Process Intensification for Enhanced Fluoride Removal and Recovery as Calcium Fluoride Using a Fluidized Bed Reactor.

This study explored the feasibility of fluoride removal from simulated semiconductor industry wastewater and its recovery as calcium fluoride using fluidized bed crystallization. The continuous reactor showed the best performance (>90% fluoride removal and >95% crystallization efficiency) at a calcium-to-fluoride ratio of 0.6 within the first 40 days of continuous operation. The resulting particle size increased by more than double during this time, along with a 36% increase in the seed bed height, indicating the deposition of CaF2 onto the silica seed. The SEM-EDX analysis showed the size and shape of the crystals formed, along with the presence of a high amount of Ca-F ions. The purity of the CaF2 crystals was determined to be 91.1% though ICP-OES analysis. Following the continuous experiment, different process improvement strategies were explored. The addition of an excess amount of calcium resulted in the removal of an additional 6% of the fluoride; however, compared to this single-stage process, a two-stage approach was found to be a better strategy to achieve a low effluent concentration of fluoride. The fluoride removal reached 94% with this two-stage approach under the optimum conditions of 4 + 1 h HRT combinations and a [Ca2+]/[F-] ratio of 0.55 and 0.7 for the two reactors, respectively. CFD simulation showed the impact of the inlet diameter, bottom-angle shape, and width-to-height ratio of the reactor on the mixing inside the reactor and the possibility of further improvement in the reactor performance by optimizing the FBR configuration.

Novel pit and fissure sealant with nano-CaF2 and antibacterial monomer: Fluoride recharge, microleakage, sealing ability and cytotoxicity.

Conventional resin-based sealants release minimal fluoride ions (F) and lack antibacterial activity. The objectives of this study were to: (1) develop a novel bioactive sealant containing calcium fluoride nanoparticles (nCaF2) and antibacterial dimethylaminohexadecyl methacrylate (DMAHDM), and (2) investigate mechanical performance, F recharge and re-release, microleakage, sealing ability and cytotoxicity. Helioseal F served as commercial control. The initial F release from sealant containing 20% nCaF2 was 25-fold that of Helioseal F. After ion exhaustion and recharge, the F re-release from bioactive sealant did not decrease with increasing number of recharge and re-release cycles. Elastic modulus of new bioactive sealant was 44% higher than Helioseal F. The new sealant had excellent sealing, minimal microleakage, and good cytocompatibility. Hence, the nanostructured sealant had substantial and sustained F release and antibacterial activity, good sealing ability and biocompatibility. The novel bioactive nCaF2 sealant is promising to provide long-term F ions for caries prevention.

Mineral Nanomedicine to Enhance the Efficacy of Adjuvant Radiotherapy for Treating Osteosarcoma.

It is vital to remove residual tumor cells after resection to avoid the recurrence and metastasis of osteosarcoma. In this study, a mineral nanomedicine, europium-doped calcium fluoride (CaF2:Eu) nanoparticles (NPs), is developed to enhance the efficacy of adjuvant radiotherapy (i.e., surgical resection followed by radiotherapy) for tumor cell growth and metastasis of osteosarcoma. In vitro studies show that CaF2:Eu NPs (200 µg/mL) exert osteosarcoma cell (143B)-selective toxicity and migration-inhibiting effects at a Eu dopant amount of 2.95 atomic weight percentage. These effects are further enhanced under X-ray irradiation (6 MeV, 4 Gy). Furthermore, in vivo tests show that intraosseous injection of CaF2:Eu NPs and X-ray irradiation have satisfactory therapeutic efficacy in controlling primary tumor size and inhibiting primary tumor metastasis. Overall, our results suggest that CaF2:Eu NPs with their osteosarcoma cell (143B)-selective toxicity and migration-inhibiting effects combined with radiotherapy might be nanomedicines for treating osteosarcoma after tumor resection.

Luminescence and photoionization of X-ray generated Sm2+ in coprecipitated CaF2 nanocrystals.

