Background Anions Research Articles

Robust degradation of tetracycline hydrochloride by electro-assisted activation of peroxymonosulfate over porous cobalt-manganese oxide nanowire array in situ grown on nickel foam

The electro-assisted activation of peroxymonosulfate (PMS) with transition metals for treating antibiotics in water environment has become a research hotspot. In this work, porous cobalt-manganese oxide nanowire array was successfully in situ fabricated on nickel foam (Co2.5Mn0.5O4/NF), and the degradation efficiency of tetracycline hydrochloride (TC) by PMS activation over Co2.5Mn0.5O4/NF in the presence of an electric field (defined as E-Co2.5Mn0.5O4/NF-PMS) was further studied. The E-Co2.5Mn0.5O4/NF-PMS system showed an unexpectedly high catalytic performance for TC degradation, achieving a removal efficiency of 98.71% in 20min with a rate constant of 0.2092min−1. Thereinto, the electric field ensured a rapid redox cycle of Co(II)/Co(III) and Mn(II)/Mn(III)/Mn(IV), which activated PMS continuously and guaranteed the robustness of TC degradation process. Specifically, the catalytic system exhibited outstanding stability after ten consecutive cycles. Electron paramagnetic resonance (EPR) analysis and quenching experiments illuminated that non-radical pathway involved singlet oxygen (1O2) was dominant in TC oxidation degradation in E-Co2.5Mn0.5O4/NF-PMS system, and furthermore possible degradation routes of TC were revealed. Of note, the degradation system exhibited relatively low level of energy consumption (0.51 kWh m−3 order−1), widespread applicability in treating wastewater contaminated with different organic pollutants, and excellent resistance toward the interference from background anions.

Activation of peroxymonosulfate by MnOOH/g-C3N5: Study on highly selective removal of phenolic pollutants and its non-radical pathway

In this research, the MnOOH/g-C3N5 material was successfully synthesized, demonstrating its efficacy in selectively removing phenolic organic pollutants. This material outperformed traditional free radical pathways, exhibiting higher selectivity, enhanced persulfate utilization efficiency, and strong resistance to background anions and complex organic matter. Using phenol as the target pollutant, the MnOOH/g-C3N5/PMS system achieved 81 % mineralization, a PMS utilization efficiency of 88 %, and a 75 % process unit energy consumption value in degrading phenol. This efficient degradation is attributed to the synergistic effects of high-valence metal oxides (MnV(O)/MnIV(O)), singlet oxygen (1O2), and electron transfer complexes, as confirmed by electrochemical analysis and In-situ EPR. Additionally, Transmission Electron Microscopy observations disclosed the development of an amorphous shell on the MnOOH/g-C3N5 surface post-reaction. Electrochemical Impedance Spectroscopy analysis suggested an enhanced charge transfer resistance, further affirming the role of MnOOH/g-C3N5 as an "electron transfer station" in the electron transfer process, accompanied by the formation of electron transfer complexes. This study provides crucial scientific insights and theoretical guidance for applying MnOOH/g-C3N5 materials in environmental engineering.

Revisiting the Electron Transfer Mechanisms in Ru(III)-Mediated Advanced Oxidation Processes with Peroxyacids and Ferrate(VI).

The potential of Ru(III)-mediated advanced oxidation processes has attracted attention due to the recyclable catalysis, high efficiency at circumneutral pHs, and robust resistance against background anions (e.g., phosphate). However, the reactive species in Ru(III)-peracetic acid (PAA) and Ru(III)-ferrate(VI) (FeO42-) systems have not been rigorously examined and were tentatively attributed to organic radicals (CH3C(O)O•/CH3C(O)OO•) and Fe(IV)/Ru(V), representing single electron transfer (SET) and double electron transfer (DET) mechanisms, respectively. Herein, the reaction mechanisms of both systems were investigated by chemical probes, stoichiometry, and electrochemical analysis, revealing different reaction pathways. The negligible contribution of hydroxyl (HO•) and organic (CH3C(O)O•/CH3C(O)OO•) radicals in the Ru(III)-PAA system clearly indicated a DET reaction via oxygen atom transfer (OAT) that produces Ru(V) as the only reactive species. Further, the Ru(III)-performic acid (PFA) system exhibited a similar OAT oxidation mechanism and efficiency. In contrast, the 1:2 stoichiometry and negligible Fe(IV) formation suggested the SET reaction between Ru(III) and ferrate(VI), generating Ru(IV), Ru(V), and Fe(V) as reactive species for micropollutant abatement. Despite the slower oxidation rate constant (kinetically modeled), Ru(V) could contribute comparably as Fe(V) to oxidation due to its higher steady-state concentration. These reaction mechanisms are distinctly different from the previous studies and provide new mechanistic insights into Ru chemistry and Ru(III)-based AOPs.

