Facile Oxidation of Leucomethylene Blue and Dihydroflavins by Artemisinins: Relationship with Flavoenzyme Function and Antimalarial Mechanism of Action

The antimalarial drug methylene blue (MB) affects the redox behaviour of parasite flavin‐dependent disulfide reductases such as glutathione reductase (GR) that control oxidative stress in the malaria parasite. The reduced flavin adenine dinucleotide cofactor FADH₂ initiates reduction to leucomethylene blue (LMB), which is oxidised by oxygen to generate reactive oxygen species (ROS) and MB. MB then acts as a subversive substrate for NADPH normally required to regenerate FADH₂ for enzyme function. The synergism between MB and the peroxidic antimalarial artemisinin derivative artesunate suggests that artemisinins have a complementary mode of action. We find that artemisinins are transformed by LMB generated from MB and ascorbic acid (AA) or N‐benzyldihydronicotinamide (BNAH) in situ in aqueous buffer at physiological pH into single electron transfer (SET) rearrangement products or two‐electron reduction products, the latter of which dominates with BNAH. Neither AA nor BNAH alone affects the artemisinins. The AA–MB SET reactions are enhanced under aerobic conditions, and the major products obtained here are structurally closely related to one such product already reported to form in an intracellular medium. A ketyl arising via SET with the artemisinin is invoked to explain their formation. Dihydroflavins generated from riboflavin (RF) and FAD by pretreatment with sodium dithionite are rapidly oxidised by artemisinin to the parent flavins. When catalytic amounts of RF, FAD, and other flavins are reduced in situ by excess BNAH or NAD(P)H in the presence of the artemisinins in the aqueous buffer, they are rapidly oxidised to the parent flavins with concomitant formation of two‐electron reduction products from the artemisinins; regeneration of the reduced flavin by excess reductant maintains a catalytic cycle until the artemisinin is consumed. In preliminary experiments, we show that NADPH consumption in yeast GR with redox behaviour similar to that of parasite GR is enhanced by artemisinins, especially under aerobic conditions. Recombinant human GR is not affected. Artemisinins thus may act as antimalarial drugs by perturbing the redox balance within the malaria parasite, both by oxidising FADH₂ in parasite GR or other parasite flavoenzymes, and by initiating autoxidation of the dihydroflavin by oxygen with generation of ROS. Reduction of the artemisinin is proposed to occur via hydride transfer from LMB or the dihydroflavin to O1 of the peroxide. This hitherto unrecorded reactivity profile conforms with known structure–activity relationships of artemisinins, is consistent with their known ability to generate ROS in vivo, and explains the synergism between artemisinins and redox‐active antimalarial drugs such as MB and doxorubicin. As the artemisinins appear to be relatively inert towards human GR, a putative model that accounts for the selective potency of artemisinins towards the malaria parasite also becomes apparent. Decisively, ferrous iron or carbon‐centered free radicals cannot be involved, and the reactivity described herein reconciles disparate observations that are incompatible with the ferrous iron–carbon radical hypothesis for antimalarial mechanism of action. Finally, the urgent enquiry into the emerging resistance of the malaria parasite to artemisinins may now in one part address the possibilities either of structural changes taking place in parasite flavoenzymes that render the flavin cofactor less accessible to artemisinins or of an enhancement in the ability to use intra‐erythrocytic human disulfide reductases required for maintenance of parasite redox balance.     

Interactions between Artemisinins and other Antimalarial Drugs in Relation to the Cofactor Model—A Unifying Proposal for Drug Action

