Metal Phosphates and Phosphonates

The type of inorganic-organic hybrid polymeric material formed by the coordination of phosphonate ligands to metal ions, resulting in multi-dimensional extended assemblies is metal phosphonates (MPs). The discipline of MPs chemistry has developed progressively over the last few decades, fueled by interest in applications in a wide range of fields. Synthetic technologies of MPs are lacking on the way to domestic, more efficient alternatives. For the characterization, the advancement of electron diffraction as an instrument for crystal structure determination and the use of in situ characterization techniques have allowed for a better understanding of reaction pathways. Metal phosphonates have been discovered to be appropriate materials for a wide range of applications. This chapter continues to concentrate on advanced emerging applications of MPs in bio-ceramics, electrochemical energy devices, fuel cells, state-of-the-art hydrogen evolution rate (HER), oxygen evolution rate (OER), and water splitting catalysts. The remaining eighteen chapters in the book demonstrate the vast expansion and diversity of metal phosphonate chemistry research briefly.

The ability to create hierarchically porous nanostructures using materials based on metal phosphate and phosphonates is very astonishing. The major drivers of the scientific community are focused on the need to rationalize novel synthetic ways to synthesize these materials under controlled settings especially related to morphology. In this chapter, we have highlighted different synthetic techniques that have been employed in the synthesis of metal phosphonates and how the properties of porous metal phosphonates and phosphates are being impacted. Nanoporous metal phosphonates are proliferating rapidly owing to their versatile applications in different areas, including energy storage, catalysis, environmental intervention, and biology, among others, which are also discussed in this chaptesr. It is expected that the chemistry of porous metal phosphonates and phosphates would advance as a result of their utilization in domains like biology and fuel cells.

Transition-metal phosphates/phosphonates have demonstrated remarkable performances for their unique physicochemical properties. Compared with transition-metal oxides, phosphate/phosphonate groups in transition-metal phosphates/phosphonates show flexible coordination with diverse orientations, endowing them with an ideal platform for many promising applications. In this chapter, we focus on the rich structural chemistry and design strategies of efficient, high-valent V/Ti-containing transition-metal phosphate/phosphonate materials for emerging applications, with special emphasis on the tuning of transition-metal-center coordination environment, optimization of electronic structures, increase of catalytically active site densities, and design of heterostructures, to address the urgent issues confronted by transition-metal phosphates/phosphonates such as low intrinsic catalytic efficiency and low electronic conductivity. The major challenges, opportunities, and prospective solutions are also discussed for further development of V/Ti-containing transition-metal phosphates/phosphonates-based materials with ultimate practical applications.

Worldwide, various factors have caused an increase in energy consumption. So, the requirement for renewable and green energy sources becomes a gradually important problem. Nowadays, improvements in energy-related conversion methods such as metal-air batteries, electrochemical water splitting, supercapacitors, etc., are very significant fields of research. Nanostructures of metal phosphate and phosphonate compounds are of tremendous attention in today's technological applications, because of their presence of hollow spaces, high surface area, and straightforward adjusting composition and dimensions. Phosphorus compounds like metal phosphates and metal phosphonates have demonstrated perfect performances and excellent potential in electrochemical applications and devices. This chapter reviews some electrochemical applications such as water splitting and energy storage devices using metal phosphate and phosphonates were examined in the last two decades of improvement.

Due to their enormous theoretical capability and potential application in electrochemical energy systems, curiosity about metal phosphates and phosphonates has considerably expanded over the past couple of years in light of the significance of renewable power, economic, and ecological challenges. Several of these metal phosphates, phosphides, and hybrids outperform transition metal hydroxides/oxides, a family of electrode materials that have received substantial study for supercapacitor applications. We thoroughly cover the properties and fundamentals of metal phosphates with regard to electrochemical energy devices in this chapter. The synthetic procedures used to manufacture these metal phosphides and phosphates, as well as the underlying scientific principles, are explored since they have a significant impact on the effectiveness of electrochemical energy retention. Several aspects of metal phosphates-based electrochemical devices along with their basic operating principles and material compositions have been examined.

