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Dolomite exhibits a wide distribution in geological strata. The metabolic activities of microorganisms in marine sediments play a crucial role in the formation of dolomite. Semiconducting minerals, such as hematite, goethite, and rutile, generate photoelectrons when exposed to sunlight, which can impact the community structure and metabolic activities of microorganisms. In this study, a simulated photoelectron system was conducted to investigate the response of the microbial community, as well as the regulation of sulfate reduction, to photoelectrons using high-throughput sequencing of the 16S rRNA gene. The regulatory effect of semiconducting mineral photoelectrons on the induction of carbonate precipitation by sulfate-reducing bacteria was explored. X-ray diffraction and Raman spectroscopy were used to characterize carbonate precipitation. During cultivation, the pH values of the system increased from 8.0 to approximately 8.5 and the rate of sulfate reduction was significantly enhanced under the influence of simulated photoelectrons. The alpha diversity of the microbial community decreased, and the semiconducting mineral photoelectronic system had a promoting effect on the enrichment of sulfate-reducing bacteria, mainly Desulfovibrio. Under the regulation of photoelectrons, sulfate-reducing bacteria can effectively oxidize organic matter and reduce sulfate in the environment, and proto-dolomite can be formed at a low Mg/Ca ratio. This process has important implications for carbon and sulfur element cycling in estuarine and oceanic photic zones, and provides a new explanation for the formation of large amounts of dolomite in geological history.

Manganese (Mn) oxides have been prevalent on Earth since before the Great Oxidation Event and the Mn cycle is one of the most important biogeochemical processes on the Earth's surface. In sunlit natural environments, the photochemistry of Mn oxides has been discovered to enable solar energy harvesting and conversion in both geological and biological systems. One of the most widespread Mn oxides is birnessite, which is a semiconducting layered mineral that actively drives Mn photochemical cycling in Nature. The oxygen-evolving centre in biological photosystem II (PSII) is also a Mn-cluster of Mn4CaO5, which transforms into a birnessite-like structure during the photocatalytic oxygen evolution process. This phenomenon draws the potential parallel of Mn-functioned photoreactions between the organic and inorganic world. The Mn photoredox cycling involves both the photo-oxidation of Mn(II) and the photoreductive dissolution of Mn(IV/III) oxides. In Nature, the occurrence of Mn(IV/III) photoreduction is usually accompanied with the oxidative degradation of natural organics. For Mn(II) oxidation into Mn oxides, mechanisms of biological catalysis mediated by microorganisms (such asPseudomonas putidaandBacillusspecies) and abiotic photoreactions by semiconducting minerals or reactive oxygen species have both been proposed. In particular, anaerobic Mn(II) photo-oxidation processes have been demonstrated experimentally, which shed light on Mn oxide emergence before atmospheric oxygenation on Earth. This review provides a comprehensive and up-to-date elaboration of Mn oxide photoredox cycling in Nature, and gives brand-new insight into the photochemical properties of semiconducting Mn oxides widespread on the Earth's surface.

Calcification exists in atherosclerotic plaques in the form of nanomineral aggregates and is closely related to the development of atherosclerosis. Spheroidal and massive calcification are two major types of calcification found in atherosclerotic tissue. However, the exact difference between these two types of calcification is still not clear. Samples composed entirely of spheroidal calcifications and massive calcifications were isolated from aortic atherosclerotic plaques and tested using both bulk and microscopic analysis techniques. Scanning electron microscopy and transmission electron microscopy showed that spheroidal calcifications had a core–shell structure. Massive calcifications were composed of randomly arranged nanocrystals. Synchrotron radiation X-ray diffraction, Raman spectroscopy and selected area electron diffraction showed amorphous calcium phosphate, whitlockite and carbonate hydroxyapatite all existing in spheroidal calcification, while massive calcification only consisted of carbonate hydroxyapatite. We conclude that amorphous calcium phosphate may act as a precursor phase of spheroidal calcifications that eventually transforms into a crystalline phase, while whitlockite in lesions could aggravate the progression of atherosclerosis.

