Synthesis, Characterization andUtilization of Hydroxamic Acid Resins

Abstract

The aim of this study was to synthesize, characterize and utilize biopolymers based onhydroxamic acid chelating agents.Carboxymethyl cellulose (CMC) polymer and silica that are derived from biomass resources, were graft copolymerized with acrylamide and converted to polyhydroxamic acid resins. CMC was synthesized from cellulose that was purified after obtaining from corn cob husk fibers by etherification reaction using mono chloroacetic acid and sodium hydroxide. A degree of substitution (DS) of 0.77 was successfully achieved at a temperature of 55˚C, sodium hydroxide concentration of 40%, amount of mono chloroacetic acid of 3 grams per 1.5 grams of purified cellulose and a reaction period of 4 hours. The purified cellulose and CMC were characterized by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). FTIR spectra of CMC compared to that of the purified cellulose have displayed the presence of new characteristics peaks of carboxymethyl substituent at 1623 cm-1 and 1090 cm-1.TGA results of both polymers have shown three distinct mass losses. CMC was found to be less thermally stable compared to the purified cellulose. The XRD results indicated the conversion of the highly crystalline cellulose polymer in 2θ at20º-25ºinto an amorphous CMC by the drastic reduction in 2θ at 20º-25º from 140 to 48. Silica was synthesized from rice husk ash (RHA) using a sol-gel technique at room temperature. It was characterized using FTIR, TGA and XRD. Characteristics absorption bands of silanol and siloxane stretching vibrations as well as siloxane bending vibration appeared at 3465 cm-1, (1098, 834) cm-1 and 465 cm-1 respectively. TGA results displayed three distinct degradation stages at 100 ºC, 679 ºC and 800 ºC. The XRD results revealed the crystalline structure of silica (2θ values at 29.3º, 31.8º, 38.9º and 63.5º). CMC grafted polyacrylamide (PAAm), silica grafted PAAm and PAAm were obtained by a free-radical initiating process in which N, N-methylenebisacrylamide was used as a crosslinker and ammonium persulphate as an initiator. Conversion of the amide groups of the copolymers into hydroxamic acid was carried out by treating them with free hydroxylamine in an alkaline solution (pH>12) at 70˚C for 6 hours. The characterization of the poly(hydroxamic acid) chelating resins were performed by elemental analysis, FTIR, proton nuclear magnetic resonance (1HNMR) and TGA. The results of the elemental analysis havedemonstrated that CMC grafted hydroxamated polyacrylamide (HPAAM)is 18.50 % C, 2.53%, H and 6.75% N. whereas the silica grafted hydroxamated polyacrylamide (HPAAM) is 29.88% C, 4.85% Hand 10.64% N. Moreover, the hydroxamated polyacrylamide (HPAAM) is 29.71% C, 4.08% H and 12.66% N. Characteristics absorption bands of polyhydroxamic functional groups at 3100-3600cm-1 (OH), 1666-1690 cm-1 (C=O) and 3100-3600 cm-1(N-H) were obtained from FTIR spectrum. Furthermore, 1HNMR of CMC grafted HPAAM have shown four distinct signals that appeared at 2.3-2.7 ppm and 3.2-3.7 ppm attributed to methylene and methyne of the backbone of the CMC grafted HPAAM. The signal at 5.2 ppm is due to the proton of –NH group while the signal at 6.4 ppm is attributed to olefenic-protons signals. Silica grafted HPAAM has shown six distinct signals at 1.7 ppm, 2.3-2.7 ppm and 3.2-3.7 ppm that are attributed to methylene and methyne of the backbone of the silica grafted HPAAM. The signals 4.93, 4.94-5.2 ppm due to the proton of –NH group. The signal at 6.4 ppm is attributed to olefenic-protons signals. HPAAM has shown the disappearance of the olefenic protons and the presence of the characteristics signals of methylene and methyne of the main chain of the PAAm at 2.3-2.8 ppm and 3.2-3.7 ppm respectively. The thermal stability (TGA) of CMC grafted HPAAM, silica grafted HPAAM and HPAAM have shown three characteristics of mass losses and all hydroxamated resins are less thermally stable than their corresponding resins. The chelating reactivity of the prepared polyhydroxamic acid resins toward some metal ions were investigated using a batch technique at various pH values. Shows high binding capacities for vanadium and copper were excellent. The maximum binding capacity of these resins toward copper (II) achieved a value of 97.17%, 98.61% and 97.29 % at pH 5 after 24 hours equilibration, respectively, while the maximum binding capacity for vanadium (V) is 81.93% at pH 1, 81.16% and 97.08 % at pH 2 after 24 hours equilibration, respectively. Finally, it could be concluded that the metal ion-sorption capacities of the resins are pH-dependent and their selectivities toward the studied metal ions are in the following order copper (II)>vanadium (V)