Reaction Kinetics, Mechanisms and Catalysis最新文献

This study presents a rapid and eco-friendly method for synthesizing carbon dots (CDs) using Cleome viscosa (CV) seeds powder via microwave carbonization. The synthesized CDs exhibit bright blue fluorescence under UV light, with a relative fluorescence quantum yield of 9.3%. Transmission electron microscopy (TEM) analysis revealed that the CDs possess an average diameter of 4.9 ± 1.2 nm and a spherical morphology and X-ray diffraction (XRD) patterns indicating their amorphous nature. Moreover, the CDs demonstrate robust fluorescence emission stability under diverse conditions including exposure to salt, continuous UV irradiation, pH variations, and prolonged storage. Furthermore, catalytic studies employing NaBH₄-assisted reduction showcased the remarkable catalytic activity of the CDs towards the degradation of methylene blue (MB) and rhodamine B (RhB) dyes. The kinetics of the catalytic process followed pseudo first-order kinetics, yielding rate constants of 0.118 ± 0.002 min⁻¹ and 0.161 ± 0.007 min⁻¹ for MB and RhB, respectively. These findings underscore the potential of CV seed-derived CDs as efficient and versatile catalysts for wastewater treatment applications.

Herein, we reported the synthesis of cobalt (Co)-doped graphitic carbon nitride (Co@g-C₃N₄) and its application in photocatalytic H₂ production. The formation, phase, crystalline nature, surface morphology, and elemental composition of the Co@g-C₃N₄ have been examined by XRD, SEM, XPS, and EDX spectroscopy. The platinum has been introduced as a cocatalyst and Co@g-C₃N₄/Pt (3 wt%) exhibited excellent photocatalytic performance towards the generation of H₂. The synthesized Co@g-C₃N₄/Pt (3 wt%) material exhibited a significant amount of H₂ production rate of 6347 µmol/g surpassing that of Co@g-C₃N₄ in the presence of TEOA sacrificial agent. The improved photocatalytic performance of the synthesized photocatalyst can be attributed to the synergistic interaction and Schottky barrier formation among Pt, Co, and g-C₃N₄, facilitating efficient charge separation and transportation of photo-induced charge carriers. This study has the potential to open up new avenues for addressing energy and environmental challenges through H₂ production.

This study investigated the use of waste dragon fruit peel extract (DF) as a reducing and stabilizing agent for preparing palladium nanoparticles (PdNPs) using a microwave-assisted technique. The effects of various synthetic parameters including pH, PdCl₂ concentration, and DF concentration on PdNPs production were examined in detail. Several techniques were employed to characterize the morphology, microstructure, functional groups, and crystallinity of as obtained nanoparticles (DF@PdNPs). The formation of PdNPs in the reaction solution was confirmed by a visible black color and broad surface plasmon absorption in the UV–vis spectrum. FTIR studies revealed the role of phytochemicals in nanoparticle reduction and stability. The produced PdNPs were spherical/oval in shape, evenly polydisperse, had an average size of 9±1.5 nm, and were well stabilized (zeta potential =  − 36.3 mV) by the extract phytochemicals. They also had a face-centered cubic crystal structure. The catalytic performance of DF@PdNPs was assessed by the NaBH₄ assisted reduction of 4-nitrophenol to 4-aminophenol, with a kinetic constant value of 0.155±0.029 min⁻¹. Furthermore, the catalyst successfully reduced methylene blue dye within 6 min, with a rate constant of 0.422±0.021 min⁻¹

Adsorption and reaction site heterogeneity of titania-supported (10%Co + 0.5%Pd) catalysts in CO hydrogenation was studied by chemisorption, temperature-programmed desorption, and diffuse reflectance infrared Fourier transform spectroscopy techniques. Precursor material was treated in various media as reductive, inert, or oxidative. Cobalt metal sites and TiO₂ support heterogeneity were proved. Upon H₂ chemisorption, a pre-reduced sample exposed mostly homogeneous metal surface. Surface heterogeneity toward CO chemisorption depended on preliminary treatment. A catalyst prepared in inert medium revealed moderate activity dynamics of adsorption and reaction sites. Weak to medium strength sites toward hydrogen adsorption were relatively strong in terms of CO adsorption. Carbonate-(like) species occupied medium and strong sites on the support. Sites of weak strength for CO adsorption were active in hydrogenation but very strong in terms of CH_x intermediates adsorption.

