Adsorption of cationic and anionic dyes on photocatalytic flyash/TiO2 modified chitosan biopolymer composite

This study evaluated the performance of TiO2 loaded flyash chitosan composite for the adsorption of anionic dye (congo red-CR) and catatonic dye (methylene blue-MB) dyes. Flyash was modified using HNO3 and H2SO4 to increase its surface area. The flyash and composites were characterized using morphological (scanning electron microscopy; Brunauer, Emmett and Teller surface area), spectral (Fourier-transform infrared; X-ray diffraction) and thermogravimetric techniques. The morphological analysis of the composite adsorbent revealed an irregular and rough surface, providing more adsorption sites for dye adsorption. The acid-activated adsorbents showed higher adsorption for CR than MB dye. For CR dye, the removal efficiencies were 98 %, 97 %, and 90 % for composite adsorbents MFA-1 (H2SO4 modified), MFA-2 (HNO3 modified), and UFA (raw flyash), respectively. For MB dye, the removal efficiencies were 60 %, 58 %, and 50 % for composite adsorbents MFA-1, MFA-2, and UFA, respectively. The maximum adsorption capacities of 163.51, 160.55 and 154.21 mg g−1 for MFA-1, MFA-2 and UFA, respectively, were observed for the CR dye. While for the MB dye, the maximum adsorption capacities of 55.75, 52.64 and 35.09 mg g−1 for MFA-1, MFA-2 and UFA, respectively. The improvement of dye removal on acid composites than unmodified flys ash compsitewas credited to the increased active sites due to acid modification of fly ash. The PSO kinetic model and Langmuir adsorption isotherms were the best fit for the experimental results. The incorporation of TiO2 inculcated photocatalytic regeneration ability in the composite adsorbents. This allowed the adsorbent to be utilized in several cycles without thermal or chemical treatment. This study concluded that the proposed adsorbent could be an effective solution for textile industry wastewater treatment.