New and effective cassava bagasse-modified biochar to adsorb Food Red 17 and Acid Blue 9 dyes in a binary mixture.

A promissory technic for reducing environmental contaminants is the production of biochar from waste reuse and its application for water treatment. This study developed biochar (CWb) and NH4Cl-modified biochar (MCWb) using cassava residues as precursors. CWb and MCWb were characterized and evaluated in removing dyes (Acid Blue 9 and Food Red 17) in a binary system. The adsorbent demonstrated high adsorption capacity at all pH levels studied, showing its versatility regarding this process parameter. The equilibrium of all adsorption experiments was reached in 30 min. The adsorption process conformed to pseudo-first-order kinetics and extended Langmuir isotherm model. The thermodynamic adsorption experiments demonstrated that the adsorption process is physisorption, exhibiting exothermic and spontaneous characteristics. MCWb exhibited highly efficient and selective adsorption behavior towards the anionic dyes, indicating maximum adsorption capacity of 131 and 150 mg g-1 for Food Red 17 and Acid Blue 9, respectively. Besides, MCWb could be reused nine times, maintaining its original adsorption capacity. This study demonstrated an excellent adsorption capability of biochars in removing dyes. In addition, it indicated the recycling of wastes as a precursor of bio composts, a strategy for utilization in water treatment with binary systems. It showed the feasibility of the reuse capacity that indicated that the adsorbent may have many potential applications.

Chitosan hydrogel scaffold modified with carbon nanotubes and its application for food dyes removal in single and binary aqueous systems.

This work developed one promising adsorbent based on chitosan hydrogel scaffold modified with carbon nanotubes, for food dye removal in single and binary aqueous systems. The modified hydrogel scaffold was characterized in relation to the gel strength, swelling degree, surface attributes, and infrared spectrum. Adsorption isotherms were performed using dyes, food red 17 (FdR17) and food blue 1 (FdB1), in single and binary aqueous systems. The experimental data were adjusted to the Langmuir model and the thermodynamic parameters were estimated. The kinetic behavior was evaluated and, desorption studies were performed to verify the reuse capacity of the modified hydrogel scaffold. The results showed that maximum adsorption capacities were of 1508 and 1480 mg g-1 for the single system and of 955 and 902 mg g-1 for the binary system, for FdB1 and FbR17, respectively. The thermodynamic parameters indicated that the adsorption was the spontaneous, exothermic and favorable process. The model that best represented the kinetic data was that of Avrami. In desorption, the adsorbent can be used until four times and maintaining the adsorption capacity of the adsorbent in 71% of the initial capacity.