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

Abstract

Zinc oxide (ZnO) can adsorb ionic dyes to generate hybrid pigments. Porous zinc oxide was prepared by combining gelled citrus pectin (80 °C) with zinc nitrate, followed by calcination (600 °C). The product had a high surface area (25 m² g⁻¹), pore volume (0.049 cc g⁻¹), and pore radius (17 Å), 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.

Keywords:

• Wurtzite
• macroporous material
• citrus pectin
• Congo red
• hybrid pigment

Acknowledgments

Silvia thanks the PNPD/Capes scholarship. Thanks also to Douglas K. Silva for obtaining the SEM images.

Additional information

Funding

The authors are grateful to the Brazilian agencies CNPq (427127/2018-1 and 308625/2019-6), FINEP (01.09.0393.00 and 01.12.0471.00), Fundação Araucária (17/2017 – 4544/17), and CAPES (Capes 01) for financial support and fellowships.