Structure Of Sepiolite Research Articles

Enhancing Flame Retardancy and Smoke Suppression in EPDM Rubber Using Sepiolite-Based Systems.

The burning of Ethylene-Propylene-Diene Monomer (EPDM) rubber generates substantial smoke, posing a severe threat to the environment and personal safety. Considering the growing emphasis on safety and environmental protection, conventional non-smoke-suppressing flame retardants no longer satisfy the present application requirements. Consequently, there is an urgent need to develop a novel flame retardant capable of suppressing smoke formation while providing flame retardancy. Sepiolite (SEP), a porous silicate clay mineral abundant in silica and magnesium, exhibits notable advantages in the realm of flame retardancy and smoke suppression. This research focuses on the synthesis of two highly efficient flame-retardant smoke suppression systems, namely AEGS and PEGS, using Enteromorpha (EN), graphene (GE), sepiolite (SEP), ammonium polyphosphate (APP), and/or piperazine pyrophosphate (PPAP). The studied flame-retardant systems were then applied to EPDM rubber and the flame-retardant and smoke suppression abilities of EPDM/AEGS and EPDM/PEGS composites were compared. The findings indicate that the porous structure of sepiolite plays a significant role in reducing smoke emissions for EPDM composites during combustion.

Effect of directional arrangement one-dimensional Fe3O4-coated sepiolite structure on the Li+ conduction of PEO-based polymer electrolyte

The low Li+ conductivity and high cost of polyethylene oxide (PEO)-based polymer electrolytes still restrict their application. Herein, a natural one-dimensional sepiolite (SEP) material is coated with Fe3O4 (FSEP) to construct a FSEP-PEO composite polymer electrolyte (CPE) with a directional arrangement structure, which significantly improved the Li+ conductivity. Results show that the Li+ conductivity of CPE (9.1 ×10−5 S cm−1) based on vertical arrangement FSEP is 43 times higher than that of PEO (2.1 ×10−6 S cm−1), and 9.1 times and 3.1 times higher than that of parallel (1.0 ×10−5 S cm−1) and disordered arrangement (2.9 ×10−5 S cm−1), respectively. The arrangement direction of FSEP has no obvious effect on the crystallinity of PEO and the dissociation degree of LiTFSI, while it has a great influence on the Li+ migration number (tLi+). The tLi+ of CPE with vertical arrangement (0.333) increased by 99.4% compared with that of the parallel arrangement (0.167), suggesting a short and fast migration path. Through multi-physical field simulation, the high current density in CPE is mainly distributed at the FSEP/PEO interface, indicating that the FSEP/PEO interface plays a dominant role in Li+ conduction. In addition, lithium symmetric batteries and LiFePO4 batteries based on vertically arranged CPE have excellent cycle and rate performance.

Obtaining High Temperature Stable Sepiolite via Optimization of Acid Treatment Conditions

Acid treatment of sepiolite under different molarity of HCl at various times was studied to find the best acid treatment conditions for obtaining anhydrous sepiolite without structural folding and with fully open and empty channels. It was found that high molarity (e.g., 3 M) acid treatment causes severe acid attack and heterogeneous magnesium dissolution from sepiolite particles. In contrast, the low molarity (e.g., 0.5 M) acid treatment dissolves magnesium homogeneously through the particles. This, in turn, affects the behavior of sepiolite upon calcination at 450ºC in that homogeneous magnesium dissolution gives better structural stability and consequently higher amount of open channels with the least amount of magnesium removal (25%). This is verified by rehydration behavior and specific surface area measurements after the calcination, where over 90% of the surface area could be preserved after the calcination of the low molarity acid-treated samples. No change in the morphology of sepiolite fibers was observed after acid treatment.

