Layered Double Hydroxides for Regulating Phosphate in Water to Achieve Long-Term Nutritional Management

Abstract

Hunger and undernourishment are increasing global challenges as the world's population continuously grows. Consequently, boosting productivity must be implemented to reach the global population's food demand and avoid deforestation. The current promising agricultural practice without herbicides and pesticides is fertilizer management, particularly that of phosphorus fertilizers. Layered double hydroxides (LDHs) have recently emerged as favorable materials in phosphate removal, with practical application possibilities in nanofertilizers. This review discusses the fundamental aspects of phosphate removal/recycling mechanisms and highlights the current endeavors on the development of phosphate-selective sorbents using LDH-based materials. Specific emphasis is provided on the progress in designing LDHs as the slow release of phosphate fertilizers reveals their relevance in making agro-practices more ecologically sound. Relevant pioneering efforts have been briefly reviewed, along with a discussion of perspectives on the potential of LDHs as green nanomaterials to improve food productivity with low eco-impacts.

Figure 1

Schematic presentation of layered double hydroxides (LDHs) as favorable nanofertilizers. (a) Versatile phosphate removal/release by LDHs for long-term P fertilizers. (b) Schematic representation of the classical LDHs structure. (Panel b was reprinted with permission from ref (31). Copyright 2022 Elsevier.)

Figure 2

Schematic representation of self-assembly LDH by the reconstruction method. (a) Illustrated “memory effect” induced CuZnAl-LDH structural transformations. (b) Delamination–reconstruction process of LDH-MTT. (Panel a reprinted with permission from ref (65). Copyright 2013 Elsevier. Panel b reprinted with permission from ref (62). Copyright 2018 Elsevier.)

Figure 3

Characterization of phosphate adsorption. (a) Schematic illustration of phosphate adsorption mechanisms includes electrostatic attraction, ion exchange, and ligand exchange. (b) Illustration of d₀₀₃ basal spacing (7.57 Å), LDH layer thickness (4.8 Å), and interlayer space. (c) XRD patterns of before (MgAl-NO₃-LDH) and after phosphate adsorption (MgAl-P-LDH). (d) LDH models with different phosphate anion orientations after optimization. The blue region presents the depletion of charge density, and the red region indicates the increasing charge density. (e) Density of states (DOS) and projected density of states (PDOS) for three different models. (Panel a reprinted with the permission from ref (67). Copyright 2019 Elsevier. Panel b reprinted with permission from ref (75). Copyright 2017 Elsevier. Panel c reprinted with permission from ref (77). Copyright 2014 Elsevier. Panels d and e reprinted with permission from ref (12). Copyright 2018 Elsevier.)

Figure 4

Characterizations of LDH structural stability after phosphate adsorption. (a) Schematic illustration of the phase changes and P sorption processes, and (b) TEM images of (i) MnFe-Cl-LDH and (ii) MnFe-CO₃-LDH. (Panel a reprinted with permission from ref (40). Copyright 2020 Elsevier. Panel b reprinted with permission from ref (110). Copyright 2022 Elsevier.)

Figure 5

Versatile binary LDHs for phosphate adsorption applications. (a) Comparison of lettuce seedling growth bioassay between control and P-laden MgAl-LDHs/biochar composite. (b) Illustration of the phosphate adsorption process onto ZnFe-LDH in various pH values and reaction times. (c) TEM images of the transformation products obtained after the interaction of CaFe-LDH with a phosphate solution. (Panel a reprinted with permission from ref (117). Copyright 2017 Elsevier. Panel b reprinted with permission from ref (119). Copyright 2020 Elsevier. Panel c reprinted with permission from ref (115). Copyright 2019 Elsevier.)

Figure 6

Investigation of P desorption from LDHs. (a) Proposed mechanism of phosphate desorption from am-Zr/MgFe-LDH by NaOH solution. (b) Influence of pH value and the composition of the solution on phosphate desorption from ZnFe-LDH. The results showed that NaOH + KNO₃ could reach a higher desorption percentage of 84%. (c) LDH showed excellent reusability for six cycles, where the adsorbent retained ∼72% of its phosphate adsorption capacity. (Panel a reprinted with permission from ref (129). Copyright 2021 IOP Science. Panels b and c reprinted with permission from ref (119). Copyright 2020 Elsevier.)

Figure 7

Phosphate adsorption/desorption performances by LDH/carbon materials composites. (a) Schematic mechanism of prepared LDH/chitosan composite. (b) Adsorption capacity of different pH and (c) NaOH concentration of desorption performance. (Panel a reprinted with permission from ref (148). Copyright 2023 Elsevier. Panel b reprinted with permission from ref (150). Copyright 2019 Elsevier. Panel c reprinted with permission from ref (149). Copyright 2019 Elsevier.)

Figure 8

Phosphate removal by LDH/magnetic materials composites. (a) Schematic representation of the preparation of Fe₃O₄@LDHs. (b) Magnetization curves of LDH composites. (c) Photograph of P-adsorbed magnetic LDH composite separated by applied magnetic force. (Panels a and b reprinted with permission from ref (157). Copyright 2015 Elsevier. Panel c reprinted with permission from ref (159). Copyright 2020 Elsevier.)

Figure 9

Pollutant removal by MOFs materials composites. (a) Schematic illustration of preparing MOFs. (b) Different mechanisms of P removal using LDH/MOF. (Panel a reprinted with permission from ref (164). Copyright 2023 Elsevier. Panel b reprinted with permission from ref (163). Copyright 2022 Elsevier.)

Figure 10

Phosphate removal by versatile LDH composites. (a) Preparation of hydrogel beads of PS-LDH. (b) Phosphate adsorption–desorption schematic illustration of amorphous ZrO₂/MgFe-LDH. (Panel a reprinted with permission from ref (68). Copyright 2022 Elsevier. Panel b reprinted with permission from ref (170). Copyright 2021 Elsevier.)

Figure 11

Practical applications of SRF by LDHs. (a) Schematic presentation for growth of soybean plants by using P-adsorbed LDH. (b) Comparison of soybean plant heights after 28 days of growth, and (c) metal content analysis of plant leaves. (d) Schematic illustration of enhanced phosphorus content of LDH-fertilizers by intercalating polymeric phosphate. (Panelss a–c reprinted with permission from ref (181). Copyright 2019 Elsevier. Panel d reprinted with permission from ref (186). Copyright 2022 Elsevier.)

Figure 12

LDH-based SRFs for various nutrients. (a) Mo-loaded ZnAl-LDH SRFs demonstrated slow and completed Mo release compared to Na₂MoO_4.. (b) Evaluation of Zn-doped MgFe-LDH as a Zn fertilizer for long-term usage. (Panel a reprinted with permission from ref (191). Copyright 2021 American Chemical Society. Panel b reprinted with permission from ref (193). Copyright 2017 Elsevier.)