Oxygen Vacancy-Laden Confinement Impact on Degradation of Metal Complexes.

Oxygen vacancies (Vo) have been recognized as the superior active site for PS-mediated environmental remediation; however, the formation and activation of Vo associated with the effects of chemical and spatial environments remain ambiguous. Herein, attributing to the low defect-formation energy of Vo in the presence of sulfonate groups, an in situ nucleating Vo-laden CuO nanosheet was deliberately fabricated inside the phase of a sulfonated mesoporous polystyrene substrate (Vo-CuO@SPM). The as-prepared nanocomposite demonstrated an excellent treatment efficiency toward metal complexes [Cu-EDTA as a case] with ignorable Cu(II) leaching, and it can be repeatedly employed for 25 recycles (not limited). Mechanistically, the electron transfer and the mass transport for PDS nonradical activation were proved to be substantially enhanced by the delocalized electrons and with the assistance of the microchannel environment. This work not only establishes insight into the formation of oxygen vacancies but also reveals the PS activation mechanism in the spatially confined sites.

Pioneering Piezoelectric-Driven Atomic Hydrogen for Efficient Dehalogenation of Halogenated Organic Pollutants.

The electrocatalytic hydrodehalogenation (EHDH) process mediated by atomic hydrogen (H*) is recognized as an efficient method for degrading halogenated organic pollutants (HOPs). However, a significant challenge is the excessive energy consumption resulting from the recombination of H* to H2 production in the EHDH process. In this study, a promising strategy was proposed to generate piezo-induced atomic H*, without external energy input or chemical consumption, for the degradation and dehalogenation of HOPs. Specifically, sub-5 nm Ni nanoparticles were subtly dotted on an N-doped carbon layer coating on BaTiO3 cube, and the resulted hybrid nanocomposite (Ni-NC@BTO) can effectively break C-X (X = Cl and F) bonds under ultrasonic vibration or mechanical stirring, demonstrating high piezoelectric driven dehalogenation efficiencies toward various HOPs. Mechanistic studies revealed that the dotted Ni nanoparticles can efficiently capture H* to form Ni-H* (Habs) and drive the dehalogenation process to lower the toxicity of intermediates. COMSOL simulations confirmed a "chimney effect" on the interface of Ni nanoparticle, which facilitated the accumulation of H+ and enhanced electron transfer for H* formation by improving the surface charge of the piezocatalyst and strengthening the interfacial electric field. Our work introduces an environmentally friendly dehalogenation method for HOPs using the piezoelectric process independent of the external energy input and chemical consumption.

Complexation-based selectivity of organic phosphonates adsorption from high-salinity water by neodymium-doped nanocomposite.

Organic phosphonates have been widely used in various industries and are ubiquitous in wastewaters, and efficient removal of phosphonates is still a challenge for the conventional processes because of the severe interferences from the complex water constitutions. Herein, an Nd-based nanocomposite (HNdO@PsAX) was fabricated by immobilizing hydrated neodymium oxide (HNdO) nanoparticles inside a polystyrene anion exchanger (PsAX) to remove phosphonates from high-salinity aqueous media. Batch experiments demonstrated that HNdO@PsAX had an excellent adsorption capacity (∼90.5 mg P/g-Nd) towards a typical phosphonate (1-hydrox-yethylidene-1,1-diphosphonic acid, HEDP) from the background of 8 g/L NaCl, whereas negligible HEDP adsorption was achieved by PsAX. Attractively, various coexisting substances (humic acid, phosphate, citrate, EDTA, metal ligands, and anions) exerted negligible effects on the HEDP adsorption by HNdO@PsAX under high salinity. FT-IR and XPS analyses revealed that the inner-sphere complexation between HEDP and the immobilized HNdO nanoparticles is responsible for HEDP adsorption. Fixed-bed experiments further verified that HNdO@PsAX was capable of successively treating more than 4500 bed volumes (BV) of a synthetic high-salinity wastewater (1.0 mg P/L of HEDP), whereas only ∼2 BV of effective treatment capacity was received by PsAX. The exhausted HNdO@PsAX was amenable to a complete regeneration by a binary NaOHNaCl solution without significant loss in capacity. The capability in removing other organic phosphonates and treating a real electroplating wastewater by HNdO@PsAX was further validated. Generally, HNdO@PsAX exhibited a great potential in efficiently removing phosphonates from high-salinity wastewater.

