In recent times there has been growing environmental attention and concern about the use of synthetic dyes in printing processes, the textile industry, cosmetics, plastics, as well as in the food industry, which has caused huge pollution in wastewater, so it is necessary to solve the environmental problems associated with the use of these compounds [1]. Cationic dyes stand out, due to their toxicity, high water solubility, and low biodegradability, which present one of the main problems. Methylene blue (MB) is classified as one of these dyes [2]. Inappropriate use of MB in humans causes serious diseases such as icterus, cyanosis, quadriplegia, shock, tissue necrosis, central nervous system toxicity, gastrointestinal infections, and brain parenchyma decolorization [3,4,5].

  Adsorption is one of the methods of choice because of its removal effectiveness, low cost, recyclability of the adsorbent, simplicity of design, and low waste generation [2,6]. A graphene oxide hydrogel (GOH) is a three-dimensional macro-structure of hydrophilic nature, formed from the self-assembly of graphene oxide (GO) sheets, which can be synthesized by chemical reduction or hydrothermal reduction, the latter being of greater interest because it generates fewer impurities in the synthesis process [7].

  There are fewer studies on the kinetics and adsorption capacity as a function of temperature of MB utilizing GOH without additives nor other filling-materials. The temperature studies significantly affect adsorption [8], therefore, studies on its effects results relevant. In this research, the adsorption kinetics of hydrothermally self-assembled GOH from a GO solution prepared by the modified Hummers method is studied isothermally in MB solutions prepared with an initial concentration of 15 mg/L, under at temperatures of 17, 20, 25, 30, 35, 40 and 45°C. Through ultraviolet-visible spectroscopy (UV-VIS), the adsorbed concentrations per unit of time were obtained, studied, and modeled using the adsorption kinetics of Langmuir [9] and the algebraic expressions of the pseudo-first order and pseudo-second order models of Ho and McKay [10] and Simoni [11] derived from it. The enthalpy, entropy, and Gibbs free energy of the adsorption process at different temperatures are determined from the fit-models and the nature of the adsorption process. The identification of the main oxygenated functional groups involved in this process are also studied. Both the GO solution and GOH were chemically and morphologically characterized using XPS, EDS, SEM, and Raman techniques.

References

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[2] B. S. Rathi, et al., Science of The Total Environment, 2021, 797, 149134.

[3] M. Arami, et al., Journal of Hazardous Materials, 2006, 135 (1-3),171–179.

[4] M. Sultan, et al., Journal of hazardous materials, 2018, 344, 210–219.

[5] A. Chen, et al., American Journal of Clinical Pathology, 2018, 149 (suppl 1), S4–S4.

[6] M. Rafatullah, et al., Journal of hazardous materials, 2010, 177 (1-3), 70–80.

[7] K. C. Wasalathilake, et al., Carbon, 2018, 137, 282–290.

[8] M. E. Argun, et al., Bioresource technology, 2008, 99 (18), 8691–8698.

[9] E. D. Revellame, et al., Cleaner Engineering and Technology, 2020, 1, 100032.

[10] Y. Ho, et al., Process Biochemistry,1999, 34 (5), 451–465.

[11] J.-P. Simonin, Chemical Engineering Journal, 2016, 300, 254–263.