Naujų sluoksniuotų dvigubų hidroksidų sintezė, modifikavimas ir savybių tyrimas

Dissertation annotation Synthesis of new layered double hydroxides, modification and investigation of properties Recently layered double hydroxides (LDHs) have attracted substantial attention due to a wide range of important application areas, e.g. catalysis, photochemistry, electrochemistry, magnetization, biomedical science, environmental applications, and optics. A general chemical formula of the LDHs can be expressed as [M2+1−xM3+x(OH)2]x+(Ay−)x/y·zH2O, where M2+ (Mg, Zn, Co, Ni, Cu, Mn, . . .) and M3+ (Al, Ga, Cr, Co, Fe, V, Y, Mn, . . .) are divalent and trivalent metal cations, respectively, and Ay− is an intercalated anion which is located in the interlayer spaces along with water molecules and compensates the positive charge created by the partial substitution of M2+ by M3+ in a positively charged metal hydroxide layers. LDHs exhibit excellent ability to adopt organic and inorganic anions. LDHs can be fabricated by different synthesis methods. The most common preparation technique is co-precipitation method starting from soluble salts of the metals. The most common second technique for the preparation of LDHs is anion-exchange. The indirect sol-gel synthesis route for the preparation of LDHs recently was also developed. The synthesized precursor gels were converted to the mixed metal oxides (MMO) by heating the gels at 650 °C. The LDHs were fabricated by reconstruction of MMO in deionized water at 80 °C. The proposed sol-gel synthesis route for LDHs showed some benefits over the co-precipitation method such as simplicity, high homogeneity and good crystallinity of the end synthesis products, effectiveness, cost efficiency and suitability for different systems. The aim of this PhD thesis was to synthesize new Mg-Al-based layered double hydroxides by modifying its chemical composition, to investigate cation and anion substitution effects on the formation of the end products and to investigate properties of obtained LDHs. To achieve this, the main tasks were formulated as follows: To investigate transition metal substitution effects in Mg3-xMx/Al1 (M = Mn, Co, Ni, Cu, Zn) LDHs synthesized using the sol-gel chemistry approach. To investigate alkaline earth metal substitution effects in sol-gel derived Mg2-xMx/Al1 (M = Ca, Sr, Ba) LDHs and related mixed-metal oxides. To investigate the reconstruction peculiarities of sol-gel derived Mg2−xMx/Al1 (M = Ca, Sr, Ba) LDHs. To investigate the influence of ultrasound and cation substitution (Mn, Co, Ni, Cu, Zn) on the intercalation of organic anions (formate (HCOO−), acetate (CH3COO−), oxalate (C2O42−), tartrate (C4H6O42−) and citrate (C6H5O73−)) to the structure of Mg3/Al1 LDHs. To synthesize the Mg3Al1-xCrx LDH samples using an aqueous sol-gel method and investigate effect of Cr3+ substitution on phase purity, morphological and luminescent properties of obtained end products. The dissertation contains: introduction, five chapters and general conclusions. The first chapter investigates effect of transition metal substitution in Mg3-xMx/Al1 (M = Mn, Co, Ni, Cu, Zn) LDHs synthesized using the sol-gel chemistry approach. Iinvestigation of alkaline earth metal substitution effects in sol-gel derived Mg2-xMx/Al1 (M = Ca, Sr, Ba) LDHs and related mixed-metal oxides is in the second chapter. Results of the reconstruction peculiarities of sol-gel derived Mg2−xMx/Al1 (M = Ca, Sr, Ba) LDHs are analyzed in the third chapter. The influence of ultrasound and cation substitution (Mn, Co, Ni, Cu, Zn) on the intercalation of organic anions (formate (HCOO−), acetate (CH3COO−), oxalate (C2O42−), tartrate (C4H6O42−) and citrate (C6H5O73−)) to the structure of Mg3/Al1 LDHs is discussed in the fourth chapter. Analysis of the Mg3Al1-xCrx LDH samples using an aqueous sol-gel method and investigation of ther effect of Cr3+ substitution on phase purity, morphological and luminescent properties of obtained end products are in the fifth chapter. The novelty and originality of PhD thesis. The transition metal substitution effects in Mg3-xMx/Al1 (M = Mn, Co, Ni, Cu, Zn) LDHs synthesized by sol-gel synthesis method were investigated. The alkaline earth metal substitution effects in Mg2-xMx/Al1 (M = Ca, Sr, Ba) LDHs synthesized by sol-gel synthesis method were investigated. The reconstruction peculiarities of sol-gel derived Mg2-xMx/Al1 (M = Ca, Sr, Ba) LDHs by changing proceeding conditions were investigated. The chromium-substituted Mg3Al1-xCrx LDH samples were fabricated using an aqueous sol-gel method and luminescent properties of obtained specimens were investigated. The main results of the thesis were published in 4 scientific publications, the results were presented in 7 scientific conferences