Facile synthesis of Ag_2O-TiO_2/sepiolite composites with enhanced visible-light photocatalytic properties

Ag2O-TiO 2/sepiolite heterostructure composites were synthesized by a simple two-step method at low temperatures（100–450 °C）. Acid red G aqueous solution and gaseous formaldehyde were chosen as model organic pollutants to evaluate the photocatalytic performance of the as-prepared composites. The results showed that the Ag2O-TiO 2/sepiolite exhibited enhanced photocatalytic activity over pure Ag2O-TiO 2,TiO 2/sepiolite,and Ag2O/sepiolite under visible-light irradiation（λ 420 nm）. The excellent photocatalytic efficiency of these composites can be ascribed to the synergistic effect between the heterojunction and the porous structure of the clay layers,which induced high adsorption and efficient charge separation. In addition,the active species involved in the degradation reaction have been investigated by photoluminescence spectroscopy and quenching experiments. A possible photocatalytic degradation mechanism of acid red G dye by the Ag2O-TiO 2/sepiolite composite is also discussed.

Ni/sepiolite催化剂的改性研究Ⅱ.载体的改性

以羟基铝改性sepiolite为载体制备了一系列Ni基催化剂。采用苯加氢为探针反应及二硫化碳中毒法系统地考察了载体改性对Ni/sepiolite催化剂活性及抗毒性能的影响。结果表明 ,载体的改性增加了催化剂的活性中心数 ,提高了Ni原子分散度 ,降低了加氢反应的活化能。动力学研究亦表明 ,羟基铝的引入既有电子效应又有几何效应 。

Y对Ru/sepiolite催化剂甲苯加氢活性的影响

以海泡石为载体,Ru为活性组分,采用浸渍法制备了Ru/sepiolite和Ru-Y/sepiolite催化剂。以甲苯加氢为探针反应,利用TPR,TPD,XRD和比表面积等测试手段对催化剂进行了表征。结果表明,Y的加入提高了Ru/sepiolite的催化活性和Ru的分散度,增加了催化剂的活性中心数和吸附性能。

Carbon Dioxide/Methane Separation by Adsorption on Sepiolite

In this work, the use of sepiolite for the removal of carbon dioxide from a carbon dioxide/methane mixture by a pressure swing adsorption （PSA） process has been researched. Adsorption equilibrium and kinetics have been measured in a fixed-bed, and the adsorption equilibrium parameters of carbon dioxide and methane on sepiolite have been obtained. A model based on the LDF approximation has been employed to simulate the fixed-bed kinetics, using the Langmuir equation to describe the adsorption equilibrium isotherm. The functioning of a PSA cycle for separating carbon dioxide/methane mixtures using sepiolite as adsorbent has also been studied. The experimental results were compared with the ones predicted by the model adapted to a PSA system. Methane with purity higher than 97% can be obtained from feeds containing carbon dioxide with concentrations ranging from 34% to 56% with the proposed PSA cycle. These results suggest that sepiolite is an adsorbent with good properties for its employment in a PSA cycle for carbon dioxide removal from landfill gases.

Facile preparation of sepiolite@LDH composites for the visible-light degradation of organic dyes

Sepiolite@LDH(Sep@LDH)composites were designed and prepared based on the assembly of layered double hydroxides(LDH)on acidified sepiolites(Sep)for the simultaneous photocatalytic degradation of methyl orange(MO)and methylene blue(MB).The structure,morphology,texture,optical properties,and photocatalytic performance of the prepared Sep@LDH were studied in detail.Among the Sep@LDH composites,Sep4@LDH(4.0 g Sep)exhibited the highest photocatalytic activity under visible‐light irradiation,which could be attributed to its large surface area,high crystallinity,and plentiful active sites on its surface.The photodegradation of the dyes followed a pseudo first‐order kinetic model(Langmuir‐Hinshelwood model),indicating that the copious and homogeneous active sites on the surface of the composites contributed to the high photocatalytic activity.The photodegradation mechanism was studied by examining the active species(^-OH,h+,and·O2^-anions)using appropriate scavengers.It was found that·OH radicals played a critical role in the photocatalytic process of MO and MB,where the generation of·OH radicals occurred on the electron/hole(e^-/h+)pairs on the surface of the Sep@LDH composites.

