Desorption and photodegradation of methylene blue from modified sugarcane bagasse surface by acid TiO2 hydrosol

Waste sugarcane bagasse (SCB) was modified by pyromellitic dianhydride to improve its adsorption capacity for cationic dyes. Results showed that the adsorption capacity of the modified SCB for methylene blue was 564 mg g−1, which was about 12 times than that obtained on the unmodified SCB. Methylene blue loaded modified SCB was regenerated by a self-clean eluent: TiO2 hydrosol with pH ranged from 1 to 4, and HNO3 solution with the same pH range was tested at the same time for comparison. Results showed that desorption kinetics of methylene blue in the hydrosol systems fit two-step kinetic model and controlled mainly by the slow step. As a self-clean eluent, acid hydrosol could firstly desorb and then photodegrade methylene blue under sunlight irradiation. After five desorption–photodegradation cycles, 78.3% of the absorbed dyes could be desorbed by using hydrosol (pH 2) as eluent. The hydrosol could be continuously used in desorption and photodegradation process, which would economize large volume of the eluent and moreover it would not bring secondary pollution.