Casein phosphopeptide calcium chelation: preparation optimization, in vitro gastrointestinal simulated digestion, and peptide fragment exploration.

BACKGROUND: Calcium is important in the formation of bones and teeth, cell metabolism, and other physiological activities. In this work, casein phosphopeptide-calcium chelate (CPP-Ca) was synthesized and the optimal process parameters for the chelation reaction were obtained. The bioavailability of calcium in CPP-Ca was investigated by in vitro gastrointestinal simulated digestion. The existence of phytic acid and oxalic acid in the digestion system was evaluated to clarify the calcium holding ability of casein phosphopeptide (CPP). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify oligopeptides from CPP-Ca. RESULTS: The optimal process parameters for the chelation reaction were: peptide concentration 7.76 mgmL-1 , pH 8.54, and reaction temperature 43.3 °C. The digestion in vitro results indicated that the calcium release rate of CPP-Ca in the stomach for 2 h reached 85%, and about 50% of the ionized calcium was re-chelated with CPP in the intestine. Phytic acid and oxalic acid could lead to a sharp decrease in soluble calcium but around 50% of the calcium was still retained in the form of chelates in the presence of CPP. The LC-MS/MS identified 19 casein-derived oligopeptides after digestion, and calcium modifications were found on eight peptides derived from ß-casein and αs2 -casein. CONCLUSIONS: This study clarified the excellent calcium holding capacity of CPP in the presence of phytic acid and oxalic acid. Liquid chromatography-tandem mass spectrometry also revealed peptide changes, and identified peptides that chelate with calcium. These findings provided significant insights that could be relevant to the further utilization and product development of peptide-calcium chelate in the food industry. © 2023 Society of Chemical Industry.

Role of oxalic acid in fungal and bacterial metabolism and its biotechnological potential.

Oxalic acid and oxalates are secondary metabolites secreted to the surrounding environment by fungi, bacteria, and plants. Oxalates are linked to a variety of processes in soil, e.g. nutrient availability, weathering of minerals, or precipitation of metal oxalates. Oxalates are also mentioned among low-molecular weight compounds involved indirectly in the degradation of the lignocellulose complex by fungi, which are considered to be the most effective degraders of wood. The active regulation of the oxalic acid concentration is linked with enzymatic activities; hence, the biochemistry of microbial biosynthesis and degradation of oxalic acid has also been presented. The potential of microorganisms for oxalotrophy and the ability of microbial enzymes to degrade oxalates are important factors that can be used in the prevention of kidney stone, as a diagnostic tool for determination of oxalic acid content, as an antifungal factor against plant pathogenic fungi, or even in efforts to improve the quality of edible plants. The potential role of fungi and their interaction with bacteria in the oxalate-carbonate pathway are regarded as an effective way for the transfer of atmospheric carbon dioxide into calcium carbonate as a carbon reservoir.

No Inhibitory Effect of Heparinized Blood on Real-Time PCR Analysis of Thrombophilic Mutations.

We compared the efficiency of real-time PCR analysis of FII (c.*97G>A, G20210A) and FV Leiden (c.1601G>A) thrombophilic mutations in the samples obtained from venous blood treated with various anti coagulant agents (EDTA, heparin, and sodium fluoride with potassium oxalate), or from clotted venous blood; one hundred samples of wild-type subjects were tested. Genomic DNA extracts and whole blood specimens modified by 90 °C heating were analysed by real-time PCR analysis; cycle threshold values were subsequently evaluated. Real-time PCR analysis for the FII gene assay performed in DNA extracts from EDTA blood samples revealed a median Ct value of 19.3. Similar Ct values were apparent in the DNA extracts obtained from the heparinized blood and sodium fluoride with potassium oxalatetreated samples: 18.5 and 18.9, respectively. Significantly higher Ct values were found in extracts from clotted blood with medians of 20.6 (tubes with inert separation gel) and 20.5 (tubes without the gel, both P < 0.001). The data on the FV real-time PCR analysis were very comparable to the FII assay. In the modified whole blood, the samples treated with heparin salts showed significantly lower Ct values (P < 0.001) in both assays when compared with the samples with EDTA, sodium fluoride with potassium oxalate, and with the samples with clotted blood. Our results indicate that real-time PCR analyses of thrombophilic mutations were not negatively influenced by the presence of heparin salts in collection tubes. Blood samples with various anticoagulants might be exchangeable for each other when DNA analysis of thrombophilic mutations is required.

