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Metal phosphonates containing acidic groups exhibit a wide range of proton conduction properties, which may enhance the performance of membrane electrode assemblies (MEAs). In this work, focus is placed on proton conduction properties of coordination polymers derived from the combination of lanthanide ions with a phosphonate derivative of taurine (2-[bis(phosphonomethyl)amino]ethanesulfonic acid, HSP). High-throughput hydrothermal screening (140 °C) was used to reach optimal synthesis conditions and access pure crystalline phases. Seven compounds with the composition Ln[H(OPCH)-NH-(CH)-SO]·2HO were isolated and characterized, which crystallize in two different structures, monoclinic m-LaHSP and orthorhombic o-LnHSP (Ln = Pr, Nd, Sm, Eu, Gd, and Tb), with unit cell volumes of ∼1200 and ∼2500 Å, respectively. Their crystal structures, solved ab initio from X-ray powder diffraction data, correspond to different layered frameworks depending on the Ln cation size. In the orthorhombic series, o-LnHSP, the sulfonate group is noncoordinated and points toward the interlayer space, while for m-LaHSP, both phosphonate and sulfonate groups coordinate to the Ln centers. As a consequence, different H-bonding networks and proton transfer pathways are generated. Proton conductivity measurements have been carried out between 25 and 80 °C at 70-95% relative humidity. The Sm derivative exhibits a conductivity of ∼1 × 10 S·cm and activation energy characteristic of a Grotthuss-type mechanism for proton transfer. Preliminary MEA assays indicate that these layered lanthanide sulfophosphonates assist in maintaining the proton conductivity of Nafion membranes at least up to 90 °C and perform satisfactorily in single proton-exchange membrane fuel cells., The work at UMA was funded by MAT2016-77648-R research grant (Spain) and by Junta de Andalucía through the P12- FQM-1656 research project. M.B.-G. thanks UMA Research Plan for financial support. The work at CSIC-Madrid was funded by PROTONCELL ENE2017-86711-C3-1-R and REPICOMES ENE2017-90932-REDT and MAT2016-81001- P. The work at UoC was supported by grants from the Research Committee of the University of Crete, ELKE (grant no. KA 10329).

The interactions of six homologous diphosphonate additives, methylamine-N,N-bis(methylenephosphonate) (MBMP, C1-D), ethylamine-N,N-bis(methylenephosphonate) (EBMP, C2-D), butylamine-N,N-bis(methylenephosphonate) (BBMP, C4-D), hexylamine-N,N-bis(methylenephosphonate) (HBMP, C6-D), octylamine-N,N-bis(methylenephosphonate) (OBMP, C8-D), dodecylamine-N,N-bis(methylenephosphonate) (DBMP, C12-D), with carbon steel surfaces are studied by XPS at pH = 3.0. Structurally, all additives possess two methylenephosphonate moieties connected to a single N atom. The third substituent on N is a non-polar, variable-length alkyl chain, –(CH2)xCH3, where x = 0 (C1-D), 1 (C2-D), 3 (C4-D), 5 (C6-D), 7 (C8-D), and 11 (C12-D). XPS studies (on pristine solid diphosphonate samples and also on carbon steel specimens, immersed in aqueous solutions), indicate significant deprotonation of the diphosphonic acid molecules upon interaction with the metallic surface. They also prove that this surface interaction results in adsorption on the surface via the deprotonated phosphonic acid moieties. The adsorption of inhibitors on the metal surface was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The changes detected in the charge transfer resistance (Rct) and constant phase element (CPE) independently confirm inhibitor adsorption on metal surface. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy was used to investigate the nature of deposited film. Small alkyl chain diphosphonates (C1-D, C2-D and C4-D) exhibited lower corrosion resistance due to the thin, porous and/or incomplete layer formed on carbon steel surface. Longer alkyl chain molecules (C6-D, C8-D and C12-D) were found to adsorb more efficiently and form a more organized and thicker layer. The best results were obtained in the case of C8-D (lower corrosion current, higher Rct and surface coverage). In the presence of C8-D the corrosion rate was reduced by a factor of 6.

(Poly)phosphonic acids constitute an exciting family of phosphorus compounds. One of the attractive attributes of these molecules is the rich chemistry of the phosphonate moiety, and, in particular, its high affinity for metal ions and mineral surfaces. Whether the phosphonate group belongs to a “small” molecule or to a polymeric matrix, phosphonate-containing compounds have found a phalanx of real-life applications. Herein, we address a special category of phosphorus compounds called bisphosphonates (BPs, a.k.a. “-dronates”) and also phosphonate containing polymers. The success of BPs in mitigating osteoporosis notwithstanding, these “-dronate” drugs present a number of challenges. Nevertheless, the main drawback of BPs is their limited oral bioavailability. It is, therefore, imperative to design and fabricate “smart” systems that allow controlled delivery of the active BP agent. Here, easy-to-prepare drug delivery systems are presented based on silica gels. These have been synthesized, characterized, and studied as hosts in the control release of several BP drugs. They exhibit variable release rates and final % release, depending on the nature of bisphosphonate (side-chain length, hydro-philicity/-phobicity, water-solubility), cations present, pH and temperature. These gels are robust, injectable, re-loadable and re-usable. Furthermore, alternative drug delivery systems are presented that are based on metal-organic frameworks (MOFs). In these biologically acceptable inorganic metal ions have been incorporated, together with BPs as the organic portion. These materials have been synthesized, characterized, and studied for the self-sacrificial release (by pH-driven dissolution) of the BP active ingredient. Several such materials were prepared with a variety of bisphosphonate drugs. They exhibit variable release rates and final % release, depending on the actual structure of the metal-bisphosphonate material. Lastly, we will present the use of phosphonate-grafted polymers as scale inhibitors for water treatment applications.

