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1.
Water Res ; 173: 115596, 2020 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-32062228

RESUMO

Selective reduction of nitrate to N2 is attractive but still a difficult challenge in the water treatment field. Herein, we established a flow-through electrochemical system packed with polymeric beads supported nZVI (nZVI@D201) for selective nitrate reduction. Consequently, efficient nitrate reduction in the flow mode was achieved on nZVI@D201 under electrochemical regulation with N2 selectivity of up to 95% for at least 60 h. Otherwise, nZVI was gradually exhausted after 20 h, and the product was mainly the undesired NH4+. Through a series of comparative experiments, we clarified that the enhanced nitrate reduction on nZVI under electrochemical regulation was mainly attributed to electrons (from cathode) and active hydrogen ([H]) rather than the previously speculated H2. Combining the characterizations of nZVI during nitrate reduction by X-ray diffraction and X-ray photoelectron spectrometry, we found that nitrate reduction under electrochemical regulation was mediated by nZVI along with the resultant Fe0@FexOy-Fe(II) structure and was sustained by electrons (from cathode) and [H] via the in situ reduction of Fe(III) back to Fe(II). Meanwhile, the undesirable product NH4+ was efficiently oxidized to N2 by the active chlorine generated on the anode. This study not only clarifies the mechanism of enhanced nitrate reduction on nZVI via electrochemical regulation but also advances the technological coupling of nZVI reduction with electrochemistry.

2.
J Hazard Mater ; 381: 120961, 2020 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-31412305

RESUMO

We design a novel cationic metal-organic framework hybrid ultrafiltration polyvinylidene fluoride membrane (PVA/Cu-iMOFs/PVDF-0.05) and report its unique capture of aqueous perchlorate (ClO4-) at ppm-level. This membrane outperformed traditional adsorption materials and exhibited a specific affinity toward ClO4- in the presence of various competing anions at greater levels (up to a concentration ratio of 20). In the batch experiment, the ClO4- removal ratio reached 99.6% over a wide pH range (3˜10). Membrane filtration by using a 12.56 cm2 PVA/Cu-iMOFs/PVDF-0.05 membrane could effectively treat 4.71 L of ClO4--contaminated water before breakthrough occurred, while maintaining a satisfactory permeability (˜627.32 L/(m2 h bar)) and antifouling property. The exhausted membrane could easily be regenerated in aminoethanesulfonic acid solution for repeated use with a negligible decrease in capacity. Moreover, the membrane showed excellent long-term stability in a cross-flow filtration process due to the amido bond between the Cu-iMOFs and membrane surface as well as the "protection" of polyvinyl alcohol. Selective and reversible ion-exchange between the sulfonic acid (R-SO3) ligands of Cu-iMOFs and tetrahedral oxo-anionic species was verified to be the pathway for ClO4- trapping. Thus, other problematic elements that also occur in tetrahedral form in water can be removed by this method.

3.
Water Res ; 168: 115211, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31669780

RESUMO

It has been long desired but challenging to forward the advanced treatment of wastewater from empirical trials towards scientific design due to the lack of molecular insight into the pollutants of concern. Herein, we first established a systematic methodology to identify the ligands of Ni(II)-complexes in an electroless nickel (EN) plating effluent. The presence of N-containing groups in the ligands of most Ni(II)-complexes was verified by time-aligned ICP-MS and ESI-HRMS, implying the suitability of autocatalytic ozonation for efficient decomplexation. Thereby, a combined process was proposed on the basis of ozonation to achieve over 83% decomplexation of Ni(II) (initially at 0.36 mg/L), followed by selective Ni(II) sequestration for resource recovery. Combinational LC-MS systems revealed the ozonation-induced fragmentation or elimination of most Ni(II)-complexes as well as the structural change of the residual complexed molecules. The released free Ni(II) was further sequestrated by a nanocomposite of hydrated Zr(IV) oxide confined in a polymeric cation exchanger (nHZO@PCE). The fixed-bed working capacity of nHZO@PCE (∼550 BV) for the ozonated EN plating effluent was over 18 times that of the cation exchanger host (∼30 BV) at the breakthrough point of 0.10 mg Ni/L. More attractively, five adsorption-regeneration cycles demonstrated the great potential of the hybrid adsorbent for sustainable utilization. This study is believed to shed new light on how to design rational processes for advanced treatment of real wastewater based on molecular identification.