Engineering Nano-Au-Based Sensor Arrays for Identification of Multiple Ni(II) Complexes in Water Samples.

Advanced techniques for nickel (Ni(II)) removal from polluted waters have long been desired but challenged by the diversity of Ni(II) species (most in the form of complexes) which could not be readily discriminated by the traditional analytical protocols. Herein, a colorimetric sensor array is developed to address the above issue based on the shift of the UV-vis spectra of gold nanoparticles (Au NPs) after interaction with Ni(II) species. The sensor array is composed of three Au NP receptors modified by N-acetyl-l-cysteine (NAC), tributylhexadecylphosphonium bromide (THPB), and the mixture of 3-mercapto-1-propanesulfonic acid and adenosine monophosphate (MPS/AMP), to exhibit possible coordination, electrostatic attraction, and hydrophobic interaction toward different Ni(II) species. Twelve classical Ni(II) species were selected as targets to systematically demonstrate the applicability of the sensor array under various conditions. Multiple interactions with Ni(II) species were evidenced to trigger the diverse Au NP aggregation behaviors and subsequently produce a distinct colorimetric response toward each Ni(II) species. With the assistance of multivariate analysis, the Ni(II) species, either as the sole compound or as mixtures, can be unambiguously discriminated with high selectivity in simulated and real water samples. Moreover, the sensor array is very sensitive with the detection limit in the range of 4.2 to 10.5 µM for the target Ni(II) species. Principal component analysis signifies that coordination dominates the response of the sensor array toward different Ni(II) species. The accurate Ni(II) speciation provided by the sensor array is believed to assist the rational design of specific protocols for water decontamination and to shed new light on the development of convenient discrimination methods for other toxic metals of concern.

Identification of Co-O-Mo Active Centers on Co-Doped MoS2 Electrocatalyst.

Strategies for harmonizing the construction of an active site and the building of electron transport for a hybrid MoS2 catalyst are crucial for its application in electrochemical reactions. In this work, an accurate and facile hydrothermal strategy was proposed to fabricate the active center of Co-O-Mo on a supported MoS2 catalyst by forming a CoMoSO phase on the edge of MoS2, yielding (Co-O)x-MoSy (x = 0, 0.3, 0.6, 1, 1.5, or 2.1). The results show that the electrochemical performances (hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical degradation) of the yielded MoS2-based catalysts were positively correlated with the Co-O bonds, verifying the significant role of Co-O-Mo as the active center. The fabricated (Co-O)-MoS0.9 presented an extremely low overpotential and Tafel slope in both HER and OER, and it also demonstrated excellent BPA removal in the electrochemical degradation reaction. As compared with the Co-Mo-S configuration, the configuration of Co-O-Mo not only serves as the active center but also provides a conducting channel to facilitate electron conductivity with more accessible charge transfer at the electrode/electrolyte interface, which is favorable for electrocatalytic reaction. This work offers a new perspective for the active mechanism of metallic-heteroatom-dopant electrocatalysts and further boosts research on the development of noble/non-noble hybrid electrocatalysts in the future.

Enhanced phosphate removal from water by hydrated neodymium oxide-based nanocomposite: Performance, mechanism, and validation.

