Adsorption of phenanthrene on organoclays from distilled and saline water

Adsorption and mineralization of metalaxyl-m and chlorpyrifos in irrigated Mediterranean soil under the effects of salinity

To evaluate the effects of salinity on the fate of pesticides in a Mediterranean irrigated system, experiments were carried out under laboratory conditions to determine the adsorption, desorption, and mineralization of chlorpyrifos (CPF) and metalaxyl-M (MET) in a soil sample from an irrigated field in northern Tunisia. Adsorption/desorption isotherms and mineralization kinetics data were obtained over a realistic range of salinities via batch equilibrium and incubation techniques. On the basis of the experimental results, MET has a lower sorption capacity than CPF does, and the adsorption data for both compounds were better fitted by the Freundlich equation, with Kf values of 0.477, 0.486, 0.426, 0.444 and 0.474 L kg-1 for MET and 38.994, 39.084, 40.644, 44.055 and 45.185 L kg-1 for CPF at salinities of 0, 1, 2, 5 and 10 g L-1, respectively. According to the mineralization experiments, increasing salinity increased the half-lives of both pesticides. For MET, the DT50 values in unsterilized soil were 206.68, 220.74, 222.16, and 238.73 days, and those in sterilized soil were 2772.58, 4077.33, 6301.33, and 8664.33 days at salinities of 0, 1, 2, 5, and 10 g L⁻1, respectively. For CPF, the DT50 values were 115.52, 138.62, 157.53, and 177.73 days in unsterilized soil and 346.57, 533.19, 693.14, and 990.21 days in sterilized soil. In terms of leaching behavior, the calculated groundwater ubiquity score (GUS) values for the MET and CPF indicate that the MET is classified as a leacher and that the CPF is classified as a nonleacher.

Adsorption of sulfamethoxazole and ethofumesate in biochar- and organoclay-amended soil: Changes with adsorbent aging in the laboratory and in the field

Biochars and organoclays have been proposed as efficient adsorbents to reduce the mobility of agrochemicals in soils. However, following their application to soils, these adsorbents undergo changes in their physicochemical properties over time due to their interaction with soil components. In this study, the adsorption capacity of a commercial biochar and a commercial organoclay for the antibiotic sulfamethoxazole (SFMX) and the pesticide ethofumesate (ETFM) was evaluated over aging periods of 3 months in the laboratory and 1 year in the field, subsequent to their application to a Mediterranean soil. The results showed that the adsorption of SFMX and ETFM in the soil amended with the adsorbents was greater than in the unamended soil, but for both chemicals, adsorption decreased with aging of the adsorbents in the soil. Characterization of the adsorbents before and after aging revealed physical blocking of adsorption sites by soil components. The loss of adsorption capacity of the adsorbents upon aging led to higher leaching of SFMX and ETFM in the soil containing field-aged adsorbents, although leaching remained lower than in unamended soil. Our findings reveal that, under the Mediterranean environment studied, the efficacy of the studied materials as adsorbents is maintained to a considerable extent for at least one year after their field application, which would have positive implications in their use for attenuating the dispersion of agricultural contaminants in the environment.

Biochar/Delonix regia seed gum/chitosan composite as efficient adsorbent for the elimination of phenol from aqueous medium

In this study, biochar (BC) from Delonix regia pods peel and gum from Delonix regia seed (SG) were prepared, and also biochar/chitosan composite (BCS) and biochar/Delonix regia seed gum/chitosan composite (BCGS) were fabricated for the efficient adsorption of phenol. Various characterization tools such as SEM, TEM, ATR-FTIR, TGA, zeta potential, and textural investigation were studied to examine the features of the synthetized adsorbents, confirming their positive construction. It was fully studied how necessary factors, comprising pH, dose of adsorbent, contact shaking time, initial phenol concentration, and temperature influenced adsorption behavior. An obvious rise of the adsorption capacity from 60.16 to 165.20 mg/g was achieved by the modification of biochar with Delonix regia seed gum and chitosan under ideal circumstances of 2 h contact duration, pH 7, 15 °C, and a dose of 2.0 g/L. The phenol adsorption was well applied by Langmuir, Temkin, Dubinin-Radushkevich, and Sips isotherms, in addition to nonlinear pseudo-second-order kinetic model. Furthermore, the physisorption, endothermic, and spontaneous process was illustrated by thermodynamic investigation. Additionally, the fabricated adsorbents could be effectively used and regenerated without main losses of only 7.5, 4.6, and 4.0 % for BC, BCS, and BCGS, respectively in the removal percentage after seven cycles of application.

Single and Competitive Adsorption of Naphthalene, Phenanthrene, and Pyrene on Polystyrene Nanofibers

