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1.
Chemosphere ; 254: 126916, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32957301

RESUMO

4-Nonylphenol (4-NP), a phenolic endocrine disruptor chemical (EDC), is known to have high toxicity to aquatic organisms and humans. The remediation of 4-NP-contaminated marine sediments was studied using red algae-based biochar (RAB) thermochemically synthesized from Agardhiella subulata with simple pyrolysis process under different temperatures of 300-900 °C in CO2 atmosphere. The RAB was characterized by XRD, Raman, FTIR spectroscopy, and zeta potential measurements. The calcium in RAB efficiently activated sodium percarbonate (SPC) to generate reactive radicals for the catalytic degradation of 4-NP at pH 9.0. The oxygen-containing functional groups reacted with H2O2, which increased the generation of reactive radicals under alkaline pH condition. Ca2+ ion was the active species responsible for 4-NP degradation. CaO/CaCO3 on RAB surface enhanced direct electron transfer, increased HO production, and 4-NP degradation in marine sediments. Langmuir‒Hinshelwood type kinetics well described the 4-NP degradation process. Remediation of contaminated sediments using RAB could be a sustainable approach toward closed-loop biomass cycling in the degradation of 4-NP contaminants.


Assuntos
Carvão Vegetal/química , Disruptores Endócrinos/análise , Recuperação e Remediação Ambiental/métodos , Sedimentos Geológicos/química , Fenóis/análise , Rodófitas/química , Poluentes Químicos da Água/análise , Biomassa , Carbonatos/química , Catálise , Humanos , Peróxido de Hidrogênio/química , Cinética
2.
Ecotoxicol Environ Saf ; 204: 110977, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32739673

RESUMO

Indirect oxidation induced by reactive free radicals, such as hydroxyl radical (HO), sulfate radical (SO4-) and carbonate radical (CO3-), plays an important or even crucial role in the degradation of micropollutants. Thus, the coadjutant degradation of phenacetin (PNT) by HO, SO4- and CO3-, as well as the synergistic effect of O2 on HO and HO2 were studied through mechanism, kinetics and toxicity evaluation. The results showed that the degradation of PNT was mainly caused by radical adduct formation (RAF) reaction (69% for Г, the same as below) and H atom transfer (HAT) reaction (31%) of HO. For the two inorganic anionic radicals, SO4- initiated PNT degradation by sequential radical addition-elimination (SRAE; 55%), HAT (28%) and single electron transfer (SET; 17%) reactions, while only by HAT reaction for CO3-. The total initial reaction rate constants of PNT by three radicals were in the order: SO4- > HO > CO3-. The kinetics of PNT degradation simulated by Kintecus program showed that UV/persulfate could degrade target compound more effectively than UV/H2O2 in ultrapure water. In the subsequent reaction of PNT with O2, HO and HO2, the formation of mono/di/tri-hydroxyl substitutions and unsaturated aldehydes/ketones/alcohols were confirmed. The results of toxicity assessment showed that the acute and chronic toxicity of most products to fish increased and to daphnia decreased, and acute toxicity to green algae decreased while chronic toxicity increased.


Assuntos
Carbonatos/toxicidade , Peróxido de Hidrogênio/toxicidade , Fenacetina/toxicidade , Sulfatos/toxicidade , Testes de Toxicidade Aguda , Testes de Toxicidade Crônica , Animais , Carbonatos/química , Clorófitas/efeitos dos fármacos , Daphnia/efeitos dos fármacos , Peixes , Peróxido de Hidrogênio/química , Íons/química , Íons/toxicidade , Cinética , Modelos Químicos , Oxigênio/química , Fenacetina/química , Sulfatos/química , Água/química
3.
Nature ; 583(7814): 66-71, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32612224

