This work is dedicated to the synthesis, characterization, and adsorption performance of reduced graphene oxide-modified spinel cobalt ferrite nanoparticles. The as-synthesized reduced graphene oxide cobalt ferrite (RGCF) nanocomposite has been characterized using FTIR spectroscopy, FESEM coupled with EDXS, XRD, HRTEM, zeta potential, and vibrating sample magnetometer (VSM) measurements. FESEM proves the particle size in the range of 10 nm. FESEM, EDX, TEM, FTIR, and XPS analyses provide the proof of successful incorporation of rGO sheets with cobalt ferrite nanoparticles. The crystallinity and spinel phase of cobalt ferrite nanoparticles have been shown by XRD results. The saturation magnetization (M _s) was measured as 23.62 emu/g, proving the superparamagnetic behavior of RGCF. The adsorption abilities of the synthesized nanocomposite have been tested using cationic crystal violet (CV) and brilliant green (BG) and anionic methyl orange (MO) and Congo red (CR) dyes. The adsorption trend for MO, CR, BG, and As(V) follows RGCF > rGO > CF at neutral pH. Adsorption studies have been accomplished by optimizing parameters like pH (2-8), adsorbent dose (1-3 mg/25 mL), initial concentration (10-200 mg/L), and contact time at constant room temperature (RT). To further investigate the sorption behavior, isotherm, kinetics, and thermodynamic studies have been conducted. Langmuir isotherm and pseudo-second-order kinetic models suited better for the adsorption of dyes and heavy metals. The maximum adsorption capacities (q _m) obtained have been found as 1666.7, 1000, 416.6, and 222.2 mg/g for MO, CR, BG, and As, respectively, with operational parameters such as T = 298.15 K; RGCF dose: 1 mg for MO and 1.5 mg each for CR, BG, and As. Thus, the RGCF nanocomposite was found to be an excellent adsorbent for the removal of dyes and heavy metals.

The development of competent adsorbents based on agro-waste materials with multifunctional groups and porosity for the removal of toxic dyes from aqueous solutions is still a challenge. Herein, a bionanocomposite made up of neem leaf powder (NLP), zinc oxide (ZnO), and amino acid (l-cysteine)-functionalized polyaniline (PANI), namely, NLP/ZnO@l-cysteine-grafted-PANI (NZC-g-PANI), has been prepared by an in situ polymerization method. The as-prepared bionanocomposite was tested for the adsorptive removal of three anionic dyes, namely, methyl orange (MO), amido black 10B (AB 10B), and eriochrome black T (EBT), as well as three cationic dyes, namely, brilliant green (BG), crystal violet (CV), and methylene blue (MB), from synthetic aqueous medium. The morphological and structural characteristics of the NZC-g-PANI nanocomposite were examined with the help of HR field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopy. FTIR and Raman studies show that the formulated NZC-g-PANI have an ample number of functional moieties such as carboxyl (-COOH), hydroxyl (-OH), amines (-NH₂), and imines (-N=), thus demonstrating outstanding dye removal capacity. C-S linkage helps to attach l-cysteine with polyaniline. Moreover, the predominance of chemisorption via ionic/pi-pi interaction and hydrogen bonding between the NZC-g-PANI nanocomposite and dyes (BG and MO) has been realized by FTIR and fitting of kinetics data to the PSO model. For both BG and MO dyes, the biosorption isotherm was precisely accounted for by the Langmuir isotherm with q _max values of up to 218.27 mg g^-1 for BG at pH 6 and 558.34 mg g^-1 for MO at pH 1. Additionally, thermodynamic studies revealed the endothermic and spontaneous nature of adsorption. NZC-g-PANI showed six successive regeneration cycles for cationic (MO: from 96.3 to 90.4%) and anionic (BG: from 94.7 to 88.7%) dyes. Also, batch adsorption operations were validated to demonstrate dye biosorption from real wastewater, such as tap water, river water, and laundry wastewater. Overall, this study indicates that the prepared NZC-g-PANI biosorbent could be used as an effective adsorbent for the removal of various types of anionic as well as cationic dyes from different aqueous solutions.

This study evaluates the preparation of novel ternary functional adsorbents based on polyaniline, zinc oxide nanoparticles, and moringa oleifera gum to produce zinc oxide/Moringa oleifera gum-grafted L-methionine-functionalized polyaniline bionanocomposites (ZM-g-Pani) and employed to sequestrate divalent metal ions (Cd²⁺, Hg²⁺ and Pb²⁺) from wastewater samples. The morphological and structural properties of ZM-g-Pani were exploited using FT-IR, FE-SEM/EDS, TEM, and XRD. FT-IR and FE-SEM studies show that the as prepared nanocomposite has an abundant number of reactive groups and a porous structure, thus demonstrating outstanding divalent metal cation removal. FT-IR study confirms that the attachment of L-methionine to polyaniline is facilitated by the C-S linkage. Both TEM and FE-SEM techniques confirmed the clustered granules of ZnO over the surface of polyaniline, which ultimately provided more surface area to adsorb metal ions. The study demonstrated that Cd²⁺, Hg²⁺ and Pb²⁺ ions could undergo physical sorption and chemisorption simultaneously during the adsorption process. The maximum adsorption capacity was 840.33, 497.51, and 497.51 mg/g for Cd²⁺, Hg²⁺, and Pb²⁺, respectively. The impact of co-existing ions, including NO₃⁻, PO₄³⁻, SO₄²⁻, Cl⁻, Na⁺, Cu²⁺, and Al³⁺, showed that there were no notable alterations in the adsorption of the selected metal ions with ZM-g-Pani. ZM-g-Pani showed eight successive regeneration cycles for Cd²⁺, Hg²⁺, and Pb²⁺ with more than 85% removal efficiency.