In this investigation, polystyrene (PS) nanofibers were prepared by electrospinning for the adsorption of naphthalene (Nap), phenanthrene (Phe), and pyrene (Pyr) from an aqueous solution. Surface morphology and physicochemical characteristics of PS nanofibers were analyzed using Fourier transform infrared spectroscopy (FT-IR) and point-of-zero-charge calorimetry (pHpzc). The effects of pH, ion concentration, and temperature on the adsorption were also investigated. The adsorption mechanism of target pollutants on PS nanofibers was investigated by a batch adsorption method. The adsorption kinetic studies showed that the adsorption of the three polycyclic aromatic hydrocarbons (PAHs) on PS nanofibers conformed to the pseudo-second-order kinetic model in both single and ternary systems. Meanwhile, in a single system, the three PAHs adsorbed on nanofibers were controlled by both intraparticle diffusion and liquid film diffusion, whereas the adsorption of Nap in a ternary system was controlled mainly by intraparticle diffusion, and the adsorption of Phe and Pyr was controlled mainly by liquid film diffusion. The isotherm data indicated that the Freundlich model performed better than the Langmuir model for the adsorptions of Nap, Phe, and Pyr on PS nanofibers in both the single system and the ternary system. Due to competitive adsorption, the adsorption capacities of Nap and Pyr on PS nanofibers decreased from 105.816 and 19.098 mg g-1 in the single system to 23.626 and 12.126 mg g-1 in the ternary system, but the adsorption of Phe was not affected. π-π interactions and pore filling may be jointly involved in the adsorption of PAHs on PS nanofibers.

Polyvinyl alcohol-montmorillonite composites for water purification: Analysis of clay mineral cation exchange and composite particle synthesis

Municipal and residential water purification rely heavily on activated carbon (AC), but regeneration of AC is costly and cannot be performed at the point-of-use. Clay minerals (CMs) comprise a class of naturally abundant materials with known capacities for analyte adsorbance. However, the gel-forming properties of CMs in aqueous suspension pose problems for these materials being used in water-purification. In this study, we have taken three main steps to optimize the use of CMs in these applications. First, we produced several variants of montmorillonite CMs to evaluate the effect of interstitial cation hydrophobicity on the ability of the CM to uptake chargecarrying organic pollutants. These variants include CMs with the following cations: sodium, hexyl(triphenyl) phosphonium, hexyadecyl(triphenyl)phosphonium, and hexyl(tributyl)phosphonium. Second, we synthesized polymer-clay mineral composite films composed of polyvinyl alcohol (PVA), crosslinked in the presence of a CM variant. These films were evaluated for their ability to uptake malachite green (MG). Finally, we developed a one-pot synthetic method for the generation of polymer-clay particles for use in a continuous column process. We synthesized polymer-clay mineral particles using the highest performing CM (based on the film experiments) and evaluated the equilibrium capacity and kinetics of MG uptake from solution.

Elucidation of electrocoagulation mechanism in the removal of Blue SI dye from aqueous solution using Al-Al, Cu-Cu electrodes - A comparative study

This work presents the research on the treatment of an anthraquinone derivatives of disperse dye Blue SI from aqueous solution using aluminium for the optimization of operational parameters like pH, current density, addition of electrolyte, contact time for the color removal efficiency (CRE) and the results are compared with the performance of copper electrodes in electrocoagulation (EC). The parameters for maximum CRE was found with Al at current density 40 Am^-2, time 10 min at pH 7, and for Cu at 60 Am^-2 15 min, at pH 6 were optimized. The characterization of the treated water using HPLC, MS studies revealed intermediate compounds. From the XPS analysis of the sludge obtained, the mechanism of EC was deduced. Treated aqueous solution was studied for its phytotoxicity with Vigna radiata and ecotoxicity studies were conducted on Artemia salina to study the toxicity effect of the intermediatory products in the treated dye solution. Blue SI dye aqueous solution treated with aluminium electrodes shows no or lesser toxicity in plants as well as in ecotoxic study compared with copper electrodes.

Characterization of the fate and changes of post-irradiance fluorescence signal of filtered anthropogenic effluent dissolved organic matter from wastewater treatment plant in the coastal zone of Gapeau river

Anthropogenic effluent dissolved organic matter (DOM) plays an important role in coastal zone pollution. The objectives of the present study were to characterize the fluorescence signal of anthropogenic effluent DOM from wastewater treatment plant and to evaluate the effect of solar irradiation on the fluorescence signal in the coastal zone. Solar irradiation experiments were conducted to evaluate the effect photochemical degradation using excitation-emission matrix (EEM) method combined with parallel factor analysis (PARAFAC). Results showed high fluorescence of DOM before irradiation and the intensity tends to decrease after 4th and 15th day of irradiation. Rapid photochemical degradation of humic-like fluorophores and appearance of a post-irradiance dominant anthropogenic effluent DOM fluorophores were also observed after irradiation. Our experiments showed a sharp reduction in fluorescence intensity which occurred after 4th day of solar irradiation and the fluorescence signal did not disappeared after 15th day indicating the formation of a specific signal due to solar irradiation. PARAFAC model divided the bulk EEM spectra into three individual fluorescent components with C1 "terrestrial humic-like" and C2 "humic-like of longer wavelength" and C3 is a noisy component with two emission maxima. Multilinear regression of PARAFAC components contribution with mixing composition was most suitable according to the equation C*i = A^WW_i,0 + A^WW_i,1.f_SW + A^WW_i,2.f_RW, where C*_i is the normalized contribution of PARAFAC component number i in a given irradiation day; A^WW_i,0, A^WW_i,1, A^WW_i,2 are the multilinear regression coefficients and contain implicitly the effect of f_WW; and WW, SW, and RW are treated wastewater, sea water, and river water respectively. The values of A^WW_i,0, A^WW_i,1, and A^WW_i,2 fitted second-order kinetics with irradiation process with kinetic constant of 9.68, - 987.35, and - 977.67 respectively for C1 equation and the same trend for C2 and no values for C3 due to its noisy character indicating the rapid degradation with increase of f_SW and f_RW and the predominance of the residual fluorescence coming from f_WW which is the content fraction of anthropogenic effluent DOM because A^WW_i,0 was 100 times less sensitive to photobleaching. A suitable model for predicting the fluorescence EEMs as a function of mixing composition was developed.

