Layered Double Hydroxide Interlayer Research Articles

NiFe layered double hydroxide nanosheets self assembled and etched by phosphotungstic acid for the enhanced oxygen evolution reaction

Poor conductivity and low reaction kinetics of layered double hydroxides (LDHs) hindered their large-scale applications as catalysts in the oxygen evolution reactions (OER). The composites with vacancies, high valence cations and 3D gradient pore structures were synthesized by the ionic exchange, delamination and self-assembly methods. The nanoclusters [PW12O40]3- were successfully intercalated into the interlayers of LDHs due to the static attraction. Meanwhile, the partial metal cations in the layers were etched by its conjugate acid. The molar ratios of Ni:Fe and acid:LDH need to be modulated to achieve the optimum catalytic performances. The composite 1:4PW12–Ni3Fe exhibited a lower overpotential 270 mV at 10 mA cm−2, superior kinetics (43 mV dec−1), better conductivity (2.68 Ω cm−2) and larger turnover frequency (3.59 s−1) than the bulk and nanosheet counterparts with reevesite-like structure. [PW12O40]3- more effectively reduced the overpotentials of LDHs than other interlayer anions (e.g.WO4−, B4O72− and CnH2n+1SO42−). The favourable electrocatalytic performances were attributed to the synergistic effects. The vacancies provided new active centers with high intermediate adsorption energy. The high valances cations induced electronic coupling and spatial charge redistribution. 3D gradient pore structures with a large electrochemical active surface area exposed active sites and provided a convenient path for transferring masses and charges.

Selective Covalent Basal Plane Modification as a Probe of Hydroxide Ion Conduction Pathways in Magnesium Aluminum Layered Double Hydroxides.

Understanding ionic conduction in layered double hydroxides (LDHs) is a crucial step towards utilizing them as solid, hydroxide ion-conducting electrolytes in energy conversion applications. We selectively modified the interlayer and external surfaces of MgAl LDHs with tris(hydroxymethyl)aminomethane (TRIS) ligands. By adjusting the concentration of the TRIS surface modifier, the LDH basal plane surfaces could be functionalized everywhere (internally and externally) or only externally. External modification resulted in loss of OH-conductivity compared to pristine LDHs, confirming that external platelet surfaces are the primary ion conduction pathway.

Effects of Different Antioxidant Intercalated Layered Double Hydroxides on Anti-Aging Properties of Asphalt Binders

This research aims to prepare different antioxidant intercalated layered double hydroxides (LDHs) and compare the thermal oxidation and ultraviolet (UV) aging resistances of different modified asphalts. The ion exchange technique was used to intercalate three different antioxidants: 3-(3,5-di-tert-butyl-4-carboxyphenyl) propionic acid, antioxidant 1222, and sodium dibutyl dithiocarbamate (rubber accelerator TP) into the interlayer of LDHs. The morphology, structures, UV blocking, and free radical scavenging properties of different antioxidant intercalated LDHs were characterized, respectively. The effects of the anti-aging agents on the physical properties (penetration, softening point, ductility, and viscosity); rheological behaviors (complex modulus and phase angle); and functional groups (C=O and S=O) of asphalt both before and after thermal oxidation aging and UV aging were systematically investigated. The results of the crystal structure and functional group analysis show that the three different antioxidants can be successfully inserted into the interlayer of LDHs without destroying their layered structures. Antioxidant intercalated LDHs exhibit a remarkable capacity for absorbing UV rays, coupled with a moderate ability to reflect UV light. Moreover, the inclusion of antioxidants into the interlayers of LDHs confers upon them the ability to scavenge free radicals. After 2 h of reaction, the free radical scavenging rates of LDHs-3, LDHs-1222, and LDHs-TP were 57.7%, 35.6%, and 17.1%, respectively. With an increase in the content of the antioxidant intercalated LDHs, the performance of the modified asphalt varies, and 4% is the optimal content of the anti-aging agents. Asphalts with the three antioxidant intercalated LDHs all had favorable storage stability, and their physical and rheological properties were improved after aging compared to LDHs-modified asphalt. The LDHs-3-modified asphalt showed the best anti-ultraviolet aging effect, while LDHs-1222-modified asphalt showed the best anti-thermal oxidation aging effect. This research lays the foundation for developing aging-resistant asphalt and improving the durability of asphalt pavement.

