Titanium-based MAX-phase with sonocatalytic activity for degradation of oxytetracycline antibiotic

Dual-Phase Structure through Selective Etching of the Double A-Element MAX Phase in Lewis Acidic Molten Salts

Two-dimensional (2D) MXene materials with innovative properties and versatile applications have gained immense popularity among scientists. The green and environmentally friendly Lewis acid salt etching route has opened up immense possibilities for the advancement of 2D MXene materials. In this study, we precisely etched the Al element from the double A-element MAX phases Ti2(SnyAl1-y)C by employing Lewis molten salt guided by redox potentials. This approach led to the discovery of a novel Ti2SnyCClx dual-phase structure consisting of Ti2SnC and Ti2CClx. We then established that the etching of the MAX phase via Lewis acid salt is facilitated by the oxidation of M-site elements, with the MX sublayer acting as an electron transmission conduit to enable the oxidation of A-site elements. This work is dedicated to unraveling the underlying mechanisms governing the etching processes using Lewis molten salt, thereby contributing to a more profound comprehension of these innovative etching routes.

Continuous ultrasonic ozone coupling technology-assisted control of ceramic membrane fouling coupled enhanced multiphase mixing to treat dye wastewater and CFD flow field simulation

In this study, ozone catalysts (hydrogenation-modified red mud, HM-RM) successfully prepared by hydrogenation-modification of industrial hazardous solid waste red mud (RM) as a raw material in accordance with the viewpoint of treating waste with waste and using waste. Meanwhile, as for the common phenomenon of membrane fouling, uneven distribution of multiphase solid catalysts and ozone in liquids, the addition of ultrasound can not only disperse materials, but also play a role in online cleaning of ceramic membranes and catalysts. The optimum treatment conditions for Rhodamine B (RhB) solution with volume of 2 L and concentration of 40 mg/L were catalyst concentration of 0.4 mg/L, reaction temperature of 45 °C, ultrasonic time of 1 h, ultrasonic intensity of 600 W, removal rate of RhB was up to 90 %. In addition, the computational fluid dynamics (CFD) simulation method was used to investigate the fluid flow between the two gas-liquid phases and the effect of the negative pressure of the membrane pump on the fluid by the analysis of flow, pressure and ozone flux of the ceramic membrane(CM) reaction apparatus. The CFD simulation results showed that at the inlet gas-liquid flow rate of 3 m/s and the negative pressure of 20,000 Pa, the maximum flow rates of CM-1 were 3 m/s, 0.752 m/s for CM-2, and 0.228 m/s for CM-3, respectively. Vortices, which are beneficial to solid-liquid mixing and gas-liquid mass transfer, formed between the suction port CM-1 of CM-1 and the inlets of CM-2 and CM-3. This discovery is consistent with relevant experimental research results. Significantly higher concentrations of both •OH and dissolved ozone were observed in the US/HM-RM/O3 system compared to other systems, indicating the significant improvement in ozone utilization rate through the application of ultrasound. The superiority of the US/HM-RM/O3 device was demonstrated. The real dye effluent was tested under optimum operating conditions and the results showed that COD and TOC were reduced by 81.34 % and 60.23 % respectively after 180 min of treatment. The above research can provide technical support for the treatment of dye wastewater using Ultrasound-enhanced ozone oxidation ceramic membranes.

Sonocatalytic degrading antibiotics over activated carbon in cow milk

Herein, an efficient, simple and economical approach to remove antibiotics (ABX), i.e. ceftiofur hydrochloride, sulfamonomethoxine sodium (SMM), marbofloxacin and oxytetracycline by sonication with activated carbon (AC) from cow milk has been successfully implemented. The pseudo-first-order kinetics constants for the sonolytic and sonocatalytic degrading SMM are 0.036 and 0.093 min-1, respectively. The synergistic efficiency of removing ABX by using sonocatalysis reached 1.8-4.0. Hydrophobic ABX underwent faster degradation than hydrophilic ABX in sonocatalytic systems. Adding 0.5 mmol L-1 H2O2, the optimal concentration, improved the sonocatalytic degradation rates of ABX by 9.1%-28.5%. Surface area and dose of AC play crucial roles in the sonocatalysis of ABX. By sonicating 50 mL of 5.52 μmol L-1 ABX in milk at 500 kHz and 259 W with 20 mg AC for 20-60 min resulted in residual ABX concentrations ranging from 42.6 to 95.1 μg L-1, which meet the relative maximum residue limits set by European Commission.

