Extraction of W, V, and As from spent SCR catalyst by alkali pressure leaching and the pressure leaching mechanism

Spent selective catalytic reduction (SCR) catalysts are environmentally hazardous and resource-enriching. In this work, V, W, and As in a spent SCR catalyst was extracted by alkali pressure leaching. Results showed that the V, W, and As were loaded on the anatase TiO2 crystal grains as amorphous oxides. The optimum pressure leaching conditions were NaOH concentration of 20 wt%, reaction temperature of 180 °C, reaction time of 120 min, L/S of 10 mL/g, and stirring speed of 300 rpm. The leaching efficiency of W, V, and As reached 98.83%, 100%, and 100%, respectively. The experiment revealed the preferential leaching of V and As rather than W, and the leaching mechanisms of V, W, and As were studied through experiment and density functional theory (DFT). The leaching kinetics of W conformed to a variant of the shrinking core model and the leaching process of W is controlled by both chemical reactions and diffusion processes. During the leaching process, Na2Ti2O4(OH)2 product powder layer was generated, which affects the mass transfer of W. The destruction of the TiO2 skeleton in the spent SCR catalyst is essential for adequate W extraction, especially for the extraction of W embedded in the TiO2 lattice. The DFT simulation result indicated that the V and As loaded onto the TiO2 support are easier to absorb hydroxide ions rather than W, and the leaching reaction energy of V and As was lower than W, As, and V has leaching priority over the leaching of W. Furthermore, an anatase TiO2 photocatalyst with the {001} crystal surface exposed was successfully prepared from the alkali pressure leaching residue. This work provides theoretical support for the metal leaching and utilization of spent SCR catalysts via alkali pressure leaching.

Mechanistic vision on polypropylene microplastics degradation by solar radiation using TiO2 nanoparticle as photocatalyst

Microplastics are emerging contaminants owing to their occurrence and distribution in everywhere the ecosystem and leading to major environmental problems. Management methods are more suitable for larger-sized plastics. Here, the current study elucidates that, TiO2 photocatalyst under sunlight irradiation actively mitigates polypropylene microplastics (pH 3, 50 h) in an aqueous medium. End of post-photocatalytic experiments, the weight loss percentage of microplastics was 50.5 ± 0.5%. Fourier transforms infrared (FTIR) and nuclear magnetic resonance spectroscopy (1H NMR) spectroscopy results revealed the formation of peroxide and hydroperoxide ions, carbonyl, keto and ester groups at the end of the post-degradation process. Ultraviolet-Visible Diffuse Reflectance spectroscopic (UV - DRS) results showed variation in the optical absorbance of polypropylene microplastics peak values at 219 and 253 nm. Increased the weight percentage of oxygen level due to the oxidation of functional groups and decreased the weight percentage of carbon content in electron dispersive spectroscopy (EDS), probably owing to breakdown of long-chain polypropylene microplastics. In addition, scanning electron microscopy (SEM) microscopic analysis showed the surface having holes, cavities, and cracks on irritated polypropylene microplastics. The overall study and their mechanistic pathway strongly confirmed the formation of reactive oxygen species (ROS) with help of the movement of electrons by photocatalyst under solar irradiation which aids the degradation of polypropylene microplastics.

Removal of ethylene by synthesized Ag/TiO2 photocatalyst under visible light irradiation

Photocatalysts based on titanium dioxide (TiO₂) were widely applied to solve environmental problems such as water and air pollution treatment. Currently, the application of these compounds for food packaging is increasing. This study prepared silver (Ag) doped TiO₂ photocatalyst (Ag/TiO₂) for the decomposition of gas ethylene (Eth), which is the main factor that causes fruits to over-ripen and damage or decay. It found that the doping of Ag could improve the optical property and light adsorption ability of Ag/TiO₂ photocatalyst, which directly enhanced the photocatalytic decomposition of Eth performance. Under visible light, Ag/TiO₂ could depredate 91.2% of Eth, while the removal performance by using the original TiO₂ was 43.9%. The increased initial concentration of Eth from 5 to 30 ppm could inhibit the photocatalytic efficiency of Ag/TiO₂ from 98.6 to 69.2%. Besides, the relative humidity and gas flow rate are roles in the Eth decomposition process. The recycling experiment confirmed that Ag/TiO₂ had good reusability with a slight loss in photocatalytic performance (18.6%) after ten cycles tested. The future protective application of Ag/TiO₂ for food protection during storage and transportation is discussed. This work provides a potential method to remove gas ethylene, reduce the ripening process and extend the shelf life of fruits.

