Polyaniline (PANI) has been widely used as an electroactive material in various applications including sensors, electrochromic devices, solar cells, electroluminescence, and electrochemical energy storage, owing to PANI’s unique redox properties. However, the chemical and electrochemical stability of PANI-based materials is not sufficiently high to maintain the performance of devices under many practical applications. Herein, we report a route to enhancing the chemical and electrochemical stability of PANI through layer-by-layer (LbL) assembly. PANI was assembled with different types of polyelectrolytes, and a comparative study between three different PANI-based layer-by-layer (LbL) films is presented here. Polyacids of different acidity and molecular structure, i.e., poly(acrylic acid) (PAA), polystyrene sulfonate (PSS), and tannic acid (TA), were used. The effect of polyacids’ acidity on film growth, conductivity, and chemical and electrochemical stability of PANI was investigated. The results showed that the film growth of the LbL system depended on the acidic strength of the polyacids. All LbL films exhibited improved chemical and electrochemical stability compared to PANI films. The doping level of PANI was strongly affected by the type of dopants, resulting in different chemical and electrochemical properties; the strongest polyacid (PSS) can provide the highest conductivity and chemical stability of conductive PANI. However, the electrochemical stability of PANI/PAA was found to be better than all the other films.
Zeolite is extensively synthesized for the application in a large variety of catalysis processes such as ion exchange, hydrocarbon cracking, and organic synthesis. In order to satisfy the serious terms of sustainability that denotes to the reduction of costs and chemical waste, kaolinite‐based zeolites were produced from cheap natural resources as against to the conventional process that employs pure sodium silicate and sodium aluminate. This review paper is to highlight the current trends in the synthesis of zeolite. Prior to previous reviews, great concern is focused on the impurities effect on the catalytic performance of kaolinite‐based zeolites. This study reveals that the impact of impurities in a catalytic reaction was in fact, underestimated or neglected. For instance, it was found that Fe ion concentration as small as 60 ppm gives significant catalytic output. Hence, a new practice to report the concentration of impurities in the research publication is suggested. This undoubtedly will generate a better interpretation of the catalytic activity from the zeolite framework.
Owing to its unique structure and reduction–oxidation (redox) properties, polyaniline (PANI) has been widely used in diverse applications, including sensors, solar cells, electrochromic devices, batteries, and supercapacitors. However, irreversible redox reactions between different oxidation states of PANI often result in low chemical and electrochemical stability, deteriorating devices’ performance characteristics. Herein, we fabricated PANI-based multilayer films using spin-assisted layer-by-layer assembly, providing significantly improved chemical and electrochemical stability compared to the PANI homopolymer. More importantly, we found that the electroactivity and electrical conductivity of PANI-based films can be restored by a simple chemical reactivation process using an acidic aqueous solution. The re-doping process successfully recovers the electrochemical properties of PANI, even improving the electroactivity and conductivity characteristics of polyacid-doped PANI films, attributed to the secondary doping and rearrangement of polymers. Furthermore, we demonstrate that the performance of PANI multilayer films for ammonia sensors is successfully restored after the reactivation process.
Synthetic fragrance has dominated the perfumery industry in recent decades due to the ability to produce perfumery ingredients on a large scale at a low cost. Extensive research in the field of synthetic perfumery chemical involved the utilization of catalysts to improve the productivity. This review will discuss recent advances of heterogeneous catalysts for the synthesis of perfumery chemicals as fragrance ingredients. Transition from homogeneous to heterogeneous catalysts will be included in order to provide insight into the benefits of heterogeneous catalysts to overcome the limitation of homogeneous reaction. Isomerization, acetalization and hydrogenation were identified as three main reactions for the synthesis of perfumery chemicals based on the number of reported work since 2000. This review will focus on α‐pinene and α‐pinene oxide as the main molecular substrates, however, different molecules, for example, linalool, citronellal and cinnamaldehyde will also be included. The synthesis, modification and possible mechanisms for the reactions involving zeolite, aluminosilicate, metal oxides, metal organic framework, monometallic and bimetallic nanoparticles as heterogeneous catalysts will be discussed. Discussion on isomerization and acetalization reactions will focus on the acidity and the porosity of the catalysts as the two main factors that determine the conversion and selectivity. For perfumery chemicals produced via hydrogenation reaction, the role of monometallic and bimetallic nanoparticles catalysts will be discussed in the chemoselective reduction of cinnamaldehyde and citronellal.
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