Colloidal Water Research Articles

A dynamic model describing the effects of soil moisture on mercury speciation and migration in the plow layer

ABSTRACTA dynamic model was constructed to predict the effects of soil water movement on changes and migration of available mercury (Hg) in various layers of different soil types. Various soil types were placed in large boxes. The available Hg content was then determined in vertical layers of the soils. Simultaneously, changes in the equilibrated available Hg content with evaporation were measured. Capillary water absorption was used to maintain the soil water holding capacity. The results were as follows. 1) Soil available Hg migrated upward or downward along with water movement, achieving a stable downward migration rate of 23.5%–35.3% and an upward migration rate of 17.4%–33.3%. The migration rate of available Hg owing to water movement was in the order of sandy loam > loam > clay loam. 2) Under different soil water holding capacities, when migration reached equilibrium, the increase in the amount of bound Hg, which was desorbed into available Hg, was 1.2%–14.3% of the initial available Hg content, and this increase was in the order of sandy loam > loam > clay loam. Based on these findings, a dynamic model describing the effects of soil moisture on Hg speciation and migration in the plow layer was constructed. The model is a true reflection of the impact of variations in soil characteristics (e.g., particle size, organic matter content, pH value, water movement vector, mineral composition, and colloid properties.) with time. This model can provide new insight into the speciation transformation and distribution of Hg. It can also be applied in risk evaluation in remediation of heavy metal contaminated soils.

Synthesis of graphene-like phases in a water colloid by laser ablation of graphite

The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation to highly purified microcrystalline graphite targets immersed into a water medium. The fundamental wavelength, the second and the fourth harmonic wavelengths of a Nd:YAG laser system (λ = 1064 nm) were used. The morphology of the particles dispersed in water was studied by scanning electron microscopy. Their phase composition and structure were explored by SEM, Raman and XP spectroscopy, GIXRD, as well as TEM. We establish that besides of the main phases of reduced graphene oxide (rGO) with flakes of micro- to nano-sized area and graphite micro-particles, the colloids contain some graphene oxide and defected, multilayered and folded multilayered graphene. The spacing of {0 0 1} increases by about 5–

Effects of Early Structural Changes of Engineered Soils on Green Roof and Bioretention Performance

Engineered soils play an important role in urban hydrology e.g. in the functioning of green roofs and storm water bioretention beds. Water infiltration, colloid transport and heat transport are affected by changes in pore system geometry particularly due to development of macropores and clogging by particles. The rate of pedogenesis is often faster than in natural soils due to higher loads of particles as well as by extreme water regimes. In the presented project we assess the temporal changes of hydraulic properties of engineered soils in typical bioretention beds and green roofs by conducting field scale experiments. The aim is to elucidate changes in hydraulic properties by studying the structural changes of soils at the microscale by invasive and noninvasive methods. The outcomes of the research will lead to improved design and management procedures for green roofs and bioretention beds.

Facile synthesis of cerium-doped carbon quantum dots as a highly efficient antioxidant for free radical scavenging

Excessive reactive oxygen species (ROS) can lead to irreversible damage to the human body in vivo, therefore it is highly desirable to exploit an efficient antioxidant. Recently, cerium oxide nanoparticles have attracted extensive attention in the field of biomedicine due to their excellent antioxidant properties. In this study, cerium-doped carbon quantum dots (Ce-doped CQDs) with hydroxyl radical scavenging capacity were synthesized for first time by one-step hydrothermal carbonization method. The resultant Ce-doped CQDs with the average particle size of 2.5 nm possessed the properties of good water solubility, colloid stability, and strong fluorescence, which are similar to traditional CQDs. Meanwhile, the Ce-doped CQDs had good biocompatibility and negligible cytotoxicity. Taking advantage of inherent ultra-small size, the Ce-doped CQDs exhibited a high Ce3+/Ce4+ ratio at the surface of particles. The radical scavenging capability of the Ce-doped CQDs was proved by a simple photometric system in vitro, which provided direct evidence for its antioxidant potency. Furthermore, the Ce-doped CQDs had a high ability to protect cells from hydrogen peroxide-induced damage by scavenging hydroxyl radicals. These results suggest that Ce-doped CQDs as a new ROS scavenger may provide potential prospects for the treatment of oxidative stress-related diseases.

