Search Results (424)

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

Stainless steel dust (SSD) is a by-product generated during the smelting process of stainless steel, which is rich in valuable metals such as Fe, Cr, Ni, and Mn. To optimize the carbothermic reduction process of SSD, this study first conducted the thermodynamic analysis of the carbothermic reduction of SSD and then employed walnut shell biochar as a reductant with non-isothermal thermogravimetric analysis with linear heating rates of 5 °C/min, 10 °C/min, 15 °C/min, and 20 °C/min. The activation energies of the carbothermic reduction reactions were calculated using the FWO method, KAS method, and Friedman method, respectively. Subsequently, the corresponding kinetic models were fitted and matched using the Málek method. The results indicate that before 600 °C, the direct reduction of SSD by carbon plays a dominant role. As the temperature increases, the indirect reduction becomes the main reduction reaction for SSD due to the generation of CO. The activation energies calculated by the Flynn–Wall–Ozawa (FWO) method, Kissinger–Akahira–Sunose (KAS) method, and Friedman method are 412.120 kJ/mol, 416.930 kJ/mol, and 411.778 kJ/mol, respectively, showing close values and a general trend of increasing activation energy as the conversion rate increased from 10% to 90%. Moreover, the reduction reaction is staged. In the conversion range of 10% to 50%, the carbothermic reduction reaction conforms to the shrinking core model within phase boundary reactions, coded as R1/4. In the conversion range of 50% to 60%, it conforms to the shrinking core model within phase boundary reactions, coded as R1/2; in the conversion range of 60% to 90%, the carbothermic reduction reaction follows the second-order chemical reaction model, coded as F2. Full article

As a result of the catalytic decomposition of H₂O₂, hydroxyl radicals are produced. Hydroxyl radicals are strong oxidants and effectively inactivate bacteria, ensuring water disinfection without toxic chlorinated organic by-products. The kinetics of bacterial inactivation were studied in a laboratory-scale flow catalytic reactor. A granular cobalt ferrite catalyst was thoroughly characterized using XRD and XRF techniques, SEM with EDS, and Raman spectroscopy. At lower H₂O₂ concentrations, H₂O₂ decomposition follows first-order reaction kinetics. At higher H₂O₂ concentrations, the obtained kinetics lines suggest that the reaction order increases. The kinetics of bacterial inactivation in the developed flow reactor depends largely on the initial number of bacteria. The initial bacterial concentrations in laboratory tests were within the range typical of real river water. A regression model was developed that relates the degree of bacterial inactivation to the initial number of bacteria, the initial H₂O₂ concentration, and the contact time of water with the catalyst. Full article

In this study, the degradation of Nile Blue dye was investigated using homogeneous and heterogeneous photocatalytic methods based on the photo-Fenton reaction. More specifically, for homogeneous photocatalysis, the classical photo-Fenton (UV/Fe²⁺/H₂O₂) and modified photo-Fenton-like (UV/Fe²⁺/S₂O₈²⁻) systems were studied, while for heterogeneous photocatalysis, a commercial MOF catalyst, Basolite F300, and a natural ferrous mineral, geothite, were employed. Various parameters—including the concentrations of the oxidant and catalyst, UV radiation, and pH—were investigated to determine their influence on the reaction rate. In homogeneous systems, an increase in iron concentration led to an enhanced degradation rate of the target compound. Similarly, increasing the oxidant concentration accelerated the reaction rate up to an optimal level, beyond which radical scavenging effects were observed, reducing the overall efficiency. In contrast, heterogeneous systems exhibited negligible degradation in the absence of an oxidant; however, the addition of oxidants significantly improved the process efficiency. Among the tested processes, homogeneous techniques demonstrated a superior efficiency, with the conventional photo-Fenton process achieving complete mineralization within three hours. Kinetic analysis revealed pseudo-first-order behavior, with rate constants ranging from 0.012 to 0.688 min⁻¹ and correlation coefficients (R²) consistently above 0.90, confirming the reliability of the applied model under various experimental conditions. Nevertheless, heterogeneous techniques, despite their lower degradation rates, also achieved high removal efficiencies while offering the advantage of operating at a neutral pH without the need for acidification. Full article

