Silica Gel Layers Research Articles

On the Differences in the Mechanisms of Adsorption of Aromatic Heterocycles from Water–Acetonitrile Solutions on Octadecyl-Bonded Silica Gels

Adsorption of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions on Luna C18 and Discovery C18 silica gels with grafted octadecyl groups has been studied in a wide range of compositions at temperatures of 313.15–333.15 K. The comparative analysis of the liquid-phase adsorption of the heterocycles has revealed a number of differences between the mechanisms of binding molecules of the studied compounds by the surfaces of these octadecyl-derivatives of silica gel. The log–log dependences of the retention factor on the molar fraction of acetonitrile in the solutions are strictly linear only for adsorption on Luna C18 silica gel, which is characterized by an increased hydrophobicity. For the adsorption of the studied heterocycles on Discovery C18 silica gel, the concentration dependences of the retention at low and high acetonitrile concentrations in the solution are described by quadratic functions and characterized by higher retention values as compared with those for the linear dependence because of the lower hydrophobicity of this silica gel. It has been found that the surface layer of Luna C18 modified silica gel is enriched with acetonitrile molecules to a higher extent than the surface layer of Discovery C18 silica gel. It has been shown that one adsorbed molecule of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines displaces three and two molecules of pre-adsorbed acetonitrile from the surfaces of Luna C18 and Discovery C18 silica gels, respectively. Linear correlation equations have been proposed for calculating the retention of the studied heterocycles on Luna C18 and Discovery C18 silica gels from mobile phases of arbitrary compositions at different temperatures of chromatographic columns.

Synthesis of functionalized by an oxime group surfactants on the basis of imidazole, pyridine and alkylamines

Methods have been developed for the synthe-sis of a series of monomeric and dimeric surfactants functionalized by an oxime group based on imid-azole, pyridine and alkylamines. Alkyl radicals of varying degrees of branching were used, both as sub-stituents at the nitrogen atom of the head group and as spacers in the formation of dimeric products. This allowed to create a whole spectrum of supramo-lecular systems with different physicochemical pro-perties and reactivity.Methods of obtaining a number of intermedi-ate products were improved, primarily for the reac-tion of the imidazole alkylation using interphase ca-talysis conditons — solid phase-liquid. The method of obtaining surfactants based on imidazole consisted in the interaction of alkylimidazoles with chloro-acetaloxime in a suitable solvent or with chloro-acetone and subsequent reaction with a hydroxyla-mine solution. In the preparation of pyridine-based surfactants, the corresponding oxo-substituted pyri-dine was reacted with a hydroxylamine solution, fol-lowed by reaction of the obtained product with al-kyl halide. A method has been developed for the syn-thesis of functionalized surfactants based on alipha-tic amines, where for monomeric products a path is chosen that is associated with the sequential alkyla-tion of 1-chloroacetoxime with dimethylamine and dodecyl bromide, and for dimeric ones, the direct interaction of 1,3-dichloroacetoxime with 1,1-dime-thyl-1-dodecylamine.The composition, structure and purity of the obtained compounds were confirmed by NMR spec-troscopy, thin-layer chromatography and elemental analysis. NMR spectra were recorded on a BRUKER Avance II 400 instrument (400 MHz), TMS was used as an internal standard. Chromatography in a thin layer of silica gel was performed on Merck Si-licaGel 60 F254 plates (eluent — chloroform: meth-anol = 10:1).The data presented by us testify to the pro-spects of the chosen pathway for structural modifica-tion of surfactants functionalized by the oxime group, and give direction for the further design of such microheterogeneous systems.

Co-enhance bioactive of polymer scaffold with mesoporous silica and nano-hydroxyapatite

Mesoporous silica Santa Barbara Amorphous-15 (SBA15) and nano-hydroxyapatite (nHA) were introduced in poly-l-lactic acid (PLLA) scaffold fabricated by selective laser sintering to co-enhance the bioactivity. On the one hand, the active elements silicon and calcium released respectively by the degradation of SBA15 and nHA were favorable for stimulating cell response. On the other hand, the hydrated silica gel layer derived from SBA15 could adsorb calcium ions released from nHA, thereby co-promoting apatite nucleation and growth. The experimental results showed that the formation of bone-like apatite on the scaffold was accelerated under simulated body fluid, indicating a good biomineralization capacity. Moreover, the scaffold demonstrated a good cell response in promoting the attachment of cell and the expression of alkaline phosphatase activity. Besides, SBA15 and nHA not only improved the hydrophilicity of the scaffold (the water contact angle changed from 107.4° to 57.8°), but also retarded the pH reduction by neutralizing the acidic hydrolysate of PLLA. These results indicated that the PLLA-SBA15-nHA scaffold may be potential candidates for bone repair.