Sustained antibacterial release of zwitterionic globular hyperbranched polymer dots intercalated into layered double hydroxides.

This study introduces zwitterionic hyperbranched polymer (HBP) dots intercalated into layered double hydroxides (LDHs) for sustained antibacterial release. The proposed zwitterionic HBPs possess a three-dimensional spherical structure; unconventional blue fluorescent luminescence; water solubility; abundant COOH, amine, and amide functional groups; anionic exchangeability for intercalating into LDH interlayers; and sustained-release antibacterial activity. The intercalation for the layered nanomaterials was determined by adding different weight ratios of HBPs to Mg-Al LDHs to investigate the changes in the interlayer distance. X-ray diffraction revealed that the LDH layer spacing increased from 8.6 to 25.5 Å, effectively expanding the interlayer spacing with increasing HBP intercalation. Additionally, Fourier-transform infrared spectroscopy revealed the functional groups of the intercalated nanohybrids. Because the peripheral functional groups of HBPs are amino (-NH2) groups, preliminary evaluations revealed that pristine HBPs exhibited antibacterial properties. We further examined the antibacterial properties of the HBP/LDH nanohybrids. The results showed that HBPs combined with LDHs' controllable release properties can effectively achieve long-term sustained antibacterial release.

Tetrahydrobiopterin inhibitor-based antioxidant metabolic strategy for enhanced cancer ferroptosis-immunotherapy

The induction of immunogenic ferroptosis in cancer cell is limited by the complex and delicate antioxidant system in the organism. Synergistic induction of oxidative damage and inhibition of the defensive redox system in tumor cells is critical to promote lethal accumulation of lipid peroxides and activate immunogenic death (ICD). To address this challenge, we present a multifunctional and dual-responsive layered double hydroxide (LDH) nanosheet to enhance immunogenic ferroptosis. The MTX-LDH@MnO2 nanoplatform is constructed by intercalating methotrexate (MTX) into LDH interlayers and electrostatically absorbing biomineralized ovalbumin (OVA)-MnO2 onto the LDH surface. Specifically, the released Mn2+ from the incorporated MnO2 triggers a Fenton-like reaction, leading to reactive oxygen species (ROS) accumulation, while the depletion of reduced glutathione (GSH) further intensifies oxidative stress, resulting in the induction of ferroptosis. MTX is released in response to the acidic environment of tumor cells and inhibits the regeneration of tetrahydrobiopterin (BH4), modulating the GTP cyclic hydrolase 1 (GCH1)/BH4 axis. MTX disrupts the antioxidant metabolic activity regulated by GCH1/BH4 axis and inhibits ROS consumption, further boosting the ferroptosis effect, which promoted the release of damage-associated molecular patterns (DAMPs) and triggered ICD in the tumor. This activation subsequently leads to significant antitumor immune reactions, including DCs maturation, infiltration of CD4+/CD8+ T cells and cytokines release. The redox-controllable nanoplatform demonstrates promising anticancer efficacy in a mouse breast model providing a novel strategy for cancer immunotherapy.