Salinity profile in coastal non-agricultural land in Gaza

The objectives of this study were to characterize the electric conductivity (EC), total dissolved salts (TDS), highly soluble salts (HSS), less soluble salts (LSS), cations (Na⁺, K⁺, Ca⁺⁺ and Mg⁺⁺) and anions (Cl^-, NO^-₃, SO^--₄, PO^---₄) profiles in non-agricultural coastal land in Gaza Strip and to evaluate the effect of trees in salinity. Six locations were selected randomly in coastal zone in Gaza Strip and used for soil profile digging. Soil samples were collected from different layers between 0 and 150 cm depth, air dried and kept in plastic bags at lab temperature. Ten grams of soil were mixed with 25 mL distilled water and kept under shaking for 24 h, then EC, pH and TDS were determined. Then additional 25 ml distilled water was added to each bottle and kept for additional 24 h of shaking. EC and TDS were determined again. Then the soil filtrates were collected by centrifugation and used to determine cations and anions. Results showed that concentrations of TDS, HSS and LSS were higher at the top soil layer than at deeper soil layers. Concentrations of cations and anions have similar trends to TDS, HSS and LSS. Behavior of cations and anions in the soil profiles under trees were different from those in open field. Comparing between the data of soil profiles under trees (site 2 and 5) and those in the open field (sites 1, 3, 4 and 6) showed slight effects on availability of cations and anions. Strong correlations were found between cations and anions in soil profiles under trees, and week correlations were found in soil profile in open field. In conclusion the coastal soil profiles are characterized with elevated levels of TDS, HSS and LSS in the top soil layers. Accumulations of salts were more pronounced in top soil layers. These properties suggest high potential damage to the ecosystem.

Impact of salinity on colloidal ozone aphrons in removing phenanthrene from sediments

Polycyclic aromatic hydrocarbons (PAHs) tend to adsorb and accumulate on sediments owing to their hydrophobicity and persistence. Salinity is the predominant factor determining the PAH partition between aqueous and solid phases in freshwater, estuaries and seawater. This study focuses on the impact of salinity on the phenanthrene (PHE) removal from sediments using an in situ and targeted remediation technology - colloidal ozone aphrons (COAs). The ozone-encapsulated colloidal aphrons exhibited increasing air holdup but decreasing stability with the salinity increasing from 0.5‰ to 35‰. The hydrophobic attraction between Tween-20-coated bubbles and the hydrophobic solid surface weakened at high salinities. The presence of inorganic ions in the aqueous phase could lead to the salting-out of nonionic compounds (PHE, Tween-20 and even ozone), hindering detaching and degrading PHE from the solid phase. Anyhow, COAs achieved high efficiencies of washing (88.0-90.2%) and oxidative degradation (74.0-76.5%) particularly for the hydrophobic sediments with highly concentrated PHE (200.4 μg/kg) over the investigated salinities. The flushing effect imposed by the bubble flow played an important role, which was not greatly influenced by salinity. Although the dissolved natural organic matter competed with PHE for COAs and led to low PHE removal, the efficiency was improved by successive COA addition.

Tuning down the environmental interests of organoclays for emerging pollutants: Pharmaceuticals in presence of electrolytes

The impact of electrolytes on the adsorption of emerging pollutants: pharmaceuticals onto layered materials: a raw clay mineral and its nonionic and cationic organoclay derivatives was studied. The selected pharmaceuticals: amoxicillin, norfloxacin, sulfamethoxazole, metoprolol, carbamazepine, and trimethoprim show different electric charges: zwitterionic, anionic, cationic and neutral and hydrophobic character (different LogP). Without any salts, the set of complementary data obtained by UV and infrared spectroscopies, X-ray diffraction points out the importance of the electric charge which represents a key parameter in both the spontaneity and feasibility of the adsorption. In contrast, the hydrophobicity of the analytes plays a minor role but determines the magnitude of the adsorbed amount of pharmaceuticals onto organoclays. With a dual hydrophilic and hydrophobic behavior, nonionic organoclay appears to be the most polyvalent material for the removal of the pharmaceuticals. In the presence of electrolytes (NaCl at a concentration of 1 × 10^-2 mol L^-1), both nonionic and cationic organoclays show a decrease of their efficiencies, whereas the adsorption is particularly enhanced for Na-Mt except for the cationic species (trimethoprim and metoprolol). Thus, in realistic experimental conditions close to those of natural effluents, raw clay mineral appears as the most appropriate sorbent for the studied pharmaceuticals while it raises the question of the usefulness of organoclays in water remediation strategy.

Brief bibliometric analysis of "ionic liquid" applications and its review as a substitute for common adsorbent modifier for the adsorption of organic pollutants

The importance of improving adsorbent's adsorption efficiency in organic pollutants has been reported by many researchers. Surfactant-based modified adsorbents were a tasteful choice. As a result, the use of surfactants as a modifier for removing organic pollutants has shown to play a very big role in enhancing the adsorption efficiency of different materials. Ionic liquids are receiving extensive interest as green multipurpose compounds, primarily as a replacement for traditional chemicals that are used in many chemical processes. This work gives a brief bibliometric analysis of application of ionic liquid from 1930 to 2017, documents were collected from Scopus database and keywords from the abstracts and titles were analyzed using VOSviewer software. Furthermore, the work presents a review of conventionally known surfactants and the recent likelihood of ionic liquids for modifying adsorbents for adsorption of organic pollutants. Over the period of years between 1930 and 2017, 13,144 documents were published on the application of ionic liquids. VOSviewer software further confirms that adsorption is one of the leading areas in applications of ionic liquids. Review also showed that ionic liquid is a good modifier of adsorbents.

