The efficiency of magnetic TiO2 anatase loaded by graphen quantum dots for photocatalytic degradation of imipramine from aquatic media

The pharmaceutical industry is occurred in the fourth wastewater production with significant amounts of drugs and precursors required in pharmacy that are toxic and are not removed by traditional methods, so have to be used advanced technology for treatment. The purpose of this study was synthesis of Fe3O4, anatase TiO2, loading of TiO2 on the Fe3O4 surface, synthesis of GQD based on maltose for the first time, loading of GQD on the Fe3O4/TiO2 and investigating the efficiency of as-synthesized photocatalyst Fe3O4/TiO2/GQDs for imipramine photodegradation from aquatic media.

Firstly, prepared photocatalyst Fe3O4/TiO2/GQDs included three components, which produced in four steps. Firstly, iron oxide was prepared in the form of magnetite by co-precipitation method. Then, Fe3O4/TiO2 was synthesized by sol-gel manner and titanium iso propoxide (IV) as a titanium source in anatase crystalline form. In the third step, maltose was used as procedure for GQD production in hydrothermal method. So, as-synthesized photocatalyst was obtained by loading GQD on the Fe3O4/TiO2. Then, the structural properties and quality of the nanocomposite were investigated using FT-IR, Nitrogen adsorption/desorption isotherm, FESEM and HRTEM technique. Finally, the efficiency of photocatalytic decomposition was examined affected by different independent variables.

FT-IR results of naopowders and prepared photocatalyst indicated absorbance peaks of C=C, C-H, C-O, Fe–O and Ti-O-Ti bonds. Also, new peaks were appeared in 1400 and 1170 cm-1 which is related to forming the Fe–O bond between Fe in Fe3O4 and the carboxyl group in GQDs, showing the successful preparation of Fe3O4/TiO2/GQD. The specific surface area was 38 m²/g in Nitrogen adsorption/desorption isotherm. According to IUPAC classification, the isotherm curve of photocatalyst was the type IV and hysteresis loop of types due to mesoporous structure. FESEM images determined the almost spherical morphology of as-synthesized photocatalyst and homogenous distribution of TiO2 nanoparticles on the magnetite surface that was utilized without any changes in morphology but particle size changing after loading TiO2 on the magnetite particles. HRTEM results confirmed the spherical spherical shape with less than 50 nm diameter and the lattice spacing related to anatase (TiO2) and GQDs. Also, the photocatalytic efficiency of the as-synthesized nanocomposite were measured for achieving the maximum removal of imipramine related to different variables including photocatalyst dose, pH, ambient temperature, and irradiation time. The best yield gained exceed 90% in experimental sample and about 70% in real wastewater under the optimum condition comprising photocatalyst dose of 0.5 g/L, pH ≈3, temperature ≈40 °C for 120 minutes. The reusability of the synthesized photocatalytic material investigated which was stable and active similar to primary sample and suitable for many times.

The results showed, the dominant mechanism of imipramine degradation was oxidative decomposition via the photogenerated holes and followed by the first-order models under the UVA light irradiation. Therefore, results proved as-prepared photocatalyst Fe3O4/TiO2/GQDs could be developed for treatment of persistence organic pollutants in industrial wastewater under optimized conditions.