Cl2 Adsorption and Desorption over Ordered Mesoporous Carbon Materials as an Indicator for Catalytic Phosgene Formation

The presented work evaluates the implementation of adsorption and desorption experiments with Cl₂ over carbon materials towards the development of more active and stable catalysts for industrial phosgene synthesis. By using a soft templating method as a tool, ordered mesoporous carbon materials with tunable porosity, surface area, and degree of graphitization were synthesized and utilized as model system. The Cl₂ adsorption/desorption properties of these materials were studied and compared to commercial activated carbon. To draw correlations between Cl₂ adsorption/desorption behavior and catalytic performance, the materials were further tested in the phosgene formation in a plug flow reactor. However, the chemical reaction of Cl₂ with carbon during the adsorption/desorption experiment hinders a direct correlation.     

Adsorption of amphiphiles at an oil-water vs. an oil-metal interface

Studies were conducted to investigate whether adsorption of amphiphiles from oil onto a degreased metal can be predicted from knowledge about adsorption of the amphiphiles at the oil-water interface. The surface of a degreased metal comprises oxides, hydroxides, and adsorbed water vapor, which form from the reaction of the metal with air and moisture. If the behaviors of amphiphiles at water-oil and metal-oil interfaces are similar, this information can be useful in the development of cheaper and quicker methods of estimating amphiphile adsorption properties on degreased metals. The amphiphiles used were safflower oil (SA) and jojoba oil (JO), both of which are plant-based oils, and methyl palmitate (MP). SA is a triester whereas JO and MP are monoesters. The interfacial tension of water-hexadecane was measured as a function of amphiphile concentration in hexadecane and used to estimate an interfacial-based free energy of adsorption, ΔG _ads. The resulting interfacial-based ΔG _ads values for SA were identical to those reported from friction-based adsorption isotherms. The corresponding values for the monoesters were within the range reported from friction-based adsorption isotherms.     

含有球状和柱状超微孔SiO2的一步合成与表征

以常用的十二烷基胺为模板剂,首次以3－巯丙基－三甲氧基硅烷和三氟甲基三甲基硅烷为共模板剂,在乙氰－水溶剂中,合成了高比面积、高热稳定性、具有球状和柱状新颖形貌的超微孔分子筛,并用氮气吸附脱咐,XRD,FT－IR,SEM和TG－DSC等对其结构进行了表征,推测了合成过程.     

A new synthesis procedure for titanium-containing zeolites under strong alkaline conditions and the catalytic activity for partial oxidation and photocatalytic decomposition

A new synthesis procedure for titanium-containing aluminosilicate zeolites has been obtained using a clear colloidal dispersion (sol) which was prepared with titanium isopropoxide, water, hydrochloric acid and colloidal silica, Ludox. When NaY, KL, offretite, mordenite and ZSM-5 zeolites were crystallized from the sol following conventional hydrothermal crystallization procedures, all the aluminosilicate zeolites showed the same X-ray absorption fine structure at the Ti K edge indicating framework Ti. The zeolites showed remarkable catalytic activity for the partial oxidation of cyclohexene using H₂O₂ as an oxidant and the photocatalytic decomposition of trichloroethene using water.     

Binary Adsorption in a Fixed-Bed Column Packed with an Ion-Exchange Resin

Abstract

A mathematical model was adopted to analyze a binary fixed-bed adsorption column packed with an ion-exchange resin. Two pairs of organic compounds, o-cresol-benzoic acid and p-chlorophenol-p-nitrophenol, were employed as the adsorbates. A modified Langmuir isotherm with interaction factors η _i was found suitable for representing the adsorption equilibrium. Scale-up of the binary adsorption column with respect to column length was effective based on the proposed mathematical model and corresponding methods for estimating the model parameters. The significance of excess concentration in the breakthrough curve was related to inlet concentration, column length, and the difference in adsorption affinity.     

Electrochemical removal of boron from water: Adsorption and thermodynamic studies

The present work provides an electrochemical removal of boron from water and its kinetics, thermodynamics, isotherm using mild steel and stainless steel as anode and cathode respectively. The various operating parameters on the removal efficiency of boron were investigated, such as initial boron ion concentration, initial pH, current density and temperature. The results showed that the optimum removal efficiency of 93.2% was achieved at a current density of 0.2 A dm^?2 at pH of 7.0. First‐, second‐order rate equations, Elovich and Intraparticle models were applied to study adsorption kinetics. Adsorption isotherms of boron on Fe(OH)₃ were determined and correlated with isotherm equations such as Langmuir, Freundlich and D‐R models. Thermodynamic parameters, such as standard Gibb's free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°), were also evaluated by Van't Hoff equation. The adsorption process follows second‐order kinetics. The adsorption of boron preferably fits with Langmuir adsorption isotherm suggesting monolayer coverage of adsorbed molecules. The adsorption of boron onto Fe(OH)₃ was found to be spontaneous and endothermic. © 2011 Canadian Society for Chemical Engineering     

