Sodium hydroxide (naoh)

the ferric nitrate nonahydrate (Fe(NO₃)₃·9H₂O, 98.00%), ferric chloride (FeCl₃, 98.00%), urea (NH₂CONH₂, ≥ 99.00%), sodium hydroxide (NaOH) and polyvinylpyrrolidone (PVP) were supplied by Shanghai Titan Scientific Co., and utilized directly as received without further purification. Deionized water (H₂O) was used throughout the experiments.

The bleach bamboo pulp (α-cellulose content 88%, 1.4 × 10⁵ (Mη)) was provided by Ganzhou Hwagain Paper Co., Ltd. (Ganzhou, China) in China. Lithium chloride (LiCl, 99%, AR), N,N-dimethylacetamide (HPLC, 99.8%), methane sulfonic acid (CH₃SOOH, 90%), solid blue BB salt (AR), dimethylsulfoxide (C₂H₆OS, DMSO, 99.0%, AR), sodium hydroxide (NaOH, 98.0%), urea (AR, 99.0%), ethylene glycol ((CH₂OH)₂, 99.7%, AR), glycerol (C₃H₈O₃, 99.0%, AR), and lithium hydroxide monohydrate (LiOH·H₂O, 99.0%) were offered by Shanghai Titan Scientific Co., Ltd. (Shanghai, China) 30% hydrogen peroxide (H₂O₂, AR), ethanol (C₂H₅OH, 99.7%, AR), trisodium citrate (C₆H₅Na₃O₇, AR), citric acid monohydrate (C₆H₈O₇, 99.5%, AR), disodium hydrogen phosphate (Na₂HPO₄, 99%), and hydrochloric acid (HCl, 30–38.0%, AR) were provided by Xilong Science Co., Ltd. (Shantou, China) Ethylenediamine copper (AR) was obtained by the China National Pulp and Paper Research Institute. All chemical reagents were used without further purification.

The pristine jute fibers were provided by Redbud Textile Tech. Inc., Suzhou, China. The fibers were sufficiently dried in a vacuum drying oven at 70 °C for over 24 h. Polyvinyl alcohol with a degree of alcoholysis of 97.0–98.8 mol% was procured from Shanghai Yuanye Biological Technology Co. Ltd. (Shanghai, China) 2,2,6,6-tetrmethylpiperidine-1-oxyl radical (TEMPO, 98%), sodium bromide (NaBr, 99.6%) and sodium hypochlorite (NaClO, 6–14%) were supplied by Shanghai Macklin Biochemical Co. Ltd. (Shanghai, China) and were used as received. The sodium hydroxide (NaOH, ≥96.0%) and ethanol were purchased from Shanghai Titan Scientific Co. Ltd. and utilized without any further purification. All reagents were of analytical grade, and ultrapure water generated using the Milli-Q plus water purification system (Millipore Corporation, Billerica, MA, USA) was used.

Sinopharm Group (Shanghai, China) provided the following products: Ni(NO₃)₂·6H₂O, urea, and hydroxychloric acid (HCl). Aladdin (Shanghai, China) provided the following products: RuO₂ (99% metal basis), Co(NO₃)₂·6H₂O, Ammonium fluoride (NH₄F), and Sodium hypophosphite (NaH₂PO₂). Shanghai Titan Scientific Co., Ltd. (Shanghai, China) provided the sodium hydroxide (KOH). Dupont China Holding Co., Ltd. (Shanghai, China) was the supplier of the Nafion D-520. Shanghai HEPHAS Energy Equipment Co., Ltd. (Shanghai, China) provided the XC-72 and commercial 20 wt.% Pt/C. Cyber Electric Co., Ltd. (Hong Kong, China) supplied the Nickel foam (1.0 mm in thickness, 0.1 mm in aperture, and 97.2% porosity). Nothing was purified further.

The bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272, C₁₆H₃₅O₂P, purity: ≥92 wt%) was purchased from Zhengzhou Hecheng New Materials Tech Co., Ltd. (Zhengzhou, China). Butylamine (C₄H₉NH₂, purity: ≥99 wt%), Sodium hydroxide (NaOH, purity: ≥92 wt%), n-Hexane (C₆H₁₄, purity: ≥99 wt%), Anhydrous ethanol (≥99 wt%), NiSO₄·6H₂O (purity: ≥98.5 wt%,) CoSO₄·7H₂O (purity: ≥98 wt%), and H₂SO₄(purity: ≥98 wt%) were purchased from Shanghai Titan Scientific Co., Ltd. (Shanghai, China). Standard solutions of cobalt and nickel (1000 μg/mL) were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China). The synthesized [C₄H₉NH₃][Cyanex 272] and n-Hexane were used as extractant and diluent (Figure 1), respectively. All the chemicals and reagents were of reagent grade and used without further purification unless otherwise stated.
The simulated sulfuric acid solution containing 14 g/L of Co²⁺ and 14g/L of Ni²⁺ [4 (link),23 (link)] was prepared by dissolving the NiSO₄·6H₂O and CoSO₄·7H₂O in deionized water. With the aim of obtaining a purity solution, the simulated solutions should pass through a filtration membrane with an aperture of 0.45 microns. The pH_ini of the simulated solutions was adjusted by adding H₂SO₄ or NaOH solutions.