Enhanced CO2 adsorption of PEHA/sepiolite adsorbent by zirconium accelerator in post-combustion

The most promising approach to tackling the greenhouse gases is CO2 capture and storage (CCS), and amine solid adsorbents are the most widely investigated materials. In this work, Zr species as an accelerator promote CO2 adsorption of the Pentatethylenehexamine (PEHA)/sepiolite (SEP) adsorbents. The adsorption rate, CO2 adsorption capacity, and amine efficiency were significantly improved under various conditions (temperature, gas flow, and CO2 concentration) by the introduction of the optimal content of Zr, the optimal HSEP-Zr0.13-PEHA0.5-600 adsorbent exhibited 1.80 mmol/g at 60 °C. Adsorption experiments combine with characterization (TG, XPS, NH3-TPD, SEM and TEM) exhibited that the introduction of Zr species were high dispersion on sepiolite, and Zr-O bond was formed in the structure of sepiolite. The acidity of the sepiolite supporter was enhanced by Zr which is benefit for amine loading. Above all resulted in the regeneration and thermal stability of the adsorbent were improved together. The economic evaluation results demonstrated that the adsorbent with Zr species is low-cost for large-scale post-combustion CO2 capture.

Preparation of sepiolite-based hybrid silica sol and its application in polyester/cotton fabric flame retardant finishing

Halogen-free flame-retardant finishing of textiles is of great significance. In this study, a new type of phosphorus-rich organic-inorganic flame-retardant hybrid silica sol was prepared by the ion replacement reaction between natural sepiolite and biomass phytic acid, which was then used as the flame retardant for coating finishing of polyester/cotton (T/C) fabric. The structure and morphology of the hybrid silica sol was investigated. The results indicated that prepared silica sol maintained the fibrous structure of sepiolite, which would be helpful to reduce the damage to the mechanical properties of T/C fabric in the flame-retardant finishing process. The tests on the flame retardancy and mechanical properties of T/C fabrics show that the flame retardancy and mechanical properties of T/C fabrics coated by sepiolite-based silica sol were improved. Compared with raw T/C fabric, the limit oxygen index of the optimal sample increased by 24.8% and the char length decreased by 76%. In addition, the elongation at break at warp direction of the optimal sample was 16.3%, which was about 39.16% higher than that of raw T/C fabric. The hybrid sepiolite-based silica sol has broad application prospect.

Sustainable sepiolite-based composites for fast clotting and wound healing

Uncontrolled bleeding and bacterial coinfection are the major causes of death after an injury. Fast hemostatic capacity, good biocompatibility, and bacterial coinfection inhibition pose great challenges to hemostatic agent development. A prospective sepiolite/Ag nanoparticles (sepiolite@AgNPs) composite has been prepared by using natural clay sepiolite as template. A tail vein hemorrhage mouse model and a rabbit hemorrhage model were used to evaluate the hemostatic properties of the composite. The sepiolite@AgNPs composite can quickly absorb fluid to subsequently stop bleeding due to the natural fibrous crystal structure of sepiolite, and inhibit bacterial growth with the antibacterial ability of AgNPs. Compared with commercially-available zeolite material, the as-prepared composite exhibits competitive hemostatic properties without exothermic reaction in the rabbit model of femoral and carotid artery injury. The rapid hemostatic effect was due to the efficient absorption of erythrocyte and activation of the coagulation cascade factors and platelets. Besides, after heat-treatment, the composites can be recycled without significant reduction of hemostatic performance. Our results also prove that sepiolite@AgNPs nanocomposites can stimulate wound healing. The sustainability, lower-cost, higher bioavailability, and stronger hemostatic efficacy of sepiolite@AgNPs composite render these nanocomposites as more favorable hemostatic agents for hemostasis and wound healing.

Low Temperature Aluminothermic Reduction of Natural Sepiolite to High-Performance Si Nanofibers for Li-Ion Batteries.

