Discoloration Reaction Research Articles

Novel spherical and homogeneous Alstonia Scholaris silver nanoparticles for dual applications: Detection of ultra-trace amounts of Cr(III) ions and MB discoloration sustained by 3-input AND gate

This study unveils an effective method for detecting Cr(III) and MB dye discoloration using biosynthesized silver nanoparticles obtained from leaves of Alstonia Scholaris (AS-AgNPs). HR-TEM images showed that the mean diameter of AS-AgNPs increased from 14.68 to 37.05 nm after the interaction with Cr(III) ions. The AS-AgNPs show an impressive detection limit of 2.1 nM for Cr(III) and demonstrate high efficacy in MB discoloration of 91.27% in 12 min. The discoloration reaction fitted pseudo-first-order kinetics with the R2 value of 0.9634. When comparing the kinetics of MB discoloration by NaBH4 alone, and addition of AS-AgNPs to NaBH4 resulted in a 102 fold decrease in t1/2 and a 102 fold increase in k values. This is the first report to use spherical AS-AgNPs for dual applications, supported by 3-Input AND gate logic, and also highlights AS-AgNPs' potential application for real sample analysis.

Eco-friendly synthesis of biochar supported with zinc oxide as a heterogeneous catalyst for photocatalytic decontamination of Rhodamine B under sunlight illumination

In the current study, biochar, as a porous and low-cost carbon derived from Pontederia crassipes L. leaves, was loaded with zinc oxide for the photocatalytic discoloration of Rhodamine B dye in aqueous suspension under solar light irradiation. For the comparison, the unmodified zinc oxide and biochar samples were prepared. The synthesizing materials were investigated by X-ray powder diffraction, UV-DRS spectrophotometer, field emission scanning electron microscopy, Fourier transform infrared spectrometer, and Raman spectroscopy. The synthesized ZnO/Biochar hybrid has improved features, besides narrowing the band gap energy, and enhancing the surface area of the photocatalyst. The ZnO/biochar nanohybrid displayed an excellent photocatalytic degradation efficiency (99. 67 %) of Rhodamine B in the presence of H2O2 with 120 min of solar light irradiation. The results of recyclability study of ZnO/Biochar in the photocatalysis process verified its physical and chemical stability after five repeated cycles, hence it retained of 82.24 % of initial activity. Furthermore, the photocatalytic discoloration reaction was compatible with the pseudo-first-order kinetic model

Mechanisms of lead-containing pigment discoloration caused by Naumannella cuiyingiana AFT2T isolated from 1500 years tomb wall painting of China

Biodeterioration of ancient wall paintings is a ubiquitous phenomenon that threatens the long-term survival of invaluable cultural heritage. In this study, the Naumannella cuiyingiana AFT2T, isolated from the surface of tomb paintings dating back 1500 years, was observed to be capable of altering the appearing colors of Pb-containing pigments. By a combination of physiological and biochemical measurements and transcriptomic analysis of strain AFT2T under Pb amendment treatments, the discoloration mechanisms were investigated further in depth. Incubation experiments showed that the discoloration reaction resulted from an interaction between Pb-containing pigments and strain AFT2T cells. Subsequently, we found that strain AFT2T had ability to assimilate Pb ions from pigments by using EDX mapping. Finally, after comparing to the controls, it is speculated that the observed discoloration is the formation of cellular product PbS and a series of additional tests were conducted to verify this. In addition, controlling the chemical composition in the culture medium was utilized to confirm the source of S which might be related to the sulfur-containing amino acids of animal proteins in the medium. Transcriptomic analysis exhibited that Pb stress strongly affected the expression of some genes in strain AFT2T, such as metal ion transport and metabolism genes and genes related to the TlpA family protein disulfide reductases. Among them, the gene of the enzyme with disulfide-bond reducing properties and the gene encoding the divalent Pb ion uptake transporter are the key genes in the process of discoloration. A combination of biochemical reactions and transcriptomic analysis was utilized to reveal the key genes involved in the discoloration of Pb-containing pigments by strain AFT2T. These results provide not only new insights and a theoretical basis for the conservation of cultural relics but also a new means for the management of heavy metal pollution in the environments.