Artemisinins are proposed to act in the malaria parasite cytosol by oxidizing dihydroflavin cofactors of redox‐active flavoenzymes, and under aerobic conditions by inducing their autoxidation. Perturbation of redox homeostasis coupled with the generation of reactive oxygen species (ROS) ensues. Ascorbic acid–methylene blue (MB), N‐benzyl‐1,4‐dihydronicotinamide (BNAH)–MB, BNAH–lumiflavine, BNAH–riboflavin (RF), and NADPH–FAD–E. coli flavin reductase (Fre) systems at pH 7.4 generate leucomethylene blue (LMB) and reduced flavins that are rapidly oxidized in situ by artemisinins. These oxidations are inhibited by the 4‐aminoquinolines piperaquine (PPQ), chloroquine (CQ), and others. In contrast, the arylmethanols lumefantrine, mefloquine (MFQ), and quinine (QN) have little or no effect. Inhibition correlates with the antagonism exerted by 4‐aminoquinolines on the antimalarial activities of MB, RF, and artemisinins. Lack of inhibition correlates with the additivity/synergism between the arylmethanols and artemisinins. We propose association via π complex formation between the 4‐aminoquinolines and LMB or the dihydroflavins; this hinders hydride transfer from the reduced conjugates to the artemisinins. The arylmethanols have a decreased tendency to form π complexes, and so exert no effect. The parallel between chemical reactivity and antagonism or additivity/synergism draws attention to the mechanism of action of all drugs described herein. CQ and QN inhibit the formation of hemozoin in the parasite digestive vacuole (DV). The buildup of heme–Fe^III results in an enhanced efflux from the DV into the cytosol. In addition, the lipophilic heme–Fe^III complexes of CQ and QN that form in the DV are proposed to diffuse across the DV membrane. At the higher pH of the cytosol, the complexes decompose to liberate heme–Fe^III. The quinoline or arylmethanol reenters the DV, and so transfers more heme–Fe^III out of the DV. In this way, the 4‐aminoquinolines and arylmethanols exert antimalarial activities by enhancing heme–Fe^III and thence free Fe^III concentrations in the cytosol. The iron species enter into redox cycles through reduction of Fe^III to Fe^II largely mediated by reduced flavin cofactors and likely also by NAD(P)H–Fre. Generation of ROS through oxidation of Fe^II by oxygen will also result. The cytotoxicities of artemisinins are thereby reinforced by the iron. Other aspects of drug action are emphasized. In the cytosol or DV, association by π complex formation between pairs of lipophilic drugs must adversely influence the pharmacokinetics of each drug. This explains the antagonism between PPQ and MFQ, for example. The basis for the antimalarial activity of RF mirrors that of MB, wherein it participates in redox cycling that involves flavoenzymes or Fre, resulting in attrition of NAD(P)H. The generation of ROS by artemisinins and ensuing Fenton chemistry accommodate the ability of artemisinins to induce membrane damage and to affect the parasite SERCA PfATP6 Ca²⁺ transporter. Thus, the effect exerted by artemisinins is more likely a downstream event involving ROS that will also be modulated by mutations in PfATP6. Such mutations attenuate, but cannot abrogate, antimalarial activities of artemisinins. Overall, parasite resistance to artemisinins arises through enhancement of antioxidant defense mechanisms.     

Reactions of antimalarial peroxides with each of leucomethylene blue and dihydroflavins: flavin reductase and the cofactor model exemplified

Flavin adenine dinucleotide (FAD) is reduced by NADPH-E.?coli flavin reductase (Fre) to FADH(2) in aqueous buffer at pH?7.4 under argon. Under the same conditions, FADH(2) in turn cleanly reduces the antimalarial drug methylene blue (MB) to leucomethylene blue. The latter is rapidly re-oxidized by artemisinins, thus supporting the proposal that MB exerts its antimalarial activity, and synergizes the antimalarial action of artemisinins, by interfering with redox cycling involving NADPH reduction of flavin cofactors in parasite flavin disulfide reductases. Direct treatment of the FADH(2) generated from NADPH-Fre-FAD by artemisinins and antimalaria-active tetraoxane and trioxolane structural analogues under physiological conditions at pH?7.4 results in rapid reduction of the artemisinins, and efficient conversion of the peroxide structural analogues into ketone products. Comparison of the relative rates of FADH(2) oxidation indicate optimal activity for the trioxolane. Therefore, the rate of intraparastic redox perturbation will be greatest for the trioxolane, and this may be significant in relation to its enhanced in?vitro antimalarial activities. (1)H?NMR spectroscopic studies using the BNAH-riboflavin (RF) model system indicate that the tetraoxane is capable of using both peroxide units in oxidizing the RFH(2) generated in?situ. Use of the NADPH-Fre-FAD catalytic system in the presence of artemisinin or tetraoxane confirms that the latter, in contrast to artemisinin, consumes two reducing equivalents of NADPH. None of the processes described herein requires the presence of ferrous iron. Ferric iron, given its propensity to oxidize reduced flavin cofactors, may play a role in enhancing oxidative stress within the malaria parasite, without requiring interaction with artemisinins or peroxide analogues. The NADPH-Fre-FAD system serves as a convenient mimic of flavin disulfide reductases that maintain redox homeostasis in the malaria parasite.     