Catalysts alter the rate of reactions by providing an alternative route to the reactants for product formation. Physically feasible reactions when uncatalyzed in the real world may take hundreds of years to complete but with the help of catalysts, they take a reasonably small amount of time. There are many ways in which a particular reaction can be catalyzed. To this end, geometrical confinement provides an attractive route through which a given chemical reaction could be catalyzed. It has been shown that confining the reactants inside suitable cavitands such as cucurbit[n]urils can reduce the activation barrier associated with the reactions. Geometrical confinement impacts the nature of bonding, and energy gaps among the frontier orbitals within the concerned reactants thereby affecting their reactivity. The cavitands’ size and shape (and thereby the nature of the confining regime), however, plays a significant role in determining the rate of the reaction as shown by Diels–Alder reactions occurring inside organic hosts like ExBox⁴⁺ and cucurbit[n]uril. The cavitands (e.g. cucurbit[n]uril) which promote suitable alignment of the reactants can facilitate the reaction effectively. Furthermore, the cavitands can exhibit fluxional behavior (as in B₄₀ molecule) and thus the nature of the confining regime can change as a function of time. In such systems, the reaction dynamics get affected by this fluxional behavior of the host.

As the cleanest renewable resource with the highest gravimetric energy density, hydrogen fuel is considered the preferred alternative to fossil fuels for the supply of future energy. Water electrolysis provides an attractive strategy to achieve efficient and sustainable hydrogen generation for the future hydrogen economy. As the vital half-reaction of water electrolysis for hydrogen production, cathodic hydrogen evolution reaction (HER) is always intensely researched over the past decades. The employment of highly active HER catalysts can make water electrolysis more economical and energy-efficient. Metal phosphates/phosphonates (MPi/MPPi) are promising and burgeoning HER catalysts owing to their special electronic structure, tunable composition, and multi-functionality. In this chapter, states of the art of main metal-based phosphates/phosphonates catalysts including cobalt, nickel, iron, and other metal phosphates/phosphonates for HER are summarized. While those effective strategies for the design and construction of MPi/MPPi-based catalysts with high HER activities and the catalysis mechanisms are also introduced and discussed. In addition, the application of MPi/MPPi-based catalysts in the future for HER has been prospected.

As a kind of green energy, hydrogen is an effective way to solve energy shortages, environmental pollution, and climate change. At present, the cost of hydrogen energy production and storage is high. Metal phosphide is expected to be the upstream main raw material to support the hydrogen economy instead of precious metals due to its low hydrogen overpotential, adjustable electronic structure, high conductivity, and low price. This chapter reviews the R&D status of metal phosphates/phosphonates as electrocatalysts, photocatalysts, biological starters, and thermochemical stabilizers in hydrogen energy preparation and storage technology, respectively. The progress of phosphorous-based fuel cells is also summarized. Finally, the application of metal phosphate/phosphonates in the related fields of hydrogen energy development has prospected. This chapter aims to provide technical support and theoretical reference for researchers and beginners in related industries.

The efficient and scalable production of H₂ from the water splitting is fundamentally reliant on the development of active, robust, and economical electrocatalysts for oxygen evolution reaction (OER). Transition metal phosphates and phosphonates are promising materials due to their distinct layered architectures, high catalytic activity, low-cost, facile synthesis, and environmental friendliness. Metal phosphates with open, gigantic, framework structures, e.g., polyoxometalates (POMs), provide ion transport channels and cavities along with abundant redox active sites. POMs containing primarily oxygen atoms and transition metals like M = Mo, W, V, etc., and a central addenda heteroatom like P, Si, etc., have shown great promise toward the electrocatalytic OER. In this chapter, the overviews of the fundamentals of OER and the catalytic characteristics of POMs, and the insights into OER electrocatalysis are discussed.