A Full-Solid-State Humidity Pump for Localized Humidity Control

Summary Humidity management is essential and widely needed in various fields. Traditional moisture removal technologies are mostly based on cooling condensation or desiccant dehumidification. These methods come with inherent defects of energy efficiency and are bulky and complex for small-space humidity-control applications. Here, we demonstrate a full-solid-state humidity pump using the advantages of commercial thermoelectric coolers and silica gel materials. Silica gel is coated on the surface of heat sinks to minimize contact thermal resistance between the material and heat source while maintaining enough heat and mass transfer area between the desiccant and the air. The humidity pump device exhibits 0.61 g W−1 h−1 humidity transfer efficiency, corresponding to a humidity transfer rate of 28.38 g h−1. The proposed device neither uses refrigerant nor introduces liquid water. It opens up the possibility of use in localized humidity control applications with higher efficiency and a wider ambient temperature range than traditional technologies.

Development and Validation of New High Performance Thin Layer Chromatography Method for Determination of Aripiprazole in Bulk and Tablet Formulation

A new high performance thin layer chromatography method was established for the determination of aripiprazole in bulk and tablet formulation. The estimation of aripiprazole was performed on thin layered aluminum backed plates coated with 200 μm layer of silica gel 60 F254 (10 cm × 10 cm) using mobile phase carbon tetrachloride: methanol: triethyl amine (2.5:2.4:0.1 v/v/v). Densitometric detection of aripiprazole was performed at 255 nm. Aripiprazole show linear relationship over the desired concentration range 300-1800 ng with correlation coefficient is 0.998. The R value for aripiprazole was found to be 0.58 ± 0.02. The established method was employed for tablet formulation and percent label claim for aripiprazole was found to be in the range 98-100 % and the % amount found in range from tablet formulation show that there is no interference from excipients available in tablet formulation. As per international conference on harmonization the established method was successfully validated to various parameter like linearity, precision, accuracy, ruggedness, robustness, detection limit and quantitation limit and showed satisfactory results for all parameters hence it is proved that the established method is simple, accurate, linear, precise, rugged, robust, sensitive and economical in nature. This method can be utilized for the routine quality control analysis of aripiprazole in bulk and tablet formulation.

Photocatalytic Functionalized Aggregate: Enhanced Concrete Performance in Environmental Remediation

Engineering of effective photocatalytically active structures is of great importance as it introduces a solution for some existing air pollution problems. This can be practically achieved through the bonding of particulate photocatalysts to the surface of construction materials, such as aggregates, with a suitable stable binding agent. However, the accessibility of the photocatalytically active materials to both the air pollutants and sunlight is an essential issue which must be carefully considered when engineering such structures. Herein, different amounts of commercial TiO2 were supported on the surface of quartz sand, as an example of aggregates, with a layer of silica gel acting as a binder between the photocatalyst and the support. The thus prepared photocatalytically active aggregates were then supported on the surface of mortars to measure their performance for NOx removal. The obtained materials were characterized by electron microscopy (SEM and TEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and UV-vis Absorption Spectroscopy. Very good coverage of the support’s surface with the photocatalyst was successfully achieved as the electron microscopic images showed. FTIR spectroscopy confirmed the chemical bonding, i.e., interfacial Ti–O–Si bonds, between the photocatalyst and the silica layer. The photocatalytic activities of the obtained composites were tested for photocatalytic removal of nitrogen oxides, according to the ISO standard method (ISO 22197-1). The obtained aggregate-exposed mortars have shown up to ca. four times higher photocatalytic performance towards NO removal compared to the sample in which the photocatalyst is mixed with cement, however, the nitrate selectivity can be affected by Ti–O–Si bonding.