Aerobic Oxidation of Vicinal Diols Catalyzed by an Anderson‐Type Polyoxometalate, [IMo6O24]5–

An Anderson‐type polyoxometalate, [I^VIIMo₆O₂₄]^5–, has been used as a catalyst for the aerobic oxidation at 80 °C of vicinal diols (glycols). This is the first report on the use of such a polyoxometalate as an oxidation catalyst. Reactivity and selectivity were dependent on the substrate. Thus, aryl‐substituted diols yielded mostly the carbon‐carbon bond cleavage products, while 1,2‐cyclohexanediol yielded cyclohexanone‐2‐ol and 1,2‐cyclohexanedione. Aliphatic diols were less reactive but yielded carbon‐carbon bond cleavage products in the presence of additional acid. An abbreviated mechanistic study was carried out indicating that the polyoxometalate oxidizes the diol to the various products even under anaerobic conditions. The reduced polyoxometalates (heteropoly blues and heteropoly browns) formed in the oxidation of the diols are re‐oxidized by the molecular oxygen.     

A flavoprotein monooxygenase that catalyses a Baeyer-Villiger reaction and thioether oxidation using NADH as the nicotinamide cofactor

A gene from the marine bacterium Stenotrophomonas maltophilia encodes a 38.6 kDa FAD‐containing flavoprotein (Uniprot B2FLR2) named S. maltophilia flavin‐containing monooxygenase (SMFMO), which catalyses the oxidation of thioethers and also the regioselective Baeyer–Villiger oxidation of the model substrate bicyclo[3.2.0]hept‐2‐en‐6‐one. The enzyme was unusual in its ability to employ either NADH or NADPH as nicotinamide cofactor. The K_M and k_cat values for NADH were 23.7±9.1 μM and 0.029 s^?1 and 27.3±5.3 μM and 0.022 s^?1 for NADPH. However, k_cat/K_M value for the ketone substrate in the presence of 100 μM cofactor was 17 times greater for NADH than for NADPH. SMFMO catalysed the quantitative conversion of 5 mM ketone in the presence of substoichiometric concentrations of NADH with the formate dehydrogenase cofactor recycling system, to give the 2‐oxa and 3‐oxa lactone products of Baeyer–Villiger reaction in a ratio of 5:1, albeit with poor enantioselectivity. The conversion with NADPH was 15 %. SMFMO also catalysed the NADH‐dependent transformation of prochiral aromatic thioethers, giving in the best case, 80 % ee for the transformation of p‐chlorophenyl methyl sulfide to its R enantiomer. The structure of SMFMO reveals that the relaxation in cofactor specificity appears to be accomplished by the substitution of an arginine residue, responsible for recognition of the 2′‐phosphate on the NADPH ribose in related NADPH‐dependent FMOs, with a glutamine residue in SMFMO. SMFMO is thus representative of a separate class of single‐component, flavoprotein monooxygenases that catalyse NADH‐dependent oxidations from which possible sequences and strategies for developing NADH‐dependent biocatalysts for asymmetric oxygenation reactions might be identified.     

Synthesis of ZrC–SiC Powders from Hybrid Liquid Precursors with Improved Oxidation Resistance

ZrC–SiC powders are synthesized by high‐temperature pyrolysis of hybrid liquid precursors, which are prepared from organic Zr‐containing precursor (PZC) and liquid polycarbosilane (LPCS). Due to the excellent miscibility between PZC and LPCS, the hybrid liquid precursors are formed by dissolving PZC into LPCS without adding organic solvent. The viscosity and elemental content of Zr and Si of the hybrid precursors are readily adjustable by controlling the LPCS/PZC mass ratio. SEM and TEM observations reveal that the ZrC–SiC powders pyrolyzed at 1550°C exhibit spherical morphology with characteristic dimension of less than 60 nm, and the two phases are uniformly distributed in composite powders. The advantage of the ZrC–SiC powders synthesized by this novel method is demonstrated by investigating the oxidation behavior of powders with different amount of SiC and ZrC. Below 700°C, ZrC quickly oxidizes to generate an almost nonprotective ZrO₂ scale, whereas at ~ 1000°C, dense and protective SiO₂ forms that improves the oxidation resistance of the ZrC–SiC composite powders.     

