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Piezocatalysis is an emerging approach for degrading organic dye. However, the limited availability of ultrasonic resources in nature restricts its practical application. Our proposed peak flow kinetic energy piezocatalytic strategy, based on a “waterfall flow” model, aims to simulate the piezocatalytic degradation of pollutants in nature. This innovative strategy can enhance degradation efficiency by adjusting the flow rate and drop height. When 140mL of rhodamine B (RhB) dye solution flows at a rate of 1000mL/min from a height of 48cm and impacts a 3 cm diameter BaTiO₃ nanowires/PVDF piezoelectric composite film, a degradation rate of 90% can be achieved within 120min. This rapid degradation is primarily attributed to the efficient conversion of kinetic energy into impact force as the water falls, which triggers the generation of piezopotential in the composite film. This, in turn, drives the separation and transmission of electron–hole pairs, leading to the promotion of reactive oxygen species (ROS) generation and facilitating fast organic dye degradation. The pulsating nature of the impact force ensures a continuous generation of ROS. This approach is poised to advance piezocatalysis for the degradation of organic dyes in natural environments and presents a novel method for wastewater treatment.

Transition metal oxide photocatalysis is a relatively new method representing advanced oxidation process to be applied in industrial wastewater treatment especially for degradation of organic pollutants. We investigate TiO₂ as a photocatalyst for the photocatalytic degradation of Rhodamine B (RhB) under simulated sunlight. Various parameters and their effectiveness have been studied. The effects of processing parameters including catalyst loading and feed concentration were investigated; and the degradation pathway was proposed based on the UHPLC-MS analysis. The result showed that a higher kinetic rate can be obtained by employing low catalyst loading and feed concentration, i.e., 0.5 g/L of TiO₂ loading and 5 ppm of RhB concentration, respectively. For this particular system, the optimum degradation rate ($k$) can achieve 0.297/min. The effectiveness of solar light-TiO₂ system for RhB degradation shows this method can be used for wastewater treatment.

In this work, efficient catalyst is prepared using ZnO and $\alpha$-Fe₂O₃ along with a surface modification using 2-methylimidazole. Surface modified feature of the catalyst is confirmed by the shifting of vibrational frequency to higher wavenumber. Photocatalytic properties of the as-synthesized and surface modified composites are investigated by measuring the degradation of Methylene Blue (cationic) dye under sunlight irradiation. Both the samples exhibited a similar photocatalytic efficiency of 78% under 300 min. The effect of surface modification shows no significant enhancement on the cationic dye removal. Further, the samples are tested for the degradation of Methyl Blue (anionic) dye in dark condition to validate the effect of functionalization. Surface functionalized sample exhibits 96% efficiency compared to 86% for the pristine sample. Thus, surface modification has extended to be one of the promising techniques for enhancing the catalytic properties of composites.

The present work deals with the synthesis of bi-continuous macro and mesoporous crack-free titania–silica monoliths, with well-defined structural dimensions and high surface area. The work also highlights their potential photocatalytic environmental applications. The highly ordered titania–silica monoliths are synthesized through direct surface template method using organic precursors of silica and titania in the presence of surface directing agents such as pluronic P123 and PEG, under acetic acid medium. The monoliths are synthesized with different Ti/Si ratios to obtain monolithic designs that exhibit better photocatalytic activity for dye degradation. The titania–silica monoliths are characterized using XRD, SEM, EDAX, FT-IR, TG–DTA and BET analysis. The photocatalytic activity of the synthesized monoliths is tested on the photodegradation of a textile dye (acid blue 113). It is observed that the monolith with 7:3 ratio of Ti/Si showed significant photocatalysis behavior in the presence of UV light. The influence of various physico-chemical properties such as, solution pH, photocatalyst dosage, light intensity, dye concentration, effect of oxidants, etc. are analyzed and optimized using a customized photoreactor set-up. Under optimized conditions, the monoliths exhibited superior degradation kinetics, with the dye dissipation complete within 10min of photolysis. The mesoporous catalysts are recoverable and reusable up to four cycles of repeated usage.