Assuntos
Nanocompostos , Poluentes Químicos da Água , Adsorção , Níquel , Águas Residuárias
4.
Chemosphere ; 240: 124940, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31574446

RESUMO

Charged ultrafiltration (UF) membranes can repel electrically charged molecules that are smaller than the size of the membrane pores and display high rejection of solutes, high flux, and low operation pressures compared to uncharged UF, nanofiltration (NF) and reverse osmosis (RO). Here, a charged UF membrane composite (PANI/PVDF) was prepared and regulated via electrochemically reversible control in portions of amine/imine functional groups of PANI. As a result, the permeability and rejection ratios of CR2- on charged PANI/PVDF, with PVDF as a control, increased from 19.6 to a maximum of 183.3 L m-2 h-1 bar-1 and from 3.4% to 74%, which expands the trade-off confine benefited from surface potential change from -12.21 mV to -25.26 mV, furtherly, the rejection ratio of CR2- on PANI/PVDF reached up to 93% via the electrochemical regulation. Finally, a fixed-charge model was built that well describes the steric and electric repulsion effects on membrane performance and the important roles of the electrochemically controllable surface charge. Moreover, the contour map of rejection ratios containing the ratio of molecular size vs the average pore size of the membrane (r/R = 0.2-1.0) and the zeta potential (-10 to -60 mV) were taken into account, which can be used to visually understand the rejection performance of membranes. This model is also appropriate for varying molecular sizes and for molecules with different charges. Our work opens a new horizon for the design of electrochemically controllable charged membranes to remove charged compounds.


Assuntos
Corantes/análise , Técnicas Eletroquímicas/métodos , Ultrafiltração/métodos , Purificação da Água/métodos , Eletricidade , Membranas Artificiais , Propriedades de Superfície
5.
Environ Sci Technol ; 2019 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-31804806

RESUMO

Eutrophication of water bodies is a serious and widespread environmental problem. Achieving low levels of phosphate concentration to prevent eutrophication is one of the important goals of the wastewater engineering and surface water management. Meeting the increasingly stringent standards is feasible in using a phosphate-selective sorption system. This critical review discusses the most fundamental aspects of selective phosphate removal processes and highlights gains from the latest developments of phosphate-selective sorbents. Selective sorption of phosphate over other competing anions can be achieved based on their differences in acid-base properties, geometric shapes, and metal complexing abilities. Correspondingly, interaction mechanisms between the phosphate and sorbent are categorized as hydrogen bonding, shape complementarity, and inner-sphere complexation, and their representative sorbents are organic-functionalized materials, molecularly imprinted polymers, and metal-based materials, respectively. Dominating factors affecting the phosphate sorption performance of these sorbents are critically examined, along with a discussion of some overlooked facts regarding the development of high-performance sorbents for selective phosphate removal from water and wastewater.

