a percentage of nitrogen of approximately 8 by weight and after pyrolysis the graphitised carbon samples contain nitrogen as evidenced by combustion chemical analysis or x ray photoelectronic spectroscopy xps fig5 in contrast in the case of alginate the resulting graphene sample only has a carbon content of up to 95 the impregnation of the biopolymer with an adequate compound containing another heteroatom can occur by means of pretreatment a particular example of the present invention that leads to boron doped graphene consists of the impregnation of sodium alginate with an aqueous solution of boric acid this impregnation is carried out by agitating the sodium alginate particles in an aqueous solution of 1 m boric acid ph 5 for 1 hour at ambient temperature recovering the resulting solid after impregnation by means of filtration alternatively the impregnation can be performed by adding drops of a concentrated aqueous solution of boric acid on the crystalline biopolymer particles the pyrolysis of the material impregnated with boron or other heteroatom is carried out in the same furnace under identical conditions to those described previously finally resulting in graphitic carbonaceous material containing the heteroatom the concentration of heteroatom and its presence can be revealed as in the previous cases using an analytical technique or spectroscopy such as combustion analysis or xps spectroscopy other representative examples of the present invention for preparing graphene suspensions in different solvents are shown below samples of commercial alginic acid are placed in a ceramic crucible and introduced in a furnace without pretreatment the furnace containing the acid.