Nanocomposites of silica gel (SG) and multiwalled carbon nanotubes (MWCNTs) of relatively low concentrations (0.25, 0.50, and 0.75 wt%) were characterized before and after annealing. Adsorption is a surface phenomenon, and based on this, the morphology of the composites was investigated by scanning electron microscopy (SEM). The produced images show that the MWCNTs were embedded into the silica gel base material. Fourier transform infrared (FTIR) transmittance spectroscopy showed that MWCNTs were not functionalized within the matrix of silica gel and MWCNT composites. However, after annealing the composites at 400 °C for 4 h in air, evidence of activation was observed in the FTIR spectrum. The effects of the embedding of MWCNTs on porosity, specific surface area, and pore size distribution were studied using Raman spectroscopy. The Raman spectra of the prepared composites were mainly dominated by characteristic sharp scattering peaks of the silica gel at 480, 780, and 990 cm−1 and a broad band centered at 2100 cm−1. The scattering peaks of MWCNTs were not well pronounced, as the homogeneity of the composite is always questionable. Nanosizer analysis showed that at 0.25 wt%, the distribution of MWCNTs within the silica gel was optimal. Vickers hardness measurements showed that the hardness increased with the increasing weight percent of MWCNTs within the composite matrix, while annealing enhanced the mechanical properties of the composites. Further studies are required to investigate the pore structure of silica gel within the matrix of MWCNTs to be deployed for efficient cooling and water purification applications.
This study aimed to maximize the dependent variables [total phenolic content (TPC), antioxidant (DPPH and ABTS), and anticancer activities (against HepG2 and MCF-7 cells)] from P. schimperi aerial parts by optimizing three independent variables (extraction temperature, extraction time, and liquid-to-solid ratio) of ultrasound-assisted extraction (UAE) using the Box–Behnken design (BBD) of response surface methodology (RSM). For each of the dependent variables, the projected quadratic models were found to be very significant (p < 0.001). The extraction temperature and extraction time had a significant impact on the TPC extraction, antioxidant, and anticancer properties (p < 0.05). The best conditions were identified as an extraction temperature of 54.4 °C, extraction time of 48 min, and liquid-to-solid ratios of 20.72 mL/g for the simultaneous extraction of the TPC, antioxidant, and anticancer properties of P. schimperi. The experimental results and the expected values agreed under these circumstances. Regarding the high extraction effectiveness and antioxidant and anticancer effects at comparably low extraction temperature and duration, UAE demonstrated considerable benefits over conventional solvent extraction (CSE). This improved UAE approach has shown a potential use for effective polyphenolic antioxidant extraction from P. schimperi aerial parts in the nutraceutical sectors.
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