Tom Tat La.tieng Anh.doc

INTRODUCTION Vietnam Academy of Science and Technology Institute of Tropical Technology *** PHAM THI MINH Research characteristic of azo organic compounds mineralization in dye textile wastewater by e[.]

Vietnam Academy of Science and Technology

Institute of Tropical Technology

…… ….***…………

PHAM THI MINH

Research characteristic of azo organic compounds mineralization in dye textile wastewater by

The thesis was completed at: Institute of Tropical Technology

-Vietnam Academy of Science and Technology

Supervisors: Assoc Prof Nguyen Thi Le Hien

Assoc Prof Dinh Thi Mai Thanh

Referee 1: Assoc Prof Mai Thanh Tung

Referee 2: Assoc Prof Vu Thi Thu Ha

Referee 3: Assoc Prof Nguyen Thi Cam Ha

The thesis will be defended in front of doctoral thesis judgement, held

at Institute of Tropical Technology - Vietnam Academy of Science and Technology at 9 A.M, May 20th , 2014.

The thesis can be found at:

- Vietnam Academy of Science and Technology library

- Vietnam National library

1 The urgency of the thesis

Recently, the more strongly the process of industrialization andurbanizationdevelop, the worse the pollution problem is getting One of the most industrieswhich make highly pollution is dyeing textile industry With thousands of smallmanufactories from traditional villages, post-produced wastewater is hardlyhandled before flowing directly into lakes, rivers, which caused environmentalpollution The dye textile wastewater contains a lot of organic compounds,especially azo pigment This is a kind of the stable, persistent and toxic compound.Researching and treating wastewater containing azo compound is an importantproblem in order to remove all these substances before discharging it into theenvironment, protect human and ecological environment

There are many treatment methods of toxic organic compounds such as the method

of physics, biology or chemistry However, these direct methods are still limited

In recent times, the advanced oxidation methods have been researching by the

strong oxidizing ability, it can completely oxidize toxic organic compounds toform CO2 and H2O Many different advanced oxidation methods have beeneffectively applied such as the methods of ozone, Fenton, electro-Fenton Amongthem, electro-Fenton method not only is confirmed to have many advantages butalso can easily combine with other advanced methods to absolutely treat the toxicorganic compounds, minimize the environmental pollution Electro-Fenton method

is the oxygen reduction process to create H2O2, then H2O2 will oxidates transitionmetal ions such as Fe2+, Cu2+ to create HO• or HO2• radicals with high oxidability.The oxygen reduction creating H2O2 depends on the nature of the cathode material.The recent surveys showed that the composite electrode which was made fromspinel-structured complex oxides of transition metal mixing in with conductivepolymers such as polyanilin, polythiophen has good catalytic ability for theoxygen reduction to create H2O2 However, the research to find out the suitablematerial to apply in pollute organic compounds treatment is a new researchapproach, which has not been much interested by domestic and foreign scientists

For the reasons mentioned above, the thesis "Research characteristic of azo

organic compounds mineralization in dye textile wastewater by electro-Fenton method” has been carried out.

2 The objectives of the thesis

- Synthesize the spinel-structured complex oxide Cu1,5Mn1,5O4

- Synthesize Ppy and Ppy(oxit)/Ppy coatings on carbon substrate

- Determine the optimal mode for azo compounds mineralization

- Treat the dye textile wastewater in reality by electro-Fenton effect

3 The main contents of the thesis

- Synthesize and research the composition, structure, surface morphology ofspinel-structured complex oxide Cu1,5Mn1,5O4

- Synthesize and research the characteristics of Ppy and Ppy(oxide)/Ppy coatings

- Electrochemical characteristics of platinum anode and carbon cathode insolution containing azo compounds

- Mineralize some azo compounds by electro-Fenton methods

- Treat dye textile wastewater by electro-Fenton methods

Chapter 1 OVERVIEW 1.1 The dye textile wastewater

1.1.1 Sources of dye textile wastewater

The wastewater source arises in dye textile industry from the stages of starching,removing, cooking, easing, dyeing and finishing The main pollution problem inthe dye textile industry is water pollution Considering two factors: the volume andthe composition of wastewater, dye textile industry causes the biggest pollution

1.1.2 Characteristics of dye textile wastewater

The characteriristic of dye textile wastewater in general and the dye textilewastewater in Van Phuc and Duong Noi villages in particular is all containingcoloring organic compounds, thus indicators such as pH, DO, BOD, COD… arevery high, exceeding allowed standards to discharge into ecological environment

1.1.3 Main pollutants in dye textile wastewater

Main pollutants in textile wastewater are dyes, surface-active substances, organichalogen compounds Among them, dyes are the most difficult compositions to betreated, especially azo dyes widely-used nowadays, those account for 60-70% ofthe market share