RESUMO

Dental enamel is a principal component of teeth1, and has evolved to bear large chewing forces, resist mechanical fatigue and withstand wear over decades2. Functional impairment and loss of dental enamel, caused by developmental defects or tooth decay (caries), affect health and quality of life, with associated costs to society3. Although the past decade has seen progress in our understanding of enamel formation (amelogenesis) and the functional properties of mature enamel, attempts to repair lesions in this material or to synthesize it in vitro have had limited success4-6. This is partly due to the highly hierarchical structure of enamel and additional complexities arising from chemical gradients7-9. Here we show, using atomic-scale quantitative imaging and correlative spectroscopies, that the nanoscale crystallites of hydroxylapatite (Ca5(PO4)3(OH)), which are the fundamental building blocks of enamel, comprise two nanometric layers enriched in magnesium flanking a core rich in sodium, fluoride and carbonate ions; this sandwich core is surrounded by a shell with lower concentration of substitutional defects. A mechanical model based on density functional theory calculations and X-ray diffraction data predicts that residual stresses arise because of the chemical gradients, in agreement with preferential dissolution of the crystallite core in acidic media. Furthermore, stresses may affect the mechanical resilience of enamel. The two additional layers of hierarchy suggest a possible new model for biological control over crystal growth during amelogenesis, and hint at implications for the preservation of biomarkers during tooth development.


Assuntos
Amelogênese , Esmalte Dentário/química , Ácidos/química , Cálcio/química , Carbonatos/química , Cristalização , Teoria da Densidade Funcional , Esmalte Dentário/ultraestrutura , Durapatita/química , Fluoretos/química , Humanos , Magnésio/química , Microscopia Eletrônica de Transmissão e Varredura , Sódio/química , Tomografia , Difração de Raios X
4.
Environ Geochem Health ; 42(11): 3819-3839, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32601907

RESUMO

Monitoring the groundwater chemical composition and identifying the presence of pollutants is an integral part of any comprehensive groundwater management strategy. The present study was conducted in a part of West Tripura, northeast India, to investigate the presence and sources of trace metals in groundwater and the risk to human health due to direct ingestion of groundwater. Samples were collected from 68 locations twice a year from 2016 to 2018. Mixed Ca-Mg-HCO3, Ca-Cl and Ca-Mg-Cl were the main groundwater types. Hydrogeochemical methods showed groundwater mineralization due to (1) carbonate dissolution, (2) silicate weathering, (3) cation exchange processes and (4) anthropogenic sources. Occurrence of faecal coliforms increased in groundwater after monsoons. Nitrate and microbial contamination from wastewater infiltration were apparent. Iron, manganese, lead, cadmium and arsenic were above the drinking water limits prescribed by the Bureau of Indian Standards. Water quality index indicated 1.5% had poor, 8.7% had marginal, 16.2% had fair, 66.2% had good and 7.4% had excellent water quality. Correlation and principal component analysis reiterated the sources of major ions and trace metals identified from hydrogeochemical methods. Human exposure assessment suggests health risk due to high iron in groundwater. The presence of unsafe levels of trace metals in groundwater requires proper treatment measures before domestic use.


Assuntos
Água Subterrânea/análise , Metais/análise , Oligoelementos/análise , Poluentes Químicos da Água/análise , Qualidade da Água , Carbonatos/análise , Carbonatos/química , Exposição Dietética/efeitos adversos , Exposição Dietética/análise , Água Potável/análise , Monitoramento Ambiental/métodos , Fezes/microbiologia , Água Subterrânea/química , Água Subterrânea/microbiologia , Humanos , Hidrologia/métodos , Índia , Nitratos/análise , Medição de Risco/métodos , Águas Residuárias/análise , Águas Residuárias/microbiologia , Microbiologia da Água
5.
Chemosphere ; 260: 127460, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32673866