6.
J Colloid Interface Sci ; 557: 357-366, 2019 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-31536916

RESUMO

Hydroxyapatite (Hap) has been shown to be an excellent sorbent for F- removal of elevated levels of fluoride in groundwater worldwide; however, the molecular mechanisms of this process have not been clearly addressed. Herein, we used 19F solid-state NMR spectroscopy to investigate F- sorption mechanisms by nanosized Hap combined with 1H NMR and 1H{19F} Rotational Echo DOble Resonance (REDOR) technology in addition to other characterization methods such as Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Nanoscale Secondary Ion Mass Spectroscopy (NanoSIMS). Our experimental results showed that F- sorption mechanisms depend on solution pH and fluoride concentration ([F-]). At pH 7 and [F-] ≤ 50 mM, a single 19F NMR peak at -103 ppm was observed, which could be assigned to fluorapatite [Ca5(PO4)3F] (Fap) or fluoro-hydroxyapatite solid solution [Ca5(PO4)3Fx(OH)1-x; x = 0-1] (F-Hap). A simultaneous formation of fluorite (CaF2) precipitates (δF-19 = -108 ppm) was observed at higher [F-] (e.g., 100 mM), which was further confirmed by TEM and XRD analysis. The NanoSIMS and 1H{19F} REDOR analyses indicated that a dissolution-precipitation process was involved in the F- sorption on Hap. Our results strongly support the efficacy of Hap for F- removal even after several instances of regeneration, making it a cost-effective strategy for fluoride treatment.

7.
Chemosphere ; 234: 917-924, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31519100

RESUMO

Nickel, massively used in plating industry but detrimental to ecosystem, tends to form stable complexes with organic additives in industrial effluents. Currently, most of the available processes aim at water decontamination from free toxic metal ions and thus, could not effectively remove nickel-carboxyl complexes from water. Herein, we employed a proprietary combined process Fe(III)/UV/NaOH, namely Fe(III) displacement and UV irradiation followed by alkaline precipitation, to validate its feasibility on the efficient removal of nickel-carboxyl complexes from synthetic and authentic effluents. Fe(III)/UV/NaOH outperformed other commonly used processes including NaOH precipitation, UV/NaOH, Fe(III) coagulation, and Fenton/NaOH. Each unit of the combined process was optimized, and the underlying mechanism was elucidated. Fe(III) displacement favored the stoichiometric release of free nickel ions and formation of Fe(III)-carboxyl complexes, which could be decarboxylated via ligand-metal charge transfer under UV irradiation. The precipitation unit aims at simultaneously removing the released Ni along with Fe species. Attractively, the presence of other organic species (ethylene glycol, ethyl acetate and humic acid) and anions (chloride and sulfate) exerted very slight effect on the final Ni removal, whereas greatly adverse effect occurred on the Fenton process under similar conditions. The feasibility of the combined process was validated by testing on an authentic electroplating effluent, resulting in the residual Ni below 0.1 mg/L, the most stringent discharge standard for Ni in electroplating effluent in China.


Assuntos
Compostos Férricos/química , Níquel/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , China , Ecossistema , Galvanoplastia , Hidróxido de Sódio , Sulfatos , Raios Ultravioleta , Água , Poluentes Químicos da Água/análise
8.
Water Res ; 164: 114888, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31377525

RESUMO

Stringent regulations and deteriorating source water quality could greatly influence the water production capacity of drinking water treatment plants (DWTPs). Using models to predict the performance of DWTPs under stress provides valuable information for decision making and future planning. A hybrid statistic model named HANN was established by combining artificial neural network (ANN) with genetic algorithm (GA) aiming at forecasting the overall performance of DWTPs nationwide in China. Monthly data from 45 DWTPs across China was employed. Water quality parameters like temperature and chemical oxygen demand (COD) and operational parameters like electricity consumption and chemical consumption were selected as input variables, while drinking water production was employed as the output. Both preliminary data analysis and principal component analysis (PCA) suggested a clear non-linear relationship between the input and output variables. The structure of the HANN model was optimized by employing the lowest mean squared error (MSE) as the indicator. The resultant HANN model performed well when simulating the training datasets. Its predictive accuracy for the independent test datasets was enhanced when feeding more training datasets and the performance was constantly higher than the independent multi-layered ANN models using the coefficient of determination (R2) as the indicator, indicating the HANN model was capable of capturing complex non-linear relationship and extrapolation. Results from Accuracy test, Garson sensitivity analysis and Analysis of Variance (ANOVA) suggested the quantity of water produced by DWTPs was closely linked to water quality and operational parameters. The scenario analysis showed that the HANN model was capable of predicting water production variation based on the parameter variations, indicating that the HANN model could be a general management tool for decision makers and DWTP managers to make plans in advance of regulatory changes, source water quality variations and market demand.


