Cadmium nitrate tetrahydrate cd no3 2 4h2o

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).

The WAS used in the following AD was from a secondary sedimentation tank of a municipal wastewater treatment plant in Changsha, China, where no PAM-based wastewater treatment was carried out. The background Cd concentration detected in untreated sludge was 0.11 ± 0.02 mg L⁻¹. The collected fresh sludge was filtered through a 0.45-mm stainless steel screen to remove impurities and concentrated at 4 °C for 24 h. The supernatant liquid was removed, and the remainder was the sludge used in the experiment. The major characteristic of sludge included the following: total suspended solids (TSS) 29101 ± 345 mg L⁻¹, volatile suspended solids (VSS) 16033 ± 203 mg L⁻¹, and pH 6.8 ± 0.1.
The inoculum (sludge retention time: 20 d; TSS: 23532 ± 302 mg L⁻¹; total chemical oxygen demand (COD): 18061 ± 223 mg L⁻¹) was attained from a long-term anaerobic digester in the laboratory. APAM was purchased from Meiyuan Water Purification Agents company (Gongyi, China) with a molecular weight of 10 million Da and a charge density of 30%. As a heavy metal salt solution, cadmium nitrate tetrahydrate [Cd(NO₃)₂·4H₂O] with a purity of 99.0% was purchased from Sigma Aldrich and used in this study. Cd stock solution (6.0 g L⁻¹) was prepared with deionized water.