Elimination of hazardous methylene blue from contaminated solutions by electrochemically magnetized graphene oxide as a recyclable adsorbent

Polydopamine-modification of a magnetic composite constructed from citric acid-cross-linked cyclodextrin and graphene oxide for dye removal from waters

The effect of polydopamine (PDA) modification on aminated Fe₃O₄ nanoparticles (Fe₃O₄-NH₂)/graphite oxide (GO)/β-cyclodextrin polymer cross-linked by citric acid (CDP-CA) composites were studied for the removal of a cationic dye (methylene blue, MB) and an anionic dye (Congo red, CR) from waters. The micro-structural and magnetic characterizations confirmed the successful preparation of Fe₃O₄-NH₂/GO/CDP-CA and PDA/Fe₃O₄-NH₂/GO/CDP-CA composites. The maximum MB and CR adsorption capacities of Fe₃O₄-NH₂/GO/CDP-CA were 75 mg/g and 104 mg/g, respectively, while the corresponding amounts for PDA/Fe₃O4-NH₂/GO/CDP-CA composite were 195 mg/g and 64 mg/g, respectively. The dye sorption behaviors of these two composites were explained by their corresponding surface-charged properties according to the measured zeta potential results. Moreover, the high saturation magnetizations and the stable dye removal rate in the adsorption-desorption cycles indicated the good recyclability and reusability of the fabricated composites.

Insights on synthesis and applications of graphene-based materials in wastewater treatment: A review

Graphene has excellent unique thermal, chemical, optical, and mechanical properties such as high thermal conductivity, high chemical stability, optical transmittance, high current density, higher surface area, etc. Due to their outstanding properties, the attention towards graphene-based materials and their derivatives in wastewater treatment has been increased in recent times. Different graphene-based materials such as graphene oxides, graphene quantum dots, graphene nanoplatelets, graphene nanoribbons and other graphene-based nanocomposites are synthesized through chemical vapor deposition, mechanical and electrochemical exfoliation of graphite. In this review, the specifics about the graphenes and their derivatives, the synthesis strategy of graphene-based materials are described. This review critically explained the applications of graphene-based materials in wastewater treatment. Graphene-based materials were utilized as adsorbents, electrodes, and photocatalysts for the efficient removal of toxic pollutants such as heavy metals, dyes, pharmaceutics, antibiotics, phenols, polycyclic aromatic hydrocarbons have been highlighted and discussed. Herein, the potential scope of graphene-based material in the field of wastewater treatment is critically reviewed. In addition, a brief perspective on future research directions and difficulties in the synthesis of graphene-based material are summarized.

Removal of Methylene Blue from Aqueous Solutions by Using Nance (Byrsonima crassifolia) Seeds and Peels as Natural Biosorbents

Contamination of effluents with chemicals is a serious problem that impacts human health. Methylene blue is a cationic dye found frequently in industrial and urban sewages. In this work, dried grinded seeds and peels of nance were used as biosorbents in aqueous solutions at pH 7 and 10 (simulating urban and textile effluents) finding that Langmuir and Freundlich isotherms adequately described the sorption. Adsorption efficiencies were larger than 98% in all cases and slightly lower at pH 7 due to the closeness with the point of zero charge (pzc) of seeds and peels of nance (5.96 and 3.42, respectively). In all cases, Langmuir adsorption was favorable (RLa < 1), and Gibbs free energy of adsorption was negative indicating spontaneity, and since these values were larger than −80 but lower than 0 kJ/mol, the MB removal process was mainly due to physical interactions, a characteristic of physical adsorption. No significant differences were found amongst bulk mass transfer coefficients for the adsorption of both sorbents, indicating that both bioadsorbents had the same hydrodynamic and driving forces as well as depicted similar MB-adsorbent affinities. Interaction of MB with adsorbents was corroborated by FTIR spectroscopy, and the sorption was evidenced by scanning electron microscopy and image analysis which indicated that both adsorbents had fractal structures.

