Sonochemical activity in ultrasonic reactors under heterogeneous conditions

Due to its physical and chemical effects, ultrasound is widely used for industrial purposes, especially in heterogeneous medium. Nevertheless, this heterogeneity can influence the ultrasonic activity. In this study, the effect of the addition of inert glass beads on the sonochemical activity inside an ultrasonic reactor is investigated by monitoring the formation rate of triiodide, and the ultrasonic power is measured by calorimetry and by acoustic radiation. It was found that the sonochemical activity strongly depends on the surface area of the glass beads in the medium: it decreases above a critical area value (around 10⁻² m²), partly due to wave scattering and attenuation. This result is confirmed for a large range of frequencies (from 20 to 1135 kHz) and glass beads diameters (from 8-12 µm to 6 mm). It was also demonstrated that above a given threshold of the surface area, only part of the supplied ultrasonic power is devoted to chemical effects of ultrasound. Finally, the acoustic radiation power appears to describe the influence of solids on sonochemical activity, contrary to the calorimetric power.     

Ultrasound expands the versatility of polydopamine coatings

Polydopamine (PDA) coating of surfaces is a versatile strategy to fabricate functional films on various substrates, which typically requires oxygen and alkaline pH. Overcoming such limitations may enhance the versatility of this technique. Herein, we develop a simple and green sonochemical process for PDA coatings, which overcomes the limitations of traditional coating technique and expands the versatility of PDA chemistry. The oxidizing radicals generated by high frequency ultrasound (412 kHz) are utilized to initiate and accelerate the polymerization of dopamine. The sonochemical rate of film deposition is found to be about twice faster than that of the traditional method in the presence of oxygen. Importantly, the PDA coatings can be obtained in neutral or acidic aqueous solutions and even in the absence of oxygen. The PDA coatings can be moderated by turning on or off high frequency ultrasound. This study provides an environmentally friendly and economic method for the engineering of PDA coatings independent of the solution pH and nature of dissolved gas.     

The effect of high-intensity ultrasound on the ring-opening polymerisation of cyclic lactones

High-intensity ultrasound has been applied to the ring-opening polymerisation of δ-valerolactone and ε-caprolactone catalysed by dibutyl tin dilaurate. Sonication was found to accelerate the polymerisation. In the case of δ-valerolactone, sonication also promoted a depolymerisation reaction so that the molecular weight fell during later stages of the reaction. Co-polymers of the two monomers were synthesised and the use of ultrasound led to preferential incorporation of ε-caprolactone into the material, probably due to degradation of the valerolactone sequences.     

Ultrasound assisted ambient temperature synthesis of ternary oxide AgMO2 (M=Fe, Ga)

The application of ultrasound for the synthesis of ternary oxide AgMO₂ (M=Fe, Ga) was investigated. Crystalline α-AgFeO₂ was obtained from the alkaline solutions of silver and iron hydroxides by sonication for 40 minutes. α-AgFeO₂ was found to absorb optical radiation in the 300-600 nm range as shown by diffuse reflectance spectroscopy. The Raman spectrum of α-AgFeO₂ exhibited two bands at 345 and 638 cm⁻¹. When β-NaFeO₂ was sonicated with aqueous silver nitrate solution for 60 minutes, β-AgFeO₂ possessing orthorhombic structure was obtained as the ion-exchanged product. The Raman spectrum of β-AgFeO₂ showed four strong bands at 295, 432, 630 and 690 cm⁻¹. Sonication of β-NaGaO₂ with aqueous silver nitrate solution for 60 minutes resulted in olive green colored, α-AgGaO₂. The diffuse reflectance spectrum and the EDX analysis confirmed that the ion-exchange through sonication was complete. The Raman spectrum of α-AgGaO₂ had weak bands at 471 and 650 cm⁻¹.     

Ultrasonic assisted dyeing: Dyeing of acrylic fabrics C.I. Astrazon Basic Red 5BL 200%

The dyeing of acrylic fabrics using C.I. Astrazon Basic Red 5BL 200% has been studied with both conventional and ultrasonic techniques. The effect of dye concentration, dye bath pH, ultrasonic power, dyeing time and temperature were studied and the resulting shades obtained by dyeing with both techniques were compared. Colour strength values obtained were found to be higher with ultrasonic than with conventional heating. The results of fastness properties of the dyed fabrics were studied. X-ray and Scanning Electron Microscope SEM were carried out on dyed samples using both methods of dyeing to find out an explanation for the better dyeability of acrylic fabrics with (US) method. Dyeing kinetics of acrylic fabrics using C.I. Astrazon Basic Red 5BL 200% using conventional and ultrasonic conditions were compared. The time/dye-uptake isotherms are revealing the enhanced dye-uptake in the second phase of dyeing. The values of dyeing rate constant, half-time of dyeing and standard affinity and ultrasonic efficiency have been calculated and discussed.     

