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.

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^-, SO₄^2-, and CO₃^2-. 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.

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^-, SO₄^2-, CO₃^2- 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.

Chemical control of struvite scale by a green inhibitor polyaspartic acid

A green scale inhibitor, polyaspartic acid, is reported for the first time to effectively inhibit struvite formation and promote struvite dissolution.

Microwave-assisted preparation of sepiolite-supported magnetite nanoparticles and their ability to remove low concentrations of Cr(vi)

A sepiolite–nanomagnetite composite obtained by a facile microwave-assisted route can not only remove low concentrations of Cr(vi), but also effectively immobilize the secondary Fe³⁺in the final solution.

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.

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.

The Properties of Serum GPI-PLD

The purified glycosylphosphatidylinositol phospholipase D (GPI-PLD) is a single-polypeptide with a molecular weight of about 1OO kD. However, the enzyme is eluted in the fraction of 500 kD when human serum undergoes gel filtration chromatography. To study the natural state of GPI-PLD might help to visualize its physiological function. By using gel filtration, hydrophobic column chromatography and ultracentrifugation, and analyzing the concentration of phospholipids, triglycerides and cholesterol, we found that GPI-PLD did not exist as polymer of polypeptids in serum, but combined with the serum lipids to form a complex of lipids and proteins. As a result, it is present in a density zone similar to HDL after ultracentrifugation, this complex exists in serum separately from the subfractions of HDL which are abundant in Apo-A1. In addition it could bind on the heparin-Sepharose affinity chromatography column as Apo-E.

Deinococcus radiodurans CatB Gene Cloning and Expression in Escherichia coli

A 1 611 bp length complete coding sequence of the catalase (Cat) was obtained through bioimformatical analysis of the database of D.radiodurans genome, and then was amplified from D. radiodurans genomic DNA by polymerase chain reaction. The amplified gene was cloned into pKK223-3 vector and transformed into E.coli UM2, a Cat-deficient mutant. Staining of non-denaturing polyacrylamide gels for Cat activity demonstrated that pKK223-3 insert encoded a Cat that co-migrated with the CatB found in D.radiodurans cell lysates. Expression of CatB gene from D.radiodurans in E.coli UM2 restored the resistance to H(2)O(2) at low concentrations.

Isolation and Characterization of a Type 1 Ribosome-Inactivating Protein from Fruiting Bodies of the Edible Mushroom (Volvariella volvacea)

A novel single-chained ribosome-inactivating protein (RIP) with a molecular weight of approximately 29 000 was purified from fruiting bodies of the edible mushroom Volvariellavolvacea with a procedure involving ammonium sulfate precipitation, ion-exchange chromatography on DEAE-cellulose, and gel filtration on Superdex 75. The mushroom RIP, designated volvarin, exhibited a potent inhibitory action on protein synthesis in the rabbit reticulocyte lysate system with an IC(50) value of 0.5 nM. Like most plant RIPs, volvarin acted as an N-glycosidase that depurinated rRNA from rabbit reticulocyte lysate, releasing a characteristic RNA fragment after treatment with aniline. It also exerted a deoxyribonuclease activity on supercoiled SV-40 DNA and demonstrated a strong abortifacient effect in mice.

Demonstration of ribonuclease activity in the plant ribosome-inactivating proteins alpha- and beta-momorcharins

Alpha- and beta-momorcharins, ribosome-inactivating proteins from Momordica charantia seeds, were utilized in this investigation. Ribonucleolytic cleavage was observed after naked rRNA was incubated with either momorcharin. Beta-momorcharin, and to a lesser extent alpha-momorcharin, also acted on tRNA to release acid-soluble UV-absorbing products. Such activity was optimal at pH around 5.5. Using polyhomoribonucleotides as substrate, it was found that the momorcharins preferentially acted on polyU, but exerted negligible effects on polyA, polyC and polyG. Chromatographic analysis of the reaction product indicated that mono and/or oligo-ribonucleotides, but not free base, were generated from polyU, suggesting that the enzymatic action involved ribonucleolytic cleavage. Similar to the results obtained with tRNA as substrate, beta-momorcharin was about 15-fold more active than alpha-momorcharin on polyU.

