It has been well established that natural organic matters (NOMs) are precursors for the formation... more It has been well established that natural organic matters (NOMs) are precursors for the formation of disinfection by-products (DBPs) in drinking water supplies, thus the removal of NOMs is often used as an effective approach to limit DBPs production. In this study, we evaluated the application of oxidized multi-walled carbon nanotubes (OMWNTs)/polysulfone (PSU) nanocomposite hollow fiber membranes (HFM) for the removal of NOMs and its impact on the production of DBPs following water chlorination. Analysis of source water samples by fluorescence excitation/emission matrix (EEM) spectrometry indicated that the dominant dissolved organic matters were humic acid. Evaluation of the fabricated nanocomposite HFMs showed improved water fluxes (30~50%), better fouling resistance, and a comparable solute rejection rate when compared with the conventional PSU membranes. The flux increase was attributed to the increased surface hydrophilicity and porosity of the membrane after embedding the hyd...
Chromium contamination of the environment is of a major concern due to its extensive use in indus... more Chromium contamination of the environment is of a major concern due to its extensive use in industrial processes. In most of basic and neutral environments, Cr (III) precipitates as stable hydroxides: Cr (OH)3 and Cr, Fe (OH)3 [1]. Yet, the production of organic ligands by plants or microorganisms can increase the dissolution of Cr (OH)3 either by protons exchange or by the formation of soluble complexes [2, 3]. In order to evaluate the risk of Cr (OH)3 heterotrophic leaching, several organic acids commonly found in the soil solution and a siderophore have been tested as a function of environmentally relevant pHs. The leaching ability of a siderophore-producing strain Pseudomonas putida GB1, was also tested in the presence of increasing concentrations of Cr (OH)3.
Knowing that the world is facing a shortage of fresh water, desalination, in its different forms ... more Knowing that the world is facing a shortage of fresh water, desalination, in its different forms including reverse osmosis, represents a practical approach to produce potable water from a saline source. In this report, two kinds of Metal-Organic Frameworks (MOFs) nanoparticles (NPs), UiO-66 (~100 nm) and MIL-125 (~100 nm), were embedded separately into thin-film composite membranes in different weight ratios, 0%, 0.05%, 0.1%, 0.15%, 0.2%, and 0.3%. The membranes were synthesized by the interfacial polymerization (IP) of m-phenylenediamine (MPD) in aqueous solution and trimesoyl chloride (TMC) in an organic phase. The as-prepared membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, and salt rejection and water flux assessments. Results showed that both UiO-66 and MIL-125 could improve the membranes' performance and the impacts depended on the NPs loading. At the optimum NPs loadings, 0.15% for UiO-66 and 0.3% for MIL-125, the water flux increased from 62.5 L/m 2 h to 74.9 and 85.0 L/m 2 h, respectively. NaCl rejection was not significantly affected (UiO-66) or slightly improved (MIL-125) by embedding these NPs, always at >98.5% as tested at 2000 ppm salt concentration and 300 psi transmembrane pressure. The results from this study demonstrate that it is promising to apply MOFs NPs to enhance the TFC membrane performance for desalination.
Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthes... more Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthesized by the interfacial polymerization (IP) process. An m-phenylenediamine (MPD) aqueous solution and an organic phase with trimesoyl chloride (TMC) dissolved in isooctane were used in the IP reaction, occurring on a nanoporous polysulfone (PSU) support layer. Isooctane was introduced as the organic solvent for TMC in this work due to its intermediate boiling point. MCM-41 silica NPs were loaded in MPD and TMC solutions in separate experiments, in a concentration range from 0 to 0.04 wt %, and the membrane performance was assessed and compared based on salt rejection and water flux. The prepared membranes were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, and attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis. The results show that adding MCM-41 silica NPs into an MPD solution yields sligh...
Amide-functionalized ordered mesoporous carbon was developed for removal of mercury (Hg 2+) from ... more Amide-functionalized ordered mesoporous carbon was developed for removal of mercury (Hg 2+) from aqueous phase. Ordered mesoporous carbon was synthesized using a mesoporous silica template, SBA-15, followed by in situ polymerization of acrylic acid, carbonization and template removal. Ordered mesoporous carbon was subsequently functionalized with ethylenediamine through a combined treatment of nitric acid and thionyl chloride. Physio-chemical properties of the carbons were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform IR spectroscopy, potentiometry and N2-adsorption/desorption (BET). Adsorption kinetics and equilibrium of Hg was assessed in batch experimental systems. Results indicated that amide-functionalized carbon (FOMC) maintained the original ordered mesoporous structure and hexagonal framework with an averaged surface area of 607 m 2 g-1 , pore size of 4.1 nm and pore volume of 0.62 cm 3 g-1. The functionalization process immobilized significant amounts of amide group on the carbon surface and enhanced surface negative charges and hydrophilicity. The adsorption of mercury(II) by functionalized ordered mesoporous carbon reached equilibrium within 480 min. The adsorption capacity was 1.5-time as large as for ordered mesoporous carbon, suggesting an enhanced affinity of surface amide groups for aqueous Hg binding. The adsorption also occurred in a wider pH range (about 5.0-7.0 vs. 5.5-6.5). The Freundlich adsorption model fitted the isotherms reasonably well. A surface complexation double layer model was developed to describe the Hg 2+ adsorption, from which related H + and Hg 2+ binding constants on the surface were obtained.
