The synthesis of graphene oxide (GO) nanosheets, to be used as an adsorbent for the removal of textile dyes from wastewater, was optimized by the modified Hummers method. The GO nanosheets produced ...were compared with commercial graphene and characterized by X-ray diffractometry (XRD), Raman spectroscopy, specific surface area analysis, and zero-charge point (pHpcz). Both GO and graphene nanomaterials were originally used to adsorb two coloured dyes (direct red 81 and Indosol SFGL direct blue), which are commonly disposed in textile industrial effluents. Adsorptive assays were performed to determine and compare the variables that most influence the process, such as pH and dye concentration. The mechanisms of adsorption are proposed based on the strong interactions between the graphene oxide (due to its high functionalization with hydroxyl and carboxylic groups) and the active functional groups of the dyes (according to its colour) that, in general, overcome the weaker electrostatic forces between water/commercial graphene/dye systems.
After preparing composite PSGO films by coating electrospun polystyrene (PS) fibers with graphene oxide (GO), we examined their use as dye adsorbents for water remediation. The GO, which was ...synthesized via a modified Hummers' method, was adsorbed on the surface of the PS fibers. Through X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TGA) analyses, we characterized the structure and morphology of the composite films, confirming that the GO was successfully incorporated onto the PS fibers. SEM images revealed that the PS fibers exhibited a smooth surface and that the GO was uniformly deposited on them. TGA analysis indicated that the PSGO is composed of ∼13 wt% GO and ∼87 wt% PS, and that both components exhibited similar thermogravimetric behavior. We examined the removal of the methylene blue (MB) dye from aqueous solutions as a model system to assess the adsorptive properties of the PSGO films. The composite films had a removal capacity that was approximately 2.3 times greater than that of pure PS membranes. For all MB concentrations investigated, the removal of the dye, which was very fast in the first 30 min, the equilibrium value of the adsorption capacity (qe = 114 mg g−1) was reached after 120 min. The kinetics of the adsorption process was best described by the pseudo-second-order (PSO) model, which predicted an adsorption capacity (qt) of 116.69 mg g−1.
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•Fabrication and use of electrospun polystyrene fiber covered with graphene oxide.•GO-coated polystyrene is a promising adsorbent of the Methylene Blue dye.•Outstanding adsorptive capacity in comparison to other reported adsorbents.
The local electrical properties of a conductive graphene/polystyrene (PS) composite sample are studied by scanning probe microscopy (SPM) applying various methods for electrical properties ...investigation. We show that the conductive graphene network can be separated from electrically isolated graphene sheets (GS) by analyzing the same area with electrostatic force microscopy (EFM) and conductive atomic force microscopy (C‐AFM). EFM is able to detect the graphene sheets below the sample surface with the maximal depth of graphene detection up to ≈100 nm for a tip‐sample potential difference of 3 V. To evaluate depth sensing capability of EFM, the novel technique based on a combination of SPM and microtomy is utilized. Such a technique provides 3D data of the GS distribution in the polymer matrix with z‐resolution on the order of ≈10 nm. Finally, we introduce a new method for data correction for more precise 3D reconstruction, which takes into account the height variations.
The conductive graphene network in a conductive graphene/polystyrene composite sample is separated from electrically isolated graphene sheets by analyzing the same area with conductive atomic force microscopy (C‐AFM) and electrostatic force microscopy (EFM). The novel technique based on combination of a scanning probe microscope and microtome is utilized for 3D reconstruction of the graphene sheets in the polymer matrix with z‐resolution in the order of ≈ 10 nm.
The concept of physical adsorption was applied for the removal of direct and reactive blue textile dyes from industrial effluents. Commercial graphite nanoplatelets were used as substrate, and the ...quality of the material was characterized by atomic force and transmission electron microscopies. Dye/graphite nanoplatelets water solutions were prepared varying their pH and initial dye concentration. Exceptionally high values (beyond 100 mg/L) for adsorptive capacity of graphite nanoplatelets could be achieved without complicated chemical modifications, and equilibrium and kinetic experiments were performed. Our findings were compared with the state of the art, and compared with theoretical models. Agreement between them was satisfactory, and allowed us to propose novel considerations describing the interactions of the dyes and the graphene planar structure. The work highlights the important role of these interactions, which can govern the mobility of the dye molecules and the amount of layers that can be stacked on the graphite nanoplatelets surface.
Textile effluent is one of the most hazardous types of wastewater for both the environment and human health when discharged without proper treatment. This work stands out as one of the first to ...evaluate the parameters for the application of graphene oxide (GO) to treat real textile wastewater. A comparative analysis was conducted to investigate the removal efficiencies of turbidity and apparent colour from raw textile wastewater using GO. The effects of different parameters, such as GO dosage, pH, and contact time were discussed, considering a removal mechanism based on the salting out effect. Results regarding treatment using GO followed by centrifugation showed that in >1 hour nearly 90% turbidity was decreased, and an apparent colour removal efficiency over 76% was recorded, which is twice the value obtained with the conventional treatment applied in textile mills. Over 60% chemical oxygen demand was reduced. Tests using GO followed by sedimentation also revealed promising results, showing removal efficiencies of 66% and 88% for apparent colour and turbidity, respectively. These results suggest that GO could be promising for real wastewater treatment.
