Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 873
Filtrar
1.
Environ Monit Assess ; 192(4): 240, 2020 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-32185514

RESUMO

Metal ion contamination in wastewater is an issue of global concern. The conventional methods of heavy metal removal from wastewater have some drawbacks, ranging from generation of sludge to high cost of removal. Adsorption technique for copper(II), zinc(II), and chromium(VI) using activated carbon has been found efficient. However, it is not economical on a large scale. This, therefore, necessitates the search for economical and readily available plant biomass-based activated carbons for the sequestration of the metal ions. This review presents the state of the art on the adsorption of copper(II), zinc(II), and chromium(VI) from industrial wastewater. Based on the literature review presented, the groundnut husk and corncob based activated carbons were found to possess the maximum adsorption capacities for copper(II), zinc(II), and chromium(VI) removal, when compared with the other plant biomass-based activated carbons. The high values of the adsorption capacities obtained were as a result of the isotherms and pH of the adsorbent as well as the initial concentration of the metal solutions. From the review, the equilibrium data fitted better with Langmuir and Freundlich isotherms than with other isotherms. Research gaps were identified which include a need to investigate the kinetic and the thermodynamic behaviors of the metal ions onto the studied adsorbents. Furthermore, a comparative analysis of the three types of activation of the adsorbents should be investigated using single and multi-metals. The optimization of particle size, contact time, temperature, initial concentration, and adsorbent dosage for adsorption of copper(II), zinc(II), and chromium(VI) onto the studied adsorbents using response surface methodology is equally required.


Assuntos
Cromo , Metais Pesados , Águas Residuárias , Purificação da Água , Adsorção , Biomassa , Carvão Vegetal , Cromo/isolamento & purificação , Cobre/isolamento & purificação , Monitoramento Ambiental , Concentração de Íons de Hidrogênio , Cinética , Metais Pesados/isolamento & purificação , Zinco/isolamento & purificação
2.
Environ Sci Pollut Res Int ; 27(7): 7657-7671, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31889268

RESUMO

The metal contents of the soil and plant tissues in a large chromium salt-producing factory wasteland were determined to assess the properties of soil contamination and to identify plant species accumulating a range of heavy metals. Total metal contents in the factory soils presented a high heterogeneity, and the principal contaminants were Cd and Cr. All plant species examined were metal-tolerant, but to different extents. Especially, the maximum accumulation of Cd (15.61 mg kg-1) and Cr (925.07 mg kg-1) was found in Melia azedarach L. Subsequently, the Cd and Cr bioaccumulation and diverse physiological properties of M. azedarach seedlings exposed to different concentrations of Cd(II), Cr(VI), or Cd(II) + Cr(VI) in nutrient solutions were further investigated. All treated seedlings were able to survive under heavy metal stress, and the accumulation of both metals in plant tissues increased with elevation of metal exposure strength. M. azedarach showed a BCF greater than 147.56 for Cd and 36.76 for Cr. Meanwhile, the TF was lower than 0.25 for Cd and 0.32 for Cr. The highest bioaccumulation in root tissues was 2708.03 mg kg-1 Cd and 824.65 mg kg-1 Cr for seedlings cultured with 20 mg L-1 Cd(II) or 20 mg L-1 Cr(VI). Cd and Cr increased each other's uptake in seedlings although a reduced accumulation in roots occurred when exposed to the highest concentration of Cd(II) + Cr(VI) treatment (20 mg L-1). At either level of concentration, the degree of plant growth inhibition and oxidative damage caused by heavy metals was Cd(II) + Cr(VI) > Cr(VI) > Cd(II). Superoxide dismutase and peroxidase exhibited positive and effective responses to low-Cd(II) or Cr(VI) concentration stress, but their activities decreased with increasing metal exposure strength. The behavior of the non-enzymatic antioxidants (GSH, soluble protein, and proline) in plant involved in the detoxification of ROS induced by metal exposure was correlated well with higher Cd and Cr accumulations. Here, the potentiality of M. azedarach with the capacity to accumulate and stabilize Cd/Cr in metal-contaminated soil by phytoremediation process has been explored.


