New design to enhance phosphonate selective removal from water by MOF confined in hyper-cross-linked resin

Although polymeric anion exchange resins can remove phosphonates, they lack selectivity for target phosphonates and are susceptible to interference by anions and other substances. Here, we developed a novel strategy via confining MIL-101(Fe)-NH2 inside commercial resins IRA-900 for high-efficient and precise phosphonate removal, accompanying with the improvement of the stability and recovery of MIL-101(Fe)-NH2. The obtained nanocomposite MIL-101(Fe)-NH2@IRA-900 (MFNI) exhibited significantly enhanced phosphonate removal in the presence of competing anions (Cl-, SO42-, NO3- and CO32-) and natural organic matter (humic acid) at high concentrations (2-4 times of phosphonate concentration). Moreover, MFNI displayed the highest phosphonate adsorption capacity (12.9 mg P/g) and the fastest adsorption kinetics (120 min) than hydrated ferric oxides modified IRA-900 (HFOI) (6.7 mg P/g, 180 min), MIL-101(Fe)-NH2 (7.6 mg P/g, 240 min) and IRA-900 (5.6 mg P/g, 360 min). Such higher adsorption affinity and anti-interference ability came from the synergistic effect of the host IRA-900 (hydrogen-bond interaction and electrostatic attraction) and the embedded MIL-101(Fe)-NH2 (ligand exchange). The depleted MFNI could be regenerated with a binary NaOH-NaCl solution and reused without significant loss of capacity. Column adsorption runs by using MFNI indicated the fresh MFNI could achieve 100 % removal of PPOA in 10.5 h continuously feeding, which offered the possibility of achieving potential large-scale applications. In general, a new MOF-confined design approach was practiced to achieve selective elimination of phosphates and to improve the stability and recovery of MOF.

One-pot synthesis of novel flower-like LaCO3OH adsorbents for efficient scavenging of phosphate from wastewater

Phosphorus removal from wastewater has been considered as an effective method to control eutrophication and mitigate phosphorus deficiency. Phosphate adsorption using lanthanum-based materials has awakened much attention and triggered extensive research. In this study, novel flower-like LaCO₃OH materials were synthesized via a one-step hydrothermal method and evaluated for phosphate removal from wastewater. The adsorbent with flower-like structures prepared at the hydrothermal reaction time of 4.5 h (BLC-4.5) exhibited the optimum adsorption performance. BLC-4.5 had a rapid removal rate with more than 80% of the saturated adsorbed phosphate removed within 20 min. Furthermore, the maximum phosphate adsorption capacity of BLC-4.5 was as high as 228.5 mg/g. Notably, the La leaching amount of BLC-4.5 was negligible in the pH range of 3.0-11.0. BLC-4.5 outperformed most of the reported La-based adsorbents in terms of removal rate, adsorption capacity, and La leaching amount. Moreover, BLC-4.5 had broad pH adaptability (3.0-11.0) and high selectivity for phosphate. BLC-4.5 also displayed excellent phosphate removal efficiency in actual wastewater and great recyclability. The potential adsorption mechanisms of phosphate on BLC-4.5 were precipitation, electrostatic attraction, and inner-sphere complexation via ligand exchange. This study demonstrates that the newly developed flower-like BLC-4.5 reported here is a promising adsorbent for the effective treatment of phosphate in wastewater.

Recent developments in alginate-based adsorbents for removing phosphate ions from wastewater: a review

The huge development of the industrial sector has resulted in the release of large quantities of phosphate anions which adversely affect the environment, human health, and aquatic ecosystems. Naturally occurring biopolymers have attracted considerable attention as efficient adsorbents for phosphate anions due to their biocompatibility, biodegradability, environmentally-friendly nature, low-cost production, availability in nature, and ease of modification. Amongst them, alginate-based adsorbents are considered one of the most effective adsorbents for removing various types of pollutants from industrial wastewater. The presence of active COOH and OH^- groups along the alginate backbone facilitate its physical and chemical modifications and participate in various possible adsorption mechanisms of phosphate anions. Herein, we focus our attention on presenting a comprehensive overview of recent advances in phosphate removal by alginate-based adsorbents. Modification of alginate by various materials, including clays, magnetic materials, layered double hydroxides, carbon materials, and multivalent metals, is addressed. The adsorption potentials of these modified forms for removing phosphate anions, in addition to their adsorption mechanisms are clearly discussed. It is concluded that ion exchange, complexation, precipitation, Lewis acid-base interaction and electrostatic interaction are the most common adsorption mechanisms of phosphate removal by alginate-based adsorbents. Pseudo-2^nd order and Freundlich isotherms were figured out to be the major kinetic and isotherm models for the removal process of phosphate. The research findings revealed that some issues, including the high cost of production, leaching, and low efficiency of recyclability of alginate-based adsorbents still need to be resolved. Future trends that could inspire further studies to find the best solutions for removing phosphate anions from aquatic systems are also elaborated, such as the synthesis of magnetic-based alginate and various-shaped alginate nanocomposites that are capable of preventing the leaching of the active materials.

