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Recently, layered double hydroxides (LDHs) have been extensively researched for their anion exchange capabilities and exhibit a layered structure with a host layer of octahedrally coordinated metal cations and a guest layer (interlayer) of anions. In this study, we synthesized a CM-β-CD•Zn–Al LDH by anion exchange method to study the anionization of cyclodextrin (CD) to promote its incorporation into the LDH interlayers and its stability therein. Ni2+ adsorption by the CMCD•Zn–Al LDH by the anion exchange method was compared with the results co-precipitation method. The X-ray diffraction spectra of NO3•Zn–Al LDH and CM-β-CD•Zn–Al LDH synthesized by the anion exchange method exhibit that the product peaks were attributable to Z n 6 A l 2 O H 16 C O 3 4 H 2 O and possessed an LDH structure. Furthermore, all CM-β-CD•Zn–Al LDHs exhibited the presence of some CM-β-CD. The CM-β-CD•Zn–Al LDH was hypothesized to be composed of two types of layers: a CM-β-CD layer in which two molecules of CM-β-CD7-, with cavity axes perpendicular to the LDH host layer, are vertically overlaid, and a NO3-type Zn–Al LDH layer used as a precursor. CM-β-CD•Zn–Al LDH adsorbed Ni2+ in an aqueous solution. To determine whether Ni2+ adsorption by the CM-β-CD•Zn–Al LDH is driven chemically or physically, we fitted the data to the Freundlich and Langmuir adsorption models; the results showed that Ni2+ adsorption by the CM-β-CD•Zn–Al LDH is consistent with the Langmuir equation and could be considered a chemical adsorption. [ABSTRACT FROM AUTHOR]

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To reduce sludge volume, Mg-Al layered double hydroxide (LDH) was used to remove pollutants from mine wastewater. Mg-Al LDH can remove both cations and anions from mine wastewater via co-precipitation and anion exchange mechanisms, respectively. We herein investigated the difference in removal efficiencies between Mg-Al LDH and Ca(OH)2. Initial As and Fe concentrations of 8.4 and 308.6 mg/L led to final concentrations of <0.001 and 15.4 mg/L, respectively, when 5 g/L LDH with an Mg/Al molar ratio of 2:1 was employed. This suggests that As was removed in the form of , which exchanged with intercalated in the Mg-Al LDH structure, while Fe was removed by the formation of Fe-Al LDH via co-precipitation. In contrast, treatment with 5 g/L Ca(OH)2 gave As and Fe concentrations of 0.1 and <0.01 mg/L, respectively. Thus, under Ca(OH)2 treatment, As is removed by the co-precipitation of arsenate with the formation of ferric oxyhydroxide (FeO(OH)), while Fe is removed by co-precipitation of the formed Fe(OH)3. The sludge volume obtained using Mg-Al LDH was approximately ten times lower than that obtained when using Ca(OH)2. [ABSTRACT FROM AUTHOR]

Owing to the low atmospheric concentration of CO 2 (400 ppm), direct air capture technologies require adsorbents that offer high CO 2 adsorption capacities at low CO 2 concentrations. In this study, we investigated the potential of CO 3 ·Mg–Al layered double hydroxides (LDHs; Mg/Al molar ratio = 2, 3, and 4) as CO 2 adsorbents. The CO 2 adsorption and desorption behavior was studied at various molar ratios, adsorption/desorption temperatures, and linear speeds. CO 2 adsorption by CO 3 ·Mg–Al LDH followed the Langmuir model, indicating that monolayer adsorption occurs. The maximum CO 2 adsorption quantity calculated using the Langmuir equation was 0.794 mmol/g for CO 3 ·Mg–Al LDH with a Mg/Al molar ratio of 3. In dry CO 2 adsorption experiments, a maximum CO 2 adsorption quantity of 0.319 mmol/g was recorded with a Mg/Al molar ratio of 3 and temperature of 60 °C. In dry CO 2 desorption experiments, the CO 2 concentration and desorption quantity reached maximum values at 300 °C and a linear speed of 0.250 m/min. Notably, the maximum CO 2 concentration was 6232 ppm, showing a 15.6-fold increase in comparison with the initial concentration of 400 ppm. Overall, our results demonstrate that CO 3 ·Mg–Al LDH has high potential as a CO 2 adsorbent. The study findings have significant implications for the development of new CO 2 adsorbents for the direct air capture and storage of CO 2. • We have developed new CO 2 adsorbents for the direct air capture and storage of CO 2. • Our results demonstrate that CO 3 ·Mg–Al LDH has high potential as a CO 2 adsorbent. • CO 2 adsorption followed the Langmuir model, indicating that monolayer adsorption occurs. [ABSTRACT FROM AUTHOR]

