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Öğe A facile synthesis route to improve the catalytic activity of inherently cationic and magnetic catalyst systems for hydrogen generation from sodium borohydride hydrolysis(Elsevier Science Bv, 2015) Şahiner, Nurettin; Seven, FahriyeInherently cationic poly(3-acrylamidoproply)trimethylammonium chloride) (p(APTMACl)) as hydrogel and cryogel as nonporous and superporous structures to use as template for cobalt and Nickel metal nanoparticle preparation and then H-2 production from NaBH4 hydrolysis. Use of p(APTMACl) hydrogels in H-2 generation reactions from hydrolysis is an advantage due to their inherently cationic nature and no requirement for any modification/quaternization steps to load metal salts for in situ metal nanoparticle preparation. However, it is very well known that the metal loading processes of p(APTMACl) hydrogels are very slow. Therefore, the superporous cryogels prepared from p(APTMACl) offered great advantages in terms of swelling, metal absorption for in situ metal nanoparticle preparation, and then higher catalytic activity in hydrolysis of NaBH4. The p(APTMACl) cryogels and their metal composites provide 32, 3600, 1.5, 5.5 and 3.5 fold faster swelling degree, swelling time, metal absorption capacity, metal absorption time and H-2 generation rate, respectively than hydrogels and metal composites. In addition, p(APTMACl)-Co metal composites are shown to have highly useful characteristics in H-2 generation reaction from hydrolysis of NaBH4, due to their innate magnetic character, which allows control by an externally applied magnetic field, and reusability, with almost 80% at the end of 5th use. (C) 2014 Elsevier B.V. All rights reserved.Öğe A simple post modification method for novel porous superabsorbent p(acrylamide) hydrogels and their H2 production(Springer, 2014) Seven, Fahriye; Şahiner, NurettinPoly(Acrylamide) (AAm) hydrogels were synthesized in bulk and reacted with NH2OH center dot HCl to develop a new functional group to confer high swelling, porosity and high metal ion binding abilities. The chemically-modified hydrogels, denoted as amidoximated poly(Acrylamide) (amid-p(AAm)) showed increased water swelling ability of up to 16-fold. The chemical modification induced structural changes were examined by FT-IR spectroscopy, water and pH swelling experiments, optical microscope images, titration studies, and even TG analysis. The amid-p(AAm) hydrogels were used as template for absorption of Co(II) and Ni(II) ions from their aqueous solutions and treated with aqueous NaBH4 for in situ metal nanoparticle preparation of the corresponding ions within the amid-p(AAm) matrices. The amid-p(AAm)-M (M:Co or Ni) composites were then used as catalyst in the hydrolysis of NaBH4 for H-2 generation, and their catalytic performances were investigated. Various parameters for the hydrolysis of NaBH4 such as functionality of polymer matrices, the types of metal nanoparticles, metal catalyst amounts within hydrogel matrices, and temperature were investigated. Considerably low activation energy in comparison to similar studies in the literature were calculated for NaBH4 hydrolysis by amid-p(AAm)Co metal composite systems: E-a=17.26 +/- 0.06.