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Physical & Chemical properties

Nanomaterial Zeta potential

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Administrative data

Endpoint:
nanomaterial Zeta potential
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Limited documentation of the data evaluation was provided in the full study reports. Furthermore the procedure for subsampling and data analysis was not explained in detail. Thus, it was not possible to assess the validity of the provided data as the sample preparation could have a significant influence to the result. The provided data are not sufficient to finally conclude on the zeta potential of the 4 NMs or to identify differences or similarities. The concentration used was excessive and the results were regarded to be not self-consistent (e.g. the pH-dependence for NM111), and were not confirmed by other labs (should see positive charge at neutral pH).

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2012
Report Date:
2012

Materials and methods

Test guideline
Qualifier:
no guideline followed
GLP compliance:
no
Type of method:
Laser-Doppler
Remarks:
Laser-Doppler-Electrophoresi
Details on methods and data evaluation:
Zeta potentials of samples were determined at different pH values (pH=2, 4, 6, 8 and 10) using a Brookhaven particle size analyser 90Plus equipped with a 657 nm laser. 10 mg “as-received” ZnO sample was dispersed in a cuvette containing 3 ml DI water, and the pH was adjusted by adding either 0.1M HCl or 0.1M NaOH. The cuvette was placed in an ultrasonic bath for 10 seconds and then shaken manually to ensure good dispersion of particles in the sample. The electrode was inserted into the dispersion and the Zeta potential at each pH was measured 5 times and an average was determined. The temperature of all measurements was maintained at 25 °C. The cuvette was thoroughly washed with deionised water after each measurement.

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: nanoform

Data gathering

Instruments:
Brookhaven particle size analyser 90Plus equipped with a 657 nm laser

Results and discussion

Zeta potentialopen allclose all
Zeta potential:
-5.79 mV
St. dev.:
0.61 mV
pH:
6.2
Medium:
DI water
Remarks on result:
other: NM110
Zeta potential:
-26.78 mV
St. dev.:
1.77 mV
pH:
6.2
Medium:
DI water
Remarks on result:
other: NM111
Zeta potential:
3.74 mV
pH:
6.2
Medium:
DI water
Remarks on result:
other: NM112
Zeta potential:
-5.51 mV
St. dev.:
0.72 mV
pH:
6.2
Medium:
DI water
Remarks on result:
other: NM113
Isoelectric pointopen allclose all
Isoelectric Point:
3.9
Medium:
deionised water
Remarks on result:
other: NM110
Isoelectric Point:
2.7
Medium:
deionised water
Remarks on result:
other: NM111
Isoelectric Point:
6.5
Medium:
deionised water
Remarks on result:
other: NM112
Isoelectric Point:
5.1
Medium:
deionised water
Remarks on result:
other: NM113

Any other information on results incl. tables

The table and the figure show the relationship between zeta potential and pH for the four ZnO samples tested. The pH value at which the net surface charge is zero is called the isoelectrical point (IEP). The IEPs are 3.9 for NM110, 6.5 for NM112 and 5.1 for NM113. IEPs in the range 4-6 are consistent with the dissociation of water to H+ and OH- on the particle’s surface and, where there is no surface coating, the IEP will be due solely to this dissociation. This therefore suggests that there is no specific surface coating on NM110, NM112 and NM113.

 

The IEP of NM111 is nominally 2.7, based on the data acquired. This IEP, which is significantly lower than IEPs determined for the uncoated NM110, NM112 and NM113, is suggestive of a different surface reaction (other than water dissociation) occurring on the coated NM111. However, NM111 is hydrophobic and observed to be very difficult to disperse in aqueous solutions; it is difficult to reconcile this observation with measurements of large zeta potential in water at most pHs. One possible explanation may be that the zeta potential data pertain to a small portion of the sample that is able to disperse. Therefore these data on zeta potential for NM111 should not be considered as representative of the sample, unless supported by other evidence.

 

Table Zeta potentials for ZnO samples dispersed in DI water where the pH was adjusted by adding either 0.1M HCl or 0.1M NaOH.

pH

NM110

Zeta potential

mV

NM110

SD

NM111

Zeta potential

mV

NM111

SD

NM112

Zeta potential

mV

NM112

SD

NM113

Zeta potential

mV

NM113

SD

2.10

25.04

1.84

14.36

3.01

24.04

1.91

16.94

2.74

4.00

-1.50

0.6

-33.67

2.76

10.20

0.92

5.94

3.1

6.20

-5.79

0.61

-26.78

1.77

3.74

0.56

-5.51

0.72

8.10

-21.63

0.82

-28.20

1.5

-22.00

3.45

-13.50

0.76

10.00

-31.45

0.48

-19.25

1.06

-33.34

0.62

-37.38

1.25

 

 

Applicant's summary and conclusion

Executive summary:

CSIRO, 2012 investigated the Surface charge (zeta potential) of the nanomaterials. Zeta potentials of the samples were determined at different pH values (pH=2, 4, 6, 8 and 10) using a Brookhaven particle size analyser 90Plus equipped with a 657 nm laser. 10 mg. ZnO nano samples were dispersed in a cuvette containing 3 mL deionized water, and the pH was adjusted by adding either 0.1 M HCl or 0.1 M NaOH. The cuvette was placed in an ultrasonic bath for 10 seconds and then shaken manually to ensure good dispersion of particles in the sample. The electrode was inserted into the dispersion and the Zeta potential at each pH was measured 5 times and an average was determined. The temperature of all measurements was maintained at 25 °C. The result showed the relationship between zeta potential and pH for the four ZnO samples tested. The isoelectrical point (IEP) was determined to be 3.9 for NM‑110, 6.5 for NM‑112 and 5.1 for NM‑113. IEPs in the range 4-6 are consistent with the dissociation of water to H+ and OH- on the particle’s surface and, where there is no surface coating, the IEP will be due solely to this dissociation. This therefore it was concluded that there is no specific surface coating on NM‑110, NM‑112 and NM‑113. The IEP of NM‑111 was determined to be 2.7 which was significantly lower than IEPs determined for the uncoated test samples. NM‑111 is hydrophobic and observed to be very difficult to disperse in aqueous solutions; it is difficult to reconcile this observation with measurements of large zeta potential in water at most pHs. One possible explanation may be that the zeta potential data pertain to a small portion of the sample that is able to disperse. Therefore these data on zeta potential for NM‑111 should not be considered as representative.