Adsorption characteristics of sericite for cesium ions from an aqueous solution

To efficiently remove cesium ions from aqueous solution, sericite was used as a novel adsorbent. The silanol (SiO₂) and aluminol (Al₂O₃) groups in sericite are likely to play an important role in adsorption process. The maximum adsorption capacity (q_m) and adsorption constant (K_L) for cesium ions obtained from the Langmuir isotherm model were 6.68 mg/g and 0.227 L/mg, respectively and regression curve fit well with the experimental data as the 0.965 of correlation coefficients (r²). However, when the Freundlich isotherm model was used correlation coefficient (r²) was 0.973. Therefore, it was concluded that Freundlich model fits equilibrium data better than Langmuir model. When the 6.0 g/L of sericie concentration was added to aqueous solution, cesium ions were removed by about 80% and the increase was not happened above 6.0 g/L of sericite concentration any more. The process was determined as exothermic reaction because the removal efficiency of cesium ions decreased as temperature increased. Furthermore, all adsorption was completed in 120 min and comparing the pseudo first and second-order kinetic models indicates that the adsorption of cesium ions using sericite follows well the pseudo-second-order kinetics.     

Adsorption efficiency and photocatalytic activity of fly ash-based geopolymer foam mortar

Fly ash-based geopolymer foam mortar (GFM) was used as an adsorbent material to methylene blue (MB) and also the dye removal material using the photocatalytic mechanism. The GFM, containing 50 wt% river sand aggregate, was prepared to have approximately 46% open porosity, pore size distribution between 0.01 and 3.5 mm, and water permeability of 0.2 cm/s. The variation of adsorption efficiency and adsorption capacity with the contact time of the GFM was first evaluated using various GFM dosages (10, 20, 50, 80, and 100 g/L). The adsorption efficiency at equilibrium (AE_e) was found to linearly increase, while adsorption capacity (q_ae) exponentially decayed, with an increase of loading dosages. The photocatalytic removal efficiency of ~100% was obtained with 50, 80, and 100 g/L GFM loading dosages, with a shorter time at higher dosages. The GFM could be reused, without regeneration, for 5 cycles. The AE_e and q_ae for each reused cycle did not noticeably change suggesting the reusability. The photocatalytic removal efficiency, however, was found to decrease with an increase of the reused cycle. After the 5^th cycle, the highest removal efficiency was reduced to ~70%. The attempts to treat the GFMs with hydrochloric (HCl) and phosphoric (H₃PO₄) acid to reduce the excess alkaline did not give satisfactory results as expected. The photocatalytic removal efficiency had subsided after the treatment with both acids.     

Preparation and Adsorption Research of the Modification Macroporous Adsorption Resin (LX1180)

This work focused on the research of carboxylation modification of nonpolar macropolar adsorption resin (MAR) (LX1180) and its adsorption properties. Under optimization conditions a MAR with carboxylation degree of 23.10% (g/g, expressed as C₇H₆NO₂) was obtained. After characterizing the structures of MAR LX1180, LX1180-Cl and LX1180-COO^?, the adsorption mechanism (including isotherm kinetics) and influence of functional groups and functional degree of substrate on equilibrium adsorption capacity were also investigated systemically. The result showed the adsorption mechanism could be expressed well by an intra-particle diffusion model, and the four-parameter adsorption model was more appropriate to express the adsorption behavior of the MARs here. Moreover, it could be found that the introduction of a functional group could increase the equilibrium adsorption capacity, while the initial concentration related to the saturated adsorption capacity decreased.     

Adsorption of polyacrylamide on zirconium dioxide

The adsorption of an anionic-type polyelectrolyte (polyacrylamide) onto zirconium dioxide from aqueous dispersion has been studied as a function of pH. Polymer adsorption takes place in the acid region, obeying a Langmuir-type isotherm. Adsorption decreases with increasing pH. The zero-point of charge (zpc) at the ZrO₂–H₂O interface and the nature of the ionic charge on the polymer molecules were investigated. The behavior of polymer attachment is discussed on the grounds of a nonionic bonding mechanism including H bonding and of electrostatic interaction. It has been found that the zpc of ZrO₂ is at pH ～3.5 and that the ionic properties of the polymer molecules depend, to a noticeable extent, upon the pH of the medium.     