The oxidative degradation of anthocyanins in red wine was investigated under controlled conditions using hydroxyl radicals generated in the presence of Cu (II) as a catalyst. A full factorial experimental design with 23 replicates was used to evaluate the effects of hydrogen peroxide concentration, catalyst dosage, and reaction temperature on anthocyanin degradation over a fixed time. Statistical analysis (ANOVA and multiple regression) showed that all three variables and the main interactions significantly affected anthocyanin loss, with temperature identified as the most influential factor. The combined effects were described by a first-order polynomial model. The activation energies for degradation ranged from 56.62 kJ/mol (cyanidin-3-O-glucoside) to 40.58 kJ/mol (peonidin-3-O-glucoside acetate). Increasing the temperature from 30 °C to 40 °C accelerated the degradation kinetics, almost doubled the rate constants and shortened the half-life of the pigments. At 40 °C, the half-lives ranged from 62.3 min to 154.0 min, depending on the anthocyanin structure. These results contribute to a deeper understanding of the stability of anthocyanins in red wine under oxidative stress and provide insights into the chemical behavior of derived pigments. The results are of practical importance for both oenology and viticulture and support efforts to improve the color stability of wine and extend the shelf life of grape-based products. Full article

This work deals with the catalytic steam reforming of raw syngas to increase the efficiency of coupling gasification with downstream processes (such as fuel cells and catalytic chemical syntheses) by producing high-temperature, ready-to-use syngas without cooling it for cleaning and conditioning. Such a combination is considered a key point for the future exploitation of syngas produced by steam gasification of biogenic solid fuel. The design and construction of an integrated gasification and gas conditioning system were proposed approximately 20 years ago; however, they still require further in-depth study for practical applications. A 3D model of the freeboard of a pilot-scale, fluidized bed gasification plant equipped with catalytic ceramic candles was used to investigate the optimal operating conditions for in situ syngas upgrading. The global kinetic parameters for methane and tar reforming reactions were determined experimentally. A fluidized bed gasification reactor (~5 kWth) equipped with a 45 cm long segment of a fully commercial filter candle in its freeboard was used for a series of tests at different temperatures. Using a computational fluid dynamics (CFD) description, the relevant parameters for apparent kinetic equations were obtained in the frame of a first-order reaction model to describe the steam reforming of key tar species. As a further step, a CFD model of the freeboard of a 100 kWth gasification plant, equipped with six catalytic ceramic candles, was developed in ANSYS FLUENT^®. The composition of the syngas input into the gasifier freeboard was obtained from experimental results based on the pilot-scale plant. Simulations showed tar catalytic conversions of 80% for toluene and 41% for naphthalene, still insufficient compared to the threshold limits required for operating solid oxide fuel cells (SOFCs). An overly low freeboard temperature level was identified as the bottleneck for enhancing gas catalytic conversions, so further simulations were performed by injecting an auxiliary stream of O₂/steam (50/50 wt.%) through a series of nozzles at different heights. The best simulation results were obtained when the O₂/steam stream was fed entirely at the bottom of the freeboard, achieving temperatures high enough to achieve a tar content below the safe operating conditions for SOFCs, with minimal loss of hydrogen content or LHV in the fuel gas. Full article

Controlled iron extraction from iron-based sludge (Fe-Sludge) drainage and its use as a Fenton’s reagent is investigated in the current study for eliminating organics from launderette discharge stream. The influences of the iron dosage, hydrogen peroxide concentration, and pH are assessed as treatment factors for their direct impact on the oxidation of organic compounds. Additionally, optimal oxidation conditions are determined using the response surface methodology (RSM) technique, and the ranges of treatment variables are analyzed. The optimum values of a pH of 2.0, Fe sludge concentration of 99 mg/L, and H₂O₂ content of 402 mg/L resulted in optimal organics removal of up to 98%, expressed as Chemical Oxygen Demand (COD) removal. The oxidation efficacy attained from the design is confirmed and the model validation is assessed, and the suggestive model is accepted since it possesses a correlation coefficient of 97.7%. The thermodynamic and kinetic models are also investigated, and the reaction showed that the temperature increases resulted in the oxidation efficiency being reduced. The oxidation efficiency expressed as COD reduction is clearly characterized by first-order reaction kinetics. The thermodynamic characteristics indicated that the oxidation reaction was exothermic and not spontaneous. Full article

Spent automobile catalysts can be an important source of platinum for industry applications. Low-cost and simple technologies for platinum recovery from this source are sought, especially involving the application of green adsorbents. Honeycomb biowaste can be an excellent candidate for this purpose; n-hexane-treated honeycomb biowaste is therefore obtained for the first time. This material is characterized using several instrumental techniques, confirming the presence of O, N, and P heteroatoms on its surface and the complex morphology of its particles. The maximum static Pt(II)/Pt(IV) adsorption (46 mg/g and 60 mg/g, respectively) onto the n-hexane-extracted honeycomb biomass is reached at pH = 1.55 and a contact time of 50 h. The adsorption kinetics are best fitted to the pseudo-second-order model in both cases. The Langmuir model best described the Pt(II)/Pt(IV) adsorption isotherms on the studied material. Quantitative desorption of the Pt from the studied material is reached for 1 mol/L thiourea dissolved in HCl. The adsorption mechanism of Pt(IV) ions onto the obtained material is based mainly on the surface complexation reactions. The studied material is successfully applied for the first time for Pt(IV) removal from a spent automobile catalyst leachate. Full article

