## 3 Results
### Effect of pH and Adsorbent Dose  
The availability and accessibility of adsorption sites were significantly influenced by the adsorbent dose [66; 67; 68]. The concentration of hydrogen ions is considered to be an important factor in adsorption operations, which can have a significant effect on how heavy metals behave in aqueous solutions. One of the deciding elements is the concentration of hydrogen ions, which affects the solubility of heavy metal ions in a solution [17]. Throughout the process, it also influences the extent of ionization of the adsorbate and replaces certain positive ions that may exist in the active sites of the adsorbent [54]. An investigation was conducted to examine the effect of different dosages of DAC (10-100 g/L for the Cu solution and 5-50 g/L for the Pb solution) on two metals (Cu and Pb), with an initial concentration of 50 mg/L. The impact of varying amounts of adsorbent on the removal of Cu and Pb ions is illustrated in Figures 11 and 12 at various pH levels. The removal efficiencies of Cu\({}^{2+}\) and Pb\({}^{2+}\) by date seed activated carbon (DAC) are highly affected by adsorbent dose and pH, as illustrated in Figures 11 and 12. A strong adsorption potential of DAC was reported, which is driven by its surface chemistry and active functional groups. The results indicate a positive correlation between the dosage of adsorbent and the percentage of lead and copper removal efficiency. It is anticipated that the adsorption will rise as the dose of adsorbent increases, as a result of the expansion in the surface area of the adsorbent and the greater number of available adsorption sites [54; 66]. The Cu removal efficiency for DAC was investigated at pH 5 and pH 7, with varying adsorbent doses in g/L. At pH 7 (Figure 11) pH 7, DAC demonstrated consistent performance, achieving high Cu removal percentages, between 95% and 99%. This implies that a neutral pH is the key parameter for the adsorption of Cu ions. Paired \(t\)-test analysis showed that the Cu removal rates at pH 5 and 7 are significantly different (\(p=1.67\times 10^{-6}\) < 0.05). Figure 11: Copper removal efficiency (%) at different pH (5 and 7) levels by DAC at four different doses: 10, 25, 50, and 100 g/L. The copper removal efficiency is consistently high at pH 7, surpassing 95% for all adsorbent concentrations. This suggests that the neutral pH promotes the optimal adsorption of copper ions, presumably as a result of the reduced competition between H\({}^{+}\) ions and Cu\({}^{2+}\) ions for active adsorption sites, as observed in previous studies [69; 70]. At pH 5, however, the removal rate is comparatively lower, around 32% at the highest adsorbent concentration of 100 g/L. The inferior performance at lower pH is due to the protonation of the DAC active sites, which in turn results in the reduction of the active sites and is responsible for lower Cu removal [71]. The trend, on the other hand, shows that the increase in the adsorbent dose from 10 g/L to 100 g/L results in a better removal efficiency at both pH levels. This is due to the increased availability of surface area and active adsorption sites with the higher adsorbent doses, which aligns with findings in other previous adsorption studies [72]. The efficacy of Pb removal by DAC was evaluated at several pH values (3, 5, and 7), with varied adsorbent dosages in g/L (Figure 12). The results demonstrate that the efficacy of lead adsorbent is superior at low pH levels (pH 3 and 5), achieving around 99% to 100% effectiveness. This phenomenon may be attributed to the prevalence of Pb\({}^{2+}\) ions available for adsorption and to reduced competition for adsorption in an acidic pH environment. At pH 3 and 5, the surface charge of DAC may be more conducive to electrostatic attraction to Pb\({}^{2+}\) ions. Similar findings were observed in a prior study, indicating that pH 5 settings facilitate lead adsorption due to increased electrostatic interactions [73].