Scan Science and Technology
Contact Leading Edge Experts & Companies
The Experts below are selected from a list of 4701 Experts worldwide ranked by ideXlab platform
Xionghan Feng – One of the best experts on this subject based on the ideXlab platform.
The Influence of Zn2+ and Mn2+ on Pb2+ Adsorption Behaviors of BirnessiteMolecular Environmental Soil Science at the Interfaces in the Earth’s Critical Zone, 2020Co-Authors: Wei Zhao, Xionghan FengAbstract:
The present study comparatively investigated Pb2+ adsorption behaviors of the Birnessite with high Mn average oxidation state (AOS) before and after treatment of preadsorption with Zn2+ and Mn2+, respectively. The association of vacant Mn octahedral sites with Pb2+ adsorption was further understood from the variances of Birnessite AOS, d(110)-interplanar spacing, maximum Pb2+ adsorption, maximum Zn2+ and Mn2+ release during the Pb2+ adsorption before and after treatments. The Birnessite AOS and d(110)-interplanar spacing were almost unchanged as the concentration of Zn2+ increased, indicative of the unchanged vacant Mn octahedral sites, whereas the maximum Pb2+ adsorption decreased from 3190 to 2030 mmol·kg−1 due to occupancy of the treating Zn2+ in adsorption sites. However, the AOS of the Mn2+-treated Birnessites decreased and most of the treating Mn2+ were oxidized to Mn3+ and located below or above vacant Mn octahedral sites or migrated into vacant Mn octahedral sites. Increasing Mn2+ concentration from 1 to 2.4 mmol·L−1 increased the d(110)-interplanar spacing of the treated Birnessites from 0.1416 to 0.14196 nm but decreased the maximum Pb2+ adsorption of the treated Birnessites from 3190 to 1332 mmol·kg−1, indicating the decrease in the amount of vacant Mn octahedral sites, mainly due to the increase of the produced Mn3+ migrating into vacant Mn octahedral sites. Therefore, birnesstie Pb2+ adsorption capacity was largely determined by the number of Mn site vacancies.
Self-assembly of Birnessite nanoflowers by staged three-dimensional oriented attachmentEnvironmental science. Nano, 2020Co-Authors: Xinran Liang, Zixiang Zhao, Lijun Wang, Xionghan FengAbstract:
Birnessite (layer-type Mn(III, IV) oxides with ordered sheet stacking) is the most common mineral species of manganese (Mn) oxides and has been demonstrated to be among the strongest sorbents and oxidants in surface environments. The morphology of Birnessite is one of the key factors affecting its reactivity. Either biotic or abiotic Birnessite samples usually consist of nanoflower-like crystals. However, the governing factors and mechanisms of morphological evolution of the nanoflower-shaped Birnessite remain poorly understood. In this work, Birnessite nanoflowers, as a natural Birnessite analog, were synthesized and the intermediate products during Birnessite crystallization were captured by instant freezing using liquid nitrogen. The processes and mechanisms of crystal growth of Birnessite nanoflowers were investigated using a combination of high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that primary hexagonal nanoflakes rapidly agglomerate to form nuclei-like substrates at the initial stages, and subsequently, these nanoflakes aggregate laterally and link serially on the substrates to form nanopetals through both rotation and edge-to-edge oriented attachment (OA) mechanism. This process is likely driven by hydrogen bonding between unsaturated O atoms at the edge planes of [MnO6] sheets. Meanwhile, the OA mechanism along the (001) plane is likely driven by Coulombic interactions and hydrogen bonding during the assembly process of the adjacent nanopetals. The morphological evolution occurred by the staged three-dimensional OA process that plays an essential role in the self-assembly of flower-like Birnessite crystals. These findings provide further understanding of how nanoparticle assembly is directed to achieving desired shapes and sizes by fabricating nanomaterials through three-dimensional OA processes.
