Adsorption Of Graphene Oxide Research Articles

Colloidal graphene oxide enhances the activity of a lipase and protects it from oxidative damage: Insights from physicochemical and molecular dynamics investigations

Physical adsorption of lipase from Thermomyces lanuginosus onto single-layer sheets of graphene oxide (GO) was studied using the response surface methodology to evaluate the physicochemical factors – temperature, pH, ionic strength, and concentration – affecting the enzymatic activity and the immobilization efficiency. The immobilization efficiency and the activity of the enzyme were inversely proportional to each other. Specifically, higher pH values increased the immobilization efficacy, but produced changes in the aggregation state and secondary structure of the enzyme, thus decreasing its activity. Lower pH values, in turn, reduced the immobilization efficacy, but increased the activity of the adsorbed lipase. The adsorbed and the free lipase were followed during 600 ns and 3.5 μs, respectively, in molecular dynamics (MD) simulations. MD trajectories showed that irreversible adsorption freezes the enzyme in a state with a correctly opened catalytic cavity, while the active site remains without a direct interaction with the GO adsorbent. In contrast to the interfacial activation of lipases in a hydrophobic environment, where the catalytic pocket attaches to the hydrophobic surface, the adsorption onto GO made the active site of the lipase accessible by altering the tertiary structure of the enzyme, leading to a higher catalytic efficiency. Experimental investigations confirmed that the physical adsorption onto GO induces tertiary structure changes in the lipase and protects it from H2O2 by accepting the oxidative damage upon itself. In summary, the physical adsorption of the lipase onto GO is mainly affected by pH and could possibly provide a spreadable and robust catalytic interface for biotechnological applications.

Surface-Anchored Graphene Oxide Nanosheets on Cell-Scale Micropatterned Poly(d,l-lactide-co-caprolactone) Conduits Promote Peripheral Nerve Regeneration.

Regeneration and functional recovery of peripheral nerves remain formidable due to the inefficient physical and chemical cues in the available nerve guidance conduits (NGCs). Introducing micropatterns and bioactive substances into the inner wall of NGCs can effectively regulate the behavior of Schwann cells, the elongation of axons, and the phenotype of macrophages, thereby aiding the regeneration of injured nerve. In this study, linear micropatterns with ridges and grooves of 3/3, 5/5, 10/10, and 30/30 μm were created on poly(d,l-lactide-co-caprolactone) (PLCL) films following with surface aminolysis and electrostatic adsorption of graphene oxide (GO) nanosheets. The GO-modified micropatterns could significantly accelerate the collective migration of Schwann cells (SCs) and migration of SCs from their spheroids in vitro. Moreover, the SCs migrated directionally along the stripes with a fastest rate on the 3/3-GO film that had the largest cell adhesion force. The neurites of N2a cells were oriented along the micropatterns, and the macrophages tended to differentiate into the M2 type on the 3/3-GO film judged by the higher expression of Arg 1 and IL-10. The systematic histological and functional assessments of the regenerated nerves at 4 and 8 weeks post-surgery in vivo confirmed that the 3/3-GO NGCs had better performance to promote the nerve regeneration, and the CMAP, NCV, wet weight of gastrocnemius muscle, positive S100β and NF200 area percentages, and average myelinated axon diameter were more close to those of the autograft group at 8 weeks. This type of NGCs thus has a great potential for nerve regeneration.

Synthesis and characterization of graphene oxide/ gold nanoparticles/ dibenzothiophene heterogeneous nanostructures

This work examines the effect of gold nanoparticle (Au NP)- graphene oxide (GO) on the adsorption of dibenzothiophene (DBT) compounds. Au NP-GO were also used as an absorbent to produce nanoscale samples of DBT selfassembled monolayers (SAMs) on Au NP-GO. The influences of DBT adsorption on the size and the time of patterns were investigated. Atomic force microscopy (AFM) and Transmission electron microscopy (TEM) measurements showed that all of the uniformly distributed on Au NP- GO preliminary results indicated that the diameter and the density of DBT adsorptive can be controlled by controlling concentration of GO and Au NP and adsorption time during DBT the stage of SAMs. Photocatalytic oxidation of DBT was studied over Au NPs incorporated DBT Au NP-GO- DBT catalyst under UV radiation.

