Aniline monomer

Graphite powder (synthetic, conducting grade, 325 mesh, 99.9995%) was purchased from Alfa Aesar. RuCl₃.3H₂O, 2(2-Pyridyl) benzimidazole, aniline monomer and aluminium (Al) evaporation slug were procured from Sigma-Aldrich. Pre-patterned ITO substrates, PEDOT:PSS, P3HT, PTB7, PC₆₀BM and PC₇₀BM were purchased from OSSILA, Ossila Limited, Kroto Innovation Centre, Broad Lane, Sheffield, S3 7HQ, UK. All other solvents and reagents were received and used without further purification.

Aniline monomer (99.8%) is an analytical grade and purchased from Sigma-Aldrich Co. (Shanghai, China). MWCNTs (98%) and ethanol (AR, 98%) were obtained from Hengqiu Technology Reagent Co. (Suzhou, China) and Changzheng Chemical Reagent Co. (Chengdu, China). Ammonium persulfate, potassium hydroxide, and hydrochloric acid are all analytically pure grades, and purchased from Kelong Chemical Reagent Co. (Chengdu, China).

Aniline monomer (C₆H₅NH₂, >99%, M_w = 93.13 g/mol, d_25ºC = 1.02 g/cm³), ammonium persulfate ((NH₄)₂S₂O₈, 98%, M_w = 228.20 g/mol, d_25ºC = 1.98 g/cm³), triethylamine (TEA, >98%, M_w = 101.193 g/mol), H₂SO₄, KMnO₄, P₂O₅, K₂S₂O₈ and H₂O₂ (30 wt % in water) were obtained from Sigma-Aldrich (Madrid, Spain). Graphite powder was purchased from Bay Carbon, Inc. (Bay City, MI, USA). Hexamethylene diisocianate (HDI, >99%, M_w = 168.196 g/mol) was provided by Acros Organics (Madrid, Spain). The organic solvents were HPLC grade and were purchased from Scharlau S.L. (Barcelona, Spain). Deionized water was obtained from a Milli-Q-Water-Purification-System (Millipore, Milford, DE, USA). Aniline was stored in a refrigerator and was distilled under reduced pressure prior to use; the rest of the chemicals were used as received.

PVA (MW 89,000–98,000, +99% hydrolyzed), aniline monomer, N-methyl-2-pyrrolidone (NMP), ammonium persulfate (APS), HCl, methanol, benzimidazole (98%), sodium chloride, sodium hydroxide, chloroacetic acid (ClCH₂COOH, purum ≥ 97.0%) were purchased from Sigma-Aldrich (St. Louis, MI, USA).
The chemical composition of the cast iron sample is shown in Table 1. Cast iron specimens of dimensions 3.7 × 1.2 × 0.2 cm³ were polished to a mirror finish, degreased with trichloroethylene, and used for weight loss and surface examination studies.

The precursor of silver nitrate (AgNO₃, 99.99% purity), iron nitrate (Fe(NO₃)₃ nanohydrate ACS reagent >98%), aniline monomer (C₆H₅NH₂), and polyvinyl alcohol (PVA, 99% hydrolysis) was purchased from Sigma-Aldrich Chemicals. A strain of E. coli O157:H7 was obtained from microbiological laboratory, Universiti Kebangsaan Malaysia.

With reference to a previous study, C8F-doped PANi@HPMC core–shell nanoparticles, as sensing materials, were synthesized.^{19 (link)} First, 5 ml of 0.169 M hydroxypropyl methylcellulose (HPMC, Sigma Aldrich) was dissolved in 5 ml of deionized (DI) water to prepare an aqueous dispersion, and then 100 μl of aniline monomer (GR, Sigma Aldrich) was added, followed by stirring at room temperature for 30 min. Second, 1 ml of 1 wt% HCl was added to the solution prepared above and stirred for 30 min, and 1.25 ml of 0.8 M ammonium persulfate (APS, 98.0%, Sigma Aldrich) was continuously added. Third, the reaction was conducted for 12 h without agitation at 0 °C. The reaction product is separated and purified by centrifugation at 15 000 rpm, and the obtained spherical nanoparticles are re-dispersed in DI water. Finally, 1 wt% C8F (40% in water solution, Sigma Aldrich) compared with aniline monomer was added to the dispersion, and the mixture was stirred at 300 rpm for 12 h or more. The synthesized core–shell-structured nanoparticle sensing materials were additionally washed two to three times with methanol and DI water and finally prepared as an ink solution of DI water dispersion.