溶液酸碱性对氧化石墨烯自组装成膜结构与性能的影响

The Influence of Solution pH on the Self-Assembly Structure and Properties of Oxidized Graphene Films

相比石墨烯,氧化石墨烯(GO)在稳定性、可溶性、功能化修饰和作为载体的应用等方面颇有优势,使得其在催化、分离过滤、传感、储能等领域中更具实际可行性和应用价值。在GO的宏观组装过程中,溶液酸碱性强烈地影响GO自组装过程,但其中的影响规律尚不明晰。因此,通过调控高浓GO溶液的pH值制备GO厚膜,研究了GO与分散介质之间的相互作用力变化对GO组装及宏观组装材料性能的影响。研究结果显示,厚GO膜的各项性能随着溶液pH值的变化而有显著差异。当GO溶液的pH值为弱碱性(pH值为9)时成膜,GO膜的拉伸强度达到229.29 MPa,是pH值为4时GO膜强度的7倍以上,同时,当GO溶液的pH值为9时成膜,GO膜的电导率为27800 S/m,是pH值为4的1.7倍以上。一系列分析结果表明,当溶液pH值为弱碱性时,GO表面的部分羟基和羧基被还原,使得片层上同时存在氧化区域和sp^(2)碳区域,氢键作用力和静电排斥作用力诱导片层的面面排列,而π-π作用力驱动片层的紧密堆积,当sp^(2)碳区域的比例接近氧化区域时,其组装驱动力从氢键相互作用力主导转变为由氢键和π-π相互作用共同诱导。最终发现,当两种作用力的比例相差较大时,会导致片层堆积间距较大(氢键作用力更大)或堆积排列有序性降低(π-π相互作用更大)。因此,在以GO为主要成分制备宏观材料时,溶液的酸碱环境将极大影响组装结构的有序性和应用性能,本研究对石墨烯基宏观材料的结构设计和性能提升具有一定的启发意义,石墨烯薄膜具有优异的导热性和导电性、柔韧性和坚固性,可以作为电子产品的候选者。

Compared to graphene,graphene oxide(GO)has advantages in stability,solubility,functional modification,and application as a carrier,making it more practical and valuable in catalysis,separation and filtration,sensing,energy storage,and other fields.In the macroscopic assembly process of GO,the acidity and alkalinity of the solution strongly affect the self-assembly process of GO,but the rules of its influence are not yet clear.Therefore,by adjusting the pH of high concentration GO solution,GO thick films were prepared,and the effects of changes in the interaction force between GO and dispersion medium on GO assembly and macroscopic assembly material properties were studied.The research results show that the various properties of thick GO membranes vary significantly with the change of solution pH value.When the pH of the GO solution is weakly alkaline(pH=9),the film forms,and the tensile strength of the GO film reaches 229.29 MPa,which is more than 7 times the strength of the GO film at pH=4.At the same time,when the pH of the GO solution is 9,the film forms,and the conductivity of the GO film is 27800 S/m,which is more than 1.7 times the pH=4.A series of analysis results indicate that when the solution pH is weakly alkaline,some hydroxyl and carboxyl groups on the surface of GO are reduced,resulting in the presence of both oxidation and sp^(2) carbon regions on the layer.Hydrogen bonding and electrostatic repulsion forces induce the surface arrangement of the layer,whileπ-πforces drive the tight stacking of the layer.When the proportion of sp^(2) carbon regions approaches the oxidation region,the assembly driving force shifts from hydrogen bonding interaction to hydrogen bonding andπ-πinteractions.It was ultimately found that when the ratio of the two forces differs significantly,it can lead to a larger interlayer stacking distance(greater hydrogen bonding force)or a decrease in stacking arrangement order(greaterπ-πinteraction).Therefore,when preparing macroscopic materials with GO as the main component,the acid-base environment of the solution will greatly affect the orderliness and application performance of the assembled structure.This study has certain inspirational significance for the structural design and performance improvement of graphene based macroscopic materials.Graphene films have excellent thermal conductivity and conductivity,flexibility and robustness,and can be used as candidates for electronic products.