Phosphorus (P) control has been recognized as an imperative task to mitigate water eutrophication and settle the imminent shortage of P resources. Despite intensive effort put into this matter, it is still generally challenging for the current methods to remove and even potentially recover phosphorus (as phosphate) from complicated water matrices. To this end, we proposed a novel nanocomposite via coupling polystyrene anion exchanger (PsAX) with hydrated neodymium oxide (HNdO) nanoparticle for selective removal of phosphate. The developed nanocomposite, i.e., HNdO-PsAX, exhibited quite stable and efficient phosphate adsorption over a wide pH range of 3.0-10.0 with the maximum adsorption capacity as 85.4 mg P/g. It also showed satisfied anti-interference against various competing substances; notably, HNdO-PsAX obviously outperformed Phoslock, a commercial lanthanum-based adsorbent exclusively for phosphate sequestration, particularly under the interference of bicarbonate and humic acid, which were admitted as the paralyzing factors for Phoslock. The superior affinity of HNdO-PsAX towards phosphate, driven by the specific Nd-P inner-sphere complexation as evidenced by XPS, FT-IR, and the lattice evolution of HNdO nanoparticle, renders the nanocomposite eminently suitable for sequestrating trace phosphate. Fixed-bed treatment validated that HNdO-PsAX was capable of treating ∼11,800 bed volume of a simulated wastewater (from 2.0 to below 0.5 mg P/L), approximately 12 times higher than that of the previously reported Fe-based nanocomposite (HFO-PsAX, ∼ 900 BV); also, a satisfactory outcome in treating authentic municipal wastewater by HNdO-PsAX and the feasibility of regenerating the exhausted one by a binary NaOH-NaCl solution were recognized. This work provides a new potion of enhanced phosphorous control for surface water and wastewater.

Oxygen vacancy-mediated peroxydisulfate activation and singlet oxygen generation toward 2,4-dichlorophenol degradation on specific CuO1-x nanosheets.

Durable and stable removal of 2,4-dichlorophenpl (2,4-DCP) by CuO1-x nanosheets is reported. CuO1-x nanosheets were fabricated by a simple defect engineering strategy and greatly increased the efficiency of peroxydisulfate (PDS) activation to improve 2,4-DCP removal by introducing abundant oxygen vacancy (Vo) to produce an electron-rich surface. Results showed that CuO1-x nanosheets exposed more Vo as active sites for PDS activation as compared with that of CuO nanoparticles, giving rise to dramatic enhancement of catalytic performance with ultrahigh reaction rate that is qualified for serving in flow filtration system, completely degrading 100 mg L-1 of 2,4-DCP within 3 s of residence time. Besides, experimental studies confirmed that 1O2 generated by Vo - mediated PDS activation plays the dominate role in the degradation of contaminants. Relative to the previously reported CuO/PDS systems, the obtained CuO1-x nanosheets demonstrated 2.7 times higher specific PDS activity and 67 times higher specific CuO activity for 2,4-DCP removal. Our study not only improves the fundamental understanding of active sites in morphologically tunable metal oxides but also proposes a guideline for future research and engineering application of persulfate.

Identifying the Active Sites of Heteroatom Graphene as a Conductive Membrane for the Electrochemical Filtration of Organic Contaminants.

The dopants of sulfur, nitrogen, or both, serving as the active sites, into the graphitic framework of graphene is an efficient strategy to improve the electrochemical performance of electrochemical membrane filtration. However, the covalent bonds between the doped atoms and the substrate that form different functional groups have a significant role in the specific activity for pollutant degradation. Herein, we found that the singly doped heteroatom graphene (NG and SG) achieved superior removal efficiency of pollutants as compared with that of the double doped heteroatom graphene (SNG). Mechanism studies showed that the doped N of NG presented as graphitic N and substantially increased electron transfer, whereas the doped S of SG posed as -C-SOx-C- provided more adsorption sites to improve electrochemical performance. However, in the case of SNG, the co-doped S and N cannot form the efficient graphitic N and -C-SOx-C- for electrochemical degradation, resulting in a low degradation efficiency. Through the fundamental insights into the bonding of the doped heteroatom on graphene, this work furnishes further directives for the design of desirable heteroatom graphene for membrane filtration.

