Graphene-based Adsorbent Research Articles

A robust self-regenerating graphene-based adsorbent for pharmaceutical removal in various water environments

The presence of active pharmaceutical ingredients (APIs) in wastewater effluents and natural aquatic systems threatens ecological and human health. While activated carbon-based adsorbents, such as GAC and PAC, are widely used for API removal, they exhibit certain deficiencies, including reduced performance due to the presence of natural organic macromolecules (NOMs) and high regeneration costs. There is growing demand for a robust, stable, and self-regenerative adsorbent designed for API removal in various environments. In this study, we synthesized a self-generating metal oxide nano-composite (S-MGC) containing titanium dioxide (TiO2) and silicon dioxide (SiO2) combined with 3D graphene oxide (GO) to adsorb APIs and undergo regeneration via light illumination. We determined optimal TiO2:SiO2:GO compositions for the S-MGCs through experiments using a model contaminant, methylene blue. The physical and chemical properties of S-MGCs were characterized, and their adsorption and photodegradation capabilities were studied using five model APIs, including sulfamethoxazole, carbamazepine, ketoprofen, valsartan, and diclofenac, both in single-component and multi-component mixtures. In the absence of TiO2/SiO2, 3D graphene oxide (CGB) displayed better adsorption performance compared to GAC, and S-MGCs further improve CGB's adsorption capacity. This performance remained consistent in two complex water environments: aqueous solutions at varying NOM levels and artificial urine. TiO2 supported on the GO surface exhibits similar photocatalytic activity to suspended TiO2. In a continuous fixed-bed column test, S-MGCs demonstrated robust API adsorption performance that is maintained in the presence of NOM or urine, and can be regenerated through multiple cycles of adsorption and light illumination.

In-silico mechanistic analysis of adsorption of Iodinated Contrast Media agents on graphene surface

The study aims at assessing the potential of graphene-based adsorbents to reduce environmental impacts of Iodinated Contrast Media Agents (ICMs). We analyze an extensive collection of ICMs. A modeling approach resting on molecular docking and Density Functional Theory simulations is employed to examine the adsorption process at the molecular level. The study also relies on a Quantitative Structure-Activity Relationship (QSAR) modeling framework to correlate molecular properties with the adsorption energy (Ead) of ICMs, thus enabling identification of the key mechanisms underpinning adsorption and of the key factors contributing to it. A collection of distinct QSAR-based models is developed upon relying on Multiple Linear Regression and a standard genetic algorithm method. Having at our disposal multiple models enables us to take into account the uncertainty associated with model formulation. Maximum Likelihood and formal model identification/discrimination criteria (such as Bayesian and/or information theoretic criteria) are then employed to complement the traditional QSAR modeling phase. This has the advantage of (a) providing a rigorous ranking of the alternative models included in the selected set and (b) quantifying the relative degree of likelihood of each of these models through a weight or posterior probability. The resulting workflow of analysis enables one to seamlessly embed DFT and QSAR studies within a theoretical framework of analysis that explicitly takes into account model and parameter uncertainty. Our results suggest that graphene-based surfaces constitute a promising adsorbent for ICMs removal, π-π stacking being the primary mechanism behind ICM adsorption. Furthermore, our findings offer valuable insights into the potential of graphene-based adsorbent materials for effectively removing ICMs from water systems. They contribute to ascertain the significance of various factors (such as, e.g., the distribution of atomic van der Waals volumes, overall molecular complexity, the presence and arrangement of Iodine atoms, and the presence of polar functional groups) on the adsorption process.

Continuous adsorption of Metanil Yellow and Remazol Black B dyes onto fixed-bed of 3D graphene oxide/chitosan biopolymer