local structure of cu 2 in cu doped hexagonal turbostratic Birnessite and cu 2 stability under acid treatmentChemical Geology, 2017Co-Authors: Quanjun Xiang, Lirong Zheng, Matthew Gindervogel, Juan Xiong, Luuk K Koopal, Mingxia Wang, Xionghan FengAbstract:
Abstract Geochemical behaviors of heavy metal contaminants, such as Cu 2 + , are strongly controlled by natural Birnessite-like minerals in both marine and terrestrial environments. However, the mechanisms of the interaction of Cu 2 + with Birnessite are not fully understood yet. In the present study, Cu 2 + was coprecipitated with Mn 2 + to produce hexagonal turbostratic Birnessite, which is analogous to natural Birnessite. The obtained Cu-doped Birnessite was characterized by powder X-ray diffraction, field-emission scanning electron microscopy, and X-ray absorption spectroscopy (XANES + EXAFS). The stability of Cu(II) in the Birnessite structure was investigated by acid treatment. Increasing the dopant content reduces the mineral crystallinity in the  direction and the unit cell parameter b from the hexagonal layers. It also shortens the bond length of Mn O in the [MnO 6 ] unit and the edge-sharing Mn Mn distance in the layers, and increases the average oxidation state (AOS) of Mn and the specific surface area. Analysis of Cu K-edge XANES and EXAFS data indicates that, only a small part of Cu(II) is inserted into the Birnessite layers, while most of it is adsorbed on the vacancies. When the Cu/Mn molar ratio is increased from 0.08 to 0.23, an increasing part of Cu(II) is present as polynuclear clusters on the Birnessite edge sites in the pH range of ~ 3.3–5.3. Reaction with H 2 SO 4 solution is found to easily dissolve the polynuclear Cu clusters and the highly distorted Cu octahedra in innersphere complexes on the Birnessite-water interface, with ~ 53% of the Cu 2 + released into the solution. On the other hand, the reaction with HCl solution leads to reductive dissolution of the mineral matrix, the release of Mn 2 + into solutions, the decrease in the first Mn O and edge-sharing Mn Mn distances and Mn AOS, in addition to the release of Cu 2 + . The release rate of Cu 2 + is much faster than that of Ni 2 + in Ni-doped Birnessites, owing to the lower stability of distorted [CuO 6 ] octahedron upon proton attack. These results indicate the formation of multinuclear Cu complexes on Birnessite surfaces under the investigated conditions. The results also suggest the lower stability of Cu 2 + in these minerals and thus higher potential toxicity in acidic conditions, in comparison with other metal pollutants, such as Ni 2 + . This study provides new insights into the interaction mechanisms between Cu 2 + and Birnessite-like minerals, and help to clarify the structural stability and geochemical behaviors of Cu 2 + associated with Birnessite-like minerals in natural environments.
J P Pereiraramos – One of the best experts on this subject based on the ideXlab platform.
doping effects on structure and electrode performance of k Birnessite type manganese dioxides for rechargeable lithium batteryElectrochimica Acta, 2008Co-Authors: Atsushi Ogata, Shinichi Komaba, J P Pereiraramos, R Baddourhadjean, N KumagaiAbstract:
Abstract The potassium Birnessites doped with Al, Ni, and Co were prepared by calcination and aqueous treatment, which showed that single phase products were obtained with Ni and Al up to 5 at.% and Co up to 25 at.% addition to strating KMnO 4 . The discharge–recharge capacities and capacity retentions in an aprotic Li cell were not improved by the Ni and Al dopings, but those of the cobalt doped Birnessite were improved. The initial discharge capacities of the undoped and cobalt doped Birnessites were 170 and 200 mAh g −1 with capacity retentions of 56 and 80% during the initial 20 cycles, respectively. The reasons for the improvement of the battery performance by Co doping were considered as follows: (i) a change in the stacking structure, (ii) a decrease in the charge transfer resistance, and (iii) improved structural stability of the oxide. Their micro structures were evaluated by X-ray diffraction, photoelectron and Raman spectroscopies, and electron microscopy. Also, potassium Birnessite synthesized by adding about 3 times excess potassium indicated that the stacking structure was similar to the 30 at.% cobalt doping sample, furthermore, the better capacity retention was achieved as cathode in a Li cell.
raman spectra of Birnessite manganese dioxidesSolid State Ionics, 2003Co-Authors: C Julien, M Massot, R Baddourhadjean, Sylvain Franger, S Bach, J P PereiraramosAbstract:
Structural features of layered manganese dioxides of the Birnessite family are studied using Raman scattering spectroscopy. This local probe is capable of analysing directly the near-neighbour environment of oxygen coordination around manganese and lithium cations. Four types of sol–gel Birnessite (SGB) are considered: lithium Birnessite (Li-Bir), sodium Birnessite (Na-Bir), sol–gel Birnessite (SG-Bir), and sol–gel Co-doped Birnessite (SGCo-Bir). Thus, in a first approach, we consider the overall spectral features of Birnessites such as the superposition of the spectra of local structures, while the lattice modes are discussed in the spectroscopic symmetry. Results show the specific spectroscopic fingerprints of SG-Bir single phases, the site occupancy of Co ions in the substituted SGCo-Bir compound, and vibrations due to lithium ions with their oxygen neighbours in Li-Bir, Li0.32MnO2·0.6H2O. A correlation between the interlayer d-spacing and the stretching mode frequencies of Birnessite oxides has been established.
synthesis ion exchange and electrochemical properties of lamellar phyllomanganates of the Birnessite groupMaterials Research Bulletin, 1996Co-Authors: Le P Goff, S Bach, N Baffier, J P PereiraramosAbstract:
Synthesis of various X-Birnessites was performed using the ion exchange properties of the sodium Birnessite Na0.32MnO2,yH2O. Their structural and electro-chemical characteristics are investigated and discussed in comparison with previous data obtained for some compounds and in relation with mechanism invoked for Li electrochemical insertion into sol-gel and chemical Birnessites. Two main groups of materials are obtained with a monoclinic or hexagonal structure depending on the kind of inserted cation.
