Solution pHs Research Articles

Effect of oxide coatings, pH and competing anion on the sorption of arsenic species onto Light Expanded Clay Aggregates (LECA’s)

Abstract Arsenic (As) is a highly toxic metalloid that it causes globally serious groundwater problems. In aquatic environment it exists as arsenate (AsV) or arsenite (AsIII) which decisively differ in their p K a values and chemical behaviour. Sorption is one of the most efficient technologies applied to remove As from water. However, its efficiency depends on the chemical composition of the sorbent. In this study we compared the ability of Light Expanded Clay Aggregates (LECAs) and LECA coated with aluminium oxide (Al-LECA) or iron oxide (Fe-LECA) to remove As species from water. To unravel the optimal pH conditions for removal, sorption envelopes for AsV were prepared at pH 2–9 and those for AsIII at pH 5–11. Furthermore, effect of phosphate competing with AsV for sorption sites on LECA sorbents was studied at pH 6. The peak sorption of AsV onto LECA, Al-LECA and Fe-LECA was obtained at pH 2, 4 and 6, respectively. As for AsIII, the corresponding peak sorptions were recorded at pH 10, 9 and 10, respectively. The actual sorption capacity relevant in practice was determined on the basis of the As concentration 10 μ g L-1 ( X 10 ) in the equilibrium solution, which corresponds to the upper limit of As in water. The X 10 values estimated at varying solution pHs were decisively lower than the sorption maximum ( X m ). The oxide-coated LECAs were decisively more efficient in As removal than LECA. Furthermore, phosphate decreased the sorption of AsV onto Al-LECA more than that onto Fe-LECA. Although LECA had a lower As sorption capacity than the oxide-coated LECAs, the sorption onto it was less affected by phosphate than that onto the other sorbents. Arsenic is a highly toxic metalloid that it causes globally serious groundwater problems. Sorbent containing Al or Fe oxides as LECA can be used as sorbent for arsenic ions. Coating LECA with Al or Fe oxides decisively increased the removal efficiency.

Solvation Structure of Surface-Supported Amine Fragments: A Molecular Dynamics Study

Amine-grafted silica gel is an efficient heterogeneous catalyst for the Knoevenagel condensation and draws much attention in green chemistry for applications like heavy metal adsorption and CO2 fixation. Despite its successful usage in diverse areas, fundamental questions remain on how the silica substrate affects the local chemical environment of the tethered amines. In this work, we use all-atom molecular dynamics simulation to investigate the solvation structures of two primary amines tethered onto a silica surface at different pHs of aqueous solutions. The atomic density profiles in the solvation shell are analyzed with a spherical harmonics expansion method for both isolated and silica-supported amines in different aqueous environments. The simulation results provide direct evidence for the strong influence of the silica surface on the hydration structure that is often ignored in the theoretical analysis of surface reactions. The surface effect becomes less prominent on the tethered amine as the alky...

Sorption, kinetics and thermodynamics of phosphate sorption onto soybean stover derived biochar

Abstract Phosphorus (P) is one of the main sources of eutrophication of water bodies creating ecological problems. Biochar prepared from agricultural waste materials can be used as a potential adsorbent for removing P from waste streams. In the present investigation biochar produced from soybean stover pyrolysed at 700 °C was tested for aqueous P removal in a batch type reactor at different temperatures and solution pHs. The sorption process was evaluated through various isotherms, kinetics models and thermodynamic parameters. It was observed that with an equilibrium time of 24 h, up to 95% of P was removed from water at a temperature of 40 °C at pH 5.5. The sorption experimental data were studied through both Langmuir and Freundlich models and the Langmuir adsorption maximum (Q m ) values were 90.90 and 75.75 mg/g at pH 5.5 and 8.5, respectively while the Freundlich equilibrium constant (K f ) values were 4.67 and 4.36 mg/g at pH 5.5 and 8.5, respectively. The rate of adsorption confirmed to follow pseudo-second order kinetics with a better correlation. The thermodynamic parameters predicted that the adsorption process is an endothermic and spontaneous process.