Application of modified sepiolite as reusable adsorbent for Pd(Ⅱ) sorption from acidic solutions

The adsorption characteristics and mechanisms of modified sepiolite as an adsorbent to recover Pd(Ⅱ) from acidic solutions were studied. The Pd(Ⅱ) adsorption properties were analyzed through isotherm, kinetic and thermodynamic models. In addition, SEM-EDS, TEM and XPS were applied to investigating the Pd(Ⅱ) adsorption mechanisms onto modified sepiolite. The equilibrium data were well fitted to Langmuir isotherm model with maximum Pd(Ⅱ) adsorption capacity of 322.58 mg/g at 30 ℃. The kinetic data could be satisfactorily simulated by the pseudosecond order model, indicating that the rate-controlling step was chemical adsorption. 99% of Pd(Ⅱ) could be recovered using 1 g/L modified sepiolite when initial concentration of Pd(Ⅱ) was 100 mg/L. The results of reusability studies indicated the modified sepiolite had an acceptable stability and reusability. This study indicated that the modified sepiolite might be an efficient and cost-effective material for Pd(Ⅱ) recovery.

Sodium-treated sepiolite-supported transition metal(Cu,Fe,Ni,Mn,or Co)catalysts for HCHO oxidation

Sodium-treated sepiolite(Na Sep)-supported transition metal catalysts(TM/Na Sep;TM = Cu, Fe, Ni, Mn, and Co) were synthesized via a rotary evaporation method. Physicochemical properties of the as-synthesized samples were characterized by means of various techniques, and their catalytic activities for HCHO(0.2%) oxidation were evaluated. Among the samples, Cu/Na Sep exhibited superior performance, and complete HCHO conversion was achieved at 100 ℃(GHSV = 240000 m L/(g·h)). Additionally, the sample retained good catalytic activity during a 42 h stability test. A number of factors, including elevated acidity, the abundance of oxygen species, and favorable low-temperature reducibility, were responsible for the excellent catalytic activity of Cu/Na Sep. According to the results of the in-situ DRIFTS characterization, the HCHO oxidation mechanism was as follows:(i) HCHO was rapidly decomposed into dioxymethylene(DOM) species on the Cu/Na Sep surface;(ii) DOM was then immediately converted to formate species;(iii) the resultant formate species were further oxidized to carbonates;(iv) the carbonate species were eventually converted to CO2 and H2O.

Adsorption Properties of Calcined Modified Sepiolite on SO4^2- and Cl^-

Three different kinds of sepiolite(Type A, Type B and Sepiolite fiber) were processed by calcination and analyzed by thermogravimetric analysis(TG), X-ray diffraction diffractometer(XRD), scanning electron microscopy(SEM), BET(specific surface area from N2 adsorption isotherms), mercury intrusion porosimetry(MIP), and infrared spectroscopic analysis(IR), respectively. The results show that the adsorption performance of sepiolite can be changed by calcination and environment temperatures, especially for calcination. The adsorption capacity of sepiolite fiber is bigger than that of Type A and B, and adsorption capacity of each sepiolite to sulfate is smaller than that of the chloride ions. Especially, the maximum value for adsorption of the sepiolite fibers, calcined at 600 ℃ and water bath at 60 ℃, to chlorine ion and sulfate are 5.95 and 5.71 mg/g, respectively(mg/g : the ions quantity adsorbed by a unit of sepiolite weight). The minimum adsorption of calcined sepiolite fiber to sulfate ions increased from 5.02 to 5.55 mg/g. While microstructure analysis of sepiolite by TG indicated that its structure was, for temperature not exceeding 700 ℃, was not changed significantly. Sepiolite has a porous structure, especially for sepiolite fiber, which can be observed by SEM. BET indicates that sepiolite fiber has a larger pore volume than others and this can be increased by calcination. IR shows that the adsorption of sepiolite to Cl-and SO42- belongs to physical absorption, instead of chemisorption.

