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1.
J Environ Manage ; 268: 110340, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32383660

RESUMO

CO2 separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO2 capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO2 sorption, reusability and CO2/CH4 selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO2 capture processes including higher CO2 sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO2 over CH4. The best performance was obtained by SX- [bmim] [TF2N] (223.4 mg CO2/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF2N] showed higher CO2 sorption capacity as compared to other reported sorbents. CO2 sorption and CO2/CH4 selectivity results were submitted to an analysis of variance and the means compared using Tukey's test (5%).


Assuntos
Líquidos Iônicos , Dióxido de Silício , Ânions , Dióxido de Carbono , Cátions
2.
Chemosphere ; 255: 126950, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32380266

RESUMO

Metal-modified carbon materials have been widely used for fluoride removal, but the traditional impregnation by soaking method suffers from low loading of metals and substantial use of chemicals. This study proposed a new approach to prepare zirconium modified activated carbon fibres (Zr-ACF) by a drop-coating method. Using the same amount of chemicals, the drop-coating method yielded a 5.5 times higher fluoride adsorption capacity than the soaking method due to more effective loading of Zr(IV) onto ACF. The effects of various preparation conditions, including the addition of a complexing agent (oxalic acid) and Zr/ACF mass ratio (0.2-1), were investigated. Zr-ACF prepared by drop-coating was characterised by SEM and BET, and the functional groups involved in the anchoring of Zr(IV) on ACF and the adsorption of fluoride onto Zr-ACF were identified by FTIR and XPS. Adsorption experiments at pH between 3 and 11 revealed that ion exchange and electrostatic attraction were the main adsorption mechanisms at different pH levels. Co-existing anions such as CO32-, HCO3- and Cl- had an insignificant negative impact (<5%) on fluoride adsorption capacity while SO42- decreased fluoride adsorption capacity by 11.5%. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms followed the Langmuir isotherm model with a maximum fluoride adsorption capacity of 28.50 mg/L at 25 °C, which was higher than other carbon-based materials in the literature. The remarkable improvement of adsorption capacity and reduced chemical consumption demonstrate that Zr-ACF prepared by drop-coating is a promising adsorbent for fluoride removal.


Assuntos
Fluoretos/química , Poluentes Químicos da Água/química , Zircônio/química , Adsorção , Ânions , Fibra de Carbono , Carvão Vegetal , Concentração de Íons de Hidrogênio , Troca Iônica , Cinética , Ácido Oxálico , Água , Purificação da Água/métodos
3.
Environ Sci Pollut Res Int ; 27(21): 27124-27134, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32394260

RESUMO

A dead-end ultrafiltration cup was continuously operated to investigate the underlying mechanisms of membrane fouling caused by gel layer in this paper. Anionic polyacrylamide was used as a model foulant for gel formation process in various ultrafiltration processes by two kinds of ultrafiltration membrane, e.g., polyvinylidene fluoride (PVDF) membrane (OM) and TiO2/Al2O3-PVDF membrane (MM); then, a gel formation model was established and systematically assessed. The results show that the gel formation process in ultrafiltration can be divided into three stages: "slow-rapid-slow" flux decay curve. The R2 value of the simulation curve was still higher than 0.90 for both OM and MM. Based on the current cognition, the proposed gel layer formation mechanism and mathematical model were feasible.


Assuntos
Ultrafiltração , Purificação da Água , Resinas Acrílicas , Ânions , Membranas Artificiais
4.
J Environ Sci (China) ; 92: 141-150, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32430117

