Graphene oxide and graphene oxide functionalized with silver nanoparticles as adsorbents of phosphates in waters. A comparative study.

Phosphate removal is an important factor that must be taken into account in eutrophized waters. For this reason, many studies on different ways of removing phosphates from water have been published nowadays. In this work, a comparative study between the use of graphene oxide (GO) and graphene oxide functionalized with silver nanoparticles (GO@AgNPs) as adsorbents to remove phosphates from water samples has been carried out. Experimental conditions, including the pH, adsorbent dose, contact time and temperature, have been analyzed to achieve the highest adsorption efficiency. Although both adsorbents can be considered suitable for removing phosphates from aqueous solutions, GO@AgNPs provided a maximum removal efficiency of 100%, reaching the equilibrium conditions instantaneously under straightforward experimental conditions. Moreover, a much lower adsorbent dose was necessary than with graphene oxide. When GO was used, the maximum removal efficiency was 75%, 9 min were necessary to reach the equilibrium conditions and 20 mg of adsorbent were needed. Both adsorbents can be regenerated in an acid medium, giving recovery percentages of 98% and 80% for GO and GO@AgNPs respectively, which allows them to be recycled and used again.