Hydrophile-lipophile balance solid phase extraction of surface water organics: Fluorescent elution preference and overlooked fractions.

Fluorescent dissolved organic matter (FDOM) in surface water has broad implications on water quality research and operations. Solid phase extraction (SPE) is the most widely used technique to extract FDOM. However, fluorescent elution preferences by common solvents and content of quantifiable chromophores in waste fraction remain largely unknown, both quantitatively and qualitatively. In this work, the preferential selection of various types of FDOM captured by and lost from SPE as characterized by the fluorescence excitation-emission matrix (EEM) were investigated. Three elution solvents (methanol, acetone, and dichloromethane) were adopted to elute the DOM that was enriched on a typical SPE sorbent. Results revealed that high polarity (methanol) and medium polarity (acetone) solvents eluted the highest variety and quantity of humic acid-like substances (Region V), while the low polarity (dichloromethane) elution solvent was more suitable for eluting tyrosine (Region I) and tryptophan (Region II). Compared to eluting only with methanol, sequential elution and recombination using the three aforementioned solvents demonstrated a significant increase in not only DOC recovery (by 7%), but fluorescence integral values and fluorescence characteristics covering collectively much larger fluorescence regions that more closely resembled raw water. For the first time, the fluorescence EEM of waste after loading the sample revealed a previously overlooked FDOM loss of 20%, caused by ineffective adsorption onto the solid phase resin. Substantial carbonaceous and nitrogenous FDOM were present in this fraction (the fluorescence intensity of aromatic protein in waste exceeds 20% of that in raw water), indicating possible underestimations of FDOM-related research in areas such as disinfection byproduct and toxicity work. The results of this study provide both a qualitative and quantitative characterization of the elution and lost products of SPE in capturing FDOM.

As(III) removal by a recyclable granular adsorbent through dopping Fe-Mn binary oxides into graphene oxide chitosan.

Graphene oxide chitosan composite (GOCS) is recognized as an environmentally friendly composite adsorbent because of its stability and abundant functional groups to adsorb heavy metals, and Fe-Mn binary oxides (FMBO) have attracted increasing interest due to their high removal capacity of As(III). However, GOCS is often inefficient for heavy metal adsorption and FMBO suffers poor regeneration for As(III) removal. In this study, we have proposed a method of dopping FMBO into GOCS to obtain a recyclable granular adsorbent (Fe/MnGOCS) for achieving As(III) removal from aqueous solutions. Characterization of BET, SEM-EDS, XRD, FTIR, and XPS are carried out to confirm the formation of Fe/MnGOCS and As(III) removal mechanism. Batch experiments are conducted to investigate the effects of operational factors (pH, dosage, coexisting ions, etc.), as well as kinetic, isothermal, and thermodynamic processes. Results show that the removal efficiency (Re) of As(III) by Fe/MnGOCS is about 96 %, which is much higher than those of FeGOCS (66 %), MnGOCS (42 %), and GOCS (8 %), and it increases slightly with the increasing molar ratio of Mn and Fe. This is because amorphous Fe (hydro)oxides (mainly in the form of ferrihydrite) complexation with As(III) is the major mechanism to remove As(III) from aqueous solutions, and it is accompanied by As(III) oxidation mediated by Mn oxides and the complexation of As(III) with oxygen-containing functional groups of GOCS. Charge interaction plays a weaker role in As(III) adsorption, therefore Re is persistently high over a wide range of pH values of 3-10. But the coexisting PO43- can greatly decrease Re by 24.11 %. As(III) adsorption on Fe/MnGOCS is endothermic and its kinetic process is controlled by pseudo-second-order with a determination coefficient of 0.95. Fitted by the Langmuir isotherm, the maximum adsorption capacity is 108.89 mg/g at 25 °C. After four times regeneration, there is only a slight decrease of <10 % for the Re value. Column adsorption experiments show that Fe/MnGOCS can effectively reduce As(III) concentration from 10 mg/L to <10 µg/L. This study provides new insights into binary polymer composite modified by binary metal oxides to efficiently remove heavy metals from aquatic environments.

MiR-302c-5p affects the stemness and cisplatin resistance of nasopharyngeal carcinoma cells by regulating HSP90AA1.

