Internalization of Fluoride in Hydroxyapatite Nanoparticles

Abstract

Hydroxyapatite (HAP) is a cost-effective material to remove excess levels of fluoride from water. Historically, HAP has been considered a fluoride adsorbent in the environmental engineering community. This paper substantiates an uptake paradigm that has recently gained disparate support: assimilation of fluoride to bulk apatite lattice sites in addition to surface lattice sites. Pellets of HAP nanoparticles (NPs) were packed into a fixed-bed media filter to treat solutions containing 30 mg-F/L (1.58 mM) at pH 8, yielding an uptake of 15.97 ± 0.03 mg-F/g-HAP after 864 h. Solid-state 19 F and 13 C magicangle spinning nuclear magnetic resonance spectroscopy demonstrated that all removed fluoride is apatitic. A transmission electron microscopy analysis of particle size distribution, morphology, and crystal habit resulted in the development of a model to quantify adsorption and total fluoride capacity. Low-and high-estimate median adsorption capacities were 2.40 and 6.90 mg-F/g-HAP, respectively. Discrepancies between experimental uptake and adsorption capacity indicate the range of F − that internalizes to satisfy conservation of mass. The model was developed to demonstrate that F − internalization in HAP NPs occurs under environmentally relevant conditions and as a tool to understand the extent of F − internalization in HAP NPs of any kind.

Fluorinated Defect-Engineered Acetylenic Polymers with Separated Active Centers for Switching the Photosensitized Activation Pathway of Peroxymonosulfate

“…Meanwhile, a new peak at δ ( 13 C) ≈ 74.5 ppm in PTEB-F 15 could be assigned to the carbon atoms in the acetylene moieties at the tail end of its molecule, which was attributed to the uncoupling of carbon triplet bonds (CC) . In contrast to the pristine PTEB, the 13 C NMR spectrum of PTEB-F 15 reveals the presence of new peaks at 119.8 and 140.5 ppm, which can be ascribed to the carbon atoms bonded to fluorine atoms in the FPA. − Figure e illustrates the 19 F NMR spectrum of PTEB-F 15 , where distinct peaks appear at −109.0 ppm, confirming the integration of fluorine atoms. − In contrast, defect-free PTEB lacks these characteristic fluorine peaks, indicating that the introduction of −F defects directly results from the participation of FPA during the polymerization process. X-ray photoelectron spectroscopy (XPS) was utilized to examine the elemental composition and chemical states of the photosensitizers (Figure f,g).…”

Sulfate Doping Promotes Agglomeration of Calcium Fluoride Crystals

“…Fluoride contamination in drinking water poses a serious threat to public health, and excessive intake of fluoride results in dental or bone diseases. − About 200 million people worldwide rely on water sources with excessive fluoride ions (the World Health Organization limits the concentration of fluoride in drinking water to 1.5 mg/L). − Fluoride ions originate from the dissolution of minerals or the discharge of human industrial activities. ,− Fertilizer production (∼1700 mg/L), optoelectronic (∼2000 mg/L), aluminum electroplating (∼7000 mg/L), semiconductor manufacturing (∼1500 mg/L), photovoltaic power generation (∼2500 mg/L), and other industries produce a large amount of high-fluorine wastewater, and the discharge of these wastewater aggravates the current situation of fluorine contamination. − The concentration of fluoride ion in most of the high fluoride wastewater is at 500–2000 mg/L. Meanwhile, fluorite, as a mineral that can extract a large amount of fluorine, is the main source of fluorine in the modern chemical industry.…”

In Situ Evolution of Ionic Sites at Clay Mineral Interfaces Facilitates Fluoride and Phosphorus Mineralization

“…The activity of FF is primarily influenced by calcium, iron, and aluminum substances . Soil remediation strategies to fix F include ion exchange, surface complexation, coprecipitation, and mineralization mechanisms, such as adding hydroxyapatite, gypsum, lime, and calcite passivators. − P is a macronutrient that is essential for crop growth. Maintaining appropriate P levels in the soil is crucial to prevent eutrophication and ensure efficient P utilization .…”

“…According to crystal growth theory, the mineralization of F and P theoretically proceeds through both classical and nonclassical pathways, with the latter usually offering the advantage of lower energy crystallization . Current studies have mainly discussed surface coprecipitation and ion exchange phenomena in ideal solution states, − ,, such as the crystallization of fluorite and apatite due to the dissolution of calcium from the surfaces of calcite and hydroxyapatite. However, these studies have not yet explored their crystallization pathways in detail due to the difficulty of considering nonclassical heterogeneous crystallization pathways in complex environments.…”