Sonophotocatalytic removal of organic dyes in real water environments using reusable BiSI@PVDF-HFP nanocomposite membranes

Focusing on the uncontrolled discharge of organic dyes, a known threat to human health and aquatic ecosystems, this work employs a dual-functional catalyst approach, by immobilizing a synthesized bismuth sulfur iodide (BiSI) into a poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymeric matrix for multifunctional water remediation. The resulting BiSI@PVDF nanocomposite membrane (NCM), with 20 wt% filler content, maintains a highly porous structure without compromising morphology or thermal properties. Demonstrating efficiency in natural pH conditions, the NCM removes nearly all Rhodamine B (RhB) within 1 h, using a combined sonophotocatalytic process. Langmuir and pseudo-second-order models describe the remediation process, achieving a maximum removal capacity (Qmax) of 72.2 mg/g. In addition, the combined sonophotocatalysis achieved a degradation rate ten and five times higher (0.026 min-1) than photocatalysis (0.002 min-1) and sonocatalysis (0.010 min-1). Furthermore, the NCM exhibits notable reusability over five cycles without efficiency losses and efficiencies always higher than 90%, highlighting its potential for real water matrices. The study underscores the suitability of BiSI@PVDF as a dual-functional catalyst for organic dye degradation, showcasing synergistic adsorption, photocatalysis, and sonocatalysis for water remediation.

Advanced degradation of organic pollutants using sonophotocatalytic peroxymonosulfate activation with CoFe2O4/Cu- and Ce-doped SnO2 composites

The rampant upsurge of organic pollutants in aqueous media has become one of the major concerns nowadays. Finding non-specific catalysts that can target a wide range of organic pollutants is a key challenge. Eco-friendly oxidative radicals, such as promoted by peroxymonosulfate (PMS), are necessary for efficient water decontamination. We propose a multicomponent composite catalyst for activating PMS using a dual strategy of sonophotocatalysis. The composite integrates cobalt ferrite and Cu- or Ce-doped SnO2, with the at. % of doping metal and the mixture ratio carefully balanced. The top-performing architectures were able to decompose rhodamine B (20 ppm), a representative pollutant, in under 3 min and achieve over 70% mineralization in just 5 min. The synthesized nanocomposites demonstrated exceptional sonophotocatalytic performance, even when treating complex and diverse multipollutant solutions (80 ppm), achieving over 75% mineralization after 150 min. Considering their high stability and reusability, the proposed CoFe2O4/Cu- and Ce-doped SnO2 materials are among the state-of-the-art heterogeneous catalysts for mineralizing organic pollutants through PMS activation.

Mineralization of palm oil mill effluent by advanced oxidation processes: A review on current trends and the way forward

Palm oil mill effluent (POME) is regarded as deleterious to the environment, primarily owing to the substantial volume of waste it produces during palm oil extraction. In terms of contaminant composition, POME surpasses the pollutant content typically found in standard municipal sewage, therefore releasing it without treatment into water bodies would do irreparable damage to the environment. Main palm oil mills are normally located in the proximity of natural rivers in order to take advantage of the cheap and abundant water source. The same rivers are also used as a water source for many villages situated along the river banks. As such, it is imperative to degrade POME before its disposal into the water bodies for obvious reasons. The treatment methods used so far include the biological processes such as open ponding/land application, which consist of aerobic as well as anaerobic ponds, physicochemical treatment including membrane technology, adsorption and coagulation are successful for the mitigation of contaminants. As the above methods require large working area and it takes more time for contaminant degradation, and in consideration of the strict environmental policies as well as palm oil being the most sort of vegetable oil in several countries, numerous researchers have concentrated on the emerging technologies such as advanced oxidation processes (AOPs) to remediate POME. Methods such as the photocatalysis, Fenton process, sonocatalysis, sonophotocatalysis, ozonation have attained special importance for the degradation of POME because of their efficiency in complete mineralization of organic pollutants in situ. This review outlines the AOP technologies currently available for the mineralization of POME with importance given to sonophotocatalysis and ozonation as these treatment process removes the need to transfer the pollutant while possibly degrading the organic matter sufficiently to be used in other industry like fertilizer manufacturing.

Proficient sonophotocatalytic degradation of organic pollutants using Co3O4/TiO2 nanocomposite immobilized on zeolite: Optimization, and artificial neural network modeling

The health of all living organisms is greatly influenced by the quality of the water. Therefore, developing cost-effective, eco-friendly, and easily accessible methods is desperately needed to meet the high global demand for clean water. Recently, nanozyme-based dye degradation methods have been promising for the remediation of water pollution. In this work, peroxidase-mimic Co3O4/TiO2 nanocomposite was synthesized and characterized for its size, morphology, and crystalline structure. Colorimetric assay results showed that the peroxidase-like activity of the Co3O4/TiO2 nanocomposite was considerably enhanced compared to the pure Co3O4 NPs and TiO2 NPs. Besides excellent enzyme-mimic activity, the higher sonophotocatalytic dye degradation capability of the nanocomposite after immobilization on zeolite (Co3O4/TiO2@Ze) was also demonstrated. Under optimal conditions (pH = 5.0, 25 °C), 0.1 g/L of catalyst was able to degrade 100 % of methylene blue (MB) with 600 μM in the presence of 30 μM H2O2 within 12 min. GC/MS analysis and toxicity studies revealed less toxic metabolite production after treatment of MB with sonophotocatalytic Co3O4/TiO2@Ze. Modeling of MB degradation using artificial neural networks (ANN) with a 5:6:1 topology was successfully performed, and the results confirmed the fitness of theoretical and experimental outputs according to the calculated correlation coefficient values. The prepared nanocomposite could thus be used as a promising and highly effective catalyst for the removal of organic dyes from polluted water.

Treatment of landfill leachate by combined use of ultrasound and photocatalytic process using fly ash as catalyst

Advanced oxidation processes, such as sonophotocatalysis and photocatalysis, have been proven to be interesting alternatives for the effective treatment of old landfill leachates. Since there is no specific information about which parameters help to improve the treatment efficiency when using fly ash (FA) in a sonophotoreactor, this research focuses on evaluating the use of an ultrasound process (US) combined with a photo-Fenton process, with FA as a catalyst for the first time. The removals of colour, chemical oxygen demand (COD), and aromatic compounds (UV 254) present in landfill leachates were studied using a factorial design, where the effect of different loads of FA (1, 1.5, and 2 g FA/L), pH (pH = 3, 6, and 8.9), and US frequency irradiation (576, 864, and 1138 kHz) on the efficiency of photo-Fenton was evaluated. The highest removals of COD (40.7%), colour (36.8%), and UV 254 (50.8%) were achieved adjusting the pH to 3, adding 2 g of FA/L, and applying 576 kHz of US frequency. It was found that pH is the parameter that has the highest effect on pollutant removal (95% confidence level). In addition, the removals of COD, colour, and UV 254 increased at lower pH values and US frequency. Also, the presence of Fe2O3, SiO2, and TiO2 in the FA under UV irradiation and ultrasound process, improved the removal of complex organic matter present in the landfill leachate, where HO• was the most important radical.

