Search Results (201)

Persistent reactive azo dyes released from textile finishing are a serious threat to water systems, but effective methods using sunlight to break them down are still limited. Everzol Yellow 3RS (EY-3RS) is particularly recalcitrant: past studies have relied almost exclusively on physical adsorption onto natural or modified clays and zeolites, and no photocatalytic pathway employing engineered nanomaterials has been documented to date. This study reports the synthesis, characterization, and performance of a visible-active ternary nanocomposite, Cu₄O₃/ZrO₂/TiO₂, prepared hydrothermally alongside its binary (Cu₄O₃/ZrO₂) and rutile TiO₂ counterparts. XRD, FT-IR, SEM-EDX, UV-Vis, and PL analyses confirm a heterostructured architecture with a narrowed optical bandgap of 2.91 eV, efficient charge separation, and a mesoporous nanosphere-in-matrix morphology. Photocatalytic tests conducted under midsummer sunlight reveal that the ternary catalyst removes 91.41% of 40 ppm EY-3RS within 100 min, markedly surpassing the binary catalyst (86.65%) and TiO₂ (81.48%). Activity trends persist across a wide range of operational variables, including dye concentrations (20–100 ppm), catalyst dosages (10–40 mg), pH levels (3–11), and irradiation times (up to 100 min). The material retains ≈ 93% of its initial efficiency after four consecutive cycles, evidencing good reusability. This work introduces the first nanophotocatalytic strategy for EY-3RS degradation and underscores the promise of multi-oxide heterojunctions for solar-driven remediation of colored effluents. Full article

Water pollution caused by increasing industrial and human activity remains a serious environmental challenge, especially due to the persistence of organic contaminants in aquatic systems. Photocatalysis offers a promising and eco-friendly solution, but in the case of bismuth oxide (Bi₂O₃) there is still a limited understanding of how structural and morphological features influence photocatalytic performance. In this work, a straightforward hydrothermal synthesis method followed by controlled calcination was developed to produce phase-pure α- and β-Bi₂O₃ with tunable morphologies. By varying the hydrothermal temperature and reaction time, distinct structures were successfully obtained, including flower-like, broccoli-like, and fused morphologies. XRD analyses showed that the final crystal phase depends solely on the calcination temperature, with β-Bi₂O₃ forming at 350 °C and α-Bi₂O₃ at 500 °C. SEM and BET analyses confirmed that morphology and surface area are strongly influenced by the hydrothermal conditions, with the flower-like β-Bi₂O₃ exhibiting the highest surface area. UV–Vis spectroscopy revealed that β-Bi₂O₃ also has a lower bandgap than its α counterpart, making it more responsive to visible light. Photocatalytic tests using Rhodamine B showed that the flower-like β-Bi₂O₃ achieved the highest degradation efficiency (81% in 4 h). Kinetic analysis followed pseudo-first-order behavior, and radical scavenging experiments identified hydroxyl radicals, superoxide radicals, and holes as key active species. The catalyst also demonstrated excellent stability and reusability. Additionally, Methyl Orange (MO), a more stable and persistent azo dye, was selected as a second model pollutant. The flower-like β-Bi₂O₃ catalyst achieved 73% degradation of MO at pH = 7 and complete removal under acidic conditions (pH = 2) in less than 3 h. These findings underscore the importance of both phase and morphology in designing high-performance Bi₂O₃ photocatalysts for environmental remediation. Full article

Catalysts are ubiquitous in manufacturing industries and gas phase pollutant abatement but are not widely used in wastewater treatment, as high temperatures and concentrated waste streams are needed to achieve the reaction degradation rates required. Heating water is energy intensive, and alternative, low temperature solutions have been investigated, collectively known as advanced oxidation processes. However, many of these advanced oxidation processes use expensive oxidants such as perchlorate, hydroxy radicals or ozone to react with contaminants, and therefore have high running costs. This study has investigated microwave catalysis as a low-energy, low-cost technology for water treatment using NiO catalysts that can be heated in the microwave field to drive the decomposition of azo-dye contaminants. Using this methodology for the microwave-assisted degradation of two azo dyes (azorubine and methyl orange), conversions of >95% were achieved in only 10 s with 100 W microwave power. Full article

