Potentiometric Acid-base Titrations Research Articles

Evaluation of Brønsted acidity and proton topology in Zr- and Hf-based metal–organic frameworks using potentiometric acid–base titration

Potentiometric acid–base titration is introduced as a method to evaluate pKa values (Brønsted acidity) of protons present in the nodes of water stable Zr6- and Hf6-based metal–organic frameworks (MOFs), including UiO-type MOFs, NU-1000, and MOF-808.

Suitability of Two Methods for Determination of Point of Zero Charge (PZC) of Adsorbents in Soils

ABSTRACTThe points of zero charge (PZC) of manganese oxide (MnO2), titanium dioxide (TiO2), aluminum (Al) laterite, ferruginous (Fe) laterite, aluminum oxide (Al2O3), and a commercial activated carbon sample (AC001) were determined using acid-base potentiometric (PT) and mass titration (MT). The MT technique has been used extensively for carbonaceous materials but less for soils. In addition, little work has been done on the PZC of these metal oxides and carbon materials under similar experimental conditions concurrently. Our aim is to buttress the ease of MT usage over PT in routine laboratory analysis. The experimental PZC measured by acid-base potentiometric and mass titrations respectively were 4.97 and 4.11 for MnO2; 5.38 and 5.74 for TiO2; 4.19 and 4.08 for Al laterite; and 4.45 and 4.10 for Fe laterite. For Al2O3 and activated carbon, mass titration gave 7.53 and 8.41 respectively. Calculated standard deviations between the means of PT and MT were less than 1, and Student’s t-test at 95% confidence interval (CI) gave a P value of 0.135, suggesting that there is no significant difference between PT and MT and buttressing the reliability of the experimental procedures. In routine laboratory work, mass titration should be preferred for PZC measurement of (hydr)oxides and soil materials because it saves time.

A SOLID Fe2O3-GRAPHITE COMPOSITE ELECTRODE FOR pH MEASUREMENT

A solid Fe2O3-graphite composite electrode was prepared and investigated for use as a potentiometric pH sensor. The electrode was constructed by mixing iron (III) oxide, oxidized graphite and wax that was put over silver disc onto a polypropylene rod. The response of the electrode was investigated by measuring electrode potential as a function of pH.The effect of composition of the electrode material (Fe2O3 and oxidized graphite ration) on the electrode response was investigated. The electrode with 40% Fe2O3, 30% graphite and 30% wax by mass was found to give the best potentiometric response. This electrode behaves in Nernstian manner with a potentiometric gradient of 56.6±0.4 mV per unit change in pH at 25?C within the working range of pH 2-9.The electrode was also used for the end-point detection in potentiometric acid-base titrations and found to be an excellent electrode for pH-metric titration. The effect of oxidation of electrode on pH response was investigated by dipping electrode in 0.1N KMnO4, 1:1HNO3 and 0.1N Ce4+ solutions for different interval of time. This treatment of the electrode with oxidizing agents increased the standard electrode potential of the electrode however potential gradient per unit change in pH remains unaltered. Low cost, quick response and easy to prepare are the advantages of the iron oxide - graphite composite electrode as a pH sensor. However some metal ions and oxidising agents interfered in the determination of pH using this electrode which is the limitation of using these electrodes.Scientific World, Vol. 12, No. 12, September 2014, page 44-47

A new electrode for acid-base titration based on poly(copper phthalocyanine)

A new electrode based on poly(copper phthalocyanine) (poly(CuPc)) microparticles attached to gold is characterized and introduced as a simple, robust, and cheap tool for potentiometric acid-base titrations.

Rare earth oxides doped NiO/γ-Al2O3 catalyst for oxidative dehydrogenation of cyclohexane

The effect of rare earth oxides (RE=Ce, La, Gd, and Dy) doping of alumina support in NiO/γ-Al2O3 system was investigated on its catalytic performance in oxidative dehydrogenation (ODH) of cyclohexane. The physicochemical properties of various samples were followed up through N2 physisorption, temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and potentiometric acid-base titration techniques. In the parent NiO/γ-Al2O3 catalyst, Ni species were found to be strongly interacted with alumina surface. Addition of rare earth dopants to γ-Al2O3 in the catalyst system affected the nickel-alumina interaction and resulted in significant modifications in the catalytic performances in the ODH reaction. The results revealed the beneficial role of both La2O3 and Gd2O3 doping in enhancing the ODH catalytic activity and selectivity to cyclohexene. H2-TPR and XPS results indicated that majority of Ni species in NiO/La2O3 modified γ-Al2O3 were more weakly interacted with La2O3 and alumina whereas both NiO like species and nickel aluminate were present on the surface. Doping with cerium or dysprosium increased the nickel-support interaction and led to a decrease in surface nickel concentration. In case of doping with Ce, surface concentration of cerium oxide was higher than those of the other RE oxides; the doped catalyst reached its steady state activity faster than the other catalysts. The acid-base results suggested that RE metals were interacted most likely with acidic surface hydroxyl groups. The degree of nickel-alumina interaction decreased in the following order: LaAl>GdAl>CeAl>DyAl.