Assuntos
Água Potável , Purificação da Água , Algoritmos , China , Qualidade da Água
9.
Water Res ; 161: 78-88, 2019 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-31181449

RESUMO

Phosphonate is an important phosphorous species in the effluent of wastewater treatment plant (WWTP), contributing to eutrophication and interfering with phosphate removal in WWTP. It is particularly difficult to determine phosphonates in samples of complex solution chemistry, resulting in very limited information on their presence in environmental matrices. Herein, we proposed a sensitive method based on liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine six quantitatively most important phosphonates even at the ng/L level, i.e., 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-hydroxyethane 1,1-diphosphonic acid, nitrilotris(methylene phosphonic acid), ethylenediamine tetra(methylene phosphonic acid), hexamethylenediamine tetra(methylene phosphonic acid) and diethylenetriamine penta(methylene phosphonic acid). Trimethylsilyldiazomethane (TMSCHN2) derivatization of the target phosphonates is pre-requisite since it could greatly increase the sensitivity up to 2-3 orders of magnitude over direct analysis of the virgin ones. The sample pretreatment methods (including ion exchange and solid phase extraction(SPE)), the derivatization procedures, and the LC-MS/MS conditions were systematically optimized. The limits of quantitation for the six phosphonates in the background of tap water ranged from 1.4 µg/L to 57 µg/L for direct analysis, and from 5.0 ng/L to 200 ng/L for SPE enabled pre-concentration analysis, respectively. The reliability of the proposed method was successfully validated by analysis of authentic water samples collected from one river and three WWTPs (0.088-7200 µg/L phosphonates) with satisfactory recoveries (72-126%). To the best of knowledge, this is the first report on quantification of phosphonates in environmental samples in China.


Assuntos
Organofosfonatos , Poluentes Químicos da Água , China , Cromatografia Líquida , Metilação , Reprodutibilidade dos Testes , Extração em Fase Sólida , Espectrometria de Massas em Tandem , Águas Residuárias
10.
Environ Sci Technol ; 53(14): 8342-8351, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31246427

RESUMO

About 3.93 billion tons of wastewater containing heavy metal complexes are discharged (e.g., from the electroplating industry) every year in China alone. It is challenging to appropriately treat such wastewaters. Here, a multifunctional composite nanowires BaTiO3@graphene was designed based on Comsol simulations and made into 3D millimeter-sphere in order to facilitate practical application. Results indicate 100% of Cu-EDTA was decomplexed in situ via piezoelectric potential by BaTiO3@graphene. Notably, the addition of graphene sharply increased the surface potential (from 19.8 ± 0.97 to 96.8 ± 1.48 mV) of BaTiO3@graphene by its flexoelectric effect then effectively promoted piezoelectric electrons to be separated and transferred, which favors the piezoelectric catalysis. Moreover, the released Cu(II) from Cu-EDTA decomplexation were recovered simultaneously via the interaction on graphene groups. This method efficiently recovered Cu(II) to avoid the consumption of massive chemical reagents and the generation of secondary hazardous solid waste containing heavy metal ions, compared with the conventional oxidative decomplexation/precipitation strategy for heavy metal complexes removal. Piezoelectric catalysis paves a new possibility for advanced oxidation in wastewater treatment.


Assuntos
Grafite , Poluentes Químicos da Água , China , Cobre , Ácido Edético , Oxirredução , Águas Residuárias
11.
Sci Total Environ ; 683: 609-616, 2019 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-31146065

