Infrared photoacoustic spectroscopy of surfaces

Journal of Molecular Q Elsevier Scientific

INFRAREiJ

3l.J.D.

Structure,

PHOTOACOUSTIC

Low and

Department New York,

61 (1980)

119-124

119

Publishing Company, Amsterdam - Printed in The Netherlands

G.A.

SPECTROSCOPY OF SURFACES

Parodi

of Chemistry - New York N.Y. 10003 (U.S.A.)

University

-

4 Washington

Place

ABSTRACT photoacoustic,

A prototype coupled

with

scribed.

in

which

IR photoacoustic

several face

a reactor

computer-controlled

millimeters

sub-monolayer

spectra

thick

nodi fications

were

surface

corrosion

1 ayers.

and

were

species

of

may be treated samples

catalyst

carried

coverages

observing

samples

spectrometer,

and

on adsorbents,

have

new

been

an

to

beds

of

recorded of

technique

catalysts,

gases

of

IR absorptions The

observed.

with

consisting

pellets

out,

and

acoustic

1000°C.

and

, chars

and

dealumina

various

species

sur-

formed

is particularly

coals

is

silica

after

surface

cell

at

useful

carbons,

for

and

INTRODUCTIOll Infrared

spectroscopy

information

the

IR transmission

and

species are

present

and

study

range tial

structure

methods

so thick,

carbons, such

perhaps

that

have

of

the

been

and

such

single

molecular used

as commercial

we have

very

photoacoustic

the

effect

powerful

technique

bound

$0

extensively

There

are,

catalyst

methods

examined

most species

catalyst.

conventional

samples,

by means

the

of

on adsorbents

physically

chars to

about

is

fail.

it of

1,2),

and

of

the

so opaque, be useful

obtaining

data

describe

solids,

surface

some samples

or

would

obtaining

surfaces

studying

however,

feasibility (ref.

for

pellets, As

the

for

which such

as

to

be able

in

the

some of

our

IR ini -

results.

EXPERINEHTAL The atory

prototype 1 and

Figs.

operated

with

differential frequency

is shown

2.

The

signal

from

a l/2”

2804

power

supply

(ref.

chopper I/O The

spectrometer

a Type amp1 ifier

a generalized software.

IR-PAS

(ref. to

and 4), a Nova

monochromator

Model

124A

through

was

B&K Model 3)

lock-in

fitted

(ref.

A/D 6)

with

was

4165

led

amp1 ifier

a 15-bit

computer

schenatically

with

end-of-travel

largely

condenser

through

locked

converter

fitted

by the

a

(ref.

Model

a Model 5)

peripherals switches

microphone

P-A-R-C.

to

selfexplan-

192

variable

incorporated and and

IlC

suitable

a fiduciary

in

120

marker, and its continuous ble

by the

computer_

retained,

but

coating,

99.4%

thus

significantly

not

drive

The

additional reflective

in

the

analog

selected

:favelength

multiple

scanning,

ficult

and

range

were

so on.

dictated

by the

constant


the

LiF

-70

mm slits resp.).

was

Fig. As carrying device

shown

10)

prism

(0.50

the

tions

of

to

the

cock device

the and

region

then

lifted

worked

exploratory

of

Fig.

then

major

used

for

and

obvious

for

operating

were

available

2).

The

to

be 20,

mm slits),

and

and

the

in

and

is

expansions,

that

the

IR rather

more

than

dif-

the

The spectral

the

4 cm-’ 54

with

at and

the

spectra

ranges

slit

settings

2200

The -1 cm ,

with

CaF2

resolution.

