Materials based on silica and aluminosilicate for environmental protection
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Дата
2025
Автори
Науковий керівник
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Видавець
Igor Sikorsky Kyiv Polytechnic Institute
Анотація
Yu Junjie. Materials based on silica and aluminosilicate for environmental protection. – Qualification research work presented as a manuscript. Dissertation for the degree of Doctor of Philosophy in specialty 161 Chemical Technologies and Engineering. – National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute,” Kyiv, 2025.
This dissertation is devoted to the development of silicate materials based on natural and artificial raw materials for protecting water from pollution by various toxic substances. The development of water purification technologies for removing heavy metal ions and organic dyes using effective adsorption materials based on accessible and low-cost raw materials is economically justified. Promising materials in this regard include natural (layered aluminosilicates), artificial (synthesized silicas), and even technogenic silicates (fly ash). By applying various surface modification methods to inorganic materials using modern synthesis techniques, it is possible to obtain new chemically and thermally stable sorbents with improved structural-adsorption characteristics and physicochemical properties. The production of so-called “low-cost” materials based on natural aluminosilicate raw materials in granulated form enables quick separation of solid and liquid phases after adsorption purification, without the need for special equipment. A key and topical issue is the study of specific features of obtaining materials based on modified synthetic silicas and aluminosilicates, as well as the investigation of physicochemical patterns involved in the removal of heavy metals and cationic dyes from water using such materials. The first chapter of the dissertation presents an analytical review of scientific literature on adsorption materials used for the protection of aquatic environments. It examines the sources of heavy metal ions and organic dyes entering water, as well as existing methods for purifying natural and wastewater from such pollutants. Special attention is given to adsorption processes, the factors influencing them, and the practical application of sorption materials in water treatment technologies. The chapter also analyzes methods for obtaining mesoporous adsorbents based on syntheticsilicates (silica) and natural or artificial aluminosilicate materials. Various approaches to chemical modification of these materials and their fields of application are studied. The second chapter describes the methodologies for obtaining adsorption materials, including synthetic silica with a zero-valent iron layer, amino-functionalized silica, commercial silica gel modified with nickel oxide, granulated samples based on saponite and sodium alginate, and mesoporous adsorbents synthesized using fly ash. A list of reagents, materials, and equipment used to prepare the adsorbents is provided. The reliability of the obtained results is ensured by the use of modern instrumental research methods. Surface morphology of the materials was studied using scanning electron microscopy with energy-dispersive X-ray spectroscopy and transmission electron microscopy. Phase composition and surface chemistry were analyzed using Xray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy. Porous structure parameters were determined using low-temperature nitrogen adsorption– desorption methods. Thermal stability was assessed using differential thermal analysis and thermogravimetric analysis. In addition, the rheological properties of clay suspensions were measured, along with functional group content on the surface of the adsorbents and granule stability in aqueous media. Sorption techniques were used to study the physicochemical characteristics of heavy metal ion and dye removal from water. Inductively coupled plasma atomic emission spectrometry was applied to determine initial and equilibrium concentrations of copper ions, while the spectrophotometric method was used for determining dye concentrations in solution. The third chapter is devoted to the synthesis and characterization of dendritic mesoporous silica nanoparticles (DMSNs) modified with zero-valent iron and 3- aminopropyltriethoxysilane, as well as to the study of their efficiency in removing copper ions from aqueous solutions. The optimal synthesis parameters were determined, particularly the influence of synthesis time on the formation of monodisperse silica microspheres with controlled structural and physicochemical characteristics. X-ray diffraction analysis revealed a broad diffraction peak at 2θ = 22°, indicating the formation of amorphous silica in all samples, regardless of synthesis duration (1.5, 3, and 5 hours – labeled as