Öğe Effects of size, structure, charge, and porosity of hydrogel-metal composite catalyst systems on hydrogen generation from the hydrolysis of NaBH4(Amer Chemical Soc, 2013) Şahiner, Nurettin; Seven, Fahriye; Turhan, Tuğce; Karacan, Elif; Cağlar, AyselÖğe Energy and environmental usage of super porous poly(2-acrylamido-2-methyl-1-propan sulfonic acid) cryogel support(Royal Soc Chemistry, 2014) Şahiner, Nurettin; Seven, FahriyeSuperporous and nonporous poly(2-acrylamido-2-methyl-1-propansulfonic acid) [p(AMPS)] cryogels and hydrogels were prepared under freezing conditions (-18 degrees C) and at room temperature (25 degrees C), respectively. The swelling equilibrium values of the p(AMPS) cryogels were extremely fast, 3600 fold faster than those of conventional hydrogels. The p(AMPS) cryogels were further employed as highly effective supports for the in situ preparation of metal nanoparticles within superporous networks, by loading Co(II) and Ni(II) ions into the cryogel network from aqueous environments and reducing with NaBH4. The Co metal nanoparticle-containing cryogel composites demonstrated superior catalytic performances in comparison to nonporous p(AMPS) hydrogel composites for energy and environmental applications e. g., hydrogen production from the hydrolysis of sodium borohydride, and reduction of 4-nitrophenol to 4-aminophenol. The energy applications of cryogel-based p(AMPS)-Co metal composites, especially, were investigated in detail. The effect of various parameters on the rate of the hydrogen generation reaction, such as porosity, metal types, pH, the types of reaction water, temperature and reuse of catalyst, were examined for the p(AMPS)-Co cryogel composite materials. With the p(AMPS)-Co cryogel composite a very high hydrogen generation rate of 14 501 mL H-2 per min per g of Co was attained. This value is one of the best recorded values in comparison to the values obtained for other similar catalysts reported in the literature. p(AMPS)-Co composite cryogels were repeatedly used without significant loss of catalytic activity (82%) even after five repetitive uses for catalytic hydrolysis reactions with NaBH4. Additionally, a very low activation energy for the p(AMPS)-Co cryogel composite systems was attained: E-a = 15.40 +/- 0.3 kJ mol(-1).Öğe Enhanced catalytic performance in hydrogen generation from NaBH4 hydrolysis by super porous cryogel supported Co and Ni catalysts(Elsevier, 2014) Seven, Fahriye; Şahiner, NurettinThe neutral 3-D superporous cryogel is prepared from a poly(acrylamide) (p(AAm)) hydrogel network modified with an amidoximation reaction to induce chemical changes to produce superporous amidoximated-p(AAm) (amid-p(AAm)) cryogel. The newly-formed strongly ionizable matrices can readily absorb metal ions such as Co(II) and Ni(II) enabling in situ preparation of corresponding metal nanoparticles by NaBH4 treatments. It is found that the superporous amid-p(AAm)-Co cryogel composite is very effective as a catalyst for H-2 generation from hydrolysis of NaBH4 in alkaline medium. Furthermore, it is demonstrated that the metal ion loading capacity and catalytic activity of superporous amid-p(AAm)-Co cryogel composites increased with 2nd and 3rd Co(II) ion loading and reduction cycles. The hydrogen generation rate of p(AAm)-Co metal composites is increased to 1926.3 +/- 1.1 from 1130.2 +/- 1.5 (mL H-2) (min)(-1) (g of M)(-1). The effect of various parameters such as porosity, metal type, the number of reloading and reduction cycles of the metal ion, and temperature are investigated for the hydrolysis of NaBH4. The kinetic parameters such as energy, enthalpy and entropy are determined as Ea = 39.7 +/- 0.2 kJ mol(-1), Delta H = 37.2 +/- 0.1 kJ mol(-1) and Delta S = -171.9 +/- 0.5 J mol(-1) K-1, respectively. (C) 2014 Elsevier B.V. All rights reserved.