Nanostructure silicon is one of the most promising anode materials for the next-generation lithium-ion battery, but the complicated synthesis process and high cost limit its large-scale commercial application. Herein, a simple and low-cost method was proposed to prepare silicon nanofibers (SNF) using natural sepiolite as a template via a low-temperature aluminum reduction process. The low temperature of 260°C during the reduction process not only reduced the production cost but also avoided the destruction of the natural sepiolite structure caused by the high temperature above 600°C in the traditional magnesium thermal reduction process, leading to a more complete nanofiber structure in the final product. For the first time, the important role of Mg-O octahedral structure in the maintenance of nanofiber structure during the process of low-temperature aluminothermic reduction was verified by experiments. When used as an anode for lithium-ion batteries, SNF yield a high reversible capacity of 2005.4 mAh g−1 at 0.5 A g−1 after 50 cycles and 1017.6 mAh g−1 at 2 A g−1 after 200 cycles, remarkably outperforming commercial Si material. With a low-cost precursor and facile approach, this work provides a new strategy for the synthesis of a commercial high-capacity Si anode.

Tuning adsorption, structure and compressive strength of sepiolite- and metakaolin-based alkali activated monoliths for methylene blue removal from waste water

Adsorption is considered as the most beneficial waste water treatment method when compared to other physical, chemical, and biological treatment methods due to its economic feasibility, environmentally friendliness, and easy implementation. Alkali activated materials (AAMs) are promising materials as adsorbents for removing organic molecules from waste water owing to their low cost and availability, easy and environmentally-friendly synthesis, high adsorption capacity, chemical stability, regeneration/reusability capability, and high mechanical strength. Unfortunately, powder-formed adsorbents are mostly focused in literature although their practical utilization is limited due to problems in recovery, regeneration and mechanical performance. In this regard, a family of sepiolite (S)- and metakaolin (M)-based alkali activated monoliths (S-Monolith and M-Monolith) with varying porosities were synthesized and tested for methylene blue (MB) adsorption comparatively for the first time. Hydrogen peroxide (H2O2) is used as a foaming agent to adjust the porosity with varying concentrations in the ranges of 0–8 wt% and 0–1 wt%, for S-Monoliths and M-Monoliths, respectively. As porosity of S-Monoliths increases from 13% to 40%, MB uptake capacity rises from 6.6 to 10.3 mg g−1 while corresponding compressive strength values decrease gradually from 37 MPa to 6.5 MPa. On the other hand, as the porosity of M-Monoliths varies from 31.9% to 63.5%, corresponding MB uptake capacity increases from 4.3 to 7.8 mg s−1 whereas compressive strength values decrease from 28 MPa to 2.1 MPa. Both pseudo-first-order and pseudo-second-order adsorption kinetics show good fit to the experimental data, indicating that both physical and chemical adsorption processes govern the adsorption process. Adsorption isotherm model studies showed that Langmuir isotherm provides a better fit indicating that chemisorption controls the adsorption mechanism. Regeneration experiments conducted on samples with the highest porosities show that S- and M-Monoliths can be regenerated up to four cycles without loss in their integrity. Results show that the adsorption performance of AAM monoliths synthesized from different raw materials can be tuned by changing the porosity levels and these monoliths offer mechanically strong and sustainable options as adsorbents for industrial applications.

Understanding relationship of sepiolite structure tailoring and the catalytic behaviors in glycerol steam reforming over Co/sepiolite derived Co-phyllosilicate catalyst

Bio-glycerol Steam reforming over green and economical Co/sepiolite (SEP) catalysts was a promising strategy to hydrogen production. The activation pretreatment of SEP played a vital role for boosting catalytic behavior of Co/SEP. This work originally explored a full activation of SEP by molten NaOH for tailoring the physicochemical properties of Co-based catalysts prepared by urea precipitation method. Differing from the acid pickling/calcination and molten NaNO3 activation, the molten NaOH treatment enhanced surface area of SEP by desilicication/dealumination effect and further improved the exposure of framework Si and its surface ‘reactivity’. According to the characterization results of N2 adsorption-desorption, XRD, TEM, H2-TPR, CO/CO2-TPD and XPS, it was found that the feathered Co-phyllosilicate formed on Co/SEP-NaOH catalyst, which enhanced the metal-support interaction, surface area and basic/metallic sites. In contrast, the molten NaNO3 treatment facilitated the transformation of SEP into loughlinite and it was adverse to metal dispersion. Therefore, Co/SEP-NaOH catalyst possessed the highest conversion (92%) and H2 yield (68%) during the activity test at 600 °C and the superior resistance to amorphous coke. Additionally, DFT analysis was introduced to simulate the process of glycerol adsorption and decomposition and demonstrated the Co–CoO interface as the primary reaction sites for the catalytic process.

