Preparation And Corrosion Inhibition Of Graphene Oxide Quantum Dots

Carbon materials have been widely studied in the field of metal corrosion protection as paint dopant,there are few reports of using graphene quantum dots as liquid phase corrosion inhibitors,the inhibition efficiency of graphene quantum dots in previous studies was only71%.In this paper,the synthesis process of graphene oxide quantum dots was optimized by electrochemical method.It was found that when the graphite rod with particle size of 43?m and 1.7 g/cm³was used as the working electrode,the prepared graphene oxide quantum dots have the best inhibition efficiency of 94.6%,which is better than reported.The structure,composition,morphology and optical properties of GOQDs were studied by FTIR,XRD,TGA,HP-LC-MS,XPS,TEM,AFM,UV-Vis and PL;the corrosion inhibition behavior and mechanism of Q235 steel in 1mol/L hydrochloric acid solution containing different concentrations of GOQDs at different temperatures were studied by weight loss method,electrochemical method,SEM,AFM,EDS,XPS,Zero charge potential,corrosion thermodynamic and kinetic calculation.The results showed that the prepared GOQDs contains much oxygen-containing functional groups such as carboxyl,hydroxyl and aldehyde groups on surface and edge distributed uniformly.The structure of prepared GOQDs is similar to graphite.The lattice spacing was 0.209nm,corresponding to the crystal surface of graphite?100?.The particle size distribution was 2.5nm⁵nm,and the thickness was about 2nm⁴nm,which was equivalent to the thickness of 4⁸ single-layer graphene.HP-LC-MS indicated that the average molecular weight of prepared GOQDs was about 2873.The position of emission peak of GOQDs will redshift with the increase of excitation wavelength.The optimal excitation and emission wavelength are separately 365nm and 438nm.The fluorescence color of GOQDs is blue-green.The UV-Vis characteristic absorption peak occurs at255nm-269nm related to C=O n-?*transition and C=C?-?*transition.GOQDs is a mixed corrosion inhibitor,the adsorption on the surface of carbon steel is spontaneous which is in accordance with the Langmuir isothermal adsorption law.The adsorption of GOQDs is accompanied by entropy increase and heat release.The corrosion inhibition mechanism of GOQDs is to form an adsorption film on the surface of Q235 steel,which hinders the effective contact between corrosion factors and the surface of carbon steel and thus reduces the corrosion rate.GOQDs have no effect on corrosion reaction process.The adsorption of GOQDs includes both physical adsorption and chemical adsorption,and it's adsorption mechanisms mainly include four aspects:electrostatic attraction between deprotonated GOQDs and Fe²⁺on the surface of anode zone;electrostatic attraction between protonated GOQDs and negatively charged cathode surface;interactions between the heteroatoms?O?with free electrons in GOQDs and the unoccupied d-orbital of the iron atoms;the electron from the d-orbital of iron atoms may be transferred to vacant?*?antibonding?orbital of GOQDs.