Order Cl Research Articles

Microscopic mechanism about the selective adsorption of Cr(VI) from salt solution on O-rich and N-rich biochars

The adsorption of Cr(VI) on biochars can be suppressed by coexisting anions, but the roles of O-containing functional groups and in particular N-containing functional groups are unclear. In this study, we combined spectroscopic and molecular simulation approaches to investigate the selective adsorption of Cr(VI) on the O-rich (PB, UB1) and N-rich (UB3, UB5) biochars under strong competition of anions. The elemental analysis and pyrolysis-gas chromatography/mass spectrometry indicated that the structures of PB and UB1 were similar, and so were the UB3 and UB5. Quantification of functional groups showed that for UB1, 75.3% of Cr(VI) removal was attributed to O-containing groups, while 53.3–72.7% of that was mediated by N-containing groups in UB3 and UB5. X-ray photoelectron spectra and density functional theory calculations confirmed that for O-rich biochars, surface complexation and strong H-bonds between carboxyl/hydroxyl and HCrO4– improved Cr(VI) removal in the presence of anions, while for N-rich biochars, Cr(VI) adsorption was depressed by coexisting anions in the order of Cl–>NO3– >SO42– because of the weaker H-bond between protonated amino groups and HCrO4–. This study presents a novel approach for quantitative, molecular-level evaluation of the roles of biochar functional groups in the Cr(VI) removal from complex environmental systems.

Magnetic Fe3O4–N-doped carbon sphere composite for tetracycline degradation by enhancing catalytic activity for peroxymonosulfate: A dominant non-radical mechanism

The design of sustainable, effective and recyclable hybrid catalysts for advanced oxidation processes is highly significant for remediation of the water environment. In this study, we synthesized magnetic Fe3O4–N-doped carbon sphere composite catalysts (Fe3O4-NCS-x) for efficient removal of tetracycline by activating peroxymonosulfate (PMS). The Fe3O4-NCS-x composite was obtained by facile hydrothermal treatment of chitosan-iron complexes followed by pyrolysis. The unique structure of N-doped carbon spheres embedded in Fe3O4 nanoparticles intensified the electron transport, consequently improving the catalytic activity via a synergistic effect. Factors influencing the catalytic activity of the Fe3O4-NCS-2 were systematically investigated. High degradation efficiency of TC—97.1% within 1 h—was achieved in this Fe3O4-NCS-2/PMS system under the optimum conditions (C0 = 20 mg L−1, catalyst dosage 0.2 g L−1, PMS concentration 2.4 mM, native pH and 25 °C). The inhibitory effect of anions in the water matrix decreased in the order Cl− > NO3− > SO42− > CH3COO− > HCO3−. The obtained results from the competitive quenching tests and electron paramagnetic resonance measurements demonstrated that singlet oxygen (1O2), a non-radical species, plays a major role in TC degradation. It is estimated that 1O2 and hydroxyl radicals (·OH) contributed ∼65.2% and ∼24.2% to TC degradation in the Fe3O4-NCS-2/PMS system, respectively. The M-H hysteresis loop of Fe3O4-NCS-2 revealed that its saturation moment is 56 emu g−1. Magnetic responsive behavior and consecutive runs confirmed that Fe3O4-NCS-2 possesses remarkable separation performance and desirable reusability. This novel magnetic Fe3O4-NCS-2 composite activator for PMS promises great potential in TC degradation.

Water quality index and GIS-based technique for assessment of groundwater quality in Wanaparthy watershed, Telangana, India.