Graphene-Supported Spinel CuFe₂O₄ Composites: Novel Adsorbents for Arsenic Removal in Aqueous Media.

A graphene nanoplate-supported spinel CuFe2O4 composite (GNPs/CuFe2O4) was successfully synthesized by using a facile thermal decomposition route. Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Electron Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) were employed to characterize the prepared composite. The arsenic adsorption behavior of the GNPs/CuFe2O4 composite was investigated by carrying out batch experiments. Both the Langmuir and Freundlich models were employed to describe the adsorption isotherm, where the sorption kinetics of arsenic adsorption by the composite were found to be pseudo-second order. The selectivity of the adsorbent toward arsenic over common metal ions in water was also demonstrated. Furthermore, the reusability and regeneration of the adsorbent were investigated by an assembled column filter test. The GNPs/CuFe2O4 composite exhibited significant, fast adsorption of arsenic over a wide range of solution pHs with exceptional durability, selectivity, and recyclability, which could make this composite a very promising candidate for effective removal of arsenic from aqueous solution. The highly sensitive adsorption of the material toward arsenic could be potentially employed for arsenic sensing.

Heteroatoms doped metal iron–polyvinylidene fluoride (PVDF) membrane for enhancing oxidation of organic contaminants

Iron nanoparticles (NPs) embedded in S, N-codoped carbon were prepared by one-step pyrolysis of a homogeneous mixture consisting of Fe, S, N, C precursors, and then immobilized in poly (vinylidene fluoride) membranes as a multifunctional catalytic system (NSC-Fe@PVDF) to effectively activate peroxymonosulfate (PMS) and oxidize organic compounds in water. The NSC-Fe@PVDF membranes effectively decolorized organic pollutants at a wide pH range (2.05-10.85), due to the synergistic effects between the S, N-doped carbon and iron NPs. The efficiency depended on the doping types, amount of metal, PMS dosages, reaction temperatures, solution pHs, and organic substrates. In-situ electron spin resonance spectroscopy and sacrificial-reagent incorporated catalysis indicate radical intermediates such as sulfate and hydroxyl radicals are mainly responsible for this persulfate-driven oxidation of organic compounds. Membrane’s porous structure and high internal surface area not only minimize the NPs agglomeration, but also allow the facile transport of catalytic reactants to the active surface of metal catalysts. The results demonstrate the morphological and structural features of catalytic membranes enhance the overall catalytic activity.

Development of multifunctional self-cleaning and UV blocking cotton fabric with modification of photoactive ZnO coating via microwave method

Abstract A new self-cleaning cotton fabric coated with zinc oxide (ZnO) was obtained via a facile and effective microwave method. The solution pH was a key factor in determining the morphology of ZnO crystal growth on the cotton fibers: rod structures were apt to be formed at pH 4–5, whereas flake and flower-like structures were preferentially formed at higher solution pHs of 6–7 and 10–11, respectively. It is proved that the photocatalytic and wettability performances of ZnO could be efficiently transferred to cotton fabric, leading to a preeminent UV-blocking and self-cleaning cotton fabric. The identified UV protection factors (UPFs) indicate the excellent UV-blocking properties of the ZnO-coated textile fabric synthesized at pH 6–7, 8–9 and 10–11 with UPFs of 222.52, 162.68 and 202.57, respectively. The ZnO coating layer on the cotton fabric significantly improved the wetting behavior of the fabric, such as water absorption speed, thereby affording a self-cleaning ability for the ZnO-coated cotton fabrics. This ability was checked according to the removal degree of coffee stain under UV irradiation at different humidities (30–90% RH). The coffee stains on the ZnO-coated cotton fabrics were almost removed after 15 h without needing any water or detergent and the highest removal effect was observed at 90% humidity.

