Evaluating the abiotic synthesis potential and the stability of building blocks of life beneath an impact-induced steam atmosphere.

A prerequisite for prebiotic chemistry is the accumulation of critical building blocks of life. Some studies argue that more frequent impact events on the primitive Earth could have induced a more reducing steam atmosphere and thus favor widespread and more efficient synthesis of life building blocks. However, elevated temperature is also proposed to threaten the stability of organics and whether life building blocks could accumulate to appreciable levels in the reducing yet hot surface seawater beneath the steam atmosphere is still poorly examined. Here, we used a thermodynamic tool to examine the synthesis affinity of various life building blocks using inorganic gasses as reactants at elevated temperatures and corresponding steam pressures relevant with the steam-seawater interface. Our calculations show that although the synthesis affinity of all life building blocks decreases when temperature increases, many organics, including methane, methanol, and carboxylic acids, have positive synthesis affinity over a wide range of temperatures, implying that these species were favorable to form (>10-6 molal) in the surface seawater. However, cyanide and formaldehyde have overall negative affinities, suggesting that these critical compounds would tend to undergo hydrolysis in the surface seawaters. Most of the 18 investigated amino acids have positive affinities at temperature <220°C and their synthesis affinity increases under more alkaline conditions. Sugars, ribose, and nucleobases have overall negative synthesis affinities at the investigated range of temperatures. Synthesis affinities are shown to be sensitive to the hydrogen fugacity. Higher hydrogen fugacity (in equilibrium with FQI or IW) favors the synthesis and accumulation of nearly all the investigated compounds, except for HCN and its derivate products. In summary, our results suggest that reducing conditions induced by primitive impacts could indeed favor the synthesis/accumulation of some life building blocks, but some critical species, particularly HCN and nucleosides, were still unfavorable to accumulate to appreciable levels. Our results can provide helpful guidance for future efforts to search for or understand the stability of biomolecules on other planets like Mars and icy moons. We advocate examining craters formed by more reducing impactors to look for the preservation of prebiotic materials.

Efficient Removal of Congo Red, Methylene Blue and Pb(II) by Hydrochar-MgAlLDH Nanocomposite: Synthesis, Performance and Mechanism.

Organic dyes and heavy metals often coexist in industrial effluents, and their simultaneous removal is a grand challenge. Herein, a hydrochar and MgAl layered double hydroxide (HC-MgAlLDH) nanocomposite was prepared via a facile one-step hydrothermal route, and applied to remove anionic Congo red (CR), cationic Methylene blue (MB) and Pb(II) from aqueous solutions. The nanocomposite was formed by interweaving amorphous HC and crystalline MgAlLDH nanoplates and possessed more functional groups, lower zeta potential and larger specific surface area than uncomposited MgAlLDH. Batch removal experiments showed that the components HC and LDH dominated the CR and MB removals, respectively, whereas Pb(II) removal was conjointly controlled by the two components. The maximum Langmuir removal capacities of the nanocomposite to sole CR, MB, or Pb(II) were 348.78, 256.54 or 33.55 mg/g. In binary and ternary systems, the removal capacities of CR and MB only slightly decreased, while the capacity of Pb(II) increased by 41.13-88.61%. The increase was related to the coordination of Pb(II) with the sulfur-containing groups in dyes and the precipitation of PbSO4. Therefore, the simultaneous removal of CR, MB and Pb(II) was involved in a synergistic effect, including electrostatic adsorption, π-π interaction, coordination and precipitation. The present work shows that the HC-MgAlLDH nanocomposite has great potential for wastewater integrative treatment.

Mn3O4@polyaniline nanocomposite with multiple active sites to capture uranium(VI) and iodide: synthesis, performance, and mechanism.

