Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 14 de 14
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Colloid Interface Sci ; 614: 603-616, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35123214

RESUMO

This is the first report of the metal Fe-Ti oxide/biochar (Fe2TiO5/BC) composite for simultaneous removal of aqueous Pb2+, Cr6+, F- and methylene blue (MB). Primary Fe2TiO5 nano particles and aggregates were dispersed on a high surface area Douglas fir BC (∼700 m2/g) by a simple chemical co-precipitation method using FeCl3 and TiO(acac)2 salts treated by base and heated to 80 °C. This was followed by calcination at 500 °C. This method previously was used without BC to make the neat mixed oxide Fe2TiO5, exhibiting a lower energy band gap than TiO2. Adsorption of Cr(VI), Pb(II), fluoride, and MB on Fe2TiO5/BC was studied as a function of pH, equilibrium time, initial adsorbate concentration, and temperature. Adsorption isotherm studies were conducted at 5, 25, and 45 ℃ and kinetics for all four adsorbates followed the pseudo second order model. Maximum Langmuir adsorption capacities for Pb2+, Cr6+, F- and MB at their initial pH values were 141 (pH 2), 200 (pH 5), 36 (pH 6) and 229 (pH 6) mg/g at 45 ℃ and 114, 180, 26 and 210 mg/g at 25 ℃, respectively. MB was removed from the water on Fe2TiO5/BC by synergistic adsorption and photocatalytic degradation at pH 3 and 6 under UV (365 nm) light irradiation. Cr6+, Pb2+, F-, and MB each exhibited excellent removal capacities in the presence of eight different competitive ions in simulated water samples. The removal mechanisms on Fe2TiO5/BC and various competitive ion interactions were proposed. Some iron ion leaching at pH 3 catalyzed Photo-Fenton destruction of MB. Fe2TiO5, BC, and Fe2TiO5/BC bandgaps were studied to help understand photocatalysis of MB and to advance supported metal oxide photodegradation using smaller energy band gaps than the larger bandgap of TiO2 for water treatment. A long range goal is to photocatalytically destroy some sorbates with adsorbents to avoid the need for regeneration steps.


Assuntos
Azul de Metileno , Poluentes Químicos da Água , Adsorção , Carvão Vegetal , Cromo/análise , Fluoretos , Ferro , Cinética , Chumbo , Óxidos , Titânio , Poluentes Químicos da Água/análise
2.
J Environ Manage ; 296: 113186, 2021 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-34256294

RESUMO

Biochar adsorbents can remove environmental pollutants and the remediation of Cr(VI) and nitrate are considered. Cr(VI) is a proven carcinogen causing serious health issues in humans and nitrate induced eutrophication causes negative effect on aquatic systems around the world. Douglas fir biochar (DFBC), synthesized by fast pyrolysis during syn gas production, was treated with aniline. Then, a polyaniline biochar (PANIBC) composite containing 47 wt% PANI was prepared by precipitating PANI on DFBC surfaces by oxidative chemical polymerization of aniline in 2M HCl. PANIBC exhibited a point of zero charge (PZC) of 3.0 and 8.2 m2/g BET (N2) surface area. This modified biochar was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) morphology and surface elements, and oxidation states by X-ray photoelectron spectroscopy (XPS). PANIBC exhibited positive surface charge below pH 3, making it an outstanding adsorbent, for Cr(VI) removal. Cr(VI) and nitrate removal mechanisms are presented based on XPS analysis. DFBC and PANIBC Cr(VI) and nitrate adsorption data were fitted to Langmuir and Freundlich isotherm models with maximum Langmuir adsorption capacities of 150 mg/g and 72 mg/g, respectively. Cr(VI) and nitrate removal at pH 2 and 6 were evaluated by reducing the amount of PANI (9 wt%) dispersed on to DFBC. Adsorption capacities verses temperature studies revealed that both Cr(VI) and nitrate adsorption are endothermic and thermodynamically favored. Regeneration studies were conducted on both DFBC and PANIBC using 0.1M NaOH and PANIBC exhibited excellent sorption capacities for Cr(VI) and nitrate in lake water samples and in the presence of competitive ions.


