N2 Bubbling Research Articles

Degradation of atenolol by UV/peroxymonosulfate: Kinetics, effect of operational parameters and mechanism

Photoactivation of peroxymonosulfate (PMS) with UV (254nm) irradiation was used to generate the SO4--based advanced oxidation process, which was adopted to degrade atenolol (ATL) in water. The second-order reaction rate constants of ATL with HO and SO4- were determined, and the effects of operational parameters (dose of PMS, solution pH, HCO3-, humic acids (HA), and N2 bubbling) were evaluated as well. Finally the main transformation intermediates were identified and possible degradation pathways were proposed. The results showed that there was a linear positive correlation between the degradation rate of ATL and specific dose of PMS (1–16M PMS/M ATL). Increasing solution pH from 3 to 9 promoted elimination of ATL due to the pH-dependent effect of PMS photodecomposition, while further pH increase from 9 to 11 caused slowing down of degradation because of apparent conversion of HO to SO4-. 1–8mM HCO3- exerted no more than 5.3% inhibition effect on ATL destruction, suggesting HCO3- was a weak inhibitor. Absorption (or complexation) and photosensitized oxidation induced by HA improved ATL degradation during the first minute of degradation process, whereas photon competition and radical scavenging effects became the leading role afterward. Bubbling with nitrogen enhanced the degradation rate due to the stripping of dissolved oxygen. Hydroxylation of aromatic ring, cleavage of ether bond, oxidation of primary and secondary amine moieties, and dimerization were involved in the degradation mechanism of ATL by UV/PMS.

Estimation of N2 and N2O ebullition from eutrophic water using an improved bubble trap device

Ebullition pathway of N2 and N2O emission and its importance on nitrogen loss were quantified during a survey of a eutrophic pond located at the subtropical climate zone in China. Using an improved bubble trap device, in situ collection of N2 bubbles was achieved by avoiding the contamination of N2 in the air. Measurements using the device indicated very high ebullition rates (36.3–366.7mlm−2h−1) and N2 ebullition flux (0.025–0.297gm−2h−1) at warmer months of September and October. The ebullition rates and N2 ebullition fluxes dropped sharply in colder months of December and January, ranged 2.5–15.9mlm−2h−1 and 0.002–0.016gm−2h−1, respectively. Distinct spatial variation of ebullition rates, and N2 and N2O ebullition fluxes were observed, with the highest rate at the heavy sediment location. Ebullition of N2O was a very minor fraction of total gaseous nitrogen released to air. The data demonstrated that ebullition could contribute greatly to biogenic N2 fluxes in eutrophic waters with significant bubble emission.

Simultaneous Enhancement of Methylene Blue Degradation and Power Generation in a Microbial Fuel Cell by Gold Nanoparticles

This study examined the effect of positively charged gold nanoparticles [(+)AuNPs] on the enhancement of methylene blue (MB) degradation in a microbial fuel cell (MFC) cathode. Complete MB degradation and a maximum electricity production of 36.56 mW/m2 were achieved simultaneously. The MFC performance and MB degradation were found to be strictly dependent on the cathodic conditions, such as N2 bubbling, air bubbling, and addition of H2O2. MB was reduced rapidly under anaerobic conditions, whereas complete oxidative mineralization of MB occurred in the presence of dissolved oxygen (DO) or H2O2. (+)AuNPs enhanced the electricity generation in the MFCs involving MB degradation owing to its electron-relay effect. The presence of both (+)AuNPs and H2O2 produced the greatest enhancement in MB degradation. After 5 h, almost all of the MB (98%) and chemical oxygen demand (COD) (96%) had been removed in the presence of (+)AuNPs, whereas only 57.4% of the MB and 40% of the COD had been removed in the absence of (+)AuNPs.

CO2 switchable nanoparticles: reversible water/organic-phase exchange of gold nanoparticles by gas bubbling

Gold nanoparticles capped with oleylamine can be effectively transferred from an organic solvent to water in the presence of an acetamidine surfactant by CO2 bubbling and then effectively reverted back to the organic phase by N2 bubbling.

