The analysis of the influence of TiO2 content in the structure of the PILCs.

Table of Contents ACKNOWLEDGEMENT 1 List of Tables 4 List of Figures 4 Abbreviations 6 INTRODUCTION 7 PART 1. OVERVIEW 9 1.1. Euro standards for sulfur content 9 1.2. Hydrodesulfurization 10 1.3 Oxidative desulfurization 11 1.4. Comparations of oxidative desulfuriation to hydrodesulfurization 12 1.5. Photocatalytic oxidation desulfurization 13 1.5.1. General 13 1.5.2. Fundamental of photocatalytic process 15 1.6. Advantage and Disadvantage of using TiO2 as Photocatalytic 17 1.6.1. Introduction of TiO2 17 1.6.2. Using TiO2 as photocatalyst 18 1.6.3. Application of TiO2Mont in environmental treatment 21 1.6.4. Some photocatalytic synthesis process for TiO2Mont 23 PART 2. EXPERIMENTAL 26 2.1. Chemicals 26 2.2. Experimental 26 2.2.1 Synthesis of TiO2 solgel 26 2.2.2 Synthesis of TiO2Montmorillonlite 27 2.2.3 Inspecting photoreactivity of catalysts in oxidative desulfurization 30 PART 3. CATALYST CHARACTERIZATION 32 3.1 XRay diffraction (XRD) spectroscopy 32 3.2 Energy dispersive Xray (EDX) spectroscopy 33 3.3 Ultra violetvisible spectroscopy (UVVIS) 34 3.4 High performance liquid chromatography (HPLC) 34 PART 4: RESULTS AND DISCUSSIONS 36 4.1 Xray diffraction results 36 4.2 Energy dispersive xray spectroscopy results 37 4.3 Ultra violetvisible spectroscopy results 38 4.4 High performance liquid chromatography results 40 CONCLUSION 44 REFERENCE 45

I can complete this thesis.

I sincerely thank Advanced Program, Departure of Oil Refining andPetrochemistry, Hanoi University of Mining and Geology for providing facilities tostudy, optimal laboratory conditions, which help me complete this thesis

Finally, I would like to say thanks to my dear parents for supporting me spirituallythroughout writing this thesis and my life in general

Ha Noi, June 5th, 2017 Student

Nguyen Huy Thanh

Table of Contents

List of Tables

Table 1.1 European emission standards of sulfur contents 9

Table 1.2 Results of desulfurizaion in diesel fuel 11

Table 4.1 The content of components in TiO2/Mont and CuO-TiO2/Mont 38

Table 4.2 Band gap energy of catalyst material TiO2/Mont and CuO-TiO2/Mont 39

Table 4.3 Thiophene conversion with 2 different kinds of catalyst samples: TiO2/Mont and CuO-TiO2/Mont 43

List of Figures Figure 1.1 General mechanism of hecterogeneous photocatalysis 14

Figure 1.2 Operation of semiconducted particle being excited by light 16

Figure 1.3 Crystal structure of Titanium Dioxide 17

Figure 1.4 Energy diagram of Anatase and Rutile 20

Figure 1.5 Decomposition process of organic compound using TiO2 photocatalyst 22

Figure 1.6 Diagram for synthesis Ti(x)C16(y)-Mont 24

Figure 2.1 XRD diagram of Bentonite and Momorillonite (after purifying) 27

Figure 2.2 Preparation of Na-Montmorillonite 28

Figure 2.3 Experimental process for modifying montmorillonite 29

Figure 2.4 The Sol-gel was added to the mixture drop by drop 30

Figure 2.5 Inspecting photoreactivity of TiO2 and CuO-TiO2 Mont samples 30

Figure 4.1 XRD diagram of TiO2/Mont (a) and CuO-TiO2/Mont (b) 36

Figure 2.3: Modification process of Titanium dioxide on Monmorillonite

Figure 4.2 The EDX spectroscopy of (a) TiO2/Mont and (b) CuO-TiO2/Montsample 37Figure 4.3 UV-Vis result of (a) TiO2-Mont, (b) CuO-TiO2/Mont 38Figure 4.4 Standard curve result of Thiophene sample model with standard curveequation Spic = 66037,48 + 53521,98 x CThiophene 41Figure 4.5 The conversion result of thiophene with TiO2/Mont catalyst sample after

