ReviewAdvances in iridium nano catalyst preparation, characterization and applications
Introduction
Among top nine rare elements, iridium (Ir) is of the utmost importance in various chemical reactions. Generally, it is found in nature as native element or in the form of alloys. The important alloys are iridosmium (iridium rich), osmium iridium alloys and osmiridium (osmium rich). Maximum iridium is found in Canada, Russia and South Africa. The element was discovered by Smithson Tennant in 1803 and its name is founded on name of Greek Goddess ‘Iris’, that symbol is a ‘Rainbow’. Its catalytic activities were discovered by Lauri Vaska in 1960 [1]. It is the most active and widely used catalyst in several reactions both in basic and acidic medium [2,3]. Iridium and its complexes are utilized as homogeneous catalysts, bio-catalyst and nano-catalyst. It is most essential element of platinum group elements with wide array of oxidation positions i.e. -3 to +9 among all transition elements. Due to these facts, iridium has a wide range of uses including catalytic, medical and industrial [[4], [5], [6], [7]]. In photosynthesis process, it is responsible for cracking of water molecules into hydrogen and oxygen [[8], [9], [10]]. Therefore, iridium may be useful in solving food crises by artificial photosynthesis and energy crisis by splitting water generating hydrogen fuel (green energy).
Among various applications, catalytic action is the most significant area of iridium and its complexes for many industrial production including allylic substitution, hydrogen-transfer reactions, hydrogenation, functionalization of CH bonds, catalyzed fine chemical synthesis, 1,3-dipolar cycloadditions, etc. For long time iridium and its complexes are used as good catalysts but after the development of nanotechnology the application of this element has increased many folds. This due to the remarkable features of nanoparticles; particle size, charges, free energies etc. [[11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]] Some authors prepared nano size materials of native iridium and its compounds and used for multi-purposes [[27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42]]. The applications of nano size of iridium and its complexes are found to be remarkable with good number of publications. There is no review article on iridium based catalyst with nano concept. Because of a good growth of the research and publications and lack of review on this topic it was realized to write a review article on advances in iridium catalyst: a nano concept. The details on the synthesis, characterization, application and future perspectives are highlighted in this article. Certainly, this article will be highly useful for academicians, researchers and industrial persons.
Section snippets
Preparation
The preparations of iridium nano particles catalysts were reported by general wet chemistry methods. The various methods involved the iridium salts as the precursors. The different conditions were used by various workers. The particle sized was controlled by the experimental conditions. The nano particle catalysts were separated from reaction mixture and washed numerous times with water. Some authors washed these by alcohol. It is not possible to describe all the reported procedures. However,
Characterization
The iridium nano particle catalysts were characterized by the well-known techniques used in general nano technology. The important techniques are transmission electron microscopy (TEM), scanning electron microscope (SEM), cyclic voltammetry (CV), X-ray diffraction (XRD), electrochemically active surface area (ECSA), atomic force microscope (AFM), field ion microscope (FIM), scanning Tunneling Microscope (STM), scanning probe microscopy (SPM), energy-dispersive analysis of x-rays (EDAX), Fourier
Applications
Iridium is an important element with remarkable properties. Iridium and its complexes have extensive choice of applications in numerous area of science and technology. As a catalysis iridium is an excellent element for catalyzing various organic and inorganic reactions. It is very difficult to write the whole applications of iridium nano catalysts. However, the attempts are made to summarize some important applications so that the readers may be benefited.
Toxicity
As such iridium is not toxic as there is no report on the iridium toxicity in the literature but nano particles of non-biodegradation nature are toxic. Therefore, all the toxicity aspects of nano particles will be applicable to iridium nano particles as these nano particles are non-biodegradable. The non-biodegradable nano particles are threat to human beings and environment. The lesser size of nanoparticles creates their entrance stress-free into the living organisms. Nanoparticles have higher
Future perspectives
As discussed above iridium catalyst has an extensive range of applications and really it is the best element to produce more smart catalyst. The special features of nano particles made this element of extraordinary importance. Much work has not been done to develop the efficient iridium nano particles; especially in water splitting for hydrogen generation – a need of future. Besides, the applications of iridium nano particles are not fully developed in other areas of research and industrial
Conclusion
This review article presents the state-of-the-art of iridium nano catalysts. In this article, the attempts are made to discuss the syntheses, characterizations, applications, toxicity and future perspectives aspects. Over all, the available information on nano iridium catalysts is included in this article. The data included in this article is of great importance for researchers, academicians and industrial persons. The growth of papers and applications of iridium nano catalysts indicated bright
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