Recently, green-prepared oxidized graphenes have attracted huge interest in water purification and wastewater treatment. Herein, reduced graphene oxide (rGO) was prepared by a scalable and eco-friendly method, and its potential use for the removal of methylene blue (MB) from water systems, was explored. The present work includes the green protocol to produce rGO and respective spectroscopical and morphological characterizations, as well as several kinetics, isotherms, and thermodynamic analyses to successfully demonstrate the adsorption of MB. The pseudo-second-order model was appropriated to describe the adsorption kinetics of MB onto rGO, suggesting an equilibrium time of 30 min. Otherwise, the Langmuir model was more suitable to describe the adsorption isotherms, indicating a maximum adsorption capacity of 121.95 mg g⁻¹ at 298 K. In addition, kinetics and thermodynamic analyses demonstrated that the adsorption of MB onto rGO can be treated as a mixed physisorption–chemisorption process described by H-bonding, electrostatic, and π $-$ π interactions. These results show the potential of green-prepared rGO to remove cationic dyes from wastewater systems.

This work explores the transformative role of graphene in enhancing the performance of surface plasmon resonance (SPR)-based biosensors. The motivation for this review stems from the growing interest in the unique properties of graphene, such as high surface area, excellent electrical conductivity, and versatile functionalization capabilities, which offer significant potential to improve the sensitivity, specificity, and stability of SPR biosensors. This review systematically analyzes studies published between 2010 and 2023, covering key metrics of biosensor performance. The findings reveal that the integration of graphene consistently enhances sensitivity. Specificity, although less frequently reported numerically, showed promising results, with high specificity achieved at sub-nanomolar concentrations. Stability enhancements are also significant, attributed to the protective properties of graphene and improved biomolecule adsorption. Future research should focus on mechanistic insights, optimization of integration techniques, practical application testing, scalable fabrication methods, and comprehensive comparative studies. Our findings provide a foundation for future research, aiming to further optimize and harness the unique physical properties of graphene to meet the demands of sensitive, specific, stable, and rapid biosensing in various practical applications.

Graphene oxide (GO) exhibits different properties from those found in free-standing graphene, which mainly depend on the type of defects induced by the preparation method and post-processing. Although defects in graphene oxide are widely studied, we report the effect of drying time in GO and how this modifies the presence or absence of edge-, basal-, and sp³-type defects. The effect of drying time is evaluated by Raman spectroscopy, UV-visible spectroscopy, and transmission electron microscopy (TEM). The traditional D, G, and 2D peaks are observed together with other less intense peaks called the D’, D*, D**, D+G, and G+D. Remarkably, the D* peak is activated/deactivated as a direct consequence of drying time. Furthermore, the broad region of the 2D peak is discussed as a function of its deconvoluted 2D_1A, 2D_2A, and D+G bands. The main peak in UV-visible absorption spectra undergoes a redshift as drying time increases. Finally, TEM measurements demonstrate the stacking of exfoliated GO sheets as the intercalated (water) molecules are removed.

The use of graphene oxide (GO) in combination with mesoporous materials has gained interest in the development of adsorbents. In this study, GO was impregnated into zeolite at three concentrations (ZGO2.5, ZGO5, and ZGO10) through a simple thermal process to enhance the adsorption of methylene blue (MB). Characterization of the resulting materials was performed using spectroscopic techniques such as UV-Vis and FT-IR spectroscopy, SEM, and EDS, confirming the presence of GO on zeolite. Batch experiments were conducted to evaluate their performance, analyzing contact time, pH effect, and adsorption kinetics. Pseudo-first-order, pseudo-second-order, and Elovich kinetic models were applied, and the adsorption mechanism was studied using Langmuir, Freundlich, Temkin II, and Dubinin–Radushkevich (D-R) isotherms at different temperatures. Optimal adsorption was achieved at 273 K, 100 mg L⁻¹ of MB, adsorbent mass of 100 mg, 250 rpm, and pH 5–9, with 90% removal efficiency after 70 min. The pseudo-second-order, Freundlich, and D-R models best described the process (R² > 0.98), suggesting a mixed physisorption–chemisorption mechanism. The maximum adsorption capacity from the D-R isotherm reached 119 mg g⁻¹ at 333 K. Thermodynamic studies showed that adsorption was a spontaneous and endothermic process. These findings highlight the potential of GO-impregnated zeolite as an effective adsorbent for MB.

Graphene oxide (GO) and its reduced form, reduced graphene oxide (rGO), are among the most predominant graphene derivatives because their unique properties make them efficient adsorbent nanomaterials for water treatment. Although extra-functionalized GO and rGO are customarily employed for the removal of pollutants from aqueous solutions, the adsorption of heavy metals on non-extra-functionalized oxidized graphenes has not been thoroughly studied. Herein, the adsorption of mercury(II) (Hg(II)) on eco-friendly-prepared oxidized graphenes is reported. The work covers the preparation of GO and rGO as well as their characterization. In a further stage, the description of the adsorption mechanism is developed in terms of the kinetics, the associated isotherms, and the thermodynamics of the process. The interaction between Hg(II) and different positions of the oxidized graphene surface is explored by DFT calculations. The study outcomes particularly demonstrate that pristine rGO has better adsorbent properties compared to pristine GO and even other extra-functionalized ones.