One of the grand challenges to sustain the modern society is to secure adequate water resources o... more One of the grand challenges to sustain the modern society is to secure adequate water resources of desirable quality for various designated uses. To address this challenge, membrane water treatment is expected to play an increasingly important role in areas such as drinking water treatment, brackish and seawater desalination, and wastewater treatment and reuse. Existing membranes for water treatment, typically polymeric in nature, are still restricted by several challenges including the trade-off relationship between permeability and selectivity (also called Robeson upper boundary in membrane gas separation), and low resistance to fouling. Nanocomposite membranes, a new class of membranes fabricated by combining polymeric materials with nanomaterials, are emerging as a promising solution to these challenges. The advanced nanocomposite membranes could be designed to meet specific water treatment applications by tuning their structure and physicochemical properties (e.g. hydrophilicity, porosity, charge density, and thermal and mechanical stability) and introducing unique functionalities (e.g. antibacterial, photocatalytic or adsorptive capabilities). This review is to summarize the recent scientific and technological advances in the development of nanocomposite membranes for water treatment. The nanocomposite membranes were classified into (1) conventional nanocomposite, (2) thin-film nanocomposite (TFN), (3) thin-film composite (TFC) with nanocomposite substrate, and (4) surface located nanocomposite, based on the membrane structure and location of nanomaterial. Challenges and future research directions in developing high performance nanocomposite membranes were also be discussed.
The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was inve... more The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed that U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.9 to 9.0. For instance, at pH 6.9 the observed U(VI) reduction rates decreased by 81% and 82% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) possibly acted as an electron shuttle to ferry the electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 could facilitate U(VI) reductive immobilization in the contaminated groundwater.
The effects of soil minerals on chromate (Cr VI O 4 2-, noted as Cr(VI)) reduction by sulfide wer... more The effects of soil minerals on chromate (Cr VI O 4 2-, noted as Cr(VI)) reduction by sulfide were investigated in the pH range of 7.67 to 9.07 under the anoxic condition. The examined minerals included montmorillonite (Swy-2), illite (IMt-2), kaolinite (KGa-2), aluminum oxide (γ-Al 2 O 3), titanium oxide (TiO 2 , P-25, primarily anatase), and silica (SiO 2). Based on their effects on Cr(VI) reduction, these minerals were categorized into three groups: (i) minerals catalyzing Cr(VI) reduction-illite; (ii) minerals with no effect-Al 2 O 3 ; and (iii) minerals inhibiting Cr(VI) reductionkaolinite, montmorillonite, SiO 2 and TiO 2. The catalysis of illite was attributed primarily to the low concentration of iron solubilized from the mineral, which could accelerate Cr(VI) reduction by shuttling electrons from sulfide to Cr(VI). Additionally, elemental sulfur produced as the primary product of sulfide oxidation could further catalyze Cr(VI) reduction in the heterogeneous system. Previous studies have shown that adsorption of sulfide onto elemental sulfur nanoparticles could greatly increase sulfide reactivity towards Cr(VI) reduction. Consequently, the observed rate constant, k obs , increased with increasing amounts of both iron solubilized from illite and elemental sulfur produced during the reaction. The catalysis of iron, however, was found to be blocked by phenanthroline, a strong complexing agent for ferrous iron. In this case, the overall reaction rate at the initial stage of reaction was pseudo first order with respect to Cr(VI), i.e., the reaction kinetics was similar to that in the homogeneous system, because elemental sulfur exerted no effect at the initial stage prior to accumulation of elemental sulfur nanoparticles. In the suspension of kaolinite, which belonged to group (iii), an inhibitive effect to Cr(VI) reduction was observed and subsequently examined in more details. The inhibition was due to the sorption of elemental sulfur onto kaolinite, which reduced or completely eliminated the catalytic effect of elemental sulfur, depending on kaolinite concentration. This was consistent with the observation that the catalysis of externally added elemental sulfur (50 μM) on Cr(VI) reduction would disappear with a kaolinite concentration of more than 5.0 g/L. In kaolinite suspension, the overall reaction rate law was:-d[Cr(VI)]/dt = k obs [H + ] 2 [Cr(VI)][HS-] 0.70
Hexavalent chromium reduction by sulfide in the presence of goethite was studied through several ... more Hexavalent chromium reduction by sulfide in the presence of goethite was studied through several batch experiments. Under our specific experimental conditions including 20 µM of hexavalent chromium, 560-1117 µM of sulfide and 10.61-37.13 m 2 /L of goethite at pH of 8.45 controlled by 0.1 M borate buffer, the obtained hexavalent chromium disappearance rate was-d[Cr(VI)]/dt = k[surface area of goethite][Cr(VI)][S(-II)] T 1.5 and the determined overall rate constant (k) was 31.9 ± 4.2 (min)-1 (m 2 /L)-1 (mol/L)-1.5. Among the potential major reducing agents in our comprehensive heterogeneous system such as aqueous phase sulfide, surface-associated sulfide, dissolved ferrous iron, ferrous iron on the goethite surface, as well as fresh ferrous sulfide in the solution, it was considered that the surface ferrous irons which could be produced following sulfide adsorption, played a leading role for Cr(VI) reduction as primary electron donors. In addition, no proof of the preliminary dissolution of ferrous iron from goethite to aqueous phase was observed in the experiments. Elemental sulfur was detected as the final stabilized product of sulfide and it took in charge for the promoted Cr(VI) disappearance for the successive addition of Cr(VI) at later stage.