Delineating Areas of Past Environmental Degradation near Smelters using Rock Coatings: A Case Study at Rouyn-Noranda, Quebec

Emissions of SO2 from smelters can promote formation of acid rain, which can dissolve siliceous minerals on exposed rock surfaces and promote the formation of silica gel layers within which detrital and smelter-derived particulates can become trapped. These processes of dissolution and entrapment can result in the formation of rock coatings that contain elevated levels of heavy metals. Between 1927 and 1976, the Horne smelter processed sulfide ore derived from the Rouyn-Noranda region and became one of the largest emitters of particulates and sulfur dioxide in North America, promoting the formation of coatings on nearby rock surfaces. The reflectance spectra of these coatings are relatively flat, with typical reflectance values ranging between ~5% at visible wavelengths and ~16% in the shortwave infrared. Absorption troughs in coating spectra are consistent with the presence of materials including opaline silica, olivine, pyroxene, hydrous phyllosilicates, and sulfates. Classification of Landsat 8 Operational Land Imager data indicates that rock coatings near Rouyn-Noranda comprise a total surface area of ~1.5 km2, nearly all of which is located within ~6 km of the Horne smelter. Remote sensing techniques can used to delineate the geographic extents of coatings near smelters, highlighting areas previously subjected to severe environmental degradation.

Experimental investigation on the adsorption kinetics of silica-gel layer enhanced thermal conductivity

Desiccant air conditioning by heat exchange with an adsorbent driven by waste heat has the potential to become a highly efficient process because latent and sensible heat can be controlled independently. However, the mass and heat transfer phenomena that occur in the heat exchanger with the adsorbent are too complex to be expressed. Therefore, we attempted to elucidate the effect of thermal conductivity on adsorption kinetics by a volumetric method. In addition, we experimentally investigated the adsorption kinetics of a silica gel layer. The thermal conductivity of the silica gel layer increased in the range of 0.2–2.0 W/(m·K) at 303 K, which drastically increased adsorption kinetics. Moreover, there is an optimal point in water adsorption power per volume because of the relationship between packing density and content ratio of carbon-doped silica gel.

Studying the Sorption of Certain Benzimidazoles on Octadecyl Silica Gel from Water–Acetonitrile Solutions via Liquid Chromatography

The effect the composition of a water–acetonitrile eluent has on the sorption of benzimidazoles by octadecyl silica gel is studied using the Snyder–Soczewinski model. Three-parameter equations associating retention factors and certain physicochemical characteristic of the molecules of benzimidazoles are obtained via linear regression analysis. Standard changes in the enthalpy of the transfer of benzimidazoles from the water–acetonitrile phase to the layer of octadecyl silica gel and entropic components of the process are calculated from the temperature dependences of the retention factors. The enthalpy–entropy dependences of sorption are discussed.

Antiseptic effect of compound lysostaphin disinfectant and its preventive effect on infection of artificial dermis after graft on full-thickness skin defect wound in rats