Electrochemical investigation of adsorption of graphene oxide at an interface between two immiscible electrolyte solutions.

Graphene oxide (GO) has been recognized as an amphiphilic molecule or a soft colloidal particle with the ability to adsorb and assemble at the liquid/liquid (L/L) interface. However, most extant works concerning the adsorption behaviors of GO at the L/L interface have been limited to the non-polarized L/L interface. Here, we studied what would happen if GO nanosheets met with a polarizable L/L interface, namely an interface between two immiscible electrolyte solutions (ITIES). On one hand, the adsorption behavior of GO nanosheets at the L/L interface was electrochemically investigated firstly by using cyclic voltammetry (CV) and alternating current voltammetry (ACV). On the other hand, the influence of the adsorbed GO layers at the L/L interface on the ion transfer reactions was studied by employing ion-transfer voltammetry of TEA+ and ClO4− selected as probe ions. Capacitance measurements show that the interfacial capacitance increases greatly in the presence of GO nanosheets inside the aqueous phase, which can be attributed to the increases of interfacial corrugation and charge density induced by the parallel adsorption and assembly of GO at the L/L interface. In addition, it is found that the application of an interfacial potential difference by external polarization can promote the adsorption of GO at the L/L interface. Moreover, the ion-transfer voltammetric results further demonstrate that the GO layers formed at the interface can suppress the ion transfer reactions due to interfacial blocking and charge screening, as well as the hindrance effect induced by the GO layers. All the results with insights into the interfacial behavior of GO under polarization with an external electric field enable understanding the adsorption behavior of GO at the L/L interface more comprehensively.

Boronic acid-modified polyhedral oligomeric silsesquioxanes on polydopamine-coated magnetized graphene oxide for selective and high-capacity extraction of the catecholamines epinephrine, dopamine and isoprenaline.

Amino-functionalized polyhedral oligomeric silsesquioxanes (POSS-8NH2) were covalently bound to the surface of polydopamine-coated magnetized graphene oxide. It was then reacted with 4-formylphenylboronic acid to prepare a "cubic boronic acid"-bonded magnetic graphene oxide adsorbent. The new adsorbent exhibits better selectivity and much higher adsorption capacity for ortho-phenols over adsorbents where small boronic ligands are directly bound to the surface of the material. It is shown to enable selective and faster enrichment of the catecholamines epinephrine (EP), dopamine (DA) and isoprenaline (IP) with high selectivity over many potential interferents that can occur in urine. The analytes were then quantified by HPLC with fluorometric detection. Under optimal conditions, response is linear (R2 ≥ 0.9907), limits of detection are low (0.54-2.3ng·mL-1), and reproducibility is acceptable (inter- and intra-day assay RSDs of≤10.9%). The method was successfully applied to the determination of endogenous EP and DA and exogenous IP in urine samples. Graphical abstractSchematic of boronic acid (BA)-modified polyhedral oligomeric silsesquioxanes (POSS) on polydopamine-coated magnetized graphene oxide (magGO). The material (magGO@POSS-BA) has good selectivity and higher adsorption capacity to ortho-phenols and can be applied to enrich the catecholamines in urine.

The critical role of oxidative debris in the adsorption and desorption of Pb(II) to graphene oxides under alkaline groundwater conditions

The application of graphene oxide (GO) and its derivatives as adsorbents to remove heavy metal contaminants from industrial wastewaters has attracted increasing attention worldwide. Here, we investigated the role of oxidative debris (OD) on GO surfaces in the adsorption of Pb(II) under natural conditions. OD attached to GO surfaces can be removed under alkaline conditions, and plays a critical role in the adsorption of Pb(II) by GO. Specifically, the maximum adsorption capacity of Pb(II) on GO decreased from 926.50 to 357.64 mg·g−1 after OD removal. Under simulated natural alkaline groundwater conditions, some adsorbed Pb(II) was released with OD that was stripped from spent GO adsorbents (i.e., GO-Pb(II)). Further, batch experiments indicated that 1.30−1.43% of adsorbed Pb(II) could stably disperse in water as dissolved PbCO3 and OD-Pb(II) complexes, at a pH of ~8.3. The stripping and dissociation of OD under alkaline conditions promoted the mobility of Pb(II) on GO adsorbents. This study enhances our understanding of heavy metal transport in natural alkaline groundwater environments that contain GO particles.

