Surface Of LDH Research Articles

Modulating the synergy of Pt single atoms and quantum dots on NiFe LDH for efficient and robust hydrogen evolution

Hydrogen evolution reaction (HER) from water electrolysis is an ideal alternative solution to address the energy crisis and develop clean energy. However, the construction of an efficient electrocatalyst with multiple active sites that can ensure high metal utilization and promote reaction kinetics simultaneously still leaves a major challenge. Herein, we present a facile strategy to synthesize a HER catalyst comprising Pt single atoms (PtSA) anchored in Fe vacancies and Pt quantum dots (PtQD) on the surface of NiFe LDH. Benefitting from the hierarchical and ultrathin nanosheet arrays and strong electronic interaction between PtSA/PtQD and NiFe LDH matrix, the optimized sample (PtSA/QD-NiFeV9 LDH) exhibits outstanding HER performance in 1 M KOH with ultra-low overpotentials of 20 and 67 mV at 10 and 100 mA cm−2, respectively, outperforming the benchmark Pt/C electrocatalyst. In addition, the electrolyzer using PtSA/QD-NiFeV9 LDH as a cathode requires voltages of only 1.48 and 1.73 V to yield current densities of 10 and 1000 mA cm−2, respectively. The combination of in situ tests and density functional theory (DFT) calculations reveal that the synergy of PtSA and PtQD can optimize the kinetics of water dissociation and hydrogen desorption, thus the Volmer-Tafel pathway prevailing the HER process. This work provides a promising surface engineering strategy to develop catalysts for efficient and robust hydrogen evolution.

Uncalcined Zn/Al Carbonate LDH and Its Calcined Counterpart for Treating the Wastewater Containing Anionic Congo Red Dye

In this investigation, Zn/Al carbonate layered double hydroxide (ZAC-LDH) and its derived material on calcination were synthesized for removing the anionic azo dye Congo red (CR) from wastewater. Numerous factors were methodically investigated, including temperature, adsorbent dosage, pH, starting Dye Concentration (DC), and contact time. The CR elimination percentage dropped as the initial DC increased from 25 mg/L to 100 mg/L at 30 °C for uncalcined LDH, and from 97.96% to 89.25% for calcined LDH. The pH analysis indicates that the highest level of dye removal was recorded within the acidic pH range through the electrostatic attraction mechanism. The sorption kinetics analysis results demonstrated that the pseudo-second-order kinetic model exhibited a stronger fit to both uncalcined LDH and CZA-LDH, with the maximum correlation coefficient value. The Van’t Hoff plots indicate the spontaneous nature of the physisorption process with a negative ΔG° (<−20 kJ/mol), while the endothermic adsorption process exhibited a positive ΔH°. The X-ray diffraction of calcined LDH reveals a significant intercalation of CR dye molecules, both prior to and following adsorption, showcasing a distinctive memory effect. The Brunauer–Emmett–Teller (BET) gas sorption measurements were performed to support the mesoporous nature of ZAC-LDH and CZA-LDH. The FTIR spectrum confirms the interaction of dye molecules on the surface of uncalcined and calcined LDH. These findings emphasize the efficacy of both the synthesized LDHs in removing CR dye, with CZA-LDH demonstrating superior efficiency compared to uncalcined LDH in the context of CR removal from wastewater.

Effect of modified MgAl-LDH coating on corrosion resistance and friction properties of aluminum alloy

The in-situ growing approach was utilized in this article to construct the magnesium–aluminum layered double hydroxide (MgAl-LDH) film on the surface of a 1060 aluminum anodized film. To improve the corrosion resistance and friction qualities of aluminum alloy, the MgAl-LDH coating was treated using stearic acid (SA) and thiourea (TU). The aluminum substrate and anodized aluminum film layer corroded to varying degrees after 24 h of immersion in 3.5% (mass) NaCl solution, while the modified hydrotalcite film layer continued to exhibit the same microscopic morphology even after being immersed for 7 d. The results show that the synergistic action of thiourea and stearic acid can effectively improve the corrosion resistance of the MgAl-LDH substrate. The tribological testing reveals that the hydrotalcite film layer and the modified film layer lowered the friction coefficient of the anodized aluminum surface substantially. The results of the simulations and experiments demonstrate that SA forms the dense LDH-TU interlayer film layer by exchanging NO3– ions between TU layers on the one hand and the LDH-SA film layer by adsorption on the surface of LDH on the other. Together, these two processes create LDH-TU-SA, which can significantly increase the substrate's corrosion resistance. This synergistically modified superhydrophobic and retardant hydrotalcite film layer offers a novel approach to the investigation of wear reduction and corrosion protection on the surface of aluminum and its alloys.

