Micro-hydrogel Particles Consisting of Hyperbranched Polyamidoamine for the Removal of Heavy Metal Ions from Water

A series of micro-hydrogel particles consisting of hyperbranched polyamidoamine (HPAMAM) without any supporting core materials was synthesized via the inverse suspension condensation polymerization of A2 and B4 monomers, N,N′-methylenebisacrylamide (MBA) and ethylenediamine (EDA). The particles were found to be highly effective when used to remove heavy metal ions, such as cadmium, copper, lead, nickel, zinc, and cobalt, from water, and they could be separated from the water by a simple filtration process. The results of this study demonstrate that crosslinked HPAMAM particles, which can be prepared by a simple and environmentally friendly process, are an attractive absorbent for water purification.

1 H NMR spectra were recorded on a Bruker Fourier Transform Avance 400 spectrometer for the polymers dissolved in deuterium oxide. FT-IR spectra were obtained with a Bruker EQUINOX-55 spectrometer. Thermal stability studies of the particles were carried out using a TA 2200 thermal analyzer system with a scan rate of 10 o C min -1 under a flow nitrogen gas.
The morphology of the polymer particles was examined by optical microscopy (OM) and scanning electron microscopy (SEM). Copper ion binding capacities were measured by inductively coupled plasma optical emission spectrometer (Agilent ICP-OES 720).

Measurement of Swelling Ratio
We measured the swelling ratio (Q) by following procedure. The dry HPAMAM particles (Wdry) were placed in distilled water and kept there for at least 2 days to reach swelling equilibrium at room temperature. Equilibrated swollen HPAMAM particles were then removed from water and tapped with filter paper to dry the particle surface. And then the particles were collected and weighted (Ws). Swelling ratio (Q) was calculated from the following equation where Wdry and Ws are the weights of the dry sample and the swollen particles, respectively.

Measurement of Copper Ion Adsorption Capacity
Binding experiments were carried out in batches as follow. Stock copper solution was prepared as 10,000 ppm in distilled deionized water. The dry HPAMAM particles were placed in the stock heavy metal solution and kept there for at least 1 days to reach equilibrium at room temperature. The HPAMAM particles were separated from the metal solutions by filtration with cellulose nitrate membrane filters with a pore size of 0.45 μm. The concentration of metals in the filtrate was determined by using inductively coupled plasma optical emission spectrometer (Agilent ICP-OES 720). Copper ion binding capacity (A) was calculated from the following equation (2).

Copper ion binding capacity (
where m (g) is the weights of the dry sample, V (L) is the volume of the stock copper solution, C0 and Ce (g/L) are the initial and equilibrium copper ion concentrations, respectively.

Measurement of Gel Fraction
The dry HPAMAM particles (Wbefore) were placed in distilled water and stirred for at least 2 days to dissolve unreacted monomers and oligomers at room temperature. HPAMAM particles were then removed from water and tapped with filter paper and then dried under vacuum for 24hr at 60 o C. Then the weight of dry HPAMAM particles were measured (Wafter). Gel fraction was calculated from the following equation (3).

Metal Ion Adsorption Test Using Column Method
Glass column (Spectra/Chrom TM LC Column, diameter: 2.5 cm, volume: 4.91ml/cm) was prepared for our fixed-bed column adsorption test. 25g of P-M12/8S0.5R0.3k-500 particles were placed in glass column. In order to pack the PAMAM particles in glass column, water was injected to percolate through the column at the flow rate of 2.0 mL/min. Then, Cu 2+ aqueous solution was allowed to flow at each flow rate.

EDX analysis
Frozen HPAMAM particles with liquid nitrogen were broken by spatula, then cut HPAMAM particles were prepared for element analysis of inner part of HPAMAM particles. Element composition was determined by Hitachi SU8230.

Fig. S10
Effect of the reaction scale on swelling ratio (a) and Cu 2+ absorption capacity (b)