in Vietnam; toxicity of
textile dyeing wastewater directly and indirectly to humans, aquatic species and
the environment.
1.2. Organic color compounds - Dyes : how to classify dyes, the level of loss to
the environment of reactive dyes is the most. On that basis, focus on introducing
research subjects which are Reactive Blue 19, Reactive Blue 21, Reactive Yellow
145, Rhodamine B, Methylene Blue: structure, properties and toxicity.
1.3. Textile dyeing wastewater treatment methods: introduction of traditional
treatment methods and advanced oxidation methods. On that basis, the research
situation on the treatment method of 5 selected colorants is introduced.
1.4. Peroxymonocarbonate oxidizing agent made from hydrogen peroxide bicarbonate system: introduction to the properties of hydrogen peroxide bicarbonate system and peroxymonocarbonate is an oxidizing agent. From
there, the analytical methods to determine PMC and peracids are presented as
well as the application of PMC in the treatment of organic pollutants, especially
organic dyes.
CHAPTER 2. EXPERIMENTAL AND RESEARCH METHODS
2.1. Chemicals, tools and equipment
2.2. Experimental process
2.2.1. Develop a procedure to determine concentration of
peroxymonocarbonate in solution
a. Synthesis PMC and titration to determine PMC concentration in
solution
The process of synthesizing and determining PMC concentration by low
temperature iodine - thiosulfate titration method is diagrammed in Figure 2.1,
consisting of 2 main steps:
Step 1: Synthesize PMC.

Mix 50 mL of 1 M HCO3- solution and 10.2 mL of 30% H2O2 solution at room
temperature, make up to 100 mL with double distilled water (the initial
concentration of the substances in the solution HCO3- 0.5 M, H2O2 1 M).
Step 2: Titrate to determine the concentration of PMC by iodine thiosulfate method at low temperature.
*Cooling PMC solution:
- Prepare the mixture of ice - salt: mix 2 kg of crushed ice with 1 kg of salt (2:1
ratio in mass), the lowest temperature measured of the mixture is -20oC.


5
- Take exactly 5 mL of PMC solution into a conical flask, add 5 mL of
ethanediol to prevent the solution from solidifying at low temperatures below
0°C. Immerse the flask in the ice - salt mixture to reach the test temperature.
The initial temperature is maintained and monitored throughout the titration
using the MULTI - THERMOMETER electronic thermometer.
*Titration to determine PMC concentration by iodine - thiosulfate method:
Adjust the pH of the test solution to pH = 5 with HCl solution, add the
exact amount of 1.2450 grams of KI (which is the maximum amount of KI that
reacts completely) with 5 mL of PMC if the PMC synthesis efficiency is
considered to be 100% based on 0.5 M NaHCO3).
Close the mouth of the conical flask and leave in the dark for 5 minutes.
Titrate with 0.5 M Na2S2O3 solution until a light yellow color appears, add 2-3
drops of starch indicator and then titrate until the blue color disappears. The
experiments were repeated 3 times and the average results were taken.
HCO3- 1 M

H2O2 30%

Solution HCO4+ C2H4(OH)2.
Place in ice - salt

+ HCl (pH = 5)
+ KI, wait 5 minutes
+ Na2S2O3 0,5 M

Soution after titration

Figure 2.1. Procedure for synthesis and determination of PMC concentration by
low temperature iodine - thiosulfate titration method.
b. Investigate the effect of temperature
Preliminary investigation of the influence of temperatures below 5oC
(from -18oC to 4oC) shows that at some temperatures, volumes of Na2S2O3 are
similar, which can be considered in terms of temperature range. Therefore,
investigating the effect of low temperature below 5oC on titration of 2 solutions
of H2O2 and PMC was conducted in 3 temperature ranges: -18oC ÷ -10oC; - 8 oC
÷ -5 oC; -5 oC ÷ 4 oC.
- Take 5 mL of solution H2O2 1 M into a conical flask (control, with the same
concentration as in PMC solution, pH = 5), add 5 mL of ethanediol, cool down