Quantification of ZnO nanoparticles and other Zn containing colloids in natural waters using a high sensitivity single particle ICP-MS

Inductively coupled plasma mass spectrometry in single particle mode (SP-ICP-MS) is becoming a powerful tool of choice for the quantification and characterization of metallic nanoparticles (NP) at very low concentrations. Nonetheless, this technique has relatively high size detection limits for highly soluble nanoparticles (e.g. ZnO, CuO) or NP that are measured in the presence of high background concentrations of dissolved metal. In order to evaluate whether SP-ICP-MS could be used to measure a soluble NP under environmentally relevant conditions, an ion-exchange column (IEC) was coupled to a highly-sensitive sector-field ICP-MS (IEC-SP-ICP-MS) and then used to detect both spiked ZnO NP and natural Zn containing colloids in natural waters. The use of an ion exchange column, short dwell times (50 µs) and a high sensitivity instrument gave size detection limits for the measurement of ZnO NP of ca. 8.2 nm in pure water, 14.3 nm in a river water and 17.7 nm in a rainwater. IEC-SP-ICP-MS measured ca. 4.4 × 105 mL−1 zinc containing particles in a river water sample and ca. 1.0 × 105 mL−1 particles in a local rainwater.

Colloid clogging of saturated porous media under varying ionic strength and roughness during managed aquifer recharge

Abstract Column experiments were conducted to examine the clogging effects of colloids under controlled conditions of solution ionic strength (IS) and porous media roughness. The results showed that colloids in recharge water play an important role in the clogging process of saturated porous media, such that even a small amount of colloid may cause a large reduction in the permeability of the porous medium. Clogging at the pore throat was inferred to be the main reason for the severe permeability reduction of porous media. The characteristics of colloid clogging were clearly influenced by both IS and medium roughness. Recharge water with a higher IS facilitated greater attachment of colloids to the surface of the saturated porous medium, which lead to superficial clogging, while collectors with a rough surface resulted in greater clogging than collectors with a smooth surface.

Technology of drinking water preparation using the reactor - clarifier

Siberian surface water and groundwater are characterized by low temperatures for a long year period. Many groundwater sources’ organic composition are formed of soil and peat humus, marsh feeding of rivers, decomposition of plankton, higher water, and soil grass in reservoirs and lakes. Organic colloids in natural waters and in humic substances give the color of water. It’s yellowish coloration of varying intensity. Thus, the Om River’s water color in the city of Kuibyshev in the Novosibirsk Region is 500 degrees with feculence of less than 3 mg/l. A number of underground water sources also have an increased content of organic contaminants caused by peat bogs at great depths and high water colority with low turbidity. For example, the water color is up to 1500 degrees in the Namtsy village of the SAHA-Yakutia Republic. In addition, underground water and, to a greater extent, surface water are often characterized by a high content of iron (up to 20 mg/l), manganese (up to 4 mg/l), and other impurities of natural and anthropogenic origin. Iron and manganese are in natural waters in the form of mineral or organic complex compounds of humic or some fatty acids. In the second case, these waters are with increased oxidizability and rather aggressive nature. In particular, the iron content is 3 mg/l, manganese is 1 mg/l, the permanganate oxidizability is 50 mg/l in the water of the Om River.

Chemical sensing of water contaminants by a colloid of a fluorescent imine-linked covalent organic framework.

A two-dimensional imine-linked covalent organic framework bearing pyrene has been prepared and exfoliated in water as nanosheets to produce a stable water colloid. As a proof-of-concept, this COF colloid has been used to detect the presence of several organic dyes and polynitro-aromatic derivatives. These results show the high potential of these nanomaterials for applications in chemical sensing of pollutants directly in water.

Particle tracer transport in a sloping soil lysimeter under periodic, steady state conditions

