Nahit Aktas

Removal of toxic metal ions with magnetic hydrogels.

Hydrogels, based on 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) were synthesized via photopolymerization technique and used for the preparation of magnetic responsive composite hydrogels. These composite hydrogels with magnetic properties were further utilized for the removal of toxic metal ions such as Cd(II), Co(II), Fe(II), Pb(II), Ni(II), Cu(II) and Cr(III) from aqueous environments. It was revealed that hydrogel networks with magnetic properties can effectively be utilized in the removal of pollutants. The results verified that magnetic iron particle containing p(AMPS) hydrogel networks provide advantageous over conventional techniques. Langmuir and Freundlich adsorption isotherms were applied for toxic metal removal and both isotherms were fit reasonably well for the metal ion absorptions.

Optimization of removal conditions of copper ions from aqueous solutions by Trametes versicolor

A multi-step response surface methodology was successfully applied to optimize the biosorption conditions for the maximum removal of Cu(II) ions from aqueous solutions using Trametes versicolor fungi as a biosorbent. In the first step, the most effective medium factors, which are pH, temperature and initial Cu(II) concentration, on biosorption of Cu(II), were determined through Plackett-Burman Design. Then steepest accent followed by central composite design steps were utilized to evaluate the optimum biosorption conditions for the maximum Cu(II) ions removal. Based on the statistic analysis; the optimum conditions were obtained 5.51, 20.13 degrees C and 60.98 mg/L as medium pH, medium temperature and initial Cu(II) concentration, respectively. Finally the analysis of variance (ANOVA) of central composite design showed the proposed quadratic model fitted experimental data very well.

P(4-VP) based nanoparticles and composites with dual action as antimicrobial materials

Polymeric 4-VP (p(4-VP)) particles were synthesized in an oil-in-water microemulsion system using various amounts of ethylene glycol dimethacrylate (EGDMA) as crosslinker. The prepared p(4-VP) particles were chemically modified to obtain positively charged particles as polyelectrolytes. Furthermore, these p(4-VP) particles were used for in situ Ag and Cu metal nanoparticle syntheses to provide dual action with an additional advantage as bactericidal particles. The synthesized p(4-VP) particles with positive charges and metal constituents were tested for potential antibacterial action against various bacteria such as Staphylococcus aureus ATCC6538, Pseudomonas aeruginosa ATCC9027, Bacillus subtilis ATCC6633, Escherichia coli ATCC8739. It was found that p(4-VP) particles, especially the positively charged forms had potential as antibacterial materials. The synthesized particle dimensions were characterized with TEM, and DLS measurements. Chemical modification of the particles was confirmed by FT-IR spectroscopy and zeta potential measurements, and the metal nanoparticle contents were determined with thermogravimetric (TGA) studies.

Single step natural poly(tannic acid) particle preparation as multitalented biomaterial.

In this study, we report the preparation of poly(tannic acid) (p(TA)) particles by crosslinking with glycerol diglycidyl ether (GDE) and trimethylolpropane triglycidyl ether (TMPGDE). The p(TA) particles are negatively charged as obtained by the zeta potential measurements, -27mV. P(TA) particles are found to be an effective antioxidant material as 170mgL(-1) of p(TA) particle demonstrated the antioxidant equivalency of 82.5±7.2mgL(-1) of gallic acid (GA), used as standard in Folin-Ciocalteau (FC) method. Additionally, TA and p(TA) particles have a strong antimicrobial effect against Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, and Bacillus subtilis ATCC 6633. Furthermore, p(TA) particles were used as drug delivery materials by using model drugs such as TA itself, and GA in the release studies in PBS at pH7.4 at 37.5°C, and found that p(TA) particles can release 80.8 and 87.4% of the loaded TA and GA, respectively. Interestingly, p(TA) maintained its fluorescent property upon crosslinking of TA units. It is further demonstrated that p(TA) particles are as effective as cisplatin (a cancer drug) against A549 cancerous cells that both showed about 36 and 34% cell viability, respectively whereas linear TA showed 66% cell viability at 37.5μgmL(-1) concentration. Above this concentration p(TA) and cisplatin showed almost the same toxicity against A549 cancerous cells. Additionally, p(TA) particles are found to be much more biocompatible against L929 Fibroblast cells, about 84% cell viability in comparison to linear TA with about 53% at 75μgmL(-1) concentration.