38G0,

2300 and -1 36 cm , resp.,

frequency was 45 Hz and was chosen

ambient

reactions

3 was

requires

noise

spectrum

and,

The

constructed.

conditions. when

careful sample

Purified

the

pressures

had

was moved

the

microphone_

Turning

the

the

carriage

pressed

it

and

Its

objectionable

not

otherwise,

the

could

of

the

environment.

barrel against

steel

which

of

then

the

is

carriage

environment,

the

the

and

introduced

magnet

of

the

be degassed

equalized,

by an external

feature, is

control

he1 ium was

carriage

but

is

spectrometers

scale

the

along set

92,

The modulation in

spectrometer

beam, and digitize

difference

(ref. 9).

also

7.5

was

LH41

with

photoacoustic

ratioing,

which,

a scan),

treated

opera-

7) slits

The latter is a 2500°K carbon rod

source.

sample

we1 1 . work

is

(ref. the

in the form of a spectrum over pre-

detector

the

minimum

surface

device the

the

drive

between

Fig. 2.

gases under controlled opened,

a step

1.

out in

(ref.

throughout

(ref.

near

range

prisms

computed

this

micron

from Boyd et al .

was

because

3-25

suitable

latter

.‘jo,

mirrors

including

were

(-35,

All

The

(which

resp.,

kept

added.

of

adapted with minor modification covered

with

nonochromator

were

software

needed,

the

the sample with a "monochromatic"

and materials

are

replaced

of

from other single-beam

output

ranges;

technology

visible

the

different

filtered

was

path

mirrors

in that it will illuminate store

motor

original

large

Teflon

bottom

of

acceptable which

can

exposed

to

both

stopcock

through high the

for

the

the

the

introduce

sec-

was stopcock

vacuum celJ.

to

stopThe

present contam-

121

ination;

a quartz-enclosed

magnet

has

to

be substituted,

The sample

bed depth

was

- 2inm.

-2x3xl2

‘I

&

m

.(mgQAT

SPO%VELDED TO STEEL CARRIAGE MOVED BY EXtitiNkMAGNEf

-

TEFLON HLGNVACUUM STOPCOCK

Fig.

3.

Photoacoustic

The ordinates usually

recorded

2000 cl8 scan at

region

rate

the

are

high

a sample,

of

the

spectra

at

a rate

required

computing

units

.

the

being

were

used

, So,

at

the

were

under

double-beam

obtained

in

The range

spectra

charcoal

simu’iated

The spectra

prism

Ratioed

linear

wavelenght.

microns/step~se~.

15 min.

by the

of

are

O-00165

about

determined

S, and that

&own

of

wavenumbers.

then

spectra

and reactor.

cell

, so that covered

low

identical

by multiple

a scan

by the

instrumental

4000-

and

the

the

spectrum

conditions,

in

eight

scanning,

the

and by convenience

by recording

S/So , given

were

of

spectra

wavenumbers,

produced

spectrum

The spectra

arbitrary

of and

intensity

sequentially

recorded

added.

RESULTS Figs.

4 and 5 serve

af s , reagents,

materi surface

species

obtainable

are

of

2 mm deep sample caused

observed stretching

i?lustrate

the

and conditions

were

known

(refs.

by transmission-

The results

This

to

absorption

a sequence

band.

of

bed was first

a substantial

by the

decrease

11-14)

of

Llhen the

O-Ii

chosen

data

obtainable.

because

the

PAS data

The particular

surface

could

reactions

be compared

and with

others

methods. treatments

degassed

the

of

and the

surface

replacement

type

[A) of

band

and then

ESi-CJli and the

sample was exposed

of

to

silica

are

exposed

to

by %SI-O-SiHC72

shown CSiClS

in

Fig.

vapor

4. (B).

groups

formation

of

?IliS,

some Wi4C1 was formed

(C),

the

and can be -I 2260 cm Si -E

The

122

(Nk$

gives

halosilane

bands shifted

destroyed

these

numbers.

Treating

surface

rSi -OCH3

at

3130 the

surface the

and 3045

Si-H

species sample

4.

Surface

to

(II), with

and the 2239

and the methanol

coordination

cmW1 (ref. Si-Cl (E)

14).

stretch

then

caused

of

NH3 to

Degassing shifted the

to

the

surface

partially higher

formation

waveof

some

groups.

3900

Fig_

cm-l)

stretch

2100 cd

Modification

of

Silica.

3900

2100

123

ALUMINA DEGASSED

\/

AFTER /ESTERIFICATION

Fig.

