Synthesis and Utilization of rGO/Ultrathin Nanotube Bi5O7I for Photodegradation of Methylene Blue and Photoreduction of Cr6+ to Cr3+ toward Detoxification of Water

The reduced graphene oxide/ultrathin nanotube Bi5O7I (rGO/UN-Bi5O7I) was well synthesized via a simple method to investigate the charge transfer and light-harvesting ability and its efficient application in wastewater problems such as organic (Methylene blue) and inorganic (Cr6+) pollution. The analysis shows the synergistic effect of the graphitic structure of rGO and the ultrathin nanotube structure of Bi5O7I, leading to efficient light harvesting and charge transfer. The efficient photocatalytic activity of this photocatalyst was achieved with 20% rGO. The optimum pH, ionic strength, and time for the photodegradation of MB were 12.0, 0.05 M, and 4 min, and those for the photoreduction of Cr6+ were 2.0, 0.10 M, and 38 min, respectively. In addition, the experimental data for MB investigation show that the kinetic surface adsorption model follows the Langmuir isotherm [Qmax = 350.00 (mg/g)] model. The kinetic isotherm of the surface adsorption is observed by pseudo-first-order kinetics [Qe.cal = 136.87 (mg/g)]. Also, the photodegradation efficiency of UN-Bi5O7I and rGO/UN-Bi5O7I was compared, and the results showed that the kinetic rate constant of rGO/UN-Bi5O7I for the photodegradation of MB was 14 times, and that for the photoreduction of Cr6+ was 4.5 times higher than UN-Bi5O7I. The scavenger test showed that the hole (h+) and superoxide radical (•O2–) have the main role in the photodegradation of MB. The rGO, due to its functional groups, improved the surface adsorption of pollutants and caused the photodegradation of MB by h+ and the photoreduction of Cr6+ to Cr3+ by electrons. Consequently, rGO/UN-Bi5O7I can be efficiently utilized in environmental pollutant remediation.