Toxicity and endocrine-disrupting potential of PM2.5: Association with particulate polycyclic aromatic hydrocarbons, phthalate esters, and heavy metals.

The adverse effects of fine atmospheric particulate matter with aerodynamic diameters of ≤2.5 µm (PM2.5) are closely associated with particulate chemicals. In this study, PM2.5 samples were collected from highway and industry sites in Hangzhou, China, during the autumn and winter, and their cytotoxicity and pulmonary toxicity and endocrine-disrupting potential (EDP) were evaluated in vitro and in vivo; the particulate polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs), and heavy metals were then characterized. The toxicological results suggested that the PM2.5 from highway site induced higher cytotoxicity (cell viability inhibition, intracellular oxidative stress, and cell membrane injury) and pulmonary toxicity (inflammatory response (IR) and oxidative stress (OS)) than the samples from industry site, while the PM2.5 from industry site exhibited higher EDP (estrogenic and anti-androgenic activity). The cytotoxicity and pulmonary toxicity of PM2.5 in the winter were higher than those in the autumn, while no seasonal difference in the endocrine-disrupting potential was observed (p > 0.05). The Pearson correlation analysis between the biological effects and particulate chemicals revealed that the PM2.5-induced inflammatory response and oxidative stress were closely associated with the particulate PAHs and heavy metals (Pearson correlation coefficients: rIR, PAHs = 0.822-0.988, rIR, heavy metals = 0.895-0.971, rOS, PAHs = 0.843-0.986, and rOS, heavy metals = 0.887-0.933), while particulate di (2-ethylhexyl)phthalate (DEHP) substantially contributed to the EDP of PM2.5 (rEDP, DEHP = 0.981). This study indicated that the toxicity and EDP of PM2.5 could vary with the surrounding environment and season, which was closely associated with the variations of particulate chemicals. Further studies are needed to clarify the associations between the harmful effects of PM2.5 and other contributing factors.

Mechanistically understanding adsorption of methyl orange, indigo carmine, and methylene blue onto ionic/nonionic polystyrene adsorbents.

The involved interaction information concerning adsorbate-adsorbate and adsorbate-adsorbent is indispensable for developing and optimizing adsorption treatment of dye wastewater. Single and bi-solute adsorption of methyl orange (MO), indigo carmine (IC), and methylene blue (MB) on polystyrene anion exchanger (PsAX), defunctionalized version of PsAX (DF-PsAX), and hyper-cross-linked polystyrene adsorbent (MN200) were investigated to obtain a mechanistic understanding. Under acidic condition, higher adsorption efficiencies of PsAX due to extra intermolecular interactions of MO between the protonated tertiary amine group and the sulfate groups were observed, while strong alkaline condition is favorable for the adsorption of IC and MB by PsAX. MN200 exhibited much larger adsorption capacity toward MB than that toward MO or IC, because the fused-rings structure of MB is more polarizable and can form stronger nonionic intermolecular attractions with the matrix structure of polystyrene adsorbents. Bi-solute adsorption reveals that MO has obvious competitive effect toward IC adsorption at low concentrations, but it is not the case for the adsorption at high concentrations, where IC molecules can form intermolecular H-bonding interactions to defend the competition. the thermodynamic parameters confirm the endothermic and spontaneous nature of MO adsorption by PsAX, and ≈ 48 KJ mol-1 of the enthalpy change (∆H) imply the adsorption is not just physical absorption. Additionally, water/ethanol mixture solution of NaCl can almost thoroughly regenerate the exhausted PsAX, whereas only aqueous solution without ethanol is invalid.

Rapid start-up of an aerobic granular sludge system for nitrogen and phosphorus removal through seeding chitosan-based sludge aggregates.