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.

Highly efficient ultrasound-driven Cu-MOF/ZnWO4 heterostructure: An efficient visible-light photocatalyst with robust stability for complete degradation of tetracycline

Metal-organic frameworks (MOFs) are a significant class of porous, crystalline materials composed of metal ions (clusters) and organic ligands. The potential use of copper MOF (Cu-BTC) for the sonophotocatalytic degradation of Tetracycline (TC) antibiotic was investigated in this study. To enhance its catalytic efficiency, S-scheme heterojunction was created by combining Cu-BTC with Zinc tungstate (ZnWO4), employing an ultrasound-assisted hydrothermal method. The results demonstrated that the Cu-BTC/ZnWO4 heterojunction exhibited complete removal of TC within 60 min under simultaneous irradiation of visible light and ultrasound. Interestingly, the sonophotocatalytic degradation of TC using the Cu-BTC/ZnWO4 heterojunction showed superior efficiency (with a synergy index of ∼0.70) compared to individual sonocatalytic and photocatalytic degradation processes using the same heterojunction. This enhancement in sonophotocatalytic activity can be attributed to the formation of an S-scheme heterojunction between Cu-BTC and ZnWO4. Within this heterojunction, electrons migrated from Cu-BTC to ZnWO4, facilitated by the interface between the two materials. Under visible light irradiation, the built-in electric field, band edge bending, and coulomb interaction synergistically inhibited the recombination of electron-hole pairs. Consequently, the accumulated electrons in Cu-BTC and holes in ZnWO4 actively participated in the redox reactions, generating free radicals that effectively attacked the TC molecules. This study offers valuable perspectives on the application of a newly developed S-scheme heterojunction photocatalyst, demonstrating its effectiveness in efficiently eliminating diverse recalcitrant pollutants via sonophotocatalytic degradation.

Boosting the sonophotocatalytic performance of BiOCl by Eu doping: DFT and an experimental study

Bismuth oxychloride (BiOCl) has a unique layered structure and uneven charge distribution, resulting in an internal electric field under polarization, which promotes the efficient separation and migration of photogenerated carriers. BiOCl could be a candidate for sonophotocatalysts. However, the low utilization of visible light limits the application of BiOCl in photocatalysts. In this study, the photocatalytic performance of rare earth element (Nd, Sm, Eu, Er and Er)-doped BiOCl was studied by density functional theory (DFT) and experimentally to screen high-performance catalysts. The band structure, density of states, and optical properties were calculated by the DFT method to predict the photocatalytic activity of rare earth-doped BiOCl. The built-in electric field formed in Eu-doped BiOCl inhibiting electron and hole recombination can be observed. Subsequently, the activity of the photocatalyst and sonophotocatalysts was evaluated. The results show that the photocatalytic and sonophotocatalytic activity of Eu-doped BiOCl is improved, which is consistent with the theoretical prediction. Combining theoretical calculations with experiments, the sonophotocatalytic activity of Eu-doped BiOCl is enhanced, mainly due to the synergistic effect of inhibiting carrier recombination, and expansion to the visible light absorption region.

Synergistic effects of layered Ti3C2TX MXene/MIL-101(Cr) heterostructure as a sonocatalyst for efficient degradation of sulfadiazine and acetaminophen in water

