Mathias Strauss

Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl4– Anions and Their Conversion into Supported Gold Nanoparticles

Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ion-exchange properties of the functionalized porous solid (SBA-15/R(+)Cl(-)) toward AuCl(4)(-) anions were evaluated through an ion-exchange isotherm. The calculated values of the equilibrium constant (log β = 4.47) and the effective ion-exchange capacity (t(Q) = 0.79 mmol g(-1)) indicate that the AuCl(4)(-) species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl(4)(-) ions were submitted to a chemical reduction process with NaBH(4), converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron microscopy images of the supported gold nanoparticles before and after thermal treatment at 973 K indicate that the metal nanostructures are highly dispersed and stabilized by the host environment.

Activated carbon from pyrolysed sugarcane bagasse: Silver nanoparticle modification and ecotoxicity assessment

Activated carbon from pyrolysed sugarcane bagasse (ACPB) presented pore size ranges from 1.0 to 3.5nm, and surface area between 1200 and 1400m(2)g(-1) that is higher than commonly observed to commercial activated carbon. The ACPB material was successfully loaded with of silver nanoparticles with diameter around 35nm (0.81wt.%). X-ray photoelectron spectroscopy (XPS) analyses showed that the material surface contains metallic/Ag(0) (93.60wt.%) and ionic/Ag(+) states (6.40wt.%). The adsorption capacity of organic model molecules (i.e. methylene blue and phenol) was very efficient to ACPB and ACPB loaded with silver nanoparticles (ACPB-AgNP), indicating that the material modification with silver nanoparticles has not altered its adsorption capacity. ACPB-AgNP inhibited bacteria growth (Escherichia coli), it is a promising advantage for the use of these materials in wastewater treatment and water purification processes. However, ACPB-AgNP showed environmental risks, with toxic effect to the aquatic organism Hydra attenuata (i.e. LC50 value of 1.94mgL(-1)), and it suppressed root development of Lycopersicum esculentum plant (tomato). Finally, this work draw attention for the environmental implications of activated carbon materials modified with silver nanoparticles.

Preparation of supported AuPd nanoalloys mediated by ionic liquid-like functionalized SBA-15: structural correlations concerning its catalytic activity

Noble metal nanoalloys are very important in catalysis, sensing, electrochemistry, and plasmonics. Based on the importance of these materials and in order to overcome the synthetic limitations for the in situ synthesis of supported nanoalloys in porous supports, we extended a synthetic protocol to achieve supported AuPd nanoalloys within SBA-15 pores modified with an ionic liquid-like alkoxysilane. The synthesized materials form very small nanoparticles with non-passivated surfaces, which are highly active as heterogeneous catalysts for the reduction of 4-nitrophenol. The anion exchange ability of the functionalized SBA-15 was used to adsorb Au and Pd anionic complexes. The adsorbed species were then reduced and converted into supported monometallic nanoparticles or nanoalloys. Nitrogen physisorption isotherms showed that the synthetic process does not damage the mesoporous support nor block the pores. TEM/EDS and UV-vis analyses were used to prove alloy formation in the bimetallic materials through the concomitant presence of Au and Pd in the same particles and through the disappearance of the gold plasmon band as the palladium content increased. Finally, the catalytic activity of the materials increased as the palladium content increased, showing that it is possible to control the catalytic performance by tuning the material composition during the anion exchange step.

Synthesis and structural characterization of nanometric ceria highly dispersed in SBA-15 with oxygen exchange capacity

Nanometric ceria-decorated SBA-15 was prepared using a route involving the impregnation of SBA-15 pores by a solution of cerium(III) 2-ethylhexanoate, followed by its thermal decomposition. According to XRF analysis, the number of successive impregnation–decomposition cycles (IDC) allows control of the CeO2/SiO2 ratio in the final material, and also the tailoring of the nanoparticle size of the fluorite CeO2nanoparticles supported in the SBA-15, as confirmed by XRD, Raman and UV-Vis spectroscopies. The mean pore size of the SBA-15 decreases with successive IDC, as observed by N2 adsorption–desorption, suggesting that CeO2 nanoparticles are located inside the SBA-15 mesopores, as confirmed by TEM and HRTEM analyses. The degree of oxygen storage capacity (OSC) was measured by the number of hydrogen uptake from the temperature programmed reduction (H2-TPR). It was found that the value of hydrogen uptake of SBA-15 submitted to one IDC corresponds to 3344 μmol of O2 per gram of CeO2, whereas those of SBA-15 submitted to five and ten IDC were 1324 and 2769 μmol of O2 per gram of CeO2, respectively.