Assuntos
Biodegradação Ambiental , Cádmio/isolamento & purificação , Cromo/isolamento & purificação , Melia/metabolismo , Poluentes do Solo/isolamento & purificação , China , Metais Pesados/isolamento & purificação , Raízes de Plantas/metabolismo
3.
Chemosphere ; 241: 125044, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31683426

RESUMO

A novel ball milled Fe0-biochar composite was synthesized by ball milling the mixture of biochar (pyrolyzed at 300 °C, 500 °C, and 700 °C) and micron grade iron powder. FTIR, SEM, TEM-EDS, XRD, and XPS were applied to characterize this composite. XRD results showed that iron carbide phase was formed during the ball milling process. The ability of this synthesized composited to remove aqueous Cr(VI) was tested. Removal rates of Cr(VI) (49.6%, 65.8%, and 97.8%, respectively) by ball milled Fe0-biochar composite consisting of biochar pyrolyzed at 300 °C (300BMFe0-BC), 500 °C (500BMFe0-BC), and 700 °C (700BMFe0-BC) were much higher than those (19%, 11%, and 4%, respectively) by pristine biochar pyrolyzed at 300 °C (300BC), 500 °C (500BC), and 700 °C (700BC). Cr(VI) removal rate by 700BMFe0-BC increased from 15.4% to 97.8% when prolonging ball milling time from 6 h to 48 h. Ball milling promoted the combination of Fe0 and biochar as well as reduced the hydrodynamic diameter of the composite. Acidic conditions favored Cr(VI) removal. Ball milling exposed the functional groups of biochar and improved its Cr(VI) removal rate. Raman spectra showed that the degree of graphitization in 700 °C ball milled biochar (700BMBC) was the highest. Electrochemical analysis demonstrated that 700BMBC had the highest electron transfer capacity. In the presence of Fe0, graphitized structure in 700BMBC acted as an electron conductor, facilitating electron transfer from Fe0 to Cr(VI). Ball milling also destroyed the surface iron oxide layer to regenerate the composite.


Assuntos
Carvão Vegetal/química , Cromo/isolamento & purificação , Pirólise , Poluentes Químicos da Água/isolamento & purificação , Elétrons , Compostos Férricos , Temperatura , Poluentes Químicos da Água/análise
4.
Chemosphere ; 238: 124638, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31466006

RESUMO

In this study, we reported on the recycling of carbon materials from spent commercial supercapacitors and its application as low-cost adsorbent for high-efficiency removal of Ag(I) and Cr(VI) ions from aqueous solutions. Adsorption kinetics and isotherms, and effects of initial pH were carried out to investigate the adsorption performance of the recycled supercapacitor activated carbon (RSAC), whereas a series of characterizations such as SEM, EDX, BET, XPS, XRD and FTIR were employed to detailedly analyse the adsorption mechanism. The RSAC showed maximal adsorption capacity for Ag(I) and Cr(VI) of 104.0 and 96.3 mg g-1, respectively, with adsorbent dosage of 2 g L-1 and initial ions concentration of ∼2000 mg L-1 at room temperature (23 ±â€¯1 °C), and the adsorption was rapid and influenced by the initial pH value. The outstanding adsorption performance of RSAC was attributed to the high specific surface area (1403 m2 g-1) and abundant multifarious oxygenic groups which could participate in the electrostatic attraction and reduction reaction of Ag(I) and Cr(VI) during the adsorption process. Furthermore, the predominate species of the adsorbed toxic Ag(I) and Cr(VI) on the surface of RSAC was metallic silver particle (about 2 µm) and harmless Cr(III), respectively, thus it was possible for further recycling and disposal.


Assuntos
Carvão Vegetal/química , Cromo/isolamento & purificação , Reciclagem/métodos , Prata/isolamento & purificação , Águas Residuárias/química , Purificação da Água/métodos , Adsorção , Íons , Cinética , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
5.
Chemosphere ; 239: 124735, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31499306

RESUMO

A key challenge in adsorption process of toxic organic and inorganic species is the design and development of adsorbent materials bearing an abundance of accessible adsorption sites with high affinity to achieve both fast adsorption kinetics and elevated adsorption capacity for toxic contaminants. Herein, a novel anion-exchange adsorbent based on fibrous silica nanospheres KCC-1 was synthesized by a facile hydrothermal-assisted post-grafting modification of KCC-1 with 1-methyl-3- (triethoxysilylpropyl)imidazolium chloride for the first time. Silica fibers with micro-mesoporous structure display the proper combination of features to serve as a potential scaffold for decorating adsorption sites to create desired ion-exchange adsorbent. The obtained N-methylimidazolium-functionalized KCC-1 (MI-Cl-KCC-1) with fibrous nanosphere morphology showed a high surface area (∼241 m2 g-1) and high pore volume (0.81 m2 g-1). The adsorption behaviors of toxic hexavalent chromium from aqueous media by the MI-Cl-KCC-1 were systematically studied using the batch method. The adsorption rate was relatively fast, and MI-Cl-KCC-1 possesses a high capacity for the adsorption of Cr(VI). The maximum Cr(VI) adsorption was obtained at pH 3.0-4.0. Different non-linear isotherm equations were tested for choosing an appropriate adorption isotherm behavior, and the adsorption data for MI-Cl-KCC-1 were consistent with the Langmuir model with a maximum adsorption capacity of 428 ±â€¯8 mg g-1.