DMSN-1.5, DMSN-3, and DMSN-5). Infraredspectroscopy confirmed the presence of characteristic vibrational bands for Si – OH, O – Si – O, and Si – O – Si bonds, typical for amorphous SiO2. Surface morphology studies using scanning electron microscopy revealed that the silica microspheres synthesized under different stirring durations are monodisperse spheres with a diameter of approximately 200 nm and contain visible pores. The DMSN-1.5 sample exhibited a nanoscopic rim structure around 7 nm in thickness and well-defined mesopores. Extending the synthesis time to 3 hours caused the thin nanosheet-like edges to transform into thicker ribbon-like rims, increasing their size to 16 nm, while maintaining the overall 200 nm particle diameter. Further extending the reaction time to 5 hours resulted in edge thickening up to 22 nm, but also led to partial loss of monodispersity, suggesting that prolonging the synthesis beyond this point is not advisable. Low-temperature nitrogen adsorption–desorption analysis showed that all SiO2 microsphere samples exhibit type IV isotherms with H3-type hysteresis loops according to IUPAC classification, indicating mesoporous structures formed by uniform spherical particles. The pore sizes ranged from approximately 5 to 50 nm. The specific surface areas were 504 m²/g, 452 m²/g, and 308 m²/g for DMSN-1.5, DMSN3, and DMSN-5, respectively. It was concluded that a synthesis time of 1.5 hours is optimal for achieving a high specific surface area and favorable morphology without significant pore coalescence or excessive rim thickening. A adsorbent material (Fe⁰@DMSN) was obtained by depositing zero-valent iron particles onto the surface of DMSN-1.5. Successful modification was confirmed by scanning and transmission electron microscopy, X-ray phase analysis, and infrared spectroscopy. The low-temperature nitrogen adsorption–desorption isotherms of the studied samples correspond to type IV isotherms according to IUPAC classification, featuring H3-type hysteresis loops typical for mesoporous materials. The specific surface area of the modified sample was found to be nearly half that of the synthesized DMSN, which may be attributed to Fe⁰ occupying or partially blocking the DMSN pore channels. Pore size distribution revealed a broad range of pore diameters between 3 and 50 nm. It was established that under pH = 5.7, the maximum adsorption capacity of Fe⁰@DMSN toward copper ions reached 39.8 mg·g⁻¹, which is approximately 57times higher than that of the unmodified DMSN-1.5 (0.7 mg·g⁻¹). The kinetics of Cu²⁺ removal were described by a pseudo-first-order model. An amino-functionalized adsorbent (DMSN-NH2) was obtained by chemically modifying dendritic mesoporous silica nanoparticles with 3- aminopropyltriethoxysilane. It was determined that the content of – NH₂ groups in the modified sample is significantly higher than the content of – OH groups in the unmodified material: 2.03 meq/g versus 0.16 meq/g, respectively. Successful attachment of amino groups to the surface of the silica particles was confirmed by infrared spectroscopy and thermal analysis methods. The low-temperature nitrogen adsorption–desorption isotherms of both samples correspond to type IV isotherms with H3-type hysteresis loops according to the IUPAC classification. This is characteristic of mesoporous materials, as confirmed by the obtained pore size distribution. It was found that the unmodified DMSN exhibits almost no adsorption capacity toward copper ions at pH 6, with a removal efficiency of only 15%. In contrast, DMSN-NH₂ demonstrates highly efficient Cu(II) removal across the entire tested pH range, with only a slight decrease in removal efficiency from 99% to 87% as the pH increases from 3 to 6. The adsorption equilibrium was reached relatively quickly. Structural-sorption, morphological, and adsorption studies showed that amino functionalization of the DMSN surface significantly enhances its efficiency in removing copper ions from aqueous solutions. X-ray photoelectron spectroscopy results indicate the formation of coordination bonds between Cu²⁺ ions and amino groups, suggesting a combination of physical adsorption and chemisorption processes. Regeneration studies of the used adsorbent indicate its potential for repeated use. The forth chapter presents the results of adsorption removal of copper ions and methylene blue using materials based on commercial silica gel modified with nickel oxide at different mass ratios (SiO₂@0.5NiO and SiO₂@NiO). X-ray diffraction analysis confirmed the successful deposition of nickel oxide on the silica surface. The obtained low-temperature nitrogen adsorption–desorption isotherms correspond to type IV according to IUPAC classification, indicating a mesoporous structure. The hysteresis loop shape suggests that the porous structure of all samples is formed byspherical particles of uniform size, arranged in a homogeneous packing with cylindrical