Mechanism of in situ surface polymerization of gallic acid in an environmental-inspired preparation of carboxylated core-shell magnetite nanoparticles.

Magnetite nanoparticles (MNPs) with biocompatible coatings are good candidates for MRI (magnetic resonance imaging) contrasting, magnetic hyperthermia treatments, and drug delivery systems. The spontaneous surface induced polymerization of dissolved organic matter on environmental mineral particles inspired us to prepare carboxylated core-shell MNPs by using a ubiquitous polyphenolic precursor. Through the adsorption and in situ surface polymerization of gallic acid (GA), a polygallate (PGA) coating is formed on the nanoparticles (PGA@MNP) with possible antioxidant capacity. The present work explores the mechanism of polymerization with the help of potentiometric acid-base titration, dynamic light scattering (for particle size and zeta potential determination), UV-vis (UV-visible light spectroscopy), FTIR-ATR (Fourier-transformed infrared spectroscopy by attenuated total reflection), and XPS (X-ray photoelectron spectroscopy) techniques. We observed the formation of ester and ether linkages between gallate monomers both in solution and in the adsorbed state. Higher polymers were formed in the course of several weeks both on the surface of nanoparticles and in the dispersion medium. The ratio of the absorbances of PGA supernatants at 400 and 600 nm (i.e., the E4/E6 ratio commonly used to characterize the degree of polymerization of humic materials) was determined to be 4.3, similar to that of humic acids. Combined XPS, dynamic light scattering, and FTIR-ATR results revealed that, prior to polymerization, the GA monomers became oxidized to poly(carboxylic acid)s due to ring opening while Fe(3+) ions reduced to Fe(2+). Our published results on the colloidal and chemical stability of PGA@MNPs are referenced thoroughly in the present work. Detailed studies on biocompatibility, antioxidant property, and biomedical applicability of the particles will be published.

Detection analysis of surface hydroxyl active sites and simulation calculation of the surface dissociation constants of aqueous diatomite suspensions

The surface properties of the diatomite were investigated using nitrogen adsorption/deadsorption isotherms, TG-DSC, FTIR, and XPS, and surface protonation–deprotonation behavior was determined by continuous acid–base potentiometric titration technique. The diatomite sample with porous honeycomb structure has a BET specific surface area of 10.21m2/g and large numbers of surface hydroxyl functional groups (i.e. Si-OH, Fe-OH, and Al-OH). These surface hydroxyls can be protonated or deprotonated depending on the pH of the suspension. The experimental potentiometric data in two different ionic strength solutions (0.1 and 0.05mol/L NaCl) were fitted using ProtoFit GUI V2.1 program by applying diffuse double layer model (DLM) with three amphoteric sites and minimizing the sum of squares between a dataset derivative function and a model derivative function. The optimized surface parameters (i.e. surface dissociation constants (logK1, logK2) and surface site concentrations (logC)) of the sample were obtained. Based on the optimized surface parameters, the surface species distribution was calculated using Program-free PHREEQC 3.1.2. Thus, this work reveals considerable new information about surface protonation–deprotonation processes and surface adsorptive behaviors of the diatomite, which helps us to effectively use the cheap and cheerful diatomite clay adsorbent.

Simultaneous adsorption and reduction of U(VI) on reduced graphene oxide-supported nanoscale zerovalent iron

The reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) composites were synthesized by chemical deposition method and were characterized by SEM, high resolution TEM, Raman and potentiometric acid-base titrations. The characteristic results showed that the nZVI nanoparticles can be uniformly dispersed on the surface of rGO. The removal of U(VI) on nZVI/rGO composites as a function of contact time, pH and U(VI) initial concentration was investigated by batch technique. The removal kinetics of U(VI) on nZVI and nZVI/rGO were well simulated by a pseudo-first-order kinetic model and pseudo-second-order kinetic model, respectively. The presence of rGO on nZVI nanoparticles increased the reaction rate and removal capacity of U(VI) significantly, which was attributed to the chemisorbed OH− groups of rGO and the massive enrichment of Fe2+ on rGO surface by XPS analysis. The XRD analysis revealed that the presence of rGO retarded the transformation of iron corrosion products from magnetite/maghemite to lepidocrocite. According to the fitting of EXAFS spectra, the UC (at ∼2.9Å) and UFe (at ∼3.2Å) shells were observed, indicating the formation of inner-sphere surface complexes on nZVI/rGO composites. Therefore, the nZVI/rGO composites can be suitable as efficient materials for the in-situ remediation of uranium-contaminated groundwater in the environmental pollution management.

Acid–base properties of pillared interlayered clays with single and mixed Zr–Al oxide pillars prepared from Tunisian-interstratified illite–smectite

Interstratified illite–smectite clay samples from Tunisia have been used in order to prepare Al, Zr and Zr–Al-pillared clays. Several Al/metal, OH/metal ratios were used in order to investigate the effect on the chemical and physical properties, specifically the point of zero charge (PZC) of the synthesized pillared clays. The structure of the pillared materials is studied by XRD and cationic exchange capacity. The textural property is investigated by the nitrogen adsorption/desorption method. The acid–base chemistry “surface acidity” of these products was analysed by using mass and potentiometric titration in order to determine the PZC and the equilibrium constants (pKa) of each sample. The resulting materials exhibited basal spacings in the range of 17.4–20.5Å, with high surface areas (134–199m2g−1). Titration curves obtained by acid–base potentiometric titration for the starting material showed an indistinct cross-over point at about pH=7.3, whereas in the case of pillared samples, points were observed at the acidic region between 4 and 6. In addition, the calculated pKas values of pillared clays show a shifting to the acidic values compared to the untreated sample.

Simultaneous removal of uranium and humic acid by cyclodextrin modified graphene oxide nanosheets

Cyclodextrin-modified graphene oxide nanosheets (denoted as CD/GO) were synthesized by an in - situ polymerization method and characterized by as well as Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and potentiometric acid-base titration. The characterization results indicated that CD was successfully grafted onto GO surfaces by forming a chemical bond. Mutual effects on the simultaneous removal of hexavalent uranium and humic acid by CD/GO from aqueous solution were investigated. The results indicated that U(VI) and humic acid (HA) sorption on CD/GO were greatly affected by pH and ionic strength. The presence of HA enhanced U(VI) sorption at low pH and reduced U(VI) sorption at high pH, whereas the presence of U(VI) enhanced HA sorption. The surface adsorbed HA acted as a “bridge” between U(VI) and CD/GO, and formed strong inner-sphere surface complexes with U(VI). Sorption isotherms of U(VI) or HA on CD/GO could be well fitted by the Langmuir model. This work highlights that CD/GO can be used as a promising material in the enrichment of U(VI) and HA from wastewater in U(VI) and humic substances obtained by environmental pollution cleanup.

Electrodeposition of composites consisting of polypyrrole and microporous zeolites

Polypyrrole/zeolite composites were synthesized by electrochemical polymerization of pyrrole monomer at ambient temperature (22 ± 1 °C) in aqueous suspension of pure microporous zeolite particles. Electrodeposition was performed by using the method of constant potential. The proton form of Beta zeolites with SiO2/Al2O3 ratios of 25 and 300 and Y zeolites with SiO2/Al2O3 ratios of 12 and 80 was used in this work. The chemical compositions and the acidic properties of the zeolites were studied by inductively coupled plasma optical emission spectrometer and potentiometric acid–base titration. Polypyrrole/zeolite composite films deposited on platinum and indium tin oxide glass electrodes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy with attenuated total reflectance, X-ray diffraction, and transmission electron micrographs, and their electrochemical behavior was studied by cyclic voltammetry. These measurements showed that polymerization of pyrrole took place on the outer surfaces of the host zeolite crystals. The oxidized cationic polypyrrole was charge-balanced by the anionic groups present in the zeolite framework. Content of the anionic groups in the zeolites was found to be important for the electrochemical behavior of the polypyrrole/zeolite composites.

