Determination of catalytic properties of TiO2 coatings using aqueous solution of coumarin: Standardization efforts

Many types of supported photocatalytic TiO₂ continue to be the subject of extensive development worldwide. Besides industrial production and practical use of the new photocatalytic materials, there is an increasing need for a simple and reliable procedure for characterization of photocatalytic activities of newly developed materials. The aim of our work was to develop a method for the determination of quantum yields of supported photocatalysts by employing an aqueous solution of a model organic compound and different thin TiO₂ films. Additionally, also a newly defined parameter, the so-called mass efficiency, was introduced as an advantageous way of defining the photocatalytic activities. Coumarin (CM) was found to be an appropriate candidate for being a probe molecule when the photocatalytic degradation mainly occurs via the HO radical-mediated mechanism. An advantage of using CM is easy determination of highly fluorescent 7-hydroxycoumarin (7OHC). Different TiO₂ films were deposited via sol–gel methods on soda-lime glass slides that were precovered with a thin SiO₂ film, and via the sedimentation process from aqueous suspensions. Aqueous solutions of CM were irradiated using 365 nm radiation in the presence of titania films. Although Degussa P25 films showed approximately four times higher degradation rates compared to the sol–gel processed, its quantum yield was not more than 2.5 times higher. This could be explained by higher absorbance of Degussa P25 films per amount of the catalyst compared to sol–gel films. Since no information on the absorption characteristics of the material per unit of mass of the catalyst is included within the calculation of quantum yield, mass efficiency is suggested for the evaluation of photocatalytic properties of the coatings. It is evident from the present study that it is obligatory to evaluate the photocatalytic efficiencies of different area densities of the same photocatalyst in order to properly characterize the material's efficiency.     

Blue upconversion luminescence of CaMoO4:Li+/Yb3+/Tm3+ phosphors prepared by complex citrate method

Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ upconversion (UC) phosphor was prepared by complex citrate-gel method and UC luminescence properties were investigated. Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ has intense blue emission induced by ¹G₄??³H₆ transition at 476?nm that is improved 10 times more than that of Li⁺ undoped sample and weak red emission at 647 nm generated by ³F₂??³H₆ transition under excitation at 980?nm. The optimum doping concentration of Li⁺ ions was investigated and UC mechanism of Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ was discussed in detail.     

A new characterization of graphs based on interception relations

While graphs are normally defined in terms of the 2-place relation of adjacency, we take the 3-place relation of interception as the basic primitive of their definition. The paper views graphs as an economical scheme for encoding interception relations, and establishes an axiomatic characterization of relations that lend themselves to representation in terms of graph interception, thus providing a new characterization of graphs. © 1996 John Wiley & Sons, Inc.     

A methodology to achieve the set of operation modes of reconfigurable parallel manipulators

The demand for increasingly more versatile machinery has boosted the development of the so-called reconfigurable mechanisms. In this paper, the authors present a general methodology to assess the multioperational capacity of a 6-DOF parallel manipulator basing on the possible motion patterns having Lie group structure that the manipulator owns. This ability of having different operation modes enables the manipulator to adapt to diverse tasks. To show the potential of the methodology, this approach has been applied to the 6-DOF 3-CPCR which is capable of generating multiple motion patterns. In addition to carrying out the complete theoretical study in which all the different operation modes are obtained, and validating the procedure with GIM software designed for kinematic analysis and design of mechanisms, a demonstration prototype of the 3-CPCR parallel manipulator has been also built.

     

Photocatalytic CO2 Reduction Using TiO2-Based Photocatalysts and TiO2 Z-Scheme Heterojunction Composites: A Review