Assuntos
Cromo/isolamento & purificação , Imidazóis/química , Nanoestruturas/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Ânions , Cromo/química , Imidazóis/síntese química , Troca Iônica , Cinética , Micro-Ondas , Dióxido de Silício/química , Poluentes Químicos da Água/química , Purificação da Água/métodos
6.
Chemosphere ; 239: 124733, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31526991

RESUMO

Lignin, natural aromatic polymer derived from plant dry matter, is second abundant biopolymer. Recently, interest in applications of lignin, especially as an adsorbent material is increasing. However, the physicochemical complexity of lignin significantly reduces access to practical environmental remediation processes. Also, there is a limitation because the adsorption performance of the pristine lignin materials is not superior to that of commercial adsorbent and ion exchange resin material. In this study, spherical lignin particles with high physicochemical stability and excellent Cr(VI) adsorption capacity are prepared using a polyethylenimine (PEI) modification strategy. This modification process significantly improves the mechanical properties and water stability of lignin by complementing the instability of lignin particles. In addition, the PEI-lignin particles exhibit a superior Cr(VI) removal capability (657.9 mg/g, the highest value for a PEI-modified natural adsorbent), which is attributed to their structural stability and introduced amine functional groups. The Cr(VI) removal with PEI-lignin particles is performed via intra-particle diffusion and adsorption followed by covalent bonding combined with a reduction process. Moreover, the PEI-lignin particles exhibit excellent reusability, which sustains their high adsorption efficiency over a long and repeated adsorption period. The results herein strongly support the potential use of PEI-lignin particles as a high performance bio-sorption material for heavy metal removal and its detoxification in aqueous wastewater streams. Evidently, this lignin-based bio-sorbent manufacturing system can provide sustainable bio-resource recycling and cost efficiency.


Assuntos
Cromo/isolamento & purificação , Lignina/química , Adsorção , Cromo/química , Recuperação e Remediação Ambiental , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia Fotoeletrônica , Polietilenoimina/química , Espectroscopia de Infravermelho com Transformada de Fourier , Eliminação de Resíduos Líquidos/métodos , Água/química , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
7.
Ecotoxicol Environ Saf ; 188: 109902, 2020 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-31704325

RESUMO

In this study, polyethylene glycol (PEG)-stabilized nano zero-valent iron (nZVI) supported by biochar (BC) (PEG-nZVI@BC) was prepared to remedy Cr(VI) with high efficiency. The morphology, functional groups, and crystalline structure of PEG-nZVI@BC composites were characterized, revealing that when PEG was added, a large number of -OH functional groups were introduced, and nZVI was effectively dispersed on the BC surface with a smaller particle size. The results of Cr(VI) remediation experiments showed Cr(VI) removal rate by PEG-nZVI@BC (97.38%) was much greater than that by BC-loaded nZVI (nZVI@BC) (51.73%). The pseudo second-order and Sips isotherm models provide the best simulation for Cr(VI) removal experimental data, respectively. The main remediation mechanism of Cr(VI) was reduction and co-precipitation of Cr-containing metal deposits onto PEG-nZVI@BC. Ecotoxicity assessment revealed PEG-nZVI@BC (1.00 g/L) has little influence on rice germination and growth, but resisted the toxicity of Cr(VI) to rice. The modified Community Bureau of Reference (BCR) sequential extraction showed pyrolysis could increase the percentage of oxidizable and residual Cr and diminish the environmental risk of Cr release from post-removal composites.


Assuntos
Carvão Vegetal/química , Cromo/isolamento & purificação , Ferro/química , Polietilenoglicóis/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Precipitação Química , Cromo/química , Recuperação e Remediação Ambiental , Oxirredução , Tamanho da Partícula , Poluentes Químicos da Água/química
8.
Chemosphere ; 239: 124760, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31518923