180 minutes 41Figure 4.6 The conversion result of thiophene with CuO-TiO2/Mont catalyst sampleafter 180 minutes 42

Figure 4.7 Thiophene conversion with 2 different kinds of catalyst samples:TiO2/Mont and CuO-TiO2/Mont 42

Nowadays, environmental pollution is becoming an urgent issue EuropeanStandards for fuels now are more and more restrictive Sulfur-containing organiccompounds are potential pollutants present mainly in fuel oils which are difficult to

be removed Traditional methods used for desulfurization such ashydrodesulfurization (HDS) shows out ineffectively in deep desulfurization (forsulfur-containing heterocyclic compounds) and costly One of the new materials that

is catching the attention of scientists is TiO2 photocatalyst With the presence ofTiO2 and ultraviolet irradiation, researchers found that organic compounds,pollutants are easily disintegrated [1] This special ability of TiO2 has been applied

in water purification, air and disinfection technologies Many toxic and hazardouscompounds are efficiently degraded by heterogeneous photocatalyst The use oftitanium dioxide as photocatalyst for air and water treatment is well documented aswell as the fundamental mechanisms of the process [2] The main primary step isthe adsorption of the substrate on the support Thus, efforts have been carried out

on the synthesis of new materials having high specific surface area, low particlessize with the highest expected photoreactivity Supported TiO2 on different minerals

or TiO2 thin films appeared as solutions to overcome the recovery problem and also

to enlarge the application fields [3] Mesoporous materials which can be easilyseparated from the treated effluent, have been synthesized, and demonstrated theirfeasibility for photocatalytic treatment of fuel They are mainly based on clayminerals, zeolites, silica or activated carbons Among them, pillared clays (PILCs),constitute a group of mesoporous materials Pillared interlayered clays (PILCs)form a well-known family of microporous and mesoporous materials [4] They areprepared by multi-step molecular engineering processes The insertion of pillaringagents (organic, organometallic, or inorganic complexes) expands the interlayerspacing leading to a two-dimensional channel system with porous structurescomparable to those of zeolites [5] After the calcination process, the insertedcationic polymers yield rigid and are thermally stable leading to oxide species inform of pillars, which hold (separated) the clay layers separated and prevent theircollapse at high temperatures Thus, PILCs may be viewed as clay layers separated

by metallic oxide based pillars (alumina, titania, zirconia, iron oxide, etc.), oralternatively, as dispersed nanometric oxide particles which aggregation is hindered

by the presence of the clay layers [4] The main objective in the formation of PILCs

is to achieve as basal spacing as large as possible contributing to the development ofhigher surface area and porous volume The addition of TiO2 to the PILCs has beenpreviously studied

For this reason, the main objectives of this thesis are the analysis of theinfluence of TiO2 content in the structure of the PILCs This thesis describessynthesis and characterization of montmorillonite based porous clay heterostructurewith modified titanium dioxide in their pillars Likewise this thesis discusses therole of CuO located in the pillars and its effect in oxidative desulfurizaion leading to

an advantageous way to design functional materials with photocatalytic andadsorbent applications for deep desulfurizaion in fuel

Thesis objects:

• Modification of bentonite by titanium dioxide

• Doping copper oxide on titanium dioxide

• Investigating photocatalytic activity of synthesised samples

PART 1 OVERVIEW

1.1 Euro standards for sulfur content

Emissions of SOx, NOx, from the combustion of organic compounds whichcontain heteroatoms as sulfur, nitrogen in fuel has become an environmental issueover the world Because these emission gases are one of the main reason of acidrain, Global warming-up and atmospheric pollution [1] To minimize the amount ofSOx emissions, many countries in the world have put strict requirements on thesulfur content in fuel.The amount of sulfur contained in the material Example,sulfur content in diesel must be reduced from 500ppmw to less than 15ppmw fordiesel and from 300ppmw to less than 30 ppmw for gasoline Therefore, Deep-desulfurizaion method are increasingly interested in, recently

Table1.1 European emission standards of sulfur contents [6]

EN 228:1993(g)

October, 1994 2000

Euro 3 93/12/EEC

EN 590:1999(d)

EN 228:1999(g)

150 (gasoline)

Euro 4 98/70/EC

EN 590:2004(d)

EN 228:2004(g)

January, 2005 50*

Euro 5 2003/17/E

Note:

