## 2 Removal of Lead
### Removal of lead using GO-polymer composites
Disappearance of XRD (X-ray diffraction spectroscopy) sharp peak from 20 = 10.7\({}^{\circ}\) corresponding to 001 plane reflection from the XRD spectrum of PAM-GO indicated the complete exfoliation of GO sheets and intercalation of PAM chains into the GO layers. In the PAM-GO XPS spectrum, C1s peak at 284.4 eV binding energy was attributed to the C-C, C=C and C-H bonds and the peak appeared at 288.4 eV was correlated with the O=C-N bond of PAM [163,198]. Effect of contact time on the adsorption efficiency for PAM-GO adsorbent was studied for 45 mg/L as Pb(II) ions concentration at pH 6. The adsorption capacity of PAM-GO increased sharply within the first 20 min. and reached at equilibrium within 30 min. The short period of time for higher adsorption capacity highlights potential industrial applications of the PAM-GO adsorbent. Experimental value (440.4 mg/g) calculated from pseudo-second-order kinetic model parameters for Pb(II) ions adsorption was similar to the calculated value (458.7 mg/g). The correlation coefficient (R\({}^{2}\)= 0.999) obtained from the pseudo-second-order kinetic model suggested that the adsorption process might be controlled by chemical adsorption involving valence forces through the sharing or exchange of electrons between the sorbent and sorbate. Langmuir and Freundlich isotherms comparison were studied for GO and PAM-GO to examine the Pb(II) ions surface adsorption mechanism. The adsorption of Pb(II) for GO and PAM-GO was well fitted with the Langmuir isotherm model and higher R\({}^{2}\) value, indicated specific homogeneous adsorption (i.e., with all the adsorption sites of equal adsorbate affinity) on GO and monolayer adsorption on the PAM-GO adsorbent [199,200]. The theoretical adsorption capacity of PAM-GO, determined from the Langmuir isotherm for Pb(II) was 819.67 mg/g, which was 20 times higher than that of the GO nanosheets. Higher adsorption capacity of PAM-GO was attributed due to good water dispersibility and increased oxygen functionalities. [PERSON] et al. converted the peripheral carboxylic acid functional groups of reduced GO to amino groups using _N_-hydroxysuccinimide and 1,3-diaminopropane [201]. The free radical polymerization initiator was anchored at the surface of GO sheets and RGO-PAM polymer brushes were synthesized via in situ free radical polymerization of acrylamide. Staudenmaier method was used to prepare GO which includes the treatment of graphite with potassium chlorate in the presence of concentrated nitric and sulfuric acid. After the stipulated period of time, the reaction mixture was added to an excess of water followed by repeatedly washing till the filtrate neutrality. Free radical initiator was attached onto the surface of thermally reduced GO and used to graft PAM resulting RGO-PAM composites. Two FT-IR absorption peaks at 1384 cm\({}^{-1}\) and 1446 cm\({}^{-1}\) were attributed with the symmetric and asymmetric bending vibrations of methylene groups of an initiator attached onto the surface of reduced GO, respectively. XPS N1s binding energy absorption peak at 399.1 eV indicated that surface grafting of a free radical initiator. Additionally, the absorption peak at 2242 cm\({}^{-1}\) also confirmed the grafting of an initiator. Asymmetric C-H stretching vibration at 2925 cm\({}^{-1}\) and C=O stretching vibration at 1647 cm\({}^{-1}\) were attributed with the grafting of PAM chains. Pb(II) ions were adsorbed onto the surface of RGO-PAM using dialysis and kinetics was studied since it gives deep knowledge insight the adsorption mechanism.