Excessive intake of fluorine (F) over time can lead to acute or chronic fluorosis. In this study, a novel Fe^III–Ce^IV-based layered hydroxide composite (DD-LHC) was synthesized and applied in both batch and column modes to develop new adsorbent materials and to obtain efficient removal of fluorine (F) anions from wastewater. DD-LHC achieved better adsorption results and material stability compared to green rusts (GR, Fe^II–Fe^III hydroxide). The maximum adsorption capacity of DD-LHC for F⁻ was 44.68 mmol·g⁻¹, obtained at an initial pH of 5 and initial concentration of 80 mM. The substitution of Ce^IV for Fe^II in the intercalated layered structure of GR potentially changed the reaction pathways for F⁻ removal, which are typically dominant in the layered double hydroxides (LDHs) of Fe^II–Fe^III. The molecular structure of layered hydroxides combined with the three-dimensional (3D) metal frame of Fe-O-Ce was integrated into DD-LHC, resulting in nanoscale particle morphologies distinct from those of GR. The pseudo-first-order kinetic model effectively described the whole adsorption process of DD-LHC for F⁻. DD-LHC exhibited notable selectivity for F⁻ across a wide pH range. The removal process of F⁻ by DD-LHC was dominated by Ce–F coordination bonds, with additional influences from auxiliary pathways to different extents. Full article

During the thermal treatment of kaolinite, the main mineral phase in kaolin rock, dehydroxylation occurs, forming metakaolin through a process that has significant industrial applications. This study experimentally analyzed dehydroxylation in two kaolinite samples: a well-crystallized reference sample from the Clay Mineral Society and a locally sourced, industrial kaolin sample. The mechanism and kinetic parameters were evaluated from a series of thermogravimetric measurements. Non-isothermal kinetic analysis revealed that dehydroxylation followed a third-order (F3) reaction mechanism, with activation energies ($E_a$) ranging from 35 to 60 kcal/mol. Additionally, theoretical calculations based on Density Functional Theory were performed on four systems in which a water molecule was removed by combining OH group and H atom vacancies in the kaolinite unit cell. These models represented the onset of dehydroxylation and provided values for the reaction energy Q from first-principles calculations, which served as reference values for $E_a$. The results confirm that water molecule formation involving both OH at the kaolinite outer surface and inner surface are energetically competitive and highlight the crucial role of structural relaxations following water removal to determine Q values in the range of 30–50 kcal/mol, in very good agreement with the experiments. Full article

This study investigates the competitive dynamics of reducing sugar production and degradation during the subcritical water processing (SWP) of lyophilized grape pomace (LGP), with the goal of optimizing sugar yield. Under the SWP conditions tested (150 °C, 150 bar, pH 7, S/F of 30 g water g⁻¹ LGP, and a flow rate of 5 mL min⁻¹), we achieved a reducing sugar yield of 296.0 mg sugars g⁻¹ LGP, effectively balancing sugar production and degradation. Sugar yield decreased as the temperature increased from 150 °C to 210 °C, due to the degradation of monosaccharides into by-products like furfural and 5-HMF. A first-order reaction model was developed to better understand the kinetic competition between sugar formation and degradation at varying temperatures. The highest sugar yield occurred at 150 °C, where sugar production was maximized, and degradation was minimized. These findings offer valuable insights for subcritical water processing in the valorization of LGP into fermentable sugars while minimizing the formation of undesirable by-products. Full article

This work reports the synthesis of two monometallic catalysts, Cu/Al₂O_3, and Pd/Al₂O₃, using a green approach based on Mexican oregano (Lippia graveolens), a common food condiment. Its extract has been largely overlooked as a high-technology reactive for synthesizing catalysts, metallic or oxide nanoparticles, unlike other green leaf plants. The green synthesis was compared with a conventional catalyst synthesis methodology using commercial chemical reducing agents. Oregano extract shows promise for novel applications extending beyond its culinary use, valorizing it as a chemical reducer to produce catalysts. Thus, this kind of application could significantly elevate the value of oregano, empowering communities that rely on its cultivation for economic benefit and transforming the plant from a low-profit agro-industrial product to a high-added-value crop. The reduction kinetics involved in the formation of nanoparticles were monitored up to the first stage of nucleation and a first-order model adequately described the data. Activation energy analysis showed that the chemical reaction mechanism has a dominant role in controlling the reaction, compared to mass transfer effects. Notoriously, the Pd/Al₂O₃ green synthesis catalyst showed the smallest mean particle size (4.85 ± 1.30 nm). These findings underscore the potential of green synthesis as an economically viable and environmentally friendly alternative for producing catalysts. Concerning the 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) as a biomass-derived molecule, its oxidation with H₂O₂ using both Pd/Al₂O₃ catalysts (by green and chemical synthesis methods) exhibited significantly higher selectivity toward 2,5-diformylfuran (DFF) compared to Cu/Al₂O₃ catalysts, suggesting a possible inhibitory effect. Full article

