Removal of methylene blue using MnO2@rGO nanocomposite from textile wastewater: Isotherms, kinetics and thermodynamics studies

Process Optimization and Equilibrium, Thermodynamic, and Kinetic Modeling of Toxic Congo Red Dye Adsorption from Aqueous Solutions Using a Copper Ferrite Nanocomposite Adsorbent

In the present investigation of copper ferrite, a CuFe2O4 nanocomposite adsorbent was synthesized using the sol-gel method, and its relevance in the adsorptive elimination of the toxic Congo red (CR) aqueous phase was examined. A variety of structural methods were used to analyze the CuFe2O4 nanocomposite; the as-synthesized nanocomposite had agglomerated clusters with a porous, irregular, rough surface that could be seen using FE-SEM, and it also contained carbon (23.47%), oxygen (44.31%), copper (10.21%), and iron (22.01%) in its elemental composition by weight. Experiments were designed to achieve the most optimized system through the utilization of a central composite design (CCD). The highest uptake of CR dye at equilibrium occurred when the initial pH value was 5.5, the adsorbate concentration was 125 mg/L, and the adsorbent dosage was 3.5 g/L. Kinetic studies were conducted, and they showed that the adsorption process followed a pseudo-second-order (PSO) model (regression coefficient, R2 = 0.9998), suggesting a chemisorption mechanism, and the overall reaction rate was governed by both the film and pore diffusion of adsorbate molecules. The process through which dye molecules were taken up onto the particle surface revealed interactions involving electrostatic forces, hydrogen bonding, and pore filling. According to isotherm studies, the equilibrium data exhibited strong agreement with the Langmuir model (R2 = 0.9989), demonstrating a maximum monolayer adsorption capacity (qmax) of 64.72 mg/g at pH 6 and 302 K. Considering the obtained negative ΔG and positive ΔHads and ΔSads values across all tested temperatures in the thermodynamic investigations, it was confirmed that the adsorption process was characterized as endothermic, spontaneous, and feasible, with an increased level of randomness. The CuFe2O4 adsorbent developed in this study is anticipated to find extensive application in effluent treatment, owing to its excellent reusability and remarkable capability to effectively remove CR in comparison to other adsorbents.

Turning waste avocado stones and montmorillonite into magnetite-supported nanocomposites for the depollution of methylene blue: adsorbent reusability and performance optimization

The existence of methylene blue (MB) in wastewater even as traces is raising environmental concerns. In this regard, the performances of four adsorbents, avocado stone biochar (AVS-BC), montmorillonite (MMT), and their magnetite Fe3O4-derived counterparts, were compared. Results showed the superior performance of Fe3O4@AVS-BC and Fe3O4@MMT nanocomposites with removal percentages (%R) of 95.59% and 88%. The morphological features of AVS-BC as revealed by SEM analysis showed a highly porous surface compared to a plane and smooth surface in the case of MMT. Surface analysis using FT-IR and Raman spectroscopies corroborated the existence of the Fe-O peaks upon loading with magnetite. The XRD analysis confirmed the formation of cubic magnetite nanoparticles. The adsorption process in the batch mode was optimized using central composite design (CCD). Equilibrium and kinetic isotherms showed that the adsorption of MB onto Fe3O4@AVS-BC fitted well with the Langmuir isotherm and the pseudo-second-order (PSO) model. The maximum adsorption capacity (qm) was 118.9 mg/g (Fe3O4@AVS-BC) and 72.39 mg/g (Fe3O4@MMT). The Fe3O4@AVS-BC showed a higher selectivity toward MB compared to other organic contaminants. The MB-laden adsorbent was successfully used for the remediation of Cr (III), Ni (II), and Cd (II) with removal efficiencies hitting 100% following thermal activation.

Study on Electrochemical Performance of MnO@rGO/Carbon Fabric-Based Wearable Supercapacitors

In this work, we reported the electrochemical performance of a type of carbon fabric-based supercapacitor by coating MnOx@rGO nanohybrids on carbon fabric with a simple one-step hydrothermal method. We studied the mass ratio of MnOx to rGO on the electrochemical properties of the carbon fabric-based supercapacitors. We found that as the mass ratio is 0.8:1 for MnO@rGO, the supercapacitor with a loading of 5.40 mg cm^-2 of MnO@rGO nanohybrids on carbon fabric exhibits a specific capacitance of 831.25 mF cm^-2 at 0.1 mA cm^-2 current density. It also shows long-term cycling capacitance retention of 97.2% after 10,000 charge-discharge cycles at a current density of 0.4 mA cm^-2. We speculate that the high electrochemical performance results from the strong interfacial bonding between the hierarchical architecture of MnO@rGO nanohybrids and carbon fabric.