A kinetic study of oxidation of β-cyclodextrin by permanganate in aqueous media

Selective Oxidation of Cellulose—A Multitask Platform with Significant Environmental Impact

Raw cellulose, or even agro-industrial waste, have been extensively used for environmental applications, namely industrial water decontamination, due to their effectiveness, availability, and low production cost. This was a response to the increasing societal demand for fresh water, which made the purification of wastewater one of the major research issue for both academic and industrial R&D communities. Cellulose has undergone various derivatization reactions in order to change the cellulose surface charge density, a prerequisite condition to delaminate fibers down to nanometric fibrils through a low-energy process, and to obtain products with various structures and properties able to undergo further processing. Selective oxidation of cellulose, one of the most important methods of chemical modification, turned out to be a multitask platform to obtain new high-performance, versatile, cellulose-based materials, with many other applications aside from the environmental ones: in biomedical engineering and healthcare, energy storage, barrier and sensing applications, food packaging, etc. Various methods of selective oxidation have been studied, but among these, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) (TEMPO)-mediated and periodate oxidation reactions have attracted more interest due to their enhanced regioselectivity, high yield and degree of substitution, mild conditions, and the possibility to further process the selectively oxidized cellulose into new materials with more complex formulations. This study systematically presents the main methods commonly used for the selective oxidation of cellulose and provides a survey of the most recent reports on the environmental applications of oxidized cellulose, such as the removal of heavy metals, dyes, and other organic pollutants from the wastewater.

Kinetics and Mechanism Studies of Oxidation of Dibromothymolsulfonphthalein Toxic Dye by Potassium Permanganate in Neutral Media with the Synthesis of 2-Bromo-6-isopropyl-3-methyl-cyclohexa-2,5-dienone

The oxidation of 3',3″-dibromothymolsulfonphthalein (DBTS) in neutral medium by potassium permanganate multi-equivalent oxidant has been studied spectrophotometrically. Pseudo-first-order plots showed inverted S-shape throughout the entire course of the reaction. The initial rates were found to be relatively fast in the early stages, followed by a decrease in the oxidation rates over longer time periods in the slow stage. Under pseudo-first-order conditions where [DBTS] ≫ 10 [MnO₄ ^-], the experimental results showed a first-order dependence in [MnO₄ ^-] and fractional-first-order kinetics in the [DBTS] concentration. The formation of 1:1 coordination intermediate complex prior to the rate-determining step was revealed kinetically. In addition, the intermediate species involving complexes of Mn(V) coordination has been detected. The oxidation product of DBTS was identified by Fourier transform infrared spectroscopy, ultraviolet-visible spectrophotometry, and gas chromatography-mass analysis. The obtained results indicated the formation of 2-bromo-6-isopropyl-3-methyl-cyclohexa-2,5-dienone as a derivative oxidation of DBTS.

Bacterial cellulose-based biomaterials: From fabrication to application

Driven by its excellent physical and chemical properties, BC (bacterial cellulose) has achieved significant progress in the last decade, rendering with many novel applications. Due to its resemblance to the structure of extracellular matrix, BC-based biomaterials have been widely explored for biomedical applications such as tissue engineering and drug delivery. The recent advances in nanotechnology endow further modifications on BC and generate BC-based composites for different applications. This article presents a review on the research advancement on BC-based biomaterials from fabrication methods to biomedical applications, including wound dressing, artificial skin, vascular tissue engineering, bone tissue regeneration, drug delivery, and other applications. The preparation of these materials and their potential applications are reviewed and summarized. Important factors for the applications of BC in biomedical applications including degradation and pore structure characteristic are discussed in detail. Finally, the challenges in future development and potential advances of these materials are also discussed.

An integrated approach using ozone nanobubble and cyclodextrin inclusion complexation to enhance the removal of micropollutants

Ozone (O₃) has been widely used for the elimination of recalcitrant micropollutants in aqueous environments, due to its strong oxidation ability. However, the utilization efficiency of O₃ is constrained by its low solubility and short half-life during the treatment process. Herein, an integrated approach, using nanobubble technology and micro-environmental chemistry within cyclodextrin inclusion cavities, was studied in order to enhance the reactivity of ozonisation. Compared with traditional macrobubble aeration with O₃ in water, nanobubble aeration achieved 1.7 times higher solubility of O_3, and increased the mass transfer coefficient 4.7 times. Moreover, the addition of hydroxypropyl-β-cyclodextrin (HPβCD) further increased the stability of O₃ through formation of an inclusion complex in its molecule-specific cavity. At a HPβCD:O₃ molar ratio of 10:1, the lifespan of O₃ reached 18 times longer than in a HPβCD-free O₃ solution. Such approach accelerated the removal efficiency of the model micropollutant, 4-chlorophenol by 6.9 times, compared with conventional macrobubble ozonation. Examination of the HPβCD inclusion complex by UV-visible spectroscopy and Nuclear Magnetic Resonance analyses revealed that both O₃ and 4-chlorophenol entered the HPβCD cavity, and Benesi-Hildebrand plots indicated a 1:1 stoichiometry of the host and guest compounds. Additionally, molecular docking simulations were conducted in order to confirm the formation of a ternary complex of HPβCD:4-chlorophenol:O₃ and to determine the optimal inclusion mode. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of organic micropollutants.

