The Synthesis And Properties Of Metal Chalcogenide Semiconductors

Energy, environment and materials are three aspects that have attracted attentionfrom all over the world. Ever since the industrial revolution, fossil fuels （includingcoal, oil and natural gas） are the main sources of energy to production and life of thewhole population. Nevertheless, there’s a controversy between the continuous growthof energy needs and fossil fuel reserves. So people are paying more and moreattention to find alternative energy sources which are both effective and economical.Thermoelectric materials can convert almost all kinds of waste heat （like residentialheating, automotive exhaust and industrial processes） to electricity. For this reason, itcan also increase the efficiency of conventional energy sources besides performing asan alternative energy source. At the same time, enormous amount of organicpollutions that discharged into the environment every year have dramatically affectedour eco-system. As a large proportion of the whole organic pollutions, synthetic dyescannot be effectively degradated with conventional methods of treatment. Fentonprocess can take advantage of many other procedures for the efficiency of degradatingsynthetic organic dyes. Its efficiency can even be enhanced while radiations orultrasonics are introduced. The two main areas in this thesis focus on the three aspectsof energy, environment and materials, which makes it of good realistic meanings.1. With CuCl——2and FeCl——3as metal sources, we have synthesized uniform CuFeS2nanoparticles （with an average size of6.4±0.5nm） using a facile solution phasemethod by adding capping agents. The sample is defined as chalcopyrite CuFeS2according to XRD measurements. For the understanding of more detailed componentand valence state information, we have measured EDX and XPS spectra of oursamples. The results show that our samples are in good accordance with standardstoichiometry of chalcopyrite. At the same time, the valence states for Cu, Fe and Sare+1,+3and-2, respectively. We have also investigated thermoelectric properties of as-synthesized CuFeS₂nanoparticles in the temperature range of300K to500K. When compared withcommercialized bulk chalcopyrite, we found that the figure of merit ZT of our sampleis77times larger than the value of bulk material. With its environment-friendlyfeature, facile and reproducible synthetic method, good thermoelectric performance,as well as its low cost, we believe that CuFeS2nanoparticles can be used in industrialscale and have potential value of being made into thermoelectric devices.2. With a facile solution-phase approach, we have made uniform PbTenanocrystals （with an average size of13±3nm）. We then coated as-synthesizedPbTe nanocrystals onto glass fibers and got flexible thermoelectric fibers. We canobtain uniform nanocrystal coatings with this solution-phase deposition method, andthe coating thickness can be adjusted with tuned experimental parameters. We haveinvestigated the thermoelectric properties of the flexible thermoelectric fibers, andfound that they have an enormous figure of merit.Because of their flexible feature, the coated fibers have the potential to bewrapped onto the industrial pipes to act as both thermal insulating materials andthermoelectric convertor that can recover the waste heat back into electricity toimprove energy efficiency. Most importantly, by applying the thin coating ofthermoelectric nanocrystals onto glass fibers, significant reduction in the amount ofraw materials required to build thermoelectric devices can be achieved, dramaticallyimproving the performance/manufacture cost trade-off to enable the large scaleinstallation of thermoelectric energy harvesting device.3. We have selected the mixture of CuFeS2powers and peroxide to apply fentonreaction for the degradation of synthetic organic dyes （methylene blue, rhodamine Band rhodamine6G）. UV-vis spectrum measurements show that the mixture of CuFeS₂powers and peroxide has high degradation efficiency for all the three organic dyes. It’sthe first time that a ferric sulfide material being used in fenton process, and we arestill working on the mechanics and improvement of performance related to thissystem.