Nonporous Particles Research Articles

In-Situ Measurements of Engineered Nanoporous Particle Transport in Saturated Porous Media

Engineered nanoporous particles have become an important class of nanostructured materials that have been increasingly applied in energy, biomedical, and environmental researches and industries. The internal pore surfaces in the particles can be chemically functionalized for environmental applications to sequestrate metals and radionuclide contaminants from groundwater. The fate and transport of the nanoporous particles in subsurface environments, however, have not been studied. Here we present a scanning optical fiber fluorescence profiler that can be used to in situ monitor the transport of fluorescent particles in column systems. Engineered nanoporous silicate particles (ENSPs) that were covalently bounded with fluorescence-emitting, and uranium-chelating ligands in the intraparticle pore domains were synthesized and used as an example to investigate nanoporous particle transport and to demonstrate the application of the developed in situ measurement profiler. The profiler detected an "irreversible" or slowly detached fraction of ENSPs in a sand collector even under thermodynamically unfavorable conditions for particle attachment. Further, the in situ measurement system detected the spatial variability of ENSPs transport that deviated from one-dimensional, homogeneous assumption, which is typically used to model particle transport in column systems. Generally, however, both measured and model-calculated results indicated that the transport of ENSPs was consistent with that of nonporous colloidal particles subjected to coupled reversible attachment/detachment and straining processes. The developed system can also be applied to detect other fluorescent nanostructured or colloidal particles in porous media.

Chemical Interactions of Surface-Active Agents with Growing Resorcinol-Formaldehyde Gels

The influence of cationic, anionic, and nonionic surfactants (S) on the characteristics of carbon xerogels was analyzed. The polymerization of resorcinol (R) and formaldehyde (F) was developed in an aqueous solution of S without any additional catalyst. The gels obtained were dried in air to obtain organic xerogels and then carbonized to carbon xerogels. The prepared samples were characterized by FTIR, TG, SEM, and N(2) and CO(2) adsorption. The formation of RF-S copolymers was observed for cationic and nonionic surfactants, but this was not observed for anionic S, probably because of repulsive electrostatic interactions between the two organic phases. Nevertheless, anionic S leads to a greater morphological transformation with the formation of nonporous needle particles associated with the higher pH induced by this S. Carbon xerogels are microporous materials with interesting molecular sieve behavior. The RF-S composites undergo greater shrinkage than do the pure RF xerogel; consequently, a narrower microporosity is obtained.

Interpreting the difference between conventional and bi-directional plate-height measurements in liquid chromatography

An experimental and theoretical study was conducted of the column characterization technique in which plate heights determined using the conventional pulse-response method are compared with those determined using a bi-directional method where an eluite sample is introduced into one end of a chromatographic column and elution occurs at the same end after the flow direction is reversed inside the column. Experiments are presented for a micropellicular HPLC column before and after its performance has been degraded by repeated sample injections, for a low-pressure column containing nonporous glass particles, and for an HPLC column containing particles with 300 Å pores. The results obtained are interpreted in terms of several different theories which apply in various Fourier number ranges. It was shown that the transcolumn contribution to convective dispersion in a chromatographic column is largely responsible for the difference observed between conventional and bi-directional plate-height measurements and that a collocation method can be employed to develop a useful analytical expression for this contribution.

Controlled release of bioactive recombinant human growth hormone from PLGA microparticles

Controlled release formulation of recombinant human growth hormone (r-hGH) was achieved using poly lactide-co-glycolide (PLGA) polymer. Denaturation of r-hGH by dichloromethane during primary emulsification step of particle preparation was minimized by using human serum albumin whereas inclusion of sucrose and sodium bicarbonate helped in reducing protein denaturation during lyophilization and polymer particle degradation. Encapsulation efficiency of r-hGH entrapped in PLGA particles (size ∼30 µm) was around 45% with protein load 20 µg of r-hGH/mg of polymer particles. Porous particles showed quick release of r-hGH in comparison to non-porous particles in vitro. More than 10 ng/mL of bioactive r-hGH was found in the serum of the experimental animals observed for a 30-day period after a single intramuscular injection of the polymeric formulation. Incorporation of optimal stabilizers is thus essential for the development of a stable, month long controlled release of polymer particle based r-hGH formulation.