A visual colorimetric assay based on phage T156 and gold nanoparticles for the sensitive detection of Salmonella in lettuce

In this study, a new technique was developed for visual and precise identification of Salmonella using phage T156-mediated aggregation of gold nanoparticles. The phage binds to gold nanoparticles in a dispersed and stable state under high NaCl concentrations. When Salmonella is introduced, the phage specifically recognizes and adsorbs the targeted bacteria, causing the AuNPs to undergo a discoloration reaction resulting in aggregation, which enables Salmonella visualization. The method has a detection range of 3.8 × 101–3.8 × 109 CFU/mL and a limit of detection of 38 CFU/mL and can produce results in approximately 80 min. The technique was also tested on field samples, including spiked lettuce, and was found to be accurate with a recovery rate of 81.0–119.2% and relative standard deviations ranging from 3.3% to 14.7%. Notably, this technique utilizes phages as recognition elements in colorimetric methods, offering simplicity, speed, and the ability to effectively distinguish between live and dead Salmonella. It demonstrates remarkable sensitivity, specificity, and accuracy. Furthermore, it presents a novel avenue for the rapid detection of other pathogenic bacteria.

Sensitive and Label-Free Colorimetric Detection of Glyphosate Based on the Suppression Peroxidase-Mimicking Activity of Cu(II) Ions.

The sensitive and accurate determination of glyphosate (Glyp) is urgently demanded because it is closely correlated with human health and environmental safety. In this work, we proposed a sensitive and convenient colorimetric assay by employing copper ion peroxidases for the detection of Glyp in the environment. Free Cu(II) ions displayed high peroxidase activity and can catalytically oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB, resulting in an obviously visible discoloration reaction. Once the Glyp is added, the ability of copper ions to mimic peroxidase can be largely suppressed because of the generation of Glyp-Cu2+ chelate. The favorable selectivity and sensitivity were demonstrated in the colorimetric analysis of Glyp. Furthermore, this rapid and sensitive method was successfully applied in the accurate and reliable determination of glyphosate in the real sample, holding promising applications in pesticide determination in the environment.

Catalytic hydrogenation of organic dyes by Ag and Au magnetic nanoparticles supported on nanocellulose from waste pistachio shells

The present study reports the preparation of a novel magnetic catalyst constituted by Au/Ag/Fe3O4 nanoparticles (Au/Ag/Fe3O4 NPs), supported on nanocellulose obtained by pistachio shells wastes, for the catalytic reduction of anionic and cationic dyes. X-ray Powder Diffraction (XRD) analysis confirmed the coexistence of Fe3O4, Ag, and Au nanoparticles. The catalytic studies showed that 6 mg and 8 mg catalyst mass can promote the discoloration reaction of methylene blue (MB) at about 94.75% and 98.7%, after only 4 min, respectively. Discoloration efficiency reached 100% at longer times. Moreover, the time required for a 100% reduction of MB or methyl orange (MO) was found to be almost the same up to the 8th cycle of reuses, suggesting robust stability for our catalyst.

Synthesis and deposition of bismuth oxychloride with a rose‐type flower shape and photoelectroactivity evaluation in the methyl orange discoloration reaction

AbstractIn this work, bismuth oxychloride with a rose‐type flower shape was successfully synthesised using the easy and low‐cost successive ionic layer adsorption and reaction process. The tetragonal crystalline structure with a flower‐like shape and thickness of 150‐nm nanosheets was used as electrode material in an exciting approach for the photoelectrochemical discoloration reaction of methyl orange. The structure, morphology and optical properties of the obtained bismuth oxychloride sample were evaluated through X‐ray diffraction, Raman spectroscopy, the Brunauer–Emmett–Teller method, diffuse reflectance ultraviolet–visible spectroscopy and scanning electron microscopy. Through photoelectrochemical characterisation measurements (linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques), the bismuth oxychloride electrode showed remarkable electroactivity under ultraviolet light irradiation. The methyl orange discoloration reaction, performed under ultraviolet light incidence and potential application of −0.5 V (vs silver/silver chloride) for 60 minutes, produced a higher degradation percentage (ca. 82%) and kobs of 29 × 10−3 min−1.

