Tải bản đầy đủ - 0 (trang)
4 Photoionization of Reactive Intermediates of Atmospheric Importance with Synchrotron Radiation, Using Atomic Nitrogen as an Example

4 Photoionization of Reactive Intermediates of Atmospheric Importance with Synchrotron Radiation, Using Atomic Nitrogen as an Example

Tải bản đầy đủ - 0trang

3 Photoionization Studies of Reactive Intermediates of Importance in the Atmosphere


Some of the capabilities of this instrument, notably in areas (a) and (b), to

study reactive intermediates of atmospheric importance can be demonstrated by

considering angularly resolved PE spectra and CIS spectra of nitrogen atoms.

Photoionization of atomic nitrogen is an important process in the physics and

chemistry of the upper atmosphere.

Angle resolved PE and CIS measurements were made on N atoms using the

Elettra synchrotron radiation source (near Trieste in Italy) on the beamline BL 4.2R

[27]. The degree of linear polarization (P D 1) of the radiation is well established.

The asymmetry parameter (“) was measured for nitrogen atoms at selected photon

energies and over a photon energy range, by recording CIS spectra at two different

angles ™ (0ı and 54ı 440 ) at each photon energy. The angle 54ı 440 corresponds

to the angle at which the measurement is independent of “, thereby, permitting a

straightforward determination of the relative partial photoionization cross-section.

“ was then determined from “ D R 1, where R D I0 /I54ı 440 is the ratio of the

experimental intensities at these two angles.

Nitrogen atoms were produced by passing a flowing mixture of molecular nitrogen mixed with helium through a microwave discharge in a glass inlet tube attached

to the ionization chamber of the spectrometer. A PE spectrum recorded for discharged nitrogen is shown in Fig. 3.12 (upper panel). This shows the first band of N

atoms at 14.54 eV corresponding to the ionization NC (2s2 2p3 ,3 P) N(2s2 2p4 ,4 S).

The corresponding spectrum obtained with the discharge off is also shown in

Fig. 3.12 (lower panel).

The CIS spectrum of N atoms at ™ D 54ı 440 is shown in Fig. 3.13. This is

the relative cross-section for N atoms plotted as a function of photon energy. This

is obtained by monitoring the intensity of the first N atom PE band at 14.54 eV

as a function of photon energy. The resonances seen in this plot correspond

to excitation to N* (2s2p3 (5 S), np) states from the N(2s2 2p3 ,4 S) ground state

followed by autoionization to the NC (2s2 2p3 ,3 P) state. The resonances seen in this

plot show an asymmetric profile. This is due to interference between the direct

and indirect (resonance plus autoionization) ionization processes and results in a

characteristic Fano profile. Each resonance can be fitted to a Fano profile to obtain

Fano parameters which provide information about the excited state lifetime and

the interaction of the excited state with the continuum. Specifically, the resonance

position En , the natural line-width, €, and line-shape parameters q and ¡2 , and

the discrete oscillator strength f have been determined for the N*(2s2p3(5 S),

np) N(2s2 2p3 ,4 S) autoionization resonances for n D 5–10, and explanations of

the changes in these parameters with principal quantum number have been proposed

[27]. Fitting the resonance energies, En , obtained to the Rydberg energy expression

En D E 1



ın /2


where E1 is the ionization energy, R is the Rydberg constant and • is the quantum

defect, gave E1 D 20.39 eV for the (2s) 1 ionization and • D (0.61 ˙ 0.01). This

• value is consistent with the value expected for a p Rydberg orbital of a first row



J. Dyke


Discharge on




N (3P)










Discharge off








Ionization energy/eV

Fig. 3.12 PE spectrum recorded at photon energy hž D 21.22 eV with the microwave discharge

on (upper panel) and off (lower panel) of a He/N2 mixture The peak labelled with (*) at 16.45 eV

is a “hot-band” associated with the ionization N2 C (A 2 …u , vC D 0) N2 (X 1 †g C , v00 D 1)

