Application of Mn-Fe Layered Double Hydroxide as an Adsorbent for the Removal of Arsenic from Synthetic Acid Mine Drainage

The Mn-Fe layered double hydroxide using chloride in the interlayer anion was successfully synthesized using chemical co-precipitation methods. The Mn-Fe LDH was then applied as adsorbent for arsenic removal from synthetic acid mine drainage. The adsorbent characterizations of SEM and XRD analysis showed that the Mn-Fe LDH had many different functional groups and a high specific surface area for the adsorption processes. The morphological structure of Mn-Fe LDH by the SEM-EDS analysis method shows a round shape structure with a particle size of about 1 μm, and the XRF analysis method shows that the Mn and Fe elements dominate more than other components. Batch adsorption experimental conducted using the Mn-Fe LDH with the interlayer anion of chloride as an adsorbent to study the effect of contact time, equilibrium pH, and temperature on the arsenic removal. The Mn-Fe LDH showed high adsorption uptake capacity and selectivity for the arsenic in the synthetic acid mine drainage. The adsorption and ion exchange between interlayer chloride anions in Mn-Fe LDH and As (V) solution was the main adsorption mechanism. Therefore, the Mn-Fe LDH can be used as an adsorbent in water and wastewater treatment. In contrast, this research has the potential to be processed and developed into advanced materials.

Development of a high temperature CO2 sorbent based on hydrotalcite for a H2-rich syngas production from biomass.

In order to adapt hydrotalcite based sorbents (LDO) to high temperature CO2 sorption and suitable temperature for tar steam reforming, the addition of CaO was investigated, maintaining their structure to keep porosity and accessibility but mostly assure the CO2 sorption stability during sorption/desorption cycles. In co-precipitation synthesis, various interlayer anions with different sizes and valences (carbonate, oxalate, and stearate) and various pH values were studied for different Mg/Ca ratios. The characterization of these sorbents (LDO) by TGA, XRD, N2 adsorption, SEM, sorption capacity, and sorption/desorption stability (cyclic TGA) permitted to understand the effect of the various synthesis conditions and to highlight the interest of oxalate use as interlayer anion. Typical LDH sand roses were formed with carbonate and oxalate anions after calcination until Mg/Ca/Al ratio = 1/2/1. For carbonate, this optimal ratio reached the highest sorption capacity and CaO sites accessibility at 600°C, better than pure CaO. However, the best stability during cycles was obtained with the sorbent from oxalate and Mg/Ca/Al ratio = 1.5/1.5/1 at pH 10 for which sorption results were almost the best values observed. For these two samples, the observed macroporosity were associated to the highest specific surface area and pore volume.Statement of NoveltyIn hydrotalcite structure, a width interlayer space permits to integrate various anions (CO32-, SO4-2, or NO3-) in order to modify CO2 sorption kinetics and capacity. The spheroidal “sand rose” morphology observed with CO32- anions explained the large BET surface area and the better CO2 sorption capacity. Stearate (and longer molecules) exchange was extensively studied as long-carbon-chain organic anion and allowed a better CO2 capture performance.This work focuses on another interlayer anion (oxalate) with the same valence of carbonate (2), a shape and valence different to stearate (1), and not yet reported in the literature. The novelty is to demonstrate that oxalate can replace carbonate as interlayer anion and moreover stearate by a less toxic one.

Experimental Investigation of Chloride Uptake Performances of Hydrocalumite-Like Ca-Al LDHs with Different Microstructures

