In Situ Electrochemical Intercalation-Induced Phase Transition to Enhance Catalytic Performance for Lithium-Sulfur Battery.

Accelerating the conversion of polysulfide to inhibit shutting effect is a promising approach to improve the performance of lithium-sulfur batteries. Herein, the hollow titanium nitride (TiN)/1T-MoS2 heterostructure nanospheres are designed with efficient electrocatalysis properties serving as a sulfur host, which is formed by in situ electrochemical intercalation from TiN/2H-MoS2 . Metallic, few-layered 1T-MoS2 nanosheets with abundant active sites decorated on TiN nanospheres enable fast electron transfer, high adsorption ability toward polysulfides, and favorable catalytic activity contributing to the conversion kinetics of polysulfides. Benefiting from the synergistic effects of these favorable features, the as-developed hollow TiN/1T-MoS2 nanospheres with advanced architecture design can achieve a high discharge capacity of 1273 mAh g-1 at 0.1 C, good rate performance with a capacity retention of 689 mAh g-1 at 2 C, and long cycling stability with a low-capacity fading rate of 0.051% per cycle at 1 C for 800 cycles. Notably, the TiN/1T-MoS2 /S cathode with a high sulfur loading of up to 7 mg cm-2 can also deliver a high capacity of 875 mAh g-1 for 50 cycles at 0.1 C. This work promotes the prospect application for TiN/1T-MoS2 in lithium-sulfur batteries.

The important role of EPS in mediated biosynthesis of CdS QDs: Comparative study of EPS-intact and EPS-free.

In this study, we investigated the adsorption of Cd(II) and the biosynthesis of CdS quantum dots (QDs) mediated by cells of sulfate-reducing bacteria before and after the removal of EPS to determine whether EPS or the cell wall plays a major role. Potentiometric titration revealed that the concentration of proton-active binding sites on cells with EPS (EPS-intact) was notably higher than that on cells without EPS (EPS-free) and that the sites were predominantly carboxyl, phosphoryl, hydroxyl, and amine groups. The protein content in EPS-intact cells was higher, and thus the Cd(II) adsorption capacity was stronger. The CdS QDs biosynthesized using EPS-intact possessed better properties, including uniform size distribution, good crystallinity, small particle size, high fluorescence, and strong antimicrobial activity, and the yields were significantly higher than those of EPS-free by a factor of about 1.5-3.7. Further studies revealed that alkaline amino acids in EPS play a major role and serve as templates in the biosynthesis of QDs, whereas they were rarely detected in the cell wall. This study emphasizes the important role of EPS in the bacterial binding of metals and efficient recycling of hazardous waste in water.

Enhanced immobility of Pb(II) during ferrihydrite-Pb(II) coprecipitates aging impacted by malic acid or phosphate.

Metastable ferrihydrite is omnipresent in environments and can influence the fate of Pb(II) during ferrihydrite transformation. Ferrihydrite is rarely pure and often coexists with impurities, which may influence the mineralogical changes of ferrihydrite and Pb(II) behavior. In this work, we investigated the effect of malic acid or phosphate on Pb(II)-ferrihydrite coprecipitates (Fh-Pb) transformation and the subsequent fate of Pb(II) during the 10-day aging of Fh-Pb. Results showed that both malic acid and phosphate retarded Fh-Pb transformation and prevented the release of Pb(II) from Fh-Pb back into solutions. Pb(II) was beneficial to goethite formation by inhibiting hematite formation while both malic acid and phosphate inhibited goethite formation since they could act as templates of nucleation. Besides, malic acid and phosphate improved the proportion of non-extracted Pb(II) during Fh-Pb transformation, indicating that Pb(II) was incorporated into secondary minerals. Pb(II) could not replace Fe(III) within the crystal lattice due to its large radius but was occluded into pores and defect structures within the secondary mineral lattices. This work can advance our understanding of the influences of malic acid and phosphate on Pb(II) immobility during Fh-Pb aging.

Mobility and transformation of Cr(VI) on the surface of goethite in the presence of oxalic acid and Mn(II).