Modified sepiolite stabilized stearic acid as a form-stable phase change material for thermal energy storage

Sepiolite(ST) was used as a supporting matrix in compiste phase change materials(PCMs) due to its unique microstructure, good thermal stability, and other raw material advantages. In this paper, microwave acid treatment were innovatively used for the modification of sepiolite. The modified sepiolite(ST_(m)) obtained in different hydrochloric acid concentrations(0.25, 0.5, 0.75, and 1.0 mol·L^(-1)) was added to stearic acid(SA) via vacuum impregnation method. The thermophysical properties of the composites were changed by varying the hydrochloric acid concentration. The SA-ST_(m0.5)obtained by microwave acid treatment at 0.5 mol·L^(-1)hydrochloric acid concentration showed a higher loading capacity(82.63%) than other composites according to the differential scanning calorimeter(DSC) analysis. The melting and freezing enthalpies of SA-ST_(m0.5)were of 152.30 and 148.90 J·g^(-1), respectively. The thermal conductivity of SA-ST_(m0.5)was as high as 1.52 times that of pure SA. In addition, the crystal structure, surface morphology, and microporous structure of ST_(m)were studied, and the mechanism of SAST_(m0.5)performance enhancement was further revealed by Brunauere Emmett Teller(BET) analysis. Leakage experiment showed that SAST_(m0.5)had a good morphological stability. These results demostrate that SA-ST_(m0.5)has a potential application in thermal energy storage.

Carbon Nanotubes Grown on Sepiolite as Catalyst Carrier

Multi-walled carbon nanotubes were synthesized by the catalytic decomposition of acetylene at 750oC over sepiolite powder, which was treated with aqueous cobalt nitrate. It is expected that the composite with high specific area will have high capacity of hydrogen storage.

Lanthanum-Promoted Ru/Sepiolite in Ammonia Synthesis

A new kind of Ru supported on sepiolite catalyst with La as promoter for ammonia synthesis was prepared. The effects of reaction conditions on catalytic activity were discussed. The result shows that La is an effective promoter for sepiolite-supported Ru based catalyst. When the load of Ru is 5% (mass fraction), and the molar ratio of La/Ru is 1.5, under the condition of 10 MPa 450 ℃ 20000 h-1, the ammonia synthesis rate is 38.5 mmol NH3·g-1·h-1.

Modification of Sepiolite by Treatment with Methyl Triethoxysilane

Grafting reaction of methyltriethoxysilane on sepiolite surface was studied.The structure of the silanized product before and after thermal treatment was characterized by XRD,TG-DTA,SEM and IR.It is found that the silicon monomers are grafted on the external surface of sepiolite via silicon hydroxyls.The thermal stability remains unchanged after silanization.

Internal Curing Mechanism of Sepiolite in Cement Paste

In order to explore the internal curing mechanism of sepiolite in cement-based materials,the effects of sepiolite on the water consumption of standard consistency,setting time,viscosity,strength,pore structure characteristics,micro-hardness characteristics and two-dimensional surface characteristics of cement paste were studied,respectively.The experimental results show that the water consumption of standard consistency increases linearly with the increase of sepiolite content.The setting time and viscosity are also lengthened and increased with the addition of sepiolite,respectively.When the content of sepiolite exceeds 5%,the strength of the specimen increases significantly.The BET results show that the pore structure of the interfacial transition zone(ITZ)in hardened cement paste(HCP)with sepiolite is optimized after curing for28 d and its pore volume content with below 10 nm is decreased,especially for the specimen with a lower watercement ratio.The characteristics of microhardness and strength of specimens have the same law.Backscattered electron image(BSE-IA)shows that the ITZ of the specimen with sepiolite is denser and the unhydrated cement particles are less than the reference specimen.

Cadmium sorption from aqueous solutions onto Iranian sepiolite:Kinetics and isotherms

This work aims to investigate the efficiency of Fariman sepiolite from Iran as an adsorbent to remove Cd from aqueous solutions. The effects of different experimental factors such as the initial Cd concentration, contact time and the sorbent dose were investigated through a series of batch adsorption experiments. The results show that the adsorption capacity of sepiolite for Cd increases with the contact time, the initial concentration of Cd solutions and the sorbent dose. Sorption of Cd by Fariman sepiolite is rapid within the first hour of the experiment and then slowly increases until a pseudo equilibrium is approached at 8 h. The results also show that the time-dependent Cd sorption data are better described with pseudo second-order （7〉0.999） than that of pseudo first-order （r2〉0.971） kinetic model. Equilibrium isotherm studies show that the experimental data are better correlated by the Freundlich adsorption isotherm （7〉0.995） than the Langmuir （P〉0.825）. It is suggested that both adsorption and cation exchange reactions are responsible for the sorption of Cd by the sepiolite, and the mineral has a very good potential to remove Cd from aqueous solutions.

