Development of La2-xCexO2CO3 solid solution for low-concentration phosphate removal and recovery: manipulating Ce ratio and valence to boost phosphate capture

The removal and recovery of low-concentration phosphates from water have become crucial due to the dual challenges of eutrophication and the phosphorus crisis. Herein, we engineered a highly efficient and recyclable phosphate trapping agent of La2-xCexO2CO3 solid solution. The incorporation of Ce enhances the surface area and surface potential of La2-xCexO2CO3, providing abundant adsorption sites for phosphate. Surprisingly, we found that adjusting the Ce proportion affects the carbonate content, thereby influencing the anion-exchange capacity between carbonate and phosphate. Specifically, at 3 % Ce content (3 %-CeL), the carbonate ratio is maximized, resulting in an optimal sorption capacity (196.4 mg P/g) and a rapid removal rate (under 40 min) for phosphate, unaffected by interfering ions. Remarkably, 3 %-CeL achieved nearly 100 % phosphate removal efficiency in diverse water samples from sewage treatment plants, rivers, reservoirs, and groundwater. After five adsorption-desorption cycles, the phosphate removal and recovery efficiency of 3 %-CeL remained above 90 %. Mechanistic studies revealed that 3 % Ce content yielded the highest proportion of Ce4+/Ce3+, enabling greater carbonate binding for anion-exchange. This study proposes a high-performance phosphate trapping agent with broad applicability for treating actual waters and provides a new perspective on enhancing low-concentration phosphate removal in La-based materials through manipulating Ce ratio and valence.

Water-dispersible X-ray scintillators enabling coating and blending with polymer materials for multiple applications

Developing X-ray scintillators that are water-dispersible, compatible with polymeric matrices, and processable to flexible substrates is an important challenge. Herein, Tb3+-doped Na5Lu9F32 is introduced as an X-ray scintillating material with steady-state X-ray light yields of 15,800 photons MeV-1, which is generated as nanocrystals on halloysite nanotubes. The obtained product exhibits good water-dispersibility and highly sensitive luminescence to X-rays. It is deposited onto a polyurethane foam to afford a composite foam material with dose-dependent radioluminescence. Moreover, the product is dispersed into polymer matrixes in aqueous solution to prepare rigid or flexible scintillator screen for X-ray imaging. As a third example, it is incorporated multilayer hydrogels for information camouflage and multilevel encryption. Encrypted information can be recognized only by X-ray irradiation, while the false information is read out under UV light. Altogether, we demonstrate that the water-dispersible scintillators are highly promising for aqueous processing of radioluminescent, X-ray imaging, and information encrypting materials.

Thermal Air Oxidation-Mediated Synchronous Coordination and Carbonation of Lanthanum on Biochar toward Phosphorus Adsorption from Wastewater

Biochar has attracted increasing attention as the sustainable and structure-tunable carrier for lanthanum (La) species for diverse applications. Carbonated La species possesses a higher biocompatibility and a lower leaching potential than other commonly used La species, while less attention is paid on the application of carbonated La in phosphorus (P) adsorption. Herein, thermal air oxidation (TAO) was applied as a novel strategy for synchronously tuning the coordination environment and chemical species of La on biochar surface. The results demonstrated that TAO induced the coordination of La with oxidation-generated oxygenated functional groups (OFGs) and carbonation of La species by the oxidation-generated CO2 on the biochar surface. The batch adsorption results showed that the Qm of resultant biochar remarkably increased from 68.92 to 132.49 mg/g at 1 g/L dosage. It also showed a robust adsorption stability in pH 2-6, a strong resistance to the co-existing Cl-, SO42-, NO3-, CO32-, or HCO3-, a stable adsorption recyclability, and an ultralow La leaching potential. The P adsorption was dominated by ligand exchange-induced inner-sphere complexation. In practical swine wastewater, the resultant biochar composite (1 g/L) removed 99.87% of P from 92.3 to 0.12 mg/L at a practical pH of 7.12. The density functional theory calculation further revealed the significant role of the binding of carbonated La by the biochar surface OFGs in reducing the P adsorption energies, indicating the synergism between the oxygenated biochar carrier and the carbonated La in P adsorption. Finally, this study provided a novel route to synchronously tune the coordination environment and chemical species of La on biochar via a facile TAO process for high-efficient P adsorption from wastewater.

