Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 4Citation - Scopus: 3Atomic-Scale Insights Into Carbon Dioxide Hydrogenation Over Bimetallic Iron-Cobalt Catalysts: a Density Functional Theory Study(MDPI, 2023) Tuncer, Dilan; Kızılkaya, Ali CanThe conversion of carbon dioxide to fuels and chemicals is a promising long-term approach for mitigating CO2 emissions. Despite extensive experimental efforts, a fundamental understanding of the bimetallic catalytic structures that selectively produce the desired products is still lacking. Here, we report on a computational surface science approach into the effect of the Fe doping of Co(111) surfaces in relation to CO2 hydrogenation to C1 products. Our results indicate that Fe doping increases the binding strength of surface species but slightly decreases the overall catalytic activity due to an increase in the rate-limiting step of CO dissociation. FeCo(111) surfaces hinder hydrogenation reactions due to lower H coverages and higher activation energies. These effects are linked to the Lewis basic character of the Fe atoms in FeCo(111), leading to an increased charge on the adsorbates. The main effect of Fe doping is identified as the inhibition of oxygen removal from cobalt surfaces, which can be expected to lead to the formation of oxidic phases on bimetallic FeCo catalysts. Overall, our study provides comprehensive mechanistic insights related to the effect of Fe doping on the catalytic behavior and structural evolution of FeCo bimetallic catalysts, which can contribute to the rational design of bimetallic catalysts.Erratum Citation - WoS: 1Corrigendum: Bioactive Snail Mucus-Slime Extract Loaded Chitosan Scaffolds for Hard Tissue Regeneration: The Effect of Mucoadhesive and Antibacterial Extracts on Physical Characteristics and Bioactivity of Chitosan Matrix (2021biomed. Mater.16 065008)(NLM (Medline), 2023) Perpelek, M.; Tamburaci, S.; Aydemir, S.; Tıhmınlıoğlu, F.; Baykara, B.; Karakaşli, A.; Havitçioǧlu, H.Article Citation - WoS: 11Fabrication of Helix Aspersa Extract Loaded Gradient Scaffold With an Integrated Architecture for Osteochondral Tissue Regeneration: Morphology, Structure, and in Vitro Bioactivity [2](American Chemical Society, 2023) Tamburacı, Sedef; Perpelek, Merve; Aydemir, Selma; Baykara, Başak; Havıtçıoğlu, Hasan; Tıhmınlıoğlu, FundaRegeneration of osteochondral tissue with its layered complex structure and limited self-repair capacity has come into prominence as an application area for biomaterial design. Thus, literature studies have aimed to design multilayered scaffolds using natural polymers to mimic its unique structure. In this study, fabricated scaffolds are composed of transition layers both chemically and morphologically to mimic the gradient structure of osteochondral tissue. The aim of this study is to produce gradient chitosan (CHI) scaffolds with bioactive snail (Helix aspersa) mucus (M) and slime (S) extract and investigate the structures regarding their physicochemical, mechanical, and morphological characteristics as well as in vitro cytocompatibility and bioactivity. Gradient scaffolds (CHI-M and CHI-S) were fabricated via a layer-by-layer freezing and lyophilization technique. Highly porous and continuous 3D structures were obtained and observed with SEM analysis. In addition, scaffolds were physically characterized with water uptake test, micro-CT, mechanical analysis (compression tests), and XRD analysis. In vitro bioactivity of scaffolds was investigated by co-culturing Saos-2 and SW1353 cells on each compartment of gradient scaffolds. Osteogenic activity of Saos-2 cells on extract loaded gradient scaffolds was investigated in terms of ALP secretion, osteocalcin (OC) production, and biomineralization. Chondrogenic bioactivity of SW1353 cells was investigated regarding COMP and GAG production and observed with Alcian Blue staining. Both mucus and slime incorporation in the chitosan matrix increased the osteogenic differentiation of Saos-2 and SW1353 cells in comparison to the pristine matrix. In addition, histological and immunohistological staining was performed to investigate ECM formation on gradient scaffolds. Both characterization and in vitro bioactivity results indicated that CHI-M and CHI-S scaffolds show potential for osteochondral tissue regeneration, mimicking the structure as well as enhancing physical characteristics and bioactivity. © 2023 The Authors. Published by American Chemical Society.Article Citation - WoS: 10Citation - Scopus: 12Enhanced Model Protein Adsorption of Nanoparticulate Hydroxyapatite Thin Films on Silk Sericin and Fibroin Surfaces(Springer, 2022) Özcan, Selçuk; Çiftçioğlu, MuhsinHydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm2 on the latter surface as compared to 1.37 µg/cm2 of hydroxyapatite on glass without an intermediate silk sericin layer. [Figure