Preparation of MgAlFe-LDHs as a deicer corrosion inhibitor to reduce corrosion of chloride ions in deicing salts

This material consists of a double hydroxide consisting of Mg, Al, Fe in a 9:2:1 M ratios, which was synthesised by hydrothermal method under constant pH conditions. The products were calcined at 500 °C for use as a deicing corrosion inhibitor, which breaks through the problem that the traditional corrosion inhibitor itself doesn't have the capability of deicing. The raw material of Al and Fe was extracted from the red mud by acid leaching. Characterization by XRD, FTIR, BET, XPS, SEM and TEM revealed that the interlaminar structure of the collapsed double-layered hydroxide material after high temperature calcination was regained by adsorbing Cl^-. Cl^- was filled between the layers of double hydroxide and existed by chemical adsorption. By measuring the freezing point of mixed deicing salt and the ability to melt snow and deicing, the freezing point of the inhibitor was found. When the solution concentration was 40 wt%, the freezing point of the mixed deicing salt reached -27.6 °C. Corrosion inhibitors can reduce the amount of CaCl₂ when used in combination with anhydrous CaCl₂. In addition, the determination of the corrosion rate of carbon steel and the resistance to salt freezing of concrete has revealed that the corrosion inhibitor can adsorb Cl^- and reduce the content of free Cl^- at low temperatures. Therefore, corrosion inhibitor plays a significant role in reducing the amount of Cl^- used, the corrosion rate of carbon steel, and the salt-freezing resistance of concrete.

Ultrasound-assisted dispersive liquid-liquid microextraction followed by ion mobility spectrometry for the simultaneous determination of bendiocarb and azinphos-ethyl in water, soil, food and beverage samples

A sensitive and fast ultrasound-assisted dispersive liquid-liquid microextraction procedure combined with ion mobility spectrometry has been developed for the simultaneous extraction and determination of bendiocarb and azinphos-ethyl. Experimental parameters affecting the analytical performance of the method were optimized: type and volume of extraction solvent (chloroform, 150 µL), pH (9.0), type and volume of buffer (ammonium buffer pH = 9.0, 4.5 mL) and extraction time (3.0 min). Under optimum conditions, the linearity was found to be in the range of 2-40 and 6-100 ng/mL and the limits of detection (LOD) were 1.04 and 1.31 ng/mL for bendiocarb and azinphos-ethyl, respectively. The method was successfully validated for the analysis of bendiocarb and azinphos-ethyl in different samples such as waters, soil, food and beverage samples.

Sorption of benzene and naphthalene on (semi)-arid coastal soil as a function of salinity and temperature

Considerable activities from the oil and natural gas sector have risen some concerns about the pollution of soil and groundwater by petroleum hydrocarbons (PHCs) in (semi)-arid coastal regions. The understanding of the fate and transport of PHCs in these regions is therefore necessary to develop strategies for remediation. To quantify the sorption rates of PHCs in (semi)-arid coastal soil environments, we conducted a series of controlled-laboratory batch experiments under variable temperature and salinity conditions. The soil samples were collected from the eastern coast of Qatar which is near the two largest off-shore oil and natural gas fields of the country (North Gas and Al-Shaheen Oil Fields), and the volatile benzene and naphthalene were used as PHCs. The characterization of soil samples showed sand classification with the texture class of sabkha and saline beach sandy soils with calcite as potential dominant mineral. The concentrations of dissolved chloride and sodium were found to be high (> 400 mg L^-1) with a chloride-to‑sodium ratio of about 1.7. The results of sorption experiments showed that the rates of naphthalene sorption were more than for benzene, where the initial aqueous concentrations of benzene and naphthalene were reduced at equilibrium due to sorption by about 14-25% and 65-79%, respectively. This difference was attributed mainly to the organic carbon-water partitioning coefficient which is higher for naphthalene. The sorption rate experiments showed that sorption was stronger for benzene under higher salinity and lower temperature conditions. The sorption of naphthalene was not affected by the change in salinity but increased by 18% when the temperature decreased from 35 to 5 °C. A sorption kinetic model was also applied to define the sorption behavior of benzene and naphthalene for the coastal soil collected in Qatar and the best fits were achieved with the Langmuir sorption isotherm.