We report photoluminescence and photoionization properties of Sm2+ ions generated by X-irradiation of nanocrystalline CaF2:Sm3+ prepared by coprecipitation. The nanocrystals were of 46 nm average crystallite size with a distribution of ±20 nm and they were characterised by XRD, TEM and SEM-EDS. At room temperature, the X-irradiated sample displayed broad electric dipole allowed Sm2+ 4f55d (A1u) → 4f6 7F1 (T1g) luminescence at 725 nm that narrowed to an intense peak at 708 nm on cooling to ∼30 K. The narrow f-f transitions of Sm3+ were also observed. The X-irradiation-induced reduction of Sm3+ + e- → Sm2+ as a function of X-ray dose was investigated over a very wide dynamic range from 0.01 mGy to 850 Gy by monitoring the photoluminescence intensities of both Sm2+ and Sm3+ ions. The reverse Sm2+ → Sm3+ + e- photoionization can be modelled by employing dispersive first-order kinetics and using a standard gamma distribution function, yielding an average separation of 13 Å between the Sm2+ ions and the hole traps (e.g. oxide ion impurities). The present results point towards potential applications of Sm doped CaF2 nanocrystals in the fields of dosimetry and X-ray imaging.

Reconstruction of a Demineralized Dentin Matrix via Rapid Deposition of CaF2 Nanoparticles In Situ Promotes Dentin Bonding.

Dentin bonding based on a wet-bonding technique is the fundamental technique used daily in clinics for tooth-restoration fixation and clinical treatment of tooth-related diseases. Limited bonding durability led by insufficient adhesive infiltration in the demineralized dentin (DD) matrix is the biggest concern in contemporary adhesive dentistry. This study proposes that the highly hydrated noncollagenous protein (NCP)-formed interfacial microenvironment of the DD matrix is the root cause of this problem. Meanwhile, the endogenous phosphate groups of the NCPs are used as pseudonuclei to rapidly induce the formation of amorphous CaF2 nanoparticles in situ in the interfacial microenvironment. The DD matrix is thus reconstructed into a novel porous structure. It markedly facilitates the infiltration of dentin adhesives in the DD matrix and also endows the DD matrix with anticollapsing capability when water evaporates. Whether using a wet-bonding or air-drying mode, the bonding effectiveness is greatly promoted, with the 12 month bonding strength being about twice that of the corresponding control groups. This suggests that the nanoreinforced DD matrix eliminates the dependence of bonding effectiveness on the moisture status of the DD surface controlled only by experiences of dentists. Consequently, this bonding strategy not only greatly improves bonding durability but also overcomes the technical sensitivity of bonding operations of the total-etched bonding pattern. This exhibits the potential to promote dentin bonding and is of great significance to dentistry.

Growth of mineralized collagen films by oriented calcium fluoride nanocrystal assembly with enhanced cell proliferation.

Bone is a highly calcified tissue with 60 wt% inorganic components. It is made up of mineralized collagen fibrils, where the platelet-like hydroxyapatite nanocrystals deposit within the collagen fibrils in an oriented manner. Inspired by the special structure and biological activity of bone, we realize the intrafibrillar mineralization of collagen films with oriented calcium fluoride nanocrystals in vitro. Amorphous calcium fluoride (ACF) precursors are generated by polyacrylic acid through polymer-induced liquid precursor processes. The precursors are ready to infiltrate and fill the gap zones laterally and then diffuse to occupy the whole space inside the collagen longitudinally. Finally, the fully mineralized collagen fibrils exhibit a single-crystal-like structure after transforming precursors to co-oriented nanocrystals under the influence of arranged collagen molecules. Expanding the collagen mineralization from 1D fibrils to 2D films, the growth of mineralized areas on the films with a reaction-limited behavior is found. The kinetic rate of growth is around 0.2-0.3 µm min-1, which depends on the pH of the solution. Furthermore, the mineralized collagen films exhibit an enhanced ability of cell proliferation over the pure collagen matrices. Understanding the mineralization of artificial collagen-based scaffolds may have broad promising potentials for bone tissue regeneration and repair in the future.

A sensitive and visual molecularly imprinted fluorescent sensor incorporating CaF2 quantum dots and ß-cyclodextrins for 5-hydroxymethylfurfural detection.