Assessment of the Oral Health Impact Profile (OHIP-14) improvement of different treatments for dentin hypersensitivity in noncarious cervical lesions-a randomized clinical study.

OBJECTIVES: To assess the improvement on oral health-related quality of life (OHRQoL) of individuals with cervical dentin hypersensitivity (CDH) with the noncarious cervical lesion (NCCLs) subjected to different treatments. MATERIAL AND METHODS: A single-blind randomized clinical trial was conducted with patients (n = 74) randomly allocated into three groups according to the treatment performed: PO, potassium oxalate (Oxa-Gel BF); LL, low-power laser irradiation; and POLL, potassium oxalate (Oxa-Gel BF) associated with low-power laser irradiation. The treatments were applied in four steps, weekly. The questionnaire Oral Health Impact Profile (OHIP-14) was applied before initiating and immediately after the fourth session. The greater the sum of the score, the smaller the measurement of OHRQoL. RESULTS: The total mean values of the variables at the final moment were significantly lower than the initial one for all dimensions (p value ranging from < 0.001 to 0.006). Furthermore, the OHIP-14 scores final analysis between the groups indicated that the POLL group compared to LL had a significantly lower final score for the functional limitation (p = 0.009), physical pain (p = 0.049), and psychological discomfort (p = 0.035) dimensions and that group PO compared to group LL had a significantly lower final score for the functional limitation dimension (p = 0.024). CONCLUSIONS: There was a reduction in the OHIP-14 score for all dimensions, indicating an improvement in patients' quality of life after the use of desensitizing therapies. Patients in group LL had a higher functional limitation, physical pain, and psychological discomfort. CLINICAL RELEVANCE: This study indicated improvement of desensitizing therapies for CDH to improve patients' OHRQoL. TRIAL REGISTRATION: This trial was registered in the Brazilian Clinical Trials Registry Platform (REBEC protocol number RBR-4ybjmt).

Colonization and bioweathering of monazite by Aspergillus niger: solubilization and precipitation of rare earth elements.

Geoactive fungi play a significant role in bioweathering of rock and mineral substrates. Monazite is a phosphate mineral containing the rare earth elements (REE) cerium, lanthanum and neodymium. Little is known about geomicrobial transformations of REE-bearing minerals which are also relevant to REE biorecovery from terrestrial and extra-terrestrial reserves. The geoactive soil fungus Aspergillus niger colonized monazite in solid and liquid growth media without any apparent growth inhibition. In a glucose-minerals salts medium, monazite enhanced growth and mycelium extensively covered rock particle surfaces, probably due to the provision of phosphate and essential trace metals. Teeth-like and pagoda-like etching patterns indicated monazite dissolution, with extensive precipitation of secondary oxalate minerals. Biomechanical forces ensued causing aggressive bioweathering effects by tunnelling, penetration and splitting of the ore particles. High amounts of oxalic acid (~46 mM) and moderate amounts of citric acid (~5 mM) were produced in liquid media containing 2% (wt./vol.) monazite, and REE and phosphate were released. Correlation analysis suggested that citric acid was more effective than oxalic acid in REE mobilization, although the higher concentration of oxalic acid also implied complexant activity, as well as the prime role in REE-oxalate precipitation.

Low-power laser and potassium oxalate gel in the treatment of cervical dentin hypersensitivity-a randomized clinical trial.

