Superior selectivity of high-frequency ultrasound toward chorine containing-pharmaceuticals elimination in urine: A comparative study with other oxidation processes through the elucidation of the degradation pathways

This work considered the sonochemical degradation (using a bath-type reactor, at 375 kHz and 106.3 W L^-1, 250 mL of sample) of three representative halogenated pharmaceuticals (cloxacillin, diclofenac, and losartan) in urine matrices. The action route of the process was initially established. Then, the selectivity of the sonochemical system, to degrade the target pharmaceuticals in simulated fresh urine was compared with electrochemical oxidation (using a BDD anode, at 1.88 mA cm⁻²), and UVC/H₂O₂ (at 60 W of light and 500 mol L^-1 of H₂O₂). Also, the treatment of cloxacillin in an actual urine sample by ultrasound and UVC/H₂O₂ was evaluated. More than 90% of the target compounds concentration, in the simulated matrix, was removed after 60 min of sonication. However, the sono-treatment of cloxacillin in the real sample was less efficient than in the synthetic urine. The ultrasonic process achieved 43% of degradation after 90 min of treatment in the actual matrix. In the sonochemical system, hydroxyl radicals in the interfacial zone were the main degrading agents. Meanwhile, in the electrochemical process, electrogenerated HOCl was responsible for the elimination of pharmaceuticals. In turn, in UVC/H₂O₂ both direct photolysis and hydroxyl radicals degraded the target pollutants. Interestingly, the degradation by ultrasound of the pharmaceuticals in synthetic fresh urine was very close to the observed in distilled water. Indeed, the sonodegradation had a higher selectivity than the other two processes. Despite the sono-treatment of cloxacillin was affected by the actual matrix components, this contrasts with the UVC/H₂O₂, which was completely inhibited in the real urine. The sonochemical process led to 100% of antimicrobial activity (AA) elimination after 75 min sonication in the synthetic urine, and ∼ 20% of AA was diminished after 90 min of treatment in the real matrix. The AA decreasing was linked to the transformations of the penicillin nucleus on cloxacillin, the region most prone to electrophilic attacks by radicals according to a density theory functional analysis. Finally, predictions of biological activity confirmed that the sono-treatment decreased the activity associated with cloxacillin, diclofenac, and losartan, highlighting the positive environmental impact of degradation of chlorinated pharmaceuticals in urine.     

Sonochemical advanced oxidation process for the degradation of furosemide in water: Effects of sonication’s conditions and scavengers

The intensive consumption of pharmaceuticals and drugs in the last decades has led to their increased concentrations in wastewaters from industrial sources. The present paper deals, for the first time, with the sonochemical degradation and mineralization of furosemide (FSM) in water. FSM is a potent loop diuretic used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. The influence of several operating parameters such as acoustic intensity, ultrasonic frequency, initial FSM concentration, solution’s pH, nature of the dissolved gas (Ar, air and N₂) and radical scavengers (2-propanol and tert-butanol) on the oxidation of FSM was assessed. The obtained results showed that the degradation rate of the drug increased significantly with the increase of the acoustic intensity in the range of 0.83 to 4.3 W cm⁻² and decreased with the augmentation of the frequency in the range of 585–1140 kHz. It was also found that the initial rate of the sonolytic degradation of FSM increased with the increase of its initial concentration (2, 5, 10, 15 and 20 mg/L). The most significant degradation was achieved in acidic conditions at pH 2, while in terms of saturating gas, the rate of FSM degradation decreased in the order of Ar > air > N₂. The FSM degradation experiments with radical scavengers showed that the diuretic molecule degraded mainly at the interfacial region of the bubble by hydroxyl radical attack. Additionally, in terms of acoustic conditions, the sono-degradation of 30.24 µmol L^-1 of FSM solution demonstrate an optimal performance at 585 kHz and 4.3 W/cm², the results indicated that even if the ultrasonic action eliminated the total concentration of FSM within 60 min, a low degree of mineralization was obtained due to the by-products formed during the sono-oxidation process. The ultrasonic process transforms FSM into biodegradable and environmentally friendly organic by-products that could be treated in a subsequent biological treatment. Besides, the efficiency of the sonolytic degradation of FSM in real environmental matrices such as natural mineral water and seawater was demonstrated. Consequently, the sonochemical advanced oxidation process represent a very interesting technique for the treatment of water contaminated with FSM.     

