Search Results (43)

We investigated a novel natural dye-sensitized solar cell (DSSC) utilizing gadolinium ruthenate pyrochlore oxide Gd₂Ru₂O₇ (GRO) as a photoanode and compared its performance to the TiO₂-Gd₂Ru₂O₇ (TGRO) combined-layer configuration. The films were fabricated using the spin-coating technique, resulting in spherical grains with an estimated mean diameter of 0.2 µm, as observed via scanning electron microscopy (SEM). This innovative photoactive gadolinium ruthenate pyrochlore oxide demonstrated strong absorption in the visible range and excellent dye adhesion after just one hour of exposure to natural dye. X-ray diffraction confirmed the presence of the pyrochlore phase, where Raman spectroscopy identified various vibration modes characteristic of the pyrochlore structure. Incorporating Gd₂Ru₂O₇ as the photoanode significantly enhanced the overall efficiency of the DSSCs. The device configuration FTO/compact-layer/Gd₂Ru₂O₇/Hibiscus-sabdariffa/electrolyte(I⁻/I₃⁻)/Pt achieved a high efficiency of 9.65%, an open-circuit voltage (Voc) of approximately 3.82 V, and a current density of 4.35 mA/cm² for an active surface area of 0.38 cm². A mesoporous TiO₂-based DSSC was fabricated under the same conditions for comparison. Using impedance spectroscopy and cyclic voltammetry measurements, we provided evidence of the mechanism of conductivity and the charge carrier’s contribution or defect contributions in the DSSC cells to explain the obtained Voc value. Through cyclic voltammetry measurements, we highlight the redox activities of hibiscus dye and electrolyte (I⁻/I₃⁻), which confirmed electrochemical processes in addition to a photovoltaic response. The high and unusual obtained Voc value was also attributed to the presence in the photoanode of active dipoles, the layer thickness, dye concentration, and the nature of the electrolyte. Full article

Water pollution by dyes is a major environmental problem, particularly in the textile, food, and pharmaceutical industries. These dyes are often complex chemical compounds that are difficult to remediate due to their chemical stability, their solubility in water, and their resistance to conventional treatment processes such as filtration, coagulation, or decantation. Thus, to date, there is still a need to make water treatment processes more performant and cost-efficient. The main aim of this research is to prepare photocatalytically active MFI-type zeolites from natural clays and support iron oxide nanoparticles. These catalysts were characterized and evaluated for the capture and the photo-Fenton degradation of methylene blue (MB) in aqueous solution. After 10 min under photo-Fenton conditions, Fe/MTK-MFI presented almost complete removal of MB for up to four consecutive cycles. Full article

The purpose of this work is to establish the influence of the nature of solid alginate gels (alginic acid, AAG; calcium alginate, CAG) and the conditions of methylene blue (MB) introduction to alginate matrices upon its release into aqueous media. MB is an active photosensitizer, which is used in the photodynamic therapy of tumors and purulent wounds. Solid alginate gels based on AAG and CAG were obtained by adding hydrochloric acid and calcium chloride to sodium alginate. The dye was introduced into the matrix either at the stage of gelation or by immersing the gel in an aqueous solution of the dye. It has been shown that the strength of the dye’s attachment to AAG is higher than that of CAG, which leads to a higher rate of MB release from CAG into aqueous media. It has also been shown that, when introduced at the stage of gel formation, MB is released into both the water and buffer solutions. When MB is introduced by gel immersion into an MB solution, the dye may be released only into salt solutions. An alginate gel with immobilized MB can be used as a solid photosensitizing system with the controlled release of the photoactive agent into the wound cavity for photodynamic treatment. Full article