Picolinic Acid Promoted Permanganate Oxidation of D-Mannitol in Micellar Medium

Kinetics of permanganate oxidation of D-mannitol have been investigated spectrophotometrically under pseudo-first-order conditions in aqueous acidic media at 30 °C. The spectral analysis of hydrazone derivative of the product indicates the product to be an aldehyde. The observed rate constant value was found to be relatively slow in the uncatalyzed path, which increases by the presence of four isomeric promoters: 2-picolinic acid (2-PA), 4-picolinic acid (4-PA), 2,3-dipicolinic acid (2,3-diPA) and 2,6-dipicolinic acid (2,6-diPA). The catalytic effect of sodium dodecylbenzene sulfonate (SDBS) surfactant on the permanganate oxidation of D-mannitol has been also studied in the presence of the promoters. The critical micelle concentration (CMC) of SDBS alone and in presence of D-mannitol was determined by conductometry and spectrophotometry. The aggregation and morphological changes during reaction were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The variation of the reaction rates for the different promoters in the presence and absence of SDBS micellar catalyst is discussed qualitatively in the terms of partitioning nature of substrate, charge of surfactant and reactants. 2,3-diPA in association with SDBS as micellar catalyst accelerated the reaction velocity compared to the uncatalyzed path.

Recyclable Capture and Destruction of Aqueous Micropollutants Using the Molecule-Specific Cavity of Cyclodextrin Polymer Coupled with KMnO4 Oxidation

The removal of aqueous micropollutants remains challenging because of the interference of natural water constituents that are typically 3-9 orders of magnitude more concentrated. Cyclodextrins, which feature molecular recognition and are widely applied in separation and catalysis, are promising materials in the development of pollutant treatment technologies. Here, we described the facile integration of cyclodextrin polymer (CDP) adsorption and KMnO4 oxidation for recyclable capture and destruction of aqueous micropollutants (i.e., antibiotics and TBBPA). CDP exhibited adsorption efficiencies of 0.81-88% and 0.81-94% toward 14 pollutants at 50.0 ng/L and 50.0 μg/L, respectively, at a solid-to-liquid ratio of 1:1250. The presence of simulated or natural water constituents (e.g., Mg(2+), Ca(2+), DOC, and a combination thereof) did not decrease the adsorption potential of CDP toward these pollutants because the pollutants, based on molecular specificity, were entrapped in the CD cavity. Subsequent KMnO4 oxidation completely degraded the retained pollutants, demonstrating that the pollutants could be broken down in the cavity. Pristine CDP was rearranged into the structurally loose composites that featured a porous CDP architecture with uniform embedment of δ-MnO2 nanoparticles and different adsorption efficiencies. δ-MnO2 loading was a linear function of the number of times the integrated procedure was repeated, underlying the accurate control of CDP recycling. Thus, this approach may represent a new method for the removal of aqueous micropollutants.

β-CD assisted dissolution of quaternary ammonium permanganates in aqueous medium

The non-polar internal cavity of β-cyclodextrin (β-CD) has been exploited for the entrapment of the hydrophobic tails of two water insoluble quaternary ammonium permanganates (QAPs): cetyltrimethylammonium permanganate (CTAP) and tetrabutylammonium permanganate (TBAP), for solubilization in aqueous medium. The solubilization and organizational behavior of the QAPs in aqueous β-CD solution have been determined from the comparison of their rates of self-oxidation in presence and in absence of β-CD. Effect of QAP concentration on their observed rate constants (k(obs)) at a fixed β-CD concentration, phase solubility analysis in varying β-CD concentration, impact of quaternary ammonium bromides (QABs) on the kobs values of CTAP and TBAP at fixed QAP and β-CD concentrations, and the temperature effect have been reported. A scheme to explain the solvation of QAPs in aqueous β-CD has been proposed based on dynamic light scattering (DLS) analysis of the samples.

Studies on the kinetics of growth of silver nanoparticles in different surfactant solutions

Silver nanoparticles were prepared in aqueous silver nitrate solution using hydrazine as reducing agents in presence of two ionic surfactants (cetyltrimethylammonium bromide; CTAB and sodium dodecyl sulfate; SDS) and one non-ionic surfactant (Triton X-100). The reaction rate was determined spectrophotometrically. The nature of the head group of these surfactants is responsible for the formation of stable, yellow and transparent silver sol. For a certain reaction time, i.e., 20 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [hydrazine]. The reaction follows first-order kinetics with respect to each in [hydrazine] and [Ag(+)]. The results suggest formation of a complex between silver(I) and hydrazine, decomposes in a rate-determining step, leading in the formation of a free radical, which again reacts with the silver(I) in a subsequent fast step to yield the products. The transmission electron microscopic (TEM) images show that CTAB stabilized silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 15 nm.

Oxidative treatment of azo dyes in aqueous solution by potassium permanganate

This work was conducted to study the ability of permanganate (KMnO(4)) oxidative treatment as a method to decolourise the solutions containing azo dye C.I. Acid Orange 7, C.I. Acid Orange 8, C.I. Acid Red 14, or C.I. Acid Red 73, in a batch system. The results of the study demonstrated the complete removal of the colour and partial mineralization for each dye solution. The effect of the key operating variables such as initial dye concentration, permanganate amount, pH and temperature were studied. Decolourisation reactions were influenced by the acidity and temperature of the treated solutions. To avoid the overdose of KMnO(4), the stoichiometric amount of permanganate required for 1 mol of dye complete colour removal was determined. The reactions between permanganate and C.I. Acid Orange 7, C.I. Acid Orange 8, C.I. Acid Red 14 and C.I. Acid Red 73 dyes in acidic medium exhibit (2.05, 2.20, 2.42 and 2.79):1 stoichiometry (MnO(4)(-):dye). Dye degradation efficiency by potassium permanganate was studied, monitoring total organic carbon (TOC). The results indicated that the degradation efficiency of azo dyes increased with the increase of the potassium permanganate amount. Meanwhile, even in large excess of the oxidant, the dye mineralization was incomplete.