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. 2025 Mar 12;73(12):7131–7139. doi: 10.1021/acs.jafc.4c12454

Hybridizing Mg–Fe Layered Double Hydroxide with Pectin Natural Polymer for Organic Ligand-Responsive Phosphate Release: An Innovative Controlled-Release Phosphorus Fertilizer

Wen-Hui Li †, Liang-Ching Hsu †, Han-Yu Chen †, Yi-Chun Chen ‡, Heng Yi Teah §, Yu-Yu Kung †, Yu-Min Tzou †,∥, Yu-Ting Liu †,∥,*
PMCID: PMC11951156  PMID: 40071643

Abstract

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Phosphorus (P) is vital for plant growth, but its agricultural use is limited by soil fixation and environmental loss. This study developed an organic ligand-responsive phosphate release system by hybridizing magnesium–iron-layered double hydroxides (Mg–Fe LDH) with pectin from apple and citrus (pectin-A/C). Structural properties and phosphate (PO4) release of LDH hybrids with different concentrations of metal precursors (0.5LDH-A/C, 2.5LDH-A/C) were evaluated. All hybrids exhibited higher PO4 sorption than pristine Mg–Fe LDH, with 2.5LDH-A reaching 118.2 mg g–1. Phosphate release kinetics showed that 0.5LDH-A/C provided slow release up to 1056 h, while 2.5LDH-A/C released 87.7% PO4 with 4 mM citrate, responding to organic ligands. Synchrotron spectroscopy revealed that Fe substitution in LDH layers and Fe(III)-P species was the key influencing PO4 release. The slow-release behavior of 0.5LDH-A/C and the ligand responsiveness of 2.5LDH-A/C highlight their potential to enhance sustainable agriculture by improving fertilizer efficiency, ensuring food security, and minimizing environmental impact.

Keywords: Mg−Fe LDH, pectin, phosphate sorption and release, organic ligands responsiveness

1. Introduction

Phosphorus (P) is critical for plant growth; however, P rock is a finite resource, anticipated to deplete within 50 to 100 years.1 Agriculture consumes 80–90% of extracted P, but merely 5–30% of applied P is assimilated by plants,2 with the remainder lost via soil fixation and runoff. The biogeochemical disruption of P has surpassed planetary boundaries,3 and with global food demand projected to rise by 30–62% by 2050,4 efficient fertilizer use is crucial.

Recent studies have explored improving P use efficiency through slow-release materials, including recycled P precipitates,5 graphene-related materials,6 metal–organic frameworks,7 and adapted biochar.8 Slow-release fertilizers (SRFs) extend nutrient release over time, while controlled-release fertilizers (CRFs) precisely match nutrient release with plant growth stages.9 Among promising materials, layered double hydroxides (LDHs) stand out due to their tunable structure, pH-dependent stability, and capacity for anion exchange. LDHs, composed of di- and trivalent metal cations,10,11 can intercalate phosphate (PO4). The PO4 is used in our article as a general representation of phosphate ions, which can exist in various forms (PO43–, HPO42–, or H2PO4–) depending on the pH. However, PO4 sorption on LDH surfaces or impurities formed during preparation (amorphous metal hydroxides) may dominate PO4 retention mechanisms,12 making ion exchange, desorption, and structural weathering key for PO4 release near plant roots. Therefore, the weathering and biodegradability of LDHs over time fulfill the prerequisites for slow release and stimuli-responsive (i.e., controlled release) P fertilizers.

Traditional CRFs are often coated with synthetic polymers that have hydrophobic characteristics to create a diffusion wall or barrier.13,14 The most popular coating materials are petroleum-derived synthetic polymers, which may generate toxic byproducts upon degradation. Here, the hybridization of Mg–Fe LDH with pectin, a biodegradable, nontoxic, and natural polymer from apple and citrus,15 was investigated as a more sustainable alternative. Pectin is classified by the degree of esterification (DE) into high and low methoxyl pectin (DE ≥ and <50%).16 Low methoxyl pectin has more free carboxylic acid groups, while high methoxyl pectin has fewer. When LDH grafts with polymers, the weakened hydrogen bonding and electrostatic interactions between LDH layers promote exfoliation, reducing stacking.17 This study hypothesized that varying DE levels may impact the structure and PO4 release profile of LDH-pectin hybrids, which may increase the susceptibility to environmental weathering.

Plants under P starvation exude organic acids and ligands like citrate, oxalate, and malate, which trigger responsive PO4 release through ligand-promoted Fe complexation.18 In the rhizosphere, organic ligand concentrations can exceed 5 mM.19 This study aimed to develop CRFs responsive to organic ligands by hybridizing Mg–Fe LDH with high and low DE pectin. It investigated PO4 release mechanisms and structural characteristics of the hybrids, using synchrotron-based techniques to assess PO4 bonding and Fe coordination. These insights will inform the design of more efficient, ecofriendly P fertilizers, contributing to sustainable agriculture, preserving P reserves, and supporting global food security.

2. Materials and Methods

2.1. Hybridization between Mg–Fe LDH and Pectin

The Mg–Fe LDHs were hybridized with pectin derived from apple pomace (pectin-A, Sigma-Aldrich, 50–75% DE, Lot # BCCD1493) and citrus peels (pectin-C, Sigma-Aldrich, DE < 26%, Lot # SLCD2368) by means of in situ coprecipitation. Wherein, a 10 mL mixture comprising 1.0 and 5.0 M total Mg [Mg(NO3)2·6H2O] (Merck, 99%, Lot # A1846153 223) and Fe [Fe(NO3)3·9H2O] (Sigma-Aldrich, ≥ 98%, Lot # MKCV3716), with 3:1 molar ratio of Mg:Fe was stirred with 10 mL of 1% (weight/volume) pectin-A or pectin-C suspensions. Pectin-A and pectin-C suspensions were produced via stirring 1 g of apple pectin and citrus peel pectin (MERCK) into degassed and deionized water, adjusting to pH 9.0–10.0 with 1.0 M NaOH, and bringing the total volume to 100 mL. Hereafter, these samples were designated as 0.5/2.5LDH-A/C according to the total Mg and Fe concentration (0.5 and 2.5 M) and the polymer form. Each mixture was then dripped into 50 mL of 1.5 M NaOH, maintaining the pH at 14.0 ± 0.5. After half hour, samples were centrifuged at 9000g for 20 min to collect solids, which were rinsed five times with deionized water to eliminate residual ions and then freeze-dried.20

2.2. Phosphate Sorption and Release of Mg–Fe LDH Hybridized with Pectin-A/C

2.2.1. Sorption Isotherms

Sorption isotherms of PO4 on hybrid samples were conducted at pH 5.0 using 10 mM NaNO3 as the background electrolyte. Aliquots of 100 mM KH2PO4 were added into hybrid LDH suspensions to achieve a final ratio of 1 g L–1. The pH was maintained at 5.0 using 10 mM HNO3 or 10 mM NaOH. Suspensions were shaken for 24 h at 25 °C and then centrifuged at 9000g for 20 min. The supernatant was filtered across 0.2 μm membranes. Dissolved PO4 was determined colorimetrically via the molybdate method.21 Solids were lyophilized for subsequent testing. Sorption results were modeled by means of the Langmuir equation.22 Please see Table S1 for the equation details.

