Niobium-Titanium-Based Photocatalysts: Its Potentials for Free Cyanide Oxidation in Residual Aqueous Effluent

Photocatalytic Degradation of Phenol Red in Water on Nb(x)/TiO2 Nanocomposites

In this paper, the photocatalytic effect of Nb(x)/TiO2 nanocomposites on the degradation of phenol red (PR) was studied. Nb(x)/TiO2 nanocomposites are fabricated by a simple sol-gel route with new experimental conditions. The structural and optical properties were determined using high transmission electron microscopy (HRTEM), X-ray diffraction, Raman spectroscopy, photoluminescence, and UV-vis absorbance spectroscopy. Compared to pure anatase TiO2, the recently fabricated Nb(x)/TiO2 nanocomposite has a shift in the optical band edge to the visible wavelength. Consequently, it has high performance in adsorption capacity and photocatalytic activities. A time of 160 min has been observed to be suitable for mostly degradable 20 mgL−1 of phenol red on Nb(2.0)/TiO2 composite. The kinetic results were in good agreement with the first-order kinetic model at different concentrations. In addition, the results showed that the addition of Nb led to a significant degradation process. The decomposition of phenol red pollutants showed a synergistic effect of the Nb(2.0)/TiO2 nanocomposites on wastewater treatment.

Synergistic effect of adsorptive photocatalytic oxidation and degradation mechanism of cyanides and Cu/Zn complexes over TiO2/ZSM-5 in real wastewater

The treatment of cyanide wastewater from the gold industry is essential. Photocatalytic oxidation is an effective method for the elimination of cyanides and metal cyanide complexes. TiO₂/ZSM-5 composite photocatalysts with different SiO₂/Al₂O₃ ratios were prepared using the solid-state dispersion (SSD) method. The composite catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption-desorption, and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The catalytic efficiency of different SiO₂/Al₂O₃ ratios and the synergistic effect of adsorptive photocatalytic oxidation for the degradation of cyanide wastewater was investigated under different adsorption and illumination times. With the extension of the photocatalytic time (>2.0 h), the composite catalyst with a high SiO₂/Al₂O₃ ratio had better photocatalytic performance. A 93.97% degradation efficiency of total cyanides was observed after adsorption for 3.0 h and illumination for 4.0 h under room temperature with air as the oxidant. The removal efficiencies of the copper and zinc ions were 81.67% and 100%, respectively. The degradation of cyanide followed pseudo-first-order kinetics. Energy dispersive spectroscopy (EDS) results showed that the generally irregular surface of the catalyst with a high SiO₂/Al₂O₃ ratio contains more nano-TiO₂. The adsorption capacities of copper and zinc were relatively high. X-ray photoelectron spectroscopy (XPS) suggested that cyanide was eventually degraded to CO₂ and NO₃^-. Copper and zinc were removed in the form of Cu(II) and Zn(II).