Effect of arc current on characteristics of nanocarbons prepared by cryogenic arc discharge method

A variety of nanocarbons (nanohorns, nanoflowers and nanoclusters) could be prepared by arc discharge in cryogenic nitrogen with either graphite–graphite or iron–graphite electrodes manipulated by a strategy of automatic electrode delivering. Based on local thermal equilibrium assumption, magneto-hydrodynamic equations were taken into account for estimating the arc power efficiency of 60–84%, depending on the electrode combination. The effects of arc current on the morphology and yield of nanocarbons were investigated within a range of 75–150 A. Transmission electron microscopic analyses revealed that the synthesized product consisted of single-walled carbon nanohorns and multi-walled carbon nanoflowers with nominal diameters of 100–200 nm when graphite–graphite electrodes were employed but nanoclusters containing Fe nanoparticles inside carbon nanoshells with smaller size of 70–120 nm were mainly synthesized by iron–graphite electrodes subject to arc discharge in cryogenic nitrogen.     

Metal catalysts impregnated on porous media for aqueous phenol decomposition within three-phase fluidized-bed reactor

Performance of metal catalysts to decompose aqueous phenol was experimentally investigated. Comparison of the phenol decomposition rates within three-phase fluidized-bed reactors utilizing only O(3), TiO(2) deposited on silica beads, metal catalyst (Ni or Co) impregnated on mesoporous carbon beads, or O(3) in combination with each catalyst was thoroughly examined. It was found that the use of Co catalyst with the presence of O(3) led to the best removal condition which aqueous phenol was completely decomposed within 10 min (k = 0.1944 min(-1)). In contrast, the use of TiO(2) without O(3) resulted in the worst decomposition of phenol (k = 0.0066 min(-1)). Some intermediate products, such as hydroquinone and catechol, were also detected but their final concentrations were negligibly low.     

Role of Surface Area, Primary Particle Size, and Crystal Phase on Titanium Dioxide Nanoparticle Dispersion Properties

Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO₂ nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO₂ samples, and one commercial Degussa TiO₂ sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl₂) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO₂ isoelectric point was found to be dependent on particle size. As anatase TiO₂ primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO₂ nanoparticle IEP was found to be insensitive to particle crystal structure.     

Development of encapsulation technique for curcumin loaded O/W emulsion using chitosan based cryotropic gelation

Cryogel based encapsulation of curcumin, an herbal extract, was successfully carried out with a ternary system of colloidal chitosan, κ-carrageenan, and carboxymethylcellulose sodium salt. The effects of chitosan concentration, κ-carrageenan/CMC ratio of the polymer suspension and molecular weight of chitosan on the sol–gel formation were investigated. The effects of cooling rate during freeze-drying and oil phase composition on the encapsulation yield and the release behavior of curcumin from the hydrogel were determined. And so were the effects of pH of the phosphate-buffered media and oil phase composition on the swelling of the specimens. The microstructure of the resulting specimens revealed core-shell nanoparticles (i.e. oil droplet for core and cryogel membrane for shell) entrapped in the cryogel matrix. The encapsulation yield for two types of suspensions was in a range of 83.9 to 99.6% when a high-MW chitosan was used. Controlled release of the encapsulated curcumin in an aqueous system could be maintained for 4 days, and the releasable amount of curcumin was in a range of 41.1 to 59.9%. The encapsulation yield as well as the released pattern and releasable amount of curcumin were significantly influenced by the cooling protocol used during freezing. Irrespective of the introduced oil phase composition, controlled release of curcumin was achievable when the cooling rate was sufficiently high at ? 2.0 °C/min and, interestingly, either a burst release or a first order release could simply be achieved by changing the freezing condition.     

Application of TiO2-coated alumina beads to dielectric barrier discharge-photocatalyst hybrid process for NO and SO2 removals

NO and SO2 removal by dielectric barrier discharge-photocatalyst (DBD-P) hybrid process was examined for various conditions of process variables. Alumina beads were coated with TiO2 thin film by a rotating cylindrical PCVD reactor and they were packed inside the cylindrical reactor. The NO and SO2 removal efficiencies can be enhanced by using a combination of dielectric barrier discharge and photodegradation by TiO2. The stronger the applied voltage is, the higher the pulse frequency is, or the longer the gas residence time is, the higher the NO and SO2 removal efficiencies become. By applying additional photocatalytic effect, NO removal efficiency increased more significantly than SO2 removal efficiency, because SO2 removal efficiency was already high by dielectric barrier discharge only. In this study, we found that the alumina beads coated with TiO2 thin film by a rotating cylindrical PCVD reactor could be used effectively to remove NO and SO2 by DBD-P hybrid process.     

Preparation of a carbon monolith with hierarchical porous structure by ultrasonic irradiation followed by carbonization, physical and chemical activation

A two-step direct and simple method for the preparation of a hierarchical porous carbon monolith with micropores, mesopores and macropores is described. The two stages give more flexibility in the preparation of a porous carbon monolith. In step I a macroporous interconnected carbon monolith is prepared by ultrasonic irradiation during sol-gel polycondensation. The effects of sol-gel temperature, catalyst concentration and ultrasonic power on the structure of the monolith are investigated. In step II, mesopores are induced in the monolith by Ca(NO₃)₂ impregnation followed by CO₂ activation. The effect of activation temperature is also studied. A hierarchical interconnected carbon monolith with mean pore size diameter of 1.2 μm, BET surface area of 624 m²/g, mesopore volume of 0.38 cm³/g and micropore volume of 0.22 cm³/g has been obtained from Ca(NO₃)₂ impregnation of the macroporous carbon monolith followed by CO₂ activation at 850 °C.