Fabrication of a GNP/Fe-Mg Binary Oxide Composite for Effective Removal of Arsenic from Aqueous Solution.

Graphene nanoplates (GNPs) can be used as a platform for homogeneous distribution of adsorbent nanoparticles to improve electron exchange and ion transport for heavy-metal adsorption. In this study, we report a facile thermal decomposition route to fabricate a graphene-supported Fe–Mg oxide composite. The prepared composite was characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. Batch experiments were carried out to evaluate the arsenic adsorption behavior of the GNP/Fe–Mg oxide composite. Both the Langmuir and Freundlich models were employed to describe the adsorption isotherm, in which the sorption kinetics of the arsenic adsorption process by the composite was found to be pseudo-second-order. Furthermore, the reusability and regeneration of the adsorbent were investigated by an assembled-column filter test. The GNP/Fe–Mg oxide composite exhibited significant fast adsorption of arsenic over a wide range of solution pHs, with exceptional durability and recyclability, which could make this composite a very promising candidate for effective removal of arsenic from aqueous solutions.

Low-cost magnetic herbal biochar: characterization and application for antibiotic removal.

Magnetic biochar (M-BC) was derived from herbal medicine waste, Astragalus membranaceus residue, and was used as an adsorbent for ciprofloxacin removal from aqueous solutions. The M-BC was characterized by Brunauer-Emmett-Teller surface area analyses, Fourier transform infrared spectrometry, X-ray diffraction analysis, hysteresis loops, scanning electron microscopy energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. The BET surface area increased from 4.40 to 203.70m2/g after pyrolysis/magnetic modification. Batch experiments were performed at different dosages, initial concentrations, contact times, and solution pHs. Adsorption performances were evaluated using Langmuir and Freundlich isotherm models, and the results indicated that the Langmuir model appropriately described the adsorption process. The kinetic data were better fitted by a pseudo-second-order kinetic model. The maximum ciprofloxacin removal was observed at pH 6 (adsorption capacity of 68.9±3.23mg/g). Studies demonstrated that magnetically modified biochar might be an attractive, cost-effective, and easily separated adsorbent for contaminated water. Graphical abstract.

Rheological characterization of yield stress gels formed via electrostatic heteroaggregation of metal oxide nanoparticles.

Mixtures of fumed fractal metal oxide nanoparticles (np's) dispersed in water, at a solution pH where one species is positively charged and the other is negatively charged, form yield stress gels at volume fractions as low as 1.5%, due to electrostatic heteroaggregation into networks as confirmed by small-angle neutron scattering. These gels exhibit a measurable yield stress and an apparent viscosity that follows a power law relationship with shear rate. Rotational and oscillatory shear rheology is presented for binary mixtures of fumed silica, fumed alumina, and fumed titania in aqueous dispersions. Gels were characterized at various particle concentrations, solution pHs, mixture ratios, and salt concentrations. The strength of the gel network, as evaluated by the storage modulus and yield stress, is maximized when the mixture contains a mixture of particles with an approximately equal, but opposite, number of charged groups.

Ru-coated metal monolith catalyst prepared by novel coating method for hydrogen production via natural gas steam reforming

Ru-coated FeCrAlloy monolith catalysts were prepared by a deposition-precipitation (DP) method with different solution pHs and evaluated the catalytic activity in natural gas steam reforming (NGSR) reaction for H2 production. The characteristics of prepared monolith catalysts as to the crystallite size, surface area, pore size distribution, metal dispersion, and morphology of Ru particles were analyzed by XRD, BET, BJH, CO-chemisorption, and SEM, respectively. The solution pH had a major effect on the precipitation formation and the particle size and dispersion of Ru catalyst coated on the monolith surface. At pH 7, nano-sized Ru particles with high BET surface area (112m2/g) and metal dispersion (23.5%) were formed uniformly on the monolith surface. Among the prepared monolith catalysts, the monolith catalyst prepared at pH 7 showed the highest CH4 conversion in NGSR. Despite the less amount of Ru metal coated on the metal monolith, the monolith catalyst showed a good catalytic performance equivalent to the 2wt% Ru/Al2O3 pellet catalyst due to the high availability of the Ru active metal in NGSR. It was also confirmed that the Ru catalyst layer coated on the FeCrAlloy monolith had good adhesion via ultrasonic vibration test.

