Hydrogen peroxide h2o2 30 w w

Caffeic acid (3,4-Dihydroxycinnamic acid) was acquired from Sigma-Aldrich, St. Louis, MO, and used as received without further purification. The molecular structure of caffeic acid in non-hydrolyzed form is illustrated in Table 1. Iron (II) sulfate heptahydrate (FeSO₄•7H₂O) was acquired from Panreac, Barcelona, Spain, and hydrogen peroxide (H₂O₂ 30% w/w) and titanium (IV) oxysulfate solution 1.9–2.1%, for determination of hydrogen peroxide, were acquired from Sigma-Aldrich, St. Louis, MO, USA. Sodium sulfite anhydrous (Na₂SO₃) was acquired from Merk, Darmstadt, Germany. Trifluoroacetic acid (HPLC grade, ≥99.0%) was acquired from Riedel-de Haën, Seelze, Germany, and acetonitrile (HPLC grade, ≥99.9%) was acquired from Chem-Lab, Zedelgem, Belgium. For pH adjustment, sodium hydroxide (NaOH) from Labkem, Barcelona, Spain, it was used, along with sulfuric acid (H₂SO₄, 95%) from Scharlau, Barcelona, Spain. Deionized water was used to prepare the respective solutions.

Ferric chloride hexahydrate (FeCl₃·6H₂O) was acquired from Merck (Darmstadt, Germany). Iron (II) sulfate heptahydrate (FeSO₄·7H₂O) was purchased from Panreac (Barcelona, Spain); hydrogen peroxide (H₂O₂ 30% w/w) and titanium (IV) oxysulfate solution 1.9–2.1% were bought from Sigma-Aldrich (St. Louis, MI, USA). Sodium hydroxide (NaOH) was acquired from Labkem (Barcelona, Spain) and sulfuric acid (H₂SO₄, 95%) from Scharlau (Barcelona, Spain).
Elderberry wastewater is generated from washing and fruit processing, and it was obtained from a company in the North of Portugal.

Singlet Oxygen Sensor Green was purchased from Thermo Fisher; Chlorin-e6 (C₃₄H₃₆N₄O₆) was purchased from Bio-connect life sciences (Huissen, the Netherlands); Sodium azide, sodium acetate, ammonium molybdate ((NH₄)₆Mo₇O₂₄•4H₂O), potassium iodide (KI), sodium iodide (NaI) were obtained from Merck (Darmstadt, Germany); MEthanol, hydrogen peroxide (H₂O₂, 30% (W/W)), acetic acid, 1,3-diphenylisobenzofuran (DPBF) and 9,10-antherachenediyl-bis(methylene) dimalonic acid (ABDA) were bought from Sigma Aldrich (Zwijndrecht, the Netherlands). Ethanol was bought from Brenntag (Zwijndrecht, The Netherlands). Dimethyl Sulfoxide (DMSO) was bought from Biosolve B. V. (Valkenswaard, The Netherlands). All chemicals were used without further treatment. Water used in these experiments was prepared with the in-house Milli-Q system from Merck Millipore.