One-step preparation of photoresponsive microcapsules based on the interfacial self-assembly of an azopyridine coordination polymer

In recent decades, stimuli-responsive microcapsules have attracted increasing attention due to their potential applications as microreactors for drug delivery, catalytic reactions, etc.; however, the complicated preparation process and the difficulty of size fixation and recycling need to be addressed. In this work, we developed a one-step preparation method to fabricate photoresponsive microcapsules based on the interfacial self-assembly of an azopyridine coordination polymer. The coordination of silver ions and ligands was performed in situ at an oil–water interface, and the coordination polymer self-assembled into nanofibers, which stabilized the Pickering emulsion and produced water-in-oil microcapsules. Additionally, microcapsules with a uniform size were prepared based on a microfluidic process. Both the crystal structure and the Janus surface of nanofibers were determined to elucidate the mechanism of self-assembly and interface stabilization. When the microcapsules were irradiated with 365 nm UV light, the cis isomerization of the azo group in the coordination polymer led to the disassembly and dissolution of the nanofibers, resulting in fusion of the microcapsules and demulsification of the Pickering emulsion. Conversely, visible light and heating triggered the trans isomerization of the azopyridine coordination polymer and thus caused regeneration of the nanofibers and recovery of the microcapsules. Finally, microcapsules encapsulating several reactants were employed in the pH-indicator discoloration reaction and the enzyme-catalyzed decomposition of H2O2 to demonstrate their feasibility as photocontrolled microreactors. This kind of photoresponsive microcapsule with one-step preparation and good recyclability might have potential applications in the field of microreactors.

Crack Evaluation of Concrete Using Mechanochromic Sensor.

In this study, the deformation of concrete materials was evaluated using a mechanochromic sensor that detects the discoloration reaction caused by deformation. This sensor was attached by applying the Loctite adhesive to both ends in the longitudinal direction. The process of applying tensile stress to the specimens was videotaped, and the deformation and discoloration were examined through image analysis. The mechanochromic sensor was not affected by the finished surface condition, and the discoloration reaction was detected for a concrete material deformation level of up to 0.01 mm. The detected level was caused by the elongation of the sensor, and the discoloration compared with the initial color was identified. In addition, the integration behavior of the mechanochromic sensor under the deterioration of concrete members in cold areas and winter environments, as well as the discoloration reaction of the sensor in a low-temperature environment, was examined. It was found that the discoloration ability of the mechanochromic sensor exposed to a low-temperature environment was restored in 2 h after the end of the freeze-thaw test, and it was judged that the deformation and discoloration levels will be properly measured when the surface temperature of the sensor is restored to a room temperature of approximately 15 °C. This appeared to be due to the room temperature recovery of the dielectric spacer of the sensor and the deformation structure of the resonance condition. The sensor was also attached when diagonal cracks occurred in the concrete beam members to evaluate the strain and discoloration rate according to the deformation and discoloration levels. Accordingly, the cracks and deformation of the concrete materials were monitored using measured values from the discoloration of the mechanochromic sensors, and the possibility of measuring the crack width was reviewed only by real-time monitoring and imaging with the naked eye.

Efficient photodegradation of methyl orange dye using electrogenerated copper-zinc oxide hybrid

A photoactive Cu-doped ZnO (Cu/ZnO) hybrid was synthesized via a simple electro-generation procedure. The resultant catalyst was then subjected to UV–vis DRS and BET analysis for band gap and porosity properties studies. The photocatalytic efficiency of the Cu/ZnO hybrid was then evaluated via discoloration reaction of dye pollutant, methyl orange (MO) under visible light irradiation. To study the effect of Cu loadings on the hybrid catalyst performance, a series of catalysts with different Cu wt.% were synthesized and tested for MO degradation. As result, ZnO doped with 5 wt% Cu was found as the most active catalyst with 100 % MO removal followed by 3 wt% Cu/ZnO (94 %), 7 wt% Cu/ZnO (71 %) and 10 wt% Cu/ZnO (40 %). Whereas, in the presence of pure ZnO, only 23 % MO was managed to be degraded, remarking its low catalytic reactivity compared to Cu/ZnO hybrids, especially 5 wt% Cu/ZnO. This might be due to the increase in surface area and lower band gap of 5 wt% Cu/ZnO (3.11 eV) compared to ZnO (3.20 eV) as analyzed by BET and UV–vis DRS respectively. Meanwhile, the optimum reaction conditions were found to be pH 3, 10 mg/L initial dye concentration, and 0.38 g/L of 5 wt% Cu/ZnO. Conclusively, the electrogenerated Cu/ZnO catalyst was highly capable of degrading methyl orange dye pollutants and therefore has a high potential for future wastewater treatment application.

