Polyoxometalates for bifunctional applications: Catalytic dye degradation and anticancer activity

Improving the efficiencies of organic compound degradations by catalytic materials is a challenging materials research field. In our research, we successfully synthesized cobalt-based polyoxometalates (CoV-POMs) via a simple crystallization-driven self-assembly method. The incorporation of the newly synthesized CoV-POMs into peroxymonosulphate (PMS), forming a mixture, greatly enhancing the catalytic activation for a complete degradation of dye solution. The positive synergic effect between CoV-POMs and PMS was substantiated by a relatively meager degradation of less than 10% in the system without CoV-POMs, in which CoV-POMs played a vital role to activate PMS towards free radicals generation for dye degradation. Methylene blue (MB) and rhodamine B (RB) dyes were completely decolorized under 60 min with the presence of 40 mg/L CoV-POMs and 150 mg/L PMS. The CoV-POMs/PMS system was pH dependance with a lower dye degradation efficiency at elevated pH. The effect of pH was more prominent in RB dye, in which the degradation efficiency dropped drastically from 93.3% to 41.12% with the increase in the solution pH from 7 to 11. The quenching tests suggested that sulfate radicals were the dominant active species involving in the dye degradation reaction. Besides MB and RB dyes, CoV-POMs/PMS system also showed significant activity towards the degradation of phenol red (PR) and methyl orange (MO) dyes. In the biological test, CoV-POMs exhibited non-toxic behavior towards normal cells that reduced safety concern for the large-scale wastewater treatment application. In addition, the testing divulged the anticancer property of CoV-POMs with more than 35 % of A549 lung adenocarcinoma and MDA-MB-231 breast adenocarcinoma were killed with 250 mg/L CoV-POMs. The selective lethality of CoV-POMs towards cancer cells was found to be caused by different extents of cellular apoptosis. In overall, the synthesized bifunctional CoV-POMs manifested superior activities in the examined applications, specifically dye degradation and anticancer.

Advanced Synthesis and Characterization of Vanadia/Titania Catalysts through a Molecular Approach

Vanadia/titania catalysts were synthesized by the equilibrium deposition filtration (EDF) method, which is a synthesis route that follows a molecular-level approach. The type of interfacial deposition as well as the interfacial speciation of the deposited oxo-V(V) species were determined by means of a model that takes into account experimental “proton-ion” curves and “adsorption edges”. It is shown that at pH ≥ 9.5, the deposition proceeds exclusively through the formation of mono-substituted inner sphere monomeric species in an “umbrella”-like Ti–OV(OH)2O configuration, whilst with lowering of the pH, a second species, namely the disubstituted inner sphere quadrameric species in a (Ti-O)2V4O10 configuration possessing two mono-oxo V=O and two di-oxo V(=O)2 terminations gradually prevails, which is in co-existence with the monomeric species. Raman spectroscopy is used for verifying the solution speciation, which is different compared to the interfacial speciation of the deposited oxo-V(V) species. Furthermore, in situ Raman spectroscopy was used to verify the model-predicted interfacial speciation of the deposited oxo-V(V) species and to monitor the temperature-dependent evolution up to 430 °C. Hence, a controlled formation of a specific vanadia species on a titania surface is enabled, which, depending on the synthesis conditions, can result in specific catalyst characteristics and thus possibly different catalytic behavior for a specific reaction.

Pd-based catalysts promoted by hierarchical porous Al2O3 and ZnO microsphere supports/coatings for ethyl acetate highly active and stable destruction

Developing economical and active materials is of great significance for VOC purification. Here, hierarchical porous Al₂O₃ and ZnO microspheres (Al₂O₃-pm and ZnO-pm) were synthesized by a facile hydrothermal strategy. The urchin-like Al₂O₃-pm and flower-like ZnO-pm possess high specific surface area (especially; external surface area) obviously boost the dispersion of Pd with 29.3 % and 30.1 % over Pd/Al₂O₃-pm and Pd/ZnO-pm, respectively, over 3.4 times higher than those of commercial Al₂O₃- and ZnO-supported counterparts. Pd/Al₂O₃-pm possesses excellent activity and CO₂ yield in ethyl acetate (EA) degradation, with TOF reaches 7.76 × 10^-3 s^-1 at 160 °C under GHSV of 50,000 h^-1. Moreover, Pd/Al₂O₃-pm exhibits satisfied performance in EA-contained binary VOCs oxidation and has high long-term stability under both dry and humid conditions. Both Pd sites and Brønsted acid sites participated in reaction process and initially react with EA to form ethylene and ethanol, respectively. Larger amount Brønsted acid sites over Pd/Al₂O₃-pm promote ethanol formation and C-C cleavage, resulting in different CO₂ yields and EA activation mechanisms. The coating greatly enhances Pd dispersion over Pd supported monolithic catalyst, endowing its desired activity and stability even with a much lower Pd loading. This work promotes the potential application of noble-metal-based monolithic materials in VOC degradation.

