Effect of capping mode on control of phosphorus release from sediment by lanthanum hydroxide

The use of in situ active capping to control phosphorus release from sediment has attracted more and more attentions in recent years. It is important to identify the effect of capping mode on the control of phosphorus release from sediment by the in situ active capping method. In this study, the impact of capping mode on the restraint of phosphorus migration from sediment into overlying water (OW) by lanthanum hydroxide (LH) was studied. Under no suspended particulate matter (SPM) deposition condition, LH capping effectively restrained the liberation of endogenous phosphorus into OW during anoxia, and the inactivation of diffusive gradient in thin film-unstable phosphorus (UP_DGT) and mobile phosphorus (P_Mobile) in the topmost sediment served as a significant role in the restraint of endogenous phosphorus migration into OW by LH capping. Under no SPM deposition, although the transformation of capping mode from the single high dose capping to the multiple smaller doses capping had a certain negative impact on the restraint efficiency of endogenous phosphorus liberation to OW by LH in the early period of application, it increased the stability of phosphorus in the static layer in the later period of application. Under SPM deposition condition, LH capping had the capability to mitigate the risk of endogenous phosphorus liberation into OW under anoxia conditions, and the inactivation of UP_DGT and P_Mobile in the topmost sediment was a significant mechanism for the control of sediment phosphorus liberation into OW by LH capping. Under SPM deposition condition, the change in the covering mode from the one-time high dose covering to the multiple smaller doses covering decreased the efficiency of LH to limit the endogenous phosphorus transport into OW in the early period of application, but it increased the performance of LH to restrain the sedimentary P liberation during the later period of application. The results of this work suggest that the multiple LH capping is a promising approach for controlling the internal phosphorus loading in freshwater bodies where SPM deposition often occurs in the long run.

Stable and recyclable lanthanum hydroxide-doped graphene oxide biopolymer foam for superior aqueous arsenate removal: Insight mechanisms, batch, and column studies

In this study, a graphene oxide-based lanthanum hydroxide/chitosan foam (CSGOL foam) was synthesized for arsenate (As(V)) remediation in surface water. The synthesized CSGOL foam texture and purity was assessed using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) studies. The results proved that the foam was highly porous, stable, and had high surface functionality that facilitated adsorption for water pollutant removal. The sorption results proved that the As(V) removal was high (146.20 mg/g at pH 6 with 0.5 g/L CSGOL foam) when compared to the similar type of materials, endothermic chemisorption due to the production of monodentate and bidentate inner-sphere complexes. Furthermore, continuous column results indicated that the As(V) concentration in real surface waters was reduced to WHO standards (less than 10 μg As/L of water) of As(V) in drinking water for up to 10,000 bed volume. Further it can be used up to four cycles without loss of efficacy less than 93%. Because of its excellent removal capabilities and simple synthesis technique, CSGOL foam shows significant promise for treating As(V)-containing water. Further, the XPS analysis and batch studies results suggests that As(V) removal mechanism was involved electrostatic and surface complexation through chemical interaction predominately.

Design and optimization of an innovative lanthanum/chitosan bead for efficient phosphate removal and study of process performance and mechanisms

Presence of excessive phosphorus in surface waters is the main cause for eutrophication. In this study, a lanthanum/chitosan (La/CS) bead was prepared so as to provide a cost-effective solution to the problem. The optimization of bead for the treatment was conducted, leading to the optimal condition: 30 wt% La/CS bead at a dosage of 30 g L^-1 (wet weight). A higher phosphate removal around 90% was obtained in pH 4.0-10.0. Most of uptake occurred in the first 2 h and the equilibrium was reached in about 6 h. Coexisting ions of Cl^-, [Formula: see text] , [Formula: see text] , and [Formula: see text] had negligible effects on the treatment, while the presence of F^- reduced the uptake by 10.39%. The maximum adsorption capacity of 261.1 mg-PO₄·g^-1 (dried weight) at pH 5.0 was achieved, which is much better than many reported La-based adsorbents. The adsorbed phosphate can be effectively recovered with an alkaline solution. A multi-cycle regeneration-reuse study illustrated that the treated water still met the phosphorus discharge standard. The characterization results demonstrated the disappearance of La(OH)₃ and La₂(CO₃)₃ on the bead and the formation of NH₃⁺ … P and La-P groups after the adsorption, indicating the significant roles of ion exchange and electrostatic attraction on the uptake. The excellent performance found in this study clearly indicates that the optimized La/CS bead is promising in the treatment of phosphate and perhaps its recovery for industrial use.

