Insoluble Products Research Articles

Application of Engineered Bacteriophage T7 in the Detection of Bacteria in Food Matrices.

Detection of pathogens in a food matrix is challenging due to various constraints including complexity and the cost of sample preparation for microbial analysis from food samples, time period for the detection of pathogens, and high cost and specialized resources required for advanced molecular assays. To address some of these key challenges, this study illustrates a simple and rapid colorimetric detection of target bacteria in distinct food matrices, including fresh produce, without prior isolation of bacteria from a food matrix. This approach combines bacteriophage-induced expression of an exogenous enzyme, alkaline phosphatase, the specific colorimetric substrate that generates insoluble color products, and a simple filtration method to localize the generation of colored signal. Using this approach, this study demonstrates the specific detection of inoculated Escherichia coli in coconut water and baby spinach leaves. Without isolating bacteria from the selected food matrices and using a food sample size that is representative of industrial samples, the inoculated samples were added to the enrichment broth for a short period (5 h) and incubated with an engineered bacteriophage T7 with a phoA gene. The incubation period with the engineered bacteriophage was 30 min for liquid samples and 2 h for fresh produce samples. The samples were then filtered through a 0.2-micron polycarbonate membrane and incubated with a colorimetric substrate, i.e., nitro blue tetrazolium/5-bromo-4-chloro-3-indolyl phosphate (NBT/BCIP). This substrate forms a dark purple precipitate upon interactions with the released enzyme on a filter membrane. This approach successfully detected 10 CFU/ml of E. coli in coconut water and 102 CFU/g of E. coli on baby spinach leaves with 5 h of enrichment. Success of this approach illustrates potential for detecting target bacteria in food systems using a simple visual assay and/or quantitative colorimetric measurements.

Phthalocyanine pigments: general principles

AbstractThis chapter describes some of the fundamental chemical and structural principles underlying the phthalocyanine system. Historically, phthalocyanines had been isolated as insoluble blue products in the early twentieth century, although the structures were not established at the time. After the serendipitous re-discovery of metal complex phthalocyanines by industry, and the elucidation of their structures, copper phthalocyanine (CuPc) pigments were introduced industrially in the 1930s to become, and remain, by far the most important blue and green organic pigments, finding almost universal use as colorants for paints, printing inks, plastics, and a wide range of other applications. The phthalocyanines have become one of the most extensively studied classes of organic compounds, because of their unique molecular structures, light absorption properties that produce strong, bright colors, and their exceptionally high stability. While their dominant use is as colorants, they are also of interest for a range of other applications, for example in electronic devices, biological applications, and as catalysts.

Kinetic modeling of phosphorylase-catalyzed iterative \u03b2-1,4-glycosylation for degree of polymerization-controlled synthesis of soluble cello-oligosaccharides

BackgroundCellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes the iterative β-1,4-glycosylation of cellobiose using α-d-glucose 1-phosphate as the donor substrate. Cello-oligosaccharides (COS) with a degree of polymerization (DP) of up to 6 are soluble while those of larger DP self-assemble into solid cellulose material. The soluble COS have attracted considerable attention for their use as dietary fibers that offer a selective prebiotic function. An efficient synthesis of soluble COS requires good control over the DP of the products formed. A mathematical model of the iterative enzymatic glycosylation would be important to facilitate target-oriented process development.ResultsA detailed time-course analysis of the formation of COS products from cellobiose (25 mM, 50 mM) and α-d-glucose 1-phosphate (10–100 mM) was performed using the CdP from Clostridium cellulosi. A mechanism-based, Michaelis–Menten type mathematical model was developed to describe the kinetics of the iterative enzymatic glycosylation of cellobiose. The mechanistic model was combined with an empirical description of the DP-dependent self-assembly of the COS into insoluble cellulose. The hybrid model thus obtained was used for kinetic parameter determination from time-course fits performed with constraints derived from initial rate data. The fitted hybrid model provided excellent description of the experimental dynamics of the COS in the DP range 3–6 and also accounted for the insoluble product formation. The hybrid model was suitable to disentangle the complex relationship between the process conditions used (i.e., substrate concentration, donor/acceptor ratio, reaction time) and the reaction output obtained (i.e., yield and composition of soluble COS). Model application to a window-of-operation analysis for the synthesis of soluble COS was demonstrated on the example of a COS mixture enriched in DP 4.ConclusionsThe hybrid model of CdP-catalyzed iterative glycosylation is an important engineering tool to study and optimize the biocatalytic synthesis of soluble COS. The kinetic modeling approach used here can be of a general interest to be applied to other iteratively catalyzed enzymatic reactions of synthetic importance.