OBJECTIVE: To evaluate the effectiveness of different protocols for the treatment of cervical dentin hypersensitivity (CDH) in non-carious cervical lesions (NCCLs). MATERIALS AND METHODS: The CONSORT checklist was used to design this study. The sample with n = 74 participants (389 NCCLs) was randomly allocated into three groups: G1, potassium oxalate (Oxa-Gel BF); G2, GaAlAs (gallium-aluminum-arsenate) low-power laser (100 mW, 808nn, 60 J/cm2); and G3, potassium oxalate (Oxa-Gel BF) associated with the GaAlAs low-power laser. The CDH was triggered by the evaporative stimulus test (EST) and by the tactile stimulus test (TST). The visual analog scale (VAS) was used to quantify the degree of CDH. Changes in sensitivity were assessed from baseline over 3 weeks. Data were analyzed for NCCLs using mixed-effects models with unstructured direct product covariance structure (α = 0.05). RESULTS: After the first application, participants from G1 and G3 had a reduction in CDH (p < 0.05) compared with group G2 for TST. After the second application, G3 participants had a reduction in CDH (p < 0.05) in relation to G2 for both stimuli. Reduction in CDH (p < 0.05) occurred over 3 weeks for EST and TST for all groups; however, there was no difference between groups at the end of the therapies. CONCLUSION: Potassium oxalate was more effective in reducing immediate CDH. After four applications, all groups showed similar results for the reduction of CDH. CLINICAL RELEVANCE: GaAlAS laser irradiation and oxalate potassium gel could reduce the symptoms of CDH; thus, they are viable alternatives for the treatment of this condition. Chemical occlusion of dental tubules showed effective results after a shorter time interval. TRIAL REGISTRATION: Brazilian Clinical Trials Registration Platform under protocol number RBR-4ybjmt. http://www.braziliantrials.com/?keywords=RBR-4ybjmt&order=%7Eensaios.patrocinador_primario.

A Comparison of Dentin Tubule Occlusion Properties of Dipotassium Oxalate against Potassium Nitrate: An In Vitro Study.

AIM: The aim of this study is to compare the efficacy of dipotassium oxalate and potassium nitrate to occlude dentinal tubules. MATERIALS AND METHODS: This study utilized Parkinson model of longitudinal dentin tubule occluding properties of dentifrices under a 4-day acid challenge. Dentin disks of approximately 1.5 mm thick were sectioned from the crowns of the freshly extracted molars. The disks were randomized into three sets of 15 and treated with dipotassium oxalate, potassium nitrate, or used as a control. The disks were then subjected to a 4-day acid challenge and evaluated by scanning electron microscopy (SEM). RESULTS: On days 1, 2, and 3, dipotassium oxalate showed significant occlusion of dentinal tubules. On day 4, no significant difference was observed between dipotassium oxalate and potassium nitrate. Both test groups showed better occlusion properties in comparison to the control. CONCLUSION: Through the use of a 4-day acid challenge, this study demonstrates that both agents can indeed occlude dentinal tubules. Initially, dipotassium oxalate does occlude dentinal tubules faster than potassium nitrate. However, at the conclusion of the acid challenge, minimal differences were observed in occlusion rate among the two agents. Further studies should be conducted to determine the efficacy of these two agents. CLINICAL SIGNIFICANCE: Both dipotassium oxalate and potassium nitrate can help treat patients with dentinal hypersensitivity.

The apical anion exchanger Slc26a6 promotes oxalate secretion by murine submandibular gland acinar cells.