Modulating oxone-MnOx/silica catalytic systems towards ibuprofen degradation: Insights into system effects, reaction kinetics and mechanisms

Heterogeneous processes activated persulfate for organic degradation is increasingly recognized as an environmentally important remediation technology. However, manipulating persulfate oxidation processes with desirable decontamination effectiveness is still underdeveloped. Towards this goal, we systematically investigated the catalytic behaviors of Oxone-MnOx/silica systems towards aqueous ibuprofen (IBU) degradation in terms of system effects, reaction kinetics and mechanisms. MnOx/SBA-15 (MS) demonstrated variable catalytic Oxone efficacies towards IBU removal at different solution pHs. Meanwhile, the catalyst supports and FeOx co-doping within MS also produced significant impacts on catalytic Oxone efficacy. Moreover, the catalytic Oxone efficacies of MS for IBU degradation were generally inhibited by humic acid, NO3−, HCO3−, SO42− and PO43− to different extents at low/high levels. Interestingly, Cl− at low concentrations (2mM) obviously inhibited IBU removal by Oxone-MS, while Cl− at high concentrations (20mM) greatly enhanced IBU removal. Kinetic studies implied that IBU removal by Oxone-MnOx/silica systems using two first-order kinetic models was closely related to the extents of the interferences of synthetic conditions and water chemistry components. The surface electron transfer between MnOx(OH)y species of MS and HSO5− of Oxone was responsible for the formation of reactive oxygen radicals, thus contributing to IBU degradation. Liquid chromatography–mass spectrometry was employed to identify oxidation products of IBU, and reaction pathways of IBU oxidation were accordingly proposed.

Determination of association constants of monovalent ions to sphingomyelin and phosphatidylinositol liposomal membranes by microelectrophoresis

ABSTRACTIn this paper, we examined the effect of adsorbed monovalent ions on the surface charge of liposomal membranes formed from neutral (sphingomyelin), anionic (phosphatidylinositol) lipids mixed in various ratios. The surface charge density of the membrane was determined from electrophoretic mobility measurements at various pHs of solution. A four-quilibria model describing adsorption of ions on the sphingomyelin (SM) membrane and a two-equilibria model describing adsorption of ions on the phosphatidylinositol (PI) membrane was presented. We proposed a mathematical model for characterizing these equilibria. Using these models, together with experimental data of the membrane surface charge density, we determined association constants characterizing the equilibria. The correctness of the proposed model was proven by comparing the theoretical charge variation curves for SM and PI membranes with the experimental date.

Persulfate-assisted photodegradation of diethylstilbestrol using monoclinic BiVO4 under visible-light irradiation.

In this study, the photosynergistic performance of BiVO4 with persulfate (PS) is demonstrated under visible light irradiation for the first time. Diethylstilbestrol (DES) was selected as a reluctant compound, and factors including dosages of PS and catalyst, solution pHs, initial concertration of DES, and inorganic anions were evaluated. The morphology and chemical state of bismuth vanadate (BiVO4) was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy (DRS). It was found that the degradation of DES was promoted in either acid or alkaline solutions. The increase of PS and BiVO4 dosages was beneficial to the reactions, while incremental concentration of DES showed the inhibiting effect. By scavenging hVB+, Cl- was able to make the promotion, differentiated from the exsiting HCO- 3. Moreover, the photocatalytic mechanism for the BiVO4/PS/vis-light system was proposed by using several probe compounds (isopropanol, tert-butanol, and 1,4-benzoquinone), which consists of h+ VB/e- CB generation and recombination on the surface of BiVO4 as well as free radical oxidation in the solutions. The study provides a distinctive method to treat organic contaminants using visible light in the aqueous environment.