pore channels. These materials also exhibit a narrow mesopore size distribution in the range of approximately 2.5–3 nm, as confirmed by pore size distribution data. It was shown that in the series SiO₂ > SiO₂@0.5NiO > SiO₂@NiO, the specific surface area of the adsorbents decreased from 411 m²/g to 186 m²/g. The commercial SiO₂ exhibited practically no copper ion adsorption, with a maximum capacity of 0.2 mg/g at pH 5.5. For the modified samples, the degree of Cu²⁺ removal increased with increasing pH. The maximum adsorption capacities at pH 5.5 were 0.9 mg/g for SiO₂@0.5NiO and 1.7 mg/g for SiO₂@NiO. Copper ion removal was found to be relatively fast. Adsorption equilibrium was established within 1 hour, with 51% removal achieved within the first 15 minutes for SiO₂@NiO - significantly higher than for unmodified SiO₂. These results indicate that the sorption capacity of silica gel is significantly enhanced after surface modification with nickel oxide. Specifically, the maximum adsorption capacity increased by approximately 5 times for SiO₂@0.5NiO and by nearly 10 times for SiO₂@NiO. The study also showed that methylene blue removal from solution by the synthesized materials occurred rapidly. The highest adsorption capacity (19.3 mg/g) was observed for the sample with a SiO₂ to NiO mass ratio of 1:0.5. The fifth chapter presents experimental data on the removal of copper ions using sorbent materials based on natural and technogenic aluminosilicates. Granules were obtained using saponite modified with ferrihydrite and sodium alginate, as well as a mesoporous adsorbent derived from fly ash coated with a zeolite layer. To obtain granules that are stable in aqueous media, the rheological behavior of clay suspensions based on saponite and biopolymer with varying component mass ratios was investigated. It was established that these systems are thixotropic, and their viscosity— when the same amount of sodium alginate is added-depends on the solid phase content. Based on these results, the appropriate conditions for granulation were selected. It was found that the amount of sodium alginate added significantly affects the stability of the granules in water. The structural-sorption characteristics and thermal properties of the resulting granulated adsorbents were studied, and their potential application for theremoval of heavy metal ions from water was demonstrated. The morphology, phase composition, and chemical structure of sorbents based on aluminosilicate microspheres with a zeolite coating were examined. It was shown that during synthesis, fly ash serves as the source of silicon, while the aluminate solution provides sodium and aluminum. The deposition of a zeolite phase on the surface of fly ash increased the sorption capacity for copper ions from 4.94 mg/g to 6.53 mg/g. However, to further improve efficiency, longer synthesis durations at higher temperatures are required. This study presents, for the first time, an in-depth investigation into the synthesis of adsorption materials based on dendritic mesoporous silica and commercial silica gel with enhanced structural and sorption characteristics. These improvements were achieved through surface modification with zero-valent iron nanoparticles, 3- aminopropyltriethoxysilane, and nickel oxide. The rheological behavior of suspensions based on natural and modified saponite with sodium alginate was examined, and the optimal conditions were determined for producing granulated, water-stable, low-cost adsorbents. Additionally, a mesoporous material coated with a zeolite layer was synthesized using technogenic aluminosilicate waste (fly ash) under relatively simple synthesis conditions and with accessible laboratory equipment. The physicochemical mechanisms of copper ion and methylene blue dye removal using the synthesized adsorbents were studied. The results confirm the promising potential of these materials for efficient purification of water contaminated with such pollutants. From a practical standpoint, the functional materials obtained in this work may be applied in the development of new effective sorbents based on silicates and natural or artificial aluminosilicates for protecting aquatic environments from inorganic and organic toxicants. These sorbents are especially relevant for use in the chemical, food, and mining industries.
Опис
Ключові слова
silicon dioxide, tetraethoxysilane, silica, aluminosilicates, modification, morphology, water purification, adsorption, sorption capacity, heavy metals, organic dyes, діоксид кремнію, тетраетоксисилан, кремнезем, алюмосилікати, модифікація, морфологія, очищення води, адсорбція, сорбційна ємність, важкі метали, органічні барвники
Бібліографічний опис
Yu Junjie. Materials based on silica and aluminosilicate for environmental protection : dissertation submitted for the Doctor of Philosophy degree : 161 Chemical technologies and engineering / Yu Junjie. – Kyiv, 2025. – 194 p.