Search Results (131)

2,5-bis(hydroxymethy)lfuran (BHMF), a renewable compound with extensive industrial applications, can be obtained by selective hydrogenation of the C=O group of 5-hydroxymethylfurfural (HMF), a platform molecule derived from lignocellulosic biomass. In this work, we perform kinetic modeling of the selective liquid-phase hydrogenation of HMF to BHMF over a Cu/SiO₂ catalyst prepared by precipitation–deposition (PD) at a constant pH. Physicochemical characterization, using different techniques, confirms that the Cu/SiO₂–PD catalyst is formed by copper metallic nanoparticles of 3–5 nm in size highly dispersed on the SiO₂ surface. Before the kinetic study, the Cu/SiO₂-PD catalyst was evaluated in three solvents: tetrahydrofuran (THF), 2-propanol (2-POH), and water. The pattern of catalytic activity and BHMF yield for the different solvents was THF > 2-POH > H₂O. In addition, selectivity to BHF was the highest in THF. Thus, THF was chosen for further kinetic study. Several experiments were carried out by varying the initial HMF concentration (C⁰_HMF) between 0.02 and 0.26 M and the hydrogen pressure (P_H2) between 200 and 1500 kPa. In all experiments, BHMF selectivity was 97–99%. By pseudo-homogeneous modeling, an apparent reaction order with respect to HFM close to 1 was estimated for a C⁰_HMF between 0.02 M and 0.065 M, while when higher than 0.065 M, the apparent reaction order changed to 0. The apparent reaction order with respect to H₂ was nearly 0 when C⁰_HMF = 0.13 M, while for C⁰_HMF = 0.04 M, it was close to 1. The reaction orders estimated suggest that HMF is strongly absorbed on the catalyst surface, and thus total active site coverage is reached when the C⁰_HMF is higher than 0.065 M. Several Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic models were proposed, tested against experimental data, and statistically compared. The best fitting of the experimental data was obtained with an LHHW model that considered non-competitive H₂ and HMF chemisorption and strong chemisorption of reactant and product molecules on copper metallic active sites. This model predicts both the catalytic performance of Cu/SiO₂-PD and its deactivation during liquid-phase HMF hydrogenation. Full article

The DFT method was used to evaluate the adsorption of methyl radicals and the evolution of ethane on the M(111) (M = Co, Ni, Pd, Pt) surfaces, eight metal atoms, in aqueous medium. A maximum of five and four radicals can be adsorbed on Co(111) and Ni(111), respectively, and six on Pd(111) and Pt(111) (top site). The ethane evolution occurs via the Langmuir–Hinshelwood (LH) or Eley–Rideal (ER) mechanisms. The production of ethane through the interaction of two adsorbed radicals is thermodynamically feasible for high coverage ratios on the four surfaces; however, kinetically, it is feasible at room temperature only on Co(111) at a coverage of (5/5) and on Pd(111) at a coverage ratio of 4/6, 5/6, and 6/6. Ethane production occurs via the ER mechanism: a collision with solvated methyl radical produces either C₂H₆ or ${\mathrm{C}\mathrm{H}}_2^{\ast }+{\mathrm{C}\mathrm{H}}_{4\left(\mathrm{a}\mathrm{q}\right)}$. On Pd(111) the product is only C₂H₆, on Pt(111), both products (C₂H₆ or ${\mathrm{C}\mathrm{H}}_2^{\ast }$) are plausible, and on Co(111) and Ni(111), only ${\mathrm{C}\mathrm{H}}_2^{\ast }+{\mathrm{C}\mathrm{H}}_{4\left(\mathrm{a}\mathrm{q}\right)}$ is produced. Further reactions of ${\mathrm{C}\mathrm{H}}_2^{\ast }$ with ${\mathrm{C}\mathrm{H}}_2^{\ast }$ or ${\mathrm{C}\mathrm{H}}_3^{\ast }$ to give ${\mathrm{C}}_2{\mathrm{H}}_4^{\ast }$ or ${\mathrm{C}}_2{\mathrm{H}}_5^{\ast }$ are thermodynamically plausible only on Pt(111); however, they are very slow due to high energy barriers, 1.48 and 1.36 eV, respectively. Full article

