Németh József

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Thesis points of  Ph.D. dissertation       Structural and Photooxidation Properties of Layered Silicate Stabilized ZnO and SnO2 Nanoparticles          József Németh  Supervisor:  Dr. Imre Dékány         University of Szeged Department of Colloid Chemistry Szeged, 2004.   1 Introduction and aims of the work   In the course of the different industrial processes large amounts of toxic pollutants having harmful effects on living organisms get out into our natural environment. It is important to remove and make harmless these pollutants to protect the living environment and human health.    The first goal of  the work was the preparation of  such ZnO and SnO2 catalysts with grain size in the nanometer range, which are able to degrade these harmful pollutants in photooxidative processes with the highest possible degradation efficiency. The second goal was to develop an environmentally friendly synthesis process for the preparation of the nanoparticles avoiding the use of  the large amount of organic solvents and surfactants. Therefore, principally synthesis methods in aqueous medium were worked out, applying clay minerals as stabilizing agents which are themselves also nanostructured materials.  The third main goal of the work was to explore the effect of the structural properties of the nanocomposites on the photocatalytic efficiency. For this purpose photooxidation of organic model molecules was investigated. This way the optimization of the conditions of catalyst preparation and the improvement of the photooxidation efficiency was carried out. The final aim of the work was to develop the suitable conditions for the application of the catalysts in industrial environment. To accomplish this purpose, nanofilms were prepared containing ZnO nanoparticles and these ultrathin layers were applied in a flow photoreactor.   Experimental methods   The semiconductor content of the prepared nanocomposites was determined by chemical analysis. The structural properties of the nanomaterials were examined by X-ray diffraction (XRD), nitrogen gas adsorption, transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), Mössbauer spectroscopy, and thermal analysis (DTA-TG). The optical properties of the nanoparticles without layered silicate were examined by UV-VIS absorption spectrophotometry, the streaming potential of the nanocrystallites was measured by a particle charge detector.   Nanocomposites were selected to study the interaction between the salicylic acid model pollutant and the catalyst surface by titration microcalorimetry investigations. The photooxidation process of the model pollutants was followed by UV-VIS absorption spectrophotometry.  2 New scientific results  1. Preparation of nanoparticles and nanocomposites  1.1. New synthesis methods were worked out employing homogeneous nucleation in aqueous medium in order to prepare ZnO nanoparticles from zinc acetate precursor applying photolysis, alkaline and thermal hydrolysis. Nearly monodisperse nanoparticles in the 5-9 nm diameter range were produced by these synthesis methods.  1.2. New synthesis methods were worked out employing homogeneous and heterogeneous nucleation in dimethyl sulfoxide medium in order to prepare ZnO nanoparticles. In the presence of clay minerals the concentration of the nanoparticles can be increased without the increase of their size. This phenomenon indicates that the clay minerals – growing the crystallites on their surface – are able to stabilize the size of the nanoparticles.  1.3. In the case of the nanocomposites prepared by the heterocoagulation method an intercalated composite structure was formed as the result of the electrostatic attraction between the components having oppositely charged surfaces (between the positively charged nanoparticles and the negatively charged layered silicate lamellae).  