Enhanced ultrasonic degradation of methylene blue using a catalyst-free dual-frequency treatment

Numerical investigation of acoustic cavitation characteristics of a single gas-vapor bubble in soft tissue under dual-frequency ultrasound

The viscoelastic tissue under dual-frequency ultrasound excitation affects the acoustic cavitation of a single gas-vapor bubble. To investigate the effect of the cavitation dynamics, the Gilmore-Akulichev-Zener (GAZ) model is coupled with the Peng-Robinson equation of state (PR EOS). Results indicate that the GAZ-PR EOS model can accurately estimate the bubble dynamics by comparing with the Gilmore PR EOS and GAZ-Van der Waals (VDW) EOS model. Furthermore, the acoustic cavitation effect in different viscoelastic tissues is investigated, including the radial stress at the bubble wall, the temperature, pressure, and the number of water molecules inside the bubble. Results show that the creep recovery and the relaxation of the stress caused by viscoelasticity can affect the acoustic cavitation of the bubble, which could inhibit the bubble's expansion and reduce the internal temperature and pressure within the bubble. Moreover, the effect of dual-frequency ultrasound on the cavitation of single gas-vapor bubbles is studied. Results suggest that dual-frequency ultrasound could increase the internal temperature of bubbles, the internal pressure of bubbles, and the radial stress at the bubble wall. More importantly, there is a specific optimal combination of frequencies for particular viscoelasticity by exploring the impact of different dual-frequency ultrasound combinations and tissue viscoelasticity on the acoustic cavitation of a single gas-vapor bubble. In conclusion, this study helps to provide theoretical guidance for dual-frequency ultrasound to improve acoustic chemical and mechanical effects, and further optimize its application in acoustic sonochemistry and ultrasound therapy.

On the Valorization of Olive Oil Pomace: A Sustainable Approach for Methylene Blue Removal from Aqueous Media

Currently, industrial water pollution represents a significant global challenge, with the potential to adversely impact human health and the integrity of ecosystems. The continuous increase in global consumption has resulted in an exponential rise in the use of dyes, which have become one of the major water pollutants, causing significant environmental impacts. In order to address these concerns, a number of wastewater treatment methods have been developed, with a particular focus on physicochemical approaches, such as adsorption. The objective of this study is to investigate the potential of a bio-based material derived from olive oil pomace (OOP) as an environmentally friendly bio-adsorbent for the removal of methylene blue (MB), a cationic dye commonly found in textile effluents. The biobased material was initially characterized by determining the point of zero charge (pHpzc) and using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Subsequently, a comprehensive analysis was conducted, evaluating the impact of specific physicochemical parameters on MB adsorption, which included a thorough examination of the kinetic and thermodynamic aspects. The adsorption process was characterized using Langmuir, Freundlich, Brunauer-Emmett-Teller (BET), and Dubinin Radushkevich (D-R) isotherms. The results suggest that the equilibrium of adsorption is achieved within ca. 200 min, following pseudo-second-order kinetics. The optimal conditions, including adsorbent mass, temperature, bulk pH, and dye concentration, yielded a maximum adsorption capacity of ca. 93% (i.e., 428 mg g-1) for a pomace concentration of 450 mg L-1. The results suggest a monolayer adsorption process with preferential electrostatic interactions between the dye and the pomace adsorbent. This is supported by the application of Langmuir, BET, Freundlich, and D-R isotherm models. The thermodynamic analysis indicates that the adsorption process is spontaneous and exothermic. This work presents a sustainable solution for mitigating MB contamination in wastewater streams while simultaneously valorizing OOP, an agricultural by-product that presents risks to human health and the environment. In conclusion, this approach offers an innovative ecological alternative to synthetic adsorbents.