Defective Metal-Organic Frameworks As Unpyrolyzed Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent core electrocatalytic processes in unitized regenerative fuel cells and rechargeable metal-air batteries catalyzed by the costly platinum group metals (PGMs) materials. Finding highly efficient yet durable ORR/OER catalysts using earth-abundant, low-cost materials represents a critical path in lowering cost barrier for widespread commercialization of the devices. We herein report two approaches to construct defective metal-organic frameworks (MOFs) to remove PGM usage for oxygen electrocatalysis.In approach 1, we prepared a coordinately unsaturated Co-MOF as a bifunctional ORR/OER electrocatalyst in an alkaline electrolyte. The Co-MOF possessed great π-π stacking and hydrogen bonding interactions, giving rise to excellent structural and catalytic stabilities. Structure characterizations demonstrated that the coordination of Co(II) was largely unsaturated. Modeling simulations further confirmed that the unsaturated coordination significantly promoted the interactions with molecular water and oxygen and improved the electronic conductivity, leading to enhanced mass and charge transfer properties.In approach 2, we developed a partial ligand removal (or ligand-defect) approach to create mesopores and unsaturated coordination in a Cu-MOF. Since the micropores typically limit the mass-transfer properties (and the capability to store insoluble discharge product for aprotic metal-air battery), the mesopores of the as-prepared MOF showed less steric hindrance, and the unsaturated Cu coordination also boosted electronic conductivity and auxiliary reactant affinity, leading to high Li-air battery capacity.The defective MOFs may open up a new venue for developing effective electrocatalysts with enhanced intrinsic activity towards oxygen electrocatalysis.

Effects of Oxygen Cathode Substrates with Various Carbon Catalysts on the Discharge Capacity of Lithium-Oxygen Battery

Lithium-oxygen batteries have been considered strong candidates to supersede current rechargeable batteries especially lithium-ion batteries. Despite having tremendously high theoretical energy density, the practically achievable energy density is far from commercial application till date. The oxygen electrode is one of the major bottlenecks in maximizing the battery capacity. It is comprised of a porous structure (mainly carbon) with high surface area and sufficient reaction sites. High porosity facilitates lithium ion and oxygen mass transfer and results in high storage capacity for the insoluble discharge product during discharging. The cathode electrode is fabricated by coating a catalyst layer on a porous carbon substrate. The substrate, which contacts with oxygen channels, plays a vital role in mass transfer of oxygen from outside to the reaction sites. Therefore, it is important to select a substrate that does not clog with deposition of Li2O2 particles immediately after discharging begins and allows oxygen to reach the catalyst side for longer period of time.This study investigates the effects of oxygen electrode substrates with various coating materials on the discharge capacity of lithium-oxygen battery. For this purpose, we have compared the discharge capacity of plain carbon cloth, plain carbon paper and carbon cloth or carbon paper coated with carbon catalysts including Vulcan XC, Super P and Graphene Oxide. 1.5mg/cm2 (+/-0.3mg/ cm2) is used as catalyst loading. The electrolyte used in this study is 1M LiTFSI in TEGDME. PTFE (30wt%) is used as a binder. All experiments are conducted at room temperature with pure oxygen supply.With carbon cloth as a substrate, the discharge capacities obtained were 3 to 6 times higher (depending on the carbon catalysts coated) than the capacities obtained with carbon paper. The bare carbon cloth, Vulcan XC, Super P and Graphene oxide with carbon cloth as a substrate have discharge capacities of 0.11 mAh/mg, 13 mAh/mg, 6.8 mAh/mg, 1.5 mAh/mg respectively. On the other hand, the discharge capacities achieved with bare carbon paper, Vulcan XC, Super P and graphene oxide with carbon paper as substrate were 0.02 mAh/mg, 2.4 mAh/mg, 2.7 mAh/mg, 0.28 mAh/mg respectively. The results clearly indicate that the cathode with carbon cloth as a substrate yields significantly higher discharge capacity with all the coating materials as compared with the carbon paper. The different performances of two substrates can be attributed to their structure and pore size distribution. Carbon cloth is composed of flexible woven threads with longer lengths ( ̴ 30µm) and broader pore size distribution (5-200 µm) with peaks at 10, 70 and 100 µm. This type of structure is favorable in reducing tortuosity, enhancing mass transport of oxygen and lithium ion and improving ionic conductivity. On the other hand, the structure of carbon paper comprises of non-woven short carbon fibers ( ̴ 15µm) and smaller pore size distribution range (10-70 µm) with a peak at 50 µm. This renders poor transport of oxygen from outside to the reaction sites leading to lower discharge capacity.The primary function of coating materials is to increase surface area of cathode thereby providing more reaction sites and creating tri-phase boundaries for reaction to take place. These catalysts also have different pore size distributions and resistance to mass transfer. Therefore, various carbon catalysts used yield different discharge capacity with same substrate.