* 10ppm fuel must be available

** nonroad fuels limit

1.2 Hydrodesulfurization

Currently, in our Country, the method is mainly used to remove sulfur out ofliquid fuel is hydrodesulphurization process (HDS) using metal - sulfide catalystcarried on Al2O3-support

Chemical theory [3] of Sulfur elimination reactions: Mercaptan, sulfur anddi-sulfur compounds gently react to form aromatic and saturated compoundcorresponding Sulfur element which is linked in aromatic ring, such as thiophene is

so much harder to eliminate All of these reactions are exothermic reactions, theycreate hydro sulfur and consume hydrogen

as Co, Mo, Ni-Mo supported on solid acid Nowadays, for deep desulfurization incompounds which have high molecular weight and aromatic compounds, highactive catalysts are used such as: CoMo/Al2O3, CoMoP/Al2O3, GaCr/HZSM-5 or amixture of CoMoP/Al2O3 + GaCr/HZSM-5

Diesel fuel contains a lot of hardly reduced sulfur-containing compoundsbecause they are in heavy fractions and have high boiling temperature Normally,the amount of sulfur-containing compounds in fuel is from 9,000 to 2,000 ppmincluding compounds contain sulfur which are easy and difficult to eliminate Theproductivity of desulfurization in diesel fuel using CoMoP/Al2O3 catalyst is given

in Table 1.2

Table 1.2 Results of desulfurizaion in diesel fuel

Temperature (K) Sulfur content in products

(ppm)

Desulphurization efficiency(%)

of the products Therefore, deep desulfurization without using hydrogen and harshconditions have been developed to overcome the disadvantages of HDS process.Due to that, sulfur content in fuel can reduced below 10 ppm

1.3 Oxidative desulfurization

Oxidative desulfurization is not a new concept and has been discussed forseveral years in previous publications.The advantage that oxidative desulfurizationhas over conventional to HDS is that the difficult-to-desulfurize, sufur-containingheterocyclic compounds such as dibenzothiophenes (DBT) are easily oxidized atlow temperature and pressure conditions to form the corresponding sulfones Thisoverall process is demonstrated as below The oxidant can be supplied by eitherhydrogen peroxide/peracid sor organic peroxide [4] Note that there is no hydrogenconsumed in this reaction The sulfones are highly polar compounds and are easily

separated from the diesel product by either extraction or adsorption.For example,dibenzothiophene oxidation process:

This oxidation chemistry is complementary to hydrotreating, as other sulfurcompounds such as disulfides are easy to hydrodesulfurize, but oxidize slowly Forthis reason, oxidative desulfurization is best utilized as a second stage after anexisting HDS unit, taking a low sulfur diesel (~500 ppm) down to ULSD (<10 ppm)levels In this situation, the diesel product has been depleted of difficult-to-oxidizesulfur species and has a high concentration of the more refractory DBT constituents

In oxidative desulfurization (ODS) process the sulfur species like dibenzotiopheneare usually transformed into the corresponding sulfoxide and sulfone species Inorder to finally obtain a deeply desulfurized product, the sulfone species shouldthen be removed in a second step by extraction or adsorption

Process of oxidative desulfurization has several advantages over HDS ODScan be performed under mild conditions, atmospheric pressure and temperatures till100°C higher reactivity of aromatic compounds and no use of hydrogen Also, somedisadvantages of ODS processes can be listed; waste management of sulfonecompounds, rise in operation cost with the increase in the feed sulfur content, somedecrease of oil yield in case that extraction is applied to the sulfone separation

1.4 Comparations of oxidative desulfuriation to hydrodesulfurization

The HDS method is very effective at removing compounds that containssulfur, including saturated organic compounds and aromatics Nevertheless, withhectero-aromatic compounds which contain sulfur such as Dibenzothiophene(DBT), Benzothiophene (BT), and their derivatives, this method is not efficient.Otherwise, this method has also got restricts because it is always carried out at highpressure and temperature conditions, at about 300-340 oC and 20-100 atm, consume

a lot of energy, and large amounts of hydrogen.With the above disadvantages of theHDS method, the development of a new method to eliminate sulfur significantly isvery necessary There are some alternatives in using conventional hydrotreatingtechnology Recently, some methods for deep desulfurations, those are beingcatched attention recently are: Oxidative desulfuration (ODS), biodesulfurization,

extraction using ionic liquid, Among them, the ODS method which uses suitablecatalysts along with oxidative agent as hydroperoxide is very promising one withseveral advantages comparing to HDS such as: processes can be conducted at lowpresure and temperature conditions, no need for using hydrogen, capability ineliminating hetero-aromatic compounds more easilier.