Electronic modulation with Pt-incorporated NiFe layered double hydroxide for ultrastable overall water splitting at 1000 mA cm−2

Achieving large current density is crucial to the practical application of large-scale hydrogen production by water splitting, but it is hindered by sluggish and unstable catalysts. Herein, a Pt-induced NiFe layered double hydroxide (Pt-NiFe LDH) nanosheet is synthesized for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It affords 10 mA cm–2 at overpotentials of only 198 mV and 36 mV for OER and HER, respectively. Impressively, an alkali-electrolyzer (Pt-NiFe LDH || Pt-NiFe LDH) exhibits a stable cell voltage of 1.887 V to deliver a current density of 1000 mA cm–2 over 3000 h. The introduction of Pt modulates the electronic structure on the surface of NiFe LDH by charging redistribution at the interface and decreasing the Gibbs free energy change (ΔG) for the potential determining step (from *O to *OOH) during OER. This work provides a facile strategy for developing catalysts for large current density water splitting.

Ultrasound-assisted green synthesis of Ru supported on LDH-CNT composites as an efficient catalyst for N-ethylcarbazole hydrogenation.

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/12H-NEC) is one of the most attractive LOHCs, and it is of great significance to develop catalysts with high activity and reduce the hydrogen storage temperature. Layered double hydroxides-carbon nanotubes composites (LDH-CNT) were synthesized by a simple in-situ assembly method. Due to the introduction of CNT, a strong interaction occurred between LDH and CNT, which effectively improved the electron transfer ability of LDH-CNT. Ru/LDH-CNT catalysts were prepared via ultrasound-assisted reduction method without adding reducing agents and stabilizers. Under the cavitation effect of ultrasound, the hydroxyl groups on the surface of LDH were excited to generate hydrogen radicals (•H) with high reducibility, which successfully reduced Ru3+ to Ru NPs. Ru/LDH-3.9CNT-(300-1) catalyst was of 1.63nm average Ru particle size with CNT amount of 3.9wt% and the ultrasonic power of 300W at 1h, and its electron transfer resistance was less than that of Ru/LDH-(300-1). The synergy of ultrafine Ru NPs and fast electron transfer made it exhibit exceptional catalytic performance in NEC hydrogenation. Even if the reaction temperature was lowered to 80°C, its hydrogenation performance was better than that of commercial Ru/Al2O3 catalyst at 120°C. The ultrasound-assisted method is efficient, green and environmentally friendly, and the operation process is simple and economical. It is expected to be used in practical industrial production, which provides a reference for the preparation of high-activity and low-temperature hydrogen storage catalysts.

Enhance methanol-sensing properties based on Ag functionalized monolayer LDH nanosheet: A combined experimental and theoretical calculation investigation