A composite photocatalyst of ceria–cadmium supported on mesoporous SBA-15 silica was synthesized and employed for the aqueous methylene blue (MB) degradation. The composites were prepared using an incipient wetness impregnation technique and a conventional sol–gel approach with triblock copolymer P123 as a structure-directing agent for SBA-15 preparation, enabling the uniform dispersion of CeO₂ and Cd species within the SBA-15 framework. The physicochemical properties of both CeO₂/SBA-15 and Cd-CeO₂/SBA-15 composites were analyzed using small-angle and wide-angle XRD, FT-IR spectroscopy, SEM, TEM, EDX spectroscopy, N₂ physisorption at 77 K, and UV-Vis spectroscopy. The findings revealed that the SBA-15 support retained its well-ordered hexagonal mesostructure in both the ceria–SBA-15 and SBA-15-supported cadmium–ceria (Cd-CeO₂) composites. The highest degradation efficiency of 96.40% was achieved under optimal conditions, and kinetic analysis using the Langmuir–Hinshelwood model indicated that the MB degradation process followed pseudo-first-order kinetics, with a strong correlation coefficient (R² = 0.9925) and a rate constant (k) of 0.02532 min⁻¹. Under irradiation, the Cd-CeO₂/SBA-15 composites exhibited superior photocatalytic activity compared to the pristine components, owing to the synergistic interaction between ceria and cadmium, enhanced light absorption, and improved charge carrier separation. The recyclability test demonstrated that the degradation efficiency decreased slightly from 96.40% to 94.86% after three cycles, confirming the stability and reusability of Cd-CeO₂/SBA-15 composites. The photocatalytic process demonstrated a favorable electrical energy per order (EE/O) value of 281.8 kWh m⁻³, indicating promising energy efficiency for practical wastewater treatment. These results highlight the excellent photocatalytic performance and durability of the synthesized Cd-CeO₂/SBA-15 composites, making them promising candidates for facilitating the photocatalytic decomposition of MB and other dye molecules in water treatment applications. Full article

Recently, aquatic life and human health are seriously threatened by the release of pharmaceutical drugs. For a sustainable ecosystem, emerging contaminants like antibiotics must be removed from drinking water and wastewater. To address this issue pure and cerium-doped titanium dioxide (CeT) nanoparticles were produced with stable tetragonal (anatase) lattices by room temperature sol–gel method and employing the inorganic titanium oxysulfate (TiOSO₄) as titanium precursor. The structural analysis by X-ray diffraction (XRD) revealed that at calcination temperature of 600 °C all (un and doped) powders were composed of crystalline anatase TiO₂ with the crystallite sizes in the range of 13.5–11.3 nm. UV–vis DRS spectroscopy revealed that the most narrowed bandgap value of 2.75 eV was calculated for the 0.5CeT sample containing the optimum dopant content of 0.5 weight ratio. X-ray spectroscopy (XPS) confirmed the presence of the impurity level Ce³⁺/Ce⁴⁺, which became responsible for the decrease in bandgap as well as for the photoinduced carriers recombination rate. Photocatalytic tests showed that the maximum decomposition of the model spiramycin (SPR) antibiotic pollutant was 88.0% and 77.0%, under UV and visible light, respectively. According to the reaction kinetics, SPR decomposition adhered to the Langmuir–Hinshelwood (L–H) model and via ROS experiments mainly hydroxyl radicals (OH^•) followed by photogenerated holes (h⁺s) become responsible for the pollutant degradation. In summary, this study elaborates on the role of xCeT nanoparticles as an efficient photocatalyst for the elimination of organic contaminants in wastewater. Full article