Chromate (Cr VI) reduction by sulfide was conducted in anaerobic batch experimental systems. The ... more Chromate (Cr VI) reduction by sulfide was conducted in anaerobic batch experimental systems. The molar ratio of the reduced Cr VI to the oxidized S-II was 1:1.5 during the reaction, suggesting that the product of sulfide oxidation was elemental sulfur. Under the anaerobic condition, the reaction was pseudo first order initially with respect to Cr VI , but the rate was dramatically accelerated at the later stage of the reaction. The rate acceleration was due to catalysis by elemental sulfur nanoparticles; dissolved species such as monomeric elemental sulfur and polysulfides appeared to be ineffective catalysts. Elemental sulfur nanoparticles were capable of adsorbing sulfide and such adsorbed sulfide exhibited much higher reactivity toward Cr VI reduction than the aqueous-phase sulfide, resulting in the observed rate acceleration. Kinetic data under various reactant concentrations can be represented by the following empirical kinetic equation:-d[Cr VI ]/dt) k 1 [Cr VI ][H 2 S] 0.63 + k 3 [Cr VI ][tSsSH] 0.57. The first term on the right-hand side corresponds to the noncatalytic pathway, with k 1) 1.0 × 10-3 (µM)-0.63 min-1 at pH 7.60 and 8.2 × 10-5 (µM)-0.63 min-1 at pH 8.10. The second term, k 3 [Cr VI ][tSsSH] b , is the catalytic term with [tSsSH] representing the adsorbed concentration of sulfide on the elemental sulfur nanoparticles (µM). The catalytic term is more important at the later stage of the reaction, as indicated by the observed kinetics and the enhancement of the reaction rate by externally added elemental sulfur nanoparticles. At pH 8.10, k 3) 0.0057 (µM)-0.57 min-1 .
In Situ Gaseous Reduction (ISGR) using hydrogen sulfide (H 2 S) is a technology developed for soi... more In Situ Gaseous Reduction (ISGR) using hydrogen sulfide (H 2 S) is a technology developed for soil remediation by reductive immobilization of contaminants such as hexavalent chromium (Cr(VI)). Deploying the technology requires us to obtain a much-improved understanding of the interactions among the contaminants, H 2 S, and various soil components. In this study, Cr(VI) reduction by gaseous H 2 S was examined under various relative humidities (0-96.7%), concentrations of Cr(VI) (127-475 µg/g of solid), and H 2 S (0-800 ppm v) and by using Cr(VI) compounds with different solubilities. Glass beads with various average diameters (GA) 0.600 mm; GB) 0.212-0.300 mm; and GC) 0.106 mm) and silica (SA) 0.075-0.150 mm) were used as matrices to support K 2 CrO 4 , CaCrO 4 , PbCrO 4 , or BaCrO 4 , and reduction of these compounds by gaseous H 2 S was monitored by Cr(VI) analysis following extractions with distilled water or hot alkali solution. The results showed that Cr(VI) reduction relied on both the relative humidity of the gaseous stream and the size of particles onto which Cr(VI) was deposited. The relative humidity required for fast Cr(VI) reduction was 85% for GA, 61% for GB, 6% for SA, and 0% for GC. It was believed that a water film formed on the particle surfaces under appropriate humidity conditions, resulting in Cr(VI) compound dissolution and subsequent reduction. For nonsoluble Cr(VI) compounds including PbCrO 4 and BaCrO 4 , no reduction by H 2 S was observed, even at high relative humidity (96.7%), due to lack of dissolution. This study indicated that ISGR treatment in soils requires appropriate moisture content in the subsurface or maintaining a suitable humidity in the treatment gas stream to maximize chromium immobilization.
Hg(II) sorption by polyaniline is impacted by both water chemistry and the polymer's physicochemi... more Hg(II) sorption by polyaniline is impacted by both water chemistry and the polymer's physicochemical properties.