RESUMO

Bauxite residue, a byproduct of alumina manufacture, is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds. Four typical anions of CO32-, HCO3-, Al(OH)4- and OH- (represented caustic compounds) and metal ions (As, B, Mo and V) were selected to assess their leaching behavior under dealkalization process with different conditions including liquid/solid ratio (L/S ratio), temperature and leaching time. The results revealed that washing process could remove the soluble composition in bauxite residue effectively. The leaching concentrations of typical anions in bauxite residue decreased as follows: c(CO32-) > c(HCO3-) > c[Al(OH)4-] > c(OH-). L/S ratio had a more significant effect on leaching behavior of OH-, whilst the leaching concentration of Al(OH)4- varied larger underleaching temperature and time treatment. Under the optimal leaching, the total alkaline, soluble Na concentrations, exchangeable Ca concentrations were 79.52, 68.93, and 136.0 mmol/L, respectively, whilst the soluble and exchangeable content of As, B, Mo and V in bauxite residue changed slightly. However, it should be noted that water leaching has released metal ions such as As, B, Mo and V in bauxite residue to the surrounding environment. The semiquantitative analysis of XRD revealed that water leaching increased the content of gismondine from 2.4% to 6.4%. The SEM images demonstrated the dissolution of caustic compounds on bauxite residue surface. The correlation analysis indicated that CO32- and HCO3- could effectively reflect the alkalinity of bauxite residue, and may be regarded as critical dealkalization indicators to evaluate alkalinity removal in bauxite residue.


Assuntos
Óxido de Alumínio , Cáusticos , Ânions , Metais , Água
5.
Chemosphere ; 256: 127044, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32428741

RESUMO

Various surfactants, such as nonionic Triton X-100 and Simple Green™ (SG), and anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were utilized to remove polycyclic aromatic hydrocarbons (PAHs) from heavily contaminated harbor sediments dredged from Kaohsiung Harbor in Taiwan. Desorption/re-sorption equilibrium, kinetics, and washability of PAHs using the selected surfactant were evaluated under different critical micelle concentrations (CMC). Experimental results revealed that the desorption rate of high molecular weight PAHs was greater than those of low molecular weight PAHs, and the anionic SDS was relatively effective in the removal of total PAHs (>50%) compared to the other surfactants. The correlation between the effectiveness of the surfactant washing processes and the physicochemical properties of individual PAH was statistically analyzed. The resulting data suggested that hydrophobic factors (Kow, Koc and Sw) affected PAH treatability more than the reactivity of PAH (electron affinity and ionization potential). Since the adsorption of anionic surfactant altered the hydrophobicity of organic matter in the sediment, PAHs preferred transferring from the sediment to the hydrophobic core of micelles in aqueous solution. Nevertheless, the nonionic surfactant enhanced the PAH partition in the aqueous phase, thus increasing the micellar solubilization of PAH.


Assuntos
Monitoramento Ambiental , Hidrocarbonetos Policíclicos Aromáticos/análise , Poluentes Químicos da Água/análise , Adsorção , Ânions , Micelas , Octoxinol/química , Dodecilsulfato de Sódio , Solubilidade , Tensoativos/química , Taiwan , Água/química
6.
Water Res ; 178: 115846, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32375112

RESUMO

Anion exchange resin (AER) adsorption is an established technology for water treatment and groundwater remediation. Two contaminants amenable to AER treatment are natural organic matter (NOM) and per- and polyfluoroalkyl substances (PFAS), specifically anionic perfluoroalkyl acids (PFAAs) such as perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). NOM is ubiquitous in natural waters and is often targeted for removal. PFAS occurrence in water resources is a human health concern. Accordingly, the goal of this research was to provide new insights on the use of AER for water treatment considering separate and combined removal of NOM and PFAAs. Batch experiments were conducted comparing polystyrene and polyacrylic AER in both chloride- and sulfate-forms using natural groundwater spiked with Suwannee River natural organic matter (SRNOM) and/or six PFAAs. The polymer composition of the AER had a significant impact on contaminant removal with polystyrene resin more effective for PFAA removal and polyacrylic resin more effective for SRNOM removal. Both resins had type I quaternary ammonium functional groups; however, the polyacrylic resin had trimethyl ammonium whereas the polystyrene resin had triethyl ammonium. Therefore, the influence of polymer composition could not be isolated conclusively from functional group chemistry. Polystyrene AER showed greater removal of PFAAs with sulfonate than carboxylate head group and 8-carbon than 4-carbon chain length. Removal of SRNOM and PFAAs by both resin polymer compositions were greater when sulfate was the mobile counterion ion than chloride. The results of this research have important implications for using AER for water treatment and remediation. Foremost, polymer composition and mobile counterion form of the resin can be selected to target specific contaminants and maximize contaminant removal. When contaminants have unique interactions with AER such as SRNOM and polyacrylic resin and PFAAs and polystyrene resin, the presence of one contaminant does not impact removal of the other contaminant.


