Water has always been one of the most important and precious natural resources. However, due to the rapid growth of the population and industrial progress, the available resources of freshwater are decreasing in an alarming manner. The contamination of water by hazardous pollutants has prompted researchers to develop new, efficient and low-cost methods and materials for water treatment. Adsorption is one of the most effective ways to remove many pollutants, even at very low concentrations. Recently, new adsorbent nanomaterials, whose efficiency can be improved when exposed to external influences such as pH, agitation, and temperature have been used in research on wastewater treatment. Graphene oxide based nanomaterials and their composites are considered as promising adsorbents for the removal of heavy metals, dyes, and other hazardous pollutants from aqueous environments due to its distinctive physicochemical properties, such as chemical stability, huge surface area, high adsorption capacity and recyclability. The present review, with 198 articles included, summarizes the methods of synthesis and characterization of graphene oxide-based adsorbents, as well as their adsorption characteristics, mechanisms and kinetics of pollutants’ removal processes, the experimental parameters to be optimized, and the adsorption–desorption recycling processes. Several representative examples are reported in details. Also, the main challenges, treatment system economic, and future perspectives in the field are also highlighted. 

Removal of heavy metals and dyes from wastewater using graphene oxide-based nanomaterials: A critical review

The use of carbon-based nanomaterials, including carbon nanotubes, carbon dots, graphene/graphene oxide, fullerene, and their derivatives, in the removal of emerging pollutants from wastewater has become a promising method in water treatment. These nanomaterials exhibit exceptional adsorption capabilities and selectivity due to their extensive surface area, customizable surface chemistry, and unique structural features, which involve factors like π-π interactions, electrostatic interactions, and specific surface functional groups. A notable experiment demonstrated the effectiveness of carbon nanotubes as adsorbents for removing Ismate violet 2R dye from contaminated water. The results showed a remarkable maximum removal efficiency of 91.71 % at a concentration of 10 mg/L within a brief 120-min period. This article conducts a comprehensive evaluation of the adsorptive removal of emerging pollutants from wastewater using carbon-based nanomaterials, with a focus on developments between 2015 and 2023. An in-depth bibliometric analysis of 1285 research publications retrieved from the Web of Science (WOS) and Scopus databases reveals a substantial increase in the number of publications, rising from 50 in 2015 to 158 in 2023. This signifies a burgeoning emphasis on both practical application and technological advancement in this domain. Furthermore, this review explores the intricacies of adsorption mechanisms, factors influencing the adsorption performance of carbon-based nanomaterials, and the associated challenges and limitations when applied in wastewater treatment. By thoroughly investigating these constraints and potential advantages, this article provides valuable insights for the development of future carbon-based nanomaterials, aiming to enhance their efficiency and expand their applications in the field of wastewater treatment. 

Adsorptive removal of heavy metals, dyes, and pharmaceuticals: Carbon-based nanomaterials in focus

Graphene oxide (GO) and reduced graphene oxide (rGO) were synthesized from graphite powder to compare the adsorption capacity of GO and rGO towards a cationic dye-methylene blue (MB). These synthesized nanomaterials were analyzed by Fourier Transform-Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and Field Emission Scanning Electron Microscope (FESEM). FTIR results indicated the presence of larger number of oxygenated functional groups in the GO as compared to rGO surface suggests the conversion of GO to rGO. Scattered layers of graphite sheets with chunks of pores present in the GO surface were marked by FESEM. The effect of contact time and adsorbent dosage have been studied to make an efficient comparison between the adsorption capacity of GO and rGO for removing MB. GO showed an excellent adsorption capacity by removing 98.67% of MB dye within 4 h, while rGO could remove 93.47% of MB within 7 h from the aqueous solution. The maximum adsorption capacities of GO and rGO were 3333 mg/g and 2000 mg/g, respectively. The findings reveal the contribution of electrostatic interaction, H-bonds, and π–π interactions for the sorption of MB onto GO and rGO. The abundance of oxygen-containing functional groups substantially raised the sorption capacity of GO compared to rGO by at least 60%. The higher specific surface area of GO (9.10 m2/g) compared to rGO (0.60 m2/g) was another contributing factor to higher MB sorption. The sorption process was well described by a pseudo-second-order kinetics model, suggesting that the adsorption of MB by GO and rGO was mostly controlled by chemisorption. The Langmuir isotherm model fitted best (R2 > 0.9) for both adsorbents indicating monolayer sorption on a uniform surface with a finite number of adsorption sites. These results suggest that GO can be preferred over rGO for removing cationic pollutants from wastewater. 

