Capacitive deionization of high concentrations of hexavalent chromium using nickel-ferric-layered double hydroxide/molybdenum disulfide asymmetric electrode.

To decontaminate wastewater affected by high concentrations of aqueous hexavalent chromium (Cr(VI)) and improve the capability of layered double hydroxide (LDH) as an electrode in the capacitive deionization (CDI) process, nickel-ferric-LDH (NiFe-LDH) and NiFe-LDH/molybdenum disulfide (NiFe/MoS2) were synthesized using a hydrothermal method. Characterization results indicated that the flower-like cluster framework of MoS2 was decorated with the NiFe-LDH. Addition of MoS2 improved the conductivity, capacitance reversibility, charge efficiency, coulombic efficiency, and stability of NiFe/MoS2. The CDI performance of aqueous Cr(VI) was evaluated using NiFe/MoS2 and activated carbon as the anode and cathode, respectively. The process reached equilibrium within 240 min. The deionization capacity and removal ratio for Cr(VI) (100 mg/L, 100 mL) were 49.71 mg/g and 99.42 %, respectively, at 1.2 V and 20 mL/min. The isothermal data were accurately described using the Langmuir model, and the theoretical maximum deionization capacity of NiFe/MoS2 for Cr(VI) was 106.2 mg/g. The interaction mechanisms included electrostatic attraction, surface complexation, and reduction. These findings indicate that NiFe/MoS2 has feasible applications in practical wastewater treatment for Cr(VI) removal.

Synthesis of calcium-aluminum-layered double hydroxide and a polypyrrole decorated product for efficient removal of high concentrations of aqueous hexavalent chromium.

To efficiently remove high concentrations of hexavalent chromium (Cr(VI)), calcium-aluminum-layered double hydroxide (CaAl-LDH, denoted as CAL), and polypyrrole-modified CAL (CAL-PPy) were prepared by hydrothermal and in situ polymerization methods, respectively. The chemical structure, morphology, and elemental results indicated that the chain-like polypyrrole was decorated with hexagonal CAL. The specific surface area of CAL-PPy increased from 8.746 m2/g to 24.24 m2/g. The adsorption performances of CAL and CAL-PPy for aqueous Cr(VI) were investigated using batch equilibrium experiments. The decontamination process of aqueous Cr(VI) (100 mg/L) reached the equilibrium state within 50 min, and the kinetic data met the pseudo-second-order kinetic equation. The Langmuir model described the isothermal data properly, and the obtained theoretical adsorption capacity of CAL for Cr(VI) at 318 K was 34.06 mg/g, while that of CAL-PPy was 66.14 mg/g. The removal mechanisms involved electrostatic attraction, surface complexation, anion exchange, and reduction to low-toxicity Cr(III). Therefore, CAL and CAL-PPy have underlying applications in treating real wastewater containing Cr(VI).

A dual signal-amplified electrochemiluminescence immunosensor based on core-shell CeO2-Au@Pt nanosphere for procalcitonin detection.

A dual signal-amplified sandwich electrochemiluminescence (ECL) immunosensor was fabricated for trace detection of procalcitonin (PCT). CeO2-Au@Pt composed of sea urchin-like Au@Pt nanoparticles coated on CeO2 hollow nanospheres was immobilized on electrode surface to electrochemically catalyze H2O2 to produce a large number of superoxide anion (O2•-). The immunosensor was prepared by linking the capture antibody on immobilized CeO2-Au@Pt with heptapeptide (HWRGWVC), which could maintain the activity of the antibody. The prepared Au star@BSA was used to bind abundant luminol for labeling the secondary antibody (Ab2). Upon the sandwich-typed immunoreactions, the O2•- could react with the introduced luminol on the immunosensor surface to produce strong ECL intensity. With an outstanding linear detection range and a low detection limit of 17 fg/mL, the ECL immunosensor permitted ultrasensitive detection of PCT at a low H2O2 concentration and demonstrated its high application potential in the clinical assay.

Oxidative transformation of 1-naphthylamine in water mediated by different environmental black carbons.