6
to different temperature ranges. Add KI and titrate with Na2S2O3 0.5 M.
Particularly with the temperature of -18 oC ÷ -10 oC, preliminary survey shows
that the volume of Na2S2O3 0.5 M is very small, so Na2S2O3 0.1 M solution is
used instead. H2O2 reacts with I- according to the reaction:
H2O2 + 3I- + 2H+ → I3- + 2H2O
(2.1)
Titrate the amount of I3 produced with solution Na2S2O3 according to the
reaction:
I3- + 2 S2O32- → S4O62- + 3I(2.2)
Therefore, the concentration of H2O2 in the solution is calculated by the formula:

𝐶𝐻2 𝑂2 =

𝐶𝑁𝑎2𝑆2𝑂3 . 𝑉𝑁𝑎2𝑆2𝑂3
2. 𝑉𝐻2𝑂2

- Take 5 mL of PMC solution, add 5 mL of ethanediol, cool down to
different temperature ranges, add 14 mL of HCl 3 M to adjust to pH = 5, add KI
and titrate with solution Na2S2O3 0.5 M.
Immediately after adding KI to the flask, the solution appears yellowbrown due to the reaction between PMC and I- to produce I2 according to the
reaction:
HCO4- + 3I- + 2H+ → HCO3- + I3- + H2O
(2.3)
Titrate the amount of I3 produced with Na2S2O3 according to the reaction 2.2.
Therefore, PMC concentration is calculated by the formula:
𝐶𝑃𝑀𝐶 =

𝐶𝑁𝑎2𝑆2𝑂3 . 𝑉𝑁𝑎2𝑆2𝑂3
2. 𝑉𝑃𝑀𝐶

2.2.2. Investigate factors affecting peroxymonocarbonate formation and
decomposition
2.2.2.1. Effect of molar ratio H2O2 : HCO3- Mix 50 mL of solution HCO3- 1 M with volumes of H2O2 30% solution (9.8
M) to obtain the molar ratios of the two substances, add volumes of HCl 3 M,
make up to 100 mL with double distilled water to adjust to pH = 8. The specific
conditions are presented in Table 2.1. In which, the concentration of HCO 3- 0.5
M is fixed, the concentration of H2O2 is in turn 1; 2; 2.5; 3; 4 and 4.5 times the
concentration of HCO3-. The reaction mixtures were conditioned for 40 min to
reach equilibrium at room temperature of 25 ± 1°C. Take exactly 5 mL of
sample solution, add KI, and determine the concentration of PMC according to
the iodine-thiosulfate titration method.

Table 2.1. Synthesis of PMC at different molar ratios of H2O2 : NaHCO3
Molar ratio H2O2 : HCO31 : 1 2 : 1 2.5 : 1 3 : 1 4 : 1 4.5 : 1
Volume HCO3 1 M (mL)
50
50
50
50
50
50
Volume H2O2 30% (mL)
5.10 10.20 12.75 15.30 20.40 22.95
pH H2O2 : HCO3 initial
8.62 8.55 8.37
8.27 8.11 8.08
Volume HCl 3M (mL)
0.4
0.25 0.2
0.15 0.1
0.05
Distilled water (mL)
Define level 100 mL


7
Investigate the variation of PMC concentration generated from the H2O2 :
NaHCO3 system with the molar ratio = 2 : 1 and 2.5 : 1 in about 240 minutes
starting from the time of mixing, taking 5 mL of PMC solution every 10
minutes, add KI and titrated to determine PMC concentration.
2.2.2.2. Effect of pH
The HCO4- preparation experiment was conducted at six different pH

values pH = 5; 6; 7; 8; 9; 10; fixed concentration of HCO3- 0.5 M, H2O2 1M,
room temperature 25 ± 1oC. Adjust the pH with HCl 3M or NaOH 2M
solutions. At each pH value, analyze the PMC concentration over
approximately 240 min starting from mixing.
2.2.2.3. Studying the stability of PMC in solution
The H2O2 concentration in the experiments was fixed at 0.4 M, pH = 9
was adjusted with 2 M NaOH solution, room temperature, the reaction flask
volume was 50 mL. The specific experimental conditions are presented in Table
2.3.
Table 2.3. Experimental conditions to study the stability of PMC
Sample [H2O2] M
[HCO3-] M
Co2+ mg/L
1.
0.4
2.
0.4
0.1
3.
0.4
0.2
4.
0.4
0.2
0.1
Take 5 mL of each solution, add 1 mL of H2SO4 2 M solution, and titrate with
KMnO4 0.05 M solution at room temperature:
5 H2O2 + 2 MnO4– + 6 H+ → 2 Mn2+ + 5 O2 + 8 H2O
(2.4)
–