Based on the most active hydrosphere on the earth, the interplay between adjacent semiconducting minerals and electrochemically active microorganisms was scientifically researched in the marine eup...

Tungstate oxide is a new kind of anionic semiconductor material, which has been received much attention due to its good photocatalytic performance and long-term stability. To facilitate large-scale application, the natural counterpart of tungstate oxide, wolframite, was firstly used as a visible-light mineral photocatalyst in this study. Its mineralogical and photocatalytic properties were characterized and compared with two synthetic end-member minerals, FeWO4 and MnWO4. The results showed natural wolframite in the form of (Fe,Mn)WO4, had a bandgap of only 1.5 eV, far lower than that of FeWO4 (2.3 eV) and MnWO4 (2.6 eV). Under visible-light, natural wolframite exhibited remarkable photoactivity towards degradation of methylene blue (MB, 5 mg/L) and disinfection of Escherichia coli K-12 (107 cfu mL−1) under neutral pH. The MB degradation rate in the presence of both wolframite and H2O2 was as 3-fold or 14-fold as that in the controls without light or H2O2, respectively. And the disinfection rate using wolframite was at least 5 times higher than that using MnWO4 or FeWO4. Hydroxyl radical (OH•), as detected by electron paramagnetic resonance, was demonstrated as the major reactive oxygen species by using different scavengers in the photocatalytic reactions. The production of OH• was due to both photocatalytic and photo-Fenton effects. Recycling experiments were conducted to demonstrate the long-term stability and photoactivity of wolframite, in which the MB degradation rate almost kept unchanged after three experimental rounds. Our results indicated that natural wolframite could be used as a promising visible-light driven photocatalyst applied for large-scale wastewater treatment.

The photoelectrochemical characteristic of semiconducting minerals plays an imperative role in supporting the growth of many electroactive microorganisms. In order to study the effects of photoelectrons triggered from semiconducting mineral by solar energy on the marine microbial growth, metabolism, and community structure, a dual-chamber electrochemical system was established by incubating seawater microbial community with varying simulated electrochemical conditions. The absolute quantifications of 16S rRNA and 18S rRNA genes suggested that photoelectrons could support the growth and reproduction of bacteria with an increase of two magnitudes from 1.34 ± 0.76 × 1012 to 1.41 ± 0.93 × 1014, and archaea with a slight increase from 0.50–8.74 × 1011 to 2.37–14.80 × 1011, whereas not for the growth of eukaryote in consideration of the complicated regulating mechanism of eukaryotic cells. The bacterial and archaeal communities were shaped by the supplement of photoelectron, also not for the eukaryotic community. Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria accounted for over 80% of the total bacterial community. Photoelectrons with appropriate energy could stimulate the diversity and maintain the community structure of bacteria and archaea while lower or higher electric potential caused lower diversity and more divergent microbial assemblages. The abundance of genes related to the electron transport chain was significantly higher in photoelectron regulated setups than that in open circuit ones, indicating that the extracellular photoelectrons experienced the transmembrane transition and entered the bacterial electron transport chain coupling cell anabolism and catabolism. This study proposed the potential impact of photoelectrons produced by semiconducting minerals on marine microorganisms and the putative electron flow under sunlight in the natural environments.

Rock varnish is a widespread Mn-rich rock coating commonly developed in arid environments, but the mechanism for its formation is still under debate. In this study, rock varnish and adjacent soil dust collected from Gobi Desert were analyzed for exploring the possible abiotic oxidation mechanism of Mn oxides. The occurrence of rock varnish shows a direct and close relationship with strong irradiation of sunlight, giving the first evidence of photochemical genesis. Abundant caves and tunnels with average diameter of ~1–5 μm are observed on varnish surface regions, which facilitate the penetration of sunlight and water. Metal (oxyhydr)oxides, including birnessite, hematite, goethite, rutile and anatase, account for the major components of rock varnish, which are all solar light-responsive semiconducting minerals. The trace elements enrichment patterns revealed by LA-ICP-MS provide the indication of an aqueous origin. The positive Ce anomalies in varnish in contrast to the rock substrate, as well as the positive correlation between Ce and Mn suggest a strong oxidizing environment in the genesis of rock varnish. Therefore, the photo-generated holes and reactive oxygen species (ROSs) on metal oxides in varnish can promote Mn(II) oxidation, which are further demonstrated from thermodynamic and kinetic considerations. ROSs including 1O2 and OH with strong oxidizing capability are detected by EPR in varnish suspension, providing the direct evidence for Mn(II) oxidation. Laboratory experimental simulations show the photocatalysis of metal oxides in rock varnish greatly promote Mn(II) oxidation by 2.10–7.97 times in comparison with homogenous solution oxidation. All these lines of evidence suggest that light-induced abiotic process may play important roles in the formation of rock varnish together with other abiotic and biotic pathways, which can even provide implications for the evolution of Mn oxides on surface of terrestrial planets.