Objective: To study the antiseptic effect of compound lysostaphin disinfectant and its preventive effect on infection of artificial dermis after graft on full-thickness skin defect wound in rats. Methods: (1) Each one standard strain of Klebsiella pneumoniae, Acinetobacter baumannii, and Staphylococcus aureus were selected. Each 20 clinical strains of Klebsiella pneumoniae, Acinetobacter baumannii, and Staphylococcus aureus were collected from those isolated from wound exudates of burn patients hospitalized in our wards from January 2014 to December 2016 according to the random number table. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of compound lysostaphin disinfectant to above-mentioned strains were detected. The experiment was repeated 3 times. Compared with the corresponding standard strain, the clinical strain with higher MIC and/or MBC was considered as having decreased sensitivity to the disinfectant. The percentage of strains of each of the three kinds of bacteria with decreased sensitivity was calculated. (2) Artificial dermis pieces were soaked in compound lysostaphin disinfectant for 5 min, 1 h, 2 h, and 4 h, respectively, with 21 pieces at each time point. After standing for 0 (immediately), 12, 24, 36, 48, 60, 72 h (with 3 pieces at each time point), respectively, the diameters of their inhibition zones to standard strains of Klebsiella pneumoniae, Acinetobacter baumannii, and Staphylococcus aureus were measured. The experiment was repeated 3 times. The shortest soaking time corresponding to the longest standing time, after which the disinfectant-soaked artificial dermis could form an effective inhibition zone (with diameter more than 7 mm), was the sufficient soaking time of the disinfectant to the artificial dermis. (3) Forty Sprague-Dawley rats were divided into post injury day (PID) 3, 7, 14, and 21 sampling groups according to the random number table, with 10 rats in each group. A full-thickness skin defect wound with a diameter of 20 mm was made on both sides of the spine on the back of each rat. Immediately after injury, the artificial dermis without any treatment was grafted on the wound on left side of the spine (hereinafter referred to as control wound), while the sufficiently soaked artificial dermis with compound lysostaphin disinfectant was grafted on the wound on right side of the spine (hereinafter referred to as disinfectant wound). On PID 3, 7, 14, and 21, the gross condition of wounds of all the surviving rats was observed, and the new infection rates of control wounds and disinfectant wounds were calculated. Then, the rats in the sampling group with corresponding time were killed, and the full-thickness wound tissue containing artificial dermis was collected for quantitative analysis of bacteria. Bacteria content of the uninfected control wounds and that of the uninfected disinfectant wounds were compared. Data were processed with chi-square test and Wilcoxon rank sum test. Results: (1) The MIC of compound lysostaphin disinfectant to standard strains of Staphylococcus aureus, Klebsiella pneumoniae, and Acinetobacter baumannii were 1/32, 1/32, and 1/512 of the original concentration of the disinfectant, respectively, and the MBC were 1/32, 1/16, and 1/512 of the original concentration of the disinfectant, respectively. The percentages of clinical strains of Klebsiella pneumoniae, Acinetobacter baumannii and Staphylococcus aureus with decreased sensitivity to compound lysostaphin disinfectant were 15% (3/20), 20% (4/20), and 10% (2/20), respectively. (2) After being soaked in compound lysostaphin disinfectant for 2 and 4 h, the longest standing time, after which the artificial dermis could form an effective inhibition zone against Klebsiella pneumoniae, Acinetobacter baumannii, and Staphylococcus aureus, were 24, 36, and 48 h respectively, longer than 12, 24, and 24 h of soaking for 5 min and 24, 24, and 36 h of soaking for 1 h. The sufficient soaking time of compound lysostaphin disinfectant to artificial dermis was 2 h. (3) On PID 3, no infection symptom was observed in all the wounds, and so both the new infection rate of control wounds and that of disinfectant wounds were 0. The artificial dermis was transparent but not well connected with the wound. On PID 7, the new infection rate of control wounds was 20.00% (6/30), which was obviously higher than 3.33% (1/30) of disinfectant wounds, χ(2)=4.043, P 0.05). Conclusions: Compound lysostaphin disinfectant has quite strong antibacterial ability against Klebsiella pneumoniae, Acinetobacter baumannii, and Staphylococcus aureus. Clinical strains of the three kinds of bacteria were highly sensitive to compound lysostaphin disinfectant. Saturation of absorption of compound lysostaphin disinfectant achieves in artificial dermis after 2 hours' soaking. After 24, 36, and 48 hours' standing, the soaked artificial dermis still has the antibacterial effect on Klebsiella pneumoniae, Acinetobacter baumannii, and Staphylococcus aureus, respectively. The infection rate and the bacteria content of full-thickness skin defect wound in rats are all decreased when grafted with soaked artificial dermis.

Analysis and optimisation of an insulated water tank for the domestic purpose

Hot water storage in the insulated tank is an effective method of energy storage and also fills the permanent and intermittent domestic need for hot water. In this study, an insulated water tank with 29 litres capacity is developed, and its energy storage performance is analysed through numerical simulation method. Silica gel and Polyurethane are the insulation materials attached to the concrete tank. This water tank is optimised for minimum cost and temperature loss using grey relation analysis (GRA) and response surface method (RSM). The thickness of concrete, polyurethane and silica gel layer are the considered control parameters. The best value obtained from the two optimisation methods are compared, and from GRA method, thickness of concrete, polyurethane and silica gel are identified as 7.5cm, 0.25cm and 0.25cm, respectively. Finally, from the confirmation test, the temperature loss in 24 hours is predicted as 6.29°C with a minimum material cost for the tank as 5914 INR.