The Structure and Properties of Sepiolite with Partial Lattice Ions Substituted by Aluminum Ions.

Sepiolite was modified with Al3+ via hydrothermal reaction. The substitution amount of Al3+ for Mg2+ and Si4+ located at sepiolite lattice and the influence of substitution amount on the structure, specific surface area, and surface acidity of Al-modified sepiolite were investigated. On this basis, indigo–sepiolite composite pigments were prepared by Al-modified sepiolite and indigo via grinding method to evaluate the influence of Al-modified sepiolite on the structure, bonding strength, and weather resistance of composite pigment. The crystal structure of Al-modified sepiolite had no obvious change after modification. Al3+ mainly substituted Mg2+ located at the octahedron of the sepiolite lattice, and the substitution amount was positively related to the dosage of Al3+. The specific surface area of Al-modified sepiolite decreased and the distribution of channel size became wider after Al modification. In addition, the absolute value of zeta potential decreased as well as the solid acid sites increased with the increase of Al substitution in Al-modified sepiolite. For indigo–sepiolite composite pigments, the structure of Al-modified sepiolite had no obvious change as well. The adsorption amount of indigo in composite pigment after treating by DMSO and Al content as well as weak acid amount in Al-modified sepiolite presented linear correlation, indicating that Al modification could enhance the bonding strength between indigo and Al-modified sepiolite by increasing the amount of coordinated water with Al. For indigo, Al-modified sepiolite could brighten the color and reduce the weather resistance of the prepared composite pigment. The results of this study provide a new idea and basis for regulating the structure and properties of clay and for studying the preparation of composite pigment and clay functional materials.

Rehabilitation of a complex industrial wastewater containing heavy metals and organic solvents using low cost permeable bio-barriers – From lab-scale to pilot-scale

This work addresses the treatment of a complex industrial effluent containing high concentrations of metals and spiked with two organic solvents (diethylketone – DEK, and methyl ethyl ketone - MEK) using an eco-friendly approach. The treatment system herein proposed consists of a bio-barrier that combines the adsorption capacity of sepiolite with the properties of a Streptococcus equisimilis biofilm with proven ability in the degradation and bioremoval of a wide range of pollutants.Results from the open-systems experiments conducted with raw sepiolite exposed to a binary mixture of DEK and MEK revealed the preference of the sorbent towards DEK. The results from the biodegradation experiments also revealed the preference of S. equisimilis to degrade/bioremove DEK over MEK independently of their initial concentration (100 mg/L to 3200 mg/L). Bioremoval percentages higher than 95% were reached for all the concentrations of DEK tested. The lab-scale experiments conducted in open-system with sepiolite and sepiolite covered with biofilm, and the pilot-scale experiment conducted in closed-loop, revealed similar performances on the rehabilitation of an industrial effluent containing heavy metals and additionally spiked with DEK and MEK. Regarding the selectivity towards the different pollutants, Cu was preferentially removed over Cr and Ni, and DEK over MEK. The presence of the biofilm allowed an improvement on the removal of heavy metals, particularly Cr, besides preventing the leaching of Al, Fe, and Mg from the sepiolite structure, an extremely important advantage in comparison to the system without biofilm. EDS analyses performed in sepiolite samples revealed the presence of several metals (Cr, Cu and Ni), proving thus the occurrence of sorption processes by sepiolite and by sepiolite covered by biofilm. The breakthrough data obtained in the open-systems were properly described by the Dose Response and the Yoon and Nelson mathematical models. More research work needs to be performed with complex industrial effluents aiming the optimization of the treatment systems to be applied in real context scenarios.

