The efficiency of polysiloxane surfaces modified with ortho, meta and para-nitrophenyl moieties as a low cost
adsorbent for removing lead ions from aqueous solution has been investigated in this paper. Batch experiments were
conducted to study the effects of the main parameters such as contact time, initial concentration of Pb(II), adsorbent
dose, solution pH, and temperature on the adsorption of Pb(II) by polysiloxane surfaces. The maximum removal of
lead(II) is found to be 97 % at pH 8 for (Si-p-NO2), 95.9 % for(Si-o-NO2) and 93.7% for (Si-m-NO2) initial Pb(II)
concentration of 10 mg·L−1, adsorbent dose of 1 g·L−1, agitation speed of 200 rpm, and temperature of 25 °C. The
same study was done for the effect of dose (5 mg) and showed 99 % removal using the (Si-p-NO2).Dynamics of the
adsorption process were studied, and the values of rate constants of pseudofirst-order and pseudosecond-order
were calculated. Equilibrium isotherms for the adsorption of Pb(II) were analyzed by the Langmuir and Freundlich
isotherm models. The Langmuir isotherm model was found to represent better the data of Pb(II) sorption onto
polysiloxane surfaces. Different thermodynamic parameters, namely, changes in standard Gibbs energy, enthalpy,
and entropy, were also evaluated from the temperature dependence, and the results suggest that the adsorption
reaction is non-spontaneous and endothermic in nature. The prepared compound was characterized using solid 13CNMR,
TGA, FT-IR, UV-vis and SEM.
Keywords: groundwater, adsorption, isotherm, desorption, heavy metals, kinetics.