Applicative study (Part I): the excellent conditions to remove in batch direct textile dyes (Direct red, Direct blue and Direct yellow) from aqueous solutions by adsorption processes on low-cost chitosan films under different conditions

摘要

In recent years the development of chitosan (CH) based materials as useful adsorbent polymeric\udmatrices is an expanding field in the area of adsorption science. Even though CH has been successfully\udused for dye removal from aqueous solutions due to its low cost, no considerations have\udbeen made about, for example, the effect of changing the pH of chitosan hydrogelor about the dehydrating\udeffect of Ethanol (EtOH) treatment of chitosan film on the dyes removal from water.\udConsequently in our laboratory we carried out a study focusing the attention, mainly, on the potential\uduse of CH films under different conditions, such as reducing the intrinsic pH, increasing the\udhydrophobic character by means of ethanol treatment and neutralization of CH films to improve\udtheir absorption power. Textile anionic dyes named Direct Red 83:1, Direct Yellow 86 and Direct Blue 78 have been studied with the aim of reducing the contact time of CH film in waste water improving\udthe bleaching efficiency. Neutralized acid CH film and longtime dehydrated one result to\udbe the better films in dye removal from water. Also the reduction of the CH solution acidity during\udthe film preparation determines the decreasing of the contact time improving the results. The effect\udof initial dye concentration has been examined and the amount of dye adsorption in function\udof time t, qt (mg/cm2), for each analyzed film has been evaluated comparing the long term effect\udwith the decoloration rate. A linear form of pseudo-first-order Lagergren model has been used and\uddescribed. The best condition for removing all examined dyes from various dye solutions appears\udto be the dehydration of a novel projected CH film obtained by means of the film immersion in\udEtOH for 4 days. Also CH films prepared by well-known literature procedure and neutralized with\udNaOH treatment appear having an excellent behavior, however the film treatment requires a large\udquantity of water and time.