Density Of Functional Groups Research Articles

Preparation of porous biomass-derived hydrothermal carbon modified with terminal amino hyperbranched polymer for prominent Cr(VI) removal from water

Herein, a series of functionalized hydrochars with high density of nitrogen-containing functional groups were engineered by co-processing of terminal amino hyperbranched polymer and walnut shell biomass in the hydrothermal carbonization media. Hydrothermal Carbonization with optimized key parameters was implemented to determine the impact of added polymer to the biomass on the properties of the obtained hydrochars. Consequently, the optimum hydrochar which was achieved with the values of 250 °C, 60 min, and 50% (w/w) for temperature, time, and polymer/biomass weight ratio, demonstrated a highly improved surface area of 544 m2.g−1 and the highest adsorption capacity for Cr(VI) removal which was obtained from Freundlich isotherm model and described by the pseudo-second-order kinetic model to be 363.22 mg.g−1 (at pH = 2.0). This work suggests that the co-hydrothermal carbonization promotes the uniform incorporation of polymers into the hydrochar matrix and provides adsorbents for the effective removal of Cr(VI) from water.

Direct/Alternating Current Electrochemical Method for Removing and Recovering Heavy Metal from Water Using Graphene Oxide Electrode.

Treatment of heavy-metal pollution in both point-of-use water and industrial wastewater is critical in protecting human health and the environment. Current methods for heavy-metal treatment in both sources have limitations. For point-of-use water, current methods usually suffer from limited capacity and difficulties in spontaneously removing multiple heavy metals. For industrial wastewater, current methods greatly reduce the value of heavy metal by precipitating them as sludge which requires further treatment. Here we developed an electrochemical method that can treat both low-concentration and high-concentration heavy-metal pollution using either direct current (DC) or alternating current (AC) electrodeposition with graphene-oxide-modified carbon felt electrode (CF-GO). The graphene oxide provides a high density of surface functional groups to assist the electrodeposition. The electrodeposition method showed 2 orders of magnitude higher capacity (>29 g heavy metal for 1 g of graphene oxide) compared with traditional adsorption methods. For low levels of heavy-metal pollution in point-of-use water, DC electrodeposition with a CF-GO electrode can reduce single heavy-metal ion pollution (Cu, Cd, and Pb) as well as multiple ion mixtures to below safe water drinking levels. This method can tolerate a much wider range of heavy-metal pollution in point-of-use water than traditional adsorption methods. For high-level pollution in industrial wastewater, AC electrodeposition can recover >99.9% heavy-metal ions. By tuning the AC frequency and voltage, the electrodeposition method can further selectively recover Cu, Cd, and Pb separately, which adds values to the heavy-metal removal process.

Ecological engineers’ nests benefit plant recovery following fire in a semiarid grassland, New Mexico, USA

AbstractQuestionsAnts and rodents are recognized as ecosystem engineers worldwide creating soil‐modified nests and adjacent edges with superior resources. The influence of Dipodomys spectabilis (rat) and Pogonomyrmex rugosus (ant) on nests and edges would be similar in burned and unburned habitat on functional groups’ cover, density, number of inflorescences and species number. We hypothesize that annual and perennial dicots would recover faster on rat patches than on burned grassland, dicots and grasses would recover faster on ant patches than on burned grassland, and annual dicots would recover faster on rat than on ant patches, whereas grasses would recover faster on ant than on rat patches.LocationSemiarid grassland, Sevilleta National Wildlife Refuge, New Mexico, USA.MethodsWe analyzed annual and perennial dicots, grasses and subshrubs in burned and unburned plots at 80 nests during cool‐ and warm‐seasons two years post‐fire. Data were collected at nest top (mound), edge, and 20 m (control) from the edge.ResultsCover, density and species richness of different functional groups were low on animal mounds in unburned and burned plots. Ant edges had greater perennial dicot cover, grass cover and richness while rat edges had lower grass density and richness than control sites at unburned and burned plots. Perennial dicot density and richness recovered faster at rat mounds and edges than control. Ant edges yielded faster recovery of grass inflorescences than control. Dicots recovered faster on rat than ant mounds whereas grasses grew faster on ant edges.ConclusionsRats create nests enhancing density of recovering dicots and ant edges facilitate reproduction of recovering grasses. Equal regeneration between animal nests and grassland occurred commonly when fire reduced grass competition. Dysochory, granivory and fire intensity may influence recovery. Nests may be sources of reestablishment and seed dispersal. Recovery of grassland may be amplified as plants infill from engineered nests.

