Article pubs.acs.org/Langmuir
Synthesis, Characterization, and Catalytic Properties of Cationic Hydrogels Containing Copper(II) and Cobalt(II) Ions Lucía Victoria Lombardo Lupano,† Juan Manuel Lázaro Martínez,*,‡ Lidia Leonor Piehl,§ Emilio Rubín de Celis,§ Rosa María Torres Sánchez,∥ and Viviana Campo Dall’ Orto*,† †
IQUIFIB-CONICET & Departamento de Química Analítica y Fisicoquímica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín, 956 (1113) CABA, Argentina ‡ CONICET, Av. Rivadavia 1917 (1033), CABA, Argentina & Departamento de Química Orgánica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín, 956 (1113) CABA, Argentina § Departamento de Fisicomatemática, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín, 956 (1113) CABA, Argentina ∥ CETMIC−CONICET, Camino Centenario y 506, M. B. Gonnet, 1897, Argentina S Supporting Information *
ABSTRACT: Here, we report the synthesis and characterization of a hydrogel based on ethylene glycol diglycidyl ether (EGDE) and 1,8-diamino-3,6-dioxaoctane (DA). Chemically stable Co(II) and Cu(II) coordination complexes were prepared with this nonsoluble polyelectrolyte, poly(EGDEDA), and studied by ss-NMR, FT-IR, thermogravimetry, and microscopy. Mesopores were found in all the samples, the thermal stability of the polymer matrix was highly affected by the presence of metal ions, and the 13C CP-MAS spectrum for the Cu(II)-complex evidenced a significant increase in the reticulation degree by Cu(II) ions. The catalytic activity of these materials on H2O2 activation was studied by electron spin resonance (ESR). The Co(II)-poly(EGDE-DA)/H2O2 heterogeneous system produced O2, an anion superoxide (O2•¯), and a hydroxyl radical (OH•), which diffused into the solution at the time that a decrease in pH was detected. In the same way, the Cu(II)-poly(EGDE-DA)/H2O2 heterogeneous system produced O2 and OH•. H2O2 activation by the poly(EGDE-DA) complexes with Co(II) and Cu(II) were applied on the decolorization of solutions of the azo-dye methyl orange (MO). In the presence of 63 mM H2O2, 87% of MO was removed in 10 min with Cu(II)-poly(EGDE-DA) and in 110 min with Co(II)-poly(EGDE-DA). In addition, the pharmaceutical product epinephrine was partially oxidized to adrenochrome by the O2•¯ released from the Co(II)-poly(EGDE-DA)/H2O2 heterogeneous system.
1. INTRODUCTION The coordination of a polymeric ligand by a transition metal ion is an efficient way to obtain processable materials with unique and valuable properties. Polymer networks offer new possibilities to scientists for the creation of artificial materials. In recent years, hydrogels with chelating ligands attracted the attention for industrial applications.1 In particular, polyelectrolyte and polyampholyte hydrogels have become of great interest in the macromolecular chemistry area due to their versatility as excellent adsorbents of chemical compounds.2 Stimuli-sensitive hydrogels are used in a variety of novel applications, including controlled drug delivery, immobilized enzyme systems, separation processes, fuel cells, and sensor development.3,4 We have previously demonstrated that nonsoluble polymers can be prepared from ethylene glycol diglycidyl ether (EGDE) using methacrylic acid (MAA) and/or N-heterocycles. The synthetic process involves the opening of the epoxy groups © XXXX American Chemical Society
from EGDE by the reaction with MAA, and a peroxide-initiated radical polymerization of MAA segments covalently bound to EGDE to give a polyelectrolyte [poly(EGDE-MAA)]. When imidazole (IM) is added to the reaction mixture, the epoxy groups are opened up by both the carboxylic acid of the MAA and the pyridine-type nitrogen of the N-heterocycle, yielding a polyampholyte [poly(EGDE-MAA-IM)].5−7 When EGDE and IM are mixed in the absence of the radical polymerization initiator [poly(EGDE-IM)], a polyelectrolyte is also synthesized. The respective polyampholytes and polyelectrolytes were derived from a variety of N-heterocycles such as 2methylimidazole (2MI), pyrazole (PYR), and triazole (TRZ).8,9 These materials offer the versatility to complex different metal ions due to the presence of the imidazole ligand, Received: December 17, 2013 Revised: January 28, 2014
A
dx.doi.org/10.1021/la404799t | Langmuir XXXX, XXX, XXX−XXX
Langmuir
Article
The FT-IR spectra of the polymers and their copper complexes were recorded on a Nicolet 380 spectrometer using KBr pellets. SEM imaging and EDS were carried out with a scanning electron microscope field emission SEM (Zeiss Gemini DSM 982) operated at a 0.3 kV acceleration voltage and an INCA Energy (Oxford Instrument), respectively. Elemental analysis was performed with a Carlo Erba EA 1108 device. A nitrogen adsorption isotherm was collected at 77 K on a Micromeritics Gemini 2360 system. Specific surface area was calculated using the BET (Brunauer−Emmett− Teller) equation. The electron spin resonance (ESR) spectra were obtained at 20 °C using an X-band ESR Spectrometer Bruker EMX plus (Bruker Instruments, Inc., Berlin, Germany). Partial pressure of O2 was measured with an Orbisphere A1100-Oxygen Sensor. UV− visible spectrophotometric measurements were made on a HewlettPackard instrument, HP 8452A model with diode array. The isoelectric point (IEP) value was obtained by diffusion potential determination as described elsewhere.18 Electromotive force (EMF) measurements were carried out with a Keithley 616 digital electrometer instrument with Metrohm calomel electrodes. Potentiometric titration of the polyelectrolyte was performed with a HANNA Instrument pH meter as elsewhere.5,6 2.3. Synthesis of Poly(EGDE−DA). An aliquot of 176 μL (1.2 mmol) of 1,8-diamino-3,6-dioxaoctane (DA) and 0.4 mL (1.28 mmol) of ethylene glycol diglycidyl ether (EGDE; 50 wt % in ethylene glycol dimethyl ether) was mixed with 0.4 mL of acetonitrile. The solution was placed in a tube glass and thermostatted at 60 °C for 24 h. The product was placed at 20 °C, milled, washed three times with distilled water, and dried at 60 °C during 24 h. The polyelectrolyte was used without further purification. 2.4. Swelling Equilibrium. Equilibrium swelling measurements were performed in triplicate at pH 3.00 with an ionic strength (I) of 0.50 and
