| Nano-CuO is a kind of p-type semiconductor photocatalytic material with narrow band gap,which has wide application prospect in many fields such as environmental pollution control.However,the conventional nano-CuO powder has the defects of complicated preparation process and not easy recycling,which seriously restricts its practical application in environmental pollution control.Therefore,the development of a simple and inexpensive synthesis method of nano-CuO material,as well as the interaction relationship among its preparation process,structural characteristics and photocatalytic performance plays an important role in the field of environmental modification.In this paper,the nano-CuO films were prepared by electrochemical deposition process,and the effect of process parameters on the structure of nano-CuO was studied.The controllability of the preparation process was realized.On this basis,the growth mechanism of different kinds of nano-CuO and its photocatalytic mechanism in the field of environmental pollution control system were systematically investigated.The main findings are as follows:Firstly,the nano-CuO film with micro-morphology as snowflake was prepared by using the electrochemical deposition process.The preparation process conditions were optimized via adjusting the preparation parameters(including electrodeposition voltage,pH value of electrolyte,electrodeposition time,electrodeposition temperature,etc.).At the same time,doping of transition metal ions has a certain effect on the microstructure of CuO,which can improve the photocatalytic performance of the nano-CuO in some extent.Secondly,we found that different electrolyte compositions have an important effect on the structure of nano-CuO.When the CuSO4/lactic acid mixed electrolyte system was selected,the octahedral structure and the nano-CuO with needlelike microstructure were obtained.When the Cu(NO3)2/NH4 Cl mixed electrolyte system was used,the obtained microstructure of nano-CuO was composed of nanosheets as the basic unit.According to different superposition methods,the cross structure,beam structure and flower cluster structure were formed.When the Cu(NO3)2/NH4NO3 mixed electrolyte system was used,the nano-CuO with fibrous or flower-like microstructure was obtained.The results of the organic pollutants degradation experiment reveal that all the above nano-CuO with different microstructure show good photocatalytic activity.Thirdly,the Full-prof software was used to refine the XRD patterns of nano-CuO samples which prepared under different conditions.It was found that nano-CuO with high purity and good crystallinity could be obtained in acid-to-alkaline electrolytes.However,the effect of CuO prepared by different electrolyte systems on the crystal structure is small,and the experimental value is slightly lower than the theoretical value.In addition,the nano-CuO structure doped with lanthanum ions is basically consistent with the theoretical structure.The doping of lanthanum ion can improve the photocatalytic efficiency of nano-CuO.Fourthly,the nano-CuO films prepared by different electrolytic solutions were in accordance with the multi-layer structure.In the acetic acid electrolyte environment,the snow-like nano-CuO is mainly affected by the micellar effect.To be more precisely,the growth of the Cu2 O nucleus in the specific crystal plane is limited,while the other crystal faces are not hindered,so that the crystal growth rate along different crystal surfaces differentiate from each other,resulting in a preferred orientation during the crystal growth of Cu2 O.The octahedral and acicular structures prepared in the environment of lactic acid electrolyte are divided into upper and lower layers,and the lower layer is arranged closely together by CuO nanoparticles,which is closely connected with ITO conductive glass.The upper layer is octahedral or sea urchin(Spherical surface attached to the needle-like protrusion)structure.The needle-like structure is mainly affected by lactic acid,because lactic acid molecules are easy to dehydrate and condense to form acid anhydride or lactide.The formation of crosslinked,fibrous and flower globules microstructures are mainly due to the fact that NH4+ is easy to form Cu-NH2 complex(Cu(NH3)42+),which thereby altered the electrochemical deposition process,namely crosslinked together in the processes of directional attachment and Ostwald ripening.Fifthly,during the photocatalytic reaction of nano-CuO,the electrons captured on the surface of the sample react with the oxygen molecules adsorbed on the surface to form superoxide radical negative ions(·O2-),and ·O2-reacts with water or protons to generate HO2-and H2O2.These active substances will continue to react with O2 and H2 O to form a series of intermediates and eventually convert to hydroxyl radicals(·OH).At the same time,these active substances react with the organic matter in the system to generate various reactive oxygen free radicals.On the other hand,the photogenerated holes can be directly reacted with the water molecules after being captured on the surface of the sample to form hydroxyl radicals.Experiments have shown that hydroxyl radicals have a strong ability to oxidize almost all of the organic molecules and decompose them.In this paper,based on the morphology-controlled preparation,the nano-CuO samples were subjected to full-spectrum fitting and structural refinement,and the corresponding relationship between the preparation conditions and the microstructure of the samples was obtained.On the basis of the above,the growth mechanism and the photocatalytic mechanism of the nano-CuO samples were systematically studied.The results of the photocatalytic characterization were ascribed to its structure,namely the structure and properties of nano-CuO.These provide effective theoretical and data support for the application of other nanomaterials in the field of environmental pollution control. |
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