Assuntos
Cromo , Poluentes Químicos da Água , Adsorção , Compostos de Anilina , Carvão Vegetal , Cromo/análise , Humanos , Concentração de Íons de Hidrogênio , Cinética , Nitratos , Água , Poluentes Químicos da Água/análise
3.
Chemosphere ; 269: 128409, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33069440

RESUMO

Biochar has become a popular research topic in sustainable chemistry for use both in agriculture and pollution abatement. To enhance aqueous Cr(VI), Pb(II) and Cd(II) removal efficiency, high surface area (535 m2/g) byproduct Douglas fir biochar (DFBC) from commercial syn-gas production obtained by fast pyrolysis (900-1000 °C, 1-10 s), was subjected to a KOH activation. KOH-activated biochar (KOHBC) underwent a remarkable surface area increase to 1049 m2/g and a three-fold increase in pore volume (BET analysis). Batch sorption studies on KOHBC verses pH revealed that the highest chromium, lead and cadmium removal capacities occurred at pH 2.0, 5.0 and 6.0, respectively. KOHBC exhibited much higher adsorption capacities than unactivated DFBC. Heavy metal loadings onto KOHBC were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Sorption of Cr(VI), Pb(II) and Cd(II) all followed pseudo-second order kinetics and the Langmuir adsorption model. The highest Langmuir adsorption capacities at the respective pH's of maximum adsorption were 140.0 mg g-1 Pb(II), 127.2 mg g-1 Cr(VI) and 29.0 mg g-1 Cd(II). Metal ions spiked into natural and laboratory waste water systems exhibited high sorption capacities. Desorption studies carried out using 0.1 M HCl revealed that Pb(II) adsorption onto the KOHBC surface is reversible. Portions of Cd(II) and Cr(VI) adsorbed strongly onto KOHBC were unable to be desorbed by 0.1 M HCl and 0.1 M NaOH.


Assuntos
Pseudotsuga , Poluentes Químicos da Água , Adsorção , Cádmio , Carvão Vegetal , Cromo/análise , Concentração de Íons de Hidrogênio , Cinética , Chumbo , Poluentes Químicos da Água/análise
4.
J Colloid Interface Sci ; 587: 767-779, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33309243

RESUMO

Commercialization of novel adsorbents technology for providing safe drinking water must consider scale-up methodological approaches to bridge the gap between laboratory and industrial applications. These imply complex matrix analysis and large-scale experiment designs. Arsenic concentrations up to 200-fold higher (2000 µg/L) than the WHO safe drinking limit (10 µg/L) have been reported in Latin American drinking waters. In this work, biochar was developed from a single, readily available, and taxonomically identified woody bamboo species, Guadua chacoensis. Raw biochar (BC) from slow pyrolysis (700 °C for 1 h) and its analog containing chemically precipitated Fe3O4 nanoparticles (BC-Fe) were produced. BC-Fe performed well in fixed-bed column sorption. Predicted model capacities ranged from 8.2 to 7.5 mg/g and were not affected by pH 5-9 shift. The effect of competing matrix chemicals including sulfate, phosphate, nitrate, chloride, acetate, dichromate, carbonate, fluoride, selenate, and molybdate ions (each at 0.01 mM, 0.1 mM and 1 mM) was evaluated. Fe3O4 enhanced the adsorption of arsenate as well as phosphate, molybdate, dichromate and selenate. With the exception of nitrate, individually competing ions at low concentration (0.01 mM) did not significantly inhibit As(V) sorption onto BC-Fe. The presence of ten different ions in low concentrations (0.01 mM) did not exert much influence and BC-Fe's preference for arsenate, and removal remained above 90%. The batch and column BC and BC-Fe adsorption capacities and their ability to provide safe drinking water were evaluated using a naturally contaminated tap water (165 ± 5 µg/L As). A 960 mL volume (203.8 Bed Volumes) of As-free drinking water was collected from a 1 g BC-Fe fixed bed. Adsorbent regeneration was attempted with (NH4)2SO4, KOH, or K3PO4 (1 M) strippers. Potassium phosphate performed the best for BC-Fe regeneration. Safe disposal options for the exhausted adsorbents are proposed. Adsorbents and their As-laden analogues (from single and multi-component mixtures) were characterized using high resolution XPS and possible competitive interactions and adsorption pathways and attractive interactions were proposed including electrostatic attractions, hydrogen bonding and weak chemisorption to BC phenolics. Stoichiometric precipitation of metal (Mg, Ca and Fe) oxyanion (phosphate, molybdate, selenate and chromate) insoluble compounds is considered. The use of a packed BC-Fe cartridge to provide As-free drinking water is presented for potential commercial use. BC-Fe is an environmentally friendly and potentially cost-effective adsorbent to provide arsenic-free household water.