Willow tree-like functional groups modified magnetic nanoparticles for ultra-high capacity adsorption of dye

Abstract In this paper, magnetic nanoparticles (MNPs) modified with willow tree-like functional groups were designed and prepared by grafting polyethyleneimine (PEI) chain on the poly glycidyl methacrylate (PGMA) polymer chain anchored on the magnetic nanoparticles, named as Fe3O4-g-PGMA-g-PEI. Quantitative measurement of surface groups and adsorption performance test showed that these nanoparticles with willow tree-like modification (28.30 mmol/g) had much higher surface functional groups density than magnetic nanoparticles with PGMA polymer chains by ethylene diamine (EDA) (Fe3O4-g-PGMA-EDA) (16.98 mmol/g). The Congo red (CR) adsorption was significantly pH dependent. The adsorption process followed the pseudo-second-order kinetics (R2 = 0.9999) and Langmuir isotherm model (R2 = 0.9924). The developed adsorbent showed ultrahigh maximum adsorption capacity for CR (2047.5 mg/g), and fast adsorption rate (the equilibrium within 1 min). The regeneration study proved that the nano-adsorbent could be repeatedly utilized without significant loss of adsorption efficiency. The developed nanoadsorbents are a promising efficient adsorbent for removal of CR from wastewater.

Structural design of a high sensitivity biomass cellulose-based colorimetric sensor and its in situ visual recognition mechanism for Cu2+

A novel biomass cellulose-based colorimetric sensor (DAC-PDH) was prepared by a Schiff base reaction between the aldehyde groups of dialdehyde cellulose (DAC) and the amino groups of 2,6-pyridine dihydrazide (PDH). The as-prepared sensor (DAC-PDH) showed selective recognition of Cu2+ and a visual colour change from white to green. The visual limit of detection for Cu2+ was 10−7 mol/L. Furthermore, DAC-PDH responded to Cu2+ within 30 s by the method of dynamic condition. The sensor possessed the properties of a high density of functional groups (CO, NH, NH2), a large external surface area, a short transit distance and flexibility; thus, Cu2+ can be rapidly absorbed and enriched on the DAC-PDH through multi-dentate ligand chelation between Cu2+ and the carbonyl groups (CO) and the amino groups (NH, NH2) of DAC-PDH. The as-prepared DAC-PDH colorimetric sensor exhibits promising prospects for in situ identification of Cu2+.

Effects of oxidation degree on photo-transformation and the resulting toxicity of graphene oxide in aqueous environment

Graphene oxide (GO) has been demonstrated to be key component for diverse applications. However, their potential environmental reactivity, fate and risk have not been fully evaluated to date. In this study, we investigated the photochemical reactivity of four types of GO with different oxidation degrees in aqueous environment, and their related toxicity to two bacterial models Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was further compared. After UV-irradiation, a large amount of oxygen functional groups on GO were reduced and the electronic conjugations within GO were restored as indicated by UV–visible absorption spectra, X-ray photoelectron spectroscopy and Raman spectroscopy analysis. Moreover, the higher the oxidation degree of the pristine GO was, the more obvious of the photo-transformation changes were. In order to further reveal the photochemical reactivity mechanisms, the reactive oxygen species (ROS) generation of GO was monitored. The quantity of ROS including singlet oxygen (1O2), superoxide anions (O2·-), and hydroxyl radicals (·OH) increased with increasing oxidation degree of GO, which was in accordance with the previous characterization results. Scanning electron microscopy and cell growth analyses of E. coli and S. aureus showed that the photochemical transformation enhanced the toxicity of GO, which might be due to an increase in functional group density. The higher conductivity of the reduced graphene oxide (RGO) was responsible for its stronger toxicity than GO through membrane damage and oxidative stress to bacteria. This study revealed that the oxidation degrees play important roles in photochemical transformation and the resulting toxicity of GO, which is helpful for understanding the environmental behaviors and risks of GO in aquatic environments.

Formaldehyde adsorption in carbon nanopores – New insights from molecular simulation

Adsorption of formaldehyde is profoundly affected by both the pore structure and the surface chemistry of an adsorbent. Understanding the mechanism of adsorption of formaldehyde in carbonaceous materials at the molecular level is instrumental for the rational design of suitable adsorbents. While most experimental studies have focused on the synthesis and modification of adsorbent materials, the key question of how formaldehyde adsorbs at the microscopic level remains unanswered. To this end, we have conducted a comprehensive Monte Carlo simulation of formaldehyde adsorption in functionalized carbon nanopores and have compared our molecular model with experimental data. The effects of the functional group density and distribution, pore size, and temperature were investigated with the detailed analysis of the isotherm, the isosteric heat and the density distribution, and we particularly highlight the importance of the guest-guest and guest-host interactions. Our investigation also includes a special study of adsorption at ultralow pressures, typically found in practical applications, and provides insight in the search for an effective and water-resistant adsorbent for formaldehyde.