The solute carrier family 26 (SLC26) gene family encodes at least 10 different anion exchangers. SLC26 member 6 (SLC26A6 or CFEX/PAT-1) and the cystic fibrosis transmembrane conductance regulator (CFTR) co-localize to the apical membrane of pancreatic duct cells, where they act in concert to drive HCO3- and fluid secretion. In contrast, in the small intestine, SLC26A6 serves as the major pathway for oxalate secretion. However, little is known about the function of Slc26a6 in murine salivary glands. Here, RNA sequencing-based transcriptional profiling and Western blots revealed that Slc26a6 is highly expressed in mouse submandibular and sublingual salivary glands. Slc26a6 localized to the apical membrane of salivary gland acinar cells with no detectable immunostaining in the ducts. CHO-K1 cells transfected with mouse Slc26a6 exchanged Cl- for oxalate and HCO3-, whereas two other anion exchangers known to be expressed in salivary gland acinar cells, Slc4a4 and Slc4a9, mediated little, if any, Cl-/oxalate exchange. Of note, both Cl-/oxalate exchange and Cl-/HCO3- exchange were significantly reduced in acinar cells isolated from the submandibular glands of Slc26a6-/- mice. Oxalate secretion in submandibular saliva also decreased significantly in Slc26a6-/- mice, but HCO3- secretion was unaffected. Taken together, our findings indicate that Slc26a6 is located at the apical membrane of salivary gland acinar cells, where it mediates Cl-/oxalate exchange and plays a critical role in the secretion of oxalate into saliva.

Effect of Organic Acids on Molecular Mobility, Physical Stability, and Dissolution of Ternary Ketoconazole Spray-Dried Dispersions.

In an earlier investigation, ketoconazole (KTZ)-organic acid coamorphous systems were prepared, wherein, in the solid-state, there was ionic and/or hydrogen bonding interactions between the drug and the acid ( Fung , M. ; Berzins , K. ; Suryanarayanan , R. Mol. Pharmaceutics , 2018 , 15 ( 5 ), 1862 -1869 ). While the coamorphous systems accelerated KTZ dissolution, the organic acids were not effective in maintaining supersaturation, and drug precipitation was observed. Ternary drug-polymer-acid amorphous solid dispersions (ASDs) were prepared with KTZ, polyvinylpyrrolidone (PVP), and each oxalic (OXA), tartaric (TAR), citric (CIT), or succinic (SUC) acid. When compared with amorphous KTZ, solid dispersions of KTZ-PVP exhibited a moderate reduction in molecular mobility and small improvement in dissolution performance. The incorporation of acid (OXA, TAR, or CIT) in PVP-KTZ solid dispersion led to orders of magnitude increase in α-relaxation times and decrease in the crystallization propensity. These ternary ASDs were stable while crystallization of the cocrystal was observed in the SUC system. Moreover, the addition of acids also dramatically improved the dissolution performance of KTZ, a result attributed to KTZ-acid interactions.

Microwave-Assisted Oxalic Acid Pretreatment for the Enhancing of Enzyme Hydrolysis in the Production of Xylose and Arabinose from Bagasse.

In this study, highly-efficient hydrolysis of bagasse into xylose and arabinose sugars (C5 sugars) was developed by microwave-assisted oxalic acid pretreatment under mild reaction conditions. The effects of acid and hydrolysis conditions on the C5 sugar yields were discussed. The results showed that oxalic acid performed better than hydrochloric acid and maleic acid, and was a promising alternative to sulfuric acid for xylose production at the same acid concentration. The maximum yields of xylose (95.7%) and arabinose (91.5%) were achieved via the microwave-assisted oxalic acid pretreatment (120 °C, 10 min, 0.4 mol/L, solid-liquid ratio of 1:50 g/mL), indicating that almost all xylan-type hemicelluloses were released from the cell wall and hydrolyzed into C5 sugars. After pretreatment, more than 90% of the cellulose in the residual bagasse was converted to glucose (92.2%) by enzymatic hydrolysis. This approach could realize the highly-efficient hydrolysis of xylan from bagasse into C5 sugars, which would enhance the enzyme hydrolysis of treated bagasse into glucose.

In-office Treatments for Dentin Hypersensitivity: A Randomized Split-mouth Clinical Trial.