A critical review on the sonochemical degradation of organic pollutants in urine,seawater, and mineral water

Substances such as pharmaceuticals, pesticides, dyes, synthetic and natural hormones, plasticizers, and industrial chemicals enter the environment daily. Many of them are a matter of growing concern worldwide. The use of ultrasound to eliminate these compounds arises as an interesting alternative for treating mineral water, seawater, and urine. Thereby, this work presents a systematic and critical review of the literature on the elimination of organic contaminants in these particular matrices, using ultrasound-based processes. The degradation efficiency of the sonochemical systems, the influence of the nature of the pollutant (volatile, hydrophobic, or hydrophilic character), matrix effects (enhancement or detrimental ability compared to pure water), and the role of the contaminant concentration were considered. The combinations of ultrasound with other degradation processes, to overcome the intrinsic limitations of the sonochemical process, were considered. Also, energy consumptions and energy costs associated with pollutants degradation in the target matrices were estimated. Moreover, the gaps that should be developed in future works, on the sonodegradation of organic contaminants in mineral water, seawater, and urine, were discussed.     

High frequency ultrasound as a selective advanced oxidation process to remove penicillinic antibiotics and eliminate its antimicrobial activity from water

This work studies the sonochemical degradation of a penicillinic antibiotic (oxacillin) in simulated pharmaceutical wastewater. High frequency ultrasound was applied to water containing the antibiotic combined with mannitol or calcium carbonate. In the presence of additives, oxacillin was efficiently removed through sonochemical action. For comparative purposes, the photo-Fenton, TiO₂ photocatalysis and electrochemical oxidation processes were also tested. Therefore, the evolution of the antibiotic and its associated antimicrobial activity (AA) were monitored. A high inhibition was found for the other three oxidation processes in the elimination of the antimicrobial activity caused by the additives; while for the ultrasonic treatment, a negligible effect was observed. The sonochemical process was able to completely degrade the antibiotic, generating solutions without AA. In fact, the elimination of antimicrobial activity showed an excellent performance adjusted to exponential kinetic-type decay. The main sonogenerated organic by-products were determined by means of HPLC-MS. Four intermediaries were identified and they have modified the penicillinic structure, which is the moiety responsible for the antimicrobial activity. Additionally, the possible oxacillin sonodegradation mechanism was proposed based on the evolution of the by-products and their chemical structure. Furthermore, the high-frequency ultrasound action over 120 min readily removed oxacillin and eliminated its antimicrobial activity. However, the pollutant was not mineralized even after a long period of ultrasonic irradiation (360 min). Interestingly, the previously sonicated water containing oxacillin and both additives was completely mineralized using non-adapted microorganisms from a municipal wastewater treatment plant. These results show that the sonochemical treatment transformed the initial pollutant into substances that are biotreatable with a typical aerobic biological system.     

Degradation of Acid Blue 25 in aqueous media using 1700 kHz ultrasonic irradiation: ultrasound/Fe(II) and ultrasound/H2O2 combinations

In this work, the sonolytic degradation of an anthraquinonic dye, C.I. Acid Blue 25 (AB25), in aqueous phase using high frequency ultrasound waves (1700 kHz) for an acoustic power of 14 W was investigated. The sonochemical efficiency of the reactor was evaluated by potassium iodide dosimeter, Fricke reaction and hydrogen peroxide production yield. The three investigated methods clearly show the production of oxidizing species during sonication and well reflect the sonochemical effects of high frequency ultrasonic irradiation. The effect of operational conditions such as the initial AB25 concentration, solution temperature and pH on the degradation of AB25 was studied. Additionally, the influence of addition of salts on the degradation of dye was examined. The rate of AB25 degradation was dependent on initial dye concentration, pH and temperature. Addition of salts increased the degradation of dye. Experiments conducted using distilled and natural waters demonstrated that the degradation was more efficient in the natural water compared to distilled water. To increase the efficiency of AB25 degradation, experiments combining ultrasound with Fe(II) or H₂O₂ were conducted. Fe(II) induced the dissociation of ultrasonically produced hydrogen peroxide, leading to additional OH radicals which enhance the degradation of dye. The combination of ultrasound with hydrogen peroxide looks to be a promising option to increase the generation of free radicals. The concentration of hydrogen peroxide plays a crucial role in deciding the extent of enhancement obtained for the combined process. The results of the present work indicate that ultrasound/H₂O₂ and ultrasound/Fe(II) processes are efficient for the degradation of AB25 in aqueous solutions by high frequency ultrasonic irradiation.     