Physical insights into the sonochemical degradation of recalcitrant organic pollutants with cavitation bubble dynamics

This paper tries to discern the mechanistic features of sonochemical degradation of recalcitrant organic pollutants using five model compounds, viz. phenol (Ph), chlorobenzene (CB), nitrobenzene (NB), p-nitrophenol (PNP) and 2,4-dichlorophenol (2,4-DCP). The sonochemical degradation of the pollutant can occur in three distinct pathways: hydroxylation by OH radicals produced from cavitation bubbles (either in the bubble–bulk interfacial region or in the bulk liquid medium), thermal decomposition in cavitation bubble and thermal decomposition at the bubble–liquid interfacial region. With the methodology of coupling experiments under different conditions (which alter the nature of the cavitation phenomena in the bulk liquid medium) with the simulations of radial motion of cavitation bubbles, we have tried to discern the relative contribution of each of the above pathway to overall degradation of the pollutant. Moreover, we have also tried to correlate the predominant degradation mechanism to the physico-chemical properties of the pollutant. The contribution of secondary factors such as probability of radical–pollutant interaction and extent of radical scavenging (or conservation) in the medium has also been identified. Simultaneous analysis of the trends in degradation with different experimental techniques and simulation results reveals interesting mechanistic features of sonochemical degradation of the model pollutants. The physical properties that determine the predominant degradation pathway are vapor pressure, solubility and hydrophobicity. Degradation of Ph occurs mainly by hydroxylation in bulk medium; degradation of CB occurs via thermal decomposition inside the bubble, degradation of PNP occurs via pyrolytic decomposition at bubble interface, while hydroxylation at bubble interface contributes to degradation of NB and 2,4-DCP.     

Sonochemical growth of antimony sulfoiodide in multiwalled carbon nanotube

This paper presents for the first time the nanocrystalline, semiconducting ferroelectrics antimony sulfoiodide (SbSI) grown in multiwalled carbon nanotubes (CNTs). It was prepared sonochemically using elemental Sb, S and I in the presence of methanol under ultrasonic irradiation (35 kHz, 2.6 W/cm²) at 323 K for 3 h. The CNTs filled with SbSI were characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, and optical diffuse reflection spectroscopy. These investigations exhibit that the SbSI filling the CNTs is single crystalline in nature and in the form of nanowires. It has indirect forbidden energy band gap E_gIf = 1.871(1) eV.     

Imparting superhydrophobic and biocidal functionalities to a polymeric substrate by the sonochemical method

Multifunctional substrates with superhydrophobic and biocidal properties are gaining interest for a wide range of applications; however, the production of such surfaces remains challenging. Here, the sonochemical method is utilized to impart superhydrophobicity and antimicrobial properties to a polyethylene (PE) sheet. This is achieved by sonochemically depositing nanoparticles (NPs) of a hydrophobic fluoro-polymer (FP) on the PE sheets. The polymer is a flexible, transparent fluoroplastic composed of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride in the form of a powder. The NPs of polymers are generated and deposited on the surface of the PE using ultrasound irradiation. Optimizing the process results in a homogeneous distribution of 110–200 nm of NPs on the PE surface. The coated surface displays a water-contact angle of 160°, indicating excellent superhydrophobicity. This superhydrophobic surface shows high stability under outdoor conditions for two months, which is essential for various applications. In addition, metal-oxide nanoparticles (CuO or ZnO NPs) were integrated into the polymer coating to achieve antibacterial properties and increase the surface roughness. The metal oxides were also deposited sonochemically. The antibacterial activity of the FP@ZnO and FP@CuO PE composites was tested against the bacterium Staphylococcus aureus, and the results show that the FP@CuO PE can effectively eradicate the bacteria. This study highlights the feasibility of using the sonochemical method to deposit two separate functions, opening up new possibilities for producing “smart” novel surfaces.     

Sonochemical synthesis of PdO@silica as a nanocatalyst for selective aerobic alcohol oxidation

A sonochemical method has been employed for the synthesis of palladium oxide (PdO) nanoparticles deposited on silica nanoparticle. By sonochemical process, the PdO nanoparticles were doped on the surface of silica at room temperature and atmospheric pressure with short reaction time. Silica nanoparticles were used as a supporting material to suppress aggregation and thereby to increase surface area of PdO nanoparticles. Fabricated PdO-doped silica nanoparticle (PdO@SNP) was applied as a nanocatalyst for selective alcohol oxidation reaction in the presence of molecular oxygen. The PdO@SNP composite showed higher catalytic activity and selectivity than unsupported PdO nanoparticle for aerobic alcohol oxidation reaction.     

Preparation of metal–ceramic composites by sonochemical synthesis of metallic nano-particles and in-situ decoration on ceramic powders

Copper and nickel nanoparticles were synthesized using reducing agents in the presence of direct high energy ultra-sonication. The metallic nanoparticles were decorated on various ceramic substrates (e.g. α-Al₂O₃, and TiO₂) leading to metal reinforced ceramics with up to 45% metallic content. Different parameters, such as the amount of precursor material or the substrate, as well as the intensity of ultrasound were examined, in order to evaluate the percentage of final metallic decoration on the composite materials. All products were characterized by means of Inductively Coupled Plasma Spectroscopy in order to investigate the loading with metallic particles. X-ray Diffraction and Scanning Electron Microscopy were also used for further sample characterization. Selected samples were examined using Transmission Electron Microscopy, while finally, some of the powders synthesized, were densified by means of Spark Plasma Sintering, followed by a SEM/EDX examination and an estimation of their porosity.