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Phosphoric Acid Catalysis
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
Exploring the idea of utilizing chiral phosphates as PTCs, Toste and coworkers described the first example of catalytic chiral anion PTC in 2008 (Figure 3.18).52 Starting with racemic β-chloro tertiary amine, meso-aziridinium ion was generated in situ in the presence of CPA P and solid Ag2CO3 in toluene. The lipophilic chiral phosphate transferred silver cation from the surface of silver carbonate into the bulk solution where it abstracted chloride and triggered the ring closure to form chiral azridinium ion pair. The formation of insoluble AgCl salt drove the formation of aziridinium-phosphate ion pair, which then underwent enantioselective ring opening through the nucleophilic attack by alcohol. The proposed roles of chiral phosphate and the intermediacy of aziridinium ion were supported by several observations: (1) only double inversion products were isolated, (2) the reaction did not proceed in the absence of either CPA P or Ag2CO3, and (3) low enantioselectivity (56%) was obtained when more soluble AgOTf was used. In other words, silver cation was essential for the reaction to proceed, and there was no silver cation in the bulk solution without the presence of CPA as the phase transfer agent. The authors also discovered that the silver phosphate preformed from CPA P was equally effective in catalyzing this reaction.
Basic of the Chalcogenides
Published in Abhay Kumar Singh, Tien-Chien Jen, Chalcogenide, 2021
Abhay Kumar Singh, Tien-Chien Jen
Ravaine and Souquet proposed a model in 1977. It was based on data obtained by thermodynamic activity measurements on a series of sodium silicate glasses [137]. Later Reggiani et al.[138] and Levasseur et al. [139] studied this model’s utility for silver phosphate and lithium borates glasses. They demonstrated that the data of the glasses acted as weak electrolytes. With this in mind, Ravaine and Souquet demonstrated that glass acts as an electrolyte with the glassy network being the solvent and the modifier being the solute. In any weak electrolyte, the solute would be weakly disassociated leading to only a small fr action of the cations mobility at time t.
Photocatalysts Based on Covalent Organic Frameworks
Published in Tuan Anh Nguyen, Ram K. Gupta, Covalent Organic Frameworks, 2023
Nazanin Mokhtari, Mohammad Dinari
Traditionally, the leading position of photocatalysis has been occupied by inorganic semiconductors, including silver phosphate ( Ag3PO4 ) [3], zinc oxide (ZnO) [4], cadmium sulfide (CdS) [5], and titanium dioxide ( TiO2 ) [6]. The diversity of inorganic semiconductors has increased over the past several decades; however, the popularity of TiO2 is maintained due to its low cost, relatively high availability, and durability. Besides TiO2 , other oxides and sulfides of transition metals such as Ag3PO4 and CdS represent the excellent capacity of charge carrier transportation. However, environmental concerns of heavy metal usage and the photo-corrosion effect limited their practical applications [7]. Therefore, finding new semiconductors becomes a long-lasting challenge for investigators. Organic semiconductors have come to the attention of researchers as a new solution to face the challenge of environmental issues. Graphitic carbon nitride (g- C3N4 ) [8], metal-organic frameworks (MOFs) [9], and covalent organic frameworks (COFs) [10] were introduced to be used as promising alternatives for photocatalytic solar energy conversion.