Photochemical Oxidation of Americium in Dilute Nitric Acid Solution with the Addition of Ozone

Abstract

A trial to oxidize americium (Am) from the trivalent to the hexavalent form in dilute nitric acid solution was undertaken by emitting light from a deuterium lamp as well as by blowing ozone into the solution. It was found out that trivalent Am in dilute nitric acid solution (～0.1 N) can be photooxidized to its hexavalent form by a deuterium lamp which emits lines below 170 nm. Photooxidation, however, cannot be effected unless the oxidation rate exceeds the rate of autoreduction of Am which is caused by radicals and ions formed by alpha radiolysis. Ozone was introduced into the solution to maintain Am in its hexavalent form because ozone, which does not oxidize Am³⁺ to Am⁶⁺ in acid media, readily oxidizes Am^{5 +} to Am⁶⁺ in HNO₃ solution. Photooxidation can be effectively carried out by a combination of photolysis and ozone. Its oxidation rate was about 5%/h in 0.1 N nitric acid solution at 65°C. The oxidation rate decreased with increasing nitric acid concentration.     

Initial reaction steps in photocatalytic oxidation of aromatics

Transient reaction at 273 and 300 K was used to study the initial steps in the photocatalytic oxidation (PCO) of benzene, toluene, p-xylene, mesitylene, benzyl alcohol, benzaldehyde, and m-cresol adsorbed on a thin film of TiO₂ catalyst. Adsorbed aromatics were oxidized by O₂ photocatalytically in the absence of gas-phase aromatics, and the compounds remaining on the surface were characterized by temperature-programmed oxidation and desorption (TPO, TPD). Benzene and methyl benzenes oxidize rapidly at 273 or 300 K to form adsorbed intermediates that are more strongly adsorbed and much less reactive than the original aromatic, which is relatively weakly adsorbed on TiO₂. The catalyst is expected to be covered with these intermediates during steady-state reaction. The rates of PCO of benzene and methyl benzenes to CO₂ are slow relative to complete oxidation of alcohols or chlorinated hydrocarbons. The intermediates do not appear to be alcohols or aldehydes formed by oxidation of a methyl group, nor do they correspond to addition of an hydroxyl to the aromatic ring. Benzyl alcohol oxidizes photocatalytically to benzaldehyde and then to CO₂ and H₂O during PCO, but adsorbed m-cresol does not photocatalytically oxidize.     

Photocatalytic Performance of Nitrogen‐Doped and Cu2+ and Ag+ Co‐Doped Sodium Trititanate

Nano‐sized (i) N‐doped sodium trititanate and (ii) N and Cu²⁺ (Ag⁺) co‐doped sodium trititanates CuTi₃NO_6?x (Ag₂Ti₃NO_6?x) were prepared by a solid‐state and ion‐exchange methods, respectively. The materials were characterized by EDS, PXRD, XPS, FESEM, TEM, UV–visible DRS, and Raman spectroscopy. All the materials were crystallized in monoclinic lattice with P21/m space group. The bandgap energy of all the samples was deduced from their UV–visible DRS profiles. Visible‐light‐induced photocatalytic oxidation of the methylene blue (MB) and methyl orange (MO), cyclohexene and phenol, was examined. The Ag⁺ co‐doped trititanate exhibited the highest photocatalytic activity among the materials investigated.     

Nanocomposite of polyaniline and a layered niobate acid host: Synthesis,electrochemical studies,and photocatalytic properties

The synthesis of polyaniline (PANI) with H₄Nb₆O₁₇ (HNbO) to form PANI/HNbO lamellar nanocomposite by in situ polymerization using aniline (ANI) intercalation compound ANI/HNbO as the intermediate has been investigated. The properties of the samples were characterized by means of XRD, SEM, TEM, FT‐IR, UV–vis spectroscopy, and TG‐DTA. The in situ polymerization of ANI packed in a regular orientation in a mono‐ and bilayers (i.e., pseudo‐bilayers) structure within the HNbO interlayers led to PANI/HNbO nanocomposite powder using (NH₄)₂S₂O₈ as the catalyst with PANI monolayer packing orientation within the HNbO interlayers. PANI/HNbO nanocomposite showed improved thermal stability compared with original PANI by TG analysis. The PANI/HNbO nanocomposite was studied by cyclic voltammetry (CV), which indicated the good redox activity and electrochemical‐cycling stability in acidic solution. The interaction between PANI and nanosheets greatly affected the electrochemical behavior of PANI/HNbO nanocomposite. Two couples of redox peaks corresponded to two oxidation process of PANI in acid conditions. The PANI/HNbO nanocomposite exhibited much higher photocatalytic activities for the degradation of methylene blue (MB) in aqueous solution under visible light irradiation than HNbO itself. POLYM. COMPOS., 34:834–841, 2013. © 2013 Society of Plastics Engineers     