Theoretical and experimental adsorption studies of sulfamethoxazole and ketoprofen on synthesized ionic liquids modified CNTs

The adsorption of sulfamethoxazole (SMZ) and ketoprofen (KET) using carbon nanotubes (CNTs) and CNTs modified with ionic liquids (ILs) was investigated. Two ionic liquids (1-benzyl, 3-hexyl imidazolium, IL1 and 1-benzyl, 3-decahexyl imidazolium, IL2) were synthesized, and characterized by nuclear magnetic resonance (¹H and ¹³C NMR) and high resolution-mass spectrometry (HR-MS). CNTs and modified CNTs were characterized using FT-IR, X-ray diffraction (XRD), surface area and porosity analysis, thermal gravimetric analysis (TGA), Zeta potential, Raman and scanning electron microscopy (SEM). Kinetics, isotherm and computational studies were carried out to determine the efficiency and adsorption mechanism of SMZ and KET on modified CNTs. A density functional theory (DFT) method was applied to shed more light on the interactions between the pharmaceutical compounds and the adsorbents at the molecular level. The effects of adsorbent dosage, concentration, solution pH, energetics and contact time of SMZ and KET on the adsorption process were investigated. The adsorption of SMZ and KET on CNTs and modified CNTs were pH dependent, and adsorption was best described by pseudo-second-order kinetics and the Freundlich adsorption isotherm. Ionic liquid modified CNTs showed improved adsorption capacities compared to the unmodified ones for both SMZ and KET, which is in line with the computational results showing performance order; CNT+KET/SMZ < CNT-ILs+SMZ < CNT-ILs+KET.

Examination of the influence of phenyltrimethylammonium chloride (PTMA) concentration on acetochlor adsorption by modified montmorillonite

The results presented in this paper show an impact of the concentration of the aromatic organic cation on the adsorption of acetochlor on the surface of the organic-modified montmorillonite. Natural montmorillonite from Bogovina (Boljevac municipality, Serbia) was used for organic modification in this experiment. Cation exchange capacity of this montmorillonite (86 mmol 100 g^-1 of clay) was determined using the methylene blue method. In pretreatment, montmorillonite was modified with NaCl. For the purpose of organic modification, three different concentrations of phenyltrimethylammonium chloride (PTMA) have been selected, based on calculated CEC value: 43 mmol 100 g^-1 of clay (0.5 CEC), 86 mmol 100 g^-1 of clay (1 CEC) and 129 mmol 100 g^-1 of clay (1.5 CEC). The changes in the properties of the inorganic and organic modified montmorillonite were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and batch equilibrium method. Freundlich coefficients show higher uptake of the herbicide by montmorillonite modified with PTMA, compared to inorganic-modified montmorillonite. The results also indicate the influence of the organic cation concentration on the adsorption of the selected herbicide.

Toxicity of some aquatic pollutants to fish

Pesticide residues threaten fish that live in rivers. This study investigated the effects of Nemacur, malathion, and diuron on freshwater fish behavior, mortality, acetylcholinesterase (ACHE) activity, liver biomarkers, and residue accumulation. Fish were exposed to individual concentration of Nemacur, malathion, and diuron at 1 mg/L and to binary mixtures in glass aquarium 16 L capacity. Mortality of fish was also investigated at a range of 0.0-1 mg/L of Nemacur and malathion. The biochemical effects of the tested compounds were recorded. The results showed abnormal fish behavior at low concentration (0.1 mg/L) of malathion, high fish mortality at 0.1 mg/L of Nemacur and mixtures with Nemacur, and no mortality with diuron. Mortality increased and became more intense after 48 h rather than after 24 h. Diuron increased the effect of Nemacur and malathion at low concentration. ACHE was inhibited at different percentages in the blood serum and brain homogenate due to exposure to Nemacur, malathion, diuron, and/or a combination of these pesticides. Liver biomarker levels were higher in the blood serum of the treated fish than the control group. The interesting outcome of the study is that Nemacur is several folds more toxic than malathion and diuron. Mixtures showed synergistic effects. The pesticide residues in the fish muscles were less than those in the water. It can be concluded that low concentrations of Nemacur, malathion, and diuron are negatively affecting fish in rivers.

Adsorption performance of polydopamine-modified attapulgite granular adsorbent for methylene blue

Polydopamine-modified granule organo-attapulgite adsorbent (PDA-GOAT) was facilely prepared via a dip-coating approach. The samples were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Surface area and pore size were calculated from the Brunauer-Emmett-Teller method by N₂ adsorption-desorption isotherm. The adsorption behaviour of methylene blue (MB) onto PDA-GOAT was systematically investigated. The experimental data revealed that the adsorption process fitted well with the pseudo-second-order kinetics equation and the adsorption isotherm fitted better with the Langmuir model. Thermodynamic analyses illustrated that MB adsorption onto PDA-GOAT was a physisorption endothermic process. Importantly, PDA-GOAT can be regenerated by NaBH₄ aqueous solution. The obtained results prove that PDA-GOAT can be a superior reusable adsorbent for the removal of MB from effluent.

Immobilization of phenanthrene onto gemini surfactant modified sepiolite at solid/aqueous interface: Equilibrium, thermodynamic and kinetic studies

The immobilization of phenanthrene from aqueous phase onto natural and gemini surfactant modified sepiolite was investigated with respect to contact time, pH, ionic strength and temperature. The surface modification was examined through FT-IR characterization, SEM technique, and the thermogravimetric analysis. The maximum sorption capacity of phenanthrene on modified sepiolite was 95.15μgg^-1 with initial PHE concentration 1.0mgL^-1, temperature 293K, pH7, and ionic strength 1M. The corresponding PHE removal efficiency was higher than 95%. The Langmuir, Freundlich and Temkin isotherm models were applied to describe the phenanthrene sorption behavior and the Freundlich equation agreed well with the experimental data. The evaluation of the thermodynamic parameters indicated that the immobilization of phenanthrene onto gemini surfactant modified sepiolite was a spontaneous and exothermic process from 283 to 313K. The pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models were used to evaluate the kinetic data. According to the calculated kinetic parameters, the immobilization process of phenanthrene followed the Elovich kinetic model with the highest correlation coefficients. The obtained results show that gemini surfactant modified sepiolite could be effectively utilized as one type of low-cost clay material to remove polycyclic aromatic hydrocarbons from water effluents.