Öğe Imprinting hydrogels with metal ions for metal nanoparticle preparation and use in hydrogen production as catalysis media(Amer Chemical Soc, 2013) Seven, Fahriye; Yetişkin, Berkant; Turhan, Tuğce; Karacan, Elif; Şahiner, NurettinÖğe Kriyojellerin sentezi, karakterizasyonu ve bazı uygulamaları(Çanakkale Onsekiz Mart Üniversitesi, 2014) Seven, Fahriye; Şahiner, NurettinBu tez çalışması kapsamında kriyopolimerizasyon yöntemine göre sentezlenen süpergözenekli p(AMPS), p(VI), p(AAm) ve p(HEMA) kriyojelleri bazı katalitik çevre ve enerji uygulamalarında katalizör destek maddeleri olarak kullanılmışlardır. Bazik ve nötral fonksiyonelliğe sahip kriyojellere çeşitli modifikasyon yöntemleri uygulanarak metal iyonlarını tutma özelliği kazandırılmıştır. Süpergözenekli kriyojel ağ yapıları içerisinde güçlü indirgeyici ajan sodyum bor hidrür (NaBH4) kullanılarak kobalt (Co), nikel (Ni) ve bakır (Cu) gibi çeşitli metal nanopartiküller sentezlenmiştir. Kriyojeller ve metal kompozitleri, şişme çalışmaları, optik mikroskop, SEM ve TEM görüntüleri, FT-IR, AAS ve TGA analizleri gibi çeşitli yöntemlerle karakterize edilmiştir. Sentezlenen kriyojel-metal kompozit malzemeler NaBH4 ve amonyum boren (NH3BH3) gibi kimyasal hidrürlerin hidrolizinden hidrojen (H2) üretimi ve metilen mavisi (MB), eozin Y (EY) boyar maddeleri, 2- ve 4-nitrofenol (2- ve 4-NP) gibi toksik bileşiklerin indirgenme reaksiyonuyla giderimi çalışmalarında katalizör olarak kullanılmışlardır. Bor hidrür bileşiklerinin hidrolizinden H2 üretimi ve toksik bileşiklerin indirgenmesi reaksiyonlarına gözeneklilik, metal nanopartikül türü, metal nanopartikül miktarı, sıcaklık vb birçok parametrenin etkisi detaylı olarak incelenmiştir. Süpergözenekli kompozit malzemelerin bor bileşiklerinin hidrolizinden H2 üretimi ve toksik bileşiklerin giderimi reaksiyonlarına ait hidrojen üretimi hızı (HGR) ve toplam dönüşüm frekansı (TOF) gibi hız değerleri ve aktivasyon enerji (Ea), entalpi (?H) ve entropileri (?S) gibi aktivasyon parametreleri hesaplanmıştır. Süpergözenekli kriyojel destekli katalizörlerin literatürde yer alan benzer katalitik çalışmalarla kıyaslanabilen oldukça iyi katalitik performans değerlerine sahip oldukları bulunmuştur. Kriyojellerin yapı ve fonksiyonelliğine bağlı olarak kriyojel-Co metal kompozitlerin bor bileşiklerinin hidrolizinden H2 üretimi ve toksik bileşiklerin indirgenme reaksiyonlarına ait 15-40 kjmol-1 arasında değişen aktivasyon enerjisi (Ea) değerleri elde edilmiştir.Öğe Metal ion-imprinted hydrogel with magnetic properties and enhanced catalytic performances in hydrolysis of NaBH4 and NH3BH3(Pergamon-Elsevier Science Ltd, 2013) Seven, Fahriye; Şahiner, NurettinMetal ion-imprinted (IIH) poly(2-acrylamido-2-methyl-1-propansulfonic acid) p(AMPS) hydrogels were prepared by using a free-radical polymerization technique in the presence of metal ions (M = Co (II) or Ni (II)). Using metal ion-imprinted hydrogels (IIHs), and non-metal ion-imprinted (NIH) hydrogels as template for the preparation of Co and Ni catalyst systems, the hydrolysis kinetics of NaBH4 and NH3BH3 were investigated. The catalytic performances of IIHs and NIHs were compared in terms of effect on hydrolysis kinetics of NaBH4 and NH3BH3. To increase the amounts of Co nanoparticles within p(AMPS) hydrogel for better catalytic activity, several reloading and reduction cycles of Co (II) ions were carried out, and the prepared p(AMPS)-Co composite catalyst systems were tested for hydrogen generation from the hydrolysis of NaBH4. As the number of Co (II) loading and reduction cycles increased, the amount of metal catalysts and the catalytic performance of composites increased. Kinetics studies were carried out on three times Co (II) ion loaded and reduced p(AMPS)-Co catalyst systems (containing 36.80 mg/g Co). Three time Co (II)-loaded catalyst systems provided very fast hydrolysis kinetics for NaBH4, and provided magnetic field responsive behavior. The hydrolysis reaction of NaBH4 was completed within 50 s, under the described conditions at 60 degrees C. It was demonstrated that the synthesized catalyst systems can be used ten times repetitively without significant loss of catalytic activity (86.5%). Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Modified macroporous P(2-hydroxyethyl methacrylate) P(HEMA) cryogel composites for H2 production from hydrolysis of NaBH4(Elsevier Science Bv, 2014) Seven, Fahriye; Şahiner, NurettinMacroporous p(2-hydroxyethyl methacrirlate) p(HEMA) cryogel was synthesized at 18 degrees C via cryopolymerization technique and chemically modified with a quaternization agent (QA), 3-chloro-2hydroxypropyl trimethyl ammonium chloride in basic medium to produce Q-p(HEMA). Then superporous p(HEMA) cryogel was used as template for in situ Co and Ni metal nanoparticle preparation and used as soft reactors in H-2 generation reactions from hydrolysis of NaBH4. To increase the catalyst contents of the cryogel composites, multiple metal ion loading and reduction steps were carried out for faster H-2, generation from the hydrolysis reaction. The effects of several parameters, such as number of reloading-reduction cycles (1st, 2nd and 3rd), metal nanoparticle types, concentration of NaBH4, alkalinity of reaction medium, and temperature on the H-2 generation reactions were investigated. It was found that the 3rd time Co(II) loaded-reduced Q-p(HEMA)-Co cryogel composite is highly active as the turn over frequency (TOF) and the hydrogen generation rate (HGR) values were 62.9 +/- 1.8 (mot H-2) (mol catalyst minri and 26,641.0 +/- 3.6 (ml H-2) (min)(-1) (g of M)(-1) at 70 degrees C which is even better than the fastest known catalyst, ruthenium. (C) 2014 Elsevier B.V. All rights reserved.Öğe NaOH Modified P(acrylamide) Hydrogel Matrices for In Situ Metal Nanoparticles Preparation and Their Use in H2 Generation from Hydrolysis of NaBH4(Wiley-Blackwell, 2014) Seven, Fahriye; Şahiner, NurettinCrosslinked poly(acrylamide) (p(AAm)) as neutral hydrogel is synthesized via photo polymerization technique, and the amide groups within p(AAm) matrices are converted to strongly ionizable carboxylic acids groups via facile modification route by simple treatment of NaOH to obtained NaOH-p(AAm) hydrogels. Because of the highly ionizable nature of carboxylate groups within mod-p(AAm), the swelling and metal ion absorbing capacities are increased tremendously, almost 40 and 7.5 folds, respectively. The Co(II) and Ni(II) metal ions are loaded into NaOH-p(AAm) hydrogels, and are treated with NaBH4 to form corresponding metal nanoparticles in situ within mod-p(AAm) matrices, and used in H-2 generation production from hydrolysis of NaBH4. Various parameters such as functionality of polymeric matrices, the kinds and the amount of metal nanoparticles, and the temperature effecting the H-2 generation are investigated. Comparable low E-a with the similar researches in the literature, E-a = 20.07 +/- 0.05 kJ mol(-1) is obtained in NaBH4 hydrolysis catalyzed by NaOH-p(AAM)-Co composite system. (C) 2014 Wiley Periodicals, Inc.Öğe Poly(acrylamide-co-vinyl sulfonic acid) p(AAm-co-VSA) hydrogel templates for Co and Ni metal nanoparticle preparation and their use in hydrogen production(Pergamon-Elsevier Science Ltd, 2013) Seven, Fahriye; Şahiner, NurettinP(AAM-co-VSA) hydrogel was prepared at different mole ratios form the corresponding monomers and used in absorption of metal ions such as Co and Ni from aqueous environments. Then, these bound metal ions within the hydrogel matrices were reduced to their metal nanoparticles by aqueous NaBH4 treatment. Finally, p(AAm-co-VSA)-M (M: Co or Ni) composites were used as reactor in the hydrolysis of NaBH4 for hydrogen generation. The amounts of metal ions before and after metal nanoparticle formation were determined by Atomic Absorption Spectroscopy (AAS). P(AAm-VSA) hydrogel showed greater absorption tendency for Ni(II) ions than Co(II) ions, and the metal ion binding capacity of these hydrogels was increased with an increase in the amount of VSA in the copolymeric hydrogel. It was also found that although the amount of Ni ions loaded into the hydrogel matrices were more than Co ions, Co metal nanoparticle-containing hydrogel produced hydrogen faster than Ni metal nanoparticle-containing hydrogel composites. The activation energy for the Co nanoparticle-embedded p(AAm-co-VSA) was found as 34.505 kJ mol(-1)k(-1), and other thermodynamic parameters were also calculated. The p(AAm-co-VSA)-Co hydrogel can be used up to 5 times repetitively without any loss of yield but with 55% of catalytic activity. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Super poroushydrogels as coordinating templates for in situ metal nanoparticle preparation and use as soft reactors in hydrogen production from the hydrolysis of hydrides(Amer Chemical Soc, 2012) Şahiner, Nurettin; Sağbaş, Selin; Turhan, Tuğçe; Karacan, Elif; Seven, Fahriye; Yaşar, Alper; Alpaslan, Duygu[Anstract Not Available]Öğe Super-fast hydrogen generation via super porous Q-P(VI)-M cryogel catalyst systems from hydrolysis of NaBH4(Pergamon-Elsevier Science Ltd, 2015) Şahiner, Nurettin; Seven, Fahriye; Al-Lohedan, HamadNovel poly(1-vinyl imidazole) p(VI) cryogels were synthesized via cryopolymerization technique where simultaneous polymerization and crosslinking occur around ice crystals under freezing conditions. The superporous p(VI) cryogels were modified with various alkyl bromides possessing different chain lengths such as 1.2-Dibromoethane (1,2-BE), 1.4-Dibromobutane (1,2-BB) and 1.6-Dibromohexane (1,6-BH), and used as template for in situ metal nanoparticle (M) synthesis (M: Co-0 or Ni-0). The prepared p(VI)-M cryogel composites were used in hydrogen (H-2) generation from the hydrolysis of sodium borohydride (NaBH4). Very high turnover frequency (TOP) and H-2 generation rate (HGR) values, of 34.4 (mol H-2) (mol catalyst min)(-1) and 14566.9 (mL H-2) (min)(-1) (g of M)(-1), respectively, were obtained at 70 degrees C for 3rd time Co (II) loaded and reduced 1.2-BE modified p(VI)-Co composite catalyst system compared with other imidazole-based catalyst systems reported in the literature. Moreover, modified p(VI) cryogels possess inherently magnetic behavior even after a single Co(II) loading-reduction step. Due to their superior properties, such as being recoverable via external applied magnetic field, fast HGR, and reusability, 1.2-BE-p(VI)-Co metal composites were found to be a highly attractive catalyst system for catalytic hydrolysis of NaBH4. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Superporous Cryogel-M (Cu, Ni, and Co) Composites in Catalytic Reduction of Toxic Phenolic Compounds and Dyes from Wastewaters(Springer International Publishing Ag, 2015) Şahiner, Nurettin; Seven, Fahriye; Al-lohedan, HamadP(Acrylamide) (p(AAm)) cryogel with superporous structure was synthesized by employing a cryopolymerization technique under freezing conditions. The prepared cryogels were modified by amidoximation to generate new functional groups as amid-p(AAm) cryogel, that binds metal ions, and the metal nanoparticles of those ions were prepared via in situ reduction method. The prepared amid-p(AAm)-M cryogel composites (M: Cu, Ni, and Co) were used as superporous reactor for the catalytic reduction of toxic phenol compounds 2- and 4-nitrophenol (2- and 4-NP) and some dyes methylene blue (MB) and Eosin Y (EY). P(AAm) cryogels and their metal composites were characterized by using FT-IR analysis, SEM images, and AAS measurements. The impact of porosity, the types and amount of metal catalyst, temperature of reaction medium, and so on were investigated for toxic 2-NP reduction by amid-p(AAm)-M cryogel composites. Very high total turnover frequencies (TOF) and low activation energy (Ea) values of 2.46 (mole 2-NP) (mole Cu. min)(-1) and 20.2 kJmol(-1) were obtained for catalytic reduction of 2-NP compound catalyzed by amid-p(AAm)-Cu cryogel composites. Consequently, superporous p(AAm) cryogel is the perfect support material for metal nanoparticle preparation and use in catalytic reduction reactions.