Granular activated carbon-based, iron-containing adsorbents (As-GAC) were developed for effective... more Granular activated carbon-based, iron-containing adsorbents (As-GAC) were developed for effective removal of arsenic from drinking water. Granular activated carbon (GAC) was used primarily as a supporting medium for ferric iron that was impregnated by ferrous chloride (FeCl 2) treatment, followed by chemical oxidation. Sodium hypochlorite (NaClO) was the most effective oxidant, and carbons produced from steam activation of lignite were most suitable for iron impregnation and arsenic removal. Two As-GAC materials prepared by FeCl 2 treatment (0.025-0.40 M) of Dacro 20 × 50 and Dacro 20 × 40LI resulted in a maximum impregnated iron of 7.89% for Dacro 20 × 50 and 7.65% for Dacro 20 × 40LI. Nitrogen adsorptiondesorption analyses showed the BET specific surface area, total pore volume, porosity, and average mesoporous diameter all decreased with iron impregnation, indicating that some micropores were blocked. SEM studies with associated EDS indicated that the distribution of iron in the adsorbents was mainly on the edge of As-GAC in the low iron content (∼1% Fe) sample but extended to the center at the higher iron content (∼6% Fe). When the iron content was > ∼7%, an iron ring formed at the edge of the GAC particles. No difference in X-ray diffraction patterns was observed between untreated GAC and the one with 4.12% iron, suggesting that the impregnated iron was predominantly in amorphous form. As-GAC could remove arsenic most efficiently when the iron content was approximately 6%; further increases of iron decreased arsenic adsorption. The removal of arsenate occurred in a wide range of pH as examined from 4.4 to 11, but efficiency was decreased when pH was higher than 9.0. The presence of phosphate and silicate could significantly decrease arsenate removal at pH > 8.5, while the effects of sulfate, chloride, and fluoride were minimal. Column studies showed that both As(V) and As(III) could be removed to below 10 µg/L within 6000 empty bed volume when the groundwater containing approximately 50 µg/L of arsenic was treated.
Aqueous U(VI) reduction by hydrogen sulfide was investigated by batch experiments and speciation ... more Aqueous U(VI) reduction by hydrogen sulfide was investigated by batch experiments and speciation modeling; product analysis by transmission electron microscopy (TEM) was also performed. The molar ratio of U(VI) reduced to sulfide consumed, and the TEM result suggested that the reaction stoichiometry could be best represented by UO2(2+) + HS- = UO2+ S* + H+. At pH 6.89 and total carbonate concentration ([CO32-]T) of 4.0 mM, the reaction took place according to the following kinetics: -d[U(VI)]/dt = 0.0103[U(VI)][S2-]T0.54 where [U(VI)] is the concentration of hexavalent uranium, and [S2-]T is the total concentration of sulfide. The kinetics of U(VI) reduction was found to be largely controlled by [CO32-]T (examined from 0.0 to 30.0 mM) and pH (examined from 6.37 to 9.06). The reduction was almost completely inhibited with the following [CO32-]T and pH combinations: [(> or = 15.0 mM, pH 6.89); (> or = 4.0 mM, pH 8.01); and (> or = 2.0 mM, pH 9.06)]. By comparing the experimental results with the calculated speciation of U(VI), it was found that there was a strong correlation between the measured initial reaction rates and the calculated total concentrations of uranium-hydroxyl species; we, therefore, concluded that uranium-hydroxyl species were the ones being reduced by sulfide, not the dominant U-carbonate species present in many carbonate-containing systems.
Arsenic (As) accumulation in rice grains is a threat to human health and marketability of rice pr... more Arsenic (As) accumulation in rice grains is a threat to human health and marketability of rice products. In an effort to minimize As uptake by rice grains, field experiments were conducted to investigate As accumulation in rice grains of three cultivars in monosodium methanearsonate-treated soil under saturated and flooded water management practices. Results indicated that As concentrations in rice grains were cultivar-dependent and influenced by water management. Soil flooding would substantially enhance the As accumulation with a great variation among cultivars. Extractable As in the soil was positively correlated with sodium dithionite-sodium citrate-sodium bicarbonate solution-extractable Fe, suggesting a strong association of As with ferric (hydr)oxide. Additional laboratory studies showed a strong affinity of synthetic ferric (hydr)oxide with monosodium methanearsonate. This study demonstrated that selection of less As-responsive rice cultivars and use of saturated water management in paddy fields could be an effective means to minimize As accumulation in rice grains.
Water samples from 56 lakes of Missouri, USA, were analysed for their fluorescence excitation/emi... more Water samples from 56 lakes of Missouri, USA, were analysed for their fluorescence excitation/emission matrix (EEM) spectroscopy and the formation potentials of total trihalomethanes (TTHM) and N-nitrosodimethylamine (NDMA). Comparing the excitation/emission matrix fingerprints with trihalomethanes formation revealed that water with higher fluorescence intensity generally exhibited higher trihalomethanes formation potential. Moreover, waters with fluorescence centre at excitation: 290-310 nm/emission: 330-350 nm were related to high N-nitrosodimethylamine and trihalomethanes formation potentials. The results suggest that excitation/emission matrix fingerprints could be used as surrogate parameters for monitoring trihalomethanes and N-nitrosodimethylamine formation potentials.
This study is to develop a carbon-based adsorbent containing multiple functional ligands for effe... more This study is to develop a carbon-based adsorbent containing multiple functional ligands for effective removal of lead ions from aqueous media. Activated carbon was oxidized by nitric acid, followed by chlorination with thionyl chloride and reaction with ethylenediamine. Modified activated carbon (MAC) was characterized using scanning electron microscopy in conjunction of energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), and potentiometric titration. Surface characterizations confirmed that carboxyl, amine, and chlorine functional groups were effectively introduced onto the carbon surface by the treatments. The modifications lowered the pH at the point of zero charge (pH pzc) from 9.6 to 2.55 and resulted in more negatively charged surfaces. Adsorptive experiments showed that aqueous Pb removal by MAC was faster, with a 62% higher capacity than the original activated carbon (60.2 vs. 37.2 mg g-1).