Assuntos
Fluorcarbonetos , Poluentes Químicos da Água , Purificação da Água , Ânions , Humanos , Polímeros , Rios
7.
Chemosphere ; 256: 127124, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32450354

RESUMO

In the present work, talc (a low-cost clay) encapsulated salts alginate (TAL) beads were synthesized by cross-linking with lanthanum ion and tested for phosphate adsorption. Multiple methods were applied for the characterization of composites. The combined effect of talc and lanthanum improved phosphate removal performance of TAL beads. Factors such as talc content, La3+ concentration, adsorbent dosage, pH, co-existing ions (Cl-, NO3- and SO42-) were studied in batch experiments. The optimized TAL-7 beads exhibited satisfactory selectivity towards phosphate in the coexistence of competing anions and could remain efficient phosphate removal in the pH range of 4-6. The phosphate removal efficiency reached to 95% with a maximum uptake of 16.4 mg P/g obtained at the optimal pH 4. Further experiments suggested that Langmuir isotherm model and the pseudo-second-order kinetic model could well describe the phosphate adsorption process of TAL-7 beads. Moreover, TAL-7 beads exhibited superior phosphate fixation performance in the long-term experiment. The results from adsorption experiment and characterization analysis demonstrated that TAL-7 beads could be a cost-effective and promising biosorbent for phosphate adsorption and fixation in the aqueous environment.


Assuntos
Alginatos/química , Hidrogéis/química , Lantânio/química , Fosfatos/análise , Talco/química , Poluentes Químicos da Água/análise , Adsorção , Ânions , Concentração de Íons de Hidrogênio , Íons/química , Cinética , Fosfatos/química , Água/química , Poluentes Químicos da Água/química , Purificação da Água/métodos
8.
J Chromatogr A ; 1621: 461075, 2020 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-32354558

RESUMO

The role of individual functional groups has been assessed with regard to surface charge and chromatographic retention. Coatings were prepared from various fragments of the chiral zwitterionic materials Chiralpak ZWIX(+) and ZWIX(-). The different chromatographic ligands allowed fine tuning of the surface charge. Chiralpak ZWIX phases showed strongly negative ζ-potentials over the entire pH-range. Zwitterionic congeners with quinuclidine and sulfonic acid moieties but lacking the quinolone ring in the ligand structure exhibited shifted ζ-potentials of around + 5 to 20 mV depending on the surrounding residues. Capillary electrophoretic mobilitiy measurements with the chromatographic ligands and molecular dynamics simulations were carried out to offer some explanation of these surface charge differences of the distinct zwitterionic stationary phases. The new mixed-mode phases were also chromatographically characterized by simple RP and HILIC tests. The results allowed their positioning within a large variety of different commercially available RP, HILIC and mixed-mode phases, which were evaluated as well, by multivariate data processing using principal component analysis. The new mixed-mode phases overall exhibit reasonable hydrophilicity-lipophilicity balance and enable retention of ionic compounds by additional ionic interactions through weak anion-exchange (WAX-type), strong cation-exchange (SCX-type) or both (RP/ZWIX-type). Hence, the new RP/ZWIX phases can be flexible tools for selectivity tuning in RP and HILIC separations.