RESUMO

Advanced oxidation processes (AOPs), such as photolysis, photocatalysis, ozonation, Fenton process, anodic oxidation, sonolysis, and wet air oxidation, have been investigated extensively for the removal of a wide range of trace organic contaminants (TrOCs). A standalone AOP may not achieve complete removal of a broad group of TrOCs. When combined, AOPs produce more hydroxyl radicals, thus performing better degradation of the TrOCs. A number of studies have reported significant improvement in TrOC degradation efficiency by using a combination of AOPs. This review briefly discusses the individual AOPs and their limitations towards the degradation of TrOCs containing different functional groups. It also classifies integrated AOPs and comprehensively explains their effectiveness for the degradation of a wide range of TrOCs. Integrated AOPs are categorized as UV irradiation based AOPs, ozonation/Fenton process-based AOPs, and electrochemical AOPs. Under appropriate conditions, combined AOPs not only initiate degradation but may also lead to complete mineralization. Various factors can affect the efficiency of integrated processes including water chemistry, the molecular structure of TrCOs, and ions co-occurring in water. For example, the presence of organic ions (e.g., humic acid and fulvic acid) and inorganic ions (e.g., halide, carbonate, and nitrate ions) in water can have a significant impact. In general, these ions either convert to high redox potential radicals upon collision with other reactive species and increase the reaction rates, or may act as radical scavengers and decrease the process efficiency.


Assuntos
Poluentes Químicos da Água/análise , Purificação da Água , Benzopiranos , Carbonatos/química , Substâncias Húmicas , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Oxirredução , Fotólise , Raios Ultravioleta
6.
Chemosphere ; 257: 127223, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32534295

RESUMO

The degradation performance of trichloroethylene (TCE) by sodium percarbonate (SPC) activated with citric acid (CA) chelated Fe(II) in the presence of nonionic surfactant Tween-80 was investigated. The addition of CA successfully prevented the precipitation of iron and facilitated TCE degradation. However, Tween-80 had an inhibitory effect on TCE degradation mainly due to the competition of ∗OH between Tween-80 and TCE. The effect of SPC and Fe(II) dosage on TCE degradation was also explored and the results displayed that 87.2% of TCE could be degraded in 15 min at the SPC/Fe(II)/CA/TCE molar ratio of 3/4/2/1. Free radical probe tests confirmed that both O2-∗ and ∗OH were generated in the SPC/Fe(II)/CA system. Free radical scavenging tests implied that the degradation of TCE in the SPC/Fe(II)/CA system was mainly attributed to ∗OH, while O2-∗ was only partially involved in the degradation of TCE. In addition, TCE removal was suppressed with the raising of the initial solution pH from 3.0 to 9.0. The actual groundwater (containing Tween-80) tests confirmed that 93.2% of TCE degradation could be achieved at the SPC/Fe(II)/CA/TCE molar ratio of 30/40/10/1 and strongly demonstrated that the SPC/Fe(II)/CA process has potential for the in situ treatment of TCE contaminated groundwater in the presence of surfactant Tween-80. In conclusion, TCE degradation by Fe(II) activated SPC system in the presence of Tween-80 can be significantly enhanced with the addition of CA, and this finding offers an innovative direction for removing chlorinated organic contaminants from groundwater in contaminated site after surfactant solubilization treatment.


Assuntos
Carbonatos/química , Tensoativos/química , Tricloroetileno/química , Poluentes Químicos da Água/química , Quelantes , Ácido Cítrico , Compostos Ferrosos/química , Água Subterrânea , Ferro , Oxirredução , Polissorbatos , Surfactantes Pulmonares , Poluentes Químicos da Água/análise
7.
PLoS One ; 15(6): e0234136, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32520947

RESUMO

Groundwater treatment sludge is a Fe/Mn-bearing waste that is mass produced in groundwater treatment plant. In this study, sludge was converted to a magnetic adsorbent (MA) by adding ascorbate. The sludge was weakly magnetised in the amorphous form with Fe and Mn contents of 28.8% and 8.1%, respectively. After hydrothermal treatment, Fe/Mn oxides in the sludge was recrystallised to siderite and rhodochrosite, with jacobsite as the intermediate in the presence of ascorbate. With an increment in ascorbate dosage, the obtained magnetic adsorbent had a significant increase in chromate adsorption but a decrease in magnetisation. When the Mascorbate/MFe molar ratio was 10, the produced MA-10 was a dumbbell-shaped nanorod with a length of 2-5 µm and a diameter of 0.5-1 µm. This MA-10 showed 183.2 mg/g of chromate adsorption capacity and 2.81 emu/g of magnetisation. The mechanism of chromate adsorption was surface coprecipitation of the generated Cr3+ and Fe3+/Mn4+ from redox reaction between chromate and siderite/rhodochrosite on MA-10, separately. This study demonstrated an efficient recycling route of waste sludge from groundwater treatment to produce MA for treating chromate-bearing wastewater.


