Search Results (19)

This study explores the photocatalytic efficiency of Zn/Fe/TiO₂ catalysts, synthesized via the wet impregnation method, for degrading the food colorings Allura Red and Tartrazine Yellow. A 2² factorial design with a central point replication guided the catalyst synthesis. Characterization involved BET surface area analysis, SEM-EDX, XRD, and PZC determination. Photocatalytic tests were conducted in batch mode under natural sunlight with 10 mg L⁻¹ food coloring solutions. Kinetic modeling and statistical analysis were performed, and catalyst reuse was evaluated under artificial light. Results showed that low calcination temperatures (200–273 °C) and Zn loadings of 2–10% led to nearly 99% discoloration and degradation efficiency. The Behnajady–Modirshahla–Ghanbery kinetic model best described the discoloration data, confirming the significant impact of both variables. The optimal catalyst for Allura Red degradation was 2%Zn/2%Fe/TiO₂ calcined at 200 °C, while for Tartrazine Yellow, 6%Zn/2%Fe/TiO₂ calcined at 300 °C was most effective. Both catalysts exhibited excellent stability, maintaining efficiency over four reuse cycles. These findings demonstrate the potential of Zn/Fe/TiO₂ catalysts for sustainable wastewater treatment. Full article

To address the protective demands of marine engineering equipment in complex corrosive environments, this study proposes an environmentally friendly composite coating based on carboxylated graphene oxide (CGO)-modified water-based epoxy organosilicon resin. By incorporating varying mass fractions (0.05–0.25%) of CGO into the resin matrix via mechanical blending, the microstructure, corrosion resistance, and long-term corrosion kinetics of the coatings were systematically investigated. The results demonstrate that the coating with 0.15 wt.% CGO (designated as KCG15) exhibited optimal comprehensive performance: its corrosion current density (I_corr = 4.37 × 10⁻⁸ A/cm²) was two orders of magnitude lower than that of the pure resin coating, while its low-frequency impedance modulus (∣Z∣_0.1Hz = 4.99 × 10⁶ Ω⋅cm²) is significantly enhanced, accompanied by improved surface compactness. The coating achieved a 97% inhibition rate against sulfate-reducing bacteria (SRB) through synergistic physical disruption and electrostatic repulsion mechanisms. Long-term corrosion kinetics analysis via 60-day seawater immersion identified three degradation phases—permeation (0–1 day), blockage (1–4 days), and failure (7–60 days)—with structural evolution from microcrack networks to foam-like blistering ultimately reducing by 97.8%. Furthermore, a 180-day atmospheric exposure test confirms the superior weatherability and adhesion of the KCG15 coating, with only minor discoloration observed due to its hydrophobic surface. This work provides theoretical and technical foundations for developing marine anti-corrosion coatings that synergize environmental sustainability with long-term protective performance. Full article

The suitability of steel shavings (SS) as a low-cost waste catalyst in catalytic ozonation and the heterogeneous Fenton process was evaluated. Three dyes were selected for the research: Indigo Carmine, Tartrazine, and Allura Red AC. Single processes (oxidation by H₂O₂, O₃, and heterogeneous Fenton process) and hybrid processes (O₃ + Fenton) were applied. The Fenton process had the highest efficiency at pH = 3 and with the highest dose of catalyst (5 mg of SS) and hydrogen peroxide (30 µL). More than 98% discoloration of the solution was observed in 10 min. Analyzing ozone-based processes, they can be ranked with the highest efficiency as follows: (O₃ + H₂O₂ + SS) > (O₃ + H₂O₂) > O₃ > (O₃ + SS). The combination of the Fenton process (5 mg of SS + 15 µL of H₂O₂) with ozonation accelerated the reaction rate in the case of Indigo Carmine. In the hybrid process, only 5 min were enough for complete decolorization, while more than 98% in the Fenton process was reached after 30 min. Kinetic studies revealed that the degradation of dyes in an aqueous solution through advanced oxidation processes followed first- and second-order reaction kinetics. The calculation of the energy requirement confirmed that the most economic process for removing Indigo Carmine was the O₃+Fenton process (SS dose = 5 mg, H₂O₂ dose = 15 µL, pH = 3). Full article