Assuntos
Cromatografia por Troca Iônica/métodos , Ânions/química , Cátions/química , Eletroforese Capilar , Interações Hidrofóbicas e Hidrofílicas , Ligantes , Simulação de Dinâmica Molecular
9.
Water Sci Technol ; 81(2): 293-300, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32333662

RESUMO

Boron removal from water containing 5 mg L-1 of boron using electrodialysis (ED) was studied as a function of several parameters such as flow rates, initial pH, coexisting anions and ED time. An ED cell, equipped with three cation exchange membranes (fumasep FKB) and two anion exchange membranes (fumasep FAB), was applied. The central composite design, which is the standard design of response surface methodology, was used to evaluate the effects and interactions of studied factors on boron removal efficiency. The effectiveness of the considered design parameters was well examined to find the optimum condition. The experimental data obtained were analyzed by analysis of variance for the polynomial model with 95% confidence level. Boron removal by ED showed to be independent of the electrodialysis time, whereas flow rate as well as the pH of the feed solution and also the coexisting anions on the feed solution play a significant role on the deboronation efficiency. According to the desirability function, the maximum response of 43.5% was predicted for boron removal at a pH equal to 10, a flow rate of 10 L h-1, a ratio between sulfates and that of boron equal to 2 and a reaction time of 25 minutes.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Ânions , Boro , Concentração de Íons de Hidrogênio , Água
10.
Water Sci Technol ; 81(1): 148-158, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32293598

RESUMO

The microbubble pretreated resin was used for demulsification and deoiling of the simulated O/W emulsion. The demulsification and deoiling performance and the influencing factors were investigated systematically. Experimental results indicate that the microbubble pretreated resin reaches a 97% oil removal within 80 min; on the contrary, oil removals are 90% and 85% for NaOH solution soaked and un-pretreated resins respectively. After five repeated runs, the oil removal of microbubble pretreated resin can be maintained at over 70%. The demulsification mechanism was revealed by comparing zeta potential, surface tension, contact angle of the emulsion in treatment, and the characterization results of the resin before and after use. Three possible pathways of demulsification were concluded and the ranking contributions can be shown below. Pathway 1: Competitive trapping of surfactant. The cationic groups of the resin combine with the anionic groups of the surfactant and drag them away from the oil particle surface. Pathway 2: Distribution equilibrium of surfactant. Free surfactants in the emulsion are captured by resin and reduce the concentration of uncombined surfactant. This results in surfactants on the oil particle partly detaching from the oil surface to maintain the adsorption-desorption equilibrium of the surfactant. Pathway 3: Adsorption coalescence.


Assuntos
Microbolhas , Tensoativos , Adsorção , Ânions , Emulsões
11.
Environ Sci Pollut Res Int ; 27(17): 21506-21516, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32277410

RESUMO

The ability of vetiver grass (Chrysopogon zizanioides L.) for the reduction of anions and cations especially inorganic nitrogen compounds from the influent and effluent of sewages was investigated. Vetiver grass was grown hydroponically in influent (IN) and four different effluent (EF) sewages including control, 125 (EF125), 250 (EF250), and 500 (EF500) mg L-1 Ca(NO3)2. During 18 days, phosphate concentration gradually declined in both influent and all effluent treatments. Unlike effluent treatments, the amount of ammonium in influent was greater than the standard (39.52 mg L-1) and decreased severely down to 4.85 mg L-1 at the end of the experiment. After just 48 h, the concentration of nitrate in EF treatment reached 2.25 mg L-1 that is lower than the standard. The decrease of nitrate to concentrations less than the standard was also observed at days 8, 11, and 18 in EF125, EF250, and EF500 treatments, respectively, and about 90% of nitrate had been removed from 500 mg L-1 Ca(NO3)2 treatment. Other ions such as Cl-, Ca2+, and K+ decreased in influent and all effluent sewages due to phytoremediation process. Accordingly, phytoremediation by vetiver grass could decrease concentrations of nitrate, ammonium, phosphate, chloride, and calcium in influent and all effluent sewages. Increasing the concentration of nitrate resulted in the increase in its uptake rate. In addition, a positive correlation was shown between the uptake rate of nitrate by vetiver grass and the duration of cultivation of this plant in nitrate-containing medium.