Öğe Superporous P(2-hydroxyethyl methacrylate) cryogel-M (M:Co, Ni, Cu) composites as highly effective catalysts in H2 generation from hydrolysis of NaBH4 and NH3BH3(Pergamon-Elsevier Science Ltd, 2014) Seven, Fahriye; Şahiner, NurettinHighly porous p(2-hydroxyethyl methacrylate) p(HEMA) cryogels were synthesized via cryopolymerization technique and used as template for Co, Ni, and Cu nanoparticle preparation, then as composite catalyst systems in H-2 generation from hydrolysis of both NaBH4 and NH3BH3. Due to their highly porous and open microstructures, p(HEMA)-Co cryogel composites showed very effective performances in H-2 production from hydrolysis of both chemical hydrides. The characterization of p(HEMA) cryogels, and their metal composites was determined via various techniques including swelling experiments, digital camera images, SEM and TEM images, AAS and TGA measurements. The effect of various parameters on the hydrolysis reaction of NaBH4 such as metal types, concentration of chemical hydrides, amounts of catalyst, alkalinity of reaction medium and temperature were investigated in detail. It was found that Co nanoparticles are highly active catalysts in H-2 generation reactions from both hydrides. The hydrogen generation rate (HGR) of p(HEMA)-Co was 1596 (mL H-2) (min)(-1) (g of Co)(-1) which is quite good in comparison to reported values in the literature. Furthermore, kinetic parameters of p(HEMA)-Co metal composites such as energy, enthalpy and entropy were determined as Ea = 37.01 kJmol(-1), Delta H# = 34.26 kJmol(-1), Delta S# = -176,43 Jmol(-1) K-1, respectively. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe The use of superporous p(AAc (acrylic acid)) cryogels as support for Co and Ni nanoparticle preparation and as reactor in H2 production from sodium borohydride hydrolysis(Pergamon-Elsevier Science Ltd, 2014) Şahiner, Nurettin; Seven, FahriyeHere, we report for the first time the use of p(AAc (p(acrylic acid)) cryogel for in situ metal nanoparticle preparation, and their use as a superporous reactor for H-2 generation from hydrolysis of NaBH4. Superporous p(AAc) cryogels and conventional hydrogels were prepared via free radical polymerization technique at low (-18 degrees C) and moderate (40 degrees C) temperatures, respectively. They were characterized by employing various methods such as swelling experiments, optical imaging, and SEM (Scanning Electron Microscopy) analysis. By reducing Co2+ and Ni2+ ions within p(AAc) cryogel and hydrogel matrices, the obtained Co and Ni metal nanoparticles were employed for H-2 generation from NaBH4 hydrolysis. Various factors such as porosity, metal type, temperature, and the amount of sodium hydroxide were investigated to determine their effects on hydrogen generation from NaBH4 hydrolysis. Activation energy (Ea), enthalpy (Delta Eta(#)) and entropy (Delta S-#) for NaBH4 hydrolysis by superporous p(AAc)-Co metal composites were 2935 kJ mol(-1),=36.85 kJ mol(-1), and 157.88 J mol(-1)K(-1), respectively. Cryogels showed better catalytic activity than conventional hydrogels in the hydrolysis reaction, and have a higher TOF (turnover frequency) value of 4.10 mol H-2 (mol catalyst min)(-1) compared to conventional hydrogels, due to its highly porous nature, short diffusion distances and fast response times. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Use of cryogels for in situ metal nanoparticle preparation and catalysis for hydrogen generation(Amer Chemical Soc, 2014) Şahiner, Nurettin; Seven, Fahriye; Yıldız, Sema; Aktaş, Nahit[Anstract Not Available]