Multi-scale evaluation of sodium dodecyl sulfate intercalated LDHs on the ageing resistance of SBS modified bitumen

Sodium dodecyl sulfate (SDS) intercalated layered double hydroxides (LDHs) were prepared to enhance the ageing resistance of SBS modified bitumen (SMB). X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) showed that SDS has been intercalated into the interlayers of LDHs. Compared to LDHs, the interaction between SDS intercalated LDHs (OLDHs) and SMB was obviously stronger, and OLDHs exhibited better dispersity and stability in SMB. After ageing, the viscoelastic properties of SMB were deteriorated. LDHs and OLDHs could obviously alleviate the deterioration of ageing on the properties of SMB, which could improve the ageing resistance of SMB, especially OLDHs. Additionally, the enhancement mechanisms of OLDHs and LDHs for the ageing resistance of SMB at the microscopic scale were investigated by molecular dynamics. The incorporation of LDHs could obstruct the invasion of oxygen into the interior of SMB and inhibit the diffusion rate of oxygen in SMB, which reduced the oxidation reaction probability of SMB during ageing, and eventually achieved the improvement on ageing resistance of SMB. The effectiveness of LDHs was further improved after SDS intercalated modification, that was, SDS intercalated modification was beneficial to enhance the ageing resistance of LDHs for SMB.

Synthesis of phenylalanine and tartaric acid intercalated layered double hydroxide (LDH): Investigation of two kinds of chiral molecules interaction in interlayer space of LDH using solid-state vibrational circular dichroism

Recently, the applicability of solid-state vibrational circular dichroism (SD-VCD) for the evaluation of organoclay nanohybrids has attracted much attention. Herein, the intercalation of two kinds of chiral molecules, phenylalanine (Phe) and tartaric acid (Tart), into Zn-Al layered double hydroxide (LDH) was carried out by a standard coprecipitation method. The Phe/Tart/LDH was characterized by XRD, FT-IR, TG-DTA, and SD-VCD. The chemical composition and interlayer distance expansion of Phe/Tart/LDH indicated that Phe and Tart were intercalated into the LDH. The VCD and theoretical calculation results showed that Phe and Tart coexisted in the same interlayer space of LDH with the formation of electrostatic interaction and hydrogen bonding between Phe-Tart, LDH-Phe, and LDH-Tart. The results demonstrated the utility of the SD-VCD method for determining the detailed conformation of chiral molecules in the LDH interlayer space.

Hybridize magnesium-iron layered double hydroxide with biopolymers to develop multiple pathways for phosphate sorption and release: A potential slow release phosphorus fertilizer

The intensive use of chemical fertilizers presents a dilemma for sustaining food production or causing soil degradation and posing agricultural contamination. The reduction of phosphorus (P) fertilizer usage is particularly crucial because it is a limited resource. This situation calls for the development of efficient P fertilizers to address the impending P deficiency. Mg-Fe layered double hydroxides (LDH) with 0.5 and 2.5 M metal precursors were hybridized with chitosan (CTS) and carboxymethyl cellulose (CMC) to design alternatives of slow release P fertilizers. While phosphate (PO4) sorption capacities were in the order of Mg-Fe LDH > 2.5LDH-CTS/CMC > 0.5LDH-CTS/CMC, PO4 release from 0.5LDH-CTS exhibited a rate constant ∼2.6–7.6 times lower than that of other samples, which had not reached equilibration even after 2688 h. Fe-EXAFS data implied the greatest degree of isomorphic substitution into LDH interlayer of 0.5LDH-CTS. In addition to intercalated PO4, P-XANES data also suggested the organic-P and Fe(III)-P on 0.5LDH-CTS, causing versatile retention processes. After 2688 h of PO4 release, LDH structure gradually weathered and transformed primarily into a structure dominated by ferric (oxyhydrox)oxides. On 0.5LDH-CTS, however, 14.3% of Fe inventory was contributed by Fe(II) species. The Fe(II) domains in conjunction with the likely remaining Mg-Fe LDH structure and amorphous Mg(OH)2 provided bonding sites for PO4, serving as the key factor for the continuous PO4 release beyond 2688 h. Such extended duration of PO4 release warrants the use of LDHs hybridized with biopolymers as promising substitutes for slow release P fertilizers.

