Browsing by Author "Alkan, Mehmet Huseyin"

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Cryogel-Immobilized Catalase as a Biocatalyst with Enhanced Stability Against Microplastics
(MDPI, 2025) Erol, Kadir; Alkan, Mehmet Huseyin; Alacabey, Ihsan
Catalase is a pivotal antioxidant enzyme that decomposes hydrogen peroxide and reduces oxidative stress. However, its low thermal and operational stability limits applications in challenging environments, particularly those contaminated with emerging pollutants such as polystyrene-based microplastics (PS-MPs). In this study, cryogels composed of Poly(2-hydroxyethyl methacrylate-co-allyl glycidyl ether) [Poly(HEMA-co-AGE)] were synthesized and evaluated as immobilization matrices to enhance catalase stability. Cryogels containing varying AGE concentrations were characterized using FT-IR, SEM, TEM, TGA, and BET analyses. The formulation with 250 mu L AGE exhibited optimal physicochemical properties, including improved water retention, increased surface area, and high immobilization capacity (356.3 mg center dot g(-1)). Immobilized catalase maintained superior activity under PS-MP-induced stress across a range of concentrations (0-1.0 mg center dot mL(-1)), temperatures (4-60 degrees C), and exposure times (up to 5 h). Kinetic modeling revealed a significant improvement in substrate affinity, with Km decreasing from 54.9 to 17.1 mM, while Vmax decreased moderately. Long-term stability tests showed that immobilized catalase retained similar to 80% activity after 70 days at 4 degrees C and 55% after 15 reuse cycles. Desorption studies confirmed the reusability of the cryogel system. These findings suggest that Poly(HEMA-co-AGE) cryogels provide a robust and reusable platform for catalase stabilization, offering potential for applications such as wastewater treatment and biosensing in microplastic-contaminated systems.
Citation - WoS: 7
Citation - Scopus: 7
Efficient Removal of Ciprofloxacin From Water Using High-Surface Activated Carbon Derived From Rice Husks: Adsorption Isotherms, Kinetics, and Thermodynamic Evaluation
(MDPI, 2025) Demirdag, Esra; Demirel, Mehmet Ferit; Benek, Veysel; Dogru, Elif; Onal, Yunus; Alkan, Mehmet Huseyin; Alacabey, Ihsan
Activated carbon is widely recognized as an effective material for removing pollutants, especially pharmaceutical residues, from water. In this study, high-surface-area activated carbon derived from rice husks (RHAC) was synthesized via KOH activation and used for the adsorption of ciprofloxacin, a widely used fluoroquinolone antibiotic. Its adsorption behavior was systematically investigated through batch experiments varying the pH, adsorbent dosage, contact time, initial concentration, and temperature. The RHAC exhibited a high surface area of 1539.7 m(2)/g and achieved a maximum adsorption capacity of 398.4 mgg(-1). The Freundlich isotherm best describes its adsorption equilibrium, suggesting multilayer adsorption on a heterogeneous surface. Kinetic modeling revealed that the adsorption process followed a pseudo second-order model (R-2 = 0.9981), indicating chemisorption as the rate-limiting mechanism. Thermodynamic parameters (Delta H degrees = 6.61 kJ/mol, Delta G degrees < 0) confirmed that the process was endothermic and spontaneous. These findings demonstrate that RHAC is a highly efficient, low-cost, and sustainable adsorbent for removing ciprofloxacin from aqueous environments.
Engineering Polyethylenimine-Metal Functionalized Cryogels for Superior Catalase Binding, Activity, and Long-Term Durability
(Nature Portfolio, 2026) Alkan, Mehmet Huseyin; Erol, Kadir; Alacabey, Ihsan
Cryogels with interconnected macroporous architectures offer significant advantages as enzyme immobilization supports due to their high permeability, mechanical robustness, and tunable surface chemistry. In this study, a novel Poly(HEMA-co-GMA) cryogel was synthesized and subsequently modified through polyethyleneimine (PEI) grafting and transition-metal chelation to create high-affinity matrices for catalase immobilization. Among the metal ions tested with Cu(II), Ni(II), and Co(II), the Cu(II)-functionalized cryogel exhibited superior physicochemical properties, including the highest water retention capacity (438.4%), well-preserved porosity, and strong coordination interactions with amine-rich PEI domains. FT-IR, SEM, TGA, BET, elemental analysis, and ICP-OES results confirmed successful stepwise modification and metal loading. Catalase immobilization studies revealed that the Poly(HEMA-co-GMA)-PEI-Cu(II) cryogel achieved the highest enzyme loading (391.9 mg & centerdot;g(-)& sup1;), with an optimal immobilization time of 8 h and optimum pH near neutrality. Kinetic analysis demonstrated a substantial decrease in K-m (from 57.3 to 14.4 mM), indicating enhanced substrate affinity, while k(cat)/K-m increased 2.8-fold relative to the free enzyme. The immobilized catalase exhibited improved thermal tolerance, strong operational stability (34.2% activity after 15 cycles), high desorption efficiency (96% in the first cycle), and markedly superior storage stability (62.1% activity after 70 days at 4 degrees C) compared to its free counterpart. These results validate the Cu(II)-chelated Poly(HEMA-co-GMA)-PEI cryogel as a highly efficient and reusable biocatalytic platform with significant potential for industrial and environmental enzyme-based applications.