The alternative use of layered double hydroxides as extraction medium coupled with microcomplexation for determination of phosphate in water samples

Preconcentration of phosphate ions on graphene oxide decorated with lanthanum oxide from waters followed by energy dispersive X-ray fluorescence spectrometric determination

A method for energy dispersive X-ray fluorescence spectrometric (EDXRF) determination of phosphate ions via the PKα line in diverse types of water samples is described. The method is based on ultrasonically assisted dispersive micro-solid phase extraction (USA-DMSPE) using lanthanum oxide supported on graphene oxide (La2O3-GO) as a solid adsorbent. Under optimal preconcentration conditions, i.e. sample pH = 5, sample volume 50 mL, adsorbent dose 0.8 mg, sonication time 30 min, a linear response was obtained between the phosphate concentration and the measured analytical signal in the range of 2-300 ng mL-1 with a correlation coefficient of 0.9995. The developed procedure is characterized by good detection and quantification limits of 0.4 and 1.32 ng mL-1. The inter-day and infra-day precision of the method tested at analyte ion concentrations of 5, 50, and 200 ng mL-1 ranges from 1.1 to 4.4% and 1.2-4.7%, respectively. The accuracy of the method was verified by the standard addition method and the inductively coupled plasma atomic emission spectrometry (ICP-OES) comparative technique. The method was implemented for the analysis of various water samples, including artificial seawater. The phosphate content in studied water samples ranges from 23.8 to 121 ng mL-1. Recoveries in samples enriched with phosphates with a known concentration of 94-102%, as well as a relative difference of 1.5-3.8% between results obtained by USA-DMSPE/EDXRF and ICP-OES indicate the usefulness of the method for the quantitative determination of phosphate ions in natural waters. Moreover, the mechanism of chemisorption in the tested system was discussed and the maximum adsorption capacity of La2O3-GO towards phosphate ions (90.1 mg g-1) was determined.

Eco-Friendly Starch Composite Supramolecular Alginate–Ca2+ Hydrogel as Controlled-Release P Fertilizer with Low Responsiveness to Multiple Environmental Stimuli

Environmentally friendly fertilizers (EFFs) have been developed to improve fertilizer efficiency and minimize adverse environmental impacts, but their release behavior under various environmental conditions has been less explored. Using phosphorus (P) in the form of phosphate as a model nutrient, we present a simple method for preparing EFFs based on incorporating the nutrient into polysaccharide supramolecular hydrogels using Cassava starch in the Ca2+-induced cross-link gelation of alginate. The optimal conditions for creating these starch-regulated phosphate hydrogel beads (s-PHBs) were determined, and their release characteristics were initially evaluated in deionized water and then under various environmental stimuli, including pH, temperature, ionic strength, and water hardness. We found that incorporating a starch composite in s-PHBs at pH = 5 resulted in a rough but rigid surface and improved their physical and thermal stability, compared with phosphate hydrogel beads without starch (PHBs), due to the dense hydrogen bonding-supramolecular networks. Additionally, the s-PHBs showed controlled phosphate-release kinetics, following a parabolic diffusion with reduced initial burst effects. Importantly, the developed s-PHBs exhibited a promising low responsiveness to environmental stimuli for phosphate release even under extreme conditions and when tested in rice field water samples, suggesting their potential as a universally effective option for large-scale agricultural activities and potential value for commercial production.

Progress in pre-treatment and extraction of organic and inorganic pollutants by layered double hydroxide for trace-level analysis

Continuous release of pollutants into the environment poses serious threats to environmental sustainability and human health. For trace-level analysis of pollutants, layered double hydroxide (LDH) is an attractive option to impart enhanced sorption capability and sensitivity toward pollutants because of its unique layered structure, tunable interior architecture, high anion-exchange capacities, and high porosity (e.g., Zn/Cr LDH/DABCO-IL, Ni/Al LDH, CS-Ni/Fe LDH, SDS-Fe₃O₄@SiO₂@Mg-Al LDH, Boeh/Mg/Al LDH/pC, and Fe@NiAl LDH). In concert with the well-defined analytical methodologies (e.g., HPLC and GC), the LDH materials can be employed to detect trace-level targets (e.g., as low as ∼ 20 fg/L for phenols) in aqueous environments. This review highlights LDH as a promising material for pre-treatment of a variety of organic and inorganic target pollutants in complex real matrices. Challenges and future requirements for research into LDH-based analytical methods are also discussed.