1.1.4 The dyes commonly used in Vietnam

Today, Vietnamese often use dyes such as direct dyes, acid dyes, active dyes,bases dyes, reverted dyes, sulfur dyes, dispersed dyes, azo dyes and pigment dyes.Most of them contain azo link (- N=N-) in the molecular

1.1.5 The general concept of azo coloring compounds

Azo compounds, the synthetic coloring compounds, contain the -N=N- link andpopularly applied in many industries (foodstuff, printing and dyeing ) This is the

1.2 The methods of dye textile wastewater treatment

1.2.1 The actuality of dye textile wastewater pollution in Vietnam

In recent years, although the environmental field has been particularly concerned

by the state, a number of companies, factories and most of the handicraft dyetextile villages still directly discharge post-produced untreated wastewater intorivers, lakes and canals which causes serious environmental pollution

1.2.2 The actuality of azo-inflected wastewater treatment technologies

1.2.2.1 The traditional methods

The traditional methods of dye textile wastewater treatment have been applied,including: absorbing methods, physical methods, oxidative methods andmicrobiological methods

1.2.2.2 The advanced oxidative methods

Advanced oxidative method is the process of decomposition compounds based on

selecting organic compounds to form CO2, H2O and mineral salts

1.2.2.3 Some common advanced oxidative processes

In recent time, many advanced oxidative methods have been applied quiteeffectively, such as ozonation, Fenton, electro-Fenton, photo-Fenton

1.2.3 Electrochemical method

Electrochemical process allows eliminating or minimizing the pollutants bydirectly oxidizing way of pollutants on the electrode by currents or creating oxygenagents in the environment which is capable of oxidizing toxic organic compounds.There are two methods to create hydroxyl radical: directly oxidizing at the anode

or indirectly oxidizing on the cathode by electro-Fenton effect

1.2.3.1 Directly electrochemical oxidation at the anode to create hydroxyl radical

This method allows oxidating water to create hydroxyl radical absorbed on theanode surface with high overpotential:

O2 + 2H+ + 2e → H2O2 (2)

Fe2+ + H2O2 → Fe(OH)2+ + •OH (3)Although Fe2+ is rapidly decomposed by HO• to form Fe2+ and HO- (reaction 4),the reaction 3 still continues due to the regeneration of Fe2+ according to thereaction 5,6,7

Fe3+ + R• → Fe2+ + R+ (6)

Fe3+ + H2O2 → Fe2+ + HO2• + H+ (7)Ion Fe2+ regenerates mainly due to the reduction of Fe3+ by H2O2 according to

the diagram:

Organic compounds + HO•, HO2• → products ( 8 )

Organic compounds treated by Electro-Fenton method was assessed quiteeffectively because the HO• radical was not only created in the solution from thereaction 2 but also formed on the anode electrode from the H2O oxidation (reaction9)

Dissolved oxygen reduction process that occurs according to the mechanism ofreceiving 2e to create H2O2 (reaction 2) depends on the nature of the cathodematerial Therefore, cathode material which are capable of electrochemicallycatalyzing for oxygen reduction in order to create H2O2 is one of the mostimportant factors that decide the performance of wastewater treatment by electro-Fenton method

1.2.4 Application of electro-Fenton effect for mineralizing azo compounds in dye textile wastewater

In recent years, the researches on applications of electro-Fenton method to treatazo dyes in dye textile wastewater have been interested by many domestic andforeign scientists However, the way of researching which uses composite cathodematerial with the catalytic ability to oxygen reduction reaction to create H2O2 isstill very limited Hence, the thesis focused on researching to produce and usingthe composite cathode materials based on the basis of Cu1,5Mn1,5O4 complex oxideand conductive Ppy

Recent researches show that Ppy coating, especially Ppy(oxide)/Ppy has goodcatalytic ability for the reduction of the oxygen to produce H2O2 on the cathode,setting the basis for research of the application this material in polluted organiccompounds treatment.

Chapter 2 CONDITION AND EXPERIMENTAL METHOD

2.1 Chemicals and equipments

* Chemicals: The chemicals which were used in this study have high-purity,

including: CuSO4.5H2O, MnSO4.H2O, KOH, Pyrol, KCl, H2SO4, NaOH, Na2SO4,

textile villages: Van Phuc and Duong Noi

* Equipment:

- Electrochemical measurement equipment AUTOLAB 30 (Eco., Co.,Netherlands)

- STEREOSCAN 440 LEICA equipment paired with LEO software

- UV-Vis equipment (UV-spectrometer, CINTRA 40 – The USA)

- pH measurement equipment named PHM 210 Standard pH Meter (France)

- Annealed machine named DRB 200 HACH- Japan - The USA

- Magnetic stirrer heating machine

- Analytical Electronic scale, Toledo manufacturer (Switzerland)

2.2 Condition and experimental method

2.2.1 Synthesize complex oxides of Cu and Mn:

Complex oxides of Cu and Mn were synthesized by co- precipitation method fromCuSO4, MnSO4 and KOH solution

- Steady-potential method: Determine the value of feedback current at steady-state,which characterizes the electrochemical reaction speed at the researched potential

2.3.3 The analysis method:

- The methods of SEM, TEM, EDX, X - Ray: Analyze the surface morphology,composition and structure of oxide and Ppy(oxit)/Ppy coating.

