Oxidative Discoloration Research Articles

Analysis of Grindability and Surface Integrity in Creep-Feed Grinding of High-Strength Steels.

Creep-feed grinding of high-strength steel is prone to excessive wheel wear and thermal damage defects, which seriously affects the service performance of parts. To solve the above-mentioned issue, a creep-feed grinding test was carried out on high-strength steel using SG and CBN abrasive wheels. The grindability of high-strength steel was scrutinized in terms of grinding force, machining temperature and grinding specific energy. Moreover, the effects of operation parameters and grinder performances on the surface integrity of the workpiece such as surface morphology, roughness, residual stress and hardness were rigorously studied. The results indicate that, when the instantaneous high temperature in the grinding area reaches above the phase transition temperature of the steel, the local organization of the surface layer changes, leading to thermal damage defects in the components. The outstanding hardness and thermal conductivity of CBN abrasives are more productive in suppressing grinding burns than the high self-sharpening properties of SG grits and a more favorable machining response is achieved. The effects of thermal damage on the surface integrity of high-strength steel grinding are mainly in the form of oxidative discoloration, coating texture, hardness reduction and residual tensile stresses. Within the parameter range of this experiment, CBN grinding wheel reduces grinding specific energy by about 33% compared to SG grinding wheel and can control surface roughness below 0.8 µm. The weight of oxygen element in the burn-out workpiece accounts for 21%, and the thickness of the metamorphic layer is about 40 µm. The essential means of achieving burn-free grinding of high-strength steels is to reduce heat generation and enhance heat evacuation. The results obtained can provide technical guidance for high-quality processing of high-strength steel and precision manufacturing of high-end components.

Degradation of cellulose polymorphs into glucose by HCl gas with simultaneous suppression of oxidative discoloration

As cellulose is the main polysaccharide in biomass, its degradation into glucose is a major undertaking in research concerning biofuels and bio-based platform chemicals. Here, we show that pressurized HCl gas is able to efficiently hydrolyze fibers of different crystalline forms (polymorphs) of cellulose when the water content of the fibers is increased to 30–50 wt%. Simultaneously, the harmful formation of strongly chromophoric humins can be suppressed by a simple addition of chlorite into the reaction system. 50–70 % glucose yields were obtained from cellulose I and II polymorphs while >90 % monosaccharide conversion was acquired from cellulose IIIII after a mild post-hydrolysis step. Purification of the products is relatively unproblematic from a gas-solid mixture, and a gaseous catalyst is easier to recycle than the aqueous counterpart. The results lay down a basis for future practical solutions in cellulose hydrolysis where side reactions are controlled, conversion rates are efficient, and the recovery of products and reagents is effortless.

Stepwise cooling mediated feasible supercooling preservation to extend freshness of mackerel fillets

This study investigated the effect of supercooling preservation on the freshness and quality parameters to mackerel in comparison to chilled (refrigerated) and freezing condition. Stepwise cooling by 0.5 °C every 18 h was applied to preserve mackerel under a supercooled state for 12 days, and physicochemical properties were compared with chilled and frozen samples. The mean preservation temperatures (Tm) were 1.01 °C, −1.42 °C and −17.5 °C for the chilled, supercooled and frozen treatments, respectively. Freshness parameters indicated that supercooling effectively delayed both oxidative and microbial deteriorations, including total aerobic count (TAC), thiobarbituric acid reactive substances (TBARS), total volatile basic nitrogen (TVBN) and trimethylamine (TMA), compared to chilled conditions. Based on kinetic analysis, the freshness holding period of supercooled mackerel was 9.51 days compared to 4.53 days of chilled mackerel. Although oxidative discoloration could not be prevented by supercooled preservation, supercooled mackerel showed better water-binding and textural properties than chilled or frozen mackerel after 12 days of storage. From the results, supercooling was effective to maintain fresh conditions (sashimi or sushi grade) of mackerel for more than twice the duration of chilled preservation.

Acetylated Resveratrol and Oxyresveratrol Suppress UVB-Induced MMP-1 Expression in Human Dermal Fibroblasts.