Utilization of minute-bubble technique on crystallization: Application to antisolvent crystallization of sodium chloride

A crystallization technique to accelerate the nucleation of NaCl crystals utilizing local supersaturation regions around the gas-liquid interfaces of nitrogen (N2) minute-bubbles was developed. The effects of N2 bubble supply and minimizing bubble diameter on antisolvent crystallization phenomena of NaCl were examined. The initial concentration of NaCl in the saturated solution was set at 5.50mol/l, and ethanol (EtOH) was added as an antisolvent to the saturated NaCl solution where the added volume ratio of EtOH became 10vol%. N2 minute-bubbles with an average bubble diameter (dbbl) of 40μm were continuously supplied to the suspended solution using a self-supporting bubble generator, and NaCl was crystallized. Furthermore, dbbl was varied in the range of 100–2000μm by changing the hole size (5–120μm) on the gas dispersion plate using a dispersing-type bubble generator. Consequently, the average size of NaCl crystals while supplying N2 minute-bubbles was about 7μm at 1min crystallization and almost same profile in size distribution was obtained independent of the crystallization time. When minute-bubbles were not supplied, the average size was shifted up to 13μm and the size distribution width was expanded in comparison with that obtained under supplying N2 minute-bubbles. The supply of minute-bubbles at a dbbl of 40 μm into antisolvent crystallization of NaCl is effective in obtaining fine crystals with narrow distribution width.

Polymorph control of glycine by antisolvent crystallization using nitrogen minute-bubbles

In this study, utilizing the gas–liquid interfaces around minute-bubbles as new nucleation fields, a crystallization technique to control polymorphism under constant temperature was developed. Glycine, which has three polymorphs of stable γ-form, metastable α-form, and unstable β-form under atmospheric temperature and pressure, was crystallized using the antisolvent method supplying nitrogen (N2) minute-bubbles. In the regions near the minute gas–liquid interfaces, higher local supersaturation generates because of the accumulation of glycine and antisolvent caused by the negative electric charge on the minute-bubble surface; hence, the nucleation rate is higher and a less stable polymorph can be expected to crystallize. At a solution temperature of 303K, methanol as an antisolvent was mixed into the saturated glycine solution. The mixture ratio of methanol was varied in the range of 20–60vol% to control supersaturation of glycine in the bulk solution. While mixing methanol with the saturated glycine solution, N2 bubbles with different average diameters of 10–2000μm were continuously supplied to the mixed solution, and glycine was produced within the crystallization time of 5min. Antisolvent crystallization without the bubble supply was carried out for comparison. The results indicated that bubble injection and minimizing bubble size led to the expansion of the generation region of β-form and the reduction of supersaturation ratio in the bulk solution necessary for the generation of β-form during antisolvent crystallization.

Visible-light-driven photocatalytic and photoelectrocatalytic debromination of BDE-47 on a macroporous silicon/graphene heterostructure

Macroporous silicon/graphene (MPSi/Gr) heterostructure was fabricated by electrophoresis depositing Gr sheets on the surface of MPSi and then annealing the samples to improve adhesion and electrochemical property. In the photoelectrochemical measurements, MPSi/Gr heterostructure displayed stable and high photocurrent compared with MPSi. The stability profits from protection of Gr layer, and the enhancement of photocurrent is ascribed to effective photogenerated charge separation of MPSi/Gr heterostructure. The results of photocatalytic and photoelectrocatalytic debromination of BDE-47 showed MPSi/Gr possesses excellent photocatalytic capability, and this capability can be enhanced by applying a bias potential. The kinetic constant of MPSi/Gr (1.13h−1) heterostructure in photoelectrocatalytic process was five times as much as that of MPSi/carbon film heterostructure (0.22h−1), indicating Gr, as a charge collector which can promote separation and transfer of photogenerated carries, is superior to other carbon materials for building heterostructures. The majority (87.1%) of debromination was induced by visible light which was confirmed by comparing reaction efficiency under xenon lamp irradiation to that under the same lamp irradiation via a 422nm filter. According to the results of photocatalytic debromination experiments with O2 or N2 bubbling, debromination mechanism of BDE-47 was proposed as a reductive debromination by photogenerated electrons.

Solvent-free lipase-catalysed synthesis of saccharide-fatty acid esters: closed-loop bioreactor system with in situ formation of metastable suspensions