Enhanced recovery of water due to ammonia nitrogen contamination caused by mining processes

During in situ mining processes, high concentrations of ammonium sulfate solution are directly injected into the mountain to replace the rare earth. However, the residual ammonia nitrogen (AN) in the vadose zone from this injected solution is a serious pollutant of groundwater and soil. Unfortunately, in situ leaching methods using clean water are not effective at removing the AN. In this work, we developed a novel leaching method and examined its efficiency, as well as studied the mechanisms behind the adsorption and desorption of AN. It was found that the majority of the ammonium adsorbed in the soil was in soluble and exchangeable forms. The saturated adsorption capacity under mining conditions was 810 mg kg−1, where only 36 % of the adsorbed AN was able to be leached out by water. However, the amount of AN leached out increased to 85 % when a KCl solution was used as the leaching agent at an optimized concentration of 2.8 mM. Furthermore, this improved leaching agent worked well at a wide range of solution pHs. Therefore, this method is an efficient means by which to remediate AN contamination after mining processes of RE ores.

산성수 침수 및 하중 조건에서의 암석물성변화 연구

본 연구에서는 산성수 및 하중의 화학 역학적 영향이 암석 물성에 미치는 영향을 파악하기 위한 실내 실험을 실시하였다. 실험에서는 암석시료에 pH 및 하중조건을 부여한 후, 유효 공극률을 포함한 다양한 암석 물성 변화를 측정하였다. 실험결과, 일정한 하중조건에서 암석을 침수시킨 산성수의 pH가 낮을수록 물성 변화가 증가하는 것으로 나타났다. 이는 산성수의 pH가 낮을수록 암석과 산성수 사이의 화학반응 속도가 증가했기 때문으로 예측된다. 또한 일정한 pH의 산성수에 침수된 암석에서 가해진 하중이 증가함에 따라 암석물성 변화가 감소하는 것으로 나타났다. 이는 균열개시응력 이하의 하중에서 발생된 압축으로 암석과 산성수 사이의 화학반응 영역이 감소했기 때문으로 여겨진다. This paper presents experimental results to investigate the affects of acidic solution under loading condition on rock properties. In the experiment, the variations of various rock properties including effective porosity, thermal conductivity, and etc were investigated with different pHs of solution and magnitudes of loading. The results show that the rock property change was increased with low pH under loading. It was predicted that chemical reaction rate would be increased in low pH. Below the crack initiation stress of the rock specimen, the variation of rock property change was reduced with increased loading. It could be explained with the reduced chemical reaction area by the compressional loading if there is no crack generation.

Room temperature aqueous self-assembly of poly(ethylene glycol)-poly(4-vinyl pyridine) block copolymers: From spherical to worm-like micelles

The solution self-assembly and the formation, at room temperature, of a wide range of nanostructures based on monomethyl ether poly(ethylene glycol)-b-poly(4-vinyl pyridine) (mPEG-b-P4VP) block copolymer is reported. Copolymers with different compositions and molecular weights were synthesized through Atom Transfer Radical Polymerization (ATRP) method. The solution self-assembly of the block copolymers was studied by transmission electron microscopy (TEM) for different solution pHs. It was found that the formation of non-spherical nanostructures, such as rod- and worm-like micelles can be easily achieved, at room temperature, by simply varying the molecular weight of the different segments as well as the mPEG to P4VP ratio in the block copolymer structure. Because P4VP segments are known to form strong complexes with metals, the nanostructures prepared in this manuscript can find innovative applications in the biomedical field and be used as nano-templates for inorganic materials.

