Ultrasound in Nanochemistry: Recent Advances

Green Synthesis of Nanomaterials

Nanotechnology is considered one of the paramount forefronts in science over the last decade. Its versatile implementations and fast-growing demand have paved the way for innovative measures for the synthesis of higher quality nanomaterials. In the early stages, traditional synthesis methods were utilized, and they relied on both carcinogenic chemicals and high energy input for production of nano-sized material. The pollution produced as a result of traditional synthesis methods induces a need for environmentally safer synthesis methods. As the downfalls of climate change become more abundant, the scientific community is persistently seeking solutions to combat the devastation caused by toxic production methods. Green methods for nanomaterial synthesis apply natural biological systems to nanomaterial production. The present review highlights the history of nanoparticle synthesis, starting with traditional methods and progressing towards green methods. Green synthesis is a method just as effective, if not more so, than traditional synthesis; it provides a sustainable approach to nanomaterial manufacturing by using naturally sourced starting materials and relying on low energy processes. The recent use of active molecules in natural biological systems such as bacteria, yeast, algae and fungi report successful results in the synthesis of various nanoparticle systems. Thus, the integration of green synthesis in scientific research and mass production provides a potential solution to the limitations of traditional synthesis methods.

Ultrasound-Assisted Hydrothermal Synthesis of V2O5/Zr-SBA-15 Catalysts for Production of Ultralow Sulfur Fuel

This work reports the results of the ultrasound-assisted hydrothermal synthesis of two sets of V2O5 dispersed on SBA-15 and Zr doped SBA-15 catalysts used for the oxidation of dibenzothiophene (DBT) in a model diesel via the combination of oxidation, catalysis, and extraction technical route. These catalysts contained Lewis acidity as major and Brønsted acidity as minor. The amount of acidity varied with the content of vanadia and zirconium doping. It was found that DBT conversion is very sensitive to the Lewis acidity. DBT conversion increased by increasing the vanadium content and correlated well with the amount of surface Lewis acidity. Under the optimal experimental condition (Reaction temperature: 60 °C, reaction time 40 min, catalyst concentration: 1 g/L oil; H2O2/DBT mole ratio = 10), the 30% V2O5/SBA-15 and 30% V2O5/Zr-SBA-15 catalysts could convert more than 99% of DBT. Two reaction pathways of DBT oxidation involving vanadia surface structure, Lewis acidity, and peroxometallic complexes were proposed. When the vanadia loading V2O5 ≤ 10 wt%, the oxidative desulfurization (ODS) went through the Pathway I; in the catalysts with moderate vanadia content (V2O5 = 20–30 wt%), ODS proceeded via the Pathways II or/and the Pathway I.

Ultrasonically-assisted surface modified TiO2/rGO/CeO2 heterojunction photocatalysts for conversion of CO2 to methanol and ethanol

Converting CO₂ to usable fuel may contribute to lowering of global warming, thus this study developed effective heterojunction photocatalysts for the photoreduction of CO₂ with water into methanol and ethanol fuels. The photocatalysts were prepared from combining surface modified titanium dioxide (TiO₂) nanoparticles with reduced graphene oxide (rGO) and cerium oxide (CeO₂). The TiO₂ surfaces were firstly modified via the sono-assisted exfoliation, with high intensity ultrasonic waves (ultrasonic horn, 20 kHz, 150 W/cm²) in 10 M NaOH for 1 h. Highly reactive nanosheets delaminated from outer surfaces of the primary TiO₂ crystals leading to an increase in specific surface active area, light absorption and decrease in electron-hole recombination rate, which enhanced photocatalytic activity. Then, 0.75 wt% rGO and 1 wt% CeO₂ were incorporated into the surface modified TiO₂ to promote photogenerated charge separation, electron mobility and CO₂ absorptivity. The modified TiO₂/rGO/CeO₂ photocatalysts exhibited superior photocatalytic performance by producing methanol at 641 μmol/g_cath and ethanol at 271 μmol/g_cath, almost 7 times higher than rates from pure TiO₂. The significant improvement in CO₂ photoconversion activity was mainly attributed to the high interfacial contact area and strong connection between the reactive delaminated TiO₂ nanosheets, rGO and CeO₂, which, in turn, facilitated the flow of large number of photogenerated charge carriers to react with the absorbed species, and the multi-step charge transportation due to the heterojunction effect that effectively retarded electron-hole recombination.

