Efficient utilization of biogenic manganese oxides in bioaugmentation columns for remediation of thallium(I) contaminated groundwater.

Little attention has been paid to the in situ-generated biogenic manganese oxides (BMnOx) for practical implementation in continuous groundwater remediation systems. The enrichment effects of manganese oxidizing bacteria (MOB) in bioaugmentation columns and the in situ-generated BMnOx for continuous thallium(I) (Tl(I)) removal from groundwater were investigated. Results indicated that Pseudomonas Putida MnB1 (strain MnB1) attached on the groundwater sediments (GS) can achieve a maximum of 97.37 % Mn(II) oxidation and generate 29.6 mg/L BMnOx, which was superior than that of traditional quartz sand (QS). The in situ-generated BMnOx in MOB_GS column effectively removed 10-100 µg/L Tl(I) under the interference of high concentrations of Fe(II) and Mn(II) in groundwater. Distinctive microbial enrichment effects occurred in the bioaugmentation columns under the competition of indigenous microbes in groundwater. The release of Mn(II) from the BMnOx inhibited with the decrease in Tl(I) removal efficiency. XAFS analysis revealed Tl(I) was effectively adsorbed by BMnOx and Mn-O octahedra with Tl-O tetrahedral coordination existed in BMnOx. This study provides an in-depth understanding of the in situ-generated BMnOx for the Tl(I) removal and contributes to the application of BMnOx in groundwater remediation.

Insights into the synergistic removal mechanisms of thallium(I) by biogenic manganese oxides in a wide pH range.

The behavior and mechanism of thallium (Tl) adsorption by biogenic manganese oxides (BMnOx) are poorly understood. In this study, BMnOx was applied for Tl(I) removal from aqueous solution, and the adsorption interactions were systematically revealed for the first time. BMnOx was successfully prepared with high productivity by effectively oxidizing Mn(II) with a manganese oxide bacterium in an optimal Mn(II) concentration range of 4.0-28 mg/L. Compared with other adsorbents, the prepared BMnOx achieved high Tl(I) adsorption capacity over a wide pH range from 3.0 to 9.0 and high humic acid (HA) concentration (40 mg/L) interference. The experimental results were well depicted by pseudo-second-order kinetics and the Langmuir isotherm model, indicating that chemisorption played the dominant role during the adsorption process. The adsorption mechanisms were verified as synergetic interactions of oxidation-precipitation, electrostatic attraction, ion exchange and surface complexation. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) results suggested that 19.46% of the highly toxic Tl(I) was transformed into the much less toxic product Tl2O3 after adsorption onto BMnOx. This study provides theoretical guidance for high-concentration Tl(I) decontamination from groundwater by biogenic manganese oxides.

Facile Preparation of Oxygen-Vacancy-Engineered MoOx Nanostructures for Photoreversible Switching Systems.

Photochromic materials have attracted increasing attention. Here, we report a novel photo-reversible color switching system based on oxygen-vacancy-engineered MoOx nanostructures with water/N-methyl-2-pyrrolidone (NMP) as solvents. In this work, the system rapidly changed from colorless to blue under UV irradiation (360-400 nm) and slowly recovered its colorless state under visible light irradiation. The obtained oxygen vacancy-engineered MoOx nanostructures exhibited good repeatability, chemical stability, and cycling stability. Upon UV light irradiation, H+ was intercalated into layered MoOx nanostructures and the Mo6+ concentration in the HxMoOx decreased, while the Mo5+ concentration increased and increased oxygen vacancies changed the color to blue. Then, it recovered its original color slowly without UV light irradiation. What is more, the system was highly sensitive to UV light even on cloudy days. Compared with other reported photochromic materials, the system in this study has the advantage of facile preparation and provides new insights for the development of photochromic materials without dyes.

Microwave-assisted functionalization of PAN fiber by 2-amino-5-mercapto-1,3,4-thiadiazol with high efficacy for improved and selective removal of Hg2+ from water.

Mercury (Hg2+) contamination in water is associated with potential toxicity to human health and ecosystems. Many research studies have been ongoing to develop new materials for the remediation of Hg2+ pollution in water. In this study, a novel thiol- and amino-containing fibrous adsorbent was prepared by grafting 2-amino-5-mercapto-1,3,4-thiadiazol (AMTD) onto PAN fiber through a microwave-assisted method. The synthesized functional fiber was characterized by FTIR, SEM, and elemental analysis. Adsorption tests depicted that for mercury uptake, PANMW-AMTD fiber exhibited enhanced adsorption capacity compared with other fibrous adsorbents and selective adsorption feature under the interference of other metal ions, including Pb2+, Cu2+, Cd2+, and Zn2+. The influence of pH on the adsorption process was investigated and the effect of temperature revealed that the adsorption sorption process was endothermic and the adsorption performance of PANMW-AMTD was elevated with the increase of temperature. Kinetic studies of PANMW-AMTD fiber followed the pseudo-second-order and the adsorption isotherm of Hg2+ was well fitted by Sips and Langmuir equations, given the maximum adsorption amount of 332.9 mg/g. XPS results suggested that a synergetic coordination effect of sulfur and nitrogen in functional fiber with mercury took responsibility for the adsorption mechanism in the uptake process. In addition, the prepared PANMW-AMTD fiber could easily be regenerated with 0.1 M HCl for five times without significant reduction of mercury removal efficiency. Thus, this study will facilitate the research on novel functional material for the removal of mercury from water.