Mn carbonate is the main MnII mineral phase that precipitates in suboxic to anoxic environments. The coupled processes of MnIV oxide bioreduction and organic oxidation serve as dominant factors leading to Mn carbonate precipitation. This study examined the simultaneous respiration of oxygen and birnessite by a facultatively anaerobic bacterium, the Dietzia strain DQ12-45-1b (45-1b), and discussed the possible mechanism of rhodochrosite precipitation under general oxic environments. Compared to anaerobic experiments, the more rapid growth of 45-1b under aerobic conditions caused faster oxidation of acetate (1.0 × 103 μM h−1) and accumulation of HCO3− (5.5 × 102 μM h−1) within 72 h, which was coupled to a dramatic increase in pH from 7.0 to more than 9.2. By virtue of the higher biomass and bioactivity in the aerobic condition, the bioreduction of MnIV was accelerated and it caused a higher accumulating rate of soluble reduced Mn (4.0 μΜ h−1) than that in the anaerobic condition (2.0 μΜ h−1). Those rates indicated that an anaerobic-aerobic sub-interface was present in the aerobic system, in which anaerobic and aerobic respiration co-occurred to give rise to sufficient Mn(II) and alkalinity, thus, increased the supersaturation index (SI) for rhodochrosite. The mineral intermediates and products were identified by time-course XRD, SEM, and Raman spectra. Manganite (MnOOH) was found as the transient intermediate, which suggested the stepwise one-electron transfer mechanism of birnessite reduction. The dialysis tube, lysed cells, dead cells and two-compartment experiments suggested that the living 45-1b not only carried out a direct extracellular electron transfer for birnessite reduction but also provided necessary nucleation sites for rhodochrosite precipitation. Furthermore, both the isotope experiments and Raman analysis showed that the carbon source in rhodochrosite was mainly 13C isotope-labeled acetate, which corresponded well with the geological isotopic records. Finally, a conceptual model of Mn carbonate precipitation at oxic-suboxic/anoxic interfaces that could be possibly present in soil and sedimentary environments was proposed based on three prerequisites: (i) sufficient Mn(II) produced on an aerobic-anaerobic sub-interface, (ii) adequate alkalinity, and (iii) nucleation sites provided by cell surfaces. This model highlights the role of aerobic respiration in Mn(IV) reduction and Mn-carbonate formation, and may suggest a realistic way for inorganic carbon storage.

