Semiconductor Minerals Research Articles

Pathways for the Photoreduction of Fumarate on ZnS

Semiconductor mineral particles can act as photocatalysts for organic redox reactions that occur enzymatically in modern biological metabolic pathways. Semiconductor mineral-mediated photocatalysis...

Heterogeneous catalytic degradation of methylparaben using persulfate activated by natural magnetite; optimization and modeling by response surface methodology

AbstractBACKGROUNDIn this study, a naturally magnetic semiconductor mineral (NM‐SCM) was used as a highly active, easily separable and green catalyst to activate persulfate (SPS) for the degradation of methylparaben (MeP) in aqueous solution by a heterogeneous catalyst system (SPS/NM‐SCM). NM‐SCM properties were characterized using field emission scanning electron microscope (FESEM), Brunauer–Emmett–Teller (BET), X‐ray diffraction (XRD), energy‐dispersive X‐ray (EDX) and vibrating sample magnetometer (VSM) analyses. The effects of contributing factors such as solution pH, NM‐SCM loading, SPS dosage and initial MeP concentration on MeP degradation were analyzed using response surface methodology (RSM) and Box–Behnken design (BBD).RESULTSThe RSM model obtained from the present study (R2 > 0.99) showed a suitable correlation between the predicted values and experimental results of MeP degradation. Under optimized conditions (pH 6.5, SPS 5 mmol L−1, NM‐SCM 0.3 g L−1 and MeP 10 µmol L−1), a removal efficiency of 99.5% and a mineralization degree of 37% were achieved. The removal efficiency of MeP was reduced in the presence of inorganic ions as follows: chloride > nitrate > carbonate > phosphate. After five successive catalyst reuses, the degradation efficiency was >90%, indicating the excellent potential reusability of NM‐SCM catalyst.CONCLUSIONOwing to the generation of highly reactive oxidizing species (SO4•−) and easy separation of the catalyst, the integration of NM‐SCM and SPS has great potential for the degradation of MeP from water and wastewater matrices. © 2019 Society of Chemical Industry

Bioavailable iron production in airborne mineral dust: Controls by chemical composition and solar flux

A large part of oceanic biological production is limited by the scarcity of dissolved iron. Mineral dust aerosol, processed under acidic atmospheric conditions, is the primary natural source of bioavailable iron to oceanic life. However, synergistic and antagonistic effects of non-Fe-containing minerals on atmospheric processing of Fe-containing minerals and Fe solubilization are poorly understood. The current study focuses on mineralogical influences of non-Fe-bearing semiconductor minerals, such as titanium dioxide (TiO2), on the dissolution of iron in selected natural mineral dust aerosols under atmospherically relevant conditions. Further, the role of elevated Ti concentrations in dust is evaluated using magnetite, a proxy for Fe(II) containing minerals, under both dark and light conditions. Our results highlight that relatively higher Ti:Fe ratios, regardless of their total Fe content, enhances the total iron dissolution in mineral dust aerosols as well as in magnetite. Moreover, elevated Ti percentages also yield high Fe(II) fractions in mineral dust systems under dark conditions. Upon irradiation however, dissolved Fe(II) is suppressed by high Ti levels due to the involvement of photochemical redox cycling reactions with hydroxyl radicals (•OH). These synergistic and antagonistic effects of Ti are further evaluated by altering the chemical composition of natural dusts with artificially added anatase (TiO2) and synthetic amorphous titania. The current study reveals important mineralogical controls by non-Fe-bearing minerals on dust iron dissolution to better understand global iron mobilization.

Features of 63,65Cu NMR Spectra in the Local Field of Samples of CuFeS2 Semiconductor Mineral from Oceanic Sulfide Deposits

The results of studying natural samples of CuFeS2 chalcopyrite mineral from hydrothermal ore manifestations of island arcs of the Pacific Ocean by 63Cu nuclear magnetic resonance (63Cu NMR) in a local field at room temperature are presented. The asymmetric shape of the detected resonance lines in the 63Cu NMR spectrum indicates the presence of at least two overlapping lines. The presence of two overlapping central components can be a consequence of the occurrence of regions with different types of structural distortion near the resonant nuclei. These results show that the pulsed 63Cu NMR method can be an effective method for studying the physical properties of deep-sea polymetallic sulfides of the global ocean.

