Preparation of trimethylchlorosilane-modified acid vermiculites for removing diethyl phthalate from water

Flame Retardancy and Thermal Stability of Rigid Polyurethane Foams Filled with Walnut Shells and Mineral Fillers

Recently, the influence of the concept of environmental sustainability has increased, which includes environmentally friendly measures related to reducing the consumption of petrochemical fuels and converting post-production feedstocks into raw materials for the synthesis of polymeric materials, the addition of which would improve the performance of the final product. In this regard, the development of bio-based polyurethane foams can be carried out by, among other things, modifying polyurethane foams with vegetable or waste fillers. This paper investigates the possibility of using walnut shells (WS) and the mineral fillers vermiculite (V) and perlite (P) as a flame retardant to increase fire safety and thermal stability at higher temperatures. The effects of the fillers in amounts of 10 wt.% on selected properties of the polyurethane composites, such as rheological properties (dynamic viscosity and processing times), mechanical properties (compressive strength, flexural strength, and hardness), insulating properties (thermal conductivity), and flame retardant properties (e.g., ignition time, limiting oxygen index, and peak heat release) were investigated. It has been shown that polyurethane foams containing fillers have better performance properties compared to unmodified polyurethane foams.

Effective stabilization of heavy metals in solid waste and sludge pyrolysis using intercalated-exfoliated modified vermiculite: Experiment and simulation study

Pyrolysis is effective in reducing the volume of solid waste and sludge, and produces less pollutants than incineration and landfill, but the process still suffers from heavy metal pollution. Four types of intercalated-exfoliated modified vermiculite (UIV, DIV, TIV and 3IV) were prepared using urea, dimethylsulfoxide, tributyl phosphate and 3-aminopropyltriethoxysilane as intercalators for the control of Cd, Cr, Cu, Pb and Zn in municipal sewage sludge (MSL), paper mill sludge (PML), municipal domestic waste (MWA) and aged refuse (AFE). The larger the interlayer spacing of the vermiculite, the more favorable the retention of heavy metals. 3IV was the most effective additive, with an average retention of more than 75 % of all heavy metals at 450 ℃ for the four raw materials. Cr, Cu, Pb and Zn were all at low potential ecological risk (Pr), while Cd was moderate or considerable Pr, and the addition of 3IV reduced the Pr. Distribution of intercalators between vermiculite interlayers was haphazard, and interlayer spacing results were close to those of the experiment (except for tributyl phosphate). The reactive electrons mainly flowed from the Highest Occupied Molecular Orbital (HOMO) of vermiculite flakes to the Lower Unoccupied Molecular Orbital (LUMO) of heavy metal chlorides. In contrast, the reactive electrons mostly flowed from the HOMO of heavy metal oxides to the LUMO of vermiculite flakes. Heavy metal oxides were more readily adsorbed on vermiculite flakes than heavy metal chlorides, and the adsorption capacity of Cr and Zn was stronger than that of Cd, Pb and Cu.

Stabilization of heavy metals in solid waste and sludge pyrolysis by intercalation-exfoliation modified vermiculite

Increasing amounts of solid waste and sludge have created many environmental management problems. Pyrolysis can effectively reduce the volume of solid waste and sludge, but there is still the problem of heavy metal contamination, which limits the application of pyrolysis in environmental management. The intercalated-exfoliated modified vermiculite (IEMV) by intercalators of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide were used to control the release of Cd, Cr, Cu, Zn and Pb during pyrolysis process of sludge or solid waste. The retention of heavy metals in sludge was generally better than that in solid waste. The IEMV by octadecyltrimethylammonium bromide as the intercalator calcined 800 °C (STAB-800) was the best additive for heavy metal retention, and the retention of Cr, Cu and Zn was significantly better than that of Pb and Cd. Cr, Cu, Zn and Pb were at low risk, while Cd had considerable risk under certain circumstances. New models were proposed to comprehensively evaluate the results of the risk and forms of heavy metals, and the increasing temperature was beneficial in reducing the hazards of heavy metals by the addition of STAB-800. The reaction mechanism of heavy metals with vermiculite was revealed by simulation of reaction sites, Fukui Function and Frontier Molecular Orbital. Thermal activation-intercalated-exfoliated modified vermiculite (T-IEMV) is more reactive and had more active sites for heavy metals. Mg atoms and outermost O atoms are the main atoms for T-IEMV to react with heavy metals. The Cr, Cu and Zn have better adsorption capacity by T-IEMV than Pb and Cd. This study provides a new insight into managing solid waste and sludge and controlling heavy metal environmental pollution.

Effective Adsorption of Methyl Orange on Organo-Silica Nanoparticles Functionalized by a Multi-Hydroxyl-Containing Gemini Surfactant: A Joint Experimental and Theoretical Study

A novel multi-hydroxyl-containing gemini surfactant (G₁₆) is first designed for modifying silica precursors (SiNPs), with the purpose of fabricating organic adsorbents targeted at methyl orange (MO). The purity of G₁₆ and structural character of the resultant G₁₆-SiNPs are unveiled through Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry-derivative thermogravimetry, scanning electron microscopy, and surface analysis (BET). Compared with SiNPs, G₁₆-SiNPs exhibit enhanced hydrophobicity, enlarged interlayer spacing, and increased thermal weight losses with the modifier availability reaching as high as 100%. Enhanced MO adsorption is obtained from the higher adsorption capacity of G₁₆-SiNPs (401.88 mg/g) than SiNPs (64.72 mg/g), which is more effective than most of the existing silica-based adsorbents. Pseudo-second-order and Langmuir models conform to all adsorption processes, indicating that the adsorption mainly relies on the availability of adsorption sites and characterized by a homogeneous adsorption form. By combining the experimental study and theoretical calculation methods, it can be demonstrated that the as-synthesized adsorbent G₁₆-SiNPs own multi-active sites that contribute to multi-adsorption mechanisms. The partition process, electrostatic interactions, and OH-π interactions are all responsible for the adsorption performance of G₁₆-SiNPs. This study throws light on the exploration of the superb MO adsorbent in aspects of not only the novel structured modifier and precursor but also theoretical analysis for gaining insights into the adsorption mechanism.

