Sonorex rk 52 h

The synthesis of CeO₂ nanoparticles based on the principle of Chen and Chang [53 (link)–54 (link)] and is described by Herrmann et al. [55 ]. SiO₂ nanoparticle samples were synthesized as described previously [56 (link)].
The SiO₂ nanoparticles were stored in water and the CeO₂ nanoparticles were stored in ethanol as a solvent. Before starting the experiments, the ethanol was replaced by Millipore water by four centrifugation/redispersion (1.0 mL water) steps. To prepare nanoparticle working suspensions, the stock suspensions were vortexed and placed in an ultrasound bath (Bandelin Sonorex RK 52 H, Bandelin electronic GmbH & Co. KG, Germany; HF-power: 60 W (effective)) for 10 min.

The parameters for the optimization of extraction were selected based on the internal industrial extraction guidelines for the preparation of SFBE: water solvent (ratio of water: branches of 1:5) was heated to 70–90 °C for 30–60 min. The obtained samples were extracted using water solvent at different temperatures (60, 80, 100 °C) and extraction times (30, 60, 90 min) in an ultrasonic bath (Bandelin Sonorex RK 52 H, Bandelin electronic GmbH & Co. KG, Berlin, Germany). The volume of solvent was 5, 7.5 or 10 mL per 1 g of sample. Twenty extracts were prepared with different combinations of these three variables obtained with Design-Expert^® 7.0 software (Stat-Ease, Inc., Minneapolis, U.S.A.) (central composite design (CCD) with the responses of the dependent variables). Liquid extracts were separated by filtration and kept at 4 °C until further analysis of the antioxidant and phenol content over a maximum period of two days. An optimization experiment was carried out using response surface methodology for the extraction of total phenols and the ABTS and DPPH test results.