V-doped TiO2 photocatalysts and their application to pollutant degradation

Degradation of carbamazepine in surface water: performance of Pd-modified TiO2 and Ce-modified ZnO as photocatalysts

Carbamazepine is a widely used antiepileptic drug to control and treat a variety of disorders that is frequently detected in surface water, and in municipal and urban wastewater. This recalcitrant pollutant could be removed by alternative advanced oxidation technology such as heterogeneous photocatalysis. Ce-modified ZnO and Pd-modified TiO2 were synthesized by a microwave-assisted sol-gel method. According to the characterizations (Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy), a mixture of oxides was determined in both materials: CeO2/ZnO and PdO/TiO2. Photocatalytic degradation of carbamazepine in pure water under visible light (3 h) was assayed. The degradation percentage obtained with each catalyst was 80%, 53%, 20%, and 9% for ZnO, Ce-modified ZnO, TiO2, and Pd-modified TiO2, respectively. The leaching of Zn as a possible source of water contamination was tested, finding the lowest value for Ce-modified ZnO by adjusting the initial pH up to neutrality. Later, an environmentally relevant concentration of carbamazepine (228 µg L-1) was assayed, using local surface water (pH = 8.3). Despite the presence of other compounds in the real water matrix, after 5 h of photocatalysis, a 56% of degradation of the pharmaceutical and low leaching of Zn were achieved. The use of Ce-modified ZnO activated by visible light is a promising strategy for the abatement of pharmaceutical active compounds.

Zeolite Y-supported carbon-doped TiO2 nanocomposites: Efficient solar photocatalysts for the purification of medicinal wastewater

The existence of antibiotics in aquatic streams destroys water quality and thereby poses serious ecological hitches. Photocatalysis involving nanosemiconductors is an environmentally benign technique for the mineralization of antibiotics. Herein, we prepared a new visible light-sensitive photocatalyst, zeolite Y-supported carbon-doped TiO₂ nanocomposite (zeolite Y-c-TiO₂), for the elimination of cefazolin antibiotic in wastewater systems. The structural and optical properties of the synthesized nanocomposites were investigated by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller surface area analysis (BET) as well as diffuse reflectance spectroscopy (UV-DRS) and photoluminescence spectroscopy (PL). The UV-Vis absorbance spectrum of zeolite Y-c-TiO₂ exhibited a red shift towards longer wavelength with an increase in visible light absorption as compared to pure TiO₂ nanoparticles and zeolite Y-supported TiO₂ nanocomposites (zeolite Y-TiO₂). Accordingly, the photocatalytic action of the zeolite Y-c-TiO₂ for the degradation of methylene blue was evaluated under solar simulator, and it turned out to be highly efficient (100%) mineralization as compared to TiO₂-nanoparticles (42%) and zeolite Y-TiO₂ (62%) after 70 min irradiation for a 50mg L^-1 methylene blue solution. Radical scavenging experiments revealed the involvement of hydroxyl radicals, superoxide radicals, and photogenerated holes in the degradation process. Consequently, zeolite Y-c-TiO₂ was applied for the photocatalytic degradation of the cefazolin antibiotic in water, and complete degradation of cefazolin (50 mg L^-1) was observed within 6 h of solar light irradiation on zeolite Y-c-TiO₂. The degradation pathway of cefazolin was proposed by considering various intermediates detected via LC-MS analysis. The study points to the significant potential of zeolite Y-c-TiO₂ photocatalyst for the purification of medicinal wastewater under sunlight.

Palladium-modified TiO2 films in a photocatalytic microreactor: evaluation of radiation absorption properties and pollutant degradation efficiency

Pure (TiO₂) and 0.1 nominal atomic percent of palladium-modified TiO₂ (Pd-TiO₂) films were synthesized via a sol-gel method and compared through their physicochemical properties and photocatalytic activity in the degradation of an emerging contaminant, 17-α-ethinylestradiol (EE2). The activity of the films was studied using a continuous flow, planar microreactor under simulated sunlight. Catalysts characterization included X-ray diffraction, UV-Visible diffuse reflectance and transmittance spectroscopy, atomic force microscopy, transmission electron microscopy, Raman spectroscopy, N₂ physisorption analysis, and X-ray photoelectron spectroscopy. The modification of TiO₂ with palladium confined the size of anatase phase crystallites, increased the specific surface area and improved radiation absorption. PdO domains on TiO₂ were observed. In all the tested conditions, higher conversion of EE2 was achieved with the Pd-TiO₂ film compared with the TiO₂ film, presenting an 80% increase in the reaction rate. The performance of the catalytic films was also assessed by the calculation of two efficiency parameters: radiation absorption efficiency and quantum efficiency of reaction. The Pd-TiO₂ film showed a notable enhancement of the absorption of the incident radiation and a more efficient utilization of the absorbed photons to degrade the target pollutant.

Rational construction of Co-promoted 1T-MoS2 nanoflowers towards high-efficiency 4-nitrophenol reduction

Developing efficient and cost-effective non-noble metal catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) is of great importance. Herein, Co-promoted 1T-MoS₂ nanoflowers were synthesized via a one-step hydrothermal method. The influence of Co content on the structure and catalytic performance of 1T-MoS₂ was studied in detail. It was found that Co doping not only enhanced the electronic conductivity but also increased the hydrogen adsorption ability of 1T-MoS₂. Meanwhile, the highest activity was achieved due to the synergy effect of Co-Mo-S and CoS₂ active phase. In the catalytic reduction of 4-NP, the reaction rate constant of Co/1T-MoS₂-0.3 was as high as 0.908 min^-1 and the catalyst exhibited excellent stability after recycling five times. The present work provides new insights for the rational design of highly efficient metal-doped MoS₂ catalysts towards 4-NP reduction in wastewater.

Controllability of β-Ga2O3 single crystal conductivity by V doping

Strategy for realizing the tunability of the effective carrier concentration of β-Ga2O3 single crystals using V as a dopant.