Calcium fluoride (CaF2) quantum dots have many applications in various fields. But there is no report on fluorescent characteristics of CaF2 quantum dots (CaF2 QDs). Here, a synthesis of multiple-color emission CaF2 QDs by changing the temperature, time and raw ratio is reported, by which the CaF2 QDs with purple, blue, green, and yellow emission can be obtained, respectively. They were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). On this basis, a novel molecular imprinting ratiometric fluorescence sensor (MIR sensor) had been constructed based on the prepared CaF2 QDs and CdTe QDs, in which the yellow emission CaF2 QDs was used as a responsive signal material and the red emission CdTe QDs was served as a reference signal material. And the ß-CD and methylacrylic acid (MAA) as bifunctional monomers were used for constructing the specific molecularly imprinted polymers (MIPs) in MIR sensor. This MIR sensor was applied for highly selective and excellent sensitive detection of 5-hydroxymethylfurfural (HMF). Under optimum conditions, it exhibited an excellent linear relationship between the fluorescence intensity ratio (I599/I625) and the concentration of HMF in the range of 0.1-6.0 µg/mL with a detection limit of 0.043 µg/mL. Finally, the established HMF-MIR sensor was successfully utilized to detect HMF in honey with satisfactory results. This work provided a reference for the application of the CaF2 QDs and the detection of the furfural substances.

Decoding the molecular water structure at complex interfaces through surface-specific spectroscopy of the water bending mode.

The structure of interfacial water determines atmospheric chemistry, wetting properties of materials, and protein folding. The challenge of investigating the properties of specific interfacial water molecules has frequently been confronted using surface-specific sum-frequency generation (SFG) vibrational spectroscopy using the O-H stretch mode. While perfectly suited for the water-air interface, for complex interfaces, a potential complication arises from the contribution of hydroxyl or amine groups of non-water species present at the surface, such as surface hydroxyls on minerals, or O-H and N-H groups contained in proteins. Here, we present a protocol to extract the hydrogen bond strength selectively of interfacial water, through the water bending mode. The bending mode vibrational frequency distribution provides a new avenue for unveiling the hydrogen bonding structure of interfacial water at complex aqueous interfaces. We demonstrate this method for the water-CaF2 and water-protein interfaces. For the former, we show that this method can indeed single out water O-H groups from surface hydroxyls, and that with increasing pH, the hydrogen-bonded network of interfacial water strengthens. Furthermore, we unveil enhanced hydrogen bonding of water, compared to bulk water, at the interface with human serum albumin proteins, a prototypical bio-interface.

Development and Characterization of Bioadhesive Film Embedded with Lignocaine and Calcium Fluoride Nanoparticles.

The formation of biofilm by Streptococcus mutans on the tooth surface is the primary cause of dental caries and periodontal diseases, and fluoride (F) has shown tremendous potential as a therapeutic moiety against these problems. Herein, we report an efficient multi-ingredient bioadhesive film-based delivery system for oral cavity to combat dental problems with an ease of administration. Thiolated chitosan-based bioadhesive film loaded with calcium fluoride nanoparticles (CaF2 NPs) and lignocaine as a continuous reservoir for prolonged delivery was successfully prepared and characterized. The polygonal CaF2 NPs with an average particle size less than 100 nm, PDI 0.253, and + 6.10 mV zeta potential were synthesized and loaded in film. The energy dispersive x-ray (EDX) spectroscopy confirmed the presence 33.13% F content in CaF2 NPs. The characterization of the three film trials for their mechanical strength, bioadhesion, drug release, and permeation enhancement suggested film B as better among the three trials and showed significant outcomes, indicating the potential application of the medicated bioadhesive film. In vitro dissolution studies revealed sustained release pattern of lignocaine and CaF2 NP following Krosmeyer-Peppas model over 8 h. Franz diffusion studies showed the prolonged contact time of film with mucosa that facilitated the transport of CaF2 NPs and lignocaine across the mucosa. Hence, the prepared bioadhesive film-based system showed good potential for better management of dental problems. Graphical Abstract.