Effects of Promoters on a Ru/Sepiolite Catalyst for Carbon Dioxide Methanation

In this work, CO_2 methanation has been investigated over Ru-based catalysts.The effects of promoters on the activity, selectivity and reduction properties of the Ru/sepiolitecatalyst were analyzed by kinetic and thermodynamic methods. The catalysts were characterized bymeans of TPD, and the results revealed that the addition of Mo, Mn or Co improved the properties ofthe Ru/sepiolite catalyst. The effects of promoters could affect the change of enthalpy, entropy andchemical potential.

Study on Modification of Sm_2O_3 by Ni/Sepiolite Catalyst

A series of Ni Sm/sepiolite catalysts were prepared by impregnation. The modification of Sm 2O 3 for Ni/sepiolite was investigated by TPR, XPS and poisoning of CS 2, respectively. The results indicate that the addition of Sm 2O 3 improves the activity of hydrogenation and anti poisoning ability of Ni/sepiolite catalyst, and it also increases the dispersion of nickel atoms over support and the amount of active nickel atoms in catalyst. Effect of Sm 2O 3 on Ni/sepiolite catalyst includes not only electronic effect but also steric effect, whereas electronic effect seems to be principal.

Preparation and Properties of Organically Modified Sepiolite/High-performance Epoxy Nanocomposites

Fibrous organic sepiolites （OSEP） and novel epoxy/OSEP nanocomposites were prepared, and different methods were investigated to produce an intercalated/exfoliated structure of OSEP. Experimental results show that the modifier molecules can be easily adsorbed by the sepiolite, but the layer space （d001 of the sepiolite, linked by means of covalent bond, remains unchanged. A proper method to solve this problem appears to exert large shearing force on the original sepiolite followed by its organic modification （OSEP2）. The morphology observation shows that there are formed an even dispersion of nano-sized OSEP2 fibers in epoxy resin and a structure intercalated by epoxy molecules, which lead to significantly improved mechanical properties. Impact strength of the epoxy/OSEP2 nanocomposite increases from 32.1 kJ/m^2 to 44.4 kJ/m^2, 38.3% higher than that of pristine matrix with 3 wt% OSEP2 content. It is also noted that the flexural strength of the OSEP/epoxy composites has risen by about 3% higher than that of the pure epoxy resin.

Effect of Transition Metals on Catalytic Performance of Ru/Sepiolite Catalyst for Methanation of Carbon Dioxide

The effects of Mo, Mn and Zr transitional metals on the catalytic performance of Ru/sepiolite for CO2 methanation were investigated. The results indicated that addition of the transitional metals affected the activity of the Ru/sepiolite remarkably, and the activities of the catalysts were closely associated with the electronic state of the ruthenium surface. The addition of Mo increased the active surface area, the Ru dispersity, the number of active sites, and the resistance to poisoning. According to the Transition State Theory, when Mo is added into the Ru/sepiolite catalyst, the decrease in surface energy is at a cost of an increment in steric hindrance. When T≤674 K, the energy factor was dominating, and resulted in a decreasing in the ratio of S(CU4)/S(CO). Otherwise, the steric factor dominated the reaction course.

RESEARCH ON CLEANUP AND ACTIVATION OF SEPIOLITE

A simple process of purifying and activating sepiolite is introduced. Impure minerals in sepiolite can be removed by fully agitating the sepiolite suspension to which a few amount of disperser has been added. After being purified and activated, fine sepiolite particles present prior properties such as increased specific area,better dispersiveness and increased adsorptivity, moreover, the pulping ratio can be raised from original 4-5m3/2 to 20m3 /t. The process with simple technique and utilizing cheap chemical agents extends the application of low-grade sepiolite.

DEVELOPMENT OF SEPIOLITE TYPE FILTER TIPS OF CIGARETTE

Activating conditions of sepiolite are studied by determining specific surface method. Sepiolite is used in processing filter tip of cigarette of acetate silk and paper type first. Tar of cigarette with sepiolite filter tip is lowered to a lower tar level. Mechanism of the lowered tar content by sepiolite is analysed.