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    A Comprehensive Review on Red Mud-Based Catalysts: Modification Methods and Applications in Thermal- and Photocatalysis
    (Wiley-V C H Verlag Gmbh, 2025) Sekizkardes, Busra; Soyer-Uzun, Sezen; Uzun, Alper; Kuhn, Simon; Kaya-Ozkiper, Kardelen; Kurtoglu-Oztulum, Samira F.
    Red mud (RM), waste of the Bayer process for aluminum production, is mostly stored in landfill areas, creating serious environmental and economic problems. It offers substantial potential for catalytic applications, primarily because of its cost efficiency and rich chemical composition, including Fe, Si, Al, and Ti oxides. Using RM as a catalyst not only contributes to environmental protection but also offers economic advantages as it can potentially reduce the reliance on expensive noble metals typically used in solid catalyst formulations. RM is predominantly used in thermal- and photocatalysis, serving as a bulk catalyst, support material, promoter, additive, or as a host material for heterojunction catalysts. Before use, RM is generally modified to enhance its textural properties and tailor its composition. This review provides a comprehensive analysis of the utilization of RM in catalytic applications. The structural changes resulting from various pretreatments and their impact on catalytic properties are discussed. Key thermal- and photocatalytic reactions involving RM-based catalysts are presented to highlight their industrial and environmental significance. Potential pathways for further optimization of RM-based catalysts are also proposed, offering a broad perspective on future directions in the field.
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    Mechanically Strong Superabsorbent Terpolymer Hydrogels Based on AMPS via Hydrogen-Bonding Interactions
    (Amer Chemical Soc, 2023) Sekizkardes, Busra; Su, Esra; Okay, Oguz
    Polymers based on 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) attract significant attention due to their large water absorption capacity when swollen in water. Poly(AMPS) (PAMPS) hydrogels are usually synthesized via free-radical cross-linking copolymerization of AMPS and a chemical cross-linker in aqueous solutions. Owing to the covalently cross-linked network structure of PAMPS hydrogels preventing dissipation of the crack energy, they exhibit poor mechanical properties. Herein, we demonstrate that the terpolymerization of AMPS, methacrylic acid (MAAc), and N,N-dimethylacrylamide (DMAA) in an aqueous solution under UV light without a chemical cross-linker produces mechanically strong hydrogen-bonded hydrogels that are durable in water. The terpolymer hydrogels formed at a MAAc/DMAA molar ratio of 4:1 exhibit a high Young's modulus (26 +/- 2 MPa) and toughness (31 +/- 5 MJ center dot m-3) and are able to absorb 2035 +/- 255 times their mass in water without dissolving. The water content at the gel preparation, denoted by w, significantly affects the microstructure of terpolymer hydrogels. Decreasing the water content w at gelation increases the length of the primary chains forming the three-dimensional (3D) network and hence the number of interchain H-bonds due to the proximity effect. An optically transparent-to-opaque transition accompanied with a strong-to-weak transition in the mechanical properties was detected with increasing w due to the transformation of the uniform network into a colloidal network composed of phase-separated and highly hydrogen-bonded AMPS-poor aggregates interconnected by AMPS-rich terpolymer chains.
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    Modified Fly Ash: An Eco-Friendly, Cost-Free, and Efficient Iron-Based Catalyst for Ammonia Decomposition to COx-Free Hydrogen
    (Wiley-V C H Verlag Gmbh, 2024) Sekizkardes, Busra; Kurtoglu-Oztulum, Samira F.
    Fly ash (FA), an industrial waste produced in large amounts, is rich in metal oxides such as Al2O3, SiO2, and Fe2O3, making it an ideal candidate for use as a catalyst in ammonia decomposition. However, FA's surface area is very low (<1.0 m(2) g(-1)), limiting its potential. This study investigates the modification of FA by calcination at various temperatures (550, 700, and 1000 degrees C), HCl treatment, and HCl treatment followed by calcination at 500 degrees C to convert FA into a catalyst by utilizing its iron content as active sites. The catalyst obtained by treating FA with HCl at 220 degrees C, calcining at 500 degrees C, reducing in H-2 at 700 degrees C, and activating in ammonia at 700 degrees C achieved 86.0% ammonia conversion at a reaction temperature of 700 degrees C and a space velocity of 30,000 mL NH3 h(-1) gcat(-1), remaining stable for 140 h following an induction period of 30 h. Enhanced textural properties (18.5 m(2) g(-1)), elimination of S and Cl impurities, and the formation of relatively small Fe crystallites (23.8 nm determined by Scherrer equation and 24.0 nm measured by transmission electron microscopy (TEM)) when reduced in H-2 were responsible for this performance.