Salt effect and comparative analysis of micro and nano-bentonite in blue dye removal: Surface morphology and adsorption efficiency

Addressing contaminated water from various industrial practices has become a pressing concern. Methylene Blue (MB) dye is a prevalent industrial pollutant used in printing, dyeing, textiles, paper, plastics, and leather production. This study employed an efficient, cost-effective, environmentally friendly, and abundant adsorbent to remove Methylene Blue. Bentonite has been utilized as an adsorbent under varying dosages, acidity (pH), agitation, and salinity of contaminated wastewater. The adsorption capacity is enhanced by increasing the surface area and pore volume of the bentonite particles when they are transformed into nanoparticles. The adsorption capability increased with higher doses (10–50 mg) and longer shaking times (10–40 min), as well as with the concentration of the contaminated dye (5–25 ppm), but it decreased with rising pH values (2−12). The impact of temperature on the adsorption process was examined within the range of 25–55 °C. The results indicated that the adsorption capability is largely unaffected by wastewater salinity up to 10,000 ppm. The maximum adsorption capacities achieved under optimal conditions were 24.25 mg/g for micro-bentonite (μB) and 40.75 mg/g for nano-bentonite (nB), respectively. FTIR was employed to examine the adsorption of methylene blue dye by bentonite. BET, BJH, T-plots, and AFM analyses were conducted to determine the surface area, pore volume, pore diameter, and mean particle diameters for micro and nano bentonite. The results correlated more accurately using the Freundlich isotherm compared to the Langmuir and Tempkin models, due to its superior regression value (R²). The most suitable kinetic model for this investigation was the pseudo-second-order, in contrast to the pseudo-first-order, Elovich, and intra-particle diffusion models.