Preparation and catalytic evaluation of Au/γ -Al2O3 nanoparticles for the conversion of 4-nitrophenol to 4-aminophenol by spectrophotometric method

Study of amorphous alumina coatings for next-generation nuclear reactors: High-temperature in-situ and post-mortem Raman spectroscopy and X-ray diffraction

The present work focuses on the investigation of the thermal stability and structural integrity of amorphous alumina coatings intended for use as protective coatings on cladding tubes in Generation IV nuclear reactors, specifically in the Lead-cooled Fast Reactor (LFR) type. High-temperature Raman spectroscopy and high-temperature X-ray diffraction analyses were carried out up to 1050 °C on a 5 µm coating deposited by the pulsed laser deposition (PLD) technique on a 316L steel substrate. The experiments involved the in-situ examination of structural changes in the material under increasing temperature, along with ex-situ Raman imaging of the surface and cross-section of the coating after thermal treatments of different lengths. As it was expected, the presence of α-alumina was detected with the addition of other polymorphs, γ- and θ-Al2O3, found in the material after longer high-temperature exposure. The use of two structural analysis methods and two lasers excitation wavelengths with Raman spectroscopy allowed us to detect all the mentioned phases despite different mode activity. Alumina analysis was based on the emission spectra, while substrate oxidation products were identified through the structural bands. The experiments depicted a dependence of the phase composition of oxidation products and alumina's degree of crystallization on the length of the treatment. Nevertheless, the observed structural changes did not occur rapidly, and the coating's integrity remained intact. Moreover, oxidation signs occurred locally at temperatures exceeding the LFR reactor's working temperature, confirming the material's great potential as a protective coating in the operational conditions of LFR nuclear reactors.

Catalytic innovations: Improving wastewater treatment and hydrogen generation technologies

The effective reduction of hazardous organic pollutants in wastewater is a pressing global concern, necessitating the development of advanced treatment technologies. Pollutants such as nitrophenols and dyes, which pose significant risks to both human and aquatic health, making their reduction particularly crucial. Despite the existence of various methods to eliminate these pollutants, they are not without limitations. The utilization of nanomaterials as catalysts for chemical reduction exhibits a promising alternative owing to their distinguished catalytic activity and substantial surface area. For catalytically reducing the pollutants NaBH4 has been utilized as a useful source for it because it reduces the pollutants quiet efficiently and it also releases hydrogen gas as well which can be used as a source of energy. This paper provides a comprehensive review of recent research on different types of nanomaterials that function as catalysts to reduce organic pollutants and also generating hydrogen from NaBH4 methanolysis while also evaluating the positive and negative aspects of nanocatalyst. Additionally, this paper examines the features effecting the process and the mechanism of catalysis. The comparison of different catalysts is based on size of catalyst, reaction time, rate of reaction, hydrogen generation rate, activation energy, and durability. The information obtained from this paper can be used to steer the development of new catalysts for reducing organic pollutants and generation hydrogen by NaBH4 methanolysis.

A study on rapid and stable catalytic reduction of 4-nitrophenol by 2-hydroxyethylamine stabilized Fe3O4@Pt and its kinetic factors

The successful development of efficient and stable catalysts for 4-NP reduction reactions is beneficial to the environment and ecology. Fe3O4@Pt exhibits excellent catalytic performance for 4-NP reduction reaction due to the synergistic effect between Fe and Pt. But its structure and catalytic performance are extremely unstable. Here, we utilized the small-scale organic compound 2-hydroxyethylamine as surfactant to construct a stable composite nanomaterial. Then investigated the influence of monochromatic light (650 nm, 808 nm and 980 nm) and temperature on the kinetics of 4-NP reduction reaction by 2-hydroxyethylamine stabilized Fe3O4@Pt. The results indicate that both temperature and monochromatic light radiation can affect kinetic regulation. Increasing temperature can promote the catalytic rate, while monochromatic light radiation can induce agglomeration and inhibit the catalytic rate. This study opens up a new way for developing and regulating catalysts for heterogeneous catalysis reactions.

Enhancing catalytic activity of gold nanoparticles in a standard redox reaction by investigating the impact of AuNPs size, temperature and reductant concentrations

In this work, the catalytic activity of three different sizes of gold nano particles (AuNPs) (12, 30, and 45 nm) synthesized by the citrate reduction process studied in the conventional redox reaction of K₃Fe (CN₆)^-3 to K₄Fe (CN₆)^-4 using NaBH₄(reductant) at four different temperatures (5 °C, 10 °C, 15 °C, and 20 °C) and measured by UV-visible spectrophotometry. Comparative kinetic analysis of different sizes of AuNPs including rate constant, activation energy, Entropy values and Frequency of collisions are reported for the first time. Transmission electron microscopy analysis is employed to investigate morphology and particle size. Spherical nanoparticles of size 12, 30, and 45 nm were observed. The UV-visible spectra were recorded at regular intervals, and it was seen that the peak of K₃Fe (CN₆)^-3 decreased gradually with time, at the same time surface plasmon resonance of AuNPs remained constant. As reaction catalysts, AuNPs maintain their optical density which shows their stability during the course of reaction. The kinetic parameters i.e., rate constant, and activation energy (k, t_1/2, E_a) were determined for three distinct sizes of gold nanoparticles (AuNPs) using the reductant at various concentrations. The value of k increases by increasing reductant concentration. This rise was significant for the small AuNPs. Increasing gold nanoparticle size (12, 30, 45 nm) decreased rate constant. As the size of AuNPs decreased the E_a reduced as well, i.e. 17.325 k cal mol^-1 for 12 nm, 19 k cal mol^-1 for 30 nm and 21 k cal mol^-1 for 45 nm AuNPs. For 50 mM of NaBH₄, k for 45 nm AuNPs is 0.10728 s^-1, but for 12 nm AuNPs, the value of k is 0.145 s^-1, indicating that the 12 nm AuNPs have the greatest rate constant values. The rate of reaction rises with an increase in reductant concentration and temperature, but this increase is significant in the case of small-sized nanoparticles, i.e., 12 nm, which have a high surface area and low E_a. Besides being a model redox reaction, the reduction of K₃Fe (CN₆)^-3 to K₄Fe (CN₆)^-4 has industrial use in making fertilizers and paint industry, anti-coating agent in colour photography, in dot etching and in amperometric biosensors.

Remarkably and stable catalytic activity in reduction of 4-nitrophenol by sodium sesquicarbonate-supporting Fe2O3@Pt

Reasonable design of bimetallic nanomaterials with support is beneficial to improve catalytic performance. This work reports a new kind of sodium sesquicarbonate-supporting Fe₂O₃@Pt via etching Fe₃O₄@Pt@SiO₂, which exhibits highly efficient and stable catalytic reduction performance towards 4-NP. Sodium sesquicarbonate-supporting Fe₂O₃@Pt has an interconnected one-dimensional network structure that provides sufficient channels for mass transfer. At the same time, a large amount of Fe₂O₃@Pt is exposed on its surface, which hinders the aggregation of pt clusters and Fe₂O₃ nanoparticles, and facilitates the direct contact of Fe₂O₃@Pt reaction sites with reactant molecules, thus improving the catalytic rate of 4-NP reduction reaction. Moreover, the introduction of non-metallic Fe can not only reduce the consumption of precious metal Pt, but also improve the catalytic efficiency due to the synergistic effect. This study opens up a new avenue to develop robust catalysts for heterogeneous catalytic reactions.

A study on the high efficiency reduction of p-nitrophenol (4-NP) by a Fe(OH)3/Fe2O3@Au composite catalyst

Precious metal nanometric catalysts are widely used in the removal of harmful substances. In the process of synthesis and catalytic reaction, it is particularly important to study green and simple synthesis methods and high catalytic efficiency. In this paper, a green one-step method was used to synthesize the Fe(OH)₃/Fe₂O₃@Au composite catalyst, in which Au was single atom-dispersed. The removal of 4-nitrophenol (4-NP), a typical dangerous chemical widely existing in factory waste gas, waste water and automobile exhaust gas, was catalysed by Fe(OH)₃/Fe₂O₃@Au. The catalytic performance of Fe(OH)₃/Fe₂O₃@Au with different synthesis conditions (different amounts of MES, NaBH₄, FeSO₄, Au and Pt) on the 4-NP reduction reaction were systematically studied. Finally, the stability and recyclability of Fe(OH)₃/Fe₂O₃@Au composite nanocatalyst were investigated thoroughly.