Activated carbon

Activated carbon, N-methyl pyrrolidone (NMP), and sodium tungstate (Na₂WO₄) were purchased from Sigma-Aldrich. Orthophosphoric (85%), NH₄Cl, KCl, distilled water, HPLC grade water, and methanol were all obtained from Loba Chemie. PVDF was purchased from Alfa Aesar. In this study, all analytical grade reagents were used without further purification.

Zinc sulfate heptahydrate (ZnSO₄·7H₂O) (99.0%), sodium hydroxide (NaOH) (98.0%), acetic acid (99.7%), copper nitrate trihydrate (Cu (NO₃)₃·3H₂O) (99.0%), zinc nitrate hexahydrate (Zn (NO₃)₂·6H₂O) (98.0%), trisodium citrate (99.0%), copper sulfate pentahydrate (CuSO₄·5H₂O) (98.9%), ammonium hydroxide (NH₄OH) (28.0%), pyrrole (99.0%), iron (III) chloride hexahydrate (FeCl₃·6H₂O) (98.0%), methyl orange (85.0%), ethanol (96.0%), sodium borohydride (NaBH₄) (99.0%), potassium hydroxide (85.0%), 4-Bromo butyric acid (98.0%), dimethylformamide (99.8%), zeolite, activated carbon, and polyvinylpyrrolidone (PVP) were all purchased from Sigma-Aldrich (Barcelona, Spain). A mixed-gas bottle of carbon dioxide and hydrogen with a molar ratio of 1:3, respectively, was provided by Carburos Metálicos, S.A. (Barcelona, Spain).

The indole (C₈H₇N, >99%), sodium dodecyl sulfate (CH₃(CH₂)₁₁OSO₃Na, >95%), benzoyl peroxide (C₁₄H₁₀O₄, >98%), Malachite Green (C₂₃H₂₅N₂·C₂HO₄·0.5C₂H₂O₄, >99%), sodium hydroxide (NaOH, >99.8%), hydrochloric acid (HCl, 37%), and activated carbon (AC, 98%) were purchased from Sigma Aldrich (St. Louis, MO, USA). Chloroform (CHCl₃, >99%) and ethanol (C₂H₅OH, >99%) were obtained from BDH(Poole, UK). Phosphoric acid (H₃PO₄, 85%) and perchloric acid (HClO₄, >70%) used in the experiment were borrowed from Scharlau (Barcelona, CAT, Spain). Malachite Green stock solution (1 g L⁻¹) was prepared by dissolving an accurately weighed amount of dye in deionized water, and the desired working concentrations were prepared using the stock solution. All these research grade chemicals were used as received without any further processing.

Whey protein isolate (WPI) was purchased from Davisco Foods International Inc. (Eden Prairie, MN, USA) and it was 97% protein of which approximately 69% was β-Lactoglobulin and 22% was α-lactalbumin. β-Lactoglobulin (>90%), mercury chloride (II), sodium chromate and activated carbon (particle size of 45 µm) were obtained from Sigma Aldrich (St. Louis, MO, USA). All reagents were analytical grade and used as received. Nitrocellulose membranes (Sartorius Stedim Biotech, Goettingen, Germany) with a pore size of 0.22 µm were used to produce the hybrid membrane.

We synthesised 5.00 g of carbon-supported 5 wt.% Ru catalyst. Ru (II) nitrosyl nitrate solution (16.67 g) (Sigma-Aldrich, 1.5% Ru) was slowly added to 4.75 g of activated carbon (Norit) dispersed in deionised water (55 cm³/support-g), the mixture was vigorously stirred at 333 K for 4 hours under reflux. The mixture was left to cool to room temperature overnight and its pH was adjusted to between 9 and 10 units using sodium hydrogen carbonate (0.90–1.10 g) (99%). Subsequently, 50 g of diethylene glycol (Sigma-Aldrich, 99%) was added to the solution under vigorous stirring for a period of 10–15 minutes and heated under reflux to 433 K for 4 h. The solution was then cooled again to room temperature and the carbon-supported Ru catalyst was separated from the aqueous solution by filtration. The resultant solid was extensively washed with 2.5 L of deionised water until the filtrate solution achieved neutral pH. The solid was finally dried at 363 K for 16 h and reduced in a 10% H₂-Ar mixture at 723 K for 4 h using a heating rate of 0.083 K.s⁻¹ and a weight time space velocity of 1.67 mL(g.s)⁻¹.

Methane with a purity of 99.99% was supplied by Beijing Haipu Gas Co., Ltd. Double distilled water was prepared in our laboratory. ZIF-8 was synthesized in our laboratory. Activated carbon with particle size of 100 mesh was purchased from Sigma-Aldrich.