Thin films (TFs) of TiO₂ and ZrO₂ were prepared and characterized to evaluate their structural and optical (SO) properties and, later, to test their efficiency for the photocatalytic degradation (PD) of methylene blue (MB) in aqueous solution. The X-ray diffraction patterns showed that the TiO₂ TFs had an anatase crystalline structure, unlike the ZrO₂ TFs, which showed a tetragonal crystalline structure that was verified by Raman spectroscopy. The band gap (BG) energies, as calculated from UV-Vis spectroscopy and diffuse reflectance spectroscopy, corresponded to 3.2 and 3.7 eV for the TiO₂ and ZrO₂ TFs, respectively. SEM examination of the obtained materials was also carried out to assess the surface morphology and topography. The comparative study of the FTIR spectra of the TiO₂ and ZrO₂ TFs successfully confirmed the composition of the two-metal oxide TFs. The electrical properties of the films were studied by conductivity measurements. The two films also showed a similar thickness of about 200 nm and a substantially different photocatalytic performance for the discoloration of MB in aqueous solution. The corresponding rate constants, as obtained from a pseudo-first-order kinetic model, revealed that TiO₂ films promote color removal of the model dye solution almost 20 times faster than the rate observed for ZrO₂ modified glass substrates. We suggest that this difference may be related to the hydrophilic character of the two films under study, which may affect the charge carrier injection process and, therefore, the overall photocatalytic performance. Full article

This paper presents the results of investigations on the kinetic modeling of Brilliant Blue FCF (BB) discoloration reactions in aqueous solutions with different ozone concentrations and pH conditions. Kinetic studies involve knowledge of the structure and properties of dye and ozone, as well as of the experimental conditions. In general, scientists admit that the predominant oxidation pathway is direct (by free oxygen atoms) or indirect (by free hydroxyl radicals); this will depend on influencing factors such as the physicochemical properties of the dye, the pH of the aqueous solution, ozone concentration, reaction time, and the contact mode with/without stirring. In this experimental research, two pathways were chosen following C_BB = f(t)—1. a constant dye concentration and different ozone concentrations, in the concentration range of 100–250 mg/L, in three pH media (acidic, neutral, and basic), with and without stirring; 2. a constant concentration of ozone and different dyes in the concentration range of 2.5–10 mg/L, under the conditions of point 1. With the obtained experimental data, the curves C_BB = f(t) were drawn and processed according to the integral method of classical kinetics, based on first- and second-order equations. Unfortunately, this simple procedure did not give any results for the pH values studied. The rate constants were negative, and/or the reaction order depended on the initial conditions. Due to its structure, the BB dye has several chromophore groups, and thus multiple attack centers, resulting in several oxidation by-products, which is why the ¹H-NMR spectrum was recorded for the discoloration of BB with ozone. Since the stoichiometry of the overall oxidation reaction, as well as the relationship between the rate constant and the reaction conditions mentioned above, is not known, a kinetic model based on mass transfer coupled with a chain reaction in the bulk liquid phase was proposed and successfully tested at pH = 7. This research approach also involves the consolidation of the theoretical bases of the ozonation process through the kinetic study carried out, as well as the proposal of a kinetic model. These systematics lead to results that are applicable to other aqueous systems that are impure with dyes, allowing for generalizations and the development of the field, ensuring the sustainability of the research. Full article

