Tailored novel nanocomposites for advanced disposal of crystal violet dye from water

Abstract

Crystal violet is a toxic cationic dye that poses substantial threats to aquatic biota and public health because of its persistence, bioaccumulation potential, and documented cytotoxic and carcinogenic effects. Efficient removal of this pollutant from contaminated water therefore remains an urgent environmental challenge. In this study, novel SrCO 3 /ZnO/MgO/C and SrCO 3 /ZnO/MgO/Sr(OH) 2 (H 2 O)/C nanocomposites were synthesized via a Pechini sol–gel route at 600 and 800 °C to yield SZM600 and SZM800, respectively. The two calcination temperatures were selected to examine how thermal treatment controls phase development, crystallinity, surface chemistry, pore structure, morphology, and adsorption performance. XRD confirmed the coexistence of crystalline oxide and carbonate phases, with average crystallite sizes of 69.38 nm for SZM600 and 81.72 nm for SZM800, while the calculated crystallinity increased from 76.4% to 84.8%. EDX, FE-SEM, HR-TEM, and BET/BJH analyses revealed that SZM600 retained finer particles, slightly higher surface area, higher residual carbonaceous contribution, and more accessible surface domains, whereas SZM800 showed stronger crystallization, particle coalescence, and pore enlargement after higher-temperature calcination. HR-TEM particle-size analysis, performed using ImageJ from calibrated micrographs, gave average particle diameters of 61.45 nm for SZM600 and 146.78 nm for SZM800. Adsorption experiments demonstrated maximum capacities of 446.43 mg/g for SZM600 and 306.75 mg/g for SZM800. The superior uptake of SZM600 was attributed to the combined effects of favorable surface charge, finer particle size, lower sintering degree, slightly higher accessible surface area, residual carbonaceous contribution, and greater availability of effective uptake sites. Thermodynamic analysis confirmed that adsorption was spontaneous, exothermic, and predominantly governed by physical interactions. The kinetic data followed the pseudo-first-order model, while the equilibrium data were best represented by the Langmuir model, indicating monolayer coverage on a finite population of relatively uniform accessible adsorption sites under the studied conditions without implying complete structural homogeneity of the multiphase nanocomposite surfaces. Both materials exhibited good regeneration through acid treatment and maintained high efficiency over repeated reuse cycles. Application to real wastewater matrices confirmed strong dye removal despite competitive ions, highlighting the practical potential of these nanocomposites for treating crystal violet-contaminated effluents.