RESUMO

Excess fluoride in water can be efficiently removed by lanthanum based material, however, different lanthanum species exhibited distinct fluoride removal capability. In this study, three typical lanthanum based nanoparticles denoted as L1, L2 and L3 in the form of La(OH)3, La2O3·nH2O and LaCO3OH respectively were synthesized and well characterized for fluoride removal. They differ in terms of morphology, surface charge, water content, specific surface area and crystallinity. L2 (La2O3·nH2O) exhibited the highest adsorption capacity (~28.9 mg/g) and selectivity towards fluoride, followed by L3 (LaCO3OH) (~25.1 mg/g) and L1 (La(OH)3) (~6.03 mg/g). Despite the relatively low capacity for L1, it could be efficiently regenerated by alkaline solution for repeated use. However, both L2 and L3 suffered significant from capacity loss after regeneration. X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis and molecular configuration modelling suggested the distinct mechanism of fluoride adsorption onto the three materials. Fluoride was captured by L1 and L3 via electrostatic attraction and ligand exchange of different bond strength. However, a stronger LaF interaction via chemical adsorption by L2 was observed. This study provided new insights into the role of commonly used La species for fluoride removal.

12.
Sci Total Environ ; 675: 62-72, 2019 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-31026644

RESUMO

A new composite catalyst, i.e., Fe doped g-C3N4/graphite (Fe-CN/G), was successfully constructed to activate peroxymonosulfate (PMS) for efficient phenolic compounds (i.e., p-chlorophenol, 4-CP) degradation in the pH range of 3-10. The optimized Fe-CN/G, i.e., Fe3.75-CN/G5.0, was fabricated at the dosage of 3.75 mmol FeCl3·6H2O, 5.0 g dicyandiamide, and 5.0 mmol glucose. Fe complexed in the nitrogen pots of Fe3.75-CN/G5.0 was demonstrated to be the primary active site for PMS activation, and the introduction of graphite favored the exposure of more accessible active sites in Fe3.75-CN/G5.0, suggesting a synergistic effect between the Fe and graphite of Fe3.75-CN/G5.0 on 4-CP degradation. Multiple experiments confirmed that sulfate radical (SO4-), hydroxyl radical (HO), singlet oxygen (1O2) and superoxide radical (O2-) exerted negligible contribution on 4-CP degradation. The in-situ Fe K-edge X-ray absorption near-edge structure (XANEX) analysis revealed a redox cycle of Fe in PMS/Fe3.75-CN/G5.0, suggesting the formation of high-valent iron-oxo species (FeIVO) was responsible for 4-CP degradation. In addition, PMS/Fe3.75-CN/G5.0 exhibited acceptable degradation of 4-CP in the presence of coexisting anions and natural organic matters (NOM). We believe this study provides new insights into the design and development of Fe-based heterogeneous catalysts for PMS-based wastewater treatment.

13.
Water Res ; 157: 472-482, 2019 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-30981978

RESUMO

As one of the key economic modes in China, chemical industry park (CIP) has made great contribution to the Chinese rapid economic growth. Concomitantly, how to effectively and safely dispose of the CIP wastewater (CIPWW) has been an unavoidable issue. Molecular transformation of dissolved organic matter (DOM) in CIPWW treatment is essential to optimize the employed process and to provide solid basis for risk evaluation of the discharged effluent as well. In this study, electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) was used to characterize the molecular transformation of DOM during full-scale treatment of integrated chemical wastewater in a centralized wastewater treatment plant (CWWTP), where the combined process follows hydrolysis/acidification (HA)-flocculation/precipitation (FP)-A2/O-membrane bioreactor (MBR)-ultrafiltration (UF)-reverse osmosis (RO). Compared to municipal wastewater, DOM in CIPWW exhibited higher unsaturation degree, lower molecular weight, and higher toxicity. In FP unit, DOM of C<24 and higher nominal oxidation state of carbon (NOSC) values was preferentially removed. The HA and anaerobic units are capable of significantly degrading DOM, resulting in great changes in molecular composition of DOM. However, the anoxic, oxic, and MBR units only lead to a slight change of the molecular formulae. The terminal units of UF and RO can remove most DOM, with the concentration of dissolved organic carbon (DOC) declining by 19.2% and 94.6% respectively. The correlation between spectral indexes and acute toxicity with the molecular formulae of DOM suggested that polyphenols and highly unsaturated phenols were positively correlated with the specific UV absorbance at 254 nm (SUVA254). In addition, both compounds (0.32 < O/C < 0.63) as well as the aliphatic ones (0.22 < O/C < 0.56) presented positive correlation with acute toxicity. Further, the pairwise correlation analysis illustrated that SUVA254, O/Cwa, double bond equivalence (DBEwa), and NOSCwa were positively correlated with each other, whereas the acute toxicity was positively correlated with humification index (HIX), O/Cwa, and DBEwa.


