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0D, 1D, 2D, and 3D Soft and Hard Templates for Catalysis
(Elsevier Science Bv, 2017) Bütün, Sultan; Demirci, Şahin; Yaşar, Alper O.; Sağbaş, Selin; Aktaş, Nahit; Şahiner, Nurettin
Catalytic reactions are generally catalyzed by metal nanoparticles, metal oxides, or their bi- or trimetallic forms with various formulations, morphology, composition, and shapes. The metal nanoparticle catalytic performances are directly related to the surface features of particles such as crystal structure, atomic stacking and order, surface area, roughness and atomic and/or spatial organizations, and the catalyst environments. It's very well-known that the high surface energy of the metal nanoparticles, which is one of the most important challenges to be considered to overcome, leads to aggregation, deactivation, and oxidation problems. Therefore, many templates such as nanoemulsions prepared from surfactant and polymers and nanogels as zero-dimensional (0D) soft templates; cylindrical or tubular natural or synthetic structures derived from again surfactants, polymers, or peptides or self-assembled structures as one-dimensional (1D) templates; graphene oxide, mica, clay, and silicates as two-dimensional (2D) hard templates; and microgel, bulk hydrogel, and cryogels as three-dimensional (3D) soft templates that are used as stabilizing media will be discussed. Regardless of the sizes of templates, various parameters such as morphology, e.g., core-shell, capsules, guiding direction, porosity, and compartmentation features of the templates, have paramount significance on composition, crystallinity, and shape of the resultant nanoparticle to be used as catalyst. Metal nanoparticles, metal oxides, and metal nanoparticles doped with various elements have been extensively investigated due to their unique physical and chemical properties, and even their bi- or trimetallic forms have been under examination due to synergistic potential application of each of the components. The main concern regarding the nanoparticle synthesis is to overcome their agglomeration, due to their high surface area, high energy, and high surface reactivity resulting in strong tendency to aggregate, leading to deactivation and oxidation. There are a variety of methods available in the synthesis of metal nanoparticles to prevent some of these shortcomings with some catalytic performance sacrifices or with some economical infeasibilities. Nevertheless, the key issue with these methods is the control of the particle size and shapes and the morphology and crystallinity. Therefore, a wide range of templates such as nanoemulsions using surfactant and polymers and nanogels as 0D soft templates; cylindrical or tubular natural or synthetic structures derived from again surfactants, polymers, or peptides or self-assembled structures as 1D templates; graphene, mica, clay, and silicates as 2D hard templates; and microgel, bulk hydrogel, and cryogels as 3D soft templates as stabilizing environments and particle compartments will be discussed. In general, polar molecules or polyelectrolytes stabilizers can be used in both controlling the size and preventing the metal nanoparticles from precipitation processes. Water-soluble polymers, including polyelectrolytes, are the commonly employed stabilizing and/or chelating agents in the preparation of metal ultrafine particles.
A comparison study about antibacterial activity of zeolitic imidazolate frameworks (ZIFs) prepared with various metal ions
(Elsevier Science Sa, 2022) Demirci, Şahin; Yıldırım, Yıldız; Şahiner, Nurettin
Herein, the synthesis of zeolitic imidazolate framework particles in water at room temperature using 2-methylimidazole (HmIm) as organic linker, and Co(II), Ni(II), Cu(II), Fe(II), Mg(II), Zn(II), Ce(III), La(III), Fe(III), and Ti (IV) ions is reported. The colors of the prepared ZIF particles varied depending on the metal ions used. The disappearance of N-H-ring-N out of plane bending peak at 1845 cm(-1) and weakening of the N-H bending peak at 1597 cm(-1) in the FT-IR spectrum of HmIm after ZIF synthesis confirmed successful preparation. Higher surface area values were observed for ZIF-Co(II) and ZIF-Zn(II) with values of 1423.4 and 1467.1 m(2)/g, respectively. The prepared ZIF-Fe(II) particles showed magnetic property. The antibacterial activities of ZIF particles also varied depending on metal ions. The highest antibacterial activities were observed for ZIF-Co(II) and ZIF-Cu(II) particles against P. aeruginosa (gram -, ATCC 10145), S. aureus (gram +, ATCC 6538), and C. albicans (fungi, ATCC 10231). The MIC values of ZIF-Co(II) particles were determined as 0.125, 0.25, and 1.0 mg/mL against P. aeruginosa, S. aureus, and C. albicans, whereas MBC values were determined as 0.25, 1.0, and 5.0 mg/mL, respectively. The inhibition zones for P. aeruginosa, S. aureus, and C. albicans in the presence of 10 mg ZIF-Cu(II) particles were measured as 22.7 +/- 1.5, 24.3 +/- 1.1, and 25.7 +/- 0.6 mm, respectively.