PURPOSE: To assess the effectiveness of four in-office therapies used for the treatment of dentin hypersensitiviy (DH) after one single application. MATERIALS AND METHODS: A randomised, controlled, split-mouth clinical trial was designed to evaluate the following treatments: 5% sodium fluoride varnish (positive control); 3% potassium oxalate; two-step self-etching adhesive; high power diode laser. Nineteen patients were selected and one tooth per quadrant was included in the study. After evaporative stimulation, pain was quantified by the Visual Analog Scale (VAS) at baseline, immediately after treatment, and after 15, 30 and 60 days. RESULTS: Compared to the baseline values, fluoride varnish (p = 0.00) and potassium oxalate (p = 0.00) presented an immediate desensitising effect that remained constant at 15, 30 and 60 days. The high-power diode laser presented significant reduction in VAS scores after 15 days (p = 0.00), while in the self-etching adhesive group, a significant reduction in VAS scores was observed only after 60 days (p = 0.03). The change in VAS ([VAS x days] - VAS baseline) differed among the groups immediately after treatment, being higher in the fluoride varnish and lower in the adhesive groups, but no statistically significant difference was found at time intervals of 15, 30 and 60 days. CONCLUSION: When an immediate desensitising effect is desired after one single application, fluoride varnish and potassium oxalate should be used. High-power diode laser and self-etching adhesive may not be clinically considered an appropriate desensitising therapy after one single application.

[Determination of the content of organic acids in the saliva of patients with breast cancer by capillary electrophoresis.]

A technique for quantitative determination of low molecular weight organic acids in saliva by the method of capillary electrophoresis has been developed. The method was tested on volunteers, divided into 3 groups: the main one (breast cancer, n=21), the comparison group (fibroadenomas, n=29) and the control group (conditionally healthy, n=26). It is shown that the concentration of lactic, acetic and propionic acids increases uniformly when passing from the control group to the comparison group, and then to the main group. Against the background of breast cancer, the concentration of oxalic and formic acids decreases in comparison with the control, whereas in fibroadenomas the concentration of oxalic acid decreases, and the formic acid grows. In general, the proposed method can be a valuable tool in the study of metabolic changes associated with cancer.

Evaluating decontamination protocols for the isolation of Mycobacterium ulcerans from swabs.

BACKGROUND: Mycobacterium ulcerans (M. ulcerans) is the causative agent of Buruli Ulcer (BU) disease. In order to inhibit the growth of the microbial contaminants during culture of M. ulcerans, it is necessary to decontaminate BU samples with effective chemical agents. This study aimed at investigating some selected chemicals as potential decontamination agents for the isolation of M. ulcerans from swabs. RESULTS: Povidone iodine at 0.5 and 1% exhibited the lowest contamination and recovery rate for microbial contaminants and M. ulcerans. The most effective decontamination method was the protocol using 2% cetylpyridinium chloride/4% sodium chloride (recovery rate = 53%, contamination rate = 14%). The observed difference between the recovery rate of 2% CPC/4% NaC and the other protocols was however not statistically significant (p = 0.76). CONCLUSIONS: Two percent (2%) cetylpyridinium chloride/4% sodium chloride can be conveniently used as an alternative decontamination method for the isolation of M. ulcerans from swabs.

Oral microbe-host interactions: influence of ß-glucans on gene expression of inflammatory cytokines and metabolome profile.