The textile industry is known for its excessive water consumption and environmental impact. One of the major challenges it faces is managing pollution generated by dyes, particularly bifunctional dyes, such as sumireact supra yellow s-hbu, with a red appearance and sumifix supra lemon-yellow e-xf, with a yellow appearance. This study aimed to investigate the decolorization kinetics of synthetic solutions of said bifunctional dyes, which comprise triazine and vinylsulfon. We conducted various tests, including modifications of pH, the addition of TiO₂ P-50 nanoparticles, exposure to solar radiation, limited contact with oxygen, and eolic agitation. The initial solutions had a concentration of 1000 ppm of textile dye. The study showed that the reaction order for the “red” solutions in the R6 and R9 reactors and all the yellow solutions was ½. The concentration of nanoparticles and pH had a significant impact on the reaction rate. The yellow solutions with a concentration of 800 ppm and pH levels of 3.15, 4.13, and 2.25 demonstrated 100% color discoloration, followed by solutions with a concentration of 400 ppm and pH levels of 3.15, 2.25, and 4.13. The analysis of variance confirmed the reaction rate constants for the yellow solutions and emphasized the significance of pH in this process. Full article

This study investigates the biodegradation of Reactive Red 141 (RR 141), an azo dye prevalent in the textile industry, by bacteria isolated from activated sludge in a textile effluent treatment plant. RR 141, characterized by nitrogen–nitrogen double bonds (-N=N-), contributes to environmental issues when improperly disposed of in textile effluents, leading to reduced oxygen levels in water bodies, diminished sunlight penetration, and the formation of potentially carcinogenic and mutagenic aromatic amines. This research focuses on identifying bacteria from activated sludge with the potential to decolorize RR 141. Microbiological identification employs MALDI-TOF-MS, known for its precision and rapid identification of environmental bacteria, enhancing treatment efficiency. Results highlight Bacillus thuringiensis and Kosakonia radicincitans as the most promising strains for RR 141 decolorization. Analysis of micro-organisms in activated sludge and database exploration suggests a correlation between these strains and the decolorization process. It is worth noting that this is the first report on the potential use of K. radicincitans for azo dye decolorization. Three distinct culture media—BHI, MSG, and MS—were assessed to investigate their impact on RR 141 decolorization. Notably, BHI and MSG media, incorporating a carbon source, facilitated the bacterial growth of both tested species (B. thuringiensis and K. radicincitans), a phenomenon absent in the MS medium. This observation suggests that the bacteria exhibit limited capability to utilize RR 141 dye as a carbon source, pointing towards the influence of the culture medium on the discoloration process. The study evaluates performance kinetics, decolorization capacity through UV-VIS spectrophotometry, potential degradation pathways via HPLC-MS analysis, phytotoxicity, and enzymatic activity identification. B. thuringiensis and K. radicincitans exhibit potential in decolorizing RR141, with 38% and 26% removal individually in 120 h. As a consortium, they achieved 36% removal in 12 h, primarily through biosorption rather than biodegradation, as indicated by HPLC-MS analyses. In conclusion, the research emphasizes the importance of exploring bacteria from activated sludge to optimize azo dye degradation in textile effluents. B. thuringiensis and K. radicincitans emerge as promising candidates for bioremediation, and the application of MALDI-TOF-MS proves invaluable for rapid and precise bacteria identification. Full article

