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Organic dyes play vital roles in the textile industry, while the discharge of organic dye wastewater in the production and utilization of dyes has caused significant damage to the aquatic ecosystem. This review aims to summarize the mechanisms of photocatalysis, sonocatalysis, and sonophotocatalysis in the treatment of organic dye wastewater and the recent advances in catalyst development, with a focus on the synergistic effect of ultrasound and light in the catalytic degradation of organic dyes. The performance of TiO2-based catalysts for organic dye degradation in photocatalytic, sonocatalytic, and sonophotocatalytic systems is compared. With significant synergistic effect of ultrasound and light, sonophotocatalysis generally performs much better than sonocatalysis or photocatalysis alone in pollutant degradation, yet it has a much higher energy requirement. Future research directions are proposed to expand the fundamental knowledge on the sonophotocatalysis process and to enhance its practical application in degrading organic dyes in wastewater.

Sonochemistry is a significant contributor to green science as it includes: (i) the use of less toxic compounds and environmentally safe solvents, (ii) improvement of reaction conditions and selectivity, (iii) no toxic sludge generation, (iv) reduction in the energy use for chemical transformations, (v) reusability of materials. In water and wastewater treatment, ultrasound is used as an advanced oxidation process to eliminate refractory pollutants. Ultrasound is also used as a very effective sludge pretreatment technology in wastewater treatment plants to facilitate biogas production. Moreover, sonochemical synthesis of nanoparticles has recently attracted great attention as a greener protocol. This paper presents the main applications of ultrasound in environmental remediation and protection. The study also introduces mechanism for the degradation of pollutants from water via sonication in aqueous media and the principle factors affecting the cavitational effect.

Water recycling is of increasing concern due to the shortage of natural resources, calling for advanced methods to remove contaminants. Indeed, the transfer of contaminants to living organisms may lead to bioaccumulation and diseases. In particular, the overuse of antibiotics for human and animal health has led to antibiotic pollution in waters, sludges and crop soils, and, in turn, to the unintended development of multi-resistant bacteria, named antibiotic resistance. Here we review antibiotic properties, antibiotic occurrence in wastewater, and antibiotic removal. Remediation techniques include electrocoagulation, photocatalysis, Fenton process, sonocatalysis, ozonation, membrane filtration, adsorption and ionizing irradiation. Nanofilters and reverse osmosis showed the highest removal of antibiotics in a bioreactor, averaging at 95%. Recently developed methods such as photocatalysis, sonocatalysis and ozone oxidation show a removal of about 98%.

Cu(II) and Mn(II) coordination polymers [Cu(ttpa)(sub)]n (Cuttpa or 1) and [Mn2(ttpa)2(nip)2(H2O)2]·3H2On (Mnttpa or 2) (ttpa = tris(4-(1,2,4-triazol-1-yl)phenyl)amine, H2sub = suberic acid, nip = 5-nitroisophthalicate) were hydrothermally prepared and the structures were characterized. Cuttpa exhibited a 2D (4,4) network based on [Cu2(COO)4] dimers with upper and lower dangled ttpa ligands and a 2D → 3D polythreaded network. Mnttpa showed a 2D (4,4) network with dangled uncoordinated triazole rings from ttpa ligands and nitro groups from nip2− ligands and a 2D → 3D polythreaded network. Eg data of Cuttpa and Mnttpa were 1.88 eV and 2.11 eV. Cuttpa and Mnttpa exhibited good catalytic activity for the decomposition of methyl blue (MB) under visible light and supersound irradiation. The decomposition mechanism using Cuttpa was explored. The holes (h+) and •OH hydroxyl radicals played the main roles, and the •O2− superoxide radicals played certain auxiliary roles in the decomposition of MB within the Cuttpa catalyst.

In this study, cobalt ferrite/mesoporous graphitic carbon nitride (CoFe 2 O 4 /mpg-C 3 N 4 ) nanocomposites were successfully synthesized by using a two-step protocol. Firstly, monodispersed CoFe 2 O 4 nanoparticles (NPs) were synthesized via thermal decomposition of metal precursors in a hot surfactant solution and then they were assembled on mpg-C 3 N 4 via a liquid phase self-assembly method. The sonocatalytic performance of as-synthesized CoFe 2 O 4 /mpg-C 3 N 4 nanocomposites was evaluated on the methylene blue (MB) removal from water under ultrasonic irradiation. For this purpose, response surface methodology (RSM) based on central composite design (CCD) model was successfully utilized to optimize the MB removal over CoFe 2 O 4 /mpg-C 3 N 4 nanocomposites. Analysis of variance (ANOVA) was applied to investigate the significance of the model. The results predicted by the model were obtained to be in reasonable agreement with the experimental data ( R 2  = 0.969, adjusted R 2  = 0.942). Pareto analysis demonstrated that pH of the solution was the most effective parameter on the sonocatalytic removal of MB by CoFe 2 O 4 /mpg-C 3 N 4 nanocomposites. The optimum catalyst dose, initial dye concentration, pH, and sonication time were set as 0.25 g L −1 , 8 mg L −1 , 8, and 45 min, respectively. The high removal efficiency of MB dye (92.81%) was obtained under optimal conditions. The trapping experiments were done by using edetate disodium, tert-butyl alcohol, and benzoquinone. Among the reactive radicals, • OH played a more important role than h + and O 2 − • in the MB dye removal process. Moreover, a proposed mechanism was also presented for the removal of MB in the presence of CoFe 2 O 4 /mpg-C 3 N 4 nanocomposites under the optimized sonocatalytic conditions. Finally, a reusability test of the nanocomposites revealed a just 9.6% decrease in their removal efficiency after five consecutive runs.