BACKGROUND: The aim of this study was to evaluate the effects of ß-glucan on the expression of inflammatory mediators and metabolomic profile of oral cells [keratinocytes (OBA-9) and fibroblasts (HGF-1) in a dual-chamber model] infected by Aggregatibacter actinomycetemcomitans. The periodontopathogen was applied and allowed to cross the top layer of cells (OBA-9) to reach the bottom layer of cells (HGF-1) and induce the synthesis of immune factors and cytokines in the host cells. ß-glucan (10 µg/mL or 20 µg/mL) were added, and the transcriptional factors and metabolites produced were quantified in the remaining cell layers and supernatant. RESULTS: The relative expression of interleukin (IL)-1-α and IL-18 genes in HGF-1 decreased with 10 µg/mL or 20 µg/mL of ß-glucan, where as the expression of PTGS-2 decreased only with 10 µg/mL. The expression of IL-1-α increased with 20 µg/mL and that of IL-18 increased with 10 µg/mL in OBA-9; the expression of BCL 2, EP 300, and PTGS-2 decreased with the higher dose of ß-glucan. The production of the metabolite 4-aminobutyric acid presented lower concentrations under 20 µg/mL, whereas the concentrations of 2-deoxytetronic acid NIST and oxalic acid decreased at both concentrations used. Acetophenone, benzoic acid, and pinitol presented reduced concentrations only when treated with 10 µg/mL of ß-glucan. CONCLUSIONS: Treatment with ß-glucans positively modulated the immune response and production of metabolites.

In vitro efficacy of a novel potassium oxalate hydrogel for dentin hypersensitivity.

A novel potassium oxalate-based hydrogel is proposed for treating dentin hypersensitivity and this study evaluates its in vitro performance as a remineralizing, desensitizing agent. Etched disks of human dentin were treated for 10 or 20 min using the test hydrogel, to mimic a professional application with dental mouth guards. Dentin disks were evaluated in terms of permeability indexes in a fluid-filled system, the surface morphology was assessed by scanning electron microscopy, and the structural properties were studied using X-ray diffraction analysis. The potassium oxalate hydrogel significantly reduced dentin permeability, in a time-dependent manner, and occluded most of the patent dentinal tubules via crystal precipitation, forming a remineralized layer. After hydrogel treatments, an acid solution (pH 4.2) was applied to the disks for 30 s, or 1, 2, or 5 min, in order to reproduce a plaque-like oral acidity, and further analysis showed a good resistance of the remineralized layer to the acid challenge. The potassium oxalate-based hydrogel showed a better performance over commercially available products and artificial saliva, appearing a promising candidate for the treatment of dentin hypersensitivity.

Enhancing the enzymatic saccharification of bamboo shoot shell by sequential biological pretreatment with Galactomyces sp. CCZU11-1 and deep eutectic solvent extraction.

In this study, sequential biological pretreatment (BP) with Galactomyces sp. CCZU11-1 at 30 °C for 3 days and deep eutectic solvent (DES) choline chloride: oxalic acid (ChCl:OA, 1 mol/2 mol) extraction at 120 °C for 1.5 h was used for pretreating BSS. It was found that combination pretreatment could effectively remove xylan and lignin for enhancing enzymatic saccharification. The reducing sugars and glucose from the hydrolysis of 100 g/L pretreated BSS with complexed cellulases of Galactomyces sp. CCZU11-1 were obtained in the yields of 81.0% and 74.1%, respectively. The BSS-hydrolyzates had no inhibitory effects on the lipid-accumulating microorganism Bacillus sp. CCZU11-1, and the cell mass and TAG accumulation were 4.8 g CDW/L and 2.2 g TAG/L, respectively. Fatty acids including palmitic acid (C16:0; 25.3%), palmitoleic acid (C16:1; 24.4%), stearic acid (C18:0; 15.1%), and oleic acid (C18:1; 21.6%) were accumulated in cells. Clearly, this combination pretreatment has high potential application in future.

Acidic Deep Eutectic Solvents As Hydrolytic Media for Cellulose Nanocrystal Production.