Effects of reaction conditions on laccase-catalyzed α-naphthol polymerization

Enzymatic oxidative polymerization of α-naphthol was carried out batch-wise with the laccase enzyme, produced by Trametes versicolor (ATCC 200801). The polymerization reaction was conducted in a closed, temperature controlled system containing acetone (solvent) and sodium acetate buffer for pH control. The effects of the organic solvent (acetone) composition, monomer (α-naphthol) and enzyme concentrations, buffer pH and temperature on the polymerization rate were investigated with respect to initial reaction conditions and depletion rate of dissolved oxygen. The optimum acetone composition, pH, monomer, dissolved oxygen and enzyme concentrations were determined as 50% (v/v), 5, 3409 gm−3, 20.3 gm−3 and 0.173 U cm−3, respectively; these values provided the most desirable conditions for initial reaction rate. Temperature rise supported the rate increase up to 37 °C, after which the rate tended to be stable due to a drop in dissolved oxygen concentration. The product polymer, poly(α-naphthol), with an average molecular weight of 4920 Da was soluble in common organic solvents. © 2000 Society of Chemical Industry

Utilization of Environmentally Benign Hydrogels and Their Networks as Reactor Media in the Catalytic Reduction of Nitrophenols

Iron particles were synthesized inside poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) and used as a catalyst in the reduction of nitro benzene and 4-nitrophenol to aniline and 4-aminophenol, respectively, in acidic medium. It was demonstrated that hydrogel networks can be used effectively as catalysis media in the reduction of some organic toxic materials. The results verified that iron particles containing p(AMPS) hydrogel networks yield faster conversion rates. Additionally, iron nanoparticles containing p(AMPS) hydrogel networks could catalyze the reaction, giving 32% yield without any added cocatalyst, providing self cocatalyst mission.

Magnetic Co–Fe bimetallic nanoparticle containing modifiable microgels for the removal of heavy metal ions, organic dyes and herbicides from aqueous media

Poly(methacrylic-co-acrylonitrile) (p(MAc-co-AN)) microgels were prepared and nitrile groups were converted to amidoxime groups by chemical modification. Amidoximated microgels, amid-p(MAc-co-AN) microgels were used for in situ synthesis of cobalt–iron (Co–Fe) bimetallic magnetic nanoparticles by simultaneous reduction of Co(II) and Fe(II) ions within microgel. The prepared magnetic microgels as amid-mag-p(MAc-co-AN) microgel were found to be very effective adsorbents for the removal of metal ion such as Cd(II), Cr(III), and organic dyes e.g., methylene blue (MB), rhodamine 6G (R6G) and a herbicide, paraquat (PQ). A tremendous increase in the adsorption capacities of amid-p(MAc-co-AN) microgels was found as 88.1, 89.9, 190.0, 334.5 and 166.5 mg g−1 from 40.2, 37.4, 75.3, 57.4, and 56.3 for MB, R6G, PQ, Cd(II), and Cr(III), respectively. Moreover, a further increase in adsorption capacity of amid-mag-p(MAc-co-AN) microgel composites were also accomplished with the existence of magnetic particles. Adsorption of these contaminants from tap, river and seawater was also studied. The effects of different parameters i.e., pH, concentration of adsorbent solution and amount of adsorbate was also studied. Langmuir, Freundlich and Temkin adsorption models were applied, and the adsorption of Cd(II) and Cr(III) was found to obey Langmuir adsorption isotherm better.