Removal of methylene blue (aq) using untreated and acid‐treated eucalyptus leaves and GA‐ANN modelling

In the present batch study, eucalyptus leaves (EUL), H₂SO₄‐treated eucalyptus leaves (SEUL), and H₃PO₄‐treated eucalyptus leaves (PEUL) are used as bio‐adsorbents for the removal of methylene blue (MB). The bio‐adsorption is executed to inspect the results of the variation between different experimental variables such as pH (2–10), adsorbent dose (1–10 g/L), contact time (5–360 min), and temperature (298–318 K) on the bio‐adsorption of MB. The Langmuir isotherm (R² = 0.99) fitted adequately to the bio‐adsorption data for the initial MB concentrations of 10–300 mg/L. It is also necessary to mention that the MB bio‐adsorption occurred in the order of a monolayer on the EUL, SEUL, and PEUL. The bio‐adsorption kinetics have been fitted by the pseudo‐second‐order model (R² ≥ 0.99) for various MB concentrations. The maximum bio‐adsorption capacity was 194.34 mg/g and was achieved for the H₃PO₄‐treated eucalyptus leaves (PEUL). These results showed that EUL, SEUL, and PEUL may be utilized as a favourable low‐cost bio‐adsorbent to eliminate MB from aqueous solutions. With safe disposal methods in mind, this investigation has revealed the eco‐friendliness of the bio‐adsorbents. A prediction of the removal percentage of methylene blue using a genetic algorithm (GA) from the data collected from the experiment has also been tested. The results related to the prediction using the GA‐ANN are accurate.     

Kinetics of catalyzed and non‐catalyzed soot oxidation with nitrogen dioxide under regeneration particle trap conditions

BACKGROUND: For compliance with the regulations on diesel particulate matter, car manufacturers have developed diesel particulate filters (DPF). These technologies require a regeneration method which oxidizes soot deposits in the filter. In diesel exhaust emissions there are two suitable oxidizing gases: oxygen and nitrogen dioxide. Nitrogen dioxide is much more active than O₂ and can directly attack the carbon surface. This work describes the kinetics of the oxidation of soot by NO₂ over a wide range of conditions relevant for DPF. RESULTS: The catalyzed and the non‐catalyzed oxidation of soot have been performed in a fixed‐bed reactor. The experimental results show that the overall oxidation process can be described by two additive parallel reactions: a direct C ? NO₂ reaction catalyzed by H₂O and a cooperative C ? NO₂ ? O₂ reaction catalyzed by the Pt/Al₂O₃ catalyst. The results obtained allow to propose the following kinetic law for the specific rates of the catalyzed and the non‐catalyzed oxidation of soot in the regeneration filter conditions: CONCLUSION: The kinetic parameters describing the oxidation rate of soot by NO₂ over a range of temperature and gas composition have been obtained. The extracted kinetics data are relevant for modeling the removal of trapping soot in automotive gas exhaust technology. Copyright © 2009 Society of Chemical Industry     

Preparation,characterization, and thermal properties of polystyrene‐block‐quaternized poly(4‐vinylpyridine)/Montmorillonite nanocomposites

Polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) was synthesized by two steps of reversible addition‐fragmentation transfer (RAFT) polymerization of styrene (St) and 4‐vinylpyridine (4VP) successively. After P4VP block was quaternized with CH₃I, PS‐b‐quaternized P4VP/montmorillonite (PS‐b‐QP4VP/MMT) nanocomposites were prepared by cationic exchange reactions of quaternary ammonium ion in the PS‐b‐QP4VP with ions in MMT. The results obtained from X‐ray diffraction (XRD) and transmission electron microscopy (TEM) images demonstrate that the block copolymer/MMT nanocomposites are of intercalated and exfoliated structures, and also a small amount of silicates' layers remained in the original structure; differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results show that the nanocomposites displayed higher glass transition temperature (T_g) and higher thermal stability than that of the corresponding copolymers. The blending of PS‐b‐QP4VP/MMT with commercial PS makes MMT to be further separated, and the MMT was homogeneously dispersed in the polymer matrix. The enhancement of thermal stability of PS/PS‐b‐QP4VP/MMT is about 20°C in comparison with commercial PS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1950–1958, 2006     

