New insights in the treatment of waste water with graphene: dual-site adsorption by sodium dodecylbenzenesulfonate

For the adsorption of sodium dodecylbenzenesulfonate (SDBS) in aqueous solution on reduced graphene oxide (rGO), it is demonstrated that the dual-site mechanism is strongly favored over the conventional single-site one. The dual-site adsorption isotherm is derived, and regression analysis is successfully applied to experimental UV-vis data (1 g L-1 rGO; 298-318 K; 100-900 mg L-1 SDBS; pH: 4-11), considering reparametrization to minimize the correlation between the parameter estimates (dual site: Delta H degrees = -37.1 +/- 1.3 kJ mol(-1); Delta S degrees = 35.5 +/- 4.1 J mol(-1) K-1; q(infinity) = 546.9 +/- 8.6 mg(SDBS) g(rGO)(-1)). A temperature of 298 K is identified as the optimal operating temperature with contact times of ca. 30 h (700 mg L-1 SDBS). An improved regression analysis strategy, carefully selecting only low contact times (maximal 10 h), allowed assessment of the dual-site adsorption and desorption coefficient as (1.2 +/- 0.3) x 10(-4) L mg(SDBS)(-1) h(-1) and (2.8 +/- 0.7) x 10(-3) h(-1). Moreover, by the additional presence of sodium chloride (1.2 x 10(4) mg L-1), a much lower contact time of ca. 10 h can be selected to ensure an as good as complete SDBS removal, highlighting the potential of the SDBS/rGO system for wastewater treatment