Ceramic Microbeads as Adsorbents for Purification Technologies with High Specific Surface Area, Adjustable Pore Size, and Morphology Obtained by Ionotropic Gelation

Abstract

In this study, we present an ionotropic gelation route for obtaining porous alumina/silica microbeads (MBs) with tailorable morphology, specific surface area (SBET), and pore size, which can directly be sintered into porous, monolithic adsorbents (MAds). After sintering, SBETs from 20 m2/g up to 70 m2/g with open porosities up to 90% could be achieved depending on the silica nanoparticle addition. Due to the significantly increased SBET, a more than 100‐fold faster uptake of model dye molecules was obtained. Pore sizes ranged between 13 and 184 nm with adjustable mono‐ and bimodal size distributions. Depending on silica content and sintering temperature, the MBs were also found to be chemically stable in technologically relevant solvents such as water, acetone, acetonitrile, hydrochloric acid, and methanol for at least 1 week except for sodium hydroxide. By adjusting the processing parameters, spherical, fibrous or irregular microbead morphologies could be obtained. The same route was also successfully applied for obtaining calcium phosphate, titania, and zirconia microbeads. The presented straight‐forward ionotropic gelation route is basically applicable to any other ceramic material and therefore extremely versatile. The obtained MBs and MAds can be further adapted to any type of environmental or biotechnological purification process by additional functionalization steps.

Rapid Sintering of Porous Monoliths Assembled from Microbeads with High Specific Surface Area and Multimodal Porosity

“…Sintering at 1200°C for 1 min resulted in a S BET of 58 m 2 g À1 , which is %57% higher compared to the conventionally sintered MAds. Klein et al [12] showed that conventionally sintered alumina/silica microbeads did not show second phase formation (e.g., mullite) at 1200°C, which was also not observed for rapidly sintered MAds (data not shown). Mesopores in the range of 5-50 nm were found.…”

“…[7,8] Subsequently their application in filtration is limited to gases and small molecules. [12] These microbeads exhibited a S BET of up to 37 m 2 g À1 and a bimodal pore size distribution at 14 and 40 nm when conventionally sintered at 1000°C. [9] However, these materials exhibit often low specific surface areas, [10] which are disadvantageous for the adsorbents' efficiency.…”

“…[12] (b) Adsorption test with methylene blue (c ¼ 450 mmol L À1 ). A highly acidic (1 M HCl), highly basic (1 M NaOH), and intermediate (deionized water) solution were used.…”

Tuning the phase composition and particle characteristics of partially stabilized yttria and ceria co-doped zirconia nanocrystals via a sol–gel process with sodium chloride as an additive

“…The most important application areas for ZrO 2 include toughened ceramics [2,3], refractories [4], piezoelectrics [5], solid electrolytes [6], active component and/or supports in catalysis [7,8], and photonics [9]. The crystal structure of ZrO 2 has a substantial influence on its characteristics and applications.…”

Recent advances in the synthesis of hierarchically porous silica materials on the basis of porous glasses

“…It is a very recent finding that large silica beads in the range of 2 to 4 mm with a bimodal pore system including leaching-based pores between 20 and 120 nm as well as additional pores with diameters between 1 to 50 mm can be synthesized via ionotropic gelation 31 of a phase separable sodium borosilicate glass followed by subsequent thermal and leaching treatment. 32 The synthesis route is presented in Fig.…”