A sensitive electrochemical aptasensor based on MB-anchored GO for the rapid detection of Cronobacter sakazakii

Cronobacter sakazakii (C. sakazakii) can cause extremely high mortality diseases especially in infants, so it is necessary to rapidly and specifically detect C. sakazakii in powdered infant formula (PIF). In this work, the amplification strategy of methylene blue (MB)-anchored graphene oxide (GO) was used to develop an electrochemical aptasensor for detecting C. sakazakii easily and quickly. In the absence of C. sakazakii, GO would be bound to the aptamer of C. sakazakii by π-π interaction, and then adsorbed MB through electrostatic adherence; thus, the electrochemical signal of MB amplified. While in the presence of C. sakazakii, the bacteria would be specifically combined with the aptamer, and hindered the electrostatic adsorption of GO and MB to the aptamer, resulting in the decreasing electrochemical signal of MB. The fabricated electrochemical aptasensor showed a wide linear range from 2 × 101 to 2 × 106 CFU mL−1 of the bacteria concentration, and its limit of detection reached 7 CFU mL−1 (S/N = 3). In addition, the applicability of the aptasensor in PIF for the analysis of C. sakazakii was successfully demonstrated. This aptasensor would provide a new method for the detection of C. sakazakii but also a novel sensing platform for the rapid detection of pathogen bacteria.

Covalently decorated crown ethers on magnetic graphene oxides as bi-functional adsorbents with tailorable ion recognition properties for selective metal ion capture in water

Metal ions (Mn+) in water are considered as environmental pollutants, as industrial impurities or as potential secondary sources for valuable metals. Increasing generation of complex feed streams has raised the need for more specialized adsorbents that could preferentially capture the target Mn+. While graphene oxide (GO) is an effective adsorbent, its indiscriminate sequestration negatively affects its selectivity. To meet the growing demand for more Mn+-selective materials, GO adsorbents with dual features of ion recognition and magnetic responsiveness were developed. The bi-functional GOs were fabricated by in-situ nucleation of Fe3O4 nanoclusters on GO oxygenous groups and by direct grafting of ethynylbenzene linkers on its backbone, which served as tethering sites for the macrocyclic crown ether (CEs) ligands with tunable Mn+ affinities (i.e. CE@Fe3O4-rGO). As proof-of-concept, 12CE4@Fe3O4-rGO was proven highly selective for Li+ capture, achieving α = 367–14,513 against Na+, K+, Mg2+, Ca2+ in seawater. Its Langmuir-type Li+ adsorption achieved nearly ~100% 12CE4 utilization (1.03 mmol g−1 CE loading). Its pseudo-second uptake rate demonstrated its rapid Li+ capture. 12CE4@Fe3O4-rGO is water-dispersible, magnetically retrievable, and recyclable with consistent Li+ uptake performance. By replacing the CEs with aza15CE5, aza18CE6 and dibenzo-24CE8, three more types of CE@Fe3O4-rGOs (1.24–1.71 mmol CE g−1) were successfully synthesized with varying affinities towards heavy metals, radionuclides and alkali metal ions. These findings highlight the versatility of the proposed technique in producing a wide selection of CE@Fe3O4-rGOs which can be used for selective Mn+ capture in various application for water decontamination, salts removal, and resource recovery.