RESUMO

Plant growth and yield are adversely affected by the uptake of toxic hexavalent chromium (Cr(VI)) from soil. The present study describes a facile technique to minimize the uptake of Cr(VI) by chickpea (Cicer arietinum) plant from soil using microporous activated carbon microfiber (ACF). Simultaneously, nano-sized carbon nanofibers (CNFs), grown over the ACF substrate, are used as an efficient carrier of the Cu micronutrient from soil to root, shoot and leaf of the plants. Adsorption, seed germination and plant growth experiments are performed in Cr-stressed medium. The ACF, used as the adsorbent for Cr(VI) in metal-stressed soil (100 mg Cr kg-1 of soil) shows the metal loading of ∼23 mg g-1. Cr(VI) up to 50 mg L-1 concentration causes no stress during germination of chickpea seeds in Murashige and Skoog (MS) medium. A dose of 500 mg-mixture (treatment) per kg-soil increases root and shoot lengths by 52 and 11%, respectively than the control, during plant growth in the metal-stressed soil, attributed to an effective translocation of Cu-CNF through plant cells. Whereas Cr uptake by plant decrease to ∼46%, Cu uptake increase up to ∼120% in comparison to control by the mixture treatment. Protein and chlorophyll contents also significantly increased (*p < 0.05) with the application of treatment. The data clearly show that the mixture of ACF and Cu-CNF can be successfully used for the simultaneous scavenging of Cr(VI) from soil by adsorption over ACF and increased uptake of Cu by plants using the CNFs as the micronutrient carrier.


Assuntos
Cromo/farmacocinética , Cicer/crescimento & desenvolvimento , Nanofibras/química , Poluentes do Solo/farmacocinética , Adsorção , Carvão Vegetal/química , Clorofila/metabolismo , Cromo/isolamento & purificação , Cicer/efeitos dos fármacos , Cicer/metabolismo , Cobre/farmacocinética , Recuperação e Remediação Ambiental/métodos , Germinação , Folhas de Planta , Proteínas de Plantas/metabolismo , Raízes de Plantas/metabolismo , Brotos de Planta/metabolismo , Solo/química , Poluentes do Solo/isolamento & purificação
9.
Nat Commun ; 10(1): 5212, 2019 11 18.
Artigo em Inglês | MEDLINE | ID: mdl-31740677

RESUMO

Redox interactions between electroactive bacteria and inorganic materials underpin many emerging technologies, but commonly used materials (e.g., metal oxides) suffer from limited tunability and can be challenging to characterize. In contrast, metal-organic frameworks exhibit well-defined structures, large surface areas, and extensive chemical tunability, but their utility as microbial substrates has not been examined. Here, we report that metal-organic frameworks can support the growth of the metal-respiring bacterium Shewanella oneidensis, specifically through the reduction of Fe(III). In a practical application, we show that cultures containing S. oneidensis and reduced metal-organic frameworks can remediate lethal concentrations of Cr(VI) over multiple cycles, and that pollutant removal exceeds the performance of either component in isolation or bio-reduced iron oxides. Our results demonstrate that frameworks can serve as growth substrates and suggest that they may offer an alternative to metal oxides in applications seeking to combine the advantages of bacterial metabolism and synthetic materials.


Assuntos
Cromo/isolamento & purificação , Estruturas Metalorgânicas/química , Shewanella/metabolismo , Oxirredução , Shewanella/genética , Shewanella/crescimento & desenvolvimento
10.
Int J Nanomedicine ; 14: 8105-8119, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31632021

RESUMO

Background: Super-paramagnetic iron oxide nanoparticles (SPIONs) are widely used metal nanoparticles for various applications for its magnetic property and biocompatibility. In recent years, pollution of our environment especially with heavy metals in waterbodies has become a major threat and has left us very minimal sources of freshwater to drink. SPIONs or surface modified SPIONs can be used to remove these heavy metals. Methods: SPIONs were synthesized by co-precipitation method and further coated with a biopolymer, chitosan. Chromium solution was treated with the synthesized SPIONs to study the efficiency of chromium removal by surface adsorption. Later, the adsorption was analysed by direct and indirect analysis methods using UV-VIS spectrophotometry and isotherm studies. Results: Stable chitosan-coated SPIONs were synthesized and they adsorbed chromium better than the uncoated SPIONs, where it was adsorbing up to 100 ppm. Adsorption was found to be increasing with decrease in pH. Conclusion: The surface-modified SPIONs expressed cumulative adsorption action. Even after the adsorption studies, chitosan-coated SPIONs were possessing magnetic property. Thus, the surface-modified SPIONs can become an ideal nanotechnology tool to remove the chromium from groundwater.