A comparative study on sorption behavior of graphene oxide and reduced graphene oxide towards methylene blue

Abstract Mercury (Hg(II)) has been classified as a pollutant and its removal from aqueous sources is considered a priority for public health as well as ecosystem protection policies. Oxidized graphenes have attracted vast interest in water purification and wastewater treatment. In this report, a partially reduced graphene oxide is proposed as a pristine adsorbent material for Hg(II) removal. The proposed material exhibits a high saturation Hg(II) uptake capacity of 110.21 mg g −1 , and can effectively reduce the Hg(II) concentration from 150 mg L −1 to concentrations smaller than 40 mg L −1 , with an efficiency of about 75% within 20 min. The adsorption of Hg(II) on reduced graphene oxide shows a mixed physisorption–chemisorption process. Density functional theory calculations confirm that Hg atom adsorbs preferentially on clean zones rather than locations containing oxygen functional groups. The present work, therefore, presents new findings for Hg(II) adsorbent materials based on partially reduced graphene oxide, providing a new perspective for removing Hg(II). 

/pdf/removal-of-mercury-ii-from-aqueous-solution-by-partially-3o3x6xex.pdf

Removal of mercury(II) from aqueous solution by partially reduced graphene oxide

Carbon-based materials, especially graphene nanocomposites (GNS) have attracted wide attention in recent years. In this study, graphene oxide (GO) and reduced graphene oxide (rGO) were prepared using the Improved Hummers method and were investigated for their adsorption behavior of emerging contaminants such as tetrabromobisphenol A (TBBPA), bisphenol A (BPA), and a conventional contaminant, phenol. The adsorption capacity seemed to slightly increase with increasing reduction degree of GO, highlighting its hydrophobic effect. The adsorption kinetics and isotherms were well delineated using pseudo-second-order and Langmuir equations respectively. At higher temperatures, the adsorption of these selected organic contaminants on GO and rGO slightly increased, also indicating the slight effect of temperature on the adsorption in the environment. From a thermodynamic analysis, the endothermic and spontaneous reaction was observed. The adsorption mechanisms included hydrophobicity, π- π interactions and π electron acceptor and donor ones. GNS can suspend in water even after adsorbing pollutants at the water interface. This would enhance the transport of these contaminants with nanomaterials in the environment. These findings are valuable to elucidate the interaction mechanism between phenol, BPA, and TBBPA on GNS while further understanding the physicochemical behavior of these organic contaminants in the environment. Summary: Adsorption capacities of emerging contaminants, BPA and TBBPA, as well as phenol on graphene oxide (GO) and reduced GO (rGO), were similar. Higher temperatures slightly increased the adsorption of these phenolic compounds on GO and rGO, which also indicated an endothermic and spontaneous process. 

Surface Interaction of Tetrabromobisphenol A, Bisphenol A and Phenol with Graphene-based Materials in Water: Adsorption Mechanism and Thermodynamic Effects

We present an analysis of the electronic and plasmonic behavior of periodic planar distributions of sufficiently wide graphene nanoribbons, for which a thorough ab initio investigation is practically unfeasible. Our approach is based on a semi-analytical model whose only free parameter is the charge carrier velocity, which we estimate by density-functional theory calculations on graphene. By this approach, we show that the plasmon resonance energies of the scrutinized systems fall in the lower THz band, relevant for optoelectronic and photonic applications. We further observe that these energies critically depend on the charge carrier concentration, ribbon width, electron relaxation rate, and in-plane transferred momentum angle, thus, suggesting a tunability of the associated light-matter modes.

https://www.mdpi.com/2079-4991/12/12/2028/pdf?version=1655109679

Calibration of Fermi Velocity to Explore the Plasmonic Character of Graphene Nanoribbon Arrays by a Semi-Analytical Model

Reduced graphene oxide (rGO) is one of the most well-known graphene derivatives, which, due to its outstanding physical and chemical properties as well as its oxygen content, has been used for wastewater treatment technologies. Particularly, extra functionalized rGO is widely preferred for treating wastewater containing dyes or heavy metals. Nevertheless, the use of non-extra functionalized (pristine) rGO for the removal of cationic pollutants is not explored in detail or is ambiguous. Herein, pristine rGO—prepared by an eco-friendly protocol—is used for the removal of cationic pollutants from water, i.e., methylene blue (MB) and mercury-(II) (Hg-(II)). This work includes the eco-friendly synthesis process and related spectroscopical and morphological characterization. Most importantly, the investigated rGO shows an adsorption capacity of 121.95 mg g−1 for MB and 109.49 mg g−1 for Hg (II) at 298 K. A record adsorption time of 30 min was found for MB and 20 min for Hg (II) with an efficiency of about 89% and 73%, respectively. The capture of tested cationic pollutants on rGO exhibits a mixed physisorption–chemisorption process. The present work, therefore, presents new findings for cationic pollutant adsorbent materials based on oxidized graphenes, providing a new perspective for removing MB molecules and Hg(II) ions.

/pdf/cationic-pollutant-removal-from-aqueous-solution-using-2j07vn2e.pdf

Cationic Pollutant Removal from Aqueous Solution Using Reduced Graphene Oxide

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Calibration of Fermi Velocity to Explore the Plasmonic Character of Graphene Nanoribbon Arrays by a Semi-Analytical Model

Cationic Pollutant Removal from Aqueous Solution Using Reduced Graphene Oxide