| The rapid development of human society has increased its reliance on traditional fossil fuels,and the combustion of fossil fuels has also given rise to a series of environmental issues.In the wake of global energy and environmental issues,great efforts have been devoted to the search for clean and renewable fuels.The high specific energy of combustion and clean combustion products of hydrogen make it a promising candidate to replace traditional fossil fuels.Hydrogen generation via semiconductor photocatalytic water splitting has been identified as an ideal solution to the current environmental and energy problem in view of the abundance of solar energy.Till now numerous semiconductors have been exploited and used for photocatalysis.However,their real application is still limited due to their low efficiency.So enormous efforts have been made in the search of highly efficient and stable photocatalysts.The last few years have witnessed a growing research enthusiasm toward graphene-like structures.As a typical kind of transition metal dichalcogenides,Mo S2 is one of the most studied material.The layer of Mo S2 is composed of covalent Mo–S bonding,while interactions between the layers are weak van der Waals forces.When it was exfoliated from bulk to monolayer,it will change from an indirect bandgap semiconductor to a direct bandgap semiconductor.Such thickness-dependent electronic structures make it a promising candidate in various areas.The layer-structured Mo S2 can be used as effective supports for anchor of semiconductor nanoparticles.A more efficient charge transport will be achieved through the formed heterojunctions between Mo S2 nanosheets and semiconductors.Besides,density functional theory calculations and pioneer experimental works found that the catalytic activity stems from the active sites anchored in the exposed and under-coordinated edge sites.Thus transition metal dichalcogenides are widely accepted as a promising cocatalyst for semiconductor photocatalysts and show great potential as substitute of noble metal co-catalysts.The application of TMDs in photocatalysis is an attractive research topic.The contents of this study and important conclusions were summarized as follows:(1)A two-step hydrothermal method was employed to synthesize the Zn In2S4/Mo S2composite.In the first step,few-layer Mo S2was prepared by a ultrasonic method.And then the obtained Mo S2 nanosheet was used as a supporting substrate for the in situ growth of Zn In2S4 nanoparticles.The photocatalytic H2 production activities of the samples were evaluated using Na2S/Na2SO3 as sacrificial agents.The rate of H2 evolution is increased and reaches a maximum when the loading amount of Mo S2 reached about 0.5%.The total yield of H2 exhibit four-time higher than pure Zn In2S4,which demonstrates it is quite effective to employ Mo S2 as cocatalyst for improving efficiency of Zn In2S4 photocatalytic activity.We also prepared the composite of zinc indium sulfide and Mo S2 before and after ultrasound effect.No obvious enhancement of the H2 production rate was observed when zinc indium sulfide was coupled with bulk Mo S2.It is mainly due to the poor dispersion,small surface area and resulting less active sites of Mo S2.(2)A series of Ag In Zn S/Mo S2 nanocomposites with different content were successfully synthesized by adjusting the loading amount of Mo S2.The obtained Ag In Zn S/Mo S2nanocomposites show high efficiency for water splitting under visible light irradiation.When the loading amount of Mo S2 reached about 0.5 wt%,the yield of hydrogen reached 944?mol?g-1?h-1,which are ca.7 times as high as that of pure Ag In Zn S.A plausible mechanism was proposed for the charge transfer in the AIZS/Mo S2 composites.The enhanced photocatalytic activity towards water splitting arises from the more effective charge transfer and active sites on the edge of Mo S2.(3)A simple hydrothermal method was used to synthesize Mo S2-GO hybrid using GO as substratre.Although Mo S2 is an efficient cocatalyst for photocatalysis,the further advancement of their photocatalytic performance is still limited by their poor electrical conductivity.To couple graphene oxide with Mo S2 might overcome such drawback.By varying the feeding ratio of precursors,we obtained a series of Mo S2-GO hybrid with different mass ratios.The morphology change of different Mo S2-GO hybrid was observed.The large specific surface area of graphene oxide can improve the dispersion of Mo S2,inhibit its aggregation and expose more active sites.The hybrid of Mo S2 and GO can make good use of the high electrical conductivity of graphene oxide and the active sites of Mo S2,which make it a promising co-catalyst for photocatalytic hydrogen production.(4)A ternary heterostructured Cu In Zn S/Mo S2-GO photocatalyst was constructed by a simple two-step hydrothermal method using Mo S2 and GO as cocatalysts.When Mo S2 and GO were used as an independent cocatalyst,the nanocomposites showed moderate H2evolution rate.While Mo S2 and GO work together,the H2 evolution rate of the as-obtained catalysts were dramatically enhanced.When the mass ratio of Mo S2 to GO is 90:10 and the loading amount is at 1 wt%,the nanocomposite exhibited highest H2 evolution rate,which is27 times higher than the pure one.The dramatically enhanced photocatalytic performance toward hydrogen evolution could be attributed to the synergetic effect of Mo S2 and GO.GO served as an electron collector and transporter while Mo S2 provide more active sites for hydrogen evolution.(5)A ternary complex of Ag In Zn S/Mo S2-GO was successfully synthesized via a two-step hydrothermal method.Layered structured Mo S2-GO plays a key role in enhancing the photocatalytic performance for hydrogen evolution.The H2 evolution rate of pure Ag In Zn S is relatively low,while the nanocomposite with 1 wt%Mo S2-GO in the heterojunction photocatalyst exhibits the highest rate of hydrogen evolution rate of 1302?mol?g-1?h-1,which is 9 times as high as the pure one.A detailed mechanism has been developed to explain the significantly enhanced catalytic activities. |
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