Preparation of Activated Carbon-Reinforced Composite Beads Based on MnO2/MCM-41@Fe3O4 and Calcium Alginate for Efficient Removal of Tetracycline in Aqueous Solutions

Tetracycline (TC) is a common antibiotic; when untreated TC enters the environment, it will cause a negative impact on the human body through the food chain. In the present study, MnO2/MCM-41@Fe3O4 (FeMnMCM) prepared using a hydrothermal and redox method and Camellia oleifera shell-activated carbon (COFAC) prepared through alkali activation were encapsulated using alginate (ALG) and calcium chloride as a cross-linking matrix to give the composite beads COFAC-FeMnMCM-ALG. The resultant COFAC-FeMnMCM-ALG composite beads were then carefully characterized, showing a high immobilization of MnO2/MCM-41@Fe3O4, with porous COFAC as an effective bioadsorbent for enriching the pollutants in the treated samples. These bead catalysts were subsequently applied to the oxidative degradation of TC in a Fenton oxidation system. Several parameters affecting the degradation were investigated, including the H2O2 concentration, catalyst dosage, initial TC concentration, and temperature. A very high catalytic activity towards the degradation of TC was demonstrated. The electron paramagnetic resonance (EPR) and quenching results showed that ·OH and ·O2- were generated in the system, with ·OH as the main radical species. In addition, the COFAC-FeMnMCM-ALG catalyst exhibited excellent recyclability/reusability. We conclude that the as-prepared COFAC-FeMnMCM-ALG composite beads, which integrate MnO2 and Fe3O4 with bioadsorbents, provide a new idea for the design of catalysts for advanced oxidation processes (AOPs) and have great potential in the Fenton oxidation system to degrade toxic pollutants.

Simple Ultraviolet-Visible Spectroscopy-Based Assay for Fast Evaluation of Magnetic Nanoparticle Selectivity Changes After Doping

Simple ultraviolet-visible spectroscopy-based methodology was proposed and utilized for the initial characterization of potential changes in selectivity of doped magnetic nanoparticles. Doped and undoped iron(II,III) (Fe₃O₄) magnetic nanoparticles were synthesized by the coprecipitation method. The doping processes of nanoparticles were confirmed using optical emission spectrometry, while the sizes of undoped and Cu-doped nanoparticles were investigated using a high-resolution field emission scanning electron microscope. The average diameters of nanoparticles were 8.34±1.78 nm and 9.12±1.93 nm, for doped and undoped materials, respectively. The influence of the nanoparticle's doping on their selectivity towards chosen analyte was monitored by the spectral techniques such as ultraviolet-visible and optical emission spectrometry. The interaction between Cu-doped Fe₃O₄ nanoparticles and cuprizone (a compound forming the characteristic colorful complex with copper) was confirmed. The elaborated studies proved the potential of ultraviolet-visible spectroscopy for the fast qualification of magnetic nanoparticles in terms of their ability to separate the selected analyte from the sample matrix.

Overview on magnetically recyclable ferrite nanoparticles: synthesis and their applications in coupling and multicomponent reactions

Nanocatalysis is an emerging area of research that has attracted much attention over the past few years. It provides the advantages of both homogeneous as well as heterogeneous catalysis in terms of activity, selectivity, efficiency and reusability. Magnetically recoverable nanocatalysts provide a larger surface area for the chemical transformations where the organic groups can be anchored and lead to decrease in the reaction time, increase in the reaction output and improve the atom economy of the chemical reactions. Moreover, magnetic nanocatalysts provide a greener approach towards the chemical transformations and are easily recoverable by the aid of an external magnet for their reusability. This review aims to give an insight into the important work done in the field of magnetically recoverable nanocatalysts and their applications in carbon-carbon and carbon-heteroatom bond formation.

Design and synthesis of a new magnetic metal organic framework as a versatile platform for immobilization of acidic catalysts and CO2 fixation reaction

The first report of the use of an acidic magnetic metal organic framework for the chemical fixation of CO2 as an environmentally friendly reaction.