• Simultaneous removal of HCl, SO 2 , and NO from the mixed gas was performed using MnO 2 /Mg–Al LDH. • Regenerated MnO 2 /Mg–Al LDH could remove HCl, SO 2 , and NO gases. • We efficiently removed the gases from the mixed gas by applying the two-step treatment process. Combustion methods are popularly used to treat acidic exhaust gases to reduce the emission of pollutants. However, exhaust gas treatment can be difficult and expensive, rendering it essential to develop a new treatment process for acidic exhaust gases. In the present study, we investigated the removal of NO from the HCl–SO 2 –NO mixed gas using MnO 2 /Mg–Al layered double hydroxide (MnO 2 /Mg–Al LDH). We analyzed the influence of CO 2 gas on the NO removal. Additionally, we regenerated MnO 2 /Mg–Al LDH after the acid gas adsorption using the wet method and examined the possibility of its cyclical use. MnO 2 /Mg–Al LDH could simultaneously remove HCl, SO 2 , and NO from the mixed gas. Because HCl and SO 2 influenced the NO removal rate, we proposed a two-step treatment process with MnO 2 /Mg–Al LDH and CO 3 •Mg–Al LDH to efficiently remove HCl, SO 2 , and NO from the HCl–SO 2 –NO mixed gas. The NO removal rate decreased with an increase in the CO 2 concentration, confirming the influence of CO 2. Additionally, the results confirmed the possible cyclic use of MnO 2 /Mg–Al LDH after removing acid gases. However, the Mn elution and Mn(IV) concentration decreased the removal rates of SO 2 and NO, respectively. Thus, it is necessary to develop the regeneration method further. [ABSTRACT FROM AUTHOR]

• CO 3 ·Mg–Al LDH can be regenerated by treatment of Cl, SO 4 , NO 3 ·Mg–Al LDH with gaseous CO 2. • The desorption of Cl−, SO 4 2−, and NO 3 − follows the intraparticle diffusion model. • This is limited by the step of CO 3 2− diffusion between LDH layers. Carbonate-intercalated Mg–Al layered double hydroxides (CO 3 ·Mg–Al LDHs) are examined as a means of sequestering gaseous pollutants, such as HCl, NO x , and SO x , which are bound to afford X·Mg–Al LDH (X = Cl, SO 4 , or NO 3). In view of the fact that the common regeneration method of CO 3 ·Mg–Al LDH (agitation in aqueous Na 2 CO 3) poses a number of problems, we herein develop a new method of regenerating CO 3 ·Mg–Al LDH by treatment of X·Mg–Al LDH with gaseous CO 2 under neutral or alkaline conditions. The desorption of X is shown to follow the intraparticle diffusion model, featuring the diffusion of CO 3 2− in between LDH layers as the rate-determining step. Given the importance of LDHs for wastewater treatment and gaseous pollutant removal, the obtained results pave the way to the efficient utilization of these adsorbents and contribute to the development of next-generation decontamination techniques. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adsorption follows a pseudo-second-order kinetic equation. • The Δ G values for adsorption systems ranged from − 20 to 0 kJ/mol. • It indicates that adsorption could be classified as physical adsorption. • NP was adsorbed on OS•Cu-Al LDH by hydrophobic interaction. • AP was adsorbed on SCD•Cu-Al LDH by CH/π interactions. Our previous study revealed that Cu-Al layered double hydroxides (LDHs) intercalated with 1-octanesulfonate and sulfonated β-cyclodextrin showed good adsorption selectivity toward m -nitrophenol (NP) and m -aminophenol (AP), respectively. We also found that the adsorption behaviors of these LDHs fit the Freundlich equation. Herein, we performed a kinetic analysis to elucidate the adsorption mechanism of the LDHs for phenols in greater detail. The adsorption results were fitted to a pseudo-first-order kinetic equation, a pseudo-second-order kinetic equation, and an intraparticle diffusion model. The correlation coefficients of the pseudo-second-order kinetic equation for each adsorption process were fairly high, and the measured and calculated equilibrium adsorption amounts were relatively close. Thus, the adsorption of NP and AP by OS•Cu-Al LDH and SCD•Cu-Al LDH, respectively, fits the pseudo-second-order kinetic equation. Because the ΔG values for each system ranged from − 20 to 0 kJ/mol, the adsorption processes in these systems may be classified as physical adsorption. Specifically, NP was adsorbed on OS•Cu-Al LDH by hydrophobic interactions, whereas AP was adsorbed on SCD•Cu-Al LDH by CH/π interactions. Our findings provide new insights into the adsorption of phenols onto modified Cu-Al LDHs and could serve as a foundation for future studies on the adsorption properties of LDHs intercalated with anions as guest layers. [ABSTRACT FROM AUTHOR]

