Вестник НЯЦ РК выпуск 4, декабрь 2022 63 https://doi.org/10.52676/1729-7885-2022-4-63-73 УДК 534.222.2 SYNTHESIS OF DIFFERENT METAL DOPED ZnAl-LDH/PVA NANOCOMPOSITES FOR ADSORPTION AND PHOTOCATALYTIC APPLICATIONS O.O. Balayeva Baku State University, Baku, Azerbaijan E-mail for contacts: oobalayeva@gmail.com; ofeliyabalayeva@bsu.edu.az Due to their high surface area, electronic properties, energy storage performance and catalytic activity, two-dimensional (2D) nanostructures have attracted significant interest and great attention in developing science. Layered double hydroxides (LDHs) belong to 2D nanostructures and have a high surface area, very important physicochemical properties, and biological activity. However, there has always been great interest in their doping to enhance and improve these unique properties, especially photocatalytic activity. In this work, ZnAl-based LDHs were synthesized and their doping with active- (Ca, Sr), transition- (Co, Cu, Cd, Ni, Pb, Fe), noble- (Ag) and rare earth- (La) metals were carried out by impregnation method. The removal of cationic and anionic dyes from aqueous solutions by adsorption and photodegradation on as-synthesized and doped ZnAl-LDH/PVA nanocomposite was also studied. The obtained results were correlated with the structure and physicochemical properties of the nanocomposites. Keywords: Layered Double Hydroxides (LDH); metal-doped, sorption; photodegradation; Rhodamine 6G; Ponceau 4R. 1. INTRODUCTION 2D nanomaterials are generally layered materials can be classified according to their chemical composition, properties, and application. They are classified based on different criteria like sheets layered nanostructures, films, nano-patterned surfaces, and coatings [1]. Graphene [2, 3], graphene oxide (GO) [4], Mxenes [5], silicate clays [6], hydroxides, and layered double hydroxides (LDHs) [7], [8], some of transition metal chalcogenides [9–11], some of transition metal oxides (TMOs) or mixed metal oxide (MMO) [12, 13], black phosphorus nano- sheets (BPN), Boron and boron nitride nanosheet, antimonene (AM) and antimonene oxide nanosheet [14] are sheet-like layered nanostructures possess excellent physical, mechanical, chemical and biochemical proper- ties due to structures, high surface area and surface charge. In order to obtain new physicochemical proper- ties in nanomaterials, new 2D nanomaterials are currently being synthesized in science, or modification of known nanostructures is being carried out. In layered nano- structures, atoms on the layer chemically bonded each other and there are physical interactions between the layers to form bulk crystals [1], [15, 16]. This research article will focus on layered double hydroxides (LDHs) which are very important represen- tatives of 2D nanostructures containing positively charged layers and their compositional properties will be discussed in detail. LDHs are layered crystalline hydro- xides with excellent conductivity, surface active, optical, electrical, mechanical, thermal, magnetic, catalytically properties which have broad application in photocatalysis [17–19] supercapacitors [20, 21], fire retardant [22, 23], energy storage [24, 25], anion exchange materials [26, 27], biomedicine [28, 29], electrochemical sensors [30], and other field. As known, to enhance or change the electrical, optical and structural properties of semi- conductor nanoparticles, it is very important to include or dope small or large amounts of other elements on their surface or inside. Many experiments on metal doping to TiO2 have been carried out in the literature [31]. Depending on the nature and amount of the dopant and method, various but excellent results have been obtained [32]. However, since LDHs themselves are formed from atoms of various elements, their doping has not been widely studied. It is for this reason that by taking LDH with a uniform composition (ZnAl), it was doped by the method of impregnation with metals of different activity. The photocatalytic activity of doped materials was studi- ed by decomposition of dye compounds under sun light and explained in detail. 2. EXPERIMENT 2.1. Synthesis of Zn Al LDH in PVA matrix Zinc-aluminum layered double hydroxide (ZnAl LDH) nanoparticles in polyvinyl alcohol (PVA) matrix was synthesized via co-formation method [33]. 40 mL of 10% PVA solution was added into the mixed metal salt solution before the co-precipitation with Zn/Al = 3/1 molar ratio and mixed for 30 min. 25 mL of 5 M sodium hydroxide (NaOH) solution was drop wise added to the mixed salt solution. The pH of the sample was adjusted to ~10 by adding some additional drops of NaOH solution. The obtained slurry was aged for 2 weeks and heated at 90 o C for four days, washed with hot distilled water (~98 o C), dried at room condition (at 25 o C), cuted into pieces and used for the adsorption and sunlight photodegradation of anionic and cationic dyes like Ponceau 4R (P4R) and Rhodamin 6G (R6G). The chemical structures of ponceau 4R and Rhodamin 6G are shown at Scheme 1: