Development of sonophotocatalytic process for degradation of acid orange 7 dye by using titanium dioxide nanoparticles/graphene oxide nanocomposite as a catalyst.

In the present study, the sonophotocatalytic degradation of acid orange 7 (AO7) dye was evaluated. The catalyst used was the titanium dioxide nanoparticles/graphene oxide (TiO2/GO) nanocomposite, which was synthesized using the Hummers and Hoffman's method and the liquid phase deposition method. TiO2/GO nanocomposite was characterized through the analyses of transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy Dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. In addition, properties of the surface area and pore size were determined by N2 adsorption-desorption and the Barrett-Joyner-Halenda methods. After modification, the nanocomposite properties showed successful stabilization of TiO2 on the graphene substrate and reduction of the recombinant carrier loads. By utilizing the proposed treatment, complete degradation of AO7 could be achieved under optimal operating parameters (pH = 5, initial concentration of AO7 dye = 50 mg/L, TiO2/GO nanocomposite dose = 0.5 g/L, UV light intensity = 36 W, ultrasonic wave intensity = 35 kHz, and reaction time = 30 min). Scavenging experiments confirmed that OH and h+ radicals were the predominant species in the sonophotocatalytic degradation reactions of the AO7 dye. The stability study confirmed the excellent shelf life of the TiO2/GO nanocomposite, with only a slight reduction in the degradation efficiency of the AO7 dye (<8.27%) detected, after six consecutive cycles of the sonophotocatalytic process. Studies related to the degradability of the AO7 dye and the biodegradability of the effluent from the process showed that the applied sonophotocatalytic system was able to remove the TOC concentration by 83% after a reaction time of 30 min. Moreover, the increase in the BOD5/COD ratio was also a confirmation for the increase in biodegradability of the treated AO7 dye effluent. Finally, the toxicity test showed that the growth inhibition rate of Escherichia coli (E. coli), as a viability index, decreased to about 7.34% after a reaction time of 180 min. This result indicated the formation of compounds with low toxicity and molecular weight over the reaction time of the sonophotocatalytic process of AO7 dye.

Photocatalytic degradation of amoxicillin from aqueous solutions by titanium dioxide nanoparticles loaded on graphene oxide.

The photocatalytic degradation of amoxicillin (AMX) by titanium dioxide nanoparticles loaded on graphene oxide (GO/TiO2) was evaluated under UV light. Experimental results showed that key parameters such as initial pH, GO/TiO2 dosage, UV intensity, and initial AMX concentration had a significant effect on AMX degradation. Compared to the photolysis and adsorption processes, the AMX degradation efficiency was obtained to be more than 99% at conditions including pH of 6, the GO/TiO2 dosage of 0.4 g/L, the AMX concentration of 50 mg/L, and the intensity of 36 W. Trapping tests showed that all three hydroxyl radical (OH•), superoxide radical (O2•-), and hole (h+) were produced in the photocatalytic process; however, h+ plays a major role in AMX degradation. Under UV irradiation, GO/TiO2 showed excellent stability and recyclability for 4 consecutive reaction cycles. The analysis of total organic carbon (TOC) suggested that AMX could be well degraded into CO2 and H2O. The formation of NH4+, NO3-, and SO42- as a result of AMX degradation confirmed the good mineralization of AMX in the GO/TiO2/UV process. The toxicity of the inlet and outlet samples of the process has been investigated by cultivation of Escherichia coli and Streptococcus faecalis, and the results showed that the condition is suitable for the growth of organisms. The photocatalytic degradation mechanism was proposed based on trapping and comparative tests. Based on the results, the GO/TiO2/UV process can be considered as a promising technique for AMX degradation due to photocatalyst stability, high mineralization efficiency, and effluent low toxicity.