Purpurin intercalated layered double hydroxide nanocomposites for improved CO2 visible photocatalytic reduction: Dye-intercalation stabilization and sensitization

Purpurin(pp) can be used as a photosensitive molecule in photocatalytic systems due to its excellent absorption of visible light, but its application is limited due to its poor stability under light. Layered double hydroxides (LDHs) can act as molecular containers due to their interlayer anion exchangeability, introducing target anions into the interlayer of LDHs and improving the instability of anions by utilizing the 2D confinement environment between LDHs layers. A series of co-intercalation materials with different ratios of pp and dodecyl sulfonate (SDS) were prepared through the hydrothermal method in this work, denoted as SDS-pp(x%)/LDHs. Compared with pp, the absorbance retention rate of SDS-pp(x%)/LDHs increased from 12.5% to 90% after 5 h of light exposure. Then its potential application in visible photocatalytic reduction of CO2 was explored. When the intercalation ratio of pp is 3%, the performance is optimal. Compared with ZnAl LDHs, the yield of CO produced by SDS-pp(3%)/LDHs was increased by 12 times and a small amount of 8-electron reduction product CH4 appeared. Through mechanism exploration, the matching energy level relationship between pp and LDHs promotes electron transfer from pp to LDHs. In addition, the catalyst exhibits good cyclic photocatalytic reduction performance for CO2 due to its stable intercalation structure.

Recyclable and reusable layered double hydroxide beads for soil remediation: Conveying belt recovery model, mechanism, bioavailability and microbial communities

Soil heavy metal remediation has always been the focus of research. This work synthesized a recoverable, reusable, and efficient material for Cr(VI)-contaminated soil through a new strategy. The main structure is a bead that encapsulates the layered double hydroxides(LDHs) and magnetic particles into an alginate bead (LDHs-M). Varying applications in soil suggested LDHs-M showed high immobilization performance. Including LDHs interlayer ions, proportion of components, pH, dosage, and initial Cr(VI) concentration, many influence factors were systemically explored, suggesting that LDHs contained in the bead played a prominent role during the immobilization and LDHs-M with the interlayer anions of NO3- showed excellent immobilization efficiency. Different characterizations were used to investigate the immobilization mechanism, indicating that interlayer anion exchange and electrostatic adsorption were the main ways for soil Cr(VI) immobilization. The toxicity also decreased with the reduction of Cr(VI). Meanwhile, the simulation of natural aging processes, plant growth, and changes in the microbial community in the soil after remediation were also investigated, which verified the immobilizing stability and bioavailability of LDHs-M. Furthermore, the magnetic belt recovery system showed superior recovery performance in solid phase separation. Then, the separated beads were regenerated in an electrolyte solution and reused in soil remediation. The perfect immobility, instantaneous separation, and regenerability made it a promising material in heavy metal contaminated soil.

Retention of Iodide by Chloride Green Rust and Magnetite.

Green rust (GR), a layered double hydroxide (LDH) containing Fe, and magnetite can be found in natural and engineered environments. The ability of chloride GR (GR-Cl) and magnetite to retain iodide as a function of various parameters was investigated. Sorption equilibrium is achieved within 1 day of contact time between iodide and preformed GR-Cl in suspension. pHm variations (7.5-8.5) have no significant influence, but the iodide sorption decreases with increasing ionic strength set by NaCl. Sorption isotherms of iodide suggest that the uptake operates via ionic exchange (IC), which is supported by geochemical modeling. The short-range binding environment of iodide associated with GR is comparable to that of hydrated aqueous iodide ions in solution and is not affected by pHm or ionic strength. This finding hints at an electrostatic interaction with the Fe octahedral sheet, consistent with weak binding of charge balancing anions within an LDH interlayer. The presence of sulfate anions in significant amounts inhibits the iodide uptake due to recrystallization to a different crystal structure. Finally, the transformation of iodide-bearing GR-Cl into magnetite and ferrous hydroxide resulted in a quantitative release of iodide into the aqueous phase, suggesting that neither transformation product has an affinity for this anionic species.

