Copper 2 nitrate hemi pentahydrate

To surface oxidation (NiO) of the Ni foam (0.7 cm × 0.7 cm) substrate, etching with HCl (5 M) for 30 min was carried out, and the residual acid was removed from the substrate by washing with deionized (DI) water [30 (link),31 (link)]. To prepare the electrodeposition solution, copper (II) nitrate hemi(pentahydrate) (10 mM, Cu(NO₃)₂·2.5H₂O, ≥98%, Sigma-Aldrich Co., Ltd., St. Louis, MO, USA) and cobalt (II) nitrate hexahydrate (50 mM, Co(NO₃)₂·6H₂O, ≥98%, Sigma-Aldrich Co., Ltd., St. Louis, MO, USA) were prepared in 500 mL of DI water and stirred for 30 min. The Ni foam substrate with surface oxide removed, a Pt mesh (3 cm × 4 cm), and a saturated calomel electrode (SCE) were used as the working (cathode), counter (anode), and reference electrodes, respectively (the distance of each electrode is 1 cm). Then, a constant potential of −1 V vs. SCE was applied for 5 min at 30 °C. After this process, the color of the nickel foam turned dark green. The electrode made by electrodeposition was washed with prepared DI water, and the dried at room temperature. Subsequently, heat treatment (annealing) was performed on the electrodeposited catalysts by heating at a rate of 1 °C/min to 150, 200, 250, and 300 °C in air for 3 h. The catalysts are labeled as CCO-x °C.

Copper(II) acetate monohydrate (puriss. p. a., ≥99.0 %), zinc(II) acetate dihydrate (puriss. p. a., ≥99.0 %), manganese(II) acetate tetrahydrate (99+%) copper(II) nitrate hemipentahydrate, zinc(II) nitrate hexahydrate, manganese(II) nitrate tetrahydrate, cerium nitrate, magnesium(II) nitrate hexahydrate, sodium carbonate, and cerium acetylacetonate hydrate were all purchased from Sigma–Aldrich. Magnesium(II) acetate tetrahydrate (analytical) was obtained from Amresco. Ethanol (absolute 99.8 %, Certified AR) was purchased from Fischer Scientific and CO₂ (CP grade) was provided by BOC. All purchased materials were used as received. Deionised water was provided in‐house.

All chemicals were purchased from Sigma-Aldrich Co., Ltd and utilized without further purification: poly(vinylpyrrolidone) (PVP) (wt 360000), zinc acetatedihydrate (ZnAc) (Zn(CH₃COO)₂ ·2H₂O, 99.99%), zinc nitratehexahydrate (Zn(NO₃)₂.6H₂O, 98%), hexamethylenetetramine (HMTA) (C₂H₁₂N₄, 99%), Copper (II) nitrate hemi(pentahydrate) (Cu(NO₃)₂.2.5H₂O, 98%), distilled water (DI, 18.4 MΩ/cm), N,N-dimethylformamide (DMF) (HCON(CH₃)₂, ≥99%), and ethyl alcohol (C₂H₅OH).

Iron(II) chloride tetrahydrate (FeCl₂·4H₂O, 99%), sodium hydroxide (NaOH, 99.99%), diethylene glycol (DEG, 99%), N-methyldiethanolamine (NMDEA, 99%), nitric acid (HNO₃, 70%), copper(II) nitrate hemi(pentahydrate) (Cu(NO₃)₂·2.5H₂O, ≥99.99%), polyvinylpyrrolidone (PVP, Mw 55 kDa), poly(ethylene glycol) methyl ether thiol (PEG-SH, Mw 2 kDa) hydrazine hydrate (55%), ammonium sulfide solution ((NH4)₂S, 20%), glutaraldehyde solution (25% in H₂O), and sodium cacodylatetrihydrate (≥98%) were purchased from Sigma-Aldrich (Saint-Quentin-Fallavier, France). Iron(III) chloride hexahydrate (FeCl₃·6H₂O, 99%) and ethanol were obtained from VWR (Rosny-sous-Bois, France).

Landfill leachate samples were collected in polyethylene bottles from a landfill site located in Friuli Venezia Giulia, Italy, and were preserved at 4 °C. The preparation of the copper supported over zirconia (5 wt% Cu/ZrO₂) and the catalytic activity experiments were carried out as previously described by Hussain et al. (Hussain et al. 2020 (link)). Briefly, 5% Cu/ZrO₂ was prepared by incipient wetness impregnation of ZrO₂ (MEL Chemicals) with an aqueous solution of copper (II) nitrate hemi pentahydrate (Sigma-Aldrich). After impregnation the material was dried overnight at 100 °C and calcined for 3 h at 500 °C.