In this paper, a highly catalytic and nanosized Ag/Co₃O₄ composite for rhodamine B(RhB) degradation was fabricated by using the co-precipitation method at room temperature. The Ag/Co₃O₄ structure and catalytic properties were characterized through scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) gas-sorption measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. The results showed that the Co₃O₄ nanosheets prepared by hydrothermal synthesis mainly exposed (2 2 0) and (1 1 1) facets, which played an important role in determining its catalytic oxidation performance. The Co₃O₄ nanosheets doped with Ag nanoparticles by a simple silver-mirror reaction exhibited a stable and well-dispersed property in dye solution. Compared to the Ag and Co₃O₄ nanostructure, the Ag nanoparticles with bigger diameter (10 nm) on Co₃O₄ surface also readily produced surface-active oxygen species and exhibited a higher catalytic activity for the degradation of RhB solution (5 mg ⋅ L^-1) under the visible light. The kinetic constant K of Ag/Co₃O₄ catalyst for RhB degradation reaction was evaluated to 0.02724 min^-1, which is relatively higher than those reported in the literatures.

In this study, LaFeO₃/ZnIn₂S₄ composites were synthesized via in situ synthesis. The composition, structure and optical absorption properties of LaFeO₃/ZnIn₂S₄ were characterized by X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy, fluorescence spectroscopy (PL), Fourier Transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The photocatalytic activity of the LaFeO₃/ZnIn₂S₄ photocatalyst was determined based on the degradation of methyl orange (MO). LaFeO₃/ZnIn₂S₄ composites showed much better photocatalytic performance compared with pure LaFeO₃ and ZnIn₂S₄. The enhanced photocatalytic performance was attributed to intimately contacted interfaces and charge transfer channels which can effectively transfer and separate the photogenerated charge carriers.

The manufacture of diatomite-supported composite catalyst with enhanced photocatalytic activity is of great interest for wastewater treatment. In this study, the pretreated diatomite (PD) with 5wt.% NaOH solution possessed better pore structure and large specific surface area. A facile hydrothermal-photoreduction method was adopted to prepare Bi/BiVO₄/PD composite. The chemical composition, microstructure morphology and pore structure of samples were investigated by means of XRF, XRD, SEM, TEM, EDS, XPS and BET methods. The results showed that the metallic Bi was uniformly deposited on the BiVO₄. After loaded on PD, both surface area and total pore volume had a significant increase. In addition, UV-vis diffuse reflectance spectra presented that the absorption capacity of Bi/BiVO₄/PD-25% composite in the visible light range was remarkably high due to the surface plasmon resonance (SPR) caused by metallic Bi. From photoluminescence (PL) spectra and transient photocurrents, the heterojunction formed between Bi/BiVO₄ and PD helped promoting the separation and migration of photo-generated carriers, which in turn led to higher photocatalytic activity. Compared with Bi/BiVO₄, Bi/BiVO₄/PD loaded with 25wt.% PD showed highest decolorization rate for rhodamine B (RhB), malachite green (MG), methylene blue (MB), methyl orange (MO) and lemon yellow (LY) under visible light irradiation. According to trapping experiments on free radicals, the active species that played a decisive role in RhB degradation were h${}^{+}$ and $•{\text{O}}_2^{-}$. Findings from this study suggest that Bi/BiVO₄/PD-25% composite holds great promise for dye degradation and wastewater treatment.

The rapid removal of organic textile dye (Acid Red-85) using mesoporous TiO₂–SiO₂ monoliths as photocatalyst material has been studied. The 7:3 mole% ratios of TiO₂ and SiO₂ within the framework provided a well-ordered cage-like monolithic design with high surface area and pore volume that facilitated faster and efficient degradation of the dye effluents. The photocatalyst has been characterized using XRD, TEM-SAED, UV–Vis-DRS, PL, TGA and BET analysis. The influence of various photocatalytic operational parameters, such as solution pH, dopant stoichiometry, catalyst dosage, dye concentration, kinetics, photo-oxidizers, etc., which could influence on the degradation efficiency, has been studied.

Spin-coated poly (vinylidene fluoride) (PVDF) membrane and electrospun PVDF nanofibers were fabricated and surface modified with in-situ self-polymerization of dopamine or surface deposition of polydopamine. The morphology, composition and phase, hydrophilicity and dye degradation effects of these composite were quantitatively investigated. The results indicated that surface modified PVDF membrane and nanofibers exhibited excellent dye degradation capacity. Specifically, in-situ self-polymerization of dopamine could induce homogeneous distribution of polydopamine on the piezo-catalysis materials, providing favorable spatial conditions for the adsorption of dye molecules and enhancing dye degradation.