Assuntos
Arsênio , Sasa , Poluentes Químicos da Água , Purificação da Água , Adsorção , Arsênio/análise , Carvão Vegetal , Compostos Férricos , Ferro , Cinética , Transferência de Tecnologia , Poluentes Químicos da Água/análise
5.
Sci Total Environ ; 706: 135943, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31862592

RESUMO

Discarded bamboo culms of Guadua chacoensis were used for biochar remediation of aqueous As(V). Raw biochar (BC), activated biochar (BCA), raw Fe3O4 nanoparticle-covered biochar (BC-Fe), and activated biochar covered with Fe3O4 nanoparticles (BCA-Fe) were prepared, characterized and tested for As(V) aqueous adsorption. The goal is to develop an economic, viable, and sustainable adsorbent to provide safe arsenic-free water. Adsorbents were characterized using scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (SEM-EDX), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (TEM-EDS), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller surface area measurements (SBET), point of zero charge determinations (PZC), and elemental analysis. Activation with KOH increased the O/C ratio and the surface area of BC from 6.7 m2/g to 1239.7 m2/g (BCA). As(V) sorption equilibrium was achieved within <2 h for all four adsorbents and kinetics followed the pseudo-second-order model. At a 10 mg/L initial As(V) concentration, BC-Fe achieved a 100% removal (5 mg/g) over a pH 5 to 9 window. Sorption was endothermic on all four adsorbents and the capacities rose with the increasing temperature. Langmuir capacities at 40 °C for BC, BCA, BC-Fe, and BCA-Fe were 256, 217, 457, and 868 mg/g, respectively, and capacities were compared with other sorbents. Breakthrough fixed-bed column sorption was carried out for BC and BC-Fe producing 6.6 mg/g and 13.9 mg/g bed capacities, respectively. Potassium phosphate was a better As stripping agent than sodium bicarbonate. Performance of the adsorbents in an As(V)-spiked natural water and a naturally As(V)-contaminated domestic water were assessed. Robust arsenate sequestration occurred generating As-safe water (As <0.01 mg/L), despite the presence of competing ions. Stoichiometric precipitation of iron-arsenate complexes triggered by iron dissolution was also established.


