4. Conclusions
Batch experiments were conducted to adsorb and remove Cu, Pb, and Cd heavy metals in aqueous solution using RPL and DPL. Persimmon leaves include many hydroxyl groups (eOH) and contain 13.03% of tannin and catechin, which are effective in removing heavy metals. Moreover, according to the FT-IR analysis, RPL and DPL had a structure which facilitates the adsorbtion of heavy metals because it has Carboxylic group, C]O carbonyl groups, CH stretching, OeH carboxylic acid, and bonded eOH groups. The removal of heavy metals by using RPL and DPL resulted in 10%e15% removal efficiency of DPL than RPL. The removal rates were in the order of Pb > Cu > Cd. The heavy metal adsorption experiments using RPL and DPL were more suitable for the pseudosecond order than the pseudo-first order depending on the coefficient of determination. The adsorption of Cu, Pb, and Cd by DPL was more suitable for Freundlich isothermal adsorption than Langmuir isothermal adsorption. The adsorption of Cu, Pb, and Cd was concluded to be ion exchange reaction on an uneven adsorption surface layer. The maximum adsorption capacity (qm) of DPL by Langmuir was determined to be 22.59 mg/g, 19.42 mg/g, and 18.26 mg/g for Pb, Cu, and Cd, respectively. As a result of the adsorption experiments on heavy metals in DPL, the n value was higher than 2 regardless of dose, indicating that the adsorption was easy. The adsorption constant KF of Cu was 0.6816, Pb was 0.7962, and Cd was 0.6742, indicating that Pb had the highest adsorption constant. That is, the adsorption rate of PB was faster than that of Cu and Cd in heavy metal adsorption experiments using DPL. In the thermodynamic experiment, DG exhibited a negative value and decreased as the temperature increased, resulting in a spontaneous process. DH and DS showed positive values, and heavy metal adsorption reaction using DPL was an endothermic process. Therefore, it can be seen that, as the temperature increases, the adsorption improves, and the affinity of heavy metal to DPL in the adsorption process is very good. Based on these experimental results, we conclude that DPL is an inexpensive, efficient, and commercially viable new eco-friendly adsorbent for removing heavy metal ions from the polluted water. In addition, bioadsorbent, DPL, is very economical because it can be easily applied without remodeling existing sewage treatment plants and could be employed as a low-cost alternative to commercial activated carbon in the removal of heavy metal ions from wastewater.