This study presents a novel strategy to accelerate the start-up of aerobic granular sludge (AGS) system and ensure the nutrient removal during cultivation. This new method consists of preparing the chitosan-based sludge aggregates outside the reactor and then seeding the reactor with such sludge aggregates. To prepare chitosan-based sludge aggregates, chitosan was dissolved in acetic acid solution acting as a cationic flocculant to bind negatively charged sludge together, and then the dissolved chitosan was in situ precipitated by readjusting pH to form stable sludge aggregates. The chitosan-induced charge neutralization and water-insolubility of chitosan were the two main reasons for the super-rapid formation of chitosan-based sludge aggregates. The as-prepared chitosan-based sludge aggregates had a much lower sludge volume index at 30 min (SVI30) (90.1 mL/g) than the original sludge (SVI30 = 328.0 mL/g). They also had some AGS-like characteristics such as large particle size (1300 µm) and fast settling velocity (23.8 m/h). Consequently, short settling time can be achieved and excessive biomass wash-out can be avoided in the rapid start-up of AGS system with chitosan-based sludge aggregates as inoculant, which was beneficial to accelerating sludge granulation while maintaining nutrient removal. Additionally, the abundances of filamentous bacteria and Candidatus Accumulibacter and the content of extracellular polymeric substances increased during cultivation, which could also contribute to the AGS formation. By seeding chitosan-based sludge aggregates in the anaerobic/oxic sequencing batch reactor, complete granulation was rapidly achieved in 10 days, and good removals of nitrogen and phosphorus was obtained after 14-18 days of cultivation.

Enhanced BiFeO3/Bi2Fe4O9/H2O2 heterogeneous system for sulfamethoxazole decontamination: System optimization and degradation pathways.

Sulfonamides as the major antibiotic have become emerging contaminants worldwide in aquatic environments. Herein, a heterogeneous Fenton-like oxidation driven by a novel BF-PMCs bismuth ferrites reported firstly for efficient degradation of sulfamethoxazole (SMX) in which the possible degradation pathways are thoroughly analyzed through identifying some of key intermediates (i.e., C8H11N3O4S, C4H4NO2, etc.) using liquid chromatography-mass spectrum (LC-MS), monitoring organic acids (i.e., acetic acid, pyruvic acid) and inorganic anions (i.e., sulfate, nitrate) using ion chromatography (IC), and detecting radical species (i.e., HO) using both chemical quenchers and fluorescence technique, simultaneously. The optimal operations in BF-PMCs/H2O2 system for SMX degradation are recommended at the conditions of initial pH ~4.5, 1.5 mg L-1 [SMX], 70 mM [H2O2], and BF-PMCs loading of 0.2 g L-1. The degradation rates (kinetic value of kapp) for SMX, azoxystrobin, bisphenol A, and 2,4-dichlorophenol are 9.5 × 10-3, 13.6 × 10-3, 7.3 × 10-3, and 5.9 × 10-3 min-1, respectively. Meanwhile, the degradation rates in BF-PMCs/H2O2 system for SMX degradation are slightly slower in the presence of inorganic anions (e.g., Cl-, NO3-) and NOM (e.g., humic acid). Based on an overall consideration, the BF-PMCs/H2O2 system has great potential for degradation of emerging organic pollutants (EOPs) in natural water systems.

Selective adsorption of molybdate from water by polystyrene anion exchanger-supporting nanocomposite of hydrous ferric oxides.

