Turning harmful Mn2+ to treasure: In-situ formed ε-MnO2 for removing heavy metals from acid mine drainage.

Acid mine drainage (AMD) contains high concentrations of heavy metals, causing serious environmental pollution. Current neutralization techniques fail to recover and utilize valuable heavy metals, and generate large quantities of hazardous sludge. Manganese (Mn) is generally present at high levels in AMD. Therefore, this paper proposed a technology to recover Mn from AMD, by adding KMnO4 to converting Mn into ε-MnO2. Ultra-Violet C (UVC) was used to photolyze the residual KMnO4. The study then evaluated the processes and mechanisms involved in the technology. The photolysis of KMnO4 in strong acidic conditions was determined, and new mechanisms were proposed. MnO2 produced by the photolysis process was formed through the reaction between Mn(III) and KMnO4. In the absence of KMnO4, Mn(III) underwent further photolysis and was reduced to Mn2+. The maximum adsorption capacities of in-situ formed ε-MnO2 for Pb2+, Cd2+, and Fe3+ were 449.80, 122.05, and 779.88 mg/g, respectively. Higher Mn-OH levels and MnO2 regeneration were crucial in improving adsorption performance. Proton exchange and inner-circle complexation were the main pathways for Pb2+ and Cd2+ adsorption by in-situ formed ε-MnO2. A phase transformation occurred when a substantial amount of Fe3+ was adsorbed, leading to the gradual transformation to MnFe binary oxides. When applying in-situ formed ε-MnO2 technology for actual AMD treatment, 98.62 % of Mn in AMD was recovered within 24 h in the presence of ε-MnO2 for possible further reuse in industries, with a final recovery of 0.76 kg/m3. Further, this technique removed other heavy metals and reduced the sludge volume by 20.99 % when used as a pre-treatment step for neutralization. These results demonstrated the broad potential of this treatment technology.

Retraction: Co3 O4 Polyhedron@MnO2 Nanotube Composite as Anode for High-Performance Lithium-Ion Batteries.

Small 2021, 17, 2008165 DOI: 10.1002/smll.202008165 The above article in Small, published online on 26 March 2021 in Wiley Online Library (https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.202008165),[1] has been retracted by agreement between the authors, the Editor-in-Chief, José Oliveira, and Wiley-VCH GmbH. The retraction has been agreed following an investigation by the corresponding author. The electrochemical measurements on the anode were performed in a wrong manner and cannot reliably be reproduced. The conclusions of this article are considered to be invalid. The authors agree with the retraction but were not available to confirm the final wording of the retraction. [1] Z. Cao, Y. Yang, J. Qin, J. He, Z. Su, Small 2021, 17, 2008165.

Effects of synthesis temperature on ε-MnO2 microstructures and performance: Selective adsorption of heavy metals and the mechanism onto (100) facet compared with (001).

The heavy-metal adsorbent ε-MnO2 was produced through a simple, one-step oxidation-reduction reaction at three different synthesis temperatures (25 °C, 50 °C and 75 °C) and their morphology and chemical-physical properties were compared. Of the three materials, MnO2-25 had the largest specific surface area and the highest surface hydroxyl concentration. Its optimal performance was demonstrated by batch adsorption experiments with Pb2+, Cd2+ and Cu2+. Of the three metals, Pb2+ was adsorbed best (339.15 mg/g), followed by Cd2+ (107.50 mg/g) and Cu2+ (86.30 mg/g). When all three metals were present, Pb2+ was still absorbed best but now more Cu2+ was adsorbed than Cd2+. In order to explore the mechanism for the inconsistent adsorption order of Cd2+ and Cu2+ in single and competitive adsorption, we combined experimental data with density functional theory (DFT) calculations to elucidate the distinct adsorption nature of MnO2-25 towards these three metals. This revealed that the adsorption affinity of the (100) facet was superior to (001), and since the surface complexes were also more stable on (100), this facet was most likely determining the adsorption order for the single metals. When the metals were present in combination, Pb2+ preferentially occupied the active adsorption sites of (100), forcing Cu2+ to be adsorbed on the (001) facet where Cd2+ was only poorly bound. Thus, the adsorption behavior was affected by MnO2-25 surface chemistry at a molecular scale. This study provides an in-depth understanding of the adsorption mechanisms of the heavy metals on this adsorbent and offers theoretical guidance for production of adsorbent with improved removal efficiency.

Co3 O4 Polyhedron@MnO2 Nanotube Composite as Anode for High-Performance Lithium-Ion Batteries.