Early hMSC morphology and proliferation on model polyelectrolyte multilayers.

Polyelectrolyte multilayers (PEMs) are a category of materials commonly used as coatings on surfaces that interact with cells. The properties of PEMs have been established to be controlled by not only polyelectrolyte choice, but by the identity of the initially applied (bottom) layer. In this work, 5-bilayer PEMs consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) were coated on gold-sputtered quartz substrates with different first layer materials. A final poly-l-lysine (PLL) layer was added to all PEMs to provide identical top layers conducive to cell growth. As in previous work, initial layer selection affected PEM roughness. All coated surfaces, including the PLL-only control, showed increased dispersive surface energy but decreased polar surface energy, as compared to uncoated surfaces. When human mesenchymal stem cells (hMSCs) were cultured on these surfaces, analysis through lateral cell imaging for the first 90 min and fluorescent staining after 1 day showed improved attachment on surfaces with a PDADMAC bottom layer. However, after 4 days, a higher cell density was observed on the PLL-only and uncoated control surfaces, indicating that the PEMs negatively affected hMSC proliferation. Both the long and short time period results did not correlate to any of the roughness and surface energy trends, indicating more complex interactions between the cells and the surface relating to charge distribution and functional group density.

Understanding fouling dynamics on functionalized CNT-based membranes: Mechanisms and reversibility

Herein, we explored resistance to fouling and the bactericidal potential of a functionalized carbon nanotube (CNT)-based polyvinylidene fluoride (PVDF) membrane. Humic acid (HA), a main constituent in natural organic matter was used as an indicator for the estimation of organic fouling, while Escherichia coli was employed as a model bacterium for biofouling investigation. In-situ fouling characterization was performed using a non-destructive optical coherence tomography. Results revealed that a thin CNT layer on the PVDF surface effectively prevented HA molecules from interacting directly with the porous structure of membrane, thereby averting the possibility of pore blockage (irreversible fouling). Moreover, the CNT membranes offered higher permeability, increased HA rejection, and better flux restoration capacity as compared with pristine PVDF membrane. This superior anti-HA-fouling performance of CNT membrane was accredited to the electrostatic repulsions between the CNT layer and HA molecules, both carrying a strong negative charge and high density of hydrophilic functional groups on the CNT surface. Antibacterial results from the ultrastructural examination of cell membrane integrity authenticate the bactericidal potential of CNT membrane toward biofouling causing bacteria. Finally, when tested with real sea water, CNT membrane with less organic and biofouling propensity outperformed commercial PVDF, indicating their suitability for seawater reverse osmosis (SWRO) pretreatment.

Nanotubols under H2O2 exposure: is it possible to poly-hydroxylate carbon nanotubes?

We present a combined experimental and theoretical study dedicated to analyze the variations in the surface chemistry of hydroxylated multiwalled carbon nanotubes (MWCNTs), so called nanotubols, when exposed to H2O2 at high temperatures. The formation, surface density, and distribution of oxygen-containing functional groups are studied by infrared (IR) and X-ray photoelectron spectroscopy (XPS), as well as density functional theory (DFT) calculations performed on model functionalized carbon nanotubes (CNTs). After H2O2 exposure, the initial composition of -OH, -C[double bond, length as m-dash]O, and -COOH substituents notably changes, with carbonyl -C[double bond, length as m-dash]O groups being the ones that show the most notable increase on the carbon surface. Our highly oxidized MWCNTs are partially soluble and form complex two-dimensional patterns at the air-water interface, as evidenced by Brewster angle microscopy. In a second step, these films can be transferred to solid substrates to form porous multilayered carbon nanostructures with complex morphologies. In particular, and for the first time, we report the synthesis of "stadium-like" configurations made of MWCNT units whose formation and stability are a direct consequence of the self-assembly process occurring at the air/water interface. DFT calculations suggest the formation of molecular islands of oxygen-containing functional groups on the CNT surface. In addition, nudged elastic band studies reveal that, for these adsorbed phases, the reaction between two neighboring OH groups to produce atomic oxygen and a physisorbed water molecule is characterized by energy barriers of ∼0.2 eV. These small values could be at the origin of the sizable increase in chemisorbed single-oxygen species determined by XPS data after H2O2 treatment at 60 °C. The simulation of the C 1s binding energies (BE) allows us to more clearly identify the different oxygen-containing functionalities as well as to reveal how the local atomic environment affects their characteristic BEs. Even if we were unable to polyhydroxylate our carbon nanotubes, we believe that H2O2-treated MWCNTs are interesting materials for more complex post-functionalization procedures that might lead to the fabrication of novel carbon nanostructures.

