Photochemical transformation of graphene oxide in sunlight

Photochemistry dominates over photothermal effects in the laser-induced reduction of graphene oxide by visible light

Graphene oxide (GO) possesses specific properties that are revolutionizing materials science, with applications extending from flexible electronics to advanced nanotechnology. A key method for harnessing GO's potential is its laser-induced reduction, yet the exact mechanisms - photothermal versus photochemical effects - remain unclear. Herein, we discover the dominant role of photochemical reactions in the laser reduction of GO under visible light, challenging the prevailing assumption that photothermal effects are dominant. Employing a combination of Raman thermometry, X-ray photoelectron and photoluminescence spectroscopies, and electrical atomic force microscopy, we quantify the temperature and map the reduction process across micro and nano scales. Our findings demonstrate that the photochemical cleavage of oxygen-containing groups below a reduction threshold temperature is a decisive factor in GO reduction, leading to distinct characteristics that cannot be replicated by heating alone. This work clarifies the fundamental mechanisms of GO transformation under visible laser irradiation, highlighting the dominant role of photochemical processes. Distinguishing these subtleties enables the development of laser-reduced GO platforms for graphene-based applications compatible with industrial scales. We illustrate this potential by encoding information on GO surfaces as optical storage, allowing us to write binary sequences in long-term memory encoding invisible even through an optical microscope.

Carbon Adsorbent Properties Impact Hydrated Electron Activity and Perfluorocarboxylic Acid (PFCA) Destruction

Carbon-based adsorbents used to remove recalcitrant water contaminants, including perfluoroalkyl substances (PFAS), are often regenerated using energy-intensive treatments that can form harmful byproducts. We explore mechanisms for sorbent regeneration using hydrated electrons (eaq -) from sulfite ultraviolet photolysis (UV/sulfite) in water. We studied the UV/sulfite treatment on three carbon-based sorbents with varying material properties: granular activated carbon (GAC), carbon nanotubes (CNTs), and polyethylenimine-modified lignin (lignin). Reaction rates and defluorination of dissolved and adsorbed model perfluorocarboxylic acids (PFCAs), perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), were measured. Monochloroacetic acid (MCAA) was employed to empirically quantify eaq - formation rates in heterogeneous suspensions. Results show that dissolved PFCAs react rapidly compared to adsorbed ones. Carbon particles in solution decreased aqueous reaction rates by inducing light attenuation, eaq - scavenging, and sulfite consumption. The magnitude of these effects depended on adsorbent properties and surface chemistry. GAC lowered PFOA destruction due to strong adsorption. CNT and lignin suspensions decreased eaq - formation rates by attenuating light. Lignin showed high eaq - quenching, likely due to its oxygenated functional groups. These results indicate that desorbing PFAS and separating the adsorbent before initiating PFAS degradation reactions will be the best engineering approach for adsorbent regeneration using UV/sulfite.

Photo-transformation of graphene oxide in synthetic and natural waters

Graphene oxide (GO) is widely employed due to its outstanding properties, leading to an increasing release into the environment and natural waters. Although some studies have reported on the photo-transformation of GO, its behavior in complex natural waters remains inadequately explored. This study demonstrates that different types of ions may promote the photoreduction of GO in the order of Ca2+ > K+ > NO3- > Na+ by interacting with the functional groups on the surface of GO, and the photoreduction is enhanced with increasing ion concentrations. Additionally, natural organic matter (NOM) can inhibit the photoreduction of GO by scavenging reactive oxygen species. However, with increasing NOM concentrations (≥ 5 mgC/L), more NOM adsorb onto the surface of GO through hydrogen bonding, Lewis acid-base interactions, and π-π interactions, thereby enhancing the photoreduction of GO. On this basis, our results further indicate that the combined effects of different ions, such as Ca2+, Mg2+, NOM, and other complex hydrochemical conditions in different natural waters can promote the photoreduction of GO, resulting in a reduction in oxygen functional groups and the formation of defects. This study provides a theoretical basis for assessing the long-term transformation and fate of GO in natural waters.

Mapping Photogenerated Electron-Hole Behavior of Graphene Oxide: Insight into a New Mechanism of Photosensitive Pollutant Degradation

The use of graphene oxide (GO) photogenerated electron-hole (e-h+) pairs to degrade pollutants is a novel green method for wastewater treatment. However, the interaction between photosensitive pollutants and a GO-light system remains unclear. In this work, the mechanism of degradation of photosensitive pollutant tetracycline (TC) promoted by GO photogenerated e-h+ pairs was studied. Our studies encompassed the determination of TC removal kinetics, analysis of active substances for TC degradation, identification of degradation products, and computational modeling. Clear evidence shows that a new reaction mechanism of enhanced adsorption and induced generation of reactive oxygen species (ROS) was involved. This mechanism was conducive to significantly enhanced TC removal. Kinetic studies showed a first-order behavior that can be well described by the Langmuir-Hinshelwood model. Radical scavenging experiments confirmed that 1O2, •O2-, and holes (h+) were the main active substances for TC degradation. Electron spin resonance analysis indicated that photoexcited TC molecules may transfer electrons to the conduction band of GO to induce the generation of additional ROS. A major transformation product (m/z 459) during TC degradation was identified with liquid chromatography-mass spectrometry. Density functional theory calculation indicated a stronger adsorption between TC and GO under photoirradiation. This mechanism of photo-enhanced adsorption and synergistic induced generation of ROS provides a new strategy for the removal of emerging pollutants in water. Overall, the new mechanism revealed in this work expands the knowledge of applying GO to wastewater treatment and is of great reference value for research in this field.

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

Application of Nanomaterials in the Production of Biomolecules in Microalgae: A Review

Nanomaterials (NMs) are becoming more commonly used in microalgal biotechnology to empower the production of algal biomass and valuable metabolites, such as lipids, proteins, and exopolysaccharides. It provides an effective and promising supplement to the existing algal biotechnology. In this review, the potential for NMs to enhance microalgal growth by improving photosynthetic utilization efficiency and removing reactive oxygen species is first summarized. Then, their positive roles in accumulation, bioactivity modification, and extraction of valuable microalgal metabolites are presented. After the application of NMs in microalgae cultivation, the extracted metabolites, particularly exopolysaccharides, contain trace amounts of NM residues, and thus, the impact of these residues on the functional properties of the metabolites is also evaluated. Finally, the methods for removing NM residues from the extracted metabolites are summarized. This review provides insights into the application of nanotechnology for sustainable production of valuable metabolites in microalgae and will contribute useful information for ongoing and future practice.