Synthesis of gas-permeable membranes via crosslinking of poly(diphenylacetylene)s by cationic polymerization and radical coupling of side chains

Four types of diphenylacetylene monomers [Me3SiC6H4CCC6H4R; R = OCH2CH2Br (M1), CH2CH3 (M2), OCHCH2 (M3), and CHCH2 (M4)] were synthesized to facilitate the crosslinking of poly(diphenylacetylene)s via post-polymerization modification. Metathesis polymerizations of M1 and M2 using TaCl5/n-Bu4Sn afforded corresponding high-molecular-weight poly(diphenylacetylene)s (P1 and P2; Mw = 1,370,000 and 1,410,000, respectively). However, the polymerization of M3 and M4 afforded a low-molecular-weight polymer (Mw of 6290) and an insoluble product, respectively. The elimination reaction of the side groups in P1 using t-BuOK yielded poly(diphenylacetylene) with vinyl-ether side groups (P1–V). A crosslinked poly(diphenylacetylene) (C–P1–V) was subsequently synthesized via cationic polymerization of the vinyl-ether side groups of P1–V using BF3·OEt2. Another crosslinked poly(diphenylacetylene) (C–P2–Br) was synthesized via radical coupling of the side chains in P2 using N-Bromosuccinimide/benzoyl peroxide. The crosslinked poly(diphenylacetylene)s exhibited relatively low gas permeability among the poly(diphenylacetylene) derivatives, with oxygen permeability coefficients of 35 and 6.8 barrer for C–P1–V and C–P2–Br, respectively.

Kraft Process-Formation of Secoisolariciresinol Structures and Incorporation of Fatty Acids in Kraft Lignin.

The complex chemical structure and the fact that many areas in pulping and lignin chemistry still remain unresolved are challenges associated with exploiting lignin. In this study, we address questions regarding the formation and chemical nature of the insoluble residual lignin, the presence of fatty acids in kraft lignin, and the origin of secoisolariciresinol structures. A mild thermal treatment of lignin at maximum kraft-cooking temperatures (∼170 °C) with tall oil fatty acids (TOFA) or in an inert solvent (decane) produced highly insoluble products. However, acetylation of these samples enabled detailed chemical characterization by nuclear magnetic resonance (NMR) spectroscopy. The results show that the secoisolariciresinol (β–β) structure in kraft lignin is formed by rearrangement of the β-aryl ether structure. Furthermore, fatty acids bind covalently to kraft lignin by reacting with the stilbene structures present. It is highly probable that these reactions also occur during kraft pulping, and this phenomenon has an impact on controlling the present kraft pulping process along with the development of new products from kraft lignin.

Application of Eh-pH Diagrams on Acid Leaching Systems for the Recovery of REEs from Bastnaesite, Monazite and Xenotime

Bastnaesite, monazite and xenotime are rare earth minerals (REMs) that are typical sources for rare earth elements (REEs). To advance the understanding of their leaching and precipitation behavior in different hydrometallurgical processes, Eh-pH diagrams were constructed and modified using the HSC 9.9 software. The aqueous stability of rare earth elements in H2O and acid leaching systems, i.e., the REE-Ligands-H2O systems, were depicted and studied based on the Eh-pH diagrams. This study considers the most relevant lixiviants, their resulting equilibrium states and the importance in the hydrometallurgical recovery of rare earth elements (REMs). A literature review was performed summarizing relevant Eh-pH diagrams and associated thermodynamic data. Shifting stability regions for REEs were discovered with additions of acid ligands and a narrow stability region for soluble REE-(SO4/Cl/NO3) complexes under highly acidic conditions. As such, the recovery of REEs can be enhanced by adjusting pH and Eh values. In addition, the Eh-pH diagrams of the major contaminants (i.e., Fe, Ca and Al) in leaching systems were studied. The resulting Eh-pH diagrams provide possible insights into potential passivation on the particle surfaces due to the formation of an insoluble product layer.

Исследование процессов гидродинамической очистки артезианских вод

The paper aims to investigate hydrodynamic treatment processes of raw (artesian) groundwater to be used for household needs and drinking. The main advantage of hydrodynamic raw water treatment is that a single device, a so-called hydrodynamic vibration generator, is enough to perform the most important processing (deferrization, manganese removal, aeration) without any additional reactants. A hydrodynamic vibration generator contributes to accelerating mass exchange processes without using additional chemical reactants, solely by means of the kinetic energy inherent in the raw water flow undergoing treatment, which is generated when the hydrodynamic properties of the flow itself change dramatically. The generator by itself does not purify water; it processes raw water so as to derive insoluble products by recombining the forms in which the substances to be removed are found in the water, that is, by transforming dissolved manganese and iron compounds into insoluble compounds and decreasing carbon dioxide content in the water so as to precipitate insoluble calcium compounds. The resulting insoluble compounds are easy to remove via further processing in a ceramic membrane filtration system. Hydrodynamic vibration generator efficiency depends on many factors, which means that, when implementing hydrodynamic raw water treatment in real life, obtaining fundamental laws governing the treatment processes as functions of respective parametric characteristics is a necessary stage so as to ensure maximum efficiency. Our experiment confirmed that a phenomenon known as sonoluminescence occurs in raw water subjected to hydrodynamic treatment. We propose a monitoring technology indirectly confirming the efficiency of the hydrodynamic raw water treatment implemented, which is based on recording the sonoluminescence phenomenon via an acoustic technique

A standardised approach for determining heat tolerance in cotton using triphenyl tetrazolium chloride

Improving the heat tolerance of cotton is a major concern for breeding programs. To address this need, a fast and effect way of quantifying thermotolerant phenotypes is required. Triphenyl tetrazolium chloride (TTC) based enzyme viability testing following high-temperature stress can be used as a vegetative heat tolerance phenotype. This is because when live cells encounter a TTC solution, TTC undergoes a chemical reduction producing a visible, insoluble red product called triphenyl formazan, that can be quantified spectrophotometrically. However, existing TTC based cell viability assays cannot easily be deployed at the scale required in a crop improvement program. In this study, a heat stress assay (HSA) based on the use of TTC enzyme viability testing has been refined and improved for efficiency, reliability, and ease of use through four experiments. Sampling factors that may influence assay results, such as leaf age, plant water status, and short-term cold storage, were also investigated. Experiments conducted in this study have successfully downscaled the assay and identified an optimal sampling regime, enabling measurement of large segregating populations for application in breeding programs. The improved HSA methodology is important as it is proposed that long-term improvements in cotton thermotolerance can be achieved through the concurrent selection of superior phenotypes based on the HSA and yield performance in hot environments. Additionally, a new way of interpreting both heat tolerance and heat resistance was developed, differentiating genotypes that perform well at the time of a heat stress event and those that maintain a similar performance level to a non-stressed control.