Macadamia nutshells-derived activated carbon and attapulgite clay combination for synergistic removal of Cr(VI) and Cr(III)

A physical mixture of Macadamia-derived activated carbon and cationic attapulgite clay was investigated for total chromium removal in aqueous solution. The parameters influencing the adsorption of chromium on the sorbents were investigated, and it was shown that pH 3, contact time 2 hours, concentration 50 mg L−1 and calculated adsorption capacity of 96.28 mg g−1 were the optimal parameters. The process of adsorption was better described by Freundlich adsorption isotherm, and the kinetic modelling data suggested a chemisorption mechanism described by pseudo-second-order (PSO) rate model. Ionic strength studies demonstrated that the removal of anionic Cr(VI) species was mostly affected by the presence of anions like Cl− and [Formula: see text], while the removal of the cationic Cr(III) species was affected largely by cations [Formula: see text]>Na+>K+. Overall, the removal mechanism involved adsorption, reduction and ion exchange processes.

Pentynyl Ether of β-Cyclodextrin Polymer and Silica Micro-Particles: A New Hybrid Material for Adsorption of Phenanthrene from Water

A new hybrid material for the removal of polycyclic aromatic hydrocarbons (PAH) from water was prepared by the polymerization of pentynyl beta-cyclodextrin (PyβCD) and silica micro-particles (SMP). Phenanthrene, being one of the important members of the PAH family and a potential risk for environmental pollution, was selected for this study. Results show that phenanthrene removal efficiency of the SMP was improved significantly after hybridization with PyβCD-polymer. Approximately 50% of the phenanthrene was removed in the first 60 min and more than 95% was removed in less than 7 h when 25 mL of the 2 ppm aqueous phenanthrene solution was incubated with the 100 mg of SMP-PyβCD-polymer material. Infrared spectroscopy and thermal gravimetric analysis show that the enhanced efficiency of the SMP-PyβCD-polymer compared to the unmodified SMP was due to the formation of the inclusion complexation of phenanthrene with the PyβCD. These results indicate that SMP-PyβCD polymers have a potential to be applied as molecular filters in water purification systems and also for waste water treatment.

Specific adsorption of cadmium on surface-engineered biocompatible organoclay under metal-phenanthrene mixed-contamination

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) is extremely challenging when they coexist with heavy metals. This constrain has led to adsorption-based techniques that help immobilize the metals and reduce toxicity. However, the adsorbents can also non-selectively bind the organic compounds, which reduces their bioavailability. In this study we developed a surface-engineered organoclay (Arquad^® 2HT-75-bentonite-palmitic acid) which enhanced bacterial proliferation and adsorbed cadmium, but elevated phenanthrene bioavailability. Adsorption models of single and binary solutes revealed that the raw bentonite adsorbed cadmium and phenanthrene non-selectively at the same binding sites and sequestrated phenanthrene. In contrast, cadmium selectively bound to the deprotonated state of carboxyl groups in the organoclay and phenanthrene on the outer surface of the adsorbent led to a microbially congenial microenvironment with a higher phenanthrene bioavailability. This study provided valuable information which would be highly important for developing a novel clay-modulated bioremediation technology for cleaning up PAHs under mixed-contaminated situations.

Insights into asphaltene aggregation in the Na-montmorillonite interlayer

This study aimed to provide insights into the diffusion and aggregation of asphaltenes in the Na-montmorillonite (MMT) interlayer with different water saturation, salinity, interlayer space and humic substances. The molecular configuration, density profile, diffusion coefficient and aggregation intensity were determined by molecular dynamic simulation, while the 3D topography and particle size of the aggregates were characterized by atomic force microscopy. Results indicated that the diffusivity of asphaltenes was up to 5-fold higher in the MMT interlayer filled with fresh water than with saline water (salinity: 35‰). However, salinity had little impact on the asphaltene aggregation. This study also showed a marked decrease in the mobility of asphaltenes with decrease in the pore water content and the interlayer space of MMT. This was more pronounced in the organo-MMT where the humic substances were present. The co-aggregation process resulted in the sequestration of asphaltenes in the hollow cone-shaped cavity of humic substances in the MMT interlayer, which decreased the asphaltene diffusion by up to one-order of magnitude and increased the asphaltene aggregation by about 33%. These findings have important ramifications for evaluating the fate and transport of heavy fractions of the residual oil in the contaminated soils.

Polycyclic aromatic hydrocarbons (PAHs) removal by sorption: A review

Polycyclic aromatic hydrocarbons (PAHs) are organic micro pollutants which are persistent compounds in the environment due to their hydrophobic nature. Concerns over their adverse effects in human health and environment have resulted in extensive studies on various types of PAHs removal methods. Sorption is one of the widely used methods as PAHs possess a great sorptive ability into the solid media and their low aqueous solubility property. Several adsorbent media such as activated carbon, biochar, modified clay minerals have been largely used to remove PAHs from aqueous solution and to immobilise PAHs in the contaminated soils. According to the past studies, very high removal efficiency could be achieved using the adsorbents such as removal efficiency of activated carbon, biochar and modified clay mineral were 100%, 98.6% and >99%, respectively. PAHs removal efficiency or adsorption/absorption capacity largely depends on several parameters such as particle size of the adsorbent, pH, temperature, solubility, salinity including the production process of adsorbents. Although many studies have been carried out to remove PAHs using the sorption process, the findings have not been consolidated which potentially hinder to get the correct information for future study and to design the sorption method to remove PAHs. Therefore, this paper summarized the adsorbent media which have been used to remove PAHs especially from aqueous solutions including the factor affecting the sorption process reported in 142 literature published between 1934 and 2015.