Asymmetric fabrication and in vivo evaluation of the wound healing potency of electrospun biomimetic nanofibrous scaffolds based on collagen crosslinked modified-chitosan and graphene oxide quantum dot nanocomposites

Asymmetric scaffolds were developed through electrospinning by utilizing biocompatible materials for effective wound healing applications. First of all, the chitosan surface was modified with decanoyl chloride and crosslinked with collagen to synthesize collagen crosslinked modified-chitosan (CG-cross-CS-g-Dc). Then, the asymmetric scaffolds were fabricated through electrospinning, where the top layer was a monoaxial nanofiber of the PCL/graphene oxide quantum dot (GOQD) nanocomposite and the bottom layer was a coaxial nanofiber having PCL in the core and the CG-cross-CS-g-Dc/GOQD nanocomposite in the shell layer. The formation of monoaxial (∼130 ± 50 nm) and coaxial (∼320 ± 40 nm) nanofibers was confirmed by transmission electron microscopy (TEM). The presence of GOQDs contributed to antioxidant and antimicrobial efficacy. These scaffolds showed substantial antibacterial activity against the common wound pathogens Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The scaffolds exhibited excellent cytocompatibility (MTT assay) and anti-inflammatory behaviour as analysed via the cytokine assay and biochemical analysis. The in vivo wound healing potential of the nanofibrous scaffolds was assessed with full-thickness excisional wounds in a rat model. The scaffolds accelerated the re-epithelialization as well as the collagen deposition, thereby facilitating the wound healing process in a very short span of time (10 days). Both in vitro and in vivo analyses thus provide a compelling argument for the use of these scaffolds as therapeutic biomaterials and their suitability for application in rapid wound regeneration and repair.

Removal of carboxylated multi-walled carbon nanotubes (MWCNT-COOH) from the environment by Trametes versicolor: a simple, cost-effective, and eco-friendly method

Nanotechnology has increased the release of nanoparticles into the environment, which poses a risk to human health and the ecosystem. Therefore, finding ways to eliminate these hazardous particles from the environment is crucial. This research studied the ability of Trametes versicolor fungi to remove carboxylated multi-walled carbon nanotubes. The study analyzed the impact of pH, MWCNT-COOH concentration, and initial fungal growth time on the removal process. The properties of the adsorbent were measured before and after the biosorption process using SEM, FTIR, and EDS techniques. The results showed that the live biomass of T. versicolor was more effective in removing nanoparticles than dead biomass at 30 °C and pH 7. An increase in carbon nanotube concentration from 5 to 20 mg. mL-1 decreased biosorption potential from 100% to 28.55 ± 1.7%. The study also found that an increase in initial fungal growth time led to higher biomass production and adsorption capacity, increasing biosorption ability for concentrations > 5mg. ml-1. The biosorption kinetics followed a pseudo-second-order model and corresponded most closely to the Freundlich isotherm model. The adsorption capacity of live fungal biomass to remove multi-walled carbon nanotubes was 945.17 mg. g-1, indicating that T. versicolor fungi have significant potential for removing carbon nanostructures from the environment.

Long-Term Exposure of Graphene Oxide Suspension to Air Leading to Spontaneous Radical-Driven Degradation

Understanding the environmental transformation and fate of graphene oxide (GO) is critical to estimate its engineering applications and ecological risks. While there have been numerous investigations on the physicochemical stability of GO in prolonged air-exposed solution, the potential generation of reactive radicals and their impact on the structure of GO remain unexplored. In this study, using liquid-PeakForce-mode atomic force microscopy and quadrupole time-of-flight mass spectroscopy, we report that prolonged exposure of GO to the solution leads to the generation of nanopores in the 2D network and may even cause the disintegration of its bulk structure into fragment molecules. These fragments can assemble themselves into films with the same height as the GO at the interface. Further mediated electrochemical analysis supports that the electron-donating active components of GO facilitate the conversion of O2 to •O2- radicals on the GO surface, which are subsequently converted to H2O2, ultimately leading to the formation of •OH. We experimentally confirmed that attacks from •OH radicals can break down the C-C bond network of GO, resulting in the degradation of GO into small fragment molecules. Our findings suggest that GO can exhibit chemical instability when released into aqueous solutions for prolonged periods of time, undergoing transformation into fragment molecules through self-generated •OH radicals. This finding not only sheds light on the distinctive fate of GO-based nanomaterials but also offers a guideline for their engineering applications as advanced materials.

rGO outperforms GO in generating oxidative stress and DNA strand breaks in zebrafish liver cells

Graphene oxide (GO) and reduced graphene oxide (rGO) are both widely applicable and there is a massive production throughout the world which imply in inevitable contamination in the aquatic environment by their wastes. Nevertheless, information about their interaction at the cellular level in fish is still scarce. We investigated the metabolic activity, reactive oxygen species (ROS) production, responses of antioxidant defenses, and total antioxidant capacity (TAC) as well as oxidative stress and DNA integrity in zebrafish liver cells (ZFL) exposed to (0.001, 0.01, 0.1 and 1 µg mL-1) of GO and rGO after two exposure period (24 and 72 h). Higher ROS production and no significant changes in the antioxidant defenses resulted in lipid peroxidation in cells exposed to rGO. Cells exposed to GO increased the activity of antioxidant defenses sustaining the TAC and avoiding lipid peroxidation. Comet assay showed that both, GO and rGO, caused DNA strand breaks after 24 h of exposure; however, only rGO caused DNA damage after 72 h of exposure. The exposure to rGO was significantly more harmful to ZFL cells than GO, even at very low concentrations. The cells showed a high capacity to neutralize ROS induced by GO preventing genotoxic effects and metabolic activity, thus sustaining cell viability. The time of exposure had different impacts for both nanomaterials, GO caused more changes in 24 h showing recovery after 72 h, while cells exposed to rGO were jeopardized at both exposure times. These results indicate that the reduction of GO by removal of the oxygen functional groups (rGO) increased toxicity leading to adverse effects in the cells, even at very low concentrations.