A comprehensive study of 58 groundwater samples collected in the virgin area of Wanaparthy watershed (1600km2), Telangana, India, to assess the hydrochemistry, quality, water types and potability using hydrogeochemical characterization, WQI and GIS technique. Major ions concentration of Na+, K+, Ca2+, Mg2+, Cl-, F-, NO3- and SO42- in groundwater were analysed using ion chromatography (IC). Physicochemical values of the potential of hydrogen (pH), total dissolved solids (TDS) and electrical conductivity (EC) were determined using Hanna portable meters, while total hardness (TH), alkalinity and bicarbonates are estimated by titrimetric methods. Results obtained enlighten the major anions and cations, which are found in order of Cl- > HCO3- > SO42- > NO3- > F- and Na+ > Ca+2 > Mg+2 > K+ respectively. Among various ions measured, fluoride (18.97%), chloride (3.44%), nitrate (8.62%), sulphate (5.17%), sodium (34.48%) and calcium (1.72%) were found to above acceptable limit values of Bureau of Indian Standards (BIS) for drinking purposes. According to Piper trilinear diagram, two dominant hydrochemical facies, Na-Cl-SO4 and Ca-Na-HCO3 types, were identified. Gibbs diagram imparted the dominancy of samples in the territory are rock-water reaction and evaporation dominance. WQI shows 67.79% of samples pertain to the excellent to good water types reveal fit for drinking. Drainage pattern enumerated the concentration of the parameters measured are exceeding towards the downstream region, which might be due to the chemical reaction of rock-water interaction (infiltration and recharge). As the groundwater is the major source of drinking in the study area, a proper management plan has to implement before its quality deteriorated.

Clean Production of Levulinic Acid from Fructose and Glucose in Salt Water by Heterogeneous Catalytic Dehydration.

Levulinic acid (LA) is considered to be one of the promising organic bio-platform chemicals and intermediates for the synthesis of fuels, chemicals, and polymers. In the present study, heterogeneous catalytic dehydration of hexose sugars, fructose and glucose, using a strong cation exchange resin (hydrogen form) as an acid catalyst, was performed to produce LA in an aqueous medium. The effect of salts such as NaCl, KCl, CaCl2, Na2CO3, and Na2SO4 in the medium on the rate of sugar conversion and LA yield was evaluated. Under optimum reaction conditions, 10% (w/w) fructose was dehydrated to LA (with 74.6% yield) in 10% (w/w) NaCl aqueous solution in 24 h at 110 °C using the catalyst at 30% (w/w sugar). Even 10% (w/w) glucose monohydrate was directly dehydrated to LA (with 70.7% yield) under similar conditions but at 145 °C. This study shows that the salts enhance the rate of catalytic dehydration in the order of Cl– > CO32– > SO42–. Thus, the combination of high sugar concentration and heterogeneous catalysis in an aqueous system under relatively mild conditions could provide a high-yielding and sustainable process for bio-based LA production.

Effectiveness of a 3-liter reactor with UV and persulfate in degrading chloramphenicol in water

The effectiveness of a 3-liter reactor with UV and persulfate (PS) in the degradation of chloramphenicol (CAP) in water was investigated. The UV-254 nm/PS process degraded CAP much more efficiently than the UV-254 nm process or the PS process alone. The dependences of the degradation of CAP on the UV wavelength, PS dosage, and addition of anions in the UV/PS process were examined. The UV-254 nm/PS process was much more effective than the UV-365 nm/PS process in degrading CAP. In the UV-254 nm/PS process, the efficiency and rate of degradation of CAP increased with the PS dosage from 1 to 10 mM. However, at a PS dosage of 20 mM, the degradation of CAP was lower. Hence, the UV-254 nm/PS process was most effective with a PS dosage of 10 mM. In the UV/PS process, the degradation of CAP exhibited a pseudo-first-order kinetic model. In the UV-254 nm/PS process, the addition of anions (Cl−, NO3−, and SO42−) limited the degradation of CAP in the order Cl−>NO3−>SO42−. In the absence of anions, the UV-254 nm/PS process with an initial CAP concentration of 10 mg/L and a PS dosage of 10 mM provided complete degradation of CAP in 4 min and 94% mineralization of CAP in 10 min. Therefore, a 3-liter reactor with the UV-254 nm/PS process is greatly effective in degrading CAP in water.

A computational study of hydrogen bonding motifs in halide, tetrafluoroborate, hexafluorophosphate, and tetraarylborate salts of chiral cationic ruthenium and cobalt guanidinobenzimidazole hydrogen bond donor catalysts; acceptor properties of the “BArf” anion