Over the past few years, many substances have been investigated for their potential application as adsorbent materials. The combination of a layered double hydroxide (LDH) and CH/π interactions enables selective adsorption through the differences in the electron density of the aromatic ring. Thus, in this study, two organic anions, namely the linear 1-octane sulfonate (OS-) and cyclic sulfonated-β-cyclodextrin (SCD13-), were intercalated into the interlayers of a Cu-Al LDH by coprecipitation (Cu/Al ratio, 3.0; chemical ratio, 2.0). The SCD13- anion was selected because β-cyclodextrin comprises hydrophobic cavities that allow the formation of inclusion compounds. X-ray diffraction (XRD), total organic carbon (TOC) analysis, and inductively coupled plasma-atomic emission spectrometry (ICP-AES) revealed that the as-synthesized OS-Cu-Al LDH and SCD-Cu-Al LDH were both oriented perpendicular to the LDH layer. Subsequent absorption experiments with m -aminophenol (AP) and m -nitrophenol (NP), which have similar structures but different aromatic ring electron densities, confirmed a Freundlich-type adsorption mechanism and revealed that adsorption occurred on a non-uniform surface for both LDHs. The results also revealed excellent NP and AP adsorptions for the linear OS•Cu-Al LDH and cyclic SCD•Cu-Al LDH, respectively. This was attributed to the strong hydrophobic interactions in the former and strong CH/π interactions in the latter. This study shows the potential of using linear and cyclic organic sulfonic acid-modified LDHs for the selective recovery of the desired aromatic organic compounds. [Display omitted] • Cu-Al LDHs with 1-octane sulfonate and sulfonated cyclodextrin from coprecipitation. • OS•Cu-Al LDH/SCD•Cu-Al LDH selectively adsorb m-nitrophenol/m-aminophenol. • Selectivity due to hydrophobic and CH/π interaction in their respective guest layers. [ABSTRACT FROM AUTHOR]