The “-parameter plot is shown in Fig. 3.14. As can be seen, resonances are

observed in this plot in the same positions as are observed in the CIS plot shown in

Fig. 3.13. “ values are in general in the range 1 to C2 and interpretation of a “-plot

of the type shown in Fig. 3.14 provides information about the angular momentum

carried away by the free electron. For an electron with orbital angular momentum

quantum number l in an atom before photoionization, free electron waves with l 1

3 Photoionization Studies of Reactive Intermediates of Importance in the Atmosphere




N (5S)



np 4P







Photon Energy/eV

Fig. 3.13 Relative integrated cross section of atomic nitrogen across the NC (2s2 2p3 , 3 P) N*

(2s2p3 (5 S) np)4 P N(2s2 2p3 , 4 S) autoionizing resonances for n 5, over the photon energy range

19.4–20.5 eV The spectrum was recorded at ™ D 54ı 440


Asymmetry Parameter













Photon Energy/eV

Fig. 3.14 Asymmetry parameter for atomic nitrogen across the NC (2s2 2p3 ,3 P) N* (2s2p3 (5 S)

np)4 P N(2s2 2p3 , 4 S) autoionizing resonances for n 5, over the photon energy range 19.4–

20.5 eV


J. Dyke










Photon Energy

Fig. 3.15 TPE spectrum recorded for the NC (3 P2,1,0 )

the three ionic state components 3 P0 , 3 P1 and 3 P2

N(4 S) ionization showing ionization to

and l C 1 will be produced on photoionization. The value of “ depends not only on

the strengths of the two partial waves but also on their phases, which control the

interference between them.

For non-resonant ionization of a 2p electron in nitrogen, both an s and a d

free electron wave can be produced. For a p ! s ionization “ D 0 and for a p ! d

ionization “ D 1.00. The off-resonant background level in Fig. 3.14 of approximately “ D C0.2 indicates that both s and d free electron waves are contributing

off resonance. Further insight into the values of “ both on and off resonances can

be obtained by using angular momentum transfer theory, for the angular momentum

transferred between the molecule, and the ion and photoelectron. This has been

applied to the results shown in Fig. 3.14 for N atoms and has also recently applied

to similar angular distribution plots obtained for atomic iodine [28].

An example of the use of threshold PE spectroscopy is shown in Fig. 3.15,

where the first photoelectron band of N atoms is shown. This corresponds to the

NC (3 P0,1,2 ) N(4 S3/2 ) ionization. The resolution is 3 meV and as can be seen bands

corresponding to ionization to the spin-orbit components of the 3 P ionic state, at

14.534, 14.540 and 14.550 eV, are resolved. This illustrates the extra information

that can be obtained from TPES studies.

3.5 Conclusions

In this review lecture, an attempt has been made to demonstrate the range and detail

that can be obtained on studying atmospherically important reactive intermediates

with photoionization methods. Much of the information obtained is relevant to

3 Photoionization Studies of Reactive Intermediates of Importance in the Atmosphere


understanding the photoionization, and reactivity of reactive intermediates and their

ions in the atmosphere as well as in deriving thermochemical quantities which can

be used in calculations relevant to atmospheric chemistry.

Acknowledgements I would like to thank EPSRC and NERC (UK), and the many co-workers

who have collaborated in this research. I am particularly indebted to Dr Edmond Lee and Dr

Alan Morris with whom I have collaborated over a significant number of years. Ed has been

responsible for most of the theory and calculations and Alan has designed and built all of the

spectrometers used. I am also very grateful to the organisers of ICPAC 2010 for the opportunity to

present this paper.


