Browsing by Author "Sahiner, Nurettin"

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Boric Acid Versus Boron Trioxide as Catalysts for Green Energy Source H2 Production From Sodium Borohydride Methanolysis
(2021) Demirci, Sahin; Ari, Betul; Sengel, Sultan B.; Inger, Erk; Sahiner, Nurettin
Here, boric acid (H3BO3) and its dewatered form, boron trioxide (B2O3) were tested as catalysts for hydrogen (H2) evolution in the methanolysis of sodium borohydride (NaBH4) in methanol. Parameters such as catalyst types and their amounts, NaBH4 concentration, and the reaction temperature affecting the hydrogen generation rate (HGR) were studied. It has been found that H3BO3 and B2O3 catalyzed methanolysis reaction of NaBH4 follow up first-order kinetics relative to the concentration of NaBH4. Furthermore, the conversion and activity of these catalysts were examined to determine their performance in ten consecutive use. Interestingly, H3BO3 and B2O3 have demonstrated superior catalytic performances in methanolysis of NaBH4 comparing to the studies published in literature with the activation energy of respectively 22.08 kJ.mol-1, and 23.30 kJ.mol-1 in H2 production. The HGR was calculated as 6481 mL.min-1.g-1 and 5163 mL.min-1.g-1 for H3BO3 and B2O3 catalyst, respectively for 50 mg catalyst at 298 K. These results are comparably better than most metal nanoparticle catalysts used for H2 production in addition to the naturally occurring boron-based environmentally friendliness of these materials.
Citation - WoS: 27
Citation - Scopus: 29
Catalytic activity of metal-free amine-modified dextran microgels in hydrogen release through methanolysis of NaBH₄
(Wiley, 2020) Inger, Erk; Sunol, Aydin K.; Sahiner, Nurettin
Polymeric microgels were prepared from dextran (Dex) by crosslinking linear natural polymer dextran with divinyl sulfone (DVS) with a surfactant-free emulsion technique resulting in high gravimetric yield of 78.5 +/- 5.3% with wide size distribution. Dex microgels were chemically modified, and then used as catalyst in the methanolysis of NaBH4 to produce H-2. The chemical modification of Dex microgel was done on epichlorohydrin (ECH)-reacted Dex microgels with ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetraamine (TETA) in dimethylformamide (DMF) at 90 degrees C for 12 hours. The modified dextran-TETA microgels were protonated using treatment with hydrochloric acid (HCl) and m-Dex microgels-TETA-HCl was found to be a very efficient catalyst for methanolysis of NaBH4 to produce H-2. The effects of reaction temperature and NaBH4 concentration on H-2 generation rates were investigated and m-Dex microgels-TETA-HCl catalyst possessed excellent catalytic performances with 100% conversion and 80% activity at end of 10 consecutive uses and was highly re-generatable with simple HCl treatment. Interestingly, m-Dex microgels-TETA-HCl catalyst can catalyze NaBH4 methanolysis reaction in a mild temperature range 0 to 35 degrees C with Ea value of 30.72 kJ/mol and in subzero temperature range, -20 to 0 degrees C with Ea value of 32.87 kJ/mol, which is comparable with many catalysts reported in the literature.
Citation - WoS: 4
Citation - Scopus: 3
Crosslinked Polyethyleneimine-Based Structures in Different Morphologies as Promising Co₂ Adsorption Systems: a Comprehensive Study
(Wiley, 2024) Demirci, Sahin; Inger, Erk; Bhethanabotla, Venkat; Sahiner, Nurettin
Although there are many studies on CO2 adsorption via PEI-modified carbon particles, metal-organic frameworks, zeolitic imidazolate frameworks, and silica-based porous structures, only a limited number of studies on solely cross-linked PEI-based structures. Here, the CO2 adsorption capacities of PEI-based microgels and cryogels were investigated. The effects of various parameters influencing the CO2 adsorption capacity of PEI-based structures, for example, crosslinker types, PEI types (branched [bPEI] or linear [lPEI]), adsorbent types (microgel or cryogel), chemical-modification including their complexes were examined. NaOH-treated glycerol diglycidyl ether (GDE) crosslinked lPEI microgels exhibited higher CO2 adsorption capacity among other microgels with 0.094 +/- 0.006 mmol CO2/g at 900 mm Hg, 25 degrees C with 2- and 7.5-fold increase upon pentaethylenehexamine (PEHA) modification and Ba(II) metal ion complexing, respectively. The CO2 adsorption capacity of bPEI and lPEI-based cryogels were compared and found that lPEI-GDE cryogels had higher adsorption capacity than bPEI-GDE cryogels with 0.188 +/- 0.01 mmol CO2/g at 900 mm Hg and 25 degrees C. The reuse studies revealed that NaOH-treated GDE crosslinked bPEI and lPEI microgels and cryogels showed promising potential, for example, after 10-times repeated use >50% CO2 adsorption capacity was retained. The results affirmed that PEI-based microgels and cryogels are encouraging materials for CO2 capture and reuse applications.