Ag/AgCl-decorated layered lanthanum oxide (La₂O₃) and niobium pentoxide (Nb₂O₅) plasmonic photocatalysts are fabricated through an ionic liquid-mediated co-precipitation method. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) techniques were used to illustrate the physicochemical properties of the materials. The photoactivity was evaluated for the degradation of Acid Blue 92 (AB92) azo dye, a typical organic contaminant from the textile industry, and U251 cancer cell inactivation. According to the results, Nb₂O₅–Ag/AgCl was able to remove >99% of AB92 solution in 35 min with the rate constant of 0.12 min⁻¹, 2.4 times higher than that of La₂O₃–Ag/AgCl. A pH of 3 and a catalyst dosage of 0.02 g were determined as the optimized factors to reach the highest degradation efficiency under solar energy at noon, which was opted to have the highest sunlight intensity over the reactor. Also, 0.02 mg/mL of Nb₂O₅–Ag/AgCl was determined to be of great potential to reduce cancer cell viability by more than 50%, revealed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and mitochondrial membrane potential (MMP) examinations. The mechanism of degradation was also discussed, considering the key role of Ag⁰ nanoparticles in inducing a plasmonic effect and improving the charge separation. This work provides helpful insights to opt for an efficient rare metal oxide with good biocompatibility as support for the plasmonic photocatalysts with the goal of environmental purification under sunlight. Full article

This review discusses natural and synthetic azo compounds found in bacteria, fungal endophytes, fungi, plants, and invertebrates. More than 100 of these compounds have demonstrated significant pharmacological activity, including antitumor, antimicrobial, and antibacterial effects. Using mathematical algorithms and the PASS program, researchers predict new potential applications based on their structure–activity relationships. This review emphasizes the importance of natural azo compounds as promising drug prototypes and key players in drug discovery. It also explores the synthesis and degradation of azo dyes and their potential uses in medicine, food, cosmetics, and related fields. Additionally, the role of microorganisms in producing natural azo compounds and their synthetic counterparts is examined, showcasing their potential in drug development and human health advancements. Full article

Nanoparticles (especially zinc and titanium oxide) have been found to be effective in photodegrading pollutants (organic/inorganic) from industrial wastewater. Presently, this study aimed at biosynthesizing zinc oxide nanoparticles (ZnO-NPs) from the leaf extract of Pavonia zeylanica, a plant with significant medical value, and evaluating their photocatalytic properties against methylene blue (MB), an azo dye (100 mg L⁻¹, pH 7), using solar irradiation, along with the measurement of their reusability and mineralization efficiency. The characterization of the Pz-ZnO-NPs showed an absorbance peak at 313 nm, with a bandgap value of 3.04 eV and a size of 19.58 nm. This study’s results show that the synthesized Pz-ZnO-NPs, upon treatment with MB dye after 2 h of solar irradiation, showed an 89.32% degradation, which was concentration-dependent and followed pseudo-first-order kinetics. The reusability studies indicated that the Pz-ZnO-NPs were able to degrade MB dye after five repeated cycles of its usage. The structural composition of the Pz-ZnO-NPs evaluated by XRD showed that the peak position stayed constant. Nevertheless, the peak intensity dropped, indicating that the ZnO-NPs’ crystal structure was unaffected. Furthermore, advanced oxidation process studies, which included an evaluation of COD and TOC, revealed that both the contents decreased significantly during the photocatalysis process, wherein the electron-rich organic dyes were converted to nontoxic products through mineralization. Full article