Microwave-assisted purification of detonation nanodiamond

In the present work microwave-assisted purification approaches for detonation nanodiamond (DND) are considered, and the resultant impurity content of purified DND revealed by direct ICP-MS and elemental analysis. A significant reduction in noncarbon contaminants as compared with detonation soot was achieved with resulting purity of 99.95%. Surface characterisation including scanning electronic microscopy, low temperature adsorption of nitrogen, acid–base potentiometric titration, zeta potential measurements and particle size distribution of the DND in suspensions revealed distinctive surface properties for each purified DND sample. Results highlight the suitability of the microwave purification approach using acid reagents, allowing nanodiamonds with different and reproducible surface properties to be produced or modified. Contamination effects from laboratory glassware used to store samples were carefully considered. Refined DND with impurity levels over two orders of magnitude lower than commercially available samples was prepared. The profile and concentration levels of residual impurities in purified samples of nanodiamond are discussed with identification of possible reasons for contamination.

Surface complexation of the phototrophic anoxygenic non-sulfur bacterium Rhodopseudomonas palustris

This work extends our knowledge of anoxygenic phototrophic bacteria (APB) interactions and contributes to the database of aquatic microorganism trace element adsorption parameters, such as heavy metal pollutants and limiting micronutrients. The surface properties of a phototrophic anaerobic non-sulfur bacterium (Rhodopseudomonas palustris KR-95p), which is often considered a model microorganism for Precambrian anoxygenic primary producers, were studied using potentiometric acid-base titration at various ionic strengths. The electrophoretic mobility of viable cells was measured as a function of pH and ionic strength, as well as cation (Zn, Cd, and Pb) and anion (Mo, W, and Cr) concentration. Zn, Cd, Sr, Pb, Cu, Cs, Al, Ga, Sb, As, Ge, Tl, W, and Mo adsorption was studied as a function of pH at a constant initial element concentration, yielding the pH-dependent adsorption edge. Zn, Cd, Sr, Cu and Pb adsorption was also studied as a function of metal concentration in solution at a constant pH, producing a “Langmuirian” adsorption isotherm. The non-electrostatic linear programming method (LPM) was used to fit the experimental data and assess the number of surface sites and adsorption reaction constants involved in heavy metal and anion binding to the cyanobacteria surface.The total H/OH binding site number (80–480μmol/gwet) for Rps. palustris encompasses the values reported for other APB (60–120μmol/gwet) and cyanobacteria (50–200μmol/gwet) examined using the same technique. For the cations, the adsorption edge follows the order Pb2+>Cu2+≫Cd2+≈Zn2+>Sr2+>Tl+>Cs+, which is similar to the element hydrolysis order. Trivalent hydrolysates (Al3+ and Ga3+) demonstrated increased adsorption with a pH increase at 2≤pH≤4 followed by desorption from the bacterial surface at pH>5–6 as negatively charged Al(OH)4− and Ga(OH)4−, similar to anions, such as MoO42− and WO42−. This behavior directly reflects the level of trace element complexation with two primary binding sites at the surface, carboxylate and phosphorylate, and certain electrostatic-like interactions between negatively charged anions and positive amine groups in acidic solutions. The main results of the present study are that the Rps. palustris exhibit trace element binding properties through their pH-dependence and overall adsorption capacity, which are similar to properties described earlier for other phototrophic bacteria, both anoxygenic bacteria and cyanobacteria. The absolute adsorption capacities for metal cations follow the order Rps. palustris<APB Rdb. blasticus<cyanobacteria Gloeocapsa sp, which presumably reflects a greater concentration of free metal cations in the external milieu for this species. Correspondingly, the adsorbed anion concentration is greatest for Rps. palustris, which therefore yields a higher proportion of positively charged amine groups or fewer negative charges overall due to a lower fraction of carboxylates and phosphorylates.

Potentiometric and spectrophotometric study of the stability of magnesium carbonate and bicarbonate ion pairs to 150 °C and aqueous inorganic carbon speciation and magnesite solubility

The formation constants of magnesium bicarbonate and carbonate ion pairs have been experimentally determined in dilute hydrothermal solutions to 150°C. Two experimental approaches were applied, potentiometric acid–base titrations at 10–60°C and spectrophotometric pH measurements using two pH indicators, 2-naphthol and 4-nitrophenol, at 25 and 80–150°C. At a given temperature, the first and second ionization constants of carbonic acid (K1, K2) and the ion pair formation constants for MgHCO3+(aq) (KMgHCO3+) and MgCO3(aq) (KMgCO3) were simultaneously fitted to the data. Results of this study compare well with previously determined values of K1 and K2. The formation constants of MgHCO3+(aq) and MgCO3(aq) ion pairs increased significantly with increasing temperature, with values of logKMgHCO3+=1.14 and 1.75 and of logKMgCO3=2.86 and 3.48 at 10°C and 100°C, respectively. These ion pairs are important aqueous species under neutral to alkaline conditions in moderately dilute to concentrated Mg-containing solutions, with MgCO3(aq) predominating over CO32-(aq) in solutions at pH >8. The predominance of magnesium carbonate over carbonate is dependent on the concentration of dissolved magnesium and the ratio of magnesium over carbonate. With increasing temperature and at alkaline pH, brucite solubility further reduced the magnesium concentration to levels below 1mmolkg−1, thus limiting availability of Mg2+(aq) for magnesite precipitation.

