Many efforts have been made in fabricating three-dimensional (3D) ordered hydroxyapatite (Ca10(PO4)6(OH)2, HAp) nanostructures due to their growing applications as a bone cement, drug deliverer, ...tooth paste additive, dental implant, gas sensor, ion exchange, catalyst, etc. Here, we developed a new synthetic route to 3D HAp-based hollow microspheres through a water-soluble biopolymer (polyaspartic acid) assisted assembly from HAp nanorods. The as-obtained products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Brunauer–Emmett–Teller (BET) gas sorptometry. SEM and TEM results showed that 3D HAp hollow microspheres are constructed by a number of one-dimensional (1D) nanorods as primary building units. The influences of the additive polyaspartic acid and reaction time on final morphology and assembled structure of the products were systematically investigated. On the basis of our experimental results, a phenomenological elucidation of the mechanism for growth of the hollow HAp architectures has been proposed. The time-dependent experiments unveil that the HAp hollow microspheres are fabricated following initial formation and subsequent transformation of amorphous calcium phosphate (ACP) spheres. In-depth investigations, based on control experiments and FT-IR, EDX, and XPS analyses, reveal that polyaspartic acid acts as both a chelating and a surface capping agent in the synthesis process. First, polyaspartic acid molecules via calcium ion accumulation induce formation of ACP. At the subsequent stage Ostwald ripening contributes to formation of the hollow microspheres, and polyaspartic acid molecules capping to the surface of HAp crystallites control growth of the short nanorod subunits. Moreover, the adsorption experiments of the hierarchical hollow HAp for different heavy metal ions were conducted, and the results exhibit that the hierarchical hollow HAp have unique selective adsorption activity for heavy metal Pb2+. In-depth investigation is still in progress.
One of the primary objectives of Mars exploration missions is to search for traces of past or present life. The search for bioorganic molecules is highly desirable because they have diagnostic ...features to indicate the presence of life. Lipids and amino acids are particularly favored because of their high preservation potential in the geological record. Raman spectroscopy has emerged as a promising tool for detecting and identifying organic molecules on extraterrestrial planets. However, cautions should be exercised in operating Raman instruments to detect organic samples, especially concerning laser power. Excessive laser power can potentially alter spectral characteristics and even damage samples, while low power levels suffer from attenuation of the measured Raman signal, making it challenging to interpret. Therefore, it is crucial to determine the optimal Raman laser power for organic detection and build a laser power-based spectral library to increase our capability to interpret the Martian spectroscopic data. As such, we performed a comprehensive Raman analysis of several lipids (decanol, hexadecane, and palmitic acid) and amino acids (alanine, aspartic acid, glycine, histidine, and tyrosine). The Raman laser power varies in two modes, i.e., increasing from 1% (0.63 ± 0.01 mW) to 100% (66.40 ± 1.85 mW) and vice versa, within the operational range of Raman payloads of Mars rovers. The results show that different spectra can be obtained for the organic samples when using different excitation powers. Using high-power lasers could cause damage to lipid samples, whereas amino acids exhibit stability even under the strong irradiation of 100% laser power. In addition, low-power lasers significantly reduce the Raman signal of lipids, while amino acids remain detectable at low laser powers even as low as 1%. Therefore, the most effective and secure operation is to gradually increase the laser power in the Raman analyses for detecting various organic compounds. Our study serves as a reference for operating Raman instruments and contributes to the accurate interpretation of spectral data returned from spacecraft. The supplementary material provides all the spectral data, facilitating further comparisons with future in situ and orbital measurements on Mars.
•Excitation power-dependent Raman spectra are studied for lipids and amino acids.•Excessive high or low excitation power is not conducive to the detection of lipids.•Raman spectra of amino acids show minimal influence over entire excitation power.•Systematic spectral database for lipids and amino acids are established.•Incremental mode of excitation power is recommended for extraterrestrial mission.
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•Vaterite spherolites as a green scavenger are obtained by a facile injection-precipitation route.•Simultaneous removal of Cd(II) and dye Congo red (CR) by the spherolites is firstly ...investigated.•Excellent performance for Cd(II) and CR removal can be achieved by the spherolites.•A multistep mechanism for concurrent removal Cd(II) and CR by the spherolites is proposed.