One-pot synthesis of siliceous ferrihydrite - coated halloysite nanorods in alkaline medium: Structure, properties and cadmium adsorption performance

The application of amorphous ferrihydrite (Fh) for Cd(II) removal is restricted by its unstable and easily transformable nature. Although doping with silicates stabilized ferrihydrite, its product siliceous ferrihydrite (SiFh) again suffered from the disadvantage of spontaneous agglomeration. Herein, ferrihydrite was hybridized with halloysite nanotubes (HNTs) to prepare a novel siliceous ferrihydrite - coated halloysite nanorods (SiFh@HNTs) in alkaline medium, to break through the current barriers. The characterization results showed that SiFh@HNTs could simultaneously overcome the defects of easy phase transformation of ferrihydrite and easy aggregation of SiFh nanoparticles (NPs). Meanwhile, the optimal SiFh@HNT₄₀ with halloysite content of 40 % formed a well-developed mesoporous structure and exhibited the desired surface properties: a high specific surface area of 303.4 m²/g, an isoelectric point as low as pH_iep = 4.5, and rich functional Fe - OH groups. The formation mechanism of such excellent sturcture-properties of SiFh@HNT₄₀ were mainly attributed to two factors: the generation of smaller (∼5 nm) SiFh NPs induced by the integration of halloysite-derived SiO₄^4- into ferrihydrite, and the dispersion of SiFh NPs on clay nanotubes. Furthermore, the adsorption capacity of SiFh@HNT₄₀ for Cd(II) was up to 137.8 mg/g at 30 °C and pH 6, which was much higher than that of aggregated ferrihydrite (11.2 mg/g), halloysite (18.8 mg/g) and goethite (49.4 mg/g). The adsorption thermodynamics study revealed the adsorption of Cd(II) on SiFh@HNT₄₀ was clearly chemisorption with a (ΔH_ads)_q of 43.3 kJ/mol. Characterization results of XPS and FTIR confirmed that the rich Fe - OH groups on SiFh@HNT₄₀ was the main adsorption sites, and Cd(II) was specifically adsorbed by inner-sphere surface complexation. In addition, SiFh@HNT₄₀ had application potential in the mixed-metal wastewaters treatment. Cyclic regeneration experiments showed that SiFh@HNT₄₀ had good regeneration performance and could be reused many times.

Converting Chrysotile Nanotubes into Magnesium Oxide and Hydroxide Using Lanthanum Oxycarbonate Hybridization and Alkaline Treatment for Efficient Phosphate Adsorption

Magnesium oxide and hydroxide nanomaterials comprise a class of promising advanced functional metal nanomaterials whose use in environmental and material applications is increasing. Several strategies to synthesize these nanomaterials have been described but are unsustainable and uneconomic. This work reports on a processing strategy that turns natural magnesium-rich chrysotile into magnesium oxide and hydroxide nanoparticles via nanoparticle hybridization and an alkaline process while enabling La-based nanoparticles to coat the chrysotile nanotube surfaces. The adsorbent's resulting hybrid nanostructure had an outstanding capacity for phosphate uptake (135.2 mg P g^-1) and enhanced regeneration performance. Furthermore, the adsorbent featured wide applicability with respect to the coexistence of competitive anions and a broad range of pH conditions, and its high-performance phosphate removal from sewage effluent was also demonstrated. Spectroscopic and microscopic analyses revealed the scavenging ability of phosphate by the La-based and Mg-based nanoparticles and the multiple capture mechanisms involved, including surface complexation and ion exchange. This proposed approach expands chrysotile's potential use as a magnesium-rich nanomaterial and harbors great promise for the removal of pollutants in a variety of real-world settings.