Properties of silica and silica-titania layers fabricated from silica sols containing fumed silica

Silica layers fabricated by the sol-gel method are usually amorphous and exhibit a relatively low refractive index (n∼1.46 at about 0.6 μm), high optical transmittances at UV-VIS and near-IR ranges, as well as high thermal stability. Such layers can be used as high reflection or antireflection coatings, dielectric mirrors, bandpass filters, etc. However, crack-free layers with a maximum thickness of about 400 nm can be prepared in one coating cycle from sols of simple silicon alkoxides. This paper presents an approach for the preparation of crack-free silica layers that allows us to increase this maximum thickness. The approach is based on the dip-coating technique used for applying stable silica sols containing fumed silica. These sols were obtained from input silica sols based on tetraethyl orthosilicate (TEOS) with concentrations 1 and 2 mol/l, ethanol, HCl and water (RW 1.75). Fumed silica was dispersed in water/TritonX-100 solution and added into some of the input sols. Zeta potentials, average dimensions and diffusion coefficients of silica agglomerates in sols containing fumed silica are presented. Both types of sols were deposited onto silica slides and silicon wafers by the dip-coating technique using different withdrawing velocities 100,200 and 300 mm/min. Prepared silica gel layers were thermally treated at 450 or 900 °C. One of silica sols with fumed silica has also been used for the preparation of a silica-titania sol with a molar ratio Ti/Si = 3/7. Both these sols have been employed for the preparation of a Bragg mirror consisting of three pairs of high-index silica-titania and low index silica layers on a silica slide.The appearance and thickness of prepared single silica and silica-titania layers have been characterized by optical microscopy and scanning electron microscopy. Optical properties of layers have been determined by spectral ellipsometry and UV-VIS-NIR transmission spectrometry. The measurements have shown that characteristics of layers fabricated from both types of the sols differ and that one can obtain stable transparent silica layers with thicknesses up to 650 nm and refractive indices in a range from 1.41 to 1.44 at 600 nm using TEOS sols containing fumed silica. It has been found that larger layer thicknesses can be achieved by using silica sols with fumed silica, by increasing the alkoxide concentration, by using increased withdrawing velocities, and by decreasing heat-treatment temperatures.

Compatibility and bone bonding efficiency of gamma irradiated Hench's Bioglass-Ceramics

Samples of Hench's bioglass-ceramic derived from thermal heat treatment of parent Hench's bioglass of the normal composition (45SiO2−24.5Na2O-24.5CaO-6P2O5 wt%) were prepared. Combined collective characterization of the effects of both gamma irradiation with varying doses (1→10Mrad) and immersion times in SBF (1→4 weeks) through specific analytical techniques including FTIR, X-Ray diffraction and SEM investigations. The overall extended studies are focused on justifying the bone-bonding efficiency with the interference of both X-Ray diffraction and immersion times. Experimental data indicate the stability of FTIR spectra upon the increase of gamma irradiation but prolonged immersion times cause distinct variations which touch the vibrational bands in consequence to the ion exchange or preferential attack and replacement of modifiers by hydronium ions leading to the surface silica gel layer from the SBF and the final formation of hydroxyapatite as an indicator for bone-bonding ability. The FTIR spectra show some variations as visualized from the IR spectra of the only un-irradiated samples and that for irradiated samples upon prolonged immersion. X-ray diffraction patterns are found to change by gamma irradiation dose and/or immersion time in SBF. Hydroxyapatite and silicon phosphate crystalline phases are identified to be formed upon gamma irradiation alone or with combined immersion and gamma irradiation beside the formation of crystalline sodium calcium silicate phase formed with both the un-irradiated and un-immersed samples.

Preparation of C@silica core/shell nanoparticles from ZIF-8 for efficient ciprofloxacin adsorption

Ciprofloxacin (CIP) in water is harmful to fish, human body and potentially harmful to ecological system, thus it needs to be removed. Adsorption is a simple treatment method, but the reported adsorbents rarely showed high adsorption performance. Herein, we present the preparation of a C@silica core/shell nanoparticles material for removal of CIP from aqueous solution. The nanoparticles were prepared by first coating a layer of silica gel on ZIF-8 nanoparticles via hydrolysis of tetraethoxysilane (TEOS), followed by carbonization. XRD, FT-IR, TEM, and N2 adsorption–desorption analysis were employed to examine the obtained products. TEM images clearly show the core/shell structures with a thickness of the silica layer of 13–28 nm. N2 adsorption–desorption results exhibit the textural properties of the products with both micro- and meso-pores and a high surface area of 594.4 m2/g. More CIP amount can be adsorbed from water with higher surface area. The equilibrium adsorption amount reaches a climax at pH 6. The maximum CIP adsorption amount of the C@silica core/shell nanoparticles is 516.8 mg/g, much higher than the parental carbon. In addition, the maximum CIP adsorption amount is significantly increased to 1575 mg/g with the presence of Cu(II) in the aqueous solution. We investigated the mechanism for the increased adsorption capacity of the C@silica core/shell nanoparticles materials, indicating that the silica coating makes these nanoparticles more negatively charged and thus benefits the adsorption of CIP via stronger electrostatic interaction. The C@silica nanoparticles can be easily prepared and their CIP adsorption capacity is very high. The results show that the C@silica nanoparticles are promising candidates for removal of CIP from water.