This research work explores the green synthesis of silver nanoparticles using Quassia indica (QI-Ag NPs), a natural plant extract, as a stabilizing and reducing agent. The synthesized QI-Ag NPs were characterized using various analytical techniques, including UV-Visible spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (HR-TEM) and Selected Area Electron Diffraction (SAED). The UV-Visible analysis revealed a characteristic peak at 430 nm, indicating the successful formation of AgNPs. XRD analysis unveiled the crystalline nature of the nanoparticles, with four distinctive peaks corresponding to the silver crystallographic planes. SEM and EDX provided insights into the morphology and chemical composition of the QI-AgNPs. Moreover, TEM and SAED elucidated the structural attributes and crystallinity of the nanoparticles. The Ag NPs exhibited a spherical structure and crystalline nature, as supported by both SAED and XRD findings. The zeta potential of QI-Ag NPs exhibited a value of −24.2 mV. The synthesized QI-Ag NPs were evaluated for their photocatalytic potential, demonstrating a remarkable 97% degradation of Crystal Violet dye. Furthermore, comprehensive studies encompassing antioxidant, antimicrobial and cytotoxicity assessments were conducted, showcasing the multifaceted applications of these nanoparticles. This research underscores the promising potential of Q. indica-mediated silver nanoparticles as environmentally benign and versatile nanomaterials.

Piezocatalysis has emerged as a promising environmental remediation technique, and the exploration of environmentally friendly and high-performance piezocatalysts is crucial for their practical applications. In this work, the bismuth sodium titanate (Na${}_{0.5}$Bi${}_{0.5}$TiO₃ (NBT)) exhibited efficient piezocatalytic activity toward typical organic pollutants degradation, including acid orange 7, methylene blue, rhodamine B and methyl orange. Notably, rhodamine B was degraded by 98.1% within 30min with a reaction rate constant of 0.130min${}^{-1}$. Furthermore, the NBT achieved a hydrogen peroxide production efficiency of 538$\mu$mol/g⋅h without the sacrificial agent, indicating that the NBT is a superior piezocatalyst for dye degradation and hydrogen peroxide generation. This work demonstrated that by using mechanical energy, the NBT can be used for degrading organic pollutants in wastewater and hydrogen peroxide generation.

In this work, a series of BiFeO₃/ZnO composites with varying molar ratio of BiFeO₃ to ZnO (Bi:Zn = 2.5:1, 5:1, 10:1, 20:1) have been synthesized via a one-step hydrothermal method and evaluated for their efficiency in rhodamine B (RhB) degradation performance. The morphology results reveal that the microsphere-shaped ZnO is dispersed on the surface of the blocky-like BiFeO₃, with intimate contact between the two phases. It has been found that the maximum piezocatalytic activity could be achieved at BiFeO₃/ZnO molar ratio of 5:1, with a degradation rate up to 92% for RhB. Compared with pure BiFeO₃ and ZnO, the composites have superior piezocatalytic degradation performance. The reason for the enhanced piezocatalytic dye degradation rate may be that the BiFeO₃/ZnO composites effectively separate the positive and negative charges to reduce the recombination of positive and negative charges. These active species, such as superoxide radicals (${\text{O}}_2•-$) in the process of piezocatalytic, are proved on the active species capture experiments. The BiFeO₃/ZnO composites have good piezocatalytic degradation performance, which provides an option for collecting vibration energy to degradation dye wastewater in the future.

A novel heterogeneous Fenton catalyst was prepared by immobilizing iron(II) phthalocyanine (FePc) onto the amidoximated Polyacrylonitrile (PAN) fiber through axial coordination bonds. The obtained catalyst was characterized using XRD and DRS technique, and then used for the degradation of Rhodamine B under visible irradiation. The results indicated that optimum FePc concentration in the dispersion solution is 7.5 g/L, and the amidoxime groups having great coordination ability significantly facilitate anchoring FePc onto the catalyst. FePc immobilization led to the catalyst with decreased crystallinity region and obvious absorption feature in the visible region. In addition, the catalyst was found to be an efficient catalyst for oxidation elimination of RhB by activating H₂O₂ under visible irradiation.

A discovery on the effect of tosyl group(s) number which acts as the initiator of dye degradation during the coagulation-flocculant process using laterite soil. In this study, acid orange 7, cibacron brilliant yellow 3G-P and reactive red 120 which contained one, three and six tosyl(s), respectively were selected. The optimum coagulant-flocculant dosage used to degrade each dyes are: 6000 mg/L for reactive red 120 with 99.53 % degradation rate; 8000 mg/L for cibacron brilliant yellow 3G-P with 99.46 % degradation rate; 10000 mg/L for acid orange 7 with 90.17 % degradation rate. Tosyl group(s) was able to enhance the performance of coagulation-flocculation process by laterite soil through substitution on the silica bonding. Ascertainment of the degradation was characterized by UV-Vis and FT-IR techniques. The product formed is nmethyldisilathiane which has the capability of forming larger and denser floc. Indirectly enhance the settling rate.