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«Dissertation zur Erlangung des akademischen Grades Doktoringenieurin (Dr.-Ing.) von: Yashodhan Pramod Gokhale geboren am: 05. October 1981 in Pune, ...»

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Synthesis and Modeling of Silver and Titanium dioxide

Nanoparticles by

Population Balance Equations


zur Erlangung des akademischen Grades



von: Yashodhan Pramod Gokhale

geboren am: 05. October 1981 in Pune, India

genehmigt durch die Fakultät für Verfahrens- und Systemtechnik

der Otto-von-Guericke-Universität Magdeburg

Gutachter: Prof. Dr.-Ing. habil Jürgen Tomas

Prof. Dr.-Ing. habil Andreas Seidel-Morgenstern Eingereicht am: 30. November 2009 Promotionskolloquium: 23. March 2010


When you set out on your journey to Ithaca, pray that the road is long, full of adventure, full of knowledge.

The Lestrygonians and the Cyclops,

the angry Poseidon do not fear them:

You will never find such as these on your path, if your thoughts remain lofty, if a fine emotion touches your spirit and your body.

The Lestrygonians and the Cyclops, the fierce Poseidon you will never encounter, if you do not carry them within your soul, Ithaca if your soul does not set them up before you.

Pray that the road is long.

That the summer mornings are many, when, with such pleasure, with such joy you will enter ports seen for the first time;

stop at Phoenician markets, and purchase fine merchandise, mother-of-pearl and coral, amber and ebony, and sensual perfumes of all kinds, as many sensual perfumes as you can;

visit many Egyptian cities, to learn and learn from scholars.

Always keep Ithaca in your mind.

To arrive there is your ultimate goal.

But do not hurry the voyage at all.

It is better to let it last for many years;

and to anchor at the island when you are old,

–  –  –

Magdeburg and river Alba will always remain very close to my heart. They will remain special for the friends they gave me, and ofcourse for the Otto-von Guericke University where I studied for the past four years. The university not only opened doors to scientific research, but also broadened my views in many aspects of the world. Many individuals provided support, help and encouragement during my time in the graduate school. Now I would like to express my gratitude for them.

I am eternally thankful to Prof.-Dr. - Ing. habil. Jürgen Tomas, the best advisor one could find. Not only did he teach me scientific thinking of the highest caliber but more importantly, he taught me-through his own example-to be considerate, forthcoming, balanced and patient during interactions with colleagues, teachers and students. His keenness about knowing the basics and about questioning assumptions is an important lesson, which I shall carry with me throughout my career. He molded me from being just a student to, hopefully, being a researcher. Besides being a good professor, he has been a warm and cheerful person.

I am thankful for the financial support I received from the DFG-Graduiertenkolleg-828,” Micro-Macro-Interactions in Structured Media and Particle Systems”, Otto-von-Guericke-Universität, Magdeburg for this PhD program. I would like to thank Prof. Dr. Gerald Warnecke, and Prof. Dr.-Ing.

Albrecht Bertram for giving me valuable advice and also an opportunity to work in an interdisciplinary project.

I would like to express my sincere and deep gratitude to Dr. rer. nat. Jitendra Kumar. His advice and encouragement during the course of my research has been great help.

I am also very grateful to Dr. rer. nat. Werner Hintz who has shown considerable interest in my work.

Moreover, I value my scientific discussions during experimental work with Dipl.-Ing. Veselina Yordanova. Also, I am thankful to Dr. rer. nat. Peter Veit for TEM micrographs and Dr. rer. nat.

Hartmut Heyse for SEM images. I would like to thank other members of the chair for their useful comments and suggestions for the work included in this thesis. I have enjoyed working with Peter, Martin, Sebastian, and Dipl.-Ing. Bernd Ebenau, and would appreciate their cooperation.

To Rajesh Kumar and Ankik Kumar; who deserve a special mention for sharing the triumphs with me.

They made me truly appreciate mathematics and left me with memories of hilarious and enlightening moments to be treasured forever. I have thoroughly enjoyed all of our dinners, and delightful conversations, which made our life in Magdeburg entertaining as well as memorable.

To the great writers and scientists who through their writings have provided me with immense intellectual and moral inspiration; they have taught me more than I realize. Especially, I would like to acknowledge the work and words of George Washington Carver and Richard Feynman. I have often seen the world through their eyes, and I am sure they will continue to motivate me.