In this work, a novel lollipop nanostructure of Co3 O4 @MnO2 composite is prepared as anode material in lithium-ion batteries (LIBs). Cobalt metal-organic framework (ZIF-67) is grown on the open end of MnO2 nanotubes via a self-assembly process. The obtained ZIF-67@MnO2 is then converted to Co3 O4 @MnO2 by a simple annealing treatment in air. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction characterizations indicate that the prepared Co3 O4 @MnO2 takes a lollipop nanostructure with a stick of ≈100 nm in diameter, consisting of MnO2 nanotube, and a head part of ≈1 µm, consisting of Co3 O4 nanoparticles. The charge-discharge tests illustrate that this unique novel configuration endows the resulting Co3 O4 @MnO2 with excellent electrochemical performances, delivering a capacity of 1080 mAh g-1 at 300 mA g-1 after 160 cycles, and 696 mAh g-1 at 1 A g-1 after 210 cycles, compared with 404 mAh g-1 and 590 for pure Co3 O4 polyhedrons and pure MnO2 nanotubes at 300 mA g-1 after 160 cycles, respectively. The lollipop configuration consisting of porous Co3 O4 polyhedron and MnO2 nanotube shows excellent structural stability and facilitates lithium insertion/extraction, leading to excellent cyclic stability and rate capacity of Co3 O4 @MnO2 -based LIBs.

Adsorption of sulfamethoxazole and sulfadiazine on phosphorus-containing stalk cellulose under different water pH studied by quantitative evaluation.

To improve the high-value application of corn stalk, phosphorus-containing stalk cellulose (PFC) was prepared, characterized, and utilized for the adsorption of sulfamethoxazole (SMZ) and sulfadiazine (SD), with maximum adsorption capacities of 1.385 and 2.527 mg/g at pH 7. As expected, the adsorption efficiency of PFC was strongly affected by pH, and the preferential adsorption order of SMZ- (SD0) > SMZ0 (SD-) > SMZ+ (SD+) was obtained from the experimental results and due to the charges of PFC and the SMZ and SD species. Furthermore, these results were qualitatively linked to the adsorption mechanism, e.g., π+-π electron donor-acceptor (EDA), anion-π bond electrostatic, and hydrophobic interactions. In particular, the adsorption mechanism was further characterized in terms of structure and analyzed systematically using density functional theory (DFT), frontier orbital theory (FOT), and molecular dynamics (MD) simulation, with the aim to explain the theoretical calculation and experimental results. As a result, the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) orbitals revealed the key role of the rings and functional groups of PFC and SMZ (or SD) and validated the optimized structures of PFC+ sulfonamides (SAs)+, PFC- SAs0, and PFC- SAs-, in which their binding energy values, energy gaps, and relevant molecular lengths determined their stability. Additionally, the van der Waals (vdW) energy confirmed the effect of various interactions on adsorption.

Adsorption behavior and mechanism of sulfonamides on phosphonic chelating cellulose under different pH effects.

Phosphonic chelating fiber (PCCSF) as a novel adsorbent was produced through alkalization, etherification, amination and phosphonation, and then it was applied to adsorb sulfonamides (SAs), such as sulfadiazine (SD), sulfamonomethoxine (SMM) and sulfamethoxazole (SMZ). Specially, their adsorption behavior at different pH values was studied. As a result, PCCSF was provided with amino (NH2 or NH) and PO(OH)2 (PO) groups, and its equilibrium data were generally represented by both Langmuir and Freundlich models. Combining adsorbent-to-solution distribution coefficients (Kd) values and the effect of pH, the primary mechanism suggested that adsorption capacity of PCCSF was lower in strong acid and alkali solution, due to the electrostatic repulsion and hydrophobic interactions. By contrast, its adsorption affinity became more excellent at 3 < pH < 9 owing to the π-π electron-donor-acceptor (EDA) charge-assisted H-bond, Lewis acid-base interaction and charge-assisted H-bond (CAHB).

Absorption of cadmium (II) via sulfur-chelating based cellulose: Characterization, isotherm models and their error analysis.

Sulfur-chelating based cellulose was produced successfully through alkali-pretreatment, etherification-substitution, amination-crosslinking and sulfurate-reaction. Further, its physico-chemical properties were characterized thoroughly, and several impact factors, i.e. adsorbent dosage, pH, co-existing ions, temperature and contact time were discussed in details. Particularly, the linear and non-linear isotherm models were used to determine the best-fitting one with the verification of 8 error functions. As a result, the adsorbent had more excellent adsorption capacity of 54.71 mg g-1 at the optimal conditions, i.e. dosage of 4 g L-1; 5.1 of pH value (50 mL of solution), 298 K of temperature, at least 180 min of contact time, and 5 cyclical regeneration of the adsorbent with 0.1 g L-1 ethylenediaminetetraacetic. The Fritz-Schlünder as 4-parameter isotherm model gave the best correlation of the experimental data. Moreover, a complex formation between Cd (II) and the CS, NH2 and NH groups was confirmed as the dominant chemical adsorption interactions.