Colloid transport through complex and dynamic (i.e. non-steady-state) hydrologic systems is rarely studied, owing to the difficulty of constraining initial and boundary conditions and quantifying colloid-porous media and colloid-colloid interactions in transient flow systems. Here we present a particle tracer experiment conducted on a sloped lysimeter receiving periodic rainfall events for 10 days. Four unique, DNA-labelled particle tracers were injected both in sequence and in parallel, together with a conservative tracer (deuterium), over the course of the first day and allowed to move through the system. Discharge-particle tracer concentration curves and the spatial distribution of particle tracer mass retained in the soil at the end of the experiment were found to be highly dependent on the timing of the tracer injection and the precipitation input and subsequent dynamic response of the water table. Overall, neglecting the total DLT recovery rate, the DLT particle tracer breakthrough trend (DNA-labelled particle tracer 4) was similar to deuterium and decreased over time with the exception of a few peaks later in the experiment. The individual particle tracer breakthrough curves suggest a complex system with different fast transport mechanisms (e.g. capillary barrier and size exclusion effect) and slow retention-release mechanisms (e.g. straining, physical-chemical adsorption), which resulted in particle tracers transferring faster than deuterium in the first 10 h of the experiment but being exceeded by deuterium soon after deuterium started to break through. The experiment not only highlights the interaction of repeated colloidal pollution events in hydrologic systems with different pre-event saturation conditions, but also the benefits of using multiple synchronous or sequential tracer applications to dissect explicit formulations of water flow and colloid transport processes in complex and dynamic hydrological systems. Such explicit process formulations could help improve understanding hydrologically-controlled transport through catchments and the quantitative prediction of these processes with water quality models.

Does sulfur fertilizer influence Cu migration and transformation in colloids of soil pore water from the rice (Oryza sativa L.) rhizosphere?

Colloids are ubiquitous in soils, and it has been reported that colloids can act as carriers to increase the mobility of poorly soluble contaminants in subsurface environments. Addition of sulfur (S) fertilizer greatly influences on heavy metal behavior in paddy soil, while the influence of S fertilizer on Cu migration and transformation in colloids of soil pore water has not yet been studied. The influence of S fertilizer (S0 and Na2SO4) applied in paddy soils on Cu migration and transformation in colloids of soil pore water from the rice rhizosphere region was explored in this study. The speciation of Cu in colloids of soil pore water from the rice rhizosphere region was explored by advanced synchrotron-based X-ray absorption near-edge spectroscopy (XANES) techniques. The morphology of colloids was characterized by field emission scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX). At a depth of 20 cm, the concentration of Cu in colloids of the rhizosphere soil pore water in the control was 2.4- and 6.5- fold higher than that in treatments of S0 and Na2SO4, respectively. The colloids in soil pore water were all positively charged, ranging from 2.4 to 7.8 mV, and the size of colloids was 440–740 nm. The proportion of Fe in colloids in the rhizosphere region decreased with S fertilizer application, while the proportions of C and O increased. Sulfur fertilizer application, increased the proportion of Cu-Cysteine, while the proportion of Cu2S decreased in soil colloids. In conclusion, application of sulfur fertilizer in paddy soil decreased the Cu concentration in soil pore water and colloids of the rhizosphere region, thereby decreasing the vertical migration of Cu in soil pore water.

Geochemistry of Al and Fe in freshwater and coastal water colloids from the west coast of Southern Africa

Suspended iron-rich colloids play an important role in nutrient and contaminant transport in fluvial systems, and may ultimately provide an important source of Fe which is required for marine biological productivity. Despite being fundamental to Fe colloid behaviour in biogeochemical systems, the physical and chemical characteristics of these colloids are poorly constrained, especially at the molecular level. Here we combine traditional chemical extraction techniques with X-ray Absorption Near-edge Structure (XANES) spectroscopy to investigate and compare the bulk and molecular-level speciation of Fe and Al in suspended colloids from fluvial (Berg, Olifants and Orange Rivers) and marine sampling sites on the western margin of Southern Africa. The bulk extraction methodology shows a variable distribution of Fe among five different operationally-defined Fe pools, yet our spectroscopy results reveal that the majority of particles in the 10 nm–4 µm size fraction do not match crystalline or residual Fe spectral signatures and are thus likely to be poorly-crystalline. Aluminium K-edge XANES reveals that the Al coordination environment in aquatic colloids is diverse (e.g., relative to oxo ligands, the number of coordinated OH− ligands ranges between 0 and 6), and that the smallest sized colloids are always highly hydroxylated (i.e., their coordination environment is similar to Al in Al(OH)3 or 1:1 clays). The Al XANES further reveals a common association between Al and Fe-rich colloids, where the average measured Al/Fe ratio is 0.10 (±0.09) among all the particles measured in this study. The Al that co-occurs with Fe preferentially has a coordination environment similar to Al in 1:1 clays (i.e., two oxo ligands and four hydroxyl ligands), either further implying the amorphous nature of the Fe colloids or reflecting Al as surface complexes or as inclusions of nano-sized Al clusters. The observed high degree of disorder and the presence of Al association/substitution in iron-rich colloids observed in the Southern African systems will strongly influence the biogeochemical behaviour of these colloids (e.g., surface sorption capacity, solubility and dissolution rates). These findings contribute greatly to our understanding of natural Fe colloid and nanoparticle speciation and are anticipated to have global relevance to other aquatic systems in which ‘reactive’ or ‘poorly crystalline’ classes of suspended particulate Fe have been identified.