Birnessite, primarily formed by biooxidation, is a common semiconducting Mn oxide in nature and a major controller of heavy metals cycling processes. In turn, the heavy metal sorption pathway alters its structural chemistry and thus the electronic structure. We synthesize three kinds of birnessite, namely biogenic (bio-birnessite), Cu coprecipitated (co-birnessite) and Cu adsorbed birnessite (ad-birnessite), to investigate the influence of Cu(II) occupancy on the structure, semiconducting property and photostability of birnessite. XRD show co-birnessite holds the same hexagonal symmetry as bio-birnessite, whereas ad-birnessite transforms to triclinic symmetry as reflected by the splitting reflections at 2.44 and 1.42 A. The adsorption process is accompanied by a more intense releasing of Mn(II) (156.88 μM/L) from a bio-birnessite analog δ-MnO2 in light than in dark (19.55 μM/L), suggesting the photoreductive releasing of Mn(II) promotes structure transformation. Conformably, both the Mn average oxidation state (AOS) (3.32) and mole ratio of Cu/Mn (0.08) in ad-birnessite is lower than those in co-birnessite (AOS: 3.47, Cu/Mn ratio: 0.17). EXAFS demonstrate different Cu complexing features in ad- and co-birnessite that the ratio of Cu incorporated (INC) into vacancies is 1.16 and 0.45 for ad- and co-birnessite, respectively. UV–vis diffuse reflection spectra (DRS) and photoelectron spectrometer (PS) exhibit the band gap (Eg) and valence band (VB) of bio-birnessite are 2.05 and −5.58 eV, while there is 0.1 and 0.05 eV decrease of Eg, and 0.08 and 0.16 eV lowering of VB in co- and ad-birnessite, respectively. The reduced Eg guarantee them to generate photoelectron-hole pairs under mild indoor visible light, and the lower energy level of VB in ad-birnessite makes its VB holes more reactive to accept electrons from electron donors. Further density functional theory (DFT) calculations focus on interpreting the fine structures brought by different Cu sorption pathways on the electronic structure of birnessite. A Mn vacancy in a 2 × 2 × 1 hexagonal birnessite cell significantly reduces Eg from 1.60 to 0.28 eV by hybridizing Mn 3d and O 2p states in VB. The doped Cu reduces Eg mainly through incorporating Cu 3d orbital in VB. The INC Cu in hexagonal birnessite contributes more to reduce Eg (1.60–0.34 eV) than TCS Cu (1.60–1.20 eV), while in triclinic birnessite cell, TCS Cu causes more obvious reduction of Eg (1.68–0.28 eV) than INC Cu (1.68–1.55 eV). Thus, we conclude the vacancy imposes more effect on the electronic structure of hexagonal co-birnessite than doped Cu in TCS or INC sites; and the band structure of co-birnessite is more sensitive to INC Cu, in contrast to TCS Cu affecting more in ad-birnessite. Overall, the crystal structure differs according to Cu fixation pathway, which imposes a comprehensive effect on band structure and photostability contributed by vacancies, Cu occupancy sites and structural symmetry. Cu coprecipitating with birnessite is suggested as a preferred method in practical clean-up of metals such as Cu, due to the higher adsorption capacity for Cu, better stability of TCS Cu and better photostability influenced by Cu.

Sunlight drives photosynthesis and associated biological processes, and also influences inorganic processes that shape Earth’s climate and geochemistry. Bacterial solar-to-chemical energy conversion on this planet evolved to use an intricate intracellular process of phototrophy. However, a natural nonbiological counterpart to phototrophy has yet to be recognized. In this work, we reveal the inherent “phototrophic-like” behavior of vast expanses of natural rock/soil surfaces from deserts, red soils, and karst environments, all of which can drive photon-to-electron conversions. Using scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray absorption spectroscopy, Fe and Mn (oxyhydr)oxide-rich coatings were found in rock varnishes, as were Fe (oxyhydr)oxides on red soil surfaces and minute amounts of Mn oxides on karst rock surfaces. By directly fabricating a photoelectric detection device on the thin section of a rock varnish sample, we have recorded an in situ photocurrent micromapping of the coatings, which behave as highly sensitive and stable photoelectric systems. Additional measurements of red soil and powder separated from the outermost surface of karst rocks yielded photocurrents that are also sensitive to irradiation. The prominent solar-responsive capability of the phototrophic-like rocks/soils is ascribed to the semiconducting Fe- and Mn (oxyhydr)oxide-mineral coatings. The native semiconducting Fe/Mn-rich coatings may play a role similar, in part, to photosynthetic systems and thus provide a distinctive driving force for redox (bio)geochemistry on Earth’s surfaces.

