Role of Iron (Fe) dopant concentration on titania phase transformation and photocatalytic performance
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Date
2022
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Department of Physics, NITS
Abstract
The technological and industrial progress achieved by the humankind has come at a cost of the environment. Uncontrolled expansion of industry is destroying the fragile ecology and polluting the environment. Among the different environmental pollutions, water pollution needs special attention since water is an indispensable part of human life. Water pollution not only lead to physiological issues in human body, but also affect the entire livelihood of the affected area. Among the different water pollutants, Emerging Contaminates deserves special attention. These organic pollutants are usually found in wastewater discharged from industries. These contaminants have far reaching consequences in the environment. There are many methods for treating the wastewater containing the pollutants. The conventional methods are expensive, less effective and may use energy source to carry out the process which will mostly non-renewable source of energy. A class of wastewater treatment method known as advanced oxidation process (AOP) shows to be promising. Although still at lab scale, this emerging method is considered to superior in many aspects while compared to the conventional method. AOP’s includes the formation hydroxyl species which then mineralize the organic pollutants by oxidising them. Thus, AOP does not produce any harmful by-products. Among the different AOP methods, photocatalysis is receiving wide attention. This is due to the its cost effective nature, non-lethal procedure and its ability to utilize the solar energy. The hydroxyl radicals are produced when solar light is irradiated on the photocatalytic surface causing charge carrier separation. Semiconductor metal oxides such as TiO2, ZnO, Fe2O3 etc are widely used photocatalysts. Among them TiO2(titania) is the most preferred photocatalyst due its non-toxic nature, high stability better electron transport. But the wide bandgap (3.2 eV for anatase) restricts performance of titania to UV region of solar spectra and also higher probability of charge carrier recombination further limits its performance. Various methods have been adopted to overcome the limitations of titania such doping, forming heterojunction, sensitizing it with noble metals etc. Among these doping with metals/non-metals is one of the widely used strategy. Doping with metal/nonmetals causes a shift in the conduction/valence band causing a decrease in the bandgap and facilitating the visible light absorption. Moreover, it is observed that existence of titania as a mixed phase(anatase-rutile) rather than single has shown better photocatalytic performance due to better charge carrier separation and transportation property. Considering this the present study aims to synthesis metal doped (Iron-Fe) mixed phase titania and test its photocatlytic performance. Sol-gel route was used as the synthesis method. X-ray diffraction, UV-Vis spectroscopy and photoluminescence spectroscopy studies of the samples were carried out to study the structural and optical properties. Incorporation of Fe initiates a phase transformation from rutile to anatase. Samples with different anatase-rutile(A/R) ratio were obtained by varying the Fe dopant concentration. It is further observed that the dopant concentration also affected the PL intensity. At higher dopant concentration low PL intensity was observed indicating interaction between the dopant ion causing non radiative recombination. Finally, solar photocatalytic activity test was carried out using methylene blue as the probe pollutant. Photocatalytic activity was found to decrease with increase in doping. Also, sample calcined at 4000C and having a dopant concentration of 0.1% of Fe showed highest performance. This can be attributed to the optimum level doping due to which trap centres were created which prevents charge carrier recombination. The superior performance can also be attributed to the optimum A/R ratio(A>R) which facilitates better charge carrier separation and charge transport.