Aa700

In this work, five factors, namely pH, temperature, initial concentration of metal ions, CaCl₂, and HA, were screened for their effects on the adsorption capacities of NMGO for Cu(II) and Cr(VI) ions (response) using a 2⁵⁻¹ FFD with resolution V. The experimental factors and their levels used in the 2⁵⁻¹ FFD were demonstrated in Table 1. The software of Design Expert 8.0.6 (Stat-Ease Inc., Minneapolis, MN, USA) was used for the FFD of the experiments and regression analysis of the obtained experimental data. The full design matrix of the 2⁵⁻¹ FFD is shown in Supplementary Table S4. All adsorption experiments were performed in a 150 mL conical flask containing 50 mL aqueous solution of Cu(II) or Cr(VI), and the samples were agitated at 150 rpm for 24 h in a rotary shaker. Then, the mixture in the conical flask was separated using a permanent magnet. The Cu(II) and Cr(VI) concentrations in the supernatant were analyzed by a flame atomic absorption spectrometry (PerkinElmer AA700, USA) and an UV-visible spectrophotometer (Pgeneral T6, Beijing) at 540 nm, respectively16 (link). The adsorption capacity (q_e) of NMGO was calculated from the difference between the initial concentration (C₀) and the equilibrium concentration (C_e).

For the measurement of Cd, 0.5 g dried plant material was acid digested using HNO₃ (nitric acid) and HClO₄ (perchloric acid) in 4:1 ratio at 60 °C by adopting the hot plate block method depicted by Jackson³⁴ . The sample analysis for Cd was conducted through an atomic-absorption spectrophotometer (AAS) (Perkin Elmer AA700, USA). Cadmium translocation factor was determined as per the method of Bose and Bhattacharyya. Bioconcentration factor (BCF) was computed as heavy metal accumulated in each plant tissue to that dissolved in the soil medium as shown below: $$\text{Shoot}\text{bioconcentration}\text{factor}:{\text{BCF}}^{\text{s}}={\text{C}}^{\text{shoot}}/{\text{C}}^{\text{soil}}$$ $$\text{Root}\text{bioconcentration}\text{factor}:{\text{BCF}}^{\text{r}}={\text{C}}^{\text{root}}/{\text{C}}^{\text{soil}}$$
Translocation factor (TF) of cadmium was computed using the above equations as follows: $$\text{TF}={\text{BCF}}_{\text{shoot}}/{\text{BCF}}_{\text{root}}$$