Adsorptive Removal of Cd, Cu, Ni and Mn from Environmental Samples Using Fe3O4-Zro2@APS Nanocomposite: Kinetic and Equilibrium Isotherm Studies

An exploration of RSM, ANN, and ANFIS models for methylene blue dye adsorption using Oryza sativa straw biomass: a comparative approach

This study focused on simulating the adsorption-based separation of Methylene Blue (MB) dye utilising Oryza sativa straw biomass (OSSB). Three distinct modelling approaches were employed: artificial neural networks (ANN), adaptive neuro-fuzzy inference systems (ANFIS), and response surface methodology (RSM). To evaluate the adsorbent's potential, assessments were conducted using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The evaluation of RSM, ANN, and ANFIS included the quantification of R2, mean squared error (MSE), root mean square error (RMSE), and mean absolute error (MAE) metrics. The regression coefficients from the process modelling demonstrated that RSM (R2 = 0.9216), ANN (R2 = 0.8864), and ANFIS (R2 = 0.9589) all accurately predicted MB adsorptive removal. However, comparative statistical analysis revealed that the ANFIS model exhibited superior accuracy in data-based predictions compared to ANN and RSM models. The ideal pH for MB adsorption utilizing OSSB was established as 7. Additionally, favourable outcomes were obtained with 60-minute contact durations, 20 mg adsorbent quantities, and temperatures of 30 °C. The pseudo 2nd -order kinetic model for MB adsorption by OSSB was confirmed. The equilibrium data exhibited a superior fit with the Langmuir isotherm model in comparison to the Freundlich model. The thermodynamic adsorption parameters, including (∆G = -9.1489 kJ/mol), enthalpy change (∆H = -1457.2 kJ/mol), and entropy change (∆S = -19.03 J mol-1 K-1) indicated that the adsorption of MB onto the OSSB surface is exothermic and spontaneous under the experimental conditions. This research effectively showcased the potential of RSM, ANN, and ANFIS in simulating dye removal using OSSB. The generated parameter data proved valuable for the design and control of the adsorption process.

Cell Morphology, Material Property and Ni(II) Adsorption of Microcellular Injection-Molded Polystyrene Reinforced with Graphene Nanoparticles

Graphene's incorporation into polymers has enabled the development of advanced polymer/graphene nanocomposites with superior properties. This study focuses on the use of a microcellular foamed polystyrene (PS)/graphene (GP) nanocomposite (3 wt%) for nickel (II) ion removal from aqueous solutions. Adsorption behavior was evaluated through FTIR, TEM, SEM, TGA, and XRD analyses. Key factors, including initial ion concentration, pH, temperature, and sorbent dosage, were examined. Results showed optimal nickel removal at specific pH levels with removal efficiency decreasing from 91 to 80% as Ni (II) concentrations increased from 10 to 100 mg/L. The adsorption capacity improved from 11 to 130 mg/g. Equilibrium data aligned with Langmuir and Freundlich isotherm models, while adsorption kinetics followed a second-order kinetic model. These findings highlight the potential of PS/GP nanocomposites for nickel ion removal, offering a promising solution for small-scale industrial applications.

Comparative Seasonal Trends and Potential Health Impacts of Arsenic and Chromium in Surface Water after Adsorption Using Highly Dispersed Fe3O4 Nanoparticles

Surface water from springs, rivers, and dams is often used as an unconventional drinking water source in rural areas where potable water is often unavailable. However, this practice carries significant health risks due to potential contaminants. In this study, the concentrations of arsenic (As) and chromium (Cr) were assessed seasonally using graphite furnace atomic absorption spectrometry (GFAAS). Highly dispersed Fe3O4 nanoparticles were synthesized, characterized, and utilized as adsorbents to remove As and Cr ions from various water matrices. The removal process was optimized by adjusting the mass of the nanoparticles, pH levels, and sonication time. To further understand the adsorption process, adsorption isotherms and kinetics were conducted. Physicochemical properties such as pH, electrical conductivity, and total dissolved solids were seasonally evaluated. The average As concentrations were in the range of 13.3-46.8 µg/L, while Cr was in the range of 1.02-5.04 µg/L. Expectedly, higher concentrations of As and Cr were observed in summer when there was intense precipitation, and the lowest concentrations were observed in winter, with little to no precipitation. The calibrated GFAAS displayed an excellent limit of detection, limit of quantification, and linearity of 0.092-0.13, 0.27-0.34, and 0.27-70 µg/L for As, while 0.031-0.07, 0.16-0.21, and 0.16-70 µg/L were attained for Cr, respectively. Arsenic levels exceeded 10 µg/L in all seasons, indicating that these concentrations were above the maximum permitted levels set by the World Health Organization and the South African National Standards. According to the health risk assessment, high As concentrations were alarming, as they were seasonally increasing, with the chronic daily intake exceeding the oral reference dose, whilst the incremental lifetime cancer risk was significantly high.