A major challenge for radioactive wastewater treatment and associated environmental remediation is how to simultaneously remove cationic and anionic radionuclides. Herein, a series of Mn3O4@polyaniline (Mn3O4@PANI) nanocomposites were successfully prepared and used to remove U(VI) and I- from aqueous solution, two highly concomitant species in nuclear pollution settings. Batch adsorption experiments reveal that the component Mn3O4 is predominantly responsible for U(VI) removal, but PANI for I-. The nanocomposite with 24.2 wt% Mn3O4 possesses high removal percentages (> 85%) either for U(VI) or I- over a wide pH range, fast removal kinetics, and excellent adsorption selectivity at high concentrations of competing ions. Benefiting from the contributions of the two components and the high adsorption affinities, the nanocomposite achieves the simultaneous removal to coexisting U(VI) and I-, with a maximum adsorption capacity 102.6 mg/g for U(VI) and 126.1 mg/g for I-. X-ray photoelectron spectroscopy (XPS) results reveal that the U(VI) adsorption occurs via coordination bonding with Mn-O, -NH- , and =N- groups in the nanocomposite, whereas I- adsorption proceeds mainly through I anionic species exchange with Cl- and interactions with π-bonds in PANI, as well as the electrostatic attraction onto Mn3O4. Considering the excellent performance and multiple active sites, the Mn3O4@PANI nanocomposite is promising to remove practical radioactive U(VI) and I-.

Fe3O4-Mg(OH)2 nanocomposite as a scavenger for silver nanoparticles: Rational design, facile synthesis, and enhanced performance.

Silver nanoparticles (AgNPs) are considered as emerging contaminants because of their high toxicity and increasing environmental impact. Removal of discharged AgNPs from water is crucial for mitigating the health and environmental risks. However, developing facile, economical, and environment-friendly approaches remains challenging. Herein, an Fe3O4-Mg(OH)2 nanocomposite, as a novel magnetic scavenger for AgNPs, was prepared by loading Fe3O4 nanoparticles on Mg(OH)2 nanoplates in a one-pot synthesis. Batch removal experiments revealed that the maximum removal capacities for the two model AgNPs (citrate- or polyvinylpyrrolidone-coated AgNPs) were 476 and 442 mg/g, respectively, corresponding to partition coefficients 8.03 and 4.89 mg/g/µM. Removal feasibilities over a wide pH range of 5-11 and in real water matrices and scavenger reusability with five cycles were also confirmed. Both Fe3O4 and Mg(OH)2 components contributed to the removal; however, their nanocomposites exhibited an enhanced performance because of the high specific surface area and pore volume. Chemical adsorption and electrostatic attraction between the coatings on the AgNPs and the two components in the nanocomposite was considered to be responsible for the removal. Overall, the facile synthesis, convenient magnetic separation, and high removal performance highlight the great potential of the Fe3O4-Mg(OH)2 nanocomposite for practical applications.

Abiotic Formation of Calcium Oxalate under UV Irradiation and Implications for Biomarker Detection on Mars.

A major objective in the exploration of Mars is to test the hypothesis that the planet has ever hosted life. Biogenic compounds, especially biominerals, are believed to serve as biomarkers in Raman-assisted remote sensing missions. However, the prerequisite for the development of these minerals as biomarkers is the uniqueness of their biogenesis. Herein, tetragonal bipyramidal weddellite, a type of calcium oxalate, is successfully achieved by UV-photolyzing pyruvic acid (PA). The as-prepared products are identified and characterized by micro-Raman spectroscopy and field emission scanning electron microscopy. Persistent mineralization of weddellite is observed with altering key experimental parameters, including pH, Ca2+ and PA concentrations. In particular, the initial concentration of PA can significantly influence the morphology of weddellite crystal. Oxalate acid is commonly of biological origin; thus calcium oxalate is considered to be a biomarker. However, our results reveal that calcium oxalate can be harvested by a UV photolysis pathway. Moreover, prebiotic sources of organics (e.g., PA, glycine, alanine, and aspartic acid) have been proven to be available through abiotic pathways. Therefore, our results may provide a new abiotic pathway of calcium oxalate formation. Considering that calcium oxalate minerals have been taken as biosignatures for the origin and early evolution of life on Earth and astrobiological investigations, its formation and accumulation by the photolysis of abiological organic compounds should be taken into account.