Utilizing green nanomaterials in a biomimetic setting to treat wastewater emulates the sustainability and efficiency of natural systems. In this study, wood apple (WA) outer shell extract was used as a reducing and stabilizing agent in a simple, inexpensive, and environmentally friendly green approach to synthesize Ag nanoparticles (NPs), ZnO NPs, and Ag@ZnO nanocomposites (NCs) as potential photocatalysts for the degradation of an industrial dye known as Brilliant Blue (BB). Synthesis parameters of Ag NPs, ZnO NPs, and Ag@ZnO NCs were evaluated in this research utilizing various analytical methods. Surface plasmon resonance peaks for Ag NPs, ZnO NPs, and Ag@ZnO NCs were observed at 400–470 nm, 320–370 nm, and 400–500 nm, respectively. The appearance of a Fourier transform infrared band in the 500–700 cm⁻¹ region is attributed to the Zn-O bond stretching mode, indicating the formation of ZnO NPs and Ag@ZnO NCs. The SEM images of WA-mediated Ag NPs, ZnO NPs, and Ag@ZnO NCs illustrate spherical, flake, and flower-shapes, respectively, while the average sizes of these three types of particles are determined to be 15.04 ± 5.40 nm, 82.40 ± 3.24 nm, and 12.08 ± 2.91 nm, respectively, as per transmission electron microscopic investigation. Moreover, X-ray diffraction patterns confirm the synthesis of pure crystalline structures, with a face-centered cubic structure for Ag and a hexagonal wurtzite structure for ZnO NPs during the synthesis of Ag@ZnO NCs. The biogenic WA-mediated ZnO NPs show a remarkable photodegradation efficiency of 65.8% under the optimum conditions of catalytic load, pH, and dye concentration, whereas WA-mediated Ag NPs and Ag@ZnO NC show 13.9% and 63.7% photodegradation efficiency, respectively, at 240 min. The study reveals that WA-mediated ZnO NPs and Ag@ZnO NCs exhibit nearly identical photo-catalytic activity against the BB dye, presenting new opportunities for sustainable use in textile and wastewater treatment. Full article

Photoactive artificial nanocatalysts that mimic natural photoenergy systems can yield clean and renewable energy. However, their poor photoabsorption capability and disfavored photogenic electron–hole recombination hinder their production. Herein, we designed two nanocatalysts with various microstructures by combining the tailored self-assembly of the meso-tetra(p-hydroxyphenyl) porphine photosensitizer with the growth of titanium dioxide (TiO₂). The porphyrin photoabsorption antenna efficiently extended the absorption range of TiO₂ in the visible region, while anatase TiO₂ promoted the efficient electron–hole separation of porphyrin. The photo-induced electrons were transferred to the surface of the Pt co-catalyst for the generation of hydrogen via water splitting, and the hole was utilized for the decomposition of methyl orange dye. The hybrid structure showed greatly increased photocatalytic performance compared to the core@shell structure due to massive active sites and increased photo-generated electron output. This controlled assembly regulation provides a new approach for the fabrication of advanced, structure-dependent photocatalysts. Full article

Titania nanoparticles (NPs) find wide application in photocatalysis, photovoltaics, gas sensing, lithium batteries, etc. One of the most important synthetic challenges is maintaining control over the polymorph composition of the prepared nanomaterial. In the present work, TiO₂ NPs corresponding to anatase, rutile, or an anatase/rutile/brookite mixture were obtained at 80 °C by an inverse microemulsion method in a ternary system of water/cetyltrimethylammonium bromide/1-hexanol in a weight ratio of 17:28:55. The only synthesis variables were the preparation of the aqueous component and the nature of the Ti precursor (Ti(IV) ethoxide, isopropoxide, butoxide, or chloride). The materials were characterized with X-ray diffraction, scanning/transmission electron microscopy, N₂ adsorption–desorption isotherms, FTIR and Raman vibrational spectroscopies, and diffuse reflectance spectroscopy. The synthesis products differed significantly not only in phase composition, but also in crystallinity, textural properties, and adsorption properties towards water. All TiO₂ NPs were active in the photocatalytic decomposition of rhodamine B, a model dye pollutant of wastewater streams. The mixed-phase anatase/rutile/brookite nanopowders obtained from alkoxy precursors showed the best photocatalytic performance, comparable to or better than the P25 reference. The exceptionally high photoactivity was attributed to the advantageous electronic effects known to accompany multiphase titania composition, namely high specific surface area and strong surface hydration. Among the single-phase materials, anatase samples showed better photoactivity than rutile ones, and this effect was associated, primarily, with the much higher specific surface area of anatase photocatalysts. Full article