Functionalized Ordered Mesoporous Silicas (MCM-41): Synthesis and Applications in Catalysis

Mesoporous silica sieves are among the most studied nano-objects due to their stable pore structure and easy preparation. In particular, MCM-41 have attracted increasing research attention due to their chemical versatility. This review focuses on the synthesis and regioselective functionalization of MCM-41 to prepare catalytic systems. The topics covered are: mono and di-functionalized MCM-41 as basic and acid catalysts, catalysts based on metallic complexes and heteropolyacids supported onto MCM-41, metallic nanoparticles embed onto functionalized MCM-41 and magnetic MCM-41 for catalytic purposes.

Optimization of effective parameters in the synthesis of nanopore anodic aluminum oxide membrane and arsenic removal by prepared magnetic iron oxide nanoparicles in anodic aluminum oxide membrane via ultrasonic-hydrothermal method

In this study, a new anodized aluminum oxide (AAO) nanostructure membrane was synthesized by anodization process under a constant voltage, in oxalic acid solution that was improved with trace amounts of sulfuric acid at room temperature. The effect of various parameters on the morphology of the synthesized nanostructures such as voltage, electrolyte composition, anodization time and type of stripping solution were investigated. According to the results, corrosion of the walls, size regularity, diameter and number of the pores increased in the presence of sulfuric acid (0.018 mol.L^-1). Nitrogen adsorption-desorption analysis confirmed significant porosity, array and uniformity of the pore size in the synthesized nanoporous membrane. A new modification method was used based on ultrasonic-hydrothermal method to modify the synthesized AAO with Fe₃O₄/SiO₂ nanoparticles for metals and metalloids removal from aqueous solution. In this method, Fe₃O₄/SiO₂ nanoparticles were placed very regularly and uniformly on the surface and inside the pores. This modification was confirmed by characterization techniques. The modified AAO@Fe₃O₄/SiO₂ membrane showed excellent results for removing arsenic from aqueous media.

Synthesis of α-functionalized α-indol-3-yl carbonyls through direct SN reactions of indol-3-yl α-acyloins

A new and efficient synthesis of α-functionalized α-indol-3-yl ketones from easily available indolyl α-acyloins is reported. This process, catalyzed by Brønsted or Lewis acids, involves an uncommon direct nucleophilic substitution reaction of a secondary α-carbonyl-substituted hydroxyl group. The described methodology allows the introduction of a variety of nucleophiles such as (hetero)arenes, thiophenols, nitroanilines and 1,3-dicarbonyl derivatives. The synthesized α-indol-3-yl carbonyl compounds are important synthetic targets also useful for accessing functionalized tryptophols and furan-3-yl indoles.

Sulfonyl Azoles in the Synthesis of 3-Functionalized Azole Derivatives

Sulfonyl indoles, as well as related azolyl derivatives, have been recently introduced in synthesis as stable precursors of reactive indolenine intermediates. This personal account reports on the discovery of sulfonyl azoles and their practical utilization in many synthetic processes for the preparation of functionalized 3-substituted indoles, indazoles, and pyrroles. The indolenine intermediates obtained by treatment of sulfonyl azoles with Brønsted bases or Lewis acids can be considered as vinylogous imino derivatives that can be made to react with different nucleophilic reagents. These include organometallic reagents, reducing agents, stabilized carbanions, and heteronucleophiles. The controlled and mild conditions for the generation of indolenines from sulfonyl azoles make these substrates particularly useful in asymmetric synthesis, exploiting organo- or metal-catalyzed processes. Although less exploited, sulfonyl indoles can also be involved in photochemical processes for the preparation of polycyclic derivatives.

A highly enantioselective thiolation of sulfonyl indoles to access 3-sec-sulfur-substituted indoles in water

Highly enantioselective organocatalytic Michael addition of thiol to vinylogous imine intermediates generated in situ from sulfonylindoles in aqueous medium is presented.