Biomass-derived graphene modified gamma-Fe2O3/N,Fe-TiO2@GO: a prolific photoactive material with extended visible to near IR harvesting

This study reports the development of a novel ternary self-assembled gamma-Fe2O3/N,Fe-TiO2@GO nanocomposite as a visible to near IR (NIR) active photocatalyst prepared by ultrasonic activation followed by hydrothermal treatment. Band gap engineering of gamma-Fe2O3/N,Fe-TiO2 was performed by varying graphene oxide (GO) content, and the band gap of gamma-Fe2O3/N,Fe-TiO2@1.5%GO was narrowed to 1.5 eV due to large interfacial contact of graphene oxide and TiO2 leading to Ti-O-C bond formation causing a red shift due to the upward shift of the valance band edge. The formation of an additional band gap due to the Ti-O-C bond was also confirmed by FTIR and XPS analysis. The low-cost bioinspired GO was derived from the rice husk, which further provides efficient enhanced charge transportation and also reduces the recombination rate. The ultrafast degradation of the mixed disperse dyes (Navy Blue 3G, Scarlet RR, Scarlet 3R) with nine times enhanced photoactivity, as compared to those previously reported, was achieved with gamma-Fe2O3/N,Fe-TiO2@1.5%GO. The combined effect of operational parameters was assessed by studying the effect of various parameters on the photodegradation and obtained results indicated 100% decoloration and 85% COD reduction under sunlight. The mineralization studies and transient intermediates formed from the residue collected at the interval of thirty minutes each were analyzed through LC-MS and the obtained results demonstrated the successful mineralization of mixed disperse dyes within two hours. Also, the synthesized gamma-Fe2O3/N,Fe-TiO2@GO showed excellent recycling performance of up to eight cycles. This work highlights the potential of visible to NIR-responsive magnetically separable graphene-based titania as a broad spectrum photoactive material and the development of cost-effective technology for wastewater remediation under broad spectrum sunlight.