Phosphate removal and recovery by lanthanum-based adsorbents: A review for current advances

Controlling eutrophication and recovering phosphate from water bodies are hot issues in the 21st century. Adsorption is considered to be the best method for phosphate removal because of its high adsorption efficiency and fast removal rate. Among the many adsorbents, lanthanum (La)-based adsorbents have been paid more and more attention due to their strong affinity to phosphorus. This paper reviews research of phosphate adsorption on La-based adsorbents in different La forms, including lanthanum oxide/hydroxide, lanthanum mixed metal oxide/hydroxide, lanthanum carbonate, La³⁺, La-based metal-organic framework (La-MOF) and La-MOF derivatives. The La-based adsorbents can be loaded on many carriers, such as carbon material, clay minerals, porous silica, polymers, industrial wastes, and others. We find that lanthanum oxide/hydroxide and La³⁺ adsorbents are mostly studied, while those in the forms of lanthanum carbonate, La-MOF, and La-MOF derivatives are relatively few. The kinetic process of most phosphate adsorption is pseudo-second-order and the isotherm process is in accordance with the Langmuir model. The cost of La-based and other traditional adsorbents was compared. The adsorption mechanisms are categorized as electrostatic attraction, ligand exchange, Lewis acid-base interaction, ion exchange and surface precipitation. Besides, regeneration methods of La-based adsorbents are mainly acid, alkali, and salt-alkali. In addition, the La-based adsorbents after absorbing phosphate can be directly used as a slow-release fertilizer. This review provides a basis for the research on phosphate adsorption by La-based adsorbents. It should be carried out to further develop La-based materials with high adsorption capacity and good regeneration ability. Meanwhile, studies have been conducted on the reuse of phosphate after desorption, which needs more attention in future research.

Self-supported trimetallic NiZnLa nanosheets on hierarchical porous graphene oxide-polymer composite fibers for enhanced phosphate removal from water

Phosphate-induced water eutrophication has attracted global attention. Fabricating adsorbents with both high phosphate adsorption affinity and accessible separation property is challenging. Herein, PG@NZL, a hierarchical nanocomposite fibrous membrane, was fabricated via in-situ growth of La-doped NiZn-LDH (NiZnLa_0.1) over electrospun graphene oxide-polymer composite fibers (PG). The porous surface of the PG fibers provided abundant anchor sites for the vertical self-supported growth of NiZnLa_0.1 nanosheets, contributing to a high surface area. The La-doped NiZnLa_0.1 trimetallic LDH achieved a much higher adsorption capacity than NiZn-LDH. The negative adsorption energy (-1.45 eV), calculated with DFT, confirmed its spontaneous adsorption potential for phosphate. Interestingly, the PG fibers contributed to oxygen vacancies and the metal center electronic structure evolution of NiZnLa_0.1, thus strengthening the coordination with phosphate. Mechanistic analysis revealed that the high adsorption capacity of PG@NZL is attributed to its superior anion exchange property, oxygen vacancies, and inner-sphere complexation. Therefore, the flexible and easily separated PG@NZL nanocomposite fibrous membrane is a promising adsorbent for effectively treating phosphate-bearing wastewater.

Investigation of the efficient adsorption performance and adsorption mechanism of 3D composite structure La nanosphere-coated Mn/Fe layered double hydrotalcite on phosphate

