Natural Extracellular Electron Transfer Between Semiconducting Minerals and Electroactive Bacterial Communities Occurred on the Rock Varnish

Rock varnish is a thin coating enriched with manganese (Mn) and iron (Fe) oxides. The mineral composition and formation of rock varnish elicit considerable attention from geologists and microbiologists. However, limited research has been devoted to the semiconducting properties of these Fe/Mn oxides in varnish and relatively little attention is paid to the mineral–microbe interaction under sunlight. In this study, the mineral composition and the bacterial communities on varnish from the Gobi Desert in Xinjiang, China were analyzed. Results of principal components analysis and t-test indicated that more electroactive genera such as Acinetobacter, Staphylococcus, Dietzia, and Pseudomonas gathered on varnish bacterial communities than on substrate rock and surrounding soils. We then explored the culture of varnish, substrate and soil samples in media and the extracellular electron transfer (EET) between bacterial communities and mineral electrodes under light/dark conditions for the first time. Orthogonal electrochemical experiments demonstrated that the most remarkable photocurrent density of 6.1 ± 0.4 μA/cm2 was observed between varnish electrode and varnish microflora. Finally, based on Raman and 16S rRNA gene–sequencing results, coculture system of birnessite and Pseudomonas (the major Mn oxide and a common electroactive bacterium in varnish) was established to study underlying mechanism. A steadily growing photocurrent (205 μA at 100 h) under light was observed with a stable birnessite after 110 h. However, only 47 μA was generated in the dark control and birnessite was reduced to Mn2+ in 13 h, suggesting that birnessite helped deliver electrons instead of serving as an electron acceptor under light. Our study demonstrated that electroactive bacterial communities were positively correlated with Fe/Mn semiconducting minerals in varnish, and diversified EET process occurred on varnish under sunlight. Overall, these phenomena may influence bacterial–community structure in natural environments over time

Hierarchical nano-porous carbon from semi-coke via a MgO template preparation strategy for ONP adsorption

O-Nitrophenol(ONP) industrial wastewater causes serious harm to human body and aquatic environment. In this paper, we adopted a recycled MgO template preparation strategy to design series of semicoke derived hierarchical porous carbons. The prepared samples were characterized by N2 adsorption and desorption and scanning electron microscope. The analysis showed that the HPC-1 had a high specific surface area of 723.3m2/g with a huge pore volume of 1.64 cm3/g and exhibited remarkable adsorption capacity of 503.02 mg/g in batch adsorption test for ONP. Adsorption isotherms and adsorption kinetics revealed the adsorption mechanism of ONP molecules on HPCs surfaces, which followed the langmuir monolayer adsorption and pseudo-second-order kinetic. Furthermore, the HPC-1 exhibited good reusability and recycling performance, reflecting its great potential in practical application

Natural Hematite as a Low-Cost and Earth-Abundant Cathode Material for Performance Improvement of Microbial Fuel Cells

Developing cheap electrocatalysts for cathodic oxygen reduction in neutral medium is a key factor for practical applications of microbial fuel cells (MFCs). Natural hematite was investigated as a low-cost cathode to improve the performance of microbial fuel cells (MFCs). With hematite-coated cathode, the cell current density stabilized at 330.66 ± 3.1 mA·m−2 (with a 1000 Ω load) over 10 days under near-neutral conditions. The maximum power density of MFC with hematite cathode reached to 144.4 ± 7.5 mW·m−2, which was 2.2 times that of with graphite cathode (64.8 ± 5.2 mW·m−2). X-ray diffraction (XRD), Raman, electrode potential analysis, and cyclic voltammetry (CV) revealed that hematite maintained the electrode activities due to the stable existence of Fe(II)/Fe(III) in mineral structure. Electrochemical impedance spectroscopy (EIS) results indicated that the cathodic electron transfer dynamics was significantly improved by using hematite to lower the cathodic overpotential. Therefore, this low-cost and earth-abundant natural mineral is promised as an effective cathode material with potential large-field applications of MFCs in future