Chlorination of hafnium dioxide by gaseous chlorine in the presence of carbon

The thermodynamic simulation of chlorination of hafnium oxide by gaseous chlorine in the presence of carbon at T = 450–1000°C is performed. It is shown that the main reaction products are gaseous hafnium tetrachloride, carbon monoxide, and carbon dioxide; as the temperature increases, the partial pressure of CO increases, while that of CO2 decreases. In the mentioned temperature range, the variations in the enthalpy, entropy, and the Gibbs energy of chlorination reactions are calculated and the composition of the gas phase under the conditions of thermodynamic equilibrium is determined. In the course of studying the kinetics of chlorination of HfO2 in the presence of carbon in the range T = 600–950°C, it is established that its limiting stage depends on the process temperature. Below 700°C, its rate is limited by the chemical reaction on the surface of nonporous solid spherical particles of the body with the formation of the volatile product; above 700°C, it is limited by the mass transfer of gaseous substances.

Non-Ideal Flow in Liquid-Solid Fixed Beds of Irregular-Shaped Particles: A Critical Review

Available data and correlations for non ideal flow in liquid-solid fixed beds are summarized and reviewed with focus on irregular-shaped particles as packing material. The reason is that in many industrial applications (adsorption, ion exchange, catalysis, etc.) the particles used are of irregular shape while the vast majority of available data on dispersion and non ideal flow is on non-porous spherical or other ordered-shaped particles (saddles, rings, cylinders, tablets, etc.). In the same time, dispersion plays an important part, for example, in reactant and product transport in packed bed reactors, in adsorption, leaching, etc. In the present review all available correlations and data for liquid-solid fixed beds packed with irregular-shaped particles are collected for the prediction of the dispersion coefficients over a wide range of practical values particle Reynolds number. For the current review, 198 experimental points used and 6 Ped – Rep correlations are presented, all derived for irregular-shaped particles.

A drag correlation for a nonporous sphere steadily approaching an impermeable plane at finite Reynolds numbers

A particle experiences resistance while moving in a viscous fluid and this drag force increases in the vicinity of no-slip surfaces due to the wall effect. For a nonporous solid spherical particle steadily approaching an impermeable plane, Brenner analytically obtained the wall effect correction factor for the small Reynolds number (Brenner, 1961). For finite Reynolds numbers Wu and Lee calculated the correction factor from their numerical simulation (Wu, 1998). Unifying the results of these previous studies, we propose a compact form of the wall effect correction factor that is valid for Reynolds numbers less than 40.

Heat transfer coefficients of natural volcanic clasts

Heat transfer coefficients used in numerical simulations of volcanic eruptions are typically borrowed from industrial settings where the coefficients are well determined for non-permeable, machined (spherical) materials. Volcanic clasts, in contrast, are permeable and have irregular shapes. We performed a series of laboratory experiments to determine heat transfer coefficients for natural volcanic particles. We measured the surface and interior temperatures during cooling at wind speeds ranging from 0 to 10 m/s. We also measured the permeability and density of the particles. We find that the permeability of the particles has little effect on clast cooling. In the absence of any wind, heat loss occurs by free convection, and we find no relationship between the heat transfer coefficient and particle density. However, for non-zero Reynolds numbers (finite wind speed), the heat transfer coefficient decreases with increasing porosity. We obtain a correlation for the dimensionless heat loss, or Nusselt number, of the form Nu = 2 + aRe 1/2Pr 1/3 where a is a density dependent coefficient given by a = 0.00022ρ + 0.31, with ρ in kg/m 3, and Re and Pr are the Reynolds number and Prandtl number, respectively. Compared with non-porous particles, heat transfer coefficients for natural pumice clasts are reduced by a factor of 2–3 for particles with similar Re. Numerical simulations show that this leads to an increase in depositional temperature by 50–90 °C.

Multifunctional Mesoporous Composite Microspheres with Well-Designed Nanostructure: A Highly Integrated Catalyst System

The precise control of the size, morphology, surface chemistry, and assembly process of each component is important to construction of integrated functional nanocomposites. We report here the fabrication of multifunctional microspheres which possess a core of nonporous silica-protected magnetite particles, transition layer of active gold nanoparticles, and an outer shell of ordered mesoporous silica with perpendicularly aligned pore channels. The well-designed microspheres have high magnetization (18.6 emu/g), large surface area (236 m(2)/g), highly open mesopores (approximately 2.2 nm), and stably confined but accessible Au nanoparticles and, as a result, show high performance in catalytic reduction of 4-nitrophenol (with conversion of 95% in 12 min), styrene epoxidation with high conversion (72%) and selectivity (80%), especially convenient magnetic separability, long life and good reusability. The unique nanostructure makes the microsphere to be a novel stable and approachable catalyst system for various catalytic industry processes.