Ferrous oxalate dihydrate (α-FOD) was synthesized from Ecuadorian black sands for phenol removal from aqueous solutions. Visible light-driven photodegradation kinetics were studied by varying the initial pollutant concentration, solution pH, and α-FOD dosage and by adding peroxydisulfate (PDS), including quenching tests. A representative model of phenol photodegradation was obtained by the Langmuir–Hinshelwood mechanism over a large range of concentrations (apparent kinetic constant, k = 0.524 h⁻¹). Almost complete removal was reached within 1 h under dark + 9 h under visible irradiation. The degradation rate was slightly affected by pH in the range of 3 to 9, with a significant improvement at pH 11 (k = 1.41-fold higher). The optimal α-FOD dosage was ~0.5 g/L. Two regimes were observed when using PDS: first, a heterogeneous Fenton-like process during the first few minutes after PDS addition; second, pure photocatalysis to completely remove the phenol. When comparing the two systems, without and with PDS, the half-life time for pure photocatalysis was 2.5 h (after the lamp was switched on). When adding PDS (1.0 mM), the half-life time was reduced to a few minutes (5 min after PDS addition, phenol removal was 66%). The photocatalyst presented remarkable degradation efficiency up to five repeated cycles. Full article

Ensuring effective water purification is essential for addressing freshwater scarcity and achieving the United Nations Sustainable Development Goals (SDGs). An efficient hybrid mixture, composed of FeCr quantum dots doped into mesoporous silica SBA-15 support and activated carbon (AC) derived from olive mill solid wastes, has been developed for treating high optical density polluted aqueous environments. This hybrid, denoted as FeCr-SBA-15/AC, was examined for its efficacy in the adsorption and photo-Fenton degradation of met orange dye (MO), a model high-optical-density pollutant, under visible light exposure. Characterization of the prepared samples was conducted using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) surface area analysis, diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Key parameters investigated included catalyst dosage, dye concentration, solution pH, and H₂O₂ concentration. Remarkably, the FeCr-SBA-15/AC hybrid exhibited superior photocatalytic activity, achieving a degradation efficiency of 97% for MO under optimized conditions (catalyst dosage = 0.75 g L⁻¹, dye concentration = 20 mg L⁻¹, pH = 5.47, and 0.5 mL H₂O₂) after 180 min of irradiation with visible light. This performance surpassed that of FeCr-SBA-15 alone by 20%, due to the synergistic effects of adsorption and photo-Fenton. The adsorption of MO onto AC followed the Freundlich model equilibrium isotherm, while the experimental data for the hybrid mixture aligned well with the pseudo-first-order Langmuir–Hinshelwood kinetic model with a rate constant of 0.0173 min⁻¹. The leaching of Cr in the solution was very low—0.1 ppm—which is below the detection limit. These findings underscore the potential of the synthesized FeCr-SBA-15/AC hybrid as a cost-effective, environmentally friendly, and highly efficient photo-Fenton catalyst for treating wastewater contaminated by industrial effluents. Full article

In this study, the heterogeneous reaction of oleic acid droplets with gas-phase ozone was studied by an ATR-FTIR flow reactor. The effects of droplet size, relative humidity, and ozone concentration on the reaction kinetics were carefully investigated. Specifically, the pseudo-first-order rate constant k_app and the uptake coefficient γ displayed a size dependence, with k_app decreasing from ~4.5 × 10⁻³ to ~3.2 × 10⁻³ and γ linearly increasing from ~4.4 × 10⁻⁵ to ~3.2 × 10⁻⁴ as the suspended droplet diameter increased from 0.1 to 1.0 μm. It is believed that the reaction kinetics were the major contributor to the reactive uptake in the reaction between the oleic acid droplets and gas-phase ozone observed in this study. In addition, RH showed no obvious influence on the heterogeneous reaction kinetics, in agreement with findings from previous studies. Furthermore, the k_app was found to display a Langmuir–Hinshelwood dependence on the gas-phase ozone concentration with K_O3 = (3.29 ± 0.46) × 10⁻¹⁵ molecules cm⁻³ and k[S] = 0.153 ± 0.007 s⁻¹, which is consistent with observations of the ozonolysis of unsaturated organic materials in the literature. Kinetics data related to the heterogeneous reaction of ozone and oleic acid under different conditions could be used in chemistry transport models and air quality models to better understand air pollutants’ adverse health impacts. Full article