Layered double hydroxides has been greatly explored for gas sensor applications due to their highly tunable chemical composition and unique layer structure. In this work, an investigation combined experimental and theoretical on Ag functionalized monolayer ZnAl-LDH (Ag/LDH) is performed for excellent methanol sensing performance. The monolayer ZnAl-LDH nanosheets was firstly prepared via an inverse-microemulsion method to reduce the stacking of LDHs. Then Ag nanoparticles (NPs) were successfully introduced on the surface of monolayer LDH by glucose reduction method. The Ag/LDH nanocomposite shows Ag NPs uniformly attached on the monolayer LDH nanosheet with large specific surface area. Benefiting from the unique microstructure of monolayer LDH and Ag functionalization, the Ag/LDH gas sensor exhibits about 23-fold enhancement in response value to 25 ppm methanol at room temperature compared with multilayer LDHs sensor. Meanwhile, the as-prepared sensor can detect 500 ppb methanol and exhibits extremely fast response-recovery characteristics upon 10–200 ppm methanol. Further gas adsorption calculations based on first principles were performed to clarify the key contribution of Ag NPs to methanol adsorption and the corresponding gas mechanism is also proposed. Above all, the present work indicates that the functionalization of Ag NPs is highly potential for enhancing the response LDH towards methanol vapor. • Combination of experiment and first-principles calculations. • Monolayer LDH nanosheets with uniformly attached Ag NPs were prepared. • The Ag/LDH sensor shows rapid response and recovery characteristic to methanol at room temperature. • The as-fabricated gas sensor could detect as low as 500 ppb methanol with a response of 3.35% at room temperature.

Particle size and interlayer anion effect on chromate adsorption by MgAl-layered double hydroxide

The chromate adsorption efficacy of MgAl-layered double hydroxide (LDH) was investigated along with the two aging conditions (room temperature and post hydrothermal treatment) and two intercalated anions (Cl− and CO32−). Based on the adsorption isotherm, Cl-intercalated LDH (Cl-LDH) followed the Langmuir isotherm model, and its adsorption capacity (60–70 mg/g) was 4–15 times higher than that of CO3-LDH to the affinity of anions to LDH. Moreover, adsorption kinetics results indicated that fast chromate adsorption occurred within 30 min, and reached a plateau within 1 h due to chemical interactions. After the chromate adsorption, the characteristic crystal structure and morphology were well preserved, and based on the powder X-ray diffraction (PXRD), zeta-potential, and scanning electron microscopy (SEM) results, most of the chromate ions were possibly adsorbed on the surface of LDH with partial intercalation interlayer spaces. The X-ray photoelectron spectroscopy (XPS) Cr 2p spectra of the chromate-adsorbed LDH exhibited characteristic peaks attributed to trivalent chromium and chromate ions, indicating the reduction of hexavalent chromium by adsorption onto the hydroxyl groups (-OH) in LDH. The Cl-LDH aged at room temperature (Cl-RT) exhibited 100% adsorption efficacy during the fifth cycle and an average desorption efficacy of 80% in the recyclability test. Moreover, the practical applicability of the LDH was further confirmed by conducting a simulated box test, where the box was filled with silicate sand, in which it exhibited a high chromate removal efficacy (around 70%) during 180 min. Therefore, it could be confirmed that the LDH prepared in this study is an effective material for in-situ soil and groundwater remediation.

Efficient removal of Pb(II) and Hg(II) with eco-friendly polyaspartic acid/ layered double hydroxide by host-guest interaction

The eco-friendly polyaspartic acid/layered double hydroxide (PASP/LDH) intercalation compound was synthesized and applied for the removal of heavy metal ions from aqueous solutions. The maximum adsorption capacities were 229.2 mg/g and 208.6 mg/g for the adsorption of Pb2+ and Hg2+ ions, respectively. Further, the PASP/LDH displayed high adsorption selectivity (Pb2+ > Hg2+ > Cd2+ > Ni2+ > Cu2+ > Zn2+). The effects of contact time, ions concentrations, pH and coexisting ions on the removal of metal ions were investigated. The adsorption kinetics followed the pseudo-second-order kinetic model, which indicated that the adsorption processes were chemisorption. The adsorption isotherms were agreed with Langmuir model. The excellent adsorption properties mainly originated from inner-sphere complexation between -COO− groups on the surface of LDH and heavy metal ions. DFT calculations and the experimental results revealed that the host-guest interaction would enhance adsorption capacity of PASP/LDH though the change of surface charge and wettability of LDH laminate.