Morphogenesis and evolution mechanisms of bacterially-induced struvite.

Bacteria are able to induce struvite precipitation, and modify struvite morphology, leading to the mineral with various growth habits. However, the relevant work involving the morphogenesis is limited, thereby obstructing our understanding of bacterially mediated struvite mineralization. Here, an actinomycete Microbacterium marinum sp. nov. H207 was chosen to study its effect on struvite morphology. A combination of bacterial mineralization and biomimetic mineralization techniques was adopted. The bacterial mineralization results showed that strain H207 could induce the formation of struvite with grouping structure (i.e., a small coffin-like crystal grown on a large trapezoid-like substrate crystal), and the overgrowth structure gradually disappeared, while the substrate crystal further evolved into coffin-like, and quadrangular tabular morphology with time. The biomimetic experiments with different organic components confirmed that the soluble macromolecules rich in electronegative carboxyl groups secreted by strain H207 dominate the formation of the struvite grouping. The time-course biomimetic experiments with supernatant testified that the increase in pH and NH4+ content promoted the evolution of crystal habits. Moreover, the evolution process of substrate crystal can be divided into two stages. At the first stage, the crystal grew along the crystallographic b axis. At the later stage, coupled dissolution-precipitation process occurred, and the crystals grew along the corners (i.e., [110] and [1-10] directions). In the case of dissolution, it was also found that the (00-1) face of substrate crystal preferentially dissolved, which results from the low initial phosphate content and high PO43- density on this face. As a result, present work can provide a deeper insight into bio-struvite mineralization.

Removal and recovery of silver nanoparticles by hierarchical mesoporous calcite: Performance, mechanism, and sustainable application.

The widespread use of silver nanoparticles (AgNPs) inevitably leads to the environmental release of AgNPs. The released AgNPs can pose ecological risks because of their specific toxicity. However, they can also be used as secondary sources of silver metal. Herein, hierarchical mesoporous calcite (HMC) was prepared and used to remove and recover AgNPs from an aqueous solution. The batch experiments show that the HMC has high removal percentages for polyvinylpyrrolidone- and poly (vinyl alcohol)-coated AgNPs (PVP- and PVA-AgNPs) over a wide pH range of 6-10. The adsorption isotherms indicate that the maximum removal capacities are 55 and 19 mg g-1 for PVP-AgNPs and PVA-AgNPs, respectively, corresponding to partition coefficients (PCs) of 0.55 and 0.77 mg g-1 µM-1. Furthermore, the removal performance is also not impaired by coexisting anions, such as Cl-, NO3-, SO42-, and CO32-. Their removal mechanisms can be ascribed to the electrostatic attraction and chemical adsorption between the HMC and polymer-coated AgNPs. Calcium ions on the HMC surface serve as active sites for coordination with the oxygen-bearing functional groups of AgNP coatings. Moreover, the AgNPs adsorbed onto HMC show high catalytic activity and good reusability for the reduction of the organic pollutant 4-nitrophenol. This work may pave the way not only to remove metal nanopollutants from waters but also to convert them into functional materials.

Controlled Synthesis and Microstructure of Metastable Flower-Like Vaterite.

Developing a simple morphology-controlled synthesis of metastable vaterite is a goal in the field of materials research. In this paper, we successfully synthesized flower-like dendritic vaterite crystals using a microwave method with 2-naphthaleneacetic acid (2-NAA) and ethylene glycol (EG) as the regulating additives. The results show that the morphology of vaterite could be regulated by inducing a monolayer or multilayer flower-like structure with the appropriate choice of regulators. Interestingly, the microstructure analysis showed that such flower-like vaterite dendrites host two different kinds of crystal cells. The negative carbonate 2-NAA effectively neutralized the charge of the vaterite (001) plane, resulting in the crystalline growth along the direction parallel to it and inducing a flower-like morphology. This experiment reveals an alternative approach to controlling hierarchical structures during the synthesis of similar classes of minerals.