Ultrasonic degradation of acetaminophen in water: Effect of sonochemical parameters and water matrix

This paper deals about the sonochemical water treatment of acetaminophen (ACP, N-acetyl-p-aminophenol or paracetamol), one of the most popular pharmaceutical compounds found in natural and drinking waters. Effect of ultrasonic power (20–60 W), initial ACP concentration (33–1323 μmol L⁻¹) and pH (3–12) were evaluated. High ultrasonic powers and, low and natural acidic pH values favored the efficiency of the treatment. Effect of initial substrate concentration showed that the Langmuir-type kinetic model fit well the ACP sonochemical degradation. The influence of organic compounds in the water matrix, at concentrations 10-fold higher than ACP, was also evaluated. The results indicated that only organic compounds having a higher value of the Henry’s law constant than the substrate decrease the efficiency of the treatment. On the other hand, ACP degradation in mineral natural water showed to be strongly dependent of the initial substrate concentration. A positive matrix effect was observed at low ACP concentrations (1.65 μmol L⁻¹), which was attributed to the presence of bicarbonate ion in solution. However, at relative high ACP concentrations a detrimental effect of matrix components was noticed. Finally, the results indicated that ultrasonic action is able to transform ACP in aliphatic organic compounds that could be subsequently eliminated in a biological system.     

Effects of Na2SO4 or NaCl on sonochemical degradation of phenolic compounds in an aqueous solution under Ar: Positive and negative effects induced by the presence of salts

Sonochemical degradation of 4-chlorophenol, phenol, catechol and resorcinol was studied under Ar at 200 kHz in the absence and presence of Na₂SO₄ or NaCl. The rates of sonochemical degradation in the absence of salts decreased in the order 4-chlorophenol > phenol > catechol > resorcinol and this order was in good agreement with the order of log P (partition coefficient) value of each phenolic compound. The effects of salts on the rates of sonochemical degradation consisted of no effect or slight negative or positive effects. We discussed these unclear results based on two viewpoints: one was based on the changes in pseudo hydrophobicity and/or diffusion behavior of phenolic compounds and the other was based on the changes in solubility of Ar gas. The measured log P value of each phenolic compound slightly increased with increasing salt concentration. In addition, the dynamic surface tension for 4-chlorophenol aqueous solution in the absence and presence of Na₂SO₄ or NaCl suggested that phenolic compounds more easily accumulated at the interface region of bubbles at higher salt concentration. These results indicated that the rates of sonochemical degradation should be enhanced by the addition of salts. On the other hand, the calculated Ar gas solubility was confirmed to decrease with increasing salt concentration. The yield of H₂O₂ formed in the presence of Na₂SO₄ or NaCl decreased with increasing salt concentration. These results suggested that sonochemical efficiency decreased with decreasing gas amount in aqueous solution: a negative effect of salts was observed. Because negative and positive effects were induced simultaneously, we concluded that the effects of salts on the rates of sonochemical degradation of phenolic compounds became unclear. The products formed from sonochemical degradation of 4-chlorophenol were also characterized by HPLC analysis. The formation of phenol and 4-chloro-1,3-dihydroxy benzene was confirmed and these concentrations were affected by the presence of salts.     

Sonochemical degradation of trimethoprim in water matrices: Effect of operating conditions,identification of transformation products and toxicity assessment

The sonochemical degradation of trimethoprim (TMP), a widely used antibiotic, in various water matrices was investigated. The effect of several parameters, such as initial TMP concentration (0.5–3 mg/L), actual power density (20–60 W/L), initial solution pH (3–10), inorganic ions, humic acid and water matrix on degradation kinetics was examined. The pseudo-first order degradation rate of TMP was found to increase with increasing power density and decreasing pH, water complexity (ultrapure water > bottled water > secondary wastewater) and initial TMP concentration.TMP degradation is accompanied by the formation of several transformation products (TPs) as evidenced by LC-QToF-MS analysis. Nine such TPs were successfully identified and their time-trend profiles during degradation were followed. An in silico toxicity evaluation was performed showing that several TPs could potentially be more toxic than the parent compound towards Daphnia magna, Pimephales promelas and Pseudokirchneriella subcapitata.     

