Efficient Decontamination of Cationic Dyes from Synthetic Textile Wastewater Using Poly(acrylic acid) Composite Containing Amino Functionalized Biochar: A Mechanism Kinetic and Isotherm Study

Hydrogel-incorporated adsorbents are promising adsorbents for organic dyes due to their three-dimensional structure, economical nature, ease of use, and modifiable functional groups. To this aim, new poly acrylic acid/modified biochar composite hydrogel was synthesized using Melamine functionalized biochar and acrylic acid, employing in-situ radical polymerizations. The chemical structure of the prepared hydrogel was confirmed using Fourier transform infrared (FT-IR) spectroscopy. Thermal stability and morphology of adsorbents were determined using Thermo-gravimetric analysis (TGA) and Scanning electron microscope (SEM), respectively. The removal efficiency and adsorption capacity of the synthesized hydrogel were measured by analyzing the impact of influential parameters such as pH, initial dye concentration, contact time, and dosage in the elimination of methylene blue, crystal violet, and safranin O from synthetic textile wastewater. The kinetic study of the adsorption process was performed by using pseudo-first-order and pseudo-second-order models. Langmuir, Freundlich, and Temkin isotherms were implemented to investigate the adsorption mechanism. The experimental values are in line with the calculated results obtained from the Langmuir isotherm and the pseudo-second-order model which indicates the chemical and monolayer adsorption mechanism is the favored process. In addition, the R-2 values obtained from pseudo-first-order model, Freundlich and Temkin isotherms indicates the auxiliary involvement of physisorption and multilayer mechanisms. The maximum adsorbent capacity of 638.436 mg.g(-1), 462.550 mg.g(-1), and 711.340 mg.g(-1) was obtained for Methylene blue, Crystal violet, and Safranin O dyes, respectively. Adsorbent recovery and reusability during seven cycles divulge acceptable results.

Automated summary

Hydrogel-incorporated adsorbents are promising for the removal of organic dyes in wastewater. A new poly acrylic acid/modified biochar composite hydrogel was synthesized and demonstrated high removal efficiency for methylene blue, crystal violet, and safranin O dyes. The adsorbent exhibited stable performance and the adsorption mechanism was determined to be chemical and monolayer adsorption.