Treatment of dye polluted water using sustainable and efficient approaches is essential to mitigate the detrimental effects of dyes. The present work reports on the adsorption effectiveness of a graphene-based adsorbent configured into a practical engineering structure, namely three-dimensional graphene oxide integrated with chitosan biopolymer (3D-GCB). This unique graphene configuration enabled its application in continuous fixed-bed adsorption of Metanil Yellow (MY) and Remazol Black B (RBB) dyes from polluted water for the first time. The breakthrough attributes of the fixed-bed of 3D-GCB were established in terms of bed depth (3 – 5 cm), influent concentration (100 – 200 mg/L for MY and 100 – 300 mg/L for RBB) and feed flowrate (2 – 4 mL/min). The greatest bed adsorption capacities attained were 157.06 and 247.96 mg/g for MY and RBB, respectively. The column parameters for obtaining these results were 5 cm bed depth, 2 mL/min feed flowrate, and 150 and 200 mg/L influent concentrations respectively for MY and RBB. The fixed-bed performance of the 3D-GCB was well correlated to the Thomas and Yoon-Nelson models, and the corresponding kinetic properties were determined. Furthermore, the higher affinity of the 3D-GCB for RBB as compared to MY was elucidated based on the ionic strengths of the dye molecule. The utilisation of sustainable and renewable raw materials, such as graphite and chitosan, have resulted in a 3D-GCB production cost of approximately RM 10.72 per gram. This work revealed the suitability of 3D-GCB as the state-of-the-art graphene composite for continuous adsorption of anionic dyes, specifically MY and RBB.

Deep analysis of adsorption isotherm for rapid sorption of Acid Blue 93 and Reactive Red 195 on reactive graphene.

Graphene-based adsorbent was prepared by adopting a green synthetic route via the chemical exfoliation of graphite and low-temperature thermal activation. Prepared reactive graphene (RG) was characterized through various techniques, and its adsorption capabilities for textile dye removal were investigated for Acid Blue-93 (AB) and Reactive Red-195 (RR) under different operational conditions. The dye sorption equilibrium and mechanism were comprehensively studied using isotherm and kinetic models and compared statistically to explain the sorption behavior. Results show AB and RR adsorption by RG attains equilibrium in 60min and 70min, with a high sorption quantity of 397mgg-1 and 262mgg-1 (initial dye concentration of 100mg L-1), respectively. The dye sorption anticipates that the high surface area (104.52 m2 gm-1) and constructed meso-macroporous features of RG facilitated the interaction between the dye molecules and graphitic skeleton. The R-P isotherm fitted the best of equilibrium data, having the least variance in residuals for both dyes (AB = 0.00031 and RR = 0.00047). The pseudo-second order model best fitted the kinetics of sorption on RG, with chemisorption being the predominant process delimiting step. The overall results promise the dye removal capability of RG to be an efficient adsorbent for azo-based dyes from textile effluents.

A high-performance 3D phosphorus-doped graphene oxide adsorbent for imipramine wastewater treatment

The presence of pharmaceutical wastes in the environment has adversely impacted the marine biodiversity due to their hazardous and bioaccumulation nature. This research focussed on the development of an effective phosphorus-doped 3D graphene oxide with bentonite and carboxymethyl cellulose crosslinking (PG/BCC) for the removal of imipramine in wastewater. The impacts of single factor (adsorbent dosage, initial imipramine concentration, system temperature and contact time) on imipramine adsorption were examined by batch experiments while the interactive impacts of multiple factors and process optimisation were investigated by central composite design (CCD). The greatest adsorption capacity evaluated was 458.95 mg/g at the following CCD optimised operating parameters: 10 mg PG/BCC, 250 ppm initial concentration, 34 min contact time and 321 K temperature. The Langmuir model described well the equilibrium of imipramine adsorption whilst the pseudo-second-order model correlated closely to the kinetic data. The imipramine-PG/BCC system was spontaneous (-19.24 to −27.58 kJ/mol) and endothermic (1.23 to 14.56 kJ/mol) as evaluated from thermodynamic modelling. Characterisation of PG/BCC by various microscopy and spectroscopy analyses has validated the incorporation of imipramine into PG/BCC adsorbent. Regeneration of used PG/BCC was proven to be highly feasible with methanol eluent. Conclusively, the findings strongly advocate PG/BCC as a highly feasible and sustainable graphene-based adsorbent for imipramine separation from pharmaceutical wastewater.