A highly efficient procedure for purifying the ribosome-inactivating proteins alpha- and beta-momorcharins from Momordica charantia seeds, N-terminal sequence comparison and establishment of their N-glycosidase activity

A new purification scheme, involving two successive ion exchange chromatographic steps on DEAE-cellulose and Mono-S FPLC, was developed for the isolation of the ribosome-inactivating proteins, alpha- and beta-momorcharins, from the Chinese herb Kuquazi (seeds of Momordica charantia). This simple and rapid procedure yielded 3.1 and 1.7 mg of alpha- and beta-momorcharins, respectively, from 2.5 g of decorticated seeds in only two days. The N-terminal amino acid sequence of beta-momorcharin was found to be DVNFDLSTATAKTYTKFIED. It differed from that of alpha-momorcharin (DVSFRLSGADPRSYGMFIKD) in 10 out of the 20 positions investigated. Like other ribosome-inactivating proteins, the purified momorcharins showed specific N-glycosidase activity at nanomolar concentrations, when rRNA from rabbit reticulocyte lysate was used as substrate. The N-glycosidase activity of both momorcharins was optimal at pH7, not inhibited by K+ and not appreciably affected by NH4+. The activity of alpha-momorcharin was not drastically altered by Mn2+ but (1-10mM) Mn2+ inhibited the activity of beta-momorcharin by about 40%.

Creatine kinase is modified by 2-chloromercuri-4-nitrophenol at the active site thiols with complete inactivation

Creatine kinase modified by mercurials has been reported to be fully reactive as the native enzyme. This was ascribed to the modification of a second class of thiol groups instead of the reactive thiols at the active site (Laue, M.C. and Quiocho, F.A. (1977) Biochemistry 16, 3838-3845). It has now been shown by spectrophotometric titration and fluorescence studies that 2-chloromercuri-4-nitrophenol (MNP) reacts preferentially with the active-site thiol. Moreover, if the activity of the modified enzyme is determined in the absence of added bovine serum albumin or other enzymes, as usually employed in coupled activity assay systems for creatine kinase, the modified enzyme is completely inactive. Addition of an excess of bovine serum albumin or rabbit muscle glyceraldehyde-3-phosphate dehydrogenase restores the activity of the enzyme to over 80% of its original level. It appears that the active thiol groups at the active site of creatine kinase are after all modified by MNP with complete inactivation.

C-terminal angiogenin peptides inhibit the biological and enzymatic activities of angiogenin

Synthetic peptides corresponding to the C-terminal region of angiogenin (Ang) inhibit the enzymatic and biological activities of the molecule while peptides from the N-terminal region do not affect either activity. The peptide Ang(108-121) transiently abolishes the inhibition of cell-free protein synthesis caused by angiogenin coincidentally with its cleavage of reticulocyte RNA. Several C-terminal peptides also inhibit nuclease activity of angiogenin when tRNA is the substrate. Furthermore, peptide Ang(108-123) significantly decreases neovascularization elicited by angiogenin in the chick chorioallantoic membrane assay.

Angiogenin mRNA in human tumor and normal cells

Angiogenin mRNA was characterized in HT-29 human colon adenocarcinoma cells and its distribution in other human cell types was studied. Several RNA species ranging from 800 to 6000 nucleotides hybridized to the angiogenin probes with the smallest being the major poly(A)-containing transcript. This transcript was detected in tumor cells of diverse cellular origin. Expression of angiogenin mRNA is not limited to neoplastic cells and is detected in normal epithelial cells, fibroblasts and peripheral blood cells. The latter, when induced by mitogens, expressed more mRNA than did unstimulated or HT-29 cells. Transformed fibroblasts did not contain higher levels of angiogenin mRNA than their normal counterparts, demonstrating that increased angiogenin mRNA expression does not necessarily occur upon neoplastic transformation. This study demonstrates that angiogenin mRNA is expressed in a wide spectrum of cells and is not correlated to a particular cell phenotype.

Changes in circular dichroism and exposure of buried thiol groups during denaturation of rabbit muscle creatine kinase

The denaturation of creatine kinase in guanidine solutions has been followed by both CD changes and the increase in rapid reacting SH groups. The rates of the exposure of SH groups are in general agreement with the ultraviolet absorbance and fluorescence changes reported previously whereas changes in the ellipticity of the enzyme molecule can be detected at low guanidine concentrations before significant changes in the exposure of the aromatic residues could be observed. On the other hand, the rates of changes in the mean residue ellipticity at 220 nm are clearly slower than the changes in ultraviolet absorbance, fluorescence and exposure of SH groups. It is suggested that the secondary structure of the external regions of the peptide chains is affected at low guanidine concentrations followed by gross changes in the tertiary structure of the molecule resulting in the exposure of the buried aromatic residues. The destruction of ordered secondary structure of the peptide chain is a slower process than the opening up of the folded tertiary structure of the molecule.