Metal phosphates and phosphonates have been extensively studied for applications in membranes due to their desired features including coordination capacity, ion exchange ability, controllable morphology, and good thermal/chemical stability. The membrane performances are influenced by several factors including the types of metal ions, the structure of phosphoric or phosphonic acids, the ratios between them, and the synthetic methods. In this chapter, metal phosphates are discussed in the first section, which is further divided into four sub-sections including metal salts of phosphoric acid, metal salts of pyrophosphoric acid, metal salts of hydrocarbyloxy phosphoric acids, and other inorganic metal phosphates. The second section focused on metal phosphonates for membranes, contains three sub-sections including metal salts of alkyl phosphonic acids, metal salts of aryl phosphonic acids, and other metal salts of phosphonic acids. The synthesis and structure of metal phosphates and phosphonates were introduced while the membrane fabrication and performances were discussed. Next-generation high-performance membranes applied in ion exchange, gas separation, liquid–liquid separation and catalysis can be developed under the guidance of the valuable studies established in this field.

The rapid development of the era of social electrification has put forward higher requirements for sustainable and clean energy. The development of high-performance energy storage devices is the key to meeting the above requirements, among which fuel cells have been widely used due to their high work efficiency, high energy density, and long cycle life. In recent years, metal phosphates/phosphonates have attracted extensive research as fuel cell materials due to their abundant resources, environmental protection, and low cost. It is worth noting that the nanostructure design of metal phosphates and phosphonates has an important impact on improving their performance. In this chapter, we introduce the synthetic strategies of metal phosphates/phosphonates and the recent progress in their applications in the field of fuel cells. The phosphate/phosphonate moiety can act as a ligand site/linker due to its strong affinity for the metal center, which enables diverse synthetic strategies for metal phosphates/phosphonates. Through the structural design of metal phosphates/phosphonates, great progress has been made in the application of metal phosphates/phosphonates as functional materials in the field of fuel cells. However, there are still some key problems to be solved in the practical application process. Metal phosphates/phosphonates as functional materials have made great progress in the field of fuel cells; however, there are still many key problems to be solved. Finally, the future development direction of enhancing the electrochemical properties of metal phosphates/phosphonates-based fuel cells has been prospected.

Exigency and depletion of fossil fuels have resulted in the generation of alternative fuels i.e., biodiesel, drop-in diesel, methanol, ethanol, solar energy, and methane gas. Production of biofuel and their utilization in transportation and industries have alleviated the utilization of fossil fuels. The formation of biofuels from biomass including soybean, palm oil, vegetable oil, animal fat, and algae employs a variety of catalysts. This chapter provides a comprehensive assessment of metal phosphates and phosphonates, a class of heterogeneous catalysts, for the production of biofuels. In addition to biodiesel production, biomass is also used for the fabrication of liquid hydrocarbon drop-in fuels. The chapter discusses the environmental waste management issues raised due to the consumption of waste biomass as well as outlines the development of low-cost catalysts to yield sustainable biofuels. The potential of heterogeneous metal phosphate and phosphonates for the formation and upgradation of biofuels has a high impact on the fuel sector worldwide.

Issues that make up the world's agenda and seek urgent solutions, such as the increasing need for energy with the depletion of fossil fuels, environmental pollution, increase in carbon dioxide emission rates, and climate change, encourage using the least damaging chemicals, producing low waste production, and reducing energy consumption to prevent environmental and health hazards. Because of their enormous potency to address global energy and environmental challenges by harnessing solar light energy, semiconductor photocatalysts, a significant class of functional materials, have gained growing interest. In this book chapter, photocatalyst efficiencies of phosphates and phosphonates in environmental and energy applications are examined in detail. Compared to similar photocatalysts, phosphate and phosphonates are seen as excellent alternatives due to their structural diversity, and surface, magnetic, electronic, and catalytic properties.