Saccharide-fatty acid esters – biodegradable, biocompatible and non-ionic bio-based surfactants derived from inexpensive renewable agricultural sources, utilized in foods, cosmetics and pharmaceuticals, have been synthesized under solvent-free conditions using a closed-loop system operated under continuous recirculation consisting of a reservoir, a peristaltic pump and a packed-bed bioreactor containing immobilized Rhizomucor miehei lipase (RML). Metastable suspensions of saccharide crystals were formed through continuous stirring in the reservoir with an in-line filter of 180 µm normal size preventing larger crystals from clogging the tubing. The initial reaction medium consisted of oleic acid/fructose-oleic acid esters 95/5 w/w, with saccharide added periodically to the reservoir to replace consumed acyl acceptor substrate. The liquid-phase water concentration was retained at a previously determined optimal value of ∼0.4 wt % through free evaporation of the co-product, water, in the reservoir during the initial phase of the reaction, and N2(g) bubbling and vacuum pressure after 40 h of reaction. After 200 h, the reaction mixture contained 84 wt % ester, of which 90% of the ester consisted of monoester. Equivalently, the productivity was 0.195 mmolEster h− 1 gRML− 1. The resultant technical grade product can potentially be used directly, without further purification. A mathematical model based on mass balances and a zeroth-order kinetic model was successfully developed to predict the concentration of substrates (oleic acid and saccharide) in the reservoir during the time course of reaction.

Photo-induced DNA scission by Cu(ii)-meso-tetrakis(n-N-methylpyridiniumyl)porphyrins (n = 2, 3, 4) and their binding modes to supercoiled DNA

The photo-induced cleavage of pGEM-7zf-NIS super-coiled DNA by Cu(ii)-meso-tetrakis(n-N-methylpyridiniumyl)porphyrins (n = 2, 3, 4 referred to as o-, m- and p-CuTMPyP, respectively) and their binding mode were investigated in this study. m-CuTMPyP was most efficient in cleavage than o- and p-CuTMPyP isomers. Cleavage was suppressed by N(2) bubbling, suggesting that the cleavage occurred by an oxidative cleavage mechanism. Sodium azide, an (1)O(2) quencher, and DMSO, a hydroxyl radical scavenger, inhibited cleavage, indicating that hydroxyl radicals and singlet oxygen were likely reactive species responsible for the cleavage. Reduced linear dichroism spectroscopy showed angles of o-CuTMPyP's electric transition moments, in which the periphery pyridinium ring was prevented from free rotation, of 59° and 61° with respect to the local DNA helix axis. The spectra of m- and p-CuTMPyP complexed with pGEM-7zf-NIS DNA were characterized by large signals in the Soret band, coincident with those of known intercalated porphyrins.

Solubility of Nitrogen in High Manganese Steel (HMnS) Melts: Interaction Parameter between Mn and N

Nitrogen solubility in Fe-Mn melts was measured using a N2 bubbling and sampling method at temperatures from 1823 K to 1923 K (1550 °C to 1650 °C) for manganese content to about 25 mass pct. The effect of temperature on the nitrogen solubility was well described based on the thermodynamic behavior of Fe-Mn system. Furthermore, the interaction parameter between Mn and N was evaluated as a function of temperature. The present results can be used in thermodynamic analyses of the formation of nitride compounds such as AlN or TiN in high manganese steel melts for example, transformation induced plasticity (TRIP) and twin induced plasticity (TWIP) aided steels as well as high Mn-N alloyed stainless steels.

Effect of Sampling Methods on N Detection in High Nitrogen Steel

The effect of sampling methods on the detection of N content in the high nitrogen steel (HNS) was studied by variance analysis method. In the experiments, two kinds of samples (rod sample and chip sample) were chosen. It was showed that when the N content was in the range of 0.06%∼0.4%, the results obtained by two methods were almost the same, indicating that both were suitable to identify the N in the steel. However, when the N content was higher than 0.4%, the result obtained using chips as sample was lower than that using rod. The N2 bubble in the rod sample might cause error since it didn't comprise the N content. Hence, the N content could be reflected more accurately by the chip samples. Based on the difference of N content detected by two methods, the shrinkage rate was analyzed theoretically and found to be inversely proportional to the pressure of N2 bubbles in steel.

Physical properties and chemical efficiency of an underwater dc discharge generated in He, Ar, N2 and air bubbles

A dc excited discharge generated in bubbles (He, Ar, Air, N2) in liquid phase is investigated in this work. Voltage/current characteristics and emission spectra of the discharge are recorded in the current range 10–30 mA. Electron density in the discharge is measured from Stark broadening of the Hβ line and is of the order of 2–6 × 1020 m−3, depending on the feed gas. Estimation of electron temperature is carried out based on the balance of charged particles. Gas temperature is estimated by the slope of the Boltzmann plot and by the simulation of the OH band with different , and Tvib. Rotation temperature in the He discharge is 1200 K at I = 10 mA and linearly increases with current up to 1600 K. In the plasma of molecular gases the temperature is higher and almost constant at different currents. Chemical efficiency of the plasma is measured by the production of H2O2 and by the destruction of Direct Blue 106 dye. The highest energy consumption of H2O2 generation is achieved in the air discharge and it decreases up to 50% in the He plasma. Maximal efficiency of dye destruction is observed in the N2 plasma characterized by an energy consumption of dye decomposition of 0.86 g kWh−1.

