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    Development of a superhydrophobic and superoleophilic halloysite nanotube/phenyltriethoxysilane-coated melamine sponge sorbent material with high performance in supercritical CO2 atmosphere for the selective and effective oil spill cleanup and oil-water separation
    (Academic Press Ltd- Elsevier Science Ltd, 2025) Duman, Osman; Cengiz, Candan; Diker, Ceren Ozcan; Cengiz, Ugur; Guresir, Suleyman Mert; Tunc, Sibel
    In this study, activated halloysite nanotube (HNT) and phenyltriethoxysilane (PTES) were utilized for the first time to fabricate modified HNT materials and coat them onto melamine sponge (MS) substrate in the supercritical carbon dioxide (scCO2) atmosphere. The successful coating of MS substrate was confirmed using SEM, EDS, XPS, and contact angle measurements. The drainage technique applied in the CO2 medium achieved the uniform coating of both the inner and outer surfaces of the MS. Water and oil contact angles of the fabricated sorbent material (MS-PTES) were measured as 167.1 degrees and 0 degrees, respectively. MS-PTES sorbent having superhydrophobic and superoleophilic properties demonstrated sorption capacities ranging from 47.6 g/g to 132.2 g/g for 13 different pollutants, including various petroleum products, oils, and organic solvents. Moreover, the MSPTES sorbent material showed outstanding separation efficiency (99.99%) for the diesel-water mixture using a continuous separation process. It also displayed high selectivity for oil and organic solvent pollutants under acidic, saline, and alkaline conditions, along with excellent reusability, chemical stability, robustness, and mechanical flexibility. MS sorbent material coated with HNT-modified PTES nanoparticles, produced in the scCO2 atmosphere using the drainage technique, represents a promising solution for the removal of petroleum derivatives, oils, and organic solvents from water.
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    Effect of alkoxysilane chain length on the surface, stability, sorption and oil-water separation properties of novel superhydrophobic porous sorbent materials produced using innovative drainage technique in scCO2 atmosphere
    (Elsevier, 2024) Duman, Osman; Cengiz, Candan; Diker, Ceren Ozcan; Cengiz, Ugur; Guresir, Sueleyman Mert; Tunc, Sibel
    Alkoxysilanes play an important role in the development of new superhydrophobic sorbent materials with high sorption capacity for the cleanup of oil spills from water. Here, three different alkoxysilanes with 1, 8 and 16 carbon (C) chains were used for the first time to elucidate the role of alkoxysilanes and to determine the relation between the functional alkyl chain length of alkoxysilane compound within the coating formulation and the surface, sorption and separation properties of novel superhydrophobic sorbent materials fabricated in scCO2 atmosphere. Both the modification of activated halloysite nanotube (HNT) with each methyltrietoxysilane (METES), octyltriethoxysilane (OTES) and hexadecyltrimethoxysilane (HDTMS) separately and the direct fabrication of melamine sponge (MS)-HNT/alkoxysilane hybrid composite sorbents (MS-METES, MS-OTES and MS-HDTMS) were achieved by innovative drainage technique in scCO2 atmosphere. The surface properties of superhydrophobic sorbents were examined using contact angle, SEM, EDS, FTIR, XPS and 29Si-MAS NMR techniques. Maximum sorption capacity of melamine sponge-based hybrid materials decreased from 122.2 g/g to 90.4 g/g as the chain length of alkoxysilane was increased from C1 to C16. Water contact angle, density and porosity of superhydrophobic MS-METES, MS-OTES and MS-HDTMS sorbents were determined to be 153.0 degrees, 13.56 mg/cm3 and 99.10 %; 159.4 degrees, 16.58 mg/cm3 and 98.90 %; and 165.4 degrees, 18.90 mg/cm3 and 98.75 %, respectively. All sorbents exhibited excellent thermal stability, good chemical stability, good robustness, and high mechanical durability. Experimental results revealed that the novel coating technique applied to porous MS have a significant potential for the direct fabrication of new superhydrophobic and superoleophilic sponge-based sorbent materials.