Assuntos
Sasa , Purificação da Água , Adsorção , Arsênio , Carvão Vegetal , Compostos Férricos , Cinética , Nanopartículas Metálicas , Poluentes Químicos da Água
6.
Chemosphere ; 239: 124788, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31521935

RESUMO

Digestion of biomass derived carbonaceous materials such as biochar (BC) can be challenging due to their high chemical recalcitrance and vast variations in composition. Reports on the development of specific sample digestion methods for such materials remain inadequate and thus require considerable attention. Nine different carbonaceous materials; slow-pyrolyzed tea-waste and king coconut BC produced at 300 °C, 500 °C and 700 °C, sludge waste BC produced at 700 °C, wet fast-pyrolyzed Douglas-Fir BC and steam activated coconut shell BC have been tested to evaluate a relatively fast and convenient open-vessel digestion method using seven digestion reagents including nitric acid (NA), fuming nitric acid (FNA), sulfuric acid (SA), NA/SA, FNA/SA, NA/H2O2 and SA/H2O2 mixtures. From the tested digestion reagents, SA/H2O2 mixture dissolved low temperature produced BC (LTBC) within 2 h with occasional shaking and no external heating. Except peroxide mixtures, the other reagents were used to evaluate microwave digestion (MWD) efficiency. Nitric acid mixture was capable of only completely digesting LTBC in the MWD procedure whereas FNA, NA/SA and FNA/SA mixtures resulted in the successful dissolution of all tested carbonaceous materials. Amongst them, FNA provided the least matrix effect in the quantification of the four metals tested using flame atomic absorption spectrophotometry. Tested recoveries for FNA were satisfactory as well. It was concluded that FNA is a preferable reagent for microwave digestion of BC.


Assuntos
Carvão Vegetal/química , Resíduos , Cocos , Indústria de Laticínios , Peróxido de Hidrogênio , Metais/análise , Micro-Ondas , Ácido Nítrico/química , Pirólise , Esgotos , Espectrofotometria Atômica/métodos , Ácidos Sulfúricos/química
7.
J Anal Methods Chem ; 2019: 1690153, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30881724

RESUMO

Xylitol, a sugar substitute frequently used in sugar-free gum, is generally considered harmless to humans but it can be extremely toxic to dogs. Dog-owning customers are becoming increasingly aware of the risks associated with xylitol-containing chewing gums. However, there remains some uncertainty if these chewing gums are still dangerous to dogs after they have been partially consumed. In this work, a reliable low-cost analytical method has been developed to quantify the xylitol in sugar-free gum samples. Xylitol was extracted from gum samples using water as a solvent. Extractions were analyzed by GC-MS with direct aqueous injection (DAI). This method was successfully applied to over 120 samples including fresh gum and 5 min, 15 min, and 30 min chewed gum samples.

8.
Environ Sci Technol ; 53(5): 2635-2646, 2019 03 05.
Artigo em Inglês | MEDLINE | ID: mdl-30695634

RESUMO

Biochar has been proposed as a soil amendment in agricultural applications due to its advantageous adsorptive properties, high porosity, and low cost. These properties allow biochar to retain soil nutrients, yet the effects of biochar on bacterial growth remain poorly understood. To examine how biochar influences microbial metabolism, Escherichia coli was grown in a complex, well-defined media and treated with either biochar or activated carbon. The concentration of metabolites in the media were then quantified at several time points using NMR spectroscopy. Several metabolites were immediately adsorbed by the char, including l-asparagine, l-glutamine, and l-arginine. However, we find that biochar quantitatively adsorbs less of these metabolic precursors when compared to activated carbon. Electron microscopy reveals differences in surface morphology after cell culture, suggesting that Escherichia coli can form biofilms on the surfaces of the biochar. An examination of significant compounds in the tricarboxylic acid cycle and glycolysis reveals that treatment with biochar is less disruptive than activated carbon throughout metabolism. While both biochar and activated carbon slowed growth compared to untreated media, Escherichia coli in biochar-treated media grew more efficiently, as indicated by a longer logarithmic growth phase and a higher final cell density. This work suggests that biochar can serve as a beneficial soil amendment while minimizing the impact on bacterial viability. In addition, the experiments identify a mechanism for biochar's effectiveness in soil conditioning and reveal how biochar can alter specific bacterial metabolic pathways.


