Sodium chloride (nacl)

All reagents were of analytical reagent grade and were used without further purification. Urea was purchased from the Hedong District of the Tianjin Hongyan Reagent Factory (Tianjin, China). Sodium citrate was purchased from the Beijing Chemical Factory (Beijing, China). p-Acetaminophenol and quinine sulfate were purchased from Aladdin Co., Ltd. (Shanghai, China). Sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium chloride, H₂O₂, and chromium chloride (CrCl₃·6H₂O) were purchased from the Tianjin Damao Chemical Reagent Factory (Tianjin, China). The preparation reagents for the metal ion solutions were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shenyang, China). Anhydrous ethanol was purchased from Xinxiang Zhengxin Chemical Co., Ltd. (Henan, China).

The local reed biomass, collected from the bank of the Hunhe River in Shenyang city, Liaoning province, China, was used as the raw material to prepare the biochar. The chemicals, including ferrous sulphate heptahydrate (FeSO₄·7H₂O, ≥98%), sodium hydroxide (NaOH, ≥99%), sodium chloride (NaCl, ≥99.5%) and hydrochloric acid (HCl, ≥99.5%), were purchased from Tianjin Damao Chemical Reagent Factory, Tianjin, China. The real shallow groundwater was collected from Qianjin Farm, Shenbei New District, Shenyang China (burial depth less than 20 m). The main components and physicochemical properties of the groundwater have been reported in our previous study [51 (link)]. Briefly, the average levels of total dissolved solids and pH of the groundwater were 0.59 g/L and 7.11, respectively. The oxidation-reduction potential (Eh) was within −43.2–80.2 mV. The hardness of groundwater was relatively high, within 354.1–540.2 mg/L (measured with CaCO₃) with an average of 424.4 mg/L. Moreover, the main cationic components included Ca²⁺, Na⁺, K⁺, Mg²⁺ and some trace elements (e.g., Fe, Mn), and the main anion components were HCO₃⁻, Cl⁻ and SO₄²⁻. During the experiment, a certain amount of potassium dichromate (K₂Cr₂O₇, ≥99.5%) was added into the groundwater to synthesis the Cr contaminated groundwater. All chemicals and reagents used were of analytical grade.

α-HCH (purity > 98.1%), β-HCH (purity > 98.6%), γ-HCH (purity > 98.8%), and δ-HCH (purity > 99.2%) were purchased from Dr. Ehrenstorfer (Augsburg, Germany). USGS40 and USGS42 were purchased from US Geological Survey (Reston, VA, USA). Analytical grade HCH mixes (α:β:γ:δ = 1:1:1:1) (98.1% purity) were obtained from TMRM (Shanghai, China) and Agro-Environmental Protection Institute, Ministry of Agriculture (Tianjin, China). Hexane and methanol (purity > 99.5%) were obtained from Fisher Scientific (Waltham, MA, USA). Anhydrous sodium sulfate (Na₂SO₄, purity ≥ 99.5%), sodium chloride (NaCl, purity > 99.0%), and ferrous sulfate heptahydrate (FeSO₄∙7H₂O, purity > 99.0%) were purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China). Calcium peroxide (CaO₂, 70.0%) was obtained from Shandong Xiya Chemical Co., Ltd. (Shandong, China). Helium, carbon dioxide, oxygen (purity ≥ 99.999%), and dry compressed air were also prepared. Milli-Q water (resistivity of 18.2 MΩ·cm) was obtained using a Millipore ultra-pure water system.

The monomers acrylamide (AAm, 98%) and acrylic acid (AAc, AR grade) and the initiator potassium persulfate (KPS, AR grade) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), H₂SO₄, HCl, NaOH, MgCl₂, and NaCl were purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China), N,N’-Methylenebis(acrylamide) (MBA) was supplied by Shanghai Mackin Biochemical Co., Ltd. (Shanghai, China), doxorubicin hydrochloride (DOX-HCl) was purchased from Dalian MeiLun Biotechnology Co., Ltd. (Dalian, China), and methylene blue (MB) and methyl orange (MO) were purchased from Wenzhou Red Flag Auxiliary Factory (Wenzhou, China). Milli-Q water was used in all experiments.