Phosphate removal from river water using a highly efficient magnetically recyclable Fe3O4/La(OH)3 nanocomposite

Lanthanum based nanocomposites have attracted much attention for their efficiency and capacity in removing phosphate from water. This study developed a Fe₃O₄/La(OH)₃ nanocomposite through a precipitation route at room temperature and used the nanocomposite to remove phosphate from river water. Performance of the Fe₃O₄/La(OH)₃ nanocomposite was evaluated in terms of sorption kinetics, sorption isotherms, different solution pH values, competing ions, and regenerative ability. The Fe₃O₄/La(OH)₃ nanocomposite showed a nanosphere-like morphology with 97% magnetic separation efficiency, excellent phosphate removal capacity of 253.83 mg/g, 99% phosphate selectivity in the presence of chloride, nitrate, sulfate, fluoride, and calcium as competing ions and excellent reusability in ten cycles. Based on these findings, the Fe₃O₄/La(OH)₃ nanocomposite was used to remove phosphate from river water. It was found that, in 60 min, a 0.1 g/L dosage of the nanocomposite was able to reduce the phosphate in the water from 0.087 mg/L to 0.002 mg/L. Moreover, studying of the removal mechanism of the nanocomposite revealed that surface complexation and the electrostatic interaction between phosphate species and lanthanum hydroxide played a prominent role in the sorption of phosphate.

Lanthanum hydroxide: a highly efficient and selective adsorbent for arsenate removal from aqueous solution

In the present work, a lanthanum hydroxide adsorbent was prepared by a simple precipitation process, and its arsenic removal performances and adsorption mechanisms were investigated by batch experiments and various techniques including field emission scanning electron microscopy with energy-dispersive X-ray spectrophotometry (FESEM-EDX), Brunauer-Emmett-Teller (BET) analysis, powder X-ray diffraction (p-XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The influence of pH on arsenic removal showed that the lanthanum hydroxide adsorbent can effectively remove As(V) from solution, whereas the As(III) removal was very low, indicating that the lanthanum hydroxide adsorbent can selectively remove As(V) but not As(III). The isotherm study showed that the maximum adsorption capacities of As(V) at pH 5.0 and 9.0 were 299.4 and 192.3 mg/g, respectively, much higher than those of the widely used ferrihydrite. Significant interference on As(V) removal was caused by the presence of phosphate and natural organic acids (NOAs), such as citric acid. Powder XRD, FTIR, and XPS analysis showed that the lanthanum hydroxide was almost transformed into lanthanum arsenate after As(V) adsorption at pH 4.0, while a portion of lanthanum hydroxide remained after As(V) adsorption at pH 6.0 and 9.0. Furthermore, ligand exchange between the hydroxyl groups of the adsorbent and As(V) and the formation of inner-sphere surface complexes could play a central role in arsenic removal which needs further investigation.

Highly sensitive and selective determination of p-nitrophenol at an interpenetrating networks structure of self-assembled rod-like lanthanum hydroxide-oxidized multi-walled carbon nanotubes nanocomposite

In this study, a novel electrochemical sensor based on self-assembled rod-like lanthanum hydroxide-oxidized multi-walled carbon nanotubes (La(OH)₃-OxMWCNTs) nanocomposite was developed for sensitive determination of p-nitrophenol (p-NP). The La(OH)₃-OxMWCNTs nanocomposite with an interpenetrating networks structure was characterized by field emission electron microscope (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, Raman spectra and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were performed to study the electrochemical behaviors of La(OH)₃-OxMWCNTs modified glassy carbon electrode (La(OH)₃-OxMWCNTs/GCE). The La(OH)₃-OxMWCNTs/GCE was used for sensitive determination of p-NP by CV and linear sweep voltammetry (LSV). Under the optimum conditions, the peak currents of LSV versus the concentrations of p-NP in the range 1.0-30.0 μmol L^-1 showed a good linear relationship (R²=0.9971), and the limit of detection (LOD) was calculated to be 0.27 μmol L^-1 (signal-to-noise ratio of 3, S/N=3). The recoveries of p-NP in real samples of industrial wastewater and Xiangjiang water at La(OH)₃-OxMWCNTs/GCE were in the range of 95.62-110.75% with relative standard deviation (RSD) in the range of 1.65-3.85%. The intra-day and inter-day precisions were estimated to be less than 2.76% (n= 5), indicating that La(OH)₃-OxMWCNTs/GCE possessed highly stability. In addition, La(OH)₃-OxMWCNTs/GCE sensor showed good anti-interference ability for determination of p-NP in aqueous mixtures containing high concentrations of inorganic and organic interferents, and a decrease of oxidation peak currents by less than 3.57% relative to the initial levels indicated it possessed excellent selectivity. Therefore, La(OH)₃-OxMWCNTs/GCE could be used as a fast, selective and sensitive electrochemical sensor platform for the selective determination and quantification of aqueous p-NP.