Hierarchical vaterite spherulites, synthesized by a simple injection-precipitation method at room temperature, were applied for the simultaneous removal of heavy metal Cd(II) and dye Congo red (CR) from aqueous solution. Batch experiments reveal that the maximum removal capacities of as-prepared vaterite spherulites to Cd(II) and CR are 984.5 and 89.0 mg/g, respectively, showing excellent removal performance for Cd(II) and CR. Furthermore, in the binary Cd(II)-CR system, the removal capacity of vaterite to Cd(II) is significantly enhanced at lower CR concentration (<100 mg/L), but inhibited at higher CR concentration (>100 mg/L). In contrast, the concurrent Cd(II) shows negligible effect on the CR removal. The simultaneous removal mechanism was investigated by FESEM, EDX, XRD, FT-IR and XPS techniques. The simultaneous removal of Cd(II) and CR in the binary system is shown to be a multistep process, involving the preferential adsorption of dye CR, stabilization of CR to vaterite, coordination of the adsorbed CR molecules with Cd(II), and transformation of vaterite into otavite. Given the facile and green synthesis procedure, and effective removal of Cd(II) and CR in the binary system, the obtained vaterite spherulites have considerable practical interest in integrative treatment of wastewater contaminated by heavy metals and dyes.
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•Hierarchical Mg(OH)2-MnO2 nanocomposite (MMNC) was successfully synthesized.•The MMNC exhibits a breakthrough dye removal capacity.•Different removal mechanisms for different ...concentrations of dye.•The MMNC exhibits excellent visible light photocatalytic activity.•Synergistic effects of adsorption, precipitation, and photocatalysis for dyes removal.
Hierarchical Mg(OH)2-MnO2 nanocomposite (MMNC) was successfully synthesized by a facile water-bath method, and further applied to Congo red (CR) and methyl orange (MO) removal. Batch experiments revealed that the maximum removal capacity of the nanocomposite to CR and MO reached 17,100 and 7300 mg g−1, respectively. The CR removal mechanism was systemically investigated by FESEM, XRD, EDX and XPS techniques. The results showed that the CR removal proceed mainly through chemisorption on MMNC at low concentration. However, at high concentration, Mg2+ will release from the nanocomposite and react with CR to form a precipitate (Mg-CR), leading to a huge removal capacity. Moreover, MMNC also exhibits excellent performance for photodegradation of CR under visible light irradiation. The active species trapping experiments revealed holes in MMNC and superoxide radical anions as the major active species responsible for photodegradation of CR. The synergistic effects of adsorption, precipitation, and photodegradation enable higher CR removal efficiency, making Mg(OH)2-MnO2 nanocomposite an ideal material for dyes removal from water samples in both low concentration and scabrous high concentration dye-containing wastewater scenarios.
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 NH
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 PO
density on this face. As a result, present work can provide a deeper insight into bio-struvite mineralization.
Highly oriented aragonite tablets have been found in the nacre layers of molluscan shell (or mother of pearl). In this article, we show that highly organized aragonite rods can be prepared over a ...broad range of pH values (1.5 to 6.9) and in the absence of any bio- or organic macromolecules. The organized rods were characterized by XRD, FTIR, FESEM, TEM, SAED, and EDX techniques. FESEM results reveal that the mesoscale aragonite rods are not only assembled with aragonite microrods end-to-end, and side-to-side, but are also partially fused to one another, forming flat, faceted surfaces, i.e., mesocrystal structure. TEM and SAED analyses confirm that the organized rods have the same crystallographic symmetry as single-crystal aragonite, and thus the self-assembly process is energetically favorable. Similar assembly processes also occur for the mineral strontianite of the aragonite group, revealing the occurrence of a general self-assembly process. The driving force controlling the self-assembly process may originate from the inherent anisotropic dipole-dipole interactions between the assembled units. Such dipole interaction may generally occur in biomineralization of nacre layers in molluscan shell, and orchestrate aragonite nanocrystals in an aragonite tablet to coherently orient and array. Furthermore, the dipole-dipole interactions may also contribute to the co-orientation of the aragonite tablets in the same nacreous column. Therefore, our experimental results may provide insight into biomineralization mechanisms. It appears that biological genetic and crystallochemical factors may synergistically operate in biomineralization.