Real textile wastewater treatment using graphene‐based material.
ABSTRACT The functionalization of graphene nanosheets is the cutting edge of materials sciences nowadays. Such research promotes the development of innovative, low cost and highly capable sorbents. ...This review article aims to assemble the available information on functionalized graphene used for the adsorption of organic pollutants and establishes a critical comparison between the data reported in the literature. Various optimal experimental conditions (pH, temperature, contact time, adsorbent dosage) and adsorbent characterization methods (FTIR, Raman, XPS spectra, XRD, TEM and AFM) have been listed to enlighten adsorption mechanisms, capacity and limiting aspects. Moreover, adsorption isotherms, kinetics and thermodynamic data of different functionalized graphene-based materials towards a wide range of organic pollutants were analyzed and tabulated. In each evaluation topic, environmental and human health protection is subject for discussion, as well as the scientific breakthrough works available in high impact journals in the field.
Commercial microporous polyamide (PA) membranes were smoothly coated with different aliquots of graphene oxide (GO) water solution and crosslinked with polyvinyl alcohol (PVA)/citric acid (CA). The ...functionalized membrane was attached to a low-cost and easy-to-assemble portable filtration unit for the removal of mono- and bivalent salt from brackish water. The structure and morphology of GO, which was synthesized via a modified Hummers method, and the as-prepared membranes, were characterized through X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). FTIR revealed the same bands for GO and the modified membranes, typical of oxygenated groups vibrations. XRD of crosslinked membranes exhibited traces of crystalline phases probably induced by GO-PVA interactions. SEM images revealed that the PA membranes exhibited an irregular porous geometry and that the GO sheets were uniformly deposited on them, forming a multilayer coat ranging from ∼0.3 to ∼0.5 µm thickness, depending on the amount of GO deposited. Tests using ultrasonic bath showed that the PVA/CA reticulation enhanced the mechanical stability of the membranes, by promoting esterification crosslinking reactions of the carboxyl groups, from the citric acid, with the hydroxyl groups, from the PVA and GO. The membranes were evaluated through salt rejection capacity for magnesium sulfate (MgSO4) and sodium chloride (NaCl) ions in aqueous solutions. Polyamide membranes modified with GO aliquots of 0.75 mg exhibited the best performance, with rejection of 55 % and permeability of 1.42 L/m².h.bar for Mg+2, and rejection of 37 % and permeability of 2.08 L/m².h.bar for Na+. Furthermore, they can guarantee> 29 % retention for Mg+2 ions on the third reuse. These results indicate the potential for desalination of solutions with divalent and monovalent ions. The advances achieved during this work showed practical potentialities to be applied in portable desalination systems.
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•PA membranes were functionalized with graphene oxide and PVA/citric acid.•A low-cost and portable filtration unit was built to treat brackish water.•Most divalent ions, and a part of the monovalent ions, could be separated.•The results showed practical potentialities to be applied in desalination systems.
In the present study, we have investigated the influence of La3+ cations insertion on the crystallography, morphology, and magnetic properties of Y3Fe5-xLaxO12 compound, (x = 0.00 and 0.03) obtained ...by the sol-gel method. To confirm the Fe3+ by La3+ cations replacement and quantify the structural parameters, the Rietveld refinement method was used. The quantitative analysis confirmed that, the La3+ cations insertion in the YIG crystal structure affect significative the lattice constant, crystallite size, microstrain, sites occupancy, bond angles and distances. Room temperature Raman spectra also confirmed the YIG single phase structure. The spectra deconvolution pointed shifts for smaller wavenumber in the sample containing La3+ cations, specifically in the region between 400 and 800 cm−1, correlated with the octahedral and tetrahedral sites. The coral format morphology was confirmed by Scanning and Transmission Electron Microscopies. Lastly, room temperature magnetic measurements demonstrated that the La3+ cations insertion in the YIG crystal structure, provokes an increase in the saturation magnetization (Ms), remanent magnetization (Mr) and magnetocrystalline anisotropy (K1) of 24.8, 17.5, and 9.3%, respectively, respect to the values obtained for undoped YIG sample.
A latex technique is used to prepare graphene/polystyrene and graphene/poly(propylene) composites with varying GR loadings. Their electrical properties and the corresponding volume organisation of GR ...networks are studied. Percolation thresholds for conduction are found to be about 0.9 and 0.4 wt% for GR/PS and GR/PP with maximum obtained conductivities of 12 and 0.4 S m−1 for GR loadings of 2 wt%, respectively. Investigations using SEM and electrical conductivity measurements show that for the preparation conditions used GR forms an isotropic 3D network in the PS matrix, but GR forms a 2D network in the PP matrix. The different GR network organisations are possibly forced by the different melt flow behaviour of the matrix polymers during processing and the subsequent crystallisation of PP.
Graphene forms different networks in the volume of PS and PP matrixes, which are visualised by means of SEM and confirmed by electrical conductivity measurements performed in various directions. The different network organisation can be explained by the different flow and crystallisation behaviour of the polymer matrixes during processing.
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