Impact of Organic Contamination on Some Aquatic Organisms

Background:

Contamination of water systems with organic compounds of agricultural uses pose threats to aquatic organisms. Carbaryl, chlorpyrifos, and diuron were considered as model aquatic pollutants in this study. The main objective of this study was to characterize the toxicity of organic contamination to two different aquatic organisms.

Materials and Methods:

Low concentrations (0.0–60 µmol/L) of carbaryl, diuron and very low concentration (0.0–0.14 µmol/L) of chlorpyrifos and their mixtures were tested against fish and Daphnia magna. Percentage of death and immobilization were taken as indicators of toxicity.

Results:

Toxicity results to fish and D. magna showed that chlorpyrifos was the most toxic compound (LC₅₀ to fish and D. magna are 0.08, and 0.001 µmol/L respectively), followed by carbaryl (LC₅₀ to fish and D. magna are 43.19 and 0.031 µmol/L), while diuron was the least toxic one (LC₅₀ values for fish and D. magna are 43.48 and 32.11 µmol/L respectively). Mixture toxicity (binary and tertiary mixtures) showed antagonistic effects. Statistical analysis showed a significant difference among mixture toxicities to fish and D. magma.

Conclusion:

Fish and D. magam were sensitive to low concentrations. These data suggest potent threats to aquatic organisms from organic contamination.

Impact of salinity and dispersed oil on adsorption of dissolved aromatic hydrocarbons by activated carbon and organoclay

Adsorption capacity of phenol and naphthalene by powdered activated carbon (PAC), a commercial organoclay (OC) and a lab synthesized organoclay (BTMA) was studied using batch adsorption experiments under variable feed water quality conditions including single- and multi- solute conditions, fresh water, saline water and oily-and-saline water. Increasing salinity levels was found to reduce adsorption capacity of OC, likely due to destabilization, aggregation and subsequent removal of organoclay from the water column, but did not negatively impact adsorption capacity of PAC or BTMA. Increased dispersed oil concentrations were found to reduce the surface area of all adsorbents. This decreased the adsorption capacity of PAC for both phenol and naphthalene, and reduced BTMA adsorption of phenol, but did not negatively affect naphthalene removals by either organoclay. The presence of naphthalene as a co-solute significantly reduced phenol adsorption by PAC, but had no impact on organoclay adsorption. These results indicated that adsorption by PAC occurred via a surface adsorption mechanism, while organoclay adsorption occurred by hydrophobic or pi electron interactions. In general, PAC was more sensitive to changes in water quality than either of the organoclays evaluated in this study. However, PAC exhibited a higher adsorption capacity for phenol and naphthalene compared to both organoclays even in adverse water quality conditions.

Phytotoxicity of Alachlor, Bromacil and Diuron as single or mixed herbicides applied to wheat, melon, and molokhia

This study investigated the phytotoxicity of herbicides applied singly or as mixtures to different crops under greenhouse conditions. Growth inhibition of the crops was taken as an indicator of phytotoxicity. Phytotoxicity of mixtures was estimated by calculating EC₅₀ value in toxic units. EC₅₀ (mg/kg soil) of Alachlor, Bromacil and/or Diuron were: 11.37, 4.77, 1.64, respectively, on melon; 0.11, 0.08, 0.24, respectively, on molokhia, and 3.91, 3.08, 1.83, respectively, on wheat. EC₅₀ values of binary mixture tests of (Alachlor + Bromacil), (Alachlor + Diuron), and (Bromacil + Diuron) were 12.21, 5.84, 10.22 on melon, 0.982, 925.4, 38.1 on molokhia, and 0.673, 1.34, 0.644 on wheat. Tertiary mixture tests showed EC₅₀ values (TU/kg soil) of (Alachlor + Bromacil + Diuron) was 633.9 on melon, 3.02 on molokhia and 32.174 on wheat. Diuron was more toxic than Alachlor and Bromacil to the tested crops based on individual tests. Molokhia was the most sensitive crop to herbicides. Binary mixtures showed a synergistic effect as compared to the tertiary mixtures.

Removal of 8-quinolinecarboxylic acid pesticide from aqueous solution by adsorption on activated montmorillonites

Sodium montmorillonite (Na-M), acidic montmorillonite (H-M), and organo-acidic montmorillonite (Org-H-M) were applied to remove the herbicide 8-quinolinecarboxylic acid (8-QCA). The montmorillonites containing adsorbed 8-QCA were investigated by transmission electron microscopy, FT-IR spectroscopy, X-ray diffraction analysis, X-ray fluorescence thermogravimetric analysis, and physical adsorption of gases. Experiments showed that the amount of adsorbed 8-QCA increased at lower pH, reaching a maximum at pH 2. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. The Langmuir model provided the best correlation of experimental data for adsorption equilibria. The adsorption of 8-QCA decreased in the order Org-H-M > H-M > Na-M. Isotherms were also used to obtain the thermodynamic parameters. The negative values of ΔG indicated the spontaneous nature of the adsorption process.

