Adsorptive removal of Congo red by macroporous ZnO obtained from citrus pectin gelation and reuse as a hybrid pigment

Zinc oxide (ZnO) can adsorb ionic dyes to generate hybrid pigments. Porous zinc oxide was prepared by combining gelled citrus pectin (80 degrees C) with zinc nitrate, followed by calcination (600 degrees C). The product had a high surface area (25 m(2) g(-1)), pore volume (0.049 cc g(-1)), and pore radius (17 angstrom), indicative of a macroporous structure. ZnO comprised the wurtzite phase, as characterized by X-ray diffraction. Owing to its textural properties, ZnO effectively removed textile dyes, such as carcinogenic Congo red, from aqueous media. The adsorption of Congo red on the porous ZnO was monitored using UV-vis spectroscopy at aqueous dye concentrations ranging from 100 to 250 mg L-1. Porous ZnO with the adsorbed dye was applied as a hybrid pigment and dispersed in white real estate paint. The resulting colors were evaluated by colorimetry measurements, according to the CIE L*a*b* method.