not available: see fulltext.].Article Citation - WoS: 5Citation - Scopus: 5Flat sheet metakaolin ceramic membrane for water desalination via direct contact membrane distillation(IWA Publishing, 2022) Zewdie, Tsegahun Mekonnen; Habtu, Nigus Gabbiye; Dutta, Abhishek; Van der Bruggen, BartHydrophobic metakaolin-based flat sheet membrane was developed via phase inversion and sintering technique and modified through 1H,1H,2H,2H-perfluorooctyltriethoxysilane grafting agents. The prepared membrane was characterized by different techniques such as XRD, FTIR, SEM, contact angle, porosity, and mechanical strength. Their results indicated that the wettability, structural, and mechanical properties of the prepared membrane confirm the suitability of the material for membrane distillation (MD) application. The prepared metakaolin-based flat sheet membrane acquired hydrophobic properties after surface modification with the water contact angle values of 113.2° to 143.3°. Afterward, the membrane performance was tested for different sodium chloride aqueous solutions (synthetic seawater) and various operating parameters (feed temperature, feed flow rate) using direct contact membrane distillation (DCMD). Based on the findings, the prepared membrane at metakaolin loading of 45 wt.% and sintered at 1,300 °C was achieved the best performance with >95% salt rejection and permeate flux of 6.58 + 0.3 L/m2 · h at feed temperature of 80 °C, feed concentration of 35 g/L, and feed flow rate of 60 L/h. It can be con-cluded that further optimization of membrane porosity, mechanical, and surface properties is required to maximize the permeate flux and salt rejection.Article Citation - WoS: 6Citation - Scopus: 9Mechanistic Insights Into the Effect of Sulfur on the Selectivity of Cobalt-Catalyzed Fischer–tropsch Synthesis: a Dft Study(MDPI, 2022) Dağa, Yağmur; Kızılkaya, Ali CanSulfur is a common poison for cobalt-catalyzed Fischer–Tropsch Synthesis (FTS). Alt-hough its effects on catalytic activity are well documented, its effects on selectivity are controversial. Here, we investigated the effects of sulfur-covered cobalt surfaces on the selectivity of FTS using density functional theory (DFT) calculations. Our results indicated that sulfur on the surface of Co(111) resulted in a significant decrease in the adsorption energies of CO, HCO and acetylene, while the binding of H and CH species were not significantly affected. These findings indicate that sulfur increased the surface H/CO coverage ratio while inhibiting the adsorption of carbon chains. The elementary reactions of H-assisted CO dissociation, carbon and oxygen hydrogenation and CH coupling were also investigated on both clean and sulfur-covered Co(111). The results indicated that sulfur decreased the activation barriers for carbon and oxygen hydrogenation, while increasing the barriers for CO dissociation and CH coupling. Combining the results on elementary reactions with the modification of adsorption energies, we concluded that the intrinsic effect of sulfur on the selectivity of cobalt-catalyzed FTS is to increase the selectivity to methane and saturated short-chain hy-drocarbons, while decreasing the selectivity to olefins and long-chain hydrocarbons.Article Citation - WoS: 8Citation - Scopus: 7Cvd-Deposited Oxygen-Selective Fluorinated Siloxane Copolymers as Gas Diffusion Layers(American Chemical Society, 2022) Cihanoğlu, Gizem; Ebil, ÖzgençCopolymer thin films of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexylethylacrylate) (PFHEA), and 2-(perfluoroalkylethylmethacrylate) (PFEMA) were synthesized via initiated chemical vapor deposition (iCVD) as potential candidates for gas diffusion layers (GDLs) in gas diffusion electrodes (GDEs) for aqueous metal–air batteries. Thin-film GDLs exhibited an average water vapor transmission rate of 7.5 g m–2 day–1 and enhanced oxygen diffusion with oxygen permeabilities as high as 3.53 × 10–15 mol m m–2 s–1 Pa–1 (10.5 Barrer). The electrochemical performance of GDEs fabricated using commercial catalysts, current collectors, and synthesized GDLs was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and potentiodynamic polarization measurements. The fabricated GDEs exhibited higher oxygen reduction current densities (228.2 mA cm–2) compared to commercial GDEs (132.7 mA cm–2). Copolymer GLDs exhibited an order of magnitude higher oxygen diffusion (39.5 × 10–8 cm2 s–1) in GDEs compared to commercial counterparts (1.84 × 10–8 cm2 s–1). Due to the high oxygen solubility of V4D4 and excellent hydrophobic behavior of PFHEA and PFEMA, their copolymers can effectively promote the diffusion of oxygen and restrict moisture intake, making them ideal materials for GDLs. Combining well-balanced properties of siloxane and fluorinated polymer chemistries, the iCVD process is an excellent low-cost method for