Piezo-enhanced photocatalytic diclofenac mineralization over ZnO

Ultrasonics and sonochemistry: Editors' perspective

Ultrasonic waves can induce physical and chemical changes in liquid media via acoustic cavitation. Various applications have benefitted from utilizing these effects, including but not limited to the synthesis of functional materials, emulsification, cleaning, and processing. Several books and review articles in the public domain cover both fundamental and applied aspects of ultrasonics and sonochemistry. The Editors of the Ultrasonics Sonochemistry journal possess diverse expertise in this field, from theoretical and experimental aspects of acoustic cavitation to materials synthesis, environmental remediation, and sonoprocessing. This article provides Editors' perspectives on various aspects of ultrasonics and sonochemistry that may benefit students and early career researchers.

Ternary Polyaniline@Bi2O3-BiOCl Nanocomposites as Innovative Highly Active Photocatalysts for the Removal of the Dye under Solar Light Irradiation

Ternary PANI@Bi₂O₃-BiOCl nanocomposites were successfully synthesized during the oxidative polymerization of aniline monomer in the presence of Bi₂O₃. PANI@Bi₂O₃-BiOCl nanocomposites were characterized by several analytical techniques, including X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), N₂ physisorption, UV-Vis Diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The effective PANI-semiconductor interaction promotes the fast separation and transfer of photogenerated electrons and holes, enhancing the photocatalytic efficiency of the materials towards methylene blue (MB) degradation under solar light irradiation. The best results were obtained by 0.5%PANI@Bi₂O₃-BiOCl, leading to 80% MB degradation in 2 h, four times higher than pristine Bi₂O₃-BiOCl. Moreover, 0.5%PANI@Bi₂O₃-BiOCl maintained stable photocatalytic performances for four cycles without significant activity loss. Various scavengers (isopropyl alcohol, formic acid, and benzoquinone) were used to identify the active species by trapping holes and radicals generated during the photocatalytic degradation process. Finally, a probable photocatalytic mechanism of PANI@Bi₂O₃-BiOCl photocatalyst was suggested.

Decoration of alumina hollow fibers with zinc oxide: improvement of the photocatalytic system for methylene blue degradation

The photocatalytic degradation of methylene blue (MB) in aqueous solutions and under visible light was investigated with dispersed and supported zinc oxide (ZnO) as catalysts. The ZnO catalyst was successfully impregnated in asymmetric alumina hollow fibers by the simple vacuum-assisted dip-coating method. According to energy-dispersive analyses, the photocatalyst was homogenously distributed in the substrate. A strong correlation was observed between the initial dye concentration and the efficiency of the supported photocatalyst. For the initial MB concentration of 5 mg L^-1 and catalyst dosage of 1 g L^-1, the photocatalytic system with both dispersed and supported catalysts reached almost 100% of MB degradation. The photocatalytic process followed the pseudo-first-order kinetic model, and, for the initial MB concentration of 5 mg L^-1, the apparent constants were 0.05415 and 0.00642 min^-1 for suspended and supported catalysts, respectively. The treated MB solutions presented low phytotoxicity to the germination Lactuca sativa seeds with germination indexes greater than 80% after irrigation with the treated MB solutions. The produced supported ZnO catalyst showed suitable photocatalytic stability even after several reuse cycles.

One-step, highly stable Pickering emulsions stabilized by ZnO: tuning emulsion stability by in situ functionalization

HYPOTHESIS

Oxide-stabilized emulsions generally require a surface functionalization step to tune the oxide wettability, often involving hazardous hydrophobizing agents. Here, we propose the in situ functionalization of ZnO in vegetable oils without the addition of any modifier, resulting in the one-step formation of highly stable Pickering emulsions.

EXPERIMENTS

The role of ZnO surface features was studied by modifying the particles' wettability through surface functionalization and by comparing different oil phases. The emulsion stability was assessed through aging tests, multiple hot-and-cold cycles, centrifugation, and addition of multiple electrolytes.

