Engineering novel nanocomposites containing multiphase metal borates and carbon for basic blue 41 sequestration from wastewater

Basic blue 41 is a persistent cationic dye whose intense color and high stability threaten aquatic ecosystems and degrade water quality even at low levels. Continued exposure can promote oxidative stress and possible genotoxic effects in living organisms, so its removal from wastewater is essential. In this study, the precursor produced by a facile Pechini sol–gel route was calcined at 500 and 700 o C to obtain Mg 2 B 2 O 5 /Sr 2 B 2 O 5 /MnO 2 /C (MBSM500) and Mg 2 B 2 O 5 /SrB 2 O 4 /Mn 2 (BO 3 )O/C (MBSM700) nanocomposites, respectively, for efficient adsorption of basic blue 41 from wastewater. XRD verified the production of well-crystallized multiphase structures with average crystal sizes of 49 nm concerning MBSM500 as well as 63 nm concerning MBSM700. EDX revealed B, C, O, Mg, Mn, and Sr in both materials, with MBSM500 containing more residual carbon, while MBSM700 exhibited relatively higher Mg, Mn, and Sr contents. FE-SEM and HR-TEM images showed highly agglomerated plate- and flake-like particles for MBSM500 and denser aggregates of larger quasi-spherical nanograins for MBSM700. Under the optimal operating conditions (initial dye concentration = 250 mg/L, pH = 10, and T = 298 K), MBSM500 removed 98.58% of basic blue 41 within 60 min, whereas MBSM700 achieved 73.03% removal in 80 min. Adsorption studies yielded maximum Langmuir capacities of 373.13 mg/g concerning MBSM500 as well as 290.69 mg/g concerning MBSM700. Thermodynamic and kinetic analyses demonstrated that basic blue 41 uptake is physically exothermic and spontaneous and follows the pseudo-first-order rate model and Langmuir monolayer isotherm behavior. Both nanocomposites could be effectively regenerated by acid elution and reused over several cycles while maintaining high performance in real laboratory wastewater, which highlights their promise as practical adsorbents for treating basic blue 41 contaminated effluents.