Therefore, the total of concentration of HCO4 + H2O2 in the solution is
calculated by the formula:
C(H2O2+ PMC) =

5. CKMnO4 . VKMnO4
2. Vdung dịch

2.2.2.4. Study on kinetic model of peroxymonocarbonate formation and
decomposition
The process of formation and decomposition of PMC in solution occurs as
follows:
HCO3- + H2O2

k
- H2O

HCO4-

k'

HCO3- + O2

Since H2O2 is used excess than HCO4-, it can be assumed that the
concentration of H2O2 is stable throughout the reaction. The formation reaction
rate (vht) is assumed to follow the first order kinetic model:
vht = k. [HCO3-]
(eq.2.1)
For the decomposition, the decomposition reaction rate (v ph) depends only
on the amount of HCO4- formed and is assumed to follow the first order kinetic

8
model:
vph = k’. [HCO4-]
(eq.2.2)
Overall rate of both formation and decomposition:
d[HCO4-]/dt = vht – vph = k. [HCO3-] – k’. [HCO4-]
(eq.2.3)
The concentrations of HCO3 and HCO4 were obtained from
experimental data when studying the influence of pH on the PMC formation
according to the procedure described in section 2.2.2.2. The rate constants of
formation (k) and decomposition (k') in the above equation are determined by
the model optimization method with experimental data, using the Solver
function in MS Excel to find a suitable value for the model. The computational
model best describes the experimental curve. Optimization steps include:
Step 1: Divide the reaction time into successive simulation steps with
duration = 1 minute. With each step, the differential equation (eq.2.3)
becomes
∆ [HCO4-]/∆t = k. [HCO3-] – k’. [HCO4-]
(eq.2.4)
’
Hay ∆ [HCO4 ] = ( k. [HCO3 ] – k . [HCO4 ])∆t
(eq.2.5)
Step 2: In each simulation step, the variation of HCO3 concentration in step
i is calculated according to step (i - 1):
∆ [HCO3-]i = k. [HCO3-]i-1 ∆t
(eq.2.6)
Concentration of HCO3 after step i:
[HCO3-]i = [HCO3-]i-1 - ∆ [HCO3-]i
(eq.2.7)

Instead into (eq.2.5) to determine the concentration HCO4 .
Step 3: Enter any two values of k and k', calculate according to the theory
of concentration of substances in step 2.
Step 4: optimize the values of k and k' using the Solver function so that
the error between the theoretical value and the experimental measurement result
is minimal.
2.2.3. Evaluation ability of decoloration RB19 by peroxymonocarbonate
2.2.3.1. Construction and statistical processing of RB19 standard curve
Investigate the absorbance spectrum of the dye according to pH = 6, 8, 10,
12 in the wavelength range 200 nm to 800 nm. Select the measurement
wavelength that has maximum optical absorbance and is stable under pH changes.
From the stock solution RB19 1 g/L, prepare standard solutions with
concentrations of 4, 6, 8, 12, 20, 30, 40, 70, 80, 100, 130 mg/L, respectively.
Measure the absorbance on a UV-Vis Biochrom Libra S60 spectrophotometer
at the maximum wavelength. Construct a standard curve showing the
dependence of the absorbance on the RB19 concentration and statistical
processing of the standard curve.
From the measured absorbance of 11 standard solutions with
concentrations from 4 to 130 mg/L, set the R2 value to evaluate the linearity of
the calibration curve. The linearity of the absorbance on the concentration of