Alpha-Glucosidase Enzyme Immobilized Dextran-Co Metal Nanoparticle Cryogel Composite Systems as Dual Catalyst with Enhanced Stability and Catalytic Activity
(John Wiley and Sons Inc, 2023) Demirci, Şahin; Şahiner, Nurettin
Here, dextran (Dex) cryogels were prepared and used for the immobilization of α-Glu enzyme via two different techniques of entrapment and covalent linking. The entrapment of α-Glu enzyme within Dex cryogels (α-GluE@Dex) during the synthesis process caused almost 70 % activity loss. On the other hand, the Dex cryogels with α-Glu enzyme immobilized via covalent linking (α-GluC@Dex) maintained 91±1.1 % activity and afforded 10 consecutive usages and could be stored at 25 °C for 10 days with more than 50 % activity. Moreover, we prepared Cobalt (Co) metal nanoparticle containing Dex-Co cryogel composite to be used to immobilize the α-Glu enzyme via covalent linking to attain an α-GluC@Dex-Co catalyst system with dual catalytic performance e. g., enzymatic and chemical reduction of the substrate and its’ by-product for the first time. The prepared α-GluC@Dex-Co cryogels system was used for enzymatic hydrolysis of 4-nitrophenyl-α-D-glucopyranoside to glucose and 4-nitrophenol, and then the reduction of 4-nitrophenol to 4-aminophenol catalyzed by the Co metal nanoparticles present as co-catalyst within the cryogel network. The enzymatic activity of α-GluC@Dex-Co cryogels was calculated as 72±3.1 % and the cryogel reduced the enzymatic reaction by-product of 4-nitrophenol to 4-aminophenol in 7 min in the presence of NaBH4.
Amidoximated poly(acrylonitrile) particles for environmental applications: Removal of heavy metal ions, dyes, and herbicides from water with different sources
(Wiley, 2016) Ajmal, Muhammad; Demirci, Şahin; Siddiq, Mohammad; Aktaş, Nahit; Şahiner, Nurettin
Monodispersed poly(acrylonitrile) [p(AN)] particles were prepared by surfactant free emulsion polymerization and the hydrophobic nitrite groups were converted to hydrophilic amidoxime groups by treatment with hydroxylamine hydrochloride (NH2OH center dot HCl) in water. The p(AN) and amidoximated p(AN) [amid-p(AN)] particles were characterized by Fourier transformation infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM). The prepared particles were used as adsorbents in the removal from aqueous media of three different types of pollutants; organic dyes methylene blue (MB), and rhodamine 6 G (R6G), a heavy metal ion Cd (II), and a herbicide paraquat (PQ). The effects of various parameters such as amidoximation, pH of solution, amount of particles, and the initial concentration of solution were investigated. Upon amidoximation, a great increase in the adsorption capacity of the prepared particles was observed as the adsorbed amounts were increased to 87, 91, 74, and 91 mg/g from 5, 1.54, 1.06, and 1.22 mg/g for Cd (II), MB, R6G, and PQ, respectively. The amid-p(AN) particles were also able to remove considerable amounts of these pollutants from tap, river, and sea water. Langmuir, Freundlich, and Temkin adsorption isotherms were applied and it was found that the adsorption of Cd (II) and PQ followed the Langmuir adsorption model, whereas the adsorption of MB was found to obey the Freundlich adsorption isotherm. Pseudo first-order and pseudo second-order kinetics were also applied and the results showed that the adsorption processes of Cd (II), PQ, MB, and R6G follow pseudo second-order kinetics. (C) 2015 Wiley Periodicals, Inc.