One-step synthesis of Ag2O@Mg(OH)2 nanocomposite as an efficient scavenger for iodine and uranium.

Ag2O nanoparticles anchored on the Mg(OH)2 nanoplates (Ag2O@Mg(OH)2) were successfully prepared by a facile one-step method, which combined the Mg(OH)2 formation with Ag2O deposition. The synthesized products were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and nitrogen physisorption analysis. It was found that Ag2O nanoparticles anchored on the Mg(OH)2 nanoplates show good dispersion and less aggregation relative to the single Ag2O nanoaggregates. In addition, iodide (I-) removal by the Ag2O@Mg(OH)2 nanocomposite was studied systematically. Batch experiments reveal that the nanocomposite exhibits extremely high I- removal rate (<10min), and I- removal capacity is barely affected by the concurrent anions, such as Cl-, SO42-, CO32- and NO3-. Furthermore, I- and UO22+ could be simultaneously removed by the nanocomposite with high efficiency. Due to the simple synthetic procedure, the excellent removal performances for iodine and uranium, and the easy separation from water, the Ag2O@Mg(OH)2 nanocomposite has real potential for application in radioactive wastewater treatment, especially during episodic environmental crisis.

Biomimetic synthesis of struvite with biogenic morphology and implication for pathological biomineralization.

Recent studies have found that certain urinary proteins can efficiently inhibit stone formation. These discoveries are significant for developing effective therapies for stone disease, but the inhibition mechanism of crystallization remains elusive. In the present study, polyaspartic acid (PASP) was employed as a model peptide to investigate the effect of urinary proteins on the crystallization and morphological evolution of struvite. The results demonstrate that selective adsorption/binding of PASP onto the {010} and {101} faces of struvite crystals results in arrowhead-shaped morphology, which further evolves into X-shaped and unusual tabular structures with time. Noticeably, these morphologies are reminiscent of biogenic struvite morphology. Concentration-dependent experiments show that PASP can inhibit struvite growth and the inhibitory capacity increases with increasing PASP concentration, whereas aspartic acid monomers do not show a significant effect. Considering that PASP is a structural and functional analogue of the subdomains of aspartic acid-rich proteins, our results reveal that aspartic acid-rich proteins play a key role in regulating biogenic struvite morphology, and aspartic acid residues contribute to the inhibitory capacity of urinary proteins. The potential implications of PASP for developing therapeutic agents for urinary stone disease is also discussed.

Biomineralization mediated by anaerobic methane-consuming cell consortia.

Anaerobic methanotrophic archaea (ANME) play a significant role in global carbon cycles. These organisms consume more than 90% of ocean-derived methane and influence the landscape of the seafloor by stimulating the formation of carbonates. ANME frequently form cell consortia with sulfate-reducing bacteria (SRB) of the family Deltaproteobacteria. We investigated the mechanistic link between ANME and the natural consortium by examining anaerobic oxidation of methane (AOM) metabolism and the deposition of biogenetic minerals through high-resolution imaging analysis. All of the cell consortia found in a sample of marine sediment were encrusted by a thick siliceous envelope consisting of laminated and cementing substances, whereas carbonate minerals were not found attached to cells. Beside SRB cells, other bacteria (such as Betaproteobacteria) were found to link with the consortia by adhering to the siliceous crusts. Given the properties of siliceous minerals, we hypothesize that ANME cell consortia can interact with other microorganisms and their substrates via their siliceous envelope, and this mechanism of silicon accumulation may serve in clay mineral formation in marine sedimentary environments. A mechanism for biomineralization mediated by AOM consortia was suggested based on the above observations.

Preparation of hollow core/shell microspheres of hematite and its adsorption ability for samarium.