Cu nanoparticles-dispersed Mg-Al layered double hydroxides as efficient catalysts for CO2 conversion with propargyl alcohols

Upgrading carbon dioxide (CO2) into valuable products is a highly promising strategy of artificial carbon cycle. In this study, a series of in situ reduced CuMgAl layered double hydroxides (R-CuMgAl-LDHs) composites were synthesized, in which Cu nanoparticles were effectively dispersed and anchored on MgAl-LDHs with formation of Cu+ and Cu0 species. The optimized R-Cu1.5Mg1.5Al1-LDH exhibited excellent catalytic performance for the carboxylative cyclization of 2-methyl-3-butyn-2-ol with CO2 (turnover number of 243) under mild conditions. The layered structure of LDH stabilized the active Cu species with high dispersion, enhancing the catalytic efficiency of this carboxylative cyclization reaction. Simultaneously, the dual-activation of both CO2 and propargylic alcohol by Cu0/Cu+ species generated on the surface of LDH contributed significantly to the catalytic efficiency enhancement. Furthermore, R-Cu1.5Mg1.5Al1-LDH catalyzed the reaction of a wide range of terminal or internal propargyl alcohols with CO2, yielding various functionalized α-alkylene cyclic carbonates. Finally, a reasonable reaction mechanism was put forward according to the comprehensive analysis.

Highly thermally stable zirconium oxide deposited layered double hydroxide for enhancing flame retardancy of waterborne epoxy coatings

Inspired by the multifunctional adhesion ability of poly dopamine (PDA), ZrO2 and aluminum magnesium hydroxide (LDH) were combined by PDA, which increased the function of this material in intumescent fire retardant (IFR) coatings. Briefly, PDA was coated on the surface of LDH to improve its dispersion stability in water. Then, the high thermal stability ZrO2 nanoparticles were immobilized in situ on the LDH/PDA surface to improve the strength and temperature resistance of the char layer by a hydrothermal strategy. The fire protection performance of [email protected]@ZrO2 (LPZ) modified intumescent fire retardant (IFR) coatings was performed by large plate method, thermogravimetric analysis (TGA) and furnace experiments. From the results, the IFR coating loaded with 2.5% LPZ exhibited the lowest backside temperature and the highest heat insulation, which reached 177.9 °C and 64.42, respectively. Besides, the coating exhibited the greatest expansion height (23.65 mm) and expansion rate (18.92), which is significantly higher than that of other coatings. Moreover, the maximum thermal degradation temperature (Tmax) and residual char of LPZ2.5%/EP were significantly higher than other samples. Further, the LPZ2.5%/EP based sample indicated the lowest smoke density rating (SDR) due to its excellent smoke suppression performance. The residual carbon analysis showed that ZrO2 nanoparticles and LDH nanosheets remained in the char layer during the combustion process, which is beneficial to increase the strength of the char layer and its barrier effect on heat and oxygen.

Electronic Metal-Support Interactions for Electrochemiluminescence Signal Amplification.

Au nanoparticle-amplified electrochemiluminescence (ECL) signals are generally realized by nanoparticle morphology modification, functionalization, and nanoalloys formation. It remains a great challenge to utilize the intrinsic catalytic activity of spherical Au nanoparticles for ECL performance improvement. In this work, we prepared the oxygen vacancy-rich CoAl-layered double hydroxide (LDH-Ov)-supported spherical Au nanoparticles via alkali etching of LDH and electrodeposition of Au nanoparticles on the surface of LDH. It was found that the luminol ECL signals of the as-prepared system were significantly enhanced by forming the strong electronic metal-support interaction (EMSI) between Au nanoparticles and LDH-Ov. The further mechanism study demonstrated that EMSI can increase the electron density of interfacial Au atom (Auδ-) due to a redistribution of charge and promote electron transfer between Au species and LDH-Ov. This study not only introduces EMSI to the ECL field but also paves a new way to the applications of the intrinsic activity of spherical Au nanoparticles in ECL signal amplification. We anticipate that EMSI would be applied to other metal nanocatalysts for the development of highly efficient ECL systems.