Sequential Nucleophilic "Click" Reactions for Functional Amphiphilic Homopolymers.

Amphiphilic homopolymers with high densities of functional groups are synthetically challenging. Thiol-yne nucleophilic click reactions have been investigated to introduce multiple functional groups in polymers with high density. An electron deficient alkyne group bearing methacrylate monomer was polymerized using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Subsequently, the electron deficient alkyne group on polymer side chain was readily reacted with a thiol reagent using triethylamine (TEA) as the organocatalyst. This reaction was found to be very efficient under mild conditions. The resultant homopolymer bearing thiol vinyl ether functional groups could perform a second thiol addition with a stronger base, such as triazabicyclodecene (TBD), to prepare multifunctional homopolymers. This stepwise addition process was monitored by 1H NMR as well as gel permeation chromatography. The fidelity of this method was demonstrated by attaching four different functionalities, including both hydrophobic and hydrophilic moieties. Furthermore, these dual functionalized polymers bearing dithio-acetal groups are sensitive to reactive oxygen species (ROS), which compromises the host-guest properties of the assembly in response to this stimulus. The ROS responsive polymers reported here may have potential use in therapeutic delivery.

Design and Application of Cisplatin-Loaded Magnetic Nanoparticle Clusters for Smart Chemotherapy.

One of the major challenges of drug delivery is the development of suitable carriers for therapeutic molecules. In this work, a novel nanoformulation based on superparamagnetic nanoclusters [magnetic nanocrystal clusters (MNCs)] is presented. In order to control the size of the nanoclusters and the density of magnetic cores, several parameters were evaluated and tuned. Then, MNCs were functionalized with a polydopamine layer (MNC@PDO) to improve their stability in aqueous solution, to increase density of functional groups and to obtain a nanosystem suitable for drug-controlled release. Finally, cisplatin was grafted on the surface of MNC@PDO to exploit the system as a magnetic field-guided anticancer delivery system. The biocompatibility of MNC@PDO and the cytotoxic effects of MNC@PDO-cisplatin complex were determined against human cervical cancer (HeLa) and human breast adenocarcinoma (MCF-7) cells. In vitro studies demonstrated that the MNC@PDO-cisplatin complexes inhibited the cellular proliferation by a dose-dependent effect. Therefore, by applying an external magnetic field, the released drug exerted its effect on a specific target area. In summary, the MNC@PDO nanosystem has a great potential to be used in targeted nanomedicine for the delivery of other drugs or biofunctional molecules.

A Stretchable Strain-Insensitive Temperature Sensor Based on Free-Standing Elastomeric Composite Fibers for On-Body Monitoring of Skin Temperature.

To realize the potential applications of stretchable sensors in the field of wearable health monitoring, it is essential to develop a stable sensing device with robust electrical and mechanical properties in the present of varying external conditions. Herein, we demonstrate a stretchable temperature sensor with the elimination of strain-induced interference via geometric engineering of the free-standing stretchable fibers (FSSFs) of reduced graphene oxide/polyurethane composite. The FSSFs were formed in serpentine structures and enabled the implementation of a strain-insensitive stretchable temperature sensor. On the basis of the controlled reduction time of graphene oxide, we can modulate the response and thermal index of the device. These results are attributed to the variation in the density of oxygen-containing functional groups in the FSSFs, which affect the hopping charge transport and thermal generation of excess carriers. The FSSF temperature sensor yields increased responsivity (0.8%/°C), stretchability (90%), sensing resolution (0.1 °C), and stability in response to applied stretching (±0.37 °C for strains ranging from 0 to 50%). When the sensor is sewn onto a stretchable bandage and attached to the human body, it can detect the temperature changes of the human skin during different body motions in a continuous and stable manner.

Optimizing the Coverage Density of Functional Groups over SiO2 Nanoparticles: Toward High-Resistant and Low-Friction Hybrid Powder Coatings.