Severe water eutrophication due to large releases of phosphorus has become a worldwide environmental problem. Adsorption active sites is less of traditional adsorbents in the phosphorus removal process resulting in low removal efficiency, so the new high-efficiency phosphorus removal adsorbents become an effective way to solve the problem. In this work, quercetin modified MnFe layered double hydrotalcite three-dimensional composites structures encapsulated by lanthanum (La(III)) nanoparticles (QLa@MnFe-LDH) were successfully prepared by a classical hydrothermal method. The results of the adsorption experiments show that La(III) nanosphere-encapsulated MnFe-LDH provides a more adequate binding site for phosphate adsorption. The adsorption performance of QLa@MnFe-LDH for phosphate was outstanding, the maximum adsorption capacity was 346.5 mg/g at 298.15 K, which was 300 % higher than that of MnFe-LDH. Moreover, QLa@MnFe-LDH retained its high adsorption capacity (>315.5 mg/g) over a wide range of pH (4.0 ∼ 7.0). The active sites of the reactions were predicted by Multiwfn and Visual Molecular Dynamics (VMD), and novel visualization studies of weak interactions were applied to theoretical studies. The modified MnFe-LDH encapsulated by La nanospheres has a strong adsorption capacity for phosphate adsorption. Therefore, the modified QLa@MnFe-LDH was expected to become an effective adsorption material for phosphorus removal.

Structural insight into the alginate derived nano-La(OH)3/porous carbon composites for highly selective adsorption of phosphate

In this study, a novel nano-La(OH)3/porous carbon composites derived from La alginate xerogel with egg-box structure had been successfully synthesized by a gradient heat treatment in nitrogen atmosphere. This facile fabrication strategy can be easily employed to considerably encapsulate La(OH)3 nanoparticles uniformly into the porous carbon matrix derived from the alginate macromolecule framework. The optimized sample, labeled as LS-550(N), exhibited extremely high phosphate uptake and great selectivity. The adsorption kinetic process dramatically followed pseudo-second-order model. The Langmuir model fitted maximum equilibrium adsorption capacity is 133.58 mg·g-1. The phosphate adsorption mechanisms could be consist of electrostatic interaction, complexation and ligand exchange interaction on the surface of LS-550(N). The prominent practical applicability of LS-550(N) in the regeneration test suggests that the LS-550(N) could be a potential adsorption candidate for the decontamination of phosphate-containing natural water bodies.

Co-application of nanosized halloysite and biochar as soil amendments in aided phytostabilization of metal(-oid)s-contaminated soil under different temperature conditions

The threat posed by the degradation of the soil environment by metal (-oid)s has been lead to the improvement of existing or search for new remediation methods; in this case, the application of environmentally friendly nanomaterials falls into this trend. The study applied a technique of aided phytostabilization for the immobilization of metal (-oid)s in soil with the application of nanosized halloysite and biochar (nBH), along with Lolium perenne L. Its effectiveness was assessed in terms of changing temperature conditions (16 cycles of freeze and thaw cycles, (FTC)) on the content of As, Cu, Pb and Zn in the soil, roots, and above-ground parts of the tested plant, chemical fraction distributions of metal (-oid)s and their stability (based on reduced partition index, I_r). The biomass yield in nBH-amended soil was 2-fold higher compared to control soil, but it decreased by 1.6-fold after FTC. nBH facilitated more bioaccumulation of As, Pb and Zn than Cu in plant roots, before than after FTC. nBH increased pH in phytostabilized soil, but it was not affected by changing FTC. In soil nBH-phytostabilized total concentration of metal (-oid)s significantly decreased compared to control soil, for As and Cu below permissible value, regardless of FTC. Soil amendment and changing temperature conditions affected metal (-oid)s redistribution in soil. As a result, the stability of As increased from 0.50 to 0.66, Cu from 0.49 to 0.52, Pb from 0.36 to 0.48 and Zn from 0.39 to 0.47. These findings suggest that nBH can immobilize metal (-oid)s in phytostabilized soil under changing temperature conditions.