High-efficiency adsorption of methylene blue dye from wastewater by a thiosemicarbazide functionalized graphene oxide composite

With the aim of developing an improved adsorbent material for the treatment of printing and dyeing wastewater, we prepared a novel thiosemicarbazide functionalized graphene oxide (GO-TSC-GO) adsorbent by condensation reaction of the thiosemicarbazide amino group with the graphene oxide carboxyl group. This material was characterized by SEM, XPS, FTIR, Raman, XRD, UV–Vis, TGA, and BET then used to conduct adsorption experiments on simulated printing and dyeing wastewater containing methylene blue (MB). We investigated the effects of temperature, time, pH, salt ionic strength, initial MB solution solubility, and the activation and regeneration of the adsorbent on adsorption performance. The adsorption behavior was consistent with the pseudo-second-order adsorption kinetic model and the Langmuir adsorption isotherm model. Thermodynamic analysis indicated an exothermic chemical adsorption reaction. In addition, the GO-TSC-GO exhibited excellent reusability. The maximum adsorption capacity of GO was 196.8 mg/g whereas the maximum adsorption capacity of GO-TSC-GO was 596.642 mg/g, verifying that the GO-TSC-GO composite has important applications for the treatment of printing and dyeing wastewater.

New effective 3-aminopropyltrimethoxysilane functionalized magnetic sporopollenin-based silica coated graphene oxide adsorbent for removal of Pb(II) from aqueous environment

A new effective adsorbent, 3-aminopropyltrimethoxysilane functionalized magnetic sporopollenin (MSp@SiO2NH2) based silica-coated graphene oxide (GO), (GO@SiO2-MSp@SiO2NH2) was successfully synthesized and applied for the first time in the removal of hazardous Pb(II) ions from aqueous solution. The properties of the composite were characterized using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and vibrating-sample magnetometery (VSM). Evaluation of GO@SiO2-MSp@SiO2NH2 adsorption performance at optimum conditions revealed that the adsorbent has a maximum adsorption capacity of 323.5 mg/g for Pb(II) using 50–200 mg/L initial Pb(II) ions concentrations. Initial and final concentrations of Pb(II) ions in aqueous solution were analyzed using graphite furnace atomic absorption spectroscopy (GF-ASS). The adsorption behavior of Pb(II) ions onto GO@SiO2-MSp@SiO2NH2 was studied using Langmuir, Freundlich and Temkin isotherms models. The values of coefficient of determination showed that the adsorption best fitted the Langmuir model (R2 = 0.9994). Kinetic studies suggested that the adsorption of Pb(II) ion followed a pseudo-second-order rate model (R2 = 1.00) and thermodynamic studies revealed that the adsorption process is endothermic and spontaneous. The effect of co-existing ions on Pb(II) ion adsorption were also studied and found to have considerable effects only at higher matrix concentration. The adsorbent can be reused up to ten times and retain its good adsorption capacity. In addition, GO@SiO2-MSp@SiO2NH2 showed great potential for Pb(II)removal from industrial wastewater samples.

Highly Efficient Removal of Uranium(VI) from Wastewater by Polyamidoxime/Polyethyleneimine Magnetic Graphene Oxide

Highly efficient removal of U(VI) from mine radioactive wastewater has received a lot of attention. Herein, the polyamidoxime/polyethyleneimine magnetic graphene oxide (mGO-PP) adsorbent was succes...

Relations between metal ion characteristics and adsorption performance of graphene oxide: A comprehensive experimental and theoretical study