Very fast catalytic reduction of 4-nitrophenol, methylene blue and eosin Y in natural waters using green chemistry: p(tannic acid)–Cu ionic liquid composites

Using tannic acid (TA) as a biopolymer, poly(tannic Acid) (p(TA)) microgels were obtained by cross-linking TA with trimethylolpropane triglycidyl ether (TMPGDE) as cross-linker in a water-in-oil micro emulsion system. Ionic liquid forms of p(TA) micro particles were prepared as Ionic Liquid Colloids (ILC) by post chemical modification of p(TA) particles using quaternization agents such as 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPACl) and ammonia (NH3) in aqueous solution to generate positively-charged ammonium salts on the network. Then the modified p(TA) micro particles were used as template for Co, Ni, and Cu metal nanoparticle preparation in situ after loading of metal salts such as CoCl2, NiCl2, and CuCl2 from ethyl alcohol solution into the p(TA) network, and consequent reduction with sodium borohydride (NaBH4). The prepared metal nanoparticle-containing ILCs of p(TA) microgel composites were used as catalysts in the reduction of toxic organic compounds such as 4-nitrophenol (4-NP), eosin Y (EY), and methylene blue (MB). Various parameters affecting the 4-NP and MB reduction were investigated. The activation energy, enthalpy, and entropy for the reduction of 4-NP to 4-AP catalyzed by ILC p(TA)-co composite catalyst system were calculated as 26.19 kJ mol−1, 23.12 kJ mol−1, and −182.35 J mol−1 K−1, respectively.

Biocompatible and biodegradable poly(Tannic Acid) hydrogel with antimicrobial and antioxidant properties

A novel resourceful bulk poly(Tannic Acid) (p(TA)) hydrogel was prepared by crosslinking TA molecules with an epoxy crosslinker, trimethylolpropane triglycidyl ether (TMPGDE), in an autoclave at 90°C for 2h. The obtained p(TA) hydrogels were in disk form and have highly porous morphology. The swelling characteristics of p(TA) hydrogels were investigated in wound healing pH conditions of pH 5.4, 7.4, and 9 at 37.5°C, and the hydrogels showed good swelling and moisture content behavior. Especially, p(TA) hydrogels were found to be sensitive to pH 9 with 1669% maximum swelling. P(TA) hydrogels were completely degraded at pH 9 hydrolytically in 9 days. Total phenol contents and the effects of scavenging ABTS(+) radicals of degraded p(TA) hydrogels at pH 5.4, 7.4, and 9 were evaluated and calculated in terms of gallic acid equivalent and trolox equivalent antioxidant capacity, respectively, and found to be very effective. Moreover, degraded p(TA) hydrogels display strong antimicrobial behavior against gram positive Staphylococcus aureus, Bacillus subtilis, gram negative Pseudomonas aeruginosa bacteria strains and Candida albicans fungus strain. The WST-1 results indicated that bulk p(TA) hydrogels have no cyctotoxicity to the L929 fibroblast cell line in vitro.

Hydrogels as a Potential Chromatographic System: Absorption, Speciation, and Separation of Chromium Species from Aqueous Media

Hydrogels with highly charged forms and amphiphilic character, based on an anionic monomer 2-acrylamido-2-methyl-1-propansulfonic acid sodium salt (AMPSNa) and a cationic monomer 3-acrylamidopropyltrimethylammoniumchloride (APTMACl), were synthesized via a photo-polymerization technique and investigated for potential use in the separation of chromium species with different oxidation states. They were used for three main purposes. First, a single chromium species was successfully removed from an aqueous medium in the presence of other forms using the appropriate design and synthesis of the hydrogels. Secondly, the copolymerized p(AMPSNa-co-APTMACl) hydrogels were used to remove two chromium species simultaneously from an aqueous medium. Lastly, in addition to speciation of the chromium species, their separation and removal by an externally applied magnetic field using magnetically responsive hydrogels was demonstrated.