To all my friends in Magdeburg who provided support and encouragement to me during my stay here;

my heartfelt regards to all of them- Stan, Bhooshan, Rajesh,Vikrant, Bala, Ayan, Sagar, Yogesh, Thiru, Reza, Chris, Katja, Maren, Penka, Marc, and Frau. Martina. They are truly wonderful people who are now my family. I will always cherish the time I spent with them. To Alex, Thomas, Kai who are my best friends outside the graduate school and with whom I spent many enjoyable weekends. I also appreciate the support of friends-Chinmay, Harshada, Vikrant, Janhavi, Vivek,- and teachers from far away Pune, India.

My special thanks to Dr. Aniket, Dr. Ashutosh and Ritwik; my long friendship with these dear friends grew stronger in the course of my doctoral studies. I shall always owe them for the intellectually stimulating, academic and non-academic discussions.

Most importantly, my deepest regard to the closest persons of my life who have given me all I could ask for and much, much more that can ever be expressed in words; my family-Aai-Baba, grandparents and brother Pushkaraj. I also want to thank my other parents, Mr. and Mrs. Deshpande for their warmth and affection.

My mother and father are among the kindest and the most patient people I know. My grandfather had one of the finest and the most intelligent scientific minds I have encountered. I will be eternally indebted to him for constantly arousing in me a sense of curiosity and wonder about both the physical and the human world.

Last but not the least; I would make a special mention of my soul mate, Ashwini-to whose opinion I am addicted. Her kindness and grace, and her untiring contribution in reading, reading, and editing every draft of this thesis, have been invaluable to me. Her presence has been my strength all through.

Abstract The present scenario of well-controlled large-scale production of nanoparticles is a very important aspect in nanotechnology. The present work aims at investigating different engineering aspects of the production of silver and titanium dioxide nanoparticles using different chemical methods. Eventually, this leads to possible process control. Silver and Titania is one of the most extensively used materials for research, application and production of nano size materials.

This thesis reports detailed synthesis of silver nanoparticles produced from the reduction of silver nitrate by stabilizing and reducing agents. Silver nanoparticles have a strong tendency to agglomerate. This reduces the surface to volume ratio and hence the resultant is the catalytic effect. Silver nanoparticles are produced in the batch reactor at a different shear rate and are investigated experimentally. Finally, the colloidal solution of capped silver nanoparticles is free from agglomeration for several months.

To control the particle size and morphology of nanoparticles is of crucial importance from a fundamental and also an industrial point of view. Titanium dioxide (TiO2) is one of the most useful oxide materials, because of its widespread applications in photocatalysis, solar energy conversion, sensors and optoelectronics. Controlling particle size and monodispersity of TiO2 nanoparticles is a challenging task. The control and prediction of these dynamics are based on the conditions of the process and the nature of chemicals. This work discusses a new approach for simultaneous agglomeration and disintegration of Titanium dioxide nanoparticles. The precipitation of nanoparticles in the batch reactor is investigated experimentally at different shear rates as well as by numerical simulations based on the population balance equations.

The population balance model for agglomeration and disintegration leads to a system of integro-partial differential equations, which can be solved by several numerical methods. The shear rate influences the particle size distributions.

This work also investigates the effect of the surface stabilization with varied surfactants on the Titanium dioxide particles. The steric stabilization of polymer and various functional groups of dispersants is also considered. The interaction between different particles greatly affects both, the total energy potential and the stability ratio. Employing energy to the flow field escalates the energy barrier in the colloidal system. Eventually this leads to lower stability. Monodispersed spherical titania particles in the size range 10-100 nm are produced in a sol-gel synthesis from titanium tetra-isopropoxide.

The silver and titania nanoparticles were characterized by dynamic light scattering, scanning electron microscopy and transmission electron microscopy to determine particle size distribution and shape. Also the specific surface area is measured by BET method.

The population balance model in this work is numerically solved by cell average technique.

The experimental results are compared with the simulation using different agglomeration and disintegration kernels. It is found that the experimental results of the particle size distributions at different shear rates of TiO2 are in good agreement with the simulation results. This includes a comparison of the derived particle size distributions, moments and their accuracy depending on the starting particle size distributions.

This study shows that particle sizes, morphology and monodispersity of colloidal particles of silver and TiO2 can be controlled by two processes – one, by making appropriate choice of stabilizing and reducing agents; two, by adding surfactants and polymers or salt during the synthesis.