Synthesis of nickel–iron layered double hydroxide via topochemical approach: Enhanced surface charge density for rapid hexavalent chromium removal

Hexavalent chromium (Cr(VI)) is considered to be a potential metal contaminant because of its toxicity and carcinogenicity. In this work, the surface charge density of nickel–iron layered double hydroxide (NiFe LDH) is tuned through iron valence change to improve the performance in adsorption of Cr(VI). The addition of iron divalent in the precursor enhances the surface positivity and reducibility of Fe2+-NiFe LDH, resulting in a nearly 150% Cr(VI) maximum adsorption capacity improvement. The increase of hydroxyl groups and charge density on the surface of NiFe LDH is due to the topological chemical transition from Ni2+-Fe2+ LDH to Ni2+-Fe3+ LDH. The adsorption of Cr(VI) onto Fe2+-NiFe LDH prepared via topochemical approach is highly pH-dependent. The adsorption dynamics and isotherms results may be clearly elucidated by the pseudo-second-order model and Langmuir isotherm model. Electrostatic attraction, interlayer anion exchange and adsorption-coupled reduction are proven to be the main Cr(VI) removal mechanisms for Fe2+-NiFe LDH. This finding demonstrates that Fe2+-NiFe LDH adsorbents have potential application for efficient removal of Cr(VI) pollutants.

Adsorption Mechanism of Methylene Blue by Graphene Oxide-Shielded Mg-Al-Layered Double Hydroxide From Synthetic Wastewater.

Pollution of water resources by various pollutants is a global environmental issue, particularly, dye pollution has a major contribution to it. From various studies, it is confirmed that adsorption is an excellent remediation technique compared to others. Mg-Al-layered double hydroxides (LDHs) intercalated with NO3- ions act as an effective adsorbent-removing ionic species like heavy metal and dyes. Another popular nanomaterial is graphene oxide (GO), which is successfully used as an adsorbent for different pollutants like dye and heavy metal ions. It is prepared based on the modified Hummers method. In this study, GO was introduced on the surface of LDH to improve its adsorption capacity. The adsorption process is well described by the Freundlich model. The maximum adsorption capacity was obtained at around 0.5 and 0.85 mmol of methylene blue (MB) per gram of Mg-Al LDH and modified Mg-Al LDH with GO, respectively. The reaction kinetics of MB with both adsorbents is determined to be the pseudo-second-order. To get more insights of the mechanism, molecular dynamics (MD) simulation was conducted among the modified Mg-Al LDH with GO and MB molecules at both low- and high-concentration environments, which demonstrated that the developed composite adsorbs MB molecules predominantly onto its GO surface and then the MB molecules are adsorbed by the LDH surface. C-H···O (2.49-3.04 Å) and pi-donor···H-O (2.45-3.05 Å) are the major driving forces behind the strong adsorbability. Besides, S···H-O, S···O,N···O-H, pi···lone pair, pi···sigma, pi···cation, and alkyl···hydrophobic interactions play important roles in stabilizing the MB molecules onto the surface of the composite.

Direct Z-scheme CeO2@LDH core–shell heterostructure for photodegradation of Rhodamine B by synergistic persulfate activation

Photocatalytic activation of persulfate (PAPS) is considered an efficient and green approach for the mitigation of organic pollutants because of its advantages in low energy consumption and high reusability of photocatalysts. Herein, direct Z-scheme CeO2@LDH heterojunction photocatalyst with a core–shell structure is constructed. We reveal that CeO2@LDH exhibits excellent persulfate (PS) activation performance and high degradation efficiency of RhB under visible light irradiation. Control experiments by quenching catalytically active radicals and analysis of electron paramagnetic resonance (ESR) spectra suggest that the sulfate radical (SO4·−) generated by photocatalytic activation of PS, together with superoxide radical (·O2−) and hydroxyl radical (·OH), degrade pollutants synergistically. Density functional theory (DFT) calculations indicate that the built-in electric field across the surface of CeO2 and LDH is the intrinsic driving force for the efficient transfer of hot carriers in the Z-scheme heterojunction. The construction of this transfer path can effectively engineer the interfacial band structure and inhibit the recombination of photogenerated electron-hole pairs and promote their transportation. Meanwhile, electrons were found to accumulate at the conduction band (CB) of LDHs and holes populate at valence band (VB) of CeO2, generating more active species for photodegradation of RhB. We demonstrate that the Z-scheme heterojunction photocatalyst activated PS system (Z-scheme/PS) is a promising method to degrade RhB and potentially organic pollutants in general.