Size controlled synthesis of highly dispersed anatase/rutile nanoparticles with photocatalytic activity toward salicylic acid degradation

TiO2 nanocrystals supported in SBA-15 pores were prepared by a simple route of successive cycles of impregnation of SBA-15 with titanium(IV) di-(n-propoxy)-di-(2-ethylhexanoate) followed by thermal treatment. Anatase and rutile phases were identified by XRD in the materials obtained after cycles 1, 3, 5, 7 and 10. Raman scattering combined with XRD and TEM shows that titania is in a nanometric regime. Increases in the size of the titania nanocrystals, as well as increases in the TiO2 content in the final material (XRF), occur after successive cycles. SAXS and N2 sorption indicate that the nanocrystals are formed inside the SBA-15 mesopores, which remain unblocked even after 10 cycles. UV-Vis (DRS) spectroscopy indicates important changes in electronic properties. The ability of SBA-15-supported titania nanocrystals to photodegrade salicylic acid was tested. There is a clear relation between the TiO2 nanoparticle size and the photocatalytic activity. Among all samples tested, the best result was obtained for the materials with the highest band-gaps and with the smallest sized titania.

Structural aspects of graphitic carbon modified SBA-15 mesoporous silica and biological interactions with red blood cells and plasma proteins

Functional mesoporous materials have been worldwide studied for different applications. Mesoporous silicas are highlighted due to the synthetic possibilities for the preparation of such materials with different particle sizes and morphologies, and controlled pores sizes and structures. Moreover, the silica superficial silanol groups are explored in several chemical modifications, leading to functional materials with tuned functionalities and properties. In this work, an organo-functionalization and pyrolysis synthetic procedure is used to obtain graphitic carbon modified mesoporous SBA-15 silica. The carbon content was tuned during the functionalization step, and the graphitic nanodomains were formed in the pores surface and particles outer surface. Textural and small angle X-ray diffraction analysis accessed the presence of the carbon nanostructures inside the SBA-15 mesopores. Advanced microanalysis using electron energy loss spectroscopy coupled to a transmission electron microscope had confirmed the carbon distribution along the silica pores, which gives higher hydrophobicity and changed the interaction of the mesoporous material with biological systems. Finally, the influence of the surface modification with graphitic carbon species over the interaction with human red blood cells (hemolysis) and human blood plasma (protein corona formation) was elucidated for the very first time for this kind of functional materials. It was observed that the graphitic carbon species considerably reduced the hemolytic effect of the silica particles, and was responsible for modulating the loading and composition of the hard corona plasma proteins. This work deepness the fundamental knowledge on the interaction between such nanomaterials and biological systems, one step further the use of these modified silicas in biomedical applications.

Analysis of the effects of mesoporous silica particles SBA-15 and SBA-16 in Streptococcus pneumoniae transformation process

Streptococcus pneumoniae are natural competent bacteria which requires the presence of a pheromone-like molecule to do the transformation process. This study verified the influence of mesoporous silica (SBA-15 and SBA-16) on the transformation process in S. pneumoniae using a donor DNA obtained from a mutant strain of this microorganism (Sp360∆luxS). The results showed that mesoporous silica SBA-15 and SBA-16 particles doubled the transformation ratio frequency compared with negative control (without nanoparticles) in using SBA-15 (ratio 1.81 ± 0.04) and SBA-16 (ratio 2.18 ± 0.22). We demonstrated the how mesoporous silica nanoparticles were able to increase the pneumococcus transformations, which could possibly lead to the acquisition of virulence factor genes and resistance of antibiotics.

The positive fate of biochar addition to soil in the degradation of PHBV-silver nanoparticles composites

The environmental contamination of soils by polymeric and nanomaterials is an increasing global concern. Polymeric composites containing silver nanoparticles (AgNP) are collectively one of the most important products of nanotechnology due to their remarkable antimicrobial activity. Biochars are a promising resource for environmental technologies for remediation of soils considering their high inorganic and organic pollutant adsorption capacity and microbial soil consortium stimulation. In this work we report, for the first time, the use of biochar material as a tool to accelerate the degradation of polyhydroxybutyrate- co-valerate (PHBV) and PHBV composites containing AgNP in a tropical soil system, under laboratory conditions. This positive effect is associated with microbial community improvement, which increased the degradation rate of the polymeric materials, as confirmed by integrated techniques for advanced materials characterization. The addition of 5-10% of sugarcane bagasse biochar into soil has increased the degradation of these polymeric materials 2 to 3 times after 30 days of soil incubation. However, the presence of silver nanoparticles in the PHBV significantly reduced the degradability potential of this nanocomposite by the soil microbial community. These results provide evidence that AgNP or Ag+ ions caused a decline in the total number of bacteria and fungi, which diminished the polymer degradation rate in soil. Finally, this work highlights the great potential of biochar resources for application in soil remediation technologies, such as polymeric (nano)material biodegradation.

Tetralkylammonium bromide salts as directing agents for the CAL family molecular sieves

Abstract The use of zeolites and molecular sieves as acid catalysts is an important tool of the modern chemical and petrochemical industry, resulting in great advantages in economic grounds, safety and reduction of pollutants. The applications of molecular sieves are basically related to their structure and composition. A recent synthetic process starting from lamellar AlPO, analogous to siliceous kanemite, as Al and P source, was used to synthesize new materials: the CAL family. The use of tetralkylammonium salts, in the preparation of the gel, as structure directing agents, allowed the synthesis of new materials.