Coupled catalytic dephosphorylation and complex phosphate ion-exchange in networked hierarchical lanthanum carbonate grafted asymmetric bio-composite membrane

The remediation of non-reactive phosphate pollutants in the aquatic system is essential for protecting the ecological niche. In this work, a highly robust protein nanoparticles networked rare-earth metal carbonate-grafted bio-composite membrane (abbreviated as REMC) was fabricated via chemical crosslinking of three-dimensional (3D) hierarchical lanthanum carbonate (mREM) and casein nanoparticles (CsNPs) for selective rejection of non-reactive phosphates. The main components of the REMC membrane are mREM and CsNPs, which were prepared via SDS/CTAB templated homogeneous precipitation and the coacervation/desolvation hybrid method, respectively. The active lanthanum ion (La³⁺) on the 3D spherulitic surface of mREM exhibited excellent phosphate adsorption capacity (maximum adsorption capacity was 358 mg.g^-1) across a wide pH range and in a multi-ionic environment. A series of batch testing and characterizations revealed that the active La³⁺ and dominating phosphate centers in the REMC membrane framework enable non-enzymatic phosphatase-like activity, cleaving the phosphate ester bond of organic phosphates and releasing free phosphate anions. These released phosphate ions are retained in the REMC membrane via an ion exchange mechanism, where they contribute to improved phosphate removal capacities. Furthermore, CsNPs have a dual function in the membrane, acting as a matrix in the REMC membrane framework and contributing to phosphate ion sequestrations in a synergistic manner. The catalysis of para-nitrophenyl phosphates (pNPP) to paranitrophenol (pNP) in a sequential dephosphorylation by REMC offers an estimate of reaction kinetics and elucidates the underlying mechanism of improved phosphate selectivity in a multi-ionic environment. Furthermore, phosphate specificity, homogeneous binding capacity, reusability, and visual observation of REMC membrane saturation binding direct it's useful economic, industrial applications in aqueous phosphate contaminant removal, which could be beneficial for the active recovery of the aquatic ecosystem.

The hollow core-shell ferric oxide entrapped chitosan microcapsules as phosphate binders for phosphorus removal in vitro

Patients in hyperphosphatemia are orally prescribed with phosphate binders to excrete the non-metabolic phosphorus. Aiming for the bio-compatibility and binding efficacy, the Fe-based phosphate binders of low toxicity have been explored and improved. Herein, the hollow core-shell microcapsules as Fe@CH (nano ferric oxide entrapped in the polymerized chitosan) were constructed via emulsion interface polymerization, to enhance the phosphate binding from -NH₂ group and iron complex, and limit iron leakage significantly. Via the double emulsion polymerization based on the primary Pickering emulsion stabilized by oleic acid-modified ferric oxide, Fe@CH performed as the rough polymerized-chitosan microcapsules entrapping well-distributed ferric oxide for the phosphate adsorption in vitro. At pH 3 and pH 5, Fe@CH bound phosphorus efficiently, with the capacity of 55 mg/g and 65 mg/g respectively, along with the excellent shell isolation from iron leakage and remarkable safety. Prospectively, the Fe@CH micro-sorbent is the proper candidate as the phosphate binder for hyperphosphatemia.

Highly Efficient Low-Concentration Phosphate Removal from Effluents by Recoverable La(OH)3/Foamed Nickel Adsorbent

Lanthanum-based materials have attained increasing attention because of their high adsorption property of phosphate ions and their environmental harmlessness. However, challenges still remain to improve the phosphate adsorption capacity and find suitable materials for the lanthanum attachment substrate. Nickel foam with characteristics such as excellent uniformity, large specific surface area, high porosity, and low conductivity is considered to be the alternative for the preparation of lanthanum-based adsorption materials. An efficient adsorbent foamed nickel-based La (OH)₃ nanowire was first prepared with a facile one-step electrodeposition method. The batch static adsorption tests of simulative wastewater (e.g., coexisting ions and solution pH values) were employed to investigate the phosphate adsorption kinetics and solution matrix effects of the materials. The results indicate that the composite exhibits fast adsorption kinetics within 30 min and high selectivity to phosphate under interference from competing ions. The pH value of wastewater has great influence on the absorption of phosphate, and optimal adsorption capacity can be achieved over a pH 4-6 range. Various findings revealed that the adsorption behavior of lanthanum hydroxide/foamed nickel [La(OH)₃/Ni] followed inner-sphere adsorption through the ligand-exchange mechanism. The prepared material is expected to be an enormous potential candidate for the removal of low-concentration phosphorus from effluents.