1.5 Photocatalytic oxidation desulfurization

1.5.1 General

Traditionally, ODS operates at temperatures between 60 and 80oC [5,7] Atthese temperatures, the oxidation of desired fuel constituents, such as alkenesand aromatics, can occur, which consumes part of the oxidant and decreasesthe overall octane rating of the fuel [8] Unlike ODS, photocatalytic oxidativedesulfurization (PODS) can be conducted at ambient temperature andatmospheric pressure with high product selectivity PODS is essentially anadvanced version of ODS with a photocatalyst and UV light irradiation thatare used to increase the oxidation rate It is a desirable process because ofits low operating costs and the potential for a free source of radiation(natural sunlight) [8] PODS is characterized by three phases: oil, solvent andcatalyst (solid) Thiophene molecules in the oil phase are oxidized at thecatalyst surface increasing the molecular polarity, thus causing extraction intothe solvent phase (polar) [8] To increase the oxidation of thiophenes,oxidants are generally added to increase the concentration of hydroxylradicals, subsequently increasing the sulfone production rate Pure oxygen andair have also been reported as successful oxidants for the oxidation process,with overall desulfurization levels of 98% being reported for 5 h trials [8].The investigation into photocatalyst structures and their compositions hasreceived much interesting in the recent years [8] Li et al reported a mixed-phase Fe2O3 catalyst prepared by solution combustion method that gave 92.3%sulfur removal of DBT in n-octane using air flow and simulated sunlight.Wang et al prepared TiO2 in ionic liquid via microwave radiation for PODSand achieved 98.2% of DBT removal from model oil after 10 h UVirradiation [9] More complicated photocatalysts structures such as anatasenanocomposite polyoxometalate (Bu4N)7H3[P2W118Cd 4(Br)2O68]-TiO2 [10] andtitanium silicalite-1 [11] were also reported to be able to increase the overallsulfur removal efficiency PODS using advanced catalytic material, such as

those mentioned above, appear to be a promising method for deepdesulfurization; nonetheless, the complexity in the synthesis of thesephotocatalysts and their costs make commercialization and scaling - updifficult Therefore, PODS using simple reagent is still considered the bestapproach from industrial perspective However, systematic evaluation on theoptimum reaction conditions for PODS and the effect of the presence ofmultiple thiophenes are still insufficient In this study, TiO2 was used as thephotocatalyst, and the effects of catalyst loading, pH, temperature, the oxidantdose (H2O2) and solvent use were investigated Thiophen were used as modelaromatic sulfur compounds, as these compounds are not easily treated usingHDS The reaction rate constants were calculated for the reactions of Thiophene.The effect of thiophene on the overall sulfur removal was also investigated Toremove any matrix effects that may be experienced by the application of realfuel, acetonitrile was used as solvent for model oil.

Figure 1.1 General mechanism of hecterogeneous photocatalysis

The photocatalytic process is based on the following basic principle: Whenthe semiconductor particle is illuminated by light sources having a greater energythan the Band Gap, electrons in the Valence Band are excited and having enoughenergy to occupy up on empty spaces in the Conduction Band, leaving vacancies inthe Valence Band These charged particles will move to the surface of thesemiconductor particles and participate in reduction/oxidation reactions withadsorbed matters on the surface of the semiconductor particles However, due tolower energy levels in the Valence Band, electrons then tend to jump back into theValence Band to recombine with vacancies, along with releasing of energy in form

of photons or heat

1.5.2 Fundamental of photocatalytic process

Photocatalytic processes only occur with light radiation of sufficient lightenergy to break chemical bonds in materials In case of smaller light radiationenergy than chemical bond energies, the photocatalytic processes only occur withthe presence of photocatalyst Photocatalyst contains photosensitives that has theeffect of accelerating speed of chemical reactions