Assuntos
Ultrafiltração , Águas Residuárias , China , Filtração , Espectrometria de Massas
14.
Environ Sci Technol ; 53(9): 5319-5327, 2019 05 07.
Artigo em Inglês | MEDLINE | ID: mdl-30946783

RESUMO

Toxic metals are usually present as organic complexes in high-salinity effluents from various industries. The efficient removal of such metal complexes is an imperative but still challenging task due to their stable structure and high mobility. Herein, we propose a new strategy to remove Cu-carboxyl complexes from high-salinity water by using a commercially available nanocomposite HZO-201, i.e., nanohydrated zirconium oxide (HZO) confined inside anion exchanger D201. In contrast to D201 and a cation exchanger D001, which both adsorb Cu-citrate negligibly, HZO-201 exhibits preferable adsorption toward Cu-citrate (∼130 mg Cu/g-Zr) at high salinity (1.5 wt % NaCl). On the basis of scanning transmission electron microscopy energy-dispersive spectrometry (STEM-EDS), attenuated total reflection Fourier transform infrared (ATR-FTIR), and X-ray photoelectron spectrometry (XPS) analysis, the formation of ternary complex among Cu(II), citrate, and the embedded nano-HZO is evidenced to be responsible for the removal of Cu-citrate. The exhausted HZO-201 can be regenerated with a binary HCl-NaCl solution for repeated use for 5 cycles without capacity loss. Fixed-bed adsorption demonstrates that HZO-201 column is capable of producing ∼1150 bed volume (BV) clean water (<0.5 mg Cu/L) from simulated high-salinity wastewater, whereas only ∼10 BV and ∼60 BV was produced for the D001 and D201 columns, respectively. Furthermore, HZO-201 shows excellent removal of Cu(II) complexes with three other carboxyl ligands (oxalate, tartrate, and succinate).


Assuntos
Salinidade , Poluentes Químicos da Água , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Zircônio
15.
Proc Natl Acad Sci U S A ; 116(14): 6659-6664, 2019 04 02.
Artigo em Inglês | MEDLINE | ID: mdl-30872470

RESUMO

For several decades, the iron-based Fenton-like catalysis has been believed to be mediated by hydroxyl radicals or high-valent iron-oxo species, while only sporadic evidence supported the generation of singlet oxygen (1O2) in the Haber-Weiss cycle. Herein, we report an unprecedented singlet oxygen mediated Fenton-like process catalyzed by ∼2-nm Fe2O3 nanoparticles distributed inside multiwalled carbon nanotubes with inner diameter of ∼7 nm. Unlike the traditional Fenton-like processes, this delicately designed system was shown to selectively oxidize the organic dyes that could be adsorbed with oxidation rates linearly proportional to the adsorption affinity. It also exhibited remarkably higher degradation activity (22.5 times faster) toward a model pollutant methylene blue than its nonconfined analog. Strikingly, the unforeseen stability at pH value up to 9.0 greatly expands the use of Fenton-like catalysts in alkaline conditions. This work represents a fundamental breakthrough toward the design and understanding of the Fenton-like system under nanoconfinement, might cause implications in other fields, especially in biological systems.

