Preparation And Photocatalytic Performance Of Composites Based On Sulfur-Doped Carbon Nitride

Nowadays,the issues of environmental pollution and energy shortage become more and more serious.As a new advanced oxidation technology,photocatalytic technology has been widely used in the field of hydrogen energy generation and pollutant removal due to its low energy consumption and high efficiency in pollutant removal.As a non-metallic photocatalyst,carbon nitride(g-C3N4)has several advantages,such as good response capability in visible light,high stability,simple preparation processes.However,these disadvantages,including small specific surface area,poor light absorption and fast recombination of photogenerated electron hole heavily restrict its usage.Various attempts have been reported,such as morphology and structure regulation,element doping and heterojunction structure construction etc.to tackle the drawbacks of g-C3N4.In this study,the sulfur-doped g-C3N4(S-C3N4)was obtained by modifying g-C3N4 with non-metallic element sulfur(S),which greatly improved the photocatalytic performance of D-C3N4.In order to further improve the performance of S-C3N4,it is separately combined with TiO2 and C-dot to form a composite photocatalyst.Furthermore,the morphology,photoelectric chemical properties and photoinduced carriers separation of mono and binary photocatalysts were studied by microscopic characterization.The photocatalytic performance of photocatalysts was evaluated by removal of methyl orange and antibiotic.Finally,trapping experiments and intermediate product analyses were also carried out to understand the antibiotics removal mechanism and pathways.The main research contents and results are as follows:(1)Sulfur-doped g-C3N4 was successfully synthesized by screening sulfur precursors and optimizing preparation conditions.Microscopic characterization shows that the introduction of sulfur regulated the morphology of g-C3N4 leading to the formation of unique bar-like structure with ultrathin g-C3N4 layer nanosheet assemblies,which effectively inhibited the recombination of e--h+pairs.In addition,the increased specific surface area promoted the adsorption of pollutants by S-C3N4 and its enhanced light absorption ability further enhances the utilization of visible light.It was found that the photocatalytic activity of S-C3N4 was nearly twice as much as that of pure g-C3N4 in methyl orange removal,indicating that sulfur doping was an effective modification method.(2)Carbon nanoparticles were synthesized by alkali-assisted ultrasound method using glucose as the precursor.The S-C3N4/C-dot composite with uniform porous structure was successfully synthesized by calcinating the mixture of S-C3N4 precursor and C-dot without using template.It was found that the existence of carbon dot promoted the formation of porous structure by oxidizing itself into gaseous product as a pore-forming agent.At the same time,the content of carbon in the raw material plays a key role in controlling the crystal structure,morphology and photocatalytic performance of the final product.Compared with the pure S-C3N4,the S-C3N4/C-dot composite exhibited excellent photocatalytic performance when the carbon content was 5%,which is 1.8 times higher than that of the pure S-C3N4.(3)The nanoparticles of TiO2 were prepared by solvothermal method,and then the obtained TiO2 was mixed with S-C3N4 by a facile impregnation method to form S-C3N4/TiO2 nanocomposite.Compared with pure TiO2 and g-C3N4/TiO2,nanocomposites exhibited excellent photocatalytic activity in the removal of methyl orange,and their rate constants were 8.6 times and 2.6 times higher than that of TiO2 and g-C3N4/TiO2.Enhanced photocatalytic activity is attributed to the matching energy band position and close interface contact between S-C3N4 and TiO2,resulting in forming a unique heterojunction structure,which effectively inhibits the recombination of photogenerated electron-hole pairs.In addition,the main active species of S-C3N4/TiO2 in photocatalytic reaction were determined by capture experiments,and the mechanism of pollutants degradation was proposed.(4)The degradation pathway and mineralization degree of antibiotics were analyzed through the HPLC-MS and TOC test,and the effects of water quality factors such as inorganic ions,humus and pH on the degradation process were further studied in order to broaden the efficient application of photocatalysts.