We study the interaction of six systematically varied tetraphosphonate molecules with carbon steel surfaces by XPS at pH 3. All tetraphosphonates [EDTMP (C2), TDTMP (C4), HDTMP (C6), ODTMP (C8) and DDTMP (C12)] belong to the aminomethylene-phosphonate family, and they possess systematically elongated backbone (from two to twelve methylene groups separating the N atoms). XPS studies were performed on powdered samples and also on immersed carbon steel specimens in aqueous solutions. The XPS results also suggest that the tetraphosphonic acid molecules become significantly deprotonated upon interaction with the carbon steel surface and that the surface interaction of the tetraphosphonic acid family leads to additive adsorption on the steel surface via the phosphonate groups. The mode of corrosion inhibition was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The changes observed in the impedance parameters, like charge transfer resistance (Rct) and constant phase element (CPE) confirm the strong adsorption on the metal surface. The nature of the protective layer formed on the carbon steel surface was examined by Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and optical microscopy.

The formation, precipitation, and deposition of so-called “magnesium silicate” in geothermal waters have been subjects of intense interest. Such scaling poses a severe threat to the smooth process ...

M.T is supported by funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 663830. In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective article is to provide a critical overview of the topics discussed during the workshop, which are divided into two main areas: synthesis and characterisation, and applications. In terms of synthetic methods, there has been a push towards cleaner and more efficient approaches. This has led to the introduction of high-throughput synthesis and mechanochemical synthesis. The recent success of metal–organic frameworks has also promoted renewed interest in the synthesis of porous metal phosphonates and phosphinates. Regarding characterisation, the main advances are the development of electron diffraction as a tool for crystal structure determination and the deployment of in situ characterisation techniques, which have allowed for a better understanding of reaction pathways. In terms of applications, metal phosphonates have been found to be suitable materials for several purposes: they have been employed as heterogeneous catalysts for the synthesis of fine chemicals, as solid sorbents for gas separation, notably CO2 capture, as materials for electrochemical devices, such as fuel cells and rechargeable batteries, and as matrices for drug delivery. Publisher PDF

The structural variability of two series of Mg2+- and Zn2+- 2-hydroxyphosphonoacetates have been studied in the range of 25–80°C and 95% relative humidity in order to correlate the structure with the proton conductivity properties. In addition to selected previously reported 1D, 2D and 3D materials, a new compound, KZn6(OOCCH(OH)PO3)4(OH)·5H2O (KZn6-HPAA-3D), has been prepared and thoroughly characterized. The crystal structure of this solid, solved ab initio from synchrotron X-ray powder diffraction data, consists of a negatively charged 3D framework with K+ ions, as compensating counterions. It also contains water molecules filling the cavities in contrast to the potassium-free 3D anhydrous NH4Zn(OOCCH(OH)PO3) (NH4Zn-HPAA-3D). In the range of temperature studied, the 1D materials exhibit a 1D→2D solid-state transition. At 80°C and 95% RH, the 2D solids show moderate proton conductivities, between 2.1×10−5 S·cm−1 and 6.7×10−5 S·cm−1. The proton conductivity is slightly increased by ammonia adsorption up to 2.6×10−4 S·cm−1, although no ammonia intercalation was observed. As synthesized KZn6-HPAA-3D exhibits a low proton conductivity, 1.6×10−6 S·cm−1, attributed to the basic character of the framework and a low mobility of water molecules. However, this solid transforms to the 2D phase, Zn(OOCCH(OH)PO3H)·2H2O, upon exposure to dry HCl(g), which enhances the proton conductivity with respect to the as-synthesized 2D material (4.5×10−4 S·cm−1). On the other hand, NH4Zn-HPAA-3D exhibited a higher proton conductivity, 1.4×10−4 S·cm−1, than the K+ analog.

Silicic acid polycondensation leads to the formation of amorphous silica. This process is of great importance to the survival of certain living organisms, such as diatoms and sponges, but presents a significant problem in various production facilities that use water for heating or cooling. In the latter, amorphous silica can be a recalcitrant deposit that can hamper proper system operation. Hence, inhibition of silicic acid polycondensation by chemical inhibitors is an intensely sought strategy by water system operators. In this manuscript, we report the inhibitory effect of zwitterionic phosphonated analogs (PPEI’s) of the cationic polymeric chemical additive polyethyleneimine (PEI) in mildly supersaturated silica solutions (500 ppm/8.3 mM “Si”) at pH=7. The inhibition efficiency of PPEI’s depends on a variety of parameters, such as concentration and degree of phosphonomethylation of the parent PEI polymer.