Mechanism of surface corrosion resistance of 304 stainless steel processed by nanosecond laser pulses

AbstractA nanosecond pulsed fiber laser was used to modify the surface of 304 stainless steel. The compactness, microstructure, chemical composition, and corrosion resistance of the stainless steel passive film were observed by the blue dot detection method, scanning electron microscopy, x‐ray photoelectron spectroscopy, and electrochemical methods. The influence of different laser fluences on the stability and corrosion resistance of the stainless steel passive film was studied. The results show that with increasing laser fluence, the discoloration reaction time of the stainless steel surface increases first and then decreases, while the surface roughness decreases first and then increases. When the laser fluence is lower than 11.19 J/cm2, a compact and uniform passive film is formed. When the laser fluence is larger than this value, the stainless steel substrate is prone to secondary corrosion. Chromium oxides are enriched in the passive film, and the anodic dissolution rate decreases, which promotes a positive shift in the corrosion potential of the stainless steel, decreases the corrosion current density and increases the polarization resistance and the corrosion resistance. The surface corrosion resistance is thus significantly improved.

Comparative transcriptome and proteome provide new insights into the regulatory mechanisms of the postharvest deterioration of Pleurotus tuoliensis fruitbodies during storage

The Pleurotus tuoliensis (Pt), a precious edible mushroom with high economic value, is widely popular for its rich nutrition and meaty texture. However, rapid postharvest deterioration depreciates the commercial value of Pt and severely restricts its marketing. By RNA-Seq transcriptomic and TMT-MS MS proteomic, we study the regulatory mechanisms of the postharvest storage of Pt fruitbodies at 25 ℃ for 0, 38, and 76 h (these three-time points recorded as groups A, B, and C, respectively). 2,008 DEGs (Differentially expressed genes) were identified, and all DEGs shared 265 factors with all DEPs (Differentially expressed proteins). Jointly, the DEGs and DEPs of two-omics showed that the category of the metabolic process contained the most DEGs and DEPs in the biological process by GO (Gene Ontology) classification. The top 17 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways with the highest sum of DEG and DEP numbers in groups B/A (38 h vs. 0 h) and C/A (76 h vs. 0 h) and pathways closely related to energy metabolism were selected for analysis and discussion. Actively expression of CAZymes (Carbohydrate active enzymes), represented by laccase, chitinase, and β-glucanase, directly leads to the softening of fruitbodies. The transcription factor Rlm1 of 1,3-β-glucan synthase attracted attention with a significant down-regulation of gene levels in the C/A group. Laccase also contributes, together with phenylalanine ammonia-lyase (PAL), to the discoloration reaction in the first 76 h of the fruitbodies. Significant expression of several crucial enzymes for EMP (Glycolysis), Fatty acid degradation, and Valine, leucine and isoleucine degradation at the gene or protein level supply substantial amounts of acetyl-CoA to the TCA cycle. Citrate synthase (CS), isocitrate dehydrogenase (ICDH), and three mitochondrial respiratory complexes intensify respiration and produce high levels of ROS (Reactive oxygen species) by significant up-regulation. In the ROS scavenging system, only Mn-SOD was significantly up-regulated at the gene level and was probably interacted with Hsp60 (Heat shock protein 60), which was significantly up-regulated at the protein level, to play a dominant role in antioxidation. Three types of stresses - cell wall stress, starvation, and oxidative stress - were suffered by Pt fruitbodies postharvest, resulting in cell cycle arrest and gene expression disorder.

Biomass impregnated zero-valent Ag and Cu supported-catalyst: Evaluation in the reduction of nitrophenol and discoloration of dyes in aqueous medium

The stem part of the Melia Azadarach (MA) plant species was impregnated with Ag and Cu ions and subsequently reduced with NaBH4 in aqueous medium and were named as MA@Ag and MA@Cu. These nanocatalysts were characterized through FTIR, XRD, TGA, EDS and FESEM. Various analysis was performed to evaluate the inherent functional groups, crystallinity, thermal stability, elemental analysis and surface characteristics of the catalysts. Both catalysts were applied for the discoloration of dyes and reduction of PNP in the presence of NaBH4 in aqueous medium. Initially, both the catalysts were applied for the reduction of PNP (p-nitrophenol) and discoloration MO (methyl orange) dye. Pseudo-1st order kinetics was applied for calculating kapp and R2 values. The apparent rate constant (kapp) was highest for the discoloration reaction of RB (122.85 min-1) and MB (14.534 min-1) in which the catalyst was MA@Ag thus, indicating strongest catalytic activity. Similarly, 0.9574 and 0.9572 are the best-fitted adjacent R2 values obtained from MO and MB degradation using MA@Ag. Both the rate constant value and turnover frequency (TOF) indicated that MA@Ag exhibited higher activity.