In the photocatalytic oxidation reactions with no photocatalyst, most ofhydrocarbons are oxidized slowly Photocatalyst has got an effect of reducing theactivation energy of reactions In the processes of light irradiation, the catalystoften creates particles which is capable of strong oxidation and reduction Ahecterogeneous catalytic system contains semiconductor particles play the role asphotocatalysis When these particles are radiated, they will be in excited states.These states will create next states such as reduction/oxidation reactions andmolecular changing Figure 1.2 is the mechanism diagram of photocatalyticreactions The electron structure is determined by Valance Band (VB) andConductive Band (CB) Semiconductors (such as ZnO, TiO2, Fe2O3) can be used assensitive factor for reduction/oxidation reaction with photocatalytic sources Thedifference in energy level between the lowest enegy level of CB and the highestenergy level of VB is called as band gab energy Eg It corresponds to the minimumenergy of light needed to make materials become conductive

Subtances contain excited charges can be created by three differentmechanisms: thermal stimulation, photo stimulation and mixing If the band gapenergy smaller enough (smaller than a half of electron - volt), the themalstimulation can push electron from the VB to the CB Similarly to photostimulation, suppose that an electron can be pushed from the VB to the CB by theabsorption of a photon of light The third mechanism created excited - chargesubstance is mixing The transmission of charges creates unequal conditions, lead tothe reduction or oxidation of absorbent on the surface of semiconductor

Figure 1.2 Operation of semi-conducted particle being excited by light

When a photon has energy level is hv which is higher than band gap energy, anelectron (e-) were pushed out of the VB to the CB and leaving a hole (h+) Inconductive materials (metals), these substances which carry electron instantlyrecombined again In semiconductors, some pairs of electron-vacancy which arebeing excited by light diffues on the surface of catalyst particles (electron-vacancypairs were retained on the surface) and participate in chemical reactions with otheracceptor-molecules (A) or donored-molecules (D) which have been absorbed Thevacancies can oxidize the donored-molecules (1) and electrons in CB can reducedmolecules which get appropriate electrons (2)

SC + hv → SC (e- + h+)

D + h+ → D• + (1)

A + e- → A•- (2)Another characteristic of the metal oxides which are used as semiconductor isvacances h+ have got strong oxidation powers They can react in an oxidation stage

of an electron with a water molecular (3) to generate strongly activated hydroxyl(•OH) Both vacancies and the hydroxyl are strongly oxidized agents , they can beused to oxidize most organic substances

1.6 Advantage and Disadvantage of using TiO 2 as Photocatalytic

1.6.1 Introduction of TiO 2

TiO2 is one of the basic materials in life It is widely used in making whitepigment in paint, cosmetics and food TiO2 exists under three kinds of crystal:anatase, brookite and rutile Usually, the TiO2 semiconductor materials can beactivated (chemical activation) by sun light The photoreactivity of TiO2 has beenknown for nearly 60 years and being researched popularly Under the effect of sunlight, this material can decompose organic materials This effect is resulting in aphenomenon that organic components in paint are decomposed due to impact of thephotocatalytic process

TiO2 is a high density material and a characterized white pigment which issold in the market This compound has a high refractive index, high inert surface areand nearly colorless, all of the above properties make it nearly identical to pigment.TiO2 has sold in the market in two kinds of crystal: Anatase and Rutile: Rutilehas a density of 4.2 g/cc, and Anatase is 3.9 g/cc This difference can be explained

by their different structures The structure of rutile crystals folded more tightly andfitter than anatase crystals

Rutile is the most durable crystal phase of TiO2 Rutile phase has got the width

of band gap energy approximately 3.02 eV Rutile has got the highest fold levelcomparing to the 2 remaining phases, the density equals 4.2 g/cm3 Rutile hastetrahedron network (Bravais) with octahedron arranging contacted at peaks(Figure 1.3a)

Figure 1.3 Crystal structure of Titanium DioxideAnatase is the highest photochemical activity phase of TiO2 Anatase phasehas got the width of band gap energy approximately 3.23 eV and 3.23 g/cm3 indensity Anatase also has Bravais network type (tetragonal) as rutile but the

octahedrons fold contacting edges together and the c axis of crystals is stretched(Figure 1.3b).

