Hydrochloric acid (hcl)

Chinese fir (Cunninghamia lanceolate), sourcing from Fujian, China, was used as a raw material. Phosphoric acid, phenol, hydrochloric acid, hexamethyleneteramine, formaldehyde, sodium thiosulfate, disodium hydrogen phosphate, monopotassium phosphate, copper sulfate pentahydrate and zinc chloride were purchased from Beijing Chemical Works (Beijing, China). Soluble starch was purchased from Xilong Chemical Co. Ltd. (Shantou, China). Potassium iodide and iodine was purchase from Guangdong Guanghua Sc-tech Co. Ltd. (Shantou, China). Methylene blue was purchase from Tianjin Jinke Fine Chemicals Co. Ltd. (Tianjin, China) All the chemicals were of reagent grade and used without further purification.

Analytic grade reagents, hydrochloric acid, and tetraethyl ortho-silicate were provided by Beijing Chemical Works. Ethanol absolute, diethyl ether, concentrated nitric acid, and perchloric acid were provided by Tianjin Fine Chemical Co., Ltd.
Although the green wings of butterfly Trogonoptera brookiana possess a light trapping property which was confirmed as reported in our previous work [22 (link)], this study found that the black wing scales had the better light trapping characteristic compared with the previous study. Thus, the black wings were selected as a biological prototype in this work. Butterfly wing samples of uniform size (15 mm in length and 10 mm in width, rectangular) were cut off from the black areas in a perpendicular and parallel direction to the ridge veins, respectively. In order to confirm that the butterfly wing samples were clean, some pre-processing was conducted. Firstly, each sample was soaked by aether for 10 min to remove proteins and fattiness on the samples’ surface. Afterwards, the dehydration treatment in ethanol absolute with duration time of 15 min for each specimen was taken. The purpose of conducting the dehydration pre-processing was to increase the mechanical strength and stability of the treated tissues. Then, the samples were dried naturally in air.

Sodium 3-(trimethylsilyl)propionate-2,2,3,3-d₄ (batch no. 1668-E) was purchased from Merck. Deuterium oxide (D₂O) was purchased from Cambridge Isotope Laboratories. Methanol and acetonitrile (HPLC grade) were purchased from Beijing Chemical Works. Water (HPLC grade) was purchased from Hangzhou Wahaha Group. Dipotassium hydrogen phosphate (K₂HPO₄·3H₂O), sodium dihydrogen phosphate (NaH₂PO₄·2H₂O), and hydrochloric acid (analytical grade) were purchased from Beijing Chemical Works.

Ferric trichloride (FeCl₃, AR), sodium hydroxide (NaOH), hydrazine (N₂H₄·H₂O, 98%), and (3-Aminopropyl)triethoxysilane (APTES) were purchased from Aladdin Industrial Co., Ltd. (Shanghai, China). GO (powder in a single layer) was purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. (Nanjing, China). Cupric chloride (CuCl₂, AR) was purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. (Beijing, China). Humic acid (HA, CP) was purchased from Guangfu Chemical Reagent Company (Tianjin, China). Anhydrous ethanol and hydrochloric acid (HCl, 37%) were purchased from Beijing Chemical Reagent Company (Beijing, China). Deionized water was made in the laboratory and used for experiments.