Effective degradation of recalcitrant naphthenic acids by the Fe(III)/peroxymonosulfate oxidation enhanced by molybdenum disulfide: Degradation performance and mechanisms

In this study, molybdenum disulfide (MoS2) has been investigated as a catalyst to boost the redox cycle of Fe(III)/Fe(II) to activate peroxymonosulfate (PMS) to effectively break down cyclohexanecarboxylic acid (CHA), which is a model naphthenic acid (NA) pollutant. The optimum conditions of pH 3, MoS2 concentration of 0.4 g/L, Fe(III) concentration of 0.3 mmol/L, and PMS concentration of 2 mmol/L has been applied for complete degradation of 0.1 mmol/L CHA in 10 minutes reaction time. Based on results of electron paramagnetic resonance analysis, chemical probe and quenching experiment, it was found that all of •OH, SO4•−, 1O2, and Fe(IV) contributed to the MoS2/Fe(III)/PMS oxidation system. Eighteen CHA byproducts and three primary CHA degradation pathways were revealed according to the results of UHPLC-QTOF-MS analysis. By using XPS, SEM, and XRD to characterize the MoS2 powders before and after the reaction, MoS2 was found with high stability and the oxidation of Mo(IV) on the surface was negligible. The impacts of background anions on CHA degradation were found to be nonimportant, and commercial NAs mixture were verified to be efficiently degraded in current system. Overall results indicate the capacity and potential of MoS2/Fe(III)/PMS system to be utilized for future treatment of authentic oil and gas field wastewater.

N, O co-doping enhanced the ability of carbon/Fe composites for peroxymonosulfate activation to degrade sulfadiazine: The advantages of nitrate saturated MOFs as precursors

Using nitrate saturated metal–organic frameworks (MOFs) MIL-101-NH2(Fe) as precursors, N, O co-doped carbon/Fe composites (NOC/Fe-MIL) were synthesized by carbonization for activating peroxymonosulfate (PMS) to degrade sulfadiazine (SDZ). N and O species were doped into the carbon matrix by adsorbed nitrate, increasing the degradation rate of SDZ by 2.80 times compared to the original materials (NC/Fe-MIL). N, O co-doping not only increased the charge transfer rate on the materials surface, but also provided more pyridine N, CO groups and defects as main active sites for enhancing the adsorption to PMS indicated by DFT calculations, thus promoting the generation of O2− and 1O2 to degrade SDZ. More importantly, the NOC/Fe-MIL/PMS system still exhibited stable degradation performance in a wide pH range and in the presence of background anions, which can be used in a variety of complex water matrices and regenerated by heating, enabling it to be applied to practical wastewater treatment. This work will provide a general approach for preparing heteroatom modified materials and new insights for exploring critical roles of N and O species in PMS activation.

Oxidative treatment of bisphenol A by Fe(VI) and Fe(VI)/H2O2 and identification of the degradation products