Resveratrol (RES) and oxyresveratrol (OXYRES) are considered and utilized as active ingredients of anti-aging skin cosmetics. However, these compounds are susceptible to oxidative discoloration and unpleasant odor in solutions, limiting their use in cosmetics. Accordingly, RES and OXYRES were chemically modified to acetylated derivatives with enhanced stability, and their anti-aging effect on the skin and detailed molecular mechanism of their acetylated derivatives were investigated. Acetylated RES and OXYRES lost their acetyl group and exerted an inhibitory effect on H2O2-induced ROS levels in human dermal fibroblast (HDF) cells. In addition, RES, OXYRES, and their acetylated derivatives suppressed UVB-induced matrix metalloproteinase (MMP)-1 expression via inhibition of mitogen-activated protein kinases (MAPKs) and Akt/mTOR signaling pathways. Furthermore, RES, OXYRES, and their acetylated derivatives suppressed type I collagen in TPA-treated HDF cells. Collectively, these results suggest the beneficial effects and underlying molecular mechanisms of RES, OXYRES, and their acetylated derivatives for anti- skin aging applications.

Azo dyes degradation and mutagenicity evaluation with a combination of microbiological and oxidative discoloration treatments

This work evaluated the degradation of the Acid Blue 161 and Procion Red MX-5B dyes in a binary solution by the filamentous fungus Aspergillus terreus and the yeast Saccharomyces cerevisiae in systems with and without electrochemical oxidation as the pretreatment process. UV–Vis spectrophotometry, high-performance liquid chromatography with (HPLC), Fourier transform infrared (FT-IR) spectroscopy and Salmonella/microsome assay (Ames test) were applied towards the degradation analysis of the dyes. Adsorption tests with white clay immobilized on alginate were also conducted after the discoloration treatments to remove intermediate metabolites formed during the degradation of the dye molecules. The discoloration treatments led to the complete color removal of the solutions in all the systems tested. The clay demonstrated affinity for the metabolites formed after discoloration treatments, the removal rates were variable, but the all systems has proved efficient. The Salmonella/microsome assay (Ames test) with strains TA98 and TA100 in the absence and presence of exogenous metabolism (S9 microsomal system, Moltox) revealed that the initial molecules and by-products of the metabolism of the dyes were direct mutagens. The electrochemical/A. terreus/clay system was able to discolor the solutions and transform the direct mutagens into non-mutagenic compounds in addition to reducing the mutagenic potency of the pro-mutagens to the Salmonella strain TA100/S9, which demonstrates the high efficiency of this system with regard to discoloring and degrading azo dye molecules and their by-products. Therefore, this study showed that although not having standard treatment system for this type of pollutant, the combination of treatments can be considered promising. The use of electrochemical oxidation along with microbiological treatment may lead to the degradation and mineralization of these compounds, reducing or eliminating the environmental impact caused by the improper disposal of these dyes in aquatic environments.

Solar-driven advanced oxidation process catalyzed by metal–organic frameworks for water depollution

Phosphonate-based MOF materials namely, STA-12(M) (M = Mn, Fe, Co, Ni), show photocatalytic activity for the degradation of methylene blue (MB) and methyl Orange (MO) from aqueous solution under natural sunlight irradiation. Thus, photo-Fenton oxidative discoloration of dyes have been surveyed by H2O2 catalyzed with the STA-12(M). The degradation of the dyes, appears to be faster with STA-12(Fe) than other synthesized MOFs. The reaction is first order with respect to MO and MB dyes and the synergistic index in the STA-12(Fe)/sunlight/H2O2system reached as high as 431%. Mineralization of dyes was discussed by spectroscopic and TOC measurement. Besides, the efficiency of STA-12(Fe) used in photo-Fenton process was attentively investigated through the characterization of reactive radicals, the stability and reusability of the photocatalyst, also the effect of operational parameters such as H2O2 dosage, solution pH and initial dye concentration. This work demonstrates the first example of facilitating photo-Fenton excitation of H2O2 via phosphonate based metal organic frameworks as photocatalysts and explained a new opportunity for sunlight-induced photocatalytic environmental remediation and protection.