Analysis of aortic wall stress and morphology in patients with type B aortic dissection

Risk assessment is critical in preventing aortic dissection (AD). This study aims to evaluate the wall stress (WS) distribution, especially at the locations of proximal tears in patient-specific type-B aortic dissection (TBAD) to explore the pathogenesis of dissection. In addition, the shape of the aortas were assessed and associated with TBAD risk. In this paper, 30 three-dimensional models were reconstructed based on patient-specific CT angiography images, and finite element analysis (FEA) was used to analyze the admission blood pressure. In addition, the anatomic variables including the head vessel angles, the aorta diameters, curvatures and torturosity ware measured. Tears occurred at either local high WS or low WS region, and these acute TBAD patients can be classified into three groups based on the location of initial intimal tears. In addition, the WS values at tear sites of each group showed significant difference (P＜0.001). Moreover, the angles of the left subclavian and brachiocephalic arteries were statistical different among three groups. Increased wall stress or decreased wall strength both contribute to the pathogenesis of aortic dissections. In addition, abnormal head vessel angles may be monitored as an important risk factor for aortic dissection, and its specific features may further help to determine the potential tear location

Natural Wolframite Used as Cathode Photocatalyst for Improving the Performance of Microbial Fuel Cells

Developing simple and cheap electrocatalysts or photocatalysts for cathodes to increase the oxygen reduction process is a key factor for better utilization of microbial fuel cells (MFCs). Here, we report the investigation of natural wolframite employed as a low-cost cathode photocatalyst to improve the performance of MFCs. The semiconducting wolframite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The band gap and photo respond activities were determined by UV-vis spectroscopy and linear sweep voltammetry (LSV), respectively. Compared with the normal graphite cathode, when MFCs were equipped with a wolframite-coated cathode, the maximum power density was increased from 41.47 mW·m−2 to 95.51 mW·m−2. Notably, the maximum power density further improved to 135.57 mW·m−2 under light irradiation, which was 2.4 times higher than with a graphite cathode. Our research demonstrated that natural wolframite, a low-cost and abundant natural semiconducting mineral, showed promise as an effective photocathode catalyst which has great potential applications related to utilizing natural minerals in MFCs and for environmental remediation by MFCs in the future

Enhanced Performance for Treatment of Cr (VI)-Containing Wastewater by Microbial Fuel Cells with Natural Pyrrhotite-Coated Cathode

Here we reported the investigation of enhanced performance for the removal of hexavalent chromium (Cr (VI)) by a new microbial fuel cell (MFC) with natural pyrrhotite-coated cathode. By comparisons of the graphite-cathode, the MFCs equipped with a pyrrhotite-coated cathode generated the maximum power density of 45.4 mW·m−2 that was 1.3 times higher than that of with bare graphite cathode (35.5 mW·m−2). Moreover, the Cr (VI) removal efficiency of 97.5% achieved after 4.5 h compared with only 46.1% by graphite cathode MFC. In addition, Cr (VI) removal rate with different initial Cr (VI) concentrations for 10 mg/L and 30 mg/L was investigated and a decreased removal percentage with increasing Cr (VI) concentration was observed. Batches of experiments of different pH values from 3.0 to 9.0 in catholyte were carried out to optimize system performance. The complete Cr (VI) removal was achieved at pH 3.0 and 99.59% of Cr (VI) was removed after 10.5 h, which met the requirement of the Cr (VI) National Emission Standard. When the value of pH was decreasing, the removal rate was obviously increased and Cr (VI) could be removed successfully with a broad pH range indicating pyrrhotite-coated cathode MFC had more extensive usage scope. Furthermore, cathode treatment products were studied by X-ray photoelectron spectroscopy (XPS), Cr2O3, Cr (III)-acetate were detected on the cathode by the XPS Cr2p spectra and no Cr (VI) founded, indicating that the Cr on the surface of cathode was Cr (III) and Cr (VI) were reduced. On cathode, pyrrhotite not only played a significant role for catalyst of MFCs, but also acted as reactive sites for Cr (VI) reduction. Our research demonstrated that pyrrhotite, an earth-abundant and low-cost natural mineral was promised as an effective cathode material. Which had great potential applications in MFCs for reduction of wastewater containing heavy metals and other environmental contaminants in the future