Hybrid powder coatings (HPC) with low friction and high hardness enhance the sliding speed and allow interlocking or meshing products to slide effortlessly within each other, saving energy. In automobiles, they decrease fuel consumption and greenhouse gas emission. In the present work, a new insight of the key role played by the coverage density of triethoxyphenylsilane (TPS) grafted to SiO2 nanoparticles over the friction coefficient, hardness, elastic modulus, and roughness of HPC is presented for the first time. In all cases, a very low amount (0.1 wt %) of functionalized or unfunctionalized SiO2 nanoparticles were added to a powder-coating formulation based on polyester resin. HPC formulated with functionalized nanoparticles at a suitable coverage density (HPC–TPS3) exhibited significantly low friction coefficient (μ = 0.12), strong wear resistance (under dry sliding conditions at 1 and 5 N of load), low roughness (Rq = 3.5 nm), and high hardness and elastic modulus on the surface. We demonstrated that it is possible to tune the macroscopic properties by varying only the coverage density of TPS that is chemically attached to SiO2 nanoparticles. Also, a physicochemical explanation was disclosed, wherein a hydrophilic–hydrophobic balance between −OH and phenyl groups was proposed. In all cases, the phenyl group allows the migration of functionalized nanoparticles through the polyester matrix, enhancing the hardness and elastic modulus on the surface. Thus, the functional nanomaterial design with tunable coverage density is a powerful tool to improve the physical and superficial properties of powder coatings using low amounts of nanomaterial.

Functionalized TiO2 Surfaces Facilitate Selective Receptor-Recognition and Modulate Biological Function of Bone Morphogenetic Protein-2

Titanium dioxide (TiO2) is a promising biomedical material because it can be modified with various functional groups. However, the mechanism of the interaction between functionalized TiO2 and biomolecules, especially how the modified TiO2 regulates subsequent protein functions, still needs further investigation. In this study, we studied the interaction of bone morphogenetic protein-2 (BMP-2) with hydroxyl- and phosphite-grafted TiO2 surfaces. A set of force field parameters was developed for hydroxyl and phosphite groups on TiO2 surfaces, and the adsorption energy between the surface of the functionalized TiO2 and BMP-2 was calculated. Different coverages of functional groups were applied to the surface to investigate the influence of the functional group density. Grafting phosphite groups on the surface of TiO2 can significantly increase the adsorption energy of the protein and change the orientation of BMP-2 so that the wrist epitope of the BMP-2 molecules is pointing upward. This configuration specifically binds to the BMP receptor type-I on the cell membrane and activates the SMAD1/5/8 signaling pathway for the purpose of enhancing the expression of bone growth and regeneration-related protein. This study shows that it is possible to regulate the function of a protein by deliberately modifying the material surface, which can guide the design of new materials through function-oriented surface modification.

On the intriguing emission characteristics of size tunable carbon dots derived from functionalized multi-walled carbon nanotubes

Abstract Aqueous dispersions of carbon dots (C-dots) showing size tunable multi-colours in day light are obtained through surface functionalization of multi-walled carbon nanotubes (MWCNTs). The size of the C-dots varies with the functionalization temperature and smaller C-dots are found to be formed, at higher temperatures. The average size of the C-dots synthesized at temperatures of 100 °C, 80 °C and 60 °C lies in the range 6 nm–18 nm, based on transmission electron microscopy (TEM) images. The C-dots synthesized at these temperatures exhibit blue, green and golden yellow colours in day light without being excited by any external source. The structural characterizations using X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy confirm the presence of a high density of functional groups on the surfaces of the C-dots, giving rise to high aqueous solubility. Compared to the Raman spectrum of the MWCNTs, the spectrum of the C-dots shows a significant increase in the intensity of the defect related D band with respect to that of the crystalline G-band, which indicates the presence of a high concentration of defects and the formation of smaller sp2 carbon clusters. The synthesized C-dots exhibit size dependent optical absorption and emission characteristics. The intriguing optical properties of these C-dots, which include the multi-colour emission at day light and the excitation wavelength and the pH dependent photoluminescence emission, can be mainly attributed to the formation of sp2 clusters of different sizes embedded in the sp3 carbon matrix.