The chiral complexes [(η5-C5H5)Ru(CO)(GBI)]+ X− and mer-[Co(GBI)3]3+ 3X−, where GBI is the chelate ligand 2-guanidinobenzimidazole (HN=C(NHH′)NHC(NHR)=NR′), are effective hydrogen bond donor catalysts for a variety of organic reactions. Salts with X− = halide, BF4−, PF6− and BArf− (B(3,5-C6H3(CF3)2)4−) are studied computationally as an initial step in rationalizing reactivity trends and enantioselectivities. A variety of cation/anion hydrogen bonding motifs are identified, some involving a dyad of synperiplanar NH linkages (HN=C(NHH′)NHC(NHR)=NR′), and others (more stable) involving a triad (HN=C(NHH′)NHC(NHR)=NR′). Within each series, the gas phase ΔG values follow the order Cl− (most negative ΔG) < BF4−< PF6− < BArf−, paralleling catalytic activities and (inversely) hydrogen bond acceptor strengths suggested experimentally. With BF4−, all hydrogen bonds involve F-B-F units; with PF6−, both cis-F-P-F and mer-F-PF-F units can bind; with BArf− the isomers feature 2–6 NH⋯FC− and 1–2 NH⋯π interactions. The ΔG values in CH2Cl2 show a few differences in relative stabilities, which are analyzed; in the ruthenium series, free or solvent separated ions are predicted to be the major species for all PF6− and BArf− salts. Crystallographically characterized BArf− salts where the cations possess NH donor groups are analyzed.

High CO2 absorption capacity of metal-based ionic liquids: A molecular dynamics study

The absorption of CO2 is of importance in carbon capture, utilization, and storage technology for greenhouse gas control. In the present work, we clarified the mechanism of how metal-based ionic liquids (MBILs), Bmim[XCln]m (X is the metal atom), enhance the CO2 absorption capacity of ILs via performing molecular dynamics simulations. The sparse hydrogen bond interaction network constructed by CO2 and MBILs was identified through the radial distribution function and interaction energy of CO2-ion pairs, which increase the absorption capacity of CO2 in MBILs. Then, the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO2 in ILs. That's to say, the MBILs can enhance the CO2 absorption capacity and the diffusive ability simultaneously. Based on the analysis of structural, energetic and dynamical properties, the CO2 absorption capacity of MBILs increases in the order Cl− → [ZnCl4]2−→ [CuCl4]2−→ [CrCl4]− → [FeCl4]−, revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO2 absorbing process. These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO2 absorption process, which can also shed light on the rational molecular design of MBILs for CO2 capture and other key chemical engineering processes, such as IL-based gas sensors, nano-electrical devices and so on.

Yttrium complexation and hydration in chloride-rich hydrothermal fluids: A combined ab initio molecular dynamics and in situ X-ray absorption spectroscopy study

Accurate knowledge of rare earth elements (REE) speciation in high pressure – high temperature fluids is required to model REE transport and precipitation in subduction zones and magmatic-hydrothermal environments, and the formation of rare metal deposits. Recent experiments (lanthanum, ytterbium, erbium) have demonstrated that REE chloride complexes are the main REE form in many hydrothermal fluids (Migdisov et al., 2016). However, the speciation of yttrium (Y(III)), a cation with an ionic radius similar to that of Ho(III), remains poorly constrained in chloride-rich hydrothermal solutions.We used ab initio molecular dynamics (MD) simulations to calculate the nature of Y(III)-Cl complexes and the thermodynamic properties of these species at temperatures up to 500 °C and pressures of 800 bar and 1000 bar. The MD results were complemented by in situ X-ray absorption spectroscopy (XAS) measurements. Our results indicate that at temperatures below 200 °C, chloro-complexes do not form readily, even in highly concentrated brines. At ambient condition, the Y(III) aqua ion binds to eight water molecules in a square antiprism geometry, which is consistent with previous ab initio studies (Ikeda et al., 2005a). The thermodynamic integration method was employed to calculate the formation constants (logKΘ) of Y(III)-Cl− complexes in two simulation boxes containing different Y:Cl ratios; we obtained very consistent results of the standard logKΘ of the individual complexes from the two independent calculations, which confirms that the thermodynamic integration method is reliable and not significantly affected by technical limitations in box size, box composition, or simulation time.Based on the derived formation constants, we fit modified Ryzhenko–Bryzgalin (MRB) equation of state parameters, which enable extrapolation of the formation constants at elevated temperature and pressure. The results are consistent with the XAS data, and show that the stability of Y(III)-Cl complexes increases with increasing temperature, Y(III) forming high order Cl− complexes (up to YCl4−) in high salinity solutions at high temperature and pH = 3. We also compare the extrapolated logKΘ with the available data for other REE at 150 °C, 200 °C and 250 °C. At 200 °C, yttrium behaves more like a heavy REE, but from 200 °C to 250 °C, the formation constants of Y(III)-Cl complexes increase dramatically and behave more like the light REE. The difference of Cl− dominant species between Ho(III) (HoCl2+) and Y(III) (YCl2+) may account for the formation of anomalous Y/Ho ratios in some hydrothermal environments.

