Inorganic Chemistry Frontiers Blog

Since Wilson and Flanigen found the first microporous aluminophosphate (AlPO) in 1982, the synthesis of AlPO materials with novel frameworks and study their potential properties, such as adsorption, catalysis, and separation, has attracted intense interest of researchers. As the main family of AlPO based materials, 2D layered materials show a rich variety of structures and compositions depending on the diverse coordination and connection modes of Al and P atoms. In recent years, 2D materials, possessing highly exposed surfaces and diverse structures, have become a dramatic category of supports. However, 2D molecular sieves are serving as catalyst supports are very few.

Recently, Prof. Jiuxing Jiang at Sun Yat-sen University and Dr. Jiang-Zhen Qiu of Zhongkai University of Agriculture and Engineering synthesized a new 2D layered aluminophosphate compound by adopting rigid and bulky template of 3,5,N,N-tetramethyladamantane-1-amine (ada) through hydrothermal conditions, which is named the Zhongkai University of Agriculture and Engineering NO.1 (ZHKU-1), with the composition |Hada|₆[Al₆(PO₄)₈](H₂O)₁₁. The structure of ZHKU-1 was constructed from the alternate connection of AlO₄ and triply bridged PO₄ tetrahedra ([O=PO₃]^3-) to form a 4, 6, 12-net (Figure 1). The inorganic sheets are linked and separated by protonated amine and H₂O molecules by extensive H-bonds, giving a new 2D structure with an interlayer space of 19.6 Å.

ZHKU-1, as a 2D material with a more exposed surface, could be adapted for encapsulating metal nanoparticles (NPs). Ag species are immobilized on the supports of ZHKU-1 by UV reduction and deposition, forming the catalyst of Ag@ZHKU-1 with high loading of 4.9 wt%. The HRTEM images reveal the highly uniform Ag clusters with visually observed sizes of 1.9 nm (Figure 2).

Since 4-nitrophenol (4-NP) is a notorious industrial pollutant, Ag@ZHKU-1 is applied to the model reaction for 4-NP reduction. The catalytic results show that the reduction reaction of 4-NP into 4-aminophenol could be completely performed within 75 s in NaBH₄ solution (Figure 3). Moreover, the catalytic activity was almost the same, with almost 99% conversion after eight cycles. The remarkable catalytic activity and recyclability of Ag@ZHKU-1can be attributed to the high dispensability of Ag nanoclusters confined to the 2D support, which provides more accessible Ag active sites to 4-NP.

This work reports a new 2D layered aluminophosphate compound, which expends the aluminophosphates family. Furthermore, the confinement of metal Ag on this new layer structure through photodeposition gives rise to a small size (~1.9 nm) of AgNPs with homogeneous dispersion. The catalyst of Ag@ZHKU-1 shows excellent catalytic activity and high conversion for 4-nitrophenol reduction. This work is significant for designing 2D aluminophosphate materials to confine small metal nanoparticles for catalytic application.

Prof: Jiuxing Jiang (ORCID: 0000-0001-9664-3235). I received Ph.D degree from Jilin University in 2010. Afterward, I spent 5 years for a Post Doc. stay in Instituto Technologia Quimica (UPV-CSIC) in Valencia Spain supervised by Prof: Avelino Corma. After independent work in Sun Yat-sen University (2015-now), I keep my interesting on the topologically new zeolite synthesis (four three letter code, IRR, -IRY, -IFU, -SYT were granted by Structure Committee of Internation Zeolite Association), and zeolite based heterogeneous catalysis, such as: acid-base catalysis, catalytic ammonium synthesis, NH₃-SCR for deNOx reaction, porous materials for energy storage, etc. I have published more than 20 high-impact journal articles, such as Science, Angew. Chem. Int, Ed, Chem.Sci, Chem. Mater. etc. Among them, the work on the synthesis and structure of zeolite ITQ-43 was published in Science, 2011, 333, 1131-1134 and was selected as annually breakthrough of 2011 by Science. Currently serve as a member of Zeolite Committee of Chinese Chemical Society and youth editorial member of Journal of Chemical Research in Chinese University.

Jiang-Zhen Qiu: She received her Ph.D. degree in 2019 from Sun Yat-sen University with M.S. Supervisor Prof. Ming-Liang Tong and Ph.D. Supervisor Prof. Jiuxing Jiang. In 2020, she was introduced to Chemical Engineering of Zhongkai University of Agriculture and Engineering as an “Excellent Doctor”. Her interested research fields include synthesizing new topological structures of zeolite and exploring multifunctional materials with novel functionalities such as light, conductivity, magnetism, or catalysis. Currently, she and her collaborators published 10 papers in related fields, such as Chem. Mater., Chem. Sci., Inorg. Chem. Front., Chem. Commun., Chem. Eur. J.

 

Magnetic Resonance Imaging (MRI) is one of the most important and prominent techniques in in clinical diagnostic medicine, in preclinical studies and in biomedical research. As well as many other imaging modalities, MRI also makes extensive use of contrast agents (CAs) that allow achieving remarkable improvements in medical diagnosis in terms of higher specificity, better tissue characterization and functional information. For the vast majority, the clinically used CAs are coordination complexes in which a Gd^III ion is encapsulated within octadentate chelators based on polyaminocarboxylate anions and has a directly bound water molecule. Their use is widespread and is estimated to correspond to approximately 40 million administrations per year of Gd^III chelates worldwide.

Their effectiveness (relaxivity; the increase in the relaxation rate R₁ of the water protons normalized to a 1 mM concentration of the paramagnetic ion) at the magnetic fields of clinical interest is dominated and limited by the fast rotational dynamics and tends to decrease with the increased magnetic field. However, the current trend in MRI development is towards higher magnetic field strengths and most scanners operate at 1.5 or 3 T, while there is increasing use of those at 7 T. Therefore, a different approach for the relaxivity enhancement of Gd-based CAs becomes necessary for the modern high-field systems.

Recently, the group of Mauro Botta and colleagues from the University of Eastern Piedmont in Alessandria (Italy) investigated the optimization of the efficacy of Gd-based CAs, between 1 and 7 T, by systematically modulating the rotational dynamics through the synthesis of polynuclear systems containing between two and eight Gd^III chelates (Figure 1).

The [Gd(AAZTA)(H₂O)₂]^– chelate was used as a building block due to its remarkable properties: a) ease and high-yield synthesis, presence of two inner sphere water molecules in fast exchange with the bulk; b) high thermodynamic stability; c) kinetic inertness in the presence of physiological concentrations of Cu^II and Zn^II higher than that of the clinical agent [Gd(DTPA)]^2-; d) negligible tendency to formation of ternary complexes with endogenous anions. The study demonstrates that the strategy for relaxation enhancement varies with the strength of the magnetic field used.

Up to 3 T, efficacy is limited by molecular rotation and therefore increases proportionally with the increase in molecular size. Between 3 and 7 T, the issue of local flexibility or anisotropic rotation, evaluated with NMR techniques and computational models, becomes more and more relevant and medium-sized rigid systems (tri- or tetranuclear) provide the best results. At ultra-high fields (> 7 T), small and compact mono- or binuclear complexes are most effective (Figure 2).

 

The results of this study allow identifying the most effective strategy for optimizing the CAs, each suited to a well-defined range of applied magnetic field strength.

 

Mauro Botta is full professor of Inorganic Chemistry in the Department of Sciences and Technological Innovation at the University of Eastern Piedmont (Italy). He received the “Laurea” cum laude in Chemistry at the University of Turin in 1985. His scientific interests have focused on the use of NMR techniques for the characterization of inorganic systems, starting from organometallic clusters and then moving on the complexes of the f-elements. Recipient of the “Raffaello Nasini” gold medal award for Inorganic Chemistry of the Italian Chemical Society and of the “GIDRM gold medal for magnetic resonance”. He has published over 280 papers (index H = 63; citation: 12800) and several book chapters on these topics and filed 5 patents.