WS2-intercalated Ti3C2Tx MXene/TiO2-stacked hybrid structure as an excellent sonophotocatalyst for tetracycline degradation and nitrogen fixation

Designing a heterostructure nanoscale catalytic site to facilitate N2 adsorption and photogenerated electron transfer would maximize the potential for photocatalytic activity and N2 reduction reactions. Herein, we have explored the interfacial TiO2 nanograins between the Ti3C2TxMXene-WS2 heterostructure and addressed the beneficial active sites to expand the effective charge transfer rate and promote sonophotocatalytic N2 fixation. Benefiting from the interfacial contact and dual heterostructure interface maximizes the photogenerated carrier separation between WS2 and MXene/TiO2. The sonophotocatalytic activity of the MXene@TiO2/WS2 hybrid, which was assessed by examining the photoreduction of N2 with ultrasonic irradiation, was much higher than that of either sonocatalytic and photocatalytic activity because of the synergistic sonocatalytic effect under photoirradiation. The Schottky junction between the MXene and TiO2 on the hybrid MXene/TiO2-WS2 heterostructure resulted in the sonophotocatalytic performance through effective charge transfer, which is 1.47 and 1.24 times greater than MXene-WS2 for nitrogen fixation and pollutant degradation, respectively. Under the sonophotocatalytic process, the MXene/TiO2-WS2 heterostructure exhibits a decomposition efficiency of 98.9 % over tetracycline in 90 min, which is 5.46, 1.73, and 1.10 times greater than those of sonolysis, sonocatalysis, and photocatalysis, respectively. The production rate of NH3 on MXene/TiO2-WS2 reached 526 μmol g-1h-1, which is 3.17, 3.61, and 1.47 times higher than that of MXene, WS2, and MXene-WS2, respectively. The hybridized structure of MXene-WS2 with interfacial surface oxidized TiO2 nanograins minimizes the band potential and improves photocarrier use efficiency, contributing directly to the remarkable catalytic performance towards N2 photo fixation under visible irradiation under ultrasonic irradiation. This report provides the strategic outcome for the mass carrier transfer rate and reveals a high conversion efficiency in the hybridized heterostructure.

Ultrasound assisted fabrication of InVO4/In2S3 heterostructure for enhanced sonophotocatalytic degradation of pesticides

A cost effective and environmentally benign ultrasonic method has been developed for the synthesis of InVO4 (InV), In2S3 (InS) and the InVO4/In2S3 heterostructure (InV/InS). All the designed materials were evaluated for their structural, morphological, spectroscopic, and electrochemical characterizations. Materials were examined for photocatalytic, sonocatalytic, and sonophotocatalytic degradation of carbofuran (CBF) and diazinon (DZN) pesticides under visible light. InV/InS showed enhanced degradation of CBF and DZN when compared to InV and InS. Photocatalytic degradation was accelerated by ultrasonication and found to degrade 97 and 98 % of CBF and DZN in 60 and 70 min, respectively. The reaction conditions, like pH, catalyst dosage, acoustic intensity, and ultrasound power, were carefully optimized. Electron spin resonance (ESR) spectroscopy shows the generation of superoxide radical anion and hydroxyl radicals as reactive species during photoredox reaction. The CBF and DZN degradation intermediates were analyzed using liquid chromatography mass spectroscopy (LC-MS) that shows the mineralization of the CBF and DZN to CO2 and H2O. The effect of Cl-, and PO43- were examined towards degradation of CBF and DZN under optimal conditions in the presence of InV/InS. The degradation of CBF and DZN is decreased in presence of Cl-, CO32- and NO3- but PO43- ions does not show any effect on degradation. The bandgap and Mott-Schottky results suggest the existence of type-II heterostructure between InV and InS through the interface. The synthesis of heterostructure and degradation of pesticides utilizes ultrasonic waves, which prove their multiple applications and attract researchers towards the effective use of sonication.

Harnessing ultrasound in photocatalysis: Synthesis and piezo-enhanced effect: A review

The photocatalytic technique has drawn far-ranging interests in addressing the current issues; however, its property suffers from the limited visible light response and rapid recombination of carriers. To address these issues, two specific approaches have been proposed to enhance the photocatalytic activity: (1) ultrasound-assisted synthesis has been utilized to prepare photocatalysts, resulting in refined grain size, increased specific surface area, and reduced photogenerated carrier recombination; (2) sonophotocatalysis and piezoelectric enhanced photocatalysis have been developed to accelerate the reaction, which utilizes the synergism between ultrasound and light. On one side, sonophotocatalysis generates cavitation bubbles which induce more reactive radicals for redox reactions. On the other side, ultrasound induces deformation of the piezoelectric material structure, which changes the internal piezoelectric potential and improves the photocatalytic performance. Currently, intensive efforts have been devoted to related research and great progress has been reached with applications in pollutant degradation, new energy production, and other fields. This work starts by elucidating the fundamental concept of ultrasound-assisted photocatalyst synthesis and photocatalysis. Then, the synergistic behavior between ultrasonic and light in ultrasonic-assisted photocatalysis has been thoroughly discussed, including pollutant degradation, water splitting, and bacterial sterilization. Finally, the challenge and outlook are investigated and proposed.

Mechanistic insight into humic acid-enhanced sonophotocatalytic removal of 17β-estradiol: Formation and contribution of reactive intermediates

In this study, humic acid (HA) enhanced 17β-estradiol (17β-E2) degradation by Er3+-CdS/MoS2 (ECMS) was investigated under ultrasonic and light conditions. The degradation reaction rate of 17β-E2 was increased from (14.414 ± 0.315) × 10-3 min-1 to (122.677 ± 1.729) × 10-3 min-1 within 90 min sonophotocatalytic (SPC) reaction with the addition of HA. The results of quenching coupled with chemical probe experiments indicated that more reactive intermediates (RIs) including reactive oxygen species (ROSs) and triplet-excited states were generated in the HA-enhanced sonophotocatalytic system. The triplet-excited states of humic acid (3HA*), hydroxyl radical (•OH), and superoxide radical (•O2-) were the dominant RIs for 17β-E2 elimination. In addition, the energy- and electron-transfer process via coexisting HA also account for 12.86% and 29.24% contributions, respectively. The quantum yields of RIs in the SPC-ECMS-HA system followed the order of 3HA* > H2O2 > 1O2 > •O2-> •OH. Moreover, the spectral and fluorescence characteristics of HA were further analyzed during the sonophotocatalytic reaction process. The study expanded new insights into the comprehension of the effects of omnipresent coexisting HA and RIs formation for the removal of 17β-E2 during the sonophotocatalytic process.