2.2.2. Release Kinetics

Solids with the highest observed PO4 sorption capacity collected upon sorption isotherms were employed to determine the release behavior. This experiment was performed under 1 g L–1 proportion with 3.0 mM NaHCO3 at pH 5.5 to mimic plant root environments.23 Suspensions were shaken at 25 °C for 1056 h. At predetermined time intervals, aliquots of the suspensions were collected and filtered across 0.2 μm membranes. Dissolved PO4 content was determined colorimetrically, while solids were lyophilized for subsequent testing. Results were modeled by the Korsmeyer–Peppas equation.24 Please see Table S2 for the equation details.

2.2.3. Phosphate Release with Organic Ligand Addition

Two sets of incubations were performed to test the effect of organic ligands on the PO4 release. Both experiments were conducted by using solid samples with the highest observed PO4 sorption capacity. Release of PO4 was carried out under 1 g L–1 proportion, with 3.0 mM NaHCO3 at pH 5.5. First, hybrid LDHs with the lowest PO4 release efficiency determined via the release kinetics were selected to test the effects of types and concentrations of organic ligands on PO4 release. Citrate [HOC(COOH)(CH2COOH)2 · H2O], oxalate (HO2CCO2H), and malate [HO2CCH2CH(OH)CO2H] were added at concentrations of 1.0, 2.0, and 4.0 mM at the start of PO4 release, and the incubations were conducted for 48 h. Next, the organic ligand with the greatest impact on PO4 release was added to individual LDH suspensions at concentrations of 1.0, 2.0, and 4.0 mM. This was done at two different time points: simultaneously with the start of the PO4 release and after 360 h of release. The incubations were conducted for 24 h. After incubation, suspensions were centrifuged, and supernatants were filtered. Dissolved PO4 in the filtrates was then determined by using a colorimetric method. The flowchart of the experimental procedures, including the hybridization of Mg–Fe LDH with pectin-A/C, PO4 sorption on the hybrid LDH, and PO4 release from the hybrid LDH with and without organic ligand addition, was presented in Figure S1 of the Supporting Information to enhance clarity and facilitate understanding of the workflow.

2.3. Crystallographic and Morphological Analyses of Mg–Fe LDH Hybridized with Pectin-A/C

The crystallographic analysis for hybrid LDHs was performed using the X-ray diffraction (XRD) (PANalytical X’Pert Pro MRD). The patterns were acquired from 5 to 65° (2θ) at a scanning rate of 1° (2θ) min–1 using Cu-Κα radiation (λ = 1.5406 Å).

A field emission scanning electron microscope (FE-SEM, Ultra Plus, ZEISS) was employed to determine the morphology of hybrid LDHs. Samples were mounted by using copper tape, coated with platinum, and placed in an evacuated chamber. The images were then characterized once the chamber reached the required pressure.

2.4. Synchrotron-Based Analyses for Mg–Fe LDH Hybridized with Pectin-A/C Collected during PO4 Release

2.4.1. Iron K-Edge Extended X-ray Absorption Fine Structure (EXAFS) Spectroscopy

The local structure of Fe octahedra in hybrid LDHs was analyzed by using Fe K-edge EXAFS spectroscopy. Spectra were acquired at Taiwan Light Source (TLS) beamline 17C1 and Taiwan Photon Source (TPS) beamline 44A at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan. Monochromator energy was calibrated to 7112 eV using Fe foil and monitored during data collection. Data were obtained at energies between −200 and +700 eV relative to 7112 eV. A 0.5 eV step was adopted in the near edge section, and a step size of k = 0.05 Å–1 was used at higher energies.

Repeated scans per sample were integrated, background removed, and standardized in IFEFFIT software (version 1.2.10).25 For EXAFS fitting, the FEFF64 was used to generate the Fe–O, Fe–Mg, and Fe–Fe pairs to 3.50 Å separation according to structural developments of two-line ferrihydrite with limited Mg substitution. The single scattering Fe–C pair was derived from the [Fe(C2O4)3]3– structure.26 Coordination number (CN), interatomic distance (ΔR), and mean-square displacement of interatomic distance (σ2) for all EXAFS data were fitted using a set amplitude reduction factor (S02 = 0.78), based on the first shell analysis of ferrihydrite and goethite.27

2.4.2. Phosphorus K-Edge X-ray Absorption Near Edge Structure (XANES) Spectroscopy

The P K-edge XANES spectra were collected at TPS beamline 32A at the NSRRC. Its monochromator energy was calibrated to 2222.3 eV in accordance with the absorption edge of the Zr L3-edge. The harmonic symptoms were minimized by detuning up to 50% of flux at 100 eV higher than the P K-edge absorption edge. The data were acquired between 2090 and 2300 eV, with a 0.2 eV step between 2146 and 2161 eV. Self-absorption effects were deemed negligible since no reduced magnitude of the white-line peak was detected with rising PO4 concentrations.27

For each sample, data were integrated, the background was removed, and the data were standardized in the interface described above for Fe EXAFS analysis. The P species on hybrid LDHs were identified and quantified by linear combination fitting (LCF) over the spectral section from 2141 to 2181 eV with Athena software. The LCF analyses were performed with end member standards of KH2PO4 (labile-P), phytic acid (organic-P), and PO4 sorbed on ferrihydrite [Fe(III)-P]. Refer to Li et al. (2023)26 for more information on P K-edge XANES fitting.

3. Results

3.1. Characteristics of Mg–Fe LDH Hybridized with Pectin-A/C

The XRD patterns for all hybrid LDHs showed peaks centered at 2θ values of 11.48, 21.45, 34.16, 37.97, and 59.58° (Figure 1), corresponding to reflections for crystal planes (003), (006), (012), (015), and (110) of Mg–Fe LDH.28,29 In contrast to hybrid 2.5LDHs, hybrid 0.5LDHs displayed additional peaks around 60.70°, consistent with the (113) plane for Mg–Fe LDH. This observation suggested that structures of hybrid 0.5LDHs were more crystalline compared with those of hybrid 2.5LDHs. Hence, it can be inferred that the total metal concentrations in LDH precursors played a crucial role in influencing structure development, rather than the type of pectin used.

Figure 1.

Figure 1

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X-ray diffraction patterns of Mg–Fe LDH hybridized with pectin-A/C. Numbers of 2.5 and 1.5 refer to total metal concentrations in LDH precursors. Data were collected by using Cu Kα radiation.

The SEM morphology of hybrid 2.5LDHs revealed the emergence of three-dimensional flowerlike structures with diameters ranging from 1 to 2 μm (Figure 2a,b). This hierarchical architecture mirrors the structural characteristics of pristine Mg–Fe LDH,26 facilitating enhanced exposure of particle surfaces. However, such superstructural development was less pronounced in hybrid 0.5LDHs, as evidenced in the random aggregation of particles into clusters with rough shapes, contrasting with the clearly defined microstructural developments observed in hybrid 2.5LDHs (Figure 2c,d).

Figure 2.

Figure 2

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SEM images of Mg–Fe LDH hybridized with pectin-A/C. Numbers of 2.5 and 1.5 refer to total metal concentrations in LDH precursors.