Amine-modified halloysite nanotube embedded PEI cryogels as adsorbent nanoarchitectonics for recovery of valuable phenolic compounds from olive mill wastewater
(Elsevier Ltd, 2024) Demirci, Şahin; Sağbaş Suner, Selin; Yılmaz, Selehattin; Bağdat, Sema; Tokay, Feyzullah; Şahiner, Nurettin
Here, natural tubular clays, halloysite nanotubes (Hal), were modified with ethylenediamine (EDA), triethylenetetramine (TETA), pentaethylenehexamine (PEHA), and polyethyleneimine (PEI) to enhance their adsorption capabilities for phenolic compound for the treatment of olive mill wastewater (OMWW). Among the modified Hal adsorbents, Hall-PEHA adsorbent demonstrated a higher surface charge of +15.9 ± 1.9 mV and a larger surface area of 24.8 m2/g. The hydroxytyrosol, tyrosol, and oleuropein adsorption from their 1000 mg/L 10 mL single aqueous solutions were determined as 696 ± 44, 536 ± 36 and 91 ± 22 mg/g, respectively. Furthermore, it was determined that 90 ± 8%, 45 ± 0%, and 35 ± 3% of hydroxytyrosol, tyrosol, and oleuropein phenolic compounds were recovered from their 10 mL of 1000 mg/L aqueous mixture solution. On the other hand, the Hal-PEI adsorbents were able to adsorb 7.1 ± 1.2, 3.3 ± 0.5 and 0.5 ± 0.05 mg/g of hydroxytyrosol, tyrosol, and oleuropein compounds, respectively, from the actual OMWW. These values correspond to approximately 85 ± 8%, 71 ± 10%, and 70 ± 7% of the total amount of these compounds present in the OMWW. The PEI cryogel composite system, where Hal-PEHA was embedded into PEI cryogels (Hal-PEHA@PEI), exhibited improved adsorption amount for hydroxytyrosol, tyrosol, and oleuropein compounds from the actual OMWW compared to Hal-PEHA alone. The Hal-PEHA@PEI composite system adsorption amount was determined as 7.6 ± 1.6, 3.4 ± 0.2 and 0.7 ± 0.02 mg/g of hydroxytyrosol, tyrosol, and oleuropein compounds, respectively. These values correspond to approximately 90 ± 3%, 73 ± 3%, and 92 ± 3% of the total amount of these compounds present in the OMWW.
An amino acid, L-Glutamic acid-based metal-organic frameworks and their antibacterial, blood compatibility, biocompatibility, and sensor properties
(Elsevier, 2020) Can, Mehmet; Demirci, Şahin; Sunol, Aydın K.; Şahiner, Nurettin
In this study, metal-organic frameworks (MOFs) based on L-Glutamic acid (L-Glu), a natural amino acid as organic linker and Co (II), Ni (II), and Cu (II) metal ions were used in construction with 37.1 +/- 5.3%, 41.4 +/- 6.1%, 49.2 +/- 4.9% yields, respectively in ethanol under reflux. The prepared L-Glu-M (M: Co(II), Ni(II), and Cu (II)) MOFs were characterized in terms of their porosity, optical, thermal, electrical, and structural properties. Correspondingly, 102.1 m2/g, 83.7 m2/g, and 71.0 m2/g specific surface areas and 2.72 cm3/g, 0.46 cm3/g, and 0.07 cm3/g pore volumes were measured for L-Glu-based Co, Ni, and Cu MOFs. Moreover, the antimicrobial studies of L-Glu-M MOFs on Escherichia coil ATCC 8739, as gram-negative, and Staphylococcus aureus ATCC 6538 as gram-positive bacteria revealed that the highest inhibition zones with 42 +/- 2 mm and 44 +/- 1 mm were observed for L-Glu-Co MOFs. The hemolysis induction of L-Glu-M MOFs was evaluated, except L-Glu-Cu that induced 8.3 +/- 0.4% hemolysis, and the hemolytic characters of other MOF preparations were found to reside in safety margins possessing <= 4% hemolysis ratios. The blood clotting index of L-Glu-M MOFs were measured as 87.4 + 6.3% (Co(II)), 91.8 +/- 10.1% (Ni(II)), and 95.7 +/- 4.8% (Cu(II)) with neglectable interference to clotting mechanisms. Cytocompatibility of L-Glu-based MOFs were demonstrated that all MOF preparations with 25 mu g/mL concentrations maintained approximately 90% cell viabilities. Furthermore, Glu-based MOFs were demonstrated to possess sensory properties for NH3 vapor and could be employed in at least five cycles of repeated use. Therefore, L-Glu-M based MOFs can provide useful avenues in material science for a variety of biomedical and industrial applications.