Optimization of the Solvent‐Free Lipase‐Catalyzed Synthesis of Fructose‐Oleic Acid Ester Through Programming of Water Removal

AbstractFructose oleate, an environmentally‐friendly biobased surfactant, was prepared using solvent‐free suspensions of saccharide in a mixture of acyl donor and monoester (the latter present at ≥5 wt% initially) continuously recirculated through a closed‐loop packed bed bioreactor (PBBR)‐based system at 53 °C, with the PBBR containing immobilized Rhizomucor miehei lipase (Lipozyme®IM, Novozymes, Franklinton, NC, USA). To replenish the acyl acceptor consumed during the time course of reaction, the medium was isolated, fructose added, and a suspension formed by rigorous stirring at 80 °C for 6 h followed by centrifugation to remove larger particles, with the placement of the acyl acceptor replenishment treatments during the time course of reaction were optimized. Water removal via free evaporation was augmented during the latter portion of the time course (using a molecular sieve packed column, N2 bubbling, vacuum pressure, or a combination of the latter two), with an optimal performance achieved when initiating N2 + vacuum ( removal rate) upon reaching 60% ester, to maintain the liquid‐phase water content near 0.40 wt%. When employing the above‐mentioned conditions, 92.6 wt% fructose oleate was produced within 132 h, yielding a productivity of .

Uniform ZnSe microspheres self-assembled from ZnSe polyhedron shaped nanocrystals

Large-scale and uniform ZnSe solid and hollow microspheres have been prepared via controllable self-assembly of ZnSe faceted nanocrystals under hydrothermal conditions. During the process, using the surfactant or not plays a key role in the ZnSe faceted nanocrystals' self-assembly into the ZnSe microspheres. Using PVP as the surfactant, the ZnSe monodisperse faceted shaped (including cubes, hexagons, and pentagons) nanocrystals with a diameter of ∼50 nm have been obtained; without using PVP surfactant, the ZnSe solid microspheres with a diameter of ∼3 μm have been achieved by the self-assembly of ZnSe faceted shaped nanocrystals; while using oleyl amine as the surfactant, which combines with N2 bubbles from the decomposition of N2H4·H2O, forming a new “soft-template”, the ZnSe hollow microspheres have been synthesized through as-called “soft-template” process. Meanwhile, hydrothermal temperature, time, and reducing agent have significant effects on the surface morphology of the ZnSe microspheres, i.e., a suitable temperature (e.g., 180 °C), longer reaction time, and using a small quantity of N2H4·H2O could be beneficial to the growth of the well-defined ZnSe faceted nanocrystals and their self-assembly into microspheres. A possible mechanism for the formation of ZnSe nanocrystals and their self-assembly into ZnSe microspheres has been proposed.

Sodium Fluoride at the Air/Water Interface

The zeta potentials of a single N2 bubble in near neutral aqueous solutions of 10–5 to 10–2 M NaF have been measured with a rotating cell zetameter. The zeta potentials in the NaF solutions are slightly more negative than those of comparable NaI concentrations. A simple interpretation of this observation is that the small size of the fluoride ion leads to its stronger adsorption at the interface, despite its smaller dielectric decrement. This would not be consistent with independent electrospray results from 100 µM solutions that bromide ion is less strongly adsorbed than iodide ion, i.e. that surface affinity increases with ion size. An alternative interpretation of the fluoride experiment is that the fluoride surface affinity is the consequence of stronger ion pairing with the NaOH that spontaneously forms at the interface.

Gas–liquid flow stability and bubble formation in non-Newtonian fluids in microfluidic flow-focusing devices

This communication describes the gas–liquid two-phase flow patterns and the formation of bubbles in non-Newtonian fluids in microfluidic flow-focusing devices. Experiments were conducted in two different polymethyl methacrylate (PMMA) square microchannels of, respectively, 600 × 600 and 400 × 400 μm. N2 bubbles were generated in non-Newtonian polyacrylamide (PAAm) solutions of different concentrations. Slug bubble, missile bubble, annular and intermittent flow patterns were observed at the cross-junction by varying gas and liquid flow rates. Gas and liquid flow rates, concentration of PAAm solutions, and channel size were varied to investigate their effect on the mechanism of bubble formation. The bubble size was proportional to the ratio of gas/liquid flow rate for slug bubbles and could be scaled with the ratio of gas/liquid flow rate as a power–law relationship for missile bubbles under wide experimental conditions.

