Current Organocatalysis - Volume 7, Issue 3, 2020

Nanostructured materials often exhibit unique physical properties, such as fast carrier transport, subwavelength optical waveguiding, and a high surface-area-to-volume ratio. When the size of a material is reduced to nanoscale dimensions, its physical and chemical properties can change dramatically. In addition, nanostructures offer exciting new opportunities for environmental applications. In this review, we aim to provide an up-to-date summary of recent research related to multifunctional TiO2-based inorganic and organic semiconductor nanomaterials, covering both their synthesis and applications. After a brief introduction of the definition and classification of TiO2-based inorganic and organic semiconductor nanomaterial structures, we discuss various application strategies, such as sewage treatment, heavy metal removal, and the oxidation of alcohols to the corresponding aldehydes. In our previous work, we fabricated a variety of TiO2-based hollow spheres using a diverse range of materials from inorganic semiconductors to organic semiconductors and applied these structures as photocatalysts. Further, the development of these nanostructures may enable numerous applications in the field of environmental technology.

Catalytic air oxidation (CAO) is an economical, environmentally friendly, and efficient technology used to treat wastewater that contains refractory organics. This review analyzes recent studies regarding five common types of CAO that use external energy sources (heat, light radiation, microwave, and electricity) or non-oxidizing chemical promoters (nitrites and sulfites). Methods include hydrothermal, electro-assisted, photocatalytic, microwave-assisted, and non-oxidizing chemical-assisted CAO. The associated catalytic mechanisms are discussed in detail in order to explain the connections between CAO catalytic pathways. Mechanisms include O2 activation via excitation, free-radical autocatalytic reactions, and coordination catalysis. Classical kinetic mechanisms, including Mars-van Krevelen and Langmuir-Hinshelwood, are also proposed to reveal overall CAO dynamic processes. The catalysts used in each CAO technology are summarized, with a focus on their catalytic pathways and the methods by which they might be improved. Finally, important challenges and research directions are proposed. The proposals focus on further research regarding catalyst mechanisms, mechanism-guided catalyst design, and process improvement.

Wet air oxidation (WAO) is an attractive technique for sewage sludge treatment. The WAO process and the factors influencing the process are examined in detail, together with the advantages and disadvantages. Catalytic wet air oxidation (CWAO) is emphasized because it can lower operational conditions, and the commonly-used and new homogeneous and heterogeneous catalysts are introduced. Homogeneous catalysts tend to be more appropriate for the CWAO treatment of sewage sludge, and Cu-based homogeneous catalysts such as CuSO4 are the most popular for industrial applications. Heterogeneous catalysts include non-noble metal catalysts, noble metal catalysts, metal-organic frameworks (MOFs) catalysts, and non-metal catalysts. Non-noble metal catalysts typically contain hetero-elements as in Mo-based, Ce-based, Cu-based, Fe-based catalysts, multi-metal supported catalysts, and polyoxometalates catalysts. In general, Mo-based catalysts and Ce-based catalysts have higher activities than other metal-based catalysts. The commonly-used noble metal elements are based on Ru, Pt, Pd, Rh, and Ir. The MOF catalysts tend to have high catalytic activity, and the non-metallic carbon catalysts may be used in environments that would otherwise be toxic to traditional metal catalysts. To conclude, a summary of the challenges and prospects of WAO technology in sewage sludge treatment is given.

Ascorbic acid is the most well-known vitamin found in different types of food. It has tremendous medical applications in several different fields such as in pharmaceuticals, cosmetics, and in organic synthesis. Ascorbic acid can be used as a substrate or mediator in organic synthesis. In this review, we report ascorbic acid-catalyzed reactions in organic synthesis. Several examples are included in this review to demonstrate that ascorbic acid is a versatile catalyst for the synthesis of diverse organic compounds. Reactions catalyzed by ascorbic acid are performed in organic or aqueous media. The ready availability and easy handling features of ascorbic acid make these procedures highly fascinating.

Background: Due to the ubiquitous nature of the ketone functionality, it is considered an important functional group in organic chemistry. Hence, the synthesis of ketones from readily available starting materials is an important chemical transformation in organic synthesis. Consequently, several research efforts have been reported in the literature for the transformation of carboxylic acids to ketones in a one-pot synthesis. However, some of the procedures have limitations, such as long reaction times, harsh reaction conditions, and usage of expensive metal catalysts. Thus, a simple and convenient one-pot conversion of carboxylic acids to ketones remains desirable. Objective: We intended to develop a simple and convenient one-pot methodology for the synthesis of ketones from carboxylic acids. Our objective was to build up a carboxylic acid-based chemical template where various types of organometallic reagents can interact to produce the desired ketone. Methods: In this procedure, a carboxylic acid was converted to a mixed anhydride using mesyl chloride in the presence of a base. This mixed anhydride was then reacted with a suitable organometallic reagent at -20°C to obtain the desired ketone. The reaction was performed in a one-pot fashion. Results: Under the optimized reaction conditions, various aromatic and heteroaromatic carboxylic acids were converted to the corresponding ketones using organolithium and organomagnesium reagents with short reaction times. Moderate to good yields of the desired ketones were observed in many of these transformations. Conclusion: A simple and convenient one-pot method for the conversion of carboxylic acids to ketones has been reported. Specifically, various aromatic and `heteroaromatic carboxylic acids have been converted to the corresponding ketones in moderate to good yields. Organomagnesium and organolithium reagents were used as nucleophiles for this reaction.

Background: In this study, we show that the AFM method not only allows monitoring the morphological changes in biological structures fixed on the surface due to H-bonds, but also makes it possible to study the self-organization of metal complexes by simulating the active center of enzymes due to intermolecular H-bonds into stable nanostructures; the sizes of which are much smaller than the studied biological objects. The possible role of intermolecular hydrogen bonds in the formation of stable supramolecular metal complexes, which are effective catalysts for the oxidation of alkyl arenes to hydroperoxides by molecular oxygen and mimic the selective active sites of enzymes, was first studied by AFM. Methods and Results: The formation of supramolecular structures due to intermolecular hydrogen bonds and, possibly, other non-covalent interactions, based on homogenous catalysts and models of active centers enzymes, heteroligand nickel and iron complexes, was proven by AFM-technique. AFM studies of supramolecular structures were carried out using NSG30 cantilever with a radius of curvature of 2 nm, in the tapping mode. To form nanostructures on the surface of a hydrophobic, chemically modified silicon surface as a substrate, the sample was prepared using a spin-coating process from solutions of the nickel and iron complexes. The composition and the structure of the complex Ni2(acac)(OAc)3·NMP·2H2O were determined in earlier works using various methods: mass spectrometry, UV- and IR-spectroscopy, elemental analysis, and polarography. Self-assembly of supramolecular structures is due to intermolecular interactions with a certain coordination of these interactions, which may be a consequence of the properties of the components themselves, the participation of hydrogen bonds and other non-covalent interactions, as well as the balance of the interaction of these components with the surface. Using AFM, approaches have been developed for fixing on the surface and quantifying parameters of cells. Conclusion: This study summarizes the authors' achievements in using the atomic force microscopy (AFM) method to study the role of intermolecular hydrogen bonds (and other non-covalent interactions) and supramolecular structures in the mechanisms of catalysis. The data obtained from AFM based on nickel and iron complexes, which are effective catalysts and models of active sites of enzymes, indicate a high probability of the formation of supramolecular structures in real conditions of catalytic oxidation, and can bring us closer to understanding enzymes activity. With a sensitive AFM method, it is possible to observe the self-organization of model systems into stable nanostructures due to H-bonds and possibly other non-covalent interactions, which can be considered as a step towards modeling the active sites of enzymes. Methodical approaches of atomic force microscopy for the study of morphological changes of cells have been developed.

Background: A vital section of water pollution mostly comes from the dying industry, which contaminates the water bodies by discharging the effluents into them. Naturally, it is carcinogenic as it contains harmful chemicals and minerals. To prevent this , many researchers have studied the issue and came to an inference that Methylene blue should be removed from wastewater. Many researchers and scientists proposed that Zeolite with little modifications could be one of the feasible options for catalytic oxidation of dyes in wastewater. Our focus is mostly based on Molybdenum impregnated H-ZSM-5 to catalytically oxidize methylene blue present in wastewater. Objective: This method examined the Catalytic oxidation of wastewater containing Methylene Blue by the application of Mo-ZSM-5. Methods: Raw H-ZSM-5 was activated and impregnated with previously prepared MoCl5 and allowed to dry and calcine at the required temperature. The product was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and BET Surface Area Analyser methods. Catalytic oxidation reactions were carried out at room temperature using hydrogen peroxide as oxidant. The effect of each parameter was investigated vividly. Results: From the Energy Dispersive X-ray Spectroscopy method, it was observed that the percentage for Molybdenum over H-ZSM-5 was 9%. Surface area analysis suggested that the value for the surface area of unimpregnated H-ZSM-5 was 511 m2/g for 5% impregnation and 307 m2/g for 10% metal impregnation. A sharp decrease in the surface area was observed. Scanning Electron Microscopy images depict that the crystalline structure of raw H-ZSM-5 would not be damaged due to metal impregnation. Its shape and size were unaltered. In the images, the porous surface was observed. Conclusion: Zeolites are an important catalyst in active phases for acidic/basic/redox catalysed reactions. Its activity and selectivity affected by the crystalline structure as well as morphological properties. Molybdenum impregnated H-ZSM-5 catalyst is best popularly known for its shape selectivity property. It promotes faster decomposition of H2O2 to non-reactive O2, which shows poor oxidation activity.