Ultrasound-assisted cleaning chloride from wastewater using Friedel's salt precipitation.

The chloride salt derived from the rare earth smelting wastewater was effectively dislodged using Friedel's salt precipitation assisted with ultrasonic enhancement. Various single factors such as the reagent ratio, temperatures, reaction time and agitation speed were determined and investigated systematically. Results showed that the optimal single-stage removal efficiency were 88.22% and 80.89% with and without ultrasonic strengthen, respectively. The particle size distribution, morphology and elemental analysis of the precipitation were carried out by TEM, SEM, EDS and XRD analysis. These results revealed that the effect of ultrasonic has been given prominence to the removal efficiency of chloride salt. It is attributed to the cavitation and mechanical disturbance effect of ultrasound. In order to further decline the chloride, a two-stage de-chlorination carried out, the result indicated that the concentration of chloride was 120 mg/L and 430 mg/L with and without ultrasonic strengthening afterwards two-stage de-chlorination, respectively. The chloride concentration can fully meet the effluent concentration requirement under the effect of ultrasonic enhancement.

Decomposition Study of Praseodymium Oxalate as a Precursor for Praseodymium Oxide in the Microwave Field.

Micron-sized praseodymium oxide powders are prepared successfully from the praseodymium oxalate in a microwave field at 750 °C for 2 h in the present study. X-ray diffraction (XRD) analysis demonstrates that the presence of cubic structured crystalline Pr6O11 and complete decomposition of the precursor are confirmed by Fourier transform infrared (FT-IR) analysis. The scanning electron microscopy (SEM) results show yield powders with the desired particle size and uniform morphologies. Particle size analysis demonstrates that the median diameter (D 50) becomes stable at 750 °C. The D 50, average surface area, pore diameter, and pore volume calculated by Brunauer -Emmett-Teller (BET) are 4.32 µm, 6.628 m2/g, 1.86 nm, and 0.026 cm3/g at 750 °C for 2 h, respectively. Moreover, loss on ignition (L.O.I.) analysis indicates that the L.O.I. is as low as 0.39%, meeting the enterprise requirement (<1%). In comparison, conventional calcination experiments are carried out in the electric furnace. Both XRD and FT-IR analyses are in consistence with thermogravimetry-differential scanning calorimetry, which indicates that the temperature required for the decomposition of praseodymium oxalate hydrate is higher than that of microwave heating. Furthermore, SEM, particle size distribution, and BET analysis indicate that agglomeration generates, particle size enlarges, and average surface area increases. In all, it is confirmed that preparing rare-earth oxides from rare-earth oxalates is feasible using microwave heating to replace conventional heating.

Ce-Doped Graphitic Carbon Nitride Derived from Metal Organic Frameworks as a Visible Light-Responsive Photocatalyst for H2 Production.

Novel fibrous graphitic carbon nitride (g-C3N4) derivatives prepared from metal organic frameworks (MOFs) were doped with Ce3+ (Ce-C3N4) as photocatalytic materials. Ce-C3N4 was characterized using various techniques, revealing its high specific surface area, excellent photocatalytic activity, and stability for H2 evolution under visible light irradiation. The fluorine modified samples show superior photocatalytic activity under visible light irradiation, which is due to the presence of more active sites and enhanced absorption of solar energy. This work provides a new synthetic route for MOF-derived g-C3N4 that can be doped with different metal ions. The fluorine modified Ce-C3N4 is an efficient photocatalyst with potential for many applications related to energy and the environment.

Multifunctional Zn-Al layered double hydroxides for surface-enhanced Raman scattering and surface-enhanced infrared absorption.

Surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) are complementary techniques, and both provide fingerprint structural information on various materials with a high sensitivity. Herein, Zn-Al layered double hydroxides (LDHs) are proposed for the first time as highly sensitive and uniform substrates for both SERS and SEIRA. Zn-Al LDHs show a remarkable SERS effect with an enhancement factor (EF) as high as 1.637 × 104 by using 4-mercaptobenzoic acid (4-MBA) as the probe molecule, where the charge transfer and hydrogen bonds are believed to result in the SERS effect. Interestingly, Zn-Al LDHs also exhibit SEIRA by using 4-methoxybenzenethiol (4-MTP), where the resultant substrates possess excellent long-term stability. This study not only presents a facile route to fabricate LDH materials, but also provides a novel substrate that can be used in both SERS and SEIRA.