In this paper the effect of two synthetic, pH-responsive co-polymers, U-PVPyPEGMA-H and Q-PVPyPEGMA-H, with pyridine and polyethylene glycol grafts, on silicic acid polymerization is presented. The scope of this work was to evaluate the impact of several experimental parameters, such as working pH, polymer MW, polymer concentration, state of the pyridine ring (non-protonated, protonated, quaternized) on the anticipated inhibitory and/or enhancement activity with regards to silicic acid autocondensation to produce amorphous silica. It was found that pH substantially influences the silicification reaction, either in the absence or presence of the polymers. pH also affects the protonation state of the pyridine N atom. For example, pH switching from 5.0 to 7.0 transforms U-PVPyPEGMA-H from a silica formation catalyst (pH = 5.0) to a silicic acid stabilizer (pH = 7.0). Concentration enhances the role of the polymers, either as silicic acid stabilizers or catalysts. Polymer MW appears to have no effect on their activity either as stabilizers or catalysts. Polymer entrapment in the precipitated amorphous silica matrix occurs under these experimental conditions, affecting particle size, morphology and tendency for aggregation. The state of the N atom on the pyridine ring (non-protonated, protonated, quaternized) exhibits a profound effect on silicic acid autocondensation to produce amorphous silica. Based on our results, a “free” (non-protonated) pyridine ring induces silica inhibition, whereas protonation or quaternization enhances silica formation.

Phosphonate ligands demonstrate strong affinity for metal ions. However, there are several cases where the phosphonate is found non-coordinated to the metal ion. Such compounds could be characterized as salts, since the interactions involved are ionic and hydrogen bonding. In this paper we explore a number of such examples, using divalent metal ions (Mg2+, Ca2+, Sr2+ and Ni2+) and the phosphonic acids: p-aminobenzylphosphonic acid (H2PABPA), tetramethylenediamine-tetrakis(methylenephosphonic acid) (H8TDTMP), and 1,2-ethylenediphosphonic acid (H4EDPA). The compounds isolated and structurally characterized are [Mg(H2O)6]&middot, [HPABPA]2&middot, 6H2O, [Ca(H2O)8]&middot, [HPABPA]2, [Sr(H2O)8]&middot, [HPABPA]2, [Mg(H2O)6]&middot, [H6TDTMP], and [Ni(H2O)6]&middot, [H2EDPA]&middot, H2O. Also, the coordination polymer {[Ni(4,4&rsquo, bpy)(H2O)4]&middot, H2O}n was synthesized and characterized, which contains a bridging 4,4&rsquo, bipyridine (4,4&rsquo, bpy) ligand forming an infinite chain with the Ni2+ cations. All these compounds contain the phosphonate anion as the counterion to charge balance the cationic charge originating from the metal cation.

Numerous publications report the existence of intracellular “Si” storage pools in diatoms representing intracellular concentrations of ca. 19–340 mM depending on the species. “Si” storage pools in diatom cells, if present, are supposed to accumulate “Si” for the production of new valves. The accumulated “Si” is then transported into the silicon deposition vesicle (SDV) where the new cell wall is synthesized. Interestingly, the reported concentrations of intracellular “Si” within the storage pool sometimes strongly exceed the solubility of monosilicic acid (ca. 2 mM pH in situ supramolecular assemblies that can also affect the condensation of silicic acid. Possible mechanisms for their effect on the condensation reaction are presented, with an eye towards their relevance to the “Si pools,” from a bioinspired/biomimetic point of view.

[EN] The chemistry of metal phosphonates has been progressing fast with the addition of new materials that possess novel structural features and new properties, occasionally in a cooperative manner. In this paper, we report a new family of functional lanthanide-carboxyphosphonate materials. Specifically, the lanthanide is La, Ce, Pr, Sm, Eu, Gd, Tb, or Dy and the carboxyphosphonate ligand is 2-hydroxyphosphonoacetic acid (H(3)HPA). All reported LnHPA compounds, Ln(3)(H0.73O3PCHOHCOO)(4)center dot xH(2)O (x = 15-16), crystallize in the orthorhombic system. Two types of structures were isolated: series I and II polymorphs. For both series, the three-dimensional (3D) open frameworks result from the linkage of similar organo-inorganic layers, in the ac-plane, by central lanthanide cations, which yield trimeric units also found in other metal-HPA hybrids. Large oval-shaped 1D channels are formed by the spatial separation of the layers along the b-axis and filled with lattice water molecules. LnHPA materials undergo remarkable crystalline-to-amorphous-to crystalline transformations upon dehydration and rehydration cycles, as confirmed by thermodiffraction and NMR spectroscopy. The highest proton conductivity was observed for GdHPA (series II), 3.2 X 10(-4) S cm(-1) at 98% RH and T = 21 degrees C. The dehydration-rehydration chemistry was also followed by photoluminescence spectroscopy. It was shown that loss and reuptake of water molecules are accompanied by clear changes in the photoluminescence spectra and lifetimes of the Eu analog (series II). Our present results reveal a wide family of well-characterized, multifunctional lanthanide-based phosphonate 3D-structured metal-organic frameworks (MOFs) that show reversible crystalline-to-amorphous-to-crystalline transformations and, at the same time, exhibit high proton conductivity., The work at UMA was funded by MAT2010-15175 research grant (Spain), which is cofunded by FEDER. The work at the UoC was supported by a grant from the Research Committee of the University of Crete, ELKE, (KA 3517). The project "Factoria de Crystalizacion, CONSOLIDER INGENIO-2010" provided X-ray structural facilities for this work.