Brookite has very weak photochemical activity Brookite has got the width ofband gap energy approximately 3,4 eV and 4,1 g/cm3 in density (Figure 1.3c)

Because, thin membrane material and nano TiO2 only exist in the form ofanatase and rutile phase and the ability in photochamical activity is totally none, wewill not consider the brookite phase in the rest of the thesis

1.6.2 Using TiO 2 as photocatalyst

TiO2 is a semiconductor that has the width of band gap energy Eg = 3.2 eV If

it was irradiated by photons that has enrgy higher than 3.2 eV (wavelength < 388

nm ), the band gap would be exceeded and an electron would be pushed from VB to

CB Accordingly, the primary process is to make up an electric charge substance (5) TiO2 + hv → h + + e-(5)

The ability of the semiconductor that transmiss photosensitive (photoinducedelectrion transfer) to adsorbent are impacted by positions of band gap energy ofsemiconductors and subtituted reduction/oxidation of adsorbent The level ofsubstituted reduction/oxidation which is respective to acceptor in thermaldynamicneed to be lower than of conductive band

* Photocatalytic process on TiO2 [10,11,12]

The heterogeneous photocatalysis process can be proceed in either gas phase orliquid phase Like other heterogeneous catalysis, the heterogeneous photocatalysis

is divided in 6 phases as follows:

• Phase 1: Diffusing subtances on gas or liquid phase to surface of catalyst

• Phase 2: Adsorption of substances which is involved in reaction onto surface

of catalyst

• Phase 3: Adsorption of light photons, molecules move from basic stages toexcited stage of electrons At this stage, photocatalytic reactions are different fromother chemical catalytic reactions by the activation of catalyst For other catalyticreactions, catalysts are activated by heat; and for the photocatalytic process,catalysts are activated by light adsorption

• Phase 4: Photocatalytic reactions, are divided into 2 phases:

+ Primary photocatalytic reactions, in which molecules are excited (molecularsemiconductors) join directly reaction with adsorbents

+ Secondary photocatalytic reaction, that is the phase response of the products

in the primary stage

• Phase 5: Deadsorption of products

• Phage 6: Diffusing products into gas or liquid

Molecules which participate in adsorption on surface of catalyst includes 2types:

- Molecules which have got ability as electron donor

- Molecules which have got ability as electron acceptor

Electron transfering process will be more effective if organic and inorganiccompounds are adsorbed initially on semiconductor surface (SC) Then photon-electron in conduction band will transfer to molecular acceptors (A) and reductionoccurs Vacancies will move to molecular donors (D) to carry out oxidation:

e- + h+ → (SC) + E

Where:

(SC) is the center neutral semiconductor

E is energy that is released in the form of electromagnetic radiation (hv ' ≤ hv).Anatase TiO2 is in form of the highest activation This can be explained based

on the structure of energy bands As we know, in structure of solids have 3 bandenergies: Valance band, Band gap and Conduction band All chemical phenomenaoccurence are due to shifting of electrons among bands Anatase has got the bandgap energy of 3.2 eV, which is leading to a 388 nm wavelength photon, rutile hasgot band gap energy of 3.0 eV, which is leading to a 413 nm wavelength Thediagram of energy is shown in Figure 1.4

Figure 1.4 Energy diagram of Anatase and Rutile

The Valance band of anatase and rutile has approximately the same value.Thismeans that both anatase and rutile forms have the same ability in strong oxidation.When it is excited by lights which have appropriate wavelengths, valence electronsare separated from bonds, moving up to conduction band and creating a vacancy invalance band which is a positive charge Other electrons can jump up to thisposition for saturatng charge and creating a new vacancy at the position that it hasjust come out So, vacancies that own positive charge can freely move in valanceregion These vacancies have oxidative characteristic and capable of oxidizingwater

*Mechanism of TiO2 catalysis

When anatase TiO2 crystals are activated by light (wavelength λ) , electronstransfer from Vanlance band to Conduction Band In valance band, it will happenthe formation of OH• and RX+:

TiO2(h+) + H2O → OH• + H+ + TiO2TiO2 (h+) + OH- → OH• + TiO2TiO2 (h+) + RX → RX+ + TiO2

In Conduction band, it has the formation of O2- , HO2•:

TiO2 (e-) + O2 → O2- + TiO2

O2- + H+ →HO2•2HO2• → H2O2 + O2TiO2 (e-) + H2O2 → HO• + HO-+ TiO2

H2O2 + O2 → O2 +HO• + HOThe anatase form can reduce O2 to O2- and rutile can not, thus anatase cansimultaneously take oxygen and vapor of water from air along with ultraviolet light

to decompose organic compounds Anatase crystals with the effect of ultraviolet

light play a roll as a bridge which transfers electrons from H2O to O2, move the twomoleculars into O2- and •OH which are high oxidative activity forms and havecapable of decomposing organic compound into H2O and CO2.