Assuntos
Escherichia coli , Metabolômica , Carvão Vegetal , Solo
9.
RSC Adv ; 9(31): 17612-17622, 2019 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-35520596

RESUMO

Tea-waste is an abundant feedstock for producing biochar (BC) which is considered to be a cost effective carbonaceous adsorbent useful for water remediation and soil amendment purposes. In the present study, tea-waste BC (TWBC) produced at three different temperatures were subjected to nitric, sulfuric and hydrochloric acid modifications (abbreviated as NM, SM and HM respectively). Characteristics of the raw and modified BC such as ultimate and proximate analyses, surface morphology, surface acidity and functionality, point of zero charge, cation exchange capacity (CEC) and thermal stability were compared to evaluate the influence of pyrolysis temperature and of modifications incorporated. The amount of carboxylic and phenolic surface functionalities on TWBC was seen to decrease by 93.44% and 81.06% respectively when the pyrolysis temperature was increased from 300 to 700 °C. Additionally, the yield of BC was seen to decrease by 46% upon the latter temperature increment. The elemental analysis results provided justification for high-temperature BC being more hydrophobic as was observed by the 61% increase in H/C ratio which is an indication of augmented aromatization. The CEC was the highest for the low-temperature BC and was seen to further increase by NM which is attributed to the 81.89% increase in carboxylic functionalities. The surface area was seen to significantly increase for BC700 upon NM (∼27 times). The SM led to pore wall destruction which was observed in scanning electron microscopy images. Findings would enable the rational use of these particular modifications in relevant remediation and soil amendment applications.

10.
Bioresour Technol ; 246: 150-159, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28789905

RESUMO

Utilization of biochar (BC) as a low cost adsorbent for water remediation has gained an immense research interest due to their surface functionality and porosity. Although many reports on the BC based sorptive removal of Sulfonamides (SA) and Tetracyclines (TC) are available in literature, a deep insight into sorption mechanisms is yet to be reviewed. Objective of this review is to fill the research gap of a methodological understanding of sorption mechanisms and characteristics which is essential to develop efficient methods for contaminant removal. The most common adsorption mechanism can be considered as electron donor-acceptor interactions of electron withdrawing moieties with surface arene rings. The strongest adsorption of both antibiotics occurs at mildly acidic pH where the dominant species are zwitterionic or cationic. Smaller SAs exhibit micro pore-filling effects while bulky TCs experience size exclusions. Furthermore, the effect of matrix components and modifications are also been taken into account.


Assuntos
Antibacterianos , Sulfonamidas , Adsorção , Carvão Vegetal , Tetraciclinas
11.
J Org Chem ; 82(11): 5678-5688, 2017 06 02.
Artigo em Inglês | MEDLINE | ID: mdl-28488857

RESUMO

A regioselective synthesis of 6-alkyl- and 6-aryluracils was developed by the dimerization of 3-alkyl- and 3-aryl-2-propynamides promoted by either Cs2CO3 or K3PO4. A range of 3-aryl-2-propynamides, with both electron-deficient and electron-rich 3-aryl substituents, were successfully reacted in high yields. Cs+ acts as a soft Lewis acid to polarize the carbon-carbon triple bond, and solid K3PO4 interacts with carbonyl oxygen, promoting intermolecular nucleophilic attack by the only weakly nucleophilic amide nitrogen. Experiments were conducted to support the proposed mechanism.

12.
J Environ Sci (China) ; 35: 38-42, 2015 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-26354690

RESUMO

An improved method for trace level quantification of dicyandiamide in stream water has been developed. This method includes sample pretreatment using solid phase extraction. The extraction procedure (including loading, washing, and eluting) used a flow rate of 1.0mL/min, and dicyandiamide was eluted with 20mL of a methanol/acetonitrile mixture (V/V=2:3), followed by pre-concentration using nitrogen evaporation and analysis with high performance liquid chromatography-ultraviolet spectroscopy (HPLC-UV). Sample extraction was carried out using a Waters Sep-Pak AC-2 Cartridge (with activated carbon). Separation was achieved on a ZIC(®)-Hydrophilic Interaction Liquid Chromatography (ZIC-HILIC) (50mm×2.1mm, 3.5µm) chromatography column and quantification was accomplished based on UV absorbance. A reliable linear relationship was obtained for the calibration curve using standard solutions (R(2)>0.999). Recoveries for dicyandiamide ranged from 84.6% to 96.8%, and the relative standard deviations (RSDs, n=3) were below 6.1% with a detection limit of 5.0ng/mL for stream water samples.