The effects of interaction between vermiculite and manganese dioxide on the environmental geochemical process of thallium

The interaction among various soil minerals can significantly impact on the environmental geochemical process of contaminants. Therefore, this study investigated the effects of interaction between vermiculite (VER) and manganese dioxide (MnO₂) on the migration and transformation of Tl(I). The VER exhibited typical layered structure and MnO₂ possessed a flower-like structure with serious reunion phenomenon, while the production of interaction between vermiculite and manganese dioxide, labeled VER-MnO₂, illustrated as fish scales evenly spread over a large sheet, suggesting that MnO₂ could triumphantly be anchored on the VER and the aggregation of MnO₂ was prevented. Compared with the pure MnO₂, VER acted as template substrate contributed the higher specific surface area (298.18 m²·g^-1) and the oxidation degree of Mn. VER-MnO₂ showed the highest fixation capacity (144.29 mg·g^-1) than other two materials in the order VER-MnO₂ > MnO₂ > VER, and there was no risk derived from Mn dissolution. The influence mechanism of VER-MnO₂ on Tl(I) migration and transformation lied in immobilization, ion exchange and oxidization. Fixed-bed column immobilization experiments showed that VER-MnO₂ could purify drinking water contaminated by Tl (20 μg·L^-1) and the effective breakthrough volumes were 900 bed volumes until reaching the maximum limits allowed in drinking water (0.1 μg·L^-1). VER-MnO₂ excellently catches Tl to prevent groundwater pollution. This study provides a theoretical guidance for environmental fate and restoration of soil heavy metal pollution.

Thermal insulation with 2D materials: liquid phase exfoliated vermiculite functional nanosheets

Phyllosilicates are layered materials possessing unique thermal properties, commonly exploited in their multilayered crystalline form as refractory insulators and heating elements. A more versatile use of such materials, however, would require their existence in the form of inks and dispersions ready to be patterned. Within this framework, the liquid-phase exfoliation of low-cost, low-purity materials such as bulk multiphasic minerals and powders represents an economically advantageous approach for the production of 2D nano-sized objects with a defined composition, size and morphology. Here, ultrasound-assisted exfoliation and shear-mixing of a multi-phasic vermiculite in mild acidic aqueous solutions were employed to successfully obtain dispersions of mono- and few-layer thick clay nanosheets. The exfoliated materials were thoroughly investigated through granulometry, X-Ray Diffraction (XRD), specific surface area measurements and AFM imaging. Despite the fact that the lateral size and the thickness distribution of exfoliated flakes obtained with the two approaches appear similar, the ultrasound-assisted exfoliation process yielded a larger amount of mono- and bi-layer thick flakes as well as materials with a higher specific surface area. XRD analysis revealed that the use of ultrasound waves in an acidic environment results in the complete exfoliation of the vermiculite layer, whereas the use of shear forces under the same conditions results in the exfoliation of hydrobiotite and mica crystalline phases. Thermal conductivity measurements provided clear evidence on how the structural changes - arising from the exfoliation process - have a direct impact on the properties of the exfoliated clay. Remarkably, compared to the raw material, the thermal conductivity of the exfoliated material decreases by 25%, reaching the ultra-low thermal conductivity regime (<0.1 W m^-1 K^-1). Our approach may enable in the future the generation of patterns of thermal insulators onto different surfaces by applying vermiculite nanosheets in the form of dispersions and printable inks.

Selective Adsorption of Pb(II) from Aqueous Solution by Triethylenetetramine-Grafted Polyacrylamide/Vermiculite

Amine groups play significant roles in polymeric composites for heavy metals removal. However, generating a composite with a large number of functional and stable amine groups based on clay is still a challenge. In this work, a new amine-functionalized adsorbent based on acid-activated vermiculite (a-Verm) was prepared by organic modification of silane coupling agent as bridge, followed by in situ polymerization of acrylamide (AM) and further grafting of triethylene tetramine (TETA). The obtained polymeric composite g-PAM/OVerm was characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared (FTIR), thermal analysis (TG/DTG), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analyses, confirming that amine groups were successfully grafted onto the surface of Verm. The efficacy g-PAM/OVerm for removing Pb(II) was tested. The adsorption equilibrium data on g-PAM/OVerm was in good accordance with the Langmuir adsorption isotherms, and the adsorption maximal value of Pb(II) was 219.4 mg·g⁻¹. The adsorption kinetic data fit the pseudo-second-order kinetic model well. Additionally, g-PAM/OVerm has better selectivity for Pb(II) ion in comparison with Zn(II), Cd(II) and Cu(II) ions. The present work shows that g-PAM/OVerm holds great potential for removing Pb(II) from wastewater, and provides a new and efficient method for the removal of heavy metal ions from industrial wastewater.