This study explores the efficiency of heterogeneous photocatalysis in wastewater treatment, which is recognized for inducing significant rates of degradation and mineralization of various contaminants, including dyes. The study focuses on the development of an innovative composite via a combination of the sillenite type semiconductor Bi₁₂ZnO₂₀ and the halide-type semiconductor AgI. Both semiconductors were synthesized via co-precipitation, and their phases were identified using X-ray diffraction and characterized by scanning electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller analysis for specific surface area, UV–Visible diffuse reflectance spectroscopy, and the point of zero charge. The evaluation of the photocatalytic activity of the Bi₁₂ZnO₂₀/AgI heterosystem was carried out by monitoring the degradation process of Basic Blue 41 (BB41) under solar irradiation conditions. The results of this study revealed that the Bi₁₂ZnO₂₀/AgI heterosystem achieved the efficient degradation of BB41, with a removal rate of 98% after 150 min of treatment. The mineralization study showed that the TOC value decreased from 19.89 mg L⁻¹ to 6.87 mg L⁻¹, indicating that a significant portion of BB41 was mineralized. Via kinetic research, it was established that the degradation process followed a pseudo-first-order mechanism. Furthermore, recycling tests showed that the synthesized heterostructures maintained good structural stability and acceptable reusability over several cycles. These findings highlight the potential of heterogeneous photocatalysis as a promising approach to addressing environmental challenges associated with azo dyes. Full article

Herein, flower-like Zn₃In₂S₆ (ZIS₃) crystallites were grown onto acorn leaf-like CdS assemblies via a two-step hydrothermal approach. Under visible light irradiation, the Zn₃In₂S₆-enriched heterostructures demonstrated an enhanced azo-dye degradation rate, with the majority of the organic analyte (Orange G) being degraded within 60 min. In contrast, the CdS-enriched hybrids showed poor photocatalytic performance. The optimized hybrid containing a nominal CdS content of 4 wt% was characterized by various physicochemical techniques, such as XRD, SEM, XPS and Raman. XPS analysis showed that the electron density around the Zn and In sites in Zn₃In₂S₆ was slightly increased, implying a certain charge migration pattern. Complementary information from scavenging experiments suggested that hydroxy radicals were not the exclusive transient responsible for oxidative degradation of the organic azo-dye. This research provides new information about the development of metal chalcogenide-based heterostructures for efficient photocatalytic organic pollutant degradation. Full article

To fabricate recyclable catalytic materials with high catalytic activity, Se⁴⁺@TiO₂ photocatalytic materials were synthesized by the sol–gel method. By introducing free radicals on the surface of polyester (PET) fabrics through plasma technology, Se⁴⁺@TiO₂/PET composite photocatalytic materials with high photocatalytic activity were prepared. The surface morphology, crystal structure, chemical composition, and photocatalytic performance were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible absorption spectroscopy (UV–Vis), and photoluminescence spectroscopy (PL), respectively. The photocatalytic degradation performance was determined by assessing the degradation of azo dye methyl orange under simulated solar irradiation. The results demonstrated that Se⁴⁺@TiO₂/PET exhibited a superior degradation rate of methyl orange, reaching up to 81% under simulated sunlight. The PL spectra indicated that the electron–hole pair separation rate of Se⁴⁺@TiO₂/PET was higher than that of TiO₂/PET. Furthermore, UV–Vis spectroscopy demonstrated that the relative forbidden band gap of Se⁴⁺@TiO₂/PET was determined to be 2.9 eV. The band gap of Se⁴⁺@TiO₂/PET was narrower, and the absorption threshold shifted toward the visible region, indicating a possible increase in its catalytic activity in simulated solar irradiation. In addition, the antibacterial properties of Se⁴⁺@TiO₂/PET were subsequently investigated, achieving 99.99% and 98.47% inhibition against S. aureus and E. coli, respectively. Full article