Sonochemical water splitting in the presence of powdered metal oxides

Kinetics of hydrogen formation was explored as a new chemical dosimeter allowing probing the sonochemical activity of argon-saturated water in the presence of micro- and nano-sized metal oxide particles exhibiting catalytic properties (ThO₂, ZrO₂, and TiO₂). It was shown that the conventional sonochemical dosimeter based on H₂O₂ formation is hardly applicable in such systems due to catalytic degradation of H₂O₂ at oxide surface. The study of H₂ generation revealed that at low-frequency ultrasound (20 kHz) the sonochemical water splitting is greatly improved for all studied metal oxides. The highest efficiency is observed for relatively large micrometric particles of ThO₂ which is assigned to ultrasonically-driven particle fragmentation accompanied by mechanochemical water molecule splitting. The nanosized metal oxides do not exhibit particle size reduction under ultrasonic treatment but nevertheless yield higher quantities of H₂. The enhancement of sonochemical water splitting in this case is most probably resulting from better bubble nucleation in heterogeneous systems. At high-frequency ultrasound (362 kHz), the effect of metal oxide particles results in a combination of nucleation and ultrasound attenuation. In contrast to 20 kHz, micrometric particles slowdown the sonolysis of water at 362 kHz due to stronger attenuation of ultrasonic waves while smaller particles show a relatively weak and various directional effects.     

Degradation of methylparaben by sonocatalysis using a Co–Fe magnetic carbon xerogel

The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo–first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near–neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be >45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.     

Dual-high-frequency from single-piezoelectric crystal for ACE degradation by hybrid advanced oxidation UV-sonochemistry process

This study investigates the combination of two waves emitted from a single-piezoelectric crystal by use of a dual-frequency generator in a sonochemical reactor. The dual-frequency configurations analyzed were the double-modulated fundamental frequency (376–376 kHz), resonant and second harmonic, termed 376D, 376R and 376H respectively. The effect of the phase shift (Φ) and the percentage of modulation between added waves were described by the total acoustic power distribution (P_t) measured inside the sonoreactor. Moreover, optimal angle alignment and modulation between dual-frequency waves for 376D, 376R and 376H cases were selected in order to evaluate the ultrasonic synergy by sonochemical reactivity in production of H₂O₂, in degradation rate of a model emerging pollutant ACE, and in the TOC and biodegradability evolution in the treated effluent. Phase shift and percentage of modulation had strong effect on the resulted waveform and on the sonochemical efficiency for all, harmonic and non-harmonic, dual-frequency combinations created. In the 376D case, the best reinforcement conditions are founded at 0° and 360°. In the 376H the maximum power distribution presents a 90° period. Shift phase does not determines any cyclic pattern in the total power distribution for the 376R case. The highest H₂O₂ production rate was observed for the 376H case followed for 376D and 376R configurations with 1.61, 1.12 and 0.58 μM/min by angle alignment in 105, 0 and 110° respectively. The highest initial degradation rate of ACE was observed for the 376D case followed for 376H and 376R with 0.56, 0.42 and 0.33 μM/min at 100% modulation. Reduced mineralization was observed in all dual-frequency configurations (8.54% for 376D and approximately 4.5% for 376R and 3756H modes). Contrasting results are observed regard to biodegradability ratio following the next sequence 376D < 376H≈376R with 0.9, 2.30 and 2.33 respectively. Relevant intensification in hydroxyl radicals production is observed by the UV-US system increasing up three folds the ACE removal and mineralization and two folds higher biodegradability of effluent in particular for 376R and 376H cases at optimal operation condition of dual-frequency signal.     

