Controllable Synthesis Of Novel Tellurium-Sulfide Heterogeneous Nanocomposites For Energy Conversion And Storage Applications

Metal sulfides（MSs）nanomaterials play a pivotal position in the applications of catalysis,sensing and energy,due to their unique properties in light,electricity,heat and magnetism endowed by their rich bandgap structures,which have become a hot research focus in recent years.However,the single-component MSs nanomaterials exhibit low light absorption efficiency,low electron transmission efficiency and insufficient stability,which seriously restrict their applications in the fields of optics and energy conversion.Recently,it has been widely demonstrated as one of the most effective strategies to enhance the performances of MSs nanomaterials by utilizing the synergistic effect of the composites of two semiconductor materials with different energy band structures after constructing appropriate heterogeneous interfaces.Tellurium（Te）is a typical p-type narrow band gap semiconductor material（0.35V）,whose electrons in the valence band can easily transition to the conduction band under light,resulting in strong near-infrared absorption.In addition,Te also possesses good conductivity and is considered a quasi-metal.It has been reported that the heterogeneous materials of tellurium and sulfides can broaden the optical absorption range and increase the electronic conductivity.Moreover,the introduced compact heterogeneous interfaces can promote the transmission and separation of electrons and increase the structural stability.Therefore,the development of heterogeneous Te-MSs composites provides an unprecedented opportunity for improving and broadening the applications of energy conversion materials.Recently,it is highly desirable to establish a controllable and efficient strategy to craft Te-MSs nanomaterials with novel heterojunction structures and remarkably enhanced performances.In this thesis,for designed construction of novel Te-MSs based heterogeneous nanomaterials,a facile yet robust microwave assisted one-step electrochemical strategy was explored for the successful synthesis of a series of heterogeneous Te-Pb S,Te-Cu₂S,Te-Ni S/Cd S,Tex Sy@PANI nanomaterials with unique morphologies,followed by mechanism study based on the characterizations of morphology,structure and component.Their performances in photothermal convention,photocatalytic water splitting and lithium ion battery were systematically studied.The main research contents are as follows:（1）Novel structured Pb S based light response material was synthesized by a microwave-assisted one-step quick controlled strategy.With Pb（DMDC）₂,TDEC and ethylene glycol as Pb source,Te source and reducer,respectively,samples with different morphologies and structures were obtained by microwave heating control program.The effects of microwave heating control program on the sizes,morphologies and structures of Te-Pb S nanocrystals were investigated as well as the SERS and photothermal properties.It was found that when the final microwave temperature of Pb（DMDC）₂ was controlled at 130℃,the rod-like hybrid material of Pb S QDs/Pb（DMDC）₂ was obtained with Pb S quantum dots uniformly dispersed on the rods.The rod-like complexes exhibited excellent performance as SERS substrate,with enhancement effect close to that of gold nanometer rods.When the reaction final temperature was controlled at 140,160 and 180°C,six-branched Pb S nanocrystals with different sizes were obtained.Under the irradiation of 980nm laser,the Pb S nanomaterials prepared at180°C show excellent photothermal performance with a photothermal conversion efficiency of 9.5%for the Pb S nanomaterials at 50 ug/m L.Further,novel dumbbell-shaped Te-Pb S heterogeneous junction materials were obtained by microwave simultaneous reduction of Pb（DMDC）₂ and TDEC.The influence of precursor ratios on the morphology,the growth process mechanism and the photothermal properties of materials were investigated.It was demonstrated that the size of Te-Pb S can be modified by regulating the molar ratio of Pb（DMDC）₂ and TDEC under certain microwave conditions,which has a novel dumbbell-shaped structure with Te tubes as supports and octahedral Pb S at both ends.The photothermal conversion performance of Te-Pb S could reach 12.1%under 980 nm laser when the molar ratio of the Pb（DMDC）₂ and TDEC is 1:1.The conversion efficiency and stability of the heterogeneous structured Te-Pb S are better than that of the single-component Pb S nanoparticles prepared under the same conditions,which can be attributed to the enhanced optical absorption capacity in the presense of Te.The one-step synthesis method enables Te and Pb S to form compact heterogeneous interfaces,thus improving the stability.