Hydroxyl Radical Oxidation Processes For The Removal Of Triazine From Natural Water

The purpose of this study was to point out processes that can provide triazine oxidation via hydroxyl radical production in a water treatment line. We focus our attention on:

- oxido-flocculation, using Fe²⁺, H₂O₂

- inter-oxidation, using O₃, H₂O₂ and eventually an heterogeneous catalyst.

- disinfection, using UV, O₃ and H₂O₂ combinations.

Results show that triazines can be removed by all these processes with different efficiencies. At full scale, the O₃/H₂O₂ process presents the best performances from an economical and technical point of view.     

Synthesis of Porous Submicron Gd0.1Ce0.9O1.95 Particles by Carbon Nanoparticle-Addition Ultrasonic Spray Pyrolysis (CNA-USP) and Nanoparticle Preparation by Ball Milling

A new ultrasonic spray pyrolysis method, called carbon nanoparticle-addition ultrasonic spray pyrolysis (CNA-USP), is developed to synthesize nanoparticles of electrolyte material for solid oxide fuel cell applications. In CNA-USP, carbon nanoparticles are added in a precursor solution. First, Gd_0.1Ce_0.9O_1.95 (GDC) particles were synthesized from an aqueous solution of Ce(NO₃)₃ 6H₂O and Gd(NO₃)₃ 6H₂O by using the CNA-USP method. The resulting synthesized GDC particles were agglomerated, porous, primary particles on the order of 10 nm in diameter. EDX images revealed uniform distributions of Ce, Gd, and O in these porous particles. Then, these agglomerated, porous submicron GDC particles were ground into primary nanoparticles by ball milling for 24 h. The average diameter of the ground GDC nanoparticles was about double of their average crystallite size.

Copyright 2014 American Association for Aerosol Research     

Cluster formation mechanisms of titanium dioxide during combustion synthesis: Observation with an APi-TOF

Few studies reported the formation of Ti-containing clusters in the initial stages of TiO₂ flame synthesis. The conversion from synthesis precursor to TiO₂ monomers was commonly assumed to take place through global reaction such as thermal decomposition and/or hydrolysis at high temperatures. More recent studies have been able to identify stable intermediates of Ti-containing monomers, most commonly Ti(OH)₄, as the final step before the formation of TiO₂. However, no larger Ti-containing cluster formation mechanisms or interactions between these monomers have been tracked. To investigate cluster formation pathways of TiO₂ during flame synthesis, Charged clusters were measured in an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer. TiO₂ nanoparticles were synthesized by adding titanium tetraisopropoxide (TTIP) precursor to a premixed CH₄/O₂/N₂ flat flame aerosol reactor. Pure TiO₂ clusters were not detected by the APi-TOF. Results from measured mass spectra and mass defect plots show that for positively charged clusters, the abstraction of CH₂ groups occurs simultaneously with the clustering of larger intermediate organometallic species. For negatively charged clusters, NO_x formation pathways in the flame may play a role during the initial stages of TiO₂ formation, since a lot of Ti-containing clusters were attached with nitrate-related species. These research findings provide insights on quantum dot synthesis and molecular doping where rapid dilution of the flame synthesized nanoparticles is needed to better control the particle size and chemical composition. The possible influences of and potential artifacts brought by the dilution system on observing the incipient particle formation in flames were also discussed.

© 2017 American Association for Aerosol Research     

Aerosol Process for the In Situ Coating of Nanoparticles with a Polymer Shell

This article presents a novel method to encapsulate gas-borne nanoparticles with a polymeric shell. This method implies heterogeneous condensation of monomer vapor around the surface of nanoparticles as nuclei and polymerization is then subsequently started by addition of NH₃ as aerosol initiator. Ag and SiO₂ nanoparticles were generated as inorganic core by spark discharge and nebulization, respectively, and glycidyl methacrylate (GMA) was used as organic monomer. The effect of several parameters, including vapor pressure of monomer and properties of inorganic core such as morphology, material, particle size, and production method on the thickness of polymeric shell and morphology of resulting nanocomposites has been investigated. The particle size distribution and morphology of the resulting core-shell nanoparticles have been studied via scanning mobility particle sizer (SMPS) and transmission electron microscope (TEM). Finally, the coating efficiency was determined by aerosol photoemission (APE) and the results show that monomer and polymer coating efficiency are 99% and 60%, respectively.

Copyright 2014 American Association for Aerosol Research     

Silver-incorporated poly vinylidene fluoride nanofibers for bacterial filtration

An anti-bacterial filter was developed using poly vinylidene fluoride (PVDF) nanofibers using electrospinning method blended with silver nanoparticles (AgNO₃) of varying weight percentages of filler. Polypropylene (PP) non-woven substrate was used as base material for collecting the nanofibers. It also acted as a barrier to protect the fibers. UV-visible spectroscopy and fourier transform infra red spectroscopy confirmed the uniform dispersion of silver nanoparticles throughout the nanofibers. The experiment was designed using Box–Behnken statistical tool through three different variables namely, PP non-woven sheets (GSM), electrospinning time (hours), concentration of silver (wt%) in 15 runs. Surface morphology was analyzed using scanning electron microscopy and atomic force microscopy. Thermogravimetric analysis was performed for the analyses of mass decomposition of the material. Bacterial filtration efficiency and anti-bacterial activity studies were tested against Staphylococcus aureus and Escherichia coli for both PVDF + 0?wt% Ag fibers and PVDF-Ag nanofibers. This research shows the bacterial filtration efficiency for the prepared PVDF-Ag nanofibers as 99.86%. The prepared nanofilter was shown providing greater possibilities towards the application for clean air management.

© Copyright 2019 American Association for Aerosol Research     

Do ozone and boric acid affect microleakage in class V composite restorations?

The aim of this in vitro study was to evaluate the effects of chlorhexidine gluconate (2%), sodium hypochloride (2.5%), ozone gas, and boric acid at different concentrations (1%, 3%, 5%, and 7%) on microleakage from composite restorations.

In a total of 80 extracted human canine teeth, a class V cavity was opened on the buccal surface and the samples were separated into eight groups. In the control group, no procedure was applied for cavity disinfection, then composite restoration (Z250, 3M) was made using single-stage, self-etch adhesive (Single Bond 3M). In the other groups, seven different disinfectants were used, then the cavity was restored. The teeth were split into two in the buccolingual direction, parallel to the long axes. Stain penetration was examined under stereomicroscope and scored. Examination with SEM was made on one sample from each group, selected at random. Statistical evaluations were made using Dunnett C Post Hoc Comparison and Kruskal–Wallis H tests.

In the occlusal region evaluation, the groups with the lowest level of leakage were the 3% and 5% boric acid groups, and the highest levels of microleakage were determined in the chlorhexidine group and the 1% boric acid group. In the gingival region, the lowest level of microleakage was in the 5% boric acid group and the highest levels were determined in the 1% and 7% boric acid groups.

Boric acid disinfectants used at suitable concentrations were not seen to create a risk in respect of microleakage.     

RADIAL FLOW HOLLOW FIBERREVERSE OSMOSIS: EXPERIMENTS AND THEORY

The performance of a hollow fiber reverse osmosis system is studied both theoretically and experimentally. Experiments were carried out for applied pressure ranging from 200 to 400 psig, feed rates varying from 75 to 380 cc/sec and for feed concentrations up to 34,000 ppm of sodium chloride.

A mathematical model is proposed to predict productivity, ?, and product concentration, θ_p. The model involves solving membrane transport equations simultaneously with the hydrodynamic equations. The solubility-diffusion-imperfection, or pore diffusion model, is used to describe solute and solvent transport across the membrane. The axial gradients of shell side concentration, neglected in previous investigations, are taken into account. The differential equations are solved numerically by the 4th Order Runge-Kutta method.

Predicted values of ? and θ_p agree within 8% and 17% respectively, with experimental data over the entire range of operating conditions. However, membrane transport coefficients were found to be concentration dependent.

An approximate analysis shows that the concentration polarization is negligible in present day hollow fiber systems.     

“SPURT FRACTURE” IN CAPILLARY FLOW

The critical conditions under which flow curves in capillary flow abruptly change their slope to zero (spurt) and the influence of solvent additive and solvent power on this phenomenon have been investigated. Based on a forced high elastic state concept an expression for the so-called spurt phenomenon, i.e. fracture-induced slip at the wall in a capillary of a capillary rheometer, is deduced. It is found that the spurt fracture stress, τ^s _cr, and the spurt fracture shear rate, γ^s _cr, can be represented by the master curve log (τ ^s _crr ((p/M_c)PE(M_c/p))^2/3 against log (a_T γ^s _cr), where a_T is the WLF shift factor, M_c the molecular weight between entanglements and p the density.

Estimation of slip rates at the wall and measurements on slightly crosslinked high density polyethylene supports the assumption that spurt results from melt fracture at the capillary wall.

Only addition of the non-solvent calcium stearate (with high density polyethylene) results in flow behavior which significantly deviates from that found for samples containing good solvents. Gel permeation chromato-graphy indicates that if chain scission resulting in lower molecular weight takes place, it will be limited to thin layers near the capillary wall.

melt fracture in the capillary cannot be reached. The flow behavior is influenced by addition of the non-solvent calcium stearate. The slopes of the flow curves is changed at relatively low shear rates but the high molecular weight polymer DMDS 5140 never the less shows spurt behavior at the same stress as for the pure sample.

This behavior may tentatively be interpreted as being caused by the formation of a boundary layer of non-solvent at low shear rate the thickness of which depends on the polymer and flow field. At stresses corresponding to the critical conditions, fracture in the polymer takes place. The interface between the non-solvent layer and the polymer matrix must according to Han61 be expected to be unstable     

Comparative study of composite membranes from nano‐metal‐oxide‐incorporated polymer electrolytes for direct methanol alkaline membrane fuel cells

A series of six composite membranes was prepared with two polymer electrolytes and three inorganic fillers, namely, silica, titania, and zirconia by a solution casting method. Two polymer electrolytes, that is, anion‐exchange membranes, were prepared from polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (PSEBS) and polysulfone by chloromethylation and quaternization. A preliminary characterization of the ionic conductivity, methanol permeability, and selectivity ratio was done for all of the prepared composite membranes to check their suitability to work in direct methanol alkaline membrane fuel cells (DMAMFCs). The DMAMFC performance was analyzed with an in‐house fabricated single cell unit with a 25‐cm² area. Maximum performance was achieved for the composite membrane quaternized PSEBS/7.5% TiO₂ and was 74.5 mW/cm² at 60°C. For the comparison purposes, a commercially available anion‐exchange membrane (Anion Membrane International‐7001) was also investigated throughout the study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of size and shape on filtration of TiO2 nanoparticles

Titanium dioxide (TiO₂) is one of the most widely used nanoscale materials to date and could result in human exposures. The main objective of this study was to perform detailed characterization of TiO₂ agglomerate particles and how these properties influence particle penetration in a screen filter. Transmission electron microscope (TEM) photos showed compact agglomerates of nanoscale primary particles. The projected area diameter was close to the mobility diameter, where the length was about 25% larger than the mobility diameter. The mean aspect ratio of TiO₂ agglomerate was constant between 1.39 and 1.55. Using the tandem differential mobility analyzer-aerosol particles mass analyzer (DMA-APM) technique, we were able to measure aerodynamic diameter, mass, and fractal dimension. The value of fractal dimension based on mass and mobility diameter was 2.8. Penetration of classified TiO₂ particles through a screen filter was measured. Penetration increased with increasing mobility diameter and flow rate indicating that diffusion and interception were the main filtration mechanism. The measured physical dimensions, mobility diameter, and aerodynamic diameter were used in a single-fiber filtration theory for the fan model filter to predict the penetration of TiO₂ particles. The interception parameter was the key to estimate the penetration. Experimental penetration data were in best agreement with the model in which the maximum length was used to calculate the interception model. This result was consistent with the assumption that the rotation time of a non-spherical particle of small aspect ratio was much less than the transport time for the particle to pass through the filter fiber.