Formation mechanism and size prediction of bubble in opposite-flowing T-shaped microchannel

Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.

Strong Specific Hydroxide Ion Binding at the Pristine Oil/Water and Air/Water Interfaces

Despite claims, based largely on molecular dynamics simulations, that the surface of water at the air/water interface is acidic, with a positive charge, there is compelling experimental evidence that it is in fact basic, with a negative charge due to the specific adsorption of hydroxide ions. The oil/water interface behaves similarly. The pH dependence of the zeta potentials of oil drops has been measured by two very different techniques: on a single drop in a rotating electrophoresis cell and on about 10(14) submicrometer drops in a 2 vol % emulsion by an electroacoustic method to give similar results with a sigmoidal pH dependence characterized by an isoelectric point at pH 2-3 and a half adsorption point about pH 5.5, or at 10(-8.5) M hydroxide ion. This indicates that hydroxide ion is absorbed much more strongly than other anions. The pH dependence of a single N(2) bubble has also been measured and has the same pH dependence, independently of whether HCl or HI is used to adjust the pH. These similarities between the pH dependences of the zeta potentials of air bubbles and oil drops, as well as those reported from streaming potentials on solid inert surfaces such as Teflon, indicate that water behaves similarly, with only subtle differences, at each of these low dielectric hydrophobic surfaces, with an isoelectric point of pH 2-4. In acidic solutions at pH's below the isoelectric point, the surface is indeed positive, consistent with spectroscopic observations of the adsorption of hydrogen ions.

WO3 thin film coating from H2O-controlled peroxotungstic acid and its electrochromic properties

We prepared PTA coating solution by hot plate evaporation, N2 bubbling evaporation, and rotary evaporation. N2 bubbling and rotary evaporation are very efficient way to synthesize PTA which reduces the synthesis process time to 1/5, compared to hot plate evaporation method. Another strong point is that N2 bubbling and rotary evaporation make it possible to control excess hydrogen peroxide and water contents in PTA. The PTA formula were WO3·0.13H2O2·10.0H2O for hot plate method, WO3·0.16H2O2·7.1H2O for N2 bubbling method, and WO3·0.15H2O2·3.00H2O for rotary evaporation method. Thermal analysis and mass spectroscopy analysis show that water is evaporated at around 100 °C and hydrogen peroxide is dissociated at the range of 150 and 250 °C. Amorphous phase of WO3 thin film prepared from rotary evaporated PTA solution has the best electrochromic property, light transmission difference from 91% at its bleached state and 5.5% colored state, and charge density of 22 mC/cm2. It is thought that the control of excess hydrogen peroxide and water contents in PTA is very important to enhance the electrochromic properties of WO3 thin film.

Re-examination of Dynamics of Polyeletrolytes in Salt-Free Dilute Solutions by Designing and Using a Novel Neutral−Charged−Neutral Reversible Polymer

By using the Staudinger ligation to attach 4-{5′-[1′′-(dimethylamino)-ethylideneamino]pentyl}-1-methyl-2-(diphenylphosphino)terephthalate to poly(p-azidomethylstyrene)-co-polystyrene (PAMS-co-PS), we successfully prepared a novel polymer that can undergo a neutral−charged−neutral transition in DMF with 0.5% H2O when the solution is alternatively bubbled with CO2 and N2. Such a reversible change is confirmed by its sharp conductivity variation. Armed with this polymer, we re-examined dynamics of salt-free polyelectrolyte dilute solutions by using laser light scattering (LLS). As expected, there exists only one diffusive relaxation mode in the neutral state. The bubbling of CO2 decreases the scattering intensity and splits this initial diffusive relaxation mode into a fast and a slow diffusive mode, and their scattering intensity contributions are independent of the scattering angle, indicating that the slow mode is not related to some scattering objects larger than the LLS observation length (∼35 nm < 1/q < ∼190 nm). The bubbling of N2 gradually diminishes the slow mode and returns both the scattering intensity and solution dynamics back to their initial neutral state. The change from dilute to semidilute solution slows the fast relaxation down and suppresses the slow mode. On the other hand, the addition of LiBr (50 mM) can completely suppress electrostatic interaction.