Zusammenfassung Gegenwärtig stellt die gezielte Herstellung von Nanopartikeln im technischen Maßstab einen wichtigen Forschungsgegenstand in der Nanotechnologie dar. Es werden verschiedene ingenieurwissenschaftliche Aspekte zur Herstellung von Nanopartikeln aus Silber und Titan(IV)-oxid mit Hilfe verschiedener Prozesse untersucht, mit dem Ziel, diese möglichst zu steuern und zu kontrollieren. Dabei zählen insbesondere das Silber und das Titan(IV)-oxid zu den am meisten untersuchten Stoffen hinsichtlich der Forschung, Produktion und Anwendung nanoskaliger Materialien.

Die vorliegende Arbeit beschreibt im einzelnen die Herstellung von Nanopartikeln aus Silber durch eine Reduktion von Silbernitrat unter Zusatz von Stabilisatoren und Reduktionsmitteln.

Silber-Nanopartikel zeigen dabei eine starke Tendenz zur Agglomeratbildung. Diese verringert die spezifische Oberfläche und daraus resultierend die katalytische Wirkung der Partikel. Die Herstellung der Silber-Nanopartikel erfolgte in einem Labor-Rührreaktor, die Partikelbildung wurde experimentell bei unterschiedlichen Schergeschwindigkeiten untersucht. Dabei ist es möglich, eine kolloidale Suspension aus stabilisierten Nanopartikeln herzustellen, die für mehrere Monate stabil gegen Agglomeration ist.

Die Steuerung der Partikelgröße und der Morphologie der Nanopartikel ist von äußerster Wichtigkeit, sowohl aus wissenschaftlicher als auch aus technischer Sicht. Titan(IV)-oxid stellt eines der interessantesten Oxide auf Grund seiner Anwendung in der Photokatalyse, Solarenergietechnologie, Optoelektronik und als Sensormaterial dar. Die Steuerung der Partikelgröße und der Morphologie ist hierbei eine besondere Herausforderung. Grundlegend sind für die Steuerung und Vorhersage der dieser dynamischen Prozesse einerseits die Prozessparameter, andererseits die chemischen Eigenschaften des Stoffsystems. Die vorliegende Arbeit diskutiert einen neuen Ansatz für die gleichzeitig ablaufende Agglomerations- und Desintegrationsprozesse der Titan(IV)-oxid-Partikel. Die Fällung der Nanopartikel wurde experimentell in einem Labor-Rührreaktor bei verschiedenen Schergeschwindigkeiten untersucht und auf Basis von Populationsbilanzgleichungen numerisch simuliert. Das Populationsbilanz-Modell für die Agglomerations- und Desintegrationsprozesse führt zu einem System von Integro-Partial-Differentialgleichungen, die mit Hilfe verschiedener numerischer Methoden gelöst wurden. Die Schergeschwindigkeit beeinflußt die Partikelgrößenverteilungen.

Diese Arbeit untersucht außerdem die Wirkung der Oberflächenstabilisierung durch unterschiedliche Tenside auf die Titan(IV)-oxid-Partikel. Die sterische Stabilisierung mit Hilfe von Polymeren und Dispergierhilfsmitteln mit verschiedenen funktionellen Gruppen wird ebenfalls betrachtet. Das Zusammenspiel zwischen verschiedenen Partikeln beeinflußt wesentlich sowohl das Gesamtwechselwirkungspotential als auch den Stabilitätsfaktor. Indem Energie dem Strömungsfeld zugeführt wird, kann die Energiebarriere im kolloidalen System überwunden werden. Möglicherweise führt dies zu einer geringeren Stabilität.

Die mit Hilfe des Sol-Gel-Prozesses aus Tetraisopropyl-orthotitanat hergestellten monodispersen kugelförmigen Titan(IV)-oxid-Partikel haben eine Größe zwischen 10 und 100 nm.

Die Nanopartikel aus Silber bzw. Titan(IV)-oxid wurden mittels dynamischer Lichtstreuung, Raster- und Transmissionselektronenmikroskopie charakterisiert, um entsprechend die Partikelgrößenverteilung und die Partikelform zu bestimmen. Die spezifische Partikeloberfläche wurde mit Hilfe der BET-Methode erhalten.

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