Ammonium hydroxide

MWCNTs (JENO20) were procured from JEIO (Yusong, Korea). For the purification process, which involves the removal of amorphous carbon present on the surface of the CNTs and the formation of an oxygen functional group, sulfuric acid (98%) and nitric acid (60%) were procured from DAEJUNG Chemicals (Siheung-si, Korea). For the formation of transition metal oxides on the surface of CNTs, cobalt (II) nitrate hexahydrate, iron (III) nitrate nonahydrate, manganese (II) nitrate hexahydrate, and nickel (II) nitrate hexahydrate were procured from Sigma-Aldrich (Burlington, MA, USA) and used as transition metal hydrates. Deionized water (DIW) was used to dissolve the transition-metal hydrates. Ethyl alcohol (99.9%), procured from DUKSAN (Ansan, Korea), was used as a solvent to disperse the CNTs, and ammonium hydroxide was procured from JUNSEI (Tokyo, Japan).

The details of the synthesis method were described in our previous report15 (link). Briefly, acid-treated CNTs (0.1 g) were sonicated in diethylene glycol (DEG, >99%, Fluka, 80 mL), after which FeCl₂ ∙ 4H₂O (0.062 g, Aldrich), FeCl₃ ∙ 6H₂O (0.087 g, Junsei), and ammonium hydroxide (15 ml, 30 wt%, Junsei) were added to the solution. The solution was then loaded into 100 ml Teflon vessels that were sealed and placed in a microwave system (MARS-5, CEM Corporation). The reaction mixture was heated to 200 °C and maintained at that temperature for 10 min.

All chemicals used were of analytical grade. Potassium chromate, 0.1 N Sodium hydroxide, silver nitrate, methyl alcohol, ethyl alcohol, and sodium chloride were obtained from Duksan Pure Chemicals (Ansan, Gyeonggi-do, Korea). Sodium hydroxide, sodium hydrogen carbonate, and ammonium hydroxide were purchased from Junsei Chemicals (Tokyo, Japan). Formalin solution, standard methanol, ethanol, pentanol, propanol, and butanol were purchased from Sigma-Aldrich (St. Louis, MO, USA). Plate count agar, nutrient agar, potato dextrose agar (PDA), and potato dextrose broth were purchased from Difco (Becton, Dickinson and Company, Sparks, MD, USA). Mannitol egg yolk polymyxin agar (MYP), egg yolk emulsion, and polymyxin B supplement were purchased from Oxoid LTD (Basingstoke, Hampshire, UK). 3M Yeast and Mold Petrifilm was purchased from 3M Health Care (St. Paul, MN, USA). API 50CHB and API 20E were obtained from bioMerieux (Marcy I’Etoile, France).

All chemicals and solvents were of the analytical and chromatographic grade. Standard biogenic amines (agmatine sulfate, tryptamine hydrochloride, 2-phenylethylamine, putrescine dihydrochloride, cadaverine dihydrochloride, histamine dihydrochloride, tyramine hydrochloride, spermidine trihydrochloride, and spermine tetrahydrochloride), dansyl chloride, and acetone were purchased from Sigma-Aldrich (St. Louis, MO, USA). Sodium hydroxide, sodium hydrogen carbonate, ammonium hydroxide, and perchloric acid were purchased from Junsei Chemicals (Tokyo, Japan). High-performance liquid chromatography (HPLC) grade acetonitrile and ammonium acetate were obtained from Merck (Darmstadt, Germany). Nutrient agar was purchased from Difco (Sparks, MD, USA). API kits were purchased from BioMerieux (Marcy I’ Etoile, France).