Textile dyes pose a major environmental threat due to their toxicity, persistence in water bodies, and resistance to conventional wastewater treatment. To address this, researchers have explored biological and physicochemical degradation methods, focusing on microbial, photolytic, and nanoparticle-mediated approaches, among others. Microbial degradation depends on fungi, bacteria, yeasts, and algae, utilizing enzymatic pathways involving oxidoreductases like laccases, peroxidases, and azoreductases to breakdown or modify complex dye molecules. Photolytic degradation employs hydroxyl radical generation and electron-hole pair formation, while nanoparticle-mediated degradation utilizes titanium dioxide (TiO₂), zinc oxide (ZnO), and silver (Ag) nanoparticles to enhance dye removal. To improve efficiency, microbial consortia have been developed to enhance decolorization and mineralization, offering a cost-effective and eco-friendly alternative to physicochemical methods. Photocatalytic degradation, particularly using TiO₂, harnesses light energy for dye breakdown. Research advancements focus on shifting TiO₂ activation from UV to visible light through doping and composite materials, while optimizing surface area and mesoporosity for better adsorption. Nanoparticle-mediated approaches benefit from a high surface area and rapid adsorption, with ongoing improvements in synthesis, functionalization, and reusability, particularly through magnetic nanoparticle integration. These emerging technologies provide sustainable solutions for dye degradation. The primary aim of this review is to comprehensively evaluate and synthesize current research and advancements in the degradation of azo dyes through microbial methods, photolytic processes, and nanotechnology-based approaches. The review also provides detailed information on salient mechanistic aspects of these methods, efficiencies, advantages, challenges, and potential applications in industrial and environmental contexts. Full article

Based on the magnetic sensitivity of Fe₃O₄ in various fields, we aimed to propose a one-step solvothermal process for the synthesis of single-phase Fe₃O₄ induced by the reaction medium and urea, avoiding high-temperature reduction in H₂ or N₂ atmospheres. Feasibility was tested with purified water (H₂O), methyl alcohol (MA), ethyl alcohol (EA), and ethylene glycol (EG) as reaction media. The findings indicated that the solvothermal reaction system utilizing EA was more effective for the synthesis of cubic magnetic Fe₃O₄. Optimal conditions for synthesizing pure Fe₃O₄ were obtained by optimizing the urea amount and solvothermal reaction parameters. The optimal formulation consisted of 10 mmol of FeCl₃, 80 mmol of urea, and 60 mL of EA subjected to a solvothermal process at 200 °C for 12 h. The resulting Fe₃O₄ (magnetite, cubic) exhibited commendable crystallization with a morphology of acicular aggregates and displayed excellent magnetic sensitivity properties with a magnetization of 92.2 emu/g at 15,000 Oe. The photocatalytic degradation behaviors of the resulting Fe₃O₄ to Methyl Orange, Orange G, and Acid Red 37 azo dyes and the repeated degradation performance of Methyl Orange dye were investigated. Nearly complete degradation of Methyl Orange dye occurred after 2.0 h of photocatalytic reaction, while Orange G and Acid Red 37 dyes achieved similar results after 3.5 and 4.5 h, respectively. The exploration strategy in this work for synthesizing magnetic Fe₃O₄ can be applied to design and fabricate other metal oxides or composites, potentially resulting in novel discoveries in morphology or performance. Full article

This study presents the development and application of a batch-type photoelectrochemical reactor employing advanced oxidation processes (AOPs) with in situ generated TiO₂ particles for the efficient degradation of azo dyes. The reactor uses titanium sheets as electrodes, facilitating the electrochemical generation of TiO₂, which acts as a photocatalyst under UV light. This study specifically targets azo dyes frequently encountered in industrial wastewater, focusing on Brilliant Blue, Erythrosine, and Tartrazine, which together form the Navy Blue dye composition. The experimental methodology replicates real-world conditions, ensuring the results are representative of practical scenarios. Key findings demonstrate that the in situ production of TiO₂ enables effective heterogeneous photocatalysis, achieving significant dye degradation rates. This research highlights the novelty of combining in situ TiO₂ generation with a batch-type reactor, offering advantages in cost-effectiveness, scalability, and environmental impact. Comparative analysis with existing methods underscores the reactor’s potential for industrial applications, particularly in wastewater treatment. Furthermore, this study outlines the mechanistic insights into dye degradation and provides a foundation for optimizing photocatalytic processes to address environmental challenges. Full article