Enhanced Fenton-like catalysis for pollutants removal via MOF-derived CoxFe3-xO4 membrane: Oxygen vacancy-mediated mechanism

Traditional batch configuration is not sustainable due to catalyst leaching and ineffective recovery. Herein, a novel membrane-based catalyst with oxygen vacancies is developed, which assembled metal-organic-framework cobalt ferrite nanocrystals (MOF-d Co_xFe_3-xO₄) on polyvinylidene fluoride membrane to activate peroxymonosulfate (PMS) for catalytic degradation of emerging pollutants. MOF-d Co_xFe_3-xO₄ are synthesized by one-step pyrolysis using Co/Fe bimetallic organic frameworks (Co_xFe_3-x bi-MOF) with tunable cobalt content as a template (x/3-x represented the molar ratio of Co and Fe in MOF). Intriguingly, MOF-d Co_1.75Fe_1.25O₄ membrane exhibits excellent PMS activation efficiency as indicated by 95.12% removal of the probe chemical (bisphenol A) at 0.5 mM PMS (∼100 L m^-2 h^-1 at the loading of 10 mg), which is significantly higher than the traditional Co_1.75Fe_1.25O₄ suspension system (34.16%). Experimental results show that the membrane has excellent anti-interference ability to anions and dissolved organic matter, and can effectively degrade a variety of emerging pollutants, and its performance is not inhibited by the change of solution pH (3-9) or the long-term (20 h) continuous flow operation. EPR and quenching experiments show that catalytic degradation is the result of the synergistic effect of radicals and non-radicals. The oxygen vacancy-mediated mechanism can explain the formation of active substances, and the formation of ¹O₂ plays an important role in the degradation of bisphenol A. This study provides a membrane-based strategy for effective and sustainable removal of emerging pollutants.

Fabrication of Porous Phosphate/Carbonate Composites: Smart Fertilizer with Bimodal Controlled-Release Kinetics and Glyphosate Adsorption Ability

A simple method to prepare phosphate/carbonate composites for use as porous sponge-like phosphate fertilizers (ps-PO₄Fs) is presented. The composites ps-PO₄Fs were prepared by ion-exchange implantation of phosphate onto the surface of vaterite-phase calcium carbonate (CaCO₃) microparticles. The ps-PO₄Fs obtained under the optimized conditions were found to contain a nanoscale porous network of calcium phosphate covering the CaCO₃ support. In addition, ps-PO₄Fs exhibited two distinct phosphate release modes having different kinetics: a fast-release step over the initial 24 h period following a parabolic diffusion model, indicating controlled diffusion from external surfaces/edges, and a second slow-release step over the course of a month following the Ritger-Peppas model, indicating the release and diffusion of phosphate adsorbed at specific sites. The ps-PO₄Fs also adsorbed glyphosate well because of their porous structure and large surface area. However, glyphosate adsorption prevented phosphate release at concentrations greater than 10 mg L^-1. The ps-PO₄Fs were tested for their effects on plant growth and showed effects similar to commercial fertilizers. In summary, these smart, eco-friendly, and multifunctional fertilizers having two-stage phosphate release could enable the application of lower amounts of fertilizer and remove excess glyphosate from the environment.

In-Situ Formation of Modified Nickel–Zinc-Layered Double Hydroxide Followed by HPLC Determination of Neonicotinoid Insecticide Residues

A single-step preconcentration procedure using the in-situ formation of modified nickel–zinc-layered double hydroxides (LDHs) prior to high-performance liquid chromatography (HPLC) is investigated for the determination of neonicotinoid insecticide residues in honey samples. The LDHs could be prepared by the sequential addition of sodium hydroxide, sodium dodecyl sulfate, nickel nitrate 6-hydrate and zinc nitrate 6-hydrate, which were added to the sample solution. The co-precipitate phase and phase separation were obtained by centrifugation, and then the precipitate phase was dissolved in formic acid (concentrate) prior to HPLC analysis. Various analytical parameters affecting extraction efficiency were studied, and the characterization of the LDHs phase was performed using Fourier-transformed infrared spectroscopy and scanning electron microscopy. Under optimum conditions, the limit of detection of the studied neonicotinoids, in real samples, were 30 μg L⁻¹, for all analytes, lower than the maximum residue limits established by the European Union (EU). The developed method provided high enrichment, by a factor of 35. The proposed method was utilized to determine the target insecticides in honey samples, and acceptable recoveries were obtained.

Co-precipitation based on layered double hydroxides and anionic surfactants for preconcentration of six benzoylurea insecticides in soft drinks before simultaneous analysis by high-performance liquid chromatography

Layered-double hydroxides (LDHs) modified with anionic surfactants via a co-precipitation method were developed for preconcentrating and simultaneous analysis of six benzoylurea insecticides (BUs) by high-performance liquid chromatography (HPLC). The anionic surfactants with different chain lengths, including sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), sodium 1-nonane sulfonate (SNS), and sodium 1-hexane sulfonate monohydrate (SHS) were investigated to improve the extraction efficiency of LDHs. The SDBS-LDHs provided the highest efficiency for the enrichment of the BUs studied. Under the chosen conditions, enrichment factors in the range of 38-69 and detection limits in the range of 0.1-0.3 μg L^-1 were achieved. Good reproducibilities (RSD < 13.8%) and recoveries (71.4-118.7%) were also obtained. The proposed preconcentration method, used as an in situ procedure offers rapid and simple simultaneous preparation of LDHs and extraction of BUs. The method was successfully applied for residue analysis of BUs in fruit- and flower-derived soft drink samples.