Great enhancement in phosphate uptake onto lanthanum carbonate grafted microfibrous composite under a low-voltage electrostatic field

Removal of phosphorus from water via cost-effective measures becomes important for water industry mainly due to eutrophication in waterbody. In our lab, a novel lanthanum carbonate-microfibrous composite (LC-MC) with good performance was previously synthesized for the removal of phosphorus. In this study, we further improved our technology by applying the electrostatic field (direct current, DC) to the adsorption system. It was showed that the applied DC can greatly improve the adsorption of phosphate in particular the adsorption capacity. Better removal was seen in the pH range of 5-9 at a higher temperature. The maximum adsorption capacity of 47.57 mg-PO₄^3- g^-1 was achieved, which was 1.4 times of that operated in the absence of applied DC. The adsorption equilibrium was established at the contact time of 240 min; the adsorption history was well described by the intraparticle surface diffusion model. The negative effect from oxygen-containing anions on the phosphate uptake followed the decreasing sequence of: humic acid > carbonate > nitrate > sulfate; on the other hand, the halogen anions had almost no influence on it. Finally, the mechanism study by XPS, XRD, and IR demonstrated that the ligand exchange played an important role in the electro-assisted phosphate uptake process.

Novel talc encapsulated lanthanum alginate hydrogel for efficient phosphate adsorption and fixation

In the present work, talc (a low-cost clay) encapsulated salts alginate (TAL) beads were synthesized by cross-linking with lanthanum ion and tested for phosphate adsorption. Multiple methods were applied for the characterization of composites. The combined effect of talc and lanthanum improved phosphate removal performance of TAL beads. Factors such as talc content, La³⁺ concentration, adsorbent dosage, pH, co-existing ions (Cl^-, NO₃^- and SO₄^2-) were studied in batch experiments. The optimized TAL-7 beads exhibited satisfactory selectivity towards phosphate in the coexistence of competing anions and could remain efficient phosphate removal in the pH range of 4-6. The phosphate removal efficiency reached to 95% with a maximum uptake of 16.4 mg P/g obtained at the optimal pH 4. Further experiments suggested that Langmuir isotherm model and the pseudo-second-order kinetic model could well describe the phosphate adsorption process of TAL-7 beads. Moreover, TAL-7 beads exhibited superior phosphate fixation performance in the long-term experiment. The results from adsorption experiment and characterization analysis demonstrated that TAL-7 beads could be a cost-effective and promising biosorbent for phosphate adsorption and fixation in the aqueous environment.

An innovative lanthanum carbonate grafted microfibrous composite for phosphate adsorption in wastewater

Excessive presence of phosphorus in waters can cause eutrophication, a global unsolved environmental problem that has caused harmful effects to our eco-system and the source of our drinking water. In the study presented in this paper, a novel lanthanum carbonate grafted microfibrous composite (LC-MC) adsorbent was synthesized aiming at removing large amount of phosphate in wastewater efficiently. An optimized LC-MC was firstly prepared. The most suitable pH for the phosphate uptake was pH 7 to 9. The adsorption showed similar behavior in a wide range of ionic strength. The presence of co-existing anions was proved to have a less significant effect on the removal. The adsorption isotherm data were better fitted by the Freundlich isotherm than the Langmuir isotherm. The equilibrium was reached at about 300 min of contact time. 80 % of original adsorption capacity can be achieved even after 5 cycles of adsorption- desorption operations, indicating great regenerative performance of the adsorbent. The adsorption mechanism study showed that the ligand exchange played a key role during the phosphate adsorption.

Enhanced Phosphate Removal by Nanosized Hydrated La(III) Oxide Confined in Cross-linked Polystyrene Networks

A new nanocomposite adsorbent La-201 of extremely high capacity and specific affinity toward phosphate was fabricated and well characterized, where hydrated La(III) oxide (HLO) nanoclusters were immobilized inside the networking pores of the polystyrene anion exchanger D-201. La-201 exhibited enhanced phosphate adsorption in the presence of competing anions (chloride, sulfate, nitrate, bicarbonate, and silicate) at greater levels (up to molar ratio of 20), with working capacity 2-4 times higher than a commercial Fe(III) oxide-based nanocomposite HFO-201 in batch runs. Column adsorption runs by using La-201 could effectively treat ∼6500 bed volumes (BV) of a synthetic feeding solution before breakthrough occurred (from 2.5 mg P/L in influent to <0.5 mg P/L in effluent), approximately 11 times higher magnitude than that of HFO-201. The exhausted La-201 could be regenerated with NaOH-NaCl binary solution at 60 °C for repeated use without any significant capacity loss. The underlying mechanism for the specific sorption of phosphate by La-201 was revealed with the aid of STEM-EDS, XPS, XRD, and SSNMR analysis, and the formation of LaPO4·xH2O is verified to be the dominant pathway for selective phosphate adsorption by the immobilized nano-HLO. The results indicated that La-201 was very promising in highly efficient removal of phosphate from contaminated waters.