Surface-initiated photopolymerization has been run to synthesize a hydrogel with ZnO particles distributed uniformly along its structure, which has been loaded onto a polyamide fabric. Three samples have been obtained at different concentrations of zinc nitrate (10% (sample PA10); 20% (sample PA20) and 30% (sample PA30) of the weight of the fabric, respectively)) and subjected to gravimetric analysis, scanning electron microscopy and transmission electron microscopy. The effect of the adsorption parameters of the composite material on the removal Drimaren Rot K-7B dye from water has been studied. The Freundlich isotherm describes this process better than the Langmuir isotherm. As the results of the adsorption kinetics show, the process fits well with a pseudo-second-order equation and depends both on the boundary layer and on the structure of the adsorbent itself. The thermodynamic parameters have demonstrated that the process is endothermic and physical. When exposed to ultraviolet light, the discoloration of the dye solution accelerates due to the photocatalytic properties of the composite materials. The addition of H₂O₂ also speeds up further the process, while the reuse of the materials slows it down, gradually changing the kinetic parameters. The reaction has been attributed to first-order kinetic model, when the active centers of the materials and the number of oxidative radicals formed are numerous and to the second-order kinetic model at a lower reaction activity. Moreover, 52% decolorization of the dye solution (50 mg L⁻¹) in the dark was achieved from composite material PA 30 (13.3 g L⁻¹) in 120 min and 89% under UV light irradiation. The H₂O₂ addition (0.14 mmol L⁻¹) enhanced it up to 98%. In the second and third use of the photocatalyst, the dye removal decreased to 80% and 60%. Composite material PA30 exhibits antibacterial activity against Gram-negative bacteria E. coli, being most effective at eliminating Gram-positive bacteria S. aureus. Full article

Water pollution by dyes is a huge environmental problem; there is a necessity to produce new decolorization methods that are effective, cost-attractive, and acceptable in industrial use. Magnetic cyclodextrin polymers offer the advantage of easy separation from the dye solution. In this work, the β-CD-EPI-magnetic (β-cyclodextrin-epichlorohydrin) polymer was synthesized, characterized, and tested for removal of the azo dye Direct Red 83:1 from water, and the fraction of non-adsorbed dye was degraded by an advanced oxidation process. The polymer was characterized in terms of the particle size distribution and surface morphology (FE-SEM), elemental analysis (EA), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), infrared spectrophotometry (IR), and X-ray powder diffraction (XRD). The reported results hint that 0.5 g and pH 5.0 were the best conditions to carry out both kinetic and isotherm models. A 30 min contact time was needed to reach equilibrium with a qmax of 32.0 mg/g. The results indicated that the pseudo-second-order and intraparticle diffusion models were involved in the assembly of Direct Red 83:1 onto the magnetic adsorbent. Regarding the isotherms discussed, the Freundlich model correctly reproduced the experimental data so that adsorption was confirmed to take place onto heterogeneous surfaces. The calculation of the thermodynamic parameters further demonstrates the spontaneous character of the adsorption phenomena (ΔG° = −27,556.9 J/mol) and endothermic phenomena (ΔH° = 8757.1 J/mol) at 25 °C. Furthermore, a good reusability of the polymer was evidenced after six cycles of regeneration, with a negligible decline in the adsorption extent (10%) regarding its initial capacity. Finally, the residual dye in solution after treatment with magnetic adsorbents was degraded by using an advanced oxidation process (AOP) with pulsed light and hydrogen peroxide (343 mg/L); >90% of the dye was degraded after receiving a fluence of 118 J/cm²; the discoloration followed a pseudo first-order kinetics where the degradation rate was 0.0196 cm²/J. The newly synthesized β-CD-EPI-magnetic polymer exhibited good adsorption properties and separability from water which, when complemented with a pulsed light-AOP, may offer a good alternative to remove dyes such as Direct Red 83:1 from water. It allows for the reuse of both the polymer and the dye in the dyeing process. Full article

In recent years, iron oxides-based nanostructured composite materials are of particular interest for the preparation of multifunctional thin films and membranes to be used in sustainable magnetic field adsorption and photocatalysis processes, intelligent coatings, and packing or bio-medical applications. In this paper, superparamagnetic iron oxide (core)-silica (shell) nanoparticles suitable for thin films and membrane functionalization were obtained by co-precipitation and ultrasonic-assisted sol-gel methods. The comparative/combined effect of the magnetic core co-precipitation temperature (80 and 95 °C) and ZnO-doping of the silica shell on the photocatalytic and nano-sorption properties of the resulted composite nanoparticles were investigated by ultraviolet-visible (UV-VIS) spectroscopy monitoring the discoloration of methylene blue (MB) solution under ultraviolet (UV) irradiation and darkness, respectively. The morphology, structure, textural, and magnetic parameters of the investigated powders were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) measurements, and saturation magnetization (vibrating sample magnetometry, VSM). The intraparticle diffusion model controlled the MB adsorption. The pseudo- and second-order kinetics described the MB photodegradation. When using SiO₂-shell functionalized nanoparticles, the adsorption and photodegradation constant rates are three–four times higher than for using starting core iron oxide nanoparticles. The obtained magnetic nanoparticles (MNPs) were tested for films deposition. Full article