3.2. Phosphate Sorption Isotherms

Phosphate sorption isotherms on hybrid LDHs were suitably modeled by the Langmuir equation (Figure 3 and Table S1), suggesting nearly monolayer PO4 sorption on hybrid LDHs.22,30 Regarding modeled maximum sorption capacity, 2.5LDH-A and 2.5LDH-C exhibited comparable amounts of 118.2 and 115.1 mg g–1, respectively (Table S1), surpassing that of the hybrid 0.5LDHs (79.1–102.0 mg g–1). This sequence of PO4 sorption capacities aligned with the structural characteristics of the hybrid LDHs. Wherein, the relatively poor crystalline and microstructural developments of hybrid 2.5LDHs (Figures 1 and 2) demonstrated greater PO4 sorption capability.

Figure 3.

Figure 3

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Phosphate sorption isotherms on Mg–Fe LDH hybridized with pectin-A/C. Numbers of 2.5 and 1.5 refer to total metal concentrations in the LDH precursors. The sorption data were fitted using the Langmuir model shown as dashed lines.

Although 0.5 M metal concentration in LDH precursors and the addition of pectin-C tended to decrease PO4 sorption, PO4 sorption capacities of hybrid LDHs here still exceeded that of pristine Mg–Fe LDH [71.8 mg g–1, Li et al. (2023)26]. For LDHs employing other metal precursors, like Mg–Al LDH and Zn–Al LDH, their PO4 sorption capacities varied from 23 to 53 mg g–1, contingent upon metal ratios and experiment pH.22,31 Moreover, upon hybridizing Mg–Fe LDH with chitosan (CTS) and carboxymethyl cellulose (CMC), the resulting hybrid LDHs exhibited PO4 sorption capacities ranging from 58.5 to 66.5 mg g–1.26 These comprehensive observations essentially suggested that the integration of pectin in Mg–Fe LDH hybridization significantly bolstered its capability for PO4 retention.

3.3. Phosphate Release Kinetics

In 24 h, 5.7, 7.2, 4.7, and 4.8% of the sorbed PO4 was dissolved from 2.5LDH-A, 2.5LDH-C, 0.5LDH-A, and 0.5LDH-C (Figure 4), suggesting that the PO4 release was relatively lower in hybrid LDHs with 0.5 M precursor concentrations. However, by 96 h, the proportions of PO4 release had enhanced by an extra 1.3, 1.6, 2.2, and 4.8% for 2.5LDH-A, 2.5LDH-C, 0.5LDH-A, and 0.5LDH-C. Remarkably, the PO4 release from 0.5LDH-C doubled between 24 and 96 h. Within 96 to 360 h, the PO4 release improved by another 1.4–1.6% for hybrid 2.5LDHs, whereas for hybrid 0.5LDHs, it notably increased by 5.1–6.0%. Reflecting the nearly equilibrated PO4 release, hybrid 2.5LDHs only released an additional 1.4–1.7% of sorbed PO4 between 360 and 1056 h, while an extra 2.5–5.0% of sorbed PO4 was released from hybrid 0.5LDHs. At the end of the incubation, 9.8, 12.0, 17.0, and 18.1% of preloaded PO4 was dissolved from 2.5LDH-A, 2.5LDH-C, 0.5LDH-A, and 0.5LDH-C. Based on the fitting results obtained from the Korsmeyer–Peppas equation (Figure S2 and Table S2), the release rate constants of hybrid 2.5LDHs (4.0–5.2 h–1) were 1.7 to 2.3 times greater than those of hybrid 0.5LDHs. Considering that a lower rate constant designates slower PO4 release, and vice versa, collective results from modeling and experimental data demonstrated that hybrid 0.5LDHs not only released a relatively high proportion of sorbed PO4 but also provided protection against rapid PO4 release.

Figure 4.

Figure 4

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Phosphate release kinetics from Mg–Fe LDH hybridized with pectin-A/C. Numbers of 2.5 and 0.5 refer to total metal concentrations in LDH precursors.

Recently, LDH has emerged as a promising material for producing slow-release PO4 fertilizers, with Mg–Al LDH commonly used to assess PO4 release. Depending on the synthesis conditions of Mg–Al LDH, PO4 release in deionized water can range from 60–90% over 53 to 150 min.31,32 While equilibrated at pH 8.3 in anion exchange membranes containing 2.0 mM NaHCO3, PO4 release from Mg–Al LDH can be extended to 650 h.33 In our previous study, where Mg–Fe LDH was hybridized with CTS or CMC, the hybrid LDHs with 0.5 M metal precursor (0.5LDH-CTS/CMC) exhibited PO4 release that persisted continuously for 2688 h and beyond.26 In this study, preloaded PO4 amounts on 0.5LDH-A and 0.5LDH-C were 102.0 and 79.0 mg g–1, considerably higher than that of 0.5LDH-CTS/CMC (58.5–60.3 mg g–1). While only 17.0–18.1% of PO4 released from 0.5LDH-A/C at 1056 h, 0.5LDH-CTS/CMC exhibited 20.4–26.5% of PO4 release at 1200 h. These comparisons suggested that although 0.5LDH-A/C could lessen the barrier of low PO4 loading for practical applications, enhancing PO4 release efficiency to align with plant growth time scales and reducing the portion of unreleased PO4 in the soil remain significant challenges. According to Everaert et al. (2017),29 granulated Mg–Al LDH as SRF did not demonstrate higher agronomic effectiveness compared to the commonly used monoammonium phosphate (MAP) fertilizer. As applied in the form of granule Mg–Al LDH, 74–90% of PO4 still remained on the solids upon 100 days of incubation. Although the PO4 release efficiency was slightly improved as Mg–Al LDH was applied as a powder, the slow release of PO4 could only supplement the dissolved PO4 to comparable levels as struvite and MAP did. The PO4 release efficiency of our hybrid LDHs has improved compared to that of pristine LDHs, but further enhancing PO4 availability is crucial to increase their practical applicability.

3.4. Phosphate Release with Organic Ligand Addition

When P is deficient, plants exude organic ligands like citrate, oxalate, and malate around their roots.18 Given that up to 5 mM of organic ligands was found as the plant exudation near the rhizosphere,19 the organic ligands, including citrate, oxalate, and malate, were added at concentrations from 1 to 4 mM simultaneously during the PO4 release. The 2.5LDH-A was selected to test the effects of organic ligands on PO4 release over 48 h as its overall PO4 release was generally lower than other hybrid LDHs.

