Solvent-resistant CTAB-modified polymethylsilsesquioxane aerogels for organic solvent and oil adsorption

Recent advances in hydrophobic nanocellulose aerogels for oil spill applications: A review

In a rapidly growing world, petroleum is used extensively in various industries, and the extraction, processing, and transportation of petroleum generates large amounts of petroleum-containing wastewater. Conventional oil/water separation methodologies are often ineffective and costly. Nanocellulose-based aerogels (NA) have emerged as a possible solution to this problem. However, hydrophobic modification is required for effective use in oil/water separation. This review on materials commonly used in these processes and outlines the requirements for adsorbent materials and methods for creating unique lipophilic surfaces. New trends in hydrophobization methods for NA are also discussed. Additionally, it includes the development of composite nanocellulose aerogels (CNAs) and cellulose based membrane specially developed for oil/water (o/w) separation considering different separation requirements. This analysis also examines how CNAs have evolved by introducing special properties that facilitate oil collection or make the adsorbent recyclable. We also discuss the difficulties in creating effective NAs for these important applications in a changing society, as well as the difficulties in creating oil recovery equipment for oil spill cleanup.

Synthesis, structures and properties of hydrophobic Alkyltrimethoxysilane-Polyvinyltrimethoxysilane hybrid aerogels with different alkyl chain lengths

HYPOTHESIS

Alkyltrimethoxysilane (ATMS) is among most widely used silane coupling agents. These commercially available, reasonably priced chemicals are often utilized to improve the compatibility of inorganic surfaces with organic coatings. With three hydrolysable moieties, ATMS is an outstanding candidate for solving the hydrophilicity, moisture sensitivity and high cost of silica aerogels. However, ATMS has a non-hydrolysable alkyl chain that undergoes cyclization reactions. The alkyl chain prevents ATMS from being incorporated in aerogel structures. Polyvinyltrimethoxysilane (PVTMS) is a silica precursor that offers two types of crosslinking to the final aerogel product. This strong doubly-crosslinked network can potentially suppress the cyclization reactions of ATMS and include it in aerogel structure.

EXPERIMENTS

PVTMS was used with ATMS having different alkyl lengths (3-16 carbons) and loadings (25 or 50 wt%) as the silica precursors. Acid and base catalysts were used to perform hydrolysis and condensation reactions on the mixture and ATMS:PVTMS aerogels were obtained via supercritical drying.

FINDINGS

The incorporation of ATMS in the aerogels was approved by different characterization methods. Results showed that ATMS:PVTMS aerogels possess hydrophobicity (θ ∼ 130°), moisture resistance, varying surface area (44-916 m²·g^-1), meso/microporous structure and thermal insulation properties (λ ∼ 0.03 W·m^-1K^-1). These samples also showed excellent performance in oil and organic solvent adsorption.

Enhancing the Water Resistance and Stability of CsPbBr3 Perovskite Quantum Dots for Light-Emitting-Diode Applications through Encapsulation in Waterproof Polymethylsilsesquioxane Aerogels

Highly stable all-inorganic perovskite quantum dot/polymethylsilsesquioxane aerogel (CsPbBr₃/PMSQ AG) composites were first produced using two-step hot-injection and encapsulation processes by embedding green-emitting CsPbBr₃ PQDs into modified hydrophobic mesoporous silica AGs. The unique structure of the composites not only considerably enhances the chemical stability of CsPbBr₃ PQDs against moisture, humidity, and blue-light irradiation in air but also prevents anion exchange reactions during light-emitting diode (LED) manufacturing processes. In addition, the composition-optimized CsPbBr₃/PMSQ AG exhibited excellent stability when soaked in water for more than 14 days and retained half of its initial intensity. Finally, white LED devices were fabricated by combining a blue-emitting GaN-based chip, green-emitting CsPbBr₃/PMSQ AG, and red-emitting K₂SiF₆:Mn⁴⁺ phosphors.

Facile synthesis of ternary flexible silica aerogels with coarsened skeleton for oil–water separation

The effect of the skeleton morphology on the properties of flexible silica aerogels.

Uniformly Structured Methyltrimethoxysilane-Based Silica Aerogels with Enhanced Mechanical Property by Surfactant-Free Fabrication

The uniformity, elasticity and hydrophobicity of methyltrimethoxysilane (MTMS)-based silica aerogels, which were prepared by using dimethyl sulfoxide (DMSO) as the solvent, were investigated. The as-prepared silica aerogels were characterized by means of scanning electron microscope, Fourier transform infrared, contact angle/interface system and electronic universal testing machine. The hydrophobicity of the MTMS-based silica aerogels could be adjusted by tuning the MTMS/DMSO molar ratios. The water contact angle of the MTMS-based silica aerogels could be as high as 160.2∘, suggesting its superhydrophobic property. It was found that all the MTMS-based silica aerogels had the typical three-dimensional porous structure. The failure strain of MTMS-based silica aerogels could be as high as 66.14%.