Phase transition of Mg/Al-flocs to Mg/Al-layered double hydroxides during flocculation and polystyrene nanoplastics removal

Nanoplastics, a kind of emerging pollutant in natural environments, have now drawn tremendous attention worldwide. Flocculation with Mg/Al-layered double hydroxides (LDH) precursor solutions has showed great potential for removing negatively charged nanoparticles from water. In this study, the flocculation behavior and mechanism for the removal of polystyrene nanoplastics (PSNP) with Mg/Al flocs or Mg/Al LDH were systematically analyzed and investigated. During the process of flocculation, it was observed that in situ Mg/Al LDH can be gradually formed with increasing pH, in addition, PSNP were captured or attached to the surface of LDH with a turning point around pH of 5.0. In acidic solutions with pH < 5.0, the negative surface charges of PSNP were diminished mainly due to the high concentrations of hydrogen ions and the positive charges from Mg and Al ions. In a moderately alkaline solution, Mg and Al ions gradually formed crystals capturing PSNP. Electrostatic adsorption and intermolecular force are the main mechanisms via which PSNP are captured on Mg/Al flocs. Herein, PSNP removal efficiencies from water were more than 90.0%. As the problem of plastic pollution becomes more severe, in situ LDH growth flocculation can provide an efficient way for the removal of PSNP.

Efficient degradation of lomefloxacin by Co-Cu-LDH activating peroxymonosulfate process: Optimization, dynamics, degradation pathway and mechanism

In this study, bimetal layered double hydroxides (CoxCuy-LDHs) containing a carbonate interlayer were synthesized using coprecipitation with a variety of Co/Cu mole ratios. Meanwhile, the corresponding layered double oxides (CoxCuy-LDOs) were prepared as controls. In this study, Electrical energy per order was performed to evaluate economic analysis. Correspondingly, we found that CoxCuy-LDHs possessed a significantly better PMS activation capability than the corresponding metal oxide composite (Co3O4/CuO). Compared with other CoxCuy-LDHs, Co2Cu1 LDH possessed the best PMS activation capability for LOM degradation and the lowest electrical energy per order (EE/O) value during the reaction. Additionally, Co2Cu1 LDH presented an excellent stability and worked over a wide pH range. The hydroxide states of Co(III), Co(II), Cu(I) and Cu(II) were all able to activate PMS, indicating that there were many active sites on the surface of Co2Cu1 LDH. The involvement of radicals in this reaction system was determined via scavenger experiments and electron paramagnetic resonance (EPR). Meanwhile, it's worth noting that a mathematical model was developed to quantify the involvement of SO4− and OH. Subsequently, we determined PMS activation mechanism and LOM decomposition pathway for the PMS/Co2Cu1 LDH system.

Strained heterointerfaces in sandwich–like NiFe layered double hydroxides/Co1-xS for highly efficient and superior long–term durable oxygen evolution reaction

Sandwich–like NiFe layered double hydroxides/Co1-xS (NiFe LDH/Co1-xS) heterostructure with synergistic electrocatalytic effects for highly efficient oxygen evolution reaction is successfully prepared by electrodepositing Co1-xS on the surface of NiFe LDH grown on nickel foam (NF). The NF supported heterostructure possesses three-dimensional (3D) catalytic space and strained heterointerface. Thereinto the Co1-xS layer provides extra active sites over the original NiFe LDH. Besides, the lattice mismatch in the surface of NiFe LDH induces the formation of lattice strain in Co1-xS, which thus modulates the local electronic structures. Density functional theory (DFT) calculations validate that the strained heterointerface has advantageous OER activity. From the results of electrochemical tests, the NiFe LDH/Co1-xS possesses large number of active sites and fast charge transfer. More importantly, optimized structure and interface characteristics improve the electrocatalytic stability, resulting in long–term durability with almost no attenuation after 150 h constant current test.