Photocatalytic Destruction of Caffeine on Sepiolite-Supported TiO2 Nanocomposite

The study is about the degradation of a common pharmaceutical and personal care product (PPCP) caffeine by photocatalysis under UV–visible light using pristine TiO2 (P-25) and a lab-made nanocomposite of sepiolite–TiO2. It was found that the dark adsorption of caffeine on P-25 was insignificant, but considerably high on the nanocomposite, owing to the high porosity and unique structure of sepiolite. The degradation of the compound in the presence of P-25 and Sep–TiO2 followed the pseudo-first order and exponential decay kinetics, with a rate constant of 0.12 min−1 and 0.50 min−1, respectively. The efficiency of both catalysts for carbon mineralization was better at acidic pH, but that of the nanocomposite was significantly higher at all pH than that of the unmodified P-25 (36.1 against 9.6% at pH 6.0). The loading of TiO2 on sepiolite was an important factor in the activity of the catalyst, as the maximum activity was observed at a loading ratio of 12.5 mmol per g sepiolite, which decreased at higher ratios of the semiconductor to sepiolite. Exposure of the treated samples to high-frequency ultrasound at pH 6 was found to enhance the degree of mineralization to 65.1 and 52.1% in the presence of the nanocomposite and P-25, respectively. The outcome was attributed to the unique properties of ultrasound for the cleaning of solid surfaces, for enhancing the mass transfer of solutes to heterogeneous interfaces, and for generation of excess hydroxyl radicals. Finally, the nanocomposite was found to be considerably stable, as it was easily recovered and used four times without a significant loss in activity.

Possible Use of Sepiolite as Alternative Filler for Natural Rubber

The use of mineral fillers in rubber industry has been increasingly focused. Sepiolite is considered as one of the mineral fillers that exploits unique characteristics. This is due to its unique needle-like fibrous and a tunnel-like micro-pore channel structures. Therefore, adding this filler in natural rubber (NR) matrix would bring tremendous advantage. The study was carried out in the form of curing characteristics, tensile properties and morphology together with the dynamic properties. Filling sepiolite to NR has brought to a noticeable enhancement of curing characteristics, tensile properties and morphology. This is contributed to the distinctive structure of sepiolite itself, it provides a better dispersion to the NR. Surface roughness of the composites is visibly found which is responsible for the mechanical properties. Further verification was also monitored through the dynamic properties of the composites. The obtained profiles are in good agreement to the tensile properties and morphological characteristics observed.

Effect of surfactants on CO2 solubility and reaction in CO2-brine-clay mineral systems during CO2-enhanced fossil fuel recovery

The effect of surfactants (alkyl olefin sulfonate and cetyltrimethylammonium bromide) on the chemical reactions in CO2-brine-clay mineral systems (montmorillonite and sepiolite) was studied under subcritical to supercritical CO2 conditions (10–150 bar at 45 °C). Compared to the CO2-brine-clay mineral system without surfactants, the introduction of surfactants increased CO2 solubility. Dissolution of Si from montmorillonite and sepiolite increased significantly on addition of the surfactants, which was unlike the results from the system without surfactants. The structural changes of the clay minerals after reaction in the CO2-brine medium with surfactants were analyzed using various techniques. The pore structure of montmorillonite and sepiolite was changed after reaction in the systems with surfactants, and the adsorption of surfactants on the clay minerals led to more significant change of pore structure. The added surfactants conserved the micro-crystallinity of montmorillonite, which otherwise collapsed considerably after dissolution reactions conducted without surfactants. The experimental and calculated results indicated that the structural changes and dissolution of clay minerals could be accelerated by adding surfactants during CO2 geological sequestration combined with enhanced oil and gas recovery (CO2 foam-EOR and EGR).