Screening antibody and immunosorbent selectivity by two‐dimensional liquid chromatography‐MS/MS (2‐D LC‐MS/MS)

Selectivity of both peptide- and glycan-targeting antibodies was examined by 2-D LC-MS/MS. Proteins selected from biological extracts immunospecifically in a first chromatography dimension using antibodies immobilized by either covalent coupling or adsorption to protein G were desorbed with a denaturing mobile phase and transferred to a 1.5 microm nonporous particle RP chromatography (NP-RPC) column in a second dimension. Protein peak capacity of the NP-RPC column was approximately 50. Peaks collected from the RPC column were tryptic digested and the peptide fragments were identified by MALDI-MS/MS. The objective of this analytical strategy was to discriminate between protein antigens and nonantigens through identification of their peptides, leading to an evaluation of the selectivity of antibodies and immunosorbents. Quantification of the relative amount of antigen and nonantigen species captured by immunosorbents was achieved by absorbance, along with the likely capture mechanism. A limitation of the approach was in discriminating between isoforms of an antigen in which neither the antibody nor the LC-MS system targeted the differentiating feature in the isoforms.

Effects of Pluronics surfactants on morphology and porosity of hematite particles produced from forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl3 solution, were controlled by using Pluronics as nonionic surfactants (0–4 wt.%). Pluronics possess a nominal formula of (PEO)x–(PPO)y–(PEO)x. The effect of Pluronics with low hydrophilicity (PEO contents were less than 50 mol%) was small and provided spherical particles the same as that of the system without Pluronics (control system). However, Pluronics with higher hydrophilicity (PEO contents were over 50 mol%) gave ellipsoidal hematite particles. This effect on the particle morphology was enhanced by an increase in their molecular weight. On the other hand, the Pluronics possessing an opposite nominal formula [(PPO)x–(PEO)y–(PPO)x] exhibited no effect on the particle shape; it only depressed phase transformation from ⎕-FeOOH to hematite. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to mesoporous by using Pluronics. The N2 adsorption experiment and t-plot curve analysis revealed that the hematite particles changed from mesoporous to microporous by an increase in the concentration of Pluronics. On the other hand, in the presence of very low amounts of Pluronics molecules (0.1 wt.%), nonporous hematite particles were produced via strong aggregation of PN particles by their hydrogen bonding between hydroxyl and PEO or PPO groups. The dynamic light scattering measurement for the system with Pluronics clarified the existence of polynuclear (PN) particles with a hydrodynamic particle diameter (Da) of ca. 40 nm after these were aged for 6 h. The size of PN particles remained constant at ca. 40 nm during aging time of 12 h∼3 days, but the scattering intensity was decreased. This decrease in the scattering intensity reveals that the number of PN particles is reduced by aggregation. The transmission electron microscope, inductively coupled plasma atomic emission spectroscopy, and total organic carbon analysis measurements employed on the systems produced for ellipsoidal particles elucidated that the formation of ellipsoidal hematite particles is attributed to the adsorption of Pluronics on the surfaces of PN and growing hematite particles.

Core−Shell Diamond as a Support for Solid-Phase Extraction and High-Performance Liquid Chromatography

We report the formation of core-shell diamond particles for solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) made by layer-by-layer (LbL) deposition. Their synthesis begins with the amine functionalization of microdiamond by its immersion in an aqueous solution of a primary amine-containing polymer (polyallylamine (PAAm)). The amine-terminated microdiamond is then immersed in an aqueous suspension of nanodiamond, which leads to adsorption of the nanodiamond. Alternating (self-limiting) immersions in the solutions of the amine-containing polymer and the suspension of nanodiamond are continued until the desired number of nanodiamond layers is formed around the microdiamond. Finally, the core-shell particles are cross-linked with 1,2,5,6-diepoxycyclooctane or reacted with 1,2-epoxyoctadecane. Layer-by-layer deposition of PAAm and nanodiamond is also studied on planar Si/SiO(2) surfaces, which were characterized by scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Core-shell particles are characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), environmental scanning electron microscopy (ESEM), and Brunauer-Emmett-Teller (BET) surface area and pore size measurements. Larger (ca. 50 microm) core-shell diamond particles have much higher surface areas and analyte loading capacities in SPE than nonporous solid diamond particles. Smaller (ca. 3 microm), normal and reversed-phase, core-shell diamond particles have been used for HPLC, with 36,300 plates/m for mesitylene in a separation of benzene and alkyl benzenes and 54,800 plates/m for diazinon in a similar separation of two pesticides on a C(18) adsorbent.

