3 nitrophenol

All the chemicals used were at least of analytical grade. Toluene was purchased from Honeywell (Honeywell, Charlotte, NC, USA). 4-nitrophenol, 2-nitrophenol, 3-nitrophenol, 2-methyl-4,6-dinitrophenol, 2,4-dichlorophenol, 2,3,5-trichrolophenol, humic acids, ammonia solution, ammonium chloride, sodium chloride and sodium sulfate were purchased from Sigma-Aldrich (Sigma-Aldrich, Steinheim, Germany). Quinine hemisulfate monohydrate (98%, suitable for fluorescence) was purchased from Alfa Aesar (Alfa Aesar, Karlsruhe, Germany). Stock metal solutions (Mn²⁺, Fe³⁺, Ag⁺, As⁵⁺, Se⁴⁺, Cr³⁺, Cu²⁺, Co²⁺, Ni²⁺, Li⁺, Cd²⁺, K⁺, Na⁺, Hg²⁺ and Ca²⁺) were obtained from Merck (Merck, Darmstadt, Germany). Amino acids (lysine, methionine, phenylalanine, leucine, histidine, arginine, tyrosine, threonine, proline, serine, glycine, tryptophan, asparagine, glutamine, cysteine, alanine and valine) were acquired from Fluka (Fluka, Seelze, Germany). Stock solutions of 4-NP were prepared in amber glass vials and stored at room temperature. All the experiments were conducted using double distilled water (DDW).

The analytical grade of chemicals such as 2-nitrophenol, 3-nitrophenol, 4-nitrophenols, thionine, catechol, K₂HPO₄, and KH₂PO₄ were bought from Sigma-Aldrich (USA). Other reagents purchased were of analytical reagent quality without extra purification. Phosphate buffer saline (0.1 M, PBS) was prepared by mixing K₂HPO₄ and KH₂PO₄ solutions followed by altering the pH with sodium hydroxide (NaOH) or phosphoric acid (H₃PO₄). All the target analytes’ (3-NP and 4-NP) stack solutions (0.01 mM) were prepared with deionized water. All the stock solutions were placed in a black place to eliminate the direct contact of sunlight. All the aqueous solutions used for the electrochemical experiment were prepared using double distilled water that was collected from the Milli-Q water cleansing chamber (18.2 MΩ cm). All electrochemical experiments were carried out at room temperature (26 ± 1 °C) and purified inert nitrogen gas was purged in the electrolyte for 300 s before electrochemical measurements.

2-2′-Azo-bis-isobutyronitrile (AIBN), vinyl acetate (>99%), tetrachlorauric acid (HAuCl₄·3H₂O), sodium borohydride (NaBH₄, 99%), activated carbon NORIT SX1G, sulfuric acid (H₂SO₄, 96%), 4-nitrophenol (>99%), 3-nitrophenol (>99%), 2-nitrophenol (>99%), polyvinyl alcohol 88 (Mw: 13,000–23,000, 88–89% hydrolyzed), polyvinyl alcohol 2 (Mw: 13,000–23,000, 98–99% hydrolyzed), polyvinyl alcohol 3 (Mw: 31,000–50,000, 98–99% hydrolyzed), and polyvinyl alcohol 4 (Mw: 146,000–186,000, 98–99% hydrolyzed) were purchased from Sigma Aldrich (Italy). The other polymers were properly synthesized in the laboratory and experimental protocols are presented below. The solvents were used without further processes of purification.