The rate and efficiency of photocatalysis in decomposition of organicsubstances are enhanced by the participance of oxygen The dependence of reactionrate on oxygen concentration are explained by the adsorption of oxygen in bothilluminated irradiation and non-irradiation on surface of catalyst Oxygen moleculesacts as the center of electronic traps, which is catching electron in Conduction band,have completely or partially block combination of e-/h+ pairs along with creating aneffective oxidation agent as superoxide anion

As the catalytic processes occurring on metal oxide, photocatalytic process onTiO2 is also affected by hydrogen power (pH) pH of aqueous reaction significantlyinfluent to combination of size , electric charge on surface and oxidation-reductionpotential of boundary energy region of catalyst However, the change in rate of thephotocatalytic process in different pH is usually no more than a degree ofmagnitude It is also an advantage of photcatalytic process on TiO2 comparing toother processes

Kinetic in photocatalytic decompositions are based on Hinshel-Woodequation: the change in rate of reaction r is proportional to the part of surfaceswhich are covered by the reactants With diluted solution, reactions takes the form

of the first order dynamic, with high concentration, rate is maximum and dynamicform of zero order

Because, the nature of photocatalytic processes are electrical particles whichborn e-/h+ and join in mechanism of reaction, so that the rate of photocatalysis isproportional to the intensity of radiation in UV-A region: Rate of photocatalysisprocess increase linearly along with intensity of radiation in the range of 0-20mW/cm2 If intensity of radiation surpasses a certain value (about 25 mW/cm2), rate

of photocatalytic process is proportional ½ to the rate of irradiation ’s intensity

1.6.3 Application of TiO 2 /Mont in environmental treatment

Dye was widely used in textile industry, paper and other industrial processes,they produce a large amount of organic compounds and are taken into normalwastewater treatment process and cause water pollution seriously even at lowconcentrations [14, 15, 16] These dyes are generally not disintegrated and can notremove effectively out of water through processes of traditional wastewater

treatment The adsorption and photocatalytic decomposition has been reported to beeffective in handling dye [17, 18].

Photocatalyst TiO2 is a typical photocatalyst with many special advantages,such as high chemical stability in large pH range, there is no or low restraint of ions

in water currently,and easy conditions for decomposition of pollution those arehardly decomposed toxic [19] Nevertheless, it’s productivity depends practically oncrystallization and crystal size/its particle size The study is mostly focusing onanatase nano-TiO2 photocatalysis Zhu and Orthman (2002) reported thatphotocatalyst TiO2 which are sized smaller than 3 nm are often formless and haveweak catalytic activity The optimal size is expected to be in the limit range of 6-8

nm (< 10 nm) [20] However, nano-TiO2 particles are very difficult to separate andrecycle from water [21] In addition, the combination of nano particles in watercontains quantum excited effects, surface effects, and reduce catalytic activity [22].Thus, fixing nano-TiO2 up on support is very important and necessary to enhancethe catalytic activity and convenient to catalyst recycle

As we know, Mont is a kind of clay with natural layer form, is being used as asupport in composite material productions such as photocatalyst or absorbedmagnetic substances by ion exchange [23] The precursors of nano-TiO2 arepositive sol particles of titanium hydrate, [TiO (OH)x]mn + which is1-2 nm in size,and can replace sodium ions in inner layers of clay through ion exchange reaction toform an intermediate layer in spacing structure of Mont This pillaring method isnot only to prepare nano-TiO2 but also used to fix nano-TiO2 on Mont, this is useful

to keep nano-TiO2 split and increase surface activity center [24]

The decomposition process of organic compounds, dyes by TiO2 photocatalystoccur in sequence as Figure 1.5

Figure 1.5 Decomposition process of organic compound using TiO2 photocatalyst

-TiO2 molecules adsorb light irradiation energy as the mechanism waspresented above.