Separation performance of 1-μm silica particles as stationary phase for pressurized electrochromatography

Bare nonporous silica particles with diameter around 1 microm were prepared. A 20 cm section of a total length of 45 cm capillary (100 microm i. d.) was packed electrokinetically and the separation performance of basic compounds was investigated in the pressurized capillary electrochromatography (pCEC) system using 1 microm nonporous bare silica spheres as stationary phase and acetonitrile-water as mobile phase. The effects of the composition of the mobile phase, the concentration of the buffer, pH value, applied voltage and so on on the separation performance were investigated. The experimental results demonstrated that the bare silica column showed a typical reversed phase separation mechanism when it was used for separation of basic compounds. The separation performance changed slightly with changing buffer concentration. Since the degree of dissociation of the basic compounds depended greatly on the pH value, the interaction between the compounds and stationary phase changed with the changing of pH value, thereby changing the resolution of the compounds. The separation performance increased with the increase of applied voltage. A column efficiency of 35 000 for o-toluidine was obtained when a voltage of 1 kV was applied.

Sulfur-Functionalization of Porous Silica Particles and Application to Mercury Vapor Sorption.

Silanol (SiOH) groups on silica particle surfaces undergo silylation reactions with organosilane molecules to give functionalized particles, which are used in many applications. The determination of the extent of this reaction is important for proper design of functionalized materials, depending upon the application. Two types of porous silica particles (206 and 484 m2 g-1; 9.6 and 2.9 nm average pore diameter, respectively), and colloidal silica (Ludox) with a nonporous base particle of 22 nm diameter, were functionalized with sulfur-containing silanes, 3-mercaptopropyl trimethoxy silane (MPTMS), and bis[3-(triethoxysilyl) propyl]-tetrasulfide (S4). Maximum extent of functionalization was determined with S4 using Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), and total S analysis. For the two types of porous silica particles, FTIR indicated that 54 and 17% of the silanol groups were functionalized with S4, and TGA indicated that the functionalized particles were 12 and 11 mass % MPTMS, respectively. These results were independently confirmed with total sulfur analysis. Extents of functionalization were determined for varying the silane structure on the same silica particle. MPTMS reacted with 38% of functional groups, while S4 reacted with 17%; the mass % of silane is the same regardless of silane structure on the same silica particle. Characterization by DSC indicated a glass transition occurs in the silane layer of the S4-functionalized silica at about 85 °C, but not in the MPTMS functionalized particles. Finally, mercury sorption breakthrough curves indicate the pore characteristics of the S4 functionalized samples.

Mechanistic modelling of kinetics and mass transfer for a solid–liquid system: Leaching of zinc with ferric iron

A systematic approach was developed to consider liquid–solid reactions with rough solid particles and shrinking particle model. The model is able to predict the reactivities of both non-porous and porous solid particles; the reaction order with respect to the solid material varies from zero (non-porous slab) to one (porous particle). As a model system, leaching of zinc sulphide (sphalerite) with ferric iron in an acidic environment was considered. The modelling was based on experimental data obtained in a batch reactor system, for which both conventional mixing and ultrasound was applied. Rival models based on plausible reaction mechanisms were derived and discriminated qualitatively and with regression analysis. The best model described the leaching reaction as a stepwise process, where ferric ions react with solid zinc sulphide in consecutive surface reaction steps. Shrinking particle model along with the surface roughness approach was used. The model predicts first order behaviour with respect to zinc sulphide, while the reaction order with respect to ferric iron varies from one to two as the reaction progresses. This is in accordance with experimental observations. The intrinsic kinetics, liquid–solid mass transfer and the effect of ultrasound were well described by the best kinetic model.

Peak parking-moment analysis: A strategy for the measurement of molecular diffusivity in liquid phase

The peak-parking (PP) method permits the measurement of molecular diffusivities ( D m) in solutions. D m is first measured for benzene in pure methanol and acetonitrile (ACN), using an empty open tube. This yields an effective axial diffusion coefficient ( D ax,m) equal to D m because there is no tortuosity nor constriction in the flow channel. The same measurements made for the same combinations of solute and solvents, using a column packed with non-porous silica particles provides the obstructive factor ( Y m), defined as the ratio D ax,m/ D m, which accounts for the influence of tortuosity and constriction of the interparticulate space in packed columns on axial molecular dispersion. The value obtained for Y m, 0.74–0.75, is constant, irrespective of the solvent. Then, PP experiments were made with the same apparatus and column to measure D m for benzene, toluene, and ethylbenzene in aqueous solutions of methanol and ACN. The values of D m obtained by correcting the experimental D ax,m values with Y m were compared with values previously reported and those estimated by several literature correlations. They were in good agreement with each other. The average relative error is estimated at 4.5–10%, demonstrating that the PP method is practically effective for experimental measurements of D m.

