Adsorption of methylene blue and acid blue 40 on titania from aqueous solution

Langmuir type adsorption was observed for two systems: methylene blue (MB) on TX titania and acid blue 40 (AB40) on P25 titania at an ambient temperature of (23 +/- 2) degreesC and ambient pH initially at 4.6 +/- 0.2 for P25 titania and 7.8 +/- 0.2 for TX titania. Based on a Langmuir analysis, values for maximum surface coverage, N-max, and adsorption intensity, b, are 1.6 x 10(-5) mol MB.g(-1) and 3.6 x 10(4) L.mol(-1), respectively, for TX titania. An N-max value of 5.0 x 10(-5) mol AB40.g(-1) was determined for P25 titania. The TX titania adsorption surface area is estimated to be 12 m(2).g(-1) based on maximum adsorption of methylene blue. Results of gel electrophoresis on both dyes at pH values of 4 and 9 indicate that methylene blue remains cationic and acid blue 40 remains anionic in this pH range. Single-point adsorption experiments at selected pH values other than ambient were performed. Experimental evidence clearly indicates that electrostatic attraction is a reasonable explanation for the observed adsorption process in the MB/TX system. Although the evidence is less conclusive, electrostatic attraction may also influence the adsorption process of the AB40/P25 system.