Rapid and economical synthesis of magnetic multiwalled carbon nanotube/iron oxide composite and its application in preconcentration of U(VI)

Magnetic multiwalled carbon nanotube/iron oxide composite (Fe3O4/MWCNT) was synthesized as an adsorbent for the preconcentration of U(VI) from aqueous solutions. The surface properties of Fe3O4/MWCNT were characterized via adopting FTIR, SEM and potentiometric acid–base titration. The sorption behaviors of U(VI) on the surface of Fe3O4/MWCNT were investigated under environmental conditions by using batch technique, such as pH, ionic strength and contact time. The pH-dependent U(VI) sorption behavior on Fe3O4/MWCNT illustrated that sorption mechanism of U(VI) was achieved by outer-sphere surface complexation at low pH values, while the sorption of U(VI) was achieved by inner-sphere surface complexation and simultaneous precipitation at high pH values. Besides, the pH-dependent sorption also demonstrated an optimal and feasible pH value of 7.0 by adopting Fe3O4/MWCNT in the preconcentration of U(VI) from aqueous solutions. The sorption kinetic experimental data could be well simulated by using the pseudo-second-order pattern. The Langmuir and Freundlich patterns were employed to simulate sorption isotherms of U(VI) at three different temperatures, the experimental results demonstrated that sorption process was favorable at higher environmental temperature. The maximum sorption capacity of U(VI) on Fe3O4/MWCNT was higher than that of major materials reported. Related experimental data further indicated that Fe3O4/MWCNT had satisfactory treatment performance for the simulated wastewater. The Fe3O4/MWCNT particles having strong magnetism could be favorably and easily separated from aqueous solution under an external magnetic field. The correlative experimental results further demonstrated that the Fe3O4/MWCNT composite could be a promising adsorbent for the preconcentration of radionuclides from large volumes of aqueous solution.

Potentiometric Titration of ${\rm NH}_{4}{\rm VO}_{3}$ and ${\rm Na}_{2}{\rm HAsO}_{4}$ in Molten ${\rm NaNO}_{3}$ at 623 K Using a Novel Solid-State Glass/${\rm Nb}_{2}{\rm O}_{5}$ pH Indicator Electrode

A solid state glass/ Nb2O5 electrode was prepared by the sol-gel process using the sonocatalytic method. The film reported here was prepared from an NbCl5 as precursor and butanol as solvent. The relation between log [O2-] and glass/ Nb2O5 electrode potential in molten KNO3 at 623 K is linear with a slope of 59.1 mV at 623 K. This value is closer to the theoretical value 2.303 RT/F (61.6 mV at 623 K). The standard potential of this electrode, E0, is computed as -984.7 mV relative to the Ag/Ag reference. The electrode was investigated as an oxide ion indicator electrode in potentiometric titrations between acids and bases in fused salts. This electrode behaves reversibly and responds to the oxide ion concentration in molten nitrate. Two oxide ion acceptors (acids), NH4VO3 and Na2HAsO4, were titrated with oxide ion donors (bases) in fused KNO3 at 625 K. The electrode was found to serve as an excellent indicator for acid base potentiometric titrations in molten salts.

Functionalisation of mesoporous silica gel with 2-[(phosphonomethyl)-amino]acetic acid functional groups. Characterisation and application

A new complexing adsorbent was prepared by chemical modification of mesoporous silica Kieselgel 60 (dp=37–63μm, average pore size 6nm, specific surface area 425m2g−1) with 3-glycidoxypropyltrimethoxysilane and 2-[(phosphonomethyl)amino]acetic acid (PMA), commonly known as glyphosate. The prepared adsorbent was fully characterised using elemental analysis, thermal gravimetric analysis (TGA), acid–base potentiometric titration, Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption isotherms at 77K (BET), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The concentration of bonded PMA groups calculated from the nitrogen content was 0.38mmol per gram. The adsorption of transition metal ions on PMA functionalised silica (HEPMAS) was studied from aqueous solutions having different pH and the following selectivity was established, Zn(II)<Co(II)<Cd(II)<Mn(II)<Ni(II)<Cu(II). The calculated values of distribution coefficients D for the adsorption of ecotoxic metal ions on HEPMAS are 5.0×104, 4.9×105 and 2.6×104 for Zn(II), Pb(II) and Cd(II), respectively.