Transient Behavior and Stability in Miniaturized Multiphase Packed Bed Reactors

The step response, including various startup procedures, in a three-phase microreactor of 2 mm internal diameter packed with nonporous particles of 100 μm is reported. We demonstrate that the bed behaves reproducibly through many cycles of operating conditions. Interestingly, we find that the different startup procedures have little effect on the steady state that is achieved. In other words, minimal hysteresis was observed, in sharp contrast to larger-scale reactors with larger particles where prewetting has a remarkable impact on the hydrodynamic behavior. The powder-packed beds have very high liquid saturation values, and prewetting is not needed. At least four liquid-residence times were needed to achieve stable pressure drop and dispersion values over the bed. This indicates that the hydrodynamic response into a stable operation may well be the limiting factor that determines the rate at which kinetic experiments can be performed in high-throughput equipment.

Reaction kinetic studies of strontium hexaferrite nanoparticles synthesized by co-precipitation method

Nano crystalline strontium hexaferrite, SrFe12O19 powders have been synthesized using co-precipitation method. The ferrite precursors were obtained from aqueous mixtures of strontium chloride and ferric chloride by precipitating strontium and iron using 7.5 M sodium hydroxide solution. These precursors were heat treated at 800 and 1200°C in nitrogen atmosphere. The decomposition behaviour and reaction kinetics were investigated by means of DSC/DTG/TG for three heating rates. The various phases associated therein were identified by X-ray diffraction (XRD). From field emission scanning electron microscopy (FESEM) study, the formations of nonporous ultrafine particles have been confirmed. About 5 to 10% of the needle like crystals in the ‘as synthesized, condition were transformed to pyramidal structure and most of the crystals are found to have plate like hexagonal structures with increase in heat treatment temperatures. Activation energies and Avrami index ‘n’ were obtained using Johnson-Mehl-Avrami (JMA) equation. The reaction in the temperature range of 800 to 1200°C, proceeds as, instantaneous nucleation and three dimensional growth with activation energy of 168.33 kJ/mole.

Impact of retention on trans‐column velocity biases in packed columns

AbstractThe heights equivalent to a theoretical plate of a weakly and strongly retained compounds were measured on two packed columns having different average mesopore sizes. The measurements were carried out in two different cases, with access to the mesopores by the sample molecules blocked (filled with n‐nonane) or not. The experimental results demonstrate that the eddy dispersion terms of both columns are significantly smaller for porous than for nonporous particles. Two simultaneous phenomena explain this observation. First, packed columns are radially heterogeneous which causes significant trans‐column velocity biases warping the bands. Second, radial dispersion contributes to mass transfer across the column, relaxing the radial concentration gradients that are caused by these velocity biases. The impact of these biases is minimized when the pores of the particles are not blocked; it decreases with increasing residence time and radial dispersion coefficient of the solutes. © 2009 American Institute of Chemical Engineers AIChE J, 2009

The effect of citric acid on the sintering of calcium phosphate bioceramics

Biphasic calcium phosphate particles were prepared using a rapid increase of the pH value by adding an amount of concentrated ammonia solution, into a well-mixed solution containing Ca(H 2PO 4) 2·H 2O and CaCl 2 with Ca/P = 1.667 molar ratio; with or without the presence of citric acid (CiA). The precipitation of Calcium Phosphates took place at 97 °C using high-speed dispersing equipment. The samples were characterized using XRD, FT-IR, BET and SEM techniques. The thermal behaviour was studied by TG, DTG and DTA techniques. The modified precipitation method leads to the formation of biphasic needle-like particles consisted of crystalline hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP). The presence of CiA in the initial solution leads to the formation of aggregated nonporous small spheroidal particles consisted of low crystallinity phases of HA and octacalcium phosphate (OCP). The later facilitates the sintering process. The calcined samples at 900 °C were consisted of calcium pyrophosphate (CPP) and TCP. α-TCP is formed in the presence of a large amount of calcium citrate complexes. The main sintering process took place at the temperature range between 750 and 1150 °C, which were strongly depended on the initial amount of the CiA in the precipitation process. These results indicated that the citrate presence in the initial solution have a strong influence on the nucleation and growth processes by complexation with calcium ions and incorporation into the solid structure during particle growth.