Potassium dichromate

Cadmium nitrate tetrahydrate (Cd(NO₃)₂·4H₂O), sodium sulfide nonahydrate (Na₂S·9H₂O) and potassium dichromate (K₂Cr₂O₇) were provided by Xilong Scientific Co., Ltd (Guangdong, China). p-Nitrophenol (C₆H₅NO₃), p-aminophenol (C₆H₆N₂O₂) and ammonium formate (CH₅NO₂) were supplied by Macklin Biochemical Co., Ltd (Shanghai, China). Attapulgite was purchased from Xuyi (Jiangsu, China). All the reagents were AR (analytical reagent) grade in purity. Deionized water used in all the processes was from local sources.

2-Aminoterephthalic acid H₂N-C₆H₃-1,4-(COOH)₂ (NH₂-TPA) (99 wt%), iron(iii) chloride hexahydrate FeCl₃·6H₂O (99 wt%), methanol CH₃OH (MeOH) (anhydrous, 99.8 v/v%), sodium acetate CH₃COONa (99 wt%), acetic acid CH₃COOH (99.5 wt%), cadmium nitrate tetrahydrate Cd(NO₃)₂·4H₂O (99 wt%), lead nitrate Pb(NO₃)₂ (99 wt%), and copper sulfate pentahydrate CuSO₄·5H₂O (99 wt%.) were purchased from Sigma-Aldrich. Cobalt sulphate heptahydrate (CoSO₄·7H₂O 99.5 wt%), nickel sulphate hexahydrate (NiSO₄·6H₂O 98.5 wt%), potassium dichromate (K₂Cr₂O₇ 99.8 wt%), and zinc chloride (ZnCl₂ 98 wt%.) were supplied by Xilong Chemical Co., China. The appropriate amounts of sodium acetate and acetic acid were used to prepare acetate buffer solution 0.1 M (ABS) with pH 6.0. Dimethylformamide C₃H₇NO (DMF) (99.94 v/v%) was purchased from Fisher Chemical. Polyethylene glycol 2000 (H(OCH₂CH₂)_nOH, PEG 2000) was supplied by Alfa Aesar.
A Siemens D5005 diffractometer (Cu K_α radiation, λ = 1.54056 Å), a NICOLET iS50FT-IR spectrometer, a Hitachi S4800 scanning electron microscope (SEM), and a TECNAI F20-G2 high-resolution transmission electron microscope (TEM) were used to perform X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), SEM, and TEM measurements, respectively. Electrochemical measurements were conducted using a PGSTAT302N AutoLab electrochemical workstation (Metrohm, Netherlands).