Nasopharyngeal carcinoma (NPC) is one of the most frequent malignant tumors diagnosed in China. Cisplatin is one of the most commonly used anticancer drugs containing platinum in combined chemotherapy. The molecular mechanism of NPC is still largely unknown, and we aim to spare no effort to elucidate it. Normal human nasopharyngeal epithelial cells and NPC cell lines were cultured. The expression levels of miR-302c-5p and HSP90AA1 were detected with quantitative real-time PCR. Western blotting was used to analyze levels of the HSP90AA1, protein kinase B (AKT), p-AKT, CD44 and SOX2 proteins. The interaction between miR-302c-5p and HSP90AA1 was detected using a luciferase reporter assay. The bicinchoninic acid assay was used to observe cisplatin resistance in NPC cells. Our records confirmed that the expression of miR-302c-5p was substantially reduced and HSP90AA1 was increased in NPC cells. Additionally, miR-302c-5p inhibited cisplatin resistance and the traits of stem cells in NPC. A luciferase assay confirmed that miR-302c-5p is bound to HSP90AA1. Overexpression of HSP90AA1 may reverse the effects of overexpressed miR-302c-5p and inhibit cisplatin resistance and stem cell traits of NPC. This study investigated whether miR-302c-5p inhibited the AKT pathway by regulating HSP90AA1 expression and altered the resistance of NPC cells to cisplatin and the traits of tumor stem cells, which has not yet been reported.

Iron modified chitosan/coconut shell activated carbon composite beads for Cr(VI) removal from aqueous solution.

Iron modified chitosan/coconut shell activated carbon (Fe/CSCC) composite bead is synthesized to remove Cr(VI) and is characterized to reveal the influencing factors and reaction mechanism. Results show that the adsorption capacity (Qe) of Cr(VI) increases with the increase of iron loading, contact time (t), Cr(VI) initial concentration (C0), and temperature (T), but decreases with the increase of pH, and mass and volume ratio (m/v). After 0.1 mol FeCl3 modification, the removal efficiency of Cr(VI) by Fe/CSCC reaches as high as 97.25 % at pH = 3, m/v = 1.0 g/L, t = 2880 min, C0 = 25 mg/L, and T = 25 °C. The coexisting ions of SO42-, HPO4-, and Ca2+ lead to the decrease of Qe by 7.82, 5.05, and 5.50 mg/g, respectively, and the inhibition effect increases with their increasing concentrations. Fe/CSCC adsorption for Cr(VI) is an endothermic spontaneous process, and a chemical and monolayer adsorption, which is better fitted to a pseudo-second-order kinetic. The fitted maximum Qe is 64.49 mg/g by using the Langmuir model. Moreover, after five cycles of regeneration, the Qe value only drops about 3.46 mg/g. Characterization analysis of BET, XRD, FTIR, XPS, and SEM-EDS indicates that Cr(VI) is mainly adsorbed by Fe/CSCC through electrostatic attraction and complexation, which is related to the -COOH and - NH2 groups, and Fe - O groups, respectively.

On As(III) Adsorption Characteristics of Innovative Magnetite Graphene Oxide Chitosan Microsphere.

A magnetite graphene oxide chitosan (MGOCS) composite microsphere was specifically prepared to efficiently adsorb As(III) from aqueous solutions. The characterization analysis of BET, XRD, VSM, TG, FTIR, XPS, and SEM-EDS was used to identify the characteristics and adsorption mechanism. Batch experiments were carried out to determine the effects of the operational parameters and to evaluate the adsorption kinetic and equilibrium isotherm. The results show that the MGOCS composite microsphere with a particle size of about 1.5 mm can be prepared by a straightforward method of dropping FeCl2, graphene oxide (GO), and chitosan (CS) mixtures into NaOH solutions and then drying the mixed solutions at 45 °C. The produced MGOCS had a strong thermal stability with a mass loss of <30% below 620 °C. The specific surface area and saturation magnetization of the produced MGOCS was 66.85 m2/g and 24.35 emu/g, respectively. The As(III) adsorption capacity (Qe) and removal efficiency (Re) was only 0.25 mg/g and 5.81% for GOCS, respectively. After 0.08 mol of Fe3O4 modification, more than 53% of As(III) was efficiently removed by the formed MGOCS from aqueous solutions over a wide pH range of 5−10, and this was almost unaffected by temperature. The coexisting ion of PO43− decreased Qe from 3.81 mg/g to 1.32 mg/g, but Mn2+ increased Qe from 3.50 mg/g to 4.19 mg/g. The As(III) adsorption fitted the best to the pseudo-second-order kinetic model, and the maximum Qe was 20.72 mg/g as fitted by the Sips model. After four times regeneration, the Re value of As(III) slightly decreased from 76.2% to 73.8%, and no secondary pollution of Fe happened. Chemisorption is the major mechanism for As(III) adsorption, and As(III) was adsorbed on the surface and interior of the MGOCS, while the adsorbed As(III) was partially oxidized to As(V) accompanied by the reduction of Fe(III) to Fe(II). The produced As(V) was further adsorbed through ligand exchange (by forming Fe−O−As complexes) and electrostatic attraction, enhancing the As(III) removal. As an easily prepared and environmental-friendly composite, MGOCS not only greatly adsorbs As(III) but also effectively removes Cr(VI) and As(V) (Re > 60%) and other metals, showing a great advantage in the treatment of heavy metal-contaminated water.