Simultaneous catalytic degradation of 2,4-D and MCPA herbicides using sulfate radical-based heterogeneous oxidation over persulfate activated by natural hematite (α-Fe2O3/PS)

Herein, a sulfate radical (SO4–)-based oxidation process was utilized for simultaneous degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicides using mesoporous hematite-based natural semi-conductor minerals (HM-NSMs) as efficient activators of persulfate (PS). The features of the catalyst were characterized using field emission scanning electron microscopy (FESEM); Brunauer, Emmett and Teller (BET) analysis; X-ray diffraction (XRD); and energy-dispersive X-ray spectroscopy (EDS). The effect of some operational parameters, including solution pH, catalyst loading, PS dosage and temperature, on the performance system of PS/HM-NSMs was examined. A plausible oxidation mechanism for degradation of both pollutants was also proposed. Increasing the removal efficiency of herbicides follows the order of PS/HM-NSM > HM-NSM > PS. In all experiments, the 2,4-D removal rates were slightly lower than those for MCPA, indicating that 2,4-D has a more recalcitrant nature than MCPA. Under optimized conditions, degradation rates of 68.1% and 74.5% were achieved for 2,4-D and MCPA, respectively, during a 120-min reaction. HM-NSM displays a highly synergistic effect on the degradation of herbicides in the presence of PS. The trapping experiments demonstrated that both OH and SO4– radicals contribute significantly during the degradation of 2,4-D and MCPA and that sulfate radicals were the dominant species. A mineralization degree of 36% was obtained under optimum conditions. In conclusion, the coupling of PS and HM-NSM is a promising and effective technique to degrade organic matter for the treatment of herbicide-contaminated waters and wastewaters under real conditions.

Understanding galvanic interactions between chalcopyrite and magnetite in acid medium to improve copper (Bio)Leaching

Chalcopyrite is the main ore mineral used in industrial copper extraction. However, when passivation processes occur during hydrometallurgical treatment, a large percentage of the mineral being treated is not solubilized, so the copper recovery is limited. Galvanic interactions between semiconductor minerals are the basis of many strategies to achieve a more efficient process for increasing copper dissolution. These interactions concern generally two metallic sulfides. The present study describes a new galvanic interaction between chalcopyrite-magnetite (CuFeS2-Fe3O4) in an acid microbial culture medium, used routinely in biomining processes. The electrochemical characterization of CuFeS2, Fe3O4 and a mineral containing CuFeS2-Fe3O4 is performed. Galvanic interactions are demonstrated by comparing Evans diagrams constructed from current transients obtained by imposing the potential pulses to each species studied. It is determined that CuFeS2 and Fe3O4 fulfil the role of anode and cathode, respectively, in the behavior of the corresponding mineral. Stripping voltammetry is used to quantify electro-dissolved ions; the electrooxidation of CuFeS2-Fe3O4 mineral in acid culture medium releases twice as many copper ions as pure chalcopyrite. This corroborates that the galvanic interactions prevent the formation of typical passivating components observed in chalcopyrite.

Catalyzed Synthesis of Zinc Clays by Prebiotic Central Metabolites

How primordial metabolic networks such as the reverse tricarboxylic acid (rTCA) cycle and clay mineral catalysts coevolved remains a mystery in the puzzle to understand the origin of life. While prebiotic reactions from the rTCA cycle were accomplished via photochemistry on semiconductor minerals, the synthesis of clays was demonstrated at low temperature and ambient pressure catalyzed by oxalate. Herein, the crystallization of clay minerals is catalyzed by succinate, an example of a photoproduced intermediate from central metabolism. The experiments connect the synthesis of sauconite, a model for clay minerals, to prebiotic photochemistry. We report the temperature, pH, and concentration dependence on succinate for the synthesis of sauconite identifying new mechanisms of clay formation in surface environments of rocky planets. The work demonstrates that seeding induces nucleation at low temperatures accelerating the crystallization process. Cryogenic and conventional transmission electron microscopies, X-ray diffraction, diffuse reflectance Fourier transformed infrared spectroscopy, and measurements of total surface area are used to build a three-dimensional representation of the clay. These results suggest the coevolution of clay minerals and early metabolites in our planet could have been facilitated by sunlight photochemistry, which played a significant role in the complex interplay between rocks and life over geological time.

Investigations of CuFeS2 semiconductor mineral from ocean rift hydrothermal vent fields by Cu NMR in a local field

The results of investigating natural samples of chalcopyrite mineral CuFeS2 from massive oceanic sulfide ores of the Mid-Atlantic ridge by the 63Cu nuclear magnetic resonance (NMR 63Cu) in a local field at room temperature are presented. The significant width of the resonance lines found in the 63Cu NMR spectrum directly testifies to a wide distribution of local magnetic and electric fields in the investigated chalcopyrite samples. This distribution can be the consequence of an appreciable deviation of the structure of the investigated chalcopyrite samples from the stoichiometric one. The obtained results show that the pulsed 63Cu NMR can be an efficient method for studying the physical properties of deep-water polymetallic sulfides of the World Ocean.

