Sulphuric acid

Aniline (C₆H₂NH₂, MW = 93.13, 99.5%), N,N-dimethylformamide (DMF) (linear formula HCON(CH₃)₂, >99.8%, molecular weight (MW): 73.09 g mol⁻¹, d = ∼0.944 g ml⁻¹ (lit.)), polystyrene (linear formula [CH₂CH(C₆H₅)] n, average MW: ∼280.000 g mol⁻¹, T_g = 100 °C, d = 1.047 g ml⁻¹ at 25 °C), and graphite (empirical formula (Hill Notation) C, MW: 12.01 g mol⁻¹, powder, <20 μm, synthetic, mp = 3652–3697 °C (lit.)) are purchased from Sigma Aldrich Co., Ltd, USA. Hydrochloric acid 37% (HCL, MW: 36.46, d = 1.18 g cm⁻³ (20 °C)), ammonium peroxodisulphate (APS) ((NH₄) ₂S₂O₈, MW: 228.2 g mol⁻¹, d = 1.98 g cm⁻³ (20 °C)), sodium nitrate (NaNO₃, MW: 84.99 g mol⁻¹, d = 2.26 g cm⁻³ (20 °C)), and sulphuric acid 95% (H₂SO₄, MW: 98.08 g mol⁻¹, d = 1.84 g cm⁻³ (20 °C)) are purchased VWR CHEMICALS Analwr Normapur. Potassium permanganate (KMnO₄, >99.0%, d = 158.04 g mol⁻¹) and hydrogen peroxide 30% (H₂O₂, 29.0% specific gravity) are purchased from BDH Laboratory Supplies Pools, BH15 TD, England. All the chemicals are used without further treatment.

Molybdenum hexacarbonyl (Mo(CO)₆, ≥99.9% trace metals basis), tungsten hexacarbonyl (W(CO)₆, 99.99% trace metals basis, excluding Mo), selenium (99.99% trace metals basis, 100 mesh), trioctylphosphine (TOP; 90%, technical grade), oleic acid (90%, technical grade), nitric acid (90%, ACS Reagent), and graphitic carbon foil (CF, 99.8%) were purchased from Sigma-Aldrich. Acetone (≥99%, technical grade), ethanol (96%, AnalaR NORMAPUR), and sulphuric acid (95%, AnalaR NORMAPUR) were purchased from VWR. Toray carbon paper (CP) was purchased from Alfa Aesar. Tungsten (Pure standard, 1000 μg mL⁻¹ in H₂O), molybdenum (Pure standard, 1000 μg mL⁻¹ in H₂O), and selenium (Pure standard, 1000 μg mL⁻¹ in H₂O, 2% HNO₃) reference standards for ICP were purchased from PerkinElmer. All reagents were used without purification. trioctylphosphine was stored in an Ar filled glovebox to prevent oxidation.
1 M trioctylphosphine selenide (TOP:Se) stock solution was prepared by dissolving 5 mmol (395 mg) of Se powder in 5 mL of trioctylphosphine at room temperature under dry N₂ atmosphere. 0.0125 M tungsten and molybdenum stock solutions were prepared by dissolving 0.125 mmol of the respective hexacarbonyl (either 33 mg of Mo(CO)₆ or 44 mg of W(CO)₆) in 10 mL of degassed oleic acid for 1 hour at 200 °C under vacuum. The ready stock solutions were stored in sealed glass vials in a drying desiccator.