Mechanistic aspects for the removal of Congo red dye from aqueous media through adsorption over N-doped graphene oxide nanoadsorbents prepared from graphite flakes and powders

Publication date: Available online 4 August 2018Source: Physics and Chemistry of the Earth, Parts A/B/CAuthor(s): Kholiswa Yokwana, Alex T. Kuvarega, Sabelo D. Mhlanga, Edward N. NxumaloAbstractThis work reports the mechanistic models responsible for the adsorptive removal of Congo red (CR) dyes by nitrogen-doped graphene oxide nanosheets (NGO) prepared via a one-pot modified Hummer's method using either graphite powder (to form NGOp) or graphite flakes (to form NGOf) as starting materials. The microstructural properties, surface chemistry and thermal stability of the produced NGO adsorbents were ascertained using a range of characterization techniques. The effects of adsorbent dosage, CR dye initial concentration, contact time and solution pH on removal of CR dye were studied. The NGO adsorption process was highly dependent on initial dye concentration, contact time, adsorbent dosage, pH, NGO surface area and nanosheet size. The NGOp nanoadsorbents exhibited excellent selectivity towards the removal of CR dye molecules than NGOf. NGOp adsorbents achieved maximum removal of 98 - 99% at a pH of 2 compared to NGOf that achieved 96 - 98%. The adsorption kinetics and isotherms for CR dye on the NGO adsorbents were well fitted to the pseudo second-order kinetic model. The Langmuir isotherm model which indicated that the adsorption behavior occurred via chemisorption and in a homogeneous monolayer on the surface of the NGO. Our findings suggest that the adsorption mechanism involve...
Source: Physics and Chemistry of the Earth, Parts ABC - Category: Science Source Type: research

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