2D/2d heterojunction of MoS2/g-C3N4 nanoflowers for enhanced visible-light-driven photocatalytic and electrochemical degradation of organic pollutants

Photodegradation of toxic pollutants is a promising approach to deal with wastewater management. In this regard, MoS₂/g-C₃N₄ (MSC) derived composites with varying weight-ratios were prepared via fast (30 min) one step microwave-assisted method. The materials were characterized by XRD, XPS, EDS, FESEM and HRTEM to validate their flower-like and sheet-like morphologies. The PL and UV-vis DRS spectra exhibited low recombination-rate and band-gap (1.7 eV), which is appropriate for an effective visible-light degradation. Photocatalytic performance of the catalysts was analyzed by investigating the degradation of methylene blue (MB) as well as pesticide fipronil. Best results were obtained by 5:1 MSC (98.7% degradation efficacy; rate constant 0.0261 min^-1) in 80 min under the sunlight. The effects of solution pH, catalyst-dose, scavengers and illumination-area were also explored. The catalyst was reusable as confirmed by degradation studies (~82% efficiency) even after 5-cycles. The photocatalytic treatment of real industrial-wastewater was also conducted. The TOC and COD analysis validated that the treatment by as-prepared catalyst is more proficient for effluent-treatment than the industrial physico-chemical treatments. Electrochemical degradation of MB was also investigated using the glassy carbon electrode modified with different MSC-ratios. The electrode modified with 5:1 MSC at pH 7 manifested the maximum peak current. The plausible mechanisms for photocatalytic and electrochemical degradations were proposed, which suggested the remarkable potential the prepared nanocomposites for wastewater treatment.

A simple synthesis of ZnO:Co2O3 nanocomposites by pulsed laser irradiation in liquid

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ZnO:Co₂O₃ nanocomposites by pulsed laser irradiation in water.

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Morphology was modified by laser irradiation and Co₂O₃ content.

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Elemental composition and their chemical states were confirmed by XPS.

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Nanocomposites showed higher visible light absorption compared to ZnO.

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Thin films of the ZnO:Co₂O₃ nanocomposites showed visible light photocatalysis.

Nanocomposite materials are emerging in popularity due to their enhanced performance over the constituent materials. In this work, we report the fabrication of zinc oxide: cobalt oxide nanocomposites in a simple, fast and room temperature synthesis with good productivity. The nanocomposites synthesized were characterized by SEM, XPS and UV–Visible spectroscopy to analyze their morphology, composition, chemical states, optical absorption, band gap etc. The nanocolloids of the composite were drop casted to form thin films for photocatalytic studies. In SEM analysis, the morphological transformation of the material is observed where it transformed from agglomerated spherical particles to petals shaped and then to partially spherical forms due to pulsed laser irradiation. XPS analysis showed a gradual change in oxygen high resolution spectra in the samples with respect to the concentration difference of cobalt oxide. The optical studies show an enhanced absorption in visible region for the nanocomposite and the energy band gap reduced to 2.4 eV. All the thin films of nanocomposite showed photocatalytic decay of methylene blue dye under visible light irradiation. The results of this study support the effective use of laser irradiation in liquid to obtain nanocomposites of metal oxides for photocatalytic applications.

Highly Efficient Removal of Methylene Blue Dye from an Aqueous Solution Using Cellulose Acetate Nanofibrous Membranes Modified by Polydopamine

A new type of deacetylated cellulose acetate (DA)@polydopamine (PDA) composite nanofiber membrane was fabricated by electrospinning and surface modification. The membrane was applied as a highly efficient adsorbent for removing methylene blue (MB) from an aqueous solution. The morphology, surface chemistry, surface wettability, and effects of operating conditions on MB adsorption ability, as well as the equilibrium, kinetics, thermodynamics, and mechanism of adsorption, were systematically studied. The results demonstrated that a uniform PDA coating layer was successfully developed on the surface of DA nanofibers. The adsorption capacity of the DA@PDA nanofiber membrane reached up to 88.2 mg/g at a temperature of 25 °C and a pH of 6.5 after adsorption for 30 h, which is about 8.6 times higher than that of DA nanofibers. The experimental results showed that the adsorption behavior of DA@PDA composite nanofibers followed the Weber's intraparticle diffusion model, pseudo-second-order model, and Langmuir isothermal model. A thermodynamic analysis indicated that endothermic, spontaneous, and physisorption processes occurred. Based on the experimental results, the adsorption mechanism of DA@PDA composite nanofibers was also demonstrated.