Sonolysis of levodopa and paracetamol in aqueous solutions

Pharmaceutical products are often present in wastewater treatment effluents, rivers, lakes and, more rarely, in groundwater. The advanced oxidation methods, like ultrasound, find a promising future in the area of wastewater treatment. The aim of this paper is to evaluate the influence of several parameters of the ultrasound process on the degradation of paracetamol, a widely used non-steroidal anti-inflammatory recalcitrant drug found in water and levodopa, the most frequently prescribed drug for the treatment of Parkinson disease. Experiments were carried out at 574, 860 and 1134 kHz of ultrasonic frequency with horn-type sonicator and actual power values of 9, 17, 22 and 32 W at 20 °C. Initial concentrations of 25, 50, 100 and 150 mg L^?1 of both products were used. Treatment efficiency was assessed following changes in pharmaceuticals concentration and chemical oxygen demand.The sonochemical degradation of both products follows a pseudo-first-order reaction kinetics. Complete removal of pharmaceuticals was achieved in some cases but some dissolved organic carbon remains in solution showing that long lived intermediates were recalcitrant to ultrasound irradiation. Pollutants conversion and COD removal were found to decrease with increasing the initial solute concentration and decreasing power. The best results were obtained with 574 kHz frequency. Investigations using 1-butanol as radical scavenger and H₂O₂ as promoter revealed that pollutants degradation proceeds principally through radical reactions, although some differences were observed between both molecules. Addition of H₂O₂ had a positive effect on degradation rate, but the optimum concentration of hydrogen peroxide depends on the pollutant.     

Effects of gas sparging and mechanical mixing on sonochemical oxidation activity

The effects of air sparging (0–16 L min⁻¹) and mechanical mixing (0–400 rpm) on enhancing the sonochemical degradation of rhodamine B (RhB) was investigated using a 28 kHz sonoreactor. The degradation of RhB followed pseudo first-order kinetics, where sparging or mixing induced a large sonochemical enhancement. The kinetic constant varied in three stages (gradually increased → increased exponentially → decreased slightly) as the rate of sparging or mixing increased, where the stages were similar for both processes. The highest sonochemical activity was obtained with sparging at 8 L min⁻¹ or mixing at 200 rpm, where the standing wave field was significantly deformed by sparging and mixing, respectively. The cavitational oxidation activity was concentrated at the bottom of the sonicator when higher sparging or mixing rates were employed. Therefore, the large enhancement in the sonochemical oxidation was attributed mainly to the direct disturbance of the ultrasound transmission and the resulting change in the cavitation-active zone in this study. The effect of the position of air sparging and mixing was investigated. The indirect inhibition of the ultrasound transmission resulted in less enhancement of the sonochemical activity. Moreover, the effect of various sparging gases including air, N₂, O₂, Ar, CO₂, and an Ar/O₂ (8:2) mixture was compared, where all gases except CO₂ induced an enhancement in the sonochemical activity, irrespective of the concentration of dissolved oxygen. The highest activity was obtained with the Ar/O₂ (8:2) mixture. Therefore, it was revealed that the sonochemical oxidation activity could be further enhanced by applying gas sparging using the optimal gas.     

Critical factors in sonochemical degradation of fumaric acid

The effects of critical factors such as Henry’s Law constant, atmospheric OH rate constant, initial concentration, H₂O₂, FeSO₄ and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1 mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H₂O₂ under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H₂O₂ under sonication. 0.1 mM of fumaric acid suppresses H₂O₂ formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO₄) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.     

Intensification of sonochemical decolorization of anthraquinonic dye Acid Blue 25 using carbon tetrachloride

In this work, the influence of CCl₄ on the sonochemical decolorization of anthraquinonic dye Acid Blue 25 (AB25) in aqueous medium was investigated using high frequency ultrasound (1700 kHz). This frequency, reputed ineffective, was tested in order to introduce the ultrasound waves with high frequency in the field of degradation or removal of dyes from wastewater, due to its limited use in this field, and to increase the application of high frequency ultrasound wave in the field of environmental protection. The effects of various parameters such as the concentration of CCl₄, frequency (22.5 and 1700 kHz), solution pH, temperature and tert-butyl alcohol adding on the decolorization rate of AB25 was studied. The obtained results clearly demonstrated the significant intensification of AB25 decolorization in the presence of CCl₄. The enhancement effect of CCl₄ increased by decreasing temperature and by increasing the CCl₄ concentration. The pH has a significant influence on the bleaching of dye both in the absence and presence of CCl₄. The three investigated dosimeter methods (KI oxidation, Fricke reaction and H₂O₂ production) well corroborate the improvement of the sonochemical effects in the presence of CCl₄. The best sonochemical decolorization rate of AB25 in aqueous solution both in the absence and presence of CCl₄ is observed to occur at 1700 kHz compared to 22.5 kHz. The sonochemical oxidation of CCl₄ generates oxidizing species in the liquid phase that are highly beneficial for oxidation of hydrophilic and non-volatile pollutant, such as dyes, because they are less susceptible to free radical attack due to lower stability of the generated free radicals.     

