Acid-treated Sepiolite Research Articles

Highly efficient CO2 capture on acid-treated sepiolite impregnated with mixed polyethyleneimine and diethanolamine

Amine-functionalized solid adsorbents exhibit broad prospects in CO2 capture from flue gases due to their high adsorption capacity and selectivity. However, reported adsorbents are still facing challenges, including high costs, the easy agglomeration of polyamines, and limited adsorption temperature ranges. In this study, sepiolite-based mixed amine adsorbents are prepared by synergistically impregnating acid-treated sepiolite with a mixture of polyethyleneimine (PEI) and diethanolamine (DEA). Results show that at a PEI/DEA loading ratio of 1:1 and a mixture loading of 60wt%, the CO2 adsorption capacity of the resulting adsorbent increases from 0.58mmol/g for acid-treated sepiolite to 2.89mmol/g at 60°C, and remains above 2.50mmol/g after 10 cycles. Meanwhile, the optimized adsorbent maintains a capacity of over 2.44mmol/g within the temperature range of 30–70°C. Additionally, the CO2 selectivity and maximum heat of adsorption for the optimized adsorbent are calculated to be 1184 and 60.08kJ/mol, respectively. An improved CO2 adsorption capacity is obtained, an increase from 0.052mmol/g for acid-treated sepiolite to 1.60mmol/g. Furthermore, an in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) analysis reveals that the introduction of DEA into PEI helps in polyamine dispersion, thereby enhancing CO2 adsorption capacity. The CO2 capture mechanism follows a zwitterionic reaction, where CO2 is ultimately converted into carbamate and carbamic acid. Overall, the as-prepared sepiolite-based mixed amine adsorbents, which are characterized by high CO2 adsorption capacity and selectivity, low cost, broad adsorption temperature range, moderate heat of adsorption, and good cycle stability, show promising potential for industrial applications.

Effect of acid treatment on the reactivity of natural sepiolite used as a supplementary cementitious material

In this study, natural sepiolite samples were treated with hydrochloric and acetic acid solutions at three different concentrations (0.1 M, 0.5 M, and 1.0 M). The effect of acid treatment on the reactivity of natural sepiolite and the change in cement hydration following the addition of natural sepiolite were studied using X-ray diffraction, particle size distribution analysis, inductively coupled spectrometry, thermogravimetric analysis, and isothermal calorimetry. Although acid treatment leads to a slight decrease in the amorphous phase content in natural sepiolite, the reactivity of sepiolite increased. The results indicate that the increase in sepiolite reactivity most likely stemmed from the activation of the Si phase. In addition, acid-treated sepiolite can modify the hydration of cement during the early curing period and hinder the hydration of cement during the later curing period. The compressive strength of specimens with strong acid-treated sepiolite was higher compared with specimens with weak acid-treated sepiolite.

Optimisation of sepiolite clay with phosphoric acid treatment as support material for CoB catalyst and application to produce hydrogen from the NaBH4 hydrolysis

Herein, the CoB catalyst supported on the sepiolite clay treated with phosphoric acid was utilized to produce hydrogen from the NaBH4 hydrolysis. In order to analyse the performance of the phosphoric acid treated sepiolite clay supported-CoB catalyst, the NaBH4 concentration effect, phosphoric acid concentration effect, phosphoric acid impregnation time effect, CoB catalyst percentage effect, and temperature effect were studied. In addition, XRD, XPS, SEM, TEM, BET, and FTIR analysis were performed for characterization of Co–B catalyst supported on the acid-treated sepiolite. The completion time of this hydrolysis reaction with Co–B (20%) catalyst supported on the sepiolite treated by 5 M phosphoric acid was approximately 80 min, whereas the completion time of this hydrolysis reaction with acid-free sepiolite-supported Co–B (20%) catalyst was approximately 260 min. There is a five-fold increase in the maximum production rate. The maximum hydrogen production rates of this hydrolysis reaction at 30 and 60 °C were found as 1486 and 5025 ml min−1g−1catalyst, respectively. Activation energy was found as 21.4 kJ/mol. This result indicates that the acid treatment on sepiolite is quite successful. The re-usability of NaBH4 hydrolysis reaction by CoB catalyst supported on sepiolite treated phosphoric acid for successive five cycles of NaBH4 at 30 °C was investigated.

