Amino-Acid Surfactant Induced Structure Control Of G-C₃N₄ And Its Application In Photocatalytic Degradation Of RhB

Nowadays,environmental pollution is becoming more and more serious with the rapid development of economy and increasingly frequent human activities.People are facing and urgently need to solve the energy crisis and greenhouse effect.As a kind of clean energy,light energy has been paid to more and more attention.The conversion from light energy to chemical energy can be effectively accomplished by photocatalytic reaction.As a new type of metal-free photocatalyst,g-C3N4 has attracted wide interest of scholars.However,the catalyst itself has many defects,such as low specific surface area,relatively narrow visible light absorption edge(460 nm),weak photocatalytic oxidation ability and rapid recombination of photogenerated electrons and holes,which greatly hinder the performance of g-C3N4 photocatalysis.In order to overcome the obstacles to further improve the photocatalytic performance of g-C3N4,the structure and morphology of g-C3N4 must be thoroughly modified.At present,the technology of preparing g-C3N4 by hard template method is relatively mature.The principle of hard template method is not only uncomplicated,but the structures of products are more regular and easy to control.However,HF or NH4HF2 used in the process of template removal is corrosive and harmful to the environment and human body.Besides,the overall steps are cumbersome and the preparation cycle is long.These become the biggest bottleneck restricting the development of hard template method.Compared with the hard template method,surfactant-induced methods are easier to operate,and the raw materials are economical and easy to obtain.However,the preparation of g-C3N4 by the surfactant-induced method is only based on the use of non-ionic surfactants at the moment.Compared with traditional surfactants,amino acid surfactants have excellent surface activity,fast biodegradability,low toxicity,excellent antimicrobial and antifungal activities,so they are of great significance in the research field of new surfactants.On account of the above backgrounds,histidine-based surfactants were designed and synthesized.The structures and properties of g-C3N4 formed by L-C12His-induced can be studied to explore the role of amino acid surfactants in the induction process.This paper mainly includes the following aspects:1.Amino acid surfactants with diferent chain lengths were synthesized definitely via the characteriation of FT-IR,1H NMR and MS.The surface activity of L-CnHis(n=8,10,12)in NaOH solution with pH=13 was researched by slice method.The aggregation behavior of amino acid surfactants was characterized by circular dichroism,dynamic light scattering and negative-dyed transmission electron microscopy.CD results showed that with the increase of L-C12His concentration,the aggregates of amino acid surfactants underwent an ordered-disordered-ordered aggregation process.DLS results showed that with the increase of concentration,aggregates underwent a process from one peak type to two peak types and then to one peak type,which was consistent with the ordered-disordered-ordered aggregation process reflected by CD spectra.NS-TEM results also more intuitively verified this change process.2.Melamine was added to amino acid surfactant(L-C12His)solution to induce the formation of graphite carbon nitride.The influence of concentration of amino acid surfactants(L-C12His)and stirring time were investigated by XRD,SEM,FTIR,PL,DRS,EA and TRES.The results showed that the photocatalytic activity of graphite carbon nitride increased first and then decreased with the increase of surfactant concentrations and stirring time.When the stirring time was 24 hours and the concentration was near the CMC,the photocatalytic degradation of RhB by M-C3N4 was the best.3.Amino acid surfactants(L-C12His)were used to induce cyanuric acid-melamine(CM)complex to prepare CM-C3N4.The structures and properties of CM-C3N4 induced by amino acid surfactants with different concentrations were investigated by various technical means.The effects of chain length and head group on photocatalytic properties were compared with amino acid surfactants with different chain lengths and different types of surfactants.The results revealed that the photocatalytic degradation of RhB by CM-C3N4 was the best at the concentration close to the CMC of L-C12His.The longer the chain length,the better the photocatalytic degradation properties.