Synthesis of Mg–Al Mixed Oxides with Markedly High Surface Areas from Layered Double Hydroxides with Organic Sulfonates

Abstract

Mg–Al mixed oxides with record-high surface areas and basic site concentrations were synthesized from Mg–Al layered double hydroxides with interlayer isethionate (Ise) or 3-hydroxy-1-propanesulfonate (HPS). Anion exchange of interlayer CO 3 2– in synthetic hydrotalcites with the organic sulfonates induces disorders in layer stacking as characterized by powder X-ray diffraction and enables facile delamination in water. Thermal treatment of materials anion-exchanged by Ise (MgAl–Ise) and HPS (MgAl–HPS) in N 2 and H 2 resulted in the formation of Mg–Al mixed oxides with marked enhancement in Brunauer–Emmett–Teller (BET) surface area relative to those treated in air. Treatment in a flow of H 2 is particularly effective, doubling the surface area of mixed oxides derived from MgAl–Ise relative to those obtained in a flow of N 2 . A higher degree of disorder in layer stacking in MgAl–HPS than MgAl–Ise resulted in the formation of Mg–Al mixed oxides with higher surface areas than those from MgAl–Ise. As a result, thermal activation of MgAl–HPS in a flow of H 2 yielded Mg–Al mixed oxides with the highest BET surface area (410 m 2 g –1 ) and CO 2 uptake (1.6 mmol g –1 at 25 °C and 100 kPa) in all samples. These values are significantly higher than those obtained from the initial hydrotalcites as well as those reported in the literature with similar Mg–Al ratios. Investigation of the thermal activation steps by thermogravimetric analysis and mass spectrometry indicates that the key factors to achieve high surface area and CO 2 uptake are to weaken interactions between layers by inducing stacking disorders and to facilitate the removal of interlayer sulfonates by preventing the formation of sulfates from them via thermal activation under a reducing environment.

Selective Removal of Anionic Dyes by Metal–Organic Framework-Anchored CoAl-Layered Double Hydroxide Nanosheets

“…Additionally, due to the presence of the Cu-(tpa) MOF structure in the nanocomposite, the dye molecules can interact with terephthalate moieties of the MOF structure by surface hydrogen bond/π−π stacking interaction (through phenyl rings). 64 The BET surface area of the CoAl-LDH/Cu-(tpa) MOF nanocomposite (221.778 m 2 g −1 ) is significantly higher in contrast to the control experiment with CoAl-(tpa) LDH (11.42m 2 g −1 ). This observation confirms the formation of a mesopore with increased surface area upon growth of Cu-(tpa) MOF on CoAl-LDH surfaces.…”

“…The positively charged LDH layers of the nanocomposite strongly interact with anionic dye molecules by electrostatic interaction. Additionally, due to the presence of the Cu-(tpa) MOF structure in the nanocomposite, the dye molecules can interact with terephthalate moieties of the MOF structure by surface hydrogen bond/π–π stacking interaction (through phenyl rings) …”

ZnAl–LDH/MOF-5 heterostructure nanocomposite for photocatalytic degradation of organic dyes under sunlight irradiation

“…Additionally, due to the presence of MOF-5 structure in the nanocomposite, the dye molecules can interact with the benzene dicarboxylate moieties of the MOF-5 by surface hydrogen bonds/π–π stacking interactions (through phenyl rings). 48 Hence, adsorption efficiency of the nanocomposite is much higher than the adsorption efficiencies of pure MOF-5 or pure ZnAl–(BDC) LDH. The photocatalytic activity of the nanocomposite originates from the metal cluster moieties of the MOF-5 structure.…”

Olive Mill Wastewater Valorization through Steam Reforming Using Multifunctional Reactors: Challenges of the Process Intensification

“…A nis a charge balancing anion (usually CO 3 2− ) located in the interlayer volume and x is generally between 0.2 and 0.4, while y is the number of moles of water located in the interlayer space [209,210]. Similar layered structures of HTCs could be produced with several interlayer anions [222,224,246,247,[250][251][252][253][254][255][256][257]. (a) Sorption capacity of the fresh sorbent.…”

“…The morphology and the thermal stability of the synthesized HTCs affect CO 2 sorption performance. The physicochemical properties of HTCs can be modified by combining adequate cations and anions [222,224,246,247,[250][251][252][253][254][255][256][257]263,264], by varying the molar ratio of M 2+ /M 3+ [211,212,246], by changing the preparation conditions such as pH [222] (pH values between 8-10 can be used to synthesize HTCs [258]), calcination temperature [246,265,266], or aging process (e.g., microwave, ultrasonication, etc.) [209,223,267] among other parameters.…”