Adsorptive Removal of Bismarck Brown Dyes from Aqueous Media: A Comparative Review of Natural, Carbon-Based, Chitosan, Magnetic and Nanomaterial Adsorbents

Bismarck Brown dyes (R, Y and G) are synthetic azo colorants used in the textile, leather, printing and paper industries, and their release in effluents colors natural waters, limits light penetration and harms aquatic life. Adsorption is widely preferred for dye removal because it is simple, efficient and inexpensive. This review compares 17 studies on the removal of Bismarck Brown dyes from aqueous media using natural and waste biomass, activated carbons, chitosan-based materials, magnetic materials, and other nanomaterials and polymers. The effects of pH, contact time, adsorbent dose, initial dye concentration and temperature are summarized together with the kinetic, isotherm and thermodynamic findings. Most systems followed pseudo-second-order kinetics and the Langmuir or Freundlich isotherms, and adsorption was generally spontaneous, although the sign of ΔH° depended on the adsorbent. Activated carbons, graphene oxide composites, magnetic carbon nanotubes and MCM-48 generally showed the highest adsorption efficiencies, whereas biosorbents offered economical and sustainable alternatives. Magnetic adsorbents eased separation and regeneration, and f-CdWO₄ combined adsorption with photocatalytic degradation