https://orcid.org/0000-0003-4891-340X
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ABSTRACT
In this study, the functionalised henna powder was tested for the adsorption of the lead, copper, and nickel. The method of making this adsorbent is very easy, as it can be prepared with the materials available in the kitchen. Three metals with equal concentration are used as multi-metals adsorption. The experiment was conducted at varying contact time(30–180), adsorbent dose(0.05–0.25 g), adsorbate concentration(10-50 mg/l), temperature(15, 25, 40 and 60ºс), and pH(2–8). Most of the significant changes were observed at 30 min, 0.25 g, 20 mg/l and 5 for the contact time, adsorbent dosage, adsorbate concentration, and pH, respectively. At pH 5, the lead, copper, and nickel removal percentage were 99.96%, 97.90%, and 86.2%, respectively. In this condition, the total surface coating is less than 40% in henna, meaning that over 60% of the adsorption sites have been left unsaturated and free, so more metal ions can be adsorbed with the increase in the initial concentrations of the metal solutions. From the results, it can be concluded that the best adsorption isotherm model and correlation coefficient (R2) were followed for Pb (Langmuir, 0.997), Cu(Langmuir, 0.992) and Ni(Freundlich, 0.965). Of four kinetic models, the highest values of correlation coefficient (R2) were obtained in the Pseudo-second-order model for adsorption of Pb(1), Cu(1) and Ni(0.999). At all temperature ranges, ΔG is negative (spontaneous reaction) for lead and copper, it is positive(non-spontaneous reaction) for nickel(except at 25°C). The ΔG becomes more negative with increasing temperature for copper and this means that increasing temperature effects copper adsorption. The results are shown that thermodynamic properties such as ΔH and ΔS are for lead(−58.4, 0.151), copper(15.4, −0.07), and nickel(2.44, −0.006), respectively. The negative ΔH and ΔS are indicated that exothermic reaction(lead) and the regular arrangement of the adsorbed molecules on the adsorbent(copper and nickel), respectively.
Symbols
| Ce | = | Equilibrium concentration of solution, mg/l |
| Ci | = | Initial concentration of solution, mg/l |
| qe | = | Amount of metal adsorbed per unit mass of adsorbent at equilibrium, mg/g |
| qm | = | Langmuir constant, mg/g |
| qt | = | Amount of metal adsorbed per unit mass of adsorbent at time t, mg/g |
| KF | = | Freundlich constant, L/mg |
| KL | = | Langmuir constant, L/mg |
| Εa | = | Dubinin–Radushkevich isotherm constant, kj/mol |
| KT | = | Temkin isotherm equilibrium binding constantm, L/g |
| K1 | = | Rate constant of the pseudo-first-order adsorption process, min-1 |
| K2 | = | Rate constant of pseudo-second-order adsorption, g mg-1min-1 |
| Kid | = | The intra-particle diffusion constant, mg/g min 0.5 |
| KR | = | The Ritchie constant, 1/min |
| n | = | Freundlich constant, L/g |
| R | = | Gas constant, 8.314 J/mol/K |
| T | = | Temperature, K |
| β | = | The mean free energy of adsorption, mol2/kj2 |
| t | = | Time, min |
| bT | = | The adsorption constant, J/mol K |
| R | = | Universal gas constant, 8.314 J/mol K |
| T | = | Absolute temperature value, K |
| B | = | A constant related to the heat of sorption, J/mol |
| w | = | Weight adsorbent, g |
| ∆G | = | Gibbs free energy, kj/mol |
| ∆H | = | Enthalpy, kj/mol |
| ∆S | = | Entropy, kj/mol |
| B.P | = | Boiling Point, °C |
Acknowledgments
The authors would like to greatly appreciate Dr.Ahadianand the lab staff, as well as the Institute for Nanoscience& Nanotechnology (INST) of Sharif University of Technology that cooperated for doing this research.
Disclosure statement
No potential conflict of interest was reported by the authors.