Sub-microsecond-resolved multi-speckle X-ray photon correlation spectroscopy with a pixel array detector.

Small-angle X-ray photon correlation spectroscopy (XPCS) measurements spanning delay times from 826 ns to 52.8 s were performed using a photon-counting pixel array detector with a dynamic range of 0-3 (2 bits). Fine resolution and a wide dynamic range of time scales was achieved by combining two modes of operation of the detector: (i) continuous mode, where data acquisition and data readout are performed in parallel with a frame acquisition time of 19.36 µs, and (ii) burst mode, where 12 frames are acquired with frame integration times of either 2.56 µs frame-1 or 826 ns frame-1 followed by 3.49 ms or 1.16 ms, respectively, for readout. The applicability of the detector for performing multi-speckle XPCS was demonstrated by measuring the Brownian dynamics of 10 nm-radius gold and 57 nm-radius silica colloids in water at room temperature. In addition, the capability of the detector to faithfully record one- and two-photon counts was examined by comparing the statistical distribution of photon counts with expected probabilities from the negative binomial distribution. It was found that in burst mode the ratio of 2 s to 1 s is markedly smaller than predicted and that this is attributable to pixel-response dead-time.

Colloid Transport in Aggregated Porous Media with Intra- and Interaggregate Porosities

Column tracer and colloid transport experiments were performed under both saturated and unsaturated steady state flow conditions in an aggregated porous medium with a bimodal pore size distribution (PSD): intra-aggregate porosity with a pore radius between 10–2 and 10–1 μm and interaggregate porosity ranged between 101 and 103 μm (interporosity). All experiments were carried out under unfavorable conditions for physicochemical attachment to solid–water interfaces, using negatively charged porous media and latex microspheres (1 μm). Both porous media and colloids used in this work were hydrophobic. The results obtained through experimental observations and numerical simulations in the aggregated medium were confronted with those obtained for a sandy medium, characterized by a narrow unimodal PSD with a pore radius which ranged between 101 and 102 μm (interporosity), to explore the relative importance of the PSD on water flow, colloid transport, and deposition. Physicochemical interactions between colloids ...

Study of the contrasting effectiveness of various tumors types using cubic magnetite nanoparticles

Currently magnetic resonance imaging (MRI) is one of the key diagnostics methods of various diseases. Utilizing various contrast agents based on magnetic nanoparticles can improve the diagnostic efficiency and, consequently, the quality of the subsequent treatment. The most promising contrast agents are cubic magnetite nanoparticles, due to their high relaxation rates, as well as biocompatibility and biodegradability. Thereby, the purpose of this work was to evaluate the effectiveness of MRI imaging of tumors by cubic magnetite nanoparticles (CMN). Materials and methods. For this purpose, the synthesis of 15 nm CMN modified with biocompatible copolymer plurlonic F127 was carried out. Synthesized CMN and their water colloids were characterized by a complex of physicochemical methods of analysis. Then, using MRI a study of the effectiveness of contrasting of various tumor types after intravenous administration of CMN aqueous colloids was made. Three models of mouse tumors were used for a comprehensive assessment of obtained results: breast cancer 4T1, colon cancer CT-26 and melanoma B16. MRI studies were performed prior to the administration of the particles, and also after 15 min, 6 hours and 24 hours after injection in T2-weighted regime in two mutually orthogonal projections. Results. The analysis of the obtained results showed that the most effective accumulation of particles was found in the 4T1 (100%) and B16 (57%) models, and in the case of CT-26 model the accumulation efficiency was 50% due to the effect of the permeability of blood vessels.

