A green approach of preparation of fine active alumina with high specific surface area from sodium aluminate solution

Abstract

A green preparation of fine active alumina from saturated sodium aluminate solution by phase evolution is presented. High capillary pressure, numerous mesopores, and the inhibition of aggregation produced FAA with an extremely high specific surface area.

Simplified waste-free process for synthesis of nanoporous compact alumina under technologically advantageous conditions

“…Recently, synthesis of ammonium aluminium carbonate hydroxide (AACH, NH 4 Al(OH) 2 CO 3 ) has become a promising alternative for preparation of nanostructured Al 2 O 3 . [1][2][3]9,14,[20][21][22][23] AACH is typically prepared by liquid-liquid precipitation using different aqueous aluminium solutions (NH 4 Al(SO 4 ) 2 , Al(NO 3 ) 3 , AlCl 3 , and NaAlO 2 ). 3,9,14,20 It has been shown that the choice of an appropriate precipitating agent is crucial for preparation of pure AACH.…”

“…[1][2][3]9,14,[20][21][22][23] AACH is typically prepared by liquid-liquid precipitation using different aqueous aluminium solutions (NH 4 Al(SO 4 ) 2 , Al(NO 3 ) 3 , AlCl 3 , and NaAlO 2 ). 3,9,14,20 It has been shown that the choice of an appropriate precipitating agent is crucial for preparation of pure AACH. The product of precipitation using NH 4 HCO 3 is a mixture of boehmite (AlO(OH)) and AACH, 14,20 whereas using (NH 4 ) 2 CO 3 results in formation of only the AACH phase with low crystallinity.…”

“…14 However, precipitation of AACH is very pH sensitive (optimal pH range 9.92-10.28), because AACH can change to AlO(OH) or [Al(OH) 4 ] À in concentrated alkaline solution. 3 An alternative novel technique for AACH synthesis that enables control of the morphology of the particles is hydrothermal treatment. Reaction of Al(NO 3 ) 3 aqueous solution or aluminium hydroxide xerogel with a signicant stoichiometric excess of ammonium carbonate solution at high temperature and vapour pressure leads to ake-like 2 or rod-like 9 particles.…”

“…25 Although synthesis of nanostructured Al 2 O 3 from Al precursors prepared by precipitation has been widely performed, the nanoparticles tended to strongly agglomerate, which caused an increase of the particle size and decreased the specic surface area. 3,14,27 Agglomeration is greatly affected by the aging time of the precipitated precursor. 14 Thus, alumina prepared by precipitation generally exhibits a surface area lower than 300 m 2 g À1 .…”

“…20 Various approaches have been applied to prevent undesirable aggregation of the nanoparticles during precipitation from solution, as well as during the following drying and thermal treatment, such as addition of organic solvents, surfactants, or chelators. 3,8,11 Even though these dispersants can improve the colloid stability, reduce the temperature required for sintering, enhance green densication, and control the particle morphology, 8 they affect the product crystallinity and are difficult to completely remove from the nal materials. 10 In this context, phase transformation of ammonium aluminium carbonate hydroxide to alumina can be helpful to suppress agglomeration, because the CO 2 , NH 3 , and H 2 O gases released during thermal treatment play signicant roles in reducing agglomeration of the nal Al 2 O 3 particles.…”