9
RB19 with each data range from 1 to 3, 1 to 4, ..., 1 to 11 is evaluated through
the square of the correlation value R2. The expression R2 is calculated in MS
Excel software by the statement:
“= CORREL (range of y values; range of x values)^2”
To calculate statistical values according to the principle of least squares,
use the LINEST function in MS Excel to conduct regression analysis of the
equation of the form y = ax + b. If ∆𝑏 (t 0.05;f) > b, then it is necessary to

consider whether the non-zero b value is significant or not statistically
significant, it is necessary to reprocess the standard curve in the form y = ax.
Evaluate the two variances of two regression equations according to Fisher's
standard. If
𝐹𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡 =

𝑆𝑦2
2
𝑆𝑦′

< 𝐹𝑡𝑎𝑏𝑙𝑒 (0,95,𝑓1=𝑛−3, 𝑓2 =𝑛−2) , a non-zero value of b has no

meaning, so b = 0.
From there determine the limit of detection (LOD) and limit of quantitation
(LOQ) according to the 3σ and 10σ principles:
3.Sy
10.Sy
𝐿𝑂𝐷 =
; 𝐿𝑂𝑄 =
a
a
2.2.3.2. General procedure for decolorization experiments
Take 100 mL of the PMC solution synthesized after 50 minutes mix H2O2
and HCO3- into a Schott Duran flask (Figure 2.2), place it on a magnetic stirrer
with an appropriate stirring speed, add H2SO4 2M or NaOH 2M to adjust the pH
with the previously investigated volumes. The convention t = 0 is the time when
adding the amount of colorant with concentration of Co (mg/L), Mn+ catalyst (with
catalyzed reactions) added simultaneously. At this time, consider the colorant
concentration C = Co (mg/L). The variation in the concentration of the dyes with
time was determined by sampling the reaction time and then determining the

absorbance. The reactions were carried out at room temperature 25 ± 1°C.

Figure 2.2. The reaction system non UV for the decolorization.
2.2.3.3. Evaluation of the H2O2 decolorization ability
To be able to confirm that the main color processing ability is due to PMC, the
experiments to evaluate the decolorization ability of H2O2 were conducted
independently at room temperature, pH = 8, H2O2 concentration 20 mM, RB19 100
mg/ L without and with catalyst Co2+ 0.1 mg/L in 120 minutes.
2.2.3.4. Evaluation of the effect of PMC concentration
To investigate the effect of PMC concentration (through the effect of


10
NaHCO3 concentration), the experiment was conducted with the general
procedure for decolorization experiments with RB19. In which, NaHCO3
concentration changed from 10, 20, 30, 50, 70, 100 mM, keeping the molar
ratio H2O2 : NaHCO3 = 2 : 1, pH = 8, room temperature 25 ± 1oC, Co2+ 0.1
mg/L within 200 minutes.
2.2.3.5. Evaluation of the catalytic effect of metal ions on the decolorization
process
Testing the experimental activity of metal ions was performed with Ni 2+,
Mn2+, Zn2+, Co2+ all having a concentration of 0.1 mg/L at pH = 8, NaHCO 3 10
mM, H2O2 20 mM, RB19 100 mg/L, temperature 25 ± 1 oC.
To known role of Co2+ in to the RB19 process by H2O2 + HCO3-,
variation of RB19 is researched through 4 independent experiments, including:
1. RB19 + H2O2.
2. RB19 + H2O2 + Co2+.
3. RB19 + H2O2 + HCO3-.
4. RB19 + H2O2 + HCO3- + Co2+.
Conditions are the same in all experiments: NaHCO3 10 mM, H2O2 20

mM, RB19 100 mg/L, Co2+ 0,1 mg/L, pH = 8.
2.2.3.6. Evaluation of the effect of catalyst concentration
The experiment was conducted with the general procedure for
decolorization experiments with Co2+, RB19 100 mg/L, NaHCO3 20 mM, H2O2
40 mM, pH = 8. In which, the concentration of Co2+ changed from 0.01; 0.02;
0.04; 0.06; 0.1 mg/L.
2.2.3.7. Evaluation of the effect of pH
To study the influence of pH on the color processing, RB19 was
investigated at different values. In fact, textile dyeing wastewater has an
alkaline environment, so the selected pH values for investigation are pH = 7, 8,
9 and 10, other experimental conditions are kept constant: RB19 100 mg/L,
NaHCO3 10 mM, H2O2 20 mM, Co2+ 0.1 mg/L, room temperature 25 ± 1oC.
2.2.3.8. Kinetic model of decolorization by concentration of HCO3- and
metal ions
To study the kinetics of the reaction and determine the partial reaction
order of HCO3-, make surveys with concentrations of HCO3- 5, 10, 15, 25, 30
mM, H2O2 40 mM, Co2+ 0.1 mg/L, pH = 8 at room temperature 25 ± 1oC.
To study the kinetics of the reaction and determine the partial reaction
order of Co2+, make survey with concentrations of Co2+ 0.01; 0.02; 0.04; 0.06;
mg/L, HCO3- 20 mM, H2O2 40 mM, pH = 8 at room temperature 25 ± 1oC.
2.2.3.9. Evaluation of the effects of UVC radiation
Studying 10 independent experiments (without UVC and UVC irradiation
for 5 reaction systems respectively), kept fixed RB19 100mg/L; pH = 8,
temperature 25 ± 1oC.


11
1. RB19.
2. RB19 – H2O2 20 mM.
3. RB19 – H2O2 20 mM – Co2+ 0,1 mg/L.

4. RB19 – H2O2 20 mM – HCO3- 10 mM.
5. RB19 – H2O2 20 mM – HCO3- 10 mM – Co2+ 0.1 mg/L.
Decolourization experiments without UVC irradiation for comparison
were performed as described in Figure 2.2. Decolourization experiments with
UVC irradiation were performed as described in Figure 2.3.

Figure 2.3. The continuous UV- irradiated system for the decolorization.
2.2.4. Evaluation ability of decoloration other color compounds by
peroxymonocarbonate
Experiments to evaluate PMC's ability to process RY145, RB21, RhB and
MB dyes were conducted similarly to those of RB19 in order to compare and
then make general rules. In addition, a number of surveys on UVA rays and
ultrasonic vibration are presented to obtain more information when applying
PMC to degrade various dyes in practice.
2.2.4.1. Construction standard curve of dyes
2.2.4.2. Evaluation of PMC to treat dyes according to the concentration of
oxidants
2.2.4.3. Evaluation of PMC to treat dyes with metal ion catalysis
2.2.4.4. Evaluation of PMC to treat dyes by pH
2.2.4.5. Evaluation of PMC to handle dyes when combining PMC and UV
2.2.5. Comparison of the degradability of dyes
2.3. Research Methods
2.3.1. Nuclear magnetic resonance spectroscopy 13C NMR.
2.3.2. Iodine - thiosulfate titration methods
2.3.3. Molecular absorption spectroscopy UV-Vis.
2.3.4. High performance liquid chromatography HPLC.
2.3.5. Method analysis COD index.
2.3.6. Method analysis TOC index.

12
CHAPTER 3. RESULTS AND DISCUSSION
3.1. Formation and decomposition of peroxymonocarbonate in solution
3.1.1. Formation of peroxymonocarbonate in the reaction system
The presence of ion HCO4- in the solution is proved by 13C NMR of HCO3+ H2O2 solution with D2O solvent. The results are presented in figure 3.1.

Figure 3.1. Nuclear magnetic resonance spectroscopy 13C of HCO4- and HCO33.1.2. Analytical procedure for the determination of peroxymonocarbonate
At temperatures below -10°C, the iodine-thiosulfate titration almost exactly
reacts to the amount of HCO4- present in the solution. Therefore, in the process of
synthesizing and determining PMC concentration by low temperature iodine thiosulfate titration method (Figure 2.1), the temperature of the analytical solution
is always maintained below -10oC. The reaction should be titrated at a moderate
rate so that the temperature does not change suddenly.
3.1.3. Factors affecting the formation and decomposition of peroxymonocarbonate
3.1.3.1. Effect of molar ratio H2O2 : HCO3PMC concentration (M)

0,4
0,35
0,3
0,25
0,2
0,15
0,1
0

1

2
3
4
Molar ratio H2O2 : NaHCO3

5

Figure 3.2. Effect of molar ratio H2O2 : NaHCO3 on the amount of HCO4-.