-Oxidation of organic compounds:

R + • OH → CO2 + inorganic substances (decomposing)

In case of dye products that contain nitrogen, azo, oxidation mechanisms are:

R • N = N-R ' + • OH → R-N = N• + R '-OH

R-N = N-R ' + H• → R-N = N• + R '-H R-N = N• → R• + N2

1.6.4 Some photocatalytic synthesis process for TiO 2 /Mont

Synthesising of nano TiO2 by hydrothermal method in presence of organicsurfactants has been shown to be improving the distribution and degree ofcrystallization of nano particles [25] The organic surfactants can increase theuniformity of distribution of TiO2 pillars in Mont, due to the interaction amongfunctional groups of surfactants [26] Based on the common processes, puttingsurfactants and inorganic compounds occurred in the inner space of Mont, formingporous clay structure and a large amount of pillars with extended sizes by usingappropriate surfactant which can increase the number of active center of catalyst

[27, 28] In addition, organic surfactants has enhanced affinity for TiO2/Montcomposite with organic waste by increasing the hydrophobicity [29].

Yuan (2011) has studied a new method of fixing nano-particles TiO2 onsurface of Montmorillonite with the presence of cetyltrimethylammonium bromides(CTABr) as surfactants The synthesis catalyst has been proven to have highercatalytic activity than normal due to their optimized structures by interacting ofDiethanolamine (DEA) with CTABr [30]

Nano - TiO2 particles are synthesized by hydrothermal method with dispersing

of DEA Titannium tetrachloride (TiCl4) is added into the mixture of HCl and(NH4)2SO4 and stirring strongly in N2 gas Then the temperature of reaction isincreased to 95oC in 1 h Then, DEA dispersal is added into the solution with themolar proportion (DEA: Ti4+) = 1:2 and stirring in same condition in 1 h more toform DEA-TiO2 Then, CTABr is added into sol DEA-TiO2 at room temperatureand stir in 4 hours, forming the dispersaal DEA-TiO2 -CTABR (TC) Fixing TiO2onto Mont process was implement by dropping TC on Mont dispersant in theproportion Ti4 /CEC (Mont) equal 15:1 (cation exchange capacity: CEC) of Mont is58.3 meq/g) and stirring lightly at 70oC in 5 h After the cleaning process, weobtained TCM and calcining at 500oC to obtain TCM-500 with surface area of about62.6 m2/g, capillary volume is 10.41 volume cm3/g which are much larger thanMont clay (28.09 m2/g in surface area and capillary is 0.09 cm3/g [31]

A new method to fix nano-TiO2 particles onto the Mont surface, which isbeing developed, is using surfacatants supporting for the process of synthesisingTiO2 -Mont, as shown in the Figure 1.6:

Figure 1.6 Diagram for synthesis Ti(x)C16(y)-Mont

According to the above diagram, the synthesis proess of TiO2-Mont can bedevided into 2 steps: the first step is modification of Mont by surfactant and thesecond step is formation of TiO2 particles Mont has two tetrahedral siloxan layersknit with an octahedral aluminum layer The isomorphic replacement of Al3+ to Si4+

in tetrahedral-layers and Mg2 + or Zn2 + to Al3 + in octahedral layer forming negativenetwork cover on clay surface Therefore, at the first step, surfactant are insertedinto the inside space of Mont by processes of ion exchange and physical adsorptionprocesses, increasing-zeta potential surface of clay In the second step, the precursor

of titanium dioxide with negative charge, Titanium (IV) bis (ammonium lactatodihydroxide) (Ti-BALDH), are allowed to hydrolysis and condensate aroundsurfactanrs, inside space or on surface of Mont TiO2 are formed on both surfaceand inside Mont

In this process, the key steps are the ion exchange of surfactant into layers inclay and the adsorption of Ti-BALDH Because layers carry negative charge, it isdifficult for Ti-BALDH to insert into layers of Mt Using surfactants into the layers

of Mont is leading to increase zeta-potential surface of clay, and promote theabsorption of Ti-BALDH, then increase amount of TiO2 in Ti-Mont

In this method, cation surfactants are considered physically as oriented factors,are not only suitable with the formation of TiO2 but also control amount of TiO2 inmixture The nano TiO2 capillaries were evenly distributed uniformly on surface ofTiO2-Mont Resulting in high capillary comparing to raw clay and the surface area

of TiO2/Mont which are synthesized by the method is up to 209.5 m2/g expressingfull advanced properties such as photocatalyst and chemical adsorptions , useful forenvironment application[32]