Bisphenol A (BPA) is classified as a xenoestrogen compound and has caused adverse effects in humans and animals. Ferrate(VI) (Fe(VI)) and the combination of Fe(VI) and hydrogen peroxide ( H 2 O 2 ) were investigated to degrade BPA in water. This study evaluated the impact of BPA initial concentration (50, 200, and 1, 000 μ g L −1 ) and background anions ( Cl − , PO 4 3 − , and NO 3 − ) on the degradation efficiency of the combined oxidants. The results showed that Fe(VI)/H 2 O 2 performed significantly better than Fe(VI) or H 2 O 2 alone. BPA degradation ( 50 μ g L −1 ) using Fe(VI)/H 2 O 2 was recorded at 99.8% within 60 min at pH 8.0 with [Fe(VI)]/[H 2 O 2 ] molar concentration ratio of 250:2,500. At the same initial concentration of BPA and pH condition, the degradation of BPA using Fe(VI) and H 2 O 2 was recorded as 89% ([Fe(VI)]/[BPA]=5) and 33.5% ([H 2 O 2 ]=2, 500 μ g L −1 ), respectively. BPA degradation using Fe(VI)/H 2 O 2 was 99.8%, 85.3%, and 43.8% for an initial concentration of 50, 200, and 1, 000 μ g L −1 , respectively. The presence of Cl − and NO 3 − ions had no obvious effects on BPA degradation; however, a considerable reduction in the degradation efficiency was observed for PO 4 3 − ( 350 μ g L −1 ) due to the complexation between PO 4 3 − ion and ferric oxy/hydroxides. There were eleven intermediates detected in BPA degradation using Fe(VI)/H 2 O 2 , and three degradation pathways were proposed, including hydroxylation, cleavage of the C-C bond, and oxidation to form ring opening products. A reduction in ecotoxicity was observed after 60 min of reaction for both Fe(VI) and Fe(VI)/H 2 O 2 . • Bisphenol A (BPA) degradation using Ferrate(VI) (Fe(VI)) and Fe(VI)/H 2 O 2 was studied. • Nearly a complete degradation of BPA in water was achieved with Fe(VI)/H 2 O 2 . • BPA degradation by Fe(VI)/H 2 O 2 was affected by PO 4 3 − , but not by Cl − and NO 3 − . • Eleven intermediates in the BPA degradation were detected. • BPA degradation pathways during the oxidative treatments were proposed.

Suppressing the Hofmeister Anion Effect by Thermal Annealing of Thin-Film Multilayers Made of Weak Polyelectrolytes.

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F-, Cl-, and ClO4 -). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F- < Cl- < ClO4 -. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer-air interface in the sense of reorientation and migration of polymer chains.

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface.

Developing better separation technologies for rare earth metals, an important aspect of a sustainable materials economy, is challenging due to their chemical similarities. Identifying molecular-scale interactions that amplify the subtle differences between the rare earths can be useful in developing new separation technologies. Here, we describe the ion-dependent monolayer to inverted bilayer transformation of extractant molecules at the air/aqueous interface. The inverted bilayers form with Lu3+ ions but not with Nd3+. By introducing Lu3+ ions to preformed monolayers, we extract kinetic parameters corresponding to the monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the character of the background anion, although anions are expected to be repelled from the interface. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods.

Hydrogen bonding-orientated selectivity of phosphate adsorption by imine-functionalized adsorbent

• N C@CMPS was successfully grafted with imine group. • imine group can distinguish protonated phosphate from deprotonated competing anions. • imine group has stronger interaction force toward P(V) than that of amine group. • P(V) adsorption on N C@CMPS is slightly exothermic. • N C@CMPS can be repeatedly used for P(V) adsorption. The development of phosphate-selective adsorbents is essential for addressing eutrophication-associated problems and issues about lack of phosphorus resources. In this study an imine-functionalized adsorbent (N C@CMPS) was synthesized for this purpose; briefly, the commercially available precursor, chloromethylated polystyrene adsorbent (CMPS), was grafted with ethylenediamine (EDA) to yield the intermediate (EDA@CMPS), which was subsequently subjected to synchronous elimination to yield the product with imine functional group (N C@CMPS). Spectroscopic analyses and macroscopic experiments were then employed to evaluate the as-prepared adsorbent. As compared with CMPS, EDA@CMPS, and two commercial amine-based adsorbents, N C@CMPS exhibited much higher adsorption capacity and selectivity toward phosphate [P(V)]; such improvement can be primarily attributed to the imine group of N C@CMPS and their difference in the acid-base property. The imine group, acting as the recognition unit to distinguish P(V) from background anions, can solely serve as H-bond acceptors and exclusively interact with the protonated P(V) species (H 2 PO 4 - and HPO 4 2- , H-bond donors) under neutral pH but not with the deprotonated anions such as Cl - , NO 3 – , and SO 4 2- . the thermodynamic parameters confirm the spontaneous and slightly exothermic nature of P(V) adsorption on N C@CMPS, according with the domination of hydrogen bonding interactions. N C@CMPS also exhibited very broad applicability for P(V) adsorption over a wide range of pH (3 ∼ 10). Furthermore, the exhausted N C@CMPS can be efficiently regenerated with the combination of dilute NaOH solution and dilute HNO 3 solution for repeated use.

