Hydrofluoric acid

PLA granules (Goodfellow, UK) were dissolved in a glass container containing 5% acetone, heated to 50°C, and stirred vigorously for approximately 4 h. Mg alloy AZ91 (9 wt% Al, 1 wt% Zn), both coated and bare, was applied as a reinforcement core. Coated samples were made as follows: AZ91 strips with specific size were rinsed in 35% hydrochloric acid (OCI, Korea) to clean the surface and immersed in 50% hydrofluoric acid (Duksan, Korea) for 8 h to form the fluoride coating. Then, AZ91 strips were washed using deionized water and ethanol. Finally, AZ91 strips were wholly blow-dried. Bare samples (uncoated) were treated in the same way, except for being immersed in HF (Table 1).
The PLA solution was first laid in a metal mold, followed by a Mg alloy AZ91 strip, and then a layer of PLA solution was laid on the AZ91 strip. Next, the solvent was put in a drying oven at 100°C to evaporate for 6 h and produce a Mg-reinforced PLA-integrated membrane. The fabrication method of the integrated membrane in the control group is the same as above, except that the magnesium strip was replaced by a PLA strip. The average thickness of the integrated membranes was 120 μm. The integrated membranes were cut into the desired dimensions (Figure 1).

2,2,2-Trifluoroethyl methacrylate (TFEMA, Fluorochem, Hadfield, UK) and 4-vinyl pyridine (VP, 95%, Aldrich, St. Louis, MO, USA) were used after purification by an inhibitor remover column (inhibitor removers, Aldrich). 4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid (CTP, 97%, Aldrich), 1,4-dioxane (99.5%, Acros, Geel, Belgium), hexane (95%, Duksan, Ansan, Korea), tetrahydrofuran (THF, 99.5%, Duksan), toluene (anhydrous, 99.8%, Aldrich), chloroform (extra pure grade, Duksan), methanol (99.8%, Duksan), and hydrofluoric acid (50.0%, Duksan) were used as received without further purification. 2,2′-Azobisisobutyronitrile (AIBN, 98%, Junsei, Tokyo, Japan) was used after recrystallization in methanol. HOPG (graphene nanoplatelets, M-25 grade, XG Sciences, Lansing, MI, USA) was used as a source of graphene nanoplatelets. Ultra-pure water (resistivity > 18.2 MΩ·cm, Purelab, Elga, High Wycombe, UK) was used throughout the experiments.