Dye-containing industrial effluents create major concern nowadays. To address the problem, magnetic nickel oxide nanoparticles (NONPs) were synthesized using the autopropagator combustion technique assisted by sucrose as fuel and used for the removal of toxic malachite green (MG) from water. The material was characterized by scanning electron microscopy (SEM–EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating sample magnetism (VSM), point of zero charge (pH ZPC ), and Brunauer–Emmet–Teller surface area analysis. SEM images show flowerlike texture with the presence of multiple pores. VSM reveals a well-defined hysteresis at room temperature, confirming a permanent magnetic nature of the material. pH ZPC was found to be 6.63, which enables dye separation in the drinking water pH range. MG removal from water was carried out in the batch mode with optimized physicochemical parameters such as contact time, pH, temperature, and dose. Langmuir adsorption capacity was estimated to be 87.72 mg/g. Pseudo-second order kinetics ( R 2 = 0.999) and Langmuir isotherm model ( R 2 = 0.997) were found to best fit. The magnetic nature facilitates fast and quantitative separation of NONPs from solution using a hand-held magnet. Dye-loaded NONPs can be easily regenerated up to 89% and reused up to five cycles without significant loss of activity. The mechanism of adsorption is proposed to be a combination of electrostatic attraction and weak hydrogen bonding. Strategically designed straightforward synthetic protocol, low cost, high uptake capacity, and sustainable use render NONPs an ideal alternative for future dye treatment.

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Designing a stable and efficient adsorbent for removal of pollutants such as dyes is of serious concern nowadays. In view of that, magnetic cobalt oxide nanoparticles (CONP) were synthesized in a multigram scale using a modified self-propagator combustion method triggered by sucrose as the fuel. The material was characterized by Fourier-transform infrared spectroscopy, Xray diffraction, vibrating sample magnetism (VSM), scanning electron microscopy (SEM)−energy-dispersive system, highresolution transmission electron (HRTEM), pH ZPC , and Brunauer−Emmet−Teller surface area. SEM and HRTEM images confirm the presence of distinct pore channels. Room temperature VSM reveals weak hysteresis, indicating that the CONP is a soft but robust magnetic material. pH ZPC was found to be 6.45. Removal of malachite green from simulated water was tested in a batch mode and found to be promising. Physiochemical parameters such as pH, contact time, dose, and temperature were optimized. The maximum Langmuir adsorption capacity was found to be 238.10 mg/g. Adsorption is best described by the Langmuir isotherm model (R 2 = 0.999) and pseudo-second order kinetics (R 2 = 0.999). Regeneration (83%) with dilute acid enables its successive use. Its magnetic nature facilitates the rapid separation of the CONP after adsorption using a hand-held magnet. Easy synthetic protocols, robustness, high removal efficiency, and reusability make the material an ideal future choice for dye detoxification.

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Dewaxed honeycomb powder (HCP) was used as a promising adsorbent for removal of malachite green (MG) from aqueous solution. Raw honeycomb was strategically dewaxed by petroleum ether, and the purified product was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), pH zpc , and proximate analysis. A high uptake capacity (123 mg/g) was found at neutral pH. Experimental data follow pseudo-second-order kinetics ( k 2 as 0.45 × 10 –2 g/min/mg, R 2 = 0.986) and Langmuir isotherm with R 2 0.999. Thermodynamic parameters suggested a spontaneous (Δ G = −26.28 kJ/mol) and exothermic (Δ H = −11.61 kJ/mol) process, which suggests increased randomness (Δ S = 0.0486 kJ/mol) at the solid–liquid interface during the adsorption process. The material can be regenerated by ordinary salt solution (1 M NaCl) and efficiently reused for three cycles with a minimal loss in efficiency. Adsorption mechanism is proposed to be a combination of electrostatic interaction and π–π stacking between aromatic units of HCP and MG. Abundant availability, possibility of wax commercialization, economic sustainability, and comprehensive waste management make HCP an ideal choice for dye decolorization.