Efficient sonochemical degradation of perfluorooctanoic acid using periodate

A rapid and efficient treatment method, using periodate (PI) for sonochemical oxidation of persistent and bioaccumulative perfluorooctanoic acid (PFOA) was developed. With an addition of 45mM PI, 96.5% of PFOA was decomposed with a defluorination efficiency of 95.7% after 120min of ultrasound (US). The removals of PFOA were augmented with an increase in PI doses. In all the PI+US experimental runs, decomposition efficiencies were essentially similar to those of defluorination, indicating that PFOA was decomposed and mineralized into fluoride ions. Lower solution pHs resulted in an increase in decomposition and defluorination efficiencies of PFOA due to acid-catalyzation. Dissolved oxygen increased the amount of IO4 radicals produced, which consumed the more effective IO3 radicals. Consequently, presence of oxygen inhibited the destruction of PFOA. The PFOA degradation rates with different gases sparging are in the following order: nitrogen>air>oxygen. Effects of anions follow the Hofmeister effects on PFOA degradation (i.e., Br−>none⩾Cl−>SO42−). Br− could react with OH to yield radical anion Br2− that enhances the PFOA degradation. A reaction pathway was also proposed to describe the PI oxidation of PFOA under US irradiation.

Synthesis of three-dimensional carbon felt supported TiO2 monoliths for photocatalytic degradation of methyl orange

Three-dimensional carbon felt supported TiO2 (TiO2@CF) monoliths were synthesized via a solvothermal process. The structural properties of TiO2@CF were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption–desorption, Raman and contact angle tests. The as-prepared TiO2@CF monoliths exhibited a large surface area, hydrophilic surface as well as a well-defined three dimensional structure. Using methyl orange as a model pollutant, the photocatalytic activity of TiO2@CF monolith was studied. The effects of substrate concentrations, pHs of pollutant solutions and H2O2 concentrations in the degradation of methyl orange were examined. It was revealed that a low pollutant concentration, adequate H2O2 concentration and acidic environment facilitated the degradation of methyl orange. To explore the mechanism, controlled experiments were conducted by adding three scavengers including isopropanol, p-benzoquinone and ethylenediaminetetraacetic acid disodium salt. Mechanistic studies suggested that in the presence of H2O2, hydroxyl radicals played a dominant role in the degradation of methyl orange while the photo-induced holes were mainly responsible in the absence of H2O2. The TiO2@CF monolith catalysts could be easily regenerated via combustion and showed excellent recyclability.

Neodymium(III) and lanthanum(III) separation by magnetic nanohydrometallurgy using DTPA functionalized magnetite nanoparticles

A successful nanohydrometallurgical separation of neodymium and lanthanum ions has been demonstrated by using superparamagnetic nanoparticles functionalized with ethylenediaminepropylsilane/diethylenetriaminepentaacetic acid, as complexing agents. Neodymium is preferentially captured in relation to lanthanum, reflecting the trends of the stability constants dictated by the lanthanide contraction. A high separation efficiency (>99%) has been achieved after three successive complexation and releasing stages. The overall process can be performed under green and sustainable conditions, e.g., at room temperature, in aqueous solution and mild pHs, allowing the nanoparticles recycling, and dispensing the use of more time/energy consuming physical separation processes.

On the gas-phase reforming of glycerol by Pt on carbon black: Effects of metal particle size and pH value of the glycerol stream

We investigate the effect of the platinum particle size and the pH of the feed solution in the glycerol gas-phase reforming reaction at low-temperature (623K) over carbon black-supported Pt catalyst with different platinum loadings (1, 3, 5, and 10wt.%). We also verify the influence of the aqueous glycerol (30wt.%) feeding solution pH in the reaction at low-temperature (WHSV=33min−1 and P=1bar) over the 5wt.% Pt/C catalyst. Glycerol gas-phase reforming demonstrates being a structure-sensitive reaction and it has its activity and selectivity changed with the size of the platinum particle size. The size increasing leads to an increasing of the CO and Glycerol TOF and selectivity towards gaseous products, formed by consecutive CC cleavages. Despite no remarkable change is observed in the selectivity under the reaction condition with different pHs of the glycerol aqueous solution, there is an activity decrease.