It has been well established that natural organic matters (NOMs) are precursors for the formation... more It has been well established that natural organic matters (NOMs) are precursors for the formation of disinfection by-products (DBPs) in drinking water supplies, thus the removal of NOMs is often used as an effective approach to limit DBPs production. In this study, we evaluated the application of oxidized multi-walled carbon nanotubes (OMWNTs)/polysulfone (PSU) nanocomposite hollow fiber membranes (HFM) for the removal of NOMs and its impact on the production of DBPs following water chlorination. Analysis of source water samples by fluorescence excitation/emission matrix (EEM) spectrometry indicated that the dominant dissolved organic matters were humic acid. Evaluation of the fabricated nanocomposite HFMs showed improved water fluxes (30~50%), better fouling resistance, and a comparable solute rejection rate when compared with the conventional PSU membranes. The flux increase was attributed to the increased surface hydrophilicity and porosity of the membrane after embedding the hyd...
Chromium contamination of the environment is of a major concern due to its extensive use in indus... more Chromium contamination of the environment is of a major concern due to its extensive use in industrial processes. In most of basic and neutral environments, Cr (III) precipitates as stable hydroxides: Cr (OH)3 and Cr, Fe (OH)3 [1]. Yet, the production of organic ligands by plants or microorganisms can increase the dissolution of Cr (OH)3 either by protons exchange or by the formation of soluble complexes [2, 3]. In order to evaluate the risk of Cr (OH)3 heterotrophic leaching, several organic acids commonly found in the soil solution and a siderophore have been tested as a function of environmentally relevant pHs. The leaching ability of a siderophore-producing strain Pseudomonas putida GB1, was also tested in the presence of increasing concentrations of Cr (OH)3.
Knowing that the world is facing a shortage of fresh water, desalination, in its different forms ... more Knowing that the world is facing a shortage of fresh water, desalination, in its different forms including reverse osmosis, represents a practical approach to produce potable water from a saline source. In this report, two kinds of Metal-Organic Frameworks (MOFs) nanoparticles (NPs), UiO-66 (~100 nm) and MIL-125 (~100 nm), were embedded separately into thin-film composite membranes in different weight ratios, 0%, 0.05%, 0.1%, 0.15%, 0.2%, and 0.3%. The membranes were synthesized by the interfacial polymerization (IP) of m-phenylenediamine (MPD) in aqueous solution and trimesoyl chloride (TMC) in an organic phase. The as-prepared membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, and salt rejection and water flux assessments. Results showed that both UiO-66 and MIL-125 could improve the membranes' performance and the impacts depended on the NPs loading. At the optimum NPs loadings, 0.15% for UiO-66 and 0.3% for MIL-125, the water flux increased from 62.5 L/m 2 h to 74.9 and 85.0 L/m 2 h, respectively. NaCl rejection was not significantly affected (UiO-66) or slightly improved (MIL-125) by embedding these NPs, always at >98.5% as tested at 2000 ppm salt concentration and 300 psi transmembrane pressure. The results from this study demonstrate that it is promising to apply MOFs NPs to enhance the TFC membrane performance for desalination.
Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthes... more Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthesized by the interfacial polymerization (IP) process. An m-phenylenediamine (MPD) aqueous solution and an organic phase with trimesoyl chloride (TMC) dissolved in isooctane were used in the IP reaction, occurring on a nanoporous polysulfone (PSU) support layer. Isooctane was introduced as the organic solvent for TMC in this work due to its intermediate boiling point. MCM-41 silica NPs were loaded in MPD and TMC solutions in separate experiments, in a concentration range from 0 to 0.04 wt %, and the membrane performance was assessed and compared based on salt rejection and water flux. The prepared membranes were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, and attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis. The results show that adding MCM-41 silica NPs into an MPD solution yields sligh...
Amide-functionalized ordered mesoporous carbon was developed for removal of mercury (Hg 2+) from ... more Amide-functionalized ordered mesoporous carbon was developed for removal of mercury (Hg 2+) from aqueous phase. Ordered mesoporous carbon was synthesized using a mesoporous silica template, SBA-15, followed by in situ polymerization of acrylic acid, carbonization and template removal. Ordered mesoporous carbon was subsequently functionalized with ethylenediamine through a combined treatment of nitric acid and thionyl chloride. Physio-chemical properties of the carbons were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform IR spectroscopy, potentiometry and N2-adsorption/desorption (BET). Adsorption kinetics and equilibrium of Hg was assessed in batch experimental systems. Results indicated that amide-functionalized carbon (FOMC) maintained the original ordered mesoporous structure and hexagonal framework with an averaged surface area of 607 m 2 g-1 , pore size of 4.1 nm and pore volume of 0.62 cm 3 g-1. The functionalization process immobilized significant amounts of amide group on the carbon surface and enhanced surface negative charges and hydrophilicity. The adsorption of mercury(II) by functionalized ordered mesoporous carbon reached equilibrium within 480 min. The adsorption capacity was 1.5-time as large as for ordered mesoporous carbon, suggesting an enhanced affinity of surface amide groups for aqueous Hg binding. The adsorption also occurred in a wider pH range (about 5.0-7.0 vs. 5.5-6.5). The Freundlich adsorption model fitted the isotherms reasonably well. A surface complexation double layer model was developed to describe the Hg 2+ adsorption, from which related H + and Hg 2+ binding constants on the surface were obtained.