© 2017 American Association for Aerosol Research     

Comparative Efficiency Of Three Systems (O3, O3/H2O2, and O3/TiO2) For The Oxidation Of Natural Organic Matter In Water

CATAZONE is a new process of heterogeneous catalytic ozonation in which water is ozonated in the presence of a solid catalyst composed of titanium dioxide. The efficiency of this O₃/TiO₂ system has been compared to the two well-known oxidant systems: ozone alone and ozone combined with hydrogen peroxide.

This comparison was undertaken on three models of natural organic compounds : an aquatic fulvic acid, a protein and a disaccharide. The first results showed the following order of relative efficiency: O₃/TiO₂ > O₃/H₂O₂ > O₃ as far as Total Organic Carbon (TOC) removal was concerned.     

Shear bond strength of PEEK and PEEK-30GF cemented to zirconia or titanium substrates

Objectives: The aim of this study was to evaluate the use of dual-cure resin cement to promote the bonding between a veneering PEEK and zirconia or titanium surfaces.

Materials and methods: The surface of titanium and sintered zirconia disks were gritblasted, ultra-sonically cleaned in distilled water, and dryed by oil-free air. Then, a adhesive system was applied on the clean and dry surfaces. Disks of PEEK or 30% glass-reinforced PEEK were cut from a rod and their surface were acid etched and therefore the PEEK roughness was analysed using a contact profilometer. A resin cement was then applied between the substrates and the veneering PEEK and light cured for 4 Shear bond strength tests were performed on PEEK-cement to zirconia or titanium interfaces. Scanning electron microscopy (SEM) analyses were performed to evaluate the samples surface, interface and failure mode.

Results: Surface treatment with acid etching decreased the average roughness of PEEK-based surfaces. oMicroscopic analyses by SEM revealed morphological aspects of a poor bonding between the resin-based cement and PEEK. Those aspects could be confirmed by the low mean values in shear bond strength. The fracture analysis showed that the main failure mode was adhesive, which explain the low values of shear bond strength.

Conclusion: PEEK is a promising material for dental applications. However, significant improvements on surface modifications and in chemical composition of the cement are still required for dental applications involving cementation of PEEK or PEEK-30GF to zirconia or titanium concerning a desirable long-term clinical performance of prosthetic structures.     

Break-Up and Bounce of TiO2 Agglomerates by Impaction

In this study, the impaction behavior of titanium dioxide (TiO₂) agglomerates is evaluated, and the described method allows for the break-up and bounce of the particles to be monitored simultaneously. The degree of sintering and the primary particle size of the TiO₂ agglomerates were varied. The agglomerates were impacted onto the impaction plate of a single-stage micro-orifice uniform impactor, after which the bounced particles were collected in a low-pressure sampling chamber for subsequent analyses. The particle trajectories were simulated to accurately estimate the impaction velocity, which is one of the key parameters in the impaction process. A high degree of sintering significantly reduced the number of broken bonds, whereas reducing the primary particle size caused only minor differences in the number of broken bonds. The particles that bounced but did not break up either had a smaller primary particle size or were sintered. Decreasing the primary particle size also reduced the mass-based fraction of the bouncing particles.