Assuntos
Cromo/isolamento & purificação , Compostos Férricos/química , Nanopartículas de Magnetita/química , Nanotecnologia/métodos , Adsorção , Concentração de Íons de Hidrogênio , Nanopartículas de Magnetita/ultraestrutura , Nanopartículas/química , Espectrometria por Raios X , Espectroscopia de Infravermelho com Transformada de Fourier , Eletricidade Estática , Propriedades de Superfície , Temperatura , Fatores de Tempo , Difração de Raios X
11.
Environ Sci Pollut Res Int ; 26(32): 32928-32941, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31512128

RESUMO

In this study, MgAl-LDHs and MgFe-LDHs were synthesized via co-precipitation method and in situ coated on pre-washed zeolites through dipping process in beaker. The obtained modified zeolites and original zeolites were utilized as substrates of constructed rapid infiltration systems (CRIS) to remove hexavalent chromium (Cr(VI)) in wastewater. Micro-morphology features and chemical composition of zeolites before and after modification were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence spectrometer (XRF). The SEM, XRD, and XRF results demonstrated the feasibility of LDHs coated on the surface of the original zeolites. Purification experiments in simulated CRIS showed that the Cr(VI) removal rates of zeolites/MgAl-LDHs increased by 110.03% on average every concentration (0.5-16 mg L-1) compared with the original zeolites under 24-h HRT. The adsorption capacity of zeolites/MgAl-LDHs reached 66.98 mg kg-1 at 32 mg L-1 initial Cr(VI) concentration, which is nearly twice that of the original zeolites (33.24 mg kg-1) and 1.5 times higher than that of zeolites/MgFe-LDHs (42.01 mg kg-1). Isothermal adsorption tests showed that the Freundlich isotherm equations gave better fitting to the adsorption process. And zeolites/MgAl-LDHs showed a best fit with pseudo-second-order model which meant that the adsorption of Cr(VI) by zeolites/MgAl-LDHs was dominated by chemisorption. Thermodynamic parameters showed that the process of adsorption for the three substrates was spontaneous and endothermic intrinsically. Zeolites/MgAl-LDHs also displayed nearly 60% desorption rate with low concentration eluent (0.01 mol L-1 NaCl). Therefore, zeolites/MgAl-LDHs were chosen out as an optimal substrate for removing Cr(VI) from wastewater in CRIS. Graphical Abstract.


Assuntos
Cromo/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Zeolitas/química , Adsorção , Cromo/química , Cinética , Hidróxido de Magnésio/química , Microscopia Eletrônica de Varredura , Espectrometria por Raios X , Termodinâmica , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Poluentes Químicos da Água/química , Difração de Raios X
12.
Chemosphere ; 237: 124457, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31382197

RESUMO

It is of significant importance to realize the efficient wastewater treatment and energy recovery. This study presents a multi-functional photocatalytic fuel cell (PFC), which could reductively treat Cr(VI) contaminant and oxidatively degrade organic pollutant simultaneously along with electricity production in an economical strategy. TiO2 nanotube arrays (TNA) and graphite were used as photoanode and cathode in two separated chambers, respectively. The optimized PFC with open circuit voltage of 1.06 V, maximum power density of 1 W m-2 and short circuit current density of 3.7 A m-2 can be obtained by increasing Cr(VI) concentration and decreasing pH values in catholyte. Under optimized PFC conditions, more photogenerated electrons will be transferred to cathode for Cr(VI) reduction, and accelerating electron-hole separation in the photoanode, then facilitating the oxidation of organic pollutants on anode. More than 96.8% removal efficiency for 6.8 mM Cr(VI) with a cathodic efficiency of 95.1% can be achieved within 6 h. Methylene blue (MB), an organic model pollutant, is totally decolorized on photoanode, which is significantly improved compare to photocatalysis (61.5% removal efficiency). The stable cycle operation of this economical PFC has obtained owing to the stable and low cost materials of both photoanode and cathode. This work may provide an efficient and economical method to simultaneously remove two types of pollutants with electricity harvested in one cell.


Assuntos
Cromo/isolamento & purificação , Fontes de Energia Elétrica , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/isolamento & purificação , Cromo/química , Eletricidade , Eletrodos , Desenho de Equipamento , Grafite/química , Concentração de Íons de Hidrogênio , Azul de Metileno/química , Azul de Metileno/isolamento & purificação , Nanotubos/química , Compostos Orgânicos/química , Compostos Orgânicos/isolamento & purificação , Oxirredução , Titânio/química , Eliminação de Resíduos Líquidos/instrumentação , Águas Residuárias/química , Poluentes Químicos da Água/química
13.
Artigo em Inglês | MEDLINE | ID: mdl-31382525