Citation - WoS: 6
Citation - Scopus: 6
Optimized Porous Carbon Particles From Sucrose and Their Polyethyleneimine Modifications for Enhanced Co₂ Capture
(Mdpi, 2024) Ari, Betul; Inger, Erk; Sunol, Aydin K.; Sahiner, Nurettin
Carbon dioxide (CO2), one of the primary greenhouse gases, plays a key role in global warming and is one of the culprits in the climate change crisis. Therefore, the use of appropriate CO2 capture and storage technologies is of significant importance for the future of planet Earth due to atmospheric, climate, and environmental concerns. A cleaner and more sustainable approach to CO2 capture and storage using porous materials, membranes, and amine-based sorbents could offer excellent possibilities. Here, sucrose-derived porous carbon particles (PCPs) were synthesized as adsorbents for CO2 capture. Next, these PCPs were modified with branched- and linear-polyethyleneimine (B-PEI and L-PEI) as B-PEI-PCP and L-PEI-PCP, respectively. These PCPs and their PEI-modified forms were then used to prepare metal nanoparticles such as Co, Cu, and Ni in situ as M@PCP and M@L/B-PEI-PCP (M: Ni, Co, and Cu). The presence of PEI on the PCP surface enables new amine functional groups, known for high CO2 capture ability. The presence of metal nanoparticles in the structure may be used as a catalyst to convert the captured CO2 into useful products, e.g., fuels or other chemical compounds, at high temperatures. It was found that B-PEI-PCP has a larger surface area and higher CO2 capture capacity with a surface area of 32.84 m(2)/g and a CO2 capture capacity of 1.05 mmol CO2/g adsorbent compared to L-PEI-PCP. Amongst metal-nanoparticle-embedded PEI-PCPs (M@PEI-PCPs, M: Ni, Co, Cu), Ni@L-PEI-PCP was found to have higher CO2 capture capacity, 0.81 mmol CO2/g adsorbent, and a surface area of 225 m(2)/g. These data are significant as they will steer future studies for the conversion of captured CO2 into useful fuels/chemicals.
Citation - WoS: 15
Citation - Scopus: 16
Pei Modifiednatural Sands of Florida as Catalysts for Hydrogen Production From Sodium Borohydride Dehydrogenation in Methanol
(Wiley-hindawi, 2021) Inger, Erk; Demirci, Sahin; Can, Mehmet; Sunol, Aydin K.; Philippidis, George; Sahiner, Nurettin
Sand samples from Tampa (T) and Panama (P) City beaches in Florida were used as catalysts for dehydrogenation of NaBH4 in methanol. T and P sand samples were sieved to <250, 250 to 500, and >500 mu m sizes, and the smallest fractions resulted in faster hydrogen generation rates (HGR), 565 +/- 18 and 482 +/- 24 mL H-2 (min.g of catalyst)(-1), respectively. After various base/acid treatments, HGR values of 705 +/- 51 and 690 +/- 47 mL H-2 (min g of catalyst)(-1) for HCl-treated T and P sand samples were attained, respectively. Next, T and P sand samples were modified with polyethyleneimine (PEI) that doubled the HGR values, 1344 +/- 103, and 1190 +/- 87 mL H-2 (min.g of catalyst)(-1) and increased similar to 8-fold, 4408 +/- 187, and 3879 +/- 169 mL H-2 (min g of catalyst)(-1), correspondingly after protonation (PEI+). The Ea values of T and P sand samples were calculated as 24.6 and 25.9 kJ/mol, and increased to 36.1, and 36.6 kJ/mol for T-PEI(+)and P-PEI(+)samples, respectively.
Citation - WoS: 51
Citation - Scopus: 52
Porous Carbon Particles as Metal-Free Superior Catalyst for Hydrogen Release From Methanolysis of Sodium Borohydride
(Pergamon-elsevier Science Ltd, 2020) Demirci, Sahin; Yildiz, Mustafa; Inger, Erk; Sahiner, Nurettin
Carbon materials can be readily prepared from wood derivatives, monosaccharaides such as pentose/hexose and/or polysaccharides in addition to many starting materials by treatment of thermal, chemical and hydrothermal methods. Here, the porous carbon (PC) particles were prepared by removal of silica particles from previously prepared carbon-silica composites by hydrothermal and carbonization process from sucrose. Then, PC particles were modified with polyethyleneimine (PEI) to prepared amine functionalized PC-PEI particles and protonated with hydrochloric acid, PC-PEI+. Finally, these prepared carbon-based particles were used as catalyst for H-2 release from NaBH4 methanolysis and PC-PEI+ was found as the most effective catalyst at 25 degrees C with 4040 +/- 126 mL H-2. min(-1).g(-1) HGR value. The E s value of 23.9 kJ/mol in H-2 release reaction from NaBH4 methanolysis catalyzed by PC-PEI+ that is comparable and/or better than most of studies reported in literature. The activity% of PC-PEI+ catalyst was 72% after fifth consequential runs. Additionally, the regeneration ability of PC-PEI+ catalyst was also shown that after fifth regeneration process, there is only 5% decrease in activity%. (C) 2019 Elsevier Ltd. All rights reserved.