Assuntos
Cromatos/química , Magnetismo , Nanotubos/química , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/química , Adsorção , Carbonatos/química , Compostos Férricos/química , Ferro/química , Cinética , Manganês/química , Oxirredução , Óxidos/química
8.
Chemosphere ; 255: 127010, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32416397

RESUMO

The present work demonstrated the invention of synergistically strengthen of chemical and biological removal of phosphorus (P) in biological wastewater treatment, which was achieved by exposure the bioreactors to different levels of La-based-adsorbents. We fabricated a high-performance La2O2CO3 micro-adsorbent (H-La2O2CO3) and added it into sequencing batch reactors. When activated sludge was exposed to 40 mg/L H-La2O2CO3 for 40 d, effluent total phosphorus (TP) concentration significantly decreased to approximately 0.18 mg/L, with the steady removal efficiency of 96.4%, which is superior to the biological phosphorus removal (BPR). The effect of H-La2O2CO3 dosages on P removal in biological wastewater treatment was also detailedly investigated. The H-La2O2CO3 adsorbent could not only capture P by chemical bonding itself, but also increased protein (PN) contents of extracellular polymeric substances (EPS) and changed the functional group of EPS to chemically adsorb P. Additionally, the results of 16s rDNA molecular analysis revealed that the species richness and microbial diversity varied with the different dosages of adsorbent. Sequence analyses showed that the appropriate concentration of H-La2O2CO3 addition increased the contents of several polyphosphate accumulating organisms (PAOs) at genus level in sludge.


Assuntos
Reatores Biológicos/microbiologia , Carbonatos/química , Lantânio/química , Fósforo/análise , Esgotos/química , Águas Residuárias/química , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Adsorção , Microbiota/efeitos dos fármacos , Polifosfatos/análise , RNA Ribossômico 16S , Esgotos/microbiologia , Águas Residuárias/microbiologia
9.
J Chromatogr A ; 1624: 461172, 2020 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-32376027

RESUMO

The enantiomers of a chiral building block to be used in pre-clinical manufacturing were separated using supercritical fluid chromatography (SFC). Despite an extensive evaluation of different columns and solvent combinations followed by a careful optimization of the chromatographic method, the preparative separation suffered from low throughput and high solvent consumption. Consequently, additional improvements were necessary. By utilizing stacked injections, the chromatographic run time was almost halved, and the high solvent consumption was reduced by recycling of the two mobile phase components, carbon dioxide and methanol. The carbon dioxide was reprocessed by the SFC instrument, whereas methanol was evaporated and recycled from the fractions collected. Hence, the originally inefficient separation method was turned into a more sustainable one, and the desired enantiopure intermediate was delivered to be used in the following synthesis of the selected candidate drug. Unfortunately, when the intermediate was used in the subsequent amide coupling, a surprisingly poor yield was obtained. This was caused by an unexpected formation of a stable carbonate salt of the intermediate under the chromatographic conditions used. By removal of the carbonate prior to the amide coupling reaction, the manufacturing campaign could be saved, and the candidate drug was successfully delivered in time.


