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Photocatalysts Based on the Nanoheterostuctures

#B-1190


Development and Investigation of the Novel Effective Photocatalysts Based on the Nanoheterostructures with P-N Junction for Water and Air Purification from Toxic Contaminations

Tech Area / Field

  • CHE-RAD/Photo and Radiation Chemistry/Chemistry
  • ENV-APC/Air Pollution and Control/Environment
  • ENV-WPC/Water Pollution and Control/Environment
  • PHY-SSP/Solid State Physics/Physics

Status
3 Approved without Funding

Registration date
10.11.2004

Leading Institute
Belorussian State Technological University, Belarus, Minsk

Supporting institutes

  • National Academy of Sciences of the Republic of Belarus / Institute of General and Inorganic Chemistry, Belarus, Minsk

Collaborators

  • University of Guelph, Canada, ON, Guelph\nUniversità degli Studi di Firenze / Dipartimento di Chimica, Italy, Florence\nUniversity of Dublin / Trinity College Dublin, Ireland, Dublin\nUniversity of Applied Sciences, Austria, Wels

Project summary

Purpose of the Project.

Creation a new generation of photocatlysts based on nano-sized heterostructures of “core-shell” type with the p-n junction and development highly productive cost-efficient apparatus for water and air cleaning from toxic contaminations under the action of solar light.

Recent state in the field of explorations.

The catalytic degradation of organic compounds under light irradiation is one of the most promising and cost-efficient technique of water and air purification and decontamination. A lot of papers concerned with the photocatalysts based on inpidual and mixed oxides (including nanostructurated ones), their synthesis and photocatlytic behaviour in different photoinduced reactions (including water splitting and degradation of toxic pollutants) have been published to date. The excellent review papers and monographs on this topic are available (e.g., D.F. Ollis, H. Al-Ekabi(Eds.) Photocatalytic Purification and Treatment of Water and Air, Elsevier, Amsterdam, 1993; M. Schiavello (Ed.) Heterogeneous Photocatalysis, Wiley, Chichester, 1997).

The efficiency of photocatalysts is governed, first of all, by quantum yield, which generally does not exceed several percent. It has been found that the most promising approach to the improving the photocatalyst performance consists in combination of two semiconductors or semiconductor and fine particles of catalytic metal by fabrication of heterostructures (TiO2/SiO2, TiO2/ZnO, TiO2/Pt, etc.). However, the substantiated concept of construction of such heterostructures still does not exist mainly due to the lack of understanding of the mechanism of spatial separation of photoproduced holes and electrons in case of nano-sized heterojunctions. The enhancement of quantum yield together with the expanding of the photosensetivity spectral range to larger wavelengths (i.e., from UV to the visible region) still remain the pressing problems of applied photocatalysis. In the framework of the proposed project these problem are expected to be solved on the basis of recent advancements in chemistry and physics of semiconductor nanoparticles.

Current Project Influence on the Progress in the Field of the Science.

In the proposed project methodology initially developed for solar cell with p-n junction will be applied to the oxide photocatalysts to achieve the radical improvement of their performance. For the first time, the systematic studies will be performed directed toward elaboration of nano-sized heterostructures of “core-shell” type with p-n junction where the “core” is made of narrow-gap semiconductor of p-type, whereas the “shell” is made of high energy-gap photosensitive oxide (TiO2, SnO2, In2O3, WO3, etc.) of n-type or, on the contrary, those with the “core” made of the semiconductor of n-type and the “shell” made of the semiconductor of p-type. The p-n junction permits to radically increase the efficiency of spatial separation of photoproduced charge carriers leading to the increase (by 40%) of quantum yield of photoinduced decomposition of toxic contaminations in water and air.

By improving the photocatalyst performance and by solving in such a way the hottest problem of applied photocatalysis it will be possible

– to change in radical way the requirements to the choice of water sources, that is of great importance especially for tropical countries with the adversary sanitary situation and large percent of sunny days;


– to revise drastically the structure of fresh water usage and utilization by putting into use previously unsuitable aquatic toxic effluents;
– to make it possible a large-scale clean-out of air.

The materials developed within the framework of the project can also be used in solar cells and for photoelectrochemical and photocatalytic water decomposition (to hydrogen and oxygen).

Project participants competence in the given area.

This project for the "weapon" scientists (specialists in missile materials) involved in it is the same scientific direction, but re-oriented to civil technologies. The Project Manager, Dr. N.Y. Shishkin (BSTU), is a well-known scientist specialized in the field of physical chemistry of solid state, including oxide materials for gas sensor applications and photocatalysts, he has authored the textbook on the chemistry of solid state. The Assistant of Project Manager, Prof. A.I. Kulak (IGIC NASB), is a well-known expert in electrochemistry, photoelectrochemistry and photocatalytic properties of nanoheterostructures based on metal oxides and other semiconductors, he has on his credit a monograph on this topic. The researchers, professors and post-graduate students experienced in synthesis of metal oxide- and chalcogenide nanostructured materials and investigation of their electrical, optical, photocatalytic, magnetic and sensory properties are incorporated in the research groups in Leading Institution (BSTU) and Participating Institution (IGIC NASB).

Expected Results and their Application.