Low-Temperature NMR Study of the Semiconductor Mineral CuFeS2

Characteristic NMR parameters of 63,65Cu in the local magnetic field of the semiconductor mineral chalcopyrite CuFeS2 were measured in the range 26–77 K. The behavior of the 63,65Cu NMR spectral and relaxation parameters in the local field indicated that a magnetic phase transition related to antiferromagnetic ordering of Cu2+ magnetic moments did not occur at ~50 K in the studied CuFeS2 sample.

Electrical property of semiconductor minerals and its role on fracture and frictional discharge

Electrical property of semiconductor minerals and its role on fracture and frictional discharge

Efficient Selection of Biomineralizing DNA Aptamers Using Deep Sequencing and Population Clustering

DNA-based information systems drive the combinatorial optimization processes of natural evolution, including the evolution of biominerals. Advances in high-throughput DNA sequencing expand the power of DNA as a potential information platform for combinatorial engineering, but many applications remain to be developed due in part to the challenge of handling large amounts of sequence data. Here we employ high-throughput sequencing and a recently developed clustering method (AutoSOME) to identify single-stranded DNA sequence families that bind specifically to ZnO semiconductor mineral surfaces. These sequences were enriched from a diverse DNA library after a single round of screening, whereas previous screening approaches typically require 5-15 rounds of enrichment for effective sequence identification. The consensus sequence of the largest cluster was poly d(T)30. This consensus sequence exhibited clear aptamer behavior and was shown to promote the synthesis of crystalline ZnO from aqueous solution at near-neutral pH. This activity is significant, as the crystalline form of this wide-bandgap semiconductor is not typically amenable to solution synthesis in this pH range. High-resolution TEM revealed that this DNA synthesis route yields ZnO nanoparticles with an amorphous-crystalline core-shell structure, suggesting that the mechanism of mineralization involves nanoscale coacervation around the DNA template. We thus demonstrate that our new method, termed Single round Enrichment of Ligands by deep Sequencing (SEL-Seq), can facilitate biomimetic synthesis of technological nanomaterials by accelerating combinatorial selection of biomolecular-mineral interactions. Moreover, by enabling direct characterization of sequence family demographics, we anticipate that SEL-Seq will enhance aptamer discovery in applications employing additional rounds of screening.

Induced electromagnetic emission of rocks containing semiconductor minerals

Induced electromagnetic emission of rocks containing semiconductor minerals

The energetics and kinetics of uranyl reduction on pyrite, hematite, and magnetite surfaces: A powder microelectrode study

There are many studies describing the influence of parameters such as pH, pCO2, and complexing ligands on the sorption of the aqueous uranyl species onto mineral surfaces. However, few of these studies describe the reduction reaction mechanisms and the factors that influence the rate of reduction, despite the fact that the oxidation state of uranium is the most important factor controlling the mobility of uranium. In this study, the energetics and kinetics of the U(VI) reduction half-reaction on pyrite, hematite, and magnetite were investigated by electrochemical methods using a powder microelectrode (PME) as the working electrode. Anodic and cathodic peaks corresponding to the 1e- redox couple, U(VI)/U(V), were identified in cyclic voltammograms of pyrite, hematite, and magnetite at pH 4.5. A second oxidation peak, corresponding to the oxidation of U(IV), was identified and provides evidence for the formation of reduced uranium phase(s) on the mineral surfaces. In addition, uranium-containing precipitates were identified on pyrite surfaces after polarization in a PME. This study identifies the disproportionation of U(V) species on the surface as a possible rate-limiting step in the two-step U(VI) reduction mechanism: (1) charge transfer to form U(V) followed by, (2) a disproportionation reaction that forms U(IV) and U(VI). The Tafel slope (i.e., the derivative of the electrode potential with respect to log[current]) was used to evaluate electrochemical mechanisms. High Tafel slopes (>220mV/(logunit of current) on all minerals evaluated) suggest that uranyl reduction is mediated by insulating (hydr)oxide layers that are present on the semiconducting mineral surfaces. The onset potential for uranyl reduction was determined for pyrite (>+0.1V vs. Ag/AgCl), and hematite and magnetite (between−0.02 and−0.1V vs. Ag/AgCl). The onset potential values establish a baseline kinetic parameter that can be used to evaluate how solution conditions (e.g., dissolved reductants, complexing ligands, and polarizing ions) affect the kinetics of uranyl reduction.The results of this study demonstrate the potential for using PMEs to evaluate redox potentials and mechanisms for U(VI) reduction by Fe-oxides and sulfides under more complex solution conditions as well as other environmentally-relevant mineral-analyte systems. However, it should be noted that the determination of redox kinetics using Butler–Volmer theory has limitations when applied to semiconductor mineral electrodes. Charge depletion in semiconductor surface states can affect the kinetic values obtained for redox reactions on the surface. These limitations and a discussion of the flat band potential are considered in the interpretation of U redox kinetics in this study.

