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.

Batch Adsorption of Synthetic Dye by Maclura Pomifera, a New Eco-Friendly Waste Biomass: Experimental Studies and Modeling

The removal of Methylene blue (MB) from aqueous medium using alkaline modified Maclura pomifera (NaOH-MMP) has been studied in this work. Results showed that a pH value of 6 was favorable for the adsorption of MB. Rate constants of pseudo-first-order, pseudo-second-order and nth kinetic model were determined to analyze the dynamic of the adsorption process; they showed that adsorption kinetics followed a pseudo-second-order and nth kinetic models. The Sips isotherm model was found to be the most relevant to describe MB sorption onto NaOH-MMP with a correlation factor R2 > 0.999. The adsorption capacity of NaOH-MMP was found to be 160 mg g−1 at 25 °C, confirming its biosorbent efficiency for the removal of MB dye from aqueous solutions. Thermodynamic parameters indicated that the MB adsorption onto adsorbent was feasible in nature, spontaneous, and exothermique.

In-situ generation of gold nanoparticles on MnO2 nanosheets for the enhanced oxidative degradation of basic dye (Methylene Blue)

In this work, the gold nanoparticles (Au-NPs) were in-situ generated on the surface of MnO₂ nanosheets to form MnO₂/Au-NPs nanocomposite in a simple and cost-effective way. Multiple experiments were carried out to optimize the oxidation of basic dye (Methylene Blue (MB)), including the molar ratio of MnO₂ to chloroauric acid (HAuCl₄), the pH of the solution and the effect of initial material. Under the optimal condition, the highest degradation efficiency for MB achieved to 98.9% within 60 min, which was obviously better than commercial MnO₂ powders (4.3%) and MnO₂ nanosheets (74.2%). The enhanced oxidative degradation might attribute to the in-situ generation of ultra-small and highly-dispersed Au-NPs which enlarged the synergistic effect and/or interfacial effect between MnO₂ nanosheets and Au-NPs and facilitated the uptake of electrons by MnO₂ from MB during the oxidation, thus validating the application of MnO₂/Au-NPs nanocomposite for direct removal of organic dyes from wastewater in a simple and convenient fashion.