Remediation of Amitriptyline Pharmaceutical Wastewater by Heteroatom-Doped Graphene Oxide: Process Optimization and Packed-Bed Studies

Amitriptyline residue released into the aquatic ecosystem can have detrimental consequences on marine organisms and human wellbeing via consumption of polluted water. With a uniquely large surface area and abundant functionalities, graphene oxide adsorption offers a remediation solution for such water pollution. This study focused on synthesizing a novel graphene-based adsorbent via ice-templating of boron-doped graphene substrate. The batch adsorption performance of the as-synthesized adsorbent was explored by central composite design (CCD), while its potential large-scale application was evaluated with a packed-bed column study. The CCD optimized conditions of 12.5 mg dosage, 32 min adsorption time, 30 °C operating temperature and 70 ppm concentration produced the highest removal efficiency of 87.72%. The results of the packed-bed study indicated that continuous adsorption of amitriptyline was best performed at a graphene bed of 3.5 cm in height, with 100 ppm of the pharmaceutical solution flowing at 2 mL/min. Furthermore, the breakthrough curve was effectively portrayed by the Log Bohart–Adams model. The as-synthesized adsorbent showed a high regeneration potential using ethanol eluent via multiple adsorption–desorption cycles. The results suggest the boron-doped graphene adsorbent in packed-bed as a highly effective system to remediate amitriptyline in an aqueous environment.

Metal oxide encapsulated by 3D graphene oxide creates a nanocomposite with enhanced organic adsorption in aqueous solution.

The presence of organic contaminants (OCs) in aquatic systems is a threat to ecological and human health. Adsorption by graphene-based adsorbent is a promising technique for OC removal and we previously fabricated crumpled graphene balls (CGBs), via a novel nano-spray drying technique, which show robust adsorptive performance. Yet, since CGBs contain non-accessible surface area due to 2D graphene stacking, the goal of this research was to investigate the efficacy of maximizing the accessible CGB surface by synthesizing a nanocomposite composed of metal oxide nanoparticles encapsulated by crumpled graphene oxide (MGC). The metal oxides reduce graphene oxide stacking, expand the internal adsorptive surface area, and boost the adsorptive capacity of the MGC. MGC (fumed SiO2 or SiO2) exhibit an enhanced Langmuir adsorption capacity (qm, normalized by the % carbon) for an OC model, methylene blue (MB), achieving improvements of 60-86% compared to CGB, 3-4 fold compared to powder activated carbon (PAC) and 6-7 fold compared to granular activated carbon (GAC). MGCs display rapid adsorption reaching equilibrium after 9-12min of contact and remaining stable in wastewater effluent /surface water. A cost-efficiency comparison reveals MGCs achieve one ton of MB removal at similar or lower material costs than that of PAC/GAC.

Effects of carbonization conditions on the microporous structure and high-pressure methane adsorption behavior of glucose-derived graphene

A simple, promising, environmentally friendly, and high yield technique to synthesize high specific surface area (SSA) and porous graphene-like materials from glucose precursor through carbonization and controlled chemical iron chloride (FeCl3) activation was demonstrated. Designing this nanoporous graphene-based adsorbent with high SSA, abundant micropore volume, tunable pore size distribution, and high adsorption capacity, is crucial in order to deal with the demands of large-scale reversible natural gas storage applications. Raman spectroscopy, BET method of analysis, and N2 adsorption/desorption measurements at 196 °C were adopted to evaluate the structural and textural properties of the resultant glucose derived-graphene (gluGr) samples. The effects of different carbonization conditions, such as the inert environments (argon, helium, and argon) and temperatures (700, 800, 900, and 1,000 °C), have been studied. A glucose-derived graphene carbonized under nitrogen environment at 700 °C (NGr700) with highly interconnected network of micropores and mesopores and large SSA (767 m2/g) exhibited excellent methane (CH4) storage property with exceptionally high adsorption capacity, superior to other glucose-derived graphene (gluGr) samples. A maximum volumetric capacity up to 42.08 cm3/g was obtained from CH4 adsorption isotherm at 25 °C and 35 bar. Note that the adsorption performance of the CH4 is highly associated with the SSA and microporosity of the gluGr samples, especially NGr700 that was successfully synthesized by FeCl3 activation under N2 environment.