1. Dyke JM, Jonathan N, Morris A (1982) Recent progress in the study of transient species with

vacuum ultraviolet photoelectron spectroscopy. Int Rev Phys Chem 2:3

2. Dyke JM, Jonathan N, Morris A (1979) Vacuum ultraviolet photoelectron spectroscopy of

transient species. In: Brundle CR, Baker AD (eds) Electron spectroscopy, vol 3. Academic,

London, p 189

3. Cockett MCR, Dyke JM, Zamapour H (1991) Photoelectron spectroscopy of short-lived

molecules. In: Ng CY (ed) Vacuum ultraviolet photoionization and photodissociation of

molecules and clusters. World Scientific Co., Teaneck

4. Dyke JM (1987) Properties of gas-phase ions. JCS Faraday II 83:67

5. Chen P (1994) Photoelectron spectroscopy of reactive intermediates. In: Ng CY, Baer T,

Powis I (eds) Unimolecular and bimolecular reaction dynamics. Wiley, New York, p 372

6. Willitsch S, Innocenti F, Dyke JM, Merkt F (2005) High-resolution pulsed-field-ionization

zero-kinetic-energy photoelectron spectroscopic study of the two lowest electronic states of

the ozone cation O3 C . J Chem Phys 122:024311

7. Dyke JM, Golob L, Jonathan N, Morris A, Okuda M (1974) Vacuum ultraviolet photoelectron

spectroscopy of transient species: part 4 difluoromethylene and ozone. JCS Faraday Trans I


8. Katsumata S, Shiromaru H, Kimura T (1984) Photoelectron angular distributions and assignment of photoelectron spectrum of ozone. Bull Chem Soc Jpn 57:1784

9. Brundle CR (1974) He(I) and He(II) photoelectron spectrum of ozone. Chem Phys Lett 26:25

10. Frost DC, Lee ST, McDowell CA (1974) High resolution photoelectron spectroscopy of ozone.

Chem Phys Lett 24:149

11. Weiss MJ, Berkowitz J, Appelman EH (1977) Photoionization of ozone: formation of O4 C and

O5 C . J Chem Phys 66:2049

12. Moseley JT, Ozenne JB, Crosby PC (1981) Photofragment spectroscopy of O3 C . J Chem Phys


13. Probst M et al (2002) Ionization energy studies of ozone and OClO monomers and dimers. J

Chem Phys 116:984

14. Willitsch S, Dyke JM, Merkt F (2004) Rotationally resolved photoelectron spectrum of the

lowest singlet electronic state of NH2 C and ND2 C . Mol Phys 102:1543

15. Dyke JM, Morris A, Josland G, Hastings MP, Francis PD (1986) High-temperature photoelectron spectroscopy: an increased sensitivity spectrometer for studying vapor-phase species

produced at furnace temperatures >2000 K high temperature. Science 22:95

16. Innocenti F, Eyyper M, Lee EPF, Stranges S, Mok DKW, Chau FT, King GC, Dyke JM (2008)

Difluorocarbene studied with threshold photoelectron spectroscopy (TPES): measurement of

the first adiabatic ionization energy(AIE) of CF2 . Chem Eur J 14:11452


J. Dyke

17. Bulgin DK, Dyke JM, Jonathan N, Morris A (1979) Vacuum ultraviolet photoelectron

spectroscopy of transient species: part 9 the ClO radical. JCS Faraday II 75:456

18. Dyke JM, Gamblin SD, Hooper N, Lee EPF, Morris A, Mok DKW, Chau FT (2000) A study

of BrO and BrO2 with vacuum ultraviolet photoelectron spectroscopy. J Chem Phys 112:6262

19. Mok DKW, Lee EPF, Chau FT, Wang DC, Dyke JM (2000) A new method of calculation of

Franck-Condon factors which includes allowance for anharmonicity and the Duschinsky effect:

simulation of the He I photoelectron spectrum of ClO2 . J Chem Phys 113:5791

20. Dyke JM, Ghosh MV, Kinnison DJ, Levita G, Morris A, Shallcross DE (2005) A kinetics and

mechanistic study of the atmospherically relevant reaction between molecular chlorine and

dimethyl sulphide (DMS). PCCP 7:866

21. Dyke JM, Ghosh MV, Goubet M, Lee EPF, Levita G, Miqueu K, Shallcross DE (2006) A study

of the atmospherically relevant reaction between molecular chlorine and dimethyl sulphide

