The "End Life" of the Grape Pomace Waste Become the New Beginning: The Development of a Virtuous Cycle for the Green Synthesis of Gold Nanoparticles and Removal of Emerging Contaminants from Water

Abstract

During the last decades, the demand for processes developed according to the Circular Economy Principles has increased, searching for an alternative life for wastes. For this purpose, a one-pot green approach is exploited during this work to synthesize gold nanoparticles (AuNPs) by using grape pomace waste from Vitis vinifera. A raw aqueous extract of grape seeds, skin, and stems is used for AuNPs synthesis. UV-Vis, XPS, SEM, and ATR-FTIR spectroscopies demonstrate the main role of the extract's polyphenolic components in stabilizing nanoparticles. XRD, DLS, and Zeta Potential analyses were used to characterize AuNPs. Moreover, the ionic strength, pH, and temperature role was investigated through the Surface Plasmon Resonance (SPR) band observation to assess AuNPs' stability and photostability. For foreseeing the as-synthesized AuNPs' potential use in cosmetic and biomedical fields as multifunctional platforms, their antioxidant, and skin-lightening properties were tested, together with their sunscreen ability. A preliminary in-vitro evaluation is reported about the AuNPs' cytoprotective effects against H₂O₂ oxidative stress-induced in normal human dermal fibroblasts. Briefly, the possibility of reusing the grape pomace waste after the AuNPs synthesis as an adsorbent for the efficient removal of emergent contaminants is preliminarily discussed in the paper, further valorizing the use of waste according to a bio circular approach.

Keywords: Biomedicine; ROS; antioxidant; gold nanoparticles; grape pomace; human dermal fibroblasts.

Figure 1

Camera picture of Grape Pomace Waste (seeds, skin, and stems).

Scheme 1

The scheme depicts the aim of the present work. First, GP is placed in boiled water to obtain the raw GWE needed to induce the AuNPs formation from HAuCl₄. The exhausted GP, after the extraction, is reused to remove Ciprofloxacin (see the UV-Vis spectra collected during the adsorption process) and Tetracycline from water.

Figure 2

UV-Visible spectra of an AuNPs solution (dilution 1:5 from the stock solution), observing their typical SPR band (A). In the insets, the wavelength and FWHM time evolution registered in correspondence of the SPR are reported; TEM images of AuNPs at different magnification ratios (B); XRD diffraction patterns of AuNPs. Vertical bars: Bragg hkl reflections positions of the cubic Au crystal structure (ICSD code #044362) (C).

Figure 3

ATR-FTIR spectra of AuNPs and raw GWE referred to 500–2000 cm⁻¹ (A) and 2500–4000 cm⁻¹ (B) wavenumber regions. The signals at 1200 and 1252 cm⁻¹ (indicated with * and #) are due to vibrations of C–O and C-OH groups, respectively, attributed to hydroxyflavonoids.

Figure 4

High-resolution XPS spectra of the AuNPs: Au 4f (A), C 1s (B), O 1s (C), and N 1s (D) spectra.

Figure 5

Effect of irradiation time, by using a sun simulator lamp, on wavelength position (A) and FWHM (B) of AuNPs SPR. The inset (A) shows the intensity of the SPR band in terms of absorbance values read at the maximum of SPR at several irradiation times. ATR-FTIR spectra of AuNPs before and at the end of irradiation. Bands indicated with * at 840, 1365, and 1565 cm⁻¹ suggest the formation of surface carbonates, and the finding agrees with the well-known mechanisms of phenol photodegradation (C).

Figure 6

Percent of the antioxidant activities of raw GWE (2 mg/L), calculated at different incubation times in the presence of ABTS (A) and AuNPs at different concentrations (B).

Figure 7

Percent of tyrosinase inhibition of raw GWE (2 mg/L) (A) and AuNPs (B) at different amounts.

Figure 8

Effects of AuNPs in H₂O₂-exposed NHDFs. (A) Representative phase-contrast photomicrographs of SA-β-Gal positive cells. (B) Fibroblast morphology before and after treatments. Images are representative of cell cultures photographed using a phase-contrast microscope (100× magnification). (C) Histograms reporting viable cells (trypan blue negative) (D) Intracellular ROS scavenging activity of AuNPs in H₂O₂-exposed NHDFs. Histograms represent the percentage of cells positive for the DCF-DA probe. (E) Effects of AuNPs on H2AX and STAT5 phosphorylation were evaluated by western blot analysis. Data are presented as the mean ± standard deviation from triplicate experiments. * p < 0.05, compared with H₂O₂-treated cells.