Preparation of organic–inorganic hybrid methylene blue polymerized organosilane/sepiolite pigments with superhydrophobic and self-cleaning properties

Inspired by the self-cleaning and water-repellent properties of the lotus leaf in the natural world, a kind of organic–inorganic hybrid pigment with superhydrophobic properties was prepared by adsorption of cationic methylene blue (MB) azo dyes onto acid-treated sepiolite (SEP), and then a superhydrophobic functional group of polymerized organosilanes (POSs) obtained from hexadecyltrimethoxysilane (HDTMS) and tetraethoxysilane (TEOS) was introduced onto the composite pigments (MB/SEP). The excellent chemical, thermal and optical stability of MB@POS/SEP are due to the shielding effect caused by the chemical inertness of the POS sheet. Furthermore, the superhydrophobic MB@POS/SEP pigments show an extraordinary self-cleaning property, which is similar to the waterproof property of the lotus leaf and spider web. The superhydrophobicity is strongly linked to their chemical composition and morphology, which can be adjusted by varying the concentration of HDTMS and TEOS. This kind of superhydrophobic pigment can be applied in various fields, such as ceramics, building and daily necessities.

Purification and defibering of a Chinese sepiolite

To extend the utilization of the low-grade Human (China) sepiolite, the purification of the ore is the prerequisite for all applications. Sepiolite accompanied by quartz and calcite was effectively purified via sedimentation method and the microwave assisted acid treatment. The influence of treatment time on sepiolite purity and structure was qualitatively studied based on XRD and FESEM. Sepiolite had been successfully purified and the content was elevated from 42wt.% to more than 90wt.%. Microwave assisted acid treatment demonstrated to be an effective purification process by removing carbonates without affecting sepiolite length. Furthermore, both physical method of lyophilization and chemical method of surface modification were proposed as simple alternatives to defibering acid-treated sepiolite crystal bundles. The effects of freezing time and surfactant chain length on the disaggregation state, micro-structure and properties of treated sepiolite were analyzed comparatively using FESEM, TEM and BET. Results of FESEM and TEM indicated that the crystal structure of sepiolite was not changed after freezing at −50°C for 12h or modification with hexadecyl trimethyl ammonium bromide (HDTMA), but the aggregates were effectively disaggregated. The BET specific surface areas of the dispersed sepiolite rods obtained by these two methods increased to 144.3 and 93.1m2/g, respectively, showing good agreement with the perfect dispersion of sepiolite fibers.

Cu-Supported on Acid-Treated Sepiolite: Characterization and Selective Catalytic Reduction (SCR) of NO by Propene

H-Sep samples were taken from treating sepiolite with HCl solution. Cu/H-Sep samples were prepared by the incipient wetness impregnation method. The samples were characterized using XRF, XRD, and XPS techniques, and their catalytic activities were performed by the SCR of NO with propylene. The results show that the Cu/H-Sep catalyst exhibited the high performance in the C3H6-SCR of NO. After investigation by XRD and H2-TPR, the result showed that there are Cu2+/Cu+redox species as a reaction activity center over Cu/H-Sep.

Effect of sepiolite fibers addition on sintering behavior of sanitary bodies

The work attempts to investigate the effect of sepiolite fibers addition on sintering behavior of sanitary bodies. Raw sepiolite was found to be associated with some impurities such as calcite, amphiboles and dolomite. Sedimentation method was used, and then washed with dilute HCl solution to prepare acid-treated sepiolite fibers. Green bodies with sepiolite fibers were shaped by slip casting process, then dried and sintered in an electric furnace. After cooling to room temperature, sintered samples were characterized by bulk density, bending strength and X-ray diffraction. The results showed that 2% sepiolite fiber addition could increase the bending strength of green and sintered bodies. Sintering activation energies were determined according to the bulk density results. It was found that the activation energy rose with the increase of sepiolite addition.