5.

Surface

Similar ing

the

experiments spectrum

surface the

Al-O;1

sample

a band

Modification

had

in

the

these

being

prism

was

bands

were

were

(Fig.

groups

5)

of

used

in

not

to

to

order

to

with

alumina

showed

water

acetic

as well

attributable

out

alumina bound

exposed

region

Alumina,

carried

of

and

been C-H

of

and acid

as

a C-D

the

formation

obtain

data

broad

the

deformation

absorption

the

vapor, stretching of

below

After

(G!OM*/g).

the

band

O-H

and

band

ester,

2000

and,

cm-’

degass-

of

the

of

latter.

After

Hz0

bands declined, -1 1800 cm appeared,

near

a surface

a mild

characteristic

Al-OCOCHS.

The

unfortunately,

and

CaF2

the

C-H

resolved.

DISCUSSION It

is

about

apparent

surface

lets

(ref.

are

omitted;

most

of

tions,

15),

in

that

the

s.Si-OH

and

2260

a.

9 mono1 ayer.

to

detect

one

cm-l

will

above

which

were

Surface

treatments

amounts

bands of

Si-I-l

by the that

of

were

or

It

C,

is

For

relative

Fig.

was -1 cm

4,

2260

but,for

can

to

caused prior

peldata

note

that

to it

reac-

by molecular experience

intensities present

data

catalyst

chemisorption

were

band,

yield

brevity,

pertinent

example,

on the

the

solid

involved

species

less.

based

PAS method

included

earlier

some surface

of

IR

observed

elsewhere.

spectrum

intensity

amount.

the

examined

outlined of

species,

bands

that

species

a monolayer,

:Si-0-SiHC12

of

shown

be described

absorption

Judging tenth

solids

coal.

surface

the

present

indicates

and

results

various

examples

Other

glass

the

the

the

species.

so that

species

from

of the

should

the

extent

of

be possible

124 Some improvements resolution

will

improvement able

to

seem,

however,

examination ing

will

us has

and/or

of

in

be

instrumentation

required

for

be obtained dispersion

that

IR-PAS

the

leading technique

by employing

poor

physically

the

surfaces

a potentially

of

solids

scratched

are

sensitivity for

and

fogged

ancillary

opaque

because

and

research

monochronator;

useful

which

greater

be useful

a better

as we1 1 as

is

to to

the

only

prisms) IR

_

technique they

better

(an

are

immediate one

It

avail-

would for

highly

the absorb-

thick.

ACKNOWLEDGFMEIIT Support American

by grant Chemical

No. Society

3109-AC5 is

from

grateful

the ly

Petroleum

acknowl

Research

Fund

administered

by the

edged.

REFERENCES 1 2 3 4 5 6 7 3 9

10 11 12 13 14 15

A:. Rosencwaig, Opt. Commun. 7(1973)305. Y.-D. Pao, Optoacoustic Spectroscopy and Detection, Academic Press, N.Y., 3&K Instrument Co., Cleveland, Ohio. Princeton Applied Research Co., Princeton, N.J. Analogic Corp., Uakefield, Mass. Data General Corp., i1ew York, :i.Y. M.J.C. Low, in preparation. Laser Optics, Inc., Danbury, Conn. h’.T. Boyd, 3-E. Jennings, 1I.E. Glass, and M.N. Gailar, Rev. Sci. Instrum. 45( 1974)1236-1283. E.D. Pal ik and J.R. Stevenson, report AD $609902. L-h’. .Little, Infrared Spectra of Adsorbed Species, Academic Press, Xew York, 1966. A.V. Kiselev and V.I. Lygin, Infrared Spectra of Surface Compounds, John and Sons, Hew York, 1975. M.J.D. Low and ti. Hark, J. Catal. 44(1976)300-305. 1i.J.D. Low, A.G. Severdia and J. Chan, unpublished data. M.J.D. Low and G.A. Parodi, Spectrosc. Letters ll(8) (1978)581-588.

1977.

Cliley