The effects of hydrogen peroxide on the sonochemical degradation of phenol and bisphenol A

This report describes the effects of H₂O₂ concentration (0.01, 0.1, 1, and 10 mM) on the sonochemical degradation of phenol and bisphenol A (BPA) using an ultrasonic source of 35 kHz and 0.08 W/mL. The concentration of the target pollutants (phenol or BPA), total organic carbon (TOC), and H₂O₂ were monitored for each input concentration of H₂O₂. The effects of H₂O₂ on the sonochemical degradation of phenol was more significant than that of BPA because phenol has a high solubility and low octanol–water partition coefficient (K_ow) value and is subsequently very likely to remain in the aqueous phase, giving it a greater probability of reacting with H₂O₂. The removal of TOC was also enhanced by the addition of H₂O₂. Some intermediates of BPA have a high K_ow value and subsequently have a greater probability of pyrolyzing by the high temperatures and pressures inside of cavitation bubbles. Thus the removal efficiency of TOC in BPA was higher than that of phenol. The removal efficiencies of TOC were lower than the degradation efficiencies of phenol and BPA. This result is due to the fact that some intermediates cannot readily degrade during the sonochemical reaction. The H₂O₂ concentration decreased but was not completely consumed during the sonochemical degradation of pollutants. The initial H₂O₂ concentration and the physical/chemical characteristics of pollutants were considered to be important factors in determining the formation rate of the H₂O₂. When high concentration of H₂O₂ was added to the solution, the formation rates were relatively low compared to when low concentrations of H₂O₂ were used.     

Characteristics of photoluminescence, thermoluminescence and thermal degradation in Eu-doped BaMgAl10O17 and SrMgAl10O17

The relation between photoluminescence and thermoluminescence from Eu-doped BAM (BaMgAl₁₀O₁₇) and SAM (SrMgAl₁₀O₁₇) are investigated. The emission peak of SAM:Eu shifts from 463 to 489 nm whereas that of BAM:Eu only shifts 3 nm at 450 nm as temperature decreased from 300 to 50 K under 146 nm excitation. This can be explained by the fact that there are Beevers–Ross (BR) and mid-oxygen (mO) sites for Eu ions in SAM. The emission peak around 463 nm from SAM:Eu is ascribed to Eu ions in the mO site, while the peak around 489 nm is ascribed to ones in the BR site in SAM host. From the result of thermal degradation of SAM:Eu, it is confirmed that the Eu ions located at mO site are easy to degrade compared with those located at BR site. The thermal degradation of BAM:Eu phosphor becomes large with the increase in Eu concentration. We suggest that the thermal degradation of BAM:Eu phosphor is due to the tendency of Eu ions to occupy the mO site.     

Simultaneous hydrodynamic cavitation and glow plasma discharge for the degradation of metronidazole in drinking water

In this study, a novel hydrodynamic cavitation unit combined with a glow plasma discharge system (HC-GPD) was proposed for the degradation of pharmaceutical compounds in drinking water. Metronidazole (MNZ), a commonly used broad-spectrum antibiotic, was selected to demonstrate the potential of the proposed system. Cavitation bubbles generated by hydrodynamic cavitation (HC) can provide a pathway for charge conduction during glow plasma discharge (GPD). The synergistic effect between HC and GPD promotes the production of hydroxyl radicals, emission of UV light, and shock waves for MNZ degradation. Sonochemical dosimetry provided information on the enhanced formation of hydroxyl radicals during glow plasma discharge compared to hydrodynamic cavitation alone. Experimental results showed a MNZ degradation of 14% in 15 min for the HC alone (solution initially containing 300 × 10⁻⁶ mol L⁻¹ MNZ). In experiments with the HC-GPD system, MNZ degradation of 90% in 15 min was detected. No significant differences were observed in MNZ degradation in acidic and alkaline solutions. MNZ degradation was also studied in the presence of inorganic anions. Experimental results showed that the system is suitable for the treatment of solutions with conductivity up to 1500 × 10⁻⁶ S cm⁻¹. The results of sonochemical dosimetry showed the formation of oxidant species of 0.15 × 10⁻³ mol H₂O₂ L⁻¹ in the HC system after 15 min. For the HC-GPD system, the concentration of oxidant species after 15 min reached 13 × 10⁻³ mol H₂O₂ L⁻¹. Based on these results, the potential of combining HC and GPD systems for water treatment was demonstrated. The present work provided useful information on the synergistic effect between hydrodynamic cavitation and glow plasma discharge and their application for the degradation of antibiotics in drinking water.     