With the addition of 1 mM citrate, there was a significant increase in PO4 release, reaching 30.0% at 20 h and stabilizing at a similar range (30.7–31.5%) from 24 to 48 h (Figure 5a). This result suggested that citrate’s strong chelating properties effectively mobilize PO4 by disrupting the Mg–Fe LDH structure or competing for sorption sites. As a tricarboxylic acid, citrate has a higher charge density than dicarboxylic acids, such as oxalate and malate, enabling it to form stronger inner-sphere complexes with Fe on the LDH surface. This enhanced complexation ability reduces the availability of binding sites for PO4, thereby facilitating its desorption and increasing its mobility in solution.34,35 Observations revealed further enhancements in PO4 release efficiency at higher citrate concentrations of 2 and 4 mM (Figure 5b,c). At 2 mM, the PO4 release sharply increased, reaching 46.9% at 20 h, and maintained levels between 49.9 and 55.5% from 24 to 48 h. The influence on PO4 release became even more pronounced with a 4 mM citrate addition, where the PO4 release surged to 76.2% by 48 h, with a potential for continual increase over time. Malate, like citrate, showed a concentration-dependent impact on PO4 release but was generally less efficient than citrate at comparable concentrations. Within 48 h, PO4 releases of 12.2, 18.3, and 30.8% were observed in the presence of 1, 2, and 4 mM malate, respectively. Although oxalate also demonstrated a concentration-dependent effect on PO4 release, its pattern diverged notably from that of citrate and malate. At 1 mM, oxalate facilitated PO4 release from the onset of incubation, with the release percentages fluctuating between 14.6 and 16.7% over 48 h. This early plateau indicated that oxalate is capable of mobilizing PO4 efficiently, yet equilibrium dynamics may restrict further release over time. With 2 mM oxalate, the proportion of PO4 released stabilized between 24.5 and 28.7% across all measured time points; yet it substantially surged to 43.1–46.2% over the course of 48-h incubation in the presence of 4 mM oxalate. These findings suggested that oxalate’s impact on PO4 release from hybrid LDHs is not significantly time-dependent, underscoring its robust ability to mobilize PO4 regardless of incubation duration.

Figure 5.

Figure 5

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Phosphate release kinetics from Mg–Fe LDH hybridized with pectin-A at a metal precursor concentration of 2.5 M (2.5LDH-A) in the presence of (a) 1, (b) 2, and (c) 4 mM of citrate, oxalate, and malate.

In summary, citrate proved to be the most effective organic ligand for facilitating the PO4 release. Further tests explored the effects of citrate concentration and timing, with citrate added either at the start or 360 h into the incubation. When 1 mM citrate was added at the start of the incubation, PO4 release after 24 h from 2.5LDH-A, 2.5LDH-C, 0.5LDH-A, and 0.5LDH-C was 30.7, 31.2, 27.1, and 7.0%, which was 5.4, 4.3, 5.8, and 1.5 times their counterparts without citrate addition (Figure 6a). Clearly, citrate significantly boosted the release of PO4 from 2.5LDH-A/C and 0.5LDH-A, though its effect was less pronounced on 0.5LDH-C. As citrate concentrations increased to 2 and 4 mM, the release of PO4 also rose sharply. With 4 mM citrate, PO4 release from 2.5LDH-A/C and 0.5LDH-A reached 44.7 to 67.9%, a 9.4 to 11.7-fold increase compared to scenarios without citrate, while 0.5LDH-C showed only a 3.1-fold increase.

Figure 6.

Figure 6

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Phosphate release from Mg–Fe LDH hybridized with pectin-A/C observed at 24 h following the addition of 1, 2, and 4 mM citrate. The citrate was introduced either (a) initially or (b) at 360 h into the release incubation. The data labeled as 0 mM for parts a and (b) represent PO4 release at 24 and 384 h, respectively, in the absence of citrate addition. Numbers of 2.5 and 0.5 refer to total metal concentrations in LDH precursors.

Given that the release of PO4 from 2.5LDH-A/C plateaued around 360 h (Figure 4), citrate was introduced at this point to assess further stimulation. As shown in Figure 6b, adding 1 mM citrate increased PO4 release by 3.0 times for 2.5LDH-A/C compared with the levels without citrate at 384 h. However, for 0.5LDH-A/C, 1 mM citrate had less impact or even hindered the PO4 release. Notably, the PO4 release from 0.5LDH-C was only 90% of the level observed without citrate. Unlike the initial addition, where citrate led to similar PO4 release proportion from 2.5LDH-A and 2.5LDH-C, adding citrate at 360 h significantly boosted PO4 release from 2.5LDH-C. At 4 mM, PO4 release from 2.5LDH-C reached 87.7%, nearly 32% higher than that of 2.5LDH-A. While citrate had a lesser impact on PO4 release from 0.5LDH-A/C, their PO4 release still increased to 31.5–56.7% with 4 mM citrate (Figure 6b). In cases where 0.5LDH-A/C both released a significant proportion of PO4 and prevented its rapid dispersal, they proved to be viable candidates for slow-release PO4 fertilizers. In contrast, 2.5LDH-A/C was perceived as more suitable for controlled-release PO4 fertilizers, exhibiting a significantly higher responsiveness to citrate exudation than 0.5LDH-A/C. Nevertheless, 2.5LDH-A appeared to reach its PO4 release threshold upon citrate addition, as similar rates were observed with both initial and 360-h citrate additions (Figure 6). This suggests that 2.5LDH-A’s slow-release capacity may be compromised after citrate exposure. Regarding 2.5LDH-C, its PO4 release not only increased by 2.8 times when citrate was raised from 1 to 4 mM at 360 h but also surpassed that of the counterparts with citrate added initially by up to 1.3 times (Figure 6b). Overall, 2.5LDH-C stands out as a promising option that accommodates citrate-responsive PO4 release behaviors.

3.5. Iron Local Structures of Mg–Fe LDH Hybridized with Pectin-A/C Collected during PO4 Release

Local structural developments surrounding Fe atoms for hybrid LDHs obtained at the start, after 1056 h of PO4 release, and 24 h following citrate introduction at 360 h of the release kinetics were analyzed via Fe K-edge EXAFS spectroscopy. Fitting results showed that the first shell coordination of Fe atoms for all samples was oxygen atom with the interatomic distances from 1.97 to 2.01 Å and CN from 4.6 to 6.0 (Table 1 and Figure S3). Although the FeO6 octahedron typically coordinates with six oxygen atoms, a structural disorder in Fe domains can reduce the CN.36 Varying Fe–O distances may cause destructive interference across wave functions, contributing to this CN reduction.37

Table 1. Fitting Results of Fe-Edge EXAFS Analysis for Mg–Fe LDH Hybridized with Pectin-A/C Collected at the Start, after 1056 h of PO4 Release, and 24 h Following Citrate Introduction at 360 h of the Release Kineticsea,b.

path CNc R (Å)d σ2 (Å2)e path CN R (Å) σ2 (Å2)
2.5LDH-A 0.5LDH-A
0 h 0 h
Fe–O 5.1 2.01 0.005 Fe–O 4.6 2.01 0.005
Fe–Mg 1.7 3.12 0.007 Fe–Mg 2.7 3.14 0.006
Fe–Fe 0.5 3.31 0.005 Fe–Fe 1.0 3.54 0.007
1056 h 1056 h
Fe–O 5.4 1.99 0.009 Fe–O 5.4 1.98 0.009
Fe–C 2.5 2.82 0.013 Fe–C 3.2 2.75 0.012
Fe–Fe 2.2 2.96 0.009 Fe–Fe 3.9 2.96 0.011
Fe–Fe 3.6 3.14 0.011 Fe–Fe 3.6 3.14 0.009
Fe–Fe 1.7 3.39 0.010 Fe–Fe 1.7 3.37 0.009
360 h + CA 24 h 360 h + CA 24 h
Fe–O 5.5 1.98 0.009 Fe–O 5.9 1.98 0.009
Fe–C 1.2 2.84 0.010 Fe–C 1.5 2.88 0.009
Fe–Fe 2.4 3.03 0.010 Fe–Fe 1.7 3.05 0.010
               