The adsorption performance of graphene oxide (GO) towards metallic hard (Na+, Mg2+), soft (Cd2+ and Pb2+) and borderline ions (Ni2+, Cu2+, Zn2+, Co2+) was studied experimentally giving the sequence of maximum Langmuir adsorption capacities Qm, mmol/g, as Na+ < Mg2+ < Co2+ < Cd2+ < Zn2+ < Ni2+ < Cu2+ < Pb2+. The results showed that the adsorption capacities Qm of hard ions were substantially lower than that of soft and borderline ones. The relationship between the Qm values of metal ions and their characteristics was studied using relative correlation analysis. The ion characteristics include atomic number AN, ionic radius r, change in ionization potential ΔIP, electronegativity Xm, atomic weight AW, covalent index Xm2r, absolute difference between electrochemical potential of the ion and that of its first stable reduced state ΔE0, absolute value of the first hydrolysis constant decimal logarithm |lgKOH|, atomic radius AR, atomic radius to atomic weight ratio AR/AW, polarization force or ionic index Z2/r and softness index σp. The Qm value exhibited positive correlation with r, △IP, Xm, Z2/r, AN/△IP, AW, Xm2/r and AN, while negative correlation was observed with △E0, |lgKOH|, σp, AR and AR/AW. The results allow the Qm values being predicted by the equation, the correlation coefficient R2 of which exceeds 0.885:Qm=0.338ΔIP-0.110|lgKOH|+0.114Z2/r+26.934σp-1.479AR-1.162Xm2r+0.115AN-3.059Density functional theory (DFT) was adopted to study the adsorption mechanism of metal ions at GO, taking Na+, Cu2+ and Pb2+ ions as examples. The results showed the adsorption energy Ead of GO-Na+ bond being negative indicating Na+ adsorption less likely resulting possibly in relatively low adsorption capacity of GO towards hard ions. The Ead values of GO bonds with Cu2+ and Pb2+ comprised the rows GO(O)-Cu2+ > GO(COOH)-Cu2+ > GO(OH)-Cu2+, and GO(COOH)-Pb2+ > GO(OH)-Pb2+ > GO(O)-Pb2+, respectively. The results provide guidelines in predicting the adsorption ability of GO adsorbent towards metal ions.

One-pot synthesis of magnetic graphene oxide composites as an efficient and recoverable adsorbent for Cd(II) and Pb(II) removal from aqueous solution

It is extremely desirable but challenging to develop a facile synthesis method to directly prepare reusable and longtime stable magnetic graphene oxide (GO) adsorbent. Here, a new approach to prepare a magnetic GO for removing the heavy metal ions is reported by using n-Propyltrimethoxysilane (NPTS) as a cross-coupling agent to connect Fe3O4/SiO2 and GO. The as-prepared magnetic GO can be separated quickly from their aqueous solution by the permanent magnet and also exhibited excellent adsorption performance for Cd(II) and Pb(II) with maximum adsorption capacities for Cd(II) and Pb(II) to 128.2 and 385.1 mg/g under neutral conditions, respectively. The presence of other ions such as Na(I) and K(I), had little influence on the Cd(II) and Pb(II) removal efficiency. Moreover, the as-prepared Fe3O4/SiO2-GO adsorbents can be recycled and exhibited good reproducibility. Thus, the magnetic GO adsorbents are effective materials for the removal of heavy metal ions and thus could offer a new platform for water cleanup.

Hydrogen adsorption by g-C3N4 and graphene oxide nanosheets

The adsorption behavior of hydrogen for synthesized graphitic carbon nitride (g-C3N4) and graphene oxide nanosheets was compared. The structure of the prepared g-C3N4 and graphene oxide samples were studied using TEM, FT-IR spectroscopy and surface area analysis. Textural results of the prepared nanosheets show that the surface area, total pore volume, and average internal diameter of g-C3N4 and graphene oxide samples are similar. The hydrogen adsorption isotherms at 298 K, up to 22 bar pressures were as Type III and the maximum hydrogen storage capacities at 22 bar and 296 K were 1.06 and 1.27 mmol/g for graphite oxide and g-C3N4 samples, respectively. The adsorption results were fitted by Freundlich model, which was related to reversible multilayer adsorption on non-uniform surface active sites with different affinities of both g-C3N4 and graphene oxide adsorbents. Isosteric heat of adsorption of hydrogen on the graphene oxide varies from 8.6 kJ.mol-1 (at low hydrogen uptake) to 4.3 kJ.mol-1. These results are the range of 10.1 to 4.8 kJ.mol-1 for the prepared g-C3N4 sample at same hydrogen uptake. The results show that the interaction between hydrogen molecules and tri-s-triazine units in g-C3N4 structure are stronger than carbon atoms in graphene oxide structure.

