1
An XPS investigation on glucose oxidase and Ni/Al
hydrotalcite interaction.
Danilo Addari1 • Adriana Mignani2 • Erika Scavetta2 • Domenica Tonelli2 • Antonella Rossi*,1
1
Dipartimento di Chimica Inorganica ed Analitica, Cittadella Universitaria di Monserrato, INSTM
UdR, Cagliari, Italy
2
Dipartimento di Chimica Fisica ed Inorganica, Università di Bologna, INSTM UdR Bologna, Italy
Corresponding author: e-mail: rossi@unica.it; Tel: +39-070-6754464, Fax: +39-070-6754456
*
Abbreviations n/a: not applicable
List of XPS reference compounds
The chemicals listed in Table 1 were analyzed as reference compounds for HT surface characterization.
Table 1 List of chemicals used as reference compounds for surface analysis
Compound
Chemical formula
Supplier
Purity
State
(weight %)
Nickel metal
Ni
Johnson &
> 99.99 %
foil
Matthey
Nickel (II) oxide
NiO
Alfa Aesar
99.995%
lump
Nickel (II)
Ni(OH)2
Alfa Aesar
n/a
powder
Nickel (II) nitrate
Ni(NO3)2
Fluka
≥ 98%
powder
Aluminium
Al
Goodfellow
99.999%
foil
 alumina
-Al2O3
Buehler
n/a
powder
Aluminium nitrate
Al(NO3)3·9H2O
Aldrich
98+%
powder
Al(OH)3
Merck
n/a
powder
Type VII from
Sigma Aldrich
Minimum 60%
lyophilized
hydroxide
hydrate
Aluminium
hydroxide
Glucose oxidase
Aspergillus niger
protein
Powder compounds were pressed into pellets in a glove-box and mounted on a standard Thermo sample
holder. Glucose oxidase, aluminum and nickel nitrate samples were cooled with liquid nitrogen during
measurements to reduce outgassing.
2
Pure metals were etched for 30 s at 3 kV 1 A to remove contamination. Aluminum required a total 15
minutes etching at 3 kV 2 A in order to reduce oxygen content to less than 2% of the Al 2p signal.
Reference compounds XPS analysis
The complete list of reference compounds is reported in Table 1 and the results of the XPS analysis are
commented hereafter.
Nickel
Ni 2p of sputtered metallic nickel consists of the spin-orbit doublet and a complex satellite structure. Ni
2p3/2 is found at 852.5 eV and Ni 2p1/2 at 17.2 eV far from the main signal.
Nickel oxide
Ni 2p3/2 main peak lays at 853.6 eV and its multiplet splitting at 855.6 eV. Ni 2p1/2 is found at 871.1 eV
and the corresponding multiplet splitting signal at 872.9 eV. The multiplet splitting signals have the
same line shape and FWHM of the main peak. A complex satellite structure is observed like that of the
metal. The main component of O1s is found at 529.4 eV and is attributed to nickel oxide.
Nickel hydroxide
The position of the Ni 2p3/2 main peak is 855.9 eV and its multiplet splitting signal is at 857.3 eV. The
positions of the corresponding components of the Ni 2p1/2 are 873.5 eV and 875.4 eV, respectively. The
multiplet splitting signals have the same line shape and FWHM of the main peak. Two satellites for
each of the main peaks are detected. O 1s lays at 531.5 eV.
Nickel nitrate
The Ni 2p3/2 main signal is found at 856.6 eV and is accompanied by its satellites. The Ni 2p1/2 is found
at 874.1 eV. The oxygen component of nitrate in O 1s is at 531.9 eV, the one at 533.3 is probably due to
adsorbed water as the sample is highly hygroscopic. Four components are detected in the N 1s peak.
The most intense one, assigned to nitrate is found at 407.4 eV. The less intense signals are due to traces
of the salt impurities.
3
Aluminium
Al 2s and Al 2p peaks of etched aluminium are at 117.9 eV and 72.8 eV. The second one is an
unresolved spin-orbit doublet.
Alpha alumina
Al 2s is at 119.1 eV, the unresolved Al 2p doublet at 74.2 eV. The only oxygen component is found at
531.2 eV.
Aluminium hydroxide
Al 2s is detected at 119.0 eV, Al 2p at 74.0 eV: these values are comparable within the experimental
error to those pertaining to the alpha alumina. O 1s is detected at 531.9 eV.
Aluminium nitrate
Al 2s and Al 2p are found at 119.9 eV and 75.1 eV. O 1s is resolved into two components: one at 533.0
eV, assigned to nitrate, and the other at 533.5 eV assigned to hydration water. The same components of
nickel nitrate are found in N 1s. The one due to nitrate is at 407.8 eV.
Glucose oxidase
The elements detected in the survey spectrum of the enzyme are: C, O, N. Other elements like Na, Cl,
and P are stated in the composition of the lyophilized GOx but are below the detection limit of XPS.
The C 1s signal is resolved into four components, all assigned to the various moieties of the molecule:
285.0 eV (aliphatic), 286.6 eV (C bond to one oxygen), 288.1 eV (C liked to two oxygen atoms by
simple bonds or to one oxygen by a double bond), 288.8 eV (typical of COO, HN-C=O groups). The
corresponding O 1s components are found at 531.2 eV and 533.0 eV. Two components are found in N
1s spectrum: the more intense one at 400.3 eV, and the weaker one at 402.1 eV.
Curve fitting parameters
Details on the curve fitting parameters used in HT spectra analysis are given in Table 2.
4
Table 2 Curve fitting parameters used for data processing
Component
Position (eV)
FWHM (eV)
Line shape
Intensity ratio
with the main
peak
Al2p (alumina)
74.0 ± 0.1
1.56
GL(10)T(3)
n/a
Al2s (alumina)
119.0 ± 0.1
1.84
GL(80)T(3)
n/a
Al2p (aluminium
74.1 ± 0.1
1.38
GL(30)
n/a
119.0 ± 0.1
1.84
GL(85)
n/a
285 (reference)
1.46
GL(30)
n/a
286.7 ± 0.2
1.46
GL(30)
n/a
C1s (carbonate)
288.8 ± 0.2
1.60
GL(30)
n/a
Ca2p3/2 (from GOx)
347.3 ± 0.1
1.77
GL(60)
n/a
Ca2p1/2 (from GOx)
Ca2p3/2 + 3.6
1.77
GL(60)
0.5
Cl2p3/2 (from GOx)
198.4 ± 0.1
1.79
GL(30)
n/a
Cl2p1/2 (from GOx)
Cl2p3/2 + 1.7
1.79
GL(30)
0.5
N1s (organic)
398.4 ± 0.2
1.92
GL(30)
n/a
N1s (organic from
400.1 ± 0.2
1.92
GL(30)
n/a
N1s (nitrite)
403.6 ± 0.1
1.11
GL(30)
n/a
N1s (nitrate)
407.4 ± 0.2
1.25
GL(30)
n/a
Na1s (from GOx)
1071.4 ± 0.1
1.90
GL(55)
n/a
Ni2p3/2 metal
852.5 ± 0.1
0.92
GL(95)T(1.5)
n/a
2.75
GL(30)
0.2
4.26
GL(30)
0.5
7.32
GL(30)
0.2
hydroxide)
Al2s (aluminium
hydroxide)
C1s (aliphatic and
from GOx)
C1s (other
contaminant or from
GOx)
GOx)
Ni2p3/2 metal satellite Ni2p3/2 + 1.9
1
Ni2p3/2 metal satellite Ni2p3/2 + 5.6
2
Ni2p3/2 metal satellite Ni2p3/2 + 12.4
5
3
Ni2p1/2 metal
Ni2p3/2 + 17.2
1.51
GL(95)T(1.5)
0.5
Ni2p1/2 metal satellite Ni2p3/2 + 20.9
5.00
GL(30)
0.2
6.20
GL(30)
0.3
5.04
GL(30)
0.05
1
Ni2p1/2 metal satellite Ni2p3/2 + 22.4
2
Ni2p1/2 metal satellite Ni2p3/2 + 29.9
3
Ni2p3/2 oxide
853.6 ± 0.2
1.04
GL(90)T(0.5)
n/a
Ni2p3/2 oxide
Ni2p3/2 + 2.0
1.04
GL(90)T(0.5)
0.4
Ni2p3/2 oxide satellite Ni2p3/2 + 7.0
2.74
GL(30)
0.4
3.82
GL(30)
0.3
2.33
GL(30)
0.06
multiplet splitting
1
Ni2p3/2 oxide satellite Ni2p3/2 + 9.5
2
Ni2p3/2 oxide satellite Ni2p3/2 + 13.0
3
Ni2p1/2 oxide
Ni2p3/2 + 17.5
1.49
GL(60)T(0.5)
n/a
Ni2p1/2 oxide
Ni2p3/2 + 19.3
1.49
GL(60)T(0.5)
0.2
Ni2p1/2 oxide satellite Ni2p3/2 + 25.5
4.78
GL(30)
0.4
1.94
GL(30)
0.04
1.74
GL(30)
0.03
multiplet splitting
1
Ni2p1/2 oxide satellite Ni2p3/2 + 27.4
2
Ni2p1/2 oxide satellite Ni2p3/2 + 29.4
3
Ni2p3/2 hydroxide
855.9 ± 0.2
2.37
GL(30)
n/a
Ni2p3/2 hydroxide
Ni2p3/2 + 1.4
2.37
GL(30)
0.3
Ni2p3/2 + 6
≈5
GL(30)
1
Ni2p3/2 + 10.9
≈3
GL(30)
0.1
multiplet splitting
Ni2p3/2 hydroxide
satellite 1
Ni2p3/2 hydroxide
6
satellite 2
Ni2p1/2 hydroxide
Ni2p3/2 + 17.6
2.48
GL(30)
0.5
Ni2p1/2 hydroxide
Ni2p3/2 + 19.5
2.48
GL(30)
0.2
Ni2p3/2 + 23.6
≈ 4.5
GL(30)
0.6
Ni2p3/2 + 26.8
≈ 3.7
GL(30)
0.1
O1s oxide
530.9 ± 0.2
1.60
GL(30)
n/a
O1s hydroxide
532.0 ± 0.2
1.60
GL(30)
n/a
O1s water
533.1 ± 0.2
1.60
GL(30)
n/a
Si2p (from GOx)
102.1 ± 0.1
2.29
GL(30)
n/a
Si2s (from GOx)
153.5 ± 0.1
2.97
GL(30)
n/a
multiplet splitting
Ni2p1/2 hydroxide
satellite 1
Ni2p1/2 hydroxide
satellite 2
GL = Lorentzian to Gaussian ratio T = Tail function