Spinel ferrite minerals widely distribute in supergene environments. This study mainly focus on investigating the relationship between the crystal chemistry (structural disordering, oxygen vacancy) and semiconducting property (optical absorbance, band structure, photocatalytic activity) of spinel ferrites (Zn1−xFex)[ZnxFe2−x]O4 (x = 0, 0.03, 0.06, 0.15, 0.20). With the increase of inversion coefficient (x) from 0 to 0.20, ZnFe2O4 becomes disordered and its lattice parameter descends from 8.4407 to 8.4320 A. New polyhedrons ZnO6 and FeO4 appear since x = 0.03, which induce three new Raman bands at 299–317 (F2g(2)), 482–484 (F2g(3)) and 690–696 cm−1 (A1g), respectively. The amount of oxygen vacancy and adsorbed hydroxyl species on ZnFe2O4 surface show linear increase with increasing x (R2 = 0.943 and 0.997, respectively), as indicated by electron paramagnetic resonance and X-ray photoelectron spectroscopy. Both the spectroscopic analysis and density functional theory calculations suggest the valence band edge of ZnFe2O4 keeps unchanged as the structure goes disorderly, while its conduction band edge gradually goes lower. Therefore, the bandgap linearly decreases from 2.08 to 1.95 eV (R2 = 0.971) when x increases from 0 to 0.20. Furthermore, two impurity levels are produced in oxygen-defective ZnFe2O4 and cause dual fluorescence signals at 670 and 740–850 nm. Compared with normal ZnFe2O4, the disordered ZnFe2O4 produces more hydroxyl radical ( OH) under the same solar irradiation conditions. In summary, the structural disordering degree of spinel ferrites controls the concentration of oxygen vacancy, configuration of electronic structure and thus the photocatalytic activity, which endow natural bulk spinel ferrite minerals with surprising chemical reactivity on the surface of solid planets.

The interplay between electrochemically active microorganisms (EAMs) and adjacent minerals universally occurs in natural environments, in which soil is an extremely typical and active one. We stimu...

Anode electron transfer efficiency is one of the main bottlenecks in determining the performance of microbial fuel cells (MFCs). Here, we report for the first time a novel design of a silicon solar cell equipped MFC with one-dimensional TiO2/Fe2O3 photoanode and conventional bioanode to overcome the constraints of using traditional anodes. The novel MFC has the maximum power density of 638.3 mW m−2, which is nearly 7.6 times higher than that of general MFCs (84.2 mW m−2). In addition, the novel MFC achieves 90.9% removal of hexavalent chromium Cr(VI) with concentration of 50 ppm within 13.5 h, and this rate is significantly high at 3.67 g m−3 h−1. Efficient microbial oxidation and photoelectrocatalysis are realized after constructing the SSC with double-anode MFC, thereafter leading to enhanced electron transfer to the external circuit. In addition, the electrons are driven by the built-in electric field in silicon solar cell, in which system barriers are resolved at the same time. Power output and Cr(VI) reduction efficiency are both remarkably enhanced. Such a novel MFC strategy provides new directions for designing new systems that can increase the efficiency of MFCs by utilizing solar energy economically, which further suggest great potential in environmental remediation.

Carbonate minerals have been playing an important role in determining the history of the earth's atmosphere, geology, and hydrology and have received extensive attention. In this study, infrared spectral characteristics and infrared radiation properties of four carbonate minerals (calcite, rhodochrosite, siderite, magnesite) were highlighted and investigated by using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), energy dispersive X-ray spectrometer (EDS), differential scanning calorimeter (DSC) and infrared spectroscopy (IR) (absorption and emission spectroscopy). Infrared absorption and thermal emission spectra systematically illustrated the effect of cations (Ca2+, Mg2+, Fe2+, Mn2+) on shifting the positions and infrared performance of the carbonate absorption bands. Three specific modes of the carbonate anion (CO32−) in mid-infrared range, derived from the out-of-plane bending, asymmetric stretching, and in-plane bending vibration (ν2, ν3, and ν4 modes, respectively) were found to be blue-shifted with the decrease of cationic radius, bond length and lattice volume. The average emissivity of calcite, rhodochrosite, siderite, and magnesite were calculated as 0.954, 0.934, 0.907, and 0.883, respectively, in the temperature range of 50–155 °C and the mid-infrared range of 400–2000 cm−1. Emissivity and thermal radiation performance of carbonate minerals can be influenced by several interplaying factors. In particular, higher emissivity was proportional to longer bond length (cation-oxygen and carbon–oxygen with linear correlation coefficients (R2) of 0.751 and 0.721, respectively) and larger cationic radius (R2 = 0.872), which gave rise to lower vibrational frequency, narrower vibration range, and reduced absorbed energy. Furthermore, the heat capacity of four minerals presented a positive correlation with their infrared radiant energy within the temperature. It thus can be concluded that complex and multifactor interactions occur within the crystal structure affecting the fundamental vibrational frequencies of CO32− group, and infrared performance was consequently influenced. This paper can provide theoretical reference for demonstrating the effect of crystal structure on infrared radiation performance and spectral characteristics of various minerals, which is conducive to distinguish minerals based on their features in infrared spectroscopy.