[Display omitted] • MnO 2 /Mg–Al LDH is able to remove both HCl and SO 2 gases in addition to NO. • The HCl removal proceeds mainly through the reaction of HCl with the CO 3 2− and OH− in the LDH layers. • The SO 2 removal takes place through the adsorption of SO 2 onto the LDH and MnO 2 surfaces. • The NO removal occurs through the oxidation of NO to NO 2 by MnO 2. • It follows by the reaction of NO 2 with the CO 3 2− and OH− in the LDH layers. The gas exhaust generated by waste incinerators contains toxic acid gases such as HCl, SO 2 , and NO x , which require appropriate treatment following their release. Although several methods exist for this purpose, they have various drawbacks. Thus, toward the search for a new removal method, the ability of Mg–Al layered double hydroxide (Mg–Al LDH) to eliminate HCl, SO 2 , and NO gases from simulated exhaust gas was examined. In addition, the impact of the amount of LDH employed was investigated in terms of the toxic gas removal efficiencies and process temperature. Furthermore, the mechanism of removing HCl, SO 2 , and NO by MnO 2 /Mg–Al LDH was considered. More specifically, HCl removal proceeded mainly by the reaction of HCl with the CO 3 2− and OH− species present between the Mg-Al LDH layers, while that of SO 2 took place through the adsorption of SO 2 onto the LDH and MnO 2 surfaces. Moreover, NO was removed through the oxidation of NO to NO 2 by MnO 2 , followed by the reaction of NO 2 with the CO 3 2− and OH− species present between the Mg–Al LDH layers. These results are expected to help pave the way for the use of Mg–Al LDH to remove toxic acid gases from the gas exhausts of waste incinerators, thereby addressing the various issues related to the use of current technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Noble Zr-containing Mg-Al LDHs synthesized via sol–gel method, using two molar ratios. • These materials were employed for the adsorption of CO2. • CO2-absorbed LDHs store CO2 and accelerate ethylene urea production. • The production of ethylene urea showed an increase with the higher Zr content. • LDHs can capture and transform CO2 into valuable products. Excessive emission of greenhouse gases, such as CO 2 , from industries and the resulting global warming, has forced mankind to investigate the conversion of CO 2 into commercially valuable chemicals and achieve a sustainable carbon cycle. Therefore, various approaches have been used to uptake, harness, and transform CO 2 into valuable chemical compounds. In this study, novel Zr-containing Mg-Al layered double hydroxides (LDHs) with two distinct compositions, namely, Mg2AlZr LDH and MgAlZr2 LDH, were created using sol–gel technique. These compounds served as the adsorbent for CO 2 and an effective CO 2 source during ethylene urea (EU) production. The Mg2AlZr and MgAlZr2 LDHs exhibited specific surface areas of 171 and 197 m2/g, respectively. Increasing the Zr content played a crucial role in enhancing the generation and dissemination of zirconium hydroxide in the Mg-Al LDHs, thus resulting in an augmented surface area. The synthesized Zr-containing Mg-Al LDHs demonstrated effective CO 2 adsorption capabilities. The comparative CO 2 adsorption increased from 0.62 to 0.98 mmol/g with increasing molar content of Zr. The desorption of CO 2 occurred in the 50–250 °C temperature range from pores and surfaces. EU was successfully produced by reacting the CO 2 -adsorbed Zr-containing Mg-Al LDHs with ethylene diamine (EDA). The yield using MgAlZr2 LDH (0.06 mmol) was higher than that using Mg 2 AlZr LDH (0.02 mmol) at 160 °C. Consequently, the synthesized Zr-containing Mg-Al LDHs exhibit promising applications as efficient CO 2 gas adsorbents, CO 2 sources for further reactions, and effective accelerators to produce valuable EU. [ABSTRACT FROM AUTHOR]