Sustainable synthesis of graphene-based adsorbent using date syrup

Here we demonstrate, a facile in-situ strategy for the synthesis of environmentally benign and scalable graphene sand hybrid using date syrup as a sustainable carbon source through pyrolysis at 750 °C. Raman and SEM images revealed that the as-prepared date syrup-based graphene sand hybrid (D-GSH) had imperfections with macroporous 2-D graphene sheet-like structures stacked on the inorganic sand support. The applicability of the D-GSH for decontaminating the water from cationic (Methyl Violet, MV) and anionic (Congo Red, CR) dye and heavy metals (Pb2+ and Cd2+) was tested. Batch experiments demonstrated that D-GSH showcased exceptional capability for both dye and heavy metals removal with fast adsorption following pseudo-second-order kinetics. The adsorption capacities for MV, Pb2+, and Cd2+ were respectively 2564, 781 and 793 mg/g at 25 °C, the highest capacity graphene-based adsorbent reported in the literature to date. In addition, D-GSH also exhibited high adsorption capacity for anionic dye, CR (333 mg g−1) and good recyclability (3 cycles) for all the contaminants. The thermodynamic studies further confirmed that the adsorption of all contaminants was thermodynamically feasible, spontaneous and endothermic with ∆H° of 48.38, 89.10, 16.89 and 14.73 kJ/mol for MV, CR, Pb2+ and Cd2+, respectively. Thus, utilization of a simple one-step strategy to produce graphenic sand hybrid using date syrup helped in developing a cost-effective and environmentally friendly dye and heavy metal scavenger that can be used as a one-step solution for water decontamination.

Adsorption of Hydrogen in Microporous Carbon Adsorbents of Different Origin

Adsorption of hydrogen in four types of activated carbons of different origin with specific micropore volumes ranging from 0.46 to 0.96 cm3/g is studied at temperatures of 303, 313, 323, and 333 K and pressures up to 20 MPa. The saturation adsorption of hydrogen vapors in the considered types of activated carbons is calculated at the hydrogen boiling point (20.38 K) and a pressure of 0.101 MPa using the Dubinin theory of volume filling of micropores (TVFM). The theoretical calculations show that the type FAS-2008 adsorbent, which is produced using liquid-phase furfural polymerization, has the highest adsorption capacity. Using the TVFM and taking into account linearity of the adsorption isosteres, we also estimate adsorption of hydrogen in the type AU3:5 slit-shaped microporous carbon adsorbent at a temperature of 303 K and pressures 10 and 20 MPa. The collected experimental data and theoretical calculations are compared to the data for 101 kPa and 20.38 K. The highest hydrogen adsorption, 7.9 wt %, at 20 MPa and 303 K is predicted for a model slit-shaped microporous graphene-based adsorbent, type AU3:5.

Adsorptive decontamination of diclofenac by three-dimensional graphene-based adsorbent: Response surface methodology, adsorption equilibrium, kinetic and thermodynamic studies

Pharmaceutical residues are emerging pollutants in the aquatic environment and their removal by conventional wastewater treatment methods has proven to be ineffective. This research aimed to develop a three-dimensional reduced graphene oxide aerogel (rGOA) for the removal of diclofenac in aqueous solution. The preparation of rGOA involved facile self-assembly of graphene oxide under a reductive environment of L-ascorbic acid. Characterisation of rGOA was performed by Fourier transform infrared, scanning electron microscope, transmission electron microscopy, nitrogen adsorption-desorption, Raman spectroscopy and X-ray diffraction. The developed rGOA had a measured density of 20.39 ± 5.28 mg/cm3, specific surface area of 132.19 m2/g, cumulative pore volume of 0.5388 cm3/g and point of zero charge of 6.3. A study on the simultaneous interactions of independent factors by response surface methodology suggested dosage and initial concentration as the dominant parameters influencing the adsorption of diclofenac. The highest diclofenac adsorption capacity (596.71 mg/g) was achieved at the optimum conditions of 0.25 g/L dosage, 325 mg/L initial concentration, 200 rpm shaking speed and 30 °C temperature. The adsorption equilibrium data were best fitted to the Freundlich model with correlation coefficient (R2) varying from 0.9500 to 0.9802. The adsorption kinetic data were best correlated to the pseudo-first-order model with R2 ranging from 0.8467 to 0.9621. Thermodynamic analysis showed that the process was spontaneous (∆G = − 7.19 to − 0.48 kJ/mol) and exothermic (∆H = − 12.82 to − 2.17 kJ/mol). This research concluded that rGOA is a very promising adsorbent for the remediation of water polluted by diclofenac.