Degradation of hazardous organic dyes with solar‐driven advanced oxidation process catalyzed by the mixed metal–organic frameworks

phosphonate‐based bimetallic metal‐ organic frameworks, namely STA‐12(M1, M2) (M1, M2 = Mn, Fe, Co), show photocatalytic activity for the degradation of Rhodamine B (RhB) and Methylene blue (MB) from aqueous solution under natural sunlight irradiation. The degradation of the dyes, appears to be faster with STA‐12(Fe, Mn) than other synthesized MOFs. Thus, photo‐Fenton oxidative discoloration of dyes has been studied by H2O2 catalyzed with the STA‐12(Fe, Mn). The process is first order with respect to dyes and the synergistic index in the STA‐12(Fe, Mn)/sunlight/H2O2system reached as high as 472%. Mineralization of dyes was discussed by spectroscopic and TOC measurement. Besides, the efficiency of STA‐12(Fe, Mn) used in photocatalytic process was attentively investigated through the characterization of reactive radicals, the stability and reusability of the photocatalyst, also the effect of operational parameters such as H2O2 dosage, solution pH and initial dye concentration. This work demonstrates the first example of facilitating photo‐Fenton‐like excitation of H2O2 via phosphonate based mixed metal organic frameworks as photocatalysts and explained a new opportunity for solar‐induced AOP environmental remediation and protection.

Aging of anhydride‐hardened epoxies in lubricants at elevated temperatures

ABSTRACTIn automotive under‐the‐hood applications, electronics respectively their packaging materials come in contact with automotive fluids. The effect of automatic transmission fluid (ATF) on an anhydride‐cured epoxy was investigated at temperatures up to 180 °C for up to 1000 h. This study has shown that ATF retards the oxidative aging of the epoxy, presumably due to oxygen consumption. Whereas in air the material underwent a thermo‐oxidative aging with a mass loss of up to 4% and a strong broadening of Tg to higher temperatures, in ATF a temperature dependent distinctive drop of Tg from 142 to 126 °C after 1000 h aging at 180 °C, and a mass loss of maximum 1% was observed which might be a thermal decomposition of the epoxy material. A slight broadening of the damping factors might indicate an intrusion of ATF components. A color change of the samples could be observed after aging in air and ATF, with the discoloration in air being more intense. An explanation for the color change might be either a minor amount of oxygen causing an oxidative discoloration reaction or the intrusion of colored ATF degradation products. While the oxidation‐kinetics in air exhibited Arrhenius temperature‐dependence the mechanism in ATF changed above 165 °C. An acceleration of aging tests at temperatures beyond 150 °C is, therefore, not possible. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44877.

Structure and catalytic activity of a penta-silver supramolecular cluster through hydrogen bonding and 2,2′-bipyridine

Colorless crystals of the coordination polymer (CP) [Ag5(CN)5(2,2′-bpy)2]n, 1 were obtained by the reaction of AgNO3, 2,2′-bipyridine (2,2′-bpy) and KCN. The crystal structure of 1 consists of 1D-puckered AgCN chains which are decorated by 2,2′-bpy molecules. These chains form 2D-fused deformed six-membered rings; [Ag4(CN)2(2,2′-bpy)2] creating wide voids capable to accommodate the 2,2′-bpy molecules. 3D-network structure is created via H-bonds, π–π stacking and Ag–Ag interaction. The structure of the CP 1 was characterized by IR, UV–Vis, TGA, NMR spectra and X-ray single crystal analysis. The CP 1 was used as heterogeneous catalyst for the oxidative discoloration of methylene blue dye (MB) by H2O2.

Spectral Characteristics and Applications of Metal–Organic Frameworks Based on Copper Cyanide and Quinoline Bases

Two metal–organic frameworks (MOF), [(CuCN)2.(6-mquin)2], 1 and [Me3SnCu(CN)2.(quina)2(H2O)2], 2, where (6-mquin) = 6-methyl quinoline and (quina) = quinaldic acid, have been synthesized and structurally characterized. MOFs 1 and 2 have been characterized by IR, UV-visible, and NMR spectra, as well as TGA. The emission spectra and the thermodynamic parameters from TGA of MOFs 1 and 2 were discussed. MOFs 1 and 2 were used as heterogeneous catalysts for the oxidative discoloration of Rhodamine B dye (RhB) by H2O2. The cytotoxic effect of MOFs 1 and 2 on the viability of MCF-7 cells was also determined by MTT assay. MOFs 1 and 2 have potentially good inhibition activity to MCF-7 cells.