Promotion effect of ultraviolet light on graphene oxide aggregation in the presence of different climatic zone's humic and fulvic acid

Aggregation of graphene oxide (GO) is significantly affected by dissolved organic matter (DOM) in natural waters, while DOM's climate zone and light irradiation is seldom considered. This study investigated the effect of humic/fulvic acid (HA/FA) from various climate zones of China on aggregation of small (200 nm) and large (500 nm) GO under 120-h UV irradiation. GO aggregation was promoted by HA/FA because UV irradiation decreased hydrophilicity of GO and steric forces among particles. GO generated electron and hole pair under UV irradiation, which reduce GO with more hydrophilic oxygen-containing functional group (C-O) to rGO with high hydrophobicity and oxidize DOM into organic matter with smaller molecular weight. Most severe GO aggregation was observed with Makou HA from Subtropical Monsoon climate zone and Maqin FA from Plateau and Mountain climate zone, which was primarily because HA/FA's high molecular weight and aromaticity dispersed GO initially that facilitated UV penetration. GO aggregation ratio was positively correlated with graphitic fraction content (R2 = 0.82-0.99) and negatively correlated with C-O group content (R2 = 0.61-0.98) in the presence of DOM under UV irradiation. This work highlights different dispersity of GO during photochemical reactions in various climate zones, providing new insight into the environmental implications of nanomaterial release.

A Review of the Aquatic Environmental Transformations of Engineered Nanomaterials

Once released into the environment, engineered nanomaterials (ENMs) undergo complex interactions and transformations that determine their fate, exposure concentration, form, and likely impact on biota. Transformations are physical, chemical, or biological changes that occur to the ENM or the ENM coating. Over time, these transformations have an impact on their behaviour and properties. The interactions and transformations of ENMs in the environment depend on their pristine physical and chemical characteristics and the environmental or biological compartment into which they are released. The uniqueness of each ENM property or lifecycle results in a great deal of complexity. Even small changes may have a significant impact on their potential transformations. This review outlines the key influences and outcomes of ENM evolution pathways in aquatic environments and provides an assessment of potential environmental transformations, focusing on key chemical, physical, and biological processes. By obtaining a comprehensive understanding of the potential environmental transformations that nanomaterials can undergo, more realistic models of their probable environmental behaviour and potential impact can be developed. This will, in turn, be crucial in supporting regulatory bodies in their efforts to develop environmental policy in the field of nanotechnology.

Transformation of graphene oxide affects photodegradation of imidacloprid in the aquatic environment: Mechanism and implication

Graphene oxide (GO) is a representative novel carbonaceous nanomaterial, and neonicotinoid insecticides (NEOs) are currently the insecticides with the highest market share in the world. Their widespread application deservedly leads to their release to the environment. Thus, the complex interactions of these two types of organic compounds have attracted extensive attention. In this study, the effects of GO and its derivatives, reduced GO (RGO) and oxidized GO (OGO), on the photolysis of imidacloprid (IMD) (a typical NEO) under ultraviolet (UV) irradiation were systematically investigated. The results showed that the presence of the graphene-based nanomaterials (GNs) largely depressed the photodegradation of IMD, and the inhibition degree followed the order of RGO > GO > OGO. This was because the sp² π-conjugated structure in the GNs caused light-shielding effect and attenuated the direct photolysis of IMD, even though the GNs-generated reactive oxygen species (ROS) promoted the indirect photodegradation of IMD to a certain extent. Additionally, the rich O-functionalized GO and OGO altered the photolysis pathway of IMD and induced more toxic intermediate products. These results highlight the implication of carbonaceous nanomaterials on the behavior, fate and potential risk of NEOs in aqueous systems.

Effects of sunlight on the fate of graphene oxide and reduced graphene oxide nanomaterials in the natural surface water

Graphene nanomaterials have been commercialized for use in the electronic and biomedical industries, increasing their dissemination into surface waters and subsequent transformation in natural aquatic environment. While the photodegradation of graphene oxide nanomaterials has been investigated in the past, previous research did not consider actual natural aquatic environment and also focused on primarily graphene oxide nanomaterials. In this study, photodegradation of graphene nanomaterials with varying oxidation levels, including graphene oxide (GO) and partially reduced graphene oxide (rGO-2 h) are evaluated in Columbia River Water and compared with each other. Our results indicate that both direct and indirect photolysis of graphene-based nanomaterials will occur simultaneously in natural surface water. However, environmentally relevant concentrations of photosensitizers in surface water are not capable of producing sufficient ^·OH to initiate degradation of GO via indirect photolysis. For all conditions tested, GO showed more rapid photodegradation compared to rGO. Overall, direct and indirect photodegradation of graphene oxide nanomaterials in natural surface water is minimal and slow indicating that phototransformation of graphene-based nanomaterials will be insignificant in natural surface water.

A Novel Drug with Potential to Treat Hyperbilirubinemia and Prevent Liver Damage Induced by Hyperbilirubinemia: Carbon Dots Derived from Platycodon grandiflorum

Platycodon grandiflorum (PG) is a traditional Chinese medicine with a long history, but its active compounds have not been reported. In this study, novel carbon dots (CDs), PG-based CDs (PGC-CDs), were discovered and prepared from PG via calcinations and characterized by transmission electron microscopy; high-resolution transmission electron microscopy; X-ray diffraction, fluorescence, ultraviolet-visible, and Fourier-transform infrared spectrometers; X-ray photoelectron spectroscopy; and high-performance liquid chromatography. In addition, the safety and antioxidant activity of PGC-CDs was evaluated by RAW264.7 cells and LO2 cells. The therapeutic effects of PGC-CDs on hyperbilirubinemia and liver protection were evaluated in a bilirubin-induced hyperbilirubinemia mice model. The experiment confirmed that the diameter range of PGC-CDs was from 1.2 to 3.6 nm. PGC-CDs had no toxicity to RAW264.7 cells and LO2 cells at a concentration of 3.91 to 1000 µg/mL and could reduce the oxidative damage of cells caused by H2O2. PGC-CDs could inhibit the increase levels of bilirubin and inflammation factors and increase the levels of antioxidants and survival rate, demonstrating that PGC-CDs possessed anti-inflammatory and anti-oxidation activity. PGC-CDs may reduce the content of bilirubin, so as to reduce a series of pathological lesions caused by bilirubin, which has potential in treating hyperbilirubinemia and preventing liver damage induced by hyperbilirubinemia.