Assuntos
Compostos de Amônio , Vetiveria , Ânions , Biodegradação Ambiental , Cátions , Nitritos , Fosfatos , Esgotos
12.
J Chromatogr A ; 1622: 461127, 2020 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-32331778

RESUMO

Gas chromatographic columns based on ionic liquids (ILs) are very promising since the selectivity of these columns can be tuned by both the cation and the anion chemical nature. In this paper, efficiencies of capillary columns based on four phosphonium ionic liquids were studied. The performance of seven columns containing the cation trihexyl(tetradecyl)phosphonium and the anions bromide, chloride, and bis(trifluoromethylsulfonyl)imide was evaluated by measuring the solute band broadening as a function of gas velocities at three temperatures. Hence, classical height equivalent to a theoretical plate (H) against gas velocity (u) plots corresponding to those columns were generated and the data were fitted to the Golay-Guiochon equation with the aim of seeking the optimum conditions to be operated each of them. Band broadening at practical gas velocities is mainly due to poor mass transfer properties of solutes in the (viscous) liquid phases, which limits the achieved efficiencies. These H/u plots proved to be necessary to characterize the column quality at a given temperature, to interpret the band broadening phenomena and thus, to establish the lower temperature limits and the expected plate counts at that temperature.


Assuntos
Cromatografia Gasosa/métodos , Líquidos Iônicos/química , Compostos Organofosforados/química , Ânions , Cátions , Difusão , Dióxido de Silício/química , Temperatura
13.
J Chromatogr A ; 1621: 461066, 2020 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-32299623

RESUMO

The ion-exchange and complex forming equilibria were quantitatively described and demonstrated in order to understand major factors in the control of selectivity in the analytical separation of carboxylic acids and inorganic anions in cryptand based ion chromatography. A complex retention model has been developed for the separation on a non-conventional IC column. Changes in retention are treated both theoretically and experimentally. Retention mechanism is employed on a macrocycle-based (cryptand n-decyl-[2.2.2]) ion-exchange chromatographic phase to improve the selectivity for a mixture of model analytes. We introduced an alternative internal gradient method by mixed eluent (i.e. eluents formed by combination of two alkali hydroxide with different molar ratio). The effect of binary mixed eluent (Li/Na, Li/K) on the retention behavior and peak shape of carboxylic acids are also discussed in view of the proposed theory. It was shown that the effects of binary aqueous mobile phases, held isocratically behave very similar to the step gradient mode. The "internal gradient" separation system has advantages over traditional step gradient mode. Twenty-six anions of widely varying chemical character (mono-, di-, tri-valent inorganic anions, mono-, di-, tri-valent aliphatic carboxylic acids, aromatic- and haloacetic carboxylic acids) were investigated on the cryptand-based (D222) stationary phase using different methods by LiOH, NaOH and KOH eluent. The predicted vs measured retention data are in rather good agreement. High degree of linearity was obtained for inorganic anions, multivalent carboxylic acids, and for aromatic and haloacetic acids R2 = 0.992, 0.969, and 0.980, respectively.


Assuntos
Ácidos Carboxílicos/análise , Cromatografia por Troca Iônica/métodos , Éteres Cíclicos/química , Bases de Schiff/química , Ácidos/química , Ânions/química , Ácidos Carboxílicos/isolamento & purificação , Troca Iônica
14.
Chemosphere ; 253: 126702, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32302903

RESUMO

Iron (Fe)-based adsorbents have been promoted for aqueous arsenic adsorption because of their low cost and potential ease of scale-up in production. However, their field application is, so far, limited because of their low Fe use efficiency (i.e., not all available Fe is used), slow adsorption kinetics, and low adsorption capacity. In this study, we synthesized graphene oxide iron nanohybrid (GFeN) by decorating iron/iron oxide (Fe/FexOy) core-shell structured iron nanoparticles (FeNPs) on the surface of graphene oxide (GO) via a sol-gel process. The deposition of FeNPs on GO for the nanohybrid (GFeN) improves Fe use efficiency and arsenic mobility in the nanohybrid, thereby improving the arsenic removal capacity and kinetics. We achieved removal capacities of 306 mg/g for As(III) and 431 mg/g for As(V) using GFeN. Rapid reduction (>99% in <10 min) of As(III) and As(V) (initial concentration, C0 = 100 µg/L) was achieved with the nanohybrid (250 mg/L). There were no significant interferences by the coexisting anions and organic matters at environmentally relevant concentrations. Based on the experimental data, we have proposed that both electrostatic interaction and surface complexation contributed to ultra-high arsenic removal by GFeN. The GO sheets acted as the reservoirs for the electrons released during surface corrosion of the FeNPs and the electrons were transferred back to the FeNPs to rejuvenate the oxidized surface. The rejuvenated FeNP surface layer helped in additional arsenic removal.


