SiO₂ Template And Synergetic Catalytic Synthesis Of Hollow Carbon Spheres And Bamboo CNTs From Polyolefin

Carbon nanomaterials have always attracted people's attention.However,it is difficult to effectively control the morphology of the carbon nanomaterials prepared due to the complexity of the components produced in the cracking process of polymer resulting that the method of synthesizing carbon nanomaterials using polymers as carbon sources is still difficult to be widely used.In this work,the morphology and structure of carbon nanomaterials prepared by using silica(SiO2)particles as templates and polyolefins as carbon sources were controlled and studied.The specific work is as follows.There are already many researches on the preparation of hollow carbon spheres by SiO2 particles templates,but how to control the thickness of carbon spheres and adjust the degree of graphitization is still a great problem.In this paper,we used nano-silica particles as templates and potassium carbonate(KCI)as conditioner adjusting the degree of graphitization to prepare hollow carbon spheres from polyolefins.Research have shown that the yield can reach 32%when the ratio is PP/20 wt%SiO2/2 wt%KCl during the cracking of polypropylene catalyze by SiO2 and KCl under nitrogen.After analysis,we found that the SiO2 particles mainly act as a template,and the addition of KCl can effectively reduce the thickness of the carbon shell while increasing the degree of graphitization of the hollow carbon sphere.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffractometry(XRD),Raman spectroscopy(Raman),thermogravimetric analyzer(TGA)were used to characterize the morphology and degreeg of graphitization of the hollow carbon spheres.It was found that the hollow carbon spheres obtained by the PP/20 wt%SiO2/2 wt%KCl system were tested for specific surface area by nitrogen adsorption-desorption,and the specific surface area of the hollow carbon spheres was found to be 221 m2/g.And the hollow carbon sphere show a relatively high adsorption capacity for methylene blue when it was used to adsorb methylene blue in water.Bamboo-like carbon nanotubes have larger specific surface,higher defect density and more active sites compared with ordinary carbon nanotubes and great application advantages in adsorption,catalyst support,and composite reinforcement.However,the effective synthesis of bamboo-like carbon nanotubes has been the biggest problem in its application.In this work,bamboo-like carbon nanotubes were successfully synthesized by catalyzing polypropylene in the case of adding rice hull powder(rich in SiO2).In the research,we first studied the carbonization results of merely adding rice hull powder to polypropylene.It was found that rice hull powder did not have any catalytic cffect on PP cracking,and its products were mainly amorphous carbon and SiO2 produced by pyrolysis of rice husk.In order to increase the templating effect of rice husk silica,we further utilized Ni2O3/NH4Cl composite catalyst system.The study found that when a single catalyst of Ni2O3 and NH4Cl was added to the PP,the yield of the carbon product was only 0.2%and 13.5%.When Ni2O3/NH4Cl is added as a composite catalyst to PP,the yield of the blend can be increased to 34.6%,which indicates that the composite catalyst Ni2O3/NH4Cl is a key factor for carbonation of PP in high yield.It was found that there are great improvement in productivity which can reach to 40.1%when the amount of the rice hull powder and Ni2O3/NH4Cl added is respectively 10 wt%and 5wt%/l wt%.The carbon materials obtained were characterized by SEM,TEM,XRD,Raman,TGA and so on.It was found that the product contained more bamboo-like carbon nanotubes.By comparing the carbonized products with and without the adding of rice hull powder,it was found that rice husk powder is a necessary condition for the formation of bamboo-like carbon nanotubes,and the presence of SiO2 in rice husk powder plays a crucial role.