Fabrication of black TiO2 through microwave heating for visible light-driven photocatalytic degradation of rhodamine 6G

This study aims to prepare titanium dioxide (TiO2) with a narrower band gap, namely black TiO2, using sodium tetrahydroborate (NaBH4) as a reducing material with different mixing ratios and microwave heating, which is a faster, greener, and simpler method than the existing method using furnace heating. Scanning electron microscopy (SEM) inspections indicate that incremental changes of agglomeration are observed upon increasing the NaBH4 mixing ratio, with a moderate 2-fold increase in the particle size (up to 49.9 +/- 3.0 nm). The X-ray diffraction (XRD) patterns and Raman spectroscopy confirm that TiO2 is fully converted to the anatase phase after microwave-assisted synthesis. The gradual shift in intense E-g phonon vibration mode at 141 cm(-1) to a longer Raman wavelength infers simultaneous defect formations on both pristine and reduced TiO2 surfaces. Furthermore, high-resolution X-ray photoelectron spectroscopy (XPS) measurements confirmed the formation of Ti3+ and O-v. The photodegradation results showed that after visible light irradiation for 4 hours, the T-50 sample exhibited R6G degradation of 49.2 +/- 2.0%, outperforming the pristine P25. Moreover, bandgap reduction is successfully achieved from 3.20 eV (P25) to 1.50 eV (T-50) from diffuse reflectance UV-vis (DRUV) spectroscopy measurements. Photoluminescence (PL) spectroscopy found that the energy transfer efficiency of the T-50 sample was 30.6 +/- 4.6% during the decomposition of R6G. This combined effort promotes the use of potent black TiO2 through photocatalysis towards fabrication of highly efficient remediation materials in the future.