Multifunctional Composition Based on Surfactants and a Complex of Buffer Systems to Enhance Oil Recovery of High-Viscosity Oil Deposits

To enhance oil recovery of high-viscosity oil deposits in the temperature range of 20-210 °C, a multifunctional composition with adjustable viscosity and high oil-displacing ability has been developed based on surfactants, aluminum and ammonium salts, an adduct of inorganic acid, carbamide and polyol. High buffer capacity of the composition in a wide pH range, 2.5-10 units pH, is provided by a complex of buffer systems: in the acidic range of pH, 2.5-4.0, the system “polyolboric acid and its salt”, in the alkaline range of pH – anammonia-borate buffer system. The composition has a low interfacial tension, a prolonged reaction with carbonate rocks, prevents the precipitation of insoluble reaction products, and increases the permeability of reservoirs. The composition is both oil-displacing and flow-diverting, it provides an enhance in the oil recovery factor, both due to the increase in the displacement factor and the the reservoir sweep by waterflooding or thermal steam stimulation

Anodic dissolution characteristics of Inconel 718 in C6H5K3O7 and NaNO3 solutions by pulse electrochemical machining

The mechanism by which electrolytic products are removed during ECM of Inconel 718 in a C6H5K3O7 electrolyte was clarified. Experimental results revealed that Cit3− ions decrease the amounts of flocculent and insoluble products in the machining region considerably. The resulting passivating film presented a looser, more porous structure than that from a NaNO3 solution. This made the Inconel 718 more prone to electrochemical corrosion. The uniformity and microscale nature of the micro-pit structure dispersed on the machined surface improved substantially as the current density increased. This improved the surface quality dramatically. Finally, the anodic dissolution characteristic models were established.

Conversion of aniline contaminant to valuable polyaniline polymers from wastewater under alkaline conditions

Abstract Although the oxidation processes mediated by persulfate (PS) and peroxymonosulfate (PMS) attract more attention in the degradation of various recalcitrant contaminants, the high concentrations of oxidants required for the low concentrations of contaminants always limit their large-scale applications. In this work, aniline can be effectively oxidized by CuO and PS under pH-neutral and alkaline conditions. The increased observed rate constant (kobs) values with increasing pHs indicate that the oxidation of aniline is facilitated by solution OH−. Meanwhile, the low ratios between the removed PS and aniline (1.19 at pH 7.0 and 1.68 at pH 12.0) indicate the high catalytic oxidation efficacy of the CuO-PS system. The insignificant contributions of SO4 −, OH, 1O2 and O2 − to aniline oxidation in quenching experiments and EPR analysis suggest that PS is likely activated on the surface of CuO via the non-radical pathway. The presence of carbon-centered radicals (CCRs), as well as UV and GC MS analysis, indicates the important intermediates of PhNH2 + and PhNH radicals during the oxidation process, revealing that separate transfer of an electron from aniline to the activated PS, followed by subsequent abstraction of a H+ by OH− to form PhNH are two important steps in the oxidation process. Further coupling of PhNH radicals results in the formation of insoluble polyaniline polymers at pHs 7.0 and 12.0. The high thermal stability and ideal pseudo-capacitive properties of the insoluble products indicate that the polyaniline produced from aniline wastewater can be used for high-temperature-resistant materials or capacitors. This study provides an efficient alternative to turn aniline waste to polyaniline polymers.

