Study On The Photothermal Storage Of Close-packed BisAzo–graphene Assembly

Photo-induced isomerization of organic molecules has been proposed as an excellent way to realize the utilization of solar energy.Azobenzene(Azo)is regarded as one of important candidates for photothermal fuels(PTFs)due to its unique ability to underGO trans–cis photo-isomerization reversibly accompanied by light absorption and heat emission.Azobenzene molecules have great research value in solar energy storage.However,the short half-life and small energy storage capacity limits its practical application in solar thermal storage.Based on the density functional theory(DFT)calculations,two bisazo derivatives(bisAzo)have been designed and synthesized successfully.The results show that bisAzo molecule can enhance the intramolecular interaction and steric hindrance due to its special structure,and improve the grafting density in a disguised form.Using reduced graphene oxide as a template,rGO-bisAzo assembly with high graft density,long half-life,and high energy density is expected to be obtained by the synergetic effect of bisAzo and the graphene template.The modified Hummers method is used to prepare the reduced graphene oxide with both excellent solvent dispersibility and conjugated structure,which is beneficial to the subsequent reaction.Azobenzene units were prepared by diazonium coupling method,and two azo units were bonded by amide bond.The bisAzo molecules were covalently grafted on the surface of reduced graphene oxide layers by diazonium radical reaction.The results of thermogravimetric analysis(TGA)and X-ray photoelectron spectroscopy(XPS)showed that bisAzo molecules were covalently bonded with approximately 45 carbon atoms on rGO.The high graft density ensures sufficient steric hindrance,and hydrogen bonds can be formed between the molecules which will further increase the half-life and energy density.The UV-vis absorption spectra exhibited that the rGO-bisAzo thermal storage assembly had a half-life of 37 days and a cycle stability of more than 50 times.rGO-bisAzo hybrid materials showed that the energy density and power density had reached up to 131 Wh/kg and 2517 W/kg respectively according to the results of differential scanning calorimetry(DSC);the infrared thermal imager showed that the temperature difference between the UV irradiated part and unirradiated part of the PTF film was as high as 15 ° C.