Molybdenum is an essential trace element for humans but can be harmful with excess assimilations or chronic exposures. In this study a polymer-functionalized nanocomposite (HFO-PsAX) was fabricated for selective adsorption of molybdate from aqueous solution. HFO-PsAX was prepared by grafting hydrous ferric oxide nanoparticles (HFOs) into the porous structure of a polystyrene anion exchanger (PsAX) by in situ synthesis method. The resultant HFO-PsAX exhibited greatly enhanced selectivity toward molybdate as compared with the matrix, PsAX, which is also a fair adsorbent for scavenging molybdate. The competitive abilities of the ubiquitous anions, i.e., chloride, carbonate, sulfate, and phosphate, on the adsorption of molybdate by HFO-PsAX followed the order: chloride < phosphate < carbonate < sulfate. The unexpectedly weak competitive ability of trivalent phosphate may be due to incompletely dissociated state and formation of molybdate-phosphate complexes. The optimal pH for the adsorption of molybdate was determined as pH≈4, which is associated with the dissociation constants of molybdic acid; certain adsorption capacities were also observed even under extremely alkaline condition (pH=14) for single-component molybdate solution. Temperature (10, 25, and 40°C) has negligible effect on the adsorption capacities by HFO-PsAX, and Freundlich model and Dubinin-Radushkevich (D-R), Temkin model can describe the adsorption isotherms well. The adsorption potential of Temkin model is calculated as ≈100J/mol, which is between those of physisorption and chemisorption process. Fixed-bed column adsorption experiments validated the potential of HFO-PsAX in treating Mo(VI) contaminated water for practical application, and the exhausted HFO-PsAX can be regenerated by a binary NaOH-NaCl solution (both 5% in mass) without loss in adsorption capacities.

Differential control of anode/cathode potentials of paired electrolysis for simultaneous removal of chemical oxygen demand and total nitrogen.

Paired electrolysis can take advantage of both anodic oxidation and cathodic reduction, and thus improve current efficiency for electrochemical wastewater treatment. In this work, differential control of anode/cathode potentials of paired electrolysis for simultaneous removal of chemical oxygen demand (COD) and total nitrogen (TN, including ammonia, nitrate, and nitrite) was studied. We first determined the optimal potentials for anodic oxidation of COD/NH4+ or cathodic reduction of NO3-/NO2- (minimization of over-oxidation or over-reduction) by preliminary cyclic voltammetry and constant-potential electrolysis experiments, i.e., 1.6 V for anodic oxidation and -1.26 V for cathodic reduction in this case. The optimal working potential of the cathode was achieved at appropriate current density in the paired electrolysis system, the working potential of the anode was independently controlled by adjusting the ratio of its surface area to that of the cathode. In this way, both the cathode and anode could work under optimal potentials. At an optimized cathodic current density of 5.0 mA cm-2 and cathode/anode surface area ratio of 2:1, the removal efficiencies of COD and TN from simulated wastewater reached 91.9% and 86.2%, respectively. Additionally, the developed paired electrolysis system was validated by treating an actual pharmaceutical wastewater, results for which showed that a total current efficiency of 84.8% was achieved, which was at least twice as high as that of traditional electrochemical processes.

Treatment of reverse-osmosis concentrate of printing and dyeing wastewater by electro-oxidation process with controlled oxidation-reduction potential (ORP).

Reverse osmosis concentrate (ROC) of printing and dyeing wastewater remains as a daunting environmental issue, which is characterized by high salinity, chemical oxygen demand (COD), chroma and low biodegradability. In this study electro-oxidation process (PbO2/Ti electrode) coupled with oxidation-reduction potential (ORP) online monitor was applied to treat such a ROC effluent. The results show that with the increase of specific electrical charge (Qsp), the removal efficiencies of COD, TN and chroma increased significantly at the incipience and then reached a gentle stage; the optimal total current efficiency (12.04 kWh m-3) was obtained with the current density of 10 mA cm-2 (Qsp, 3.0 Ah L-1). Meanwhile, some inorganic ions can be simultaneously removed to varying degrees. FTIR analyses indicated that the macromolecular organics were decomposed into smaller molecules. A multi-parameter linear relationship between ORP and Qsp, COD and Cl- concentration was established, which can quantitatively reflect the effect of current density, chloride ion concentration, pollutants and reaction time on the performance of the electro-oxidation system. As compared to a traditional constant-current system, the constant-ORP system developed in this study (through the back-propagation neural network [BPN] model with ORP monitoring) approximately reduced the energy cost by 24-29%. The present work is expected to provide a potential alternative in optimizing the electro-oxidation process.