Psittacofulvins are polyenal dyes responsible for coloring parrot feathers and protecting them against photo-oxidation, harmful radicals, and bacterial degradation. To explain the unusual properties of these compounds, the thermodynamic and global chemical activity descriptors characterizing four natural and three synthetic psittacofulvins, as well as their hydroxyl, carboxyl and dialdehyde derivatives, were determined. To this aim, the DFT method at the B3LYP/QZVP theory level and the C-PCM solvation model were used. The calculations enabled the selection of the projected compounds for the greatest bioactivity and potential applicability as multifunctional ingredients in medicines, cosmetics, supplements, and food, in which they may play a triple role as preservative, radical scavenger, and coloring agent. The results obtained provide arguments for the identification of a fifth psittacofulvin within the parrot feather pigment, characterized by ten conjugated double bonds (docosadecaenal). Full article

The application of nano-TiO₂ as a photocatalytic agent in buildings’ internal surfaces has recently attracted attention to mitigate microorganism growth, soiling, and contamination in indoor environments. This work aimed at comparing the Rhodamine B (RhB) dye degradation efficiency of three different mortar compositions subjected to simulated internal radiation, in which nano-TiO₂ (10 wt% of binder mass) was dispersed by ultrasonic and mechanical methods. Mortar specimens were produced with white Portland cement, hydrated lime, sand, and water in different volume proportions of 1:1:6 (cement:lime:sand), 1:3 (cement:sand), and 1:4 (cement:sand). The first stage of the research evaluated samples exposed to the natural outdoor environment and proved the efficiency of specimens’ photoactivity when covered by a glass layer. The second and principal phase of the study simulated indoor conditions in glazed buildings through artificial weathering in which the composition of 1:1:6 was mechanically dispersed and exhibited the highest global color change (ΔE) values for RhB staining. The main finding of the study was that the mortars exposed to simulated indoor conditions presented high ΔE grades, classified as easily perceived by the human eye. This demonstrates the photocatalytic efficiency in an internal building environment that receives radiation through a glass surface. Full article

In recent years, sewage treatment plants did not effectively remove emerging water pollutants, leaving potential threats to human health and the environment. Advanced oxidation processes (AOPs) have emerged as a promising technology for the treatment of contaminated wastewater, and the addition of catalysts such as heavy metals has been shown to enhance their effectiveness. This review focuses on the use of rare earth elements (REEs) as catalysts in the AOP process for the degradation of organic pollutants. Cerium and La are the most studied REEs, and their mechanism of action is based on the oxygen vacancies and REE ion concentration in the catalysts. Metal oxide surfaces improve the decomposition of hydrogen peroxide to form hydroxide species, which degrade the organics. The review discusses the targets of AOPs, including pharmaceuticals, dyes, and other molecules such as alkaloids, herbicides, and phenols. The current state-of-the-art advances of REEs-based AOPs, including Fenton-like oxidation and photocatalytic oxidation, are also discussed, with an emphasis on their catalytic performance and mechanism. Additionally, factors affecting water chemistry, such as pH, temperature, dissolved oxygen, inorganic species, and natural organic matter, are analyzed. REEs have great potential for enhancing the removal of dangerous organics from aqueous solutions, and further research is needed to explore the photoFenton-like activity of REEs and their ideal implementation for wastewater treatment. Full article

The ever-increasing technological advancement and industrialization are leading to a massive discharge of hazardous waste into the aquatic environment, calling on scientists and researchers to introduce environmentally benign solutions. In this regard, the current work is based on introducing Fuller’s earth, which is regarded as an environmentally benign material, as an innovative Fenton oxidation technology to treat effluent loaded with Levafix Dark Blue dye. Initially, Fuller’s earth was chemically and thermally activated, then subjected to characterization using a field-emission scanning electron microscope (FE-SEM) augmented with an energy-dispersive X-ray analyzer (EDX) and Fourier transform infrared (FTIR). This detailed the morphologies of the samples and the functional groups on the catalyst leading to the reaction with the dye. Fuller’s earth, augmented with hydrogen peroxide, was then introduced as a photo-Fenton oxidation system under UV illumination for dye oxidation. Moreover, a response surface mythological analysis was applied to optimize the most effective operational parameters. The experimental data revealed that the optimal Fuller’s earth dose corresponded to 1.02 mg/L using the optimal H₂O₂ of 818 mg/L at pH 3.0, and the removal efficiency reached 99%. Moreover, the thermodynamic parameters were investigated, and the data revealed the positive ∆G′ and negative ∆S′ values that reflect the non-spontaneous nature of oxidation at high temperatures. Additionally, the negative ∆H′ values suggest the occurrence of the endothermic oxidation reaction. Furthermore, the reaction followed the second-order kinetic model. Finally, the catalyst stability was investigated, and reasonable removal efficiency was attained (73%) after the successive use of Fuller’s earth reached six cyclic uses. Full article