One of the grand challenges to sustain the modern society is to secure adequate water resources o... more One of the grand challenges to sustain the modern society is to secure adequate water resources of desirable quality for various designated uses. To address this challenge, membrane water treatment is expected to play an increasingly important role in areas such as drinking water treatment, brackish and seawater desalination, and wastewater treatment and reuse. Existing membranes for water treatment, typically polymeric in nature, are still restricted by several challenges including the trade-off relationship between permeability and selectivity (also called Robeson upper boundary in membrane gas separation), and low resistance to fouling. Nanocomposite membranes, a new class of membranes fabricated by combining polymeric materials with nanomaterials, are emerging as a promising solution to these challenges. The advanced nanocomposite membranes could be designed to meet specific water treatment applications by tuning their structure and physicochemical properties (e.g. hydrophilicity, porosity, charge density, and thermal and mechanical stability) and introducing unique functionalities (e.g. antibacterial, photocatalytic or adsorptive capabilities). This review is to summarize the recent scientific and technological advances in the development of nanocomposite membranes for water treatment. The nanocomposite membranes were classified into (1) conventional nanocomposite, (2) thin-film nanocomposite (TFN), (3) thin-film composite (TFC) with nanocomposite substrate, and (4) surface located nanocomposite, based on the membrane structure and location of nanomaterial. Challenges and future research directions in developing high performance nanocomposite membranes were also be discussed.
The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was inve... more The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed that U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.9 to 9.0. For instance, at pH 6.9 the observed U(VI) reduction rates decreased by 81% and 82% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) possibly acted as an electron shuttle to ferry the electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 could facilitate U(VI) reductive immobilization in the contaminated groundwater.
The effects of soil minerals on chromate (Cr VI O 4 2-, noted as Cr(VI)) reduction by sulfide wer... more The effects of soil minerals on chromate (Cr VI O 4 2-, noted as Cr(VI)) reduction by sulfide were investigated in the pH range of 7.67 to 9.07 under the anoxic condition. The examined minerals included montmorillonite (Swy-2), illite (IMt-2), kaolinite (KGa-2), aluminum oxide (γ-Al 2 O 3), titanium oxide (TiO 2 , P-25, primarily anatase), and silica (SiO 2). Based on their effects on Cr(VI) reduction, these minerals were categorized into three groups: (i) minerals catalyzing Cr(VI) reduction-illite; (ii) minerals with no effect-Al 2 O 3 ; and (iii) minerals inhibiting Cr(VI) reductionkaolinite, montmorillonite, SiO 2 and TiO 2. The catalysis of illite was attributed primarily to the low concentration of iron solubilized from the mineral, which could accelerate Cr(VI) reduction by shuttling electrons from sulfide to Cr(VI). Additionally, elemental sulfur produced as the primary product of sulfide oxidation could further catalyze Cr(VI) reduction in the heterogeneous system. Previous studies have shown that adsorption of sulfide onto elemental sulfur nanoparticles could greatly increase sulfide reactivity towards Cr(VI) reduction. Consequently, the observed rate constant, k obs , increased with increasing amounts of both iron solubilized from illite and elemental sulfur produced during the reaction. The catalysis of iron, however, was found to be blocked by phenanthroline, a strong complexing agent for ferrous iron. In this case, the overall reaction rate at the initial stage of reaction was pseudo first order with respect to Cr(VI), i.e., the reaction kinetics was similar to that in the homogeneous system, because elemental sulfur exerted no effect at the initial stage prior to accumulation of elemental sulfur nanoparticles. In the suspension of kaolinite, which belonged to group (iii), an inhibitive effect to Cr(VI) reduction was observed and subsequently examined in more details. The inhibition was due to the sorption of elemental sulfur onto kaolinite, which reduced or completely eliminated the catalytic effect of elemental sulfur, depending on kaolinite concentration. This was consistent with the observation that the catalysis of externally added elemental sulfur (50 μM) on Cr(VI) reduction would disappear with a kaolinite concentration of more than 5.0 g/L. In kaolinite suspension, the overall reaction rate law was:-d[Cr(VI)]/dt = k obs [H + ] 2 [Cr(VI)][HS-] 0.70
Hexavalent chromium reduction by sulfide in the presence of goethite was studied through several ... more Hexavalent chromium reduction by sulfide in the presence of goethite was studied through several batch experiments. Under our specific experimental conditions including 20 µM of hexavalent chromium, 560-1117 µM of sulfide and 10.61-37.13 m 2 /L of goethite at pH of 8.45 controlled by 0.1 M borate buffer, the obtained hexavalent chromium disappearance rate was-d[Cr(VI)]/dt = k[surface area of goethite][Cr(VI)][S(-II)] T 1.5 and the determined overall rate constant (k) was 31.9 ± 4.2 (min)-1 (m 2 /L)-1 (mol/L)-1.5. Among the potential major reducing agents in our comprehensive heterogeneous system such as aqueous phase sulfide, surface-associated sulfide, dissolved ferrous iron, ferrous iron on the goethite surface, as well as fresh ferrous sulfide in the solution, it was considered that the surface ferrous irons which could be produced following sulfide adsorption, played a leading role for Cr(VI) reduction as primary electron donors. In addition, no proof of the preliminary dissolution of ferrous iron from goethite to aqueous phase was observed in the experiments. Elemental sulfur was detected as the final stabilized product of sulfide and it took in charge for the promoted Cr(VI) disappearance for the successive addition of Cr(VI) at later stage.
