Fabrication of Zr-doped TiO2/chitosan composite catalysts with enhanced visible-light-mediated photoactivity for the degradation of Orange II dye

Microwave assisted sol-gel approach for Zr doped TiO2 as a benign photocatalyst for bismark brown red dye pollutant

A microwave supported sol-gel approach was developed in this study to fabricate Zr-doped TiO₂ mesoporous nanostructures for efficient photocatalytic activity on bismark brown red (BBR) dye under visible light illumination. Sophisticated analytical techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence analysis (XRF), Fourier transform infrared (FT-IR), ultraviolet-visible diffuse reflectance (UV-vis-DRS) spectroscopy and Brunauer-Emmet-Teller (BET) surface area analyses were used to obtain their structural, electrical: optical and spectroscopic characteristics. The analysis results revealed that the developed nanostructures exhibited strong broad absorption in the visible region with good adsorption capacity and thus enhanced photocatalytic performance. The average crystallite size was found to be 12.5 nm (UTO), 6.4 nm (ZT₄), and 4.7 nm (ZT₄M₄) respectively. The nanocatalysts (ZT₄M₄) showed a decrease in bandgap and particle size with an increase in the surface area of the Zr-TiO₂ nanoparticles (119 m² g^-1). In comparison to previous studies on the photocatalytic degradation of BBR dye under visible light irradiation employing Ni-S co-doped (110 min), Cu-doped TiO2 (75 min), etc., ZT₄M₄ exhibited a remarkable degradation rate of 99% in 50 minutes. This may be due to the hydroxyl radicals being the principle reactive species responsible for the BBR dye oxidative degradation. The present study showed that ZT₄M₄ was found to be the best photocatalyst for the BBR dye degradation under the optimal conditions.

Adsorption/photodegradation of methylene blue from synthetic wastewater on titanate nanotubes surfaces

Titanate nanotubes (TNTs) were hydrothermally synthesized from commercially available TiO₂ powder and were characterized by XRD, SEM/EDX, and TEM. The as-prepared TNTs were used to remove organic dye, Methylene Blue (MB) from aqueous media by batch mode at 25 ± 2 °C, at pH 6.8 ± 0.2. The MB removal process followed two mechanisms of adsorption (absence of UV light) and photodegradation on precursor's surfaces. Photo-illumination study revealed the ∼98% MB removal with the dose of 3 g/L TNT with an initial concentration of 10 mg/L. Adsorptive capacity of TNT was evaluated from the Langmuir isotherm and found to be 151.51 mg/g. Dimensionless equilibrium parameter R_L value suggested the favourable but the free energy changes (ΔG°) value (10.752 kJ/mol) suggested the non-spontaneity of the adsorption process. Adsorption followed the pseudo-second order kinetics model best. MB adsorption onto TNT surfaces followed neither pore diffusion nor film diffusion. Studies conducted in the presence of different foreign ions as well as varying pH of the media to understand their effects in the process if any. Turnover studies were also conducted. A probable photodegradation mechanism was proposed. Finally, TNT was used to remove MB from spiked pond water collecting from the KISS University, including pre- and post analysis of water quality.

TiO2 Co-doped with Zr and Ag shows highly efficient visible light photocatalytic behavior suitable for treatment of polluted water

The objective of this study is to analyze the effects of zirconium (Zr) and silver (Ag) doping on the photoactivity of titania (TiO2). Zr-Ag (ZA) co-doped TiO2 products were fabricated via sol-gel technique and their properties (structural and chemical) were characterized. The weight ratio of TiO2 was fixed, while weight ratios of Zr and Ag were varied from 2 to 4, 6 and 8 wt% while synthesized samples were calcined at 400 °C for 3 h. The XRD results demonstrated that the incorporation of metal doping agents failed to alter the host material's lattice structure, however, its crystallite size was reduced from 13.54 to 5.05 nm with increasing Zr4+ and Ag+ concentrations. FTIR spectroscopy was used to examine various functional groups. In the attained spectra, an ample absorption peak between 500 and 1000 cm-1 was recorded, which was ascribed to Ti-O-Ti linkage vibration mode present within TiO2. Surface morphology, microstructure, SAED patterns and elemental composition were examined with FE-SEM, HR-TEM and EDX, which served to confirm the ZA-doped TiO2 product. Band gap energy of the co-doped material was significantly reduced as indicated by a higher wavelength redshift in the spectra. The photoactivity and kinetics of photo-products were investigated by observing photo-decolorization of methylene blue (MB) under a radiation source. Photodecomposition of MB was dramatically enhanced when titania co-doped with Zr and Ag was employed compared to un-doped or mono-doped TiO2. The ZA (8 wt%) co-doped TiO2 photocatalyst depicted the maximum MB removal efficiency (∼93%) within 90 min under a light source.