Photocatalytic CO₂ reduction is a most promising technique to capture CO₂ and reduce it to non-fossil fuel and other valuable compounds. Today, we are facing serious environmental issues due to the usage of excessive amounts of non-renewable energy resources. In this aspect, photocatalytic CO₂ reduction will provide us with energy-enriched compounds and help to keep our environment clean and healthy. For this purpose, various photocatalysts have been designed to obtain selective products and improve efficiency of the system. Semiconductor materials have received great attention and have showed good performances for CO₂ reduction. Titanium dioxide has been widely explored as a photocatalyst for CO₂ reduction among the semiconductors due to its suitable electronic/optical properties, availability at low cost, thermal stability, low toxicity, and high photoactivity. Inspired by natural photosynthesis, the artificial Z-scheme of photocatalyst is constructed to provide an easy method to enhance efficiency of CO₂ reduction. This review covers literature in this field, particularly the studies about the photocatalytic system, TiO₂ Z-scheme heterojunction composites, and use of transition metals for CO₂ photoreduction. Lastly, challenges and opportunities are described to open a new era in engineering and attain good performances with semiconductor materials for photocatalytic CO₂ reduction.     

Identification of α-Glucosidase Inhibitors from Scutellaria edelbergii: ESI-LC-MS and Computational Approach

The recent study investigated the in vitro anti-diabetic impact of the crude extract (MeOH) and subfractions ethyl acetate (EtOAc); chloroform; n-butanol; n-hexane; and aqueous fraction of S. edelbergii and processed the active EtOAc fraction for the identification of chemical constituents for the first time via ESI-LC-MS analysis through positive ionization mode (PIM) and negative ionization mode (NIM); the identified compounds were further validated through computational analysis via standard approaches. The crude extract and subfractions presented appreciable activity against the α-glucosidase inhibitory assay. However, the EtOAc fraction with IC₅₀ = 0.14 ± 0.06 µg/mL revealed the maximum potential among the fractions used, followed by the MeOH and n-hexane extract with IC₅₀ = 1.47 ± 0.14 and 2.18 ± 0.30 µg/mL, respectively. Moreover, the acarbose showed an IC₅₀ = 377.26 ± 1.20 µg/ mL whereas the least inhibition was observed for the chloroform fraction, with an IC₅₀ = 23.97 ± 0.14 µg/mL. Due to the significance of the EtOAc fraction, when profiled for its chemical constituents, it presented 16 compounds among which the flavonoid class was dominant, and offered eight compounds, of which six were identified in NIM, and two compounds in PIM. Moreover, five terpenoids were identified—three and two in NIM and PIM, respectively—as well as two alkaloids, both of which were detected in PIM. The EtOAc fraction also contained one phenol that was noticed in PIM. The detected flavonoids, terpenoids, alkaloids, and phenols are well-known for their diverse biomedical applications. The potent EtOAc fraction was submitted to computational analysis for further validation of α-glucosidase significance to profile the responsible compounds. The pharmacokinetic estimations and protein-ligand molecular docking results with the support of molecular dynamic simulation trajectories at 100 ns suggested that two bioactive compounds—dihydrocatalpol and leucosceptoside A—from the EtOAc fraction presented excellent drug-like properties and stable conformations; hence, these bioactive compounds could be potential inhibitors of alpha-glucosidase enzyme based on intermolecular interactions with significant residues, docking score, and binding free energy estimation. The stated findings reflect that S. edelbergii is a rich source of bioactive compounds offering potential cures for diabetes mellitus; in particular, dihydrocatalpol and leucosceptoside A could be excellent therapeutic options for the progress of novel drugs to overcome diabetes mellitus.     

Cement Composites with Carbon-Based Nanomaterials for 3D Concrete Printing Applications – A Review

3D concrete printing (3DCP) is an emerging additive manufacturing technology in the construction industry. Its challenges lie in the development of high-performance printable materials and printing processes. Recently developed carbon-based nanomaterials (CBNs) such as graphene, graphene oxide, graphene nanoplatelets, and carbon nanotubes, have various applications due to their exceptional mechanical, chemical, thermal, and electrical characteristics. CBNs also have found potential applications as a concrete ingredient as they enhance the microstructure and modify concrete properties at the molecular level. This paper focuses on state-of-the-art studies on CBNs, 3DCP technology, and CBNs in conventional and 3D printable cement-based composites including CBN dispersion techniques, concrete mixing methods, and fresh and hardened properties of concrete. Furthermore, the current limitations and future perspectives of 3DCP using CBNs to produce high-quality composite mixtures are discussed.