Monodispersed CuO nanoparticles supported on mineral substrates for groundwater remediation via a nonradical pathway

Nonradical oxidation based on singlet oxygen (1O2) has attracted great interest in groundwater remediation due to the selective oxidation property and good resistance to background constituents. Herein, recoverable CuO nanoparticles (NPs) supported on mineral substrates (SiO2) were prepared by calcination of surface-coated metal-plant phenolic networks and explored for peroxymonosulfate (PMS) activation to generate 1O2 for degrading organic pollutants in groundwater. CuO NPs with a close particle size (40 nm) were spatially monodispersed on SiO2 substrates, allowing highly exposure of active sites and consequently leading to outstanding catalytic performance. Efficient removal of various organic pollutants was obtained by the supported CuO NPs/PMS system under wide operation conditions, e.g., working pH, background anions and natural organic matters. Chemical scavenging experiments, electron paramagnetic resonance tests, furfuryl alcohol decay and solvent dependency experiments confirmed the formation of 1O2 and its dominant role in pollutants removal. In situ characterization with ATR-FTIR and Raman spectroscopy and computational calculation revealed that a redox cycle of surface Cu(II)-Cu(III)-Cu(II) was responsible for the generation of 1O2. The feasibility of the supported CuO NPs/PMS for actual groundwater remediation was evaluated via a flow-through test in a fixed-bed column, which manifested long-term durability, high mineralization ratio and low metal ion leaching.

Efficient activation of peroxymonosulfate on CuS@MIL-101(Fe) spheres featured with abundant sulfur vacancies for coumarin degradation: Performance and mechanisms

For improving the catalytic activity and recyclability of CuS in Fenton-like reaction processes, novel sulfur vacancies-enriched CuS@MIL-101(Fe) was constructed, characterized, and examined as heterogeneous catalysts for activating peroxymonosulfate (PMS) to degrade coumarin (COU). Thanks to the redox pairs of Fe3+/Fe2+, Cu+/Cu2+, S2−/S22−/S0/sulfate species, copper-iron synergistic effect and sulfur vacancies, the CuS@MIL-101(Fe) realized a complete removal of COU (30 μM) in 10 min with reaction rate constant of 0.577 min−1, which was 11.1 and 17.0 times of CuS and MIL-101(Fe), respectively. The effect of various experimental conditions (i.e., initial pH, CuS@MIL-101(Fe) dosage, PMS concentration, and background anions) on COU degradation was discussed, and the stability and versatility of CuS@MIL-101(Fe) was studied as well. Radical scavenging experiments and electron paramagnetic resonance (EPR) spectroscopy identified •OH and 1O2 as the main reactive oxygen species (ROS). Finally, the possible mechanism of higher COU degradation efficiency in the CuS@MIL-101(Fe) activated PMS system and the degradation pathways were also deeply explored. Consequently, this work provided a novel insight into construction of sulfur vacancies-enriched heterogeneous catalysts for efficiently activating PMS for refractory organic pollutants elimination.

Removal of hexavalent chromium by encapsulated chitosan-modified magnetic carbon nanotubes: Fixed-bed column study and modelling