Hollow core/shell hematite microspheres with diameter of ca. 1-2 µm have been successfully achieved by calcining the precursor composite microspheres of pyrite and polyvinylpyrrolidone (PVP) in air. The synthesized products were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and Brunauer-Emmett-Teller (BET) gas sorptometry. Temperature- and time-dependent experiments unveil that the precursor pyrite-PVP composite microspheres finally transform into hollow core/shell hematite microspheres in air through a multistep process including the oxidation and sulfation of pyrite, combustion of PVP occluded in the precursor, desulfation, aggregation, and fusion of nanosized hematite as well as mass transportation from the interior to the exterior of the microspheres. The formation of the hollow core/shell microspheres dominantly depends on the calcination temperature under current experimental conditions, and the aggregation of hematite nanocrystals and the core shrinking during the oxidation of pyrite are responsible for the formation of the hollow structures. Moreover, the adsorption ability of the hematite for Sm(III) was also tested. The results exhibit that the hematite microspheres have good adsorption activity for trivalent samarium, and that its adsorption capacity strongly depends on the pH of the solution, and the maximum adsorption capacity for Sm(III) is 14.48 mg/g at neutral pH. As samarium is a typical member of the lanthanide series, our results suggest that the hollow hematite microspheres have potential application in removal of rare earth elements (REEs) entering the water environment.

Two-dimensional silica sieve plates mimicking the diatom valve.

Sieve and take: A biomimetic strategy was designed to fabricate two-dimensional silica sieve plates (SSP) by use of catanionic surfactants as composite template and L-tartrate with hydroxyl and carboxyl groups as regulator. Tartrate was found to combine two capabilities in the formation of SSP structures: the connection of adjacent silica structures through H bonding and the separation of adjacent structures through electrostatic repulsion.

Formation of asymmetrical structured silica controlled by a phase separation process and implication for biosilicification.

Biogenetic silica displays intricate patterns assembling from nano- to microsize level and interesting non-spherical structures differentiating in specific directions. Several model systems have been proposed to explain the formation of biosilica nanostructures. Of them, phase separation based on the physicochemical properties of organic amines was considered to be responsible for the pattern formation of biosilica. In this paper, using tetraethyl orthosilicate (TEOS, Si(OCH2CH3)4) as silica precursor, phospholipid (PL) and dodecylamine (DA) were introduced to initiate phase separation of organic components and influence silica precipitation. Morphology, structure and composition of the mineralized products were characterized using a range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), infrared spectra (IR), and nitrogen physisorption. The results demonstrate that the phase separation process of the organic components leads to the formation of asymmetrically non-spherical silica structures, and the aspect ratios of the asymmetrical structures can be well controlled by varying the concentration of PL and DA. On the basis of the time-dependent experiments, a tentative mechanism is also proposed to illustrate the asymmetrical morphogenesis. Therefore, our results imply that in addition to explaining the hierarchical porous nanopatterning of biosilica, the phase separation process may also be responsible for the growth differentiation of siliceous structures in specific directions. Because organic amine (e.g., long-chair polyamines), phospholipids (e.g., silicalemma) and the phase separation process are associated with the biosilicification of diatoms, our results may provide a new insight into the mechanism of biosilicification.

A novel intermediate-sacrificed route to polycrystalline nanorods consisting of highly oriented quantum dots of cubic CdS.

Polycrystalline nanorods of CdS were successfully prepared by a novel solvothermal method using simple initial materials of sulfur and Cd(Ac)2.2H2O in pyridine at 160 degrees C. TEM, HRTEM and SAED analyses reveal that the polycrystalline nanorods with the lengths from 400 to 1000 nm and a mean diameter of ca 40 nm are assembled with highly oriented quantum dots of face-centered cubic CdS. The chemical reactions under the current solvothermal conditions involve the first reduction of sulfur by acetate anions to S2-, and subsequently the formation of intermediate complex CdS(Py)0.5 with nanorod-like morphology, as well as finally prolonged solvothermal process to the formation of the polycrystalline nanorods. Therefore, a new intermediate-sacrificed mechanism to direct the formation of cubic CdS polycrystalline nanorods was proposed.