Preparation Of Ag-Doped Catalyst And Its Application In The Treatment Of Phenolic Wastewater

4-nitrophenol（4-NP）is a common and key chemical used in the synthesis of pesticides,drugs and synthetic dyes in various chemical and pharmaceutical industries.Because 4-NP is highly toxic and stable in water,it is harmful to the environment and human health.It not only stimulates the skin and eyes,but also damages the liver and blood cells.However,4-aminophenol（4-AP）,as a product of 4-NP reduction,can be used in the pharmaceutical industry to produce paracetamol,phenacetin and other products.Therefore,the reduction of 4-NP to 4-AP can not only purify phenol-containing wastewater,but also produce products with high added value.At present,silver nanoparticles（AgNPs）have been widely used in the reduction of 4-NP due to their large specific surface area and low cost compared with other precious metals,such as Au and Pd.However,silver nanoparticles are easy to agglomerate in the catalytic process,and the catalytic performance will be greatly reduced.A very effective strategy to solve this problem is to combine silver nanoparticles into different carriers.The incorporation of silver nanoparticles into different substrates can effectively reduce the interaction between them,thereby improving the catalytic activity.In recent years,materials such as polymers,carbon materials,oxides,and metal-organic frameworks（MOFs）have been used as common carriers for constructing silver-based nanoparticle catalysts.In this paper,zinc oxide and ZIF-67were selected as substrate materials to prepare catalysts doped with AgNPs,and used for catalytic reduction of simulated phenol-containing wastewater.（1）AgNPs were doped with ZnO by a simple one-pot hydrothermal method.Different states of Ag-ZnO nanoflower catalysts were prepared by controlling the pH value of the reaction system,the incorporation of AgNPs and different hydrothermal temperatures.By catalyzing the reduction of 4-NP by Na BH₄,the optimum preparation conditions of Ag-ZnO nanoflower catalyst were pH=7,the amount of AgNPs was 0.05 M,and the hydrothermal temperature was 160°C.The catalyst prepared under this condition can catalyze the reduction of 4-NP to 4-AP in 8 min,and the catalytic rate still reaches about 90%in the fifth cycle reaction.（2）AgNPs were doped on ZIF-67 by in-situ co-precipitation method.Water was used as solvent in the experiment,which was simpler and environmentally friendly.The prepared catalysts were characterized by SEM,XRD and XPS to explore the morphology and elemental composition of the materials.The reduction reaction of4-NP was used as a probe to test the catalytic performance of the prepared catalyst,and the reaction process was monitored by ultraviolet spectrophotometer.When Ag_0.5/ZIF-67 was used as the catalyst,the catalytic rate was 1.3038 min^-1,which was better than ZIF-67(0.3641 min^-1),Ag_0.25/ZIF-67(1.0651 min^-1),Ag_0.75/ZIF-67(0.9485min^-1),Ag₁/ZIF-67(0.7618 min^-1).Ag_0.5/ZIF-67 can completely reduce 4-NP to 4-AP in 1 min,and the catalytic efficiency is still above 90%in the sixth cycle.（3）4-NP solutions with different concentrations and different pH values were prepared to simulate phenol-containing wastewater.The catalytic effects of Ag-ZnO and Ag_0.5/ZIF-67 on the treatment of simulated phenol-containing wastewater in different states were tested,and the effects of different catalyst dosage on the catalytic effect were tested.