13
To clarify the variation of PMC concentration over time at the molar ratio
H2O2 : NaHCO3 = 2 : 1 and 2.5 : 1; pH = 8, PMC concentration was determined
over a period of 240 min from the start of mixing (Figure 3.3).
PMC concentration (M)

0,4

0,3

0,2

0,1

0
0

50

100

150

200

250

Time (min)

H2O2 : NaHCO3 = 2 : 1

H2O2 : NaHCO3 = 2,5 : 1

Figure 3.3. The concentration of PMC obtained from the system H2O2 :
NaHCO3 = 2 : 1 and 2.5 : 1.
Molar ratio of H2O2 : NaHCO3 = 2 : 1 just created HCO4- is high, it is not
necessary to use excess H2O2 so it should be used in further studies.
3.1.3.2. Effect of pH
Variation of HCO4- concentration over time at mole ratio H2O2 : NaHCO3
= 2 : 1 and different pH values are presented in Figure 3.4.

Figure 3.4. Variation of HCO4- concentration over time at different pH
Therefore, the optimal pH for PMC formation is pH = 9 ÷ 10.
3.1.3.3. Effect of metal ions on the stability of PMC


14

Figure 3.5. Variation of total concentration of HCO4– and H2O2.
A first-order kinetic model has been built to model the reaction rate of the
H2O2 - HCO3– - Co2+ system, the results are shown in Figure 3.6.

Figure 3.6. Kinetic model of the decomposition process of H2O2 - HCO3– - Co2+
3.1.3.4. Kinetic model of peroxymonocarbonate formation and decomposition

The optimal results of the PMC formation rate (k) and PMC decomposition
rate (k') values at each pH value are presented in table 3.4.
Table 3.4. Rate constant for formation and decomposition of HCO4pH k, min -1 k’, min -1 Ratio of k : k’
5 0.0203 0.0235
1:1
6 0.0205 0.0105
2:1
7 0.0379 0.0082
4.6:1


15
8 0.0454 0.0076
6:1
9 0.0598 0.0054
11:1
10 0.053
0.0050
10.6:1
The results show a trend that with increasing pH, the k:k' ratio increases,
that is, the formation of HCO4- dominates (this advantage also increases with
the increase of pH) than its decomposition.
* Discuss the mechanism of formation of peroxymonocarbonate in
solution. In a neutral and weakly alkaline environment, HCO3- ions occupy the
majority of the mole fraction compared to H2CO3 and CO32- forms, HCO3- mole
fraction dependence on pH, so pH has effect on HCO4- formation. The correlation
between the rate constant of the formation reaction k (min-1) and the mole fraction
of HCO3- according to pH is presented in Figure 3.8.

Figure 3.8. Correlation between the dependence of the molar fraction of bicarbonate

on pH and the reaction rate constant for the formation of PMC k (min-1)
Thus, there is a good agreement between the change in mole fraction of
HCO3 and the change in the constant k. As the pH increases, the molar fraction
of HCO3- and the value of the rate constant for the formation of PMC(k) also
increase accordingly and peak at about pH = 9.
3.2. Evaluation of peroxymonocarbonate to treat RB19
3.2.1. Evaluation of the RB19 calibration curve
3.2.1.1. Optimized wavelength: 592 nm
3.2.1.2. Calibration curve and statistical processing RB19
Abs = (8,4 ± 0,02).10-3.CRB19 (mg/L); R2 = 0,9999, LOD = 0,7 mg/L; LOQ =
2,3 mg/L.
3.2.2. Ability decolorization RB19 of H2O2
Under research conditions, H2O2 hardly treats the RB19. Therefore, the
influence of H2O2 can be ignored when evaluating the decolorization activity of
PMC solution in later experiments.