Electrochemical migration behavior of low-temperature-sintered Ag nanoparticle paste using water-drop method

The electrochemical migration (ECM) behavior of low-temperature-sintered Ag nanoparticle paste electrode was investigated using water-drop method. The effects of applied direct current bias voltage and NaCl concentration on ECM behavior were discussed. Results show that: at low NaCl concentration levels, mean time to failure caused by ECM decreased with increasing NaCl concentration due to the increase of solution conductivity; at medium NaCl concentration levels, dendrite growth was retarded due to the formation of AgOH or other insoluble products, while at high NaCl concentration levels, due to the turbulent hydrogen evolution, the second spreading of water drop resulted in the circuit broken and thus inhibited ECM behavior. Moreover, mean time to failure decreased with the rising applied bias voltage. More importantly, hexadecyltrimethylammonium chloride (CTAC) was proved to act as an effective inhibitor to migrate dendrite growth by selected adsorption. And the ECM inhibition efficiency increased with the concentration of CTAC. Relevant mechanisms of ECM behavior and ECM inhibition effect of CTAC for low-temperature-sintered Ag nanoparticle paste were proposed.

From a hyperbranched polyimide to a microporous network polyimide via reaction temperature change and its application in gas separation membranes

We prepared a series of microporous network polyimides (MN‐PIs) derived from tris(4‐aminophenyl)amine (TAPA), and three commercial dianhydrides such as 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,3′,4,4′‐ benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic anhydride (PMDA). Particularly, in order to obtain these free‐standing membranes before forming insoluble gel products, the self‐crosslinking rate between dianhydride and triamine functional groups was controlled via reaction temperature changing. All MN‐PIs exhibited outstanding thermal stability with high glass transition temperatures (Tg) exceeding 305°C. Gas transport experiments demonstrated that 6FDA‐derived MN‐PI membrane showed the highest gas permeabilities and well‐maintained gas‐pair selectivities rooting from the bulky ‐C(CF3)2‐ linkage groups that inhibited efficient chain‐packing and the comparable backbone rigidity relative to that of PMDA‐derived MN‐PI. The comprehensive gas transport properties of 6FDA‐based MN‐PI membrane approached the 2008 Robeson upper bound for CO2/CH4, showing CO2 permeability of 37.4 Barrer and ideal selectivity of ~56.7. Physical aging monitored for 75 days lead to a decline in gas permeabilities (e.g., 7.8% and 18.4% drop for O2 and N2) and moderately enhanced selectivity (corresponding 14.3% rise for O2/N2). Additionally, 6FDA‐derived MN‐PI also possessed excellent mixed CO2/N2 gas selectivity of 32.9, roughly equaling to its pure gas transport behaviors, which are probably related to the Lewis acid‐base interactions between CO2 and N atoms of tertiary amine in TAPA segments.

Phosphorus × Other Plant Nutrient Interactions, Reaction Products, Anion Exchange and Phosphate Fixation in Soil and Strategies to Increase Availability of the Native and Applied P to Crop Plants-A Mini Review and Critique

Phosphorus is a major plant nutrient obtained from non-renewable phosphate rock, which is not much available in India. Over and above in this its recovery efficiency in crops hardly exceeds 15-20 per cent. Utmost care is therefore required in its use. Phosphorus applied to soil gets fixed by the formation of insoluble reaction products by reacting with Fe and Al in acid soils and with calcium in saline and alkaline soils. Two techniques used for identification of reaction products are X-ray diffraction and solubility product principle. In addition, phosphate ions are also held on Fe and Al hydroxides by anion exchange. The reaction products identified are variscite and strengite minerals in acid soils and dicalcium phosphate and hydroxy apatite in calcareous soils. Methods to increase phosphorus recovery by crops include: 1) addition of organic matter to soils; 2) addition of sulphur to compost or to ground rock phosphate or directly to soil and use of phosphorus solubilising organisms including VAM/AM along with ground rock phosphate.

