Metal zirconium phosphate macroporous monoliths: Versatile synthesis, thermal expansion and mechanical properties

Abstract

A versatile synthetic method has been developed for the fabrication of metal zirconium phosphate (MZP) macroporous monoliths via a sol-gel process accompanied by phase separation. More than 30 kinds of MZP monolithic polycrystalline monoliths with co-continuous macroporous structure have been synthesized by simply adding the target metal salt in the starting solution with optimized compositions. Glycerol, due to its high boiling point, plays the key role as the solvent to prevent metal salt from recrystallization, allowing a homogeneous distribution of metal salts over the polymerizing zirconium phosphate network. Hierarchically porous polycrystalline strontium zirconium phosphate (SrZrP) monolith has been obtained when the dried gel was calcined at 800 °C. Very low thermal expansion (coefficient of thermal expansion (CTE) as 1.4 × 10 −6 K −1) over a wide temperature range (38 °C to 1000 °C) together with good mechanical properties (flexural modulus as 8.0 GPa from 3 point bending test and Young's modulus as 1.9 GPa from uniaxial compression test) has been demonstrated, while high porosity (43 %) due to the presence of macropores reduces bulk density. As compared with dense ceramics of the same composition, the CTE value is lower and can be attributed to the presence of nanometer-sized small pores, which absorbs the anisotropic thermal expansion of each crystallite in the macropore skeletons at elevated temperatures.

Revisiting the Old and Golden Inorganic Material, Zirconium Phosphate: Synthesis, Intercalation, Surface Functionalization, and Metal Ion Uptake

“…In another study, Zhu et al in 2015 reported the synthesis of highly porous monolithic ZrP by a sol−gel procedure in the presence of poly(ethylene oxide) PEO and poly(acrylamide) PAAm based polymer templates. 75,76 The synthesis was carried out in a glass bottle by dissolving 1.29 g of ZrOCl A range of macroporous structures (0.5 to 5 μm) obtained was corroborated to the copresence of PEO and PAAm polymer templates. Control over the macroporosity was obtained simply by varying the weight ratios of the two polymers.…”

“…For better ion exchange performance, ZrP should possess a high specific surface area and a suitable porosity for its use in column operation. Up to now, the use of the template method is probably the most effective route to synthesize ZrP with much higher surface area and mesoporosity (2–50 nm pore diameter). − Soft templating strategy using amphiphilic surfactants, block copolymers, and ionic liquids as structure-directing agents (SDAs) have witnessed a great achievement in the fabrication of porous micro- and nanostructured ZrP. − During soft template strategy, SDAs self-assemble in solution to form a range of structures, which will therefore affect the morphology, crystallinity, and pore dimension of the nanostructures. In the following section, we will highlight the use of the most common soft templates, namely surfactants, block copolymers, and ionic liquids.…”

“…The large mesoporous ZrP (mZrP) exhibits a wormhole-like pore structure with abundant Lewis (due to zirconium ions) and Bronsted acid (due to hydroxyl groups) sites for the efficient and catalytic dehydration of glucose to 5-hydroxymethylfurfural (HMF). In another study, Zhu et al in 2015 reported the synthesis of highly porous monolithic ZrP by a sol–gel procedure in the presence of poly­(ethylene oxide) PEO and poly­(acrylamide) PAAm based polymer templates. , The synthesis was carried out in a glass bottle by dissolving 1.29 g of ZrOCl 2 ·8H 2 O in a solution of 1.4 mL of 1 M HCl and 1.6 mL of glycerol. Different amounts of PEO and PAAm were then added to the above solution to induce phase separation in the sol–gel process.…”

“…Control over the macroporosity was obtained simply by varying the weight ratios of the two polymers. The same research group in 2016 fabricated various metal-modified zirconium phosphate (MZP) macroporous monoliths by a sol–gel process followed by phase separation . The presence of glycerol, a high boiling solvent, prevents the metal salt from recrystallization, therefore, allowing uniform distribution of metal salts.…”

Hollow Structured Transition Metal Phosphates and Their Applications

“…The whole mixture was stirred and cooled to 0 °C in an ice bath where the 0.41 ml of phosphoric acid at a temperature of 0 °C was added and stirred to obtain the wet gel. The gel was dried at 60 °C for three days followed by calcination at different temperatures [76] . Alkoxides precursors of zirconium were used to synthesize the nanostructured porous zirconium phosphate.…”