Assuntos
Arsênico/química , Poluentes Químicos da Água/química , Adsorção , Ânions , Arsênico/análise , Compostos Férricos/química , Grafite/química , Concentração de Íons de Hidrogênio , Ferro , Cinética , Nanopartículas , Oxirredução , Água , Poluentes Químicos da Água/análise , Purificação da Água/métodos
15.
Chemosphere ; 250: 126312, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32120152

RESUMO

The main aim of the study was to compare the sorption capacity of hay-based activated biochars, obtained using conventional and microwave furnance, relative to copper(II) ions and ionic polyacrylamides (PAM). Surface properties of the solids were characterized by, inter alia, N2 adsorption/desorption isotherm method, whereas their tendency to aggregation was established turbidimetrically. Adsorption capacity of biochars were performed in the simple and mixed Cu(II)/PAM systems, i.e. the examined suspensions contained one or two adsorbates at the same time. The results indicated that biochar prepared in microwave furnance was characterized by larger micropore area and, as a result, it had higher adsorption capacity relative to Cu(II) ions. At pH 6, when the initial Cu(II) concentration equaled 100 mg/L, the biochar obtained by microwave heating adsorbed 81.5% of Cu(II) ions, whereas the one obtained by conventional heating - 51.6%. Due to high molecular weight, the PAM macromolecules could not penetrate the biochar micropores and thus the polymer adsorbed amounts were similar for both materials. For initial polymer concentration equal to 100 mg/L, the solids adsorbed 65-66.2% of cationic PAM containing 25% of quaternary amine groups. In the mixed system of anionic polyacrylamide and Cu(II) ions, the formation of Cu(II)-PAM complexes occurred, which favored both heavy metal and polymer adsorption on the solid surface. On the other hand, cationic polyacrylamide and heavy metal ions made the contact with the solid difficult for each other. What is more, ionic polyacrylamide and copper(II) ions stimulated the biochar aggregation due to surface charge neutralization and flocculation.


Assuntos
Carvão Vegetal/química , Cobre/química , Calefação , Resinas Acrílicas , Adsorção , Ânions , Íons , Metais Pesados/química , Propriedades de Superfície
16.
Chemosphere ; 252: 126475, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32200180

RESUMO

Iron-impregnated food waste biochar (Fe-FWB) was synthesized for Se(Ⅵ) removal from aqueous solution. The effect and interactive effects of different parameters including pyrolysis time, temperature, and Fe concentration were explored using response surface methodology (RSM) to enhance conditions to achieve the highest Se(Ⅵ) removal using Fe-FWB. Pyrolysis time was not significant for Se(Ⅵ) adsorption capacity of Fe-FWB, but temperature and Fe concentration were found to be significant. The highest adsorption was achieved at 3.47 h and 495.0 °C with an Fe concentration of 0.44 M. Fe-FWB synthesized under optimum conditions were used to investigate the kinetic, equilibrium, and thermodynamic adsorption of Se(Ⅵ). Se(Ⅵ) adsorption reached equilibrium within 6 h, and both pseudo-second order and pseudo-first order models were suitable for describing kinetic Se(Ⅵ) adsorption. The Freundlich model was found to suitably fit the equilibrium adsorption data than the Langmuir model. The highest adsorption capacity of Fe-FWB for Se(Ⅵ) was 11.7 mg g-1. Se(Ⅵ) adsorption on Fe-FWB was endothermic and spontaneous. The enthalpy change for Se(Ⅵ) adsorption was 54.4 kJ mol-1, and the entropy change was negative at 15-35 °C. The increment of solution pH from 3 to 11 decreased the Se(Ⅵ) adsorption from 19.2 to 7.4 mg g-1. The impact of interfering anions on Se(Ⅵ) adsorption followed the lineup: HCO3- > HPO42- > SO42- > NO3-. When compared to some adsorbents, the adsorption capacity of Se(Ⅵ) onto Fe-FWB was comparable even at neutral pH and the Fe-FWB was granular. These results indicate that Fe-FWB has prospective application in the removal of Se(Ⅵ) from aqueous solutions.