Black carbons (BCs) are ubiquitous in the natural environment and can significantly influence the environmental behavior of pollutants. This work examined the mediating effects of graphite, soot, and biochar on 1-naphthylamine (1-NA) oxidation under aerobic conditions. It was shown that the three BCs significantly promoted the oxidation of 1-NA in the dark, and the mediation efficiency of graphite was much greater than that of soot or biochar. The oxidation products were the coupling oligomers (dimers and trimers) and the oxygen-containing oligomers of 1-NA (di-OH-1-NA, OH-azo naphthalene, OH-trimers and amino-naphthoquinone derivatives etc.). The phenolic OH on BCs were identified as the active sites for 1-NA oxidation, which could stimulate O2 to produce reactive oxygen species through successive single electron transfer and then cause 1-NA oxidation. Moreover, the superior catalytic performance of graphite was also related to its high electrical conductivity. The synergies between the sp2-hybridized carbon surface and the active sites (such as phenolic OH and defects) facilitated the oxidation of 1-NA on graphite. Findings in this study not only are helpful for better understanding the reactivity of environmental BCs, but also provide new insights into the risk assessment of 1-NA in the natural environment.

Phosphate adsorption performance and mechanisms by nanoporous biochar-iron oxides from aqueous solutions.

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar-iron oxides, namely biochar-magnetite (BC-M), biochar-ferrihydrite (BC-F), biochar-goethite (BC-G), and biochar-hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar-iron oxides had huge surface areas of 691-864 m2/g and average pore diameters of 3.4-4.0 nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar-iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar-iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.

Photoelectrochemical competitive immunosensor for 17ß-estradiol detection based on ZnIn2S4@NH2-MIL-125(Ti) amplified by PDA NS/Mn:ZnCdS.

A competitive-type PEC immunosensor for 17ß-estradiol (E2) detection was successfully fabricated using ZnIn2S4@NH2-MIL-125(Ti) composite as matrix. The excellent PEC behavior of ZnIn2S4@NH2-MIL-125(Ti) composite could be attributed to that the Ti4+-Ti3+ intervalence cycles in the titanium oxo-cluster of NH2-MIL-125(Ti) as well as the matching energy level between ZnIn2S4 and NH2-MIL-125(Ti) promote the migration and separation of photocarrier. Besides, polydopamine (PDA) with abundant amino- and quinone-groups was selected to further improve the PEC signals and capture antibody, which implement through the covalent bonding of PDA and BSA-E2 or carboxyl-group functionalized Mn:ZnCdS QDs in the competitive-type strategy. Concretely, the quinone functional groups in PDA film was applied to immobilize BSA-E2 through Michael reactions, and the PDA nanosphere loaded Mn:ZnCdS quantum dot (PDA NS/Mn:ZnCdS QDs) was used as antibodies' labels to amplify PEC signals. After PDA NS/Mn:ZnCdS-anti-E2 immobilized on the modified electrode, a remarkable increase of photocurrent signal was observed owing to the specific bonding of antigen and antibody. Based on the competitive binding of PDA NS/Mn:ZnCdS-anti-E2 with either free E2 or bovine serum albumin (BSA)-E2 causing the change of the photocurrent signal, the standard sample free E2 could be accuracy detect. Under optimal conditions, the competitive-type PEC immunosensor exhibited the linear range from 0.0005 ng/mL to 20 ng/mL and a limit detection of 0.3 pg/mL (S/N = 3). Meanwhile, the acceptable stability, selectivity and reproducibility of the proposed PEC immunosensing platform indicating the promising detection of small molecular environmental pollutants.

Adsorption of heavy metals by l-cysteine intercalated layered double hydroxide: Kinetic, isothermal and mechanistic studies.