Coupling Natural Halloysite Nanotubes and Bimetallic Pt-Au Alloy Nanoparticles for Highly Efficient and Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The aerobic oxidation of 5-hydroxymethylfurfural (HMF), a key platform compound derived from biomass, to 2,5-furandicarboxylic acid (FDCA) is a highly important reaction in the production of green and sustainable chemicals. Here, we developed a highly efficient and stable halloysite-supported Pt-Au alloy catalyst for the selective oxidation of HMF to FDCA. The catalyst was synthesized through the organosilane functionalization of halloysite nanotubes, followed by the in situ formation and dispersion of Pt-Au alloy nanoparticles on the internal and external surfaces of nanotubes. The composition, morphology, and structure of the prepared catalyst were characterized. The catalyst with the optimal composition of Pt/Au molar ratio of 1/4 and metal loading of 1.5 wt % exhibited outstanding catalytic activity for the oxidation of HMF to FDCA using O₂ as an oxidant with 100% conversion of HMF and 99% selectivity of FDCA. This excellent catalytic performance is mainly attributed to the high dispersion and alloying effects of bimetallic nanoparticles, which promoted the activation of reactants or intermediates and further improved FDCA selectivity. Furthermore, the halloysite-supported Pt/Au bimetallic catalyst showed high stability and reusability. This study provides a promising strategy by combining clay mineral halloysite and bimetallic alloys for developing efficient catalysts with high FDCA selectivity and stability for the oxidation of HMF to FDCA.

Mechanistic insights of hexavalent chromium remediation by halloysite-supported copper nanoclusters

Chromium (Cr) pollution is a significant environmental concern with remediation challenge. Hexavalent chromium (Cr(VI)) is more toxic than trivalent chromium (Cr(III)) due to its mutagenicity and oncogenicity. In this investigation, a multi-functional material, copper nanoclusters (CuNCs)-halloysite nanotubes (HNT) composite (CuNCs@HNT), has been synthesised in an eco-friendly manner and utilised for Cr(VI) remediation. Advanced analytical tools confirmed the seeding of ultra-fine CuNCs onto HNT surfaces. The maximum adsorption capacity of CuNCs@HNT is 79.14 ± 6.99 mg/g at pH 5 ± 0.1 with an increment at lower pHs. This performance was comparable for real surface stream water as well as other reported materials. The pseudo-second-order kinetic-, intra-particle diffusion- and Freundlich isotherm models well fit the experimental data implying that the chemisorption, multiphase diffusion and multi-molecular layer distribution occurred during adsorption. The Fourier-transform infrared and the x-ray photoelectron spectra also ensured the transformation of Cr(VI) to Cr(III) indicating the material's suitability for concurrent adsorption and reduction of Cr(VI). While coexisting cations and anions did not overwhelm this adsorption, CuNCs@HNT was regenerated and reused five successive times in adsorption-desorption cycles without significant loss of adsorption capacity and material's integrity. Therefore, this multi-functional, biocompatible, low-cost and stable CuNCs@HNT composite may have practical application for similar toxic metals remediation.

Investigation of halloysite nanotubes and Schiff base combination with deposited copper iodide nanoparticles as a novel heterogeneous catalytic system

The design, preparation and characterization of a novel composite based on functionalization of halloysite nanoclay with Schiff base followed by immobilization of copper iodide as nanoparticles is revealed. This novel nano composite was fully characterized by utilization of FTIR, SEM/EDX, TGA, XRD and BET techniques. This Cu(I) NPs immobilized onto halloysite was successfully examined as a heterogeneous, thus easily recoverable and reusable catalyst in one of classist organic name reaction so-called “Click Reaction”. That comprised a three component reaction of phenylacetylene, α-haloketone or alkyl halide and sodium azide in aqueous media to furnish 1,2,3‐triazoles in short reaction time and high yields. Remarkably, the examination of the reusability of the catalyst confirmed that the catalyst could be reused at least six reaction runs without appreciable loss of its catalytic activity.