Interaction between graphene oxide and acetaminophen in water under simulated sunlight: Implications for environmental photochemistry of PPCPs

In recent years, graphene oxide (GO) as a new carbon material has been widely investigated as adsorbent and catalyst. However, effects of GO on the micro-pollutants such as pharmaceuticals and personal care products (PPCPs) under sunlight remains unclear. In this study, the degradation of PPCPs in a simulated sunlight-GO photocatalytic system was systematically investigated. Specifically, GO rapidly degrade 95% of acetaminophen (APAP) within 10 min under simulated sunlight irradiation (λ ≥ 350 nm). The influencing factors such as APAP concentration, pH, GO dosage, water matrixes (Cl^-, NO₃^-, HCO₃^-, SO₄^2-, Ca²⁺, Fe³⁺and fulvic acid) were investigated. At a GO dosage of 100 mg L^-1 and an initial pH of 7, the APAP (5 μM) photodegradation kinetic constant k_obs was calculated to be 0.4547 min^-1. In practical applications, the GO photocatalysis system still degrade over 90% APAP within 60 min in real surface water. The electron spin resonance and radical scavenging experiments revealed that the dominated active species for degrading APAP was photogenerated holes (h⁺), while other mechanisms (¹O₂ and O₂^•-/HO₂^•) played a minor role. Furthermore, the photochemical transformation of some other typical PPCPs were comparatively studied to reveal the relationship between degradation kinetics and molecular structure. Based on descriptive variables including molar refractive index parameter, octanol-water partition coefficient, dissociation constant and dipole moment, a quantitative structural-activity relationship (QSAR) model for predicting pseudo-first-order rate constants was established with a high significance (R² = 0.996, p < 0.05). This study helps to understand the interaction between GO and PPCPs and its effects on the photochemical transformation of PPCPs in water.

Environmentally sustainable implementations of two-dimensional nanomaterials

Rapid advancement in nanotechnology has led to the development of a myriad of useful nanomaterials that have novel characteristics resulting from their small size and engineered properties. In particular, two-dimensional (2D) materials have become a major focus in material science and chemistry research worldwide with substantial efforts centered on their synthesis, property characterization, and technological, and environmental applications. Environmental applications of these nanomaterials include but are not limited to adsorbents for wastewater and drinking water treatment, membranes for desalination, and coating materials for filtration. However, it is also important to address the environmental interactions and implications of these nanomaterials in order to develop strategies that minimize their environmental and public health risks. Towards this end, this review covers the most recent literature on the environmental implementations of emerging 2D nanomaterials, thereby providing insights into the future of this fast-evolving field including strategies for ensuring sustainable development of 2D nanomaterials.

Ionic specificity mediates the transport and retention of graphene-based nanomaterials in saturated porous media

Transport of graphene-based nanomaterials in porous media is closely related to background cations. This study examines the impacts of ionic specificity on the mobility of graphene oxide (GO) and reduced GO (RGOs) in saturated quartz sand. The transport of GO/RGOs as affected by monovalent cation Na+ followed extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, whereas in solutions containing multivalent cations Zn2+ and Al3+, cation bridging effect played a dominant role in the transport inhibition. Moreover, the adverse effects of the divalent cations on GO/RGOs migration obeyed the Hofmeister series, i.e. following the order of Pb2+ > Cd2+ > Zn2+. Batch adsorption experiments and DFT calculations further confirmed that cations of higher valences, and of the same valence but with larger ionic radii (smaller hydrated radii) interacted more strongly with GO/RGOs and sand grains via forming inner-sphere complexes. Thus, more favorable retention was observed through cation bridging between particles and collectors, and also via enhanced straining caused by particles aggregation. Furthermore, the sulfide-reduced GO (SR-GO) that contained more surface O-functional groups was impacted more remarkably by strong complexing cations than the pristine GO (P-GO), while the mobility of poorly functionalized irradiation-reduced GO (IR-GO) was less affected by cation bridging effect.

Colloidal Behavior and Biodegradation of Engineered Carbon-Based Nanomaterials in Aquatic Environment

Carbon-based nanomaterials (CNMs) have attracted a growing interest over the last decades. They have become a material commonly used in industry, consumer products, water purification, and medicine. Despite this, the safety and toxic properties of different types of CNMs are still debatable. Multiple studies in recent years highlight the toxicity of CNMs in relation to aquatic organisms, including bacteria, microalgae, bivalves, sea urchins, and other species. However, the aspects that have significant influence on the toxic properties of CNMs in the aquatic environment are often not considered in research works and require further study. In this work, we summarized the current knowledge of colloidal behavior, transformation, and biodegradation of different types of CNMs, including graphene and graphene-related materials, carbon nanotubes, fullerenes, and carbon quantum dots. The other part of this work represents an overview of the known mechanisms of CNMs' biodegradation and discusses current research works relating to the biodegradation of CNMs in aquatic species. The knowledge about the biodegradation of nanomaterials will facilitate the development of the principals of "biodegradable-by-design" nanoparticles which have promising application in medicine as nano-carriers and represent lower toxicity and risks for living species and the environment.

Diesel soot photooxidation enhances the heterogeneous formation of H2SO4

Both field observation and experimental simulation have implied that black carbon or soot plays a remarkable role in the catalytic oxidation of SO₂ for the formation of atmospheric sulfate. However, the catalytic mechanism remains ambiguous, especially that under light irradiation. Here we systematically investigate the heterogeneous conversion of SO₂ on diesel soot or black carbon (DBC) under light irradiation. The experimental results show that the presence of DBC under light irradiation can significantly promote the heterogeneous conversion of SO₂ to H₂SO₄, mainly through the heterogeneous reaction between SO₂ and photo-induced OH radicals. The detected photo-chemical behaviors on DBC suggest that OH radical formation is closely related to the abstraction and transfer of electrons in DBC and the formation of reactive superoxide radical (•O₂⁻) as an intermediate. Our results extend the known sources of atmospheric H₂SO₄ and provide insight into the internal photochemical oxidation mechanism of SO₂ on DBC.

Potential source of H₂SO₄ remains unclear in the atmosphere. This work first demonstrates that the formation of photoinduced •OH radical can directly promote the heterogeneous conversion of SO₂ to H₂SO₄ on real diesel soot under light irradiation, extending the known sources of atmospheric H₂SO₄.

Size characterization of nanomaterials in environmental and biological matrices through non-electron microscopic techniques

Engineered nanomaterials (ENs) can enter the environment, and accumulate in food chains, thereby causing environmental and health problems. Size characterization of ENs is critical for further evaluating the interactions among ENs in biological and ecological systems. Although electron microscope is a powerful tool in obtaining the size information, it has limitations when studying nanomaterials in complex matrices. In this review, we summarized non-electron microscope-based techniques, including chromatography-based, mass spectrometry-based, synchrotron radiation- and neutron-based techniques for detecting the size of ENs in environmental and biological matrices. The advantages and disadvantages of these techniques were highlighted. The perspectives on size characterization of ENs in complex matrices were also presented.