Assuntos
Selênio/química , Poluentes Químicos da Água/química , Adsorção , Ânions , Carvão Vegetal/química , Alimentos , Concentração de Íons de Hidrogênio , Ferro , Cinética , Estudos Prospectivos , Selênio/análise , Temperatura , Termodinâmica , Água , Poluentes Químicos da Água/análise
17.
Phys Chem Chem Phys ; 22(14): 7193-7200, 2020 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-32195495

RESUMO

We report a joint negative ion photoelectron spectroscopy (NIPES) and computational study on the electronic structures and noncovalent interactions of a series of cyclodextrin-closo-dodecaborate dianion complexes, χ-CD·B12X122- (χ = α, ß, γ; X = H, F). The measured vertical/adiabatic detachment energies (VDEs/ADEs) are 1.15/0.93, 3.55/3.20, 3.90/3.60, and 3.85/3.60 eV for B12H122- and its α-, ß-, γ-CD complexes, respectively; while the corresponding values are 1.90/1.70, 4.00/3.60, 4.33/3.95, and 4.30/3.85 eV for the X = F case. These results show that the inclusion of B12X122- into the CD cavities greatly increases the electronic stability of the dianions. The effect of electronic stabilization for ß-CD is roughly the same as for γ-CD, both being considerably stronger than that for α-CD. Density functional theory (DFT) based geometry optimization reveals that B12X122- are inserted into CDs increasingly deeper from α-CD to γ-CD. The calculated VDEs and ADEs agree with the experiments well, particularly, reproducing the electron binding energy (EBE) trends. The molecular orbital analyses indicate that the most loosely bound photodetached electrons originate from the guest B12X122- moieties. In addition to a shift of all signals to a larger EBE, significant changes in the signal patterns are observed. At low EBE, this is due to the splitting of highly degenerate B12X122- orbitals, while at high EBE, photodetachment from CD oxygens contributes to the new bands. The guest B12X122- and host CD noncovalent, size-specific interaction based on the independent gradient model (IGM) and energy decomposition analysis (EDA) is dominated by electrostatic interactions. The analysis further unravels unambiguously the existence of dihydrogen bonding and how it affects the total energy that stabilizes the host-guest complexes of CDs·B12H122- compared to the general hydrogen bonding interaction in CDs·B12F122-. This work clearly exhibits strong influences on the electronic structures of dodecaborates upon clustering with CDs, with both size (α-, ß-, and γ-) and molecular (X = H or F) specificities, thus providing critical molecular-level information on the cyclodextrin-closo-dodecaborate interactions of interest to medical applications, e.g., boron neutron capture therapy.


Assuntos
Ânions/química , Compostos de Boro/química , Espectroscopia Fotoeletrônica , Química Computacional , Estrutura Molecular
18.
Environ Sci Pollut Res Int ; 27(14): 16754-16762, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32130638

RESUMO

This study investigated the differential toxicities of anionic and nonionic surfactants commonly used as active ingredients in household cleaning agents. The acute toxicity of the surfactants against Clarias gariepinus were investigated using static bioassays while the sublethal effects on the biochemical parameters and the histopathology of liver and gills of the fish were investigated for a period of 28 days using a static renewal bioassay. The anionic surfactants were found to be more acutely toxic against the fish than the nonionic surfactants. The evaluation of the joint action toxicity of the surfactants against the test species using the concentration-addition model showed antagonistic interactions when the surfactants are present in mixtures. The two groups of surfactants also had varying degree of effects on the antioxidant stress enzymes and the liver function enzymes of the fish. However, only the anionic surfactants caused changes in the histopathology of the gills of the fish. The results obtained from this study have shown that anionic surfactants are more toxic to fish compared to nonionic surfactants. Anionic surfactants are the most commonly used surfactants in cleaning agents, there is a need for stricter regulations governing the use of this class of surfactants in cleaning agents.