The steady increase in CO 2 levels in the atmosphere is the leading cause of climate change and global warming and is now a global concern. To reduce the impact of CO 2 , various novel routes have been proposed to capture, utilize, and convert it into valuable chemicals. In this study, a noble Ce-doped Mg–Al layered double hydroxide (Mg–Al LDH) [Mg/Al molar ratio = 3 and Ce/Al molar ratio = 0.1, 0.5, 1.0] were synthesized using co-precipitation and sol–gel method and used as an adsorbent for CO 2 gas and later on efficient source of CO 2 in the synthesis of ethylene urea (EU). The specific surface area of the Ce-doped Mg–Al LDHs prepared by sol-gel method (96.1–333 m2/g) were higher than co-precipitation method (0.5–10.6 m2/g). Each Ce-doped Mg–Al LDHs were successfully adsorbed CO 2 , where first desorption occurred at around 50–250 °C temperature. The comparative adsorption of CO 2 was observed increase with decreasing the Ce/Al molar ratio. Adsorption of CO 2 was found to be 0.05, 0.04, 0.04 mmol/g for co-precipitation method and 0.62, 0.42, 0.37 mmol/g for sol-gel method, where Ce/Al molar ratio was 0.1, 0.5, 1.0 respectively. The EU produced from the reaction between ethylenediamine (EDA) and CO 2 adsorbed Ce-doped Mg–Al LDHs, where a comparative amount of EU was observed in the order of Ce/Al molar ratio = 1.0 > 0.5 > 0.1. According to the temperature effect, EU production was increased with an increase in temperature from 120 °C to 160 °C. At 160 °C, the production of EU by co-precipitation method was found to be 0.03, 0.04, 0.07 mmol/g and by sol-gel method was found to be 0.06, 0.07, 0.16 mmol/g, where Ce/Al molar ratio was 0.1, 0.5, 1.0 respectively. A much higher production was found in all the Ce-doped Mg–Al LDHs compared to pristine Mg–Al LDH at all the temperatures. The performance of Ce-doped Mg–Al LDHs synthesized by the sol-gel method was observed to be better than that of the co-precipitation method in terms of both adsorption of CO 2 and production of EU. In this study, Ce-doped Mg–Al LDH introduced as a successful CO 2 adsorbent, a source of CO 2 and an effective promoter in the ethylene urea production. • Noble Ce-doped Mg–Al LDHs with different Ce/Al molar ratios are synthesized by co-precipitation and sol-gel method. • The materials are utilized for adsorbing CO 2. • CO 2 adsorbed materials are used as a source of CO 2 and promoter for ethylene urea (2-imidazolidinone) synthesis. • The comparative ethylene urea productions are observed to increase with an increasing Ce/Al molar ratio of 1.0 > 0.5 > 0.1. • The use of layered double hydroxide is suggested for CO 2 capture, utilize, and convert into valuable chemicals. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) nanomaterials have drawn widespread attention because of their unique physical characteristics compared to three-dimensional materials. Delamination and nanosheet formation of layered composites are necessary for 2D nanomaterials. Layered double hydroxides (LDH) exhibit anion exchange properties that can be maximized using different methods such as organic modifications and crystal growth control; delamination is one such method. Delamination of LDH render them in the form of nanosheets, which could not be expressed as interlayers, allowing them to exhibit physical properties completely different from those of bulk LDH. Herein, we propose a novel synthesis method to delaminate LDH in an aqueous solvent. In this method, heat reflux is used to break interlayer hydrogen bonds in the LDH, and the remaining hydrogen bonds are broken using ultrasonic treatment. Finally, we dispersed the material in the solvent to obtain LDH nanosheets. We compared the delamination of Mg Al LDH intercalated with lactate (lactate•Mg–Al LDH) and Mg Al LDH intercalated with NO 3 − (NO 3 ·Mg–Al LDH) in an aqueous solvent. Furthermore, we used the nanosheets obtained from NO 3 ·Mg–Al LDH and described their Ni2+ uptake characteristics. Our results show that without using organic solvents, we could delaminate lactate•Mg–Al LDH and NO 3 ·Mg–Al LDH by applying the proposed method. The lactate•Mg–Al LDH had approximately ten Mg Al LDH host layers, whereas the corresponding nanosheets had three Mg Al LDH host layers. NO 3 ·Mg–Al LDH had 14–15 Mg–Al LDH host layers, whereas the corresponding nanosheets had 2–3 Mg–Al LDH host layers. Furthermore, NO 3 ·Mg–Al LDH and its nanosheets could adsorb Ni2+ in an aqueous solvent. Thus, Ni2+ uptake capabilities were enhanced by delaminating NO 3 ·Mg–Al LDH to fabricate nanosheets. • A method for delaminating layered double hydroxides (LDHs) is proposed. • Heat reflux is used to remove hydrogen bonds in LDHs. • Remaining hydrogen bonds are removed by ultrasonic treatment. • We delaminated lactate-intercalated Mg Al LDH and NO3-intercalated Mg Al LDH. • Ni2+ uptake capabilities increased by delaminating NO3-intercalated Mg Al LDH. [ABSTRACT FROM AUTHOR]

