High Surface Area Layered Double Hydroxides via Organic Solvent Dispersion
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Solution Overview
Problem
Conventionally synthesized layered double hydroxides (LDHs) have high aggregation, resulting in low specific surface areas and non-porous structures, which limits their effectiveness in applications requiring high surface areas for adsorbents or catalyst supports.
Innovation Solution
A method involving rapid co-precipitation, aging, and dispersion in an aqueous miscible organic solvent to produce LDHs with specific surface areas exceeding 125 m²/g, utilizing a process that includes precipitation, aging, washing, dispersion in an organic solvent, and controlled drying to enhance surface area and porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional LDH synthesis methods are used, then LDHs can be produced with simple synthesis procedures, but the particles aggregate to form non-porous bodies with low specific surface area
Solution Approach 1:
The patent uses aqueous miscible organic solvents (acetone, ethanol, methanol, isopropanol, or dioxane) as intermediary dispersing media to prevent aggregation of LDH particles during synthesis and drying. These solvents act as mediators between the aqueous synthesis environment and the final dry powder, maintaining particle separation and preventing formation of dense aggregates, thereby achieving high specific surface area (125-350 m²/g) while using simple synthesis procedures.
2Productivity
If rapid co-precipitation is used, then nucleation is promoted and particle size is reduced, but the process requires vigorous stirring and precise pH control
Solution Approach 1:
The patent employs rapid addition of metal precursor solution to anion solution with simultaneous vigorous stirring to achieve rapid nucleation and formation of fine particles. The pH is precisely controlled to 10-12 using NaOH during precipitation, which promotes rapid nucleation while maintaining particle dispersion. This parameter control strategy enables high productivity through rapid nucleation while the subsequent use of organic solvent dispersion simplifies the overall process by preventing aggregation during drying.
3Ease of manufacture
If LDHs are dried conventionally, then the material can be recovered for use, but aggregation increases and surface area decreases
Solution Approach 1:
The patent disperses the precipitated LDH in aqueous miscible organic solvents (acetone, ethanol, methanol, isopropanol, or dioxane) before drying. These solvents act as intermediaries that maintain particle separation during the drying process, preventing aggregation that would otherwise occur during conventional drying. The organic solvent molecules surround and separate the LDH particles, ensuring that when the solvent evaporates, the particles remain dispersed and maintain high specific surface area (125-350 m²/g) while still allowing easy recovery of the dried material.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively increases the specific surface area and pore volume of LDHs, facilitating mass transport and providing a higher number of active sites, making them suitable for various applications such as catalysts, catalyst supports, and coatings.
Implementation Method 1
precipitating a layered double hydroxide having the formula [M z+ x M' y+ x (OH) 2 ] a+n-a/n+ bH 2 O from a solution containing the cations of the metals M and M' and the anion X n-
Implementation Method 2
The precipitated layered double hydroxide is then dispersed in an aqueous miscible organic solvent such as acetone, ethanol, methanol, isopropanol or dioxane
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
Layered double hydroxides having a high surface area (at least 125 m2/g) and the formula (I) wherein M and M' are different and each is a charged metal cation (and must be present), z = 1 or 2; y = 3 or 4, 0<x<0.9, b is 0 to 10, c = 0 to 10, X is an anion, n is the charge on the anion, and a = z(1-x)+xy-2; AMO-solvent is aqueous miscible organic solvent, may be prepared by a method which comprises a) precipitating a layered double hydroxide having the formula [Mz+ 1- x M' y + x (OH)2]a+(Xn-) a/n 'bH2O wherein M, M', z, y, x, a, b and X are as defined above from a solution containing the cations of the metals M and M' and the anion X n- ; b) ageing the layered double hydroxide precipitate obtained in step a) in the original solution; c) collecting, then washing the layered double hydroxide precipitate; d) dispersing the wet layered double hydroxide in an AMO solvent so as to produce a slurry of the layered double hydroxide in the solvent; e) maintaining the dispersion obtained in step d); and f) recovering and drying the layered double hydroxide. The high surface area products have low particle size and are particularly suitable for use as catalysts, catalyst supports, sorbents and coatings.