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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, Ca

Struvite crystallization has been regarded as a sustainable route to recover phosphorus from wastewaters. In this study, sodium alginate (SA) was chosen as model extracellular polymeric substances (EPS) to investigate its impact on struvite crystallization. The experimental results demonstrate that SA can remarkably influence struvite morphogenesis, resulting from the selective adsorption and binding of SA molecules onto the crystal faces with higher Mg content. SA concentration-dependent experiments show that SA significantly inhibits struvite growth, and the growth inhibition is caused by the adsorption of SA onto struvite surface, thus blocking the active growth sites. We also found that the elevation in Mg/P ratio or initial pH (pHi) can promote struvite growth, thus compensating the adverse effect of SA. Considering that SA is model EPS, our results provide a new insight into the role of EPS on struvite crystallization from wastewater. This will help to improve struvite crystallization technique.

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.

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 Fe

Microbial mineralization of struvite from wastewater with cheap magnesium source is a very promising means to remove and recover phosphorus and nitrogen. Seawater, as a cheap and efficient magnesium source, may be potentially applied to struvite bio-recovery. However, high salinity in seawater may have potential effect on microbial growth and its biomineralization for struvite. In present work, a halophilic marine actinomycete, Microbacterium marinum sp. nov. H207 was selected as a model microbe to induce struvite mineralization under different saline conditions. The identification and characterization of the mineralized products were done using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), and field emission scanning electron microscopy (FESEM). The results showed that this strain has good ability to mineralize struvite within the pale of seawater salinity, and the salinity levels have a negligible effect on phosphorus removal and recovery capability of this strain, but the induction period for struvite precipitation increases with elevated salinity, and such retardation can be attributed to the high salinity stress on bacterial metabolism of carbonaceous and nitrogenous organics. Meanwhile, the salinity can also affect the morphogenesis of bio-struvite, and the high saline conditions result in the significant elongations of the struvite crystals along its crystallographic [1 0 0] direction. Current results could have particular relevance to the feasibility of using seawater in microbial phosphorus recovery processes.

Controlled struvite crystallization is regarded as a promising route to phosphorus recovery from wastewaters, and has been the topic of extensive research in the last two decades. Most studies made great efforts to elevate the quantity of struvite recovered from various wastewaters, but little attention has been focused on the struvite quality which affects the agronomic response. The improvement of struvite quality can raise its value in fertilizer markets and improve the economical sustainability of struvite crystallization technology. In this study, we report a facile method for the synthesis of struvite nanowires by regulating NaCl concentration and initial pH (pHi) in synthetic wastewater. The identification and characterization of the synthesized products were done using X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and Zeta potential Analyzer....

Bacterial mineralization of struvite is one of the novel approaches for the recovery of major nutrients nitrogen and phosphorus. However, previous studies were done by using expensive water-soluble magnesium salts, like MgCl2 and MgSO4, significantly limiting its large-scale application. In this context, our objective is to examine the potential of low-cost, naturally abundant MgO as Mg source in bacterial mineralization of struvite. Shewanella oneidensis MR-1 was selected as a model microbe to induce struvite mineralization. The structure, morphology and composition of the mineralized products were identified and characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), and field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDX). Our results demonstrate that S. oneidensis MR-1 is able to enhance MgO dissolution, and transform organic nitrogen and organophosphorus into well-crystallized struvite. The process of bacterial mineralization not only increased the alkalinity of the culture, but also effectively transformed over 97% of Mg2+ from MgO into struvite, hence significantly cutting down the recovery cost of the major nutrients. Current results could provide an effective and economically feasible pathway for the nutrients removal and subsequent recovery as struvite from eutrophic waters.

Bacterial mineralization of struvite from wastewaters is one of the promising approaches to recover phosphorus. However, the information about whether and how the heavy metal Cr(VI) affect the bacterial mineralization system is still lack. Here a model microbe Shewanella oneidensis MR-1 was used to induce struvite mineralization in simulated Cr(VI)-bearing wastewaters and the composition, morphology, and Cr content of precipitates were characterized by a wide range of techniques. Our results reveal that the yield of struvite and Mg transformation efficiency are almost not affected by the concomitant Cr(VI), but pitting and roughening of struvite surfaces are observed. Meanwhile, the struvite mineralized from model wastewaters with 0.1 or 0.2 mM Cr(VI) can meet the regulatory standard of Cr content as fertilizer. Strain MR-1 can not only create an alkaline environment for struvite precipitation, but also completely reduce Cr(VI) to Cr(III), helping to form soluble organo-Cr(III) complexes in the supernatant, hence significantly reducing the Cr content in struvite. And the loaded Cr(III) exists in the form of amorphous Cr(III) species (e.g., Cr(OH)3) on the struvite surface instead of the crystal lattice substitution in abiotic case. Current results serve as a guidance for further development of struvite biomineralization and P recovery from Cr(VI)-containing wastewaters.

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.

Porous TiO2 nanotubes (PTNTs) were successfully prepared by a versatile sepiolite-sacrificed template method. The PTNTs possess a unique porous structure and a high specific surface area (120 m2 g−1). It exhibits significantly enhanced adsorption performance for azo dye Congo Red (CR, model dye pollutant) with maximum adsorption capacity of 540 mg g−1, which is much better than common TiO2-based materials, as well as some other semiconductor adsorbents. The dye-impregnated PTNTs (CR-PTNTs) were re-utilized as a photocatalyst for the visible light-induced reduction of Cr(VI). The results show that the CR-PTNTs exhibit significantly superior photocatalytic reduction ability to Cr(VI), and such performance can be attributed to the huge adsorption of CR molecules on the PTNTs and the unique porous structure of PTNTs. Current work not only reports an effective adsorbent for dye CR removal, but also put forward a reutilization strategy of the spent adsorbent for efficient visible-light photocatalytic reduction of Cr(VI), applicable to the other non-coexisting dyes and Cr(VI) pollutant scenarios.

Clays are widely used as sorbents for heavy metals due to their high specific surface areas, low cost, and ubiquitous occurrence in most soil and sediment environments. However, the low loading capacity for heavy metals is one of their inherent limitations. In this work, a novel SiO2&ndash, Mg(OH)2 nanocomposite was successfully prepared via sequential acid&ndash, base modification of raw sepiolite. The structural characteristics of the resulting modified samples were characterized by a wide range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nitrogen physisorption analysis. The results show that a hierarchical nanocomposite constructed by loading the Mg(OH)2 nanosheets onto amorphous SiO2 nanotubes can be successfully prepared, and the nanocomposite has a high surface area (377.3 m2/g) and pore volume (0.96 cm3/g). Batch removal experiments indicate that the nanocomposite exhibits high removal efficiency toward Gd(III), Pb(II), and Cd(II), and their removal capacities were greatly enhanced in comparison with raw sepiolite, due to the synergistic effect of the different components in the hierarchical nanocomposite. This work can provide a novel route toward a hierarchical nanocomposite by using clay minerals as raw material. Taking into account the simplicity of the fabrication route and the high loading capacities for heavy metals, the developed nanocomposite also has great potential applications in water treatment.

Power gating has become a popular technique to reduce the ever-increasing leakage power for commercial microprocessors or SoCs, however the wakeup energy and delay cost harm its performance. This paper proposes a fast reactivation scheme to reduce the transition delay and energy. The experiment results show that, comparing to the traditional power gating implementation, it can achieve 19.66% reactivation energy reduction, 9.28% peak leakage reduction, and 23.36% wakeup delay reduction, at the cost of 2.75% area increasing.