2.5LDH-C 0.5LDH-C
0 h 0 h
Fe–O 5.7 2.01 0.006 Fe–O 5.3 2.01 0.005
Fe–Mg 1.7 3.12 0.008 Fe–Mg 3.5 3.12 0.007
Fe–Fe 0.5 3.33 0.005 Fe–Fe 0.6 3.57 0.004
1056 h 1056 h
Fe–O 5.4 1.98 0.010 Fe–O 5.0 1.98 0.008
Fe–C 2.7 2.75 0.013 Fe–C 3.4 2.77 0.010
Fe–Fe 3.1 2.93 0.012 Fe–Fe 3.4 2.96 0.009
Fe–Fe 4.6 3.11 0.011 Fe–Fe 4.0 3.15 0.010
Fe–Fe 2.0 3.35 0.012 Fe–Fe 2.0 3.39 0.011
360 h + CA 24 h 360 h + CA 24 h
Fe–O 5.4 1.97 0.009 Fe–O 6.0 1.97 0.009
Fe–C 2.8 2.82 0.012 Fe–C 3.8 2.83 0.010
Fe–Fe 2.6 3.03 0.012 Fe–Fe 2.9 3.03 0.011
        Fe–Mg 0.9 3.10 0.015
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a

Numbers of 2.5 and 0.5 refer to total metal concentrations in LDH precursors.

b

Fitting was done across the k range of 2.5 to 10.5 Å–1 and the R range of 1.0 to 3.5 Å. All samples were fit simultaneously, yielding a normalized sum of squared residuals [R-factor = ∑(data-fit)2/∑data2)] of 0.0071 and 0.0067. Values of other EXAFS model parameters were either fixed or fitted to a common value across all samples as follows: S02 = 0.78 (fixed amplitude reduction factor based on first-shell fitting of ferrihydrite and goethite); ΔE = 0.18 and 0.15 eV (fitted energy shift parameter).

c

Coordination number.

d

Interatomic distance.

e

Mean-square displacements of interatomic distance.

In addition to the Fe–O path, samples obtained at the beginning of PO4 release showed higher-shell Fe–Mg and Fe–Fe pairs with separations of 3.12–3.14 Å and 3.31–3.57 Å (Table 1). The presence of Fe–Mg paths indicated that some Mg ions in Mg(OH)2 layers were substituted by Fe ions, creating positive charges that allowed PO4 anion insertion.38 While 2.5LDH-A/C had 1.7 Mg atoms surrounding each Fe atom, the Fe–Mg CN for 0.5LDH-A/C ranged from 2.7 to 3.5, indicating a higher degree of Fe substitution and, consequently, more positive charges on 0.5LDH-A/C. Regarding Fe–Fe pairs, interatomic distances were 3.31–3.33 Å for 2.5LDH-A/C and 3.54–3.57 Å for 0.5LDH-A/C. The shorter distance indicated FeO6 octahedra linked by sharing an edge with two OH–, while the longer distance suggested double-corner linkages dominated Fe coordination.39 However, regardless of the type of linkage, a single linkage may result in a relatively fragile FeO6 octahedral structure.

After 1056 h of PO4 release, it was noteworthy that no Fe–Mg pairs were detected in the hybrid LDHs. Instead, structural developments for FeO6 domains and bonding between FeO6 octahedra and carbon were observed in all samples (Table 1). The Fe–C paths, with distances from 2.75 to 2.82 Å, indicated partial hybridization between LDH and natural polymers, likely through the development of Fe-carbonyl assemblages via coordination between FeO6 octahedra and carbon monoxide ligands.40 Regarding FeO6 octahedral linkages, three Fe–Fe pairs with separations from 2.93 to 3.39 Å were found in all samples after 1056 h of PO4 release. These structural changes implied the emergence of ferric (oxyhydrox)oxide as it features a shared face with Fe–Fe distances of 2.88–2.90 Å, and shared edges formed by two O2–, one O2– and one OH–, and two OH–, with Fe–Fe separations of ∼2.97 Å, 3.02–3.03 Å, and 3.30–3.35 Å.39

Regarding samples obtained after 386 h of PO4 release with 4.0 mM citrate added at 360 h, the local Fe structure featured Fe–C and Fe–Fe pairs with separations of 2.82–2.88 Å and 3.03–3.05 Å (Table 1). These paths are attributed to the development of Fe-carbonyl assemblages and shared edges linked by one O2– and one OH–. Compared to the ferric (oxyhydrox) oxide structures observed after the PO4 release concluded, merely edge-shared FeO6 octahedral linkages remained after citrate addition, implying structural disruption due to ligand-promoted Fe dissolution. Beyond these structural developments, 0.5LDH-C displayed two unique features. First, the CN of the Fe–C pair in 0.5LDH-C was 3.8, 1.4–3.2 times higher than that in other citrate-treated samples, yet similar to its counterpart acquired upon 1056 h of PO4 release without citrate. Additionally, the Fe–Mg pair with a 3.10 Å separation persisted in 0.5LDH-C despite ligand-promoted dissolution. These attributes suggested a relatively robust structure, indicating that interlayers with Mg substituted with Fe ions were partially maintained in 0.5LDH-C.

3.6. Phosphorus Speciation on Mg–Fe LDH Hybridized with Pectin-A/C Collected during PO4 Release

Phosphorus species on hybrid LDHs were identified and quantified via LCF for their P K-edge XANES spectra (Figure S4). Results of LCF (Table S3 and Figure 7) showed that all tested samples contained labile-, organic-, and Fe(III)-P. Consistent with Fe local structures in hybrid LDHs, which showed Fe substitution in interlayers and the formation of Fe(III) (oxyhydrox) oxides (Table 1), labile- and Fe(III)-P can be designated as intercalated and Fe(III)-bonded PO4. The presence of organic-P suggested an alternative retention mechanism through association between PO4 and organic compounds in hybrid LDHs. Since PO4 typically bonds to Fe(III) (oxyhydrox)oxides via monodentate or bidentate inner sphere complexes,12 this P species is less prone to release compared to labile- and organic-P. Therefore, the total of labile- and organic-P represented readily releasable P. This proportion was 14.0–18.5% on 2.5LDH-A/C at the onset of PO4 release but dropped to 1.9–5.5% after 1056 h (Figure 7). Conversely, the total of labile- and organic-P on 0.5LDH-A/C initially reached 36.6–45.3% and, although decreased, remained at 15.9–16.5% after 1056 h. This relatively higher proportion at the end of the release incubation might explain why the release of PO4 from 0.5LDH-A/C had not reached a steady state, while that from 2.5LDH-A/C appeared to plateau (Figure 4).

Figure 7.

Figure 7

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Phosphorus speciation was obtained from P K-edge XANES LCF analysis. Tested samples included Mg–Fe LDH hybridized with pectin-A/C collected at the beginning and after 1056 h of PO4 release as well as those with citrate introduced either at the start or after 360 h of the release kinetics and incubated for additional 24 h. Numbers of 2.5 and 0.5 refer to total metal concentrations in LDH precursors. Reference materials used to represent labile-P, organic-P, and Fe(III)-P were KH2PO4, phytic acid, and PO4 sorbed on ferrihydrite, respectively.