A Review of Nickel, Copper, and Cobalt Recovery by Chelating Ion Exchange Resins from Mining Processes and Mining Tailings

Copper and cobalt can be found on nickel laterite ores, and cobalt can be found also on copper ores, and many contaminants such as iron, aluminum, and magnesium are associated with these ores. In hydrometallurgical process, a purification step is necessary after leaching due to the presence of these impurities. Chelating resins are more selective for some metals than others, making them more efficient than cationic resins. This overview discusses chelating resin applications to recover copper, nickel, and cobalt from mining process and mining tailings and the effect of contaminants in leach solution. Chelating resins with iminodiacetate functional group can be used for selective copper recovery, and both iminodiacetate and bis-picolylamine resins are highly selective for nickel and cobalt. Chelating resins with the same functional group can have different performances on the kinetics of loading, because of variations of structure, the density of functional group, and degree of cross-linking. This article reviews commercial chelating resins that can be applied in leach solutions with different compositions, and also possible innovations for uses of chelating resins to recover metals from mining process and mining tailings.

Influence of pyrolysis temperature on production of digested sludge biochar and its application for ammonium removal from municipal wastewater

Water contamination by ammonium (NH4+) can present considerable risks to natural ecosystems. This work evaluates the potential application of biochar, produced from the pyrolysis of digested sludge, to remove ammonium from water. Anaerobic digester sludge was collected from a municipal wastewater treatment plant in Alberta, Canada, and individual biochars were produced at 50 °C temperature increments between 350 °C and 550 °C. The chemical characteristics of the resulting biochars were determined using elemental analysis, scanning electron microscopy (SEM), BET surface area analysis, and Fourier transform infrared spectroscopy (FTIR). Our findings demonstrate that the biochar yield decreased with increasing pyrolysis temperature, and biochar produced at 450 °C (BC450) had the highest ammonium removal capacity due to its higher surface area and functional group density. The Langmuir isotherm best described the observed ammonium removal capacity by the biochars, indicating that monolayer chemical adsorption may be the dominating mechanism. Biochar ammonium removal capacity was 1.2 mg NH4N per gram of biochar in municipal wastewater, which is lower than that observed in parallel experiments using a synthetic ammonium solution (1.4 mg NH4+-N/g biochar). This phenomenon is likely due to competition between ammonia and other containments for sorption to biochar surface sites. Our results demonstrate for the first time ever that biochar produced from digester sludge is a promising adsorbent for ammonium removal from municipal wastewater.

Development of a NanoLC-MS/MS System Using a Nonporous Reverse Phase Column for Ultrasensitive Proteome Analysis.

The design of proteome projects is often restricted by the available amounts of sample, and thus there has been much effort to date to improve the sensitivity of proteome analyses. We have developed a new ultrasensitive nanoLC-MS system for the proteome analysis of microscale samples using a nonporous reverse phase column. Although nonporous particles have low binding capacity due to low functional group density, we found that the use of C30 particles compensated for this disadvantage and nanoLC-MS proteome analyses of microscale samples using a C30-packed column exhibited superior performance compared to the use of porous C18 columns. This system enabled us to identify 3278 and 1407 proteins from 1000 and 100 HEK293F cells, respectively. The results showed that the use of nonporous columns solved problems intrinsic to the analysis of microscale protein samples.

Fabrication of terminal amino hyperbranched polymer modified graphene oxide and its prominent adsorption performance towards Cr(VI).

In order to increase the density and quantity of functional groups on adsorbent, three terminal amino hyperbranched polymer modified graphene oxide adsorbents including GO-HBP-NH2-DETA, GO-HBP-NH2-TETA and GO-HBP-NH2-TEPA with N-containing functional group density of 7.21 wt%, 10.20 wt% and 12.43 wt%, respectively, were prepared and used for the adsorption and reduction of toxic hexavalent chromium Cr(VI) to less toxic Cr(III). The morphology and structure of obtained adsorbents were characterized by FT-IR, SEM, XRD, Raman, BET, XPS and zeta potential. The density of receptor sites (Nm) of the three adsorbents calculated from statistical physics model with one energy site were found to be 456.62, 604.54 and 636.03, respectively. Adsorption experiments demonstrated that the high adsorption capacities of the three adsorbents obtained from Langmuir isotherm model towards Cr(VI) were 245.01, 257.26 and 300.88 mg/g, respectively, suggesting that GO-HBP-NH2-TEPA had better adsorption ability. The density functional theory calculation (DFT) indicated that GO-HBP-NH2-TEPA was more likely to adsorb HCrO4- rather than Cr2O72- at lower pH conditions. A possible adsorption mechanism was also proposed where electrostatic interaction between Cr(VI) (HCrO4- or Cr2O72-) and the N functional group (+) on GO-HBP-NH2-TEPA dominated the adsorption of Cr(VI) and reduction mechanism dominated the reduction of Cr(VI)-Cr(III).