1.4. The structural parameters (basal distance, specific surface area, porosity) of the ZnO/layered silicate nanocomposites prepared by heterogeneous nucleation can be controlled by the appropriate regulation of pH, the concentration of the precursor ions and layered silicates. pH has a strong effect on the formation of the composite structure. As pH was increased, more zinc ions hydrolyzed, therefore increasing basal distances, decreasing specific surface areas and wider particle size distribution functions were obtained.  1.5. The basal distance of the catalysts shows a maximum as the function of the calcination temperature, however, the specific surface area continuously decreases according to the experiments investigating the structure of SnO2/layered silicate nanocomposites. Appropriate heat treatment plays a basic role in the formation of the composite structure.    3 1.6. Self-assembled ZnO/hectorite nanofilms were prepared applying negatively charged synthetic hectorite and positively charged ZnO nanoparticles synthesized by the photolysis method. The nanofilms were formed in a two dimensional heterocoagulation process and showed intercalated structure according to XRD.  1.7. A model was worked out in order to characterize the pillared structure of the nanocomposites. The specific surface area and particle size predicted by the calculations based on the model are in accordance with the experimentally obtained values. It was established that the intercalation of the nanoparticles does not unfold the complete interlamellar space of the layered silicates, but a significant part of the lamellae remains in aggregated state.   2. Photooxidation experiments  2.1. In the case of the nanocrystalline ZnO intercalated in layered silicates the specific degradation rate of salicylic acid test molecule was 0,6 – 5,4 times higher than in the case of the macrocrystalline ZnO sample. Higher degradation rate was observed for the catalysts having higher specific surface area, indicating the direct surface oxidation mechanism of the salicylic acid. When ZnO content of two nanocomposites was equivalent, we experienced higher photooxidation activity when the nanocomposite contained a layered silicate with higher transmittance (hectorite).  2.2. In the case of the nanocrystalline SnO2 intercalated in layered silicates the specific degradation rate of salicylic acid test molecule was 6,6 – 20,5 times higher than in the case of the macrocrystalline SnO2 sample. Higher degradation rate was observed when nanocomposites with higher specific surface areas were applied in the test reactions.  2.3. The photooxidation efficiency of the powder catalysts showed a maximum as the function of the catalyst concentration. This phenomenon can be explained by the self-shielding effect of the catalyst particles when high concentrations were applied. The efficiency also showed a maximum as the function of the calcination temperature, what can be explained by the not entirely developed metal oxide lattice structure at low temperatures and the significant increase of the particle size at high temperatures.  4 2.4. Applying nanofilm catalysts in the course of the experiments investigating the photooxidation of kerosene, we experienced higher degradation rate when calcinated films were used. The calcinated ZnO/hectorite films removed 39,2 % of the pollutant after 3h of the irradiation time.                                      5 Publications  Publications related to the subject of the dissertation  1. K. Mogyorósi, J. Németh, I. Dékány, J. H. Fendler: Preparation, Characterization and Photocatalytic Properties of Layered-Silicate-Supported TiO2 and ZnO Nanoparticles  (Prog. Coll. Polym. Sci. 2001, 117, 88-93)             IF: 1,132  2. Németh J., Dékány I., Süvegh K., Marek T., Klencsár Z.,Vértes A.: SnO2-montmorillonit nanokompozitok szintézise és szerkezeti paraméterei  (Magyar Kémiai Folyóirat, 2002, 108, 148-159)               IF:  0,131  3. J. Németh, I. Dékány, K. Süvegh, T. Marek, Z. Klencsár, A. Vértes,  J. H. Fendler: Preparation and Structural Properties of Tin Oxide-Montmorillonite Nanocomposites (Langmuir 2003, 19(9); 3762-3769)                IF: 3,045   4.  G. Rodríguez-Gattorno, P. Santiago-Jacinto, A. L. Rendon-Vázquez,  J. Németh,  I. Dékány, D. Díaz: Novel Synthesis Pathway of ZnO Nanoparticles from Spontaneous Hydrolysis of Zinc Carboxylate Salts  (J. Phys. Chem. B., 2003, 107, 12597-12604)              IF: 3,386  5. J. Németh, G. Rodríguez-Gattorno, A. Vazquez-Olmos, D. Díaz,   I. Dékány: Synthesis of ZnO Nanoparticles on Clay Mineral Surface in Dimethyl Sulfoxide Medium (Langmuir, 2004, 20, 2855-2860.)                IF: 3,045  6. L. Kőrösi, K. Mogyorósi, R. Kun, J. Németh, , I. Dékány: Preparation and Photooxidation Properties of  Metal Oxide Semiconductors Incorporated in Layer Silicates  (Progr.Coll.Polym. Sci ., accepted, 2003.)    IF: 1,132   6 7. L. Kőrösi, J.Németh , I. Dékány: Structural and Photooxidation Properties of SnO2/Layer Silicate Nanocomposites (Appl. Clays, accepted, 2004)                         IF: 1,115  IF: 12,986   Other publications  1. J. Németh, I. Dékány:  The Effect of Nanoparticle Growth on Rheological Properties of Silica and Silicate Dispersions  (Colloid and Polymer Sci. 2000, 278, 211-219)                 IF: 1,132 2. I. Dékány, J. Németh, M. Szekeres, R. Schoonheydt: Surfacial Liquid Sorption and Monolayer Forming Properties of Hydrophilic and Hydrophobic Stöber Silica Particles  (Colloid and Polymer Sci., 2003, 282, 727-737)                IF: 1,132 3. T. Szabó, J. Németh, I. Dékány: Zinc Oxide Nanoparticles Incorporated in Ultrathin Layer Silicate Films and Their Photocatalytic Properties  (Coll. Surf. A., 2004, 230, 23-35)     IF: 0,888  4. R.H.A. Ras, J. Németh, C. T. Johnston, I. Dékány, R.A. Schoonheydt: Infrared reflection absorption spectroscopy (IRRAS) study of smectite clay monolayers  (Thin Solid Films, accepted, 2004)             IF: 1,266   IF: 4,418 Total:     IF: 17,404  Patent  Dékány Imre, Németh József, Patzkó Ágnes, Nagy László, Molnár Árpád: Eljárás környezetszennyező modell harcanyagok fotooxidációs lebontására cink-oxid tartalmú monokationos montmorillonitok vizes szuszpenziójában Magyar Szabadalom, bejelentés ideje: 2003. január, Hiv. jel: 451/1/2002, Aktaszám: 97384-1883451   7 Oral presentations and posters:  1.  I.Dékány, J. Németh, K. Mogyorósi, Z. Király:   Nanoparticles in Clay Mineral Matrixes       EUROCLAY ’99 Conf. of the European Clay Groups Association  5-9 September, 1999, Krakow, Poland.  2.  Németh J., Dékány I.:  Nanostrukturált fém-szulfid félvezetők szintézise és vizsgálata különböző hordozók    XXII. Kémiai Előadói Napok, Szeged, 1999. nov. 1-3., Abstr. p. 78-79.  3.  I. Dékány, T. Pernyeszi, K. Mogyorósi, J. Németh, J.H. Fendler: Preparation of Semiconductors Intercalated in Clays and Their Photocatalytic Properties 13th International Conference on Photochemical Conversion and Storage of Solar Energy 30 July – 4 August, 2000, Colorado, Abs. p.W8-O-6  4.    I. Dékány, K. Mogyorósi, J. Németh, J.H. Fendler: Preparation and Structural Properties of Semiconductor Nanoparticles in  Layered Supports        14th International Symposium on the Reactivity of Solids       27-31 August 2000, Budapest, Hungary, Abstr. p.28.  5.  J. Németh, L. Kőrösi, I. Dékány,  J. H. Fendler: Preparation of ZnO and SnO2 Semiconductor Nanoparticles Intercalated in Montmorillonite  3rd International Conference of the Kolloid-Gesellschaft e. V.,   25-28 September, 2000, Budapest, Hungary, Abstr. p.145.  6.  Dékány I., Szűcs A., Németh J., Papp Sz.: Nanoszerkezetű anyagok: rétegszilikátokkal és polimerekkel stabilizált nanorészecskék előállítása  Közgyűlési előadás a Magyar Tudományos Akadémián Budapest, 2000. május, Abstr. p. 1141-1157.       8 7. L. Kőrösi, J. Németh, I. Dékány, J. H. Fendler: Preparation and Use of Layered Silicate Incorporated SnO2 Nanoparticles as Catalysts for the Photodegradation of Organic Pollutants Particles 2001 Conference,Orlando, Florida, 24-27 February 2001.   8. A. Szeri, Gy. Kőfaragó, J. Németh, K. Mogyorósi, I. Dékány,  J. H. Fendler: Semiconductor Nanoparticles in Layer-by-Layer Assembly for Photocatalytical Application Particles 2001 Conference,Orlando, Florida, 24-27 February 2001.  9. J. Németh, L. Kőrösi, I. Dékány, J. H. Fendler Photooxidation of Organic Molecules on SnO2 and ZnO/Layered Silicate Nanoparticles in Flow and Batch Reactors Hungarian-American Workshop on Molecular Catalyst Design for Green Chemistry 23-26 May, 2002, Budapest, Hungary, Abstr. p. 20.  10.  J. Németh, L. Kőrösi, I. Dékány, J. H. Fendler Photodegradation of Organic Pollutants on SnO2 and ZnO/Layered Silicate Nanocomposites Interfaces Against Pollution 2nd International Conference  27-30 May, 2002, Lillafüred, Hungary Abstr. p. 146.  11.  I. Dékány, K. Mogyorósi, J. Németh, Á. Patzkó, J. H. Fendler: Photodegradation of Organic pollutants on Semiconductor Nanoparticles Intercalated in Clay Minerals Interfaces Against Pollution 2nd International Conference  27-30 May, 2002, Lillafüred, Hungary Abstr. p. 43.  12.  J. Németh, K. Mogyorósi, I. Dékány, G. Rodríguez-Gattorno, D. Díaz: Preparation of ZnO and TiO2 Nanoparticles in Suspension of Clay Mineral Supports in Dimethyl Sulfoxide 8th Conference on Colloid Chemistry 18-20 September, 2002, Keszthely, Hungary Abstr. p. 97.   13.  K. Mogyorósi, J. Németh, L. Kőrösi, I. Dékány, J. H. Fendler: Photooxidation of Organic Molecules on TiO2 and SnO2 and ZnO/Layered Silicate Nanocomposites in Flow and Batch Reactors 8th Conference on Colloid Chemistry 18-20 September, 2002, Keszthely, Hungary Abstr. p. 94.  9  14. G. Rodríguez-Gattorno, D. Díaz, A. Vázquez-Olmos, J. Németh, I. Dékány: Synthesis of ZnO Nanoparticles from Spontaneous Alkaline Hydrolysis of Zinc Carboxylate Salts in Polar Organic Media 8th Conference on Colloid Chemistry 18-20 September, 2002, Keszthely, Hungary Abstr. p. 124.  15.   R. A. Schoonheydt, R. H. A. Ras, J. Németh, C. T. Johnston: Organization of Particles and Molecules in Clay Mineral Nanofilms Euroclay 2003, 10th Conference of the European Clay Groups Association, 22-26 June, 2003, Modena, Italy, Abstr. p. 255.  16.  J. Németh, R. H. A. Ras, E. I. Franses, C. T. Johnston,  R. A. Schoonheydt: Hybrid Langmuir-Blodgett Monolayers of Clay: an Infrared and Atomic Force Microscopy Study Euroclay 2003, 10th Conference of the European Clay Groups Association, 22-26 June, 2003, Modena, Italy  17. J. Németh, R. H. A. Ras, C. T. Johnston, I. Dékány, R. A. Schoonheydt: Hybrid Langmuir-Blodgett Monolayers of Surfactants and Clay: Molecular and Particulate Organization Workshop on Nanomaterials and Catalysis 5-6 February, 2004, Bremberg, Belgium  18. Németh József, Dékány Imre: Rétegszilikátokkal stabilizált ZnO és SnO2 nanorészecskék szerkezeti és fotooxidációs tulajdonságai Előadás (PhD elővédés) az MTA-SZAB Anyagtudományi Munkabizottság ülésén, 2004. február 19.          

Rétegszilikátokkal stabilizált ZnO és SnO2 nanorészecskék szerkezeti és fotooxidációs tulajdonságai

http://doktori.bibl.u-szeged.hu/152/9/2004_nemeth_jozsef_tezis_angol.pdf

Rétegszilikátokkal stabilizált ZnO és SnO2 nanorészecskék szerkezeti és fotooxidációs tulajdonságai

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