Polyimide derived laser-induced graphene as adsorbent for cationic and anionic dyes

Laser-induced graphene (LIG) is fabricated on polyimide films directly by irradiation with a CO2 laser. This reagent-free method to synthesize graphene in a single step is applicable for many uses including water treatment technology. Here we demonstrated that LIG is an effective adsorbent for water treatment and observed removal of methylene blue (MB) and methyl orange (MO) from aqueous solutions. LIG powder was obtained by sonication of LIG that was scraped from polyimide films. Raman and X-ray diffraction analysis confirmed the graphene component in the material, while high-resolution scanning electron microscopy and atomic-force microscopy analysis indicated the presence of multilayered graphene sheets. LIG powder showed significant removal of MB and MO dyes from the aqueous solutions where hydrophobicity played an important role, but especially a high adsorption of the MB dye was seen. Adsorption of MB and MO on LIG followed a pseudo-second-order kinetic model and the maximum adsorption capacity (Freundlich) was 926 mg g−1 and 132 mg g−1, respectively. The adsorption process was fast and exothermic, which involved both π-π interaction and electrostatic forces as observed using Raman spectroscopy. The expedient solvent-free fabrication of LIG that is generated on surfaces might be an advantageous graphene-based adsorbent for water remediation.

Synthesis, Characterization, and Adsorption Properties of a Graphene Composite Sand (GCS) and Its Application in Remediation of Hg(II) Ions

In this study, graphene-based adsorbent was successfully prepared following a thermal treatment method. The prepared material, named as graphene-coated sand (GCS), was used as an adsorbent for the removal of Hg(II) ions from aqueous solutions. Structure, composition, and morphology of the GCS were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffractometer (XRD), Raman spectroscopy, electron diffraction (ED) measurements, energy dispersive X-ray spectroscopy (EDX), surface area measurements, particle size, and zeta potential measurements, respectively. A batch adsorption method was used to assess the ability of GCS towards removal of Hg(II) ions from aqueous solutions. The results of batch studies revealed that the GCS required a pH value 6.0, contact time 120 min, and adsorbent dose of 200 mg to attain adsorption equilibrium. Langmuir, Freundlich, Temkin, and D-R adsorption isotherm models were employed to evaluate the isotherm constants and other parameters related to the adsorption process. The Hg(II) ions uptake by the GCS was found to follow Freundlich isotherm model with R 2 value of 0.97695, under optimized conditions and at 40 °C with a maximum adsorption capacity of 299.40 mg/g. The adsorption process followed the second-order kinetic path. The thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were also calculated which suggested that the adsorption processes of Hg(II) ions onto the GCS was endothermic and entropy favored. The values of ΔG° at 283, 303, and 313 K were − 1.10, − 0.025, and − 4.55 kJ, respectively, and ΔH°, ΔS° were calculated to be 26.60 kJ mol−1 and ΔS° 1.35 J mol−1 K−1, respectively. The obtained results revealed that the prepared materials could be effectively and economically beneficial.

Synergistic effects of 2D graphene oxide nanosheets and 1D carbon nanotubes in the constructed 3D carbon aerogel for high performance pollutant removal

To create interspace-enlarged and sites-exposed graphene-based adsorbents for pollutant management, three-dimensional macrostructures (3D GTs) were facilely constructed via self-assembly of two-dimensional graphene oxide nanosheets (2D GO) and one-dimensional carbon nanotubes (1D CNTs). Since the existence of CNTs acting like frames may reinforce the mechanical strength of the GO nanosheets, the density of the stable and porous 3D GTs was reduced to 0.2mg/mL which was much lower than the minimum concentration required to form pure GO 3D macrostructures. The 3D GTs exhibited superior adsorption capabilities to emerging pollutants such as oxytetracycline (1729mg/g) and diethyl phthalate (680mg/g), and traditional pollutants such as methylene blue (685mg/g), Cd2+ (235mg/g) and diesel (421g/g). The adsorption capacity of 3D GTs is higher than the reported graphene/GO and CNTs-based adsorbents, which can be attributed to the synergistic effects of GO and CNTs in micro-environment, nano-substrate, and active sites. Firstly, the assembled GO sheets were highly separated and in monolayer form, which created large interspaces in 3D GTs. Secondly, GO and CNTs provided abundant adsorption sites. Thirdly, the micro environment of interspaces in stable 3D GTs could be tuned to achieve selective adsorption to particular pollutant. In short, we propose a super graphene-based adsorbent which is competitive and scalable for water purification.