Biogenic Synthesis of Copper Oxide Nanoparticles from Aloe vera: Antibacterial Activity, Molecular Docking, and Photocatalytic Dye Degradation

Green synthesis methods offer a cost-effective and environmentally friendly approach to producing nanoparticles (NPs), particularly metal-based oxides. This study explores the green synthesis of copper oxide nanoparticles using Aloe vera (Aloe barbadensis Miller) leaf extract. The characterization revealed a unique sago-shaped morphology revealed by field-emission scanning electron microscopy and X-ray diffraction analysis. Distinctive metal-oxygen bonds at 521 and 601 cm-1 were confirmed by Fourier-transform infrared (FT-IR) spectroscopy. Furthermore, UV-visible spectroscopy revealed absorbance at 248 nm, suggesting electron transitions across energy bands and varying surface conduction electrons. The band gap value indicated the presence of quantum confinement effects, which were probably caused by the distinctive morphology and surface structure of the biogenic NPs. Additionally, molecular docking studies were carried out against key proteins of Salmonella typhi and Listeria monocytogenes, namely, listeriolysin O (PDB ID: 4CDB), internalin (InlA) (PDB ID: 1O6T), Salmonella effector protein (SopB) (PDB ID: 4DID), and YfdX (PDB ID: 6A07) using AutoDock 4.2. The results revealed binding energies against S. typhi and L. monocytogenes proteins, indicating potential interactions establishing the foundation for further in-depth understanding of the molecular basis underlying the observed antibacterial effects in vitro against S. typhi, Klebsiella pneumoniae, Pseudomonas aeruginosa, and L. monocytogenes. Antibacterial activity evaluation yielded impressive results, with CuO NPs displaying significant activity against S. typhi and L. monocytogenes, exhibiting zones of inhibition values of 13 ± 0.02 and 15 ± 0.04 mm, respectively. Moreover, the CuO NPs demonstrated remarkable photocatalytic efficacy, resulting in the degradation of 77% of the methylene blue dye when exposed to UV irradiation. This study highlighted the potential of green-synthesized CuO NPs derived from A. vera with their unique morphology, interesting spectroscopic properties, and promising antibacterial and photocatalytic activities.

Tetracycline degradation by dual-frequency ultrasound combined with peroxymonosulfate

Tetracycline has received a great deal of interest for the harmful effects of substance abuse on ecosystems and humanity. The effects of different processes on the degradation of tetracycline were compared, with dual-frequency ultrasound (DFUS) in combination with peroxymonosulfate (PMS) being the most effective for the tetracycline degradation. Free radical scavenging experiments showed that O2∙-,SO4∙- and •OH were the main reactive radicals in the degradation of tetracycline. According to the major intermediates of tetracycline degradation identified, three possible degradation pathways were proposed, which are of significance for translational studies of tetracycline degradation. Notably, these intermediates were found to be significantly less toxicity. The number of active bubbles in the degradation vessel was calculated using a semi-empirical formula, and a higher value of 1.44 × 108 L-1s-1 of bubbles was obtained when using dual-frequency ultrasound at 20 kHz (210 W/L) and 80 kHz (85.4 W/L). Therefore, compared to 20 kHz, although the yield of strong oxidizing substances from individual active bubbles decreased slightly, a significant increment of the number of active bubbles still resulted in a higher synergistic effect, and the combination of DFUS and PMS should be effective in promoting the generation of reactive free radicals and mass transfer processes within the degradation vessel, which provides a method for efficient removal of tetracycline from wastewater.

Cu/Co Bimetallic Carbon Catalyst as a Highly Efficient Promoter for Reactive Dyes Degradation with PMS

The synergistic effect between bimetallic catalysts has been confirmed as an effective method for activating persulfate (PMS). Therefore, we immobilized copper-cobalt on chitosan to prepare bimetallic carbon catalysts for PMS activation and degradation of reactive dyes. Experimental results demonstrate that the CuCo-CTs/PMS catalytic degradation system exhibits excellent degradation performance toward various types of reactive dyes (e.g., Ethyl violet, Chlortalidone, and Di chlorotriazine), with degradation rates reaching 90% within 30 min. CuCo-CTs exhibit high catalytic activity over a wide pH range of 3-11 at room temperature and under static conditions, degrading over 92% of RV5 within 60 min. ultraviolet-visible (UV-vis) spectroscopy and color changes in the dye solution confirm the effective degradation of RV5, with a degradation rate of 97.2% within 10 min. Additionally, CuCo-CTs demonstrate good stability and reusability, maintaining a degradation rate of 92.8% after eight cycles. Kinetic studies indicate that the degradation follows pseudo-first-order kinetics. Furthermore, based on the results of radical scavenging experiments, the catalytic degradation mechanism of the dye involves both radical and nonradical pathways, with 1O2 identified as the primary active species. This study provides insights and experimental evidence for the application of persulfate oxidation in the treatment of dyeing wastewater.