Superior temperature sensing of small-sized upconversion nanocrystals for simultaneous bioimaging and enhanced synergetic therapy.

The upconversion nanoparticles (UCNPs) exhibit versatility applications aiming at biological domains for decades on account of superior optical characteristics. Nevertheless, the UCNPs are confronted with tremendous difficulties in biological field owing to large grain size, low fluorescence efficiency, and single function. Herein, the small-sized CaF2: Yb3+/Er3+ UCNPs coated with NaGdF4 shells (activator and inert, UCNPs-RBHA-Pt-PEG) not only burst out strong fluorescence, but also provide prominent diagnosability by taking advantage of magnetic resonance (MR) imaging as well as temperature sensing and inhibiting capability for CT26 tumor tissues based on synergetic therapy modality of photodynamic therapy (PDT) and chemotherapy. Ultimately, the tumor sizes decrease visibly after injected with UCNPs-RBHA-Pt-PEG and simultaneously irradiated with near infrared (NIR) light at low power density (0.35 W/cm2, 6 min). In summary, the small-sized and strong-fluorescent single nanoparticles with multi-functions may provide a valuable enlightenment for diagnosis and treatment of cancer in the future.

Static Solid Relaxation Ordered Spectroscopy: SS-ROSY.

A two-dimensional pulse sequence is introduced for correlating nuclear magnetic resonance anisotropic chemical shifts to a relaxation time (e.g., T1) in solids under static conditions. The sequence begins with a preparatory stage for measuring relaxation times, and is followed by a multiple pulse sequence for homonuclear dipolar decoupling. Data analysis involves the use of Fourier transform, followed by a one-dimensional inverse Laplace transform for each frequency index. Experimental results acquired on solid samples demonstrate the general approach, and additional variations involving heteronuclear decoupling and magic angle spinning are discussed.

EDX-analysis of fluoride precipitation on human enamel.

One mechanism of action for the anticaries effect of topical fluoridation is through precipitation of CaF2. In this in vitro study energy-dispersive x-ray spectroscopy (EDX) is used as a semiquantitative method to detect enamel fluoride-precipitation under the influence of acidic and neutral pH-value and absence or presence of a salivary pellicle. Crowns of 30 human caries-free third molars were quartered into four specimens and the enamel surface ground flat and polished. Two specimens each were stored in human saliva (120 minutes pellicle formation). Teeth were randomly allocated into 6 treatment groups: NaF_a (experimental acidic sodium fluoride; 12500 ppmF-, pH 4.75); NaF_n (experimental neutral sodium fluoride; 12500 ppmF-, pH 7.0); GB_a (acidic gel base; 0 ppmF-, pH 4.75); GB_n (neutral gel base; 0 ppmF-, pH 7.0); AmF-NaF_a (experimental acidic amine/sodium fluoride; 12500 ppmF-, pH 4.75); EG_a (acidic amine/sodium fluoride; Elmex Geleé, CP-GABA GmbH; 12500 ppmF-, pH 4.75). Each gel was applied for 60 seconds to one specimen with and one specimen without pellicle. Two specimens served as controls (no gel, without/with pellicle). Atomic percent (At%) of O, F, Na, Mg, P, Ca was measured by EDX. ∆At% and Ca/P-ratios were calculated. EDX could semi-quantify superficial enamel fluoride-precipitation. Only specimens treated with acidic fluoride gels showed fluoride-precipitation, a salivary pellicle tended to decrease At%F.

CaF2 nanoparticles as peroxidase mimics for rapid and sensitive detection of aldosterone.

In this work, CaF2 nanoparticles were successfully synthesized by a simple direct precipitation method and firstly used as a peroxidase mimics for rapid and high sensitive colorimetric detection of aldosterone. The CaF2 nanoparticles were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The CaF2 nanoparticles can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue product oxidized TMB (oxTMB) in the presence of H2O2 and this peroxidase-like activity of CaF2 is found out to follow Michaelis-Menten kinetics. Experiments showed that the catalytic mechanism of CaF2 nanoparticles was attributed to that it could result in the decomposition of H2O2 to produce hydroxyl radicals (•OH). The absorbance change value of the reaction system was linear with the aldosterone concentration in the range of 2.0-40.0 nM, and the detection limit was 0.6 nM. Moreover, the developed method was applied to detect aldosterone in human serum samples. It provides a new platform for enzyme functional simulation and analytical sensing research.