Investigation of Eosin B Removal from Aqueous Solution Employing Combined Graphene Oxide Adsorption and Zinc Oxide Coagulation Processes

In this study, graphene oxide was synthesized and investigated as an adsorbent for eosin B elimination. The features and structure of graphene oxide were determined by employing scanning electron microscopy, transmission electron microscopy, Raman spectrometry, and X-ray diffractometry. Graphene oxide can remove dyes in water solutions, but it is confronted by separation challenges. Therefore, zinc oxide was used as a coagulant for separation of the dye solution from graphene oxide. Adsorption properties such as contact time, dye concentration, dosage of adsorbent, zinc oxide content, pH effect, and temperature were regularly investigated extensively. Concentrations of dyes in the supernatant suspension were evaluated employing a visible spectrophotometric method at the maximum wavelength (λmax) of 514 nm. The eosin B dye showed maximum sorption capacity of 68.027 mg/g at pH 4 and T=298 K. Isotherm models such as Freundlich and Langmuir isotherms were used to determine the better suitable isotherm model. It was discovered that this dye adsorption capacity on adsorbent particles was monolayer and had a good agreement with the Langmuir isotherm. Pseudo-first-order and pseudo-second-order kinetic models were investigated to determine adsorption kinetics. The pseudo-second-order for sorption of this dye on adsorbents was followed by kinetic data analysis. This research shows that this sorbent and coagulant are efficacious and applicable for the removal of eosin B from wastewaters.

Carbon Quantum Dot Assisted Adsorption of Graphene Oxide to the Oil–Water Interface for Copper Sensing Emulsions

AbstractA nanocomplex of graphene oxide (GO) and nitrogen‐doped carbon quantum dots (N‐CQDs) is utilized for effective stabilization of the toluene–water interface in high surface area oil‐in‐water emulsions to assist in detection and extraction of Cu(II) ions. CQDs are nitrogen‐doped to produce a positively charged material that readily adsorbs to GO through charge interactions, forming a surface‐active complex. N‐CQDs serve two key purposes: first, to screen the surface charge of GO and thereby lower the electrostatic barrier to adsorption at the toluene–water interface, and second to detect Cu(II) ions via fluorescence quenching. This combined system is far more effective in lowering the interfacial tension between toluene and water, and thus stabilizing toluene‐in‐water emulsions, than either component alone. The complex comprises cheap and easy to prepare materials, and overcomes the limitations of the individual components through synergistic effects. Additionally, the noncovalent nature and self‐assembly of this system allows for facile use and potential recovery of the materials, and therefore enables utilization in industrial applications such as solvent extraction for mineral processing.

Selective Separation of Pd(II) on Pyridine-Functionalized Graphene Oxide Prepared by Radiation-Induced Simultaneous Grafting Polymerization and Reduction

The recovery of precious metals like palladium (Pd) from secondary resources has enormous economic benefits and is in favor of resource reuse. In this work, we prepared a high efficiency pyridine-functionalized reduced graphene oxide (rGO) adsorbent for selective separation of Pd(II) from simulated electronic waste leachate, by one-pot γ-ray radiation-induced simultaneous grafting polymerization (RIGP) of 4-vinylpyridine (4VP) from graphene oxide (GO) and reduction of GO. The poly(4-vinylpyridine)-grafted reduced graphene oxide (rGO-g-P4VP) exhibits fast adsorption kinetics and high maximum adsorption capacity. The adsorption capacity is 105 mg g-1 in the first minute and reaches equilibrium within 120 min. The adsorption process follows the Langmuir model, from which the maximum adsorption capacity of Pd(II) is estimated to be 177 mg g-1. We also proved that the adsorption mechanism of Pd(II) on rGO-g-P4VP involves both ion exchange and coordination adsorption by XPS analysis. Most importantly, the loss of oxygen-containing groups due to reduction of GO not only facilitates the separation of adsorbent from aqueous solution but also reduces the electrostatic repulsion toward Pd(II)Cl42- in hydrochloric acid solution, leading to a higher adsorption selectivity of Pd(II) over some common metal cations in electronic waste including Fe(III), Cu(II), and Al(III) compared with poly(4-vinylpyridine)-grafted graphene oxide (GO-g-P4VP) prepared by atom transfer radical polymerization. Other precious metals like Pt(IV) and Au(III) can also be recovered easily and selectively by rGO-g-P4VP. This work demonstrates that rGO-g-P4VP prepared by the facile RIGP is a promising adsorbent for recovery of precious metals from secondary resources like electronic waste leachate.