(DMS): establishing the reaction intermediate and measurement of absolute photoionisation

cross-sections. Chem Phys 324:85

22. Beccaceci S, Ogden JS, Dyke JM (2010) Spectroscopic study of the reaction between Br2 and

dimethyl sulphide (DMS), and comparison with a parallel study made on Cl2 C DMS: possible

atmospheric implications. PCCP 12:2075

23. Spicer CW, Chapman EG, Finlayson-Pitts BJ, Platridge RA, Hubbe JM, Fast DJ, Berkowitz

CM (1998) Unexpectedly high concentrations of molecular chlorine in coastal air. Nature


24. Innocenti F, Eypper M, Beccaceci S, Morris A, Stranges S, West JB, King GC, Dyke JM (2008)

A study of the reactive intermediate IF and I atoms by photoelectron spectroscopy. J Phys Chem

A 112:6939

25. West JB, Dyke JM, Morris A, Wright TG, Gamblin SD (1999) Photoelectron spectroscopy of

short-lived molecules using synchrotron radiation. J Phys B 32:2763

26. Dyke JM, Gamblin SD, Morris A, Wright TG, Wright AE, West JB (1998) A photoelectron

spectrometer for studying reactive intermediates with synchrotron radiation. J Electron Spectrosc Relat Phenom 97:5

27. Innocenti F, Zuin L, Costa ML, Dias AA, Morris A, Paiva ACS, Stranges S, West JB, Dyke

JM (2005) Photoionization studies of the atmospherically important species N and OH at the

Elettra synchrotron radiation source. J Electron Spectrosc Relat Phenom 142:241

28. Eypper M, Innocenti F, Morris A, Stranges S, West JB, King GC, Dyke JM (2010) Photoionization of iodine atoms: Rydberg series which converge to the IC (1 S0 ) I(2 P3/2 ) threshold.

J Chem Phys 132:244304

Chapter 4

Synthesis and Applications of Nano Size

Titanium Oxide and Cobalt Doped

Titanium Oxide

Revannath D. Nikam, Sharad S. Gaikwad, Ganesh E. Patil, Gotan H. Jain,

and Vishwas B. Gaikwad

Abstract Using titanium isopropoxide the nano size TiO2 was prepared by new solgel method. The nano size structure of TiO2 was confirmed by ultra-violet diffuse

reflectance spectroscopy (UV-DRS), X-Ray Diffraction (XRD) Spectroscopy, Field

Emission Scanning Electron Microscopy (FESEM) and Transmission Electron

Microscopy (TEM). The gas sensitivity of material was tested by preparing thick

film by screen printing technique. For this the thixotropic paste of material was

prepared by using ethyl cellulose and butyl cellulose. The gas sensing performance

of this thick film was tested for gases like ethanol, CO2 , H2 S, NH3 , CO, Cl2 and

maximum sensitivity was observed for H2 S gas. The H2 S gas sensing ability was

also improved by doping of cobalt into TiO2 by hydrothermal method. The cobalt

doped TiO2 showed sensitivity for minimum 100 ppm of H2 S at 300ı C.