In this study, a new method to fabricate cellulose nanocrystals (CNCs) based on DES pretreatment of wood cellulose fibers with choline chloride and organic acids are reported. Oxalic acid (anhydrous and dihydrate), p-toluenesulfonic acid monohydrate, and levulinic acid were studied as acid components of DESs. DESs were formed at elevated temperatures (60-100 °C) by combining choline chloride with organic acids and were then used to hydrolyze less ordered amorphous regions of cellulose. All the DES treatments resulted in degradation of wood fibers into microsized fibers and after mechanically disintegrating, CNCs were successfully obtained from choline chloride/oxalic acid dihydrate-treated fibers, whereas no liberation of CNCs was observed with other DESs. The DES-produced CNCs had a width and length of 9-17 and 310-410 nm, respectively. The crystallinity indexes (CrIs) and carboxylic acid content of the CNCs were 66-71% and 0.20-0.28 mmol/g, respectively. CNCs exhibited good thermal stabilities (the onset thermal degradation temperatures ranged from 275-293 °C). The demonstrated acidic DES method exhibits certain advantages over previously reported CNC productions, namely, milder processing conditions and easily obtainable and relatively inexpensive biodegradable solvents with low toxicity (compared, e.g., to ILs).

Effective As(III) Removal by A Multi-Charged Hydroacid Complex Draw Solute Facilitated Forward Osmosis-Membrane Distillation (FO-MD) Processes.

Effective removal of As(III) from water by an oxalic acid complex with the formula of Na3[Cr(C2O4)3] (Na-Cr-OA) is demonstrated via an forward osmosis-membrane distillation (FO-MD) hybrid system in this study. Na-Cr-OA first proved its superiority as a draw solute with high water fluxes and negligible reverse fluxes in FO, then a systematic investigation of the Na-Cr-OA promoted FO process was conducted to ascertain the factors in As(III) removal. Relatively high water fluxes of 28 LMH under the FO mode and 74 LMH under the pressure retarded osmosis (PRO) mode were achieved when using a 1000 ppm As(III) solution as the feed and 1.0 M Na-Cr-OA as the draw solution at 60 °C. As(III) removal with a water recovery up to 21.6% (FO mode) and 48.3% (PRO mode) were also achieved in 2 h. An outstanding As(III) rejection with 30-3000 µg/L As(III) in the permeate was accomplished when As(III) feed solutions varied from 5 × 10(4) to 1 × 10(6) µg/L, superior to the best FO performance reported for As(III) removal. Incorporating MD into FO not only makes As(III) removal sustainable by reconcentrating the Na-Cr-OA solution simultaneously, but also reduces the As(III) concentration below 10 µg/L in the product water, meeting the WHO standard.

Development and Characterization of Ultrafiltration TiO2 Magnéli Phase Reactive Electrochemical Membranes.

This research focused on the synthesis, characterization, and performance testing of a novel Magnéli phase (TinO2n-1), n = 4 to 6, reactive electrochemical membrane (REM) for water treatment. The REMs were synthesized from tubular asymmetric TiO2 ultrafiltration membranes, and optimal reactivity was achieved for REMs composed of high purity Ti4O7. Probe molecules were used to assess outer-sphere charge transfer (Fe(CN)6(4-)) and organic compound oxidation through both direct oxidation (oxalic acid) and formation of OH(•) (coumarin, terephthalic acid). High membrane fluxes (3208 L m(-2) h(-1) bar(-1) (LMH bar(-1))) were achieved and resulted in a convection-enhanced rate constant for Fe(CN)6(4-) oxidation of 1.4 × 10(-4) m s(-1), which is the highest reported in an electrochemical flow-through reactor and approached the kinetic limit. The optimal removal rate for oxalic acid was 401.5 ± 18.1 mmol h(-1) m(-2) at 793 LMH, with approximately 84% current efficiency. Experiments indicate OH(•) were produced only on the Ti4O7 REM and not on less reduced phases (e.g., Ti6O11). REMs were also tested for oxyanion separation. Approximately 67% removal of a 1 mM NO3(-) solution was achieved at 58 LMH, with energy consumption of 0.22 kWh m(-3). These results demonstrate the extreme promise of REMs for water treatment applications.