ZnO and TiO₂ are both well-known electron transport materials; however, an exact comparison of their performance, when fabricated under the same synthesis conditions, is missing in the literature. Considering this, we introduced a viable electrospinning route for the development of highly polycrystalline TiO₂ and ZnO nanofibers for an electron transport material (ETM) of perovskite solar cells and photocatalysts for textiles. Thanks to the effective tuning of band structure and morphology of TiO₂, a significant improvement in performance as compared to ZnO was observed when both were used as photoanodes and photocatalysts. X-ray diffraction detected polycrystalline structural properties and showed that peaks are highly corresponding to TiO₂ and ZnO. Morphological analysis was carried out with a scanning electron microscope, which revealed that nanofibers are long, uniform, and polycrystalline, having diameter in the nano regime. TiO₂ nanofibers are more aligned and electron-supportive for conduction as compared to ZnO nanofibers, which are dense and agglomerated at some points. Optoelectronic properties showed that TiO₂ and ZnO show absorption values in the range of ultraviolet, and visible range and band gap values for TiO₂ and ZnO were 3.3 and 3.2 eV, respectively. The TiO₂ band gap and semiconductor nature was more compatible for ETL as compared to ZnO. Electrical studies revealed that TiO₂ nanofibers have enhanced values of conductivity and sheet carrier mobility as compared to ZnO nanofibers. Therefore, a higher photovoltaic conversion efficiency and antibacterial activity was achieved for TiO₂ nanofibers (10.33%), as compared to ZnO (8.48%). In addition, the antibacterial activity of TiO₂ was also recorded as better than ZnO. Similarly, compared to ZnO nanofibers, TiO₂ nanofibers possess enhanced photoactivity for antimicrobial and dye degradation effects when applied to fabrics. Full article

While various methods exist for synthesizing silver nanoparticles (AgNPs), green synthesis has emerged as a promising approach due to its affordability, sustainability, and suitability for biomedical purposes. However, green synthesis is time-consuming, necessitating the development of efficient and cost-effective techniques to minimize reaction time. Consequently, researchers have turned their attention to photo-driven processes. In this study, we present the photoinduced bioreduction of silver nitrate (AgNO₃) to AgNPs using an aqueous extract of Ulva lactuca, an edible green seaweed. The phytochemicals found in the seaweed functioned as both reducing and capping agents, while light served as a catalyst for biosynthesis. We explored the effects of different light intensities and wavelengths, the initial pH of the reaction mixture, and the exposure time on the biosynthesis of AgNPs. Confirmation of AgNP formation was achieved through the observation of a surface plasmon resonance band at 428 nm using an ultraviolet-visible (UV-vis) spectrophotometer. Fourier transform infrared spectroscopy (FTIR) revealed the presence of algae-derived phytochemicals bound to the outer surface of the synthesized AgNPs. Additionally, high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) images demonstrated that the NPs possessed a nearly spherical shape, ranging in size from 5 nm to 40 nm. The crystalline nature of the NPs was confirmed by selected area electron diffraction (SAED) and X-ray diffraction (XRD), with Bragg’s diffraction pattern revealing peaks at 2θ = 38°, 44°, 64°, and 77°, corresponding to the planes of silver 111, 200, 220, and 311 in the face-centered cubic crystal lattice of metallic silver. Energy-dispersive X-ray spectroscopy (EDX) results exhibited a prominent peak at 3 keV, indicating an Ag elemental configuration. The highly negative zeta potential values provided further confirmation of the stability of AgNPs. Moreover, the reduction kinetics observed via UV-vis spectrophotometry demonstrated superior photocatalytic activity in the degradation of hazardous pollutant dyes, such as rhodamine B, methylene orange, Congo red, acridine orange, and Coomassie brilliant blue G-250. Consequently, our biosynthesized AgNPs hold great potential for various biomedical redox reaction applications. Full article