Boron separation by adsorption and flotation with Mg–Al-LDHs and SDBS from aqueous solution

Layered double hydroxides (LDHs) have been shown to be effective adsorbents for boron. However, solid–liquid separation is still a problem when separating boron from industrial radioactive waste liquid. In this research, three types of Mg–Al-LDHs including Mg–Al-LDH(NO3–), Mg–Al-LDH(Cl–) and Mg–Al-LDH(SO42–) were applied to adsorb boron, and moreover sodium dodecylbenzenesulfonate (SDBS) was used to float the LDH particles from aqueous solution after boron adsorption. The results showed that 60 min was sufficient for the equilibrium adsorption of the three LDHs. The boron adsorption capacity of three LDHs was determined as follows: Mg–Al-LDH(NO3–) > Mg–Al-LDH(Cl–) > Mg–Al-LDH(SO42–), and was 2.0, 0.98 and 0.2 mmol·g−1, each ranging from 0 to 80 mmol·L–1 with the initial boron concentration. The efficiency of boron removal by Mg–Al-LDH(NO3–) and SDBS can reach up to 89.7%. Furthermore, the boron flotation mechanism of SDBS and LDHs has been studied, since SDBS as a flotation agent can react with LDHs and penetrate into the interlayer of LDHs in addition to electrostatic attraction. Therefore, LDHs in solution can be floated onto the foam layer to be separated from the solution, and the clarified solution was obtained. The method is simple and promising for boron removal from aqueous solution.

New insights about the intercalation of 5-Fluorouracil into 2D Mg–Al layered double hydroxide nanosheets: A theoretical and experimental investigation

Layered double hydroxides (LDH) are interesting 2D inorganic platforms for biomedical purposes. In contrast to previous studies, this work reports the intercalation of 5-Fluorouracil (5-FU) into LDH through anion exchange using a fresh LDH material without the need for any organic compound or treatment prior to the intercalation with 5-FU. The combination of experimental charaterizations and computational studies allowed us to study the intercalation process, where the presence of three phases in the hybrid material are suggested: two of them are related to different charge states of the intercalated 5-FU into 2D LDH interlayer space, and the third one might be related to some kind of distorted LDH. FTIR, XPS and DFT calculations indicated that interactions established in the host-guest system involve a complex network of hydrogen bonds, contributing to the improvement of the chemical and thermal stability of the 5-FU-LDH hybrid. Release assays of 5-FU from the 5-FU-LDH demonstrated the ability to selectively release the drug in simulated tumor microenvironment, while in vitro bioassays suggested a dose-dependent behavior of the hybrid. These results contribute to a better understanding of the chemistry of intercalation of 5-FU into 2D-LDH, and can be used to tune properties of 5-FU-LDH in antitumor therapy.

Role of Anions in Stabilizing the [Zn–Al] Layered Double Hydroxides: A Thermodynamic Study

Room-temperature acid solution calorimetry, high-temperature oxide melt solution calorimetry, and low-temperature heat capacity measurements were employed to calculate the thermodynamic stabilities of the [Zn–Al–X] layered double hydroxides (LDH) containing different anions (X = Cl–, CO32–, and SO42–). Cryogenic heat capacity measurements demonstrated a Schottky-type anomaly in the heat capacity of all three LDHs below 11 K. This anomaly is attributed to the tunneling of protons between adjacent oxygen atoms in the LDH interlayer as this creates an energy system similar to a two-level system modeled with a Schottky term. These heat capacity measurements were also used to determine vibrational entropies which, when combined with configurational entropies, provide standard entropies of these LDHs. Enthalpies of formation of LDHs from binary components were determined and combined with the entropies of formation to calculate Gibbs free energies. Based on these values, the order of stability is [Zn–Al–SO4] > [Zn–Al–CO3] > [Zn–Al–Cl]. This trend results from a combination of the interlayer spacing, amount of water in the interlayer, interactions among the interlayer species, and interactions between the metal hydroxide layer and the interlayer.

