| The discharge of modern industrial wastewater poses a great threat to both environmental safety and human health.Among them,phenolic wastewater containing 4-nitrophenol（4-NP）is highly toxic and needs to be treated urgently.The chemical reduction method is a common treatment method for phenolic wastewater,which can reduce the toxic 4-NP to harmless4-aminophenol（4-AP）.4-AP is often used as an intermediate for pharmaceuticals and other chemicals.The key to improve the reduction rate of 4-NP is to develop efficient catalysts.But conventional photocatalysts suffer from narrow light absorption range and low energy utilization,and conventional thermal catalysts suffer from high energy consumption and high pollution.In contrast,photothermal catalysts use the photothermal effect for catalytic reactions,which can use solar energy to increase the local temperature of the material surface and have the advantages of high efficiency and environmental protection.Based on this,two photothermal catalysts were developed in this paper using a strategy of loading noble metals on two-dimensional photothermal materials.Both catalysts showed enhanced photothermal catalytic efficiency under 808 nm laser irradiation.This provides new ideas for the component design and liquid-phase reaction practice of photothermal catalysts,and is expected to be extended for more complex organic reactions.The main studies are as follows.（1）Preparation of molybdenum disulfide supported palladium catalystAs a typical two-dimensional material and photothermal material,molybdenum disulfide（Mo S2）can not only be used as a carrier for active components,but also provide thermal energy for catalytic reactions.Therefore,in this paper,a two-step hydrothermal method was used to synthesize Pd/Mo S2 nanoflower composites with Mo S2 nanoflowers of about 750 nm and Pd nanoparticles of about 11 nm on the surface.When Mo S2 was loaded with Pd nanoparticles,the Pd/Mo S2 nanoflowers exhibited higher visible and near-infrared absorption in the range of 400 to1100 nm.Under 808 nm laser irradiation,Pd/Mo S2 nanoflowers exhibited a high photothermal conversion efficiency of 43.0%,which was higher than that of Mo S2（35.5%）.The apparent rate constant of the catalytic reduction reaction of 4-NP was six times higher than that of Mo S2nanoflowers when Pd/Mo S2 nanoflowers were irradiated under 808 nm laser.In addition,the photothermal catalytic rate of 4-NP reduction on Pd/Mo S2 was consistently higher than the thermal catalytic rate at a wide range of laser intensities（1-4 W/cm2）.Moreover,the photothermal catalysis showed lower activation energies than thermal catalysis with 52.94 k J mol-1 and 60.28 k J mol-1,respectively.（2）Preparation of reducing graphene oxide-supported palladium alloy catalystTo further improve the activity and stability of the catalyst,the bimetallic alloy catalyst was supported by reduced graphene oxide（r GO）.Using r GO as the carrier,palladium chloride as the palladium source,chlorauric acid as the gold source and ascorbic acid as the reducing agent,Pd-Au nanoalloy was loaded on r GO by thermal reduction method.The obtained Pd-Au/r GO has a large specific surface area and porosity,and shows strong light absorption in the range of 200-1100 nm.Under 808 nm laser irradiation,the photothermal conversion efficiency of Pd-Au/r GO can reach 43.4%.Using 4-NP catalytic reduction as the reaction model,the photothermal catalytic rate is 2.4 times of the thermal catalytic rate under 0.5 W/cm2 laser irradiation,showing the advantages of photothermal catalysis at low power density.In addition,under 1.0 W/cm2 laser irradiation,r GO-NH2,Au/r GO,Pd/r GO and Pd-Au/r GO degrade 0%,7%,25%and 92%of 4-NP in 4 min,respectively.The above results prove the enhanced catalytic activity of the alloy compared with the mono-metal. |