Colorimetric determination of trace orthophosphate in water by using C18-functionalized silica coated magnetite

In this study, we customized magnetic sorbents by functionalizing silica coated magnetite with octadecyl(C₁₈)silane (Fe₃O₄@SiO₂@C₁₈). This sorbent was intended for the determination of trace orthophosphate (o-PO₄³⁻) in unpolluted freshwater samples. The o-PO₄³⁻ was transformed to phosphomolybdenum blue (PMB), a known polyoxometalate ion. Then the PMB were coupled with cetyl trimethyl ammonium bromide (CTAB), cationic surfactant, in order to hydrophobically bound with the Fe₃O₄@SiO₂@C₁₈ particles through dispersive magnetic solid-phase extraction (d-MSPE) as part of sample preconcentration. The PMB–CTAB–magnetic particles are simply separated from the aqueous solution by the external magnet. The acidified ethanol 0.5 mL was used as PMB-CTAB eluent to produce an intense blue solution, which the absorbance was measured using a UV–Vis spectrophotometer at 800 nm. The proposed method (employing 2 mg of Fe₃O₄@SiO₂@C₁₈) yielded an enhancement factor of 32 with a linear range of 1.0–30.0 µg P L⁻¹. Precision at 6.0 µg P L⁻¹ and 25.0 µg P L⁻¹ were 3.70 and 2.49% (RSD, n = 6) respectively. The lower detection limit of 0.3 µg P L⁻¹ and quantification limit of 1.0 µg P L⁻¹ allowed trace levels analysis of o-PO₄³⁻ in samples. The reliability and accuracy of the proposed method were confirmed by using a certified reference material. Our method offers highly sensitive detection of o-PO₄³⁻ with simple procedures that can be operated at room temperature and short analysis time.

Dissolvable Mg/Al layered double hydroxides and surfactant as an extractant for trace analysis of benzoylurea insecticides by high performance liquid chromatography

A rapid and simple preconcentration method using dissolvable Mg/Al layered-double hydroxides (LDHs) and high performance liquid chromatography-photodiode array detection (HPLC-PDA) was developed for the analysis of benzoylurea insecticides (BUs) in water and honey samples. The proposed dissolvable LDHs for the extraction can be prepared in one step by the sequential addition of sodium hydroxide, magnesium chloride, aluminium chloride, and sodium dodecyl sulfate into the sample solution containing the target BUs. The co-precipitate phase was simply obtained after centrifugation, and the phase was then dissolved with formic acid before analysis by HPLC. The developed method provided an enrichment factor of 12.5-23.7. LODs were obtained in the range of 0.1-0.3 μg L^-1 for deionized water, 0.2-2.0 μg L^-1 for environmental waters, and 0.5-2.0 μg L^-1 for the analyzed honey samples. Good recoveries ranging from 78.4 to 117.8% and 72.7 to 117.9% for water and honey samples, respectively, were obtained.

A Green Chemosensor for Colorimetric Determination of Phosphate Ion in Soil, Bone, and Water Samples Using Curcumin Nanoparticles

This article presents a sensitive and straightforward colorimetric chemosensor for the determination of phosphate ion utilizing curcumin nanoparticles (CUNPs) as the sensing system. The color of as-prepared CUNPs can be changed from yellow to orange upon adding iron(III) ions due to the formation of a complex with CUNPs. However, in the presence of phosphate ions, iron(III) ions prefer to bind to phosphate ions and, subsequently the color of CUNPs is selectively recovered because of releasing the iron(III) ions from the CUNPs-iron(III) complex. Therefore, in this work the selective color changing of the CUNPs-iron(III) system upon the addition of phosphate ions was used for the quantitative sensing of phosphate ions. Various factors, such as the pH, concentration of iron(III) and volume of CUNPs, were examined and the optimum conditions were established. A linear calibration graph over the range of 10 - 400 ng mL^-1 for phosphate (r = 0.9995) was achieved using the optimal conditions. The limit of detection (LOD) of the proposed method for phosphate was 7.1 ng mL^-1 and the relative standard deviation (RSD) for measuring 50 ng mL^-1 of phosphate was 3.7% (n = 8). The developed method was applied for the measurement of phosphate in water, soil, and bone samples. Satisfactory results were obtained.

Detection of inorganic phosphor in environmental water samples using a lanthanide and nanoparticle chemosensor based on Fӧrster resonance energy transfer

A novel chemosensor is presented for the detection of inorganic phosphate (Pi) in environmental water samples. The sensing solution is comprised of terbium (Tb³⁺) chelated to ethylenediaminetetraacetic acid (EDTA) acid and cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticles (Au NPs). Upon mixing, Tb-EDTA and Au NPs undergo Fӧrster resonance energy transfer (FRET) in which the luminescence from the lanthanide ion is quenched. Upon the addition of Pi, Au NPs aggregate and precipitate out of solution. The aggregation of Au NPs results in the restoration of the Tb-EDTA luminescence signal, which correlates linearly to the Pi concentration in the matrix of analysis. The limit of detection (LOD) of the luminescence sensor (83 ng·mL^-1) is within the range of LODs previously reported for on-site monitoring of Pi. Quantitative analysis carried out via the multiple standard additions method provides accurate determination of Pi concentrations in heavily contaminated environmental waters.