Sustainable decoloration of polluted water through cellulosic TiO2 nano- crystalline material composite using sono synthesis
Published in The Journal of The Textile Institute, 2023
Syed Rashedul Islam, Md. Mehedi Hasan, Xiaolin Shen, Tayyab Naveed, Mohammed Kayes Patoary, Jinhua Jiang, Afshan Zareen
Semiconductors like bismuth oxybromide (BiOBr), tin oxide (SnO2), silver phosphate (Ag3PO4), titanium dioxide (TiO2), etc., potentially assisted in accelerating photocatalytic phenomenon (Zhao & Wu, 2018). Amongst them, TiO2 has been widely exploited due to its effectual photocatalytic degradation, low toxification, low cost, profusion, chemical, and thermal stability, corrosion resistance, and oxidative ability (Qu et al., 2018; Li et al., 2012). Further, its limitations about charge electron separation efficiency, surface wettability, and n-type wider band gap (3.2 eV) have also been improved through many strategies like metallic (Ag, Au, Bi) and non-metallic (N2, P4) doping, structural optimization, dye sensitization, and defect engineering, etc (Moridi Mahdieh et al., 2018; Pakdel et al., 2017; Yu et al., 2017; Murcia et al., 2019). For instance, semiconductor composite and heterophase interfaces have made the electronic transition easier and augmented the photocatalytic degradation through excitation of electrons under the ultraviolet light absorption thus making it more superior than anatase or rutile phase TiO2 (Lyu et al., 2020).
Photocatalytic oxidation of pollutants in gas-phase via Ag3PO4-based semiconductor photocatalysts: Recent progress, new trends, and future perspectives
Published in Critical Reviews in Environmental Science and Technology, 2022
Y. Naciri, A. Hsini, A. Bouziani, R. Djellabi, Z. Ajmal, M. Laabd, J. A. Navío, A. Mills, C. L. Bianchi, H. Li, B. Bakiz, A. Albourine
Silver phosphate is believed to be the most effective photocatalysts recorded to date since its first application in photocatalysis in 2009. Also, it is considered to be the most efficient visible-light-driven photocatalyst exhibiting remarkable photocatalytic properties than commonly employed oxidative photocatalysts such as TiO2, ZnO, BiVO4, and WO3. The only drawback for Ag3PO4 use as a photocatalyst is its photo-corrosion, which limits its potential in photocatalytic reactions. Consequently, many research efforts have been devoted to improving Ag3PO4 stability and its photocatalytic performance in environmental photo remediation studies. This review reveals that its incorporation in a Z- scheme semiconductor heterjunction with other photocatalyst or into a more conventional type-II heterojunction could effectively enhance its stability and photocatalytic activity toward gaseous pollutants elimination. The enhanced photocatalytic oxidation of gaseous contaminants is closely associated with narrow bandgap energy, improved absorption light range, reduce electron-hole pair recombination, faster charge transfer, and negligible photo-corrosion.
Improve the structure through pH-control to improve the photocatalytic performance of cubic silver phosphate photocatalyst
Published in Journal of Dispersion Science and Technology, 2022
Jin Wang, Yongfeng Cai, Hanxiao Du, Yi Shen, Fengfeng Li, Zuotao Liu, Yunfeng Liu, Chao Peng
In a typical precipitation reaction, NH3·H2O was added dropwise to the AgNO3 solution with stirring until the resulting brown precipitate just completely dissolved, getting the silver ammonia solution. The pH of the silver ammonia solution was adjusted to 6, 7, 8, 9 and 10 by slowly adding HNO3 and NH3·H2O. Then, the KH2PO4 solution was added dropwise to the silver ammonia solution with stirring for 30 min in the dark. Let the mixture stand in the dark for 5 min, and then drained the supernatant with a straw after it has settled completely. (The filtration will accelerate the oxidation of silver phosphate and the destruction of its structure, thus the milder precipitation method was used.) Finally, the as-obtained precipitate was washed twice via distilled water and ethyl alcohol absolute and kept in an oven at 70 °C for 20 min. The samples 6-Ag3PO4 (noted as A6), 7-Ag3PO4 (noted as A7), 8-Ag3PO4 (noted as A8), 9-Ag3PO4 (noted as A9) and 10-Ag3PO4 (noted as A10) were noted, respectively. When the pH < 6 or pH > 10, it is worth mentioning that the precipitate of Ag3PO4 will not be generated due to the greater solubility of Ag3PO4 in strong acids and alkalis. Therefore, only samples with pH = 6–10 are discussed in this paper.