Assuntos
Cromatografia Líquida de Alta Pressão , Monitoramento Ambiental/métodos , Guanidinas/análise , Rios/química , Extração em Fase Sólida , Espectrofotometria Ultravioleta , Poluentes Químicos da Água/análise , Limite de Detecção
13.
J AOAC Int ; 96(6): 1440-7, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24645527

RESUMO

We present an improved method for trace level quantification of five estrogens including estriol, estrone, 17alpha-estradiol, 17beta-estradiol, and 17alpha-ethinylestradiol in wastewaters. Our method includes sample preparation using SPE followed by a Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) cleanup step, a derivatization, and LC/MS/MS determination. Sample extraction was carried out using Oasis HLB cartridges and a dispersive solid-phase cleanup pack containing MgSO4 and primary-secondary amine and C18 sorbents. The resulting extract was derivatized with dansyl chloride. Separation was achieved on an Agilent Zorbax Extend C18, Narrow Bore RR 2.1 x 100 mm, 3.5 pm column; quantification was accomplished in the positive ion mode using multiple reaction monitoring. The cleanup method is quick, efficient, inexpensive, and requires only 200 mL of water. Reliable linearities were obtained for all calibration curves (r2 > 0.995). Matrix effects calculated were less than 12% for all analytes, and, hence, matrix matched calibration curves were not needed. The recoveries for the estrogens ranged from 81-103%, with a high repeatability (n = 3, RSD < or = 9%) and low LOQs (0.6-0.9 ng/L). The method was used to analyze effluent and influent wastewaters in Mississippi wastewater treatment plants, but it is broadly applicable for the determination of trace estrogens in any municipal wastewater samples.


Assuntos
Cromatografia Líquida/métodos , Estrogênios/análise , Extração em Fase Sólida/métodos , Espectrometria de Massas em Tandem/métodos , Poluentes Químicos da Água/química , Purificação da Água/métodos , Calibragem , Compostos de Dansil/química , Resíduos de Drogas/análise , Estradiol/química , Estriol/química , Estrona/química , Metanol/química , Controle de Qualidade , Reprodutibilidade dos Testes , Águas Residuárias
14.
Talanta ; 76(4): 872-7, 2008 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-18656672

RESUMO

Methyl salicylate (MeS) is used as a chemical warfare agent simulant to test chemical protective garments and other individual personal protective gear. The accurate and real-time detection of this analyte is advantageous for various testing regimes. This paper reports the results of MeS vapor exposures on polymer-filled capacitance-based sensors at temperatures ranging from 15 degrees C to 50 degrees C under dry and humid conditions. Multiple capacitors were arranged in an array on a silicon chip each having a different sorptive polymer. The sensors used parallel-plate electrode geometry to measure the dielectric permittivity changes of each polymer when exposed to water and MeS vapor. Of the four polymers tested against MeS, the optimal polymer displayed near or sub-parts-per-million detection limits at 35 degrees C (0-80%RH).


Assuntos
Técnicas de Química Analítica/instrumentação , Técnicas de Química Analítica/métodos , Polímeros/química , Salicilatos/análise , Técnicas Biossensoriais , Substâncias para a Guerra Química/análise , Eletroquímica , Desenho de Equipamento , Microquímica/métodos , Salicilatos/química , Solventes/análise , Temperatura , Volatilização , Água/análise
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...