16
3.2.3. Effect of peroxymonocarbonate oxidant concentration
Decolorization of RB19 (%)

20

15

10

5

0

0

50

100

150

200

Time (min)
10 mM

20mM

30mM

50mM

70mM

100mM

Figure 3.12. Processing performance RB19 color with different
concentrations HCO3-. Condition H2O2 : HCO3- = 2 : 1, pH = 8.
NaHCO3 concentrations are 50 and 70mM, both gave the best RB19
decolorization efficiency and were quite similar (reached nearly 20% after 200
minutes).
3.2.4. The effect of metal ion catalysis
Decolorization of RB19 (%)

100
80
60
40
20
0
0

50

100

150

200

Time (min)
Co2+

Mn2+

Zn2+

Ni2+

bare

Figure 3.13. Effect of metal ions to decolorization efficiency of RB19 100 mg/L
Condition: [HCO3-] = 10 mM, [H2O2] = 20 mM, pH = 8, [M2+] 0,1 mg/L.

Among the investigated metal ions (Ni2+, Mn2+, Zn2+, Co2+), only Co2+
catalyst showed the strongest RB19 decomposition efficiency.


17
3.2.5. Effect of catalytic ion concentration Co2+
With a concentration of 0.1 mg/L Co2+, the decolorization reaction
efficiency after 45 minutes reached the highest at 86%. However, cobalt is a
heavy metal, the allowable cobalt concentration in water is 0.1 mg/L, so the Co2+
catalyst concentration is chosen to be 0. 1 mg/L for further studies.
3.2.6. Effect of pH

Decolorization of RB19 (%)

100

80

60

40

20

0
0

50

100

150

200

Time (min)
pH = 7

pH = 8

pH = 9

pH = 10

Figure 3.16. Effect of pH to decolorization efficiency of RB19.
Condition:[HCO3-] = 10 mM, [H2O2] = 20 mM, [Co2+] = 0,1 mg/L
Although at pH = 9, 10, the decomposition of RB19 is better, but from an
economic point of view, raising the pH to high for treatment, then adding acid
to neutralize it before being discharged into the environment. It also means
consuming chemicals, increasing the cost of color treatment. Furthermore, the
HCO3- - H2O2 system itself is a buffer system with pH = 8 - 9 depending on the
molar ratio of the two substances. Therefore, pH = 8 is chosen to continue
investigating other conditions for RB19 degradation with the aim of finding the
most optimal degradation conditions for RB19 pigment both in terms of
treatment efficiency as well as economic efficiency and environmental
friendliness.
3.2.7. Kinetics of the reaction according to the concentration of HCO3- and
concentration of Co2+
3.2.7.1. Experimental reaction order for HCO3- : Order 1.7.
3.2.7.2. Experimental reaction order for Co2+ : Order 1.2.

18
3.2.8. Evaluation of color processing ability when combining PMC and UV
Table 3.9. Decolorization efficiency of RB19 in the absence of UV and with UV
of some reaction systems, [RB19] = 100 mg/L; pH = 8.
Decolorization efficiency (%)
Oxidation system
Non UV
UV
RB19
0,0
3.7 ± 0.3
0,0
83.6 ± 3.6
RB19 – H2O2 20 mM
1.8 ± 0.2
91.1 ± 2.9
RB19 – H2O2 20 mM – Co2+ 0,1 mg/L
4.7 ± 2.7
96.7 ± 2.3
RB19 – H2O2 20 mM – HCO3- 10 mM
RB19 – H2O2 20 mM – HCO3- 10 mM – Co2+ 0.1 79.9 ± 3.5
97.6 ± 3.1
mg/L
Thus, it is proved that the system H2O2 − HCO3- − Co2+ effectively treats
RB19 color even without UV rays.
3.2.9. Products after RB19 treatment with peroxymonocarbonate
3.2.9.1. HPLC results
70

Intensity (AU)

50

30

10

-10
0

2

4

6

Retention time (min)

t = 10 min

t = 30 min

8

10

t = 60 min

Figure 3.22: The chromatograms of the RB19 after degradation 10, 30, 60 min
Most of the intermediate products at 10 min were not observed after the
30 min reaction time, and the chromatogram obtained with the solution at 60
min showed no signal showed the efficiency of complete mineralization of
RB19 by the H2O2 - HCO3- - Co2+ system.
3.2.9.2. Results COD and TOC
The COD values of the initial and final reaction solutions were
determined to be 315 and 12.5 mg O2/L, respectively, of which 100 mg/L RB19
was degraded by the PMC system ([H2O2] = 20 mM, [HCO3-] = 10 mM, [Co2+]


