Easy recovery, mechanical stability, enhanced adsorption capacity and recyclability of alginate-based TiO2 macrobead photocatalysts for water treatment

Alginate-TiO2 porous beads were investigated in adsorption and removal of different organic dyes from water. The beads were fabricated from commercial HOMBIKAT type II anatase powders through ionotropic gelation, using alginate as a non-toxic, biocompatible pore-directing template and binder. Both anionic (methyl orange, MO) and cationic (methylene blue, MB) dyes were utilized as a model of organic pollutants. The photocatalytic activity of titania in solution is slightly reduced if compared with that of the nanopowders before assembly. However, the formation of the beads brings along many direct advantages. Thanks to their large size (0.5-2 mm) and good mechanical stability, the beads can be easily dispersed in polluted solutions and promptly recovered when stirring is stopped. The beads exhibited a strongly enhanced adsorption of MB in comparison to nanopowder samples (55% vs. 6.5%). Upon recovery, the adsorbed dye can be completely extracted and removed from the beads either by UV or ozone -UV cleaner treatment. The latter procedure resulted in a further increment of adsorption efficiency (up to 64%) as a function of different adsorption-removal cycles.