An overview on ZnO-based sonophotocatalytic mitigation of aqueous phase pollutants

Over the past several decades, the increase in industrialization provoked the discharge of harmful pollutants into the environment, affecting human beings and ecosystems. ZnO-based photocatalysts seem to be the most promising photocatalysts for treating harmful pollutants. However, fast charge carrier recombination, photo corrosion, and long reaction time are the significant factors that reduce the photoactivity of ZnO-based photocatalysts. In order to enhance the photoactivity of such photocatalysts, a combined process i.e., sonocatalysis + photocatalysis = sonophotocatalysis was used. Sonophotocatalysis is one of several different AOP methods that have recently drawn considerable interest, as it produces high reactive oxygen species (ROS) which helps in the oxidation of pollutants by acoustic cavitation. This combined technique enhanced the overall efficiency of the individual method by overcoming its limiting factors. The current review aims to present the theoretical and fundamental aspects of sonocatalysis and photocatalysis along with a detailed discussion on the benefits that can be obtained by the combined process i.e., US + UV (sonophotocatalysis). Also, we have provided a comparison of the excellent performance of ZnO to that of the other metal oxides. The purpose of this study is to discuss the literature concerning the potential applications of ZnO-based sonophotocatalysts for the degradation of pollutants i.e., dyes, antibiotics, pesticides, phenols, etc. That are carried out for future developments. The role of the produced ROS under light and ultrasound stimulation and the degradation mechanisms that are based on published literature are also discussed. In the end, future perspectives are suggested, that are helpful in the development of the sonophotocatalysis process for the remediation of wastewater containing various pollutants.

Tuned CuCr layered double hydroxide/carbon-based nanocomposites inducing sonophotocatalytic degradation of dimethyl phthalate

This study is the first to explore the possibility of utilizing CuCr LDH decorated on reduced graphene oxide (rGO) and graphene oxide (GO) as sonophotocatalysts for the degradation of dimethyl phthalate (DMP). CuCr LDH and its nanocomposites were successfully fabricated and characterized. Scanning electron microscopy (SEM) along with high-resolution transmission electron microscope (HRTEM) both evidenced the formation of randomly oriented nanosheet structures of CuCr LDH coupled with thin and folded sheets of GO and rGO. The impact of diverse processes on the degradation efficiency of DMP in the presence of the so-prepared catalysts was compared. Benefiting from the low bandgap and high specific surface area, the as-obtained CuCr LDH/rGO represented outstanding catalytic activity (100 %) toward 15 mg L-1 of DMP within 30 min when subjected to light and ultrasonic irradiations simultaneously. Radical quenching experiments and visual spectrophotometry using an O-phenylenediamine revealed the crucial role of hydroxyl radicals compared to holes and superoxide radicals. Overall, outcomes disclosed that CuCr LDH/rGO is a stable and proper sonophotocatalyst for environmental remediation.

Aqueous Acetamiprid Degradation Using Combined Ultrasonication and Photocatalysis Under Visible Light

Acetamiprid (ACE), a neonicotinoid pesticide widely used in pest control, was found in high concentrations in soils, rivers, and lakes. In the present study, ACE degradation was investigated using visible light driven photocatalysis over nitrogen-graphene oxide (N-GO) and palladium-graphene oxide (Pd-GO)-doped ZnO photocatalysts combined with ultrasonication implemented either as a pretreatment (sonolysis) or operated simultaneously with photocatalysis (sonophocatalysis). The effectiveness of the two ACE degradation processes was determined separately. The sonolysis pretreatment allowed reaching almost 40% acetamiprid conversion within 30 min of reaction. Pursuing with the photodegradation reaction in the presence of N-GO-ZnO and Pd-GO-ZnO resulted in a maximum conversion of 98% of ACE within 5 h. As for the sonophotocatalysis process, the reaction time was shortened from 5 to 2 h with 100% acetamiprid conversion. In addition, the photocatalysts were shown to keep their activity even after 5 sonophotocatalytic cycles, thus proving their reusability.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-022-05867-4.

Sono-photo hybrid process for the synergistic degradation of levofloxacin by FeVO4/BiVO4: Mechanisms and kinetics

A novel FeVO₄/BiVO₄ heterojunction photocatalyst was synthesized by hydrothermal method. The FeVO₄/BiVO₄ nanostructures were characterized by XRD, SEM, XPS, UV-vis, and photoluminescence spectroscopy. The effects of catalyst dosage, contaminant concentration, initial hydrogen peroxide (H₂O₂) concentration, and pH value on the degradation of levofloxacin were investigated and several repeated experiments were conducted to evaluate the stability and reproducibility. The optimized process parameters were used for mineralization experiments. Reactive oxygen species, degradation intermediates, and possible catalytic mechanisms were also investigated. The results showed that the sonophotocatalytic performance of the FeVO₄/BiVO₄ heterojunction catalyst was better than that of sonocatalysis and photocatalysis. In addition, the Type II heterojunction formed by the material still had good stability in the degradation of levofloxacin after 5 cycles. The possible degradation pathway and mechanism of levofloxacin by sonophotocatalysis were put forward. This work develops new sono-photo hybrid process for potential application in the field of wastewater treatment.

Zinc-chromium layered double hydroxides anchored on carbon nanotube and biochar for ultrasound-assisted photocatalysis of rifampicin

In this study, ZnCr layered double hydroxide (LDH), ZnCr LDH/carbon nanotube (CNT), and ZnCr LDH/Biochar (BC) were synthesized and characterized by various analyses. The successful synthesis and the great crystallinity of the samples were consented by XRD analysis. SEM and TEM were applied to study the morphology of the synthesized samples. The simultaneous presence of C, Zn, and Cr elements was well confirmed by EDX and dot mapping analyses demonstrating the successful preparation of nanocomposites. According to the BET analysis, ZnCr LDH nanocomposites with BC and CNT had more specific surface area compared to ZnCr LDH alone. The catalytic performances of the samples were determined for the degradation of rifampicin (RF). The degradation efficiency of the sonophotocatalytic process in the presence of 0.6 g L^-1 of ZnCr LDH/BC toward 15 mg L^-1 of RF under 150 W ultrasound and visible light irradiation was found to be about 100% within 40 min. The influence of the reactive species on the sonophotocatalytic process was assessed via the addition of different scavengers (para-benzoquinone (p-BQ), formic acid (FA), isopropyl alcohol (IPA)), and enhancers (hydrogen peroxide and potassium persulfate). The GC-MS analysis was carried out and eleven by-products during the RF decomposition were detected.

Graphene-based ZnCr layered double hydroxide nanocomposites as bactericidal agents with high sonophotocatalytic performances for degradation of rifampicin

Herein, ZnCr layered double hydroxide (ZnCr LDH), and its nanocomposites with GO and rGO were synthesized using the co-precipitation method. The samples were characterized using XRD, FT-IR, SEM, TEM, BET, and XPS techniques. The sonophotocatalytic activity of the ZnCr LDH, ZnCr LDH/GO, and ZnCr LDH/rGO was investigated via the degradation of rifampicin (RIF) in the ultrasonic bath under visible light irradiation. The synergy index of more than 1 determined for ZnCr LDH/rGO indicated the positive interaction of sonocatalysis and photocatalysis resulted by hybridizing the LDH nanosheets with rGO. The maximum sonophotocatalytic degradation efficiency of 87.3% was achieved in the presence of ZnCr LDH/rGO nanocomposite with the concentration of 1.5 g L^-1 for degradation of RIF with an initial concentration of 15 mg L^-1 within 60 min sonication under visible light irradiation. The addition of different scavengers indicated that hydroxyl radicals, superoxide anion radicals, and the generated holes played a dominant role in the degradation of the pollutant molecules. A possible degradation mechanism was suggested based on the intermediates. The antibacterial tests confirmed the higher antibacterial activity of ZnCr LDH/GO compared with ZnCr LDH and ZnCr LDH/rGO against Gram-positive Staphylococcus aureus.

