Methodological Study Of Continuous Synthesis Of Spherical Cu₂O Monodispersed Particles

As a p-type semiconductor with a band of 2.2 eV,cuprous oxide has been extensively used in coating,glass,ceramic,and industrial catalysis as an important inorganic material.It is well-known that the size and morphology of inorganic materials have significant effects on their properties.Hence,preparing Cu₂O crystallites or particles with different morphologies has been spotlighted in industrial application.Previous studies on the preparation of Cu₂O micro-or nano-particles reveal that the morphology and size of Cu₂O can be controlled by electrolysis,solid reaction and chemical redox in solution,etc.The Cu₂O particles prepared by the chemical redox are particularly advantageous in monodispersion,controllable morphology,non-aggregation and etc.,thus rendering the process notable.However,currently available techniques of the method require considerable additives to control morphology and size,as well as preparation of particles at low reaction concentrations,which is more appropriate on a laboratory scale rather than on an industrial one.Therefore,none of these methods can be utilized for continuous synthesis in industry.In this dissertation,Cu₂O micro-particles with different morphologies and sizes were successfully synthesized at high reaction concentrations without any surfactant.In our experiment,copper（Ⅱ）was reduced to cuprous oxide by D-glucose in a basic system.Given that the morphology and size of Cu₂O particles can be controlled by altering adding order and reaction temperature,the following aspects were studied in detail.1.Preparation of Cu₂O particles with different morphologies by discontinuous processCuprous oxide particles were synthesized by different strategies,and all the final products were sharply size-distributed and non-aggregative.Adding sodium hydroxide at different concentrations into copper sulfate solution transformed the morphology.As indicated by XRD patterns,the cuprous oxide particles were of identical cubic phase structure.Geometrical shapes of cubo-octahedral microcrystals with cubic phase structure were determined by the ratio（R）of the growth rate along the {100} direction to that along the {111} direction.Increasing the concentration of NaOH in the system increased R.When R reached 1.73,the Cu₂O particles were octahedral.It is speculated that OH-decelerated the growth along the {111} direction by being absorbed on the {111} facets.As a result,OH-affected the morphology of particles as a face-selective additive.The formation mechanism concerning the growth of cubic,polyhedral and octahedral Cu₂O particles was non-classical,which can be divided into two periods.The first major period that determines the number and size of particles is affected by the aggregation mechanism.The next period,in which the diffusion mechanism dominates,determines the morphology of final products.Besides,the species of precursory solid also changed the shape of particles.Unexpectedly,special Cu₂O particles with surprising shapes,which have not been reported yet,were obtained.Spherical Cu₂O particles were collected by programmed rise of reaction temperature,which provides a possible solution for continuous synthesis.2.Control of the shape and size of spherical Cu₂O particlesIn the gel-sol process,particle size is under the control of pH and temperature.Being able to determine the species of precursory complex,pH can also change ion strength and reaction rate.Meanwhile,temperature can affect the stabilization rate of precursory gel and reaction rate simultaneously.As the formation process of spherical particles is similar to the gel-so]route,pH and reaction temperature are the key factors for size control in our experiments,based on which the adding quantity of NaOH and the increasing rate of temperature were varied to control particle size.In addition,the quantity of D-glucose was also shape-controlling.The particles were octahedral in the presence of optimum quantity of D-glucose.In case of excess（four times）,they became spherical.Moreover,the final products were aggregative and non-polydispersive.Programmed temperature elevation lays a foundation for continuous synthesis.3.Continuous synthesis of Cu₂O particles using CSTRContinuous stirred-tank reactor（CSTR）has been widely used in industry and chemical engineering,allowing it to be used to continuously synthesize Cu₂O particles herein.Nevertheless,neither one tank reactor nor two-section serial-tank reactor managed to yield ideal products,which may be attributed to the special formation process of cuprous oxide particles and the characteristic of CSTR.Nucleation in the tank reactor cannot remain continuous,thus destabilizing the system.Consequently,ideal Cu₂O particles cannot be continuously synthesized by CSTR.4.Continuous synthesis of spherical Cu₂O particles using tubular reactorWith tubular reactor and step thermoregulation,monodispersed spherical Cu₂O particles were successfully continuously synthesized.Specifically,two and three stuff flows were pumped,respectively.As the results of programmed rising temperature method,mixing copper sulfate with glucose before adding NaOH led to the aggregation of final products.Similarly,only by pumping three stuff flows can synthesize spherical Cu₂O particles.Particles sized from 0.7 μm to 2.2 μm were controllably prepared by regulating the adding quantity of NaOH and temperature.5.Preparation of ultrafine copper powdersUtilizing the cuprous oxide powders derived from un-continuous process as the intermediate,ultrafine copper powders were synthesized by adding Arab gum,hydrazine and glycine.Furthermore,the sizes of the copper powders were controlled by varying hydrazine pH,reaction temperature and glycine concentration.