Sol–gel derived CeO2/α‐Al2O3 bilayer thin film as an anti‐coking barrier and its catalytic coke oxidation performance

A CeO₂/α‐Al₂O₃ bilayer was coated on a high temperature alloy (Incoloy 800H) by sol–gel dip‐coating and was evaluated for its potential as an anticoking barrier and coke oxidation catalyst. The bilayer effectively functioned as a barrier to metal surface catalyzed coking. The film prevented filamentous catalytic coking via blocking surface active metallic sites on the Incoloy substrate. Furthermore, the bilayer reduced the oxidation temperature of pyrolytic coke deposited on the film surface as compared to a bare oxidized Incoloy substrate, mostly owing to the oxidation catalytic activity of the CeO₂ layer. Finally, it is demonstrated that the presence of the α‐Al₂O₃ buffer layer is critically important to the overall performance. Without the α‐Al₂O₃ layer, a CeO₂ layer nearly completely lost both its barrier and oxidation catalytic functions. It is presumed that metallic species migrating from the substrate during high temperature treatments are responsible for the CeO₂ deactivation, likely by blocking catalytic sites on the CeO₂ surface. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4019–4026, 2018     

Highly effective adsorption performance of carboxymethyl cellulose microspheres crosslinked with epichlorohydrin

Different sizes of epichlorohydrin‐crosslinked carboxymethyl cellulose (E/CMC) microspheres were successfully prepared by an inverse suspension method. With further modification by monochloroacetic acid (MCA), MCA–E/CMC microspheres were successfully synthesized. The structures and morphologies of these microspheres were analyzed with polarizing microscopy, scanning electron microscopy, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, and laser particle ζ‐potential recording. The adsorption properties of the microspheres were investigated with methylene blue (MB) as a model pollutant. The highest adsorption amount of MB (998.2 mg/g) onto MCA–E_0.7/CMC which was the samples which treated with 0.7 mL of C₄H₉OH was obtained. Meanwhile, the effect of the operating parameters, such as the contact time, initial pH of the solution, temperature, and initial dye concentration, on the adsorption amount and MB removal were systematically studied. The results show that pseudo‐second‐order kinetic model provided the best correlation with the experimental data for the adsorption of MB onto the MCA–E_0.7/CMC microspheres. Both the physical and chemical adsorption played the main role in the adsorption process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44363.     

Study on electrical conductivity of 2‐vinylpyridine‐methyl methacrylate copolymer in presence of cobalt acetate

2‐Vinyl pyridine (2VP)‐methyl methacrylate (MMA) copolymers with different molar ratios were prepared. Their electrical properties were studied in the presence of Co(CH₃COO)₂. It was found that the electrical properties of the copolymer were changed by altering the molar ratio of 2VP : MMA and by varying the concentration of Co(CH₃COO)₂. The highest electrical conductivity was found when the 2VP : MMA molar ratio was 1 : 1. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2145–2153, 2001     

Novel chitosan‐TiO2 nanohybrid: Preparation,characterization, antibacterial,and photocatalytic properties

In this report, chitosan (CS) encapsulated titanium dioxide (TiO₂) nanohybrid was prepared by chemical precipitation method. Fourier transform infrared spectroscopy (FT‐IR) and X‐ray diffraction (XRD) confirmed the formation of nanohybrid. Transmission electron microscopy (TEM) analysis showed the immobilization of TiO₂ nanoparticles on the surface of CS. The nanohybrid was also characterized by thermogravimetric analysis (TGA) and zeta potential. The nanohybrid exhibited high photocatalytic activity as evident from the degradation of methylene blue (MB) dye. The result revealed substantial degradation of the MB dye (90%) under UV‐light illumination. The catalytic efficiency was unaltered even after five cycles of reuse. In addition, the nanohybrid exhibited a superior antibacterial activity of 100% within 24 h of treatment against Escherichia coli (E. coli) was measured by colony forming units (CFU). POLYM. COMPOS., 35:327–333, 2014. © 2013 Society of Plastics Engineers     

Synthesis,physical properties,and characterization of starch‐based blend films by adding nano‐sized TiO2/poly(methyl metacrylate‐co‐acrylamide)