the fabrication of GDLs for metal–air battery applications.Article Citation - WoS: 11Citation - Scopus: 12Numerical Modelling Assisted Design of a Compact Ultrafiltration (uf) Flat Sheet Membrane Module(MDPI, 2021) Bopape, Mokgadi F.; Van Geel, Tim; Dutta, Abhishek; Van der Bruggen, Bart; Onyango, Maurice StephenThe increasing adoption of ultra-low pressure (ULP) membrane systems for drinking water treatment in small rural communities is currently hindered by a limited number of studies on module design. Detailed knowledge on both intrinsic membrane transport properties and fluid hydrodynamics within the module is essential in understanding ULP performance prediction, mass transfer analysis for scaling-up between lab-scale and industrial scale research. In comparison to hollow fiber membranes, flat sheet membranes present certain advantages such as simple manufacture, sheet replacement for cleaning, moderate packing density and low to moderate energy usage. In the present case study, a numerical model using computational fluid dynamics (CFD) of a novel custom flat sheet membrane module has been designed in 3D to predict fluid flow conditions. The permeate flux through the membrane decreased with an increase in spacer curviness from 2.81 L/m(2)h for no (0%) curviness to 2.73 L/m(2)h for full (100%) curviness. A parametric analysis on configuration variables was carried out to determine the optimum design variables and no significant influence of spacer inflow or outflow thickness on the fluid flow were observed. The numerical model provides the necessary information on the role of geometrical and operating parameters for fabricating a module prototype where access to technical expertise is limited.Article Citation - WoS: 7Citation - Scopus: 8Compositional, Microstructural and Mechanical Effects of Nacl Porogens in Brushite Cement Scaffolds(Elsevier, 2021) Şahin, Erdem; Çiftçioğlu, MuhsinModification of the setting process of brushite cements by varying the concentration of ions that alter calcium phosphate crystallization kinetics, is known to enable control on the monetite conversion extent and the accompanying microporosity. This is useful because monetite serves as a suitable matrix in macroporous scaffolds due to its higher phase stability and finer crystal morphology compared to its hydrous counterpart brushite. In this study the synergistic effect of NaCl and citric acid on the microstructural evolution of brushite cement was demonstrated and microporosity of macroporous monetite-rich cement blocks was minimized by a variable NaCl porogen size distribution approach. Initially, maximum packing ratio of various combinations of NaCl size groups in PEG were determined by their rheological analysis in a range between 57% and 69%. Statistical analysis revealed a positive correlation between the amounts of NaCl particles under 38 mu m and 212 mu m and the maximum packing ratio. Further broadening the size distributions of NaCl porogens with fine cement precursors was effective in increasing the solids packing ratio of cement blocks more than the maximum packing ratio for the porogens. This improvement in packing was accompanied by a reduction in microporosity despite the increase in micropore volume with ion induced monetite formation. The detrimental effect of the microporosity introduced to the structure during monetite formation was balanced for some size distributions and not so much for others, thereby resulting in a wide range of porosities and mechanical properties. Thus, the exponential dependence of mechanical properties on porosity and the mechanical properties of monetite-rich macroporous blocks at the theoretical zero-porosity were determined according to Rice's model. Zero-porosity extrapolations were much higher than those predicted for brushite cement, contrary to the common assumption that brushite is mechanically stronger than monetite.Article Payne Cell Gravimetric Measurements in Polymer-Solvent Systems for Diffusion Coefficients and Isotherm Data(Wiley, 2021) Zielinski, John M.; Garcia, Armando R.; Alsoy Altınkaya, SacideThe discussion focuses on the application of a Payne cell to the measurement of diffusion and solubility coefficients in polymer/solvent systems. Payne cells have, thus far, been used exclusively to measure steady-state permeation rates of solvents. An analytical model has been developed to describe transient gravimetric sorption and desorption measurements performed with a Payne cell. The model has been validated by a complementary numerical simulation and has been applied to evaluate diffusion and solubility coefficients in two different toluene-silicone rubber systems. The data measured using the Payne cell are found to compare very well with diffusion coefficient and isotherm data measured by traditional gravimetric sorption experiments.