- Ultraviolet visible spectra (UV-Vis) method: This method allows evaluating theperformance of azo coloring compounds degradation through absorbed intensity bythe formula:

With:  is the degraded efficiency (%), A0 is absorbed intensity at first, At isabsorbed intensity at t time

- Chemical oxygen demand (COD) determination method:

+ COD degraded performance in mineralize process was assessed by the formula:

The results which were measured by SEM, TEM, EDX and X-Ray methodsshowed that Cu and Mn complex oxide after being synthesized is small, fineparticles, spinel-structured with molecular formula Cu1,5Mn1,5O4

(10)

Figure 3.1 SEM image

TEM Electron diffraction

Figure 3.2 TEM image

Figure 3.3 EDX spectra of Cu and

3.2 Synthesize and electrochemical catalytic ability of Ppy and Ppy(Cu 1,5 Mn 1,5 O 4 )/Ppy coatings

3.2.1 Synthesize Ppy and Ppy(Cu 1,5 Mn 1,5 O 4 )/Ppy coatings on carbon substrate electrode

The voltage change in the Ppy and Ppy(Cu1,5Mn1,5O4)/Ppy coatings in the synthesisprocess is shown in Figure 3.5 At the first phase of the synthesis process, voltagesharply increases to a stable value, equivalent to the polymerization process ofpyrol into polypyrrole which is accumulated on the anode electrode surface Withthe presence of oxide synthesis voltage significantly reduced by the activation area

of the electrode increases, which makes synthesis current density reduces and leads

to reduced potential.

Figure 3.5 Synthetic Curves of Ppy and

Ppy(Cu1,5Mn1,5O4)/Ppy coating

3.2.2 Characteristic of Ppy và Ppy(Cu 1,5 Mn 1,5 O 4 )/Ppy coatings

3.2.2.1 The component of Ppy(Cu 1,5 Mn 1,5 O 4 )/Ppy coating:

The component of Ppy(Cu1,5Mn1,5O4)/Ppy coating was analyzed by EDX spectra(figure 3.6) The results showed that Cu and Mn complex oxide was present in thecomponent of Ppy(Cu1,5Mn1,5O4)/Ppy coating after synthesizing

3.2.2.2 The electrochemical catalytic ability to oxygen reduction reaction creating hydrogen peroxide Ppy and Ppy(Cu 1,5 Mn 1,5 O 4 )/Ppy coatings

Electrochemical catalytic ability of the C/Ppy and C/Ppy(Cu1,5Mn1,5O4)/Ppycathode electrodes at different pH values was represented by the curves: current –static potential, allowing the determination speed of oxidants reduction reaction onthe studied electrode (figure 3.7) When there is the presence of oxygen, with highoxygen content, it led to cathode currents sharply increased starting with thepotential +0.2V/SCE, corresponding to the oxygen reduction reaction to create

H2O2, confirming the presence of H2O2 by KI + starch Besides, when there wasoxygen aeration, the cathode current density of Ppy coating containing oxide wasalways greater than the cathode current density of Ppy coating without oxide This

is proved that Ppy(Cu1,5Mn1,5O4)/Ppy coating had the catalytic ability for thedissolved oxygen reduction better than Ppy coating

By observing the graph describing feedback cathode current density of theC/Ppy(Cu1,5Mn1,5O4)/Ppy electrode at different pH values in potential -0.5V/SCE(figure 3.8), it showed that feedback cathode current density reached the highestvalue at pH3 This proved that the C/Ppy(Cu1,5Mn1,5O4)/Ppy cathode electrode hadthe best capable of electrochemical catalyst for oxygen reduction reaction to create

H2O2 at pH3

Figure 3.7 The variation of imposed current density at the cathode potentials in

0.05 M Na2SO4 solution, pH2,3,4,6

Figure 3.8 Cathode current density at different pH values

3.3 Electrochemical characteristics of platinum anode electrode and carbon cathode electrode in Na 2 SO 4 solution, pH3

3.3.1 The reactions on platinum anode

The anodic polarized curves in the solution with pH3 containing and uncontainingred methyl, Fe2+ and O2 were shown in figure 3.9 There was a water oxidation toform oxygen occured on the anode (starting at potential +1.1V/SCE), oxidized

Fe2+ to form Fe3+ (starting at potential +0.4V/SCE) and red methyl directly oxidated (starting

at potential +0.7 V/SCE).