Elemental Composition of Natural Nanoparticles and Fine Colloids in European Forest Stream Waters and Their Role as Phosphorus Carriers

AbstractBiogeochemical cycling of elements largely occurs in dissolved state, but many elements may also be bound to natural nanoparticles (NNP, 1–100 nm) and fine colloids (100–450 nm). We examined the hypothesis that the size and composition of stream water NNP and colloids vary systematically across Europe. To test this hypothesis, 96 stream water samples were simultaneously collected in 26 forested headwater catchments along two transects across Europe. Three size fractions (~1–20 nm, >20–60 nm, and >60 nm) of NNP and fine colloids were identified with Field Flow Fractionation coupled to inductively coupled plasma mass spectrometry and an organic carbon detector. The results showed that NNP and fine colloids constituted between 2 ± 5% (Si) and 53 ± 21% (Fe; mean ± SD) of total element concentrations, indicating a substantial contribution of particles to element transport in these European streams, especially for P and Fe. The particulate contents of Fe, Al, and organic C were correlated to their total element concentrations, but those of particulate Si, Mn, P, and Ca were not. The fine colloidal fractions >60 nm were dominated by clay minerals across all sites. The resulting element patterns of NNP <60 nm changed from North to South Europe from Fe‐ to Ca‐dominated particles, along with associated changes in acidity, forest type, and dominant lithology.

Interfacial Areas in Athabasca Oil Sands

Determination of interfacial areas is crucial for accurate identification of multiphase subsurface flow processes, e.g., in situ water treatment, contaminant transport, phase change, convection/diffusion, and colloid adsorption/desorption/migration. Pore-scale imaging and simulation techniques provide an appealing opportunity to explicitly predict such geometrical characteristics of saturated and unsaturated porous media. Here, synthetic unconsolidated sand packs in a wide range of grain arrangements and size distributions are reconstructed to extensively capture all possible heterogeneous pore-level geometries in the McMurray Formation, the primary bitumen formation in the Athabasca oil sands deposit. Multiphase fluid occupancies throughout the partially saturated media during drainage and imbibition are predicted applying a direct pixel-wised pore morphological model, incorporating a wetting phase layer covering rock/solid surfaces. The postprocessing results are verified using two-phase experimental da...

Hydrophobic Effect of Alkyl Groups Stabilizing Self-Assembled Colloids in Water.

Self-assembling behavior of hydrophobic molecules in water confirms that the hydrophobic effect (HE) of alkyl groups stabilizes the aqueous colloids. Fe(CO){CO(CH2)n-1CH3}(Cp)(PPh3) molecules (FpCn) with a Fp head and alkyl tail are water-insoluble. FpC1 aggregates in water precipitated in hours, whereas the hydrophobic interaction (HI) of long alkyl groups drove FpCn (n = 6-18) molecules assemble into colloids in water. The alkyl tails interacted and stretched as indicated by IR analysis, while the separation of Fp head groups at the surface of colloids was indicated by the redox behavior of Fe elements. The molecules therefore arranged into a proposed "Y" shape with hydration cavities. The IR and cyclic voltammetry (CV) analyses indicated that the longer the alkyl tail, the larger the hydration cavity and the stronger the HI. Both HI and hydrophobic hydration (HH) were identified as the HE stabilizing the colloids in water. This knowledge is applicable for a broad range of disciplines, including biology, chemistry, and material science.

Temperature-Induced, Selective Assembly of Supramolecular Colloids in Water.

In this article, we report the synthesis and physical characterization of colloidal polystyrene particles that carry water-soluble supramolecular N,N′,N″,-trialkyl-benzene-1,3,5-tricarboxamides (BTAs) on their surface. These molecules are known to assemble into one-dimensional supramolecular polymers via noncovalent interactions. By tethering the BTAs to charge-stabilized particles, the clustering behavior of the resulting colloids was dictated by a balance between interparticle electrostatic repulsion and the BTA-mediated attractions. Through careful tuning of the dispersing medium’s ionic strength, a regime was found in which particle aggregation could be reversibly induced upon heating the dispersion. These findings clearly indicate that hydrophobic interactions, which become stronger upon heating, play an important role during the clustering process. Besides the thermoreversible nature of the generated hydrophobic interparticle attractions, we found the clustering to be selective, that is, the BTA-functionalized colloids do not interact with nonfunctionalized hydrophobic polystyrene particles. This selectivity in the association process can be rationalized by the preferred stacking of the surface-tethered BTAs. These selective intermolecular/particle bonds are likely stabilized by the formation of hydrogen bonds, as previously observed for analogous molecular BTA assemblies. The resulting driving force responsible for particle clustering is therefore dual in nature and depends on both hydrophobic attractions and hydrogen bonding.