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•A new route linking MgO with bacterial mineralization of struvite was developed.•The strain MR-1 greatly enhanced MgO dissolution and struvite mineralization.•The bacterial ...mineralization transformed over 97% of Mg2+ from MgO into struvite.•The operating and reagent costs for struvite production were significantly cut down.•The route can also be applied to remove N and P as struvite from eutrophic waters.
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.
Nuclear energy is an important alternative energy source to non-renewable fossil fuels. Nevertheless, the nuclear contamination associated with nuclear activities and wastes is a formidable concern ...worldwide. Uranium is one of the most commonly used and discharged radionuclides, and hexavalent uranium U(VI) has significant mobility owing to its good solubility in water, leading to serious environmental and health risks. However, facile and economical solutions to effectively treating U(VI)-contaminated water are still limited. Herein, Mn3O4 nanoparticles were dispersedly anchored on sepiolite nanofibers via a facile microwave-assisted method for adsorbing U(VI) from aqueous solutions. Batch adsorption experiments showed that the nanocomposite possessed faster removal kinetics and greater removal capacity than the individual sepiolite and Mn3O4, as well as better removal performance than many reported inorganic and organic adsorbents. The nanocomposite can also reduce the U(VI) concentrations to far less than the standard of drinking water. Furthermore, a systematic investigation of the adsorption mechanism revealed that the nanocomponents Mn3O4 and sepiolite were responsible for the high-affinity U(VI) capture through the bonding of ≡Mn–O–U(VI) and ≡Si/Mg–O–U(VI), respectively, but the loaded Mn3O4 nanoparticles dominated the adsorption. Given that the simple synthesis and excellent U(VI) removal performance, the Mn3O4@sepiolite nanocomposite holds great promise for practical applications in radioactive uranium treatment.
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•A facile microwave-assisted synthesis of Mn3O4@sepiolite nanocomposite is developed.•Mn3O4 nanoparticles are high-dispersedly anchored on sepiolite nanofibers.•The nanocomposite shows excellent adsorption kinetics and capacity for U(VI).•U(VI) concentrations can be reduced to far less than the standard of drinking water.•Both Mn3O4 and sepiolite in nanocomposite contribute to the excellent removal.
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•A study linking salinity with bacterial mineralization of struvite was conducted.•Strain H207 has good ability to mineralize struvite at salinity from 0.0% to 4.0%.•The salinity has ...little effect on strain ability to removal and recovery of P and N.•Salinity prolongs struvite induction period by inhibiting biodegradation of organics.•High salinity conditions cause a preferential growth of struvite along its a-axis.
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.
Vaterite mesocrystals with a hexagonal prism structure were successfully achieved in the presence of sodium citrate (SC) and sodium dodecyl benzenesulfonate (SDBS) by use of a gas-diffusion method at ...room temperature. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), nitrogen physisorption analysis, and field-emission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray (EDX) were used to characterize the hexagonal prisms. XRD and FESEM results reveal that the superstructures are composed of hundreds of well-stacked nanoflakes, which construct the laminated hexagonal prism of vaterite. TEM and SAED analyses show that the hexagonal prism has the same crystallographic symmetry as single-crystal vaterite, confirming that the hexagonal prismatic architectures are orientationally aligned mesocrystals of vatreite. However, no hexagonal prism structures can be produced only with SC or SDBS, indicating that the cooperation of SC and SDBS is indispensable to the formation of hexagonal prismatic vaterite mesocrystals. The hexagonal prism mesocrystals of vaterite exhibit remarkable similarity to the nacreous layers of vaterite in freshwater cultured pearls from mussels and the columns/lamellae of vaterite in bivalve in architectures. Therefore, the current study on vaterite mesocrystals will be helpful for us to mimic and learn from nature and may provide another pathway toward full insight into biomineralization mechanism.
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