Visible light photodegradation of phenanthrene catalyzed by Fe(III)-smectite: role of soil organic matter

In the present study, phenanthrene is employed as a model to explore the roles played by three soil organic matter (SOM) fractions, i.e., dissolved organic matter (DOM), humic acid (HA), and fulvic acid (FA), in its photodegradation with assistance of Fe(III)-smectite under visible-light. Slight decrease in phenanthrene photodegradation rate was observed in the presence of DOM, which is explained in terms of oxidative-radical competition between DOM and target phenanthrene molecules due to the high electron-donor capacity of phenolic moieties in DOM. On the other hand, a critic content is observed with FA (0.70mg/g) and HA (0.65mg/g). Before reaching the critic content, the removal of phenanthrene is accelerated; while after that, the photodegradation rate is suppressed. The acceleration of phenanthrene degradation can be attributed to the photosensitization of FA and HA. Due to the strong interaction between phenanthrene and the phenyl rings, however, the retention of phenanthrene on SOM-Fe(III)-smectite in the presence of high content of HA or FA is enhanced, thus slowing down its photodegradation. Those observations provide valuable insights into the transformation and fate of PAHs in the natural soil environment and open a window for using clay-humic substances complexes for remediation of contaminated soil.

In Vitro Evaluations of Cytotoxicity of Eight Antidiabetic Medicinal Plants and Their Effect on GLUT4 Translocation

Despite the enormous achievements in conventional medicine, herbal-based medicines are still a common practice for the treatment of diabetes. Trigonella foenum-graecum, Atriplex halimus, Olea europaea, Urtica dioica, Allium sativum, Allium cepa, Nigella sativa, and Cinnamomum cassia are strongly recommended in the Greco-Arab and Islamic medicine for the treatment and prevention of diabetes. Cytotoxicity (MTT and LDH assays) of the plant extracts was assessed using cells from the liver hepatocellular carcinoma cell line (HepG2) and cells from the rat L6 muscle cell line. The effects of the plant extracts (50% ethanol in water) on glucose transporter-4 (GLUT4) translocation to the plasma membrane was tested in an ELISA test on L6-GLUT4myc cells. Results obtained indicate that Cinnamomon cassia is cytotoxic at concentrations higher than 100  μ g/mL, whereas all other tested extracts exhibited cytotoxic effects at concentrations higher than 500  μ g/mL. Exposing L6-GLUT4myc muscle cell to extracts from Trigonella foenum-graecum, Urtica dioica, Atriplex halimus, and Cinnamomum verum led to a significant gain in GLUT4 on their plasma membranes at noncytotoxic concentrations as measured with MTT assay and the LDH leakage assay. These findings indicate that the observed anti-diabetic properties of these plants are mediated, at least partially, through regulating GLUT4 translocation.

Stepwise adsorption of phenanthrene at the fly ash-water interface as affected by solution chemistry: experimental and modeling studies

Fly ash (FA) is predominantly generated from coal-fired power plants. Contamination during disposal of FA can cause significant environmental problems. Knowledge about the interaction of FA and hydrophobic organic pollutants in the environment is very limited. This study investigated the adsorption of phenanthrene at the interface of FA and water. The performance of phenanthrene adsorption on FA and the effects of various aqueous chemistry conditions were evaluated. The adsorption isotherms exhibited an increasing trend in the adsorbed amounts of phenanthrene, while a stepwise pattern was apparent. A stepwise multisite Langmuir model was developed to simulate the stepwise adsorption process. The adsorption of phenanthrene onto FA was noted to be spontaneous at all temperatures. The thermodynamic results indicated that the adsorption was an exothermic process. The adsorption capacity gradually decreased as pH increased from 4 to 8; however, this trend became less significant when pH was changed from 8 to 10. The binding affinity of phenanthrene to FA increased after the addition of humic acid (HA). The pH variation was also responsible for the changes of phenanthrene adsorption on FA in the presence of HA. High ionic strength corresponded to low mobility of phenanthrene in the FA-water system. Results of this study can help reveal the migration patterns of organic contaminants in the FA-water system and facilitate environmental risk assessment at FA disposal sites.

Unexpected difference in phenol sorption on PTMA- and BTMA-bentonite

The comparison of phenol sorption on phenyltrimethylammonium (PTMA)- and benzyltrimethylammonium (BTMA)-bentonite shows a clear difference as far as phenol sorption isotherms are concerned. For PTMA-bentonite the sorption isotherm is of a straight-line character which results from simple partitioning of phenol between the aqueous and organic phases sorbed on the bentonite surface. For BTMA-bentonite the isotherm has a convex shape, characteristic of physicochemical sorption. For the first time a three-parametric model, including the dissociation constant of phenol pK(a), distribution constant of phenol Kd(phen) and phenolate anion Kd(phen)(-) between the aqueous phase and the bentonite phases is used for the evaluation of phenol sorption on organoclays with pH change. The model shows that the values of Kd(phen) are higher than those of Kd(phen)(-) for all investigated initial phenol concentrations. The inspection of the FTIR spectrum of BTMA-bentonite loaded with phenol in the regions 1300-1600 and 1620-1680 cm(-1) shows the features of pi-pi electron interaction between the benzene rings of phenol and the BTMA cation together with the phenol-water hydrogen bond strengthened by this interaction.