This research investigates the enhanced photocatalytic activity of cuprous oxide (Cu₂O) nanoparticles (NPs)-titanium dioxide (TiO₂) nanotube (NT) composites for air purification, focusing on the removal of volatile organic compounds (VOCs) and Escherichia coli (E. coli) bacteria under simulated sunny light. Cu₂O-NPs were successfully deposited onto TiO₂-NTs via the successive ionic layer adsorption and reaction method. The resulting p- and n-type semiconductor heterojunction nanocomposites were characterized using various techniques, including scanning electron microscopy, transmission electron microscopy, ultraviolet–visible-light spectroscopy, and chlorinated radicals. The photocatalytic activity was evaluated for different VOCs present in indoor air (butadione, chloroform, and butyraldehyde) in the presence of E. coli bacteria. The results showed that the Cu₂O-NPs/TiO₂-NTs composites exhibited enhanced photocatalytic activity compared to pure TiO₂-NTs. The Langmuir–Hinshelwood model was used to describe the degradation kinetics, revealing that Cu₂O loading and the nature of the target pollutant influence the photocatalytic efficiency. This study has also highlighted the role of chlorinated radicals in the degradation process, especially for chloroform. The degradation process of chloroform generated chlorine radicals, which not only contributed to the degradation of other VOCs, but also enhanced the overall oxidative capacity of the system. This synergistic effect was observed to accelerate pollutant removal and improve the antibacterial efficacy against E. coli. The Cu₂O-NPs/TiO₂-NTs composites demonstrated significant reusability and antibacterial properties, highlighting their potential for sustainable indoor air purification applications. Full article

Air pollution from volatile organic compounds poses significant environmental and public health issues due to their toxicity and persistence in the environment. In this context, this experimental study explored photocatalytic degradation as a promising approach for the degradation of two polluting fatty acids, butyraldehyde (BUTY) and isovaleraldehyde, utilizing a TiO₂ photocatalyst-supported nonluminous textile within a continuous planar reactor. The impact of varying airflow rates (2 to 6 m³/h), initial pollutant concentrations (10 to 60 mg/m³), and air relative humidity (5 to 90%) on oxidation performance and removal efficiency were systematically investigated. The following optimal conditions were identified: an inlet concentration of 10 mg/m³, an airflow rate of 2 m³/h, a catalyst mass of 25 g/m², a UV intensity of 2 W/m², and 50% RH. The luminous textile photocatalytic degradation exhibited notable effectiveness for BUTY removal. To enhance our understanding, a mass transfer model using the Langmuir–Hinshelwood approach as a kinetic model was developed. This modeling approach allowed us to determine kinetic adsorption and degradation constants, reasonably agreeing with the experimental data. This study provides valuable insights into applying nonluminous textile-supported TiO₂ photocatalysts for environmental pollutant removal in continuous planar reactors. Full article

This study aimed to synthesize a multicationic hydrotalcite and transform it into mixed oxide nanostructures (ZnO/TiO₂/CeO₂/Al₂O₃, referred to as MixO) to serve as a heterogeneous photocatalyst for degrading various pollutants, including methylene blue (MB), methyl orange (MO), paracetamol (PA), and paraquat (PQ). The hydrotalcite was synthesized via an ultrasound-assisted method and calcined at 700 °C to obtain the corresponding mixed metal oxide. A comprehensive characterization of both the multicationic hydrotalcite (MC-LDH) and the mixed metal oxides (MixO) was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and pH_PZC analysis. The MixO sample exhibited an optical bandgap of 3.19 eV. Photocatalytic performance was evaluated during 240 min of UV irradiation, demonstrating high degradation efficiencies attributable to the synergistic interactions among ZnO, TiO₂, and CeO₂. Degradation efficiencies reached 99.3% for MO and 95.2% for MB, while PA and PQ showed moderate degradation rates of 60% and 15%, respectively. The degradation kinetics of all pollutant compounds followed the Langmuir–Hinshelwood model. Additionally, the MixO catalyst maintained consistent performance over four consecutive degradation cycles, highlighting its reusability and stability. These findings underscore the potential of MixO mixed oxide nanostructures as practical and recyclable photocatalysts for environmental remediation, particularly in wastewater treatment applications. Full article