Iris pseudacorus as precursor affecting ecological transformation of graphene oxide and performance of constructed wetland

The role of plants is largely unknown in constructed wetlands (CWs) exposed to phytotoxic nanomaterials. Present study investigated transformation of graphene oxide (GO) and performance of CWs with Iris pseudacorus as precursor. GO was trapped by CWs without dependence on plants. GO could move to lower substrate layer and present increases on defects/disorders with stronger effects in planted CW. Before adding GO, planted CW achieved better removal both of phosphorus and nitrogen. After adding GO, phosphorus removal in planted CW was 93.23-95.71% higher than 82.55-90.07% in unplanted CW. However, total nitrogen removal was not improved, showing 48.20-56.66% and 53.44-56.04% in planted and unplanted CWs. Plant improved urease, phosphatase, and arylsulfatase, but it decreased β-glucosidase and had less effects on dehydrogenase and catalase. Pearson correlation matrix revealed that plant enhanced microbial interaction with high degree of positive correlation. Moreover, there were obvious shifts in microbial community at phylum and genus level, which presented closely positive action on substrate enzyme activities. The functional profile was less affected due to functional redundancy in microbial system, but time effects were obvious in CWs, especially in planted CW. These findings could provide the basis on understanding role of plants in CWs for treating nanoparticles wastewater.

Impacts of photoaging on the interactions between graphene oxide and proteins: Mechanisms and biological effect

Graphene oxide (GO) are subjected to photoaging in aquatic environment, and inevitably enter biota and then interact with proteins. Here, the interactions of pristine and photoaged GO with two typical proteins (bovine serum albumin (BSA) and lysozyme) were systematically investigated. Due to long term photoirradiation (1-3 day), the lateral size of GO decreased greatly, and the oxygen-containing groups decreased as well while the graphitic carbon contents increased. Compared to pristine GO, the photoaged GO displayed stronger binding affinities with both proteins, which was mainly attributed to the increased binding sites as a result of smaller lateral size and increased hydrophobicity. The photoaging effect was more obvious for the negatively charged BSA, because hydrogen bonding and van der Waals force were mainly involved in the enthalpy-driven interactions between them. While, the strong electrostatic attraction between the positively charged lysozyme and GO diminished the photoaging effect. Analyses of synchronous, three-dimensional fluorescence spectra and fibrillation experiments intensified that the photoaged GO induced more serious changes in conformational structure of BSA and exhibited stronger inhibition on fibrillation of BSA compared to pristine GO. This study provided novel insights into the increased ecological risks of GO as a result of photoaging.

Surface conjugation of titanium dioxide nanoparticles on nano-graphene oxide enhances photocatalytic degradation of azo dyes under sunlight

Here, conjugate of nano-graphene oxide (GO) and titanium dioxide nanoparticle (nTiO₂) was proposed for the photocatalytic degradation of two toxic azo dyes, Congo red (CR) and Methylene blue (MB), under sunlight irradiation. Furthermore, the optimized weight ratio between GO and nTiO₂ of 1:5 demonstrated the highest degradation efficiency. The nanoconjugate induced 85% degradation of 40 ppm of CR in 60 min and a complete degradation within 70 min, while it degraded more than 90% of 20 ppm of MB in 80 min. The photocatalyst can be reused for five cycles of photocatalysis. Thus, the photocatalytic potential of GO/nTiO₂ under visible light may be used as a very suitable and cost-effective photocatalyst industrially for the removal of toxic dyes from water.

Impact of secondary salts, temperature, and pH on the colloidal stability of graphene oxide in water

The stability of graphene oxide (GO) in water is extremely relevant because of its application as an adsorbent material, as well as for its fate and behavior in the environment. Zeta potential was used to study the effect of secondary salts (carbonate, sulfate, and phosphate), temperature (20 to 60 °C), and pH (5 to 9) on the stability of six different GOs produced from natural, synthetic, and amorphous graphite-with and without the use of attrition milling. Generally, GOs produced with attrition-milled graphites had lower ζ-potentials than their unmilled counterparts because of their smaller particle sizes and higher concentration of oxygen-containing functional groups. It was observed that GO produced from graphite and synthetic graphite had ζ-potential values lower than -30 mV, even at 30 °C. However, it was observed that all the GOs studied were unstable in the presence of carbonate and sulfate salts at concentrations between 170 and 1695 mg L^-1, as they reached a ζ-potential of -4.1 mV. Density-functional theory electronic structure calculations suggested that the instability of GO in the presence of carbonate and sulfate was caused by the abstraction of a proton resulting in interaction energies E _int of 28.3 and 168.9 kJ mol^-1, respectively. Our results suggest that temperatures above 30 °C, as well as carbonate and sulfate salts at concentrations relevant to arid and semi-arid regions, could promote the formation of agglomerates of GO, thus limiting its use and mobility in water.

Visible-Light Assisted Covalent Surface Functionalization of Reduced Graphene Oxide Nanosheets with Arylazo Sulfones

We present an environmentally benign methodology for the covalent functionalization (arylation) of reduced graphene oxide (rGO) nanosheets with arylazo sulfones. A variety of tagged aryl units were conveniently accommodated at the rGO surface via visible-light irradiation of suspensions of carbon nanostructured materials in aqueous media. Mild reaction conditions, absence of photosensitizers, functional group tolerance and high atomic fractions (XPS analysis) represent some of the salient features characterizing the present methodology. Control experiments for the mechanistic elucidation (Raman analysis) and chemical nanomanipulation of the tagged rGO surfaces are also reported.

Bioaccumulation and depuration of TiO2 nanoparticles by zebrafish through dietary exposure: Size- and number concentration-resolved analysis using single-particle ICP-MS

The bioaccumulation and depuration of TiO₂ nanoparticles (TiO₂NPs) by zebrafish via the dietary exposure following the OECD Test Guideline 305 (OECD TG305) was evaluated using particle size- and number concentration-resolved analysis based on single-particle ICP-MS (spICP-MS). We found that using enzymatic digestion without H₂O₂ or excessive heating can recover 84.0 ± 4.0% and 94.5 ± 3.5% of TiO₂NP mass and number concentrations from fish tissue, respectively, without altering the size distribution of parent TiO₂NPs. OECD TG305 can allow for the evaluation of bioaccumulation and depuration of TiO₂NPs by fish based on the particle mass and number dose metrics. The toxicokinetic modeling can reasonably describe the mass- and number-based measurement data with the derived absorption efficiency α at ~0.2, depuration rate at ~0.5 d^-1, and kinetic biomagnification factor (BMF_k) at ~0.007 comparable with available data. The mass concentration- and number concentration-based bioaccumulation metrics including body burdens are correlated for TiO₂NPs that remained nano-sized in vivo and exhibited marginal physicochemical alterations upon uptake by fish. The result indicates that the traditional mass concentration metric may be used to represent the fish bioaccumulation potential for chemically inert NPs like TiO₂.

