A Synopsis entitled

Size and shape controlled synthesis of metal oxide nanoparticles and their applications

Submitted to

Rajiv Gandhi University

For registration of Ph.D. Degree

in Chemistry

By

Mr. Rakesh Chowdhury, M. Sc

Department of Chemistry

Rajiv Gandhi University, Rono Hills

Doimukh – 791 112 (Arunachal Pradesh)INDIA

2015

Title: Size and shape controlled synthesis of metal oxide nanoparticles and their applications

Name: Mr. Rakesh Chowdhury

Origin of the Research problem

Transition metal oxides nanoparticles (NPs) play an important role in many areas of Chemistry, Physics and Materials Science.1-3 The metal elements are able to form a large diversity of oxide compounds.4 Although, new metal oxide NPs are reported on regular basis, considerable synthetic and technological work remains to be done to fully exploit this ever increasing family of compounds for advanced materials applications. It is well known that the physicochemical properties of such metal oxide NPs are highly dependent not only on the size but also on the shape of the nanoparticles.3,5 Such size and shape dependent properties are critical parameters for their applications in various fields.6 Apart from this, the band gap energy of metal oxide NPs are also vastly influenced by the size and shape of the metal oxide NPs.7,8 As a result these nanoparticles show interesting size and shape tunable optical properties. Such interesting optoelectronic properties makes them suitable candidate for application in photocatalysis,9,10 sensor,6,11 bio-sensor,12 solar cell,13-15 battery6 etc. Consequently, during the last few years researchers have been extensively studying efficient synthetic routes to well defined nanoparticles with controlled size and shape. These include both the physical and the chemical approaches such as vapour-liquid-solid (VLS) methods,16 chemical vapour deposition (CVD) methods,17 thermal evaporation,18 and liquid–phase colloidal synthesis in aqueous or non-hydrolytic media.19-22 Relatively harsh conditions are employed in physical methods, making them unsuitable for the encapsulation of sensitive materials, and encapsulation of materials after their formation is often difficult. Other disadvantages are the lack of control over size, geometry, and uniformity of the nanoparticles produced.

Liquid-phase colloidal synthesis involves co-precipitation, sol – gel hydrothermal/ solvothermal and template based methods. For instance, Ranjit et al. synthesized MgO nanostructures by hydrolysis of magnesium methoxide in various solvent–methanol mixtures with water to methoxide ratio of 2.23 Caetano et al. reported the formation of SnO2 NPs by hydrolysis and condensation of respective precursors.20 Nedelcu et al. observed that mesoporous TiO2 are formed when polyethylene oxide (PEO) based copolymer is used as structure directing agent in a sol–gel based synthesis method. They claimed that materials structure can be systematically varied by adjustment of polymer molecular weight and titania precursor content in the reaction media.24 Sun et al. reported a generalized hydrothermal technique by which a diverse range of metal oxide nanoparticles such as manganese oxide, cobalt oxide and copper oxide can be synthesized by using respective metal formate salt in oleylamine solvent.25 Joo et al. developed a simple method to synthesize large quantities of highly monodisperse ZrO2 nanocrystals by non–hydrolytic sol–gel reaction between zirconium alkoxide and zirconium chloride at 340 ºC.26 Keeping in mind the simplicity and scalability, in the current work, we intend to use the liquid–phase colloidal synthesis methods such as co–precipitation and polymer/ surfactant micelle template–based method for the metal oxide NPs that has better control over the size and geometry of the formed nanoparticles. Although a lots of reports are available, a general, economical, environmentally friendly and scalable route to rationally fabricate metal oxide nanoparticles with controllable sizes and shapes as well as the surface functionality is still a challenge and highly desirable.

Among different types of application, metal oxide NPs are extensively used in the field of photocatalysis and sensors. For example, Kuriakose et al. reported the synthesis of flowerlike ZnO nanostructures by wet chemical technique and claimed that these flowerlike nanostructures showed enhanced photocatalytic activities towards sun–light driven photocatalytic degradation of methylene blue compared to spherical counterparts.9 Xu et al. have synthesized ZnO nanomaterials of different morphologies via simple solvothermal method with different solvents. They used these materials for phenol photodegradation and observed that ZnO with different morphologies and crystal growth habits exhibited different activities to phenol degradation.27 Davar et al. reported the synthesis of novel ZnO nanomaterials by green chemical method using lemon juice and then tested their photocatalytic activity for the degradation of methyl orange, methyl blue and methylene blue solutions.28 Zhao et al. prepared size controlled Zn–doped SnO2 hierarchical architectures by hydrothermal method and studied their gas sensor properties and photocatalytic activities towards glycol and methylene blue respectively.10

Considering the recent developments in the field of photocatalysis and sensor application, the current focus of this proposal is to design a method to prepare a diverse range of metal oxide NPs by simple chemical approach involving greener approach. In addition, a major focus will be given to the study of photocatalytic behavior of these metal oxide NPs towards degradation of pollutants and other hazardous chemicals. A detail of our objectives is outlined below:

Proposed aim and specific objectives of the investigation

i. To identify environmentally benign additives that has better control over size and shape of metal oxide nanoparticles.

ii. Design a methodology by which a diverse range of metal oxide NPs such as ZrO2, SnO2, MgO, SiO2 can be synthesized using the identified additives.

iii. To tune the size and shape of metal oxide nanoparticles.

iv. To characterize the synthesized metal oxide nanoparticles by different microscopic, spectroscopic and diffractometric techniques.

v. To study the photocatalytic and sensing activities of these metal oxide nanoparticles.

Significance of the Study

Metal oxide nanoparticles have attracted a great interest in scientific research and industrial applications, owing to their unique large surface-to-volume ratios and quantum-size effects. Since industrial catalysts usually work on the surface of metal oxides, the metal oxide NPs, which possess much larger surface area per unit volume or weight of metal than the bulk material, have been considered as promising materials for photocatalytic and sensor applications.

Methodology

In the proposed proposal, I will focus on the design and tuning of shape and size of metal oxide NPs for application in photocatalysis. The metal oxide NPs that would be considered for the current study will include ZrO2, SnO2, MgO, and SiO2. Literature surveys demonstrated that a simple synthetic method is typically easier to understand and optimize. Hence, for my study, I will adopt wet chemical methods such as co–precipitation and sol–gel techniques to synthesize the proposed metal oxide nanoparticles. A typical synthetic approach is provided schematically in Figure 1. The products and the intermediates will be characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet–visible (UV-vis) spectrometry, Fourier transform–infra red (FTIR)

Figure 1. Schematic representation of synthetic approach for metal oxide nanoparticles.

spectrometer, dynamic light scattering (DLS), X–ray photo electron spectroscopy (XPS) and fluorescence spectrometer. From the application point of view, the focus will be on the photocatalytic degradation and/ or decomposition of hazardous dyes and organic pollutants using the proposed metal oxide nanoparticles. Also emphasis will be given on the sensor applications with all types of proposed metal oxide nanoparticles.

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