Morphology engineering of type-II heterojunction nanoarrays for improved sonophotocatalytic capability

Sonophotocatalysis is one of the most significant outcomes of the exploration of the interaction between piezoelectric field and charge carriers, which exhibits potential applications in dye degradation, water splitting, and sterilization. Although several heterojunction catalysts have been applied to improve the sonophotocatalytic capability, the importance of the morphology on the sonophotocatalytic capability has not been emphasized. In this study, brush-like ZnO nanorod arrays are synthesized on a stainless-steel mesh and subsequently vulcanized into ZnO/ZnS core-shell nanorod arrays to investigate the sonophotocatalytic capability of the heterojunction. The sonophotocatalytic capability increases from 25.1% to 45.4% through vulcanization. Afterward, the ZnO/ZnS nanorods are etched to ZnO/ZnS nanotubes without affecting the crystallography and distribution of the ZnS nanoparticle shell, further improving the capability to 63.3%. The improvement can be ascribed to the coupling effect of the enhanced piezoelectric field and the reduced migration distance, which suppresses the recombination of photoexcited electron-hole pairs while transforming the morphology from nanorod to nanotube, as proven by the electron spin resonance test and numerical simulations. This study explores a novel approach of morphology engineering for enhancing the sonophotocatalytic capability of heterojunction nanoarrays.

Degradation of amoxicillin with sono, photo, and sonophotocatalytic oxidation under low-frequency ultrasound and visible light

The presence of pharmaceutically active compounds in aquatic bodies is a global concern, and suitable treatment technologies are required. In this study, the efficacy of photocatalytic, sonocatalytic, and sonophotocatalytic oxidation processes for the degradation of amoxicillin (AMX) was investigated using visible light with N doped TiO₂ (N-TiO₂) nanoparticles as the catalyst and low-frequency ultrasound in a novel multifrequency reactor. The influence of different operational parameters on the extent of AMX degradation was studied. Sonophotocatalytic oxidation was found more efficient for AMX degradation when compared to photocatalysis or sonocatalysis alone, and may be due to the reduced bandgap of the catalyst, enhanced cavitation effect due to the presence of the solid catalyst, and improved mass transfer of pollutants. AMX degradation during sono, photo, and sonophotocatalytic oxidation processes was in good agreement with pseudo-first-order kinetics. Empirical kinetic models were also developed using multiple linear regression for predicting the degradation efficiency accounting for the operational parameters. Scavenger experiments suggested that ^•OH radicals largely contributed to AMX degradation, and a plausible mechanism for degradation was proposed. Further, possible degradation pathways for all three treatment processes are also proposed after identifying the degradation products.

Application of advanced materials in sonophotocatalytic processes for the remediation of environmental pollutants

Significant advances in various industrial processes have resulted in the discharge of toxic pollutants into the environment. Consequently, it is essential to develop efficient wastewater treatment processes to reduce water contamination and increase recycling/reuse. Photocatalytic degradation is considered as an efficient method for the degradation of toxic pollutants in industrial wastewater. However, the use of photocatalytic approaches is associated with numerous limitations, such as lengthy procedures and the necessity for large amounts of catalysts. Hence, it has been proposed that photocatalysis could be combined with other techniques, including sonolysis, electrochemical, photothermal, microwave, ultrafiltration, and biological reactor. The integration of photocatalysis with sonolysis could be remarkably beneficial for environmental remediation. The combination of these processes has the advantages of using uniformly dispersed catalysts, regeneration of the catalyst surface, improved mass transfer, enhanced surface area due to smaller catalyst particles, and production of more active radicals for the degradation of organic pollutants. In this review, an overview on employing sonophotocatalysis for the removal of toxic organic contaminants from aqueous environments is provided. Additionally, the limitations of photocatalysis alone and the fundamental sonophotocatalytic mechanistic pathways are discussed. The importance of utilizing advanced two-dimensional (2D) semiconductor materials in sonophotocatalysis and the common synthetic approaches for the preparation of 2D materials are also highlighted. Lastly, the review provides comprehensive insights into different materials based on metal oxides, chalcogenides, graphene, and metal organic frameworks (MOFs), which are involved in sonophotocatalytic processes employed for the remediation of environmental pollutants.

Sonochemical processes for the degradation of antibiotics in aqueous solutions: A review

Antibiotic residues in water are general health and environmental risks due to the antibiotic-resistance phenomenon. Sonication has been included among the advanced oxidation processes (AOPs) used to remove recalcitrant contaminants in aquatic environments. Sonochemical processes have shown substantial advantages, including cleanliness, safety, energy savings and either negligible or no secondary pollution. This review provides a wide overview of the different protocols and degradation mechanisms for antibiotics that either use sonication alone or in hybrid processes, such as sonication with catalysts, Fenton and Fenton-like processes, photolysis, ozonation, etc.

Nanostructured TiO2 cavitation agents for dual-modal sonophotocatalysis with pulsed ultrasound

Current sonochemical methods rely on spatially uncontrolled cavitation for radical species generation to promote chemical reactions. To improve radical generation, sonosensitizers have been demonstrated to be activated by cavitation-based light emission (sonoluminescence). Unfortunately, this process remains relatively inefficient compared to direct photocatalysis, due to the physical separation between cavitation event and sonosensitizing agent. In this study, we have synthesized nanostructured titanium dioxide particles to couple the source for cavitation within a photocatalytic site to create a sonophotocatalyst. In doing so, we demonstrate that site-controlled cavitation from the nanoparticles using pulsed ultrasound at reduced acoustic powers resulted in the sonochemical degradation methylene blue at rates nearly three orders of magnitude faster than other titanium dioxide-based nanoparticles by conventional methods. Sonochemical degradation was directly proportional to the measured cavitation produced by these sonophotocatalysts. Our work suggests that simple nanostructuring of current sonosensitizers to enable on-site cavitation greatly enhances sonochemical reaction rates.

Doping of Mg on ZnO Nanorods Demonstrated Improved Photocatalytic Degradation and Antimicrobial Potential with Molecular Docking Analysis

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.

