Abstract
Low-ordered carbon/layered double hydroxide (LDH) nanocomposites were prepared by rehydration of the oxides produced by calcination of an organic LDH. While the memory effect is a widely recognized effect on oxides produced by inorganic LDH, it is unprecedented from the calcination/rehydration of organic ones. Different temperatures (400, 600, and 1100 °C) were tested on the basis of thermogravimetric data. Water, instead of a carbonate solution, was used for the rehydration, with CO2 available from water itself and/or air to induce a slower process with an easier and better intercalation of the carbonaceous species. The samples were characterized by X-ray powder diffraction (XRPD), infrared in reflection mode (IR), and Raman spectroscopies and scanning electron microscopy (SEM). XRPD indicated the presence of carbonate LDH, and of residuals of unreacted oxides. IR confirmed that the prevailing anion is carbonate, coming from the water used for the rehydration and/or air. Raman data indicated the presence of low-ordered carbonaceous species moieties and SEM and XRPD the absence of separated bulky graphitic sheets, suggesting an intimate mixing of the low ordered carbonaceous phase with reconstructed LDH. Organic LDH gave better memory effect after calcination at 400 °C. Conversely, the carbonaceous species are observed after rehydration of the sample calcined at 600 °C with a reduced memory effect, demonstrating the interference of the carbonaceous phase with LDH reconstruction and the bonding with LDH layers to form a low-ordered carbon/LDH nanocomposite.
Highlights
Layered double hydroxides (LDH) are materials that have attracted a lot of interest in the last few years [1,2,3] thanks to the possibility to act as a host for different inorganic or organic anions that can be intercalated between the mixed metals (e.g., Zn/Al or Mg/Al) hydroxide layers to counterbalance the positive charge of the layer
The calcination and rehydration protocol of organic layered double hydroxide (LDH) was tested and optimized, while an inorganic LDH was used as reference
In the samples prepared starting from the flurbiprofen-containing samples, Raman data confirmed the presence of low ordered carbonaceous species, possibly including graphene, in the sample calcined at 600 ◦ C
Summary
Layered double hydroxides (LDH) are materials that have attracted a lot of interest in the last few years [1,2,3] thanks to the possibility to act as a host for different inorganic or organic anions that can be intercalated between the mixed metals (e.g., Zn/Al or Mg/Al) hydroxide layers to counterbalance the positive charge of the layer. The applications of layered double hydroxides span from catalysts [4,5,6,7] to host for drugs or cosmetics [8,9,10,11,12,13] to polymers additives to improve thermal stability and flame resistance [14,15,16,17] to adsorbents for decontamination [18,19,20,21]. One of the methods used in particular for the intercalation of large organic anions is reconstruction upon hydration by exposure to air or to a solution containing the organic anion after the calcination of the inorganic LDH, exploiting the so-called “memory effect” [25]
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