4-Mercaptobenzoic acid capped terbium(III)-doped CaF2 nanocrystals: a fluorescent probe for nitroaromatic pollutants.

The authors report on an energy transfer based fluorometric approach for the detection of nitroaromatic pollutants. This is achieved using 4-mercaptobenzoic acid (4-MBA)-capped CaF2:Tb3+ nanocrystals that were synthesized by a microwave procedure. 4-MBA acts as both a capping agent and a sensitizer for the Tb3+ ions in CaF2 host matrix. This approach is different from the earlier studies where Ce3+ is generally used as the sensitizer for the Ln3+ ions. The use of capping ligand as sensitizer has the feature that binding of nitroaromatics directly to the sensitizer can alter the energy transfer efficiency between the sensitizer and the Tb3+ ions. The fluorescent nanocrystal probe doped with 2% of Tb3+ displays green emission with a peak at 542 nm if photoexcited at 311 nm. The emission is quenched if the nanocrystals are exposed to nitroaromatic compounds such as 4-nitrophenol, 2,4-dinitrophenol, 2,4,6-trinitrophenol (picric acid), 4-nitrotoluene, 2,4-dinitrotoluene and 2,4,6-trinitrotoluene. These analytes also cause a (longwave/shortwave) shift in the excitation maxima which helps in identifying the individual nitroaromatic compound using single nanoprobe. The respective detection limits (by applying the 3σ/K criterion) are 0.86 µM, 0.83 µM, 0.78 µM, 0.36 µM, 1.5 µM, and 1.96 µM. Graphical abstract Schematic illustration of the use of 4-mercaptobenzoic acid (MBA)-capped CaF2:Tb3+ nanocrystals as a fluorescent nanoprobe for the detection of nitroaromatic analytes. The Tb3+ ions show strong green fluorescence via 4-MBA-induced ligand sensitization. The specific π interaction between 4-MBA capped CaF2 nanocrystals and nitroaromatics leads to reduction in the fluorescence intensity by inhibiting the energy transfer from 4-MBA to Tb3+ ion in CaF2 nanocrystals.

Ultrasound assisted synthesis of CaF2 :Eu3+ phosphor nanoparticles.

In this work, the optical and structural properties of ultrasonically prepared CaF2 :Eu3+ nanoparticles have been reported. Ultrasonically prepared CaF2 :Eu3+ phosphor shows orange, red emission bands at 591 nm and 612 nm, respectively, when it is excited by 394 light-emitting diode (LED) excitation wavelengths. Further phosphor materials are well characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) techniques to confirm the phase purity, metal oxygen (MO) bonding and crystallites size of the materials. Here synthesized materials show a tube-like structure under 100 nm resolution and 0.1 mol% is the best doping value of the europium ion (Eu3+ ) in calcium fluoride (CaF2 ) that shows highest intensity when prepared with an ultrasound assisted method.

Fluoride Binding to Dental Biofilm Bacteria: Synergistic Effect with Calcium Questioned.

It has been suggested that fluoride binding to dental biofilm is enhanced when more bacterial calcium binding sites are available. However, this was only observed at high calcium and fluoride concentrations (i.e., when CaF2 precipitation may have occurred). We assessed fluoride binding to Streptococcus mutans pellets treated with calcium and fluoride at concentrations allowing CaF2 precipitation or not. Increasing calcium concentration resulted in a linear increase (p < 0.01) in fluoride concentration only in the pellets in which CaF2 precipitated. The results suggest that CaF2 precipitation, rather than bacterially bound fluoride, is responsible for the increase in fluoride binding to dental biofilm with the increase in calcium availability.

NaYbF4@CaF2 core-satellite upconversion nanoparticles: one-pot synthesis and sensitive detection of glutathione.