Assuntos
Carbonatos/química , Cromatografia com Fluido Supercrítico/métodos , Dióxido de Carbono/química , Metanol/química , Sais , Solventes/química , Estereoisomerismo
10.
J Chromatogr A ; 1622: 461095, 2020 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-32334852

RESUMO

A two-membrane electrodialytic carbonate eluent generator (EDG) for ion chromatography (IC) is described. It is in a sandwich-like configuration, in which the central eluent channel is spatially isolated from two outer regenerant channels by stacked cation exchange membranes (CEMs) and anion exchange membranes (AEMs). A platinum screen electrode is placed in each of two outer regenerant channels. The electrode at the CEMs side is set as an anode with respect to the electrode at the AEMs side being cathode. Potassium carbonate and/or bicarbonate solution is pumped into the regenerant channel as feed solution. The electromigration of carbonate and/or bicarbonate and potassium from feed solution respectively through AEMs and CEMs will form a gas-free eluent. With this configuration, ion transport behavior through AEMs was explored. The device demonstrated good reproducibility, as indicated by the relative standard deviation of retention time of less than 0.08%.


Assuntos
Carbonatos , Técnicas de Química Analítica , Cromatografia por Troca Iônica , Bicarbonatos/química , Carbonatos/química , Cátions/química , Técnicas de Química Analítica/instrumentação , Técnicas de Química Analítica/métodos , Cromatografia por Troca Iônica/instrumentação , Eletrodos , Potássio/química , Reprodutibilidade dos Testes
11.
Chemosphere ; 251: 126254, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32155499

RESUMO

Due to its toxicity and persistence, pesticide pollution poses a serious threat to human health and the environment. Imidacloprid or IMD is an archetypal neonicotinoid insecticide commonly used to protect a variety of crops worldwide. The present study examines the applicability of two numerical tools -- artificial neural network (ANN) and response surface methodology - Box Behnken design (RSM-BBD) -- to model and optimize oxidative IMD degradation by sodium percarbonate (SPC). The influences of SPC dose, Fe2+ catalyst dosage, and solution pH on IMD removal were evaluated. An ANN composed of an input layer with three neurons, a hidden layer with eight optimum neurons, and an output layer with one neuron was developed to map the complex non-linear process at different levels. Seventeen designed runs of different experimental conditions were derived from RSM-BBD. These experimental conditions and their response values showed to be best fitted in a reduced cubic model equation. Sensitivity analyses revealed the relative importance of the various components: Fe2+ (40.4%) > pH (31.1%) > SPC dose (28.5%). The two model were highly predictive with overall coefficients of determination and root-mean-square errors of 0.9983 and 0.31 for ANN, while 0.9996 and 0.20 for RSM-BBD. Overall, the present study established ANN and RSM-BBD as valuable and effective tools for catalytic SPC oxidation of IMD contaminants. SPC is a cleaner alternative to other oxidants for pesticide degradation as it is non-toxic, safe to handle, and produces by-products that inherently exist in the natural water matrix.


Assuntos
Carbonatos/química , Modelos Químicos , Neonicotinoides/química , Redes Neurais de Computação , Nitrocompostos/química , Catálise , Oxidantes , Oxirredução , Projetos de Pesquisa
12.
Carbohydr Polym ; 235: 115938, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32122480

RESUMO

Solvent-free protocols using microwave-assisted heating (i) or conventional heating without additives (ii) or adding K2CO3 (iii), or triturating at room temperature in the presence of K2CO3 (iv) were first used to esterify glycosaminoglycans (GAG) with maleic anhydride. High and low molecular weight hyaluronic acid (HMW and LMW HA), dermatan sulfate (Ds), heparin (HEP) and C6-oxidized HA (carboxy-HA) were used as substrates for maleation. Protocols (i)-(iii) were most effective for obtaining maleates with high DS (1.39-2.47), but had a strong degrading effect on GAG. Protocol (iv) did not have destructive effect, but was suitable for obtaining only HMW HA maleate (DS 0.71-1.15). Primary hydroxyl groups of HA and Ds showed a higher reactivity compared to the secondary ones. A specific feature of the HEP maleation was substitution of N-sulfate groups for N-maleate groups. To demonstrate the potential of the obtained maleates for thiol-ene click-chemical strategies, the reaction with l-cysteine was performed.