A catalytic ozonation advanced oxidation process (AOP) with a copper(II)-doped carbon dot as catalyst, Cu-CD (using L-cysteine and polyethylene glycol (PEG) as precursors and passivation agents), was developed for textile wastewater treatment (T = 25 °C and pH = 7). Four dyes were analyzed—Methyl Orange (MO), Orange II sodium salt (O-II), Reactive Black 5 (RB-5) and Remazol Brilliant Blue R (RBB-R), as well as a real effluent from the dying and printing industry. The Cu-CD, with marked catalytic ozonation properties, was successfully synthesized by one-pot hydrothermal procedure with a size of 4.0 nm, a charge of −3.7 mV and a fluorescent quantum yield of 31%. The discoloration of the aqueous dye solutions followed an apparent first-order kinetics with the following rate constants (k_ap in min⁻¹): MO, 0.210; O-II, 0.133; RB-5, 0.177; RBB-R, 0.086. In the presence of Cu-CD, the following apparent first-order rate constants were obtained (k_ap^c in min⁻¹) with the corresponding increase in the rate constant without catalyst (%Inc): MO, 1.184 (464%); O-II, 1.002 (653%); RB-5, 0.709 (301%); RBB-R, 0.230 (167%). The presence of sodium chloride (at a concentration of 50 g/L) resulted in a marked increase of the discoloration rate of the dye solution due to generation of other radicals, such as chlorine and chlorine oxide, resulting from the reaction of ozone and chloride. Taking into consideration that the real textile effluent under research has a high carbonate concentration (>356 mg/L), which inhibits ozone decomposition, the discoloration first-order rate constants without and with Cu-CD (k_ap = 0.0097 min⁻¹ and k_ap^c = 0.012 min⁻¹ (%Inc = 24%), respectively) were relatively small. Apparently, the Cu-CD, the surface of which is covered by a soft and highly hydrated caramelized PEG coating, accelerates the ozone decomposition and dye adsorption, increasing its degradation. Full article

The development of photocatalystsor their modification to obtain new photocatalytic performances for the removal of contaminants is a challenge. Hydroxyapatite (HAp), (Ca₁₀(PO₄)₆(OH)₂), is an inorganic component with a high superficial area and low toxicity and the presence of metal in its structure can be an interesting strategy for the photocatalytic approach. This work aimed to synthesize gallium-containing HAp (Ga-HAp) as a promising material for photocatalytic performance. The synthesis was performed by the suspension–precipitation method. The material was characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Morphological analysis employed field emission scanning electron microscope (FESEM) and the elemental analysis by energy-dispersive spectroscopy (EDS). To evaluate the photocatalytic activity, methylene blue (MB) dye was used as a pollutant model under UV light for 120 min. The influence of Ga-HAp concentration (0.25, 0.50, and 1.00 g·L⁻¹) and kinetic reaction was also studied. The Ga-HAp was successfully obtained by the suspension–precipitation method. The structural characterization by XRD and FESEM-EDS elucidated the presence of gallium in the structure of hydroxyapatite. The XPS results indicated the substitution of gallium in the crystal lattice of the material. The discoloration rate of MB dye using Ga-Hap was calculated by pseudo first-order kinetics, and the best rate constant was 7.5 × 10⁻³ min⁻¹ using 1.00 g·L⁻¹ of photocatalyst. The concentration of Ga-HAp influenced the photocatalytic process, because the discoloration rate increased as a function of the concentration of material. Therefore, Ga-HAp is a promising material for environmental remediation. Full article