One viable technical approach for achieving hydrogen-blended combustion in marine ammonia-fueled engines is to utilize online ammonia decomposition to produce hydrogen, which is then introduced into the engine for combustion. This work carried out ammonia decomposition experiments using various catalysts, examining the effects of temperature and space velocity on Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 and Ni/Ce_0.36Zr_0.64O₂ catalysts. Based on the experimental data obtained, the kinetic parameters of ammonia decomposition were fitted using four different models: mass action law, first-order reaction, Langmuir, and Temkin–Pyzhev kinetics across two catalysts, with the subsequent mechanistic analysis of catalytic reaction processes within the reactor. The results revealed that the NH₃ conversion rate of the Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 catalyst was superior to that of the Ni/Ce_0.36Zr_0.64O₂ catalyst, with temperature activity windows of 250–450 °C and 400–600 °C, respectively. Within the range of 2000–32,000 mL·g⁻¹·h⁻¹), an increase in space velocity led to a decrease in NH₃ conversion rate by approximately half. All four models were able to predict NH₃ conversion rates for the different catalysts with reasonable accuracy. The activation energies for Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 and Ni/Ce_0.36Zr_0.64O₂ catalysts were found to be 37.7 kJ·mol⁻¹ and 66 kJ·mol⁻¹, respectively. Targeting hydrogen requirements of 10–40% vol for ammonia engines, the corresponding catalytic temperatures for Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 and Ni/Ce_0.36Zr_0.64O₂ were above 267 °C and 500 °C, respectively. Full article

The widespread discharge of synthetic dyes such as Eriochrome Black T (EBT) into water bodies poses significant environmental and health concerns due to their toxicity, persistence, and resistance to degradation. In response to this issue, the removal of EBT dye from aqueous solutions using nickel-modified orange peel biochar (MOPB) was investigated in this study at various experimental conditions such as adsorbent dose, pH, concentration of dye, temperature, and contact time. Biochar was prepared from orange peels via pyrolysis, and structural characterization was performed using FTIR, XRD, and SEM to assess morphological changes, pore structure, and functional groups post-modification. MOPB exhibited significantly enhanced adsorption capacity compared to unmodified biochar. Optimal removal (at 0.1 g adsorbent dose, 25 ppm dye concentration, 90 min contact time, 35 °C, and pH 4) resulted in maximum EBT elimination. The equilibrium dataset was evaluated using Langmuir and Freundlich isotherm models. The Langmuir model (R² = 0.99) best described the uptake of EBT dye, which implies that the adsorption of EBT dye onto MOPB was monolayered. The kinetic data were also analyzed using pseudo-first-order and pseudo-second-order models. The pseudo-second-order kinetic model was found to be the best fit (R² = 0.99), indicating that it governs the rate-limiting step of the reaction. Thermodynamic parameters confirmed that the adsorption process is spontaneous and exothermic. These findings demonstrate the potential of MOPB as a low-cost, sustainable adsorbent for the efficient removal of EBT from industrial wastewater. Full article

The impact of adding 1%, 3%, and 5% by mass of kaolin residue (KR) was investigated regarding the mechanical, thermomechanical, and morphological properties, as well as the non-isothermal crystallization and melting kinetics of poly(ε-caprolactone) (PCL). The processing to obtain the PCL/KR composites was carried out through extrusion in a twin-screw extruder, followed by injection molding. This study investigated the events of first melting, fusion crystallization, and second melting using differential scanning calorimetry (DSC), with heating rates ranging from 5 to 25 °C/min. Additionally, models for the expanded Prout–Tompkins equation (BNA), the nth-order reaction with m-power autocatalysis by product (Cnm), and the Sestak and Berggren equation (SB) were tested. The PCL/KR composites exhibited an increase in the elastic modulus and the heat deflection temperature (HDT) compared to the pure PCL. Furthermore, high ductility was observed, as evidenced by the impact strength and elongation at break. The good distribution of KR in the PCL matrix was confirmed by scanning electron microscopy (SEM), which contributed to a more efficient crystallization process. The increase in KR content in the PCL matrix shifted the crystallization sigmoids to higher temperatures, acting as a nucleating agent, which reduced the energy barriers and increased the crystallization temperature by up to 5 °C. The melting events did not show significant changes with the addition of the KR. The results are important for the plastics processing industry, mainly due to the opportunity to add value to the waste and use it as an additive. Full article