Rapid and highly selective removal of lead from water using graphene oxide-hydrated manganese oxide nanocomposites

To overcome the limits of graphene oxide (GO) as a novel sorbent for heavy metal removal (e.g., low sorption selectivity and difficulty in solid-liquid separation), a nanocomposite (HMO@GO) with excellent settling ability (<2min) was fabricated through in situ growing nanosized hydrated manganese oxide (HMO) (10.8±4.1nm) on GO. As a graphene-based adsorbent, HMO@GO exhibited fast sorption kinetics (<20min). Meanwhile, the introduced HMO endowed HMO@GO with outstanding sorption selectivity and capacity toward Pb(II) (>500mgg−1) in the presence of high-level competing Ca(II). Cyclic sorption batches showed that 1kg HMO@GO can treat at least 22m3 Pb(II)-laden synthetic industrial drainage (5mgL−1 Pb(II)) and 40m3 drinking water (0.5mgL−1 Pb(II)) to their corresponding limits (0.1mgL−1 for wastewater and 10μgL−1 for drinking water) enforced in China. Additionally, the exhausted HMO@GO can be effectively regenerated using 0.3 M HCl for repeated uses. The eminent performance of HMO@GO was attributed to its specific structure, that is, the abundant oxygen-containing groups on GO mediated the growth of highly dispersed HMO that preferably sequestrated Pb(II) through specific interaction, and the host GO offered the preconcentration of Pb(II) for enhanced sequestration through the Donnan membrane effect.

Facile synthesis and characterization of thiol-functionalized graphene oxide as effective adsorbent for Hg(II)

In this work, we report the synthesized and characterization of mercaptobenzothiazole (MBT) functionalized graphene oxide (GO) as a novel adsorbent material for the adsorption of Hg(II). This adsorption process could be realized with GO and MBT acting as host-guest in the first instance followed by the subsequent complexation of Hg(II) with MBT, the soft–soft interaction between Hg(II) & sulphur enhances the effective complexation. The prepared graphene-based adsorbent was characterised by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Powder-X-ray diffraction (Powder-XRD), Transmission electron microscopes (TEM), Fourier transform infrared spectroscopy (FT-IR), UV–vis spectroscopy, scanning electron microscopes (SEM) and energy-dispersive X-ray analysis (EDX). The capability of ICP-MS for Hg(II) adsorption was extensively studied under different optimal parameters, the developed method was successfully applied to mercury adsorption from water samples.

Sulfonated graphene nanosheets as a superb adsorbent for various environmental pollutants in water.

Graphene nanosheets, as a novel nanoadsorbent, can be further modified to optimize the adsorption capability for various pollutants. To overcome the structural limits of graphene (aggregation) and graphene oxide (hydrophilic surface) in water, sulfonated graphene (GS) was prepared by diazotization reaction using sulfanilic acid. It was demonstrated that GS not only recovered a relatively complete sp(2)-hybridized plane with high affinity for aromatic pollutants but also had sulfonic acid groups and partial original oxygen-containing groups that powerfully attracted positively charged pollutants. The saturated adsorption capacities of GS were 400 mg/g for phenanthrene, 906 mg/g for methylene blue and 58 mg/g for Cd(2+), which were much higher than the corresponding values for reduced graphene oxide and graphene oxide. GS as a graphene-based adsorbent exhibits fast adsorption kinetic rate and superior adsorption capacity toward various pollutants, which mainly thanks to the multiple adsorption sites in GS including the conjugate π region sites and the functional group sites. Moreover, the sulfonic acid groups endow GS with the good dispersibility and single or few nanosheets which guarantee the adsorption processes. It is great potential to expose the adsorption sites of graphene nanosheets for pollutants in water by regulating their microstructures, surface properties and water dispersion.