Adsorption-Oxidation Mechanism of δ-MnO2 to Remove Methylene Blue

The material, δ-MnO2, has exhibited superior performance on the removal of methylene blue (MB), but the process is significantly impacted by pH, and the impacting mechanism is still unclear. In this study, the effects of pH on the removal mechanism of MB using synthesized δ-MnO2 were investigated by distinguishing the adsorption and oxidation of MB by δ-MnO2 during the removal process in the dark. The results show that the total removal efficiency of MB by δ-MnO2 decreased significantly with an increase in the pH. MB could be removed by δ-MnO2 via an adsorption mechanism and oxidation mechanism, and the proportion of adsorptive removal and oxidative removal was different under different pH conditions. With an increase in the initial pH from 2.00 to 8.05, the redox potential of δ-MnO2 decreased, and its oxidation ability for the removal of MB also gradually decreased. In contrast, the surface negative charges of δ-MnO2 increased with an increase in the pH, and the adsorption ability towards positively charged MB also gradually increased. This indicates that the effects of pH on the removal of MB by δ-MnO2 are primarily dominated by its influence on the oxidation ability of δ-MnO2. In addition, it is further proved that the pH value has a significant effect on the oxidation and adsorption of MB on δ-MnO2. Moreover, the significant effects of pH on the oxidation of MB by δ-MnO2 are further demonstrated by observing the changes in Mn2+ and the UV-Vis spectra of intermediate products during the reaction, as well as the changes in the FTIR and XPS characterizations of δ-MnO2 after the reaction.

Halloysite Nanoclay with High Content of Sulfonic Acid-Based Ionic Liquid: A Novel Catalyst for the Synthesis of Tetrahydrobenzo[b]pyrans

One of the main drawbacks of supported ionic liquids is their low loading and consequently, low activity of the resultant catalysts. To furnish a solution to this issue, a novel heterocyclic ligand with multi imine sites was introduced on the surface of amino-functionalized halloysite support via successive reactions with 2,4,6-trichloro-1,3,5-triazine and 2-aminopyrimidine. Subsequently, the imine sites were transformed to sulfonic acid-based ionic liquids via reaction with 1,4-butanesultone. Using this strategy, high loading of ionic liquid was loaded on halloysite nanoclay. The supported ionic liquid was then characterized with XRD, SEM, TEM, EDS, FTIR, BET, TGA and elemental mapping analysis and utilized as a metal-free Brønsted acid catalyst for promoting one-pot reaction of aldehydes, dimedone and malononitrile to furnish tetrahydrobenzo[b]pyrans. The catalytic tests confirmed high performance of the catalyst. Moreover, the catalyst was stable upon recycling.

Highly regenerative and efficient adsorption of phosphate by restructuring natural palygorskite clay via alkaline activation and co-calcination

Herein, we present a new strategy to create a highly regenerative and efficient phosphate adsorbent based on activating natural palygorskite structures. Both the regeneration via alkaline activation and synthesis via co-calcination restructured the palygorskite and created adsorptive metal oxides. The phosphate adsorbent exhibits excellent regeneration performance with high removal capacity.

Emerging lanthanum (III)-containing materials for phosphate removal from water: A review towards future developments

The last two decades have seen a rise in the development of lanthanum (III)-containing materials (LM) for controlling phosphate in the aquatic environment. >70 papers have been published on this topic in the peer-reviewed literature, but mechanisms of phosphate removal by LM as well as potential environmental impacts of LM remain unclear. In this review, we summarize peer-reviewed scientific articles on the development and use of 80 different types of LM in terms of prospective benefits, potential ecological impacts, and research needs. We find that the main benefits of LM for phosphate removal are their ability to strongly bind phosphate under diverse environmental conditions (e.g., over a wide pH range, in the presence of diverse aqueous constituents). The maximum phosphate uptake capacity of LM correlates primarily with the La content of LM, whereas reaction kinetics are influenced by LM formulation and ambient environmental conditions (e.g., pH, presence of co-existing ions, ligands, organic matter). Increased La solubilization can occur under some environmental conditions, including at moderately acidic pH values (i.e., < 4.5-5.6), highly saline conditions, and in the presence of organic matter. At the same time, dissolved La will likely undergo hydrolysis, bind to organic matter, and combine with phosphate to precipitate rhabdophane (LaPO₄·H₂O), all of which reduce the bioavailability of La in aquatic environments. Overall, LM use presents a low risk of adverse effects in water with pH > 7 and moderate-to-high bicarbonate alkalinity, although caution should be applied when considering LM use in aquatic systems with acidic pH values and low bicarbonate alkalinity. Moving forward, we recommend additional research dedicated to understanding La release from LM under diverse environmental conditions as well as long-term exposures on ecological organisms, particularly primary producers and benthic organisms. Further, site-specific monitoring could be useful for evaluating potential impacts of LM on both biotic and abiotic systems post-application.

