Study Of Gallic Acid Assisted Hydrothermal Synthesis Of Nanostructured Sulfides （SnS₂、Cu₂S、Cu₃SnS₄） And Their Properties

Metal sulfide semiconductor nanomaterials have found a wide of potential applications due to their excellent physicochemical properties,and received more and more researchers’ attention.With the deepening research and development,the synthesis methods of controllable microstructures,morphologies,scales and chemical compositiones of metal sulfide nanomaterials have become the hotspot in this field.Liquid-phase synthesis method is widely used in the synthesis of nanomaterials for its simple route,high efficiency,high yield,good repeatability,green and environmental protection.Among the liquid-phase processes,hydrothermal synthesis method can not only induce the synthesis of good crystalline products at low temperatures,but also control the sizes and morphologies of the resulted products.Under normal synthesis circumstances,the system requires the addition of organic surfactants or structure-directed agents so as to regulate crystal growth with the controllable the crystal morphology.Most synthetic systems can not remove organic surfactants,making the synthesis process difficult.Additionally,organic surfactants are harmful to human and environments.In this paper,a green eco-friendly gallic acid(GA)was used as crystal growth regulator and reducing agent to synthesize metal sulfides nanomaterials combined with a clean synthesis method-hydrothermal synthesis.Meanwhile,the reaction parameters were modified so as to control the microstructures,morphologies and scales of metal sulfide products.Main reaserch contents included:1.The flower-like SnS2 hierarchical structures composed of ultra-thin nanosheets have been successfully synthesized via a simple hydrothermal method using gallic acid as crystal growth modifier.The effects of concentration of gallic acid,reaction time,reaction temperature,the ratios of metal ions,thiourea doses and concentration of reactants on morphologies were investigated and formation mechanisms of the flower-like SnS2 hierarchical structures were preliminary put forward.It was found that the optimized flower-like hierarchical SnS2 structures with diameters of 1～2 μm and thickness of 2～12 nm were obtained under hydrothermal conditions of 160 ℃ and 12 h together with chemical composition molar ratios of n(GA):n(Sn4+):n(S2-)=1:1:2.Simultaneously,it was confirmed that SnS2 was formed by subsequent sulfidation reaction of SnO2 which firstly formed during the hydrothermal processing.GA molecular regulated and stimulated crystal growth along the lateral sides of SnS2 hexagonol plates resulted in forming two-dimensional nanosheets crystals,and both the orientation aggregation and Ostwald ripening played a role in the formation of flower-like SnS2 hierarchical nanostructures.SnS2 had shown good electrochemical properties being as an anode material for lithium-ion batteries.In this work,the flower-like hierarchical structures demonstrated good cycling stability,the coulombic efficiency remained at 98.8%after 50 cycles.The layer structures had a higher initial capacity of 1262 mAh g-1,the specific capacity decreased to 183.4 mAh g-1 and capacity decay was obvious after 50 cycles.2.Nanocrystalline Cu2S was successfully synthesized by a simple gallic acid assisted hydrothermal method for the first time.Different synthesis parameters such as gallic acid doses,reaction time,reaction temperature and the concentration of reactants were carried out to investigate the transformation of phase structures and morphologies of Cu2S crystals.And the effects of different solvents and surfactants contents on the dispersibility of Cu2S powder were studied.The research results showed that GA can reduce Cu2+ to Cu+ during the formation of Cu2S.In addition,n(Sn2+)=n(Sn4+)=0.01 mol and heating temperature of 200 ℃ for 12 h can be used to prepare high purity and monodispersity cubic phase Cu2S.3.High crystallinity and single-phase nano-ternary compound Cu3SnS4 has been firstly synthesized using hydrothermal synthesis method by comprehensive analysis of various influencing factors of GA molecular.Experimental parameters,such as the concentration of gallic acid,reaction time,reaction temperature,the ratios of metal ions to sulfur source,played crucial roles in determing the phase and morphologies of final products.The formation mechanism of Cu3SnS4 nanocrystallines was also discussed.It was found that hydrothermal synthesis of high purity ternary compound Cu3SnS4 required to synergetically combine with reaction parameters,such as hydrothermal temperature,reaction time,GA doses,the initial ratios of Cu:Sn:S.Single-phase ternary Cu3SnS4 nanosheets with the thickness of about 10 nm were attained under the optimized conditions of 200℃,24 h and 3:1:4.5.