Declining natural resources make the recovery of metals from waste solutions a promising alternative. Moreover, processing waste into a finished product has its economic justification and benefits. Thus, the aim of this research was developing a Waste for Product strategy, indicating the possibility of processing solutions with a low content of platinum-group metals for catalyst synthesis. The results obtained confirmed that diluted synthetic waste solutions containing trace amount of valuable metal ions (Pd, Pt) can be used for the process of catalyst synthesis. Catalysts produced in the form of palladium and platinum nanoparticles were successfully deposited on a Ni foam due to the galvanic displacement mechanism. Synthesized catalysts were characterized using UV-Vis spectrophotometry, SEM/EDS, and XRD techniques. Electro- and catalytic properties were tested for hydrogen/oxygen evolution reactions and methyl orange degradation, respectively. The results obtained from electrocatalytic tests indicated that the modification of the nickel foam surface by waste solutions consisting of noble metals ions as Pd and Pt can significantly increase the activity in hydrogen and oxygen evolution reactions in comparison to non-treated samples. Catalytic tests performed for the process of methyl orange degradation shorten the time of the process from several hours to 15 min. The most favorable results were obtained for the catalysts in the following order Pd1.0Pt0@Ni > Pd0Pt1.0@Ni > Pd0.5Pt0.5@Ni > Ni foam > no catalyst, indicating the best catalytic performance for catalyst containing pure palladium nanoparticles deposited on the nickel surface. Full article

Bentonite-supported TiO₂ (Montmorillonite (MMT)-TiO₂) and Cu₃TiO₅ oxides (MMT-Cu₃TiO₅) nanomaterials were synthesized via a facile and sustainable sol–gel synthesis approach. The XRD results indicate the presence of mixed phases, namely, TiO₂ anatase and a new semiconductor, Cu₃TiO₅, in the material. The specific surface area (S_BET) exhibits a notable increase with the incorporation of TiO₂ and Cu₃TiO₅, rising from 85 m²/g for pure montmorillonite to 245 m²/g for MMT-TiO₂ and 279 m²/g for MMT-Cu₃TiO₅. The lower gap energy of MMT-Cu₃TiO₅ (2.15 eV) in comparison to MMT-TiO₂ (2.7 eV) indicates that MMT-Cu₃TiO₅ is capable of more efficient absorption of visible light with longer wavelengths. The immobilization of TiO₂ and Cu₃TiO₅ on bentonite not only enhances the textural properties of the samples but also augments their visible light absorption capabilities, rendering them potentially more efficacious for adsorption and photocatalytic applications. The photocatalytic efficacy of both MMT-TiO₂ and MMT-Cu₃TiO₅ was evaluated through the monitoring of the degradation of Orange G, an anionic azo dye. The MMT-Cu₃TiO₅ photocatalyst was observed to induce complete degradation (100%) of the Orange G dye in 120 min when tested in an optimized reaction medium with a pH of 3 and a catalyst concentration of 2 g/L. MMT-Cu₃TiO₅ was demonstrated to be an exceptionally effective catalyst for the degradation of Orange G. Following the synthesis of the catalyst, it can be simply washed with the same recovered solution and reused multiple times for the photocatalytic process without the need for any chemical additives. Full article

Congo Red is a complex aromatic azo dye whose metabolites can be toxic due to their carcinogenicity, mutagenicity, and various associated toxic effects on flora, fauna, and humans. Different technologies have been employed to degrade this dye, including biodegradation, radiation-based degradation, and chemical degradation with catalysts and photocatalysis. Among these, the use of TiO₂-based materials combined with photocatalysis has proven to be an effective technology for its degradation. However, the wide bandgap of TiO₂ limits its efficiency under visible light, prompting the need for modifications such as doping with metals, metalloids, and organic compounds. These modifications enhance its photocatalytic performance under visible light, achieving degradation efficiencies of up to 100% under optimal conditions. This article explores recent advances (from 2020 to the present) in the degradation of Congo Red using TiO₂-based photocatalysts under visible light, focusing on their characteristics, synthesis methods, and degradation efficiencies. Additionally, it compares the TiO₂-based photocatalysis with visible light to other available technologies, emphasizing its potential as a sustainable and efficient approach while addressing the importance of monitoring degradation byproducts to prevent the generation of equally or more toxic compounds. Full article