Removal of Cr(VI) from Wastewater Using Graphene Oxide Chitosan Microspheres Modified with α-FeO(OH).

Graphene oxide and chitosan microspheres modified with α−FeO(OH) (α−FeO(OH)/GOCS) are prepared and utilized to investigate the performance and mechanism for Cr(VI) removal from aqueous solutions and the possibility of Fe secondary pollution. Batch experiments were carried out to identify the effects of pH, mass, and volume ratio (m/v), coexisting ions, time (t), temperature (T), and Cr(VI) initial concentration (C0) on Cr(VI) removal, and to evaluate adsorption kinetics, equilibrium isotherm, and thermodynamics, as well as the possibility of Fe secondary pollution. The results showed that Cr(VI) adsorption increased with C0, t, and T but decreased with increasing pH and m/v. Coexisting ions inhibited Cr(VI) adsorption, and this inhibition increased with increasing concentration. The influence degrees of anions and cations on the Cr(VI) adsorption in descending order were SO42− > PO42− > NO3− > Cl− and Ca2+ > Mg2+ > Mn2+, respectively. The equilibrium adsorption capacity of Cr(VI) was the highest at 24.16 mg/g, and the removal rate was 97.69% under pH = 3, m/v = 1.0 g/L, T = 298.15 K, and C0 = 25 mg/L. Cr(VI) adsorption was well fitted to a pseudo-second-order kinetic model and was spontaneous and endothermic. The best fit of Cr(VI) adsorption with the Langmuir and Sips models indicated that it was a monolayer and heterogeneous adsorption. The fitted maximum adsorption capacity was 63.19 mg/g using the Sips model under 308.15 K. Cr(VI) removal mainly included electrostatic attraction between Cr(VI) oxyanions with surface Fe−OH2+, and the adsorbed Cr(VI) was partially reduced to Cr(III) and then precipitated on the surface. In addition, there was no Fe secondary pollution during Cr(VI) adsorption.

Iron oxides decorated graphene oxide/chitosan composite beads for enhanced Cr(VI) removal from aqueous solution.

This study is the first to evaluate the effects of Iron oxides (FeOx) species and their decoration on graphene oxide/chitosan (GO/CS) composites for Cr(VI) removal and the possibility of Fe secondary pollution. Results show that Fe(III) is a better decoration material than Fe(II) and decoration through immersion-evaporation shows a higher adsorption capacity of Cr(VI) (Qe) than co-precipitation. Fe2O3-GO/CS as the only eco-friendly composite for enhanced Cr(VI) removal is further used for batch adsorption experiments, characterization, kinetics, isotherms, and thermodynamic studies. It is found that Cr(VI) removal mainly includes electrostatic attraction between Cr(VI) oxyanions and surface -NH3+ and -OH2+, and the adsorbed Cr(VI) partially reduces to Cr(III). Qe increases with the increasing initial Cr(VI) concentration, contact time, and temperature, while decreases with the increasing pH and mass and volume ratio (m/v). The coexisting ions (Cl-, NO3-, SO42-, PO43-, As, Fe, and Pb) can cause an obvious decrease of Qe. The removal efficiency (Re) and Qe are 94.3% and 83.8 mg/g, respectively under the optimal conditions. After five times of regeneration, Re is still as high as 84% and Qe drops about 2.6%. Cr(VI) adsorption is spontaneous and endothermic, which is best fitted with the Sips model, and the fitted maximum Qe is 131.33 mg/g.

[Adsorption of As(â ¢) in Water by Iron-loaded Graphene Oxide-Chitosan].