Application of superporous magnetic cationic cryogels for persistent chromate (toxic chromate and dichromate) uptake from aqueous environments
(Wiley, 2016) Şahiner, Nurettin; Demirci, Şahin; Şahiner, Mehtap; Yılmaz, Selehattin
Poly((3-Acrylamidopropyl) trimethylammonium chloride) (p(APTMACl)) cryogels were prepared with cryopolymerization technique and employed for the removal of toxic chromate and dichromate anions from aqueous media. The maximum adsorption capacities of 94 mg/g and 135 mg/g for chromate and dichromate anions, respectively, were determined with the application of the Langmuir isotherm. These values are very close to the experimental values of about 77 and 128 mg/g from 100 mL, 100 ppm chromate, and dichromate solutions using 0.03 g cryogel. The removal efficiency of chromate and dichromate anions were increased with the increase in the amount of cryogel and the removal percentage of chromate and dichromate toxic anions were estimated as 99.21 and 93.61%, respectively, for 0.15 g of p(APTMACl) cryogels used in 100 mL, 100 ppm chromate, and dichromate solutions. Furthermore, magnetic p(APTMACl) cryogels were also prepared and used in the removal of chromate and dichromate, and the maximum adsorption capacities were 30 mg/g and 40 mg/g, respectively. Additionally, the adsorption of these anions were investigated from different media such as drinking water, tap water, seawater, and creek water; and the maximum adsorption amounts in drinking water were 65.5 +/- 15, and 125.5 +/- 11 mg/g for chromate and dichromate anions, respectively. The reusability of p(APTMACl) cryogels for the removal of chromate and dichromate anions was also investigated, and it was found that the adsorption capacity for chromate anions decreased to 71.23 +/- 4.3 from 97.37 +/- 4.5 mg/g, whereas the adsorption capacity of dichromate anions only decreased to 123.69 +/- 3.5 mg/g from 129.9 +/- 7 mg/g at the end of five adsorption-desorption cycles. (C) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43438.
B, P, and S heteroatom doped, bio- and hemo-compatible 2D graphitic-carbon nitride (g-C3N4) with antioxidant, light-induced antibacterial, and bioimaging endeavors
(Institute of Physics, 2024) Demirci, Şahin; Sağbaş Suner, Selin; Uğuz Neli, Özlem; Koca, Atıf; Şahiner, Nurettin
The synthesis of two-dimensional (2D) graphitic g-C3N4 and heteroatom-doped graphitic H@g-C3N4 (H: B, P, or S) particles were successfully done using melamine as source compounds and boric acid, phosphorous red, and sulfur as doping agents. The band gap values of 2D g-C3N4, B50@g-C3N4, P50@g-C3N4, and S50@g-C3N4 structures were determined as 2.90, 3.03, 2.89, and 2.93 eV, respectively. The fluorescent emission wavelengths of 2D g-C3N4, B50@g-C3N4, P50@g-C3N4, and S50@g-C3N4 structures were observed at 442, 430, 441, and 442 nm, respectively upon excitation at λ Ex = 325 nm. There is also one additional new emission wavelength was found at 345 nm for B50@g-C3N4 structure. The blood compatibility test results of g-C3N4, B50@g-C3N4, P50@g-C3N4, and S50@g-C3N4 structures revealed that all materials are blood compatible with [removed]90% blood clotting indices at 100 μg ml−1 concentration. The cell toxicity of the prepared 2D graphitic structures were also tested on L929 fibroblast cells, and even the heteroatom doped has g-C3N4 structures induce no cytotoxicity was observed with >91% cell viability even at 250 μg ml−1 particle concentration with the exception of P50@g-C3N4 which as >75 viability. Moreover, for 2D g-C3N4, B50@g-C3N4, and S50@g-C3N4 constructs, even at 500 μg ml−1 concentration, >90% cell viabilities was monitored. As a diagnostic material, B50@g-C3N4 was found to have significantly high penetration and distribution abilities into L929 fibroblast cells granting a great potential in fluorescence imaging and bioimaging applications. Furthermore, the elemental doping with B, P, and S of g-C3N4 were found to significantly increase the photodynamic antibacterial activity e.g. more than half of bacterial elimination by heteroatom-doped forms of g-C3N4 under UVA treatment was achieved.
Benign Preparation of Metal-Organic Frameworks of Trimesic Acid and Cu, Co or Ni for Potential Sensor Applications
(Springer, 2015) Sel, Kıvanç; Demirci, Şahin; Meydan, Engin; Yıldız, Sema; Öztürk, Ömer Faruk; Al-Lohedan, Hamad; Şahiner, Nurettin
Metal-organic frameworks (MOFs) have been constructed using trimesic acid (TMA) as organic linker and Co(II), Ni(II) or Cu(II) metal ions from their corresponding aqueous chloride salts at room temperature. The prepared TMA-M (M: Co, Ni, and Cu) MOFs have been characterized in terms of their porosity and optical, thermal, electrical, and structural properties. The prepared MOFs were characterized in terms of their porosity through Brunauer-Emmett-Teller measurements, yielding a value of 330 m(2)/g for the TMA-Cu MOF. Structural analysis and thermal characterization of the prepared MOFs were done by using Fourier-transform infrared (FT-IR) spectroscopy, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), respectively. The optical properties were analyzed by fluorescence spectroscopy. Additionally, TMA-M MOF disks were prepared and their conductivities determined by room-temperature I-V measurements. The conductivity of the TMA-M MOFs was calculated to be between 7.97 x 10(-7) S/cm and 5.39 x 10(-9) S/cm.