• The NO 3 ⋅Mg-Al LDH and the nanosheets could adsorb the SeO 4 2− in an aqueous solution. • The adsorption capacity was greater for the delaminated NO 3 ⋅Mg-Al LDH nanosheets. • This is because the specific surface area of the NO 3 ⋅Mg-Al LDH nanosheets is larger. • The nanosheets are layered after the anion exchange on the surface of the host layer. Layered double hydroxides (LDHs) are excellent anion-exchange materials, and are useful in adsorbing hazardous anions. The LDHs form nanosheets upon delamination, which improves their efficiency. In this study, we investigated the SeO 4 2− adsorption properties of the nanosheets obtained by the delamination of NO 3 ⋅Mg-Al LDH in an aqueous solution and compared them with those of the NO 3 ⋅Mg-Al LDH. The SeO 4 2− adsorption by both substances was a "pseudo-second-order rate reaction". The reaction-rate constant during the early stage was greater for the nanosheets as their surface area was larger than the NO 3 ⋅Mg-Al LDH. The amorphous nanosheets reverted to an ordered LDH structure after the anion exchange. Atomic force microscopy (AFM) imaging and the corresponding height profile analysis of the samples confirmed the nanosheets stacking post SeO 4 2− adsorption. We propose a mechanism of the SeO 4 2− adsorption by the NO 3 ⋅Mg-Al LDH nanosheets. These findings may improve the understanding of the anion exchange by the LDHs, which may lead to the development of high-efficiency materials that extract metals such as Se from wastewater. [ABSTRACT FROM AUTHOR]

This study investigates the influence of CO 2 gas on the treatment of single acidic gases (HCl, SO 2 , and NO 2) using Mg Al layered double hydroxide intercalated with CO 3 2− (CO 3 ·Mg-Al LDH) as the adsorbent. The gas-removal kinetics is analyzed, and the reaction mechanisms are discussed. The coexisting CO 2 gas decreased the removal rate of all three acidic gases. This is likely due to the exchange reaction between intercalated CO 3 2− and gas-phase CO 2 , which inhibits the exchange between intercalated CO 3 2− and HCl, SO 2 , or NO 2. The HCl removal by CO 3 ·Mg-Al LDH follows pseudo first order kinetics, suggesting that the main removal mechanism is chemisorption (chemical reaction between CO 3 ·Mg-Al LDH and HCl). Meanwhile, the removal of SO 2 and NO 2 by CO 3 ·Mg-Al LDH also follows pseudo first order kinetics. However, the corresponding adsorption mechanisms are classified as physisorption onto the Mg Al LDH. • 10% coexisting CO 2 reduced the acidic gases absorption ratio by CO 3 ·Mg-Al LDH. • This is attributed to the exchange reaction between CO 2 gas and pre-intercalated CO 3 2−. • All the kinetic data were well fitted to pseudo-first order models. [ABSTRACT FROM AUTHOR]

Herein we studied metal ion adsorption in aqueous solution by Zn Al layered double hydroxides (Zn Al LDH) modified with carboxymethyl-β-cyclodextrin (CM-β-CD) ions (CM-β-CD•Zn-Al LDH). In single-ion solutions containing Li+, Nd3+, or Pb2+, CM-β-CD•Zn-Al LDH adsorbed Nd3+ and Pb2+ but adsorbed very little Li+. Maximum adsorption followed the order Pb2+ > Nd3+ > Li+. In a mixed solution containing Li+, Nd3+, Ni2+, Cu2+, and Pb2+, the adsorption rate followed the order Cu2+ ≫ Pb2+ > Nd3+ > Ni2+ > Li+. • CM-β-CD•Zn-Al LDH adsorbed Nd3+ and Pb2+ but adsorbed very little Li+. • In a single solution, maximum adsorption followed the order Pb2+ > Nd3+ > Li+. • In a mixed solution, adsorption followed the order Cu2+ ≫ Pb2+ > Nd3+ > Ni2+ > Li+. [ABSTRACT FROM AUTHOR]

