Hydrazine hydrate n2h4

Sodium molybdate dehydrate (Na₂MoO₄·2H₂O) (Aldrich, >99%), polyacrylonitrile (PAN, 99%, Mw: 150,000 g/mol) (Sigma Aldrich, USA), N,N-dimethylformamide (DMF) (Sigma Aldrich, USA), selenium (Se) powder (Aldrich, 99.9%), potassium ferricyanide(III) [K₃Fe(CN)₆] (Sigma-Aldrich, 99 %), hydrazine hydrate (N₂H₄) (Sigma Aldrich, 50–60%), pyrrole (PPy) (Fluka, >99%), cobalt (II) nitrate hexahydrate [Co(NO₃)₂·6H₂O] (Merck, 98%), HCl (Sigma Aldrich, 37%), sodium phosphate monobasic dihydrate (NaH₂PO₄∙2H₂O) (Sigma Aldrich), sodium phosphate dibasic dihydrate (Na₂HPO₄∙2H₂O) (Sigma Aldrich), and iron(III) chloride (FeCl₃) (CentralChem, >99.9%) were commercially supplied and used as received.

Graphite powder (<20 μm) was purchased from Sigma-Aldrich and used as received. Sulfuric acid (H₂SO₄, 98 wt.%, Merck), nitric acid (HNO₃, 69 wt.%, Honeywell), phosphoric acid (H₃PO₄, 85 wt.%, J.T. Baker), potassium permanganate (KMnO₄, Acros Organics), hydrogen peroxide (H₂O₂, 30 wt.%, Sigma-Aldrich), and hydrazine hydrate (N₂H₄, 50–60 wt.%, Sigma-Aldrich) were used as available from the supplier without any further purification.

Copper(II) sulfate (CuSO₄, reagent grade, Wako Chemicals, Tokyo, Japan) was used to prepare simulated Cu²⁺-containing wastewater. For the synthesis of the PEI@CNF aerogel, polyethyleneimine (PEI, Mw 60,000, Sigma-Aldrich, Merck, St. Louis, MO, USA) was used, along with cellulose nanofibrils (CNFs) from hard wood pulp, which were purchased from the University of Maine Process Development Center. Glutaraldehyde (25% in water, Sigma-Aldrich, Merck, St. Louis, MO, USA) was used for cross-linking the PEI@CNF aerogels. Hydrochloric acid (HCl, 36%, Junsei chemical Co., Ltd., Tokyo, Japan) was used to elute Cu²⁺ from the PEI@CNF aerogel. Sodium hydroxide (NaOH, 98%, Sigma-Aldrich, Merck, St. Louis, MO, USA) was used to adjust the solution pH. Hydrazine hydrate (N₂H₄, 50–60% in H₂O, Sigma-Aldrich, Merck, St. Louis, MO, USA) was used as a reductant. To prepare nanosized Cu⁰ particles, SDS (≥95%, Sigma-Aldrich, Merck, St. Louis, MO, USA) was used as a stabilizer.