Commonly used peroxydisulfate (PS) or peroxymonosulfate (PMS) activation methods have been limited in their practical application due to certain drawbacks, such as high cost, high energy consumption and secondary pollution. In this study, a catalyst-free alizarin green (AG) self-activating PMS catalytic system was constructed based on photosensitization properties of dye, which ultimately achieved efficient degradation of the dye activator, also the target pollutant. Here, 52.5% of the 100 mL mixture of 10 mg/L AG decomposed within 60 min with 1 mM PMS under visible-light irradiation, thereby showing a strong pH adaptation. Mechanism of AG self-activating PMS was revealed that the photo-excited AG can effectively transfer photo-induced electrons to PMS for its activation, which generates reactive oxidizing species dominated by singlet oxygen (¹O₂), and supplemented by hydroxyl radical (•OH), superoxide radical (O₂^•−) and sulfate radical (SO₄^•−) to realize the efficient self-degradation of the dye pollutants. Moreover, such self-catalytic system operated well under natural sunlight irradiation, indicating the great application potential in the actual wastewater treatment. Herein, photosensitive dye acted as an ideal PMS activator realizing its efficient self-degradation, which provides a novel idea of “using waste to treat waste” for developing wastewater treatment process in a high-efficiency and low-consumption way. Full article

Azo dyes are synthetic organic dyes used in the textile, leather, and paper industries. They pose environmental problems due to their toxic and persistent nature. The toxicity is due to the presence of azo groups in the dye molecule that can break down into aromatic amines, which are highly toxic to aquatic organisms and humans. Various treatment methods have been developed to remove azo dyes from wastewater. Conventional wastewater treatments have some drawbacks, such as high operating costs, long processing times, generation of sludge, and the formation of toxic by-products. For these reasons, a valid alternative is constituted by advanced oxidation processes. Good results have been obtained using heterogeneous photocatalysis and supercritical water oxidation. In the former method, a photocatalyst is in contact with wastewater, a suitable light activates the catalyst, and generated reactive oxygen species that react with pollutants through oxidative reactions to their complete mineralization; the latter involves pressurizing and heating wastewater to supercritical conditions in a reactor vessel, adding an oxidizing agent to the supercritical water, and allowing the mixture to react. In this review paper, works in the literature that deal with processing wastewater containing azo dyes through photocatalysts immobilized on macroscopic supports (structured photocatalysts) and the supercritical water oxidation technique have been critically analyzed. In particular, advancement in the formulation of structured photocatalysts for the degradation of azo dyes has been shown, underlying different important features, such as the type of support for the photoactive phase, reactor configuration, and photocatalytic efficiency in terms of dye degradation and photocatalyst stability. In the case of supercritical water oxidation, the main results regarding COD and TOC removal from wastewater containing azo dyes have been reported, taking into account the reactor type, operating pressure, and temperature, as well as the reaction time. Full article

This work reports the fabrication of titanium dioxide (TiO₂) nanoparticle (NPs) films using a scalable drop-casting method followed by ultra-violet (UV) irradiation for creating defective oxygen vacancies on the surface of a fabricated TiO₂ semiconductor film using an UV lamp with a wavelength oof 255 nm for 3 h. The success of the use of the proposed scalable strategy to fabricate oxygen-vacancy-rich TiO₂ films was assessed through UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Ti 2p XPS spectra acquired from the UV-treated sample showed the presence of additional Ti³⁺ ions compared with the untreated sample, which contained only Ti⁴⁺ ions. The band gap of the untreated TiO₂ film was reduced from 3.2 to 2.95 eV after UV exposure due to the created oxygen vacancies, as evident from the presence of Ti³⁺ ions. Radiation exposure has no significant influence on sample morphology and peak pattern, as revealed by the SEM and XRD analyses, respectively. Furthermore, the photocatalytic activity of the fabricated TiO₂ films for methylene-blue-dye removal was found to be 99% for the UV-treated TiO₂ films and compared with untreated TiO₂ film, which demonstrated only 77% at the same operating conditions under natural-sunlight irradiation. The proposed UV-radiation method of oxygen vacancy has the potential to promote the wider application of photo-catalytic TiO₂ semiconductor films under visible-light irradiation for solving many environmental and energy-crisis challenges for many industrial and technological applications. Full article