Evaluation of ultraviolet aging resistance of bitumen modified with isobutyltriethoxysilane surface organic grafted LDH

Isobutyltriethoxysilane surface organic grafted layered double hydroxide (OLDH) was prepared and utilized to improve the ultraviolet aging resistance of bitumen. The results of Fourier transform infrared (FTIR) and Static contact angle showed that isobutyltriethoxysilane has been grafted on the surface of LDH and the hydrophilic property of OLDH was observably weakened. The storage stability test indicated that OLDH had better compatibility and stability in bitumen compared with LDH, which was due to the decrease of hydroxyl and the introduction of organic group on the surface of LDH after isobutyltriethoxysilane organic grafting modification. Furthermore, OLDH modified bitumen showed more excellent high-temperature behavior than that of LDH modified bitumen. After ultraviolet aging, the performance of bitumen seriously deteriorated and the colloid stability notably decreased. Comparing with LDH, OLDH exhibited better in inhibiting the performance deterioration and gelefication of bitumen after ultraviolet aging, which implied that isobutyltriethoxysilane surface organic grafting modification was beneficial to strengthen the improvement of LDH on the ultraviolet aging resistance of bitumen.

Synergistic adsorption and photocatalytic reduction of Cr(VI) using Zn-Al-layered double hydroxide and TiO2 composites

Abstract Three TiO2 and Zn-Al-layered double hydroxide composites, denoted LDH-TiO2 composites, were prepared using the sol–gel method and characterized utilizing scanning and transmission electron microscopy with energy dispersive spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, X-ray diffraction, N2 adsorption–desorption, X-ray photoelectron spectroscopy, photocurrent, photoluminescence and electrochemical impedance spectroscopy techniques. The characterization results illustrated that TiO2 was attached onto the surface of LDH and the sizes of both TiO2 and LDH particles were in the nanoscale range. The combination of LDH and TiO2 promoted the photogenerated electron–hole transfer and separation. The removal abilities of the LDH-TiO2 composites for Cr(VI) were evaluated using the synergistic adsorption and photocatalytic method. The adsorption percentages of the three LDH-TiO2 composites for 20.0 mg/L Cr(VI) solutions ranged between 26% and 75%, and upon ultraviolet irradiation, the total removal percentages rapidly increased to approximately 100%. The removal efficiency for Cr(VI) depended on the TiO2 contents of the LDH-TiO2 composites. Increasing the TiO2 percentage resulted in decrease in the adsorption capacities and increase in the photocatalytic removal ratios. The kinetic and isothermal data well fitted the pseudo-second-order and Langmuir equations, respectively. The high removal efficiencies suggested that the composites were suitable for the treatment of Cr(VI)-containing wastewater.

Arginine and lysine-functionalized layered double hydroxides as efficient sorbents for radioactive Co2+ removal by chelate-facilitated immobilization

An increase in heavy metal contamination in aquatic environments require an efficient sorbent for the removal and reuse of toxic elements. We attempted to synthesize arginine/lysine-functionalized MgAl LDHs in one-pot without using any hazardous alkaline reagents. The LDHs produced at lower temperatures showed larger numbers of amino acids on their surfaces, while these are exchanged with CO32− at higher temperatures. The arginine/lysine present on the surface of LDH enhanced the adsorption of Co2+ and showed the highest adsorption capacity of 1.159 and 1.170 mmol/g for the LDHs functionalized with lysine and arginine, respectively. Kinetics studies indicated that the adsorption of Co2+ occurred by multiple mechanisms. The Co2+ adsorption on these amino acid functionalized LDHs occurs by the formation chelation complex with amino acid, which provide better vicinity of Co2+ to basic LDH that facilitating the enhanced immobilization. The sorption of other divalent metal ions on these arginine/lysine functionalized LDHs followed the order of Co2+ > Ni2+ > Mn2+ > Fe3+. The Co2+ forms diamine-like coordination that is stable on the surface of LDH and causes higher sorption densities, while other metals form partial glycine-like coordination that detaches the amino acid from the surface of LDH, thereby leading to lesser sorption capacity. The conversion of anionic LDH in to a cationic sorbent was successfully fabricated by these arginine/lysine-assisted methods and explored for the remediation of Co2+ from aqueous solution.