Novel nanocomposites including oxide, carbonate, and hydroxide phases for efficient methylene blue dye adsorption

Methylene blue is a persistent cationic dye that threatens aquatic life and can harm humans through oxidative stress and methemoglobinemia. Its strong color reduces light penetration in water and disrupts ecosystem function. Novel NiO/MgO/SrCO 3 /Sr(OH) 2 .H 2 O nanocomposites were facilely synthesized employing the Pechini sol-gel procedure at 500 o C (NSM500) as well as 700 o C (NSM700) for remarkable methylene blue dye removal. XRD confirmed all target phases and yielded average crystal sizes of 60.8 nm concerning NSM500 and 70.6 nm concerning NSM700. EDX verified homogeneous composition and showed for NSM500 20.7 %C, 41.6 %O, 14.1 % Mg, 15.8 %Ni, as well as 7.8 %Sr, while NSM700 gave 12.6 %C, 47.6 %O, 14.9 %Mg, 13.3 %Ni, and 11.6 %Sr. FE-SEM revealed compact aggregates with spherical to polyhedral grains and average grain sizes of 0.18 μm for NSM500 and 0.52 μm for NSM700. HR-TEM showed mainly spherical to faceted nanoparticles with average diameters of 25.97 nm for NSM500 and 52.09 nm for NSM700. Batch adsorption delivered maximum capacities of 340.14 mg/g concerning NSM500 as well as 267.38 mg/g concerning NSM700. Kinetic analysis matched the pseudo-first-order equation, whereas equilibrium fit the Langmuir isotherm. Thermodynamic parameters indicated a physical, exothermic, and spontaneous process. Regeneration with acid restored performance, and both adsorbents were reused over multiple cycles with high removal efficiency.