Oral health has long been a central topic among public concern, so various products were designed to keep oral health, among these, antibiotic products with whitening effect are of promising prospects. Meanwhile, some products may destroy the enamel structure, resulting in plaque adhesion and mucosal damage. Piezoelectric material is one of the candidates carrying both advantages. This study introduces the application of polytetrafluoroethylene (PTFE) electret with piezoelectric catalytic effect in tooth whitening and antibiosis, and proposes a new toothbrush design. PTFE piezoelectric electret with sonocatalytic activity can be obtained by ultrasonic treatment. Then PTFE was submitted to characterization, including piezoelectric coefficient, piezoelectric catalytic rate, cytotoxicity, antibiosis and tooth whitening effect. PTFE piezoelectric electret was successfully obtained after ultrasonic treatment, and it showed excellent piezoelectric catalytic rate and biocompatibility. After 20 h of action, the stained teeth were successfully bleached, and PTFE showed good antibacterial performance against gram-positive and gram-negative bacteria in 30 min. Only a low frequency ultrasonic power is enough to activate PTFE and produce ROS for tooth whitening and anti-bacteria, which produce prominent prospect for its application in electrical toothbrush. Graphical abstract

Various concentrations of Mg-doped ZnO nanorods (NRs) were prepared using co-precipitation technique. The objective of this study was to improve the photocatalytic properties of ZnO. The effect of Mg doping on the structure, phase constitution, functional groups presence, optical properties, elemental composition, surface morphology and microstructure of ZnO was evaluated with XRD, FTIR, UV–Vis spectrophotometer, EDS, and HR-TEM, respectively. Optical absorption spectra obtained from the prepared samples showed evidence of blueshift upon doping. XRD results revealed hexagonal wurtzite phase of nanocomposite with a gradual decrease in crystallite size with Mg addition. PL spectroscopy showed trapping efficiency and migration of charge carriers with electron–hole recombination behavior, while HR-TEM estimated interlayer d-spacing. The presence of chemical bonding, vibration modes and functional groups at the interface of ZnO was revealed by FTIR and Raman spectra. In this study, photocatalytic, sonocatalytic and sonophotocatalytic performance of prepared NRs was systematically investigated by degrading a mixture of methylene blue and ciprofloxacin (MBCF). Experimental results suggested that improved degradation performance was shown by Mg-doped ZnO NRs. We believe that the product synthesized in this study will prove to be a beneficial and promising photocatalyst for wastewater treatment. Conclusively, Mg-doped ZnO exhibited substantial (p < 0.05) efficacy against gram-negative (G-ve) as compared to gram-positive (G+ve) bacteria. In silico molecular docking studies of Mg-doped ZnO NRs against DHFR (binding score: − 7.518 kcal/mol), DHPS (binding score: − 6.973 kcal/mol) and FabH (− 6.548 kcal/mol) of E. coli predicted inhibition of given enzymes as possible mechanism behind their bactericidal activity.

Reactive Blue 19 (RB19) removal from synthetic textile wastewater was investigated by using a CoFe2O4@methylcellulose (MC) activated with peroxymonosulfate (PMS) and the ultrasound process. CoFe2O4@MC as a new magnetic nano-biocomposite was prepared using a convenient and rapid microwave-assisted technique in presence of MC as a green biopolymer, and characterized by FESEM, EDS, Mapping, TEM, FTIR, XRD, TGA, VSM, and BET techniques. Then, the effective parameters including pH (4–10), reaction time (0–30 min), CoFe2O4@MC (0.2–1 g/L), and PMS concentration (0.5–10 mM) in the sonocatalytic degradation of RB19 were investigated. The maximum removal efficiency of RB19 was achieved as 97% for synthetic wastewater under the optimal conditions of pH 4, CoFe2O4@MC dosage (0.6 g/L), reaction time = 30 min, and PMS (5 mM) in the presence of ultrasonic waves (60 kHz) at the ambient room temperature of 22 °C. The CoFe2O4@MC catalyst was simply isolated using a magnet and recycled with no remarkable loss of catalytic activity following usage in four runs. The results showed that the CoFe2O4@MC sonocatalysis process is practical, and effective for degrading complex and resistant dyes such as RB19.

