摘要
以三聚氰胺和三聚氰酸作为前驱体,将三聚氰胺和三聚氰酸的混合悬浮液通过水热反应生成超分子中间体(MCA),然后经煅烧中间体合成g-C_(3)N_(4)纳米管,最后再采用热处理向g-C_(3)N_(4)纳米管中引入Na元素,获得了Na掺杂g-C_(3)N_(4)纳米管。采用X射线衍射(XRD)、场发射扫描电镜(SEM)、能量色散X射线光谱(EDXS)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、紫外-可见漫反射(UV-Vis DRS)和光致发光(PL)对系列试样进行表征,以苯酚(Phenol)溶液为降解对象,研究了试样的光催化性能。研究表明,通过水热、煅烧和热处理过程制备的Na掺杂g-C_(3)N_(4)纳米管,不仅提升了光的吸收能力,而且使g-C_(3)N_(4)的本征吸收边红移,拓宽了其可见光的吸收范围,增强了对可见光的吸收率,从而提高了太阳光的利用率。另外,Na掺杂能够提供更多的载流子并延长载流子寿命,提高了光生载流子的分离效率。且当Na掺杂质量比为17.5%时,试样在120 min内对Phenol的降解效率达到74.7%,分别是试样CN和NC_(0)的5.05倍和2.15倍。
With the development of industrial technology,the environmental problems have become more and more serious,especial⁃ly water pollution,which will directly endanger human health.Semiconductor photocatalysis technology is a kind of solar energy driven material to degrade the pollutants in the environment by strong redox ability.However,the traditional photocatalytic materials have some disadvantages,such as small specific surface area,low visible light utilization and high recombination rate of photo-generated electrons and holes,which lead to the low photocatalytic efficiency.Therefore,it is necessary to modify the morphology and band structure of semiconductor photocatalysts to improve their photocatalytic performance.g-C_(3)N_(4)nanotubes with different Na doping con⁃centrations were prepared by hydrothermal,calcination and heat treatment methods.Firstly,a suspension mixture of melamine and cy⁃anuric acid was used as precursor and placed to an autoclave at 150℃for 20 h.After cooling to room temperature,a supramolecular intermediate(MCA)was obtained.Secondly,MCA powder was transferred into an alumina crucible,calcined in a muffle furnace at 520℃for 2 h.After cooling down to room temperature,g-C_(3)N_(4)nanotubes were obtained.g-C_(3)N_(4)nanotubes were dispersed in a NaNO_(3) solution for Na element doping,followed by a drying process at 70℃.Then the dried powder was placed in a crucible and heat treated in a muffle furnace at 520℃for 2 h.Then Na doped g-C_(3)N_(4)nanotubes were obtained.The phase composition,morphology and optical properties of the obtained samples were characterized by an X-ray diffraction(XRD),field emission scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDXS),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spec⁃troscopy(XPS),ultraviolet and visible diffuse reflectance spectrophotometer(UV-Vis DRS)and photoluminescence(PL).In addi⁃tion,the photocatalytic performance of the sample was evaluated by the degradation of a phenol solution.A 300 W xenon lamp was used as a light source for the photocatalytic activity test.And the concentration change of the phenol solution was indicated by the ab⁃sorbance change at 270 nm with the UV-Vis DRS.The results showed that when the mass ratio of Na dopant was 17.5%in g-C_(3)N_(4)nano⁃tubes,the sample showed the best photocatalytic performance with a degradation rate of 74.7%in 120 min to the phenol solution,and the degradation rate constant was 1.19×10^(-2)min^(-1).While for the bulk g-C_(3)N_(4)and g-C_(3)N_(4)nanotubes without doping samples,the degra⁃dation efficiency to phenol solution was only 14.8%and 34.7%,respectively,with the same degradation conditions.The degradation efficiency of 17.5%Na doped g-C_(3)N_(4)nanotubes was 5.05 and 2.15 times higher than that of the bulkg-C_(3)N_(4)and undoped g-C_(3)N_(4)nano⁃tubes samples,respectively.The related active groups in the photocatalytic reactions were hydroxyl radical(·OH)and superoxide an⁃ion(·O^(2-)).During the calcination process,the hydrogen bond of supramolecular hexamer obtained by hydrothermal method was bro⁃ken and the layered structure was peeled off to form g-C_(3)N_(4)nanotubes structure,which increased the specific surface area of g-C_(3)N_(4)ma⁃terial.The tubular structure was conducive to sunlight diffuse reflection,and its absorbance was thereby improved.In addition,com⁃pared with pure g-C_(3)N_(4),the intrinsic absorption edge of g-C_(3)N_(4)for the undoped g-C_(3)N_(4)nanotube sample showed a little blue-shift,which was attributed to the quantum size effect caused bythe of g-C_(3)N_(4)nanotube structure.For the Na doped g-C_(3)N_(4)samples,a redshift of the intrinsic absorption edge of g-C_(3)N_(4)was obvious,which was due to the decrease of the band gap of g-C_(3)N_(4)from 2.69 to 2.55 eV.The widened absorption range and enhanced absorbance of sunlight improve the utilization of visible light,and the photocatalytic efficiency of the samples was also improved.Due to the Na impurity energy level,the lifetime of excitons was prolonged by the effective separation of photo-generated electron-hole pairs g-C_(3)N_(4).Therefore,the photocatalytic performance of Na doped g-C_(3)N_(4)was dramatical⁃ly improved.In the studies,g-C_(3)N_(4)modifications included both morphology optimization and band structure adjustment.g-C_(3)N_(4)band structure modification was realized by Na element doping.Compared with the bulk g-C_(3)N_(4),the photocatalytic performance of Na doped g-C_(3)N_(4)nanotubes was significantly improved in the photocatalytic degradation of phenol.Although the photocatalytic performance of the modified g-C_(3)N_(4)was greatly improved,there were still some shortcomings:(1)The photocatalytic performance of g-C_(3)N_(4)needed to be further improved.It could be realized by the combination with the band structure matched semiconductor or nanoscale metal materi⁃als to further improve the separation efficiency of photo-generated electron-hole pairs in semiconductors,so that more effective photogenerated carriers could participate in photocatalytic reaction.(2)In addition to the traditional studies in photocatalytic pollutants deg⁃radation,researches and applications should be expand to other photocatalysis fields,such as photocatalytic hydrogen production,CO_(2)reduction.(3)The recycling of powder photocatalytic materials was also a challenging problem.Then the g-C_(3)N_(4)film grown on substrate should be beneficial to the recycling of materials.
作者
于富成
李圆梦
刘正艳
崔军鹏
周亚东
Yu Fucheng;Li Yuanmeng;Liu Zhengyan;Cui Junpeng;Zhou Yadong(School of Material Science and Engineering,Lanzhou University of Technology,Lanzhou 730050,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2022年第7期896-905,共10页
Chinese Journal of Rare Metals
基金
湖北省教育厅委托科技项目(B2018058)
企事业单位委托科技项目(LZSN-KJ-002,2018040-G,ky2019047)资助。