RESUMO

Soil leaching is an effective remediation technique using agents to leach the target pollutants from the soil. However, the dynamics and mechanisms for leaching of Cr and other non-pollutant metals from Cr-contaminated soils are not yet well understood. Here, column leaching experiments were conducted to determine the effect of hydrochloric acid (HCl), citric acid (CA), and oxalic acid (OX) on the leaching of Cr, as well as of Ca, Mg, Fe, and Mn, from a soil contaminated by a Cr slag heap. Acid leaching decreased soil pH and enhanced the mobility of all the surveyed metals. Leaching dynamics varied with both metals and acids. OX had the highest removal rates for Cr, Fe, Mn, and Mg, but had the poorest ability to leach Ca. HCl leached the largest amount of Ca, while CA leached similar amounts of Mg and Mn to OX, and similar amounts of Fe and Cr to HCl. Cr in the leachates was correlated with Ca, Mg, Fe, and Mn. Cr mainly interacted with soil mineral components and showed a punctate distribution in soil particles. The X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) analyses showed soil mineralogical and morphological properties were differently altered after leaching by different acids. Complexation of Cr(III), competitive desorption, and reduction of Cr(VI) make significant contribution to Cr leaching by organic acids. In conclusion, OX can be applied in leaching remediation of Cr-contaminated soil, but the concomitant removal of other non-targeted metals should be taken into account because of the loss of soil minerals and fertility.


Assuntos
Cromo/isolamento & purificação , Ácido Cítrico/química , Ácido Clorídrico/química , Ácido Oxálico/química , Poluentes do Solo/isolamento & purificação , Concentração de Íons de Hidrogênio , Metais/isolamento & purificação , Minerais/isolamento & purificação , Espectroscopia Fotoeletrônica , Solo/química , Espectrometria por Raios X , Difração de Raios X
14.
Environ Sci Pollut Res Int ; 26(29): 30463-30471, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31444721

RESUMO

The remotion of hexavalent chromium in the form of chromate in aqueous solution was done using the aquatic plant Salvinia sp as biosorbent. The chemical modification of the Salvinia surface was performed by organosolv adapted method. The untreated Salvinia and the modified were characterized by infrared spectroscopy, Boehm titration, scanning electron microscopy, energy dispersive system, point of zero charge, surface area analysis, and porosity. Batch adsorption experiments were performed to observe the effects of pH, contact time, initial concentration, and temperature on the metal removal process. The characterization results show the chemistry modifically changed the modified Salvinia structure compared with untreated Salvinia. The adsorption test results showed the maximum adsorption capacity of 26.03 mg g-1. The kinetic equilibrium was reached in about 3 h, and the better temperature and pH were 298 K and 7, respectively. The adsorption and kinetic models were Freundlich and pseud-second order, respectively. This study showed the Salvinia sp after the chemical treatment can be used with biosorbent for hexavalent chromate in the form of chromate, being a natural material with low cost and plentiful in the environment.


Assuntos
Cromo/isolamento & purificação , Traqueófitas/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Brasil , Cromo/química , Concentração de Íons de Hidrogênio , Cinética , Microscopia Eletrônica de Varredura , Soluções , Espectrofotometria Infravermelho , Temperatura , Traqueófitas/metabolismo , Poluentes Químicos da Água/química , Purificação da Água/métodos
15.
Int J Nanomedicine ; 14: 5243-5256, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31409987

RESUMO

Background: Dentin hypersensitivity is a common negative oral condition that can be treated with dentifrice containing hydroxyapatite (HA). The study evaluated the effect of nano-HA dentifrice on plugging the dentinal tubules for an anti-sensitivity reaction compared to a dentifrice containing common-sized particles. Also, the adsorption capacity of different particle sizes of HA mixed in a dentifrice and which is the optimal particle size was considered. Methods: Fourty premolar dentine discs and fourty molar dentine discs were randomly divided into 4 groups: distilled water group, ordinary dentifrice group and 80, 300 nm HA dentifrice group. Each dentin disc was brushed with a dentifrice twice daily at 7600 rpm under 100 g force for 2 mins for 7 consecutive days and divided into two parts, half of the dentin disc was detected by the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the other half was brushed with distilled water and observed by SEM. One milliliter dentifrice solution (80 nm HA dentifrice, 300 nm HA dentifrice, ordinary dentifrice) was added to 50 ml potassium dichromate solution for 1, 14, and 28 d. The residual Chromium (Cr6+) concentration in the supernatant was measured by the diphenylcarbon phthalocyanine hydrazine method. The elemental constitution in the precipitate was detected by EDS. The Kruskal-Wallis test was used to analyze surface mineralization and different plugging rates of dentinal tubules. The absorption capacity of dentifrices were also evaluated by the Kruskal-Wallis test. Results: The plugging rate in the HA dentifrice group was higher than that in the ordinary dentifrice group, and the 80 nm HA dentifrice group showed the best result. The atomic percentages of Ca and P of 80 nm dentifrice group on the surface of dentinal tubules were the highest. The 80 nm HA dentifrice group showed the best adsorption and stable effect of Cr6+, followed by the 300 nm HA dentifrice group. The 300 nm HA dentifrice and the ordinary dentifrice showed desorption phenomenon. Conclusions: The dentifrice containing HA, especially the 80 nm HA dentifrice, exerts good dentinal tubule occlusion and surface mineralization effect. This dentifrice was also a good adsorbent of Cr6+.