FINDINGS

While the wetting features of the functionalized oxide play a crucial role when the oil phase is methyl octanoate, emulsions based on vegetable oils form also using hydrophilic ZnO. During the emulsification, an in situ functionalization of bare ZnO particles takes place due to the fatty acids present in vegetable oil. These in situ-generated systems lead to stable emulsions showing < 2 μm-diameter oil droplets. The resulting emulsions display excellent stability over time (over seven months) and against temperature variations, mechanical stress and increased ionic strength. Finally, we demonstrate that this approach can be extended to a variety of vegetable oils and oxides with different morphologies.

Sustainable Solar Light Photodegradation of Diclofenac by Nano- and Micro-Sized SrTiO3

Currently, photocatalytic reactions under solar illumination have attracted worldwide attention due to the tremendous set of associated environmental problems. Taking sunlight into account, it is indispensable to develop highly effective photocatalysts. Strontium titanate, SrTiO3 (STO), is a cubic perovskite-type semiconductor, an inexpensive material with high thermal stability and corrosion resistance that exhibits a similar energy bandgap to TiO2 and can represent an interesting alternative in photocatalytic applications. Particle size can significantly affect both photocatalytic and photoelectrochemical properties of a photocatalyst, thus altering the photooxidation of organic pollutants in air or water. In this context, this research aims at investigating the photocatalytic features of nano- and micro-sized commercial STO powders towards the photodegradation of diclofenac (DFC), a non-steroidal, anti-inflammatory drug, widely used as analgesic, antiarthritic, and antirheumatic. Both nano- and micro-STO photocatalysts exhibited remarkable photocatalytic efficiency towards DCF, reaching photodegradation efficiency higher than 90% within one hour. Results obtained in simulated drinking water were also compared to those obtained in ultrapure water. Both STOs showed good stability during recycling tests, maintaining high performances after three cycles. Eventually, active species were identified using various scavengers by trapping holes and radicals generated during the photocatalytic degradation process.

Diclofenac degradation by activating peroxydisulfate via well-dispersed GO/Cu2O nano-composite

Owing to high treatment efficiency under neutral condition and no extra energy required, copper-mediated activation of persulfate (PS) has been widely used for the degradation of refractory organic pollutants in water. The dispersion stability of copper nanoparticle in water, however, remains a great challenge. Meanwhile, chemical oxidative modification of graphene oxide (GO) can improve the dispersion stability of GO in water. In this paper, cuprous oxide (Cu₂O) was deposited on the surface of GO. GO/Cu₂O nano-composites with different mass ratios, i.e., m(GO):m(Cu₂O) of 1:2, 1:5, 1:10, and 1:25, were prepared. When m(GO):m(Cu₂O) was 1:2, the amount of GO/Cu₂O nano-composite was 1.00 g/L and C_PDS:C_DCF was 15:1, and the catalytic degradation rate of diclofenac (DCF) was up to 90%. Corresponding physicochemical properties of the resulting samples were comprehensively characterized by using SEM, TEM, XRD, Raman, FT-IR, and XPS. DCF degradation by activating peroxydisulfate (PDS) via GO/Cu₂O nano-composite was also investigated in detail. It is found that the synergistic effect, namely GO adsorption and multivalent copper ion electron transfer, makes GO/Cu₂O nano-composite reveal higher reactivity. Moreover, GO/Cu₂O nano-composite possesses good stability in consecutive cycling test. EPR analyses shows that ·OH and SO₄^·- radicals are involved in DCF degradation. It is indicated that the DCF degradation process contain hydroxylation and the cleavage of C-N bond, which is explored by GC-MS. In our research, well-dispersed GO/Cu₂O nano-composite with high capacity and good cycling stability was fabricated successfully. Compared with pure Cu₂O nanoparticle, GO/Cu₂O nano-composite exhibits the better performance for DCF removal. A novel well-dispersed cuprous oxide (Cu₂O) deposited on surface of GO was fabricated with high catalytic performance. Its heterogeneous activation of peroxydisulfate (PDS) for diclofenac (DCF) degradation was investigated. GO/Cu₂O nano-composite was proved high capacity and good cycling stability. Meanwhile, the possible DCF degradation pathway was explored. Compared with pure Cu₂O nanoparticle, GO/Cu₂O nano-composite exhibits better performance for DCF removal.