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    Fabrication of superhydrophobic melamine sponge composite sorbent in supercritical carbon dioxide atmosphere for selective and effective oil removal from water
    (Elsevier Sci Ltd, 2023) Duman, Osman; Cengiz, Ugur; Diker, Ceren Ozcan; Cengiz, Candan; Guresir, Sueleyman Mert; Tunc, Sibel
    In this study, both the modification of activated halloysite nanotube (HNT) with methyltriethoxysilane (METES) and the fabrication of durable, superhydrophobic (water contact angle: 153.0 degrees) and superoleophilic (oil contact angle: 0 degrees) melamine sponge (MS)-HNT-METES sorbent material (MS-METES) were achieved in supercritical carbon dioxide (scCO2) atmosphere. For the coating of MS with clay mineral and METES through sol-gel reaction in scCO2, optimal process conditions were determined to be pressure difference of 60 bars at 35 degrees C, solvent/ METES mass ratio of 7.5, METES/MS mass ratio of 10, and degas time of 400 s. Successful preparation of MSMETES was proven by XPS, FTIR, 29Si-MAS NMR, SEM, and contact angle measurements. MS-METES displayed excellent sorption capacity for various petroleum products, oils, and organic solvents (49.6-122.4 g/g), remarkable oil-water separation efficiency (99.1%, for continuous separation technique), high selectivity for oil/ organic solvent in acidic, salty, and alkaline solution conditions, good reusability, chemical stability and robustness, and outstanding flexibility and mechanical stability. We believe that the innovative process used in this study will have great potential to be used by researchers in the direct fabrication of new superhydrophobic and superoleophilic sorbent materials for the selective removal of oil and organic solvent spills from water.
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    Fabrication of superhydrophobic sorbent material via in-situ coating of melamine sponge with halloysite nanotube and fluoroalkylsilane using supercritical CO2 coating system for efficient oily water treatment
    (Elsevier, 2025) Duman, Osman; Cengiz, Ugur; Diker, Ceren Ozcan; Guresir, Sueleyman Mert; Tunc, Sibel; Cengiz, Candan
    This study presents the preparation of a novel sorbent material with high performance and special wettability for oily water treatment, utilizing halloysite nanotube (HNT) and perfluorooctyl triethoxysilane (PFOTES). Fluoroalkyl silanes, such as PFOTES, offer significant advantages over other monomers and alkoxysilanes due to their superior water-repellent properties and high solubility in CO2 atmosphere, enabling homogeneous polymerization and coating. The modification of PFOTES with HNT was successfully achieved in the supercritical CO2 (scCO2) environment at 35 degrees C and 125 bar using a sol-gel technique. Subsequently, HNT-modified PFOTES nanoparticles were coated onto melamine sponge (MS) via a drainage technique, marking the first application of this method to create a superhydrophobic (WCA: 165.2 degrees) and superoleophilic (OCA: 0 degrees) sorbent material (MSPFOTES). The MS-PFOTES sorbent material, produced via a one-step, two-pot coating method, demonstrated exceptional sorption capacities ranging from 39.1 to 117.5 g/g for oily pollutants / organic solvents. Additionally, MS-PFOTES achieved an outstanding separation efficiency of 99.99 % for diesel-water mixtures in continuous separation processes. The fabricated material also exhibited remarkable thermal stability, chemical resistance, and robustness. Experimental findings obtained in this study highlight the significant potential of this innovative coating technique for the direct preparation of sorbent material with special wettability for oily water treatment.
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    Superhydrophobic melamine sponge-sorbent fabricated using WS2, halloysite nanotube, octyltriethoxysilane, tetraethoxysilane, and polydimethylsiloxane for the selective uptake of oil from water
    (Elsevier, 2023) Duman, Osman; Diker, Ceren Ozcan; Guresir, Sueleyman Mert; Cengiz, Ugur; Tunc, Sibel
    Here, a novel coating formulation was developed using WS2, halloysite nanotube (HNT), octyltriethoxysilane (OTES), tetraethoxysilane (TEOS), and polydimethylsiloxane (PDMS) to fabricate a new melamine sponge (MS)-based superhydrophobic sorbent material for the treatment of wastewater polluted with oily substances and organic solvents. The innovative aspect of this study lies in the alteration of WS2 particle size within the sorbent material and the chemical modification of HNT with silane compounds through the formation of reactive -OH groups on the cylindrical outer surface of clay mineral by chemical activation. The effect of nano- and micro-WS2 particle sizes on the wettability of sorbent material was investigated systematically. Successful coating of MS with the developed coating formulation was confirmed using SEM, mapping, EDS, and FTIR analyses. Sorbent material showed remarkable superhydrophobicity (WCA: 170.3 degrees), excellent thermal and mechanical stability, good chemical durability, high sorption capacity (34.0-73.8 g/g), good reusability, outstanding oil-water separation ability (>99.8 %) and flux (11,774 L/(m(2).h)), and efficient separation ability for water-in-oil emulsions (up to 99.6 %). The results of this study exhibit that MS/WS2/HNT/OTES-TEOS/PDMS sorbent material is of a great potential for the selective and effective removal of oily substance and organic solvent spills from water.