The proposed project falls in the category of applied researches, development.

The following novel results are expected as a consequence of the implementing of four main tasks of the project:

– elaboration the synthesis of nano-sized heterostructures of “core-shell” type with p-n or n-p inner junctions permitting to achieve radical enhancement of the rate of reactions of photoreduction (task 1) or photooxidation (task 2) of toxic contaminations in the water and in the air not accompanied with the formation of any harmless products;

– elaboration of metal-modified photocatalysts exhibiting a record-breaking efficiency at low loading (task 3) that enables savings in noble metals;

– elaboration of unique photocatalysts of a new generation that permits to construct highly-efficient economically sound apparatus for the removal of toxic pollutants from water and air; for this purpose, the nano-sized heterostructures with p-n junction, operating in a wide spectral range with high efficiency (up to 40%), will be developed, tested and patented (tasks 1-4) is essentially re-oriented to the civil technologies direction of earlier executed by them works.

Application of the results. Novel photocatalysts developed within the framework of the proposed project will be employed in some EU countries and in Belarus in apparatus of photocatalytic purification of water. These photocatalysts can also be used for photocatalytic and photoelectrochemical water splitting yielding hydrogen and oxygen, for photocatalytic synthesis of valuable organic compounds and in the other areas of industry and science that may promote their wide-spread applications

Meeting ISTC Goals and Objectives.

This project fully corresponds to the objectives and tasks of ISTC considering that:

– this project promote the reorientation of the abilities of experts in areas of rocket and laser materials, materials for chemical weapons to civil researches by utilizing their experience in the development of novel photocatalysts for photoassisted water purification;

– the project encourage the integration of the project participants into international scientific community by their involvement in solving the problems associated with development effective photocatalysts for the removal toxic substances from water and air;

– the project supports the basic and applied researches and the development of non-military technologies aimed to the environmental protection.

– the project contribute to the solving, on national and international level, of technical problems concerned with the development of effective photocatalysts for the removal of toxic compounds that meet the needs of chemical industry and other non-military areas of industry and science;

– the project supports, by advancing novel photocatlysts, the transition of its participants to the market economy that matches the civil needs.

Scope of Activities.

The project will last 30 months. The total labour expenses amount to 6275 man-days, including 4465 man-days for the Leading Institution (BSTU), 1810 man-day for the Participating Institution (IGIC NASB). Four tasks are to be fulfilled to achieve the goals of the project. The labour expenses for the first and the second tasks amount a 2510 man-days for each, while the labour expenses for the third task amount to 628 man-days. The fourth task (627 man-days) is the closing one. The tasks ate carried out, one by another, simultaneously by all the participants of the project which, however, use different semiconductor and oxide materials. The project participants from the Leading Institution (BSTU) are specialized in the synthesis of nano-sized semiconductors of n-and p-type. The project participants from the Participating Institution (IGIC NASB) are responsible for photoelectrochemical measurements and to construct pilot apparatus for water treatment. The coordination among three research groups in the Leading Institution (BSTU) and one research group in the Participating Institution (IGIC NASB) is performed by Dr N.Y. Shichkin. Scientific guidance of the entire project is performed by Prof. L.A. Bashkirov.

Role of Foreign Collaborators.

The collaborators Prof. Dieter Meissner (University of Applied Sciences, Wels, Austria), Prof. Ugo Bardi (Dipartmento Di Chimica Universita di Firenze, Italy), Prof. Dr Y. Gun’ko (Department of Chemistry, Trinity College, Dublin, Ireland) will be involved in the following cooperation within the framework of the Project:

– the information exchange during the course of the project dealing with the actual problems of concerned with the oxide-based photocatlysts;


– comments on the annual and the final reports, independent testing of the developed photocatalysts;
– participation in technical control of the activities due to the project by the ISTC officials;
– organization of joint seminars to discuss the obtained results and preparation of joint publications;
– organization of the tests and independent examinations of the photocatalysts developed within the framework of the project with the use of the pilot installation for water phototreatment and solar simulator in Wels, Austria (D. Meissner);
– assistance in the investigation of structure of fabricated nanostructures (U. Bardi);
– assistance in the investigation of heterostructures with p-n hetherojunction (Y. Gun’ko);
– consultations on the protection of the intellectual property and joint patenting of the developed photocatalysts;
– assistance in evaluation of the market requirements in the developed photocatalysts.

Technical Approaches and Methodology.

In the framework of this project for the first time it is proposed to use technical approaches and scientific methodology initially developed for creation of solar cells based on p-n junction of two semiconductors (or metal-semiconductor) where photogenerated electrons and holes are spatially separated between different sides of the p-n junction boundary for radical increase of efficiency of the oxide photocatalysts.

The project participants have broad experience in the complex investigations in the field of development of oxide micro- and nanostructures with desired electrical physical properties and in better understanding of the processes accompanying the interaction of these structures with the environment and some toxic compounds. The technical and methodological approaches in fields of nanochemistry, electrochemistry and photoelectrochemistry of semiconductors developed by the project participants will be employed, including the method of kinetic protection of narrow-gap semiconductor by involving the non-equilibrium charge carriers in the red-ox interfacial processes.


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