Understanding and modeling removal of anionic organic contaminants (AOCs) by anion exchange resins.

Ionic organic contaminants (OCs) are a growing concern for water treatment and the environment and are removed inefficiently by many existing technologies. This study examined removal of anionic OCs by anion exchange resins (AXRs) as a promising alternative. Results indicate that two polystyrene AXRs (IRA910 and IRA96) have higher sorption capacities and selectivity than a polyacrylate resin (A860). For the polystyrene resins, selectivity follows: phenolates ≥ aromatic dicarboxylates > aromatic monocarboxylates > benzenesulfonate > aliphatic carboxylates. This trend can be explained based on hydration energy, the number of exchange groups, and aromaticity and hydrophobicity of the nonpolar moiety (NPM) of the anions. For A860, selectivity only varies within a narrow range (0.13-1.64). Despite the importance of the NPM of the anions, neutral solutes were sorbed much less, indicating synergistic combinations of electrostatic and nonelectrostatic interactions in the overall sorption. By conducting multiple linear regression between Abraham's descriptors and nature log of selectivity, induced dipole-related interactions and electrostatic interactions were found to be the most important interaction forces for sorption of the anions, while solute H-bond basicity has a negative effect. A predictive model was then developed for carboxylates and phenolates based on the poly parameter linear free energy relationships established for a diverse range of 16 anions and 5 neutral solutes, and was validated by accurate prediction of sorption of five test solutes within a wide range of equilibrium concentrations and that of benzoate at different pH.

Reconstruction of adsorption potential in Polanyi-based models and application to various adsorbents.

The equilibrium Polanyi adsorption potential was reconstructed as ε = -RT ln(Ca(or H)/δ) to correlate the characteristic energy (E) of Polanyi-based models (qe = f[ε/E]) with the properties or structures of absorbates, where qe is the equilibriumn adsorption capacity, Ca(or H) is the converted concentration from the equilibrium aqueous concentration at the same activity and corresponds to the adsorption from the gas or n-hexadecane (HD) phase by the water-wet adsorbent, and "δ" is an arbitrary divisor to converge the model fitting. Subsequently, the modified Dubinin-Astakhov model based on the reconstructed ε was applied to aqueous adsorption on activated carbon, black carbon, multiwalled carbon nanotubes, and polymeric resin. The fitting results yielded intrinsic characteristic energies Ea, derived from aqueous-to-gas phase conversion, or EH, derived from aqueous-to-HD phase conversion, which reflect the contributions of the overall or specific adsorbate-adsorbent interactions to the adsorption. Effects of the adsorbate and adsorbent properties on Ea or EH then emerge that are unrevealed by the original characteristic energy (Eo), i.e., adsorbates with tendency to form stronger interactions with an adsorbent have larger Ea and EH. Additionally, comparison of Ea and EH allows quantitative analysis of the contributions of nonspecific interactions, that is, a significant relationship was established between the nonspecific interactions and Abraham's descriptors for the adsorption of all 32 solutes on the four different adsorbents: (Ea - EH) = 24.7 × V + 9.7 × S - 19.3 (R(2) = 0.97), where V is McGowan's characteristic volume for adsorbates, and S reflects the adsorbate's polarity/polarizability.

A modified Polanyi-based model for mechanistic understanding of adsorption of phenolic compounds onto polymeric adsorbents.

