Synthesis And Photocatalytic Water Splitting Properties Of Carbon Dots Modified Metallic Oxides

Utilizing photocatalysts and solar energy for hydrogen evolution from water is an ideal way to solve the global energy shortage and environmental pollution problem.However,it is remains challenging to search for more inexpensive,stable,and efficient photocatalysts.Carbon dots(CDs)have caused widely attention because of their unique physical and chemical properties.such as low price,low toxicity,anti-photobleaching.good water solubility,good biocompatibility and easy functionalization.What's more,CDs have been widely used in many fields,including materials science and energy.catalysis,biological labeling,bioimaging,drug delivery,etc.In this paper,three kinds of carbon modified oxide composites were synthesized,including CDs modified cobalt oxide composite(CoO1.6C0.7).WO2-NaxWO3CDs composite and MoS2-Co3O4-CDs composite.Those composites were were characterized by multiple instruments.The photocatalytic activity and corresponding reaction mechanism in these systems were also further studied.1.We designed a CoO1.6C0.7 photocatalyst using CDs and cobalt chloride as raw materials through a simple redox method.The obtained composite was used as a photocatalyst and it's photocatalytic activity for water splitting under visible light was researched.The H2 evolution rate about 2.6 ?mol/h under visible light(?>420 nm).while the H2 evolution rate increased to 18.0 pmol/h when used triethanolamine as sacrificial reagent.Moreover,the disordered CoO1.6C0.7 photocatalyst displays good stability with more than 10 cycles.The improved photocatalytic activity and favorable stability of the disordered CoO1.6C0.7 can be attributed to the addition of CDs,which enhanced the light absorption and accelerated electron transfer.2.We designed a UV-Vis-NIR broad spectrum-driven carbon dots modified WO2-NaxWO3(WO2-NaxWO3-CDs)composite as photocatalyst for overall water splitting without requirement of any sacrificial agents or cocatalysts.The WO2-NaxWO3-CDs were synthesized through a hydrothermal method.When the concentration of CDs in the composite is 0.008 gCDs/gcatalyst,the WO2-NaxWO3-CDs shows the highest photocatalytic activity with stoichiometric ratio of H2/O2 evolutions and their rates are 0.05/0.02,2.58/1.24,4.74/2.28 Eimol/h under UV(X<420 nm),visible(420 nm???760 nm)and near-infrared(?>760 nm)light irradiation,respectively.It is also impressive that the photocatalyst shows good stability for about 6 cycles of repetitive experiments.The WO2-NaxWO3-CDs composites functioned as broad spectrum-driven photocatalyst for overall water splitting should attribute to the synergistic effect of WO2-NaxWO3 and CDs,in which the WO2-NaxWO3 provides the suitable bandgap,while the CDs can enhance light absorption and accelerate separation efficiencies of photo-generated charge carriers.The photocatalytic water splitting process of WO2-NaxWO3-CDs composite is the typical concerted four-electron process as follows.The construction of WO2-NaxWO3-CDs hybrid photocatalytic system offers a new strategy for the design of broad spectrum absorption photocatalysis systems for expanding the utilization of solar light.3.We synthesized MOS2-Co3O4-CDs composite with different mass ratios of CDs by hydrothermal method.The MoS2-Co3O4-CDs composite as photocatalyst could reach overall water splitting under visible light(?>420 nm)without requirement of any sacrificial agents or cocatalysts.When the concentration of CDs in the sample is 0.03 gCDs/gcataiyst,the MoS2-Co3O4-CDs composite shows the highest photocatalytic activity and the H2 evolution rate H2/O2 are 0.13/0.04 ?mol/h.The photocatalyst shows excellent stability for about 6 cycles of repetitive experiments.The enhanced photocatalytic activity and stability of MoS2-Co3O4-CDs can be attributed to the synergistic effect between MoS2 and Co3O4 and the addition of CDs.The addition of CDs could enhance light absorption and accelerate the separation efficiencies of photo-generated charge carriers.