Assuntos
Cromo/isolamento & purificação , Dentifrícios/farmacologia , Dentina/efeitos dos fármacos , Durapatita/farmacologia , Tamanho da Partícula , Adsorção , Cálcio/análise , Humanos , Fósforo/análise , Espectrometria por Raios X , Água
16.
Environ Sci Pollut Res Int ; 26(29): 30498-30507, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31444724

RESUMO

MnFe2O4 was a magnetic material that can be used to adsorb contaminants in the wastewater. Fe(II) could act as a reductant to transfer Cr(VI) into Cr(III). In this paper, mesoporous MnFe2O4 prepared by the coprecipitation method was incorporated with Fe(II) to remove Cr(VI). The samples before and after reaction were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. A total of 98~100% of Cr(VI) in solution was removed by MnFe2O4/Fe(II) hybrid system within a wide pH range (pH 3.0-9.0), which is due to the synergetic effects of adsorption from MnFe2O4 and reduction from Fe(II). Cr(VI) was reduced to Cr(III) by ≡Mn(II) on MnFe2O4 and Fe(II). Cr(III) and Fe(III) produced during reaction formed Cr(III)-Fe(III) hydroxides/oxyhydroxides and deposited on MnFe2O4. The inhibiting action of phosphate on the removal of Cr(VI) was greater than that of sulfate. Cr(VI) removal rate retained 94.5% at the fourth recycle test, which showed excellent re-usability of MnFe2O4.


Assuntos
Cromo/isolamento & purificação , Ferro/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Precipitação Química , Cromo/química , Concentração de Íons de Hidrogênio , Hidróxidos , Magnetismo , Manganês/química , Microscopia Eletrônica de Transmissão , Fosfatos/química , Espectroscopia Fotoeletrônica , Sulfatos/química , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Poluentes Químicos da Água/química , Difração de Raios X
17.
Environ Sci Pollut Res Int ; 26(30): 31099-31110, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31452128

RESUMO

To improve the mass transfer efficiency of poly(m-phenylenediamine) for the effective removal of hexavalent chromium (Cr (VI)) from aqueous solution, a facile and one-step method to prepare two-dimensional poly(m-phenylenediamine) functionalized reduction graphene oxide (rGO-PmPD) by dilution polymerization is developed. The structure and morphology of rGO-PmPD as well as rGO and PmPD were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), Fourier-transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD). The preparation mechanism, adsorption performance, and mechanism of rGO-PmPD were then investigated in detail. The obtained rGO-PmPD exhibited thin 2D nanosheet morphology with much improved specific surface area and pore volume (18 and 25 times higher than that of PmPD, respectively). The Cr (VI) adsorption of rGO-PmPD was fitted well with the pseudo-second-order kinetic model and Langmuir isotherm model, and the maximum adsorption capacity of rGO-PmPD reached 588.26 mg g-1, higher than that of PmPD (400 mg g-1) and rGO (156.25 mg g-1). Moreover, the regeneration efficiency of the rGO-PmPD nanosheet is also promising that the adsorption performance after five times of adsorption-desorption cycles still maintains more than 530 mg g-1. The removal mechanism involved reduction coupled with adsorption and electrostatic interaction between rGO-PmPD and Cr (VI), and ~ 65% of Cr (VI) removal was attributed to reduction and ~ 35% was ascribed to adsorption and electrostatic interaction. This study thus provides a simple and effective route to achieve high accessible surface area of adsorbent materials with enhanced mass transfer efficiency and thereafter improved adsorption performance.