Copyright 2014 American Association for Aerosol Research     

Distinguishing fuel and lubricating oil combustion products in diesel engine exhaust particles

The main sources of particulate emissions from engines are fuel and lubricating oil. In this study, particles emitted by a medium speed diesel engine for locomotive use were characterized chemically by using a soot particle aerosol mass spectrometer (SP-AMS). Additionally, positive matrix factorization (PMF) was applied to the SP-AMS data for the separation of fuel from lubricating oil and/or oil additives in diesel engine emissions. The mass spectra of refractory species, i.e., metals and rBC, were included in the PMF input matrix in addition to organics in order to utilize the benefit of the SP-AMS to measure non-refractory and refractory species. In general, particulate matter emitted by the diesel engine was dominated by organics (51%) followed by refractory black carbon (rBC; 48%), trace metals and inorganic species (1%). Regarding the sources of particles, PMF indicated four factors for particle mass of which two were related to lubricating oil-like aerosol (LOA1, 29% and LOA2, 24%) and two others to diesel-like fuel aerosol (DFA1, 35% and DFA2, 12%). The main difference between LOA1 and LOA2 was the presence of soot in LOA1 and metals in LOA2 factors. DFA factors represented burned (DFA1) and unburned fuel (DFA2). The results from the PMF analysis were completed with particle size distributions, volatility measurements and particle morphology analyses.

Copyright © 2019 American Association for Aerosol Research     

Nafion-TiO2 hybrid electrolytes for stable operation of PEM fuel cells at high temperature

The fabrication and characterization of Nafion-TiO₂ hybrid electrolytes for proton exchange membrane fuel cell (PEMFC) operating at high temperature are reported. A low temperature sol-gel synthesis, based on the formation of a sol from Ti-peroxy complex, was used to effectively incorporate hydrophilic anatase TiO₂ nanoparticles into the Nafion matrix. Fuel cell testing at temperatures up to 130 °C revealed that the hybrid membranes exhibit an increasing ohmic drop with increasing TiO₂ content incorporated into the polymer. However, at high temperatures and low relative humidity (RH) the performance of fuel cells using the hybrid electrolytes was found to surpass the one of Nafion. Electrochemical impedance spectroscopy (EIS) measurements suggest that enhancement of the fuel cell performance at high temperature and low RH is related to a reduced polarization resistance, indicating that the hybrid electrolytes contribute for a better water management of the system. In addition, it was found that the inorganic phase confers stability to the polymer, allowing for the operation at high temperature and reduced RH.     

CHLORINATION KINETICS OF Nb2O5

The reaction of single sintered pellets of α-Nb₂O₅ with chlorine and carbon monoxide was studied in the temperature range from 773 K to 1073 K using a thermogravimetric apparatus. The rate controlling step of the reaction was determined from experiments carried out at variable gas flow rates, gas composition, surface geometry, pellet porosity and temperature. The vapor phase transport reaction can be written as:

Nb₂O₅(s) + 3Cl₂ (g) + 3CO(g) = 2NbOCl₃ (g) + 3CO₂(g).

Up to 60% conversion, the amount of volatilized product was found to be directly proportional to the time of reaction. The external surface area of the pellets remains unchanged up to this stage while the intergranular morphology changes.

These results were compared with reaction rates of commercial pyrochlore concentrate in order to establish the fundamental reaction stages of the process of extraction of Nb₂O₅ from pyrochlore.     

The initial stages of multicomponent particle formation during the gas phase combustion synthesis of mixed SiO2/TiO2