Immobilization of mobile and bioavailable phosphorus in sediments using lanthanum hydroxide and magnetite/lanthanum hydroxide composite as amendments

This work prepared lanthanum hydroxide (La-OH) and magnetite/lanthanum hydroxide composite (Mag-La-OH), and then La-OH and Mag-La-OH were used as sediment amendments to immobilize phosphorus (P) in sediments. The immobilization efficiency of mobile P (MobP) and bioavailable P (BIO-P) in sediments by La-OH and Mag-La-OH was investigated. Results showed that the addition of La-OH into sediment resulted in the transformation of loosely adsorbed P (LA-P) and redox sensitive P (RS-P) to sodium hydroxide extractable P (OH-P) and hydrochloride extractable P (HP) in the sediment, while the addition of Mag-La-OH into sediment led to the transformation of LA-P, RS-P and HP to OH-P and residual P (RESP) in the sediment. Both La-OH and Mag-La-OH can effectively immobilize Mob-P (LA-P + RS-P) in sediments, but La-OH had a higher Mob-P immobilization capacity than Mag-La-OH. The amendment of sediments with La-OH and Mag-La-OH both can reduce the amounts of different types of BIO-P including water soluble P (WA-P), algal available P (AL-P) and Fe oxide-paper extractable P (FE-P) in the sediments, and La-OH had a higher BIO-P immobilization capacity than Mag-La-OH. The immobilization of Mob-P in sediments by Mag-La-OH could be described by the equation: W = 0.333 × (∆Mob-P)-14.4, where ∆Mob-P (mg/kg) is the amount of Mob-P bounded in sediments and W (%) is the Mag-La-OH dosage. The immobilization of FE-P in sediments by Mag-La-OH could be described by the equation: W = 0.380 × (∆FE-P) + 1.14, where ∆FE-P is the amount of FE-P bounded in sediments. Considering that Mag-La-OH can be retrieved from the water bodies under the action of external magnetization fields after its application, Mag-La-OH could have high potential to be used as an amendment for the immobilization of Mob-P and BIO-P in sediments.

Preferable phosphate removal by nano-La(III) hydroxides modified mesoporous rice husk biochars: Role of the host pore structure and point of zero charge

Immobilizing La(OH)₃ nanoparticles (NPs) to porous hosts has been widely applied to inhibiting their inherent aggregation as well as the subsequent low utilization efficiency of La. In this study, a series of rice husk biochars (RHBCs) with high mesoporous rates were prepared and the effects of host pore structure and point of zero charge (pH_pzc) on phosphate adsorption by La-modified RHBCs was particularly focused. Characterization results confirmed that La(OH)₃ NPs were both confined in the pore channel and external surface of RHBCs. Adsorption kinetics and isotherms showed that La-modified RHBCs with higher mesoporous rates of the host showed a faster adsorption rate and La-modified RHBCs exhibited superior La utilization efficiency than many reported La-incorporated adsorbents. Phosphate could be effectively captured over a wide pH of 3-10 due to the high pH_pzc of La-modified RHBCs. Moreover, the La-modified RHBCs showed satisfactory affinity towards phosphate in the presence of coexisting anions and the phosphate adsorption by La-RHBC₉ was enhanced in the presence of Ca²⁺, while it was inhibited in the presence of Mg²⁺. The mesoporous structure of RHBCs strengthened the stability of La-modified RHBCs and weakened the inhibition of coexisting humic substances on phosphate adsorption through the "shielding effect".