The catalytic role of Mg2+ ions in the polycondensation of silicic acid to form amorphous silica has been investigated in detail. This behavior is pH-dependent. As pH increases (herein, the three p...

The effect of various fluorine-containing chemical additives on the dissolution of colloidal silica is systematically studied. These silica scale dissolvers are ammonium bifluoride (NH4·HF2), ammonium fluoride (NH4F), sodium tetrafluoroborate (NaBF4), and disodium fluorophosphate (Na2PO3F). The most effective dissolver was NH4·HF2, which was extensively studied at the pH range 2–7. The highest dissolution efficiency was demonstrated in the pH range 2–4. The dissolution capability of Na2PO3F was monitored not by the silicomolybdate method, but on the basis of a weight-loss approach. It showed substantial dissolution ability at pH’s 7 and 9.

Phosphonium-based bolaamphiphiles have been found to stabilise silicic acid beyond its solubility limit (∼150 ppm). Three bolaamphiphiles have been tested having a quaternary phosphonium group on each end, linked by a number of ethylene oxide (EO) units (5, 21, and 91, resulting in PEGP+-200, PEGP+-1000, and PEGP+-4000 dicationic bolaamphiphiles, respectively). Specifically, the ability of PEGP+-200, PEGP+-1000, and PEGP+-4000 to retard silicic acid condensation at circumneutral pH in aqueous supersaturated solutions was explored. The goal was to investigate the effect of P-based cationic molecules, EO chain length (and by inference the P-to-P spatial separation) on silicic acid stabilisation performance. PEGP+-200 showed no stabilisation ability in “long term” tests (i.e. 24, 48, 72 h). For PEGP+-1000, and PEGP+-4000, it was discovered that in “short-term” (0–8 h) and “long term” (> 24 h) studies the inhibitory activity is additive dosage-dependent, demonstrating that there is a clear increase in stabilisation ability upon phosphonium PEG dosage increase. Specifically, soluble silicic acid levels reach 420 ppm and 400 ppm after 24 h in the presence of 150 ppm PEGP+-1000, or PEGP+-4000, respectively. PEG additives (PEG-200, PEG-1000, and PEG-4000) containing no phosphonium cations were also tested. Although PEG-200 and PEG-1000 showed no silicic acid stabilisation effects, PEG-4000, surprisingly, was a strong stabiliser. In fact, the inhibitory efficiencies of PEGP+-4000 and PEG-4000 were virtually identical. These results present strong proof that the polyethylene chain beyond a certain length strongly contributes to silicic acid stabilisation. Lastly, the effects of these boloamphiphiles on silica particle morphology were investigated by SEM. Spherical particles and their aggregates, irregularly shaped particles and porous structures, are obtained depending on the additive.

The effect of various environmentally friendly chemical additives and natural products on the dissolution of amorphous silica (Aerosil 200 and laboratory-synthesized, SSD) is studied. The silica scale dissolvers tested include the following: ascorbic acid (vitamin C, ASC), citric acid (CITR), carboxymethyl inulin (CMI), 3,4-dihydroxybenzoic acid (catechuic acid, DHBA), 3,4,5-trihydroxybenzoic acid (gallic acid, GA), dopamine hydrochloride (DOPA), iminodiacetic acid (IDA), histidine (HIST), phenylalanine (PHALA), and malic acid (MAL). The chemical structures of these chemical additives contain potentially dissolution-active moieties, such as 1,2-dihydroxyethylene (ASC), α-hydroxycarboxylate (MAL and CITR), catecholate (DHBA, GA, and DOPA), α-aminocarboxylate (HIST and PHALA, both aminoacids), and finally carboxy-modified fructofuranose units (CMI). It was found that all studied molecules showed variable dissolution efficiency, with MAL, CMI, HIST, and PHALA being the slowest/least effective dissolvers, and...

The effect of various chemical additives (small molecules and polymers) on the dissolution of two kinds of colloidal silica (Aerosil 200 and laboratory-synthesized, SSD) is systematically studied at pH 10. The silica scale dissolvers tested are 5-carboxybenzotriazole (CBZT), amino-tris(methylene phosphonic acid) (AMP), a phosphino-polycarboxylic acid (PPCA), diethylenetriamine pentacarboxylic acid (DETPA), a proprietary polymer (Genesol 40), poly(acrylic acid) (PAA), ethylenediamine-tetrakis(methylenephosphonic acid) (EDTMP), phosphonobutane-1,2,4-tricarboxylic acid (PBTC), sodium metaborate, and N-phosphonomethylimino-diacetic acid (PMIDA). Of the polymeric additives only Genesol 40 shows some dissolution activity, dissolving ∼280 ppm silica at 10 000 ppm dosage after 72 h. PBTC and DETPA are the best-performing additives of all those tested. PBTC is effective even at the 2500 ppm dosage, as it solubilizes ∼290 ppm silica after 72 h. Its efficiency is dosage-dependent. DETPA is also an effective silica d...