4.1 Introduction

Metal oxide semiconductors are widely used as gas sensor materials since they show

change in conductance on exposure to gases [1]. The scientific literatures showed

that TiO2 is used as a gas sensing material in many devices [2]. The gas sensing

R.D. Nikam • S.S. Gaikwad

Department of Chemistry, K.T.H.M. College, Gangapur Road, Nashik,

422 002 Maharashtra, India

e-mail: nikam.revan@rediff.com; gaikwad.sharad85@gmail.com

G.E. Patil • G.H. Jain

Department of Physics, Arts, Commerce & Science College, Nandgaon, Nashik,

423 106 Maharashtra, India

e-mail: ganeshpatil phy@rediffmail.com; gotanjain@rediffmail.com

V.B. Gaikwad ( )

Chemistry Materials Research Laboratory, K.T.H.M. College, Nashik,

422 022 Maharashtra, India

e-mail: dr.gaikwadvb@rediffmail.com

M.G. Bhowon et al. (eds.), Chemistry for Sustainable Development,

DOI 10.1007/978-90-481-8650-1 4, © Springer ScienceCBusiness Media B.V. 2012



R.D. Nikam et al.

ability of nano size TiO2 can be increased through doping of other atoms such as

Pt, Mn, Co, Cu, Cr and Nb [3]. Hydrogen sulfide is a toxic gas generally released

from industrial effluents and coal mining processes. The permissible limit of H2 S

gas in clean environment is about 15 ppm [4]. Concentration of H2 S of more than

156 ppm is very hazardous to human health, so the measurement of released H2 S

gas is environmentally important. Numerous H2 S gas sensing devices are available

in the market, but have drawbacks of slow response and low sensitivity. This paper

presents a method of preparation of nano size TiO2 [2] and cobalt doped TiO2 ,

the semi-conducting material utilized for manufacturing the H2 S gas sensor with

maximum sensitivity for lower concentration of H2 S.

4.2 Methodology

4.2.1 Synthesis of Nano Size TiO2 by Sol-Gel Method

Titanium isopropoxide (2 ml) and dodecylamine (0.5 ml) were added to NaCl

(3.9 g) in 95% ethanol (30 ml) and the mixture was stirred for about 3 h at room

temperature. The rate of reaction was slowed down with the addition of ethanol:

NaCl mixture to obtain the product with smaller sized particle dimensions. Then the

pH of the reaction mixture was adjusted to 6.0 using 0.1 M HCl and the whitish

gel thus formed was again stirred for 2 h. The unwanted salt from gel material

was removed by washing it with a mixture of p-toluene sulphonic acid in distilled

water. The gel was dried overnight at 250ı C in an electric oven. The obtained gel

was annealed at various temperatures. The first fraction of gel annealed at 400ıC

showing black colour. The second fraction of gel annealed at 500ıC showing gray

coloured product. The third fraction annealed at 600ı C showing a white coloured

product [2]. The colour change of material was due to phase change of TiO2 from

anatase to rutile. The reaction scheme is shown in Fig. 4.1.

4.2.2 Doping of Cobalt into Nano Size TiO2

by Hydrothermal Method

The cobalt doping to nano size TiO2 was carried out by hydrothermal method by

using Teflon bottle [5, 6]. In this method 0.1 M cobalt(II) chloride solution (125 ml)

was mixed into 0.1 M NaOH solution (125 ml) in a Teflon bottle and nanoTiO 2 (1 g)

was added. The bottle was kept in an electric oven for about 2 h. Due to the internal

pressure created on the crystal lattice of titanium oxide, the cobalt got doped. The

doped material was taken into a beaker and stirred for 30 min. The product was dried

after washing it with distilled water and was fired at 250ı C for removal of unused

reagents. The cobalt doping was tested by comparing the IR absorption frequency

of doped and undoped TiO2 .

4 Synthesis and Applications of Nano Size Titanium Oxide...









Titanium isopropoxide


30ml ethanol solvent

3.9g NaCl


Stirring for 3 h

Gel Product

Stirring for 2 h.