La(OH)3 nano-rods/polyacrylonitrile nanofibers: fabrication, characterization and application for phosphate removal

In this study, an excellent phosphate adsorbent was prepared for removing phosphate to an extremely low concentration. The La(OH)₃ nano-rods stabilizing in polyacrylonitrile (PAN) nanofibers (PLNFs) were prepared by electrospinning and a subsequent in situ precipitation. PAN nanofibers were employed as the matrix of the composite nanofibers, where the well-dispersed La(OH)₃ nano-rods were encapsulated as the active species for highly efficient phosphate capture owing to the strong binding between phosphate and lanthanum. On account of the nano-structure, the maximum phosphate adsorption capacity was 151.98 mg P/g (La), much higher than the result of La(OH)₃ nano-crystal, produced by precipitation without PAN or any organic surfactants. Moreover, the PLNFs could remove phosphate (2 mg P/L) to an extremely low concentration within 20 min, which could lead to a nutrient deficient condition to protect water quality and ecosystem. The optimization of PLNFs design was implemented through parameter adjustment of electrospinning. Lanthanum salt content, humidity, concentration of solution and applied voltage were chosen to analyze the influences on the composition, diameter and morphology of the nanofibers, giving the result that the most effective adsorbent was the PLNFs with spider-web-like nano-structures.

Remarkable phosphate removal and recovery from wastewater by magnetically recyclable La2O2CO3/γ-Fe2O3 nanocomposites

Owing to the twin problems of eutrophication and global phosphorus (P) scarcity, the removal and recovery of phosphate from water and wastewater have received increasing attention. Herein, magnetically recyclable La₂O₂CO₃/γ-Fe₂O₃ adsorbents were rationally designed by derivation from La/Fe binary metal organic framework (MOF) precursors via calcination treatment. Based upon preliminary screening of as-prepared La₂O₂CO₃/γ-Fe₂O₃ nanocomposites with different La-to-Fe molar ratios in terms of phosphate sorption capacity and magnetic property as well as La content, La₂O₂CO₃/γ-Fe₂O₃ nanocomposite with a La-to-Fe molar ratio of 2:1 was selected for further characterization and adsorption performance evaluation. Batch adsorption experiments showed that La₂O₂CO₃/γ-Fe₂O₃ (2:1) adsorbent exhibited a remarkable phosphate sorption capacity of 134.82 mg P/g, a fast sorption kinetic, strong selectivity for phosphate in the presence of co-existing anions, and a wide applicable pH range of 3-9. Furthermore, La₂O₂CO₃/γ-Fe₂O₃ (2:1) sorbent displayed an excellent sorption performance for low-concentration wastewater, a low dosage of 0.1 g/L was sufficiently enough for reducing P-concentration from 0.5 mg P/L to below 10 μg P/L within 20 min. In a real sewage of 2.68 mg P/L, 0.2 g/L of sorbent could reduce the concentration of phosphate to <0.01 mg P/L within 50 min. Moreover, over 83.1 % of original sorption capacity could be retained after 5 consecutive regeneration cycles, showing great regenerative performance of the adsorbent. These development is expected to be meaningful for practical water purification.