A new type of composite adsorbent, encapsulated chitosan-modified magnetic carbon nanotubes (CS/MWCNTs/Fe) beads were used to remove hexavalent chromium (Cr(VI)) from aqueous solutions in a fixed-bed column. Among the various combination of operating parameters, we obtain a maximum volume of treated effluent (210 mL) under the following conditions: flow rate, 1 mL min−1; bed height, 8 cm; feed Cr(VI) concentration, 30 mg L−1; and solution pH, 4.0 ± 0.2. The corresponding adsorption capacity was 1.54 mg g-1 and the overall Cr(VI) removal efficiency was 54 %. In characterizing the dynamics of the adsorption process and breakthrough profiles, we found that the Thomas model and the Yoon-Nelson model both accurately described the breakthrough curves under all experimental conditions, while the Adams-Bohart model was applicable only for an early phase of dynamic behavior CtC0≤0.5 of the CS/MWCNTs/Fe beads column. Columns with shorter bed heights favored the global mass transfer rate, especially during the early breakthrough periods. Moreover, the bed depth service time (BDST) model was validated experimentally, enabling the prediction of service time of the adsorption bed at different outlet concentrations using hypothetical flow rates and inlet concentrations. Scaled-up study was performed to observe the column performance at higher throughputs. The high selectivity of Cr(VI) adsorption in the simulated wastewater in the presence of other heavy metals (copper and cadmium) and background anion (phosphate) suggests the applicability of CS/MWCNTs/Fe beads for Cr(VI) removal from industrial effluents.

Degradation of aqueous organic pollutants using an Fe2O3/WO3 composite photocatalyst as a magnetically separable peroxymonosulfate activator

Developing a cost-effective method for the separation and recovery of nanomaterials for water treatment is challenging due to the significantly high recovery cost associated with nanomaterial-based water treatment processes. In this study, we synthesized magnetically separable iron oxide/tungsten oxide (Fe2O3/WO3) composites through a chemical co-precipitation method and employed them as peroxymonosulfate (PMS) activators for the degradation of organic pollutants under visible light. Electron spin resonance analysis, chemical quenching, and photoluminescence analysis suggested that hydroxyl radicals, sulfate radicals, and valence band holes contribute to the degradation processes in the Fe2O3/WO3/PMS system under visible light. The results of the degradation and recovery experiments based on the mass ratio of WO3 to Fe2O3 ([WO3]:[Fe2O3]) in the Fe2O3/WO3 composite indicated that the Fe2O3/WO3 composite with [WO3]:[Fe2O3] = 2:1, which can be completely recovered using a magnet (magnetic flux density = 2500 G), is the optimal photocatalyst for PMS activation. The effects of reaction parameters, such as the PMS concentration, Fe2O3/WO3 dosage, solution pH, and background anions (chloride, carbonate, nitrate, and phosphate)/humic acid, on the degradation kinetics were investigated and discussed. Under visible light irradiation, the Fe2O3/WO3/PMS system efficiently degraded various organic pollutants, including 4-chlorophenol, 2-chlorophenol, 4-bromophenol, 4-methylphenol, 2,4-dimethylphenol, bisphenol A, tryptophan, sulfamethoxazole, sulfisoxazole, and furfuryl alcohol. In addition, the complete degradation of 4-chlorophenol in the Fe2O3/WO3/PMS system under visible light was achieved for up to five degradation cycles when Fe2O3/WO3 was reused after recovery using a magnet.

Electro-enhanced heterogeneous activation of peroxymonosulfate via acceleration of Fe(III)/Fe(II) redox cycle on Fe-B catalyst

Heterogeneous catalytic oxidation based on iron species for peroxymonosulfate (PMS) activation is considered as one of the most attractive strategies for wastewater treatment. However, the rate-limiting regeneration of Fe(II) from Fe(III) heavily hampers the efficient activation of PMS. In this study, the introduction of electric field to the Fe-supported bentonite (Fe-B) activated PMS process was proposed to enhance the Fe(III)/Fe(II) redox cycle. The Fe-B catalyst performed well in the removal of Acid Orange 7 (AO7) through the synergistic effect of electrolysis and the continuous redox cycle of Fe(III)/Fe(II) for PMS activation. The use of 0.5 g L−1 Fe-B catalyst and 10 mM PMS yielded nearly complete removal of the AO7 (50 mg L−1) in 60 min at 2 mA cm−2 of current density. Based on the results of electron paramagnetic resonance (EPR) spectroscopy, chemical quenching tests, X-ray photoelectron spectroscopy (XPS) analysis, and electrochemical measurements, the decolorization of AO7 was dominantly attributed to surface-bound radicals (SO4•−ads and •OHads) and also the direct electron transfer at DSA anode. Moreover, the electro/Fe-B/PMS system showed an effective pH range from 2.6 to 9.0 and the abatement of AO7 was slightly affected in the presence of natural background anions. This work provides a feasible strategy of PMS activation by cost-effective Fe-B catalyst coupling with electric field and gives an insight into the accelerated oxidation of recalcitrant pollutants.