Response of constructed wetland for wastewater treatment to graphene oxide: Perspectives on plant and microbe

The wide application of graphene oxide (GO) increases its release into environment with less known on environmental effects. This work investigated 120-day interaction between GO (500 and 5000 μg/L) and constructed wetlands (CWs) planted with Iris pseudacorus. CWs showed the effective retention for GO via mature biofilm but less biodegradation. GO significantly induced enzyme activities (urease, neutral phosphatase, and catalase), which was attributed to increases in ecological association and enzyme abundance. GO decreased microbial biomass on day 30, but it had no impacts on day 120. The microbial community showed gradual self-adaption with time due to protection of antioxidant defense system (L-ascorbate oxidase, superoxide reductase, and glutathione related enzyme). The antioxidant enzymes (superoxide dismutase and peroxidase) and lipid peroxidation of Iris pseudacorus were increased by GO, accompanied by reduction on chlorophyll biosynthesis. Overall, the separate effects of GO on micro-regions and individual bodies in CWs were obvious, but it was acceptable that variations in pollutant removal were not evident due to synergetic role of plant-substrate-microbe. Organic matter and phosphorus removals reached to above 93%, and ammonia and total nitrogen removals in GO groups were reduced by 7-8% and 9-13%, respectively.

Ionic Porous Aromatic Framework as a Self-Degraded Template for the Synthesis of a Magnetic γ-Fe2O3/WO3·0.5H2O Hybrid Nanostructure with Enhanced Photocatalytic Property

An ionic porous aromatic framework is developed as a self-degraded template to synthesize the magnetic heterostructure of γ-Fe₂O₃/WO₃·0.5H₂O. The Fe₃O₄ polyhedron was obtained with the two-phase method first and then reacted with sodium tungstate to form the γ-Fe₂O₃/WO₃·0.5H₂O hybrid nanostructure. Under the induction effect of the ionic porous network, the Fe₃O₄ phase transformed to the γ-Fe₂O₃ state and complexed with WO₃·0.5H₂O to form the n-n heterostructure with the n-type WO₃·0.5H₂O on the surface of n-type γ-Fe₂O₃. Based on a UV-Visible analysis, the magnetic photocatalyst was shown to have a suitable band gap for the catalytic degradation of organic pollutants. Under irradiation, the resulting γ-Fe₂O₃/WO₃·0.5H₂O sample exhibited a removal efficiency of 95% for RhB in 100 min. The charge transfer mechanism was also studied. After the degradation process, the dispersed powder can be easily separated from the suspension by applying an external magnetic field. The catalytic activity displayed no significant decrease after five recycles. The results present new insights for preparing a hybrid nanostructure photocatalyst and its potential application in harmful pollutant degradation.

Gentiana straminea Maxim. polysaccharide decolored via high-throughput graphene-based column and its anti-inflammatory activity

Gentiana straminea Maxim. exhibits various biological activities. However, the purification and functions of polysaccharides in Gentiana straminea Maxim. have never been reported. Herein, by proposing a flexible 3D graphene-based decoloration column (3DD column), Gentiana straminea Maxim. polysaccharide (GMP) was high-throughput obtained and its anti-inflammatory activity was investigated. Benefiting from the large macroporous network of 3D NH₂-graphene oxide hydrogel with selective adsorption towards pigments, the 3DD column exhibits high decoloration ratio (96.41%). In addition, the 3DD column provides superior practical functionality as compared to the traditional approaches, which are time-consuming and need toxic solvents, and exhibiting widespread-application for the purification of polysaccharide from other common plant species. More importantly, the decolored GMP as a natural product has promising anti-inflammatory activity on RAW264.7 cells without negative impact on cell viability. Overall, this work reveals a new functional polysaccharides and provides a flexible approach for polysaccharide decoloration, exhibiting a promising prospect for natural polysaccharides in practical application of pharmaceutical.

Insights into the transport of pristine and photoaged graphene oxide-hematite nanohybrids in saturated porous media: Impacts of XDLVO interactions and surface roughness

The transport behaviors of nanomaterials, in especial multifunctional nanohybrids have not been well disclosed until now. In this study, environmentally relevant conditions, including cation types, ionic strength and pH, were selected to investigate the transport and retention of graphene oxide-hematite (GO-Fe₂O₃) nanohybrids and a photoaged product in saturated sandy columns. Results show that more hybridization of hematite led to decreased negative surface charge, while increased particle size and hydrophobicity of the nanohybrids, which depressed their transport according to extented Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. However, the inhibitory transport of photoaged nanohybrids was attributed to their distinct surface roughness caused by relatively high hybridization and photoirradiation. Notably the restrained transport was alleviated in the CaCl₂ saturated media, since the less surface O-functional groups of the corresponding nanohybrids reduced the cation bridging effect caused by Ca²⁺. Similarly, increasing pH promoted the transport of the nanohybrids in NaCl saturated media, particularly for the nanohybrids that contained rich O-functional groups, but exerted inconspicuous effect on mobility of the nanohybrids in CaCl₂ saturated media. These observations highlight that both XDLVO interactions and surface roughness may work together to impact the transport and fate of the burgeoning, versatile nanohybrids in the environment.

A Facile and Scalable Method of Fabrication of Large-Area Ultrathin Graphene Oxide Nanofiltration Membrane

With their ultrafast water transport and excellent molecule sieving properties, graphene oxide (GO)-based membranes show great potential in the membrane filtration field for water purification and molecular separation. However, the inability of uniform GO membranes to be produced on an industrial scale and their nonenvironmentally friendly reduction treatment are the bottleneck preventing their industrial applications. Herein, we report a scalable ultrathin uniform GO membrane fabrication technique. Ultrathin GO membranes with a large area of 30 × 80 cm² and a thickness of a few nanometers were uniformly and facilely fabricated using a continuous process combining Mayer rod-coating and a short-time, high-power UV reduction. The interlayer spacing of the GO membrane could be effectively reduced and regulated to improve the salt rejection rate. The fabricated membrane showed superior water permeability of over 60.0 kg m^-2 h^-1 and a high separation efficiency of over 96.0% for a sodium sulfate (Na₂SO₄) solution. It also exhibited excellent mechanical stability under various harsh crossflow conditions. More importantly, the fabrication method developed here can be scaled up using a roll-to-roll industrial production process, which successfully solves the problem currently faced by GO membrane researchers and makes the industrial usage of GO membrane a reality.