Silica Gel Coated Spherical Micro resonator for Ultra-High Sensitivity Detection of Ammonia Gas Concentration in Air

A silica gel coated microsphere resonator is proposed and experimentally demonstrated for measurements of ammonia (NH3) concentration in air with ultra-high sensitivity. The optical properties of the porous silica gel layer change when it is exposed to low (parts per million (ppm)) and even ultra-low (parts per billion (ppb)) concentrations of ammonia vapor, leading to a spectral shift of the WGM resonances in the transmission spectrum of the fiber taper. The experimentally demonstrated sensitivity of the proposed sensor to ammonia is estimated as 34.46 pm/ppm in the low ammonia concentrations range from 4 ppm to 30 ppm using an optical spectrum analyser (OSA), and as 800 pm/ppm in the ultra-low range of ammonia concentrations from 2.5 ppb to 12 ppb using the frequency detuning method, resulting in the lowest detection limit (by two orders of magnitude) reported to date equal to 0.16 ppb of ammonia in air. In addition, the sensor exhibits excellent selectivity to ammonia and very fast response and recovery times measured at 1.5 and 3.6 seconds, respectively. Other attractive features of the proposed sensor are its compact nature, simplicity of fabrication.

The effect of experimental hyperoxia on erythrocytes’ oxygen-transport function

ABSTRACTThe aim of this study was to investigate the effect of hyperoxia, calcium ions and pH value on the composition of major phospholipids in human erythrocyte membranes and erythrocytes’ oxygen-transport function. To create a model of hyperoxia, we saturated the incubated mixture with oxygen by constant passing of oxygen–air mixture through the incubation medium. To assess the effect of elevated calcium ion concentrations, CaCl2 was added to the incubation medium. An incubation medium with different pH was used to study the effect of various pH values. Lipids were extracted from erythrocytes and chromatographic separation was carried out in a thin layer of silica gel deposited on a glass plate. The thiobarbituric acid (TBA)-active products and the content of diene conjugates (DC) in erythrocytes were determined. The oxygen-binding capacity of haemoglobin was evaluated using Raman spectroscopy. The obtained results indicated that hyperoxia causes deep changes both in the composition and character of bilayer lipids of erythrocyte membranes, which affects the functional characteristics of erythrocytes, primarily the oxygen-transport properties of erythrocyte haemoglobin. It should be noted that a combination of Ca2+ ions and change in the pH value intensify the processes associated with disruption of phospholipids’ composition. The findings indicate that the lipid phase is one of the key elements in the functioning of erythrocytes in norm as well as during development of various pathological processes.

CFD Simulation of Silica Gel as an Adsorbent on Finned Tube Adsorbent Bed

The adsorption technology is becoming the more expected solution by today’s researchers for fix the energy and environmental issues. The main part of the cooling system adsorption is adsorbent and adsorbate. One of the most widely used adsorbents in research of adsorption technology is silica gel. A new silica gel-water adsorption chiller design was developed that composed of two sorption chambers with compact fin tube heat exchangers as adsorber, condenser, and evaporator. Energy, mass, and momentum conservation equations of the adsorption systems have been used for the CFD two and three dimensional models. The geometry of simulation is simply made within silica gel layer between two fins. The simulation is also implemented using a finite volume method through the CFD software Fluent. User defined functions are given to modify the energy, mass, and momentum conservation equations. The simulation of adsorption process is adjusted at unsteady condition. Adsorption and desorption processes are simulated with room temperature for cooling water inlet at temperature 305.15 °K, hot water inlet at temperature 353.15 °K, mass flow rate cooling water inlet at 0.3 kg/s and pressure 32 KPa. For the whole adsorbent bed area, the result shows that the highest absolute adsorption rate at the outer surface, while the lowest rate is at the center. After adsorption was finished, the condition is reversed. The highest absolute adsorption rate is achieved at center, while the lowest rate is achieved at the outer surface.