Mg − Al layered double hydroxide intercalated with CO 3 2– (CO 3 ·Mg − Al LDH) was successfully used to remove SO 2 from a gas mixture at 140, 170, and 200 °C. The removal of SO 2 with CO 3 ·Mg − Al LDH occurred via surface adsorption of SO 2 and anion exchange between CO 3 2– in the interlayer of Mg − Al LDH and SO 2 from the gas mixture. The removal of SO 2 followed the order of Ca(OH) 2 > CO 3 ·Mg − Al LDH (Mg/Al = 2) > CO 3 ·Mg − Al LDH (Mg/Al = 4). The removal of SO 2 also followed the order of CO 3 ·Mg − Al LDH > Mg(OH) 2 > SO 4 ·Mg − Al LDH. CO 3 ·Mg − Al LDH was regenerated from SO 4 ·Mg-Al LDH using a Na 2 CO 3 solution through anion exchange between SO 4 2− and CO 3 2−, leading to its recyclability for removal of SO 2 from a gas mixture three times, demonstrating the feasibility of recycling the material. Unlabelled Image • This study deals with the development of CO 3 ·Mg − Al LDH for the removal of SO 2. • The SO 2 removal increased with increasing temperature and SO 2 concentration. • The removal proceeds under mass transfer control rather than surface chemical reaction control. [ABSTRACT FROM AUTHOR]

Abstract: Although effective treatments of SO x are essential for preventing air pollution, current methods pose other environmental problems such as increased amounts of desulfurized gypsum and reduced landfill lifetimes. We report a process for removing SO2 from waste streams using a Mg−Al oxide slurry. The ability of the mixed oxide to remove SO2 increased with slurry quantity and temperature but decreased with time. SO2 was removed through the reconstruction of a Mg−Al layered double hydroxide (Mg−Al LDH) intercalated with , which was derived from the dissociation of H2SO3 upon dissolution of SO2 in the slurry. SO2 was not adsorbed onto the surface of the Mg−Al oxide. These results suggest that SO2 removal using a Mg−Al oxide slurry may be possible without the concomitant problems of conventional treatment methods. [Copyright &y& Elsevier]

[Display omitted] • The mechanism of Cu(II) removal using CO 3 ·Mg-Al LDH was investigated. • Equilibrium and pH studies indicate the formation of a precipitate at the solid–liquid interface. • Solid analyses reveal the formation of CuCl 2 ·3[Cu(OH) 2 ] and its multilayer accumulation on the LDH surface. Layered double hydroxides (LDHs) are effective in removing metal cations from aqueous solutions, but the mechanism of the process has not been thoroughly investigated. In this study, we conduct the removal of Cu(II) from aqueous solutions using the CO 3 ·Mg-Al LDH and investigate the mechanism of the process based on equilibrium and pH studies and solid-state analyses. Adsorption isotherms show that the equilibrium removal of Cu follows the Freundlich and Halsey models (R2 = 0.973), inducing a multilayer adsorption process. pH studies show that Cu is removed at pH < pH PZC (=12.1), consistent with chemical binding, rather than electrostatic attraction, as the predominant mechanism of removal. XRD reveals the formation of CuCl 2 ·3[Cu(OH) 2 ] and retention of the LDH structure, and SEM images show a thick-layer morphology. Solid-state analyses confirm the formation of CuCl 2 ·3[Cu(OH) 2 ] and its multilayer accumulation on the LDH surface, in accordance with the equilibrium and pH studies. [ABSTRACT FROM AUTHOR]

