Abstract The release of industrial effluents into the environment causes widespread contamination of aquatic systems. Adsorption is seen as one of the most promising treatment processes, and lignocellulosic materials have gained prominence as adsorbents. This study investigates the potential of rice hulls, either in natura or treated with nitric acid, as adsorbents for removal of the dye. The adsorbents were characterized by infrared spectroscopy, solid state 13C-NMR, thermogravimetric analysis, and pH at point of zero charge. The dye adsorption experiments were carried out in batch mode, using different experimental conditions. The kinetic adsorption data could be fitted using the model of Elovich. The Freundlich model provided the best fit to the isothermal data. The thermodynamic parameters confirmed the spontaneity of the adsorption process. These adsorbents offer an alternative for dye removal, with advantages including biomass availability and low cost.

Activated carbon was produced from the water hyacinth (CAA) by impregnation with ZnCl2 (1:2), followed by pyrolysis at 700 ºC, under N2. CAA was used for the adsorption of phenol, m-cresol and o-cresol from aqueous solutions, using batch adsorption. The effects of contact time, pH, temperature and concentration on sorption were investigated. Adsorption capacity, calculated using the Langmuir model proved to be dependent on temperature, reaching values of 163.7, 130.2 and 142.3 mg g-1 for phenol, m-cresol and o-cresol, respectively, at 45 ºC. Thermodynamic data at the solid-liquid interface suggests an endothermic, spontaneous and environmentally-friendly process.

Cellulose was first modified with thionyl chloride, followed by reaction with 2-aminomethylpyridine to yield 6-(2'-aminomethylpyridine)-6-deoxycellulose. The resulting chemically-immobilized surface was characterized by elemental analysis, FTIR, 13C NMR and thermogravimetry. From 0.28% of nitrogen incorporated in the polysaccharide backbone, the amount of 0.10 ± 0.01 mmol of the proposed molecule was anchored per gram of the chemically modified cellulose. The available basic nitrogen centers attached to the covalent pendant chain bonded to the biopolymer skeleton were investigated for copper, cobalt, nickel and zinc adsorption from aqueous solution at room temperature. The newly synthesized biopolymer gave maximum sorption capacities of 0.100 ± 0.012, 0.093 ± 0.021, 0.074 ± 0.011 and 0.071 ± 0.019 mmol.g-1 for copper, cobalt, nickel and zinc cations, respectively, using the batchwise method, whose data was fitted to different sorption models, the best fit being obtained with the Langmuir model. The results suggested the use of this anchored biopolymer for cation removal from the environment.