Self-Exfoliated Synthesis of Transition Metal Phosphate Nanolayers for Selective Aerobic Oxidation of Ethyl Lactate to Ethyl Pyruvate

Two-dimensional (2D) transition metal nanosheets are promising catalysts because of the enhanced exposure of the active species compared to their 3D counterparts. Here, we report a simple, scalable, and reproducible strategy to prepare 2D phosphate nanosheets by forming a layered structure in situ from phytic acid (PTA) and transition metal precursors. Controlled combustion of the organic groups of PTA results in interlayer carbon, which keeps the layers apart during the formation of phosphate, and the removal of this carbon results in ultrathin nanosheets with controllable layers. Applying this concept to vanadyl phosphate synthesis, we show that the method yields 2D ultrathin nanosheets of the orthorhombic β-form, exposing abundant V⁴⁺/V⁵⁺ redox sites and oxygen vacancies. We demonstrate the high catalytic activity of this material in the vapor-phase aerobic oxidation of ethyl lactate to ethyl pyruvate. Importantly, these β-VOPO₄ compounds do not get hydrated, thereby reducing the competing hydrolysis reaction by water byproducts. The result has superior selectivity to ethyl pyruvate compared to analogous vanadyl phosphates. The catalysts are highly stable, maintaining a steady-state conversion of ∼90% (with >80% selectivity) for at least 80 h on stream. This "self-exfoliated" synthesis protocol opens opportunities for preparing structurally diverse metal phosphates for catalysis and other applications.

Bifunctional Electrocatalyst of Low-Symmetry Mesoporous Titanium Dioxide Modified with Cobalt Oxide for Oxygen Evolution and Reduction Reactions

Hybrids of low-symmetry (disordered) mesoporous titanium dioxide modified with different weight ratios of cobalt oxide nanoparticles (Co3O4(x)/lsm-TiO2) are prepared using a one-pot self-assembly surfactant template. The physicochemical characterization of Co3O4(x)/lsm-TiO2 hybrids by scanning and transmission electron microscopy, X-ray diffraction, N2 adsorption–desorption isotherms, and X-ray photoelectron spectroscopy confirm the successful incorporation of cobalt oxide nanoparticles (2–3 nm in diameter) with preservation of the highly mesoporous structure of titanium dioxide substrate. Among these mesoporous hybrids, the ~3.0 wt.% Co3O4/lsm-TiO2 exhibits the best performance toward both the oxygen evolution (OER) and reduction (ORR) reactions in alkaline solution. For the OER, the hybrid shows oxidation overpotential of 348 mV at 10 mA cm−2, a turnover frequency (TOF) of 0.034 s−1, a Tafel slope of 54 mV dec−1, and mass activity of 42.0 A g−1 at 370 mV. While for ORR, an onset potential of 0.84 V vs. RHE and OER/ORR overpotential gap (ΔE) of 0.92 V are achieved which is significantly lower than that of commercial Pt/C, hexagonal mesoporous, and bulk titanium dioxide analogous. The Co3O4/lsm-TiO2 hybrid demonstrates significantly higher long-term durability than IrO2. Apparently, such catalytic activity performance originates from the synergetic effect between Co3O4 and TiO2 substrate, in addition to higher charge carrier density and the presence of disordered mesopores which provide short ions diffusion path during the electrocatalytic process.

Highly tunable periodic imidazole-based mesoporous polymers as cooperative catalysts for efficient carbon dioxide fixation

We designed new periodic imidazole-based mesoporous polymers for cooperative catalysis, revealing the structure–activity relationships in CO₂ cycloaddition.