The removal of toxic nitric oxide (NO) from exhaust gas is challenging and expensive. MnO 2 /Mg-Al LDH, a composite of manganese dioxide and Mg-Al layered double hydroxide, was synthesized via the rehydration method for potential application in NO removal. MnO 2 /Mg-Al LDH was found to be complexed with MnO 2 , pillared between the LDH layers and intercalated with CO 3 2− and OH−. We investigated the performance of a MnO 2 /Mg-Al LDH treatment in removing NO from exhaust gas. The exhaust gas was circulated in a reaction tube filled with MnO 2 /Mg-Al LDH, CO 3 ･Mg-Al LDH, or a MnO 2 + CO 3 ･Mg-Al LDH mixture, and the NO removal efficiency of the MnO 2 /Mg-Al LDH composite was compared with that of the other compounds. When NO gas (150 ppm, linear velocity 1.0 m/min) was distributed at 170 °C, treatment with the MnO 2 ･Mg-Al LDH composite and CO 3 ･Mg-Al LDH yielded removal rates of 83.9% and 0%, respectively. The significantly higher NO removal rate of MnO 2 /Mg-Al LDH was ascribed to the transformation of NO to NO 2 via oxidation over MnO 2. Further, the NO removal rate after 90 min through the application of a simple mixture of MnO 2 and CO 3 ･Mg-Al LDH (Mn: 4.2 wt%) was only 1.4%, suggesting that a synergistic effect was generated by the MnO 2 /Mg-Al LDH composite. Though NO removal by MnO 2 /Mg-Al LDH was reduced at temperatures of 140 °C and higher, the results suggest that the synthesized compound can be much more effective than those commonly used for NO removal from exhaust gas. [Display omitted] • One-step treatment for simpler and more effective NO removal is proposed. • MnO 2 /Mg-Al LDH is synthesized via rehydration. • MnO 2 or Mn 2 O 3 is pillared to the host layer and CO 3 2−–OH intercalation occurs. • MnO 2 /Mg-Al LDH shows the highest NO removal rates. • A synergistic effect was generated by the MnO 2 /Mg-Al LDH composite. [ABSTRACT FROM AUTHOR]

Proposed molecular orientation of HEPES intercalated in the Mg–Al LDH interlayers. • Various LDH and LDO can selectively remove lactate from aqueous solution and cell culture medium. • NO 3 •Mg-Al LDH showed reasonable performance including moderately low cell toxicity. • HEPES•Mg-Al LDH is excellent adsorbent for regenerating cell culture medium by removing lactate. When cells proliferate in a culture medium, metabolites such as lactic acid gradually accumulate and eventually hinder cell growth. Herein, we considered various layered double hydroxides (LDH) and layered double oxides (LDO) for the selective removal of lactate in aqueous solution and a culture medium by anion exchange. NO 3 •Mg-Al LDH showed high lactate adsorption, low adsorption of glucose (a nutrient in culture medium), appropriate pH stability, and low cytotoxicity within a limited contact time. In contrast, NO 3 •Ni-Al LDH, NO 3 •Ca-Al LDH, Mg-Al LDO, and Cl•Mg-Al LDH had a lower performance than NO 3 •Mg-Al LDH. To further improve the performance, the anion of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES, a common pH buffer in culture media) was tested as the intercalated anion in Mg-Al LDH. HEPES•Mg-Al LDH (Mg/Al = 2) was found to be the most promising adsorbent for culture medium regeneration because its adsorption behavior was similar to that of NO 3 •Mg-Al LDH, while it had a much lower cytotoxicity. The traditional methods for regenerating a culture medium by removing accumulated lactate to increase the cell density in large-scale cell culture and lower the costs, including electrolysis, cell modification, and modification of the culture medium's composition, are complicated to operate and expensive. The adsorption method using HEPES•Mg-Al LDH presented in this study, instead, can be easily operated and has low costs. Thus, it is expected to be applied in actual cases for regenerating culture media. [ABSTRACT FROM AUTHOR]