Magnetite/Lanthanum hydroxide for phosphate sequestration and recovery from lake and the attenuation effects of sediment particles

An effective approach for eutrophication control and phosphate recovery remains a longstanding challenge. Herein, we present a new technique for phosphate sequestration in lake and phosphate recovery using novel magnetically recoverable magnetite/lanthanum hydroxide [M-La(OH)₃] hybrids that can be prepared using a simple one-pot synthesis method. Batch studies show that M-La(OH)₃ exhibits a strong sorption towards phosphate with sorption capacities of up to 52.7 mg-P/g at pH 7.0 in water. A simple model indicates that the efficiency of M-La(OH)₃ for phosphate sequestration in lake is significantly attenuated by 34-45% compared to that in water, due to interference from sediment particles. However, our results demonstrate that sediments suspensions mixed with a M-La(OH)₃ content of 1-3% exhibit a capability of up to 1.2 mg-P/g for sequestering external phosphate compared with that of 0.2 mg-P/g for pristine sediment at pH 7.3. M-La(OH)₃-mixed sediment suspensions appear to effectively sequester phosphate over an environmentally relevant pH range from 4 to 8.5. Phosphorus (P) fractionation experiments indicate that the enhanced phosphate sorption by M-La(OH)₃-mixed sediment suspensions is mainly due to the increased fractions of NaOH-P and inorganic P. This work indicates that the M-La(OH)₃ has the potential for phosphate sequestration and recovery from lake.

Lanthanum oxide nanorods for enhanced phosphate removal from sewage: A response surface methodology study

Lanthanum-based adsorbents are ideal candidates for phosphate removal because of their excellent affinity to phosphate. However, their application in the removal of trace-levels of phosphate from sewage is still unsatisfactory due to the limited adsorption capacity and inadequate optimization of the operational parameters. To overcome these drawbacks, we have developed a novel lanthanum hydroxide (LH), using a facile precipitation and hydrothermal process that involves a nanorod-like structure with the lengths ranging from 124 to 1700 nm, depending on the La/OH molar ratio. The phosphate adsorption capacity of the developed LH is up to 170.1 mg-P g^-1 in synthetic water, while a slightly lower adsorption capacity of 111.1 mg-P g^-1 is observed in a sewage sample. A polynominal model consisting of three variables (i.e. dosage, reaction time and initial phosphate concentration) for predicting efficiency of phosphate removal has been successfully developed using a face-centred central composite design (CCD)-based methodology. The results also suggest a strong interactive effect of the dosage with the phosphate concentration, and reaction time, which can significantly affect the optimization of the phosphate removal by LH. Both X-ray photoelectron spectroscopy and X-ray diffraction studies indicate that the inner sphere complexation of phosphate with LH is probably the major mechanism governing phosphate removal.

Infrared to infrared upconversion emission in Pr(3+)/Yb(3+) co-doped La2O3 and La(OH)3 nano-phosphors: a comparative study

The Pr(3+)/Yb(3+) co-doped La2O3 and La(OH)3 nano-phosphors have been synthesized through solution combustion method. The structure and morphology of the samples have been studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The physical and optical properties of the samples have been measured and compared. A broad intense infrared emission centered at 850nm due to (1)I6→(1)G4 transition along with sharp green emission centerd at 513nm due to (3)P0→(3)H4 transition are observed on excitation with 976nm laser. The emission intensity of Pr(3+) is optimized with concentration and it is maximum at 0.08mol%. The annealed samples are found to be more crystalline and emit larger photoluminescence due to removal of quenching centers. The power dependent study of green upconversion emission indicates the involvement of two photons. The phosphor in La(OH)3 phase is more stable though the photoluminescence emission is slightly weak. La(OH)3 is less toxic compared to La2O3 and is biocompatible. It generates more heat and can be used in biothermal treatment.

Facile Synthesis of Amine-Functionalized Eu(3+)-Doped La(OH)3 Nanophosphors for Bioimaging

Here, we report a straightforward synthesis process to produce colloidal Eu(3+)-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent surface modification. The La(OH)3:Eu(3+) NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission peaks at 597 and 615 nm (λex = 280 nm). The red emission, due to (5)D0 → (7)F1 and (5)D0 → (7)F2 transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)3:Eu(3+) NPs possess the potential to serve as a luminescent bioimaging probe.