Oxide Nanocomposite Hydrogels Research Articles

Poly(vinyl alcohol)/poly(acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels for pH-sensitive photocatalytic degradation of organic pollutants

Poly(vinyl alcohol)/poly(acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels were prepared using radical polymerization and condensation reaction for the photocatalytic treatment of waste water. Graphene oxide was used as an additive to improve the photocatalytic activity of poly(vinyl alcohol)/poly(acrylic acid)/TiO2 nanocomposite hydrogels. Both TiO2 and graphene oxide were immobilized in poly(vinyl alcohol)/poly(acrylic acid) hydrogel matrix for an easier recovery after the waste water treatment. The photocatalytic activity of poly(vinyl alcohol)/poly(acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels was evaluated on the base of the degradation of pollutants by using UV spectrometer. The improved removal of pollutants was due to the two-step mechanism based on the adsorption of pollutants by nanocomposite hydrogel and the effective decomposition of pollutants by TiO2 and graphene oxide. The highest swelling of nanocomposite hydrogel was observed at pH 10 indicating that poly(vinyl alcohol)/poly(acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels were suitable as a promising system for the treatment of basic waste water.

Thermo-responsive behavior of radiation-induced poly(N-isopropylacrylamide)/polyethylene oxide nanocomposite

Temperature-sensitive poly(N-isopropylacrylamide)/polyethylene oxide (PNIPAAm/PEO) nanocomposite hydrogels were successfully synthesized using γ-radiation as the initiator and crosslinking agent. The temperature-dependent swelling and shrinking behavior of PNIPAAm/PEO was exploited in order to form silver nanoparticles within the hydrogel network. Loading-temperature-responsive hybrid microgels containing silver nanoparticles (AgNPs) were readily prepared by the in situ reduction of Ag+ ions within and coordinated to PNIPAAm/PEO hydrogels. A novel method—irradiation—was utilized to generate AgNPs within the previously obtained hydrogel matrix. The newly prepared Ag-NPs/PNIPAAm/PEO hydrogels exhibited much better temperature-sensitive properties than conventional polymers. The PNIPAAm hydrogels thus prepared exhibited properties such as pore size, equilibrium swelling ratio, and swelling/deswelling rates that could be varied by modifying the feed weight ratio of NIPAAm to PEO. UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) measurements confirmed that the hydrogel possessed nanostructure, and FTIR was employed to characterize the components of the resulting nanoobjects. The hydrodynamic diameter and morphology of the microgel particles were examined by dynamic light scattering (DLS) and scanning electron microscopy (SEM), respectively. At room temperature, the hydrodynamic diameter of the PNIPAAm/PEO polymer was measured as 3.0 ± 0.7 μm, while that of the PNIPAAm/PEO-stabilized AgNPs was found to be 1.8 ± 0.1 μm. Twenty-five percent of the silver nanoparticles were less than 64.9 nm in diameter, and the mean of the particle size was 9.6 nm. These stimuli-responsive nanocomposite hydrogels have potential applications in biomedicine; for example, they could be used as drug-delivery matrices.

Temperature-sensitive poly(N-isopropylacrylamide)/graphene oxide nanocomposite hydrogels by in situ polymerization with improved swelling capability and mechanical behavior

To improve the performance of temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) hydrogels, graphene oxide (GO) was selected as a nano strengthening agent to prepare nanocomposite hydrogels. For fulfilling this purpose, in situ polymerization was carried out in colloid solution of graphene oxide, where N-isopropylacrylamide as temperature-sensitive monomer and N,N′-methylene bisacrylamide as crosslinker was initiated utilizing potassium persulfate and sodium sulfite as redox initiators. Infrared spectroscopy and transmission electron microscope was employed to characterize the structure of GO and its dispersibility in water respectively. The internal network structure of nanocomposite hydrogels was investigated by scanning electron microscope (SEM). The temperature-sensitivity, swelling and deswelling properties and mechanical performance of the as-prepared nanocomposite hydrogels was investigated preliminarily. Experimental results show that the nanocomposite hydrogels prepared not only possess good temperature-sensitivity but improved swelling capabilities. The volume-phase transition temperatures of most composite hydrogels are shifted to higher temperature than PNIPAM hydrogels. Furthermore, addition of appropriate amount of GO can dramatically enhance the mechanical performance of PNIPAM hydrogels. The compressive strength of nanocomposite hydrogels reaches a maximum of 216kPa when the weight ratio of GO to NIPAM is ∼5%, which is 4 times larger than that of PNIPAM hydrogels (54kPa). The advantageous performance of nanocomposite hydrogels over PNIPAM hydrogels is very beneficial for future applications.

Hydrogels: Photothermally Sensitive Poly(N‐isopropylacrylamide)/Graphene Oxide Nanocomposite Hydrogels as Remote Light‐Controlled Liquid Microvalves (Adv. Funct. Mater. 19/2012)

Hydrogels: Photothermally Sensitive Poly(<i>N</i>‐isopropylacrylamide)/Graphene Oxide Nanocomposite Hydrogels as Remote Light‐Controlled Liquid Microvalves (Adv. Funct. Mater. 19/2012)

Photothermally Sensitive Poly(N‐isopropylacrylamide)/Graphene Oxide Nanocomposite Hydrogels as Remote Light‐Controlled Liquid Microvalves

AbstractA photothermally sensitive poly(N‐isopropylacrylamide)/graphene oxide (PNIPAM/GO) nanocomposite hydrogel can be synthesized by in situ γ‐irradiation‐assisted polymerization of an aqueous solution of N‐isopropylacrylamide monomer in the presence of graphene oxide (GO). The colors and phase‐transition temperatures of the PNIPAM/GO hydrogels change with different GO doping levels. Due to the high optical absorbance of the GO, the nanocomposite hydrogel shows excellent photothermal properties, where its phase transitions can be controlled remotely by near‐infrared (NIR) laser irradiation, and it is completely reversible via laser exposure or non‐exposure. With a higher GO loading, the NIR‐induced temperature of the nanocomposite hydrogel increases more quickly than with a lower doping level and the temperature can be tuned effectively by the irradiation time. The nanocomposite hydrogel with its excellent photothermal properties will have great applications in the biomedical field, especially as microfluidic devices; this has been demonstrated in our experiments by way of remote microvalves to control fluidic flow. Such an “easy” and “clean” synthetic procedure initiated by γ‐irradiation can be extended for the efficient synthesis of other nanocomposite materials.

Tough and highly stretchable graphene oxide/polyacrylamide nanocomposite hydrogels

Polyacrylamide (PAM)/graphene oxide (GO) nanocomposite hydrogels (PGH) with GO nanosheets as cross-linkers were synthesized via in situ free radical polymerization of acrylamide in an aqueous suspension of GO. The tensile properties of the hydrogels were investigated in terms of type and content of cross-linkers. Compared to conventional PAM hydrogels (PBH) cross-linked chemically with N,N′-methylenebisacrylamide, PGH exhibits high tensile strength, high toughness and especially a large elongation at break. The tensile strength of PGH is about 4.5 times higher than that of PBH, and the elongation at break is over 3000%, nearly one order higher than that of PBH even when the content of GO is only 0.0079 wt%. By analyzing the cross-linked structure of PGH and the theoretical calculation on the number of cross-linked polymer chains per unit volume of gels, a structure model was thus proposed.