A Novel Degradable Adsorbent of the Hyperbranched Aliphatic Polyester Grafted Cellulose for Heavy Metal Ions

Turk J Chem 31 (2007) , 457 – 462. c TÜBİTAK
A Novel Degradable Adsorbent of the Hyperbranched Aliphatic Polyester Grafted Cellulose for Heavy Metal Ions Peng LIU Institute of Polymer Science and Engineering, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. CHINA e-mail: Received 06.12.2006 A novel degradable adsorbent for the removal of heavy metal ions from waste water, a hyperbranched aliphatic polyester grafted cellulose (HAPE-Cell), was successfully prepared by the simple one-pot method for the first time. The hyperbranched aliphatic polyester was grafted from the surface hydroxyl groups of natural cotton fibers via the solution polycondensation of the AB2 monomer, 2, 2bis(hydroxymethyl)propionic acid (bis-MPA), with the catalysis of p-toluenesulfonic acid (p-TSA). The HAPE-Cell was characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The adsorption properties of the HAPE-Cell towards the heavy metal ions (Cu(II), Hg(II), Zn(II), and Cd(II)) were also preliminarily investigated. Key Words: Hyperbranched aliphatic polyester, graft, cotton fiber, adsorbent, heavy metal ions. Introduction Cellulose is an abundant, naturally occurring, and promising low-cost material. Its modification by grafting with different vinyl monomers gives new materials for selectively permeable membranes,1 drug delivery,2 outstanding sorption agents,3−5 and enzyme immobilization.6 The modification of cellulose fibers by the grafting of vinyl polymers has been achieved by the readymade functional end-group terminated polymers, and with the surface groups of the fibers via graftingonto methods,7 or grafting-from methods, from the surface polymerizable groups8 or the surface initiating groups.9−13 The other polymers have also been grafted from the surface of the natural fibers with ringopening polymerization14 and direct condensation polymerization.15 Hyperbranched polymers are macromolecular compounds built from multifunctional monomers ABn , where the function A can couple with the function B, as proposed16 and demonstrated.17 In the last decade, the study and use of novel hyperbranched polymers for applications at surfaces and interfaces has grown.18−20 Hyperbranched polymers have been fabricated from the flat surfaces or the surfaces of porous particles for many applications, including microcolumn packing for the on-line preconcentration and separation of the 457 A Novel Degradable Adsorbent of the Hyperbranched..., P. LIU noble metal ions,21 the chiral stationary phase in HPLC,22 effective catalysts for hydroformylation and Heck reaction by being complexed with Rh and Pd,23 designable size exclusion chromatography columns,24 corrosion-resistant coatings and chemical sensing,25 photoacid-based lithography,26 and electrostatic immobilization of glucose oxidase.27 In the present work, the hyperbranched aliphatic polyester was successfully grafted for the first time from the surface hydroxyl groups of natural cotton fibers using the one-pot method via the solution polycondensation of the AB2 monomer, 2, 2-bis(hydroxymethyl)propionic acid (bis-MPA), with the catalysis of p-toluenesulfonic acid (p-TSA). The HAPE-Cell is a novel degradable adsorbent for the removal of heavy metal ions from waste water. Experimental Chemicals The cotton fiber used was absorbent cotton obtained from Shanghai Medicine Chemical Co. (Shanghai, China) and was washed with methanol, acetone, deionized water, and then dried in a vacuum oven maintained at room temperature. p-Toluenesulfonic acid (pTSA) and 2, 2-bis(hydroxymethyl)propionic acid (bis-MPA) were all analytical grade and were used as received from Tianjin Chemical Co. (Tianjin, China). Toluene, dimethyl formamide (DMF), and other solvents used were all analytical grade. Preparation of HAPE-Cell The HAPE-Cell was prepared with the following one-pot method, as previously reported:28 2.0 g of natural cotton fiber (bare Cell), 0.20 g of p-toluenesulfonic acid (pTSA), 1.0 g of bis-MPA, and 20 mL of dimethyl formamide (DMF) were mixed and refluxed for 6 h with N2 bubbling throughout. The product, a mixture of HAPE-Cell and non-grafted HAPE, was precipitated in water. The HAPECell was separated from the non-grafted HAPE by extraction with DMF, after keeping the crude on a Soxhlet apparatus until constant weight was achieved. Then, the HAPE-Cell was washed with ethanol and dried in a vacuum oven maintained at room temperature. The ideal structure of the HAPE-Cell is shown in Figure 1. O CH2O CH2 O C - C - CH3 CH2O O - C - C - CH3 CH2O CH2 O C - C - CH3 CH2O O O n Figure 1. The ideal structure of the HAPE-Cell. Characterization and analysis Elemental analysis (EA) of C and H was performed on an Elementar Vario EL instrument. A Bruker IFS 66 v/s infrared spectrometer was used for the Fourier transform infrared (FT-IR) spectroscopy analysis. X-ray diffraction (XRD) analysis was carried out with a Shimadzu XRD 6000 with Cu Kα radiation, operated at 50 kV and 80 mA over the range of 10◦ < 2θ◦ < 100◦ . The surface morphology of the fibers was observed using 458 A Novel Degradable Adsorbent of the Hyperbranched..., P. LIU scanning electron microscopy (SEM) (XL-20, Philips Corporation, the Netherlands), operating at 25 kV. The grafting parameters were estimated from the results of elemental analyses. The percentage of grafting (PG%) was calculated according to the following relationships: PG% = HAPE grafted (g)/cotton charged (g) × 100% Competitive adsorption of the heavy metal ions The heavy metal ions’ competitive uptake capacities of the bare Cell and HAPE-Cell were determined preliminary as follows: 1.0 g of fiber (bare Cell or HAPE-Cell) was wetted separately with 5 mL of distilled water for 24 h. Then, 30 mL of heavy metal ion mixture solution (containing Cu(II), Zn(II), Cd(II), and Hg(II) with the same concentration of 1.0 mg/mL in HNO3 media (pH 3.0)) was added and the mixture was shaken for 1 h at room temperature. Then, the supernatant solutions were taken out for the determination using ICP-OES performed with a Perkin-Elmer ICP/6500 inductively-coupled plasma spectrometer (RF power supply: 1100 w; Ar plasma gas flow: 14.0 L min−1 ; Ar auxiliary gas flow: 0.5 L min−1 ; Ar nebulizer gas flow: 1.0 L min−1 ; viewing height: 11 mm; detection line: Cu 327.3 nm, Hg 194.2 nm, Zn 213.8 nm, and Cd 226.5 nm). Results and Discussion The hyperbranched polymers derived from 2,2-bis(hydroxymethyl)propionic acid were previously studied with multi-hydroxyl molecules, such as 2-ethyl-2-(hydroxymethyl)-1,3-propanediol,28 1,1,1-tri(hydroxyphenyl) ethane,29 and Boltorn H4030 as the core. Differing from those works, a degradable, natural, carbohydrate polymer cotton fiber was used as the core in the present work. In the condensation polymerization, the carboxyl groups of the monomers or oligomers reacted with the hydroxyl groups of the other monomers a (...truncated)