Assuntos
Glicosaminoglicanos/química , Ácido Hialurônico/química , Maleatos/síntese química , Carbonatos/química , Calefação , Ácido Hialurônico/síntese química , Maleatos/química , Micro-Ondas , Estrutura Molecular , Potássio/química
14.
Chemosphere ; 249: 126115, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32045756

RESUMO

The BCR sequential extraction scheme (SES), initially developed for soils and sediments, is frequently adopted to evaluate the environmental risks of municipal solid waste incineration (MSWI) fly ash. Within the procedure, metals are liberated from the matrix hosting them relying on the selectivity of the chosen chemical reagents or operation conditions. However, the effect of the high content of alkaline substances in MSWI fly ash on the selectivity of acetic acid to acid-soluble fraction metals was ignored. In this study, the feasibility of the BCR SES for evaluating MSWI fly ash was assessed by adjusting the acetic acid washing times in the acid-soluble extraction step. The metal fractionation, as well as mineralogy, morphology, and surface chemistry of the residues after three successive acid washing processes, were analyzed. The results reveal that only easily soluble salts, but not hydroxides, are entirely extracted after the first acid washing (pH∼12.0). Importantly, carbonates (generally reported as an indicator of the complete release of acid-soluble metals) are mostly decomposed only after the third acid washing (pH∼3.8). The incomplete dissolution of calcium carbonates in a single-step acid washing may convey misleading results of metal fractionation and underestimates the environmental risk of potentially toxic elements. Therefore, complete removal of carbonates should be employed as the endpoint of the acid-soluble fraction extraction step in the evaluation of MSWI fly ash. This work can help in selecting proper strategies for fly ash management and developing proper sequential extraction schemes for similar high-alkalinity hazardous waste risk assessment.


Assuntos
Incineração/métodos , Metais Pesados/análise , Carbono/química , Carbonatos/química , Fracionamento Químico , Cinza de Carvão/química , Material Particulado/química , Eliminação de Resíduos , Sais , Resíduos Sólidos/análise , Oligoelementos/análise
15.
Molecules ; 25(4)2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-32093407

RESUMO

The ß-amyloid (Aß) peptide plays a key role in the pathogenesis of Alzheimer's disease. The methionine (Met) residue at position 35 in Aß C-terminal domain is critical for neurotoxicity, aggregation, and free radical formation initiated by the peptide. The role of Met in modulating toxicological properties of Aß most likely involves an oxidative event at the sulfur atom. We therefore investigated the one- or two-electron oxidation of the Met residue of Aß25-35 fragment and the effect of such oxidation on the behavior of the peptide. Bicarbonate promotes two-electron oxidations mediated by hydrogen peroxide after generation of peroxymonocarbonate (HCO4-, PMC). The bicarbonate/carbon dioxide pair stimulates one-electron oxidations mediated by carbonate radical anion (CO3•-). PMC efficiently oxidizes thioether sulfur of the Met residue to sulfoxide. Interestingly, such oxidation hampers the tendency of Aß to aggregate. Conversely, CO3•- causes the one-electron oxidation of methionine residue to sulfur radical cation (MetS•+). The formation of this transient reactive intermediate during Aß oxidation may play an important role in the process underlying amyloid neurotoxicity and free radical generation.


Assuntos
Peptídeos beta-Amiloides/química , Carbonatos/química , Radicais Livres/química , Fragmentos de Peptídeos/química , Agregados Proteicos , Humanos , Oxirredução
16.
Appl Microbiol Biotechnol ; 104(8): 3655-3673, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32095860