The purpose of this study was to improve the physical properties and to expand the application range of starch‐based blend films added nano‐sized TiO₂/poly(methyl methacrylate‐co‐acrylamide) (PMMA‐co‐AM). Starch‐based blend films were prepared by using corn starch, polyvinyl alcohol (PVA), nano‐sized PMMA‐co‐AM, nano‐sized TiO₂/PMMA‐co‐AM particles, and additives, i.e., glycerol (GL) and citric acid (CA). Nano‐sized PMMA‐co‐AM was synthesized by emulsion polymerization and TiO₂ nanoparticles were also prepared by using sol–gel method. Nano‐sized TiO₂/PMMA‐co‐AM particles were synthesized by wet milling for 48 h. The morphology and crystallinity of TiO₂, nano‐sized PMMA‐co‐AM and TiO₂/PMMA‐co‐AM particles were investigated by using the scanning electron microscope (SEM) and X‐ray diffractometer (XRD). In addition, the functional groups of the TiO₂/PMMA‐co‐AM particles were characterized by IR spectrophotometry (FTIR). The physical properties such as tensile strength (TS), elongation at break (%E), degree of swelling (DS), and solubility (S) of starch‐based films were evaluated. It was found that the adding of nano‐sized particles can greatly improve the physical properties of the prepared films. The photocatalytic degradability of starch/PVA/nano‐sized TiO₂/PMMA‐co‐AM composite films was evaluated using methylene blue (MB) and acetaldehyde (ATA) as photodegradation target under UV and visible light. The degree of decomposition (C/C₀) of MB and ATA for the films containing TiO₂ and CA was 0.506 and 0.088 under UV light irradiation and 0.586 (MB) and 0.631 (ATA) under visible light irradiation, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Antioxidative degradation mechanism of 2-mercaptobenzimidazole modified TEPA-MCM-41 adsorbents for carbon capture from flue gas

Solid amine adsorbents can efficiently adsorb CO₂, but a significant problem is that amine groups are oxidized. In this research, tetraethylenepentamine-impregnated MCM-41 adsorbents (TEPA-MCM-41) were functionally modified with sulphur-containing antioxidant 2-mercaptobenzimidazole (described as antioxidant MB) and tns-(2.4-di-tert-butyl)-phosphite (defined as antioxidant 168), respectively. The antioxidative degradation mechanism of 8% MB–50% TEPA-MCM-41 was analyzed by in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectrum and high-performance liquid chromatography/mass spectrometry (HPLC/mass). The CO₂ adsorption capacity of 50% TEPA-MCM-41 was 4.30 mmol/g under 15% CO₂/85% N₂, but decreased to 1.38 mmol/g after oxidation at 100°C for 42 h under 95% N₂/5% O₂ certain condition. The CO₂ capacity of 8% MB–50% TEPA-MCM-41 reduced from 3.90 to 2.86 mmol/g. After 30 adsorption cycles under 5% O₂/15% CO₂/80% N₂, the capacity of 8% MB–50% TEPA-MCM-41 also only decreased by 16.8%, while 50% TEPA-MCM-41 decreased by 63.2%. The reason for the excellent antioxidant stability of 8% MB–50% TEPA-MCM-41 is that MB scavenged free radicals from amine oxidation and decomposed the hydroperoxides produced by free radical reactions. The hydroperoxides were decomposed into alcohols (non-radical products), which were eventually oxidized to sulphonic compounds. The MB modification inhibited the oxidative degradation of solid amine adsorbents guided for the production of antioxidant-efficient adsorbents.     

A Comparison on Physical,Structural, and Photocatalytical Properties of TiO2 Nanopowders Produced Using Sol‐Gel and Flame Spray Pyrolysis

In this study, nanoscale photocatalyst TiO₂ powders were synthesized via sol‐gel and flame spray pyrolysis (FSP). Phase structures and ratios were analyzed by X‐ray diffractometer (XRD). Size, specific surface area, and morphologies were determined using particle size analyzer, Brunauer‐Emmett‐Teller theory, and scanning electron microscope, respectively. Anatase phase with some rutile together was obtained in XRD analysis. The degradation rates of aqueous methylene blue (MB) by TiO₂ nanopowders were calculated using UV–vis spectrophotometer. It was found that MB decomposition was successfully achieved with significantly high efficiencies for both sol‐gel and FSP‐derived powders with small differences.