Abstract
HZSM-5 (MFI type) of composition (Hx)[Al3+xSi12−xO24] × wH2O and nanocomposites NA/HZSM-5, NA:M/HZSM-5 (NA—nanoscale anatase; M = V, Ni, Ag) with Si/Al = 12, 25, 40, 300 (sp.gr. Pnma or P21/n; z = 8), as well as zeolites [(Ti4+xSi12−xO24] × wH2O (TS) with Si/Ti = 47, 53, 73.5 (sp.gr. Pnma) were studied by XRPD, XAS, FTIR-spectroscopy, BET, XPS, SEM, EDX, TPD, UV–VIS-spectroscopy, UV–DRS, and chemiluminescence methods. The results obtained together with photocatalytic, adsorption, antimicrobial, catalytic properties were analyzed using crystallochemical concepts and literature data. It was shown that NA or NA:M introduction into HZSM-5 leads, respectively, to the photodegradation of MeO dye in the UV region or difenoconazole in the visible range, and contributes to the appearance in the dark of adsorption (almost complete extraction of P(V), As(V), and Se(V) from aquatic environment) and bacteriostatic properties in respect to Staphylococcus epidermidis, Bacillus antracoides, and Escherichia coli for NA:Ag/HZSM-5(40, 300). The presence of titanium ions in NA nanoparticles on the HZSM-5 surface improves the catalytic activity in ethanol and propane (the best performance for NA/HZSM-5(25) and NA/HZSM-5(40), respectively) conversion. Determination of the composition (surface and bulk) and structure (statistical and local) of TS zeolites together with the found correlations made it possible to propose new catalysts in the reactions of propane, ethanol, and allyl chloride conversion.
Highlights
Zeolites are a large group of silicates that include several hundreds of compounds with a generalized composition formula where Mm+ denotes inorganic or organic cations and (Tn+ x Si1 −x ) denotes cations T and Si with tetrahedral coordination arranged in one crystallographic site [1]
HZSM-5 (HZSM) zeolites with MFI-type structure according to the IUPAC nomenclature show two stable structures: a low temperature phase having monoclinic symmetry
The phase transition temperature mainly depends on several parameters: (i) the chemical composition of the framework; (ii) the density of internal defects (i.e., Si vacancies generating internal hydroxyl groups [84,85,86,87,88,89]); (iii) the nature and the equilibrium pressure of adsorbed organic molecules; (iv) the presence/absence of the template [77]; and (v) as far as trivalent or with another formal charge heteroatoms are concerned, the chemical nature of the counterions [81]
Summary
Zeolites are a large group of silicates that include several hundreds of compounds with a generalized composition formula where Mm+ denotes inorganic or organic cations and (Tn+ x Si1 −x ) denotes cations T and Si with tetrahedral coordination arranged in one crystallographic site [1]. Zeolites are considered to be tetrahedral oxide structures with the skeleton density no less than 20 T atoms per 1000 Å irrespective of the material chemical composition [2]. Tetrahedra are connected by vertexes of oxygen atoms with the formation of the three-dimensional skeleton (primary structure) with voids (cavities) of 4, 5, 6, 8, 10, and. Just the general composition of the skeleton [(Tn+ x Si1 −x )O2 ], T composition, and angles between T are responsible for the configuration and sizes of cavities, and for the crystalline structure of zeolites.
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