The influence of a number of N-containing macromolecules on the polycondensation of silicic acid to form amorphous silica is studied by the combined use of 29Si NMR spectroscopy and the silicomolybdate test. Polymeric additives include poly(allylamine hydrochloride) (PAH), the poly(aminoamide) dendrimer of generation 1 (PAMAM-1), poly(ethyleneimine) (PEI), and poly(vinylpyrrolidone) (PVP). These studies were performed under biologically relevant conditions (pH 5.4 and 7.0) using aqueous solutions of isotope-labeled sodium [29Si]metasilicate as the precursor compound. It was found at pH 5.4 that all additives accelerate silicic acid polycondensation, except for PVP, which exerts a minor silicic acid stabilizing effect. At pH 7.0, polycondensation is much faster in the presence of PAMAM-1, PEI, and PAH. However, PVP significantly stabilizes mono- and disilicic acid. Silica precipitates were also studied by 29Si NMR spectroscopy. The effect observed for PVP is striking and indicates that the silicic acid pol...

Herein, the controlled release of etidronic acid (hydroxyethylidene-bis(phosphonic) acid), an important drug for osteoporotic conditions, immobilized onto cationic polymeric matrices, such as polyethyleneimine (PEI) or cationic inulin (CATIN) is reported. Several CATIN- and PEI-etidronate composites have been synthesized at various pH regions and characterized. Tablets with starch as the excipient containing the active ingredient (polymer-etidronate composite) were prepared, and the controlled release of etidronate was studied at aqueous solutions of pH 3 (to mimick the pH of the stomach) for 8 h. All studied composites showed a delayed etidronate release in the first 4 h, compared to the "control" (a tablet containing only starch and etidronic acid, without the polymer).

Reactions of M2+ (M = Mg2+ (1), Ca2+ (2), Sr2+ (3), or Ba2+ (4)) salts with R,S-hydroxyphosphonoacetic acid (HPAA) in aqueous solutions of pH 2.0−2.7 at a 1:1 ratio yield hydrated M−HPAA layered or three-dimensional coordination polymers with varying degrees of hydration (metal-coordinated water or lattice water). The crystal structures of 3 (two different phases, 3a and 3b, formed at slightly different pH) and 4 have been determined by single-crystal X-ray crystallography. Both enantiomers (R and S) of HPAA are incorporated in these metal−HPAA materials. Compounds were also characterized by a plethora of other techniques (ATR-IR, SEM, TGA, elemental analyses, powder XRD). Corrosion experiments were carried out at pH 2.0 and 7.3 to study the effect of combinations of externally added Sr2+ or Ba2+ and HPAA (1:1 ratio) on corrosion rates of carbon steel. It was found that at pH 2.0 Sr/HPAA or Ba/HPAA 1:1 combinations are not able to inhibit corrosion. However, at pH 7.3 quantitative corrosion inhibition is ...

The inhibition performance of three synthetic amine/ammonium-containing cationic polymers in colloidal silica particle growth is reported. The three additives are compared to control (no additives present during silicate polymerization). The three polymers, polyethyleneimine (PEI), polyallylamine hydrochloride (PALAM) and poly(acrylamide-co-diallyl-dimethylammonium chloride) (PAMALAM), were screened in two sets of experiments: long term (24–72 h) and short term (0–8 h). Silica inhibition performance is profoundly dependent on the polymeric additive dosage. The most effective dosages were found to be 10 ppm for PEI, 20 ppm for PALAM and 80–100 ppm for PAMALAM. The inhibitory efficiency of PEI (at 10 ppm dosage) reaches 55% at 24 h (inhibitory efficiency is defined as reactive silica in ppm at the time of measurement divided by 500 ppm, times 100). PALAM reches 65% inhibitory activity at 20 ppm, after 24 h. PAMALAM at 80 ppm dosage shows 60% inhibition. Inhibitory activity drops on longer silicate polymerization times (48 and 72 h). All three inhibitors show activity higher than the control during the first 8 h, exhibiting small variations in performance.

Mineral scale deposits in industrial waters supporting a number of process industries are a major problem that causes unexpected shutdowns and costly chemical or mechanical cleaning operations. Some deposits, although less common, are exceptionally troublesome. These include silica and magnesium silicate. Accumulation of these deposits greatly diminishes system performance. Scale prevention can be achieved by use of scale inhibitors that are added to any given treatment in minute (parts per million) quantities. Use of environmentally friendly water additives for colloidal silica scale control is a topic of great interest and intense research efforts in our laboratory. Inhibition and dispersion are two generic approaches for preventing silica scale and fouling. Inhibition stops scaleforming precipitates from forming, whereas dispersion keeps scale particles from being attached onto critical surfaces. We have pursued silicate polymerization inhibition by use of “green”, environmentally-friendly cationic macromolecules. These utilize inulin as the backbone, which has been chemically modified to introduce quaternary ammonium moieties. Three CATIN polymers (CATIN = cationic inulin) were tested: CATIN-1 (DS = 0.22), CATIN-2 (DS = 0.86), CATIN-3 (DS = 1.28), DS = degree of substitution at dosages 40, 80 and 100 ppm in supersaturated silicate solutions (500 ppm) adjusted to pH 7 for 8 h. Measurements for soluble silicate were performed every hour. After 8 h polymerization time, CATIN-1 achieves stabilization of 275 ppm silicate (~90 ppm above the control), whereas CATIN-2 and CATIN-3 exhibit virtually identical performance, stabilizing ~340 ppm silicate (~150 ppm above the control). Inhibitor dosage increase to 80 ppm does not induce any additional inhibitory performance. Further inhibitor dosage increase to 100 ppm appears to have additional detrimental effects on inhibitory activity. CATIN-1 maintains 247 ppm soluble silicate (only ~50 ppm above the control), CATIN-2 keeps ~300 ppm soluble

