Valorisation of waste rice straw for the production of highly effective carbon based adsorbents for dyes removal

Highly porous carbons have been produced through an activated pyrolysis process from waste rice straw. The methodology avoids the use of extensive pre-treatments and utilises lower temperatures than those previously reported (700 degrees C), to generate materials suitable for water purification. Activation of rice straw was achieved with carbon dioxide, potassium hydroxide and phosphoric acid to yield porous carbonaceous materials and those prepared with phosphoric acid exhibited an extremely high proportion of mesoporosity (94-95%). The characterisation of the activated carbon demonstrated that rice straw pre -carbonisation at 400 degrees C prior to activation using potassium hydroxide at 700 degrees C, resulted in a material with surface area of 1973 m(2)/g. The pre-carbonised potassium hydroxide activated carbon was demonstrated to be highly effective at the adsorption of methylene blue (cationic dye) and congo red (anionic dye) with the adsorption capacity of 527.6 and 531.4 mg/g respectively. In many cases these adsorption capacities exceeded those of other absorbents previously reported within the literature but importantly require less pre-treatment. An economic assessment of the process demonstrated that these highly porous carbons from waste rice straw are cost competitive with other commercially available activated carbons. These activated carbons may find use as an inexpensive yet effective adsorbents for dye removal and also the mesoporous carbons can be utilised in other applications including catalysis and chromatography. (C) 2017 Elsevier Ltd. All rights reserved.