Goethite is an effective adsorbent for hexavalent chromium (Cr(VI)). Oxalic acid and other organic acids will affect the release, immobilization, and bioavailability of Cr(VI) in nature on the mineral surface. Mn(II) can accelerate the reduction of Cr(VI) with oxalic acid. Herein, the effects of oxalic acid and Mn(II) on the mobilization and transformation of adsorbed Cr(VI) on the surface of goethite were investigated in this study. The results revealed that Mn(II) could increase the adsorption of Cr(VI) by increasing the positive charge on the surface of goethite. The complexation of oxalic acid with the surface of goethite caused the adsorbed Cr(VI) to be released into the solution. Moreover, oxalic acid could undergo redox with adsorbed Cr(VI) through electron conduction on the surface of goethite, thereby resulting in the transformation of adsorbed Cr(VI) to Cr(III). During the reaction in the presence of oxalic acid, the concentration of Cr(III) increased from 0 to 13.9 mg/L. In addition, Mn(II), oxalic acid, and Cr(VI) could form unstable ester-like species in the solution, which accelerated the reduction of Cr(VI) to Cr(III). These findings of this study may enrich our understanding of the behaviors of Cr(VI) in the coexistence of goethite, oxalic acid, and Mn(II).

Aquatic photodegradation of clofibric acid under simulated sunlight irradiation: kinetics and mechanism analysis.

Clofibric acid is one of the most frequently detected pharmaceuticals in various aquatic environments. Photodegradation of clofibric acid in water under simulated sunlight was investigated. The effects of different initial concentrations, pH conditions and dissolved oxygen were examined. Photodegradation of clofibric acid followed a pseudo-first-order kinetics model, and the rate decreased gradually with the increasing initial concentration of clofibric acid. Dissolved oxygen inhibited the photodegradation of clofibric acid. As a result of varying reaction species of clofibric acid, the initial pH conditions greatly influenced its photodegradation. Quenching experiments showed that the self-sensitization process via ·OH and 1O2 occured during photodegradation of clofibric acid, and the bimolecular reaction rate constants of clofibric acid with ·OH and 1O2 were determined via the competition kinetics method to be 3.93(±0.20) × 108 and 2.38(±0.12) × 106 L mol-1 s-1, respectively. In addition, the transformation products of clofibric acid were identified by the UPLC-Q-TOF-MS microsystem, and eight products were detected. It is proposed that the photodegradation of clofibric acid occurred mainly via decarboxylation, dechlorination, ·OH addition and 1O2 attack reaction.

Consecutive Reaction to Construct Hierarchical Nanocrystalline CuS "Branch" with Tunable Catalysis Properties.

New CuS nanocrystals with a 3D hierarchical branched structure are successfully synthesized through in situ consecutive reaction method with copper foam as template. The formation mechanism of the 3D hierarchical branched structure obtained from the secondary reaction is investigated by adjusting the reaction time. The morphology of CuS nanosheet arrays with the 3D hierarchical branched structure is changed through Cu(2+) exchange. In this method, the copper foam reacted completely, and the as-synthesized CuS@Cu9S5 nanocrystals are firmly grown on the surface of the 3D framework. This tunable morphology significantly influence the physical and chemical properties, particularly catalytic performance, of the materials. The as-obtained material of Cu@CuS-2 with the 3D hierarchical branched structure as catalyst for methylene blue degradation exhibits good catalytic performance than that of the material of Cu@CuS with 2D nanosheets in dark environment. Furthermore, the cation exchange between Cu and Cu(2+) indicates that Cu(2+) in wastewater could be absorbed by Cu@CuS-2 with the 3D hierarchical branched structure. The exchanged resultant of CuS@Cu9S5 retains its capability to degrade organic dyes. This in situ consecutive reaction method may have a significant impact on controlling the crystal growth direction of inorganic material.

Photodegradation of naproxen in water under simulated solar radiation: mechanism, kinetics, and toxicity variation.

The main objective of this study was to investigate the degradation mechanism, the reaction kinetics, and the evolution of toxicity of naproxen in waters under simulated solar radiation. These criteria were investigated by conducting quenching experiments with reactive oxygen species (ROS), oxygen concentration experiments, and toxicity evaluations with Vibrio fischeri bacteria. The results indicated that the degradation of naproxen proceeds via pseudo first-order kinetics in all cases and that photodegradation included degradation by direct photolysis and by self-sensitization via ROS; the contribution rates of self-sensitized photodegradation were 1.4%, 65.8%, and 31.7% via ·OH, (1)O2 and O2(•-), respectively. Furthermore, the oxygen concentration experiments indicated that dissolved oxygen inhibited the direct photodegradation of naproxen, and the higher the oxygen content, the more pronounced the inhibitory effect. The toxicity evaluation illustrated that some of the intermediate products formed were more toxic than naproxen.