Zinc oxide

Nanomaterial photocatalytic activity

Administrative data

Endpoint:

nanomaterial photocatalytic activity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Limited documentation of the data evaluation was provided in the full study reports. Nevertheless, the study was regarded as scientifically acceptable and was regarded as reliable with restrictions. This used dye was regarded as sufficient for photocatalytic activity determination in organic solvent. Furthermore DPPH and Rhodamine are recommended by OECD 2014

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Decomposition of Rhodamine-B dye in the presence of nanomaterial, detected by UV-Vis spectroscopy.

GLP compliance:

no

Type of method:

other: UV-vis

Details on methods and data evaluation:

For each measurement, 0.012g of the powder sample was added into 100 ml of Rhodamine B (RhB) aqueous solution having the concentration of 0.0096g/L. The suspension was placed in a quartz beaker with a quartz watch glass as a lid. The suspension was then stirred in the dark for 1 h to ensure the establishment of adsorption and desorption equilibrium of RhB on the particle surface. Subsequently the suspension was irradiated with simulated sunlight using an Atlas Suntest XLS+ instrument (equipped with a 150 W xenon lamp) with a flux of 300 wm-2 while continuously stirred. The temperature of the solution was regulated to 37 °C (air cooling). At given intervals, 3 mL of the suspension was extracted and then centrifuged at 6000 rpm for 10 min to separate the nanoparticles from the supernatant. UV-Vis absorbance spectra of the supernatant were measured with a Varian Cary 3E spectrophotometer. The intensity of the optical adsorption peak around 554 nm was used to monitor the rate of dye degradation. Each of the photocatalytic activity tests was repeated three times. Overall rates of the reactive dye degradation were calculated assuming the first-order kinetics. It is assumed that extraction of a small quantity of sample (3 mL each x max 6) does not alter the UV exposure conditions of the remaining sample.

Test material

Test material information

Constituent 1

Reference substance name:

Zinc oxide

EC Number:

215-222-5

EC Name:

Zinc oxide

Cas Number:

1314-13-2

Molecular formula:

ZnO

IUPAC Name:

oxozinc

Test material form:

solid: nanoform

Data gathering

Instruments:

Varian Cary 3E UV-Vis spectrophotometer:
Atlas Suntest CPS+ instrument equipped with a 150 W Xenon lamp.

Results and discussion

Photocatalytic activity equation / description:

It was found that the photocatalytic activity was the highest for NM110 and NM113 and the lowest for NM112 (Table 1). MN111 did not show the first order kinetics and hence it was not possible to estimate the rate constant. The rate constant did not show a strong correlation with specific surface area (Figure 4). Although NM113 is supposed to be a non-nano material, the photocatalytic activity was as high as NM110. When the photoactivity rates are normalised with specific surface area values, NM110 showed the highest photocatalytic activity per unit surface area (Figure 5). The results could be explained as surface defects acting as charge recombination sites to prevent photocatalysis. NM112 has near spherical shapes that are expected to have a large number of surface defects. On the other hand, MN110 and MN113 have geometrical shape particles that indicate high crystallinity and a low number of surface defects.

Applicant's summary and conclusion

Conclusions:

It was found that the photocatalytic activity was the highest for NM110 and NM113 and the lowest for NM112. NM111 did not show the first order kinetics and hence it was not possible to estimate the rate constant.

Executive summary:

The photocatalytic activity was investigated by the Deakin University, 2012. Photocatalytic activity of the ZnO samples was determined by monitoring the degradation of Rhodamine B (RhB) in aqueous solutions having the concentration of 0.0096 g/L. To quantify the photo-reactivity, the absorbance at 554 nm (the wavelength of maximum absorbance for RhB) was monitored. NM 111 did not show the first order kinetics due to the presence of a surface coating. The rate constant did not show a strong correlation with specific surface are. The photocatalytic activity of NM 0113 was as high as NM 110. When the photoactivity rates are normalised with specific surface area values, NM 110 showed the highest photocatalytic activity per unit surface area. NM 112 is the sample with the smallest primary particle size (and highest surface area), and its photocatalytic activity is less than that of its larger counterpart NM 110, and NM 113 with the largest particle size. The results could be explained as surface defects acting as charge recombination sites to prevent photocatalysis. NM 112 has near spherical shapes that are expected to have a large number of surface defects. On the other hand, MN110 and MN113 have geometrical shape particles that indicate high crystallinity and a low number of surface defects results in higher photocatalytic activities.