When 4.0 mM citrate was added, either at the start or at 360 h of PO4 release, no labile- or organic-P was found on 2.5LDH-A/C (Table S3 and Figure 7). Instead, Fe(III)-P dominated the P species. Despite cumulative PO4 release of 66.5–87.7% from 2.5LDH-A/C with 4.0 mM citrate added at the start and 360 h (Figure 6), their initial labile- and organic-P inventory was only 14.0–18.5%. This suggested Fe(III)-P was the primary source of PO4 release from 2.5LDH-A/C, making it highly responsive to citrate because of Fe(III)’s susceptibility to ligand-promoted complexation.41

For 0.5LDH-A/C, readily releasable P was still present whether citrate was added at the start or at 360 h. With 4.0 mM citrate, 6.2–9.9% of readily releasable P persisted on 0.5LDH-A after 24 or 384 h of PO4 release, while 20.6–24.5% remained on 0.5LDH-C. Notably, this proportion on 0.5LDH-C was higher than that on its counterpart collected after 1056 h of PO4 release (16.5%, Figure 4). This suggested that although Fe(III)-P on 0.5LDH-A/C underwent ligand-promoted dissolution, intercalated and organic-bound P was still retained, especially on 0.5LDH-C. Such P species distribution aligned with the relatively higher Fe–C CN and the retained layered structure with Fe substitution observed on 0.5LDH-C after PO4 release with citrate addition (Table 1). This finding explained the minimal increase in the level of PO4 release from 0.5 LDH-C in response to 4.0 mM citrate addition at the start and 360 h of incubation (Figure 6). However, multiple release mechanisms enabled 0.5LDH-C to support both slow and controlled PO4 release.

While the labile-P was designated as intercalated PO4, there might be a possible overestimation, as Mg-bonded P has a similar P-XANES spectral feature. However, Mg3(PO4)2 precipitation can be excluded as its spectral characteristics were indiscernible in any samples. Additionally, the presence of intercalated PO4 contradicted the absence of Fe–Mg paths, which would indicate Fe substitution in hybrid LDHs after 1056 h of PO4 release. The likely explication is that EXAFS analysis only captures dominant structural information with a distribution >10%.42 Therefore, the lack of Fe–Mg paths might indicate a reducing amount of Fe substitution instead of its utter lack.

4. Discussion

The 2.5LDH-A/C and 0.5LDH-A/C samples showed PO4 sorption capacities 1.6 and 1.1–1.4 times higher than those of pristine Mg–Fe LDH, indicating that pectin hybridization improved PO4 loading for practical applications. After 1056 h of incubation, 9.8, 12.0, 17.0, and 18.1% of preloaded PO4 was released from 2.5LDH-A, 2.5LDH-C, 0.5LDH-A, and 0.5LDH-C. Although 0.5LDH-A/C had higher PO4 release proportions, their release rate constants were only 0.4–0.6 times those of 2.5LDH-A/C, indicating slower PO4 release. These results suggested that 0.5LDH-A/C was better suited as a P SRF, offering protection against rapid PO4 release while maintaining agronomic effectiveness.

However, the level of release of PO4 from 2.5LDH-A/C significantly increased compared to that of 0.5LDH-A/C with organic ligand addition. Among citrate, oxalate, and malate, citrate showed the strongest impact, with 4 mM citrate triggering 76.2% PO4 release from 2.5LDH-A, which was 1.8–2.5 times greater than oxalate and malate. Citrate also showed potential for continuous PO release beyond 48 h, unlike oxalate, which peaked at the start. Citrate was further tested both initially and 360 h after release incubation. Initially, PO4 release from 2.5LDH-A and 2.5LDH-C was comparable, but adding 4 mM citrate at 360 h significantly boosted PO4 release from 2.5LDH-C to 87.7%, which is 1.3 times that of 2.5LDH-A. In contrast, PO4 release from 0.5LDH-A/C with 4 mM citrate added at 360 h was only 31.5–56.7%. These findings suggested that hybrid 2.5LDHs, especially 2.5LDH-C, are promising candidates for P CRF reagents responsive to citrate exudation.

The P K-edge XANES results showed that 0.5LDH-A/C had higher proportions of readily releasable P (36.6–45.3%, including labile- and organic-P) compared to 2.5LDH-A/C at the onset of PO4 release, explaining why PO4 release from 0.5LDH-A/C had not plateaued, unlike 2.5LDH-A/C after 1056 h. Even after citrate addition, 20.6% of readily releasable P persisted on 0.5LDH-C upon 384 h, whereas only Fe(III)-P was found on 2.5LDH-A/C. These findings aligned with Fe-EXAFS data showing Fe–Mg pairs, indicating Fe substitution in Mg(OH)2, present in all samples at the start of PO4 release but only on 0.5LDH-C after citrate incubation. Additionally, 0.5LDH-C exhibited a relatively higher Fe–C CN. This robust structural development and sustained Fe substitution made 0.5LDH-C suitable as a P SRF, even with citrate addition. Meanwhile, the dominance of Fe(III)-P on 2.5LDH-A/C, particularly on 2.5LDH-C, ensured that the PO4 release is highly responsive to citrate. Taken together, hybridizing Mg–Fe LDH with pectin created both SRF and CRF. The metal concentration in the LDH precursor and the pectin type determined the PO4 release behavior. Additionally, ferric (oxyhydrox)oxides left after PO4 release could offer additional benefits by providing retention sites for soil organic matter. Ultimately, this approach could support food security and climate change mitigation, in line with the Sustainable Development Goals.

In terms of cost analysis, the production cost of Mg–Fe LDH hybridized with pectin as P fertilizers is estimated at 2.54–2.85 USD/kg, whereas commercial SRF, such as granulated triple superphosphate (TSP), is significantly cheaper at 0.35 USD/kg. However, LDH-based P fertilizers may substantially reduce the environmental cost of excess phosphorus leaching, lowering it to 1062 USD–2667 USD per hectare, compared to 2590 USD–4604 USD per hectare for TSP application (see details in Supporting Information). A comprehensive evaluation of both production and environmental costs highlights hybrid LDH as a more sustainable and cost-effective alternative to conventional SRFs. Despite these advantages, several challenges must be addressed for their widespread adoption. Scaling up production remains a key issue as cost reductions are necessary to compete with conventional P fertilizers. Additionally, the long-term agronomic effectiveness of LDH-based fertilizers under diverse soil and crop conditions requires further validation through field trials and multiseason studies. To enhance the sustainability, feasibility, and scalability of Mg–Fe LDH hybridized with pectin, an integrated approach combining fertilizer effectiveness studies with life cycle assessment is crucial. This will provide a comprehensive evaluation of crop yield, production costs, and environmental impacts, ensuring that LDH-based fertilizers can be optimized for both economic and ecological benefits. Addressing these challenges is essential for the successful commercialization and large-scale implementation of LDH-based P fertilizers.

Acknowledgments

The research was supported by the National Science and Technology Council, Taiwan (NSTC 112-2628-B-005-002-MY3), and the Innovation and Development Center of Sustainable Agriculture from The Featured Areas Research Center Program within the framework of Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jafc.4c12454.