Comparison of the rates of inactivation and conformational changes of creatine kinase during urea denaturation

The denaturation of creatine kinase in urea solutions of different concentrations has been studied by following the changes in the ultraviolet absorbance and intrinsic fluorescence as well as by the exposure of hidden SH groups. In concentrated urea solutions, the denaturation of the enzyme results in negative peaks at 285 nm with shoulders at 280 and 290 nm and positive peaks at 244 and 302 nm in the denatured minus native enzyme difference spectrum. The fluorescence emission maximum of the enzyme red shifts with increasing intensity in urea solutions of increasing concentrations. At least part of these changes can be attributed to direct effects of urea on the exposed Tyr and Trp residues as shown by experiments with model compounds. The inactivation of this enzyme has been followed and compared with the conformational changes observed during urea denaturation. A marked decrease in enzyme activity is already evident at low urea concentrations before significant conformational changes can be detected by the exposure of hidden SH groups or by ultraviolet absorbance and fluorescence changes. At higher urea concentrations, the enzyme is inactivated at rates 3 orders of magnitude faster than the rates of conformational changes. The above results are in accord with those reported previously for guanidine denaturation of this enzyme [Yao, Q., Hou, L., Zhou, H., & Tsou, C.-L. (1982) Sci. Sin. (Engl. Ed.) 25, 1186-1193] and can best be explained by assuming that the active site of this enzyme is situated near the surface of the enzyme molecule and is sensitive to very slight conformational changes.

A comparison of denaturation and inactivation rates of creatine kinase in guanidine solutions

Both the denaturation, as followed by UV absorbance and fluorescence changes, and inactivation of creatine kinase in guanidine solutions have been found to be first order reactions. In 3 M guanidine, at 30 degrees C, the inactivation rate constant was found to be 5.9 sec-1 and the denaturation rate constant 1.9 sec-1. At lower guanidine concentrations, the inactivation rate constants were only little affected whereas the denaturation rate constants decreased markedly, being of the order of 0.04 in 1 M and 0.004 in 0.5 M guanidine. The kinetics of the inactivation reaction in 0.5 M guanidine was found to be in agreement with a combination of two first order reactions. The enzyme lost activity first by a fast reaction with a rate constant only slightly lower than the rate constant in 3 M guanidine followed by a slower reaction with a rate constant of 0.003 sec-1. In 0.3 M guanidine, very little change in either UV absorbance or in fluorescence was observed, but, in sharp contrast, the enzyme lost considerable activity by a fast reaction and this was followed by a slower reaction of inactivation. Even after prolonged denaturation in 0.5 and 0.3 M guanidine, residual activities of 3.4% and 30% remained respectively. The above results suggest a very fragile active site although dissociation of the dimer and reversible guanidine inhibition may also contribute to the initial rapid inactivation. It is also to be noted that the multiphasic courses of inactivation at lower guanidine concentrations seem to suggest the presence of partly active intermediates during denaturation.

Conformational changes of creatine kinase during guanidine denaturation

The conformational changes of creatine kinase during denaturation by different concentrations of guanidine hydrochloride have been studied by fluorescence and ultraviolet difference spectroscopic methods. At low concentrations of guanidine, less than 1 M, the denatured minus native difference spectra showed two negative peaks at 281 and 287 nm, whereas the fluorescence emission increased markedly with its maximum red-shifted from 337 to 345 nm. Control experiments showed that guanidine also increased the emission of ionized tyrosine at 345 nm. With the increase of concentrations of guanidine, both negative peaks at 281 and 287 nm increased in magnitude to reach maximal values at 3 M guanidine and at this time a small peak appeared at 292 nm. The fluorescence maximum was further red-shifted to 355 nm, whereas the emission intensity of the main peak decreased and a small shoulder appeared at 310 nm when the guanidine concentration increased from 1 to 3 M. Further increase in guanidine concentration produced little further change either in UV absorption or in fluorescence. From the above results, it seems that, in the native enzyme. Trp residues are partly buried and partly exposed and some of the Tyr residues are in ionized state. Guanidine below 1 M does not expose the buried Trp residues nor affects significantly the microenvironments of the ionized Tyr residues. At 3 M guanidine, Trp residues are exposed and the ionization state of Tyr residues is also affected. At this concentration, the peptide chain seems to be fully unfolded as evidenced by the fact that 5 M guanidine produces little further change in both UV absorption and fluorescence.