Eco-friendly Al-Bi₂WO₆ nanosheets for effective elimination of crystal violet and methylene blue dyes

Aluminum-doped bismuth tungstate (Al-Bi₂WO₆) nanostructures were synthesized through a hydrothermal method. The structural, morphological, and physicochemical properties of the as-prepared sheet-like nanostructures were systematically characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM), and Brunauer-Emmett-Teller (BET) surface area analysis. XRD results confirmed that all synthesized samples possessed an orthorhombic crystal structure. The adsorption performance of the prepared nanostructures was evaluated for the removal of crystal violet (CV) and methylene blue (MB) dyes from aqueous solutions. Batch adsorption experiments were conducted to examine the effects of key operational parameters, including solution pH, adsorbent dose, contact time, initial dye concentration, and temperature. The results demonstrated maximum removal efficiencies of 96% for CV and 98% for MB at an initial dye concentration of 20 mg L^-1, achieved within 20 and 25 min, respectively. Furthermore, the maximum adsorption capacities were determined to be 30.57 mg g^-1 for CV and 15.11 mg g^-1 for MB over a concentration range of 20-50 mg L^-1. The adsorption behavior was best described by the Langmuir isotherm model and followed pseudo-second-order kinetics, indicating monolayer adsorption with chemisorption as the rate-limiting step. Thermodynamic analysis revealed that the adsorption process was exothermic in nature.