Betaine microgel preparation from 2-(methacryloyloxy) ethyl] dimethyl (3-sulfopropyl) ammonium hydroxide and its use as a catalyst system
(Elsevier, 2015) Ajmal, Muhammad; Demirci, Şahin; Siddiq, Mohammad; Aktaş, Nahit; Şahiner, Nurettin
We demonstrate the synthesis of poly(sulfobetain methacrylate) (p(SBMA)) hydrogels of micro dimensions by inverse suspension polymerization of a zwitterionic monomer 2-(methacryloyloxy) ethyl] dimethyl (3-sulfopropyl) ammonium hydroxide (SBMA). The prepared microgels were used as microreactors for the synthesis of nickel (Ni) nanoparticles by in situ reduction of Ni (II) loaded into microgels from an aqueous medium. The prepared microgels and microgel metal nanoparticle composites were characterized by Fourier Transformation Infrared (FT-IR) Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Thermal properties of the microgels were studied by thermal gravimetric analysis (TGA). The amount of Ni nanoparticles generated within the microgels was determined by Atomic Absorption Spectroscopy (AAS) after dissolving the Ni nanoparticles to form Ni (II) ions by treating with concentrated hydrochloric acid (5 M HCl). The prepared composites were used as catalysts for the reduction of nitro aromatic compounds such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NP) and 4-nitroaniline (4-NA) and excellent catalytic performances were observed. The effects of temperature and amount of catalyst were also evaluated. A mild activation energy in comparison to the literature was calculated as 35.64 kJ/mol, and very high k p value of 0.42 min(-1) as a function of temperature was estimated for the reduction of 4-NP catalyzed by p(SBMA)-Ni composite catalyst system. (C) 2015 Elsevier B.V. All rights reserved.
Bio-MOFs Based on Natural Phenolic, Hematoxylin Leverages Biomedical Applications: Enzyme Inhibition, Antioxidant, and Antibacterial Properties
(Wiley-V C H Verlag Gmbh, 2024) Şahiner, Mehtap; Tian, Zhi; Demirci, Şahin; Sunol, Aydın; Allen-Gipson, Diane S.; Şahiner, Nurettin
Here, using natural hematoxylin (HT) as linker, metal-organic frameworks (MOFs) from Cu(II), Fe(II), and Fe(III) ions was prepared. The SEM images and DLS analyses revealed HT-based MOFs are
Biofilm inhibition and bacterial eradication by C-dots derived from polyethyleneimine-citric acid
(Elsevier B.V., 2022) Abraham, Wakeem L.; Demirci, Şahin; Wypyski, Madison S.; Ayyala, Ramesh S.; Bhethanabotla, Venkat R.; Lawson, Louise B.; Şahiner, Nurettin
Protonable polyethyleneimine (PEI) and citric acid (CA) based C-dots were prepared via a hydrothermal process, yielding particles with a hydrodynamic diameter of ~100 and ~80 nm, and zeta potential of ? 2.3 ± 0.1 and + 23.4 ± 0.2 mV for PEI-CA C-dots and their protonated form, respectively. Treating Staphylococcus aureus with these C-dots resulted in a statistically significant reduction in bacterial growth, specifically growth in the planktonic phase as well as in the development of bacterial biofilm when compared to untreated (p < 0.05). When 24 h matured S. aureus biofilms were treated with C-dots, a significant disruption and dispersion of bacteria from the existing biofilms was noted as compared to untreated (p < 0.05). Other Gram-positive microorganisms (B. cereus, S. epidermidis, S. pyogenes) and Gram-negative (P. mirabilis, E. coli, and P. aeruginosa) were also susceptible to the antimicrobial activity of the PEI-CA C-dots with significant inhibition of bacterial growth noted for all organisms after C-dot treatment. Only for B. cereus, S. epidermidis, and P. aeruginosa was this reduction in total growth reflected in decreased planktonic growth. However, biofilm formation by all organisms was reduced significantly upon treatment with the C-dots, including those for which planktonic growth was not impacted. © 2022 Elsevier B.V.
Boric acid versus boron trioxide as catalysts for green energy source H2 production from sodium borohydride methanolysis
(2021) Demirci, Şahin; Ari, Betül; Bütün Şengel, Sultan; İnger, Erk; Şahiner, 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.
