Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond Adsorption and kinetic study of Reactive Red 2 dye onto graphene oxides and graphene quantum dots Miguel de la Luz-Asunción a,b , Eduardo E. Pérez-Ramírez a,c , Ana Laura Martínez-Hernández a , Perla E. García-Casillas b , J. Gabriel Luna-Bárcenas c , Carlos Velasco-Santos a, ⁎ a Tecnológico Nacional de México - Campus Querétaro, División de Estudios de Posgrado e Investigación, Av. Tecnológico s/n Esq. Gral. Mariano Escobedo, Col. Centro Histórico, C.P. 76000 Santiago de Querétaro, México b Instituto de Ingeniería y Tecnología, Universidad Autónoma de Ciudad Juárez, Av. del Charro No. 610 Norte, Col. Partido Romero, C.P. 32320 Ciudad Juárez, Chihuahua, México c Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional Unidad Querétaro, Libramiento Norponiente No. 2000, Fraccionamiento Real de Juriquilla, C.P. 76230 Santiago de Querétaro, México ARTICLE INFO Keywords: Graphene quantum dots Graphene oxide Reactive red 2 Adsorption Dimension Elovich's equation ABSTRACT The increase of the water pollution has led to the search of new methods and materials for its remediation. In recent years, different carbon nanomaterials have gained importance in the removal of dyes from water. In this research was investigated the adsorption of Reactive Red 2 (RR2) dye onto different graphene oxides and gra- phene oxide quantum dots at pH values of 2 and 5. The graphene oxide samples were obtained modifying the amount of KMnO 4 used and replacing the magnetic stirring by ultrasonic bath in the oxidation reaction. In order to know the surface and structural properties of carbon nanomaterials, these were analyzed by infrared, Raman and energy dispersive X-ray spectroscopies, transmission electron microscopy and field emission scanning electron microscopy, nitrogen-adsorption and through potentiometric titrations was obtained the point of zero charge. The decrease in the amount of KMnO 4 used in the Hummers´ reaction induced an increase in the oxygen content of graphene oxide. All carbon nanomaterials presented a high affinity by the RR2 dye at pH = 2, however graphene quantum dots showed the best performance. The removal of RR2 is dependent of the pH, surface area, oxygenated groups and the dimensionality of the carbon nanomaterials. The experimental data are analyzed using pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models to describe the adsorption kinetics from RR2 in aqueous solutions. Based on the highest coefficient of determination values and the lowest standard deviation values, the experimental kinetic data are better adjusted by the Elovich's equation. The adsorption behavior is studied according to the R E values of the dimensionless Elovich's equation. 1. Introduction The increase in the use of dyes in industries such as paper, textile, pigments, paint, plastics, among others, has positioned to the dyes as one of the most important pollutants of water in the worldwide [1–4]. Most of these dyes are considered toxic and possess a complex and stable aromatic structure, which makes these difficult to degrade [2,5–7]. The presence of dyes in lakes, lagoon, rivers, and other water bodies can cause foul odor, increase in the chemical oxidation demand [8], decrease in the photosynthetic process of aquatic plants [1,9] and da- mages to the aquatic organisms [10,11]. In humans, the exposure to dyes can provoke respiratory problems, skin irritation, kidney dys- function, mutagenicity and toxicity [7,12–16]. Azo dyes are an important class of dyes characterized by N]N chromophore, which are used mainly in the textile industry due to af- finity with cellulosic fibers for the creation of covalent bonds. However, some groups make that these dyes have low fixation and thus produce large quantities of colored effluents [17]. For the removal of dyes from water have been employed different methods such as ozonation, ionic exchange, oxidative process, photo- catalysis and adsorption [10,18–21]. Of these methods, the adsorption is considered one of the most promising and effective on the removal of dyes [1]. Besides, its low cost and easy operation; simple design and high efficiency are another advantages versus other methods [6,12]. In this method have been used different adsorbents for the removal of dyes such as activated carbon [6], carbon nanotubes [22], zeolites [18], si- lica gel [23], clays [24], among others. https://doi.org/10.1016/j.diamond.2020.108002 Received 29 April 2020; Received in revised form 23 June 2020; Accepted 10 July 2020 ⁎ Corresponding author. E-mail address: cylaura@gmail.com (C. Velasco-Santos). Diamond & Related Materials 109 (2020) 108002 Available online 23 July 2020 0925-9635/ © 2020 Elsevier B.V. All rights reserved. T