The Fine Characterization and Potential Photocatalytic Effect of Semiconducting Metal Minerals in Danxia Landforms

The Danxia landform is representative of the Cretaceous continental red sediment. The careful identification and potential environmental effects of minerals in Danxia red beds have yet to be clearly reported. In this work, reddish sandstone samples were collected from Lang Mountain Danxia landform in Xinning, Hunan province, China, and their mineral phases, element distribution, microstructure, and the spatial relationship of different minerals were investigated using polarizing optical microscope, environmental scanning electron microscopy, energy-dispersive X-ray analysis, electron probe microanalysis, micro-Raman spectra, micro- X-ray diffraction, X-ray fluorescence spectroscopy, and high-resolution transmission electron microscopy. The results revealed that iron oxide (mainly hematite) and titanium oxide (mainly anatase) were the dominant minerals in Danxia red layers. Microcrystalline hematite was suggested as being the coloring mineral. Anatase, reported here for the first time in Danxia red beds, constituted the content of titanium in the red layer (0.17⁻0.57%) and was present in a significantly higher amount than the adjacent limestone formation (0.13%). Over 95% of Fe/Ti oxides served as a cementation agent along the framework of coarse-grain minerals (quartz and feldspar). The hematite and anatase were visible-light-responsive semiconductors, with a band gap of 2.01 eV and 3.05 eV, respectively. Photoelectrochemical experiments were performed on synthetic hematite, anatase, and their coupled material. The inactive hematite displayed an enhanced 23-fold photocurrent at 0.8 V (vs. Ag/AgCl) when coupled with anatase. Furthermore, in a photodegradation experiment using methyl orange dye under simulated sunlight, the coupled material showed decolorizing efficiency 2.4 times that of hematite. The anatase, therefore, prominently improved the photocatalytic activities of hematite. It is proposed that these semiconducting minerals in red beds produce oxygen reactive species and have significant environmental effects, which is of great importance

The Micro-Scaled Characterization of Natural Terrestrial Ferromanganese Coatings and Their Semiconducting Properties

Different types of ferromanganese coatings were collected from the Chinese mainland to study their mineralogical characteristics and semiconducting properties. Measurements, including by optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, micro-Raman spectrometer and transmission electron microscope, were employed to study their morphology, mineral assemblage, element abundance and distribution patterns. Soil Fe coatings are mainly composed of Al-rich hematite and clays. Soil Fe/Mn coatings can be divided into an outer belt rich in birnessite and an inner belt rich in hematite, goethite, ilmenite and magnetite. Goethite is the only component of rock Fe coatings. Rock Fe/Mn coatings mainly consist of birnessite and hematite, and alternating Fe/Mn-rich layers and Fe/Mn-poor layers can be observed. Powders were scraped off from the topmost part of ferromanganese coatings to conduct laboratory photochemical experiments. The photocurrent–time behavior indicates that natural coating electrodes exhibit an immediate increase in photocurrent intensity when exposed to light irradiation. Natural coatings can photo-catalytically degrade 14.3%–58.4% of methyl orange in 10 h. Under light irradiation, the photocurrent enhancement and organic degradation efficiency of the rock Fe/Mn coating, which has a close intergrowth structure of Fe and Mn components, is most significant. This phenomenon is attributed to the formation of semiconductor heterojunctions, which can promote the separation of electrons and holes. Terrestrial ferromanganese coatings are common in natural settings and rich in semiconducting Fe/Mn oxide minerals. Under solar light irradiation, these coatings can catalyze important photochemical processes and will thus have an impact on the surrounding environment