Assuntos
Cromo/química , Grafite/química , Fenilenodiaminas/química , Adsorção , Cromo/isolamento & purificação , Cinética , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Nanoestruturas , Espectroscopia Fotoeletrônica , Polimerização , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Eletricidade Estática , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação , Difração de Raios X
18.
PLoS One ; 14(7): e0219387, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31361751

RESUMO

The present study aims to address the problem of chromium (Cr) toxicity by providing important insights into the mechanisms involved in its bioremediation. Among the 22 Rhizobium and Sinorhizobium isolates obtained from Sesbania sesban root nodules, Sinorhizobium sp. SAR1 (JX174035.1) tolerated the maximum Cr concentration (1mM) and hence was used for further studies. The excess secretion of extra polymeric substances, as seen from scanning electron micrographs, could be a probable mechanism of adaptation to the Cr stress. The Energy dispersive X-ray spectroscopy data did not show any peaks of Cr. The biosorption studies done on the isolate gave maximum adsorption capacity as 285.71mg/g. The isotherm studies showed a better fit to Langmuir isotherm. The Weber and Morris plot established that the phenomenon of adsorption was governed by film diffusion mechanism. The FTIR analysis suggested the role of cell wall components and extracellular polymeric substances in Cr adsorption to the biomass of Sinorhizobium. On the basis of these results a compiled mechanism of Cr (VI) adsorption and its biotransformation into Cr (III) by Sinorhizobium sp. SAR1 is explained. This work outlines a comprehensive detail for the exact phenomenon of Cr biotransformation by Sinorhizobium sp. SAR1. These results may further help in developing and enhancing effective bioremediation approaches.


Assuntos
Cromo/metabolismo , Nódulos Radiculares de Plantas/microbiologia , Sinorhizobium/metabolismo , Adsorção , Biomassa , Biotransformação , Cromo/isolamento & purificação , Concentração de Íons de Hidrogênio , Cinética , Sinorhizobium/ultraestrutura , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura
19.
Bioresour Technol ; 291: 121856, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31357040

RESUMO

In this work, cornstalk (CS) was irradiated by high energy electron beam to obtain honeycomb-like porous CS (PCS). The PCS was loaded with ammonium sulfite (AS) and then coated by polyvinyl alcohol (PVA)-Fe3O4 to obtain PCS-AS@PVA-Fe3O4. The PCS-AS@PVA-Fe3O4 could reduce hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) by SO32-, then the Cr(III) combined with PCS-AS@PVA-Fe3O4 through hydrogen bonds. The resulting PCS-AS@PVA-Fe3O4/Cr with a high magnetism could be conveniently separated from water via a magnet. PCS-AS@PVA-Fe3O4/Cr showed a high performance on controlling Cr(VI) migration in soil and uptake by plant. Meanwhile, ammonium could be released from PCS-AS@PVA-Fe3O4, favoring plant growth. Therefore, this work not only provides a promising and low-cost approach to remove Cr(VI) and promote plant growth simultaneously, but also provides a new route for CS recycling, which might have a potential application value.


Assuntos
Compostos de Amônio/química , Cromo/isolamento & purificação , Magnetismo , Álcool de Polivinil/química , Água
20.
Int J Biol Macromol ; 136: 35-47, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31154037

RESUMO

A novel adsorbent, chitosan capsule with filler of CYPH@IL101 (CYPH@IL101/chitosan capsule), was prepared using a summary process for the adsorption of Cr(VI) from aqueous solution. The effects of CYPH@IL101 content, pH, contact time, rotational speed and Cr(VI) concentration on the adsorption were studied. The results showed that the adsorption capacity of the chitosan capsule was benefit from the increase of CYPH@IL101 content. Besides, solution pH also played an important role in the adsorption process and the maximum adsorption capacity was achieved at pH 3. Kinetic studies suggested that the adsorption rate was controlled by the diffusion step at low rotational speed (50 r/min), but was controlled by chemical reaction at high rotational speed (150 and 250 r/min). Furthermore, the adsorption isotherms were studied by using Langmuir, Freundlich, BET, and Temkin models. The results demonstrated that the adsorption process fit Langmuir and TemKin models better, which indicated that the adsorption of Cr(VI) onto CYPH@IL101/chitosan capsule mainly depended on chemisorption and the active sites were uniformly distributed on the adsorbent surface. While, the maximum adsorption capacity obtained from Langmuir model was 104.38 mg/g. Finally, XPS and FTIR analyses revealed that Cr(VI) was adsorbed and then reduced to Cr(III) by CYPH@IL101/chitosan capsule.


Assuntos
Quitosana/química , Cromo/química , Cromo/isolamento & purificação , Líquidos Iônicos/química , Purificação da Água/métodos , Água/química , Adsorção , Cápsulas , Concentração de Íons de Hidrogênio , Cinética , Soluções , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA