An Experimental Study On The Adsorption Of Thermally Reduced Graphene Oxide And The Corresponding Selectivity And Electrical Properties

Lithium,known as"the metal that advances the world",plays an increasingly important role in the development of scientific and industrial processes,and widely used in storage equipment,lithium-ion batteries（LIBs）,alloy technology,glass,and ceramics fields.Almost 60%of the world’s lithium resources are in salt lake brines,so salt lakes are considered to be the main source of lithium;with the rapid upgrading of electronic equipment,waste electronic products are increasing day by day,so waste lithium-ion batteries are considered to be a secondary source of lithium.At present,carbon neutrality and emission peak are very polular and important.To solve these problems,both energy storage and electric vehicles cannot be separated from lithium-ion batteries.Therefore,the extraction and recovery of lithium is of significance in the national strategy to achieve the double carbon goal.Various traditional separation methods are used to extract lithium from salt lakes and to recover lithium from waste lithium-ion battery leaching solution,including precipitation method,solvent extraction method,precipitation crystallization method and ion exchange method.However,effectively separating lithium from brine or the leachate of spent lithium-ion batteries is still a great challenge.Many salt-lake brines have a high Mg²⁺/Li⁺mass ratio（from 35:1to 1837:1）,and this high mass ratio and the corresponding low concentrations of Li⁺significantly limit the extraction of lithium from brines.Further,conventional methods for the recovery of lithium from leachate are usually followed by solvent extraction or precipitation,which leads to serious loss of lithium.Thus,these conventional technologies for lithium extraction and recovery are either expensive to operate,time consuming,low efficiency,or high cost and will struggle to meet future demand.Therefore,there is an urgent need to develop a more suitable method for extracting lithium to solve the limitations of the current process for extracting and recovering lithium.In this paper,we show the high-efficiency selective extraction of Li⁺by thermally reduced graphene oxide（r GO）membranes.In the mixed solution(Li⁺,Mg²⁺,Co²⁺,Mn²⁺,Ni²⁺,or Fe²⁺),the adsorption strength of Li⁺reaches up to 5 times the adsorption strength of Mg²⁺,Co²⁺,Mn²⁺,Ni²⁺,and Fe²⁺.Interestingly,the mass ratio of a mixed Mg²⁺/Li⁺solution at a very high value of 500:1 can be effectively reduced to 0.7:1within only six experimental treatment cycles,demonstrating the excellent applicability of the r GO membranes in the Mg²⁺/Li⁺separation.Conventional wisdom is that Li⁺has a low valence state so that it has a much weaker adsorption energy with the graphene than multivalent ions have,thus we do not expect that r GO membranes can preferentially selective adsorption Li⁺.In this paper,a theoretical analysis indicates that this unexpected selectivity is attributed to the competition between cation–πinteraction and steric exclusion when hydrated cations enter the confined space of the r GO membranes.Thus,the findings provide a new way to extract and recover lithium,which has the potential to contribute to sustainable lithium supplies for batteries and supercapacitors and the development of lithium-based technologies in various fields,such as the automotive,aerospace,and metallurgical industries.In addition,based on the thermal reduction method,a series of r GO membranes were conveniently prepared by thermally reduced.These prepared r GO membranes have better Ca²⁺adsorption ability,and the highest Ca²⁺adsorption capacity of the membrane is about one order of magnitude higher than the adsorption capacity of activated sludge,magnetic Fe₃O₄,functionalized silica,zeolite molecular sieve,and other reported previously.Moreover,r GO membranes show excellent stability and can be easily desorbed by water,so that the GOMs can be reused.Theoretical analysis suggests that this remarkable adsorption is attributable to the strong interactions between Ca²⁺and r GO sheets,including the ion-πinteractions between Ca²⁺and aromatic graphitic rings as well as the electrostatic interaction between Ca²⁺and oxygen-containing groups.These have potential application in the field of water purification,ion separation,capacitor and battery.