To obtain mechanistic insight into adsorption of phenolic compounds by two representative polymeric adsorbents, XAD-4 (polystyrene) and XAD-7 (polymethacrylate), a modified Polanyi-based Dubinin-Ashtakhov (D-A) model was developed based on a unique combination of the Polanyi theory, polyparameter linear energy relationships and infinitely dilute solution in n-hexadecane as the reference state. The adsorption potential in the D-A model ε = -RTln(C(w)/C(w) (sat)) was redefined by replacing the term (C(w)/C(w) (sat)) with the normalized equivalent concentration in n-hexadecane (CHD), where Cw is the aqueous equilibrium concentration and C(w) (sat) is the aqueous solubility of the solute. Using the new reference state allows quantitative comparison among various solutes. By fitting adsorption isotherms to the modified model using εHD = -RTln(CHD/10 000), a new normalizing factor (E(m)) was obtained to quantify the contributions of specific interactions (i.e., H-bonding, dipolar/polarizability, etc.) to the overall adsorption energy. Significant linear correlations were established between "A", the hydrogen-bond acidity, and "E(m)" for the investigated compounds, suggesting that, in addition to hydrophobic interactions, hydrogen-bonding is predominantly responsible for the adsorption of phenols by XAD-4 and XAD-7. Additionally, adsorption capacity and affinity of phenolates were significantly less than those of phenols; another model was proposed to accurately predict the effect of pH on the adsorption behavior of phenols.

Adsorptive selenite removal from water using a nano-hydrated ferric oxides (HFOs)/polymer hybrid adsorbent.

Selenite (SeO(3)(2-)) is an oxyanion of environmental significance due to its toxicity when taken in excess. In the present study, a hybrid adsorbent (HFO-201) was prepared by irreversibly impregnating hydrated ferric oxide (HFO) nanoparticles within a commercial available anion-exchange resin (D-201), and its adsorption towards selenite from water was investigated in batch and column tests. HFO-201 exhibited improved sorption selectivity toward selenite as compared to the polymeric anion exchanger D-201. Two possible adsorption interactions were responsible for selenite removal by HFO-201, the electrostatic interaction from the ammonium groups bound to the D-201 matrix, and the formation of inner-sphere complexes between the loaded HFO nanoparticles and selenite. In a wide pH range (i.e., 3-8), increasing solution pH was found to result in a decrease of selenite removal on HFO-201. Adsorption isotherms fit the Freundlich model well, and selenite adsorption increased with increasing ambient temperature, indicating its endothermic nature. Column adsorption tests suggested that satisfactory removal of selenite from 2 mg/L to less than 0.01 mg/L could be achieved by HFO-201 even in the presence of the commonly encountered anionic competition at greater concentration, with the treatment capacity of approximately 1200 bed volume (BV) per run, while that for D-201 was only less than 30 BV under otherwise identical conditions. Furthermore, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH-NaCl solution.

Highly efficient removal of heavy metals by polymer-supported nanosized hydrated Fe(III) oxides: behavior and XPS study.

The present study developed a polymer-based hybrid sorbent (HFO-001) for highly efficient removal of heavy metals [e.g., Pb(II), Cd(II), and Cu(II)] by irreversibly impregnating hydrated Fe(III) oxide (HFO) nanoparticles within a cation-exchange resin D-001 (R-SO(3)Na), and revealed the underlying mechanism based on X-ray photoelectron spectroscopy (XPS) study. HFO-001 combines the excellent handling, flow characteristics, and attrition resistance of conventional cation-exchange resins with the specific affinity of HFOs toward heavy metal cations. As compared to D-001, sorption selectivity of HFO-001 toward Pb(II), Cu(II), and Cd(II) was greatly improved from the Ca(II) competition at greater concentration. Column sorption results indicated that the working capacity of HFO-001 was about 4-6 times more than D-001 with respect to removal of three heavy metals from simulated electroplating water (pH approximately 4.0). Also, HFO-001 is particularly effective in removing trace Pb(II) and Cd(II) from simulated natural waters to meet the drinking water standard, with treatment volume orders of magnitude higher than D-001. The superior performance of HFO-001 was attributed to the Donnan membrane effect exerted by the host D-001 as well as to the impregnated HFO nanoparticles of specific interaction toward heavy metal cations, as further confirmed by XPS study on lead sorption. More attractively, the exhausted HFO-001 beads can be effectively regenerated by HCl-NaCl solution (pH 3) for repeated use without any significant capacity loss.