Focusing the marine euphotic zone, which is the pivotal region for interaction of solar light-mineral-microorganism and the elements cycle, we have conducted the research on the mechanism of semiconducting minerals promoting extracellular electron transfer with microorganisms in depth. Therein, anatase which is one of the most representative semiconducting minerals in marine euphotic zone was selected. The mineralogical characterization of anatase was identified by ESEM, AFM, EDS, Raman, XRD, and its semiconducting characteristics was determined by UV-Vis and Mott-Schottky plots. Determined by the electrochemical measurement of I-t curves, the photocurrent density of anatase was more prominent than dark current density. Pseudomonas aeruginosa PAO1 was widely distributed in the euphotic zone, and its mutants of operons deficient in biosynthesis pyocyanin (Δphz1Δphz2) and pili deficient (ΔpilA) were employed in this study. I-t curves indicated that both direct and indirect extracellular electron transfer processes occurred between anatase and PAO1. The indirect electron transfer depending on pyocyanin secreted by PAO1 was the main electron transfer mode. This work demonstrated the light-driven extracellular electron transfer and further revealed the photo-catalyzed mechanisms between anatase and PAO1 in marine euphotic zone.

The solar light response and photoelectrons produced by widespread semiconducting mineral play important roles in biogeochemical cycles on Earth&rsquo, s surface. To explore the potential influence of photoelectrons generated by semiconducting mineral particles on nitrate-reducing microorganisms in the photic zone, a marine heterotrophic denitrifier Halomonas sp. strain 3727 was isolated from seawater in the photic zone of the Yellow Sea, China. This strain was classified as a Halomonadaceae. Whole-genome analysis indicated that this strain possessed genes encoding the nitrogen metabolism, i.e., narG, nasA, nirBD, norZ, nosB, and nxr, which sustained dissimilatory nitrate reduction, assimilatory nitrate reduction, and nitrite oxidation. This strain also possessed genes related to carbon, sulfur, and other metabolisms, hinting at its substantial metabolic flexibility. A series of microcosm experiments in a simulative photoelectron system was conducted, and the results suggested that this bacterial strain could use simulated photoelectrons with different energy for nitrate reduction. Nitrite, as an intermediate product, was accumulated during the nitrate reduction with limited ammonia residue. The nitrite and ammonia productions differed with or without different energy electron supplies. Nitrite was the main product accounting for 30.03% to 68.40% of the total nitrogen in photoelectron supplement systems, and ammonia accounted for 3.77% to 8.52%. However, in open-circuit systems, nitrite and ammonia proportions were 26.77% and 11.17%, respectively, and nitrogen loss in the liquid was not observed. This study reveals that photoelectrons can serve as electron donors for nitrogen transformation mediated by Halomonas sp. strain 3727, which reveals an underlying impact on the nitrogen biogeochemical cycle in the marine photic zone.

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&ndash, 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&ndash, 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.