Based on the principle of self-assembly, graphene oxide, chitosan, and FeCl3·6H2O were mixed to prepare graphene oxide-chitosan coated iron-composite particles (Fe@ GOCS). Batch static experiments were carried out to investigate the kinetic and thermodynamic characteristics of As(Ⅲ) adsorption, and to identify the adsorption mechanism. Results showed that the iron on the GOCS was mainly in the form of α-FeO(OH). The As(Ⅲ) adsorption capacity increased with decreasing pH, and the highest adsorption capacity occurred at pH 3. After approximately 45 h, As(Ⅲ) adsorption reached equilibrium under the conditions of pH 3 and a temperature of 298.15, 308.15, and 318.15 K. The maximum adsorption capacity was 289.4 mg·g-1 for an optimal dosage of adsorbents of 1.0 g·L-1. After five times of repeated adsorption-desorption, the adsorption capacity increased slightly. The thermodynamic parameters showed that ΔGθ<0, ΔSθ > 0, and ΔHθ>0, thus indicating that As(Ⅲ) adsorption on Fe@GOCS was a spontaneous, endothermic, and entropy-increasing reaction, and that a higher temperature was more favorable for As(Ⅲ) adsorption. The pseudo-second-order model provided a good fit of the As(Ⅲ) adsorption kinetics for Fe@GOCS. Compared to the Langmuir isotherm, As(Ⅲ) adsorption experimental data fitted better to the Freundlich and Sips models. In combination with the characterization results, it was found that ion exchange and surface complexation were the main mechanisms of As(Ⅲ) removal from aqueous solution using Fe@GOCS.

[Characteristics and Influencing Factors of Monothioarsenate Adsorption on Goethite].

The adsorption kinetic of monothioarsenate (MTA) on goethite was characterized in this study, and batch experiments were then designed to further explore the effects of arsenate, arsenite, humic acid (HA), nitrate, and phosphate on the adsorption of MTA on goethite, and to identify the adsorption mechanism. The results showed that:① When a single arsenic species was present in a solution, the adsorption equilibrium times of MTA, arsenate, and arsenite on goethite were 8, 2, and 4 h, respectively. The adsorption experimental data of these three arsenic species were well fitted to a pseudo-second-order kinetic model. The equilibrium adsorption capacities (qe) of MTA, arsenate, and arsenite on goethite were 2129.851, 3291.838, and 1788.767 mg·kg-1, respectively. When MTA coexisted with arsenate or arsenite in a solution, MTA adsorption on goethite continued to be well fitted to a pseudo-second-order kinetic model. The value of qe for MTA was significantly reduced to 1236.941 mg·kg-1 when MTA coexisted with arsenate, and to 1532.287 mg·kg-1 when MTA coexisted with arsenite, due to the fact that arsenate and arsenite competed for adsorption sites with MTA. ② With an increase in HA concentration (10-50 mg·L-1), the qe of MTA decreased gradually, due to the fact that a large number of functional groups in HA preempted the surface adsorption sites of goethite with MTA. ③ When phosphate was added into the MTA solution, the qe values of MTA, arsenate, and arsenite on goethite were reduced greatly, to 492.802, 815.782, and 303.714 mg·kg-1, respectively, which was caused by the competitive adsorption of P and As. When nitrate was added into the MTA solution, the number of electron receptors and Eh of the solution increased, leading to the qe values of MTA, arsenate, and arsenite on goethite increasing to 2211.030, 3444.023, and 1835.537 mg·kg-1, respectively.

Highly efficient removal of As(III) from aqueous solutions using goethite/graphene oxide/chitosan nanocomposite.

A goethite/graphene oxide/chitosan (α-FeO(OH)/GO/CS) nanocomposite adsorbent was prepared and firstly used to remove As(III) from aqueous solution. The composite was characterized by FTIR, XPS, XRD, and EDS techniques. Batch experiments were conducted to investigate the effects of several factors (initial concentration, pH, m/v, contact time, co-existing ions, and temperature) on As(III) adsorption and to evaluate adsorption kinetic, equilibrium isotherm, and thermodynamics. Results showed that As(III) adsorption increased with the increasing initial concentration, contact time, and temperature, but decreased with the increasing m/v and co-existing ions concentrations of SO42-, PO43- and Fe3+. As(III) adsorption remained high at a wide pH range of 3-10. The adsorption was well fitted to a pseudo-second-order kinetic model and was endothermic and spontaneous. The best fit of As(III) adsorption with the Freundlich and Sips models indicated that it was monolayer adsorption, and the maximum adsorption capacity was 289.42 mg/g. As(III) removal was related to -NHCO-, CO, OH, and FeO groups, but the complexation between As(III) ions and hydroxyl iron oxide was the major contributor. After the fifth desorption, the removal efficiency was still as high as 79.6%, indicating excellent reusability. Thus, this composite had great potential for removing As(III) from aqueous solutions.