Study on thermal activated sepiolite for enhancing decoloration of crude palm oil

Thermal activated sepiolite was prepared and used as an adsorbent for efficient decoloration of crude palm oil. The effects of activation temperature on the structure of sepiolite were investigated by Fourier transform infrared spectroscopy, X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, Zeta potential and nitrogen adsorption–desorption isotherms techniques, and the decolorization efficiency for crude palm oil was systematically evaluated by Lovibond tone. The results indicate that the thermal activation of sepiolite affects its structure and decoloration efficiency. The Red value and content of phosphorus only reduced by 28.29 and 68.00 %, respectively, after decoloring with acid-treated sepiolite, but by 57.14 and 76.00 %, respectively, after thermal activation because that the thermal activation improved the porous structure and surface activity of sepiolite by releasing different kinds of waters and creating new adsorptive sites. In addition, the suitable activation temperature (400 °C) is significant to reach an optimal decoloring capacity.

Activity of yFe-10Cu/H-Sep and xCu/H-Sep for the Selective Catalytic Reduction of NO with Propylene

Cu supported on acid-treated sepiolite catalysts (xCu/H-Sep, x = 0  20.0 wt%) or Cu-Fe mixed supported on acid-treated sepiolite catalysts (yFe-10Cu/H-Sep, y = 0  20.0 wt%) were prepared by the incipient wetness impregnation method. The xCu/H-Sep and yFe-10Cu/H-Sep catalysts were characterized by means of XRD, BET, XRF, XPS, and H2-TPR techniques, and their catalytic activities were evaluated for the SCR of NO with propylene. XPS and XRD results indicate that there was the co-presence of Cu+-Cu2+ and Fe2+-Fe3+ over the surfaces of yFe-10Cu/H-Sep catalysts, and there was a strong interaction between Cu, Fe and sepiolite. High promotional effect of iron additive on the catalytic performance of Cu/H-Sep catalyst were found in C3H6-SCR of NO reaction. The highest activity of 65% NO conversion was obtained over 15Fe-10Cu/H-Sep catalyst at 280 oC under the condition of 1000 ppm NO, 1000 ppm C3H6, and 5% O2. The high catalytic activity of 15Fe-10Cu/H-Sep catalyst for NO reduction was due to its high reducibility to activate C3H6 to selectively reduce NO in the presence of excess O2. The high dispersion of copper oxides and strong metal-support interaction over 15Fe-10Cu/H-Sep catalyst also improve its catalytic performance.

Enhanced catalytic performance of rare earth-doped Cu/H-Sep for the selective catalytic reduction of NO with C3H6

The undoped and rare earth oxide (REOx, RE=La, Ce, Pr, Sm)-doped acid-treated sepiolite (H-Sep)-supported copper oxide catalysts (Cu/H-Sep and RE-Cu/H-Sep; Cu and RE loading=15 and 4wt%, respectively) were prepared using the incipient wetness impregnation method. The catalysts were characterized by means of the XRD, BET, XPS, H2-TPR and NH3-TPD techniques, and their catalytic activities were evaluated for the selective catalytic reduction (SCR) of NO with propylene. It is shown that the doping of REOx led to an enhancement in catalytic performance of Cu/H-Sep in the SCR of NO with C3H6. Among the RE-Cu/H-Sep catalysts, Ce-Cu/H-Sep performed the best, with 62% NO conversion being achieved at 350°C in the (NO+C3H6+O2) reaction. We believe that the high catalytic performance of Ce-Cu/H-Sep for the SCR of NO with C3H6 was associated with the good low-temperature reducibility, high copper oxide dispersion, and strong metal–support interaction.