Boron-containing magnetic nanoparticles from Co, Ni, and Fe chloride salts and their catalytic performances on 4-nitrophenol reduction
(Elsevier, 2020) Meydan, Engin; Demirci, Şahin; Aktaş, Nahit; Şahiner, Nurettin; Öztürk, Ömer Faruk
In this study, magnetic metal nanoparticles (MNP) were prepared by using Fe, Co and Ni ions and NaBH4 as reducing agents in oil-in-water microemulsion system. The prepared MNP were used as catalyst in 4-Nitro phenol (4-NP) reduction to 4-Aminophenol (4-AP). It was found that magnetic Co MNP performed superior catalytic performances than Fe and Ni MNP for 4-NP reduction. The catalytic reduction experiments revealed that as the concentration of reducing agent, NaBH4 that was used in the preparation of Co MNP was increased, the complete conversion time for 4-NP to 4-AP was decreased as the sizes of Co MNP were obatined as 75 +/- 16, 60 +/- 9, and 37 +/- 6 nm when using 0.1, 0.2 and 0.4 M NaBH, respectively. Therefore, Co MNP prepared by using 0.4 M NaBH4 was used in the detailed investigation of various parameters such as the effect Co nanoparticles, reaction temperatures and time. The activation parameters of Co nanoparticle prepared by using 0.4 M NaBH4 as reducing agent was calculated as Ea = 32.1 +/- 3.1 kJ mot(-1), Delta H = 28.8 +/- 2.2 kJ mot(-1 )and Delta S = - 162.5 +/- 9.4 J mol(-1) K-1 that is the best catalytic performance amongst the other Co MNP5. The shelf life (storage) studies of Co nanoparticles showed that smaller Co MNP obtained by using 0.4 M NaBH4 reduce catalytic performance faster than the others, e.g, in the order of Co MNP(0.4 M NaBH4) > Co MNP(0.2 M NaBH4) > Co MNP(0.1 M NaBH4) in 20 day storage at ambient temperature. The activity% of Co MNP was decreased to 58 +/- 3% after five consecutives use while maintaining 100% conversion at every use corroborating the promising industry application of this magnetic Co MNP.
Can PEI microgels become biocompatible upon betainization?
(Elsevier Science Bv, 2017) Şahiner, Nurettin; Demirci, Şahin
Polyethylene imine (PEI) microgels prepared via micro emulsion polymerization technique were treated with 1,3-propane sultone to obtained betainized PEI (b-PEI) microgels. The betainization reaction generated zwitterions on PEI microgel that are positive charges from quartemized amine groups of PEI, and the newly formed negative charges from SO3- groups from the modifying agent, 1,3-propane sultone offered interesting properties. The smaller size of b-PEI microgels that are obtained by simple filtration were increased with betainization from 512 +/- 14 to 1114 +/- 86 nm. Also, the betainization of PEI microgel provided negative zeta potential values at high pH values as 9, 10, 11, and 12. Moreover, the b-PEI microgels render more effective dye absorption capabilities for anionic or cationic organic dyes such as Methyl Orange (MO) and Methylene Blue (MB) separately with the significant increase dye adsorption capacity of 354 +/- 31 and 274 +/- 19 mg/g respectively. Moreover, antibacterial properties of b-PEI microgels tested on the E. coli ATCC 8739 and S. aureus ATCC 6538 were diminished whereas bare PEI has low MIC and MBC values (strong antibacterial properties). Interestingly, the PEI microgels known for their strong antibacterial and toxic nature found to be biocompatible upon betainization reaction. The biocompatibility test were carried with WST-1 tests and double staining methods. The cytotoxicity, apoptotic and necrotic cell tests were shown that PEI microgels induce no cytotoxicity up to 400 mu g/mL whereas PEI microgels possessed 50% toxicity at this concentration, suggesting that b-PEI microgels become biocompatible upon betainization with, 3-propane sultone. (C) 2017 Elsevier B.V. All rights reserved.