In this paper the preparation and characterization of some chelating resins, phosphonate grafted on polystyrene divinylbenzene supports, are reported. The resins were prepared by an Arbuzov-type reaction between chloromethyl polystyrene-divinylbenzene copolymers and triethylphosphite, yielding the phosphonate ester copolymer (resin A). This can be hydrolyzed by HCl to yield the phosphonate/phosphonic acid copolymer (resin B). The phosphonate resins A and B were characterized by determination of the phosphorus content, infrared spectrometry, and thermal analysis. The total sorption capacity of the phosphonate ester functionalized resin (A) and phosphonate/phosphonic acid functionalized resin (B) for divalent metal ions such as Ca 2+ , Cu 2+ , and Ni 2+ was studied in aqueous solutions. Resin A retains 3.25 mg of Ca 2+ /g of copolymer and 2.75 mg of Cu 2+ /g of copolymer, but retains no Ni 2+ at pH 1. On the other hand, resin B retains 8.46 mg of Ca 2+ /g of copolymer, 7.17 mg of Cu 2+ /g of copolymer, and no Ni 2+ at pH 1. Efficient Ni 2+ retention was observed at pH 7 only for the phosphonate/phosphonic acid functionalized resin (B) at the level of 19 mg of Ni 2+ /g of polymer B. Polymer A was incapable of retaining Ni 2+ at pH 7.

Mineral scale deposits such as calcium carbonate and phosphate, calcium oxalate, barium and strontium sulfate, magnesium silicate and others and colloidal inorganic species such as silica present important challenges for process water applications. When silica is left uncontrolled it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit silica formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. Another challenge is corrosion of critical metal surfaces of industrial equipment. Last but not least, biofouling due to the development of microorganisms. This paper is focused on the presentation of the general scope of these problems and their solutions. More specifically, it concentrates on (a) inhibition of colloidal silica formation, (b) colloidal silica dissolution, and (c) metallic corrosion, in water applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers, polyethyloxazoline and polyethyleneimine polymers. For silica dissolution the dissolvers tested were carboxymethyl inulin (CMI), Genesol 40 (a proprietary blend of additives), polyacrylic acid. In principle, silica inhibition is a function of time and inhibitor dosage. Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. Mild steel corrosion inhibition has been achieved by synergistic use of zinc ions and polyphosphonate anions that create protective films.

Supersaturated process waters high in silicates frequently result in deposition of colloidal silica or metal silicate salts. Silica cannot be inhibited by conventional phosphonate mineral scale inhibitors. Chemical cleaning poses hazards and requires operational shut-downs. This paper is focused on a dual approach for silica scale control, inhibition of colloidal silica formation and colloidal silica dissolution in water technology applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers (PAMAM) and polyethyleneimine (PEI), in combination with carboxymethyl inulin (CMI) and polyacrylate (PAA) polymers. In principle, silica inhibition is a function of time and inhibitor dosage. Amine-terminated PAMAM-1 and 2 dendrimers as well as PEI combined with anionic polymers, such as CMI and PAA, seem to have a significant inhibitory effect on silica formation, most likely at its earlier stages where the reaction products are oligomeric silicates. CMI and PAA assist the inhibitory action of PAMAM-1 and 2 and PEI by alleviating formation of insoluble SiO2-PAMAM precipitates. This most likely occurs by partial neutralization of the positive charge that exists in –NH+3 surface groups. Increase of anionic polymer dosage above a certain threshold has a detrimental effect on the activity of the cationic inhibitors. In that case the polymer’s negative charge “overwhelms” the cationic charge of the inhibitor and poisons its inhibition ability. For silica dissolution, acetic, oxalic, citric acids, histidine and phenylalanine were used as potential replacements of ammonium bifluoride (NH4F·HF). Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. This paper continues our research efforts in the discovery, design and application of antiscalant additives that have mild environmental impact. These chemicals are also known as “green additives”.

Organic, phosphorus‐based additives are commonly used in water treatment technologies such as mineral scale and corrosion inhibitors, and dispersing agents. Phosphonates find extensive use as anti‐precipitation inhibitors for sparingly soluble salts such as calcium carbonates and phosphates, calcium/barium/strontium sulfates and others, commonly formed in supersaturated process waters in a wide spectrum of industrial applications. In open recirculating cooling water systems strong oxidizing biocides (eg. ClO−, BrO−, etc.) are also added to control microbiological growth but have detrimental effects on other water treatment chemicals that are sensitive to oxidative degradation. In this paper we report the effect of a hypobromite‐based biocide towards the scale inhibitor AMP (amino‐tris‐(methylene phosphonate)). AMP reacts rapidly with the biocide at room temperature. AMP degradation continues, but it slowly reaches a plateau after 1000 minutes. Even after 50 h the reaction time, only 20% of AMP ha...