Steven L Suib – One of the best experts on this subject based on the ideXlab platform.
enhanced adsorption removal of arsenic from mining wastewater using Birnessite under electrochemical redox reactionsChemical Engineering Journal, 2019Co-Authors: Steven L Suib, Lirong Zheng, Shiming SuAbstract:
Abstract Manganese oxides have been extensively investigated for arsenic (As) adsorption from aqueous solution. However, the effect of electrochemical redox reactions on the adsorption performance and underlying mechanism remain elusive. Herein, Birnessite was used for electrochemical adsorption of As from mining wastewater at a constant cell voltage, and the effect of cell voltage and the continuous use (without desorption) performance of Birnessite electrode were also evaluated. At 1.2 V for 24 h, the concentrations of total As (As(T)) and As(III) in wastewater decreased from 3808.7 to 73.7 μg L−1 and 682.8 to 21.4 μg L−1, respectively. The As(T) removal ratio increased with increasing cell voltage and reached 98.1% at 1.2 V, which was higher than that at open circuit (84.1%). The Mn2+ concentration also significantly decreased in wastewater during As adsorption. The high potential of Birnessite anode and the generation of H2O2 on cathode facilitated As(III) oxidation, and the electrochemical redox reactions of Birnessite contributed to the enhancement of As(T) removal. The application of cell voltage reversal could improve the utilization rate of Birnessite electrodes by dissolution-recrystallization during continuous use, and the As(T) removal ratio was increased from 73.5% to 85.1% after five cycles of voltage alteration. The present work indicates that Birnessite is a promising absorbent for the electrochemical adsorption of As from real wastewaters.
Photochemical Formation and Transformation of Birnessite: Effects of Cations on Micromorphology and Crystal StructureEnvironmental Science & Technology, 2018Co-Authors: Tengfei Zhang, Steven L SuibAbstract:
As important components with excellent oxidation and adsorption activity in soils and sediments, manganese oxides affect the transportation and fate of nutrients and pollutants in natural environments. In this work, Birnessite was formed by photocatalytic oxidation of Mn2+aq in the presence of nitrate under solar irradiation. The effects of concentrations and species of interlayer cations (Na+, Mg2+, and K+) on Birnessite crystal structure and micromorphology were investigated. The roles of adsorbed Mn2+ and pH in the transformation of the photosynthetic Birnessite were further studied. The results indicated that Mn2+aq was oxidized to Birnessite by superoxide radicals (O2•–) generated from the photolysis of NO3– under UV irradiation. The particle size and thickness of Birnessite decreased with increasing cation concentration. The Birnessite showed a plate-like morphology in the presence of K+, while exhibited a rumpled sheet-like morphology when Na+ or Mg2+ was used. The different micromorphologies of bi…
enhancement of zn2 and ni2 removal performance using a deionization pseudocapacitor with nanostructured Birnessite and its carbon nanotube composite electrodesChemical Engineering Journal, 2017Co-Authors: Steven L Suib, Lirong ZhengAbstract:
Abstract Manganese oxides have been widely used as deionization capacitor electrode materials to remove heavy metal ions from aqueous solutions. However, the effect of pseudocapacitive properties of manganese oxides on the removal processes remains elusive. In this work, synthesized nanostructured Birnessite-type manganese oxide and Birnessite/carbon nanotubes (HB/CNTs) nanocomposites were used as deionization pseudocapacitor electrode materials for Zn 2+ and Ni 2+ removal from aqueous solution by constant potential electrolysis. The effects of operation potential and introduction of carbon nanotubes (CNTs) on Zn 2+ and Ni 2+ removal capacities were further investigated. The results demonstrated a significant enhancement of electrochemical removal capacities for Zn 2+ and Ni 2+ by the pseudocapacitive properties of Birnessite and the introduction of CNTs. The Zn 2+ and Ni 2+ removal capacities of Birnessite electrode increased first and then decreased with the decrease of potential from 0.2 to −0.2 V ( vs . SCE), and the highest removal capacities for Zn 2+ and Ni 2+ respectively reached 89.5 and 96.6 mg g −1 when the potential was controlled at 0 V. The HB/CNTs nanocomposite showed higher removal capacities (155.6 mg g −1 for Zn 2+ and 158.4 mg g −1 for Ni 2+ when the relative content of manganese oxide was 45.6%) and a better cycling stability (about 90% and 88% of the initial Zn 2+ and Ni 2+ removal capacity were retained after 5 cycles) than Birnessite electrode. The present study makes clear the pseudocapacitive mechanism of heavy metal ion removal using Birnessite, and proposes a facile method to remove heavy metal ions from aqueous solution.