RESUMO

Bacterially induced precipitation of minerals leading to cementation of natural geological formations has been well recorded in a variety of environments. A range of microbial pathways and geochemical processes have been found to influence the cementation processes; but detailed formation mechanisms and biogeochemical relationships are still not very clear. There has been a growing demand for the application of bacterially driven biocementation in a number of geotechnical engineering applications recently. Here, we aimed to unpin the mechanisms behind the formation of actively mineralising beachrock sediments at Lucky Bay in Western Australia to understand the natural accretionary processes and potential of indigenous bacterial communities in biocementation. We observed ferruginous, aluminosilicate and carbonate cements along with extensive extra polymeric substances, borings with possible microbial activities in certain sections of native beachrock sediments. Cement precipitation under calcium- and iron-rich microenvironments sourced from seawater and iron creek seems to be driven by both biogenic and abiogenic processes in nature. Native microbial communities with a dominance of the genera Halococcus and Marinobacter were recorded. Enrichment of native bacterial communities under seawater media conditions was conducted which lead to successful biomineralisation of calcitic and ferruginous cements under in vitro conditions although the community composition changed significantly. Nanomechanical properties of natural and laboratory synthesised cement crystals showed that engineered biocement is highly promising. The results of this study clearly demonstrate biological influence in the formation of natural cements and hint significant potential of biostimulation which can be harnessed for different engineering applications including coastal erosion.


Assuntos
Bactérias/química , Sedimentos Geológicos/microbiologia , Microbiota , Carbonato de Cálcio/química , Carbonatos/química , Minerais/química , Água do Mar/microbiologia , Austrália Ocidental
17.
Artigo em Inglês | MEDLINE | ID: mdl-32003307

RESUMO

Synthesis of hydroxyapatite coated activated carbon nanocomposite was carried out by in-situ chemical precipitation method. Different characterizations confirm that, hydroxyapatite successfully coated over activated carbon powder. Extensive sorption studies of U(VI) on the nanocomposite were conducted to know the effect of contact time, humic acid, carbonate, ionic strength and pH. The study revealed that, the composite material is a more efficient sorbent for U(VI) compared to precursors, which removes U(VI) ion without altering physicochemical properties of water. Sorption exhibits multilayer adsorption on heterogeneous surface and follows chemisorptions. Practical applicability of the material was demonsteted by spiking tap water with U(VI) ion at three different initial concentrations (50, 100 and 150 µg L-1) and the tap water was allowed to passed through a cartridge packed with composite. It was observed that, the concentration of U(VI) ion in eluted water reduced to 98.28%, 96.20% and 97.40%, respectively. This revealed that, the material possesses a huge potential for sequestrating dissolved U(VI) ion and can be used as alternate filtering material for dissolved U(VI) in complex natural water system.


Assuntos
Carvão Vegetal/química , Durapatita/química , Nanocompostos/química , Urânio/análise , Poluentes Radioativos da Água/análise , Purificação da Água/métodos , Adsorção , Carbonatos/química , Substâncias Húmicas/análise , Concentração de Íons de Hidrogênio , Modelos Teóricos , Concentração Osmolar , Pós
18.
Molecules ; 25(2)2020 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-31963280

RESUMO

Considered to be the next generation of heat transfer fluids (HTFs), nanofluids have been receiving a growing interest over the past decade. Molten salt nanofluids have been shown to have great potential as an HTF for use in high temperature applications such as direct absorption solar collector (DAC) system. Very few studies using molten salt nanofluids as the HTF in a DAC receiver can be found in the open literature. This study aimed to develop a 3D computational fluid dynamics model of the receiver of a DAC using graphite-nanoparticle-dispersed Li2CO3-K2CO3 molten salt nanofluid to investigate the effects of design and operation parameters on receiver performance. Receiver total efficiency using Li2CO3-K2CO3 salt was compared with that using solar salt nanofluid. Spectral properties of the base fluid and nanoparticles were modeled as wavelength-dependent and the absorption of the solar radiation was modeled as a volumetric heat release in the flowing heat transfer fluid. Initial results show that the receiver efficiency increases with increasing solar concentration, decreasing nanoparticle volume fraction, and decreasing receiver length. It was also found that the Carnot efficiency increases with increasing receiver length and nanoparticle volume fraction, and decreasing solar concentration and inlet velocity. Comparative study shows that solar salt HTF could provide higher total efficiency. However, a higher operating temperature of Li2CO3-K2CO3 will allow for a greater amount of thermal energy storage for a smaller volume of liquid.