19
= 0.1 mg/L, pH = 8, UVC irradiation 60 min). Total organic carbon value TOC
= TC – TIC, measured for the final solution, resulted in 15.2 mg/L in agreement
with the COD value. Thus, the H2O2 - HCO3- - Co2+ system has a good
mineralization ability of RB19 with a COD reduction efficiency of 96%.
3.3. Evaluation of peroxymonocarbonate to treat other dyes
3.3.1. The ability of peroxymonocarbonate to treat dyes according to the
concentration of oxidizing agent
Decoloraiztion of RY145 (%)

20

15

10

5

0

0
10mM

50
20mM

100
Time (min)
30mM

150

50mM

70mM

200
100mM

Figure 3.24. Effect of HCO3- concentration on RY145 decolorization efficiency.
Condition: molar ratio H2O2 : HCO3- = 2: 1, pH = 9.
Decolorization of RB21 (%)

25

20

15

10

5

0
0

60

120

180

240

300

Time (min)
10 mM

20 mM

30 mM

50 mM

70 mM

100 mM

Figure 3.25. Effect of HCO3- concentration on RB21 decolorization efficiency.

Condition: molar ratio H2O2 : HCO3- = 2: 1, pH = 9.
Summary: The dependence of decolorization efficiency on PMC
concentration (or HCO3- concentration) follows a general rule. The optimal


20
concentration of HCO3- is 50 ÷ 70 mM, when the concentration of HCO3- is too
small or too large, it is not favorable for the decolorization process.
3.3.2. The ability of peroxymonocarbonate to treat dyes with metal ion
catalysis
Decolorization of RY145 (%)

50

40
30
20
10
0
0

60

Time (min)120

bare

Mn2+

Cu 2+

180
Co 2+

Decolorization of RB21 (%)

Figure 3.26. Effect of ion metal catalyst on RY145 decolorization efficiency.
Condition: RY145 50 mg/L, HCO3– 10 mM, H2O2 20 mM, pH = 9
100
80

60
40
20
0
0

60

120

180

240

300

Time (min)
Co2+

Mn2+

Cu2+

bare

Figure 3.27. Effect of ion metal catalyst on RB21 decolorization efficiency.
Condition: RB21 50 mg/L, HCO3– 50 mM, H2O2 100 mM, pH = 9
Summary: The activity of metal ion catalysis for decolorization reactions
by PMC system follows the general rule: among the studied transition metal
ions, Co2+ 0.1 mg/L gives the catalytic efficiency outstanding.
To see more clearly the combined effect of HCO4- and Co2+, the rate of
RhB decolorization reaction was considered in systems with simultaneous
changes in HCO3- and Co2+ concentrations. The speed constant values (k, min-1)
are presented in Figure 3.28.


21

Decolorization of RY145 (%)

Figure 3.28. First-order rate constant of RhB 8 mg/L decolorization reaction
Condition: HCO3– 0, 10, 15, 20 mM; H2O2 40 mM; Co2+ 0; 0,1; 0,2 mg/L; pH 9.
Thus in the absence of Co2+, a higher concentration of HCO3– would increase
the rate of the reaction (k increases from 0.00095 to 0.00187 min-1 when [HCO3–]
from 0 to 20 mM). This enhancement is due to the formation of PMC which is more
reactive than H2O2. When 0.1 and 0.2 mg/L Co2+ were present, the reaction rate
increased nearly 10 times and 17 times, respectively. However, in the absence of
HCO3– (no HCO4–), in the presence of 0.2 mg/L Co2+, the reaction rate only
doubled. It is clear that the combination of HCO4– with Co2+ increases the reaction

rate far superior to that of HCO4– or Co2+ alone. In other words, there is a
synergistic effect when HCO4– and Co2+ are both present in the PMC-based
oxidation system.
3.3.3. The ability of peroxymonocarbonate to treat dyes according to pH
80
60
40
20
0
0

50
pH 8

100

Time (min)

pH 9

pH 10

150

200

pH 11

Figure 3.29. Effect of ion pH on RY145 decolorization efficiency.
Condition: HCO3– 50 mM, H2O2 100 mM, Co2+ 0,1 mg/L