Microbial Fuel Cell Equipped with a Photocatalytic Rutile-Coated Cathode

This study investigated semiconductor mineral (natural rutile) as a novel cathodic catalyst for microbial fuel cells (MFCs). Under the experimental conditions, MFCs installed with a natural rutile-coated cathode produced a maximal power density of 12.03 W/m3 under light irradiation, much higher than that of 7.64 W/m3 in the dark. The open circuit voltage (VOCV) of the MFC was 519 mV when irradiated with visible light, the short-circuit photocurrent density (ISC) was 50.91 A/m3, and the fill factor (FF) was 45.44%. In a separate unoptimized MFC device with a switchable cathode, the maximum power density achieved with natural rutile and platinum (Pt) as a cathode catalyst was comparably at 2.7 and 3.6 W/m3, respectively. The low “incident monochromatic photon to current conversion efficiency” (IPCE) (0.13% at 420 nm) of rutile used in this study indicates a potential for further material and system improvement. Results from this study demonstrate that natural rutile, and other expected semiconductor materia...

Laser Raman and resonance Raman spectroscopies of natural semiconductor mineral cinnabar, α-HgS, from various mines

Natural minerals α-HgS from various mines have been studied by laser Raman spectroscopy and resonance Raman spectroscopy. The crystals differ from each other in the content of selenium impurity, included in samples from some mines.Based on the Raman spectra and the factor-group analysis the classification of the first order phonons and then the comparison of the results with the results from other works were carried out. The Raman spectra analysis of minerals from various mines show the selenium impurity gap vibration at 203 cm−1 and 226 cm−1 frequencies, respectively. On the basis of statistical measurements of the Raman spectra one can conclude that impurity frequencies of α-HgS may be generally used for the identification of the mine.Resonance Raman scattering for pure minerals has been studied by a dye laser. Phonon resonance in the indirect semiconductor α-HgS is found to be far more intense than the indirect resonance detected until now in various semiconductors in the proximity of the first indirect band Eg, for instance, in GaP. In our opinion, this may be conditioned by cinnabar band structure peculiarities.Low resonance has also been fixed in ‘dirty’ minerals at the spectral band frequency of 203 cm−1 characterizing gap vibration of isomorphic impurity Se in cinnabar.

Semiconductor–metal transition of pyriteFeS2 under high pressure by full-potential linearized-augmented plane wave calculations

The effects of hydrostatic pressure on the electronic band structure of the semiconductor mineral ironpyrite FeS2 have been investigated theoretically by an ab initio full-potential linearized-augmented planewave (FPLAPW) method within a local approximation (LDA/GGA) to the density functionaltheory. The calculations predict that at a pressure of 94.1 GPa the indirect band gap of pyriteFeS2 vanishes and the material becomes a metal. This is due to the presence of the S–S and Fe–Sbonds, which provide novel energy band distortions in the process of attaining the metallicstate. Analysis indicates that, under increasing high pressure, the conduction bands(3pz ofsulfur and 3dx2−y2+3dxy of iron) intrude downwards into the valence bands, which are predominantly 3d in nature.At normal pressure, the lattice constant, the bulk modulus, sulfur position parameteru, S–S bond length, and the indirect band gap of pyriteFeS2 are calculated using a fully relaxed unit cell and found to be equal to 541.8 pm, 159.7 GPa,u = 0.383, 219.5 pm and 0.45 eV, respectively. Apart from the gap, which is too small (the usual ‘LDAerror’), these results agree well with recent experiments. The effective masses of an electronat selected points in the conduction band are reported.

Industrial and Medical Applications of Accelerators with Energies Less than 20 MeV

In this paper the medical and industrial application of small accelerators is reviewed. Most of the material is taken from the Seventh Conference on the Application of Accelerators in Research and Industry, which was held in Denton, Texas in November of 1982. The areas covered will include medical linacs, cyclotron design and production of medical radioisotopes, radiation processing, ion implantation for the metallurgical and semiconductor industries, oil and mineral exploration, trace, surface and bulk analysis, and unique accelerators for all of the above applications.

The anodic dissolution of chalcocite in an ammoniacal environment

Presented is the proposed model for the mechanism of anodic oxidation of the semiconductor mineral chalcocite in an ammoniacal environment. The kinetic parameters of the process α a, k s, j 0 0, the formal potential and the electrochemical order of the reaction in relation to ammonia are given.