The Recent Development in Chemoresistive-Based Heterostructure Gas Sensor Technology, Their Future Opportunities and Challenges: A Review

Atmospheric pollution has become a critical problem for modern society; therefore, the research in this area continually aims to develop a high-performance gas sensor for health care and environmental safety. Researchers have made a significant contribution in this field by developing highly sensitive sensor-based novel selective materials. The aim of this article is to review recent developments and progress in the selective and sensitive detection of environmentally toxic gases. Different classifications of gas sensor devices are discussed based on their structure, the materials used, and their properties. The mechanisms of the sensing devices, identified by measuring the change in physical property using adsorption/desorption processes as well as chemical reactions on the gas-sensitive material surface, are also discussed. Additionally, the article presents a comprehensive review of the different morphologies and dimensions of mixed heterostructure, multilayered heterostructure, composite, core-shell, hollow heterostructure, and decorated heterostructure, which tune the gas-sensing properties towards hazardous gases. The article investigates in detail the growth and interface properties, concentrating on the material configurations that could be employed to prepare nanomaterials for commercial gas-sensing devices.

Secondary-sphere modification in proline catalysis: Old friend, new connection

In this work, we exploit our strategy of in situ secondary-sphere modification of organocatalysts to improve the reactivity and selectivity of amino catalysts. Herein, the carboxylic acid moiety of proline...

Homochiral bifunctional L-prolinamide- and L-bis-prolinamide-catalyzed asymmetric aldol reactions performed in wet solvent-free conditions

In this study, the novel bifunctional homochiral thiourea-L-prolinamides 1-4, tertiary amino-L-prolinamide 5, and bis-L-prolinamides 6 and 7 were prepared from enantiomerically pure (11R,12R)-11,12-diamino-9,10-dihydro-9,10-ethanoanthracene 8 and (11S,12S)-11,12-diamino-9,10-dihydro-9,10-ethanoanthracene ent-8. Highly enantioselective and diastereoselective aldolic intermolecular reactions (up to 95% enantiomeric excess, 93:7 anti/syn) between aliphatic ketones (20 equiv) and a range of aromatic aldehydes (1 equiv) were successfully carried out in the presence of water (10 equiv) and monochloroacetic acid (10 mol%), solvent-free conditions, at room temperature over 24 h using organocatalysts 1-7 (5 mol%). Stereoselective induction using density functional theory-based methods was consistent with the experimental data.

Proline derived guanidine catalysts forge extensive H-bonded architectures: a solution and solid state study

The preparation of a range of amino acid derived guanidine organocatalysts is reported together with their application to the Michael addition of 2-hydroxy-1,4-napthoquinone to β-nitrostyrene, achieving a maximum ee of 56%. Some insight into the mechanism was sought by using X-ray crystallography and a detailed study of the intra- and intermolecular hydrogen bonding is reported.

Catalysts assemble! We present the design and synthesis of a large family of amino acid derived guanidine organic moieties as catalysts in the solution state and building blocks towards extended H-bonded architectures upon crystallisation.

Asymmetric Direct Aldol Reaction Catalyzed by (1R, 2R)-(+)-1, 2- Diammonium Cyclohexane-L-tartrate in Water

Background:

A cheap and commercially available organocatalyst, (1R, 2R)-(+)-1, 2- diammonium cyclohexane-L-tartrate 1 was applied in direct aldol reaction in water. The organocatalyst 1 afforded aldol products from cyclohexanone and substituted aromatic aldehydes with high yield (up to 90%) and good stereoselectivity (up to 99% ee and up to 11.5:1 dr) in large volume of water (10 ml).

Methods:

The same aldol reaction when carried out in the presence of more expensive organocatalyst e.g. (1R, 2R)-(+)-1,2-diaminocyclohexane and 1,6-hexanediaoic acid as acid additive furnished the aldol products with only 20% yield, 2:1 anti/syn ratio and 92% ee.

Results and Conclusion:

In summary, we have applied a reasonably cheap and commercially available organocatalyst 1 for highly enantioselective direct aldol reaction in water at room temperature.

A novel thiourea type organocatalyst possessing a single NH functionality

A novel thiourea organocatalyst was rationally designed by altering a typical H-bonding pattern of thiourea derivatives and utilising the potential of the 3,5-bis(trifluoromethyl)phenyl motif to participate in the H-bond formation. This unique catalyst afforded the products of the α-amination and Michael reaction in excellent yields and with a high level of stereoselectivity. Although additional studies are necessary to establish the full potential of the catalyst and to broaden its application further, the presented results may indicate alternative routes for further exploration of the thiourea class of organocatalysts.

Synthesis of Hierarchical SnO2 Nanowire-TiO2 Nanorod Brushes Anchored to Commercially Available FTO-coated Glass Substrates

Growth of single-crystal SnO₂ nanowires using a fluorine-doped SnO₂ (FTO) thin film as both the source and substrate is demonstrated for the first time at relatively low temperature (580 °C) which preserves the integrity of the underlying glass support and improves scalability to devices. Furthermore, a microwave hydrothermal process is shown to grow TiO₂ nanorods on these nanowires to create a hierarchical nanoheterostructure that will lead to efficient photogenerated charge carrier separation and rapid transport of electrons to the substrate. This process simplifies nanowire growth by using commercially available and widely used FTO substrates without the need for an additional upstream Sn source and can be used as a high surface area host structure to many other hierarchical structures.

Ionic liquid supported acid additive stabilizes the transition structure of organocatalytic asymmetric direct aldol reaction by proton donation: A quantum mechanical study

ONIOM studies were performed on the transition structure (TS) of organocatalytic direct aldol reaction by using ionic liquid supported benzoic acid (ILS-PhCO2H) as an additive. Results obtained from this computation suggest direct involvement of ILS-PhCO2H in the TS as a proton donor. It has also come out from the present study that, the counter ion of the ILS-acid additive may also play significant role to maintain the proper TS geometry by holding the organocatalyst and the acid additive close together during the course of reaction.

Highly modular dipeptide-like organocatalysts for direct asymmetric aldol reactions in brine

The dipeptide-like organocatalysts have been developed for asymmetric aldol reactions in brine to achieve high yields and enantioselectivities with 1 mol% catalyst-loading.