crystallite size reduction with possible contributions
from milling induced strain [35]. This interpretation is
consistent with the fact that significant particle size
reduction is observed in BET for dry milled NiO, but
not for slurry milled NiO.
While X-ray diffraction measurements indicate that
milling does not change the bulk crystal structure of
NiO, X-ray photoelectron spectroscopy provides clear
evidence for milling-induced chemical modification of
the NiO powder surface. The Ni 2p3/2 region of the
unmilled NiO (Fig. 3(a)) displays a multiplet which is
fitted by two peaks centered at 853.8 and 855.4 eV. It
also displays a shake-up feature fit by peaks centered
at 860.7 and 863.6 eV. The peak locations and peak
widths are consistent with the literature reports for NiO
[27,36]. In the milled NiO samples, the Ni 2p3/2
region displays subtle differences in the extent to
which the multiplet splitting peaks are resolved. This is
consistent with changes to the NiO surface either
through modification of the Ni2+/Ni3+ ratio or through
the presence of adsorbates [26,37].
The origin of the chemical modifications to the
NiO surface can be further understood by examination
of the O 1s region of the X-ray photoelectron
spectroscopy data (Fig. 3(b) and Table 3). Unmilled
NiO displays two peaks, one at 529.4 eV (full width at
half maximum (FWHM) = 1.2 eV) and the other at
531.0 eV (FWHM = 2.3 eV) (Fig. 3(b)(i)). These peaks
are frequently observed for NiO. The 529.4 eV is
assigned to oxygen in the NiO lattice [27,36]. In
previous works, the 531.0 eV has been ascribed either
to oxygen from hydroxyl or to other oxygen-containing
moieties, most likely adsorbed at defect sites [38,39]. It
has recently been shown that the 531.0 eV peak can
crystallite size reduction with possible contributionsfrom milling induced strain [35]. This interpretation isconsistent with the fact that significant particle sizereduction is observed in BET for dry milled NiO, butnot for slurry milled NiO.While X-ray diffraction measurements indicate thatmilling does not change the bulk crystal structure ofNiO, X-ray photoelectron spectroscopy provides clearevidence for milling-induced chemical modification ofthe NiO powder surface. The Ni 2p3/2 region of theunmilled NiO (Fig. 3(a)) displays a multiplet which isfitted by two peaks centered at 853.8 and 855.4 eV. Italso displays a shake-up feature fit by peaks centeredat 860.7 and 863.6 eV. The peak locations and peakwidths are consistent with the literature reports for NiO[27,36]. In the milled NiO samples, the Ni 2p3/2region displays subtle differences in the extent towhich the multiplet splitting peaks are resolved. This isconsistent with changes to the NiO surface eitherthrough modification of the Ni2+/Ni3+ ratio or throughthe presence of adsorbates [26,37].The origin of the chemical modifications to theNiO surface can be further understood by examinationof the O 1s region of the X-ray photoelectronspectroscopy data (Fig. 3(b) and Table 3). UnmilledNiO displays two peaks, one at 529.4 eV (full width athalf maximum (FWHM) = 1.2 eV) and the other at531.0 eV (FWHM = 2.3 eV) (Fig. 3(b)(i)). These peaksมักมีข้อสังเกตสำหรับ NiO 529.4 eV เป็นให้ออกซิเจนในตาข่าย NiO [27,36] ในงานก่อนหน้า 531.0 eV ได้จากนี้อย่างใดอย่างหนึ่งออกซิเจน จากไฮดรอก หรืออื่น ๆ ที่ มีออกซิเจนmoieties, adsorbed มักบกพร่องไซต์ [38,39] มันเพิ่งได้แสดงให้เห็นว่า ยอด 531.0 eV สามารถ
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