16.
Environ Sci Pollut Res Int ; 26(10): 10013-10022, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30746624

RESUMO

Millispherical nanocomposites are promising for water decontamination combining the high reactivity of the confined nanoparticles and the excellent hydrodynamic properties of the supporting host. However, the effect of three-dimensional (3-D) distribution of the nanoparticles inside the host on the performance of the nanocomposite was highly dependent on the specific decontamination process. In this study, four D201-ZVI nanocomposites from peripheral to uniform 3-D distributions of nZVI were prepared to evaluate the effect of 3-D distribution of the confined nanoparticles inside the host beads on the removal of EDTA-chelated Cu(II). The performance of Cu(II) removal increased with the 3-D distribution tailoring towards the peripheral region, which was also validated under various solution chemistry conditions in terms of initial pH, DO, and coexisting sulfate. The mechanism underlying the 3-D distribution effect may be ascribed to three perspectives. First, the dissolution of Fe was also higher from the peripherally distributed nZVI nanocomposites compared with the uniform ones. In addition, SEM-EDS analysis revealed the immobilization of Cu occurred at limited depth from the outermost surface of the composite beads, leading to the low spatial utilization of the inner core region. Furthermore, XRD and XPS analyses demonstrated the higher chemical utilization of nZVI for the outer-distributed nanocomposites owing to the shortened pathway for mass transfer. This study shed new light on the design and development of tunable nanocomposites of improved reactivity for water decontamination processes.


Assuntos
Cobre/isolamento & purificação , Ferro/química , Nanocompostos/química , Poluentes Químicos da Água/química , Purificação da Água , Ânions , Quelantes , Cobre/química , Ácido Edético/química , Polímeros
17.
J Hazard Mater ; 368: 698-704, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30739022

RESUMO

To activate zero-valent iron (ZVI) for efficient nitrobenzene (NB) reduction, a hybrid Fe0/Fe3O4/FeCl2 microcomposite (hZVIbm) was synthesized via simple ball-milling of the ternary mixture of ZVI, Fe3O4, and FeCl2·4H2O (hZVI). SEM-EDX and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) indicated the hZVIbm microcomposite (10-20 µm) consisted of Fe0 core covered by ∼3.3 µm-thick shell decorated with Fe3O4/FeCl2 fine particles (0.1-2 µm). Efficient removal (>95%) of NB (200 mg/L) was achieved by hZVIbm (2.0 g Fe/L) in 30 min over a wide pH range from 3 to 9. Notably, the NB removal efficiency of hZVIbm was over 30 times higher than the virgin ZVI or over three times higher than hZVI. The enhanced reactivity synergistically resulted from both chemical and physical aspects. Chemically, the Fe3O4/FeCl2-inlaid shell and the Fe(II) components played significant activation roles, as observed from the comparative experiments in their absence via pretreatments of hZVIbm by sonication and rinsing, respectively, with direct evidence of depassivation effect by XRD analysis. Physically, the ball-milling-induced inter-particle compaction effect was considered crucial to facilitate the interfacial mass/electron transfer processes during the reduction. The reduction pathway from NB to aniline via two intermediates was analyzed by liquid chromatography.

18.
Environ Sci Technol ; 53(4): 2036-2044, 2019 02 19.
Artigo em Inglês | MEDLINE | ID: mdl-30653306

RESUMO

Traditional processes usually cannot enable efficient water decontamination from toxic heavy metals complexed with organic ligands. Herein, we first reported the removal of Cu(II)-EDTA by a UV/chlorine process, where the Cu(II)-EDTA degradation obeyed autocatalytic two-stage kinetics, and Cu(II) was simultaneously removed as CuO precipitate. The scavenging experiments and EPR analysis indicated that Cl• accounted for the Cu(II)-EDTA degradation at diffusion-controlled rate (∼1010 M-1 s-1). Mechanism study with mass spectrometry evidence of 11 key intermediates revealed that the Cu(II)-EDTA degradation by UV/chlorine was an autocatalytic successive decarboxylation process mediated by the Cu(II)/Cu(I) redox cycle. Under UV irradiation, Cu(I) was generated during the photolysis of the Cl•-attacked complexed Cu(II) via ligand-to-metal charge transfer (LMCT). Both free and organic ligand-complexed Cu(I) could form binary/ternary complexes with ClO-, which were oxidized back to Cu(II) via metal-to-ligand charge transfer (MLCT) with simultaneous production of Cl•, resulting in the autocatalytic effect on Cu(II)-EDTA removal. Effects of chlorine dosage and pH were examined, and the technological practicability was validated with authentic electroplating wastewater and other Cu(II)-organic complexes. This study shed light on a new mechanism of decomplexation by Cl• and broadened the applicability of the promising UV/chlorine process in water treatment.