Functionalization of a cast NaAl/binary ZnO/SiO2 nanohybrid with amine and Schiff base ligands as an adsorbent of divalent cations in water system

Casting method was used to synthesize a novel sodium alginate nanohybrid functionalized with aminated ZnO/SiO2 Schiff base for adsorption of nickel (Ni2+) and copper (Cu2+) divalent cations in single and binary water systems. The cast Schiff base nanohybrids were investigated using FESEM, XRD, BET, FTIR, TGA, and XPS analyses. The influence of unfunctionalized binary ZnO/SiO2 nano oxides and aminated Schiff base ligands formed by the reaction between salicylaldehyde and O-phenylenediamine on the adsorption of Ni2+ and Cu2+ cations was evaluated. The results confirmed that the aminated Schiff base ligands led to a higher adsorption ability of the cast nanohybrids containing interaction of divalent cations with nitrogen and oxygen atoms, as well as carboxyl and hydroxyl groups. The adsorption kinetics and isotherm for both cations followed a double-exponential model and the Redlich-Peterson model, respectively. The maximum monolayer capacity was found to be 249.8 mg/g for Cu2+ cation and 96.4 mg/g for Ni2+ cation. Thermodynamic analysis revealed an endothermic and spontaneous adsorption process with an increase in entropy. Furthermore, the synthesized Schiff base adsorbent could be easily reused over five times. The simultaneous adsorption in binary system exhibited a higher adsorption selectivity of the cast Schiff base nanohybrid for Cu2+ cation compared to Ni2+ cation. It was found that the removal percentages of Cu2+ and Ni2+ from industrial electroplating wastewater were 91.3 and 64.5%, respectively. Lastly, cost analysis of the synthesized nanohybrid was investigated.

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

In this study, the adsorptive removal of methylene blue dye, which is commonly used in textile industries, was investigated using the MnO₂@reduced graphene oxide (rGO) adsorbent. The sonication-assisted synthesis from rGO nanosheets and MnO₂ nanoparticles resulted to the MnO₂@rGO nanocomposite with improved physicochemical properties. The characterization results showed the improved surface area, porous structure and adsorption sites from the nitrogen adsorption-desorption studies, improved morphology from the Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) and the improved crystal structure from X-ray powder diffraction (XRD). The improved physicochemical properties on the MnO₂@rGO nanocomposite played a significant role in enhancing the dye removal in textile wastewater. The equilibrium experimental data was best described by the Langmuir isotherm model with a maximum adsorption capacity of 156 mg g^-1, suggesting a monolayer adsorption. The kinetic data best fitted the pseudo-second order kinetic model, suggesting a chemisorption adsorption process. The thermodynamic data (ΔG°, ΔH° and ΔS°) confirmed the feasibility, randomness and spontaneous nature of the adsorption process. The mechanism of adsorption involved the hydrogen bonding, π-π interactions and electrostatic interactions. The removal of methylene blue using MnO₂@rGO nanocomposite in spiked textile wastewater yielded a 98-99% removal. The method demonstrated competitiveness when compared with literature reported results, paving way for further investigations towards industrial scale applications.

Activated carbon derived from waste orange and lemon peels for the adsorption of methyl orange and methylene blue dyes from wastewater

The study of adsorbent behaviour in laboratory conditions helps to predict the adsorption process in a large industrial scale. In this study, orange and lemon peels-derived activated carbon (OLPAC) was successfully synthesized and activated using phosphoric acid. Characterization was performed on the OLPAC and the material was used for the removal of methyl orange (MO) and methylene (MB) dyes from wastewater. The results of the scanning electron microscope and N₂ adsorption/desorption examination affirmed that the prepared nanocomposite is permeable, which is an advantage for the efficient removal of contaminants. Optimal conditions for the batch removal process were investigated using a one-factor time approach in different conditions of adsorption (Dye concentration 50–200 mg L⁻¹, pH 2–10, adsorbent mass 0.010–0.8, and contact time 5–180 min. The adsorption isotherm equilibrium data were examined by Langmuir, Freundlich, and Temkin, isotherm model. As shown by the correlation coefficient (R²), the data were best described by Langmuir isotherms with maximum adsorption capacities of 33 and 38 mg g^─1 for methyl orange and methylene blue, respectively. Adsorption kinetic data were described using the pseudo-second-order model which suggests that adsorption of MO and MB was by chemisorption mechanism. The method was applicable to real wastewater samples, with satisfactory removal percentages of OM and MB (96 and 98 %). The results of this study show that OLPAC is an inexpensive biosorbent that is successfully utilized in removing methyl orange and methylene blue dyes from wastewater.

MnO2@Reduced Graphene Oxide Nanocomposite-Based Electrochemical Sensor for the Simultaneous Determination of Trace Cd(II), Zn(II) and Cu(II) in Water Samples

The rapid detection of trace metals is one of the most important aspect in achieving environmental monitoring and protection. Electrochemical sensors remain a key solution for rapid detection of heavy metals in environmental water matrices. This paper reports the fabrication of an electrochemical sensor obtained by the simultaneous electrodeposition of MnO₂ nanoparticles and RGO nanosheets on the surface of a glassy carbon electrode. The successful electrodeposition was confirmed by the enhanced current response on the cyclic voltammograms. The XRD, HR-SEM/EDX, TEM, FTIR, and BET characterization confirmed the successful synthesis of MnO₂ nanoparticles, RGO nanosheets, and MnO₂@RGO nanocomposite. The electrochemical studies results revealed that MnO₂@RGO@GCE nanocomposite considerably improved the current response on the detection of Zn(II), Cd(II) and Cu(II) ions in surface water. These remarkable improvements were due to the interaction between MnO₂ nanomaterials and RGO nanosheets. Moreover, the modified sensor electrode portrayed high sensitivity, reproducibility, and stability on the simultaneous determination of Zn(II), Cd(II), and Cu(II) ions. The detection limits of (S/N = 3) ranged from 0.002–0.015 μg L⁻¹ for the simultaneous detection of Zn(II), Cd(II), and Cu(II) ions. The results show that MnO₂@RGO nanocomposite can be successfully used for the early detection of heavy metals with higher sensitivity in water sample analysis.