Catalytic activity of amine functionalized titanium dioxide nanoparticles in methanolysis of sodium borohydride for hydrogen generation
(Elsevier, 2020) Demirci, Şahin; Sunol, Aydın K.; Şahiner, Nurettin
Titanium dioxide (TiO2) nanoparticles, Anatase (A-TiO2), Rutile (R-TiO2), and Rutile-Anatase (RA-TiO2) mixture were modified chemically with ethylene-diamine, diethylene-tri-amine, tri-ethylene-tetra-amine, and polyethyleneimine (PEI) to functionalize their surface to catalyze sodium borohydride methanolysis to generate hydrogen. PEI modified TiO2 particles catalyzed the methanolysis reaction more effectively than amines with lesser number of amine groups for all the forms of modified TiO2 catalysts. The Hydrogen Generation Rate (HGR) values for A-TiO2, R-TiO2, and RA-TiO2 are 3121, 3525, and 2920 mL H-2/(g catalystXmin), respectively and are further increased by 25.6, 30.6, and 36.7%, respectively when protonated. The protonated catalyst, A-TiO2-PEI+, R-TiO2-PEI+, and RA-TiO2-PEI+, are effective at low temperatures, 253-313 K, with activation energies of 35.2, 36.3, and 36 kJ/mol for methanolysis, respectively. These catalysts retain over sixty percent of the original HGR at the end of fifth consecutive reuse. All the forms of the catalysts are completely regenerateable through hydrochloric acid treatment.
Catalytic performance of boron-containing magnetic metal nanoparticles in methylene blue degradation reaction and mixture with other pollutants
(Elsevier B.V., 2021) Meydan, Engin; Demirci, Şahin; Aktaş, Nahit; Şahiner, Nurettin; Öztürk, Ömer Faruk
The catalytic effects of metal nanoparticles (MNPs) synthesized in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) microemulsion system by using M(II) salts (M = Fe, Co, Ni) and NaBH4 reducing agent on methylene blue (MB) degradation reaction were investigated. It was determined that Co-MNPs gave the best catalytic activity among them. Influence of the reaction parameters e.g., reaction time, temperature, the size of catalyst and the MNP types on the catalytic performance were studied. It was found that 37 ± 6 nm Co-MNPs revealed the best catalytic activity in all studies. The best activation parameters were calculated as 13.6 ± 1.1 kJ mol−1 and ΔH = 10.7 ± 1.0 kJ mol−1 and ΔS = -87.9 ± 5.4 J mol−1 K−1. The activity % of Co-MNPs was calculated as 85.4 after 30 days on the shelf life study. The reusability studies were carried out and the activity of Co-MNPs at the 5th reuse was calculated as 70 ± 5%. Finally, the catalytic activity of Co-MNPs was investigated inside equal volumes of single and multiple solution mixtures containing MB, 4-Nitrophenol (4-NP) and Eosin Y (EY). In the examinations, it was observed that the nanocatalyst was effective as a reducing agent in all equal amount solutions (MB/4-NP, MB/EY, 4-NP/EY, and MB/4-NP/EY). And also, TOF (mole of MB/4-NP/EY) (mol catalyst.min)−1 values of catalytic activities were also calculated.
Chemically Cross-Linked Poly(?-Cyclodextrin) Particles as Promising Drug Delivery Materials
(Amer Chemical Soc, 2021) Demirci, Şahin; Khiev, Dawin; Can, Mehmet; Şahiner, Mehtap; Biswal, Manas R.; Ayyala, Ramesh S.; Şahiner, Nurettin
One-pot synthesis of poly(β-cyclodextrin) (p(β-CD)) micro-/nanoparticles was accomplished using two different cross-linkers, divinyl sulfone (DVS) as p(β-CD)-1 and trimethylolpropane glycidyl ether (TMPGDE) as p(β-CD)-2. High gravimetric yields of 84 ± 4 and 62 ± 6%, respectively, were attained for p(β-CD)-1 and p(β-CD)-2 particles. The p(β-CD)-1 and p(β-CD)-2 particles had spherical shapes with 5.09 ± 0.24 and 0.60 ± 0.01 μm diameters, respectively, and exhibited good water dispersibility at physiological pH, and their isoelectric points were calculated correspondingly to be pH 1.1 and 1.2. The surface areas of p(β-CD)-1 and p(β-CD)-2 particles were determined to be 4.76 ± 0.6 and 2.18 ± 0.2 m2/g, respectively. Moreover, p(β-CD) particles were found to be biocompatible with more than 98% cell viability on human retinal pigment epithelial (ARPE-19) cells at 0.1 mg/mL concentration. Also, p(β-CD)-1 particles exhibited 52.81 ± 9.5% Fe(II) chelation capacity at 1.0 mg/mL concentration. The hemolysis and coagulation tests revealed that p(β-CD)-1 particles possessed excellent blood compatibility with a 1.18 ± 0.60% hemolysis ratio and a 92.02 ± 1.02% clotting index even at 2.0 mg/mL concentration, whereas the safety limit of p(β-CD)-2 particles for blood interactions was determined to be 0.5 mg/mL. The in vitro drug release performances of p(β-CD)-1 and p(β-CD)-2 particles for hydrophobic acyclovir and hydrophilic vancomycin model drugs at pH 7.4 PBS showed sustained releases of 2.14 ± 0.34 and 1.34 ± 0.43 mg/g acyclovir and 51.90 ± 1.09 and 61.26 ± 3.71 mg/g vancomycin within 24 h, respectively. Kinetic modeling of experimental release data revealed the best fit for drug release from p(β-CD) particles mediated by the Korsmeyer-Peppas model. ©