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

In order to translate nanotechnology into medical practice, magnetic nanoparticles (MNPs) have been presented as a class of non-invasive nanomaterials for numerous biomedical applications. In particular, MNPs have opened a door for simultaneous diagnosis and brisk treatment of diseases in the form of theranostic agents. This review highlights the recent advances in preparation and utilization of MNPs from the synthesis and functionalization steps to the final design consideration in evading the body immune system for therapeutic and diagnostic applications with addressing the most recent examples of the literature in each section. This study provides a conceptual framework of a wide range of synthetic routes classified mainly as wet chemistry, state-of-the-art microfluidic reactors, and biogenic routes, along with the most popular coating materials to stabilize resultant MNPs. Additionally, key aspects of prolonging the half-life of MNPs via overcoming the sequential biological barriers are covered through unraveling the biophysical interactions at the bio-nano interface and giving a set of criteria to efficiently modulate MNPs' physicochemical properties. Furthermore, concepts of passive and active targeting for successful cell internalization, by respectively exploiting the unique properties of cancers and novel targeting ligands are described in detail. Finally, this study extensively covers the recent developments in magnetic drug targeting and hyperthermia as therapeutic applications of MNPs. In addition, multi-modal imaging via fusion of magnetic resonance imaging, and also innovative magnetic particle imaging with other imaging techniques for early diagnosis of diseases are extensively provided.

Surface modification of TiO2 particles with the sono-assisted exfoliation method

This study reported a novel approach to optimize the photocatalytic property of anatase TiO₂ particles by delaminating their outer surface into highly reactive nanosheets via the sono-assisted exfoliation method. To modify the surface, TiO₂ particles were dispersed in aqueous solution of 10M sodium hydroxide (NaOH) and tetrabutylammonium hydroxide (TBAOH), followed by irradiation with high intensity ultrasonic wave (20kHz, 150W/cm²) for 60min. The intercalation and exfoliation processes were accelerated with the driving force of the extreme acoustic cavitation leading to the delamination of TiO₂ nanosheets with highly reactive exposed {001} facets from the mother TiO₂ crystals. The presence of TBAOH increased yield of nanosheets formation and stabilized the nanosheet structure. The unique morphology of the surface modified TiO₂ particles provided benefits in increasing the specific surface area and lowering the optical band gap energy (E_g) and electron-hole recombination rate resulting in an enhancement of methylene blue dye degradation efficiency. The surface modification of TiO₂ particles by the sono-assisted exfoliation method can optimize the photocatalytic activity by yielding synergetic effects of the high surface reactive sites of the nanosheets and the high degree of crystallinity of the bulk structure.

Sono-assisted preparation of bio-nanocomposite for removal of Pb2+ ions: Study of morphology, thermal and wettability properties

Multi-walled carbon nanotubes (MWCNT) loaded poly(ethylene terephthalate) (PET) composites, with different CNT contents, were fabricated through an ultrasound assisted method as a fast and green way. Then, the obtained composites were fully characterized via FT-IR, UV-Vis, XRD, TGA, FE-SEM and TEM, etc. For this purpose, PET bottle was recycled and applied as matrix of nanocomposites (NC)s. Then, we dispersed the covalent functionalization of MWCNTs with a protein dispersant and obtained a powder of protein-functionalized CNTs. Bio-functionalized MWCNTs showed higher Pb²⁺ removal efficiency compared to MWCNT-COOH as ascertained via batch equilibrium adsorption experiments. Also, the results indicated the novel NCs presents a high affinity for Pb²⁺ heavy metal owing to the presence of several good sites. The contact angle results indicated that the addition of MWCNT-BSA increased significantly the contact angle compared to the pure PET. It was concluded that inflame retarding feature of NC was higher than pure polymer.