Synergetic decolorization of azo dyes using ultrasounds, photocatalysis and photo-fenton reaction

In the present work, ultrasound irradiation, photocatalysis with TiO₂, Fenton/Photo-Fenton reaction, and the combination of those techniques were investigated for the decolorization of industrial dyes in order to study their synergy. Three azo dyes were selected from the weaving industry. Their degradation was examined via UV illumination, Fenton and Photo-Fenton reaction as well as ultrasound irradiation at low (20 kHz) and high frequencies (860 kHz). In these experiments, we investigated the simultaneous action of the ultrasound and UV irradiation by varying parameters like the duration of photocatalysis and ultrasound irradiation frequency. At the same time, US power, temperature, amount of TiO₂ photocatalyst and amount of Fenton reagent remained constant. Due to their diverse structure, each azo dye showed different degradation levels using different combinations of the above-mentioned Advanced Oxidation Processes (AOPs). The Photo-Fenton reagent is more effective with US 20 kHz and US 860 kHz for the azo dyes originated from the weaving industry at pH = 3 as compared to pH = 6.8. The combination of the Photo-Fenton reaction with 860 kHz ultrasound irradiation for the same dye gave an 80% conversion at the same time. Experiments have shown a high activity during the first two hours. After that threshold, the reaction rate is decreased. FT-IR and TOC measurements prove the decolorization due to the destruction of the chromophore groups but not complete mineralization of the dyes.

Effects of catalyst preparation method and reaction parameters on the ultrasound assisted Photocatalytic oxidation of reactive yellow 84 dye

In this study, the Heterogeneous Sono-photocatalytic Process was used to degrade Reactive Yellow 84 (RY 84) dye dissolved in water over iron containing TiO₂ and TiO₂-Ce catalysts. The catalysts were prepared by sol-gel and incipient wetness impregnation methods and characterized using XRD, SEM, Nitrogen adsorption, UV-Vis DRS and ICP-AES measurements. The TiO₂ catalyst containing 1% (in weight) iron, prepared by incipient wetness impregnation technique and calcined at 300 °C (1%Fe/TiO₂-300 °C (IW)) was found to be the most effective catalyst. Parametric study was carried out over this catalyst and COD removal of 55% and TOC removal of 38% were achieved while the decolorization efficiency reached 100% after 45 min of reaction at the optimum conditions of, (25 mg/L of RY 84 solution, 0.5 g/L of catalyst, 5 mM of H₂O₂, a temperature of 25 °C, pH = 6 and US at a power of 40 W). Decolorization of RY 84 obeyed the first order kinetics with an activation energy of 20.7 kJ/mol. Sonication increased the decolorization efficiency of the heterogeneous Fenton process (UV + Catalyst+H₂O₂) from 92.7% to 97.5% after 30 min of reaction, with the COD and TOC reductions increasing from 87% to 90% and 48% to 57% after 120 min of reaction, respectively. US also decreased the toxicity of the RY 84 dye. The results obtained from this study show that, iron containing TiO₂ and TiO₂-Ce catalysts could be efficiently used in the hybrid process of ultrasound assisted heterogeneous photocatalytic oxidation in a wide range of experimental conditions.

Sonophotocatalytic activities of FeCuMg and CrCuMg LDHs: Influencing factors, antibacterial effects, and intermediate determination

Herein, FeCuMg and CrCuMg layered double hydroxides (LDHs) were synthesized and their sonophotocatalytic activities toward Acid blue 113 (AB113) were compared. Sonolysis alone (only ultrasound) led to the decolorization efficiency of 13.0 %. A similar result was obtained in the case of the utilization of photolysis alone using a 10-W LED lamp (13.5 %). The adsorption process of AB113 onto both compounds was not efficient to significantly remove the target contaminant. The bandgap energy of 2.54 eV and 2.41 eV was calculated for FeCuMg and CrCuMg LDHs, respectively, indicating relatively higher photocatalytic activity of Cr-incorporated LDH than FeCuMg LDH. The sonophotocatalysis of AB113 (50 mg L^-1) over CrCuMg LDH (81.1 %) was more efficient than that of FeCuMg LDH (57.3 %) within the reaction time of 60 min. Intermediate byproducts of the sonophotocatalytic decomposition of organic dye over the as-synthesized tri-metal layered sonophotocatalysts were also identified. Furthermore, the antibacterial activity of both LDHs was evaluated by the CFU technique and the MBC and MIC values were determined. The antibacterial assessment confirmed the higher antibacterial activity of CrCuMg LDH than that of FeCuMg LDH against Staphylococcus aureus (S. aureus).

rGO supported self-assembly of 2D nano sheet of (g-C3N4) into rod-like nano structure and its application in sonophotocatalytic degradation of an antibiotic

Graphitic carbon nitride (g-C₃N₄) is an analog of graphite due to its unique electronic structure. g-C₃N₄ based materials have been used in photocatalytic applications. However, pure g-C₃N₄ suffers from major shortcomings which include poor disparity, low surface area and a high recombination rate of photo generated electron-hole pairs that significantly reduce its photocatalytic activity. In this work, self-assembly of g-C₃N₄ sheet into rod shaped g-C₃N₄ was developed via a simple polymerisation method. A composite made of g-C₃N₄ nanorods and rGO (rGO-RCN) was also prepared. The band gap g-C₃N₄ was shifted from 2.77 to 2.6 eV evidented by UV-DRS data. As a result, rGO-RCN showed a relatively high absorption in the visible region. Moreover, a fast electron transfer rate was observed with rGO-RCN composite as conformed from PL analysis and photocurrent measurement. The formation of nanorod and sheet morphologies was confirmed via TEM analysis. The photocatalytic activities of prepared sheet-g-C₃N₄ (SCN)_, Rod g-C₃N₄ (RCN), reduced graphene oxide supported sheet-g-C₃N₄ (rGO-SCN) and reduced graphene oxide supported Rod-g-C₃N₄ (rGO-RCN) were evaluated using a commonly used antibiotic (tetracycline). Among these catalysts, rGO-RCN nanocomposite showed sonophotocatalytic activity 3 times higher compared to pure g-C₃N₄. This superior sonophotocatalytic activity could be due to enhanced visible light absorption of the material, active sites generated by ultrasound, and the high electron transport property of rGO.

Sonophotocatalytic disinfection of Shigella species under visible light irradiation: Insights into its molecular mechanism, antibacterial resistance and biofilm formation

Microbial contamination of water is one of the major sources of many diseases worldwide. Evolution of antibacterial resistance (ABR) alongside the caveats in most of the water treatment methods causes the severity of the current problem extremely vexing. This calls for an urgent need to develop new treatment methods aiming to reduce the microbial as well as ABR load in the environment. Herein, we successfully developed a visible light assisted sonophotocatalysis (SPC) using Fe/ZnO nanoparticles (NPs) for the disinfection of Shigella dysenteriae. A consortia containing S. dysenteriae and S. flexineri was also completely disinfected using SPC. Growth conditions of S. dysenteriae like growth phases and growth temperaturehad different outcomes on the overall efficacy of SPC. Compared with catalysts such as ZnO and TiO₂, Fe/ZnO resulted in better disinfection. Multi-ROS production, mostly containing h⁺ and O₂· radicals, due to the electron displacement in the catalyst and acoustic cavitation was identified as the factors behind bacterial lethality. The ROS produced was found to interfere with the metabolic activities of S. dysenteriae by causing membrane perturbation. We identified DNA damage inside the cells and the subsequent release of intracellular components. The compositional changes in the fatty acid makeup of the cells were altered as a result of SPC and few fatty acid markers indicating the stress posed by SPC were also identified. Loss of ABR in S. dysenteriae was also recorded post SPC treatment. Abatement in the biofilm forming ability of the injured bacterial cells was also recorded, proving the extremity of stress induced by SPC. Hence, the excellent efficacy of SPC in disinfecting bacteria is proposed for tertiary water treatment applications.