Assuntos
Cloro , Purificação da Água , Ácido Edético , Raios Ultravioleta , Águas Residuárias
19.
Water Res ; 153: 21-28, 2019 04 15.
Artigo em Inglês | MEDLINE | ID: mdl-30685633

RESUMO

Considerable amount of phosphorous is present as organic phosphonates (usually in the form of metal complexes, e.g., Ca(II)-phosphonate) in domestic and industrial effluents, which cannot be effectively removed by traditional processes for phosphate. Herein, we employed a proprietary process, i.e., Fe(III) displacement/UV irradiation/co-precipitation (denoted Fe(III)/UV/NaOH), to enable an efficient removal of Ca(II)-phosphonate complexes from water. The combined process includes three basic steps, i.e., Fe(III) replacement with the complexed Ca(II) to form Fe(III)-phosphonate of high photo-reactivity, UV-mediated degradation of Fe(III)-phosphonate to form phosphate and other intermediates, and the final phosphorous removal via co-precipitation at pH = 6. The operational conditions for the combined process to remove a typical phosphonate Ca(II)-NTMP (nitrilotrismethylenephosphonate) are optimized, where ∼60% NTMP is transformed to phosphate with the total phosphorous reduction from 1.81 mg/L to 0.17 mg/L. Under UV irradiation, the cleavage of NTMP is identified at the C-N and C-P bonds to form the intermediate products and phosphate in sequence. Also, the combined process is employed for treatment of two authentic effluents before and after activated sludge treatment, resulting in the phosphorous drop from 4.3 mg/L to 0.23 mg/L and from 0.90 mg/L to 0.14 mg/L respectively, which is much superior to other processes including Fenton/co-precipitation. In general, the combined process exhibits great potential for efficient removal of phosphonates from contaminated waters.


Assuntos
Organofosfonatos , Poluentes Químicos da Água , Compostos Férricos , Peróxido de Hidrogênio , Raios Ultravioleta , Água
20.
Environ Int ; 124: 393-399, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30660851

RESUMO

Heterogeneous catalysis is a promising approach to achieve efficient As(III) oxidation by H2O2 at circumneutral pH. However, radical-attack pathways dominated catalytic As(III) oxidation over most metal oxides is undesirably associated with low utilization of H2O2 induced by rapid self-quenching of radicals. In this study, we developed a non-radical catalytic route to improve H2O2 utilization efficiency for catalytic As(III) oxidation based on nanoceria. The performance and mechanism of As(III) oxidation by H2O2 was investigated by employing four types of nanoceria with different crystallite sizes (9.1-80.6 nm). At the H2O2/As(III) molar ratio of 2.0, nanoceria exhibited crystallite size-dependent catalytic activity for oxidation of As(III) over a wide pH range (5-9). Based on comprehensive study including scavenging, enzymatic, and pretreatment experiments and miscellaneous spectroscopy techniques, the catalytic As(III) oxidation over nanoceria was proved to be mainly mediated by the non-radical Ce-hydroperoxo surface complexes, whilst the surface hydroperoxyl radical served as a minor oxidant. In contrast, the roles of dissolved oxygen, homogeneous H2O2, and OH radical were all negligible. No obvious interconversion of Ce(III)/Ce(IV) was observed by XPS for the catalytic process. Such non-radical pathway enabled a stoichiometric reaction with high H2O2 utilization efficiency (90.5%-122%). Moreover, nanoceria could be recycled for five consecutive runs without desorption/regeneration treatment. This study sheds new light on the development of nanoceria-based catalytic processes for efficient oxidation of As(III).


Assuntos
Arsênico/química , Cério/química , Peróxido de Hidrogênio/química , Catálise , Oxirredução
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