Preparation of cordierite from fibrous sepiolite

Mineral sepiolite (Mg4Si6O15(OH)2·6H2O) with fibrous morphology is one of candidates for substituting asbestos. When sepiolite was used as a matrix of an inorganic insulator, it was expected that formation of cordierite (Mg2Al4Si5O18) at elevated temperatures should improve its thermal shock resistance. We investigated formation of α-cordierite by reacting two kinds of sepiolite (as-received and acid-treated sepiolite) with amorphous aluminosilicate fiber (Al2O3·1.88SiO2), γ-alumina (Al2O3) and amorphous silica (SiO2) at 1100-1300°C. A α-cordierite phase was observed above 1200°C for any starting compound, however, anorthite (CaAl2Si2O8) was produced at 1300°C when as-received sepiolite which contained calcite (CaCO3) as an impurity was used. A single phase of α-cordierite was prepared by heating the mixture of acid-treated sepiolite, amorphous aluminosilicate fiber and γ-alumina or acid-treated sepiolite, γ-alumina and amorphous silica at 1300°C.

Effect of heating and acid pre-treatment on pore size distribution of sepiolite

AbstractDue to its channels of molecular dimensions and a high specific surface area, sepiolite has many industrial applications which require high resistance to thermal effects in addition to a large surface area. On heating, sorbed water molecules are removed causing changes in the pore size distribution. In this study, the effects of thermal treatment on the pore structure of sepiolite and the acid-treated sepiolite samples were investigated. The solid density of sepiolite, measured by a He displacement technique, was 2.08 g cm-3 and total porosity was ~0.58. Both of these values showed an increase at 100°C, then decreased with further temperature increase due to crystal deformation and channel plugging which occurred at elevated temperatures. The BET surface area of the original sepiolite was 148 m2 g-1, and increased to 263 m2 g-1 at 100°C and then started to decrease. Approximately 16% of the total volume was in the micropores at 100°C. The acid pre-activation caused restrictions in possible crystal deformation during thermal treatment. The micropore volume increased to 20% and BET surface area reached values >500 m2 g-1 for the acid-treated samples.

Effect of Heating and Acid Pre-Treatment on Pore Size Distribution of Sepiolite

Due to its channels of molecular dimensions and a high specific surface area, sepiolite has many industrial applications which require high resistance to thermal effects in addition to a large surface area. On heating, sorbed water molecules are removed causing changes in the pore size distribution. In this study, the effects of thermal treatment on the pore structure of sepiolite and the acid-treated sepiolite samples were investigated. The solid density of sepiolite, measured by a He displacement technique, was 2.08 g cm-3 and total porosity was ~0.58. Both of these values showed an increase at 100°C, then decreased with further temperature increase due to crystal deformation and channel plugging which occurred at elevated temperatures. The BET surface area of the original sepiolite was 148 m2 g-1, and increased to 263 m2 g-1 at 100°C and then started to decrease. Approximately 16% of the total volume was in the micropores at 100°C. The acid pre-activation caused restrictions in possible crystal deformation during thermal treatment. The micropore volume increased to 20% and BET surface area reached values >500 m2 g-1 for the acid-treated samples.

Interaction of N-methyl 8-hydroxy quinoline methyl sulphate with sepiolite

The adsorption of N-methyl 8-hydroxy quinoline methyl sulphate—a drug generally used to protect from sunburn—by natural and acid-treated sepiolite, has been investigated. Acid treatment led to partial dissolution of the fibres of the clay, mainly in the external surface of the crystallites. Incorporation of the drug decreased the amount of water adsorbed, leading to a strong interaction between the drug and the clay, but upon acid treatment the interaction seemed to weaken. Clay-drug complexes formed by adsorption from the drug aqueous solutions and by mechanical mixing of the components in the solid state served as good sunburn shields, as indicated by the spectra of these materials in the visible-ultraviolet range of the spectrum.

Morphological, structural, and interfacial changes produced in composites on the basis of polypropylene and surface‐treated sepiolite with organic acids. III. Isothermal and nonisothermal crystallization

AbstractTwo kinetics studies with regard to isothermal and nonisothermal crystallization were conducted on composites samples containing polypropylene and sepiolite surface‐treated with isobutyric acid. Comparison of both studies allows us to demonstrate that isobutyric acid‐treated sepiolite incorporated to the polypropylene at different ratios acts as an effective nucleating agent and, due to its surface activity, generates two different crystalline structures, one of which is attributable to the formation of a mesophase on the periphery of the sepiolite particle.