Superior performance of FeVO4@CeO2 uniform core-shell nanostructures in heterogeneous Fenton-sonophotocatalytic degradation of 4-nitrophenol

Porous FeVO₄ nanorods decorated on CeO₂ nanocubes (FeVO₄@CeO₂) were successfully prepared via a facile hydrothermal route and tested in the degradation of 4-nitrophenol (4-NP) for enhanced heterogeneous oxidation using ultrasonic (US), ultraviolet (UV), and binary irradiation US/UV, respectively. The nanostructure of the core-shell FeVO₄@CeO₂ was characterised using XRD, SEM, EDS elemental mapping, TEM, HRTEM, SAED, FTIR, Raman, BET, point of zero charge (PZC), XPS analysis and UV-vis DRS. The effect of various parameters, for examples, nanostructured core-shell amounts, hydrogen peroxide concentration, initial concentration, pH and irradiation time, on 4-NP degradation were investigated for the optimisation of the catalytic performance. The durability and stability of the core-shell nanostructured materials were also investigated and the obtained results revealed that the catalysts can endure the harsh sonophotocatalytic conditions even after six cycles. Mineralisation experiments were investigated using the optimised parameters. The core-shell nanostructured FeVO₄@CeO₂ has higher PZC than pure FeVO₄ and CeO₂, leading to excellent sonophotocatalytic activity even at high pH and stability for the degradation of 4-NP after six cycles. A possible mechanism over the FeVO₄@CeO₂ was proposed based on the special three-way Fenton-like mechanism and the dissociation of H₂O₂ with the experiments of active species trapping and calculated band gap energy.

Reduced graphene oxide (rGO) supported electron deficient B-doped TiO2 (Au/B-TiO2/rGO) nanocomposite: An efficient visible light sonophotocatalyst for the degradation of Tetracycline (TC)

Incorporation of electron deficient boron atoms along with Au doped TiO₂ in the presence of rGO support was synthesized by hydrothermal method and demonstrated for the sonophotocatalytic degradation of TC under visible light illumination. The successful incorporation of electron deficient boron atoms and Au on TiO₂ was considerably enhanced the optical absorption towards visible region due to the formation acceptor energy levels below to the conduction band of TiO₂ by boron doping and surface plasmonic effect of Au. Moreover, formation of acceptor energy levels and introduction of reduced graphene oxide (rGO) support significantly improved the electron-hole pair separation and transportation which were supported by UV-vis-DRS, photo-current and photoluminescence measurements. The individual effect of photocatalysis and ultrasound for the TC degradation was found to be 45% and 12%, respectively. Importantly, a complete degradation (100%) of TC was achieved with 1.3 folds synergistic effect when ultrasound coupled with photocatalysis in 1 h. The enhanced degradation activity was mainly attributed to combined effect of rapid electron-hole pair separation facilitated by electron deficient B-atoms and rGO support and physical forces of ultrasound as well. In addition, ∼74% of Total Organic Carbon (TOC) removal was achieved within 1 h which further confirmed the effective demineralization of TC by the Au/B-TiO₂/rGO composite.

Sonophotocatalytic degradation of bisphenol A and its intermediates with graphitic carbon nitride

Since bisphenol A (BPA) exhibits endocrine disrupting action and high toxicity in aqueous system, there are high demands to remove it completely. In this study, the BPA removal by sonophotocatalysis coupled with nano-structured graphitic carbon nitride (g-C₃N₄, GCN) was conducted with various batch tests using energy-based advanced oxidation process (AOP) based on ultrasound (US) and visible light (Vis-L). Results of batch tests indicated that GCN-based sonophotocatalysis (Vis-L/US) had higher rate constants than other AOPs and especially two times higher degradation rate than TiO₂-based Vis-L/US. This result infers that GCN is effective in the catalytic activity in Vis-L/US since its surface can be activated by Vis-L to transport electrons from valence band (VB) for utilizing holes (h⁺_VB) in the removal of BPA. In addition, US irradiation exfoliated the GCN effectively. The formation of BPA intermediates was investigated in detail by using high-performance liquid chromatography-mass spectrometry (HPLC/MS). The possible degradation pathway of BPA was proposed.

Enhanced antimicrobial activity of ZnO nanofluids in sonophotocatalysis and its mechanism

This study investigated the inactivation efficiency of ZnO nanofluids against E. coli in sonophotocatalysis with the aeration of nitrogen, oxygen, argon and their mixtures. The results showed that inactivation efficiency was increased when aeration was combined with sonophotocatalysis. Addition of different types of gases could lead to the different inactivation efficiency. The inactivation efficiencies were shown in the following order: no aeration < nitrogen < argon < oxygen < Ar/O₂(3:7) < Ar/O₂(7:3) < Ar/O₂(5:5). The production of hydroxyl radicals was explored to understand the inactivation mechanism. Compared with sonophotocatalysis without aeration, more hydroxyl radicals were produced in sonophotocatalysis with aeration, which could lead to changes of cellular substances. Furthermore, characterization of E. coli cells using Raman spectroscopy and FTIR illustrated that sonophotocalysis could affect the cellular substances containing carbohydrates, proteins and P containing molecules. Results suggested that the enhanced antimicrobial activity with aeration was originated from stronger cavitational activity, together with the formation of hydroxyl radicals. Compared to sonophotocatalysis without aeration, more dissolved oxygen was existed in sonophotocatalysis with aeration, which could enhance the formation of hydroxyl radicals.

State of the art and recent advances in the ultrasound-assisted synthesis, exfoliation and functionalization of graphene derivatives

Sonochemistry, an almost a century old technique was predominantly employed in the cleaning and extraction processes but this tool has now slowly gained tremendous attention in the synthesis of nanoparticles (NPs) where particles of sub-micron have been produced with great stability. Following this, ultrasonication techniques have been largely employed in graphene synthesis and its dispersion in various solvents which would conventionally take days and offers poor yield. Ultrasonic irradiation allows the production of thin-layered graphene oxide (GO) and reduced graphene oxide (RGO) of up to 1nm thickness and can be produced in single layers. With ultrasonic treatment, reactions were made easy whereby graphite can be directly exfoliated to graphene layers. Oxidation to GO can also be carried out within minutes and reduction to RGO is possible without the use of any reducing agents. In addition, various geometry of graphene can be produced such as scrolled graphene, sponge or foam graphene, smooth as well as those with rough edges, each serving its own unique purpose in various applications such as supercapacitor, catalysis, biomedical, etc. In ultrasonic-assisted reaction, deposition of metal NPs on graphene was more homogeneous with custom-made patterns such as core-shell formation, discs, clusters and specific deposition at the edges of graphene sheets. Graphene derivatives with the aid of ultrasonication are the perfect catalyst for various organic reactions as well as an excellent adsorbent. Reactions which used to take hours and days were significantly reduced to minutes with exceedingly high yields. In a more recent approach, sonophotocatalysis was employed for the combined effect of sonication and photocatalysis of metal deposited graphene. The system was highly efficient in organic dye adsorption. This review provides detailed fundamental concepts of ultrasonochemistry for the synthesis of graphene, its dispersion, exfoliation as well as its functionalization, with great emphasis only based on recent publications. Necessary parameters of sonication such as frequency, power input, sonication time, type of sonication as well as temperature and dual-frequency sonication are discussed in great length to provide an overview of the resultant graphene products.

