Adsorption of Congo Red on the Surface of Filter Paper in Aqueous 1-Propanol and 2-Propanol Solutions

Synthetic dyes are used for dyeing in many industries and the treatment of their wastewater is highly challenging. A large number of these dyes exert detrimental effects on human health and are difficult to degrade. There are different techniques for treatment of effluents produced by industries. Among them, adsorption is an efficient and costly-economic method. On the other hand, in many cases, substances are painted through adsorption of dyes on their surface. Congo red (CR), disodium (4-amino-3-[4-[4-(1-amino-4-sulfonato-naphthalen-2-yl) diazenylphenyl] phenyl]diazinyl -naphthalene-1 -sulfonate), is an anionic dye and has many applications. In this work, adsorption of CR on the surface of filter paper was investigated in the presence of aqueous in different percentages of 1-propanol and 2-propanol solutions (structural isomerism) at 308, 318 and 328 K. Here, results were analyzed by the four-region ARIAN model. The ARIAN model is an abbreviation for adsorption isotherm regional analysis model and means Iranian. Analysis of isotherms showed that the adsorption process was a two -region one. CR molecules, in the region I were adsorbed ideally and obeyed the Henry law and, in the region II submitted the Temkin isotherm. During the process, sulfonate groups of CR molecules interacted with -OH groups of cellulose surface. Also, equilibrium binding constants (K) obtained from the Henry and Temkin isotherms were used to calculate the thermodynamic parameters of the process. The equilibrium binding constants (K) and maximum experimental adsorption capacities ( e,max q ) of filter paper for CR molecules decreased both with an increase in the concentration of the used alcohols in a certain temperature and increase in temperature in a certain alcohol concentration and adsorption in the presence of 1-propanol and 2-propanol was exothermic. Finally, in the same alcohol percentages, e,max q values of 1-propanol solutions were a little more than those observed for 2-propanol solutions and thus structural isomerism did nothave an effect on the e,max q values of the process.