Application of Graphene Oxide for Adsorption Removal of Geosmin and 2-Methylisoborneol in the Presence of Natural Organic Matter.

We investigated the adsorption characteristics of geosmin and 2-methylisoborneol (MIB) on graphene oxide (GO) in the absence and presence of natural organic matter (NOM). The graphene oxide had fast adsorption kinetics for both compounds because of its open-layered structure, with adsorption equilibrium being achieved within 15 min of contact. Although NOM did not affect the adsorption of geosmin on GO, it delayed that of MIB, probably because of competition for adsorption sites. The adsorption isotherms show that GO had a greater capacity for geosmin adsorption than for MIB because geosmin was more hydrophobic. Moreover, NOM interfered with the adsorption of MIB onto the GO, but increased the amount of adsorbed geosmin, which likely occurred because NOM increased the dispersibility of GO, which then increased the number of GO adsorption sites. The difference in the effects of NOM on GO adsorption of geosmin and MIB may be explained by their hydrophobicity. Although the adsorption of geosmin and MIB by GO was fast, its capacity to adsorb both compounds was substantially lower than that of activated carbon because of its higher hydrophilicity.

Release and transport of Pb(II) adsorbed on graphene oxide under alkaline conditions in a saturated sand column.

The use of graphene oxide (GO) adsorbents to remove Pb(II) from wastewater has attracted lots of attention, but the release of Pb(II) from Pb-laden GO in alkaline groundwater requires further investigation. The current research demonstrated that oxidative debris (OD) could be stripped gradually from the surfaces of GO in 0.01-1.0 M NaHCO3 solutions although the stripping kinetic process was very slow. Accompanied with OD detachment from GO, 5.47%-23.45% adsorbed Pb(II) on spent GO (i.e. GO-Pb(II)) was released in the form of an OD-Pb(II) complex under 0.01-1.0 M NaHCO3 conditions. OD-Pb(II) could disperse steadily in water even at pH > 7.0. The deposition and detachment of the OD in the quartz sand media were markedly affected by the ion strength of the solution, and the greater mobility of OD than GO improved the transport of OD-Pb(II) through a saturated sand column. Our results provide valuable information about the characteristics and mechanism of transport of adsorbed heavy metals on GO nanomaterials in the aqueous environment and the possible environmental risks when spent GO-based heavy mental adsorbents are discharged into natural groundwater systems.

Insight into the ultrasonication of graphene oxide with strong changes in its properties and performance for adsorption applications

A sonochemical approach is widely used as a routine protocol for graphene oxide (GO) preparation prior to adsorption applications, but there is a limited understanding of its effects on the GO sorption ability. Herein, using different types of sorbates, which are cation, cationic and anionic dye, the changes in sorption capacity along with the characteristics of sonicated GO, are shown. The ultrasound treatment unexpectedly removes oxygen functional groups from GO with a concomitant decrease in GO adsorption capacity, rather than an increase in its adsorption as expected from the use of ultrasound in dispersing or exfoliating GO. The C/O ratio increases from 2.1 in pristine GO up to 2.5 in sonicated GO. The loss of oxygen functional groups is also accompanied by an increase in disorder and defects on GO sheets, along with the weakening of π-π interaction. The pathways of GO’s structural and functional groups changed by ultrasound are proposed, based on the generation of OH· radicals from ultrasonic cavitation. These radicals can react with the facile oxygenated groups of GO, such as those of epoxide, hydroxyl, and carboxyl, leading to the partial removal of these groups and the breakage of GO sheets. GO’s adsorption capacities for cation and different dyes can decrease up to 75% after sonication, which is in agreement with the above changes in GO’s characteristics. The effects are readily observed even in mild sonication such as using an ultrasonic bath, signifying their importance in many applications employing ultrasonication to disperse GO.