Evolution 220

For determination of the photoactivity under visible-light irradiation, the aqueous phase containing 125 mg of the photocatalyst (5 g/dm³), 24 cm³ of deionized water and 1 cm³ of phenol as a model compound (Co = 500 mg/dm³) was used. The suspension was stirred and aerated (V = 5 dm³/h) for 30 min in the dark to obtain equilibrium and then the content of the reactor was photoirradiated with a 1000 W Xe lamp (Oriel, light flux 6.5–7.5 mW/cm²) which emitted both UV and visible-light irradiation. The photoreactor (V = 25 cm³, i.d. 37 mm, length 30 mm) was equipped with a quartz window and exposure layer thickness was 3 cm. The optical path included a water filter and a glass filter (GG 420) which cut-off wavelengths shorter than 420 nm. The temperature of the aqueous phase during irradiation was kept at 10 °C using a water bath. During the irradiation, the suspension (1 cm³) was collected and filtered through syringe filters (diameter 0.2 µm) to remove the photocatalyst particles. The phenol concentration was estimated by means of the colorimetric method (λ = 480 nm) after derivatization with diazo-p-nitroaniline using a UV–vis spectrophotometer (Thermo Evolution 220). The photocatalytic degradation runs were preceded by a blind test in the absence of a photocatalyst or illumination. No degradation of phenol was observed in the absence of either the photocatalyst or illumination.

The morphology of the GO-AgNPs was characterized by transmission electron microscopy (TEM, JEM-2100F, JEOL, Japan). The structure of the GO-AgNPs and GO was measured by Uv-vis spectrophotometer (Evolution 220, Thermofisher, United States), FTIR spectrophotometer (Nicolet iS10, Thermofisher, United States) and X-ray diffraction spectra (XRD, Bruker D8 Advance, Germany). The thickness and size of GO were characterized by atomic force microscopy (AFM, Multimode Nanoscope VIII Instrument Bruker, United States). The Zeta potential and average particle size of the GO-AgNPs was measured by Dynamic Light Scattering (DLS, ZS-90, Malvern, United Kingdom).

The authors described the detailed methodology of FRAP and CUPRAC determinations in a previous publication [17 (link)]. The FRAP and CUPRAC methods were analogous and consisted of the reduction of iron (Fe³⁺ → Fe²⁺) and copper ions (Cu²⁺ → Cu¹⁺), respectively. The quantitative antioxidant capacity of the samples was calculated on the basis of comparing the change in absorption (ΔA) of the analyzed sample with the value of ΔA determined for standard solutions containing no extract. The determined ΔA value of the sample is directly proportional to the concentration of antioxidant. Results are expressed as EC50 (mg/mL)—the effective concentration corresponding to half the absorbance for the reducing power for Fe³⁺ → Fe²⁺ or Cu²⁺ → Cu¹⁺. The EC50 was determined from linear regression analysis.
A UV–Vis spectrophotometer (Evolution 220, Thermo Fisher Scientific, Waltham, MA, USA) was utilized for measurements in the FRAP and CUPRAC assays. In the FRAP test, a mixture of reagents without cone extract was used as a blank, while distilled water was used in the CUPRAC method.