In this work, different mass loadings of MXene-coupled MIL-101(Cr) (MXe/MIL-101(Cr)) nanocomposites were generated through a hydrothermal process in order to investigate the potential of this nanocomposite as a novel sonocatalyst for the elimination of sulfadiazine (SD) and acetaminophen (AAP) in aqueous media. The sonocatalytic activity of different MXe/MIL-101(Cr) compositions and surface functionalities was investigated. In addition, the sonocatalytic activities at various pH values, temperatures, pollutant concentrations, catalyst dosages, initial H2O2 concentrations, and organic matter contents were investigated. The experiments on the sonocatalytic elimination of SD and AAP revealed that MXe/MIL-101(Cr) exhibited a catalytic efficiency of ∼ 98% in 80 min when the MXene loading was 30 wt% in the nanocomposite. Under optimized reaction conditions, the degradation efficiency of MXe/MIL-101(Cr) reached 91.5% for SD and 90.6% for AAP in 60 min; these values were 1.2 and 1.8 times greater than those of MXene and MIL-101(Cr), respectively. The high surface area of the MXe/MIL-101(Cr) nanocomposite increased from 4.68 m2/g to 294.21 m2/g, and the band gap of the tagged MIL-101(Cr) on the MXene surface was minimized. The superior sonocatalytic activity of MXe/MIL-101(Cr) was attributed to the effective contact interface, the effective separation rate of e- - h+ pairs through the type II heterostructure interface, and the favorable high free •OH radical production rates that promoted the degradation of SD and AAP. The solid heterointerface between MIL-101(Cr) and MXene was confirmed through Raman and FTIR analysis and was found to promote accessible •OH radical production under sonication, thus maximizing the catalytic activity of nanocomposites. The present results present an effective strategy for the design of a highly efficient, low-cost, reliable sonocatalyst that can eradicate pharmaceutical pollutants in our environment.

Application of Photocatalysis and Sonocatalysis for Treatment of Organic Dye Wastewater and the Synergistic Effect of Ultrasound and Light

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

Sonocatalytic degradation of tetracycline hydrochloride with CoFe2O4/g-C3N4 composite

In this work, different mass percent ratios of CoFe₂O₄ coupled g-C₃N₄ (w%-CoFe₂O₄/g-C₃N₄, CFO/CN) nanocomposites were integrated through a hydrothermal process for the sonocatalytic eradication of tetracycline hydrochloride (TCH) from aqueous media. The prepared sonocatalysts were subjected to various techniques to investigate their morphology, crystallinity, ultrasound wave capturing activity and charge conductivity. From the investigated activity of the composite materials, it has been registered that the best sonocatalytic degradation efficiency of 26.71 % in 10 min was delivered when the amount of CoFe₂O₄ was 25% in the nanocomposite. The delivered efficiency was higher than that of bare CoFe₂O₄ and g-C₃N₄. This enriched sonocatalytic efficiency was credited to the accelerated charge transfer and separation of e^--h⁺ pair through the S-scheme heterojunctional interface. The trapping experiments confirmed that all the three species i.e. ^•OH, h⁺ and ^•O₂^- were involved in the eradication of antibiotics. A strong interaction was shown up between CoFe₂O₄ and g-C₃N₄ in the FTIR study to support charge transfer as confirmed from the photoluminescence and photocurrent analysis of the samples. This work will provide an easy approach for fabricating highly efficient low-cost magnetic sonocatalysts for the eradication of hazardous materials present in our environment.

Catalytic activation of hydrogen peroxide by Cr2AlC MAX phase under ultrasound waves for a treatment of water contaminated with organic pollutants

This study aims to investigate the sonocatalytic activation of hydrogen peroxide (H₂O₂) using Cr₂AlC MAX phase prepared by the reactive sintering process. The hexagonal structure of the crystalline MAX phase was confirmed by X-ray diffraction. Moreover, the compacted layered structure of the MAX phase was observed via scanning electron microscopy and high-resolution transmission electron microscopy. Under the desired operating conditions, Cr₂AlC MAX phase (0.75 g/L) showed suitable potential to activate H₂O₂ (1 mmol/L) under sonication, thereby allowing a considerable removal efficiency for various organic pollutants, including dimethyl phthalate (69.1%), rifampin (94.5%), hydroxychloroquine (100%), and acid blue 7 (91.5%) with initial concentration of 15 mg/L within 120 min of treatment. Kinetic analysis proved that the degradation reaction followed pseudo-first-order kinetics. Scavenging tests demonstrated that hydroxyl radicals and singlet oxygen were effective species during degradation. Furthermore, a probable mechanism for dimethyl phthalate degradation was suggested according to gas chromatography-mass spectroscopy and nuclear magnetic resonance analyses. The obtained results confirmed the capability of the triple Cr₂AlC/H₂O₂/US process as a promising method for treating contaminated water.