Preparation and sonophotocatalytic performance of hierarchical Bi2WO6 structures and effects of various factors on the rate of Rhodamine B degradation

Hierarchical Bi₂WO₆ structures with high surface area were prepared in the presence of polyvinylpyrrolidone by using an optimized hydrothermal method. The samples prepared were characterized by X-ray diffraction, field-emission scanning electron microscopy and N₂ adsorption-desorption technique. The results of these characterizations showed the formation of the hierarchical Bi₂WO₆ structures with high surface area (51m²/g). The degradation of Rhodamine B (RhB) with or without visible light was investigated under various experimental conditions to evaluate the sonophotocatalytic activity of the hierarchical Bi₂WO₆ structures. The result showed that the degradation efficiency was found to be in the following order: sonocatalysis<photocatalysis<sonophotocatalysis. The effects of various experimental factors such as light intensity, ultrasound pulse mode and catalyst dosage on the sonophotocatalysis efficiency were also investigated. Under the optimum condition (light intensity 140W, ultrasound pulse mode: 9s on/1s off, Bi₂WO₆ catalyst dosage: 1.25g/L), the excellent sonophotocatalytic activity on the degradation of RhB was observed: the degradation ratio achieved about 99.5% at 40min. The mechanism of the sonophotocatalysis was also proposed.

Titanium dioxide-based sonophotocatalytic mineralization of bisphenol A and its intermediates

In this study, bisphenol A (BPA) removal by sonophotocatalysis coupled with commercially available titanium dioxide (TiO₂, P25) was assessed in batch tests using energy-based advanced oxidation combining ultrasound (US) and ultraviolet (UV). The kinetics of BPA removal were systematically evaluated by changing operational parameters, such as US frequency and power, mechanical stirring speed, and temperature, but also comparison of single and coupled systems under the optimum US conditions (35 kHz, 50 W, 300 rpm stirring speed, and 20 °C). The combination of US/UV/P25 exhibited the highest BPA removal rate (28.0 × 10^-3 min^-1). In terms of the synergy index, the synergistic effect of sonophotocatalysis was found to be 2.2. This indicated that sonophotocatalysis has a considerably higher removal efficiency than sonocatalysis or photocatalysis. The removal of BPA was further investigated to identify BPA byproducts and intermediates using high-performance liquid chromatography-mass spectrometry. Five main intermediates were formed during sonophotocatalytic degradation, and complete removal of BPA and its intermediates was obtained after 3 h of operation. The degradation pathway of BPA by sonophotocatalysis was also elucidated.

Synthesis of Fe-doped Bi2O3 nanocatalyst and its sonophotocatalytic activity on synthetic dye and real textile wastewater

The catalysts such as Fe, Bi₂O₃, and Fe-doped Bi₂O₃ were synthesized for the sonophotocatalytic treatment of synthetic dye and real textile wastewater. The resultant catalysts were characterized for its size and uniform shape using x-ray diffractogram (XRD) and scanning electron microscopy (SEM) which signified the nanorod shape formed Bi₂O₃. The higher ultraviolet light absorbance capacity of the catalysts was also evident using diffuse reflectance spectroscopy (DRS). Initially, the effect of conventional parameters such as initial pH, gas bubbling (argon, oxygen, air and nitrogen) and oxidant addition (H₂O₂ and peroxymonosulfate) in the presence of sonolysis (22 and 37 kHz frequency) and photolysis (UV-C light) on 10 ppm Basic Brown 1 dye was studied. The results showed that highest decolorization of 62 % was attained for 3 g/L peroxymonosulfate under 37 kHz frequency sonolysis treatment. Secondly, with the catalyst study, highest of 46 % dye color removal was obtained with 4 g/L Fe under 37 kHz frequency sonolysis treatment. The sonophotocatalytic treatment of dye with Fe-doped Bi₂O₃ catalyst in combination with peroxymonosulfate showed highest color removal of 99 %. Finally, the sonophotocatalytic treatment of real textile wastewater in the presence of 3 g/L Fe-doped Bi₂O₃ and 6 g/L peroxymonosulfate reduced the total organic carbon (TOC) and chemical oxygen demand (COD) level to 77 and 91 %, respectively, in 180 min. The reported treatment process was found to treat the synthetic dye and real textile wastewater effectively.

Sonophotocatalytic mineralization of Norflurazon in aqueous environment

Norflurazon (4-chloro-5-(methylamino)-2-[3-(trifluoromethyl)phenyl]pyridazin-3(2H)-one; C12H9ClF3N3O) is an excellent weed controlling agent being practiced in the agricultural lands. The excessive addition or the undissolved Norflurazon (maximum solubility 28 mg/L at 25 °C) enters into the aquatic environment and causes the adverse effects associated with its high concentration. To avoid the perilous effects, visible light assisted photocatalysis set-up coupled with the 42 kHz ultrasound producing bath type sonicator is used to completely mineralize the Norflurazon. TiO2, ZnO and gold loaded zinc oxide nanocatalysts were utilized to study the mineralization of Norflurazon. Au-ZnO shows the greater efficiency for the sonophotocatalytic removal of Norflurazon among the various nanocatalysts employed to study the mineralization. The order of Norflurazon mineralization was sonophotocatalysis > sonocatalysis > photocatalysis. The additive effect was achieved for the sonophotocatalytic degradation. The high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometric (LCMS) analyses were employed to identify the various intermediates produced during the mineralization. The identification of four pseudo molecular ions and various intermediates using the LCMS analysis evidently suggests the sonophotocatalytic degradation was preceded in various decay pathways. A suitable mechanism has been proposed for the sonophotocatalytic mineralization of Norflurazon.

