Preparation of Carbon Quantum Dots for Fluorescence Detection of Environmental Pollutants.

A kind of fluorescence sensing probe which used DNA aptamers as biorecognition elements and carbon quantum dots as signal amplification molecules was developed for the rapid detection of 3,3'4,4'-tetrabiphenyl (PCB77) with high selectivity. Carbon quantum dots were synthesized by hydrothermal synthesis method. Quantum dots and DNA were combined by the crosslinker. The crosslinking conditions such as pH, time, and temperature were also be explored. The sensing probe demonstrated two linear responses with PCB77 concentrations ranging from 1.0×10-9 mol L-1 to 1.0×10-8 mol L-1 and 1.0×10-7 mol L-1 to 3.0×10-6 mol L-1. The standard recovery rate was found to be 86.6% to 89.9% and the detection limit as 7.6×10-10 mol L-1. The sensing probe was also used to differentiate 3,3'4,4'-Tetrabiphenyl (PCB77) from other competing PCB congeners, including 3,3',4,4',5-pentachlorobenzene (PCB126), 4-chlorobiphenyl (PCB003) and 2,3-dichlorobiphenyl (PCB005), which showed that PCB77 could also be selectively detected when co-existing with other interference existed. Therefore, this fluorescence sensor can be a valuable tool for selective and rapid detection of PCB77 pollutant.

Spent shell as a calcium source for constructing calcium vanadate for high-performance Zn-ion batteries.

In this article, waste shell is directly used as a raw material to synthesize CaV3O7 as a cathode for aqueous zinc ion batteries. The obtained cathode material exhibits better performance than that of CaV3O7 prepared from pure calcium carbonate as a raw material. At 0.1 A g-1, the CaV3O7 prepared by spent shell as a calcium source displays a highly reversible discharge capacity of 373 mA h g-1. A high initial discharge capacity of 177.7 mA h g-1 can be gained at 5.0 A g-1, and the specific capacity remains at 133.3 mA h g-1 with a capacity retention of 75% after 3000 cycles. This work may spark inspiration for energy storage and generate more effective routes for recycling solid waste.

Performance of oxalate-doped hydroxyapatite as well as relative contribution of oxalate and phosphate for aqueous lead removal.

An oxalate-doped hydroxyapatite (O-HAP) was hydrothermally synthesized for aqueous lead (Pb) removal based on the solubility-limiting ability of oxalate and phosphate over pH range 4-9. Free Pb2+ activities in oxalate and/or phosphate systems were controlled by oxalate to form soluble ion pairs Pb-Ox (aq) and Pb-Ox22- at pH 4-7 while in preference to persist as PbHPO4 (aq) when pH ≥ 8. Both phosphate and oxalate exhibited excellent efficiency in reducing Pb solubility, causing over 99 % of Pb precipitated from solution following oxalate < oxalate-phosphate < phosphate. The Visual MINTEQ model overestimated dissolved Pb and free Pb2+ in nearly all of the reaction systems due to the ill-defined stability constants and solubility products for Pb ion-pair formation. The addition of phosphate acting as a buffer in Pb-oxalate systems tended to lessen the spontaneous pH shifts within 24 h to equilibrate proton release from Pb precipitation and hydrolysis, indicating lower solubility products and faster kinetics of Pb-phosphate mineral formation. The TEM-EDS, FTIR and XRD identified a block-shaped Pb-oxalate mineral phase as the only precipitate at acidic pH while substituted by phosphate to form rod-shaped Pb5(PO4)3OH and Pb3(PO4)2 precipitates as pH increased. The optimum hydrothermal conditions of O-HAP were 433 K, pH 9 and P/Ox doping ratio of 0.5 for 24 h. Batch experiments revealed the endothermic process of O-HAP toward Pb with the maximum adsorption capacity reaching 2333 mg/g at a pH of 7, reaction time of 12 h, initial Pb concentration of 600 mg/L and temperature of 308 K, which were best fitted with the pseudo-second-order kinetic model and Langmuir isotherm. The synergetic mechanisms of O-HAP for Pb removal involved dissolution-precipitation, adsorption and ion exchange. This study provides an insight in developing effective remediation strategies for heavy metal contamination by interacting between low-molecular-weight organic acids and secondary mineral phases.

