In this research, a nanoscale magnetic biosorbent was synthesized by incorporating magnetic nanoparticles (Fe₃O₄ NPs) into a natural carbon framework derived from black cumin (BC) seeds. The prepared Fe₃O₄/BC was utilized as a low-cost, eco-friendly, and reusable nanobiosorbent for the removal of organic (e.g., methylene blue (MB) dye) pollutants from synthetic solutions. The results indicated that Fe₃O₄/BC had extensive surface oxygenous functional groups with a high affinity for MB dye capture at different concentrations such as 10–60 mg L⁻¹. The optimization results suggested the removal of ~99% of methylene blue from its initial concentration (i.e., 10 mg L⁻¹) using 2.0 g L⁻¹ of Fe₃O₄/BC at pH = 7, temperature = 27 °C, and contact time = 120 min, with equilibrium adsorption capacity = 5.0 mg g⁻¹ and partition coefficient = ~57.0 L g⁻¹. The equilibrium adsorption efficacy at the highest initial concentration (i.e., 60.0 mg L⁻¹) was found to be 29.0 mg g⁻¹. The adsorption isotherm was well explained by the Freundlich model for MB. The renderability of this magnetic bioadsorbent by acid treatments showed a ~66% decline in removal efficiency (%) (~99% to ~33%; ~5.0 to ~1.7 mg g⁻¹) for MB after six repetitive cycles of adsorption and desorption. The current Fe₃O₄/BC gives a better partition coefficient than previously reported acid-washed BC seeds and other BC-seed-based nanobioadsorbents, Hence, a synthesized Fe₃O₄/BC nanobiosorbent demonstrates potential for use in treating water contaminated with organic pollutants.

In the present study, a photodegradation technique was employed for the removal of methylene blue dye from aqueous solution using a tungsten oxide-based photocatalyst. The photocatalyst was synthesized via a green synthesis route utilizing a plant extract (PE) under acidic conditions. The synthesized photocatalyst was characterized by various spectroscopic and microscopic techniques that confirmed the presence of various functional groups on the catalyst surface and revealed a narrow bandgap of ~3.0 eV. The synthesized particles exhibited a nanoscale dimension ranging from 10 to 15 nm. The photocatalytic activity of the material was evaluated under ultraviolet light, visible light, and sunlight irradiation, demonstrating the efficient degradation of methylene blue under all light sources. Furthermore, catalysis reusability studies indicated excellent stability, with consistent photocatalytic performance observed after five successive cycles.

This study reports the preparation of a novel hybrid composite and its application in adsorption. For this composite preparation, zirconia (ZrO₂) was precipitated onto an integrated framework of reduced graphene oxide (rGO) and black cumin (BC) seeds. Characterization using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and transmission electron microscopy confirmed the successful incorporation of ZrO₂ nanoparticles (5–20 nm) into the integrated carbon framework of rGO and seed powder. The microscopic analysis further revealed that the ZrO₂ NPs were dispersed throughout the integrated rGO-BC framework. Using the rGO-BC@ZrO₂ composite, methylene blue dye was decontaminated from water through a batch adsorption process. The rGO-BC@ZrO₂ composite achieved 96% MB adsorption at an adsorbent dose of 2.0 g/L, and nearly 100% when the adsorbent concentration was 3.0 g/L. Modeling of the experimental adsorption values was also established to verify the adsorption viability and mechanism. Thermodynamic modeling confirmed the feasibility and spontaneity of the present batch adsorption process. Isotherm modeling, which showed its compatibility with the Freundlich isotherm, suggested multilayer adsorption. rGO-BC@ZrO₂ demonstrated good persistence and reusability for methylene blue for up to five consecutive adsorption cycles. Thus, this study presents optimistic results regarding water purification.

This manuscript explores the removal of eosin yellow dye, a toxic color substance contributing to water pollution, from aqueous solutions. For this purpose, iron-zirconia binary oxide (Fe₂O₃-ZrO₂) was functionalized with eugenol oil, a natural phenolic aromatic compound extracted from the clove plant. The functional groups developed in the binary oxide were confirmed by Fourier transform infrared spectroscopy (FT-IR), and its crystal structure was determined via X-ray diffraction (XRD). The grain size analyzed by the XRD pattern was found to be 45 nanometers. The morphological analysis revealed nanoparticles of quasi-spherical type with a size ranging from 4 to 5 nanometers. The consistency between SEAD and XRD further confirmed that the material formed was iron-zirconia binary oxide. The obtained material, which was insoluble in water, was used as an adsorbent. Through the adsorption study of eosin yellow dye, the maximum monolayer adsorption capacity of approximately 91.0 mg/g at 27 °C and pH = 7.0 for the functionalized adsorbent was determined. The process was exothermic, feasible, and spontaneous. At a dose of 1.0 g/L, the adsorbent was responsible for removing more than 90% of eosin yellow with 10–70 mg/L initial concentration, while about 56% removal was achieved at a higher concentration of 150 mg/L at 27 °C and pH = 7.0. These results highlight the potential of functionalized Fe₂O₃-ZrO₂ as an effective adsorbent for water purification applications.

In this research, a tungsten oxide was prepared via a green (biogenic) synthesis route where sodium tungstate dihydrate and Punica granatum peel extract were used as a precursor and a reducing/capping agent, respectively. The characterization of the prepared tungsten oxide was performed through various spectroscopic and microscopic techniques. The characterization results revealed the preparation of highly crystalline and nanorod-shaped (length = 123 nm and width = 31.3 nm) tungsten oxide with a probable chemical formula of W₅O₁₄. Various functional groups on the W₅O₁₄ surface were also reported. The prepared nanorods were further used for the removal of Bismarck Brown R (BBR) dye from water in a batch manner. By varying the dose of nanorods (0.5–3.0 g L⁻¹), BBR solution pH (2−10), contact time (15–120 min), BBR concentration in solution (10–60 mg L⁻¹), and temperature of BBR solution (30, 40, and 50 °C), the optimized condition for maximum adsorption efficiency was measured. The results revealed that 2.0 g L⁻¹ amount of nanorods of tungsten oxide were used to remove ~98% of BBR dye from its 10 mg L⁻¹ at 30 °C and 7.0 pH. The temperature-dependent adsorption data were fitted to different types of non-linear isotherm models (e.g., Langmuir and Freundlich) to assess the adsorption potential and adsorption mechanisms in relation to temperature impacts. The synthesized nano-adsorbent fits the Langmuir as well as the Freundlich isotherm model with a maximum adsorption capacity of 17.84 mg g⁻¹. Pseudo-first-order, pseudo-second-order, and Elovich kinetic models were used for the study of adsorption kinetics. BBR adsorption onto the W₅O₁₄ nanorods follows the pseudo-second-order rates. The present adsorption is governed by physico-chemical adsorption with predominant chemical interactions.