Graphene nanoplatelet

HPLC-grade tetracycline powder (C₂₂H₂₄N₂O₈.xH₂O, ≥ 98% purity, MW: 444.43), and chitosan (high molecular weight) were purchased from Sigma-Aldrich, USA. Tetra-butyl titanate (C₁₆H₃₆O₄Ti, ≥ 98%, for synthesis, TBT), ethanol (C₂H₆O, absolute grade), nitric acid (HNO₃, 65%), hydrochloric acid (HCl, fuming 37%), sodium hydroxide (NaOH), and acetic acid (glacial 100%) were obtained from Merck, Germany, and purified sodium chloride (NaCl) was purchased from an Iranian company. Zinc acetate dihydrate (Zn(CH₃COO)₂.2H₂O, ≥ 98%, ZnAc) and graphene nanoplatelet (+ 99.5%, 2–18 nm with 32 layers) were purchased from Sigma-Aldrich, USA and US Research Nanomaterials, respectively.

Tolperisone HCl pure drug was purchased from Combi-Blocks, USA. MYDOCALM^® tablets labeled to contain 150 mg tolperisone HCl manufactured by labatec-pharma SA (Geneva), Switzerland, were obtained from local pharmacy. Paramol^® 500 mg tablets labeled to contain 500 mg paracetamol was from (Misr Co for Pharm. Ind.S.A.E., Cairo, Egypt). Voltaren^®50 tablets labeled to contain 50 mg diclofenac natrium was obtained from (Novartis, Cairo, Egypt). Poly (vinyl chloride) (PVC) of high molecular weight, dibutyl phthalate (DBP), ortho nitrophenyl octyl ether (o-NPOE), and graphene nano-platelets powder hydrophobic were purchased from (Sigma-Aldrich, St. Louis, USA). Phosphotungestic acid (PTA) was purchased from (Fluka, Switzerland). Sodium tetraphenylborate (Na-TPB) was from (oxford lab fine chem, India). Ammonium Reinecke (RKT) and monobasic sodium phosphate were from (Riedel–De Haen AG, Hannover, Germany). Graphite powder (particle size < 50 μm) was purchased from (Merck, Darmstadt, Germany). All the reagents were of analytical grade and the experiments were constructed using double distilled water.

Oil palm EFB fibers were procured from Szetech Engineering Sdn. Bhd. (Selangor, Malaysia). These were milled and sieved to obtain fibers of diameters 106–500 µm. Fractionation of lignin was performed using 90% formic acid (Merck, Darmstadt, Germany) and the lignin content was determined using 98% sulfuric acid (Merck). Graphene nanoplatelets (Sigma Aldrich, Darmstadt, Germany) was used as reinforced for the printed materials. In stereolithography 3D printing, photo-curable resin with the major composition of 45–47 wt% polyurethane acrylate, 34–36 wt% morpholine, and 15–17 wt% tripropylene glycol diacrylate was provided by Wanhao Precision Casting Co. Ltd. (Jinhua, China) and isopropyl alcohol (Merck) was used to remove the excess resin on the printed object.

The electrode slurry was fabricated by mixing active materials (80 wt%), graphene nanoplatelets with a surface area of 500 m²/g (Sigma-Aldrich) (10 wt%) as a conducting agent, and polyvinylidene difluoride (PVDF) (Sigma-Aldrich) (10 wt%) as a binder in the solvent of n-methyl-2-pyrrolidone (Sigma-Aldrich). The slurry was coated onto a copper current collector and then dried at 80 °C in a drying oven for 12 h. The coin-type of cells composed of the Cu_xS-C and Cu_1.8S-C/C as the working electrodes were assembled with cell components (Welcos, Seoul, Korea) in a glove box under an inert Ar gas environment. Coin-cells were assembled with a porous glass fiber (grade GF/F, Whatman, Little Chalfont, U.K.) film as a separator, 1 M sodium trifluoromethanesulfonate (NaSO₃CF₃) (Sigma-Aldrich) in diethylene glycol dimethyl ether (DEGDME) (Sigma-Aldrich) as an electrolyte, and a sodium (Sigma-Aldrich) foil electrode as counter and reference electrodes. The galvanostatic charge and discharge cycling test was carried out by using a multichannel battery testing unit (CTS-Lab, Asselfingen, Germany; BaSyTec). The cyclic voltammetry (CV) for the Cu_1.8S-C/C anode sample was conducted using a multi-channel potentiostat (Bio Logic, Seyssinet-Pariset, France; VMP3) in the voltage range of 0.01–3.0 V (vs. Na⁺/Na) at a scan rate of 0.2 mV/s.

Dragon skin and Ecoflex 00-30 (platinum-catalyzed silicones) were purchased from Smooth-On (USA), and Graphite flake (average size: + 20 mesh (850 microns)) was obtained from Asbury Carbons (USA). Molybdenum Disulphide (MoS₂-Powder size 1.5 μm) was provided by ACS Materials LLC. SYLGARD™ 184 Silicone Elastomer Kit was obtained from Dow Corning. Graphene nanoplatelets (surface area 750 m²/g, size ~ 2 μm) and graphite powder (~ 20 μm) were acquired from Sigma Aldrich (USA) and Fisher Chemicals respectively.

Graphene dispersion (1 mg/mL in DMF), graphene nanoplatelets (1 mg/mL, water dispersion), Fe₃O₄/graphene nanocomposite (10 mg/mL acetone dispersion, Fe₃O₄ NPs size: 5–25 nm), CoPt/graphene nanocomposite (10 mg/mL acetone dispersion, CoPt NPs size: 2–5 nm), and TiO₂/graphene nanocomposite (10 mg/mL, acetone dispersion, TiO₂ NPs size: 10–40 nm) have been purchased from Sigma Aldrich and used as received.
The size of silver interdigitates electrodes on alumina substrate was 7 mm × 13.4 mm. The interdigitates contacts consisted of 7 + 7 branches and each silver line has a 210 μm width. Figure 1a report the picture of an interdigitated substrate.
In order to prepare the sensors, 15 droplets of each graphene-based solution have been drop-casted on 5 interdigitated alumina substrates and let dry upon solvent evaporation at room temperature. The prepared samples will be labelled as Gr dispersion, Gr_nanoplatelets, Gr_Fe₃O₄, Gr_CoPt, and Gr_TiO₂.