Comparative study on CeO2 catalysts with different morphologies and exposed facets for catalytic ozonation: performance, key factor and mechanism insight.

Morphology and facet effects of metal oxides in heterogeneous catalytic ozonation (HCO) are attracting increasing interests. In this paper, the different HCO performances for degradation and mineralization of phenol of seven ceria (CeO2) catalysts, including four with different morphologies (nanorod, nanocube, nanooctahedron and nanopolyhedron) and three with the same nanorod morphology but different exposed facets, are comparatively studied. CeO2 nanorods with (110) and (100) facets exposed show the best performance, much better than that of single ozonation, while CeO2 nanocubes and nanooctahedra show performances close to single ozonation. The underlying reason for their different HCO performances is revealed using various experimental and density functional theory (DFT) calculation results and the possible catalytic reaction mechanism is proposed. The oxygen vacancy (OV) is found to be pivotal for the HCO performance of the different CeO2 catalysts regardless of their morphology or exposed facet. A linear correlation is discerned between the rate of catalytic decomposition of dissolved ozone (O3) and the density of Frenkel-type OV. DFT calculations and in-situ spectroscopic studies ascertain that the existence of OV can boost O3 activation on both the hydroxyl (OH) and Ce sites of CeO2. Conversely, various facets without OV exhibit similar O3 adsorption energies. The OH group plays an important role in activating O3 to produce hydroxyl radical (∙OH) for improved mineralization. This work may offer valuable insights for designing Facet- and OV-regulated catalysts in HCO for the abatement of refractory organic pollutants.

Sintering- and oxidation-resistant ultrasmall Cu(I)/(II) oxides supported on defect-rich mesoporous alumina microspheres boosting catalytic ozonation.

Supported copper oxides with well-dispersed metal species, small size, tunable valence and high stability are highly desirable in catalysis. Herein, novel copper oxide (CuOx) catalysts supported on defect-rich mesoporous alumina microspheres are developed using a spray-drying-assisted evaporation induced self-assembly method. The catalysts possess a special structure composed of a mesoporous outer layer, a mesoporous-nanosphere-stacked under layer and a hollow cavity. Because of this special structure and the defective nature of the alumina support, the CuOx catalysts are ultrasmall in size (1 ~ 3 nm), bivalent with a very high Cu+/Cu2+ ratio (0.7), and highly stable against sintering and oxidation at high temperatures (up to 800 °C), while the wet impregnation method results in CuOx catalysts with much larger sizes (~15 nm) and lower the Cu+/Cu2+ ratios (~0.29). The catalyst formation mechanism through the spray drying method is proposed and discussed. The catalysts show remarkable performance in catalytic ozonation of phenol wastewaters. With high-concentration phenol (250 ppm) as the model organic pollutant, the optimized catalyst delivers promising catalytic performance with 100% phenol removal and 53% TOC removal in 60 min, and a high cyclic stability. Superoxide anion free radicals (⋅O2-), singlet oxygen (1O2) and hydroxyl radicals (⋅OH) are the predominant reactive species. A detailed structure-performance study reveals the surface hydroxyl groups and Cu+/Cu2+ redox couples play cooperatively to accelerate O3 decomposition generating reactive radicals. The plausible catalytic O3 decomposition mechanism is proposed and discussed with supportive evidences.

Uniform mesoporous carbon hollow microspheres imparted with surface-enriched gold nanoparticles enable fast flow adsorption and catalytic reduction of nitrophenols.

Adsorption and catalytic conversion of nitrophenols (NPs) over carbon-based materials have attracted wide interest. Batch adsorption and catalytic reduction of NPs have been widely reported, but less attention has been paid to flow systems, which require high particle size uniformity and superior active site accessibility. Herein, uniform mesoporous carbon hollow microspheres with their surfaces enriched by Au nanoparticles (denoted as Au@UMCHMs) are synthesized. The surface-enriched Au nanoparticle loading is promoted by the unique feature, that is, relatively dense external layers and mesoporous inner shells, of the carbon microspheres and the simple impregnation-reduction method. The Au@UMCHMs possess uniform sizes of ∼82 µm, small shell thickness of ∼5.8 µm, high specific surface area (∼1587 m2/g), and uniform mesopores (2.1 and 5.8 nm). They show excellent performance for flow adsorption and catalytic reduction of 4-nitrophenol (4-NP), superior to that of conventional Au-loaded carbon materials. In flow adsorption of 4-NP, the Au@UMCHMs show a fast and complete removal efficiency with high adsorption capacities (∼223 mg/g at breakthrough). They show outstanding performance in flow catalytic reduction of 4-NP. 4-NP with high concentrations (up to 100 mg/L) can be ultrafast and completely catalytically reduced to 4-aminophenol (4-AP) under rapid flow rates (up to ∼25 mL/min).

Spray drying of monodispersed microencapsulates: implications of formulation and process parameters on microstructural properties and controlled release functionality.

Particulates for pharmaceutical applications require stringent control over their characteristics to realize the optimal therapeutic performance. By generating uniform spray-dried silica particles encapsulating different model drugs via a microfluidic jet spray drying technique, we demonstrated how the effects of formulation and process parameters on the investigated properties could be directly quantified without the complications of wide particle distributions typical of conventional spray drying. The implemented strategies included incorporating lactose to modify the internal microstructures to regulate release, and increasing drying temperature during synthesis to modify the surface features of particles. The physicochemical properties of encapsulated drugs were shown to influence particle morphologies and release profiles, while the pH of initial precursors influenced the particle morphologies with slight effects on the initial release rates. The outcomes would be useful to indentify appropriate formulations and manufacturing parameters in designing spray-dried silica-based microencapsulates with tailor-made controlled release functionalities.