A comparative study on essential parameters to minimize sealing time in wide fractures

Efficient early-time plugging of wide fractures was aimed to investigate by considering granular lost circulation material (LCM) sizes, its concentrations, and geometries as the essential parameters. Fracture sealing time was experimentally investigated using sepiolite based mud prepared considering API standards. Steady shear flow, thixotropy loop and oscillatory dynamic shear tests were conducted using Discovery Hybrid Rheometer (DHR-II) to evaluate gel structure and particle suspension ability of sepiolite based mud as carrier fluid. The set of seventeen sieves 75–3360 μm was used for analyzing grain sizes of calcium carbonate (CaCO3) as LCM. The effect of sixteen different LCM size ranges on the fracture sealing time was investigated through six slotted discs having different fracture widths (apertures) (508 μm–3048 μm) and lengths. Using wide range of sieve set allows providing uniform, bi-modal, and tri-modal particle size distribution of CaCO3 pills as the fundamentals to investigate fracture sealing time. Upward flow direction was provided using Pore Plugging Apparatus (PPA) under 1000 psi of pressure differential. Fracture sealing time values were measured using precise pressure transmitter connected between experimental setup and computer. Sealing performance of LCM sizes and concentrations was visually evaluated using optical microscope.Results reveal that rheological characteristics particularly gel structure and thixotropy of carrier fluid are highly noteworthy. High degree of thixotropy and gel structure development make the sepiolite mud an active carrier fluid. Early fracture sealing time intensely depends on accurate combination of fine, medium, and coarse LCMs, particle size distribution, particle shape and concentration of LCM. Early sealing time and plug developing in wide fractures occurs efficiently by increasing modality in particle size distribution. The fine, medium and coarse LCMs must be added with optimum concentrations to seal fracture effectively and minimize sealing time.

Fabrication of Cu2O/TiO2/sepiolite electrode for effectively detecting of H2O2

A clay-modified electrode, sepiolite modified by TiO2 nanoparticles (1–10 nm) incorporation of Cu2O particles (70–300 nm), was prepared for electrocatalytic reduction of H2O2. The morphology, structure and properties of obtained materials were characterized by XRD, BET, FT-IR, SEM and TEM and the performance of the modified electrode was evaluated by cyclic voltammetry and chronoamperometry. The results revealed that the concentration of H2O2 was proportional to the response to the current with the linear range from 20 μM to 2.36 mM and the detection limit of 10.2 μM under the working voltage. Compared with previous H2O2 sensors, the Cu2O/TiO2/sepiolite electrode possess favorable electrochemical performance can be attributed to its large specific surface area and structure of TiO2-modified sepiolite in favour of load of Cu2O.

Influence of the interaction between surfactants and sepiolite on the rheological properties and thermal stability of organo-sepiolite in oil-based drilling fluids

The influence of interaction between organic surfactants and sepiolite (Sep) on the structure and rheological properties of organo-sepiolite (OSep) in oil-based drilling fluids was investigated. Sep was modified with three kinds of cationic surfactant. X-ray diffraction, scanning electron microscope, surface properties, thermal analysis and X-ray photoelectron spectroscopy (XPS) were applied to characterize the structures of OSep and interaction between surfactants and Sep. Gel volume and dynamic rheological behavior were used to appraise the rheological properties of OSep/oil fluids. OSep keeps the crystal structure of sepiolite after organic modification and shows the more dispersed fibers. XPS results demonstrated that organic surfactants are in electronic interaction with sepiolite. Surfactants block the micropores of sepiolite by partially inserting and covering, resulting in the decrease of specific surface area. The size of the surfactants plays an important role to insert the channels. The partially insertion of surfactants into the channels leads to better rheological properties and thermal stability of OSep in oil-based drilling fluids.