To effectively remove pharmaceuticals, nitroaromatic compounds, and dyes from wastewater, an efficient multifunctional material was created based on silver nanoparticles (Ag) and MIL-125-NH 2 (MOF) immobilized on viscose fibers (VF) as a support substrate. Firstly, silver nanoparticles (Ag) were immobilized on the surface of viscose fibers (VF) via in situ synthesis using trisodium citrate (TSC) as a reducing agent to create (VF-Ag). Then, VF and VF-Ag were decorated with the titanium metal–organic framework MIL-125-NH 2 (MOF) to create VF-MOF and VF-Ag-MOF. The influence of VF-Ag, VF-MOF, and VF-Ag-MOF on the sonocatalytic or sonophotocatalytic degradation of sulfa drugs was investigated. The results show that VF-Ag-MOF showed excellent sonocatalytic and sonophotocatalytic activity towards the degradation of sulfa drugs compared to VF-Ag and VF-MOF. Furthermore, sonophotodegradation showed a dramatic enhancement in the efficiency of degradation of sulfa drugs compared to sonodegradation. The sonophotodegradation degradation percentage of sulfanilamide, sulfadiazine, and sulfamethazine drugs in the presence of VF-Ag-MOF was 65, 90, and 95 after 45 min of ultrasonic and visible light irradiation. The catalytic activity of VF-Ag, VF-MOF, and VF-Ag-MOF was evaluated through the conversion of p-nitrophenol (4-NP) to p-aminophenol (4-AP). The results demonstrate that VF-Ag-MOF had the highest catalytic activity, followed by VF-Ag and VF-MOF. The conversion percentage of 4-NP to 4-AP was 69%. The catalytic or photocatalytic effects of VF-Ag, VF-MOF, and VF-Ag-MOF on the elimination of methylene blue (MB) dye were investigated. The results demonstrate that VF-Ag-MOF showed high efficiency in removing the MB dye through the reduction (65%) or photodegradation (71%) after 60 min. VF-Ag-MOF composites structure–activity relationships represent that doping within silver NPs enhanced the photocatalytic activity of MIL-125-NH 2 , which could be explained as follows: (i) Due to the formation of a Schottky barrier at the junction between MIL-125-NH 2 and Ag NPs, the photogenerated electrons in the conduction band of MIL-125-NH 2 were supposed to be quickly transferred to the valence band of the Ag NPs, and subsequently, the electrons were transferred to the conduction band of Ag NPs. This considerable electron transferring process, which is reported as Z scheme heterojunction, can efficiently suppress the recombination of electron/hole pairs in VF-Ag-MIL-125-NH 2 composites. (ii) Sufficient separation between the photogenerated charge carriers (holes and electrons) and avoiding their recombination enhanced the photocatalytic activity of composites.

In the present work, SnO 2 -Fe 3 O 4 @MWCNT nanocatalyst was fabricated according to a sonochemical-hydrothermal procedure. The surface morphology and structure analyses of the synthesized SnO 2 -Fe 3 O 4 @MWCNT were investigated by transmission electron microscope (TEM), X-ray diffraction (XRD), Raman spectroscopy, EDS, FTIR and BET analyses. The degradation efficiency of SnO 2 -Fe 3 O 4 @MWCNT nanocatalyst in MB solution was tested by several experimental conditions such as SnO 2 -Fe 3 O 4 @MWCNT dosage (8–20 mg/L), initial MB concentration (20–50 mg/L), initial solution pH (5–9), and ultrasonic output power (37–60 kHz). SnO 2 -Fe 3 O 4 @MWCNT nanocatalyst retained its efficiency as 85% at common experimental conditions of 16 mg/L of SnO 2 -Fe 3 O 4 @MWCNTs, 45 mg/L of MB, pH of 8, H 2 O 2 of 15 mM, and 60 kHz in 60 min under ultrasonic irradiation. In addition, the optimum experiment conditions for SnO 2 -Fe 3 O 4 @MWCNTs in MB degradation were investigated. The experiment result showed that the degradation efficiency of MB was increased by adding H 2 O 2 to the reaction medium due to forming more free radicals. Further, it was detected that OH• radicals were determined to be the dominant oxidative species in MB degradation using SnO 2 -Fe 3 O 4 @MWCNT catalyst. The reuse tests showed that SnO 2 -Fe 3 O 4 @MWCNT sonocatalyst preserved its very stable structure after using the same catalyst 5 times. The intermediates and by-products after MB degradation using the catalyst were indicated by GC–MS analysis. Overall the results showed that the SnO 2 -Fe 3 O 4 @MWCNT sonocatalyst has excellent potential for treating organic pollutants in wastewater. Graphical Abstract