Preparation of CuSe-PDA/g-C3N4 and its visible-light photocatalytic performance to dye degradation.

CuSe as an excellent photocatalytic semiconductor material has wildly used in the field of photocatalysis. In this paper, CuSe-PDA/g-C3N4 was designed and synthesized, and the photocatalytic performance of CuSe was further enhanced by the addition of polydopamine (PDA) and graphite phase carbon nitride (g-C3N4). The as-prepared CuSe-PDA/g-C3N4 was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and elemental mapping. The specific surface area and porous characteristics of the material were also studied by N2 adsorption-desorption isotherm, which the specific surface area were 186.6 m2/g and pore size were of 3.1 nm by BET data analysis. The photocatalytic conditions for the degradation of methylene blue (MB) by CuSe-PDA/g-C3N4 were optimized in the experiment. The results showed that the photocatalytic performance of CuSe-PDA/g-C3N4 under visible-light illumination were better than CuSe and PDA owing to the narrow band gap energy and delayed electron-hole recombination. Under the optimized conditions, the removal rate reach to 99% of 50 mg/L MB within 60 min irradiation time. Moreover, the MB removal rate was over 90% through six repeated experiments, which proved that the CuSe-PDA/g-C3N4 composite nanomaterials have good stability and reusability.

Fe-Doped Graphitic Carbon Nitride for Methylene Blue Degradation with Visible-Light.

In the present work, degradation of methylene blue (MB) dye in aqueous solution through H2O 2and iron doped g-C3N4 (Fe-g-C3N4) was studied. The hybrid was fabricated by thermal polymerization with iron (III) nitrate nonahydrate and melamine, and it was characterized by X-ray diffraction, Fourier transform infrared, UV-Vis diffuse reflectance spectrum, X-ray photoelectron spectroscopy, transmission electron microscope and Brunner-Emmet-Teller. The various experimental conditions such as doping amount, a dose of the sample, solution pH, the addition of H2O2, and concentration of MB on the degradation of MB dye were optimized. The maximum extent of degradation of methylene blue was obtained at pH 5, doping amount of 2.7 wt% and dose of 0.07 g. The molar ratio of Fe:H2O2 is 1:1000 showed 99% of MB (30 mg/L) decolorization over 60 min. The hybrid showed good stability and recyclability after three cycles of use. Photo-Fenton reaction exhibited a higher synergetic effect than the combination of Fenton and photocatalytic process.

[Electrochemical oxidation of dual electrodes with iron promoting used for the treatment of wastewater from acrylonitrile production].

Effects and laws of electrochemical oxidation of dual electrodes with iron promoting for the treatment of wastewater from acrylonitrile production were investigated using Ti/SnO2 + Fe as combined anodes and graphite as cathode. Compared with traditional electrochemical oxidation, the higher removal of organic pollutants and current efficiency were obtained via oxidation of dual electrodes. Through the process COD removal efficiency and current efficiency were enhanced by 11.0%-13.8% and 8.0%-15.0% respectively, referred to the results from traditional electrochemical oxidation under conditions of the same voltage and no hydrogen peroxide added. With 2 200 mg x L(-1) hydrogen peroxide and voltage of 4.0 V, COD and TOC removal efficiencies increased to 74.6% and 67.9% respectively, and with the increase of hydrogen peroxide, both were enhanced obviously. During the initial reaction period, the higher hydrogen peroxide concentration and the lower Fe2+ concentration were detected, and with reaction time increased, hydrogen peroxide concentration decreased rapidly and Fe2+ concentration increased gradually. The voltage value had great effect on the concentrations of hydrogen peroxide and Fe2+, and the current efficiency was affected obviously by the time of current passed through iron anode under certain initial dosage of hydrogen peroxide. The better color removal was also obtained from electrochemical oxidation of dual electrodes. The electrochemical oxidation of dual electrodes with iron promoting presents a new alternative for the treatment of organic wastewater.