微波法合成MCM-41介孔分子筛及吸附性能研究

以十六烷基三甲基氯化铵为模板剂,在微波实验条件下合成MCM-41介孔分子筛,缩短了合成时间,降低产品成本。实验考察了多种因素对MCM-41合成的影响,并通过吸附处理亚甲基蓝溶液能力强弱,得到最佳合成条件：摩尔比1TEOS：0.2CTMACl：160H2O,pH为10,晶化时间15 min。通过红外光谱分析,MCM-41分子筛的主要特征吸收峰均已出现,说明合成分子筛MCM-41成功。     

Adsorption and desorption behaviors of S-adenosyl-L-methionine in a fixed-bed ion-exchange column

S-adenosyl-L-methionine (SAM) is one of most versatile molecules in nature and has wide medical applications. The ion-exchange separation process of SAM of the extract of yeast cells has many advantages over selective precipitation by picrolonic acid. Experiments of the dynamic column process of SAM on JK110 resin were carried out in a fixed-bed ion-exchange column. The effects of different operation parameters on the adsorption and desorption behaviors of SAM were investigated. The results show that the ion-exchange adsorption of SAM is successfully implemented at 2BV/h, 10 g/L, pH 5.0; the adsorbed SAM in the ion-exchanged bed is efficiently desorbed by 0.2 N H₂SO₄ solution at the flow rate of 2BV/h. According to material balance, the recovery yield of SAM for this ion-exchange process is 90.1%. Finally, this ion-exchange process was successfully scaled up to separate SAM at high yield and purity.     

Precursor Preparation to Promote the Adsorption of Mg‐Al Layered Double Hydroxide

This study presents an interesting phenomenon of the simultaneous occurrence of adsorption and synthesis of Mg–Al layered double hydroxide (Mg–Al–LDH) by stirring a precursor in an aqueous solution with methyl orange (MO) as target adsorbate with the precursor prepared by first milling Mg(OH)₂ for 1 h followed by another 3 h milling with Al(OH)₃.The prepared precursor and LDH samples were characterized by a set of analytical methods including X‐ray diffraction (XRD), thermogravimetry/differential scanning calorimetry (TG–DSC), and Fourier‐transform infrared (FT–IR). The maximum adsorption capacity (Q_m) of MO by the prepared precursor sample was 1110.2 mg/g, much higher than that from the synthesized LDH sample. Engineering application may be expected from the easy preparation of such precursor as adsorbent to purify the tremendous amounts of dye wastewater.     

Halloysite Nanotubes Modified by Fe3O4 Nanoparticles and Applied as a Natural and Efficient Nanocatalyst for the SymmetricalHantzsch Reaction

Halloysite as an impressive natural eco-friendly nanotube with aluminosilicate structure has been investigated recently due to its unique features such as specific morphology and excellent bio-adaptability. In this research, Fe₃O₄ nanoparticles have been loaded on the tubular halloysite by co-precipitation method in order to synthesis magnetic halloysite (Hal-Fe₃O₄₎. To characterize this recoverable nanocatalyst, applicable analyses such as Fourier-transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray (EDX) analysis, field-emission scanning electron microscopy (FE-SEM) images, X-ray diffraction (XRD) pattern, Thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) curves have been carried out. The results confirmed that Fe₃O₄ nanoparticles with cubic structure, and uniform distribution, were located at halloysite nanotubes (HNTs). This aluminosilicate nanocomposite with high thermal stability, crystalline structure, and stable morphology was evaluated as a heterogeneous catalyst in the symmetrical Hantzsch reaction for the first time. Easy synthesis process, green media, high performance, recoverable catalyst and reusing of the Hal-Fe₃O₄ as a nanocatalyst for 8 times are the main features of this protocol.

     

Combustion Synthesis of BaCO3 and its Application for Eu(III) Adsorption from Aqueous Solution

A combustion method using urea as fuel and barium nitrate as oxidant was applied for the synthesis of barium carbonate, which was characterized by XRD, IR, SEM, and BET. A batch technique was employed to study the Eu(III) adsorption from an aqueous solution using BaCO₃. It was found that the adsorption process attains equilibrium within 3 hours and depends upon the pH, europium concentration, and temperature. The kinetic data of the process could be fitted by means of the pseudo-second order and the intraparticle mass transfer diffusion models, whereas the isotherm by means of the Langmuir equation. Thermodynamic parameters indicate that the process is spontaneous and endothermic in nature. These results suggest that BaCO₃ is an effective material for Eu(III) adsorption from aqueous solutions. The findings of this study could be relevant for heterogeneous catalytic processes as well have an environmental impact.     