Photocatalytic degradation of Orange G using sepiolite-TiO2 nanocomposites: Optimization of physicochemical parameters and kinetics studies

Highly photoactive nanocomposites Sep-TiO2 with various ratios of Ti/Sep were prepared by a novel microwave-hydrothermal method and were compared for their photocatalytic activity. The catalyst with the Ti/Sep ratio of 40 mmol/g showed the highest photodegradation activity on account of its relatively intact sepiolite structure and more anatase active sites. The effects of operational conditions, including photocatalyst amount, initial dye concentration and pH on photocatalytic degradation performance were analyzed and optimized, which demonstrated low and negligible photodegradation efficiency in the presence of sepiolite only and in the absence of photocatalyst, respectively. The photocatalytic degradation kinetics under different reaction conditions was elucidated by modeling. The results showed that the photocatalytic degradation of Orange G could be described by the modified Langmuir-Hinshelwood model. The photocatalytic degradation process fits into first-order kinetics for most of the operational parameters, while follows zero-order kinetics for the condition of high dye concentration. The apparent rate constants kapp for each degradation reaction were calculated by fitting the model to experimental data and the highest value was obtained at catalyst dosage 0.8 g/L, initial dye concentration 10 mg/L and pH = 3. Moreover, the recycling experiments confirmed the stability of the catalyst.

Improvement of stability of insecticidal proteins from Bacillus thuringiensis against UV-irradiation by adsorption on sepiolite

The adsorption characteristics of protoxin and toxin from Bacillus thuringiensis by sepiolite were studied. The kinetic results showed that the protoxin and toxin could be adsorbed by sepiolite rapidly, and the equilibrium was reached within 1 h. The adsorption isotherms of both proteins followed Langmuir equation (R2>0.98) and the curves belonged to L type. The adsorption capacity, adsorption rate and the insecticidal activity of toxin were higher than those of protoxin. The results of ultraviolet irradiation showed that sepiolite could protect the toxin from ultraviolet irradiation damage, but it accelerated the damage of protoxin. Therefore, the toxin is suitable for preparing long-term formulations of B. thuringiensis using the carrier of sepiolite. The results of Fourier transform infrared, X-ray diffraction, and scanning electron microscopy indicated that toxin did not influence the structure of sepiolite and the adsorption of toxin only on the surface of sepiolite. The adsorption of toxin by sepiolite was enhanced by metal ions in the range of concentration from 0 to 4.0 mmol L−1, and the enhancement extent of metal ions on the adsorption of toxin was in the order: Ca2+>Mg2+>K+>Na+. The higher the loading of toxin per mass sepiolite, the lower the 50% of the larvae of sepiolite–toxin complex. The zeta potential of sepiolite suspension increased with the addition of metal ions, indicating that the driving forces of the adsorption of toxin to negatively charged sepiolite was electrostatic interaction.

Sepiolite-TiO2 nanocomposites for photocatalysis: Synthesis by microwave hydrothermal treatment versus calcination

Sepiolite-TiO2 nanocomposites were synthesized by conventional calcination process and microwave hydrothermal (M-H) treatment and were tested and compared for their photocatalytic activity. XRD analysis indicated that nanocomposites after calcination at 500°C or M-H treatment for 40min at about 200°C appear to be the optimal conditions, which assured the amorphous TiO2 to crystalline anatase phase transition. The deposition of the TiO2 on the surface of sepiolite by M-H treatment yielded small dispersed nanoparticles at all treatment times used in this study. However, TiO2 particle size increased with increasing calcination temperature, which was confirmed by SEM and TEM. N2-adsorption-desorption isotherms indicated that calcination process reduced the specific surface areas of the nanocomposites while the M-H treatment led to a higher surface area with better photocatalytic performance for the degradation of Orange G. The intact structure of sepiolite and the homogeneous dispersion of the TiO2 nanocrystals on sepiolite surfaces led to enhanced photocatalytic activity in M-H treated samples.