A new class of core-satellite upconversion nanoparticles (UCNPs) formed through a kinetically controlled oriented attachment is presented. The core-satellite UCNPs comprising an optically active α-NaYbF4 core and several CaF2 satellites are synthesized by a one-pot sequential injection technique. Compared to conventional core-shell UCNPs, these core-satellite UCNPs show larger surface-to-volume ratios and are suitable for further surface modifications. As a proof-of-concept, a biosensing system is constructed by coating MnO2 nanosheets on the α-NaYbF4:Tm@CaF2 core-satellite UCNPs for high-sensitivity biothiol detection. These core-satellite UCNPs show great potential in the development of UCNP-based nanohybrids for biosensing, multimodal imaging and drug delivery.

Luminescent and paramagnetic properties of nanoparticles shed light on their interactions with proteins.

Nanoparticles have been recognized as promising tools for targeted drug-delivery and protein therapeutics. However, the mechanisms of protein-nanoparticle interaction and the dynamics underlying the binding process are poorly understood. Here, we present a general methodology for the characterization of protein-nanoparticle interaction on a molecular level. To this end we combined biophysical techniques including nuclear magnetic resonance (NMR), circular dichroism (CD), resonance energy transfer (RET) and surface plasmon resonance (SPR). Particularly, we analyzed molecular mechanisms and dynamics of the interaction of CaF2 nanoparticles with the prototypical calcium sensor calmodulin (CaM). We observed the transient formation of an intermediate encounter complex involving the structural region linking the two domains. Specific interaction of CaM with CaF2 NPs is driven by the N-terminal EF-hands, which seem to recognize Ca2+ on the surface of the nanoparticle. We conclude that CaF2 NP-CaM interaction is fully compatible with potential applications in nanomedicine. Overall, the methods presented in this work can be extended to other systems and may be useful to quantitatively characterize structural and dynamic features of protein-NP interactions with important implications for nanomedicine and nano-biotechnology.

Hydrogel-Templated Solid Base Catalysts for Transesterification of Soybean Oil.

A new method for utilization of hydrogel is proposed here for the preparation of solid base catalysts for the transesterification of vegetable oil. When a solution of KF is mixed with a solution of Ca(NO3)2, CaF2 is obtained and inactive as a catalyst in the transesterification of vegetable oils. The catalysts were synthesized by the sequential incorporation of KF and/or Ca(NO3)2 solutions into the hydrogel upon microwave irradiation and then the as-obtained hydrogel was calcined at 800°C for 5 hours to eliminate the template and yield catalysts for the biodiesel productions. The prepared catalysts obtained by the different ways in the incorporation of ions into the hydrogel showed different physical properties and catalytic activities in the transesterification of soybean oil. All catalysts, except the low concentration of Ca(NO3)2, exhibiting the high activity yielding more than 90% FAME after 1 hour at 65°C, using oil to methanol molar ratio of 1:15 and 10 wt% of catalyst amounts.

Calcium-based biomaterials for diagnosis, treatment, and theranostics.

Calcium-based (CaXs) biomaterials including calcium phosphates, calcium carbonates, calcium silicate and calcium fluoride have been widely utilized in the biomedical field owing to their excellent biocompatibility and biodegradability. In recent years, CaXs biomaterials have been strategically integrated with imaging contrast agents and therapeutic agents for various molecular imaging modalities including fluorescence imaging, magnetic resonance imaging, ultrasound imaging or multimodal imaging, as well as for various therapeutic approaches including chemotherapy, gene therapy, hyperthermia therapy, photodynamic therapy, radiation therapy, or combination therapy, even imaging-guided therapy. Compared with other inorganic biomaterials such as silica-, carbon-, and gold-based biomaterials, CaXs biomaterials can dissolve into nontoxic ions and participate in the normal metabolism of organisms. Thus, they offer safer clinical solutions for disease theranostics. This review focuses on the state-of-the-art progress in CaXs biomaterials, which covers from their categories, characteristics and preparation methods to their bioapplications including diagnosis, treatment, and theranostics. Moreover, the current trends and key problems as well as the future prospects and challenges of CaXs biomaterials are also discussed at the end.