Comprehensive Study of Hydrothermal Extraction of Pectin From Sugar Beet Pulp

In this work one-stage, no presence of acidic catalyst hydrothermal extraction of pectin from sugar beet pulp (SBP) as a batch process was investigated, leading to increasing the value of this by-product of sugar beet industry. The comprehensive study of the effect of the extraction temperature and the extraction time on the yield and composition of the pectin-enriched products, the water soluble product fractions and the water insoluble product fractions, were used that are feasible for industrial upscaling. It was shown that the highest yield of satisfactory purity of pectin extract (136.3 g kg−1) was obtained at a temperature of 120 °C and a holding time of 20 min. Both further increase of the extraction temperature and extending extraction time favor the occurrence of partial hydrothermolysis of pectin and hemicellulose contained in the SBP, leading to the production of uronic acids, monosaccharides, carboxylic acids and furfurals. In the applied extraction conditions, other components of the SBP: cellulose, lignin and protein did not undergo depolymerization and were still present in the solid post-extraction residue. This work provides an important method for the recovery of pectin from SBP using environmentally friendly technique and should help to facilitate further studies to develop a new process for the hydrothermal production of pectin from waste biomass.

3D-printed cartridge system for in-flow photo-oxygenation of 7-aminothienopyridinones

A 3D-printed polypropylene (PP) continuous-photoflow cell based on a modular cartridge system was developed for the photo-oxygenation of 7-aminothieno[3,2-c]pyridin-4(5H)-ones, using ambient air as the sole co-reactant. This strategy takes advantage of the versatility of 3D-printing to construct cost-effective meso-scale reactors. In addition to scalability, a short residence time (tR 2 min) in 100-W blue LED light that minimizes the formation of dark, insoluble decomposition products is a tangible benefit of this technology.

Dark Iron-Catalyzed Reactions in Acidic and Viscous Aerosol Systems Efficiently Form Secondary Brown Carbon.

Iron-driven secondary brown carbon formation reactions from water-soluble organics in cloud droplets and aerosols create insoluble and soluble products of emerging atmospheric importance. This work shows, for the first time, results on dark iron-catalyzed polymerization of catechol forming insoluble black polycatechol particles and colored water-soluble oligomers under conditions characteristic of viscous multicomponent aerosol systems with relatively high ionic strength (I = 1-12 m) and acidic pH (∼2). These systems contain ammonium sulfate (AS)/nitrate (AN) and C3-C5 dicarboxylic acids, namely, malonic, malic, succinic, and glutaric acids. Using dynamic light scattering (DLS) and ultra high pressure liquid chromatography-mass spectrometry (UHPLC-MS), we show results on the rate of particle growth/agglomeration and identity of soluble oligomeric reaction products. We found that increasing I above 1 m and adding diacids with oxygen-to-carbon molar ratio (O:C > 1) significantly reduced the rate of polycatechol formation/aggregation by a factor of 1.3 ± 0.4 in AS solution in the first 60 min of reaction time. Using AN, rates were too slow to be quantified using DLS, but particles formed after 24 h reaction time. These results were explained by the relative concentration and affinity of ligands to Fe(III). We also report detectable amounts of soluble and colored oligomers in reactions with a slow rate of polycatechol formation, including organonitrogen compounds. These results highlight that brown carbon formation from iron chemistry is efficient under a wide range of aerosol physical states and chemical composition.

Free-standing nitrogen doped graphene/Co(OH)2 composite films with superior catalytic activity for aprotic lithium-oxygen batteries

The recent boom in large-scale energy storage system promotes the development of lithium-oxygen batteries because of their high theoretical energy density. However, their applications are still limited by the sluggish kinetic, insoluble discharge product deposition and the undesired parasitic reaction. Herein, the free-standing nitrogen doped reduced graphene oxide/Co(OH)2 (NRGO/Co(OH)2) composite films were prepared by a facile hydrothermal method. The NRGO/Co(OH)2 composite films display interconnected three-dimensional conductive network, which can not only promote the diffusion of O2 and the transport of electrolyte ions, but also provide abundant storage space for discharge products. Moreover, the introduction of nitrogen-containing functional groups results in improved conductivity and electron adsorption ability, which can facilitate electron transport and enhance the surface catalytic activity. Combining with excellent catalytic performance, the lithium-oxygen batteries with NRGO/Co(OH)2 composite film cathodes deliver low charge overpotential and excellent cycling performance.