Ammonia water

The chemicals used in the study included dopamine hydrochloride (McLean Biochemical Technology Co., Ltd.), calcium chloride (Xilong Chemical Co., Ltd.), sodium alginate, iron(iii) nitrate nonahydrate (Aladdin), anhydrous methanol, anhydrous ethanol, nitric acid (Shanghai Lingfeng Chemical Reagent Co., Ltd.), ammonia water and sodium hydroxide (Sinopharm Group Chemical Reagent Co., Ltd.). All reagents were of analytical grade, and no further purification was required prior to use. The water used in the study was ultrapure water (Millipore, ≥18.2 MΩ cm, 25 °C).

All starting chemicals were obtained commercially without further purification. Magnesium chloride hexahydrate (MgCl₂·6H₂O), sodium hydroxide (NaOH), sodium dihydrogen phosphate (NH₄H₂PO₄), triammonium phosphate ((NH₄)₃PO₄)), ammonia water (NH₃·H₂O), hydrochloric acid (HCl), and glucose are of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. The yeast extract and malt extract are of biotech grade and purchased from Oxoid Ltd. and BBI Life Sciences Ltd., respectively. Deionized water was used in all of the experiments.

Graphite (100 mesh, XFnano), ferric chloride hexahydrate (FeCl₃·6H₂O, Sinopharm), ethylene glycol (Sinopharm), polyethylene glycol (PEG 4000, Sinopharm), sodium acetate trihydrate (NaAc·3H₂O, Sinopharm), tetraethyl orthosilicate (Sinopharm), poly(diallyldimethylammonium chloride) (PDDA, Sinopharm), 3-aminopropyl triethoxysilane (APTES, Sinopharm), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, Sinopharm), n-hydroxysuccinimide (NHS, Sinopharm), ammonia water (28 wt.%, Sinopharm), hydrochloric acid (Sinopharm), lead nitrate [Pb(NO₃)₂, Sinopharm], methylene blue (MB, Sinopharm).

The para-aramid pulp with a length of 1.15 ± 0.05 mm was purchased from Cangzhou Zhongli New Material Technology Co., Ltd., Cangzhou, China and was produced from poly(p-phenylene terephthalamide) (PPTA) fibers like Kevlar of DuPont. The chemicals, including tetraethoxysilane (TEOS, m(SiO₂) ≥ 28.4%), ethanol (EtOH, 99.7%), n-hexane (97.0%), hydrochloric acid (HCl, 36.5%) and ammonia water (NH₃∙H₂O, 26.5–28.5%), were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Trimethylchlorosilane (TMCS, 98%) was bought from Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China. Deionized water (DI∙H₂O) was prepared using an ultra-pure water machine (ECO-S, HHitech, Shanghai, China) and was used to prepare 0.1 M HCl (aq) and 0.5 M NH₃·H₂O (aq), respectively.

The supports of Co_xSn_(1−x)O₂ (x = 0, 0.1, 0.2, 0.3) were synthesized by the hydrothermal method and then processed by heat treatment. One gram of hexadecyl trimethylammonium bromide (Sinopharm, Shanghai, China) was dissolved in a mixture of 20 ml of ethanol (Sinopharm) and 20 ml distilled water. Then, significant amounts of tin chloride (Sinopharm) and cobalt acetate (Sinopharm) (molar ratio (Sn²⁺ + Co²⁺): CTAB = 1 : 1.05) were added to the above solution, and continuously stirred to get a homogeneous solution. A certain amount of ammonia water (Sinopharm) was added dropwise to the solution under vigorous stirring at room temperature. The Ph value of the solution was maintained at 9 and under stirring for 2 h. After it was stirred, the mixture was transferred to a stainless Teflon-lined 100 ml autoclave and kept at 180°C for 24 h in an oven. The resulting yellow precipitate was collected by centrifugation, washed with distilled water and ethanol several times to remove the impurities, and then dried in a vacuum oven at 60°C. The dried samples were processed under 350°C for 5 h in a muffle furnace. After cooling to room temperature, Co_xSn_(1−x)O₂ nanoparticles were finally obtained.

Fresh lemons (Eureka, Anyue, Sichuan, China) were purchased from a local supermarket in Nanjing. A standard sample of Cyclohexanone (>99.9%; C6–C25) was purchased from Sigma-Aldrich Trading Co., Ltd. (Shanghai, China). Sodium chloride, amino acid standard, o-phthalaldehyde (OPA), acetonitrile, methanol, 3-mercaptopropionic acid, boric acid, potassium dihydrogen phosphate, petroleum ether (30–60 °C), absolute ethanol, phosphoric acid, hydrochloric acid, ammonia water, ether, pyrogallic acid, ethanol (95%), and other reagents were purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China).