Figure 3.9 Anodic polarized Curves Figure 3.10 Cathodic polarized

Curves

3.3.2 Reaction on carbon substrate cathode

Observing the cathodic polarized curves got on carbon substrate cathode in threesolutions (figure 3.10) showed that the cathode current began to increase atrelatively positive potentials (0  -0,5 V/SCE), which characterized the H+

reduction reaction to create H2 or oxygen reduction process to create H2O2 Inaddition, the cathode current significantly increased in the solution with oxygenaeration It proved the cathode current observed in figure 3.10 corresponded to thecontribution of oxygen reduction reaction to create H2O2

3.4 Red metyl mineralize process

3.4.1 Red methyl mineralization by Electrochemical method

0.35 mM red methyl oxidation by Electrochemical method on platinum anodeelectrode is made in 0.05 M Na2SO4 solution, pH3, 25 mA current intensity Thevariation of the COD reduction efficiency (%COD) and current efficiency (H) withoxidized time was shown in Figure 3.11 The results showed that %CODcontinuously increased with oxidation time, this proves that, red methyl wasdirectly oxidized on Pt anode electrode Besides, H gradually decreased due to thedecrease of red methyl concentration which led to red methyl oxidative speed on Ptanode electrode decrease After 180 minutes of treatment process, COD indicatorwas decreased from 250 mg/l to 145 mg/l, corresponding to the COD reductionefficiency reached 41%

3.4.2 Red methyl mineralization by Electro-Fenton method

Figure 3.12 introduce the results of red methyl treatment process in 0.05 M Na2SO4

rate, C cathode at 5 mA/cm2 current density by Electro-Fenton method The resultsshowed that the variation %COD and H with oxidative time by Electro-Fentonmethod have tend to change the same way as the red methyl directly oxidized byelectrochemical method However, the variation %COD and H with red methyloxidative time by Electro-Fenton method reached the higher value This provesthat, in the red methyl treatment process by Electro-Fenton method, not only thereoccurs the red methyl direct oxidative process on anode electrode but also thereoccurs the red methyl indirect oxidative process on the cathode electrode, somineralization efficiency reached higher values After 180 minutes ofmineralization, COD indicator decreased from 250mg/l to 115 mg/l, corresponding

to the COD reduction efficiency reached 54 %

3.4.3 Influence of factors on red methyl treatment process by electro-Fenton method

In order to determine the optimal conditions for red methyl mineralization by theElectro-Fenton method, the thesis surveyed the influence of some factors such as

rate

3.4.3.1 Influence of Fe 2+ ion concentration

Influence of Fe2+ ion concentration on red methyl mineralization by the Fenton method was made in conditions of: Na2SO4 0,05 M solution, pH3,C/Ppy(Cu1,5Mn1,5O4)/Ppy cathode electrode, 5 mA/cm2 imposed current density,1l/min oxygen aeration rate

Electro-The variation of the COD reduction efficiency (% COD) and current efficiency (H)

Figure 3.11 The variation of %COD

and H with red metyl oxidized time by

Electrochemical method

Figure 3.12 The variation of %COD

and H with red metyl oxidized time by

Electro-Fenton method

The results showed that: When [Fe2+] was lower than 1 mM, this content was notenough to completely react with H2O2 content that was generated, so the low HO•

radical concentration lead to the low mineralization efficiency When Fe2+

concentration increased to 1 mM, %COD and H reached the highest value at any

completely react with H2O2 that was created on the cathode electrode to create HO•

radical When [Fe2+] was higher than 1 mM, this content did not react completelywith H2O2 content, the surplus Fe2+ ion content would be oxidized to create Fe3+.The surplus redox couples Fe3+/Fe2+ would create a continuously redox cycle, socurrents efficiency increased

Figure 3.13 Influence of Fe2+ ion concentration for the variation of %COD and

H with time

3.4.3.2 Influence of cathode electrode material

Influence of cathode electrodes C, C/Ppy and C/Ppy(Cu1,5Mn1,5O4)/Ppy onperformance of red methyl mineralization was surveyed in 0.05 M Na2SO4

solution, pH3, 1 mM Fe2+, with 1 l/min oxygen aeration rate at 5 mA/cm2 imposedcurrent density

The variation of %COD, H and decomposing efficiency () in red methylmineralization with time was assessed by COD identify method and UV-Visspectra analysis method The results was shown in 3.14, 3.15 and 3.16 Figures, itproves that all of them had electrochemical catalytic ability for oxygen reductionprocess to produce H2O2 on cathode electrode It showed that %COD in red methylmineralization process for 3 cases also continuously increased with mineralizationtime However, in case C/Ppy(Cu1,5Mn1,5O4)/Ppy cathode electrode was used, at