HPTLC and RP-HPTLC Method Development and Validation for the Estimation of Felodipine in Bulk and Pharmaceutical Formulation

The aim of this work is to establish developed and validated method for the pharmaceutical analysis of Felodipine in bulk and pharmaceutical formulation by High Performance Thin Layer Chromatography HPTLC (NP) and Reverse Phase-High Performance Thin Layer Chromatography RP-HPTLC (RP). Chromatographic separation was performed on Pre-coated aluminum plates with 250 μm layer of Silica gel 60 F254 and Silica gel 60 RP-18 TLC F254S using Toluene: Methanol (8:2 v/v) and acetonitrile: water: glacial acetic acid (8:2:1 v/v/v) as a mobile phase, respectively. Scanning was carried out densitometrically at 237 nm. The Rf value of Felodipine in NP and RP were 0.40 and 0.53 and the reliability of the method was assessed by the evaluation of linearity which was found to be 300-1800 and 500-3000 ng/band with the r2 =0.998 correlation coefficient along with the accuracy of the method in terms of % recovery was found to be from 98-101 ± 1.04 % and 99-100 ± 0.47 % and the limit of detection and quantification were 11.51, 34.90 and 29.90, 90.61, respectively. The method can be used for routine analysis of Felodipine in bulk and pharmaceutical formulation.

Indole-3-Acetic Acid Production by Colletotrichum siamense, An Endophytic Fungus from Piper nigrum Leaves

Plant endophytic fungi have been recognized as an important and a good source of natural bioactive products with potential application in agriculture, medicine and food industry. Chemical and biological studies of fungal metabolites originating from endophytic fungi isolated in Sri Lanka are relatively less studied. Therefore we investigated the chemistry and bioactivity of endophytic fungi present in leaves of Piper nigrum L. (black pepper) of the family Piperaceae famed as the spices king due to its pungent quality. A fungal endophyte isolated from the leaves of P. nigrum was identified as Colletotrichum siamense through molecular biological means using internal transcribed spacer (ITS) region of rDNA gene. This is the first report of the isolation of C. siamense from Piperaceae. The fungus was fermented in potato dextrose media and the fungal media were extracted with EtOAc. Chromatographic separation of the EtOAc extract over silica gel, Sephadex LH-20 and preparative thin layer chromatography furnished indole-3-acetic acid (IAA) and uracil. IAA showed high antifungal activity against the common plant pathogenic fungus Cladosporium cladosporiodies by TLC bioautography method and antioxidant activity against DPPH radical by spectrophotometry method.

The Effect of Interfacial Chemical Bonding in TiO<sub>2</sub>-SiO<sub>2</sub> Composites on Their Photocatalytic NOx Abatement Performance

The chemical bonding of particulate photocatalysts to supporting material surfaces is of great importance in engineering more efficient and practical photocatalytic structures. However, the influence of such chemical bonding on the optical and surface properties of the photocatalyst and thus its photocatalytic activity/reaction selectivity behavior has not been systematically studied. In this investigation, TiO2 has been supported on the surface of SiO2 by means of two different methods: (i) by the in situ formation of TiO2 in the presence of sand quartz via a sol-gel method employing tetrabutyl orthotitanium (TBOT); and (ii) by binding the commercial TiO2 powder to quartz on a surface silica gel layer formed from the reaction of quartz with tetraethylorthosilicate (TEOS). For comparison, TiO2 nanoparticles were also deposited on the surfaces of a more reactive SiO2 prepared by a hydrolysis-controlled sol-gel technique as well as through a sol-gel route from TiO2 and SiO2 precursors. The combination of TiO2 and SiO2, through interfacial Ti-O-Si bonds, was confirmed by FTIR spectroscopy and the photocatalytic activities of the obtained composites were tested for photocatalytic degradation of NO according to the ISO standard method (ISO 22197−1). The electron microscope images of the obtained materials showed that variable photocatalyst coverage of the support surface can successfully be achieved but the photocatalytic activity towards NO removal was found to be affected by the preparation method and the nitrate selectivity is adversely affected by Ti-O-Si bonding.