Solid-State Synthesis of Direct Z-Scheme Cu2O/WO3 Nanocomposites with Enhanced Visible-Light Photocatalytic Performance

In this paper, we report the preparation of visible-light active direct Z-scheme Cu2O/WO3 nanocomposite photocatalyst by a solid-state reaction avoiding the otherwise inevitable formation of CuWO4 phase in wet syntheses. Structure, morphology, and thermal and optical properties of prepared WO3 nanoplatelets decorated by Cu2O were investigated by XRD, Raman spectroscopy, SEM/TEM, combined thermogravimetric (TG)/differential scanning calorimetry (DSC) analysis, and UV–VIS spectroscopy. The photocatalytic performance of the prepared samples under UV and visible light was studied through monitoring discoloration of methylene blue under illumination by selected wavelengths, allowing for the distinguishing between the contributions of the two semiconductive components. Experimental results showed that the decoration of WO3 nanoplates by Cu2O nanoparticles led to an improvement in photocatalytic performance, regardless of used LED (Light-Emitting Diode) wavelength, even at low concentrations. By using scavengers selectively blocking reactive species involved in the discoloration reaction, we determined that the Cu2O/WO3 nanocomposite exhibited the characteristics of direct Z-scheme-type photocatalyst.

Development of Low Power Consumption Electrochromic Device Using Spontaneous Discoloration Reaction

Recently, dimming functional materials have been attracted attention as one of the solutions to energy problems. Dimmable materials are capable of continuously adjusting the transmittance of light according to the intensity of external light, which is expected to reduce cooling and heating loads of buildings such as houses and office buildings and realize energy saving. Prussian blue (PB, KFe3+[Fe2+(CN)6]) is known as one of the dimming functional materials that shows reversible color changes upon Fe2+/Fe3+ redox reaction [1], and has been used for electrochromic devices (ECD) as an inexpensive and highly durable dimming function material. The conventional ECD is controlled by bipolar voltage applications for coloration and discoloration [2]. In contrast, , we developed here the ECD equipping a function of a spontaneous discoloration without applying voltage with the aim to reduce power consumption.ECD is consisted of indium-doped tin oxide (ITO) glass / PB / electrolyte / PB / ITO glass. The PB-coated ITO glasses were prepared by casting PB ink onto ITO glasses (15 x 15 mm) and spin-coated at 2000 rpm for 10 sec. The electrolyte used was a propylene carbonate containing potassium bis(trifluoromethanesulfonyl)imide and polymethyl methacrylate.By applying the voltage at 1.5 V to the ECD, the wavelength peak of a reflected light shifted from 460 nm (blue color) to 535 nm (yellow color) due to the reduction and oxidation of PB on the anode and the cathode, respectively. That is, KFe3+[Fe2+(CN)6] (blue) was reduced to K2Fe2+[Fe2+(CN)6] (colorless) on a cathode and KFe3+[Fe2+(CN)6] (blue) was oxidized to KFe3+[Fe3+(CN)6] (yellow) on an anode. After removing the voltage application, wavelength shifted back from 535 nm to 500 nm, indicating that PBs spontaneously changed to their original states. It is estimated that the color returns to the original color in about 3 hours. The spontaneous discoloration might be caused by the potential difference between the electrodes. The detailed discussion regarding the relationship between spontaneous discoloration and the elapsed time will be present.[1] K. Yoshino, “Prussian Blue; New applications and its nanoparticles,” THE CHEMICAL TIMES, 229(3):23-27, (2013)[2] H. Tanaka, (2010), “Development of electrochromic devices by printing processes,” NEW GLASS, 25(3): 60-63, (2010) Figure 1

Synthesis and Characterization of Ti-Nb2O5 Catalysts for Discoloration Reaction of Bromophenol Blue and Indigo Carmine Dyes