Removal of reactive blue 19 dye by sono, photo and sonophotocatalytic oxidation using visible light

An efficient sonophotocatalytic degradation of reactive blue 19 (RB 19) dye was successfully carried out using sulfur-doped TiO2 (S-TiO2) nanoparticles. The effect of various treatment processes that is sonolysis, photolysis, catalysis, sonocatalysis, photocatalysis, and sonophotocatalysis were investigated for RB 19 removal. S-TiO2 were synthesized in 1, 3 and 5 wt.% of sulfur by sol-gel process and characterized by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX), UV-Visible diffuse reflectance spectra (DRS). The results confirm anatase phase of TiO2, porous agglomerate structure, and a red shift in the absorbance spectra of S-TiO2. The dye degradation was studied by using UV-Vis spectrophotometer at λ max=594 nm. The reaction parameters such as pH, catalyst dosage, initial dye concentration, ultrasonic power and effect of sulfur doping in different weight percent were studied to find out the optimum degradation conditions. Optimum conditions were found as: S-TiO2=5 wt.%, catalyst (S-TiO2 5 wt.%)=50mg, RB 19 solution concentration=20 mg L(-1), pH=3, ultrasound power=100 and operating temperature=25°C. The response of 5 wt.% S-TiO2 was found better than 1 and 3 wt.% S-TiO2 and other forms TiO2. The sonophotocatalysis process was superior to other methods. During this process the ultrasound cavitation and photocatalysis water splitting takes place which leads to the generation of OH. As reveled by the GCMS results the reactive blue 19 (20 mg L(-1)) was degraded to 90% within 120 min. The S-TiO2 sonophotocatalysis system was studied for the first time for dye degradation and was found practicable, efficient and cost effective for the degradation of complex and resistant dyes such as RB19.

Diffused sunlight driven highly synergistic pathway for complete mineralization of organic contaminants using reduced graphene oxide supported photocatalyst

Diffused sunlight is found to be an effective light source for the efficient degradation and mineralization of organic pollutant (methyl orange as a probe) by sono-photocatalytic degradation using reduced graphene oxide (rGO) supported CuO-TiO2 photocatalyst. The prepared catalysts are characterized by XRD, XPS, UV-vis DRS, PL, photoelectrochemical, SEM-EDS and TEM. A 10 fold synergy is achieved for the first time by combining sonochemical and photocatalytic degradation under diffused sunlight. rGO loading augments the activity of bare CuO-TiO2 more than two fold. The ability of rGO in storing, transferring, and shuttling electrons at the heterojunction between TiO2 and CuO facilitates the separation of photogenerated electron-hole pairs, as evidenced by the photoluminescence results. The complete mineralization of MO and the by-products within a short span of time is confirmed by TOC analysis. Further, hydroxyl radical mediated degradation under diffused sunlight is confirmed by LC-MS. This system shows similar activity for the degradation of methylene blue and 4-chlorophenol indicating the versatility of the catalyst for the degradation of various pollutants. This investigation is likely to open new possibilities for the development of highly efficient diffused sunlight driven TiO2 based photocatalysts for the complete mineralization of organic contaminants.

Sonophotocatalytic degradation of dye C.I. Acid Orange 7 by TiO2 and Ag nanoparticles immobilized on corona pretreated polypropylene non-woven fabric

This study discusses the possibility of using corona pre-treated polypropylene (PP) non-woven fabric as a support for immobilization of colloidal TiO2 and Ag nanoparticles in order to remove dye C.I. Acid Orange 7 from aqueous solution. Dye removal efficiency by sonocatalysis, photocatalysis and sonophotocatalysis was evaluated on corona pre-treated fabric loaded with TiO2 nanoparticles, corona pre-treated fabric double loaded with TiO2 nanoparticles and corona pre-treated fabrics loaded with TiO2 nanoparticles before and after deposition of Ag nanoparticles. In addition, the stability of PP non-woven fabric during these processes was investigated. The substrates were characterized by SEM, EDX and AAS analyses. The change of the dye concentration was evaluated by UV-VIS spectrophotometry. Unlike sonocatalysis and photocatalysis, complete dye removal from both solution and non-woven fabric was obtained already after 240-270 min of sonophotocatalysis. Corona pre-treated PP non-woven fabric loaded with Ag nanoparticles prior to deposition of TiO2 nanoparticles provided excellent degradation efficiency and superior reusability. Sonophotocatalytic degradation of dye in the presence of all investigated samples was the most prominent in acidic conditions. Although this nanocomposite system ensured fast discoloration of dye solution, TOC values of water measured after sonophotocatalysis were not satisfactory because of PP degradation. Therefore, it is suggested to include TOC evaluation in each case study where different supports for TiO2 nanoparticles are used since these nanoparticles may guarantee the dye removal from solution but the stability of support could be problematic causing even more serious environmental impact.

Low frequency ultrasound (42 kHz) assisted degradation of Acid Blue 113 in the presence of visible light driven rare earth nanoclusters loaded TiO2 nanophotocatalysts

An attempt has been made to render the visible light driven photocatalytic activity to the TiO2 nanocatalysts by loading 1 wt% of rare earth (RE) nanoclusters (Gd(3+), Nd(3+) and Y(3+)) using a low frequency (42 kHz) producing commercial sonicator. The STEM-HAADF analysis confirms that the RE nanoclusters were residing at the surface of the TiO2. Transmission electron microscopic (TEM) and X-ray diffraction (XRD) analyses confirm that the loading of RE nanoclusters cannot make any significant changes in the crystal structure of TiO2. However, the optical properties of the resulted nanocatalysts were significantly modified and the nanocatalysts were employed to study the sonocatalytic, photocatalytic and sonophotocatalytic decolorization as well as mineralization of Acid Blue 113 (AB113). Among the experimented nanocatalysts maximum degradation of AB113 was achieved in the presence Y(3+)-TiO2 nanocatalysts. The decolorization of AB113 in the presence and absence of Y(3+) loaded TiO2 ensues the following order sonolysis<photocatalysis<sonocatalysis<sonophotocatalysis. The sonophotocatalytic decolorization of AB113 shows 1.4-fold (synergy index) enhanced rate when compared with the two corresponding individual advanced oxidation processes. The sonophotocatalytic mineralization shows that 65% of total organic carbon (TOC) can be removed from AB113 after the 5h of continuous irradiation however the mineralization cannot be able to show the synergetic effect.

Transformation products and reaction pathways of carbamazepine during photocatalytic and sonophotocatalytic treatment

This study examines the degradation of the antiepileptic carbamazepine (CBZ) by sonolysis, TiO2-based heterogeneous photocatalysis under UV-A and simulated solar irradiation, and by the combined use of UV-A and ultrasound irradiation (i.e. sonophotocatalysis) in demineralized water, ground water and effluent wastewater. The processes were compared with respect to substrate conversion rate and the extent of DOC reduction as a measure of mineralization. CBZ was degraded following a pseudo-first order kinetics. Sonophotocatalysis provided the highest rate of CBZ transformation over the time-course of the experiment while the degree of DOC removal in pure water was similar for all the studied treatments (around 40%), and always lower than CBZ conversion. This indicated that a considerable organic load remained in the treated solutions that could also be attributed to the presence of persistent oxidation products. UPLC-(+ESI)-QToF-MS was employed to determine major CBZ-related transformation products. Several recalcitrant hydroxy- and keto-derivatives of CBZ were tentatively identified. A Daphnia magna bioassay was used to evaluate the potential toxicity of the samples collected at different time points showing that the mixtures were highly toxic to D. magna.