Periodic pH regulation controls the phosphate uptake-release behavior and structural evolution of layered double hydroxides

Layered double hydroxides (LDH) are potentially industry-producible adsorption materials for phosphate removal from wastewater. However, the sustainable desorption strategy to support its application in practical scenarios is still lacking. In this study, we proposed to control the phosphate uptake and release behavior of LDH through periodic pH regulation. After twelve stages of regulation, the restoration rates of phosphate and pH were maintained at 86.5 % and 96.2 %, respectively, indicating that LDH was robust to resist multiple rounds of pH shock. But extremely acidic or alkaline conditions can accelerate metal ion loss from LDH laminates, so the regulation needs to be in a mild pH range (4.0–11.0). Under this condition, an alternating pattern appeared in the surface interaction of LDH and phosphate. Spectroscopic data showed that the formation of metal-phosphate coordination complexes (MOP) was the dominant mode of phosphate adsorption at high pH, while the formation of electrostatic attraction complexes dominated at low pH. For the interlayer interaction, it is interesting to find the exchanged Cl− ions would not re-enter the interlayer of LDH, suggesting that the charge-balancing anions were almost entirely composed of phosphate. Quantitative analysis revealed that the ion-exchanged phosphate amount kept increasing/decreasing in parallel with the total adsorbed amount, implying the driving effect of ion exchange on the periodic uptake/release of phosphate. Overall, the switching mechanism and reversibility of the binding state of phosphate-LDH were revealed during pH regulation. These findings may provide new insights for the development of sustainable desorption options for LDH.

Memory Effect of MgAl Layered Double Hydroxides Promotes LiNO3 Dissolution for Stable Lithium Metal Anode

AbstractLiNO3 is an effective additive for improving the performance of Li metal anodes. However, the practical application of LiNO3 is limited due to its poor solubility. Here, a novel electrolyte additive of MgAl layered double hydroxides (LDHs) with open interlayered anionic vacancies is proposed. The electropositive MgAl LDHs promote the spontaneous coordination of NO3− into anionic vacancies of LDH interlayers via memory effect, rehydrating to original NO3−‐MgAl LDHs structure and accelerating LiNO3 dissolution. The reconstructed NO3−‐MgAl LDHs play a crucial role as sustainable nitrate resources, preventing partial NO3− from participating in the Li+ solvent sheath to reduce the solvation binding energy. Moreover, MgAl LDHs absorb the anions due to electrostatic attraction, accounting for more dissociated Li+ and active Li+ migration in carbonate electrolytes. NO3− stored in MgAl LDHs is also preferentially reduced to form Li3N‐rich solid electrolyte interphase (SEI), decreasing the activation energy barrier for Li+ transport and striving to form a uniform Li deposition. The cells assembled with MgAl LDHs and LiNO3 additives deliver high Coulombic efficiency, excellent rate capability, and high capacity retention. This strategy provides new insights into LiNO3‐promotor design and excavates the potential of LDHs materials for Li metal batteries.

Preparation of lignin–MgAl layered double hydroxide composites by hydrothermal method using lignin as carrier and intercalation modifier agent

To improve the dispersion and crystallization of layered double hydroxides (LDHs), black liquor lignin was used as both the carrier and the intercalation modifier agent to prepare lignin–MgAl layered double hydroxide (Lignin-LDH) composites by a hydrothermal method. Fourier-transform infrared spectroscopy showed that the amount of NO3− inserted into the LDH interlayers decreased significantly with the increase of the lignin content. X-ray diffraction revealed that the crystallization of LDH in the Lignin-LDH composites was enhanced by the hydrothermal treatment, and the crystal structure of the LDH was more disordered with the increase of the lignin content. Thermogravimetric analysis showed that hydrothermal treatment and the addition of lignin were beneficial for enhancing the thermal stability of the Lignin-LDH composites. The basal spacing of the LDH was unchanged based on Bragg equation calculations. Based on the infrared and thermogravimetric analysis results, it can be inferred that the molecules of dissolved hydroxyl compounds were inserted into the LDH interlayers. Scanning electron microscopy showed that the hydrothermal treatment promoted the growth of LDH crystals, and the increase of the lignin amount resulted in the dispersion of LDH in lignin and a decrease of the LDH thickness.