Novel Ordered Mesoporous Carbon with Innate Functionalities and Superior Heavy Metal Uptake

Ordered mesoporous carbons with innate carbonyl functionalities (MC-icf) have been synthesized via a nanocasting process using SBA-15 as a template and acetylenedicarboxylic acid as a carbon source, instead of the commonly used sugar. The structural, textural, and surface properties of as derived mesoporous carbon material were investigated by means of spectroscopic, microscopy, and surface physicochemical methods. The experimental results showed that the new mesoporous carbons exhibit basic structural and morphological features that resemble those of CMK-3 carbons, such as hexagonally ordered structure, high specific surface area (980 m2/g), and high mesoporosity. The pore surfaces are rich in functional moieties, such as carboxylate groups, carbonyl, and free radicals. The surface charge properties of MC-icf were studied using potentiometric acid–base titrations. A surface complexation model revealed two types of H-binding sites, each one with a different degree of accessibility by positively charged species. Heavy metal, e.g., Cd2+, Pb2+, and Cu2+, uptake was also studied in detail at different pH values by the combination of analytical and EPR spectroscopic techniques. The data indicate an improved and selective capability for Cd2+, Pb2+, and Cu2+ uptake by the MC-icf compared with the standard CMK-3.

CaCO3 biomineralization on cyanobacterial surfaces: Insights from experiments with three Synechococcus strains

In the present paper, the impact of freshwater (ARC21 and LS0519) and marine (PCC8806) Synechococcus cyanobacteria on calcium carbonate (CaCO3) precipitation has been examined in respect of the formation rates and morphology of crystals. Acid–base potentiometric titrations were employed to study surface functional groups, while CaCO3 experiments have been carried out in presence and absence of cells at low to near-equilibrium conditions in respect to CaCO3. During these experiments, the pH values have been monitored, Ca and alkalinity were measured and precipitates have been investigated by Raman spectroscopy and Atomic Force and Scanning Electron microscopy.Our results showed that the Synechococcus strains exhibited different surface reactivity with total concentration of surface functional groups of 0.342 and 0.350mMg−1 of dry bact. for freshwater strains, and 0.662mMg−1 of dry bact. for the marine strain, which are on the same order of magnitude as that reported for bacterial cell surfaces. The marine strain showed the highest CaCO3 formation rate with Ca2+ removal of 18mMg−1 dry bact. compared to 6–7mMg−1 dry bact. for freshwater strains. The morphological diversity in crystals has been linked to presence of specific functional groups. The linking cell surface properties to crystal morphologies and precipitation rates propose that bacterial surfaces may modulate CaCO3 formation. Results of this work should allow better understanding of biominiralization in marine and freshwater systems as they define the precipiatation rates in typical range of pH necessary for estimation of CaCO3 formation by cyanobacterial communities.

Sorption of metal ions from aqueous solution to spruce bark

The concentrations and protonation constants of the functional groups like carboxyl and phenolic hydroxyl groups in spruce bark were determined by a potentiometric acid–base titration method. The non-cellulosic carbohydrates in spruce bark were also characterized by acid methanolysis and GC, including determination of the uronic acid units, which are the key units involved in metal sorption. Sorption of metal ions to bark takes place by ion exchange, mainly by complexation to these functional groups. The sorption equilibrium time, studied by using a batch method, was approximately 5 min. The metal sorption capacity of spruce bark and the affinity order of metal ions were studied with four different metal ion mixtures using a column chromatographic method. Because a method of competition was used, concentration of metal ions adsorbed to bark depends on the metal ions present in the mixtures studied. In the sorption experiments with same metal ion mixtures, inner bark of spruce exhibited higher sorption capacity than outer bark. By combination of the results from several experiments, the following affinity order was obtained Fe3+ ≫ Pb2+ ≫ Cu2+ ≫ Cd2+ > Zn2+ > Ni2+ > Ba2+ > Ca2+ > Sr2+ > Mn2+ > Mg2+ ≫ K+ ~ Na+ ~ Li+. Bark has a great potential as an effective and inexpensive sorbent for removal of metal ions from, e.g., waste water.