Noble Metal Promoted TiO2 from Silver-Waste Valorisation: Synergism between Ag and Au

Wastewaters from precious metal industries contain high amounts of noble metals, but their efficient recycling is hindered by the wastewater complex composition. Here, we propose an innovative approach for the efficient recovery of noble metals contained in these metal-enriched wastewaters as precursors for the synthesis of noble metal nanoparticles (NPs) and supported metal catalysts. Silver NPs were synthesized from Ag-enriched wastewater and then deposited on TiO2 to prepare photocatalysts. Then, further promotion of the photocatalytic activity of Ag-modified TiO2 was achieved by the addition of as little as 0.5 wt.% of Au. STEM-EDS analyses proved that Au NPs were located on Ag or AgOx nanoparticles. The contact between the two metal-containing NPs results in charge transfer effects, appreciable both in terms of oxidation states determined by XPS and of optical properties. In particular, the plasmon band of Au NPs shows photochromic effects: under UV light irradiation, bimetallic samples exhibit a blue-shift of the plasmon band, which is reversible under dark storage. The activity of the materials was tested towards ethanol photodegradation under UV light. Adding 0.5 wt.% Au NPs resulted in a promoted activity compared to Ag-TiO2, thus showing synergistic effects between Au and Ag. Ethanol was completely converted already after 1 h of UV irradiation, acetaldehyde was formed as the main oxidation product and fully degraded in less than 180 min. Notably, bimetallic samples showed ethylene formation by a parallel dehydration mechanism.

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.

Solar Light Photoactive Floating Polyaniline/TiO2 Composites for Water Remediation

In the present study, the development of innovative polyurethane-polyaniline/TiO2 modified floating materials applied in the sorption and photodegradation of rhodamine B from water matrix under solar light irradiation is reported. All the materials were fabricated with inexpensive and easy approaches and were properly characterized. The effect of the kind of polyaniline (PANI) dopant on the materials' behavior was investigated, as well as the role of the conducting polymer in the pollutant abatement on the basis of its physico-chemical characteristics. Rhodamine B is removed by adsorption and/or photodegradation processes depending on the type of doping agent used for PANI protonation. The best materials were subjected to recycle tests in order to demonstrate their stability under the reaction conditions. The main transformation products formed during the photodegradation process were identified by ultraperformance liquid chromatography-mass spectrometry (UPLC/MS). The results demonstrated that photoactive floating PANI/TiO2 composites are useful alternatives to common powder photocatalysts for the degradation of cationic dyes.

Novel application of Ag/PbBiO2I nanocomposite in piezocatalytic degradation of rhodamine B via harvesting ultrasonic vibration energy

Ag/PbBiO2I nanocomposite was synthesized and firstly applied in piezocatalytic degradation of rhodamine B (RhB) under ultrasonic vibration. The two-dimensional structure endows PbBiO2I nanosheets piezoelectric property, so that it can drive the piezocatalytic reaction under ultrasonic vibration. The loading of Ag nanoparticles forms Schottky barriers between the Ag-PbBiO2I contact region, which improves the separation of charge carriers and subsequently increases the piezocatalytic efficiency. The RhB degradation rate of the optimal Ag/PbBiO2I sample is 0.0165 min-1, which reaches 6.8 times that of pure PbBiO2I. This work indicates that the PbBiO2I nanosheet shows promising potential in utilizing ultrasonic vibration energy.