In this study, hydrocalumite-like Ca2Al-NO3− layered double hydroxides (Ca-Al LDHs) with different microstructures were synthesized. The crystalline properties, structure composition, morphology and particle size distribution of the Ca-Al LDH (CAL) samples were illustrated. To obtain the chloride uptake performances of CAL, the influences of contact time, initial concentration of Cl−, pH of reaction solution and coexistence anions on the chloride uptake were examined systematically. Compared to the CAL samples obtained at a higher aging temperature, CAL synthesized at 60 °C demonstrated the minimum average particle size (6.148 μm) and the best Cl− adsorption capacity (211.324 mg/g). Based on the test results, the main adsorption mechanism of chloride ion on CAL was recognized as an interlayer anion exchanging reaction other than the dissolution-precipitate mode. With the increase in the pH value of reaction solution from 7 to 13, it was found that the amount of chloride ion adsorbed by CAL increased slightly, and the solution could remain at relatively high pH value even after the adsorption. The presence of CO32− and SO42− reduced the adsorption capacity of CAL dramatically as compared with OH− due to the destruction of layered structure and the formation of precipitates (CaCO3 or CaSO4). The interference sequence of the investigated anions on the chloride uptake of CAL was SO42−, CO32− and OH−, and the order of interlayer anionic affinity was Cl− > OH− > NO3−. The results illustrated that the synthesized CAL could be used as a promising chloride ion adsorbent for the corrosion inhibition of reinforcement embedded cement-based materials.

Nanohybrid Layered Double Hydroxides Used to Remove Several Dyes from Water

For the preparation and characterization of several layer double hydroxides (LDH) with inorganic interlayer anions (carbonate and nitrate) and nanohybrids, two organo-LDHs were studied in detail. The dodecylbenzene sulfonate (DBS) was used as an organic interlayer anion to modify the hydrophilic nature of the interlayer. The aim of the modification of the layered double hydroxides (LDH) was to change the hydrophilic character of the interlayer to hydrophobic with the purpose of improving its ability to adsorb several (anionic and cationic) dyes from water. These compounds have been used as adsorbents of amaranth (Am), diamine green B (DGB) and brilliant green (BG) dyes. Adsorption tests were conducted using variable pH values, contact times and initial dye concentrations (adsorption isotherms) to identify the optimum conditions for the intended purpose. Adsorbents and adsorption products were characterized by several physicochemical techniques. The results of the adsorption tests showed that the organo-LDH nanohybrids could be efficient adsorbents in the removal of studied dyes from water. Thus, it can be concluded that nanohybrids studied in this work might act as suitable supports in the design of adsorbents for the removal of a wide spectrum of dyes with the aim of reducing the adverse effects on water resources.

Understanding the Ion Exchange Process in LDH Nanomaterials by Fast In Situ XRPD and PCA-Assisted Kinetic Analysis

Layered double hydroxides (LDHs) are nanomaterials with interesting properties finding applications in many fields, such as catalysis, environmental chemistry, and pharmaceuticals. They are anionic clays with positively charged layers and anions within the layers to reach neutrality. Their properties are defined by both composition and morphology. The composition can be tuned by exchanging the interlayer anion. The far more stable, common, and highly prevalent among natural LDHs is the carbonate anion thanks to its double negative charge. To adapt the properties of LDHs for technological applications, the challenge is to exchange the carbonate with the functionalizing monovalent anions in an effective and cheap way. In this study, the exchange of carbonate with nitrate ions is studied by in situ X-ray powder diffraction (XRPD). The exchange is carried out by a liquid-assisted grinding approach, inserting the mechanically ground dry sample in a capillary and then wetting it with a drop of nitric acid, while measuring the XRPD pattern. The kinetics of the process was investigated by the Avrami-Erofe’ev method; the reaction mechanism was determined using the advancing interface model and by analyzing the XRD peak shapes, which evidentiate changes in the crystallinity during the reaction. The reaction starts from the faces perpendicular to the layers and occurs along the channels, increasingly limited by diffusion when approaching the internal part of the crystals.

Enhanced adsorption of Cr(vi) on BiOBr under alkaline conditions: interlayer anion exchange

The first time to explore the adsorption of Cr(vi) on BiOBr in alkaline solutions, and propose an original adsorption mechanism.

Novel biomolecule-assisted interlayer anion-controlled layered double hydroxide as an efficient sorbent for arsenate removal

Novel amino acid functionalized and interlayer anion controlled layered double hydroxides were successfully obtained by a one pot synthesis, which showed enhanced arsenate adsorption capacity.