（2）Heterogeneous Te-Cu₂S nanomaterials were rapidly synthesized by a one-step microwave-assisted strategy.With Cu（DMDC）₂/TDEC as precursors,popcorn-stick-shaped Te-Cu₂S was obtained with Cu₂S nanoparticles distributed around the Te tube.The morphology,composition and optical absorption of the material were characterized.It was found that heterogeneous Te-Cu₂S nanomaterial with uniform morphology can be obtained when the final temperature of microwave reaction is180°C and the molar ratio of Cu（DMDC）₂ and TDEC is 2:3.The photothermal performance of Te-Cu₂S was evaluated to be 25.5%upon exposure of 980 nm laser and50μg/m L concentration,higher than that of single Cu₂S（20.4%）and Te nanotube（8.5%）.P-type doping in Cu₂S can induce the lack of copper ions and result in the increase of hole carriers which generate local surface plasmonic resonance under the action of near-infrared and improve the near-infrared light response for superior photothermal performance.（3）Cd S-based heterogeneous photocatalytic material was constructed in the presence of Te and cocatalyst.With cadmium diethyldithiocarbamate（CED）,tellurium diethyldithiocarbamate（TDEC）and N,N-dibutyl nickel dithiocarbamate（NBC）as precursors,the shish-kebab-like Te-Cd S/Ni S heterogeneous structure materials were synthesized by one-step microwave assisted method,followed by photocatalytic hydrolysis hydrogen production efficiency test.A shish-kebab-like Te-Cd S/Ni S heterojunction material with uniform morphology and narrow distribution was obtained when the final temperature of microwave reaction is 160°C and the mass ratio of TDEC/CED/NBC is 10:6:4.The efficiency test of hydrogen production by photocatalytic hydrolysis shows that:the hydrogen production efficiency of Te-Cd S/Ni S heterojunction is 863.9μmol/（g.h）under visible light exposure（>420nm）,which is 11 times that of the single Cd S component.Besides,the hydrogen production efficiency of Te-Cd S/Ni S keeps stable after 36 h test,and its morphology is almost unchanged.The addition of semiconductor Te broadened the light absorption in visible region,which improves the utilization of light.The loading of the Ni S cocatalyst promotes the separation of photogenerated electrons and holes,resulting in excellent stability and photocatalytic hydrogen production performance of Ni S/Cd S-Te heterojunction photocatalytic materials.（4）Te_xS_y@PANI composite was synthesized by a one-step electrochemical method as a novel cathode material for lithium ion batteries.An electrochemical-chemical-electrochemical（ECE）mechanism was established for the formation of polyaniline wrapped tellurium sulfide composites,which effectively solved the volume expansion of Te_xS_y cathode for enhanced structure stability.The specific capacity of Te_xS_y@PANI composite reaches 1141 m Ah/g at 0.1 A/g along with excellent cycling stability,which is almost three times of the theoretical value of conventional Li-Te battery（420 m Ah/g）.Notably,Te_xS_y@PANI expresses two featured discharging plateaus located at 1.75 V and 1.6 V,respectively,and exhibits Li-S battery features at a low current rate of 0.1A/g and Li-Te battery features at a high current rate of 5 A/g.The in-situ transmission electron microscopy（TEM）characterization demonstrates the volumetric variation from lithium ions insertion was efficiently suppressed due to the presence of S atoms in the Te crystal structure.Moreover,the polyaniline shell prohibits the shuttle effects of polysulfides,and the unique microstructure of Te_xS_y@PANI composite effectively inhibits the volumetric variation in the cycling process,resulting in a significant improved cycling stability.