Selective removal of Cl− and F− from complex solution via electrochemistry deionization with bismuth/reduced graphene oxide composite electrode

Electro-adsorption is attracting increasing attention as an emerging technology for removing ionic species from water but suffer from low selectivity. In this work, a bismuth/reduced graphene oxide nanocomposite electrode was fabricated by a facile and green method. Based on this material, an electrode with improved selectivity by electrochemistry deionization system was successfully fabricated. The bismuth nanoparticles were uniformly covered with reduced graphene oxide plates and the ratio of Bi on the whole materials is 79.56%. Bismuth/reduced graphene oxide showed ions selectivity in the order of Cl− > F− ≫ SO42−. The average Cl− removal capacity can reach as high as 62.59 mg g−1. Moreover, bismuth/reduced graphene oxide electrodes have good regeneration performance. Typically, in the 10 adsorption-desorption multicycles, the salt absorption/desorption capacity of the hybrid capacitive deionization system is stable and reversible. This research opened a hopeful window to design and synthesize effective materials to selectively remove the ionic species to purify the water.

Evaluation of groundwater suitability for irrigation in the coastal aquifer of Mnasra (Gharb, Morocco)

The coastal area of the Gharb plain constitutes the only hydric resource for region in terms of domestic consumption and agricultural demand which does not cease to increase. It is a very productive and easily accessible groundwater resource, used extensively for irrigation by own pumping. This study was performed to understand the impact of groundwater quality on the crop yields and its suitability for the irrigation for 63 wells and 7 boreholes. Groundwater quality in Mnasra was studied based on different indices for irrigation. The values of SAR, Na %, MAR, SSP, PI, RSC and TDS show that most of the samples fall under good to suitable category. Piper diagram reveals three facies: sodic, calcic and magnesic chlorinated. The results indicate that the order of cation dominance is Na &gt; Ca &gt; Mg &gt; K, while anion dominance is in the order Cl &gt; HCO3&gt; SO4. Stuyfzand's classification indicates that most of the waters analyzed are fresh with moderate alkalinity. Richard Plot indicates that groundwater in the study area is within the low salinity to low sodium hazard and medium salinity to low sodium hazard class (C2S1 and C3S1). Wilcox Plot shows groundwater to be within excellent to a good class.

Catalytic degradation of ciprofloxacin by magnetic CuS/Fe2O3/Mn2O3 nanocomposite activated peroxymonosulfate: Influence factors, degradation pathways and reaction mechanism

In the study, CuS/Fe2O3/Mn2O3 magnetic nanocomposite was successfully synthesized and the properties were investigated via a series of characterization. Subsequently, the magnetic nanocomposite was applied to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. The results showed that the CuS/Fe2O3/Mn2O3 magnetic nanocomposite possessed higher catalytic performance for ciprofloxacin degradation than bare CuS and Fe2O3/Mn2O3 composite. The degradation process of CIP was suitable for the pseudo-first-order kinetic model and the highest rate was reached 0.10083 min−1. And under the optimized conditions (catalyst = 0.6 g·L−1, PMS = 0.6 g·L−1, pH = 5.84, C0 = 0.2 g·L−1 and t = 120 min), the efficiency of 88% and 48.6% were corresponding to degradation and mineralization of ciprofloxacin, respectively. In addition, the key factors of degradation process such as catalyst dosage, PMS concentration, initial pH value and common anions were investigated. And the results indicated that the degradation efficiency of ciprofloxacin was reduced, which affected by the common anions in order of Cl− > SO42− > NO3− > HCO3− > Humic acid. Besides, several intermediates of ciprofloxacin were detected and the plausible degradation pathways were proposed. In addition, the underlying reaction mechanism was proposed. Meanwhile, the results of free radical quenching experiment and electron paramagnetic resonance (EPR) spectra indicated that both OH and SO4− radicals were existed in the reaction system and the OH radicals had a conquer role in the degradation progress. Moreover, the stability and reusability of CuS/Fe2O3/Mn2O3 magnetic nanocomposite were evaluated, which the degradation efficiency still reached 72% after five times used. Ultimately, the as-constructed CuS/Fe2O3/Mn2O3 magnetic nanocomposite might be a candidate to the removal of refractory pollutants in environmental remediation.

