Synthesis and Catalytic Performance of Transition Metal Dichalcogenides/Carbon Composite Nanomaterials

Author:Li Hong

Supervisor:peng zhi jian liu zuo he


Degree Year:2019





With the continuous development of the industrialization and urbanization in human society,energy shortage and environmental pollution have become two major issues of common concern for all humans.Photocatalytic and electrocatalytic technologies,as green and environmental-friendly methods that can achieve clean energy hydrogen energy and treat environmental pollutants,have received more and more attention from researchers in recent years.Transition metal dichalcogenide nanomaterials with graphene-like layered structure,as a kind of emerging candidates for highly competitive alternative to precious metals,have the advantages of low production cost and abundant resources.However,due to their poor conductivity and the easy recombination of photogenerated electron-hole pairs usually existed in semiconductor photocatalysts,the actual catalytic performance of transition metal dichalcogenide nanomaterials is poor.In addition,most of the catalysts reported so far are in the form of powders,which are difficult to recycle,thus presenting low recycling rates.As a result,they are prone to causing secondary pollution.Therefore,how to prepare transition metal disulfide-based catalysts with high activity and easy recycling is a hot research topic in the related field.In this dissertation,several transition metal dichalcogenide/carbon composite nanomaterials were successfully prepared by combining highly conductive carbon materials with transition metal dichalcogenide nanostructures,and their growth mechanism was also investigated.Moreover,their catalytic performance and catalytic reaction mechanism were studied.(1)Using WO3 as tungsten source,Se powder as selenium source,and pre-oxidized PAN fiber as carbon source,a novel carbon fibers@WSe2 nanoplates core-shell composite(C fibers@WSe2 NPCSC)was successfully prepared under the protection of high purity Ar gas,in which numerous WSe2 thin nanoplates were in situ,densely and even vertically grown on the surface of the C fibers.The presence of the carbon fibers core in the composites greatly reduces the recombination efficiency of photogenerated electron-hole pairs in the WSe2 nanoplates,and thus the catalytic activity of C fibers@WSe2 NPCSC was greatly improved.Under simulated sunlight irradiation,comparing with commercially available WSe2 powder,the as-synthesized C fibers@WSe2 NPCSC presents significantly enhanced reaction rate constants by a factor of approximately 15,9,and 3 for the degradation of aqueous methylene blue,aqueous rhodamine B,and gaseous toluene,respectively.(2)Using MoO3 as molybdenum source,S powder as sulfur source,and pre-oxidized PAN fiber as carbon source,a novel carbon fibers@MoS2 nanoplates core-shell composite(C fibers@MoS2 NPCSC)was successfully prepared under Ar gas flow,in which numerous MoS2 thin nanoplates are in-situ,densely and even vertically grown on the surface of the C fibers.The highly conductive carbon fibers core in the composites facilitate the rapid transfer of of photogenerated electrons,and thus improve the separation efficiency of photogenerated electron-hole pairs,which results in greatly enhanced photocatalytic degradation performance.(3)Through NaCl-assisted thermal evaporation method,using MoO3 and S powder as raw materials,and high-temperature carbon cloth as substrate,a series of flexible carbon cloth@MoS2 nanoflakes composites were successfully prepared at different reaction temperatures between 650850°C under the protection of Ar gas,in which ultrathin MoS2 nanoflakes are vertically grown on the surface of carbon cloth.When the reaction temperature is 750°C,the resultant composites show the highest photocatalytic hydrogen production efficiency(669.4μmol g-1 h-1),and exhibits excellent photocatalytic stability.After 5 cycles,its photocatalytic activity is still maintained at 94%.(4)Using WO3 and S powder as raw materials,and melamine foam as carbon source,a novel binder-free and free-standing N-enriched carbon foam@WS2nanoflakes composite(NE-CF@WS2 NFs)was successfully prepared under Ar gas,in which numerous ultrathin WS2 nanoflakes are vertically grown on the surface of N-enriched carbon foam with a three-dimensional cross-linked and porous network structure.The NE-CF@WS2 NFs can be directly used as the working electrode of hydrogen evolution reaction in water splitting,displaying excellent electrocatalytic activity with a low overpotential of 153 mV at the current density of-10 mA/cm2 and a small Tafel slope of 58.7 mV/dec,and superior cycle stability and long-term stability.