This paper reports the inhibition efficiency of combinations of amine-terminated polyaminoamide (PAMAM) dendrimers of generation 1 and 2 and anionic polyelectrolytes in colloidal silica particle growth. The polyelectrolytes studied were PAA = polyacrylate (low MW is 2 KDa, high MW is 450 KDa), PAM-co-AA = poly(acrylamide-co-acrylate) of MW 200 KDa, CMI = carboxymethylinulin (proprietary MW, between 2 and 3 KDa). The principle findings are summarized as follows: (1) PAMAM-1 and -2 dendrimers are effective inhibitors of silica growth at 40 ppm dosage levels. (2) The effect of anionic polycarboxylates on the inhibitory activity of PAMAM-1 and PAMAM-2 is dosage-dependent. They do not affect PAMAM-1 inhibitory activity; they increase that of PAMAM-2 at low dosage (20 ppm) but exhibit detrimental effects at high dosage (>40 ppm), with CMI exerting no adverse effects at any dosage. (3) Negative charge density on the polymer is directly proportional to inhibitor activity deterioration. (4) Addition of polymer pr...

A series of metal−phosphonate organic−inorganic polymeric hybrid materials are synthesized, structurally characterized, and evaluated for their anticorrosion properties for the protection of carbon steels. These materials are Zn−AMP (where AMP = amino-tris(methylenephosphonate)), Zn−HDTMP (where HDTMP = hexamethylenediamine-tetrakis(methylenephosphonate)), and Ca−PBTC (where PBTC = 2-phosphonobutane-1,2,4-tricarboxylate)). Their structures are described and compared. Their corrosion inhibition performances are also compared, and some interesting conclusions are drawn that relate molecular structure to inhibitory activity.

This paper reports the inhibition efficiency of a family of synthetic amine/ammonium-containing cationic polymers in colloidal silica particle growth. Three polymeric additives were tested and compared to control samples. These are polyethyleneimine (PEI), polyallylamine hydrochloride (PALAM), and poly(acrylamide-co-diallyldimethylammonium chloride) (PAMALAM). Two sets of experiments were carried out: long term (0−72 h) and short term (0−8 h). There is a strong dependence of silica inhibition on additive dosage. The optimum dosages are 10 ppm for PEI, 20 ppm for PALAM, and 80−100 ppm for PAMALAM. PEI (at 10 ppm dosage) reaches 55% inhibitory efficiency at 24 h (defined as reactive silica in ppm at the time of measurement divided by 500 ppm, or multiplied by 100 for % efficiency). PALAM shows 65% inhibitory activity at 20 ppm, after 24 h. PAMALAM at 80 ppm dosage exhibits 60% inhibition. Inhibitory activity is reduced upon longer silicate polymerization times (48 and 72 h). Inhibition within the first 8 h...

This paper is focused on a dual approach for silica scale control, inhibition and dissolution by use of designed chemical approaches. Inhibitors that are tested include the polyaminoamide STARBURST dendrimers (PAMAM) of generations 0.5, 1.0, 1.5, 2.0, and 2.5. Of these, only the NH2-terminated ones (PAMAM-1.0 and 2.0) show significant inhibitory activity, in contrast to COOH-terminated ones (PAMAM-0.5, 1.5, and 2.5), which show virtually no inhibition performance. The synergism between the above dendrimers and an anionic polyelectrolyte (poly(acrylamide-co-acrylate) copolymer) is also described. Addition of poly(acrylamide-co-acrylate) copolymer in silica supersaturated solutions containing PAMAM-1 or 2 alleviates the appearance of silica-PAMAM insoluble precipitates, resulting in stable colloids. The paper also describes silica dissolution approaches, as an alternative to inhibition, by using nonhazardous additives based on polycarboxylates with one to five −COOH groups (acetate, oxalate, citrate, diethy...

Colloidal silica (SiO2) and other sparingly soluble salts such as CaCO3 present a challenge for desalination systems used for brackish or seawater desalting. When SiO2 is left uncontrolled, it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit SiO2 formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. CaCO3 is also troublesome. This paper focused on silica and CaCO3 formation, deposition and inhibition with designed chemical approaches in water applications that require the use of membranes. It also describes SiO 2 scale removal by dissolution approaches with environmentally friendly and non-hazardous chemical additives. The general scope of silica formation and inhibition in waters relevant to desalination systems is also discussed. This paper continues our research efforts in the discovery, design and application of anti-scalant additives that have a mild environmental impact. These chemicals are also known as “green additives”. In light of increasing environmental concerns for discharge of saline water coming from desalination systems, this research is of significant interest.