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This research investigated the performance of bentonite and Al-PILC as catalysts in ethanol conversion to diethyl ether through a dehydration reaction. The natural bentonite was intercalated with the pillaring agent Keggin-ion Al₁₃ to obtain Al-intercalated bentonite. Al-intercalated bentonite has been synthesized using conventional stirring and ultrasonication. Al-intercalated bentonite was calcined at 400 °C for 4 h to produce Al₂O₃ pillared bentonite (Al-PILC). The dehydration reaction was conducted using a 0.2 g catalyst and 10 mL of ethanol with a nitrogen gas flow rate of 20 mL/min at various reaction temperatures (200, 225, and 250 °C) using a fixed bed microreactor. The characterization results reveal that Al-PILC synthesized by sonochemistry exhibits significantly higher surface area and total acidity values than bentonite and Al-PILC synthesized by conventional methods because of the formation of stable Al₂O₃ pillars in the interlayer spaces of bentonite. The sonochemically synthesized Al-PILC produces optimum ethanol conversion and diethyl ether yield of 46.05% and 41.11%, respectively. The conversion of ethanol and diethyl ether yield reaches an optimum result at 225 °C. Based on this study, the pillarization of bentonite using Al₂O₃ can enhance its catalytic properties toward diethyl ether production.

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Catalytic performance of zirconyl hydrogen tellurate (ZrOHTe) and hafnium hydrogen tellurate (HfHTe) was studied for the first time. A process of butyl acetate synthesis was used as a test reaction. A number of physicochemical techniques (XRD, SEM, TGA/DSC and XPS) was applied for catalyst characterization. Using molecular electrostatic potential and net atomic charges, both the electronic structure and the chemical reactivity of ZrOHTe and HfHTe were considered. Kinetic (activation energy, pre-exponential factor) and thermodynamic (enthalpy, entropy, Gibbs free energy barrier) parameters were calculated. A plausible reaction mechanism for esterification was offered. Particles of a low crystallinity degree or small-sized crystallites were found to form ZrOHTe and HfHTe. The fragments in ZrOHTe/HfHTe are prismatic/layered in shape with an average size around 160 μm. XPS exposed that ({text{HTeO}}_{4}^{-}) managed the surface phenomena for ZrOHTe and HfHTe. A higher butyl acetate yield using ZrOHTe than HfHTe due to higher surface acidity of the former was generated.

The present study investigated the degradation of trimethoprim using Eosin Y-sensitized ZnFe₂O₄-g-C₃N₄ photocatalyst under natural sunlight using a parabolic trough reactor. The photocatalyst performance was optimized for three independent variables: pollutant dosage (10–25 mg/l), catalyst dose (0.4–1.2 g/l), and solution pH (4–10). The central composite design (CCD) was used to generate the design matrix and the response surface for degradation and total organic carbon (TOC) removal as the responses. Multiple regression techniques for each response generated two quadratic polynomial models. The coefficient of determination (R²) for trimethoprim degradation and TOC removal was 0.99 and 0.96, respectively, and these models could explain the variability in response surface. The analysis of variance (ANOVA) revealed that the initial pollutant dose and catalyst dose were most significant (p < 0.05) in contributing to both degradation and TOC removal. The optimum parameters obtained by desirability function for pollutant concentration, pH, and catalyst concentration were 10 mg/l, 7.19, and 0.72 g/l. This yielded an optimum degradation and TOC removal of 89.52% and 49.12%, respectively. Validation studies using optimized conditions for single-factor experiments had negligible variation from the predicted values, with actual degradation and TOC removal being 87.02% and 46.33%, respectively. Considering the good predictability and validity of the models, Response Surface Methodology is a potential mathematical tool for modeling the photodegradation of different antibiotics in aquatic environments.

The present work aims to synthesize bimetallic CuZn-ZIFs using a solvothermal method to degrade Basic Fuchsin in an aqueous solution in the presence of hydrogen peroxide (H₂O₂) under ambient conditions. Zn and Cu were loaded successfully on the ZIF structure due to the linkage of Cu–N and Zn-N found by FT-IR. The combination of Cu/Zn on the ZIF structure enhanced the specific surface area up to 1568.4 m² g⁻¹ and 0.48 cm³ g⁻¹ of pore volume, which can facilitate the performance of BF degradation. Under the optimum conditions, including a reaction time of 20 min, an initial BF concentration of 30 mg L⁻¹, and catalyst dosage of 0.1 g L⁻¹, H₂O₂ level of 0.03 mol L⁻¹, the efficiency degradation of BF achieved significantly high with above 96% through Fenton-like mechanism. CuZn-ZIFs also performed higher catalytic activity compared to some homogeneous and other heterogeneous catalysts. Notably, it was observed that the catalytic activity of CuZn-ZIFs mostly remained after five cycles. The study offers valuable insights into the utilization of novel materials for potential applications in pollutant treatment and environmental remediation.

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In this study, Bi₂Fe₄O₉ photocatalysts were prepared using hydrothermal synthesis. Different morphologies of Bi₂Fe₄O₉ with a mullite-type structure were prepared using various hydrothermal synthesis methods while controlling the concentration of the mineralizer NaOH. The characterization of photocatalysts involves the use of various methods such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy, and electrochemical impedance spectroscopy. The photocatalytic performance of the samples was evaluated by testing their sterilization effect on natural seawater. The study found that when exposed to simulated sunlight using a small amount of H₂O₂, Bi₂Fe₄O₉ cubes exhibited exceptional photocatalytic activity in deactivating marine microorganisms. This was attributed to the fact that the primary exposed surface of the Bi₂Fe₄O₉ cubes was (001), which has a low recombination rate of photoelectrons and holes. Electrons can react with H₂O₂ to generate more hydroxyl radicals, thereby enhancing the photocatalytic sterilization performance. The experiment on free radical capture demonstrated that the ·OH radical was the primary active substance in the sterilization process. This paper introduces a novel concept for the photocatalytic purification of seawater.

The current investigation introduces a novel diatomite-TiO₂/ZnS photocatalyst tailored to address the challenges posed by organic dye pollution while concurrently providing antibacterial activity. The methodology commences with diatomite purification, followed by the deposition of nanoparticles forming a heterojunction system between ZnS and TiO₂ on the diatomite surface, culminating in the development of the nanocomposite. Notably, the optical absorption edge of the diatomite-TiO₂/ZnS nanocomposite resides within the UV light spectrum. Subsequent heat treatment at 500 °C heightens the system’s responsiveness to UV radiation. The nanocomposite exhibits exceptional efficacy in the photocatalytic degradation of rhodamine B dye. The optimal catalyst, DTZS 500, achieves a remarkable 98% degradation of rhodamine B within 180 min, boasting a pseudo-first-order constant of 0.03299 min⁻¹, which is twice that of P25. Furthermore, nearly complete mineralization of organic matter is evidenced by chemical oxygen demand (COD) measurements. These superior performances are ascribed to the well-dispersed TiO₂ and ZnS on the diatomite surface, the adsorption properties of diatomite, and the effective separation of photo-generated electron–hole pairs facilitated by the formation of a heterojunction system between TiO₂ and ZnS. Moreover, the nanocomposite exhibits notable antibacterial effects against S. aureus, as evidenced by substantial inhibition zones measuring 38 mm in diameter. This study thus presents a promising avenue towards the provision of highly efficient and economical solutions for water treatment, encompassing both photocatalysis and bacterial disinfection.

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