Balance of O2 and H2 content under laser-induced breakdown of aqueous colloidal solutions

Formation of molecular H2 and O2 is experimentally studied under laser exposure of water colloidal solution to radiation of a Nd:YAG laser at pulse duration of 10ns and laser fluence in the liquid of order of 100J/cm2. It is found the partial pressure of both H2 and O2 first increases with laser exposure time and saturates at exposures of order of 1h. The balance between O2 and H2 content depends on the laser energy fluence in the solution and is shifted towards H2 at high fluences. Possible mechanisms of formation of the dissociation products are discussed, from direct dissociation of H2O molecules by electrons of plasma breakdown to emission of laser-induced plasma in liquid.

Electrochemistry of Aqueous Colloidal Graphene Oxide on Pt Electrodes

Graphene oxide (GO) has received tremendous attention over the past decade, in part because it enables a route which allows graphene to be produced from aqueous solutions, which potentially enables large-scale production of graphene-based devices. The structure of GO is a two-dimensional network of carbon atoms, similar to graphene. However, whereas pristine graphene is an uninterrupted network of sp2 carbon atoms, GO contains significant interruptions to the sp2 lattice caused by the introduction of oxygen species. It is this functionalization with oxygen groups which enables GO to be soluble in water and several other organic solvents. However, breaking the sp2lattice along graphene’s basal plane diminishes the material’s electronic properties. GO can be reduced to a graphene-like material using thermal, chemical, or electrochemical means to restore the electronic properties. The electron transfer properties of GO are thus of great interest and have been investigated either by studying the heterogeneous electron transfer between a GO electrode and a redox molecule in solution, by measuring the direct reduction of GO films on various electrode substrates, or measuring the electrochemical behavior of GO in solution. With the first technique, information about the electron transfer between a species in solution and the graphene material is obtained. This can provide heterogeneous rate constants, insight into the surface chemistry and reactivity, and general electroanalytical characteristics. These experiments are useful for understanding how the GO-based material will behave in applications such as sensing or fuel cells. Such detailed characterization of the electrochemical processes provides fundamental information about the direct electron transfer processes involved with the material itself and allows a deeper understanding of GO, thus maximizing its potential for future applications. Using the second strategy, GO films are prepared (e.g., by drop casting) and subsequently reduced electrochemically. With GO fixed to the electrode surface, the current−voltage response is governed by thin-film behavior and arises from the reduction of oxygen-containing functional groups such as epoxides, hydroxides, or peroxides. With this methodology, GO is not able to diffuse to and from the electrode surface, so information about its behavior in solution is lost. To date, only two communications show the electrochemical behavior of native graphene oxide colloids. Chen et al. showed that GO can be electrodeposited onto the surface of glassy carbon electrodes directly from colloidal solutions.1 Eng and Pumera showed that the voltammetry of GO colloids depends primarily on particle size and pH.2Both of these previous investigations were conducted using carbon electrode materials, which effects the observed voltammetry due to relatively inert nature of the carbon electrode surface. Here we report a voltammetric analysis of native GO colloids in water using Pt electrodes.3Although much is known about the physical structure of GO, there is still debate concerning GO’s exact chemical properties, especially its acidity in aqueous solutions. The electrochemistry of graphene oxide in solution is shown to be significantly different from the previously reported electrochemistry of surface-bound GO films. We show that suspensions of graphene oxide exhibit a reversible oxidation and reduction that is present under a variety of conditions. We investigate the origin of this response and provide a plausible mechanism for the electrochemical behavior of GO in solution. References (1) Chen, L.; Tang, Y.; Wang, K.; Liu, C.; Luo, S. Direct Electrodeposition of Reduced Graphene Oxide on Glassy Carbon Electrode and Its Electrochemical Application. Electrochem. Commun. 2011, 13(2), 133–137. (2) Eng, A. Y. S.; Pumera, M. Direct Voltammetry of Colloidal Graphene Oxides. Electrochem. Commun. 2014, 43, 87–90. (3) O’Neil, G. D.; Weber, A. W.; Buiculescu, R.; Chaniotakis, N. A.; Kounaves, S. P. Electrochemistry of Aqueous Colloidal Graphene Oxide on Pt Electrodes. Langmuir 2014, 30, 9599–9606.