This study presents an efficient and environmentally sustainable synthesis of ZnO nanoparticles using a starch-mediated sol-gel approach. This method yields crystalline mesoporous ZnO NPs with a hexagonal wurtzite structure. The synthesized nanoparticles demonstrated remarkable multifunctionality across three critical applications. In photocatalysis, the ZnO NPs exhibited exceptional efficiency, achieving complete degradation of methylene blue within 15 min at pH 11, significantly surpassing the performance of commercial ZnO. Under neutral pH conditions, the nanoparticles effectively degraded various organic dyes, including methylene blue, rhodamine B, and methyl orange, following pseudo-first-order kinetics. The methylene blue degradation process was aligned with the Langmuir–Hinshelwood model, emphasizing their advanced catalytic properties. For supercapacitor applications, the ZnO NPs attained a high specific capacitance of 550 F/g at 1 A/g, underscoring their potential as energy storage solutions. Additionally, the nanoparticles demonstrated strong UV-induced antiradical activity, with an EC₅₀ of 32.2 μg/mL in DPPH assays. Notably, the cytotoxicity evaluation revealed an LC₅₀ of 1648 μg/mL, indicating excellent biocompatibility. This study highlights a sustainable approach for the synthesis of multifunctional ZnO NPs that offers effective solutions for environmental remediation, energy storage, and biomedical applications. Full article

Tetrafluoromethane (CF₄) is the simplest perfluorocarbon, a class of compounds with very high greenhouse gas potential. Catalytic hydrolysis offers an opportunity to convert these compounds to manageable CO₂ and HF. Recently published data showed the effectiveness of Ga-doping to overcome the fluorine poisoning of various Al₂O₃ catalysts at relatively modest temperatures. This prior work offered a partial catalytic mechanism together with kinetic and conversion data. The current paper completes the catalytic mechanism, and then analyzes it using the Langmuir–Hinshelwood algorithm for both the initial CF₄ conversion, and the catalyst site regeneration. The resulting derived rate expression, together with a catalyst activity coefficient expression, are then used in flow reactor configurations to simulate both relatively short exposure time runs with little loss of activity, as well as longer runs with severe activity loss. The reasonable agreement with the published laboratory data suggests that these expressions can be used for a larger-scale practical reactor design. Full article

The wastewater generated by the pharmaceutical industry poses a risk to the environment due to undesirable characteristics such as low biodegradability, high levels of contaminants, and the presence of suspended solids, in addition to the high load of organic matter due to the presence of drugs and other emerging products in the effluent. This study aims to reduce the impact of wastewater pollution by removing amoxicillin (AMO) antibiotics as an organic pollutant. In this concept, two synthesized catalysts, NiAl₂O₄ and ZnO, are sensitive oxides to light energy. The prepared materials were then characterized using X-ray diffraction, UV–vis solid reflectance diffuse, Raman spectroscopy, scanning electron microscopy, BET, and ATR-FTIR spectroscopy. The effects of principal operating parameters under sunlight, namely, the percentage of the mixture of NiAl₂O₄ and ZnO, the pH of the medium, and the initial concentration of the antibiotic were studied experimentally to determine the optimal conditions for achieving a high degradation rate. The results showed that photodegradation is higher at a pH of 6, with a weight percentage of the mixture of 50% for both catalysts in 1 g/L of the total catalyst dose. Then, the effect of the initial concentration of AMO on the photodegradation reaction showed an important influence on the photodegradation process; as the degradation rate decreases, the initial AMO concentration increases. A high degradation rate of 92% was obtained for an initial AMO concentration of 10 mg/L and a pH of 6. The kinetic study of degradation established that the first-order model and the Langmuir–Hinshelwood (LH) mechanism fit the experimental data perfectly. The study showed the success of using heterosystem photocatalysts and sustainable energy for effective pharmaceutical removal, which can be extended to treat wastewater with other organic emerging pollutants. On the other hand, modeling was introduced using Gaussian process regression (GPR) to predict the degradation rate of AMO under sunlight in the presence of heterogeneous ZnO and NiAl₂O₄ systems. The model evaluation criteria of GPR in terms of statistical coefficients and errors show very interesting results and the performance of the model used. Where statistical coefficients were close to one (R = 0.9981), statistical errors were very small (RMSE = 0.1943 and MAE = 0.0518). The results suggest that the model has a strong predictive power and can be used to optimize the process of AMO removal from wastewater. Full article