Assuntos
Peixes-Gato , Animais , Ânions , Antioxidantes , Brânquias , Tensoativos
19.
Environ Pollut ; 262: 114303, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32155556

RESUMO

Low pH and aluminum (Al)-toxicity often coexist in acidic soils. Citrus sinensis seedlings were treated with nutrient solution at a pH of 2.5, 3.0, 3.5 or 4.0 and an Al concentration of 0 or 1 mM for 18 weeks. Thereafter, malate, citrate, isocitrate, acid-metabolizing enzymes, and nonstructural carbohydrates in roots and leaves, and release of malate and citrate from roots were measured. Al concentration in roots and leaves increased under Al-toxicity, but it declined with elevating nutrient solution pH. Al-toxicity increased the levels of glucose, fructose, sucrose and total soluble sugars in leaves and roots at each given pH except for a similar sucrose level at pH 2.5-3.0, but it reduced or did not alter the levels of starch and total nonstructural carbohydrates (TNC) in leaves and roots with the exception that Al improved TNC level in roots at pH 4.0. Levels of nonstructural carbohydrates in roots and leaves rose with reducing pH with a few exceptions with or without Al-toxicity. A potential model for the possible role of root organic acid (OA) metabolism (anions) in C. sinensis Al-tolerance was proposed. With Al-toxicity, the elevated pH upregulated the OA metabolism, and increased the flow of carbon to OA metabolism, and the accumulation of malate and citrate in roots and subsequent release of them, thus reducing root and leaf Al and hence eliminating Al-toxicity. Without Al-toxicity, low pH stimulated the exudation of malate and citrate, an adaptive response of Citrus to low pH. The interactive effects of pH and pH on OA metabolism were different between roots and leaves.


Assuntos
Citrus sinensis , Citrus , Alumínio , Ânions , Concentração de Íons de Hidrogênio , Folhas de Planta , Raízes de Plantas
20.
Artigo em Inglês | MEDLINE | ID: mdl-32186230

RESUMO

In this study, a green adsorbent was synthesized for the removal of nitrate ions from water. The adsorbent consisted of carbonaceous particles with high specific surface area (1,240 m2 g-1) and porosity derived from pyrolysis of cornelian cherry stone and modified by protonated cross-linked chitosan. The adsorbent was characterized using various techniques like SEM, FTIR, BJH and zeta potential measurements. Dynamic behavior of the adsorbent in the nitrate adsorption was studied in a packed bed system at various operating conditions and in the presence of other competing anions (PO43-, HCO3-, SO42-). Based on the error analysis, the optimum operating conditions were considered at flow rate of 3.8 mL min-1, bed depth of 10 cm and nitrate concentration of 75 mg L-1. The kinetics of the adsorption process was studied using Adams-Bohart and Thomas models and the qmax was calculated to be about 12.4 mg g-1 at neutral pH and room temperature. Furthermore, the relationship between the bed height and the breakthrough time was described by bed depth service time (BDST) model. The experimental results suggested that the adsorbent possessed significant ability in nitrate removal from water due to the desired chemistry of the biopolymer and the excellent textural properties of the carbon support.


Assuntos
Quitosana/química , Reagentes para Ligações Cruzadas/química , Modelos Teóricos , Nitratos/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Adsorção , Ânions , Biomassa , Concentração de Íons de Hidrogênio , Cinética , Prótons , Propriedades de Superfície , Águas Residuárias/química
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