In recent years, infrared radiation materials have received extensive attention. In this study, a kind of natural carbonate rock was highlighted and its radiation mechanism investigated, using a series of mineralogical and spectroscopy studies such as optical microscope, varying-temperature X-ray diffraction (XRD), Raman spectroscopy, X-ray fluorescence spectrometer (XRF), inductively coupled plasma mass spectrometry (ICP-MS), electron microprobe analysis (EMPA), thermogravimetry, differential thermal analysis (TG/DTA), environment scanning electron microscopy (ESEM) and infrared absorption and emission spectroscopy (IR). Results indicated that micro-nanoscale calcite (95%), graphite (3%) and pyrite (0.1%) were the primary components. Additionally, Sr2+ and Mg2+ were found to substitute Ca2+ in calcite, whose content could reach 0.145% and 0.152% (wt%), respectively. On the basis of blackbody radiation theory and the radiation energy spectrum of samples from 400 to 2000 cm−1, the average emissivity of this rock, pure calcite, pyrite and graphite was calculated as 1.007, 0.986, 0.899 and 0.488, respectively, in the temperature range of 50–140 °C. Notably, the radiation energy spectrum calculated emissivity and emission spectrum of calcite showed high consistency with the natural carbonate at all temperatures, indicating that the radiation performance of the rock was principally contributed to calcite. The heat capacity of three components presented a positive correlation with their infrared emissivity values within the temperature and wavelength of this study. The highest heat capacity of calcite benefited the enhancement of the whole thermal radiation performance of carbonate rock. The vibration of C–O bonds in the narrow absorption band of emission spectrum (1350–1500 cm−1) would lead to relatively high radiation energy and emissivity. In addition, the substitution of Mg2+ and Sr2+ for Ca2+ improved the infrared radiation characteristics due to the 6–8% enhancement of average emissivity for pure MgCO3 and SrCO3 compared to CaCO3. This study can provide theoretical reference for infrared radiation material, using abundant and cheap natural minerals on the Earth as a source of raw materials for infrared functional materials.

Cs2SnBr6, one promising material applied in perovskite solar cells, has been investigated up to 20 GPa by synchrotron X-ray diffraction and Raman spectroscopy. Both experimental data demonstrate that no phase transition occurs up to 20 GPa. By fitting the third-order Birch-Murnaghan equation of state, we have obtained V0 = 1288 (14) A3, K0 = 11 (1) GPa and K0′ = 7 (1). The ultralow value of bulk modulus K0 demonstrates the soft nature of Cs2SnBr6. Combining calculated values with experimental results, we find that x coordinate of Sn (x,0,0) atoms increases and Sn Br bond lengths get shortened on compression. We have assigned vibrational peaks of Cs2SnBr6 in Raman measurements, and all the three Raman bands present nonlinear correlations with pressure.

Micrometer-scale ZnO/ZnFe2O4 coupled photocatalyst is synthesized via a simple, one-step thermal treatment performing on natural Fe-bearing sphalerite ((Zn, Fe)S). In situ high-temperature X-ray diffraction (XRD), thermogravimetry, differential thermal analysis (TG/DTA) and scanning electron microscopy (SEM) results indicated that octahedral ZnFe2O4 (∼5 μm) formed on the surface of substrate-like ZnO (tens of microns) derived from the oxidation of sulfides upon heating to 800 °C in air for 1 h, and the two components kept stable phase ratio at 3:7 (wt%) from 900 °C (sample M-900) to 1200 °C (sample M-1200). X-ray absorption spectroscopy (XAS) and Raman spectra revealed that more Zn atoms in ZnFe2O4 of M-1200 occupied tetrahedral sites than M-900, resulting in a sharper A1g mode (∼647 cm−1), more ordered spinel structure and less antisite defects. Compared with visible-light responsive sphalerite (Zn, Fe)S, M-1200 performed more 200 nm of red-shifted optical absorption, 2.5 times at most higher the incident photon-to-electron conversion efficiency (IPCE) and 2–3-fold photocatalytic efficiency towards degradation of methyl orange and inactivation of Escherichia coli K-12. Besides, the photocatalytic activities of M-1200 preponderate over M-900, typical visible-light catalyst ZnFe2O4 and ZnO/ZnFe2O4 mechanically mixed sample. The optimization of lattice structure and the establishment of special band alignment were suggested to be remarkably beneficial to the separation of photogenerated electrons-holes and promote the photocatalytic performance. This study would enlighten a feasible and efficient strategy to fabricate coupled photocatalyst by utilizing Earth-abundant and low-cost natural minerals for solving environmental problems.