Application of activated M/ZnO (M = Mn, Co, Ni, Cu, Ag) in photocatalytic degradation of diazo textile coloring dye.

Activated ZnO powder has been prepared by procedures involving first its dissolution in nitric acid, then simultaneous treatment by adding NH4OH and CO2 bubbling leading to precipitation as Zn(OH)CO3 (ZH) and further thermal decomposition of ZH at 400 °C. The gas evolution leads to formation of pores and increase in the specific surface area. Chemically activated M/ZnO powders doped with Mn, Co, Ni, Cu, and Ag have been obtained by the impregnation method. The samples have been characterized by ultraviolet-visible (UV-Vis) spectroscopy, diffuse reflectance (DR) UV-Vis, X-ray diffraction (XRD), single point Brunauer-Emmet-Teller (BET), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) methods. The experiments have shown that metal-doped activated ZnO powders possess higher photocatalytic activities in oxidative discoloration of model contaminant textile coloring dye Reactive Black 5 in slurry reactor compared to that of the pure ZnO. The XRD and XPS data have shown the presence of defects, nonstoichiometricity implying the formation of solid solutions. Copper-doped (1.5 wt%) activated ZnO (Cu(2+) replaces Zn(2+)) is outstanding in its photocatalytic performance in discoloration of the dye due to the higher specific surface area and improved charge carrier separation.

Effects of resveratrol, oxyresveratrol, and their acetylated derivatives on cellular melanogenesis

Resveratrol and oxyresveratrol are naturally occurring phenolic compounds with various bioactivities, but their uses in cosmetics have been partly limited by their chemical instabilities. This study was performed to examine the anti-melanogenic effects of the acetylated derivatives from resveratrol and oxyresveratrol. Resveratrol and oxyresveratrol were chemically modified to triacetyl resveratrol and tetraacetyl oxyresveratrol, respectively. The acetylated compounds were less susceptible than the parent compounds to oxidative discoloration. The acetylated compounds inhibited the activities of tyrosinases less than parent compounds in vitro, but they were as effective at cellular melanogenesis inhibition, indicating bioconversion to parent compounds inside cells. Supporting this notion, the parent compounds were regenerated when the acetylated compounds were digested with cell lysates. Although resveratrol and triacetyl resveratrol inhibited tyrosinase activity less effectively than oxyresveratrol and tetraacetyl oxyresveratrol in vitro, they inhibited cellular melanogenesis more effectively. This discrepancy was explained by strong inhibition of tyrosinase expression by resveratrol and triacetyl resveratrol. Experiments using a reconstituted skin model indicated that resveratrol derivatives can affect melanin synthesis and cell viability to different extents. Collectively, this study suggests that acetylated derivatives of resveratrol have great potential as anti-melanogenic agents for cosmetic use in terms of efficacy, safety, and stability.

The organotin coordination polymer [(n-Bu3Sn)4Fe(CN)6H2O] as effective catalyst towards the oxidative degradation of methylene blue

The structure of the supramolecular coordination polymer SCP 1; [(n-Bu3Sn)4Fe(CN)6H2O] consists of octahedral [Fe(CN)6]4− building blocks which are connected by the TBPY-5 configured n-Bu3Sn(CN..)2 fragments creating 3D-network structure. Fenton and photo-Fenton oxidative discoloration of Methylene Blue (MB) has been investigated by hydrogen peroxide catalyzed with the SCP 1. The reaction exhibited pseudo first-order kinetics with respect to each of MB and H2O2. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization, Kobs=0.76h−1. Mineralization of MB was investigated by FT-IR spectra. Disodium salt of terephthalic acid photoluminescence probing technology was carried out to identify the reactive oxygen species. The different parameters that affect MB degradation rate were evaluated. Moreover, the efficiency of recycled the SCP 1 and the mechanism of degradation of MB dye were investigated.

