Ferrous sulfate heptahydrate

The following chemicals were used as purchased: ferrous sulfate heptahydrate (FeSO₄·7H₂O, >99%, Panreac, Barcelona, Spain), potassium nitrate (KNO₃, >99%, Sigma-Aldrich, St. Louis, MO, USA), sodium citrate tribasic dihydrate (Na₃C₆H₅O₇·2H₂O, 99%, Sigma-Aldrich), chloroauric acid trihydrate (HAuCl₄.3H₂O, ≥99.9%, Sigma-Aldrich) and potassium hydroxide (KOH, >86%, Sigma-Aldrich), ascorbic acid (C₆H₈O₆, J. M. Vaz Pereira, Lisboa, Portugal), silver nitrate (AgNO₃, 99.9%, Sigma-Aldrich), acid chloride (HCl, 37%, AnaloR Normapur, VWR International, Radnor, PA, USA), and tetracycline hydrocloride (TC, C₂₂H₂₄N₂O₈, Sigma-Aldrich). All the solutions were freshly prepared using ultrapure water (18.2 mΩ·cm).

Chitosan (from shrimp shells, deacetylation degree ≥75%), tetraethyl orthosilicate (Si(OC₂H₅)₄, TEOS, >99%), potassium nitrate (KNO₃, >99%) and 3-(triethoxysilyl)propyl isocyanate ((C₂H₅O)₃Si(CH₂)₃NCO, ICPTES, 95%) were purchased from Sigma–Aldrich (Steinheim, Germany). Trimethyl Chitosan was obtained from Henan Tianfu Chemical Co., Ltd (Zhengzhou, China). Potassium hydroxide (KOH, >86%) was purchased from PronoLab (Lisbon, Portugal). Sulfamethoxazole (C₁₀H₁₁N₃O₃S) was obtained from Fluka Chemie (Buchs, Switzerland). Ethanol (CH₃CH₂OH, >99%) and ferrous sulfate heptahydrate (FeSO₄.7H₂O, >99%) were obtained from Panreac (Barcelona, Spain). N,N–Dimethylformamide (HCON(CH₃)₂) was obtained from Carlo Erba Reagents (Peypin, France). Ammonia solution (25% NH₃) was purchased from Riedel-de-Häen (Hanover, Germany) and methanol (CH₃OH, >99%) was purchased from VWR International (Radnor, PA, USA). Milli-Q water was obtained from the Synergy equipment from Millipore with a 0.22 μm filter (Darmstadt, Germany). All chemicals were used without any further treatment.