Kept over night at 250ЊC



Annealed at





Nanosize TiO2

Fig. 4.1 The scheme for formation of nano size TiO2

4.2.3 Preparation of Thick Film

The gas sensitivity of prepared material was tested for various gases using thick

film. The thick film of material was prepared by screen printing technique [7]. First

the thixotropic paste was prepared by mixing of the synthesized semi-conducting

nano TiO2 material (1.0 mg) with a solution of 1.0 g ethyl cellulose (binder) and

1 ml mixture of organic solvents with the following composition [Butyl cellulose

(4 parts) C Butyl carbitol acetate (3 parts) C Terpenol (3 parts)]. The film was made

uniform by application of pressure on it. The film was then fired at 475ıC to remove

organic matter. The thick film of Co-TiO2 was prepared similarly. The gas sensing

ability of both of these films was tested by their explosion with gaseous ethanol,

H2 S, NH3 , Cl2, CO and CO2 gases.

4.3 Results and Discussion

4.3.1 X-Ray Diffraction Analysis

The crystal structures of all samples were studied by X-ray diffraction technique

[8] (XRD Make-BRUKER) and the patterns are shown in Fig. 4.2. The Cu-K’

R.D. Nikam et al.












Intensity (a.u.)








600 °C

500 °C

400 °C










Fig. 4.2 XRD patterns of nano size TiO2 annealed at 400ı C, 500ı C, 600ı C and Co-doped-TiO2

radiation was used with 10–90ı angular region for identification of the specific

phase formed after heat treatment. The obtained XRD pattern of nano TiO2 was

matched with JCPDS data card no. (21–1272) and the XRD pattern of Co-doped

TiO2 was matched with JCPDS data card no. (29–0516). The comparative study

showed that the XRD pattern of sample annealed at 400ıC exhibited only anatase

phase peak at 25.5ı with (121) plane, but the peak intensity was low because

of the amorphous nature of this material. The sample annealed at 500ı C showed

anatase phases with increase in peak intensity due to increase in crystallinity. The

XRD pattern of sample annealed at 600ı C showed both anatase and rutile phases

corresponding to the peak at 25.5ı with (121) plane and 27.4ı with (111) plane.

The XRD analysis of cobalt doped material indicated the presence of crystalline

Co, judged by the diffraction signals arising from the (111) plane and (200) plane

of cobalt lattice. The XRD pattern of cobalt doped TiO2 exhibited rutile as well

as anatase peak. Overall the rutile phase formation was found to increase with

increase in annealing temperature. This effect was observed due to the increase in

surface energy with increasing annealing temperature. In gas sensing, rutile phase

was preferred because of its higher semi-conducting property [9].

4 Synthesis and Applications of Nano Size Titanium Oxide...


Fig. 4.3 FESEM images of nano size TiO2 annealed at (a) 400ı C, (b) 500ı C, (c) 600ı C and

(d) Co-doped TiO2

4.3.2 Field Emission Scanning Electron Microscopy Analysis

The nano size structures of TiO2 annealed at 400ıC, 500ı C and 600ı C and cobalt

doped-TiO2 were studied by FESEM spectroscopy. The sample for this analysis was

prepared by coating the sample of any thickness on alumina stub. The electron beam

was scanned over the surface of sample to obtain the image of surface. Due to this,

the size measured by FESEM was greater than the size measured by TEM. The result

of this analysis is represented in Fig. 4.3. When TiO2 was annealed at 400ı C, the

spherical morphology of nano TiO2 was observed with particle dimensions equal

to 28 nm (Fig. 4.3a). The particle dimensions of nano material were observed to

increase with rise in annealing temperature due to coarsening of particle. Fig. 4.3b

elucidates that, when TiO2 was annealed at 500ıC, the spherical nature of the

particle changed and its size was increased to 36 nm. Similarly, the TiO2 annealed

at 600ıC showed particle dimension equal to 56 nm with coagulated particles

(Fig. 4.3c). The FESEM image (Fig. 4.3d) of Co doped TiO2 showed spherical

morphology of particle with size 28 nm.

Tài liệu bạn tìm kiếm đã sẵn sàng tải về

4 Photoionization of Reactive Intermediates of Atmospheric Importance with Synchrotron Radiation, Using Atomic Nitrogen as an Example

Tải bản đầy đủ ngay(0 tr)