Effect of anions on electrodeposition of structured platinum nanocrystallites

Pulsed (square–wave) electrodeposition of platinum nanocrystallites with a high concentration of (100) regions from a H2PtCl6 solution with different background anions is studied. The effect of the background electrolyte is shown, namely, a more perfect cubic faceting of crystallites obtained in the 0.1 M HClO4 solution as compared to 0.5 M H2SO4. A procedure for deposit formation (secondary growth) with intermediate pulsed treatment in acid is suggested that does not involve application of high negative/positive overpotentials (no additional increasing of the mobility of platinum atoms). This allows preserving the crystallite structure and improving the overall deposit structure. In addition to conventional methods of fine surface structure determination on the basis of the hydrogen UPD region in cyclic voltammograms in sulfuric acid and SEM, we propose analysis of the Pt(100) terrace concentration/width based on the characteristic peak of nitrate ion reduction in voltammograms in perchloric acid. Stepped Pt single crystals with (100) terraces of different width are used for comparison. The effect of solution temperature on formation of faceted crystallites is shown and the optimum deposition temperature is determined: the optimum temperature in perchloric acid solution is 40 °C, while an increase in the temperature in sulfuric acid solutions results under the chosen conditions in deposition acceleration and an increase in the amount of surface defects.

Degradation of 2,4-Dinitrophenol using persulfate activated by Cu2+ in photocatalytic system (UV/SPS/Cu2+) from aqueous solution: optimisation and operational parameters

ABSTRACT The present study was developed to model and optimise 2,4-Dinitrophenol (2,4-DNP) degradation from aqueous solution using UVC/SPS/Cu2+ system based on the response surface methodology (RSM) and Box-Behenken (BBD) approach. A high removal efficiency (92.75%) and total organic carbon (TOC) reduction (61.5%) were obtained under optimum conditions, i.e. (Time = 59 min, SPS Con. = 58.74 mg/L, Cu2+ Con = 14.12 mg/L, pH = 11, Initial Con = 6 mg/L). Quenching experiments confirmed that sulphate radicals were predominant radical species for 2-4-DNP degradation. The effect of CO3 − on 2,4-DNP degradation was more complicated than other aquatic background anions. Finally, the performance of UVC/SPS/Cu2+ system for 2,4-DNP treatment in different aquatic solutions: tap water, surface runoff, treated and raw wastewater were found to be 89.76%, 81.65%, 51.22% and 75.94%, respectively.

The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate

The selective transport of trivalent rare earth metals from aqueous to organic environments with the help of amphiphilic "extractants" is an industrially important process. When the amphiphilic extractant is positively charged or neutral, the coextracted background anions are not only necessary for charge balance but also have a large impact on extraction efficiency and selectivity. In particular, the opposite selectivity trends observed throughout the lanthanide series in the presence of nitrate and thiocyanate ions have not been explained. To understand the role of background anions in the phase transfer of lanthanide cations, we use a positively charged long-chain aliphatic molecule, modeling a common extractant, and gain molecular level insight into interfacial headgroup-anion interactions. By combining surface sensitive sum frequency generation spectroscopy with X-ray reflectivity and grazing incidence X-ray diffraction, we observed qualitative differences in the orientational and overall interfacial structure of nitrate and thiocyanate solutions at a positively charged Langmuir monolayer. Though nitrate adsorbs without dramatic changes to the solvation structure at the interface or the monolayer ordering, thiocyanate significantly alters the water structure and reduces monolayer ordering. We suggest that these qualitatively different adsorption trends help explain a reversal in system selectivity toward lighter or heavier lanthanides in solvent extraction systems in the presence of nitrate or thiocyanate anions.