  • Flowchart of experimental procedures; supporting tables and figures for phosphate sorption and release models; EXAFS and XANES analysis of structural and chemical changes; and detailed description of production cost analysis and environmental impact assessment (PDF)

Author Contributions

⊥ W.-H.L and L.-C.H. contributed equally to this work. W.-H.L.: investigation, methodology, and writing–original draft. L.-C.H.: investigation, supervision, editing, and writing–review. H.-Y.C.: methodology and data curation. Y.-C.C.: conceptualization and validation. H.Y.T.: conceptualization and validation. Y.-Y.K.: investigation. Y.-M.T.: supervision. Y.-T.L.: conceptualization, investigation, supervision, writing–original draft, writing–review, and editing. W.-H.L. and L.-C.H. contributed equally to this work.

The authors declare no competing financial interest.

Supplementary Material

jf4c12454_si_001.pdf (900.1KB, pdf)

References

  1. Cordell D.; Drangert J.-O.; White S. The story of phosphorus: global food security and food for thought. Glob. Environ. Change 2009, 19 (2), 292–305. 10.1016/j.gloenvcha.2008.10.009. [DOI] [Google Scholar]
  2. Childers D. L.; Corman J.; Edwards M.; Elser J. J. Sustainability challenges of phosphorus and food: solutions from closing the human phosphorus cycle. Bioscience 2011, 61 (2), 117–124. 10.1525/bio.2011.61.2.6. [DOI] [Google Scholar]
  3. Steffen W.; Richardson K.; Rockström J.; Cornell S. E.; Fetzer I.; Bennett E. M.; Biggs R.; Carpenter S. R.; De Vries W.; De Wit C. A.; et al. Planetary boundaries: Guiding human development on a changing planet. Science 2015, 347 (6223), 1259855 10.1126/science.1259855. [DOI] [PubMed] [Google Scholar]
  4. van Dijk M.; Morley T.; Rau M. L.; Saghai Y. A meta-analysis of projected global food demand and population at risk of hunger for the period 2010–2050. Nat. Food 2021, 2 (7), 494–501. 10.1038/s43016-021-00322-9. [DOI] [PubMed] [Google Scholar]
  5. Degryse F.; Baird R.; Da Silva R. C.; McLaughlin M. J. Dissolution rate and agronomic effectiveness of struvite fertilizers–effect of soil pH, granulation and base excess. Plant Soil 2017, 410 (1), 139–152. 10.1007/s11104-016-2990-2. [DOI] [Google Scholar]
  6. Andelkovic I. B.; Kabiri S.; Tavakkoli E.; Kirby J. K.; McLaughlin M. J.; Losic D. Graphene oxide-Fe(III) composite containing phosphate–A novel slow release fertilizer for improved agriculture management. J. Clean. Prod. 2018, 185, 97–104. 10.1016/j.jclepro.2018.03.050. [DOI] [Google Scholar]
  7. Anstoetz M.; Rose T. J.; Clark M. W.; Yee L. H.; Raymond C. A.; Vancov T. Novel applications for oxalate-phosphate-amine metal-organic-frameworks (OPA-MOFs): can an iron-based OPA-MOF be used as slow-release fertilizer?. PloS ONE 2015, 10 (12), e0144169 10.1371/journal.pone.0144169. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Yao Y.; Gao B.; Chen J.; Yang L. Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slow-release fertilizer. Environ. Sci. Technol. 2013, 47 (15), 8700–8708. 10.1021/es4012977. [DOI] [PubMed] [Google Scholar]
  9. Vejan P.; Khadiran T.; Abdullah R.; Ahmad N. Controlled release fertilizer: A review on developments, applications and potential in agriculture. J. Controlled Release 2021, 339, 321–334. 10.1016/j.jconrel.2021.10.003. [DOI] [PubMed] [Google Scholar]
  10. Everaert M.; Smolders E.; McLaughlin M. J.; Andelkovic I.; Smolders S.; Degryse F. Layered Double Hydroxides as Slow-Release Fertilizer Compounds for the Micronutrient Molybdenum. J. Agric. Food Chem. 2021, 69 (48), 14501–14511. 10.1021/acs.jafc.1c06056. [DOI] [PubMed] [Google Scholar]
  11. Drits V.; Bookin A.. Crystal Structure and X-ray Identification of Layered Double Hydroxides. In Layered Double Hydroxides: Present and Future; Rives V., Ed.; Nova Science, 2001; pp 39–92. [Google Scholar]
  12. Lu C.; Qian W.; Mallet M.; Ruby C.; Hansen H. C. B. Tuning the stability and phosphate sorption of novel MnII/IVFeII/III layered double hydroxides. Chem. Eng. J. 2022, 429, 132177 10.1016/j.cej.2021.132177. [DOI] [Google Scholar]
  13. González M.; Cea M.; Medina J.; González A.; Diez M.; Cartes P.; Monreal C.; Navia R. Evaluation of biodegradable polymers as encapsulating agents for the development of a urea controlled-release fertilizer using biochar as support material. Sci. Total Environ. 2015, 505, 446–453. 10.1016/j.scitotenv.2014.10.014. [DOI] [PubMed] [Google Scholar]
  14. da Cruz D. F.; Bortoletto-Santos R.; Guimarães G. G. F.; Polito W. L.; Ribeiro C. Role of Polymeric Coating on the Phosphate Availability as a Fertilizer: Insight from Phosphate Release by Castor Polyurethane Coatings. J. Agric. Food Chem. 2017, 65 (29), 5890–5895. 10.1021/acs.jafc.7b01686. [DOI] [PubMed] [Google Scholar]
  15. Voragen A. G. J.; Coenen G. J.; Verhoef R. P.; Schols H. A. Pectin, a versatile polysaccharide present in plant cell walls. Struct. Chem. 2009, 20 (2), 263–275. 10.1007/s11224-009-9442-z. [DOI] [Google Scholar]
  16. Liang W. L.; Liao J. S.; Qi J. R.; Jiang W. X.; Yang X. Q. Physicochemical characteristics and functional properties of high methoxyl pectin with different degree of esterification. Food Chem. 2022, 375, 131806 10.1016/j.foodchem.2021.131806. [DOI] [PubMed] [Google Scholar]
  17. Choong C. E.; Wong K. T.; Jang S. B.; Saravanan P.; Park C.; Kim S.-H.; Jeon B.-H.; Choi J.; Yoon Y.; Jang M. Granular Mg-Fe layered double hydroxide prepared using dual polymers: Insights into synergistic removal of As (III) and As (V). J. Hazard. Mater. 2021, 403, 123883 10.1016/j.jhazmat.2020.123883. [DOI] [PubMed] [Google Scholar]
  18. Hinsinger P. Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review. Plant Soil 2001, 237 (2), 173–195. 10.1023/A:1013351617532. [DOI] [Google Scholar]
