Structural, Morphological, and Catalytic Properties …
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3.5 Protolytic Properties
Mechanisms of water molecule protolysis depend on the difference in strength of
acid (L) and basic (B) sites situated on the OMS-2 surfaces [23, 24] that becomes
apparent by comparison of time dependences of pH in OMS-2 suspensions [50].
Figure 5 shows the time dependences of pH in suspensions of the initial OMS-2
samples and the OMS-2 samples after their reaction with ozone.
As can be seen, profiles of the kinetic curves and values of an equilibrium pH, pH eq ,
depend on the methods of OMS-2 obtaining. For OMS-2(SSt) and OMS-2(MS), pH
of the suspension rapidly increases and a positive value of a suspension effect, pH s
= pH eq – pH 0 (Table 3), indicates that water molecules interact with basic sites:
Fig. 5 Time dependences of pH in suspensions of the OMS-2 samples before (o) and after (•) their
reaction with ozone: 1, 1 OMS-2(Ref); 2, 2 OMS-2(MS); 3, 3 OMS-2(SG); 4, 4 OMS-2(SSt)
Table 3 Values of pH 0 , pH eq , and pH s for the OMS-2 samples
Sample
Before reaction with ozone
After reaction with ozone
pH 0
pH eq
pH s
pH 0
pH eq
pH s
OMS-2(SSt)
10.5
11.6
1.1
9.0
11.0
2.0
OMS-2(Ref)
4.0
3.0
−1.0
3.5
3.2
−0.3
OMS-2(SG)
7.5
7.3
−0.2
5.8
5.5
−0.3
OMS-2(MS)
5.2
5.4
0.2
4.55
4.65
0.1
pH 0 and pH eq are pH values measured in 15 s and in the equilibrium state, respectively; pH s is a
suspension effect