Over the last few decades, bio-based polymers have attracted considerable attention from both academic and industrial fields regarding the minimization of the environmental impact arising from the excessive use of petrochemically-based polymeric materials. In this context, poly(ethylene vanillate) (PEV), an alipharomatic polyester prepared from 4-(2-hydroxyethoxy)-3-methoxybenzoic acid, a monomer originating from lignin-derived vanillic acid, has shown promising thermal and mechanical properties. Herein, the effects of three different catalysts, namely titanium butoxide (TBT), titanium isopropoxide (TIS), and antimony trioxide (Sb₂O₃), on the synthesis of PEV via a two-stage melt polycondensation method are investigated. The progress of the reaction is assessed using various complementary techniques, such as intrinsic viscosity measurement (IV), end group analysis (AV), nuclear magnetic resonance spectroscopy (NMR), Fourier-transformed infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The thermal stability of the produced polyesters is studied by evolved gas analysis mass spectrometry (EGA-MS). Moreover, as the discoloration in polymers affects their applications, color measurement is performed here. Finally, theoretical kinetic studies are carried out to rationalize the experimental observations. Full article

The scavenging activity of myoglobin toward peroxynitrite (PON) was studied in meat extracts, using a new developed electrochemical method (based on cobalt phthalocyanine-modified screen-printed carbon electrode, SPCE/CoPc) and calculating kinetic parameters of PON decay (such as half-time and apparent rate constants). As reactive oxygen/nitrogen species (ROS/RNS) affect the food quality, the consumers can be negatively influenced. The discoloration, rancidity, and flavor of meat are altered in the presence of these species, such as PON. Our new highly thermically stable, cost-effective, rapid, and simple electrocatalytical method was combined with a flow injection analysis system to achieve high sensitivity (10.843 nA µM⁻¹) at a nanomolar level LoD (400 nM), within a linear range of 3–180 µM. The proposed biosensor was fully characterized using SEM, FTIR, Raman spectroscopy, Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV), and Linear Sweep Voltammetry (LSV). These achievements were obtained due to the CoPc-mediated reduction of PON at very low potentials (around 0.1 V vs. Ag/AgCl pseudoreference). We also proposed a redox mechanism involving two electrons in the reduction of peroxynitrite to nitrite and studied some important interfering species (nitrite, nitrate, hydrogen peroxide, dopamine, ascorbic acid), which showed that our method is highly selective. These features make our work relevant, as it could be further applied to study the kinetics of important oxidative processes in vivo or in vitro, as PON is usually present in the nanomolar or micromolar range in physiological conditions, and our method is sensitive enough to be applied. Full article

This study aims to determine the physicochemical quality of seagrape (Caulerpa lentillifera) as a freshness label for products cultivated in different seasons. The applied post-harvest storage experiments compared between, within and without seawater that led to oxidative stress conditions. Water content, malondialdehyde (MDA) compound, total phenolic content (TPC), and chlorophyll content were observed at 0, 3, 6, and 9 days of storage. The storage without seawater showed sharper quality reductions by reaching 20–40% of water loss, 70–90% of MDA production, 15–25% of TPC reduction, and 40–60% of total chlorophyll degradation. The storage within seawater showed lower quality reductions due to the specific growth rates still reaching 5–10%. This study found that the greater the physicochemical quality, the slower the decomposition rates of the stored seagrape during storage. Therefore, the seagrapes’ obvious discoloration occurred earlier in winter, followed by summer and spring. Kinetics of chlorophyll degradation on seagrape in different seasons meet different order-reactions during storage. Furthermore, alternating current electric field (ACEF) treatment with 125 kV/m of intensity for 60 min can lower the spring seagrapes’ physicochemical quality by reaching 10–30% of inhibition, resulting in the shelf-life extension for up to 12 days of post-harvest storage. Full article