A new solventless process to hydrophobize silica powders in fluidized beds

Microplastics-sorbed phenanthrene and its derivatives are highly bioaccessible and may induce human cancer risks

Microplastics (MPs) are ubiquitous in environmental media and human diets and can enrich organic contaminants, including polycyclic aromatic hydrocarbons (PAHs) and their derivatives. The bioaccessibilities and triggering cancer risks of MP-sorbed PAHs and PAH derivatives are closely linked with human health, which, however, were rarely focused on. This study explored the sorption behaviors of phenanthrene (PHE) and PHE derivatives on polyethylene (PE), polypropylene (PP), and polystyrene (PS) MPs, and assessed their bioaccessibilities in gastrointestinal fluids as well as their inducing human cancer risks. PE MPs harbored the highest sorption capacity, secondly the PP MPs, then the PS ones. Sorption of PHE and PHE derivatives on MPs was positively correlated with their hydrophobicities. The bioaccessibilities of sorbed PHE and PHE derivatives could reach 53.59 %±0.46 %-90.28 %±0.92 % in gastrointestinal fluids and 81.34 %±0.77 %-98.72 %±1.44 % in gastrointestinal fluids with the addition of Tenax (more close to the bioavailability). The hydrophobicities also controlled the bioaccessibilities of PHE and PHE derivatives in gastric fluids, and those in intestinal fluids with Tenax for PS MPs. The incremental lifetime cancer risk (ILCR) values for PHE, PHE-Cl, and PHE-NO2 on MPs at tested concentrations were all higher than the USEPA-suggested safety limit (10-6), and most of them were even higher than 10-4, which thus indicates serious cancer risks. This study promoted our understanding of the potential health threats posed by organic pollutant-bearing MPs in the environment.

Development of a Hydrophobicity-Controlled Delivery System Containing Levodopa Methyl Ester Hydrochloride Loaded into a Mesoporous Silica

Background: The drug release of antiparkinsonian drugs is an important issue during the formulation process because proper release kinetics can help to reduce the off periods of Parkinson’s disease. A 2-factor, 3-level (3²) full-factorial design was conducted to evaluate statistically the influence of the hydrophobicity of mesoporous silica on drug release. Methods: Hydrophobization was evaluated by different methods, such as contact angle measurement, infrared spectroscopy and charge titration. After loading the drug (levodopa methyl ester hydrochloride, melevodopa hydrochloride, LDME) into the mesopores, drug content, particle size, specific surface area and homogeneity of the products were also analyzed. The amorphous state of LDME was verified by X-ray diffractometry and differential scanning calorimetry. Results: Drug release was characterized by a model-independent method using the so-called initial release rate parameter, as detailed in the article. The adaptability of this method was verified; the model fitted closely to the actual release results according to the similarity factor, independently of the release kinetics. Conclusions: The API was successfully loaded into the silica, resulting in a reduced surface area. The release studies indicated that the release rate significantly decreased (p < 0.05) with increasing hydrophobicity. The products with controlled release can reduce the off period frequency.

Gas Phase Modification of Silica Nanoparticles in a Fluidized Bed: Tailored Deposition of Aminopropylsiloxane

Functionalized nanoparticles have various applications, for which grafting of a chemical moiety onto the surface to induce/improve certain properties is needed. When incorporated in polymeric matrices, for instance, the modified nanoparticles can alter the interfacial characteristics leading to improvements ofthe macroscopic properties of the nanocomposites. The extent of these improvements is highly dependent on the thickness, morphology and conformity of the grafted layer. However, the common liquid-phase modification methods provide limited control over these factors. A novel gas-phase modification process was utilized, with 3-aminopropyltriethoxysilane (APTES) as precursor, to chemically deposit amino-terminated organic layers on fumed silica nanoparticles in a fluidized bed. A self-limiting surface saturation was achieved when the reaction was done at 200 °C. With this self-limiting feature, we were able to graft multiple layers of aminopropylsiloxane (APS) onto the silica nanoparticles using water as the coreactant. The feasibility of this process was analyzed using thermogravimetric analysis (TGA), diffuse reflectance IR Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and elemental analysis (EA). By altering the number of APTES/water cycles, it was possible to control the thickness and conformity of the deposited aminopropylsiloxane layer. This novel approach allows to engineer the surface of nanoparticles, by introducing versatile functionalized layers in a controlled manner.

Sulfur-Functionalization of Porous Silica Particles and Application to Mercury Vapor Sorption

Silanol (SiOH) groups on silica particle surfaces undergo silylation reactions with organosilane molecules to give functionalized particles, which are used in many applications. The determination of the extent of this reaction is important for proper design of functionalized materials, depending upon the application. Two types of porous silica particles (206 and 484 m² g^-1; 9.6 and 2.9 nm average pore diameter, respectively), and colloidal silica (Ludox) with a nonporous base particle of 22 nm diameter, were functionalized with sulfur-containing silanes, 3-mercaptopropyl trimethoxy silane (MPTMS), and bis[3-(triethoxysilyl) propyl]-tetrasulfide (S4). Maximum extent of functionalization was determined with S4 using Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), and total S analysis. For the two types of porous silica particles, FTIR indicated that 54 and 17% of the silanol groups were functionalized with S4, and TGA indicated that the functionalized particles were 12 and 11 mass % MPTMS, respectively. These results were independently confirmed with total sulfur analysis. Extents of functionalization were determined for varying the silane structure on the same silica particle. MPTMS reacted with 38% of functional groups, while S4 reacted with 17%; the mass % of silane is the same regardless of silane structure on the same silica particle. Characterization by DSC indicated a glass transition occurs in the silane layer of the S4-functionalized silica at about 85 °C, but not in the MPTMS functionalized particles. Finally, mercury sorption breakthrough curves indicate the pore characteristics of the S4 functionalized samples.