This work investigated the photodegradation of bromophenol blue (BPB) and indigo carmine (IC) dye under UV–Visible light using pure oxides of titanium and niobium, as well as TiO2-Nb2O5 oxides containing 0.5, 2.5 and 5 wt% of TiO2, prepared by wet impregnation of Nb2O5 with Ti tert-butoxide under inert atmosphere. The results of XRD and Raman spectroscopy showed the presence of anatase TiO2 phase and T-Nb2O5 phase with orthorhombic structure in the pure TiO2 and Nb2O5 oxides, respectively. The Nb2O5 oxides doped with TiO2 presented a T-Nb2O5 phase, but there was no formation of TiNb2O7. TiO2 anatase was observed in the mixed oxide with higher Ti content (5 wt% TiO2). A zeta potential analysis showed positive surface charge values for titanium oxide and negative for niobium oxide and mixed oxides. The addition of up to 5 wt% of the TiO2 fold the activity of Nb2O5 in the discoloration of both dyes. Pure TiO2 exhibits higher initial activity, which could be related to its positive PZC and higher attraction to sulphonic groups present in the dyes. Despite of the lower initial rate, 2.5 and 5% TiNb catalysts achieved full degradation of the dyes after 4 h of reaction.

Evaluation of the heterostructure ITO/BiVO4 under blue monochromatic light irradiation for photoelectrochemical application

In this paper, the semiconductor material BiVO4 was obtained by an adapted process of solution combustion synthesis, using poly(ethylene glycol) (PEG 6000) as an additional stabilizing agent, and deposited on indium-doped tin oxide (ITO) substrate, by the dip-coating deposition process, to build an ITO/BiVO4 thin film heterostructure, which can be used as photoanode in photoelectrochemical (PEC) cell. The ITO/BiVO4 photoanode has its performance evaluated by linear sweep voltammetry (LSV), chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques, under blue monochromatic light, provided by an InGaN LED source. The LSV curve shows that the photoactivity of the photoanode presents a drastic jump in the current density under illumination and negligible dark current density. Reproducibility of the electrode photoactivity is observed under light-chopped illumination. The decay profile of photocurrent suggests that despite of charge carriers recombination process occurring in the ITO/BiVO4 electrode, it still presents good photoelectrocatalytic efficiency. Additionally, the long-term current stability indicates that the current density stays stable, without considerable decay, for at least one hour. The steady-state photocurrent density obtained is equal 91 µA cm− 2. EIS results showed that under illumination, the charge transfer resistance (Rct) is considerably lower than the dark condition. The PEC performance evaluated for discoloration reaction in rhodamine B (RhB) and methylene blue (MB) shows that the photoelectrochemical system is quite efficient.

Photocatalytic methylene blue degradation on multilayer transparent TiO2 coatings

This paper presents the influence of coating thickness on the photocatalytic activity of TiO2 coatings. Methylene blue decomposition under UV light was tested. Transparent anatase TiO2 thin films were prepared by the sol-gel method using alcoholic solutions. Thin films were deposited on a borosilicate glass substrate by the multiple dip-coating technique across a much wider range than is typically described in literature, specifically, from 1 to 12 dip-coating cycles. The degradation of MB dissolvent in water was measured by UV-Vis spectroscopy. The structure, morphology and optical properties of thin film coatings were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). The crystalline structure of TiO2 films was identified as the anatase phase, consisting of uniform spherical particles from 25 to 32 nm depending on the number of dip-coatings cycles. Decreasing roughness and optical band gaps were also observed in the produced oxide films with increasing numbers of dip-coating cycles. The reaction rate of discoloration of the dye solution by photocatalytic degradation is strongly related to the thickness of the layer, the number of layers and its morphology. The thicker the oxide layer, the faster the reaction; however, this relationship is not linear. In addition, in this article, a methylene blue discoloration reaction model was proposed which takes into account stoichiometry, reagent electric charge balance and the REDOX type of reaction.