Effect of dissolved gases on sonochemical oxidation in a 20 kHz probe system: Continuous monitoring of dissolved oxygen concentration and sonochemical oxidation activity

Dissolved gases have a substantial influence on acoustic cavitation and sonochemical oxidation reactions. Little research on the changes in dissolved gases and the resultant changes in sonochemical oxidation has been reported, and most studies have focused only on the initial dissolved gas conditions. In this study, the dissolved oxygen (DO) concentration was measured continuously during ultrasonic irradiation using an optical sensor in different gas modes (saturation/open, saturation/closed, and sparging/closed modes). Simultaneously, the resulting changes in sonochemical oxidation were quantified using KI dosimetry. In the saturation/open mode using five gas conditions of Ar and O₂, the DO concentration decreased rapidly when O₂ was present because of active gas exchange with the atmosphere, and the DO concentration increased when 100% Ar was used. As a result, the order of the zero-order reaction constant for the first 10 min (k_0-10) decreased in the order Ar:O₂ (75:25) > 100% Ar ≈ Ar:O₂ (50:50) > Ar:O₂ (25:75) > 100% O₂, whereas that during the last 10 min (k_20-30) when the DO concentration was relatively stable, decreased in the order 100% Ar > Ar:O₂ (75:25) > Ar:O₂ (50:50) ≈ Ar:O₂ (20:75) > 100% O₂. In the saturation/closed mode, the DO concentration decreased to approximately 70–80% of the initial level because of ultrasonic degassing, and there was no influence of gases other than Ar and O₂. Consequently, k_0-10 and k_20-30 decreased in the order Ar:O₂ (75:25) > Ar:O₂ (50:50) > Ar:O₂ (25:75) > 100% Ar > 100% O₂. In the sparging/closed mode, the DO concentration was maintained at approximately 90% of the initial level because of the more active gas adsorption induced by gas sparging, and the values of k_0-10 and k_20-30 were almost the same as those in the saturation/closed mode. In the saturation/open and sparging/closed modes, the Ar:O₂ (75:25) condition was most favorable for enhancing sonochemical oxidation. However, a comparison of k_0-10 and k_20-30 indicated that there would be an optimal dissolved gas condition that was different from the initial gas condition. In addition, the mass-transfer and ultrasonic-degassing coefficients were calculated using changes in the DO concentration in the three modes.     

Rapid sonochemical synthesis of irregular nanolaminar-like Bi2WO6 as efficient visible-light-active photocatalysts

Irregular Bi₂WO₆ nanolaminars have been successfully synthesized via a rapid sonochemical approach using bismuth nitrate and tungstic acid as precursors in an aqueous solution. The characteristics of them were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption, pore value, PL spectroscopy and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). These irregular nanolaminars are of geometric shapes of orthorhombic Bi₂WO₆ with their basal plane being (0 0 1). They possess high crystallinity, lager surface area and pore value, which means fewer traps and stronger photocatalytic activity. The growth mechanism of such special nanolaminar was related to the sonochemical synthesis route, which played a key role in the formation of Bi₂WO₆ nanolaminar. Simultaneously, it was found that the formation of Bi₂WO₆ nanolaminar is a time dependent process. The Bi₂WO₆ nanolaminar has higher photocatalytic activity than bulk Bi₂WO₆ nanoparticle obtained by refluxing method for rhodamine B (Rh.B) degradation under visible light irradiation (λ > 400 nm).