Preparation and application of magnetic superhydrophobic polydivinylbenzene nanofibers for oil adsorption in wastewater

Superhydrophobic materials have an excellent performance in oil adsorption. In this study, a novel magnetic polydivinylbenzene (PDVB) nanofiber was synthesized by the method of cation polymerization to adsorb oil from water. The magnetic PDVB was hollow nanofiber with Fe₃O₄ nanoparticles embedded in its structure. The synthesis condition was optimized that the ratio of divinylbenzene (DVB) to boron fluoride ethyl ether (BFEE) was 10:1 (v/v), and the Fe₃O₄ dosage was 0.175 g/g of DVB. The material showed an excellent oil adsorption performance in wastewater, and the oil concentration could be reduced from 2000 to 92.2 mg/L within 5 min. The magnetic PDVB had relatively high adsorption capacity (12 g/g) for oil, which could be attributed to its super hydrophobicity and one-dimensional nanostructure with high crosslinking degree. The isotherm study indicated that the magnetic PDVB adsorbed oil was an asymmetric or multilayer adsorption process. The material could be regenerated by simple squeeze and maintain its adsorption capacity after it has been used for 10 recycles. In real coking wastewater, the magnetic PDVB kept a good oil adsorption performance without the interference of various pollutants, indicating a wide prospect in practical use.

A Co-Precursor Approach Coupled with a Supercritical Modification Method for Constructing Highly Transparent and Superhydrophobic Polymethylsilsesquioxane Aerogels

Polymethylsilsesquioxane (PMSQ) aerogels obtained from methyltrimethoxysilane (MTMS) are well-known high-performance porous materials. Highly transparent and hydrophobic PMSQ aerogel would play an important role in transparent vacuum insulation panels. Herein, the co-precursor approach and supercritical modification method were developed to prepare the PMSQ aerogels with high transparency and superhydrophobicity. Firstly, benefiting from the introduction of tetramethoxysilane (TMOS) in the precursor, the pore structure became more uniform and the particle size was decreased. As the TMOS content increased, the light transmittance increased gradually from 54.0% to 81.2%, whereas the contact angle of water droplet decreased from 141° to 99.9°, ascribed to the increase of hydroxyl groups on the skeleton surface. Hence, the supercritical modification method utilizing hexamethyldisilazane was also introduced to enhance the hydrophobic methyl groups on the aerogel’s surface. As a result, the obtained aerogels revealed superhydrophobicity with a contact angle of 155°. Meanwhile, the developed surface modification method did not lead to any significant changes in the pore structure resulting in the superhydrophobic aerogel with a high transparency of 77.2%. The proposed co-precursor approach and supercritical modification method provide a new horizon in the fabrication of highly transparent and superhydrophobic PMSQ aerogels.

Adsorption and reduction of hexavalent chromium on magnetic greigite (Fe3S4)-CTAB: leading role of Fe(ii) and S(−ii)

In this study, a facile one-step route was used to synthesize a novel magnetic mesoporous greigite (Fe₃S₄)-CTAB composite, which was utilized to remove hexavalent chromium (Cr(vi)). The optimized Fe₃S₄-CTAB_0.75 composite with a CTAB dosage of 0.75 g possessed the maximum specific surface, showing the highest Cr(vi) adsorption capacity of 330.03 mg g⁻¹. The mechanism analysis revealed that Fe(ii) and S(−ii) were critical for the reduction of Cr(vi). CTAB can promote the removal of Cr(vi) by Fe₃S₄-CTAB composites, possibly due to increased S(−ii) concentration, better dispersion of nanoparticles, and greater zeta potential. Besides, there is mild effect of Fe⁰ on Cr(vi) removal, which is confirmed by the disappearance of the Fe⁰ peak from the XPS analysis. The pseudo-second-order kinetic model could explain the Cr(vi) removal processes well. The adsorption of Cr(vi) at different initial concentrations was more consistent with a Langmuir isotherm. The existence of H⁺ was beneficial for Cr(vi) removal by Fe₃S₄-CTAB_0.75. Our work confirmed that the obtained Fe₃S₄-CTAB_0.75 composites exhibit considerable potential for Cr(vi) removal from aqueous solution.

The presence of CTAB can promote the removal of hexavalent chromium from the Fe₃S₄-CTAB surface.