Nowadays, phosphorus compounds, like metal phosphates and phosphonates have attained considerable attention as electrode materials for energy storage devices i.e., supercapacitors (SCs) and solar cells, etc., because of their high porosity, enlarged surface area, suitable pore size, well-regulated structural stability, excellent electrochemical reversibility, and rich active sites. Porous metal phosphates/phosphonates compounds are the most explored and investigated trendsetter electrode materials owing to their non-toxic, light atom weight, rich covalent states, environmental-friendly, and low-cost nature. These electrode schemes show much good performances (i.e., high specific capacitance, extraordinary energy density, long charge–discharge cycle life, and improved power density). Herein, we have focused on the topical progress and development of metal phosphates/phosphonates by concentrating on their beneficial utilization and prospective applications for the next generation as a novel class of electrode materials in SCs. Methodologies and the modified fabrication techniques to bring out the best merits of synthesized metal phosphates/phosphonates are focused, along with the technical and systematic perceptions are elaborated, as such analysis sturdily influences the electro-chemical energy storing abilities of the devices. Specific considerations have been put to such hybrid-kind of materials, where robust synergistic properties occur. Finally, the forthcoming perceptions and challenges for the metal phosphates/phosphonates are projected and discussed.

Transition metal phosphates with their tantalizing features such as low-cost, high electrochemical stability, earth abundance, environmentally benign nature, tunable functionalities, and so on have rendered them as one of the emerging families of materials for futuristic high-performance energy conversion and storage applications. Polyoxometalates (POMs), which are phosphate-based metal oxide polyanionic clusters, possessing semiconducting and acid-like natures, plentiful redox properties, and rooms for accommodating many electrons without significant structural changes have drawn much hype as supercapacitor materials. This chapter mainly discusses the promises of POM polyanionic archetype-based materials for supercapacitor applications.

The development of advanced battery technologies for portable electronic devices and electric vehicles requires highly efficient cost effective electrode materials. The fundamental challenge behind the exploration of advanced battery technologies involves the rational designing of electrode materials to meet high energy and high power density. Among the various electrode materials for energy storage applications, metal phosphates/phosphonates with the advantages of abundance, low cost, and eco-friendliness are emerging as a new class of electrode materials for lithium-ion batteries (LIBs). These transition metal phosphates/phosphonates have shown remarkable electrochemical performance for lithium-ion batteries owing to their unique physiochemical properties. In this chapter, the design engineering of transition metal phosphate and phosphonate-based electrode materials for storing lithium-ions are systematically discussed. More emphasis on the tuning of the structure–property relationship towards lithium-ion interaction/deintercation, challenges in the increase of electrochemically active sites, and construction of nanoarchitecture/heterostructures were also discussed.

The synthesis of novel materials with high affinity and high removal efficiency towards dyes is a matter of great practical importance in the remediation of wastewater treatment. In this chapter, a literature survey on metal phosphates and their hybrid systems as green and sustainable sorbent materials for the removal of dyes from industrial effluents has been presented. Following the presentation of the deleterious effects of dyes constituting the major motivation for many researchers in the field of adsorptive separations, the synthesis strategy for metal phosphates and their derivatives with the aim of better assessment of their value in the remediation of dye-polluted wastewater has been discussed. The reported works on the adsorptive removal of dyes from wastewater have then been presented in connection with the recent literature that has established the achievability and effectiveness of metal phosphates and their composites.

The field of metal phosphonates (MPs) has gained importance for sustainable energy and environmental applications over recent years. They are a prominent kind of metal–organic hybrid structures, revealing potential appliances in materials sciences, catalysis, ion- exchange, separation, and sorption, owing to their superior stability and insolubility in most solvents, which could be attributed to the hard nature of the phosphonate oxygen atoms and higher coordination affinity for metallic atoms. In the remediation of wastewater treatment, the utilization of novel materials with high adsorption capability and removal efficiency is a matter of major significance. The principal aim of this Chapter is to present a survey on the MP-based systems in the elimination of dye-polluted wastewater. The adsorptive removal of dyes from aqueous solution has been presented in the framework of the recently published works that demonstrated the feasibility and efficiency of the materials.

