Green Treatment of Phosphate from Wastewater Using a Porous Bio-Templated Graphene Oxide/MgMn-Layered Double Hydroxide Composite

Unraveling the Phosphorus Adsorption Mechanisms in Three-dimensional Reduced Graphene Oxide Materials

To prevent eutrophication, controlling the phosphate concentration levels is one of the most important issues in surface water management. One of the most utilized methods is phosphate adsorption. However, its application faces a bottleneck due to the unclear understanding of adsorption and interaction mechanisms. The present work unlocks the phosphorus adsorption mechanisms in three-dimensional reduced graphene oxide with different reduction levels and pore sizes to remove phosphate from water using experiments and multiscale simulations. Experiments were performed to evaluate the influence of pH, ionic strength, and temperature on the adsorption. Molecular Dynamics and Ab Initio simulations evaluated the influence of the pore size and oxidation degrees of the materials. We show that the adsorption capacity of the materials increases with increasing pH and ionic strength and decreasing temperature. It is observed that the more oxidized the material and the less compact the structure, the better the adsorption. These results are theoretically explained in terms of the interaction of functional groups and the clustering of phosphate ions, which results in better adsorption in materials with larger pores. The underlying mechanisms for the 3D-reduced graphene oxide performance were confirmed by spectroscopy analysis. All the results show that 3D-reduced graphene oxide can sorb phosphate in different complex water remediation systems with characteristics that can be modulated by changing the material synthesis method.

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

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.

A Green Approach for High Oxidation Resistance, Flexible Transparent Conductive Films Based on Reduced Graphene Oxide and Copper Nanowires

Copper nanowires (CuNWs)-based thin film is one of the potential alternatives to tin-doped indium oxide (ITO) in terms of transparent conductive films (TCFs). However, the severe problem of atmospheric oxidation restricts their practical applications. In this work, we develop a simple approach to fabricate highly stable TCFs through the dip-coating method using reduced graphene oxide (rGO) and CuNWs as the primary materials. Compared with previous works using toxic reduction agents, herein, the CuNWs are synthesized via a green aqueous process using glucose and lactic acid as the reductants, and rGO is prepared through the modified Hummers' method followed by a hydrogen-annealing process to form hydrogen-annealing-reduced graphene oxide (h-rGO). In the rGO/CuNWs films, the dip-coated graphene oxide layer can increase the adhesion of the CuNWs on the substrate, and the fabricated h-rGO/CuNWs can exhibit high atmospheric oxidation resistance and excellent flexibility. The sheet resistance of the h-rGO/CuNWs film only increased from 25.1 to 42.2 Ω/sq after exposure to ambient atmosphere for 30 days and remained almost unchanged after the dynamic bending test for 2500 cycles at a constant radius of 5.3 mm. The h-rGO/CuNWs TCF can be not only fabricated via a route with a superior inexpensive and safe method but also possessed competitive optoelectronic properties with high electrical stability and flexibility, demonstrating great opportunities for future optoelectronic applications.

Investigation of the efficient adsorption performance and adsorption mechanism of 3D composite structure La nanosphere-coated Mn/Fe layered double hydrotalcite on phosphate

Severe water eutrophication due to large releases of phosphorus has become a worldwide environmental problem. Adsorption active sites is less of traditional adsorbents in the phosphorus removal process resulting in low removal efficiency, so the new high-efficiency phosphorus removal adsorbents become an effective way to solve the problem. In this work, quercetin modified MnFe layered double hydrotalcite three-dimensional composites structures encapsulated by lanthanum (La(III)) nanoparticles (QLa@MnFe-LDH) were successfully prepared by a classical hydrothermal method. The results of the adsorption experiments show that La(III) nanosphere-encapsulated MnFe-LDH provides a more adequate binding site for phosphate adsorption. The adsorption performance of QLa@MnFe-LDH for phosphate was outstanding, the maximum adsorption capacity was 346.5 mg/g at 298.15 K, which was 300 % higher than that of MnFe-LDH. Moreover, QLa@MnFe-LDH retained its high adsorption capacity (>315.5 mg/g) over a wide range of pH (4.0 ∼ 7.0). The active sites of the reactions were predicted by Multiwfn and Visual Molecular Dynamics (VMD), and novel visualization studies of weak interactions were applied to theoretical studies. The modified MnFe-LDH encapsulated by La nanospheres has a strong adsorption capacity for phosphate adsorption. Therefore, the modified QLa@MnFe-LDH was expected to become an effective adsorption material for phosphorus removal.

Layered double hydroxides for removing and recovering phosphate: Recent advances and future directions

Eutrophication is a widespread environmental challenge caused by excessive phosphate. Thus, wastewater engineers primarily aim to limit the phosphate concentration in water bodies. Layered double hydroxides (LDHs) are lamellar inorganic materials containing tunable brucite-like structures. This review discusses the fundamental aspects and latest developments in phosphate removal using LDH-based materials. Based on the divalent cations, Ca, Mg, and Zn-containing LDHs are largely used along with trivalent cations such as Al and Fe owing to their limited toxicities. However, classical LDHs are affected by the presence of co-existing anions, have a narrow working pH range, and have moderate adsorption capacities. Binary LDHs have been designed to be selective towards phosphate by the addition of a third metal such as Zr⁴⁺. Developing LDH composites with magnetic, polymeric or carbon materials are feasible approaches for increasing adsorption capacity, stability, and reusability of LDHs. Biochar as a carrier material for LDHs achieved remarkable phosphate adsorption performance and improved LDH dispersion, anion exchange capacity, and ease of separation. The use of recovered phosphate as an SRF, which is a type of bioavailable fertilizer, is a promising approach.

Graphene-Based Composites for Phosphate Removal

A variety of methods, including chemical precipitation, biological phosphorus elimination, and adsorption, have been described to effectively eliminate phosphorus (P) in the form of phosphate (PO₄ ^3-) from wastewater sources. Adsorption is a simple and easy method. It shows excellent removal performance, cost effectiveness, and the substantial option of adsorbent materials. Therefore, it has been recognized as a practical, environmentally friendly, and reliable treatment method for eliminating P. Nanocomposites have been deployed to remove P from wastewater via adsorption. Nanocomposites offer low-temperature alteration, high specific surface area, adjustable surface chemistry, pore size, many adsorption sites, and rapid intraparticle diffusion distances. In this Mini-Review, we have aimed to summarize the last eight years of progress in P removal using graphene-based composites via adsorption. Ultimately, future perspectives have been presented to boost the progress of this encouraging field.

Layered Double Hydroxides in Bioinspired Nanotechnology

Layered Double Hydroxides (LDHs) are a relevant class of inorganic lamellar nanomaterials that have attracted significant interest in life science-related applications, due to their highly controllable synthesis and high biocompatibility. Under a general point of view, this class of materials might have played an important role for the origin of life on planet Earth, given their ability to adsorb and concentrate life-relevant molecules in sea environments. It has been speculated that the organic–mineral interactions could have permitted to organize the adsorbed molecules, leading to an increase in their local concentration and finally to the emergence of life. Inspired by nature, material scientists, engineers and chemists have started to leverage the ability of LDHs to absorb and concentrate molecules and biomolecules within life-like compartments, allowing to realize highly-efficient bioinspired platforms, usable for bioanalysis, therapeutics, sensors and bioremediation. This review aims at summarizing the latest evolution of LDHs in this research field under an unprecedented perspective, finally providing possible challenges and directions for future research.