Nickel-Substituted Polyoxometalate Nanomaterial as a Green and Recyclable Catalyst for Dye Decolorization

The catalytic activity of a synthesized nanopolyoxometalate $$(\upalpha _{2}\hbox {P}_{2}\hbox {W}_{17}\hbox {NiO}_{61})^{8-}$$ was investigated in the decolorization of methyl orange (MO) using KMnO $$_{4}$$ as an oxidant in aqueous medium. This catalyst was synthesized by the incorporation of nickel into the polytungstic matrix of a lacunar compound $$(\upalpha _{2}\hbox {P}_{2}\hbox {W}_{17})^{10-}$$ which was prepared from a saturated parent molecule ( $$\upalpha \hbox {P}_{2}\hbox {W}_{18})^{6-}$$ . For characterization, the applied methods, IR, UV–vis, and XRD, have been studied. The optimal experimental conditions were achieved at: pH 6, $$25\,{^{\circ }}\hbox {C}$$ , 10 mg/L of MO concentration, 0.1 mM of oxidant concentration, and 0.3 g of catalyst mass. Under these conditions, the discoloration efficiency obtained was 90.75%. The presence of chloride and sulfate ions showed the inhibitory effect on the discoloration efficiency. At the end of the discoloration reaction, the catalyst was recovered, washed, and reused in several cycles keeping its catalytic activity intact.

Antioxidant potential of some plants of Brassicaceae Burnett and Poaceae Barnhart

Objective – to estimate the antiradical scavenging ability of extracts of some plants of Brassicaceae Burnett and Poaceae Barnhart. species, to evaluate the total antioxidant activity of plants in the conditions of M.M. Gryshko National Botanical Garden of the NAS of Ukraine. Material and methods. Plant material of this investigation – species, varieties and cultivars of Brassicaceaae and Poaceae families: Brassica campestris f. annua D.C. (BCA), B. campestris f. biennis D.C.× B. napus f. biennis D.C., cv. Innovatsiia (BCBNI), B. campestris f. biennis D.C. × B. rapa L. × B. napus f. biennis D.C. (BCBRBN), B. juncea (L.) Czern. (BJ), B. juncea (L.) Czern. f. biennis, cv. Annushka (BJA), B. napus f. biennis D.C., f. EROF-5 (BNE-5), B. rapa L. (BR), B. rapa subsp. rapifera Metzger (BRR), Raphanus sativus L. var. oleiformis Pers. (RSO), Miscanthus sacchariflorus (Maxim.) Benth., cv. Snihopad (MSS), M. sinensis Anderss. f. ESBMK-6 (MSE-6), Panicum virgatum L. f. PB (PVPB), P. virgatum L. f. PL (PVPL), Sorghum bicolor (L.) Moench. f. ETSSDF-11 (SBE-11), S. nigrum Roemer et Schultes f. ETSSCHF-1 (SNE-1), S. saccharatum (L.) Moench. cv. Medove (SSM), S. sudanense (Piper) Stapf (SS), S. technicum (Koern.) Bait. et Trab. (ST). The antioxidant activity of methanol and aqueous extracts based on the discoloration reaction on the solution of DPPH (2,2-diphenyl-1-picrylhydrazyl free radical) was determined according to Brandt-Williams et al. The determination of content of ascorbic acid was conducted according to V.P. Krishchenko, the content of carotene – according to B.P. Pleshkov. Results. The antioxidant activity of methanol extracts of plants of Brassicaceae was registered in the range from 16.94±0.15 (BCA) to 36.91 ± 0.26 (BRR) % and aqueous extracts – from 26.53 ± 0.34 (BJ) to 65.85 ± 0.30 (RSO) %. This parameter for methanol extracts of Poaceae species was in range from 31.13 ± 0.32 (MSE-6) to 86.48 ± 0.49 (SNE-1) % and aqueous extracts – from 33.10 ± 0.47 (ST) to 83.14 ± 0.46 (PVPB) %. It was determined concentration of ascorbic acid from 118.67 ± 9.90 (BJA) to 566.61 ± 38.37 (BNE-5) mg% and carotene – from 0.48 ± 0.01 (BJA) to 3.11 ± 0.07 (BJ) mg% for Brassicaceae plants. Content of ascorbic acid in range from 11.80 ± 0.85 (PVPB) to 77.39 ± 1.29 (SS) mg% and carotene – from 0.05 ± 0.00 (PVPB) to 0.62 ± 0.02 (PVPL) mg% was identified for Poaceae plants. Conclusions. This study showed that plant raw material of investigated plants is a valuable source of antioxidants and vitamins. Methanol and water extracts of plants of Poaceae had higher antiradical activity against DPPH radical than extracts of plants of Brassicaceae. The higher level of ascorbic acid and carotene was observed in extracts of plants of Brassicaceae. The minimal content of ascorbic acid and carotene found for BJA (Brassicaceae) and PVPB (Poaceae).