CO2 Adsorption and Desorption for CO2 Enrichment at Low-Concentrations Using Zeolite 13X

Adsorption of CO₂ using zeolite 13X as adsorbent has been studied extensively, but little attention has been paid to CO₂ adsorption at very low concentrations such as in the ambient air. Furthermore, there is almost no information on CO₂ desorption characteristics. In a carbon enrichment for plant stimulation system, ambient CO₂ is enriched from 400 to 1000 ppm to provide an enriched CO₂ stream for plant growth in greenhouses. To provide essential design data, systematic performance tests were carried out to evaluate both the adsorption and desorption capacity, enrichment factor, moisture content, and cyclic performance. It was found that the adsorption capacity and CO₂ concentration in the enriched air are a function of adsorption temperature and the difference of adsorption and desorption temperatures, for a given adsorbent loading at a properly selected gas flow rate.     

Adsorption of p-nitrophenol on an activated carbon with different oxidations

An activated carbon prepared from olive stones has been modified through oxidation by nitric acid or sodium hypochlorite. These treatments introduced large amounts of oxygen groups, which were characterized by mass-spectrometry, temperature-programmed desorption (DTP-MS). Both CO₂- and CO-evolving groups were created by these oxidation treatments. A part of these oxidized samples was then outgassed under vacuum up to 823 K in order to remove most of the CO₂-evolving groups from their surface. Oxidized samples have a smaller surface area than the original sample. The subsequent partial outgassing increases the surface area which, however, does not reach the value it had before oxidation. p-Nitrophenol (PNP) adsorption isotherms from aqueous solutions were determined at 298 K for the original, oxidized, and partly outgassed samples. The results confirm the presence of an intermediate plateau at low equilibrium PNP concentration (at about 10 mg/l). The relative effects of textural versus surface chemistry on PNP uptakes are then discussed. The presence of CO-evolving groups showed no influence on PNP uptakes. The conclusion is that models in which carbonylic groups are basic adsorption sites for substituted phenols can be ruled out for the entire isotherm of PNP obtained with the original carbon. These models are also unlikely for PNP adsorption on oxidized and partly outgassed samples.     

Synthesis and Toluene Adsorption/Desorption Property of Beta Zeolite Coated on Cordierite Honeycomb by an In Situ Crystallization Method

The beta zeolite on cordierite ceramic monolith was synthesized by an in situ crystallization method and characterized by XRD, N₂ adsorption/desorption, SEM and NH₃‐TPD techniques. Toluene adsorption/desorption was used as probe test for the control of cold‐start emissions and treatment of volatile organic compounds. The presence of beta on the supports was confirmed by XRD, SEM, and N₂ adsorption/desorption measurements. The zeolite crystals grow both into the cordierite macropores and on the surface of the monolith channels, which form an integrated network ensuring a strong adherence. The highly dispersed beta on supports, demonstrated by larger surface area and adsorption capacity of N₂, resulted in a significant increase of the total acidity, and thus a greater adsorption capacity for toluene. Furthermore, it could trap larger amounts of toluene to higher temperature and show considerable activity for toluene cracking and oxidation. These are attributed to the greater acidity and stronger acid sites of in situ synthesized beta.     

Adsorption of heavy metals by pirymidine-derivated mesoporous hybrid material

This paper describes the synthesis of pyrimidine-derivated hybrid mesoporous material via chemical bonding. This has been done by modifying the silanol groups of the support with a synthesised pyrimidine propyl triethoxysilane. The hybrid material has been characterized by X-ray diffraction, nitrogen adsorption techniques, FT-IR, ²⁹Si and ¹³C MAS NMR. The potential of the material of removing heavy metal as copper, nickel and cobalt from water has been tested. Effects of pH, velocity of adsorption, selectivity, maximum adsorption capacity and preconcentration capacity have been determined.     

Adsorption,oxidation and effect of CO on hydrogen adsorption at smooth rhodium electrodes in acid solution

The adsorption of carbon monoxide was studied under steady state conditions on smooth rhodium electrodes in 0.5 M H₂SO₄ at room temperature. The coverage with carbon monoxide is equal to saturation coverage between 0.1 and 0.5 V vs a hydrogen electrode in the same solution. Above 0.5 V it decrease to 0 within 0.2 V. The oxidation of chemisorbed carbon monoxide at constant current is accompanied by the formation of the oxygen layer above 0.6 V. A correction for the contribution of the oxygen layer formation to the anodic charge has to be applied in the determination of the CO_ad coverage even at small current densities.The coverage with H_ad was determined as a function of potential at constant coverage with preadsorbed carbon monoxide from anodic charging curves. These curves were taken at a sufficiently small current density so that the equilibrium of the Volmer reaction remained practically established. The coverage of CO_ad, computed from the charge for the oxidation of CO_ad, agreed well with that obtained from the decrease of the length of the hydrogen branch of the charging curves. The isotherms of hydrogen adsorption are of the Temkin type at CO_ad coverages above 0.4. The characteristic parameters of the Temkin isotherm were determined as a function of the coverage with CO_ad.