The Effect of Strength of Bases and Temperature on the Synthesis of Zn‐Al Layered Double Hydroxides by a Non‐Aqueous ‘Soft Chemical’ Sol‐Gel Method and Formation of High Surface Area Mesoporous ZnAl2O4 Spinel

Abstract

AbstractLayered double hydroxides are the 2D layered material also known as the anionic clays having the general formula [M1‐x2+Mx3+(OH)2]x+[Ax/n]n−.m H2O where different M2+ ions such as Zn2+, Ni2+, Mg2+, Co2+ and M3+ ions such as Al3+, Cr3+, Ga3+, In3+, Mn3+, Fe3+ are uniformly distributed and orderly prearranged in the brucite‐like sheets and various charge‐compensating anions (An−=CO32−, NO3−, Cl−, OH− ) are present in their interlayer spaces along with the water molecules. During the synthesis of Zn−Al layered double hydroxides by non aqueous soft chemical method the strength of bases as well as the temperature influences immensely the hydrolysis of Zinc acetylacetonate (Zn(acac)2) and Aluminium acetylacetonate (Al(acac)3). Different bases such as sodium hydroxide (NaOH), piperidine, diethylamine and ammonia (NH3) was used and it was found that Zinc acetylacetonate (Zn(acac)2) directly forms Zincite (ZnO) phase without reacting with Aluminium acetylacetonate (Al(acac)3) at temperature of around 80oC. When the temperature was decreased to 0oC from room temperature as well as side by side the strength of bases were increased the formation of Zincite (ZnO) phases reduced. Thus, Zn−Al layered double hydroxide could only be synthesized at 0oC and in presence of stronger bases like sodium hydroxide (NaOH) and piperidine. The X‐ray diffraction analysis showed the presence of low intensity Zincite (ZnO) phases in Zn−Al layered double hydroxide synthesized in presence of sodium hydroxide (NaOH) which was absent in presence of piperidine. Zn−Al layered double hydroxide synthesized were further characterized by thermal analysis (TGA‐DTA), Infrared spectroscopy (FTIR), Scanning electron microscopic and energy dispersive X‐ray spectroscopic (SEM‐EDS) analysis, Brunauer–Emmett–Teller (BET) surface area and pore diameter analysis which showed their different characteristics as the base is changed. Zn−Al layered double hydroxide synthesized in presence of piperidine after thermal treatment at 800oC formed high surface area mesoporous flower platelet like Zinc‐Aluminium Oxide (ZnAl2O4) spinel which have surface area of 124.8 m2g−1 and mesopores of dimensions about 5–20 nm respectively.