New triazepine carboxylate derivatives: correlation between corrosion inhibition property and chemical structure

In this investigation, attempts have been made to study the corrosion inhibition properties of three new triazepine carboxylate compounds for mild steel in 1.0 M hydrochloric acid medium. The evaluation was carried out using mass loss, electrochemical impedance spectroscopy and polarization curves measurement. Impedance diagrams and Bode plots for uninhibited and inhibited systems were analyzed using Zview program. The fitted data observed trails in nearly the same pattern as the experimental results. It is showed that triazepine carboxylate compounds are very good inhibitors for mild steel corrosion in 1.0 M hydrochloric acid medium which act as mixed-type inhibitors. So, the inhibition efficiency was increased with inhibitor concentration in the order Cl–Me–CN > Me–CN > Cl–Me–CO2Et which depended on their molecular structures. Electrochemical impedance spectroscopy showed that all compounds act by the formation of a protective film at the metal surface. Surface analyses via SEM and Optical 3D profilometry were used to investigate the morphology of the steels before and after immersion in 1.0 M HCl solution containing inhibitors. The correspondence between inhibition property and molecular structure of the triazepine carboxylate compounds was investigated, using density functional theory (DFT). Experimental and DFT study was further supported by molecular dynamic simulations study.

Assessment of Groundwater Quality in Coastal Region a Case Study of Qayyumabad, Karachi, Pakistan

The aim of present study is to assess groundwater quality of Qayyumabad area for drinking purpose. Groundwater samples (n = 20) were collected from wellbores from variable depths (12-300 feet) occurring on both banks of the Malir River near study area. Water quality was assessed through estimation of physical parameters including, pH, Eh, TDS, EC, hardness, temperature, aesthetic character (taste, color and odor) and chemical parameters including major cations (Na, K, Ca, Mg), anions (Cl, NO3, SO4, HCO3) and minor/trace elements (Fe, As). Data revealed that groundwater of study area has very high TDS content (range: 805-40340 mg/l) and positive Eh (-180 to +125 mV), suggesting the recent recharge. The pH varies in the range of 6.55-7.75 which comply with WHO limit (6.5-8.5) for drinking water. Major solutes varied in the order of Na (mean: 2587 mg/l) > Mg (433mg/l) > Ca (231mg/l) > K (91 mg/l) while anions in the order of Cl (mean: 3385 mg/l) > SO4 (mean: 580 mg/l) > HCO3 (mean: 343 mg/l) > NO3 (11.43 mg/l). Both arsenic and iron contents occur within the WHO permissible limits except two samples which showed elevated Fe (4950 ppb) and As (100 ppb) respectively. These results suggest that groundwater in study area is unfit for drinking purpose. Principal component analysis (PCA) explained four factors where F1 suggests the salts leaching mechanism and F2 indicated anoxia prevalence due to organic matter decomposition. On the other hand, F3 confirmed water rock interaction and F4 supported the prevalence arsenic release associated with anoxia.

Localized corrosion and stress corrosion cracking of stainless steels in halides other than chlorides solutions: a review

Abstract Fluorides, bromides, and iodides, despite being less common than chlorides, are present in various environments of industrial relevance. Stainless steels suffer pitting corrosion in solutions of all halides except fluorides, which can be understood considering that fluoride is the anion of a weak acid. The aggressiveness of the rest of the halides for pitting corrosion is on the order Cl− &gt; Br− &gt; I− for stainless steels with Mo content below 3 wt.%. Mo is not as effective in inhibiting Br− pitting corrosion as it is for inhibiting Cl− pitting corrosion. Most of those observations were rationalized based on the effect of anions on pit growth kinetics. Sensitized austenitic stainless steel suffers stress corrosion cracking (SCC) in solutions of all halides, albeit chlorides seem to be the most aggressive. Fluoride SCC is relevant for SCC under insulation of stainless steels, and standards and regulations developed to mitigate this problem consider this ion as aggressive as chloride. For the solubilized stainless steels, aggressiveness toward SCC is in the order Cl− &gt; Br−. The SCC of solubilized stainless steels was not observed in solutions of F− and I−, and the possible reasons for this fact are discussed.

Hydrogeochemistry of the deglaciated lacustrine systems in Antarctica: Potential impact of marine aerosols and rock-water interactions

The deglaciated lacustrine systems in Grovnes, Larsemann Hills, East Antarctica was assessed for its solute dynamics and hydrogeochemical interactions. These pristine high latitude lacustrine systems serve as a natural laboratory to understand the interaction between hydrosphere, lithosphere and atmosphere thus providing valuable insights on the functioning of major biogeochemical cycles. A total of 14 fresh water lakes were identified and the water samples were analysed for its physico-chemical characteristics. The abundance of anions and cations in the lake water samples were in the following order of Cl− > HCO3– > SO42− > NO3− and Na+ > Mg2+ > Ca2+ > K+ respectively. Moreover, the lakes exhibit slightly alkaline condition due to dissolution of alkaline earth metals and atmospheric fallout. Na+-Cl−–HCO3– and Na+-Cl− are the commonly noticed water type in the study area and higher concentration of Na+-Cl− were due to the effect of sea spray through marine aerosols. Reverse ion exchange is noticed in most of the lakes due to saline influence. Three major mechanisms such as rock dominance, precipitation/snow and evaporation/sea spray controls the lake water geochemistry in the study area. Silicate weathering and evaporite dissolution also contribute ionic load to the lake water. Significant positive correlations (p < .01) among major ions reveal sources from bedrock weathering along with marine aerosols. Trace element chemistry shows that rock-water interaction is the primary source for dissolved metals in the lake water followed by long range atmospheric transport in the form of aeolian dust. Mineral groups such as evaporites, sulphates, carbonates, metal oxides and hydroxides are responsible for the dissolution of metal complexes in the lake water. Furthermore, lakes falling within a micro basin have shown higher Na+-Cl− content which is due to the catchment effect where snow enriched with sea spray melts during the austral summer feeding these lakes.

Electrochemical activation of persulfate on BDD and DSA anodes: Electrolyte influence, kinetics and mechanisms in the degradation of bisphenol A

The combination of electrolysis and persulfate (PS) activation was investigated to enhance the degradation of bisphenol A (BPA) using boron-doped diamond (BDD) and dimensional stable anode (DSA) in perchlorate, sulfate, and chloride media. The acceleration effect of BPA degradation followed the order of Cl−>ClO4−>SO42- in BDD/PS and BDD system, while the degradation order in DSA/PS and DSA system was Cl−>SO42->ClO4−. The contribution of radical species (SO4− and OH), active chlorine and electrolysis were confirmed for the degradation in different media with PS. Active chlorine dominated the degradation process with 85 % and 60 % removal in BDD/PS and DSA/PS system at 10 min, while the contribution of SO4− decreased from 20 % and 18 % in perchlorate to 5 % and 6 % in chloride media, respectively. The aromatic intermediates resulting from hydroxylation and carboxylation pathway and chlorinated products via hydroxylation and chlorine substitution pathway were detected in perchlorate and chloride media in BDD/PS system, respectively. The attempt of BDD/PS system in actual wastewater indicated potential for further application. This study aims to provide a deep insight to comprehensively understand the enhanced performance, contributions of different removal mechanisms, and degradation pathway of pollutants during the activation of PS in BDD and DSA systems in different media.

Quinoline-8-olato-chromium catalysts with pseudohalogen effects for the CO2/cyclohexene epoxide copolymerization

Based on our previous studies utilizing CrIII catalysts with trifluoroacetate as labile ligand and an ansa-bis-quinoline-olato ligand as a chemically more robust variant compared to known salen-type N2O2 ligands, we synthesized and investigated a series of structurally similar quinoline-8-olato chromium complexes with different active (pseudo-)halogen ligands X in [(babhq)CrX], (babhq = 2,2′-(butyl-azanediyl)bis(quinolin-8-olate), X = Cl, NCO, and N3. We demonstrate a high activity of these CrIII complexes in the solvent free carbon dioxide/cyclohexene oxide (CHO) copolymerization compared to the state of the art. In much deeper detail than in our previous communication, we altered the labile ligand X and undertook a catalyst screening on the polymerization parameters, such as pressure, temperature, and cocatalyst, i.e. [PPN]N3 (bis(triphenylphosphine)iminiun azide). The activity of the chromium systems was found to much depend on the labile (pseudo-)halogen ligand X and increases in the order Cl < NCO < N3. Especially the azide complex [(babhq)CrN3] displays a high activity, displaying a TOF of 2165 h−1 after 1 h of reaction time along with an induction period of 30 min. At longer reaction times, up to 94% monomer conversion selectively into the respective polycarbonate (pCHC) is observed.

Comparison of ReO4 − and TcO4 − in solvent extraction systems

Abstract The suitability of perrhenate (Re(VII)) to act as an analog for pertechnetate (Tc(VII)) was tested using solvent extraction and the carrier/tracer systems 99Tc(VII)/99mTc(VII) and 185/187Re/186/188Re(VII). Perrhenate is often used as a non-radioactive analogue of pertechnetate, but scarce data is available for the comparison of these metals for liquid-liquid extraction applications. Results show that neither Tc(VII) nor Re(VII) extraction is influenced by pH in the 2–8 range. The anion extractant also separates electrolyte anions, with increasing extraction following the order Cl− &lt; NO3 − ≪ ClO4 −, resulting in a decreased Tc(VII) and Re(VII) extraction in presence of salt. In particular, the extraction of Re and Tc is suppressed in presence of NaCl at concentrations higher than 1 mM. While Tc extraction is larger than that of Re in absence of electrolyte, they are statistically identical in presence of enough electrolyte. Furthermore, tetraphenylphosphonium chloride (Ph4PCl) is a stronger extractant than iodonitrotetrazolium chloride (INT).

Desalination and Li+ enrichment via formation of cyclopentane hydrate

Hydrate-based desalination is an attractive and energy-effective method. In order to obtain high water recovery and purity, the desalination and Li+ enrichment performance were examined using single-stage desalination via graphite-promoted cyclopentane (CP) hydrate formation. LiCl, LiBr and LiI aqueous solutions with concentration ranging from 0.01 to 0.6 mol/L were used as brine. The rate for CP hydrate formation is determined by concentration, independent of the type of used salts. Halide ions were found to have the different capability in hindering CP hydrate-based desalination, with an order of Cl− < Br− < I−. The desalination efficiency was improved with increased concentration. Water recovery of 40% can be obtained in 1 h reaction, demonstrating the high efficiency of hydrate-based desalination. The desalination efficiency remains constant at around 70% over 24 h reaction, which can be dramatically enhanced by multi-stage desalination. The graphite powder, as the promoter for hydrate formation shows impressive recycling stability. The finding in this study would be of great help for developing effective desalination processes to produce fresh water and enrich high-value salts via CP hydrates.

Hydrochemical and statistical evaluation of groundwater quality in coastal aquifers in Tamil Nadu, India

Groundwater samples were collected from 36 wells during summer and monsoon seasons in a coastal region in Tamil Nadu, India in 2011. The chemical analysis of groundwater samples indicated that groundwater in the region was fresh to saline with cationic concentrations in the order Na+ > Ca2+ > Mg2+ > K+ and anionic concentrations in the order Cl− > HCO3− > SO42− > NO3−. Most of the groundwater samples had a chemical composition dominated by sodium and chloride ions. Scatter plots suggested that the principal processes influencing groundwater quality in the area are likely to be: ion exchange; reverse ion exchange; silicate weathering and evaporation. A Gibbs plot indicated that evaporation was the dominant process influencing groundwater salinity in the summer season, whereas both water–rock interactions and evaporation influenced the chemical composition and salinity of groundwater in the monsoon season. A principal component analysis of the data shows four principal components for the monsoon and three components for the summer seasons, which account for 85% and 87% of the total variance, respectively. The assessment has indicated that there is widespread seawater intrusion in coastal aquifers, which has led to changes in hydrochemical processes in the study area.