Molecular Behavior of Room-temperature Ionic Liquids under Lubricating Condition

The molecular behavior of room-temperature ionic liquids (RTILs) under lubricating condition was analyzed using fourier transform infrared spectroscopy equipped with a pin-on-disk tribometer to simultaneously measure the friction force, normal load, and IR spectrum. When 1-metyl-3-butylimidazolium trifluoromethanesulfonate ([BMIM]OTf), which is miscible with water, was used as a lubricant, the water content increased with time, and the ratio of water to cation remained constant even though the film thickness reduced under the lubricating condition at a load of ~25 N. When 1-metyl-3-butylimidazolium tetrafluorophosphate ([BMIM]PF6), which is water-insoluble, was used as a lubricant, the water content was quite small and increased slightly with time, and the ratio of water to cation also remained constant even when a normal load of ~25 N was applied. The SUJ2 pin surface showed oxidative discoloration after the friction test using [BMIM]OTf, but there was little change in color when[BMIM]PF6 was used. XPS results indicated that iron oxide, chromium oxide and sulfate were observed on the worn pin surface using [BMIM]OTf and the CaF2 disk. However, iron oxide and iron phosphate were observed for the worn pin surface using [BMIM]PF6 and the CaF2 disk. These results suggest that the amount of water contained in the RTILs as well as window materials have a significant effect on the tribo-chemical reaction of RTILs.

Structure and applications of metal–organic framework based on cyanide and 3,5-dichloropyridine

The reaction of the aqueous/acetonitrile solutions of K3[Cu(CN)4] and 3,5-dichloropyridine (3,5-dClpy), in the presence of Me3SnCl affords a new metal–organic framework (MOF), 3∞[(CuCN)2·(3,5-dClpy)2], 1. The structure of the MOF 1 was characterized by IR, UV–visible, TGA and X-ray single crystal analysis. The structure of MOF 1 consists of CuCN building blocks which are connected by CN group forming 1D-zig-zag chains. Each chain is bridged to another chain by hydrogen bonding organizing 2D-sheets. The structure of 1 is further close packed by hydrogen bonds, π–π stacking and lp–π interactions creating 3D-network. The emission spectra and the thermodynamic parameters from TGA of the MOF 1 were discussed. The MOF 1 was used as heterogeneous catalyst for the oxidative discoloration of methylene blue dye (MB) by dilute solution of hydrogen peroxide as oxidant. The in vitro cytotoxic activity has been evaluated against the human breast cancer cell lines MCF-7. The cytotoxic effect of the MOF 1 on the viability of MCF-7 cells was determined by MTT assay.

Structure and Catalytic Activity of New Metal‐Organic Frameworks Based on Copper Cyanide and Quinoline Bases

AbstractTwo new metal‐organic frameworks (MOF), [(CuCN)2·(6‐mquin)2] (1) and [Me3SnCu(CN)2·(quina)2(H2O)2] (2) (6‐mquin = 6‐methyl quinolone, quina = quinaldic acid) were synthesized and characterized. Single crystals of MOF 1 were characterized by IR and NMR spectroscopy, as well as X‐ray single crystal analysis. The structure of MOF 2 was studied by IR and NMR spectroscopy as well as computational studies. The structure of MOF 1 consists of 1D (CuCN)n chains, whereas the 6‐mquin ligands alternate on both sides of the chain. Hydrogen bonds play an essential role for the construction of the 3D network structure. On the other hand, the theoretical structural analysis of MOF 2 indicated that the Cu(CN)2 fragments represent the main building blocks of the structure, which are bridged by the Me3Sn+ cations to construct 1D infinite parallel zigzag chains. MOFs 1 and 2 were used as heterogeneous catalysts for the oxidative discoloration of methylene blue dye (MB) by H2O2.

The Influence of Copper–Copper Interaction on the Structure and Applications of a Metal–Organic Framework Based on Cyanide and 3-Chloropyridine

The structure of the new metal–organic framework, [(CuCN)2·(3-Clpy)], 1, was characterized by IR, UV–visible, TGA and X-ray single crystal analysis. The structure of 1 consists of CuCN building blocks, which are connected by CN group to form two different chains; one puckered chain with TP-3 geometry around Cu(1) and a linear Cu(2)(CN)2 chain. The two kinds of chains are bonded by cuprophilic interactions creating a 3D-network. The network structure of 1 is further close-backed by π–π stacking and hydrogen bonds. The electronic absorption and emission spectra as well as the thermodynamic parameters from TGA of the MOF 1 are discussed. MOF 1 was used as an effective heterogeneous catalyst for the oxidative discoloration of methylene blue dye by dilute solution of hydrogen peroxide as the oxidant. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to determine the in vitro antitumor activity of MOF 1 on human breast cancer cell line, MCF7.