  19. Jones D. L. Organic acids in the rhizosphere - a critical review. Plant Soil 1998, 205 (1), 25–44. 10.1023/A:1004356007312. [DOI] [Google Scholar]
  20. Li M.; Dopilka A.; Kraetz A. N.; Jing H.; Chan C. K. Layered double hydroxide/chitosan nanocomposite beads as sorbents for selenium oxoanions. Ind. Eng. Chem. Res. 2018, 57 (14), 4978–4987. 10.1021/acs.iecr.8b00466. [DOI] [Google Scholar]
  21. Crouch S. R.; Malmstad H. V. Mechanistic investigation of molybdenum blue method for determination of phosphate. Anal. Chem. 1967, 39 (10), 1084. 10.1021/ac60254a027. [DOI] [Google Scholar]
  22. Hatami H.; Fotovat A.; Halajnia A. Comparison of adsorption and desorption of phosphate on synthesized Zn-Al LDH by two methods in a simulated soil solution. Appl. Clay Sci. 2018, 152, 333–341. 10.1016/j.clay.2017.11.032. [DOI] [Google Scholar]
  23. Dakora F. D.; Phillips D. A. Root exudates as mediators of mineral acquisition in low-nutrient environments. Plant Soil 2002, 245 (1), 35–47. 10.1023/A:1020809400075. [DOI] [Google Scholar]
  24. Korsmeyer R. W.; Lustig S. R.; Peppas N. A. SOLUTE AND PENETRANT DIFFUSION IN SWELLABLE POLYMERS 0.1. MATHEMATICAL-MODELING. J. Polym. Sci. B: Polym. Phys. 1986, 24 (2), 395–408. 10.1002/polb.1986.090240214. [DOI] [Google Scholar]
  25. Ravel B.; Newville M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12 (4), 537–541. 10.1107/S0909049505012719. [DOI] [PubMed] [Google Scholar]
  26. Li W. H.; Hsu L. C.; Tzou Y. M.; Chen Y. C.; Teah H. Y.; Kung Y. Y.; Chen H. Y.; Liu Y. T. Hybridize magnesium-iron layered double hydroxide with biopolymers to develop multiple pathways for phosphate sorption and release: A potential slow release phosphorus fertilizer. Chem. Eng. J. 2023, 473, 145451 10.1016/j.cej.2023.145451. [DOI] [Google Scholar]
  27. Liu Y.-T.; Hesterberg D. Phosphate bonding on noncrystalline Al/Fe-hydroxide coprecipitates. Environ. Sci. Technol. 2011, 45 (15), 6283–6289. 10.1021/es201597j. [DOI] [PubMed] [Google Scholar]
  28. Borges R.; Wypych F.; Petit E.; Forano C.; Prevot V. Potential sustainable slow-release fertilizers obtained by mechanochemical activation of MgAl and MgFe layered double hydroxides and K2HPO4. Nanomaterials 2019, 9 (2), 183. 10.3390/nano9020183. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Everaert M.; Degryse F.; McLaughlin M. J.; De Vos D.; Smolders E. Agronomic Effectiveness of Granulated and Powdered P-Exchanged Mg–Al LDH Relative to Struvite and MAP. J. Agric. Food Chem. 2017, 65 (32), 6736–6744. 10.1021/acs.jafc.7b01031. [DOI] [PubMed] [Google Scholar]
  30. Das J.; Patra B. S.; Baliarsingh N.; Parida K. M. Adsorption of phosphate by layered double hydroxides in aqueous solutions. Appl. Clay Sci. 2006, 32 (3–4), 252–260. 10.1016/j.clay.2006.02.005. [DOI] [Google Scholar]
  31. Bernardo M. P.; Guimarães G. G.; Majaron V. F.; Ribeiro C. Controlled Release of Phosphate from Layered Double Hydroxide Structures: Dynamics in Soil and Application as Smart Fertilizer. ACS Sustain. Chem. Eng. 2018, 6 (4), 5152–5161. 10.1021/acssuschemeng.7b04806. [DOI] [Google Scholar]
  32. Benício L. P. F.; Constantino V. R. L.; Pinto F. G.; Vergütz L.; Tronto J.; da Costa L. M. Layered double hydroxides: New technology in phosphate fertilizers based on nanostructured materials. ACS Sustain. Chem. Eng. 2017, 5 (1), 399–409. 10.1021/acssuschemeng.6b01784. [DOI] [Google Scholar]
  33. Everaert M.; Warrinnier R.; Baken S.; Gustafsson J.-P.; De Vos D.; Smolders E. Phosphate-exchanged Mg–Al layered double hydroxides: a new slow release phosphate fertilizer. ACS Sustain. Chem. Eng. 2016, 4 (8), 4280–4287. 10.1021/acssuschemeng.6b00778. [DOI] [Google Scholar]
  34. Caporale A. G.; Pigna M.; Azam S.; Sommella A.; Rao M. A.; Violante A. Effect of competing ligands on the sorption/desorption of arsenite on/from Mg-Fe layered double hydroxides (Mg-Fe-LDH). Chem. Eng. J. 2013, 225, 704–709. 10.1016/j.cej.2013.03.111. [DOI] [Google Scholar]
  35. Cajuste L. J.; Laird R. J.; Cajuste-B L.; Cuevas B. G. Citrate and oxalate influence on phosphate, aluminum, and iron in tropical soils. Commun. Soil Sci. Plant Anal. 1996, 27 (5–8), 1377–1386. 10.1080/00103629609369639. [DOI] [Google Scholar]
  36. Hsu L. C.; Tzou Y. M.; Ho M. S.; Sivakumar C.; Cho Y. L.; Li W. H.; Chiang P. N.; Teah H. Y.; Liu Y. T. Preferential phosphate sorption and Al substitution on goethite. Environ. Sci.: Nano 2020, 7 (11), 3497–3508. 10.1039/C9EN01435G. [DOI] [Google Scholar]
  37. Voegelin A.; Kaegi R.; Frommer J.; Vantelon D.; Hug S. J. Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy. Geochim. Cosmochim. Acta 2010, 74 (1), 164–186. 10.1016/j.gca.2009.09.020. [DOI] [Google Scholar]
  38. Rives V.Layered double hydroxides: present and future; Nova, 2001. [Google Scholar]
  39. Manceau A. Critical evaluation of the revised akdalaite model for ferrihydrite. Am. Mineral. 2011, 96 (4), 521–533. 10.2138/am.2011.3583. [DOI] [Google Scholar]
  40. Rose J.; Vilge A.; Olivie-Lauquet G.; Masion A.; Frechou C.; Bottero J. Y. Iron speciation in natural organic matter colloids. Colloids and Surfaces a-Physicochemical and Engineering Aspects 1998, 136 (1–2), 11–19. 10.1016/S0927-7757(97)00150-7. [DOI] [Google Scholar]
  41. Barreto M. S.; Elzinga E. J.; Alleoni L. R. Attenuated total reflectance–Fourier transform infrared study of the effects of citrate on the adsorption of phosphate at the hematite surface. Soil Sci. Soc. Am. J. 2020, 84 (1), 57–67. 10.1002/saj2.20005. [DOI] [Google Scholar]
  42. Finzel J.; Sanroman Gutierrez K. M.; Hoffman A. S.; Resasco J.; Christopher P.; Bare S. R. Limits of Detection for EXAFS Characterization of Heterogeneous Single-Atom Catalysts. ACS Catal. 2023, 13, 6462–6473. 10.1021/acscatal.3c01116. [DOI] [Google Scholar]

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