Ion exchange is entrenched as an efficacious contrivance in enormous water purification processes where it depends chiefly on the performance of the exchangers, utilized. Metal phosphates have played a crucial role as ion exchangers for the same processes. This chapter emphasizes the history, recognition of copious metal phosphates as ion exchangers, their classification, key characteristics of metal phosphates being used as ion exchangers, profuse stages of development with novel modifications, and a focus on current advancements in the field of analytical chemistry, especially surfactant based hybrid metal phosphates, both in fibrous and non-fibrous forms. The applications of these hybrid metal phosphates in the separation and removal of different toxic metals, in particular from the point of view of water purification are also explained.

The human body is composed of many vital elements and phosphorus is one such element that forms the basic ingredient of our biological constitution. Recently, researchers are more lenient on fabricating and applying materials for biomedical applications which pose the least threat to the human body with high mechanical strength and degradability opportunities. This provides an interesting platform and opens many avenues for the utilization of versatile metal conjugates of phosphorus in the form of phosphates/phosphonates as nanodevices or nanostructured moieties for varied biomedical applications. In this regard, metal phosphates/phosphonates have come out with such ideal properties making our biological functions better and comfortable with the least adverse reactions. Ideal metal phosphates/phosphonates are inert and degradable materials without any probability of releasing toxic contents and are generally employed for different applications namely in the field of dentistry as composite material for dental caries, cardiovascular stent fabrication, orthopedic applications, etc. As such metal phosphates are purely inorganic materials attached to phosphoric acid units and metal phosphonates are nanostructures comprising organophosphonate ligands attached to the organic–inorganic hybrid structures. These hybrid materials have a well-defined structural build triggering their usage as body implants and other in vivo applications. Thus, the current chapter highlights all the major strategies involving the fabrication of these hybrid structures with their latest biomedical applications involving biocompatibility studies.

Metal phosphate and phosphonate are hybrid materials prepared from the chemical interaction between organic and inorganic material that owns the favorable properties of both metal ions and phosphate-containing organic agents. The synthesis of metal phosphate hybrid material in mild conditions from the wide variety of existing reactants is a promising methodology to obtain new advanced materials with various building parts and chemical groups. Owing to their homogenous porosity, adjustable composition, low toxicity, and controllable structures, metal phosphates are used in lots of applications from catalysts, energy storage, and energy conversion to biotechnology, medical diagnosis, and therapy. The resolution and body retention time of metal phosphate as a medical imaging agent is significantly enhanced by using metal ions in the structure of these hybrid materials. The recent progress in cancer imaging and disease detection by metal phosphates and phosphonates are discussed in this chapter and exemplified according to the used metal types.

Recently, nanomaterials made of phosphates and phosphonates have opened up a rare occasion to create hierarchically porous nanomaterials with interconnected macropores, mesopores, and micropores. They provide appealing qualities for new applications that call for control over the interface, which is essential for functional technology, catalysis, and adsorption. For material scientists and engineers, the necessity to develop a justification for new preparation techniques that will allow for the regulated production of these materials is a crucial driving force. In this article, we will provide a quick summary of recent advancements in many development tactics, emphasizing many metal phosphonate technology and how they affect the characteristics of porous metal phosphates/phosphonates. Manufacturing of innovative metal phosphate/phosphonate-based materials with nanostructures for adsorption, catalysis, optoelectronics, fuel cells, and electrochemical cells will also be covered. The final section will give challenges and prospects for future development in the areas of mesoporous metal phosphates, increasing crystallinity, and low-cost and scalable mesoporous metal phosphide synthesis.