Chromate (Cr VI) reduction by sulfide was conducted in anaerobic batch experimental systems. The ... more Chromate (Cr VI) reduction by sulfide was conducted in anaerobic batch experimental systems. The molar ratio of the reduced Cr VI to the oxidized S-II was 1:1.5 during the reaction, suggesting that the product of sulfide oxidation was elemental sulfur. Under the anaerobic condition, the reaction was pseudo first order initially with respect to Cr VI , but the rate was dramatically accelerated at the later stage of the reaction. The rate acceleration was due to catalysis by elemental sulfur nanoparticles; dissolved species such as monomeric elemental sulfur and polysulfides appeared to be ineffective catalysts. Elemental sulfur nanoparticles were capable of adsorbing sulfide and such adsorbed sulfide exhibited much higher reactivity toward Cr VI reduction than the aqueous-phase sulfide, resulting in the observed rate acceleration. Kinetic data under various reactant concentrations can be represented by the following empirical kinetic equation:-d[Cr VI ]/dt) k 1 [Cr VI ][H 2 S] 0.63 + k 3 [Cr VI ][tSsSH] 0.57. The first term on the right-hand side corresponds to the noncatalytic pathway, with k 1) 1.0 × 10-3 (µM)-0.63 min-1 at pH 7.60 and 8.2 × 10-5 (µM)-0.63 min-1 at pH 8.10. The second term, k 3 [Cr VI ][tSsSH] b , is the catalytic term with [tSsSH] representing the adsorbed concentration of sulfide on the elemental sulfur nanoparticles (µM). The catalytic term is more important at the later stage of the reaction, as indicated by the observed kinetics and the enhancement of the reaction rate by externally added elemental sulfur nanoparticles. At pH 8.10, k 3) 0.0057 (µM)-0.57 min-1 .
In Situ Gaseous Reduction (ISGR) using hydrogen sulfide (H 2 S) is a technology developed for soi... more In Situ Gaseous Reduction (ISGR) using hydrogen sulfide (H 2 S) is a technology developed for soil remediation by reductive immobilization of contaminants such as hexavalent chromium (Cr(VI)). Deploying the technology requires us to obtain a much-improved understanding of the interactions among the contaminants, H 2 S, and various soil components. In this study, Cr(VI) reduction by gaseous H 2 S was examined under various relative humidities (0-96.7%), concentrations of Cr(VI) (127-475 µg/g of solid), and H 2 S (0-800 ppm v) and by using Cr(VI) compounds with different solubilities. Glass beads with various average diameters (GA) 0.600 mm; GB) 0.212-0.300 mm; and GC) 0.106 mm) and silica (SA) 0.075-0.150 mm) were used as matrices to support K 2 CrO 4 , CaCrO 4 , PbCrO 4 , or BaCrO 4 , and reduction of these compounds by gaseous H 2 S was monitored by Cr(VI) analysis following extractions with distilled water or hot alkali solution. The results showed that Cr(VI) reduction relied on both the relative humidity of the gaseous stream and the size of particles onto which Cr(VI) was deposited. The relative humidity required for fast Cr(VI) reduction was 85% for GA, 61% for GB, 6% for SA, and 0% for GC. It was believed that a water film formed on the particle surfaces under appropriate humidity conditions, resulting in Cr(VI) compound dissolution and subsequent reduction. For nonsoluble Cr(VI) compounds including PbCrO 4 and BaCrO 4 , no reduction by H 2 S was observed, even at high relative humidity (96.7%), due to lack of dissolution. This study indicated that ISGR treatment in soils requires appropriate moisture content in the subsurface or maintaining a suitable humidity in the treatment gas stream to maximize chromium immobilization.
Hg(II) sorption by polyaniline is impacted by both water chemistry and the polymer's physicochemi... more Hg(II) sorption by polyaniline is impacted by both water chemistry and the polymer's physicochemical properties.
