| Graphitic carbon nitride(g-C3N4)is a polymeric semiconductor photocatalyst composed of carbon-nitrogen conjugated rings and a lamellar structure.Compared with conventional metal-semiconductor photocatalysts,g-C3N4 has many superior characteristics,such as visible light responsiveness,tunable electronic structure,simple preparation and environmental friendliness.Such characteristics make g-C3N4 promise in many areas,such as energy,environment,materials,and,especially,photoinitiated polymerization and photocatalytic degradation of pollutants.Howerver,g-C3N4 also possesses some limits in the process of application currently.Firstly,the large size and serious inter-sheet aggregation of macro-prepared g-C3N4 make it difficult to be dispersed in water and most organic solvents.Secondly,due to the low density of g-C3N4 powder,its recovery and recycling performance is so poor that it needs to be loaded on appropriate media.However,its poor dispersibility is a major limitation to the loading of g-C3N4 and the construction of photocatalytically active materials based on g-C3N4.In addition,the low specific surface area,limited active sites and high composite rate of photogenerated carriers all make the photocatalytic performance of g-C 3N4 have a significant room for improvement.Therefore,based on the advantages and shortcomings of g-C3N4,following tasks were completed and related mechanisms were also explored in this thesis:the dispersibility of g-C3N4 was enhanced by selecting natural green materials as dispersants and by reducing its size;the photocatalytic activity of g-C3N4 was improved by conducting active substance-assisted ultrasonic exfoliation;and two types of eco-fiiendly photocatalytic gel materials with g-C3N4 loading were constructed in two environmentally friendly and low-energy way.bottom-up photoinitiated polymerization without the addition of cross-linking agent and physical crosslinking of naturally sourced polymers.This work not only provides materials for the efficient treatment of organic pollution,heavy metal pollution and their compound pollution in the water environment,but also provides theoretical guidance for the construction of photoactive gel materials based on g-C3N4.The research content of this thesis mainly includes the following two parts:The first part is the construction of g-C3N4/CNC/PAM composite photoactive aerogel.Natural negatively charged rod-like nanoparticle cellulose nanocrystal(CNC)was firstly selected as a disperser to disperse g-C3N4 stably and evenly.Subsequently,the monomer acrylamide(AM)was mixed with g-C3N4/CNC suspension and photocatalytically initiated by g-C3N4 under illumination to obtain polyacrylamide(PAM),which crosslinked with aldehyde-modified CNC-CHO by Schiff base reaction to obtain a composite aerogel with g-C3N4 uniform and stable loading.Research showed that the g-C3N4/CNC/PAM ternary composite aerogel has a porous structure,strong mechanical stability and excellent optoelectronic properties,and has excellent photocatalytic degradation ability for rhodamine B,methylene blue and Congo red under visible light,with treatment efficiencies up to 95%,80%and 95%,respectively.The aerogel also has strong adsorption and photoreduction ability for Cr(Ⅵ),a heavy metal,whch can reach a treatment efficiency of above 95%within 80 min.This section used natural nanoparticle CNC as dispersant,which has the advantages of low cost and eco-friendliness.CNC can also participated in the formation of aerogel skeleton without additional crosslinking agents.g-C3N4 plays the dual role of photoinitiation and photocatalytic degradation,making full use of solar energy in both preparation and application of aerogel.The g-C3N4/CNC/PAM composite aerogel has great potential in treating organic,heavy metals and their compound pollution in water.The second part of the study focused on the enhancement of the photocatalytic performance of g-C3N4.First,o-phenylenediamine(oPD)was chosen as the active substance to assist the ultrasonic exfoliation of g-C3N4 to obtain g-C3N4 nanosheets(g-C3N4 NS),which enhanced its photocatalytic performance through its enlarged specific surface area and increased active site,and its dispersion ability was also promoted due to the reduction of g-C3N4 NS size.Meanwhile,g-C3N4 was combined with oPD and its self-polymerization product poly(o-phenylene diamine)(PoPD),a conducting polymer,during the sonication process,thus its light absorption ability was enhanced and its photogenerated carrier recombination was inhibited to further enhance its photocatalytic performance.The obtained g-C3N4 NS was loaded into Ca2+ crosslinked sodium alginate(SA)hydrogel to obtained g-C3N4/SA composite hydrogel to futher the improvement of the treatment efficiency via combining the adsorption performance of the hydrogel and the photocatalytic performance of g-C3N4.The results showed that the treatment efficiency of g-C3N4 NS/SA hydrogel on organic contaminant Congo red(CR)and heavy metal Cr(Ⅵ)can both reach above 90%.This part of the work prepared a novel g-C3N4 NS with excellent optoelectronic performance and environment-friendliness by a simple and low-consumption ultrasonic method,and the hydrogel was constructed with natural polymers SA for its loading.The prepared g-C3N4 NS/SA hydrogel has excellent photocatalytic capability and eco-friendly characteristics,which ensures its efficiency in treating pollutants in water without secondary pollution.In summmary,in this work,two types of green composite photoactive gel materials,g-C3N4/CNC/PAM ternary composite aerogel and g-C3N4 NS/SA hydrogel were constructed based on g-C3N4 to solve the problems of g-C3N4 dispersion,loading and to enhance its photocatalytic properties using green materials such as CNC and SA and by low-consumption and concise methods such as ultrasound and photoinitiation.The obtained two gels have high efficiency for the treatment of organic pollutants,heavy metals and their composite pollution in the water environment,and have excellent recovery and recycling capabilities,which have broaden application prospects in the field of water pollution treatment and provided theoritic foundation of the preparation of new photocatalytic gel and its application in water pollution treatment. |
PDF Full Text Request