Adsorption can be efficiently employed for the removal of various toxic dyes from water and wastewater. In this article, the authors reviewed variety of adsorbents used by various researchers for the removal of malachite green (MG) dye from an aqueous environment. The main motto of this review article was to assemble the scattered available information of adsorbents used for the removal of MG to enlighten their wide potential. In addition to this, various optimal experimental conditions (solution pH, equilibrium contact time, amount of adsorbent and temperature) as well as adsorption isotherms, kinetics and thermodynamics data of different adsorbents towards MG were also analyzed and tabulated. Finally, it was concluded that the agricultural solid wastes and biosorbents such as biopolymers and biomass adsorbents have demonstrated outstanding adsorption capabilities for removal of MG dye.

Chitin (CH) and chitosan (CTS) beads used and compared for the adsorption of Congo Red (CR), an anionic azo dye, are reported in the present work. Initially, the adsorbents were prepared and characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) analysis. SEM images showed the heterogeneous and porous structure of the beads and FT-IR results confirm the presence of –OH, –NH₂, and–NHCOCH₃ groups which are responsible for the adsorption of CR. Further, batch studies were conducted to evaluate the adsorption capacity of CH and CTS beads and the effects of the parameters like pH, adsorbate concentration, contact time, and dosage of adsorbents on adsorption were investigated. From the analysis, it was observed that the amount of CR adsorbed on both the adsorbents increases with increasing initial dye concentration and decreasing pH. The adsorption isotherms were analyzed using the Langmuir and Freundlich isotherms. The Langmuir isotherm was the best-fit adsorption isotherm model for the experimental data obtained from the non-linear chi-square statistic test. Further, the pseudo-first-order and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The dynamical data fit well with the second-order kinetic model. The results indicate that CH and CTS beads could be employed as low-cost material for the adsorption of CR from wastewater.