Granular activated carbon-based, iron-containing adsorbents (As-GAC) were developed for effective... more Granular activated carbon-based, iron-containing adsorbents (As-GAC) were developed for effective removal of arsenic from drinking water. Granular activated carbon (GAC) was used primarily as a supporting medium for ferric iron that was impregnated by ferrous chloride (FeCl 2) treatment, followed by chemical oxidation. Sodium hypochlorite (NaClO) was the most effective oxidant, and carbons produced from steam activation of lignite were most suitable for iron impregnation and arsenic removal. Two As-GAC materials prepared by FeCl 2 treatment (0.025-0.40 M) of Dacro 20 × 50 and Dacro 20 × 40LI resulted in a maximum impregnated iron of 7.89% for Dacro 20 × 50 and 7.65% for Dacro 20 × 40LI. Nitrogen adsorptiondesorption analyses showed the BET specific surface area, total pore volume, porosity, and average mesoporous diameter all decreased with iron impregnation, indicating that some micropores were blocked. SEM studies with associated EDS indicated that the distribution of iron in the adsorbents was mainly on the edge of As-GAC in the low iron content (∼1% Fe) sample but extended to the center at the higher iron content (∼6% Fe). When the iron content was > ∼7%, an iron ring formed at the edge of the GAC particles. No difference in X-ray diffraction patterns was observed between untreated GAC and the one with 4.12% iron, suggesting that the impregnated iron was predominantly in amorphous form. As-GAC could remove arsenic most efficiently when the iron content was approximately 6%; further increases of iron decreased arsenic adsorption. The removal of arsenate occurred in a wide range of pH as examined from 4.4 to 11, but efficiency was decreased when pH was higher than 9.0. The presence of phosphate and silicate could significantly decrease arsenate removal at pH > 8.5, while the effects of sulfate, chloride, and fluoride were minimal. Column studies showed that both As(V) and As(III) could be removed to below 10 µg/L within 6000 empty bed volume when the groundwater containing approximately 50 µg/L of arsenic was treated.
Aqueous U(VI) reduction by hydrogen sulfide was investigated by batch experiments and speciation ... more Aqueous U(VI) reduction by hydrogen sulfide was investigated by batch experiments and speciation modeling; product analysis by transmission electron microscopy (TEM) was also performed. The molar ratio of U(VI) reduced to sulfide consumed, and the TEM result suggested that the reaction stoichiometry could be best represented by UO2(2+) + HS- = UO2+ S* + H+. At pH 6.89 and total carbonate concentration ([CO32-]T) of 4.0 mM, the reaction took place according to the following kinetics: -d[U(VI)]/dt = 0.0103[U(VI)][S2-]T0.54 where [U(VI)] is the concentration of hexavalent uranium, and [S2-]T is the total concentration of sulfide. The kinetics of U(VI) reduction was found to be largely controlled by [CO32-]T (examined from 0.0 to 30.0 mM) and pH (examined from 6.37 to 9.06). The reduction was almost completely inhibited with the following [CO32-]T and pH combinations: [(> or = 15.0 mM, pH 6.89); (> or = 4.0 mM, pH 8.01); and (> or = 2.0 mM, pH 9.06)]. By comparing the experimental results with the calculated speciation of U(VI), it was found that there was a strong correlation between the measured initial reaction rates and the calculated total concentrations of uranium-hydroxyl species; we, therefore, concluded that uranium-hydroxyl species were the ones being reduced by sulfide, not the dominant U-carbonate species present in many carbonate-containing systems.
Arsenic (As) accumulation in rice grains is a threat to human health and marketability of rice pr... more Arsenic (As) accumulation in rice grains is a threat to human health and marketability of rice products. In an effort to minimize As uptake by rice grains, field experiments were conducted to investigate As accumulation in rice grains of three cultivars in monosodium methanearsonate-treated soil under saturated and flooded water management practices. Results indicated that As concentrations in rice grains were cultivar-dependent and influenced by water management. Soil flooding would substantially enhance the As accumulation with a great variation among cultivars. Extractable As in the soil was positively correlated with sodium dithionite-sodium citrate-sodium bicarbonate solution-extractable Fe, suggesting a strong association of As with ferric (hydr)oxide. Additional laboratory studies showed a strong affinity of synthetic ferric (hydr)oxide with monosodium methanearsonate. This study demonstrated that selection of less As-responsive rice cultivars and use of saturated water management in paddy fields could be an effective means to minimize As accumulation in rice grains.
Water samples from 56 lakes of Missouri, USA, were analysed for their fluorescence excitation/emi... more Water samples from 56 lakes of Missouri, USA, were analysed for their fluorescence excitation/emission matrix (EEM) spectroscopy and the formation potentials of total trihalomethanes (TTHM) and N-nitrosodimethylamine (NDMA). Comparing the excitation/emission matrix fingerprints with trihalomethanes formation revealed that water with higher fluorescence intensity generally exhibited higher trihalomethanes formation potential. Moreover, waters with fluorescence centre at excitation: 290-310 nm/emission: 330-350 nm were related to high N-nitrosodimethylamine and trihalomethanes formation potentials. The results suggest that excitation/emission matrix fingerprints could be used as surrogate parameters for monitoring trihalomethanes and N-nitrosodimethylamine formation potentials.
This study is to develop a carbon-based adsorbent containing multiple functional ligands for effe... more This study is to develop a carbon-based adsorbent containing multiple functional ligands for effective removal of lead ions from aqueous media. Activated carbon was oxidized by nitric acid, followed by chlorination with thionyl chloride and reaction with ethylenediamine. Modified activated carbon (MAC) was characterized using scanning electron microscopy in conjunction of energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), and potentiometric titration. Surface characterizations confirmed that carboxyl, amine, and chlorine functional groups were effectively introduced onto the carbon surface by the treatments. The modifications lowered the pH at the point of zero charge (pH pzc) from 9.6 to 2.55 and resulted in more negatively charged surfaces. Adsorptive experiments showed that aqueous Pb removal by MAC was faster, with a 62% higher capacity than the original activated carbon (60.2 vs. 37.2 mg g-1).
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