To understand the interaction mechanisms between heavy metals and functional groups modified nanomaterials, the l-cysteine (Cys) intercalated MgAl-layered double hydroxide (MgAl-Cys-LDH) was designed by a facile co-precipitation method and used to remove Cu(II), Pb(II) and Cd(II) in water solutions. The XRD, FTIR, SEM, TEM, EDS and XPS characterization analyses proved the carboxyl, thio and amido groups were successfully introduced into MgAl-LDH. The possible mechanisms were analyzed by the XPS and XRD spectra and involved the precipitation of metal hydroxides or sulfides, surface complexation with abundant surface groups, and the isomorphic substitution of Mg(II). The adsorption kinetics and isotherms data of Cu(II), Pb(II) and Cd(II) on MgAl-Cys-LDH were well described by the pseudo-second-order kinetic equation and the Langmuir model. The influence factors such as initial solution pH of heavy metals, dosage of MgAl-Cys-LDH, adsorption time and various types of water were investigated, and the results suggested that MgAl-Cys-LDH had potential applications in real wastewater treatment containing heavy metals.

Metal ions-based immunosensor for simultaneous determination of estradiol and diethylstilbestrol.

Environmental estrogens (EEs) can cause various endocrine diseases. Herein, we designed an ultrasensitive electrochemical immunosensor for simultaneous detection of two typical EEs, estradiol and diethylstilbestrol. These two analytes were immobilized on graphene sheet (GS) modified glassy carbon electrode (GCE). Amino-group functionalized mesoporous Fe3O4 (Fe3O4-NH2) was loaded with Pb(2+) or Cd(2+), and then incubated with estradiol and diethylstilbestrol antibodies, respectively. Using an electrochemical analysis technique, two well-separated peaks were generated by the redox reaction of Pb(2+) or Cd(2+), making the simultaneous detection of two analytes on the electrode possible. Subsequently, square wave anodic stripping voltammetry (SWASV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behaviors of the immunosensor. Under optimized conditions, the SWASV peak currents were proportional to the concentrations of estradiol and diethylstilbestrol in the range from 0.050 pg mL(-1) to 100 ng mL(-1) and 1.0 pg mL(-1) to 100 ng mL(-1), respectively. The immunosensor exhibited highly sensitive response to estradiol with a detection limit of 0.015 pg mL(-1) and diethylstilbestrol with a detection limit of 0.38 pg mL(-1). Furthermore, the immunosensor was satisfactorily employed to detect estradiol and diethylstilbestrol simultaneously in water samples.

Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron-aluminum pillared bentonites.

Phosphorus removal is important for the control of eutrophication, and adsorption is an efficient treatment process. In this study, three modified inorganic-bentonites: hydroxy-aluminum pillared bentonite (Al-Bent), hydroxy-iron pillared bentonite (Fe-Bent), and mixed hydroxy-iron-aluminum pillared bentonite (Fe-Al-Bent), were prepared and characterized, and their phosphate adsorption capabilities were evaluated in batch experiments. The results showed a significant increase of interlayer spacing, BET surface area and total pore volume which were all beneficial to phosphate adsorption. Phosphate adsorption capacity followed the order: Al-Bent>Fe-Bent>Fe-Al-Bent. The adsorption rate of phosphate on the adsorbents fits pseudo-second-order kinetic models (R(2)=1.00, 0.99, 1.00, respectively). The Freundlich and Langmuir models both described the adsorption isotherm data well. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous in nature. Finally, phosphate adsorption on the inorganic pillared bentonites significantly raised the pH, indicating an anion/OH(-) exchange reaction.

Adsorption of cadmium onto Al(13)-pillared acid-activated montmorillonite.

The optimal preparation conditions for Al(13)-pillared acid-activated Na(+)-montmorillonite (Al(13)-PAAMt) were (1) an acid-activated Na(+)-montmorillonite (Na(+)-Mt) solution of pH 3.0, (2) a OH(-)/Al(3+) molar ratio of 2.4 and (3) Al(3+)/Na(+)-Mt ratio of 1.0 mmol g(-1). The effects of OH(-)/Al(3+) and Al(3+)/Na(+)-Mt ratios on the adsorption of Cd(2+) onto Al(13)-PAAMt were studied. A comparison of the adsorption of Cd(2+) onto Al(13)-PAAMt, Al(13)-pillared Na(+)-montmorillonite (Al(13)-PMt) and Na(+)-Mt suggested that Al(13)-PAAMt had higher adsorption affinity for Cd(2+) than the other two adsorbents. A pseudo-second-order model described the adsorption kinetics well. Cadmium adsorption followed the Langmuir two-site equation, while desorption was hysteretic.