Chondroitin Sulfate-Based Cryogels for Biomedical Applications
(MDPI, 2021) Demirci, Şahin; Şahiner, Mehtap; Ari, Betül; Sunol, Aydın K.; Şahiner, Nurettin
Cryogels attained from natural materials offer exceptional properties in applications such as tissue engineering. Moreover, Halloysite Nanotubes (HNT) at 1:0.5 weight ratio were embedded into CS cryogels to render additional biomedical properties. The hemolysis index of CS cryogel and CS:HNT cryogels was calculated as 0.77 ± 0.41 and 0.81 ± 0.24 and defined as non-hemolytic mate-rials. However, the blood coagulation indices of CS cryogel and CS:HNT cryogels were determined as 76 ± 2% and 68 ± 3%, suggesting a mild blood clotting capability. The maximum% swelling capacity of CS cryogel was measured as 3587 ± 186%, 4014 ± 184%, and 3984 ± 113%, at pH 1.0, pH 7.4 and pH 9.0, respectively, which were reduced to 1961 ± 288%, 2816 ± 192, 2405 ± 73%, respectively, for CS:HNT cryogel. It was found that CS cryogels can hydrolytically be degraded 41 ± 1% (by wt) in 16-day incubation, whereas the CS:HNT cryogels degraded by 30 ± 1 wt %. There is no chelation for HNT and 67.5 ± 1% Cu(II) chelation for linear CS was measured. On the other hand, the CS cryogel and CS:HNT cryogel revealed Cu(II) chelating capabilities of 60.1 ± 12.5%, and 43.2 ± 17.5%, respectively, from 0.1 mg/mL Cu(II) ion stock solution. Additionally, at 0.5 mg/mL CS, CS:HNT, and HNT, the Fe(II) chelation capacity of 99.7 ± 0.6, 86.2 ± 4.7% and only 11.9 ± 4.5% were measured, respectively, while no Fe(II) was chelated by linear CS chelated Fe(II). As the adjustable and con-trollable swelling properties of cryogels are important parameters in biomedical applications, the swelling properties of CS cryogels, at different solution pHs, e.g., at the solution pHs of 1.0, 7.4 and 9.0, were measured as 3587 ± 186%, 4014 ± 184%, and 3984 ± 113%, respectively, and the maximum selling% values of CS:HNT cryogels were determined as 1961 ± 288%, 2816 ± 192, 2405 ± 73%, re-spectively, at the same conditions. Alpha glucosidase enzyme interactions were investigated and found that CS-based cryogels can stimulate this enzyme at any CS formulation.
Conducting semi-interpenetrating polymeric composites via the preparation of poly(aniline), poly(thiophene), and poly(pyrrole) polymers within superporous poly(acrylic acid) cryogels
(Elsevier Science Bv, 2016) Şahiner, Nurettin; Demirci, Şahin
In this study, a novel and special form of hydrogel known as cryogel with super and interconnected pore structures was synthesized as p(acrylic acid) (p(AAc)) cryogel by a cryopolymerization technique. Then, the superporous p(AAc) cryogels were used as template for the synthesis of conductive polymers such as poly(aniline) (p(An)), poly(thiophene) (p(Th)), and poly(pyrrole) (p(Py)). To the best of the authors' knowledge, this is the first study of its kind to report the synthesis of conductive polymers, p(An), p(Th), and p(Py), within the superporous network of cryogel. The synthesized p(AAc)/p(An), p(AAc)/p(Th), and p(AAc)/p(Py) conducting semi-interpenetrating polymeric network (semi-IPN) cryogel composites were characterized by using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and conductivity measurements. The conductivities of p(AAc)/p(An), p(AAc)/p(Th), and p(AAc)/p(Py) toward semi-IPN cryogels were measured as 2.2 x 10(-4) +/- 1 x 10(-5),32 x 10(-4) +/- 0.9 x 10(-5), and 3.2 x 10(-3) +/- 5 x 10(-4) S cm(-1), whereas the conductivity of bare p(AAc) cryogels was calculated to be about 3.2 x 10(-9) +/- 2.1 x 10(-10) S cm(-1). (C) 2016 Elsevier B.V. All rights reserved.

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