Hydrazine monohydrate

Chitosan (deacetylation degree, 90%), nickel (II) chloride hexahydrate (NiCl₂·6H₂O; 99.9%), copper (II) chloride dihydrate (CuCl₂·2H₂O; 99.9%), ethylene glycol (EG; 99.8%), hydrazine monohydrate (N₂H₄·H₂O; 80%), SDS, and acetic acid (HAc; 98%) were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Copper plate, platinum plate, and other chemicals were obtained from commercial sources in China. All chemicals were of analytical grade and were used as received without further purification.

Rhodamine 6G (95%), 1,3-dicyclohexylcarbodiimide (DCC, 99%), N,N-dimethylpyridin-4-amine (DMAP, 99%), and 4-carboxybenzaldehyde (98%) were obtained from Aladdin Chemistry Co. Ltd. (Shanghai, China). Polyethylene glycol (PEG, M_W 4,000 Da), hydrazine monohydrate (50%), silver nitrate, chloride salts of K⁺, Na⁺, Mg²⁺, Ca²⁺, Cu²⁺, Hg²⁺, Co²⁺, Cd²⁺, Zn²⁺, Ni²⁺, Mn²⁺, Al³⁺, Cr³⁺, and Fe³⁺ were purchased from Sinopharm Chemical Reagent Co. Ltd. MTT (thiazolyl blue tetrazolium bromide) was obtained from Thermo Fisher Scientific (China). Ultrapure water (18.2 MΩ cm) was obtained from the Milli-Q system and applied throughout the experiment. Other solvents and chemicals were of analytical reagent grade and used without further treatment.

Hydrochloric acid (HCl), Urea (99 wt.%), Hydrazine monohydrate (N₂H₄·H₂O, 80 wt.%), Cobalt(II) nitrate hexahydrate (Co(NO₃)₂•6H₂O, 98.5 wt.%) and Nickel(II) nitrate hexahydrate (Ni(NO₃)₂•6H₂O, 98.0 wt.%) were purchased from Sinopharm Group Chemical Reagent Co., Ltd. Sodium hypophosphite (NaH₂PO₂, 99.0 wt.%) and Ammonium fluoride (NH₄F, 98 wt.%) were purchased from Aladdin. Sodium hydroxide (KOH, 90 wt.%) was purchased from Shanghai Titan Scientific Co., Ltd. Acetone, Ethanol, Isopropanol were purchased from Shanghai Lingfeng. Nafion D-520 dispersion (5 wt.%) was purchased from Dupont China Holding Co., Ltd. Commercial 20 wt.% Pt/C and the carbon black (XC-72) were purchased from Shanghai HEPHAS Energy Equipment Co., Ltd. Nickel foam (thickness: 1.0 mm; aperture: 0.1 mm; porosity: 97.2%) was purchased from Cyber Electric Co., Ltd. Anion exchange membrane (AEM, FAB-PK-130) was purchased from Fumasep. Composite matrix was purchased from Changsha Sipulin. All materials were used as received without further purification.

An aqueous solution of single-layered GO sheets was prepared from graphite powder following a modified Hummer’s method [47 (link)–49 (link)]. A drop of 10 µL of as-prepared GO solution (50 ng/µL) was placed onto a mica substrate. Chemical reduction of GO was performed by exposure to a saturated vapour of hydrazine monohydrate (85 wt % in water, Sinopharm) in a sealed Petri dish at 80 °C for 1 h. Thermal reduction of GO was carried out in a vacuum oven at 180 °C for 15 min. A hybrid GO/RGO sample was made by depositing another drop of GO solution onto the substrate on which reduced GO had been deposited.

Analytical grade reagents were used directly without purification. Zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) was bought from Tianjin guangcheng chemical reagent Co. LTD. Thioacetamide (TAA), Indium chloride (InCl₃), and Selenium power (Se, ≥99.99% metal basis) were bought from Shanghai Macklin biochemical technology Co. LTD. Ascorbic acid (AA) and hydrazine monohydrate (N₂H₄·H₂O, 85%) were bought from Sinopharm Chemical Reagent Co., LTD. Sodium molybdate dihydrate (Na₂MoO₄·2H₂O) was purchased from Tianjin Fengchuan Chemical Reagent Technology Co., LTD. Deionized water was obtained from local sources.