The root bark extract of the Maerua oblongifolia plant in the green synthesis of titanium dioxide nanoparticles (TiO₂ NPs) for photocatalytic degradation of toxic pollutants and antibacterial activities was implemented in this study. The root bark extract served as a novel capping and reducing agent for the first time. Characterization of the TiO₂ NPs was conducted by using visual observation, ultraviolet visible spectrometry (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques, confirming their successful synthesis. The TiO₂ NPs exhibited maximum absorbance at 323 nm and an average particle size of 19.58 nm; the conjugations and existences of Ti-O and OH vibrational bands were revealed by the FTIR spectrum. The photocatalytic activities of the TiO₂ NPs were investigated by using solar irradiation as an energy source for aqueous solutions of methyl orange (MO) and methylene blue (MB) dyes. The TiO₂ NPs showed strong photocatalytic activities by degrading 97.23% MB and 91.8% MO under optimized conditions. Degradation behavior was investigated by isotherms and kinetics models, with the Langmuir isotherms (R²: 0.996, 0.979) and Langmuir–Hinshelwood (R²: 0.998, 0.997) highest correlation coefficients for MB and MO, respectively. Moreover, the antibacterial efficacy of the green-synthesized TiO₂ NPs and the results indicated higher antibacterial activities on Gram-negative bacteria (27 ± 0.52). Full article

Community drinking water sources are increasingly contaminated by various point and non-point sources, with emerging organic contaminants and microbial strains posing health risks and disrupting ecosystems. This study explores the use of zinc oxide nanoparticles (ZnO-NPs) as a non-specific agent to address groundwater contamination and combat microbial resistance effectively. The ZnO-NPs were synthesized via a green chemistry approach, employing a sol-gel method with lemon peel aqueous extract. The catalyst was characterized using techniques including XRD, ATR-FTIR, SEM-EDAX, UV-DRS, BET, and Raman spectroscopy. ZnO-NPs were then tested for photodegradation of quinoline yellow dye (QY) under sunlight irradiation, as well as for their antibacterial and antioxidant properties. The ZnO-NP photocatalyst showed significant photoactivity, attributed to effective separation of photogenerated charge carriers. The efficiency of sunlight dye photodegradation was influenced by catalyst dosage (0.1–0.6 mg L⁻¹), pH (3–11), and initial QY concentration (10–50 mg L⁻¹). The study developed a first-order kinetic model for ZnO-NPs using the Langmuir–Hinshelwood equation, yielding kinetic constants of equilibrium adsorption and photodegradation of Kc = 6.632 × 10⁻² L mg⁻¹ and kH = 7.104 × 10⁻² mg L⁻¹ min⁻¹, respectively. The results showed that ZnO-NPs were effective against Gram-positive bacterial strains and showed moderate antioxidant activity, suggesting their potential in wastewater disinfection to achieve sustainable development goals. A potential antibacterial mechanism of ZnO-NPs involving interactions with microbial cells is proposed. Additionally, Gaussian Process Regression (GPR) combined with an improved Lévy flight distribution (FDB-LFD) algorithm was used to model QY photodegradation by ZnO-NPs. The ARD-Exponential kernel function provided high accuracy, validated through residue analysis. Finally, an innovative MATLAB-based application was developed to integrate the GPR_FDB-LFD model and FDB-LFD algorithm, streamlining optimization for precise photodegradation rate predictions. The results obtained in this study show that the GPR and FDB-LFD approaches offer efficient and cost-effective methods for predicting dye photodegradation, saving both time and resources. Full article