Dendrimers have attracted immense attention during the last decade due to their interesting properties both from a basic and an applied research viewpoint. Encapsulation of metal nanoparticles for catalysis, drug delivery and light harvesting are only some applications of dendrimers that are breaking new ground. A novel application of dendrimer technology is described in the present paper that relates to industrial water treatment. Industrial water systems often suffer from undesirable inorganic deposits. These can form either in the bulk or on metallic surfaces, such as heat exchangers or pipelines. Silica (SiO2) scale formation and deposition is a major problem in high-silica-containing cooling waters. Scale prevention rather than removal is highly desired. In this paper, benchtop screening tests on various silica inhibition chemistries are reported, with emphasis on materials with a dendrimeric structure. Specifically, the inhibition properties of commercially available STARBURST  polyaminoamide (PAMAM) dendrimers generations 0.5, 1, 1.5, 2, and 2.5 are investigated in detail together with other commonly-used scale inhibitors. Experimental results show that inhibition efficiency largely depends on structural features of PAMAM dendrimers such as generation number and nature of the end groups. PAMAM dendrimers are effective inhibitors of silica scale growth at 40ppm dosage levels. PAMAM dendrimers also act as silica nucleators, forming SiO2-PAMAM composites. This occurs because the SiO2 formed by incomplete inhibition interacts with cationic PAMAM-1 and -2. The general scope of silica formation and inhibition in industrial waters is also discussed.  2005 Society of Chemical Industry

Colloidal silica (SiO 2 ) is perhaps the most undesirable inorganic deposit formed in process industrial waters, either in bulk or on surfaces, such as membrane heat exchangers or pipelines. Conventional mineral scale inhibitors do not inhibit its formation. Chemical cleaning is difficult and not free from hazards. Research on silica scale formation and prevention is on-going and has led to various chemical approaches. This paper is focused on silica formation, deposition and its inhibition in desalination applications by following designed chemical approaches. More specifically, benchtop screening tests on various silica inhibition chemistries are reported, with emphasis on additives with dendrimeric or polymeric structure and backbone. The inhibition performance of Starburst® polyaminoamide (PAMAM) dendrimers of generations 0.5, 1, 1.5, 2, and 2.5 are investigated in detail. Experimental results show that inhibition efficiency largely depends on structural features of PAMAM's such as generation number and nature of the end groups, as well as dosage levels. Poly(2-ethyl-2-oxazoline) polymers of a variety of molecular weights are also investigated as potential SiO 2 inhibitors. The general scope of silica formation and inhibition in waters relevant to desalination systems is also discussed.

A methacrylate-based polyampholyte homopolymer was synthesized starting from N-methacryloyl-l-histidine (MHist). This paper reports the inhibitory effects of poly-N-methacryloyl-l-histidine (poly-MHist) on the in vitro silicic acid condensation. In particular, the ability of poly-MHist to retard silicic acid condensation in aqueous supersaturated solutions at three pH values, 5.5, 7.0, and 8.5, is studied. The direct role of the imidazole ring was confirmed by substantial changes in silicic acid stabilization efficiency based on the following observations: (a) the protonation degree of the imidazole ring affects stabilization. At a relatively low pH of 5.5, the imidazole is protonated and the entire polymer acquires a zwitterionic character (−COO– is also present). Inhibitory activity increases considerably. In contrast, at a high pH of 8.5, the imidazole ring is neutral and the polymer backbone is anionic due to the presence of −COO– moieties. This results in total inactivity with respect to silicic acid...

The structural and functional chemistry of a family of alkali-metal ions with racemic R,S-hydroxyphosphonoacetate (M-HPAA; M = Li, Na, K, Cs) are reported. Crystal structures were determined by X-ray data (Li+, powder diffraction following an ab initio methodology; Na+, K+, Cs+, single crystal). A gradual increase in dimensionality directly proportional to the alkali ionic radius was observed. [Li3(OOCCH(OH)PO3)-(H2O)4]·H2O (Li-HPAA) shows a 1D framework built up by Li-ligand “slabs” with Li+ in three different coordination environments (4-, 5-, and 6-coordinated). Na-HPAA, Na2(OOCCH(OH)PO3H)(H2O)4, exhibits a pillared layered “house of cards” structure, while K-HPAA, K2(OOCCH(OH)PO3H)(H2O)2, and Cs-HPAA, Cs(HOOCCH(OH)-PO3H), typically present intricate 3D frameworks. Strong hydrogen-bonded networks are created even if no water is present, as is the case in Cs-HPAA. As a result, all compounds show proton conductivity in the range 3.5 × 10−5 S cm−1 (Cs-HPAA) to 5.6 × 10−3 S cm−1 (Na-HPAA) at 98% RH and T = 24 °C. Differences in proton conduction mechanisms, Grothuss (Na+ and Cs+) or vehicular (Li+ and K+), are attributed to the different roles played by water molecules and/or proton transfer pathways between phosphonate and carboxylate groups of the ligand HPAA. Upon slow crystallization, partial enrichment in the S enantiomer of the ligand is observed for Na-HPAA, while the Cs-HPAA is a chiral compound containing only the S enantiomer. Proyectos nacionales MAT2010-15175 y MAT2013-41836-R

The synthesis and spectral profile of a cyclam-type “turn on” fluorescent sensor selective for Hg2+ ions in aqueous media is described. Its properties are compared to those of a second probe with an N-deprotected cyclam system. The vast difference in ion selectivity between the two sensors reveals the influence of functional group modifications on the selectivity of fluorescent ion probes.