Fenton Oxidation of Methyl Violet in Aqueous Solution

In this study, oxidative discoloration of methyl violet (MV) dye in aqueous solution has been studied using Fenton (Fe2+/H2O2) process. The parameters such as concentration of Fe2+, H2O2, MV, temperature, and Cl− and ions that affected of discoloration in Fenton process were investigated. The rate of degradation is dependent on initial concentration of Fe2+ ion, initial concentration of H2O2, and pH of media. Discoloration of MV was increased by increasing the temperature of reaction. Optimized condition was determined and it was found that the obtained efficiency was about 95.5% after 15 minutes of reaction at pH 3. TOC of dye sample, before and after the oxidation process, was determined. TOC removal indicates partial and significant mineralization of MV dye. The results of experiments showed that degradation of MV dye in Fenton oxidation can be described with a pseudo‐irst‐order kinetic model. The thermodynamic constants of the Fenton oxidation process were evaluated. The results implied that the oxidation process was feasible, spontaneous, and endothermic.

Degradation of methylene blue by catalytic and photo-catalytic processes catalyzed by the organotin-polymer 3∞[(Me3Sn)4Fe(CN)6

The organotin-polymer [(Me3Sn)4Fe(CN)6], 1, has been synthesized and characterized to test its potential application as catalyst. The structure of 1 consists mainly, of [Fe(CN)6]4− building blocks connected by the Me3Sn cations forming 3D-polymeric network. The iron (II) sites acquire distorted octahedral geometry while the tin atom exhibits TBPY-5 configured [Me3Sn(CN…)2] fragments. Fenton and photo-Fenton oxidative discoloration of methylene blue (MB) has been investigated by hydrogen peroxide catalyzed with the metal–organic framework, (MOF) 1. The reaction is first order with respect to MB dye. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization. Mineralization of MB was investigated by FT-IR spectra. Disodium salt of terephthalic acid photoluminescence probing technology was carried out to identify the reactive oxygen species. The different parameters that affect MB degradation rate were evaluated. Moreover, the efficiency of recycled the catalyst 1 and the mechanism of degradation of MB dye were investigated.

Effect of Edible Coatings Containing Soy Protein Isolate (SPI) on the Browning and Moisture Content of Cut Fruit and Vegetables

Effectiveness of edible coatings containing soy protein isolate (SPI), in reducing oxidative browning and moisture loss during storage (<TEX>$4^{\circ}C$</TEX>) of cut apples, potatoes, carrots, and onions was investigated. The SPI coatings were shown to have antioxidative activity. Furthermore, addition of carboxymethyl cellulose (CMC) to the formulations significantly improved its antioxidative activity. Oxidative discoloration, as determined by Commission Internationale De I'Eclairage (CIE) lightness (<TEX>$L^*$</TEX>), redness (<TEX>$a^*$</TEX>), and yellowness (<TEX>$b^*$</TEX>) color scale, was significantly reduced (p <0.05) by SPI coating treatments over a storage time of 120 min. Loss of lightness was reduced by SPI coatings with and without CMC. These respectively showed 4.03 and 3.71% change of <TEX>$L^*$</TEX> value compared to 8.56% for control. Browning of the control in cut potatoes was significantly increased by 106.6% in contrast to 34.3 and 35.2% for SPI coatings with and without CMC, respectively. The <TEX>$b^*$</TEX> values also reflected effectiveness of SPI. Moisture barrier effect was significantly better for the treatments, compared to the control. SPI coatings reduced moisture loss in apples and potatoes, respectively, by 21.3 and 29.6% over the control. Cut onions did not show any treatment effect both in terms of browning and moisture loss. SPI coatings prove to be good moisture barrier and antioxidative property.