Removal of ceftriaxone sodium antibiotic from pharmaceutical wastewater using an activated carbon based TiO2 composite: Adsorption and photocatalytic degradation evaluation

The water pollution becomes a serious concern for the sustainability of ecosystems due to the existence of pharmaceutical products (ceftriaxone (CEF) antibiotic). Even in low concentration of CEF has lethal effects on ecosystem and human health. To remove CEF, TiO₂ is considered as an effective and efficient nanoparticles, however its performance is reduced due to wider energy gap and rapid recombination of charge carriers. In this study, activated carbon based TiO₂ (ACT-X) heterogeneous nanocomposites were synthesized to improve the intrinsic properties of TiO₂ and their adsorption-photocatalytic performance for the removal of CEF. The characterization results revealed that ACT-X composites have slower recombination of charge carriers, lower energy band gap (3.05 eV), and better light absorption under visible region of light. From ACT-X composites, the ACT-4 photocatalyst has achieved highest photocatalytic degradation (99.6%) and COD removal up (99.2%). The results of radical scavengers showed that photocatalytic degradation of CEF is mainly occurred due to superoxide and hydroxyl radicals. Meanwhile, the reusability of ACT-4 up to five cycles shows more than 80% photocatalytic degradation, which make the process more economical. The highest experimental adsorption capacity is achieved up to 844.8 mg g^-1 using ACT-4. The favorable and multilayer heterogeneous adsorption is carried out according to the well-fitted data with pseudo-second-order and Freundlich models, respectively. These results indicate that the carbon-based TiO₂ composites can be used as a green, stable, efficient, effective, reusable, renewable, and sustainable photocatalyst to eliminate the pharmaceutical pollutants (antibiotics) via adsorption and photocatalytic degradation processes.

Investigation of optimum Mn dopant level on TiO2 for dye degradation

Pristine and Mn-TiO₂ photocatalysts was prepared employing sophisticated hydrothermal technique. TiO₂, 0.2 M, 0.4 M Mn-TiO₂ photocatalysts analysis were done by using standard characterization studies. The morphology of the pure TiO₂ photocatalyst showed the large agglomeration of nanoparticles. While the dopant Mn ions influenced higher on host lattice TiO₂. The 0.2 M Mn added TiO₂ photocatalyst showed no agglomeration and nanoparticles size were decreased. On increasing dopant level, there is growth of nanorods along with nanoparticles which greatly helped in dye degradation. The prepared photocatalysts photocatalytic action was investigated on reducing MG dye. Prepared photocatalyst added dye mixtures were exposed under visible light and collected for every 15 min. 0.4 M Mn-TiO₂- MG sample showed 96% efficiency on degrading MG dye. The dopant has increased electrons and holes recombination on host surface. 0.4 M Mn-TiO₂-MG sample rate constant was higher than other samples and reaction system abide by Pseudo first order kinetics. 0.4 M Mn-TiO₂ photocatalyst be an efficient and enthusiastic potential material to remove organic pollutants.

Decomposition of naproxen by plasma in liquid process with TiO2 photocatslysts and hydrogen peroxide

Naproxen (NPX), one of the representative non-steroidal anti-inflammatory drug (NSAID) ingredients, was decomposed by plasma in liquid process (PiLP). Strongly oxidized species generated in the plasma field of the PiLP, such as OH radicals, were confirmed by optical emission spectroscopy Increasing the operation parameters (pulse width, frequency and applied voltage) of the power supply promoted plasma field generation and OH radical generation, and affected the NPX decomposition rate. Although the NPX decomposition reaction rate was improved by up to 18-30% by adding TiO₂ photocatalyst powder and H₂O₂ to PiLP, but the optimal addition amount should be determined considering the plasma generation and scavenger effects. A decomposition pathway was proposed, in which NPX was mineralized into CO₂ and H₂O through five intermediates mainly by decarboxylation, demethylation, hydroxylation, and dehydration reactions via hydroxyl radicals.

Long-term and stable antimicrobial properties of immobilized Ni/TiO2 nanocomposites against Escherichia coli, Legionella thermalis, and MS2 bacteriophage

Nickel has been extensively used as a high work function metal because of its abundance, low cost, relatively non-toxic nature, and environmentally benign characteristics. However, it has rarely been extended in a form of immobilized composite, which is a practical strategy applicable for photocatalytic antimicrobial activities. In this study, a composite of nickel and TiO₂ (Ni/TiO₂) was prepared using a photodeposition method, and its antibacterial properties were investigated using Escherichia coli (E. coli). To optimize Ni/TiO₂ synthesis, the effect of various photodeposition conditions on antibacterial performance were investigated, such as the light irradiation time, metal content, TiO₂ crystalline structure, and presence or absence of electron donors (i.e., methanol). The optimized 2 wt% Ni/TiO₂ exhibited an antibacterial efficiency of 3.74 log within 7 min, which is more than 10-fold higher than that of pristine TiO₂ (2.54 log). Based on this optimized weight ratio, Ni/TiO₂ was immobilized on a steel mesh using an electrospray/thermal compression method, and its antibacterial performance was further assessed against E. coli, MS2 bacteriophage virus (MS2 phage), and a common pulmonary pathogen (Legionella thermalis, L. thermalis). Within 70 min, all target microorganisms achieved an inactivation that exceeded 4 log. Furthermore, the long-term stability and sustainable usability of the Ni/TiO₂ mesh were confirmed by performing more than 50 antibacterial evaluation cycles using E. coli. The results of this study facilitate the successful utilization of immobilized Ni/TiO₂ mesh in water disinfection applications.