Removal of anionic and cationic pollutants with bioadsorbents prepared from hemp fibers by graft copolymerization and modification

In this study, an eco-friendly approach, which takes its source from the environment, has been developed. In addition, the fact that the hemp fiber (HF) chosen as the adsorbent raw material is a natural polymeric material and the focus on grafting and modification of this natural polymer in the study indicates an innovative approach. In the first part of the study, the usability of the bioadsorbent prepared by modifying the supplied hemp fiber with H2SO4 in the removal of cationic pollutants Methylene Blue (MB), Crystal Violet (CV), Malachite Green Oxalate (MGO) dyes from aqueous solution was investigated. In the second part, hemp fiber was first grafted with Glycidyl Methacrylate (GMA) and then modified with Tetraethylenepentaamine (TEPA) to prepare semi-synthetic polymeric bioadsorbent. The usability of the prepared grafted modified bioadsorbent in the removal of anionic pollutants Remazol Brilliant Blue R (RBBR), Reactive Red (RR120) and Reactive Yellow (RY160) dyes from aqueous media was investigated. Prepared adsorbents (SHF and TEPA-(GMA-g-HF)) were characterized in detail using various techniques (SEM-EDX, STEM, FTIR, BET, XRD, TGA, Boehm Titration, pHpzc). During the adsorption studies carried out with the batch method the effects of adsorbent amount, pH, time, dye initial concentration and temperature were investigated. Kinetic, isotherm and thermodynamic parameters were determined. The effects of different ions in the solution on adsorption were investigated by conducting studies in the synthetic seawater medium. In addition, desorption and reusability studies were also carried out. From the findings of the study; for both cationic and anionic dyes, the adsorption was observed to be more consistent with the pseudo-second order kinetic model (R2 > 0.99) and the Langmuir isotherm model (R2 > 0.99). From the Langmuir model, the maximum adsorption amounts (qm) at 298 K; MB onto SKL: 500 mg/g, CV: 625 mg/g, MGO: 1250 mg/g and onto TEPA-(GMA-g-HF) RBBR: 91.74 mg/g, RR120: 76.34 mg/g, RY160: 83.33 mg/g was determined. It was observed that the adsorption capacity increased as the temperature increased. It was determined that the adsorption process for all dyes was endothermic and spontaneous. SHF and TEPA-(GMA-g-HF) appear to be highly effective adsorbents that can be used for cationic and anionic dyes, respectively, thanks to the almost unaffected adsorption efficiency and effective reusability even in synthetic seawater environment. In addition, this study, which includes the removal of both anionic and cationic dyestuffs from the water environment, brings a holistic approach. Thus, a significant contribution has been made to a vital field of application such as the fight against water pollution and to the scientific literature.