Graphitic carbon nitride embedded with graphene materials towards photocatalysis of bisphenol A: The role of graphene and mediation of superoxide and singlet oxygen

Composite photocatalysts comprising graphitic carbon nitride (g-C₃N₄) and graphene materials were synthesized and evaluated in the photocatalysis of bisphenol A (BPA) with a focus on elucidating the reaction mechanism. Embedding reduced graphene oxide (rGO) to g-C₃N₄ significantly accelerated the photocatalysis rate of BPA by three folds under visible light irradiation at neutral pH. We showed that rGO synthesized in intimate contact with g-C₃N₄ increased the surface areas and electrical conductivity of the g-C₃N₄ composites and promoted the electron-hole pair separation. The BPA photodegradation mechanism involved selective oxidants as superoxide (O₂^•-) and singlet oxygen (¹O₂) that were formed through one-electron reduction of O₂ and the unique oxidation of O₂^•- by photogenerated hole (h⁺), respectively. The synthesized photocatalyst exhibited superior visible light photoreactivity to that of N-doped P25 TiO₂, good photo-stability and reuse potential, and was operative in complex wastewater. rGO embedded g-C₃N₄ achieved good photomineralization of BPA at 80% in 4 h compared to 40% of bare g-C₃N₄. This study sheds light on the photocatalysis mechanism of BPA with a metal-free, promising rGO/g-C₃N₄ photocatalyst.

Phototransformation of Graphene Oxide on the Removal of Sulfamethazine in a Water Environment

Graphene oxide (GO) is widely used in various fields and has raised concerns regarding its potential environmental fate and effect. However, there are few studies on its influence on coexisting pollutants. In this study, the phototransformation of GO and coexisting sulfamethazine (SMZ) under UV irradiation was investigated, with a focus on the role of reactive oxygen species. The results demonstrated that GO promoted the degradation of SMZ under UV irradiation. The higher the concentration of GO, the higher the degradation rate of SMZ, and the faster the first-order reaction rate. Two main radicals, ∙OH and ¹O₂, both contributed greatly in terms of regulating the removal of SMZ. Cl⁻, SO₄²⁻, and pH mainly promoted SMZ degradation by increasing the generation of ∙OH, while humic acid inhibited SMZ degradation due to the reduction of ∙OH. Moreover, after UV illumination, the GO suspension changed from light yellow to dark brown with increasing absorbance at a wavelength of 225 nm. Raman spectra revealed that the I_D/I_G ratio slightly decreased, indicating that some of the functional groups on the surface of GO were removed under low-intensity UV illumination. This study revealed that GO plays important roles in the photochemical transformation of environmental pollutants, which is helpful for understanding the environmental behaviors and risks of nanoparticles in aquatic environments.

New insights into the colloidal stability of graphene oxide in aquatic environment: Interplays of photoaging and proteins

Wide application leads to release of graphene oxide (GO) in aquatic environment, where it is subjected to photoaging and changes in physicochemical properties. As important component of natural organic matters, proteins may greatly affect the aggregation behaviors of photoaged GO. The effects of a typical model protein (bovine serum albumin, BSA) on the colloidal stability of photoaged GO were firstly investigated. Photoaging reduced the lateral size and oxygen-containing groups of GO, while the graphene domains and hydrophobicity increased as a function of irradiation time (0-24 h). Consequently, the photoaged GO became less stable than the pristine one in electrolyte solutions. Adsorption of BSA on the surface of the photoaged GO decreased as well, leading to thinner BSA coating on the photoaged GO. In the solutions with low concentrations of electrolytes, the aggregation rate constants (k) of all the photoaged GO firstly increased to the maximum agglomeration rate constants (k_fast, regime I), maintained at k_fast (regime Ⅱ) and then decreased to zero (regime Ⅲ) as the BSA concentration increased. In both regime I and III, the photoaged GO were less stable at the same BSA concentrations, and the impacts of BSA on the colloidal stability of the photoaged GO were less than the pristine one, which was attributed to the weaker interactions between the photoaged GO and BSA. This study provided new insights into the colloidal stability and fate of GO nanomaterials, which are subjected to extensive light irradiation, in wastewater and protein-rich aquatic environment.

Nanotechnology and artificial intelligence to enable sustainable and precision agriculture

Climate change, increasing populations, competing demands on land for production of biofuels and declining soil quality are challenging global food security. Finding sustainable solutions requires bold new approaches and integration of knowledge from diverse fields, such as materials science and informatics. The convergence of precision agriculture, in which farmers respond in real time to changes in crop growth with nanotechnology and artificial intelligence, offers exciting opportunities for sustainable food production. Coupling existing models for nutrient cycling and crop productivity with nanoinformatics approaches to optimize targeting, uptake, delivery, nutrient capture and long-term impacts on soil microbial communities will enable design of nanoscale agrochemicals that combine optimal safety and functionality profiles.

Co-transport of negatively charged nanoparticles in saturated porous media: Impacts of hydrophobicity and surface O-functional groups

Graphene oxide (GO) and polystyrene nanoplastic (PSNP) are typical carbonaceous nanomaterials which likely co-exist in soil and sediment. Here, we describe the transport of GO, irradiation reduced GO (RGO) and PSNP in saturated quartz sand both in single and binary systems. In the single transport system, the materials exhibited mobility in the order of GO > RGO > PSNP, due to increased hydrophobicity and decreased negative surface charges. Nevertheless, the co-transport of (R)GO and PSNP in the binary transport system was much more intricate. In Na⁺ saturated porous media, PSNP preferred to interact with (R)GO relative to the highly negatively charged quartz sand, thus (R)GO carried PSNP to break through the sand column. However, in Ca²⁺ saturated porous media, the transport of both (R)GO and PSNP was depressed, attributed to the particle-collector and particle-particle bridging effects between Ca²⁺ and the metal-complexing moieties of the nanoparticles and sand grains. Moreover, GO influenced the co-transport of PSNP to a larger extent than RGO, especially at relatively high ionic strength, because of the more abundant surface O-functional groups on GO providing more complexion sites with Ca²⁺. These results demonstrated that the transport of negatively charged nanomaterials was greatly related to the hydrophobicity and surface O-functional groups.