The ability to properly scale the synthesis of advanced materials through combustion synthesis routes is limited by our lack of knowledge regarding the initial stages of particle formation. In flame aerosol reactors, the high temperatures, fast reaction rates, and flame chemistry can all play a critical role in determining the properties of the resulting nanomaterials. In particular, multicomponent systems pose a unique challenge as most studies rely on empirical approaches toward designing advanced composite materials. The lack of predictive capabilities can be attributed to a lack of data on particle inception and growth below 2 nm. Measurements for the initial stages of particle formation during the combustion synthesis of SiO₂ and composite SiO₂/TiO₂ using an atmospheric pressure inlet time-of-flight mass spectrometer are presented. Both positively and negatively charged clusters can be measured and results show the presence of silicic acid species which grow through dehydration, hydrogen abstraction, and interactions with hydroxyl radicals. In the case of composite SiO₂/TiO₂ particle formation, new molecular species containing Ti atoms emerge. Tandem differential mobility analysis-mass spectrometry (DMA-MS) provided further insight into the size-resolved chemistry of particle formation to reveal that at each cluster size, further hydroxyl-driven reactions take place. From this we can conclude that previous assumptions on collisional growth from simple monomer species of SiO₂ and TiO₂ do not sufficiently describe the collisional growth mechanisms for particle growth below 2 nm.

Copyright © 2018 American Association for Aerosol Research     

Synthesis of TiO2/PAA nanocomposite by RAFT polymerization

Due to the strong tendency of nanoparticles such as metal oxides to agglomerate, homogeneous dispersion of these materials in a polymeric matrix is extremely challenging. In order to overcome this problem and to enhance the filler-polymer interaction, this study focused on living polymerization that was initialized from the surface of titania nanofillers. A new method for synthesizing TiO₂/polymer nanocomposites was found with a good dispersion of the nanofillers by using the bifunctional RAFT agent, 2-{[(butylsulfanyl)carbonothioyl]sulfanyl}propanoic acid). This RAFT agent has an available carboxyl group to anchor onto TiO₂ nanoparticles, and an SC(SC₄H₉) moiety for subsequent RAFT polymerization of acrylic acid (AA) to form n-TiO₂/PAA nanocomposites. The functionalization of n-TiO₂ was determined by FTIR and partitioning studies, the livingness of the polymerization was verified using GPC and NMR, while the dispersion of the inorganic filler in the polymer was studied using electron microscopy, FTIR and thermal analysis.     

Influence of Ozone on the Photocatalytic Oxidation of Organic Compounds

Heterogeneous photocatalytic oxidation processes using titanium oxide as a photocatalyst are widely discussed topics in research for water and waste water treatment. Oxygen fed into the systems is normally used as oxidizing agent. However few investigations exist concerning the use of ozone as an additional oxidant. In this work the influence of ozone on the photocatalytic degradation of organic compounds are described. The results are compared with those by using ozone, UV/O₃ and UV/TiO₂/O₂. The oxidation reactions were performed at pH 3 and 7.

In this research compounds of the different classes were used: glyoxal, pyrrole-2-carboxylic acid, p-toluenesulfonic acid and naphthalene-1,5-disulfonic acid. Depending on the classes of compounds in some cases the elimination rates of the initial compounds is enhanced by using UV/TiO₂/O₃ compared to UV/O₃ or O₃ alone. But in all cases greatest DOC elimination is achieved by using UV/TiO₂/O₃.     

Efficient separation scheme for binary mixture of CO2 and H2S using aromatic components

Separating a mixture of CO₂ and H₂S into two products through distillation is both difficult and complicated because of similar relative volatility between the two gasses, particularly when a CO₂ concentration exceeds 80%. Therefore, the separation process can involve many separating stages. However, adding a solvent (agent) to the distillation column during the separation process makes this procedure easier.

In this study, different solvents (ethylbenzene, o-xylene, m-xylene, and toluene) and operating conditions (temperature, pressure, and reflux ratio) for separating CO₂ from H₂S have been simulated through distillation using Aspen HYSYS software. Furthermore, four different aromatic compounds (solvents) for different concentrations (from 0 to 40 mol%) have been evaluated to increase the CO₂/H₂S relative volatility, reducing the quantity of the solvent required and energy consumption.

m-xylene was found to be the best solvent for separating CO₂ from H₂S because of the significant effect on relative volatility, the low quantity required for high CO₂ recovery, and the low energy for generating the solvent.