Interleaved Electroactive Molecules into LDH Working on Both Electrodes of an Aqueous Battery-Type Device.

By selecting two electroactive species immobilized in a layered double hydroxide backbone (LDH) host, one able to act as a positive electrode material and the other as a negative one, it was possible to match their capacity to design an innovative energy storage device. Each electrode material is based on electroactive species, riboflavin phosphate (RF) on one side and ferrocene carboxylate (FCm) on the other, both interleaved into a layered double hydroxide (LDH) host structure to avoid any possible molecule migration and instability. The intercalation of the electroactive guest molecules is demonstrated by X-ray diffraction with the observation of an interlayer LDH spacing of about 2 nm in each case. When successfully hosted into LDH interlayer space, the electrochemical behavior of each hybrid assembly was scrutinized separately in aqueous electrolyte to characterize the redox reaction occurring upon cycling and found to be a rapid faradic type. Both electrode materials were placed face to face to achieve a new aqueous battery (16C rate) that provides a first cycle-capacity of about 7 mAh per gram of working electrode material LDH/FCm at 10 mV/s over a voltage window of 2.2 V in 1M sodium acetate, thus validating the hybrid LDH host approach on both electrode materials even if the cyclability of the assembly has not yet been met.

Theoretical Study on the Swelling Mechanism and Structural Stability of Ni3Al-LDH Based on Molecular Dynamics.

layered double hydroxide (LDH) as a kind of 2D layer material has a swelling phenomenon. Because swelling significantly affects the adsorption, catalysis, energy storage, and other application properties of LDHs, it is essential to study the interlayer spacing, structural stability, and ion diffusion after swelling. In this paper, a periodic computational model of Ni3Al-LDH is constructed, and the supramolecular structure, swelling law, stability, and anion diffusion properties of Ni3Al-LDH are investigated by molecular dynamics theory calculations. The results show that the interlayer water molecules of Ni3Al-LDH present a regular layered arrangement, combining with the interlayer anions by hydrogen bonds. As the number of water molecules increases, the hydrogen bond between the anion and the basal layer gradually weakens and disappears when the number of water molecules exceeds 32. The hydrogen bond between the anion and the water molecule gradually increases, reaching an extreme value when the number of water molecules is 16. The interlayer spacing of Ni3Al-LDH is not linear with the number of water molecules. The interlayer spacing increases slowly when the number of water molecules is more than 24. The maximum layer spacing is stable at around 19 Å. The interlayer spacing, binding energy, and hydration energy show an upper limit for swelling: the number of water molecules is 32. When the number of interlayer water molecules is 16, the water molecules' layer structure and LDH interlayer spacing are suitable for anions to obtain the maximum diffusion rate, 10.97 × 10-8 cm2·s-1.

Effect of different organic layered double hydroxides on the anti-aging property of bitumen

Two organic layered double hydroxides (LDHs) were synthesized and utilized to enhance the anti-aging property of bitumen. Fourier infrared spectroscopy and X-ray diffraction showed that sodium dodecyl sulfate was intercalated into the interlayers of LDHs (I-LDHs), and γ-(2,3-Epoxypropoxy)propyltrimethoxy silane was chemically grafted onto the surface of LDHs (S-LDHs). Compared with LDHs, organic LDHs possessed better compatibility and organic LDHs modified bitumen exhibited better performance in high-temperature regions, especially S-LDHs. After aging, the rheological properties dramatically deteriorated. The content of aromatic in bitumen evidently decreased, and the asphaltene noteworthy increased, the colloid structure verged on the gel system. The incorporation of LDHs could relieve the damage of aging on the rheological properties and colloid structure, and strengthen the anti-aging property of bitumen. Moreover, the consequence of LDHs had been further enhanced obviously after organic modification, and S-LDHs exhibited more excellent performance compared with I-LDHs.