Efficient removal of GenX (HFPO-DA) and other perfluorinated ether acids from drinking and recycled waters using anion exchange resins

Carcinogenic GenX chemicals, heptafluoropropylene-oxide-dimer-acid (HFPO-DA), have been recently detected in surface, ground and recycled water sources worldwide. However, GenX removals under the influence of variable characteristics of the organic and inorganic compounds present in the natural water sources, have often been overlooked in scientific literature. This is critically important given that the ionic composition and characteristics of organic matter in natural waters are spatially and seasonally variable. A strongly basic anion exchange (IX) resin was used to remove GenX and two other perfluorinated ether acids (PFEAS) from natural surface and recycled water sources. Factors influencing the uptake behavior included the PFEAS concentrations, resin dosage, and background anion characteristics. The equivalent background compound was employed to evaluate the competitive uptake between natural organic matter (NOM), inorganic ions and PFEAS in natural water matrices. Experimental data were compared with different mathematical and physical models and it was depicted that approximately 4–6% of the initial NOM competed with PFEAS for active exchange sites. Further, IX was able to achieve complete PFEAS removal (Cfinal<10 ng/L) with simultaneous removal of>60% NOM and >80% inorganic ions. Results of this study indicate that IX exhibits great potential for PFEAS removal from natural drinking water sources.

Evaluation of permeable sorption barriers for removal of Cd(II) and Zn(II) ions from contaminated groundwater.

In the present study, continuous-flow column experiments (using glass column, Tygon tubing, and peristaltic pump Manostat Carter) were conducted to investigate the performance of permeable sorption barriers for the removal of cadmium and zinc from synthetic groundwater. Zeolite, ion-exchange resin and granular activated carbon as reactive materials were used. The effectiveness and stability of reactive materials were studied by monitoring of changes of metal ions concentration and selected background anions and cations concentration in groundwater during its flow through columns. Results showed that ion exchange resin was the most effective material of permeable reactive barrier (PRB). Performance of resin barrier remained effective (>99.5% metal ions removal) for the time corresponding to on average of about 10,000 min. The high efficiency of ion-exchange resin in PRB for removal of heavy metals from groundwater was coupled with its reactivity and long barrier lifetime. The breakthroughs in the column tests on activated carbon and zeolite using synthetic groundwater occurred much earlier as compared to resin. Therefore, the system using resin requires smaller amount to treat a given volume of groundwater as compared to other materials. Moreover, the presence of other ions did not impact on activity and permeability of barrier filled with resin.

Cationic polymer for selective removal of GenX and short-chain PFAS from surface waters and wastewaters at ng/L levels

The emerging classes of perfluorinated alkyl substances (PFAS) (e.g., Perfluorobutanoic acid (PFBA), perfluorobutane sulfonic acid (PFBS), GenX, ADONA, and F–53B) are persistent and recalcitrant to removal by conventional treatment techniques. Herein, we report on poly (N-[3-(dimethylamino)propyl]acrylamide, methyl chloride quaternary, DMAPAA-Q) hydrogel matrix as an effective sorbent for sequestering PFAS from different water matrices. The selective removal of 16 PFAS from different classes using DMAPAA-Q polymer was confirmed in surface waters and treated wastewater at environmentally relevant concentration (i.e., <1000 ng/L). The results showed fast removal kinetics with equilibrium time of 60–120 min and a higher removal of sulfonated than carboxylic PFAS, regardless of their chain lengths. These observations were in agreement with adsorption energy calculations of short- and long-chain PFAS on poly DMAPAA-Q hydrogel using density functional theory (DFT). No desorption was observed when the experimental time was extended to 24 h, which gives an added advantage of poly DMAPAA-Q hydrogel over previously reported adsorbents in the literature. In addition, the removal efficiency was not affected under a varying pH range of 4–10. The impact of background anions on PFAS removal by poly DMAPAA-Q hydrogel was tested and found to follow an order of SO42− > Cl− > NO3−. The performance of poly DMAPAA-Q hydrogel was maintained in six consecutive adsorption/regeneration cycles to remove PFAS. The unique fast kinetics and high adsorption activity of poly DMAPAA-Q hydrogel towards PFAS exhibits a great potential for being a promising material for PFAS control.