Assuntos
Carbonatos/química , Grafite/química , Carbonato de Lítio/química , Nanopartículas/química , Potássio/química , Energia Solar , Adsorção , Algoritmos , Hidrodinâmica , Modelos Teóricos , Fenômenos Físicos , Reprodutibilidade dos Testes , Soluções
19.
Proc Natl Acad Sci U S A ; 117(2): 883-888, 2020 01 14.
Artigo em Inglês | MEDLINE | ID: mdl-31888981

RESUMO

Phosphate is central to the origin of life because it is a key component of nucleotides in genetic molecules, phospholipid cell membranes, and energy transfer molecules such as adenosine triphosphate. To incorporate phosphate into biomolecules, prebiotic experiments commonly use molar phosphate concentrations to overcome phosphate's poor reactivity with organics in water. However, phosphate is generally limited to micromolar levels in the environment because it precipitates with calcium as low-solubility apatite minerals. This disparity between laboratory conditions and environmental constraints is an enigma known as "the phosphate problem." Here we show that carbonate-rich lakes are a marked exception to phosphate-poor natural waters. In principle, modern carbonate-rich lakes could accumulate up to ∼0.1 molal phosphate under steady-state conditions of evaporation and stream inflow because calcium is sequestered into carbonate minerals. This prevents the loss of dissolved phosphate to apatite precipitation. Even higher phosphate concentrations (>1 molal) can form during evaporation in the absence of inflows. On the prebiotic Earth, carbonate-rich lakes were likely abundant and phosphate-rich relative to the present day because of the lack of microbial phosphate sinks and enhanced chemical weathering of phosphate minerals under relatively CO2-rich atmospheres. Furthermore, the prevailing CO2 conditions would have buffered phosphate-rich brines to moderate pH (pH 6.5 to 9). The accumulation of phosphate and other prebiotic reagents at concentration and pH levels relevant to experimental prebiotic syntheses of key biomolecules is a compelling reason to consider carbonate-rich lakes as plausible settings for the origin of life.


Assuntos
Carbonatos/química , Lagos/química , Origem da Vida , Fosfatos/química , Apatitas , Cálcio , Dióxido de Carbono , Membrana Celular , Concentração de Íons de Hidrogênio , Minerais , Modelos Biológicos , Prebióticos , Rios , Solubilidade
20.
Chemosphere ; 246: 125789, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31918099

RESUMO

Salt pollution and anthropogenic-accelerated weathering is globally shifting the ionic composition and increasing salinisation of fresh water. We analyzed a 40-year data set (1970s-2010s) to characterize the drastic change of dissolved ionic composition, conductivity and pH levels. We also identified causative factors in these highly polluted mountain streams in northeastern China. Dissolved salt ions (Ca2+, Mg2+ and SO42-) increased by 3.02-5.21 fold and conductivity (a proxy for salinisation) increased by 3.09 fold. The average pH values increased from 7.08 to 8.49. The dominant ions, Ca2+, Mg2+, SO42- and HCO3- + CO32-, accounted for ∼90% of ionic composition based on mass concentration. Between the 1970s and 2010s, the dominant anion shifted from HCO3- + CO32- to a mixture of SO42- and HCO3- + CO32-. Increasing mining and land development appear to be the primary driving factors for the change of Ca2+, Mg2+, SO42- and HCO3- + CO32- concentrations; whereas, agricultural land was the main driving factor for the variation in K+, Na+ and Cl- concentrations. The source of ions has shifted from a more natural weathering of carbonate rocks to one of mineral dissolution that is affected by anthropogenic activities. Our study shows that freshwater mountain streams are at risk of long lasting anthropogenic salinisation and should be considered in future management and conservation plans.


Assuntos
Monitoramento Ambiental , Rios/química , Salinidade , Poluentes Químicos da Água/análise , Agricultura , Ânions , Carbonatos/química , China , Água Doce , Mineração , Tempo (Meteorologia)
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