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Öğe Effect of different solvents on hydrogen production from hydrolysis of potassium borohydride with a new and active Ni-based catalyst synthesized by green synthesis(Elsevier BV, 2024-12) Ömer Şahin; Selma Ekinci; Mehmet Sait İzgi; Erhan OnatIn this study, a novel Ni-based catalyst supported on carbon quantum dots (CQDs), synthesized from caffeine via a green hydrothermal method was developed to enhance hydrogen generation. The effects of different solvents, including water, and ethanol, on the catalyst's performance were explored. The results demonstrate that the Ni@CQDs catalyst prepared in ethanol exhibited superior hydrogen production rates due to improved nickel dispersion and higher surface area, as confirmed by BET, XPS, and XRD analyses. Ethanol was found to effectively modify the catalyst, resulting in faster H₂ conversion compared to water. The HGR values obtained with catalysts synthesized in water and ethanol were 4662, and 12262 mL min−1g−1, respectively. The study also investigated the impact of KOH concentration, catalyst loading, KBH4 concentration, and temperature on the hydrolysis process. The Ni@CQDs catalyst synthesized in ethanol achieved optimal performance at higher KBH₄ and KOH concentrations, producing 100% H2 yield over six reusability cycles with minimal loss of catalytic efficiency. Thermodynamic analysis using the Arrhenius and Eyring-Polanyi equations indicated that the catalyst in ethanol had a lower activation energy, enhancing the hydrolysis reaction rate. The Ni@CQDs (ethanol) catalyst exhibited a significantly higher TOF of 1696 h⁻1 at 4% KBH4 concentration and a lower activation energy (Ea) of 33.78 kJ mol−1 compared to the Ni@CQDs (water) catalyst, which had a TOF of 601.5 h⁻1 at 2% KBH4 concentration and an Ea of 38.93 kJ mol−1, indicating superior catalytic efficiency with ethanol as the solvent.Öğe Effective and environmentally friendly Co nanocatalyst on sodium borohydride hydrolysis in different solvents(Elsevier BV, 2025-01) Erhan Onat; Selma Ekinci; Ömer Şahin; Mehmet Sait İzgiThis study investigates the development and performance of a cobalt (Co) nanocatalyst supported by carbon quantum dots (CQDs) for hydrogen production via sodium borohydride (NaBH₄) hydrolysis. The CQDs were synthesized using a hydrothermal method from caffeine and subsequently used to support the cobalt catalyst. The structure and properties of the synthesized catalyst were characterized using techniques such as X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDX). The catalytic performance was evaluated in various solvents, with the highest hydrogen production rate observed in ethanol. The optimal conditions for Co@CQDs catalyst synthesis were identified as an 8-h hydrothermal treatment with a 3 mmol metal loading. The catalyst demonstrated excellent reusability, maintaining 100% hydrogen production efficiency after seven cycles. The activation energy for the hydrolysis reaction was found to be lower for catalysts synthesized in ethanol (25.48 kJ mol−1) compared to those synthesized in water (35.57 kJ mol−1), indicating enhanced catalytic activity. Under optimum conditions, the hydrolysis reaction in the presence of Co@CQDs (water) catalyst produced 23753 mL min−1 g−1 of hydrogen, while the hydrolysis reaction in the presence of Co@CQDs (ethanol) catalyst produced 28751 mL min−1 g−1. This study highlights the potential of CQDs-supported Co nanocatalysts for efficient and sustainable hydrogen production.Öğe Green synthesis of highly efficient and stable Ni@CQD nanoparticles: Experimental and theoretical approach for hydrogen production from dimethyl aminborane and sodium borohydride hydrolysis(Elsevier BV, 2025-10) Mehmet Sait Izgi; Ömer Şahin; Sultan Faal; Fatih Ahmet Celik; Erhan Onat; Ezman KarabulutIn this study, four different catalysts (Ni(0), Ni@Urea, Ni@DOT, Ni@MOF-DOT) were synthesized. The first two of these were synthesized by the impregnation method, while the last two were obtained using the hydrothermal method. Hydrogen (H2) efficiency of catalyses were investigated by hydrolysing sodium borohydride (SBH) and dimethylamine borane (DMAB) hydrogen sources. The HGR values obtained for SBH and DMAB hydrolysis of the best catalysis Ni@MOF-DOT were determined to be 1423 and 642 (mL/min.g.cat), and the TOF values were determined to be 191/hour and 78.6/hour, respectively. Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), nitrogen adsorption/desorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) analyses were used for the characterization study of Ni@CQDs nano-catalyst. In kinetic analyses driven by Arrhenius and Eyring-Polanyi equations, the catalyst in the hydrolysing of DMAB has lower activation parameters while the catalysts have showed stability over six reusability cycles in both hydrogen sources. Also, the average particle size of the (Ni@DOT-MOF) nano catalyst is about 4.6 nm and the presence of Carbon (C), oxygen (O), nitrogen (N) and Ni (Ni) atoms in its structure is confirmed by XPS and ICP analyses. The high density of 2P1/2 and 2P3/2 spin states of Ni atoms in the Ni@MOF-DOT catalyst creates Lewis acid regions that increase the catalytic activity. The experimental results were supported by Molecular Dynamics (MD) findings based on extended tight-binding density functional theory (GFN1-xTB)