New insight into the photo-transformation mechanisms of graphene oxide under UV-A, UV-B and UV-C lights

Photo-transformation dominates the fate of graphene oxide (GO) in the environment. However, the photo-transformation mechanisms of GO under different UV bands remain unclear. Our results showed that UV bands played a crucial role in sunlight-induced GO transformation. UVA and UVB induced significant photo-reduction of GO as indicated by decreasing surface O/C ratio, which could be explained by an O₂-independent electron-hole pair-mediated mechanism (Mechanism I), and an O₂-dependent reactive oxygen species (ROS)-mediated reduction mechanism (Mechanism II). Mechanism II accounted for 62.7 % and 33.3 % of total GO photo-transformation under UVA and UVB, respectively. Different from UVA and UVB, UVC led to GO reduction under anaerobic condition via Mechanism I and Mechanism III (direct decarboxylation). However, under aerobic condition, UVC caused significant oxidation of GO, which was the combined effect of Mechanisms I-III and the oxidation of graphitic structure on GO with the assistance of O₂ (Mechanism IV). Moreover, it was demonstrated that the environmental factors (e.g., dissolved organic matter, phosphate) significantly enhanced the photo-transformation of GO in natural water. The information in the present work is useful for better understanding the fate of GO in aquatic environments.

Environmental transformation of graphene oxide in the aquatic environment

In recent years, research on graphene oxide (GO) has developed rapidly in both academic and industrial applications such as electronic, biosensor, drug delivery, water treatment and so forth. Based on the large amount of applications, it is anticipated that GO will inevitably find its own way to the environment, if used are not restricted to prevent their release. Environmental transformation is an important transformation process in the natural environment. In this review, we will summarize the recent developments on environmental transformation of GO in the aquatic environment. Although papers on environmental transformation of graphene-based nanomaterials can be found, a systematic picture describing photo-transformation of GO (dividing into different irradiation sources), environmental transformation of GO in the dark environmental, the environmental toxicity of GO are still lacking. Thus, it is essential to summarize how different light sources will affect the GO structure and reactive oxygen species generation in the photo-transformation process, how GO will react with various natural constituents in the aquatic environment, whether GO will toxic to different aquatic organisms and what will be the interactions between GO and the intracellular receptors in the intracellular level once GO released into the aquatic environment. This review will arouse the realization of potential risk that GO can bring to the aquatic environment and enlighten us to pay attention to behaviors of other two-dimensional GO-like nanomaterials, which have been intensively applied and studied in recent years.

Multicolor polymeric carbon dots: synthesis, separation and polyamide-supported molecular fluorescence

Multicolor carbon dots (CDs) have been developed recently and demonstrate great potential in bio-imaging, sensing, and LEDs. However, the fluorescence mechanism of their tunable colors is still under debate, and efficient separation methods are still challenging. Herein, we synthesized multicolor polymeric CDs through solvothermal treatment of citric acid and urea in formamide. Automated reversed-phase column separation was used to achieve fractions with distinct colors, including blue, cyan, green, yellow, orange and red. This work explores the physicochemical properties and fluorescence origins of the red, green, and blue fractions in depth with combined experimental and computational methods. Three dominant fluorescence mechanism hypotheses were evaluated by comparing time-dependent density functional theory and molecular dynamics calculation results to measured characteristics. We find that blue fluorescence likely comes from embedded small molecules trapped in carbonaceous cages, while pyrene analogs are the most likely origin for emission at other wavelengths, especially in the red. Also important, upon interaction with live cells, different CD color fractions are trafficked to different sub-cellular locations. Super-resolution imaging shows that the blue CDs were found in a variety of organelles, such as mitochondria and lysosomes, while the red CDs were primarily localized in lysosomes. These findings significantly advance our understanding of the photoluminescence mechanism of multicolor CDs and help to guide future design and applications of these promising nanomaterials.

Graphene/polymer nanocomposite degradation by ultraviolet light: The effects of graphene nanofillers and their potential for release

The ultraviolet (UV)-induced degradation of graphene/polymer nanocomposites was investigated in this study. Specifically, the effect of few-layer graphene nanofillers on the degradation of a thermoplastic polyurethane (TPU) and the release potential of graphene from the degraded nanocomposite surfaces were assessed. Graphene/TPU (G/TPU) nanocomposites and neat TPU were UV-exposed under both dry and humid conditions in the NIST SPHERE, a precisely controlled, high intensity UV-weathering device. Neat TPU and G/TPU were characterized over the time course of UV exposure using color measurements and infrared spectroscopy, for appearance and chemical changes, respectively. Changes in thickness and surface morphology were obtained with scanning electron microscopy. A new fluorescence quenching measurement approach was developed to identify graphene sheets at the nanocomposite surface, which was supported by contact angle measurements. The potential for graphene release from the nanocomposite surface was evaluated using a tape-lift method followed by microscopy of any particles present on the tape. The findings suggest that graphene improves the service life of TPU with respect to UV exposure, but that graphene becomes exposed at the nanocomposite surface over time, which may potentially lead to its release when exposed to small mechanical forces or upon contact with other materials.

Sublethal exposure of small few-layer graphene promotes metabolic alterations in human skin cells

Small few-layer graphene (sFLG), a novel small-sized graphene-related material (GRM), can be considered as an intermediate degradation product of graphene. GRMs have a promising present and future in the field of biomedicine. However, safety issues must be carefully addressed to facilitate their implementation. In the work described here, the effect of sub-lethal doses of sFLG on the biology of human HaCaT keratinocytes was examined. A one-week treatment of HaCaTs with sub-lethal doses of sFLG resulted in metabolome remodeling, dampening of the mitochondrial function and a shift in the redox state to pro-oxidant conditions. sFLG raises reactive oxygen species and calcium from 24 h to one week after the treatment and this involves the activation of NADPH oxidase 1. Likewise, sFLG seems to induce a shift from oxidative phosphorylation to glycolysis and promotes the use of glutamine as an alternative source of energy. When sub-toxic sFLG exposure was sustained for 30 days, an increase in cell proliferation and mitochondrial damage were observed. Further research is required to unveil the safety of GRMs and degradation-derived products before their use in the workplace and in practical applications.