Preparation of palladated porous nitrogen-doped carbon using halloysite as porogen: disclosing its utility as a hydrogenation catalyst

In this article, halloysite nanoclay (Hal) was used as porogen for the synthesis of nitrogen doped porous carbon material with high specific surface area and pore volume. To this purpose, polymerization of melamine and terephthalaldehyde (MT) was performed in the presence of amine-functionalized carbon coated Hal (Hal@Glu-2N) that was prepared from hydrothermal treatment of Hal and glucose. Then, the prepared nanocomposite was palladated and carbonized to afford Pd@Hal@C. To further improve the textural properties of the nanocomposite, and introduce more pores in its structure, Hal nanotubes were etched. The characterization of the resulting compound, Pd@C, and comparing it with Pd@Hal@C, showed that etching of Hal significantly increased the specific surface area and pore volume in Pd@C. Pd@C was successfully used as a heterogeneous catalyst for promoting hydrogenation of nitroarens in aqueous media using hydrogen with atmospheric pressure as a reducing agent. The comparison of the structural features and catalytic activity of the catalyst with some control catalysts, including, Pd@Hal, Pd@Hal@Glu, Pd@Hal@Glu-MT and Pd@Hal@C confirmed that nitrogen groups in C could improve the Pd anchoring and suppress its leaching, while etching of Hal and introduction of more pores could enhance the catalytic activity through facilitating the mass transfer.

Palladated Nanocomposite of Halloysite-Nitrogen-Doped Porous Carbon Prepared from a Novel Cyano-/Nitrile-Free Task Specific Ionic Liquid: An Efficient Catalyst for Hydrogenation

A novel nitrile-/cyano-free ionic liquid was synthesized and carbonized under two different carbonization methods in the presence of ZnCl₂ as a catalyst to afford N-doped carbon materials. It was found that the carbonization condition could affect the nature and textural properties of the resulting carbon. In the following, ionic liquid-derived carbon was hybridized with naturally occurring halloysite nanotubes via two procedures, that is, hydrothermal treatment of halloysite and as-prepared carbon and carbonization of ionic liquid in the presence of halloysite. The two novel nanocomposites were then used for stabilizing Pd nanoparticles. Examining the structures and catalytic activities of the resulting catalysts for the hydrogenation of nitroarenes in aqueous media showed that the carbonization procedure and hybridization method could affect the structure and the catalytic activity of the catalysts and hydrothermal approach, in which the structure of halloysite is preserved, leading to the catalyst with superior catalytic activity.

Fabricating Mechanically Robust Binder-Free Structured Zeolites by 3D Printing Coupled with Zeolite Soldering: A Superior Configuration for CO2 Capture

3D-printing technology is a promising approach for rapidly and precisely manufacturing zeolite adsorbents with desirable configurations. However, the trade-off among mechanical stability, adsorption capacity, and diffusion kinetics remains an elusive challenge for the practical application of 3D-printed zeolites. Herein, a facile "3D printing and zeolite soldering" strategy is developed to construct mechanically robust binder-free zeolite monoliths (ZM-BF) with hierarchical structures, which can act as a superior configuration for CO2 capture. Halloysite nanotubes are employed as printing ink additives, which serve as both reinforcing materials and precursor materials for integrating ZM-BF by ultrastrong interfacial "zeolite-bonds" subjected to hydrothermal treatment. ZM-BF exhibits outstanding mechanical properties with robust compressive strength up to 5.24 MPa, higher than most of the reported structured zeolites with binders. The equilibrium CO2 uptake of ZM-BF reaches up to 5.58 mmol g-1 (298 K, 1 bar), which is the highest among all reported 3D-printed CO2 adsorbents. Strikingly, the dynamic adsorption breakthrough tests demonstrate the superiority of ZM-BF over commercial benchmark zeolites for flue gas purification and natural gas and biogas upgrading. This work introduces a facile strategy for designing and fabricating high-performance hierarchically structured zeolite adsorbents and even catalysts for practical applications.