Mesoporous carbon nitride based nanomaterials for solar fuel production

Theoretical thesis.Bibliography: pages 47-56.Chapter 1. Introduction -- 2. Literature review -- 3. Experimental section -- 4. Results and discussion -- 5. Conclusions and future work.From economic and environmental aspects, the generation of hydrogen (H2) from renewable solar energy and water through photocatalytic water splitting is a promising route, but the development of an efficient catalyst remains a great challenge for its technological use on a large scale. Because of several features like being metal-free, nontoxic, low cost, and chemically stable, carbon nitride has attracted worldwide attention. Compared to bulk carbon nitride, mesoporous carbon nitride (MCN) possesses a higher surface area and plentiful accessible mesopores. For the first time, Co3O4/MCN nanocomposites were designed and synthesised for photocatalytic H2 evolution in this work. Co3O4,earth-abundant nanoparticles, were supported on MCN via an impregnation method. Complementary characterisation techniques were employed to understand the properties of the fabricated catalysts.The bare MCN prepared under optimum conditions showed high photocatalytic activity under visible light irradiation without using any co-catalyst. The Co3O4/MCN with a Co3O4 mass content of 5 wt% exhibited the optimum photocatalytic activity in H2 evolution, which was two times higher than that of the bare MCN. The improved photocatalytic performance may be attributed to the enhanced catalytic properties, visible-light harvesting and effective charge separation.Mode of access: World wide web1 online resource (ix, 56 pages) illustration

Theoretical and Experimental Analysis of Surface Roughness and Adhesion Forces of MEMS Surfaces Using a Novel Method for Making a Compound Sputtering Target

Achieving a compound thin film with uniform thickness and high purity has always been a challenge in the applications concerning micro electro mechanical systems (MEMS). Controlling the adhesion force in micro/nanoscale is also critical. In the present study, a novel method for making a sputtering compound target is proposed for coating Ag–Au thin films with thicknesses of 120 and 500 nm on silicon substrates. The surface topography and adhesion forces of the samples were obtained using atomic force microscope (AFM). Rabinovich and Rumpf models were utilized to measure the adhesion force and compare the results with the obtained experimental values. It was found that the layer with a thickness of 500 nm has a lower adhesion force than the one with 120 nm thickness. The results further indicated that due to surface asperity radius, the adhesion achieved from the Rabinovich model was closer to the experimental values. This novel method for making a compound sputtering target has led to a lower adhesion force which can be useful for coating microgripper surfaces

Tunable syngas production from biomass : synergistic effect of steam, Ni–CaO catalyst, and biochar

The production of tunable syngas from biomass will further establish the role of biomass-derived syngas as a versatile platform for liquid fuels and value-added chemical synthesis. This study introduced steam, Ni–CaO catalyst, and biochar into a proposed two-stage sorption-enhanced catalytical thermochemical conversion process, aiming to obtain the tunable syngas through the in-situ stepwise generation of high purity H2 and CO. The presence of steam and Ni–CaO catalyst shows unprecedented performance in enhancing the H2 generation due to the promotional tar steam reforming/cracking and water-gas shift reactions at the first stage, and the control experiments indicate that the steam performs a higher selectivity to H2 than the Ni–CaO catalyst. The introduction of biochar with a supplementary carbon source, remarkably promotes the CO generation at the second stage, which could be further pronounced by the addition of Ni–CaO catalyst. A synergistic effect of steam, Ni–CaO catalyst, and biochar contributes to a significant enhancement in H2 and CO generation with an inherently separated generation of H2 (88.2 ± 2.3 vol% of purity) and CO (55.6 ± 1.3 vol% of purity). And the combined use of steam, Ni–CaO catalyst, and biochar could lead to a superior syngas quality with high LHVsyngas and energy recovery efficiency