High-Efficiency Ag-Modified ZnO/g-C3N4 Photocatalyst with 1D-0D-2D Morphology for Methylene Blue Degradation

Photocatalysts with different molar ratios of Ag-modified ZnO to g-C3N4 were prepared through an electrostatic self-assembly method and characterized through techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The resulting Ag-ZnO/g-C3N4 photocatalysts exhibited a unique 1D-0D-2D morphology and Z-type heterojunction. Moreover, g-C3N4 nanosheets with large layer spacing were prepared using acid treatment and thermal stripping methods. The Z-type heterostructure and localized surface plasmon resonance effect of Ag nanowires enabled high-speed electron transfer between the materials, while retaining large amounts of active substances, and broadened the light response range. Because of these features, the response current of the materials improved, and their impedance and photoluminescence reduced. Among the synthesized photocatalysts, 0.05Ag-ZnO/g-C3N4 (molar ratio of g-C3N4/ZnO: 0.05) exhibited the highest photocatalytic performance under UV-visible light. It degraded 98% of methylene blue in just 30 min, outperforming both g-C3N4 (21% degradation in 30 min) and Ag-ZnO (84% degradation in 30 min). In addition, 0.05Ag-ZnO/g-C3N4 demonstrated high cycling stability.

Adsorbents for the Uranium Capture from Seawater for a Clean Energy Source and Environmental Safety: A Review

On the global level, uranium is considered the main nuclear energy source, and its removal from terrestrial ores is enough to last until the end of the current century. Therefore, a major focus is attracted toward the capture of uranium from a sustainable source (seawater). Uranium recovery from seawater has been reported over the last few decades, and recently many efforts have been devoted to the preparation of such adsorbents with higher selectivity and adsorption capacity. The purpose of this review is to report the advancement in adsorbent preparation and modification of porous materials. It also discusses challenges such as adsorbent selectivity, low uranium concentration in seawater, contact time, biofouling, and the solution to the problems necessary to ensure a better adsorption performance of the adsorbent.

Electrochemical Exfoliation of Graphene Oxide: Unveiling Structural Properties and Electrochemical Performance

An electrochemical exfoliation method for the production of graphene oxide and its characterization by electrochemical techniques are presented here. Graphite rods are used as working electrode in a three-electrode electrochemical cell, and electro-exfoliation is achieved by applying anodic polarization in a sulfuric acid solution. The electrochemical process involved two steps characterized by an intercalation at lower potential and an exfoliation at higher potential. The electrochemical behavior of the produced GO is studied through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). X ray Photoelectronic Spectroscopy (XPS), Raman spectroscopy, Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM) are employed to characterize the structural and chemical properties of the exfoliated GO. The results demonstrate that the electrochemical exfoliation method yields GO materials with varying degrees of oxidation, defect density, and crystallite size, depending on the applied potential and acid concentration. The graphene oxide samples exhibited distinct electrochemical properties, including charge transfer resistance, interfacial capacitance, and relaxation times for the charge transfer, as revealed by CV and EIS measurements with a specifically selected redox probe. The comprehensive characterization performed provides valuable insights into the structure-property relationships of the GO materials synthesized through electrochemical exfoliation of graphite.

Structure and functional group regulation of plastics for efficient ammonia capture

Activated carbon and metal organic frameworks have been tested as NH₃ recovery adsorbents, however, they are limited due to low NH₃ adsorption capacity and high cost, respectively. In this study, ethylene glycol dimethacrylate (EGDMA) polymers as the representative ester plastics were tested, and their structure and adsorption sites were regulated using HNO₃, HCl, or H₂SO₄ with varied H⁺ concentrations. The results showed that the EGDMA polymers all used hydrolysis which promoted NH₃ adsorption via different mechanisms. With HNO₃ and HCl optimization, an increased surface area promoted NH₃ adsorption via physical forces. H₂SO₄ optimization resulted in -COOH, -OH, and -SO₃H formation, which reacted with NH₃ by chemical adsorption and hydrogen bonds. This significantly increased the NH₃ adsorption capacity (85.99 mg·g^-1) compared to the material before optimization (0.36 mg·g^-1). This study presents a novel low-cost and efficient method to recycle waste plastics as NH₃ adsorbents.

Ni(II), Cr(VI), Cu(II) and nitrate removal by the co-system of Pseudomonas hibiscicola strain L1 immobilized on peanut shell biochar

At present, the improvement of nitrate and mixed heavy metals removal in wastewater by microorganism are urgently needed. Previous studies have shown that Pseudomonas hibiscicola strain L1 exhibited Ni(II) removal ability under aerobic denitrification. In this study, the characteristics of the free strain L1, peanut shell biochar (PBC) and further the co-system of strain L1 immobilized on PBC were investigated for the removal of Ni(II), Cr(VI), Cu(II) and nitrate in mix-wastewater. The results illustrated that strain L1 could remove 15.51% - 32.55% of Ni(II) (20-100 mg·L^-1), and removal ratios by co-system were ranked as Ni(II) (81.17%) > Cu(II) (45.84%) > Cr(VI) (38.21%). Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) images indicated that the strain L1 immobilized well on PBC and had vigorous biological activity; the crystals of Ni(OH)₂, Cu(OH)₂ and CrO(OH) etc. were formed on surface of co-system with various functional groups participated in. In Sequential Batch Reactor (SBR), the pollutant removal ratios by co-system were higher than that by free strain L1. This study illustrated that the co-system of strain L1 immobilized on PBC was qualified to be applied for practical scenarios of effective heavy metal removal of electroplating mix-wastewater.

Pomegranate seed polyphenol-based nanosheets as an efficient inhibitor of amyloid fibril assembly and cytotoxicity of HEWL

Poor water solubility and low bioavailability are considered as two main factors restricting therapeutic applications of natural polyphenols in relation to various disorders including amyloid-related diseases. Among various strategies developed to overcome these limitations, nanonization has attracted considerable attention. Herein, we compared the potency of bulk and nano forms of the polyphenolic fraction of pomegranate seed (PFPS) for modulating Hen Egg White Lysozyme (HEWL) amyloid fibril formation. Prepared PFPS nanosheets using direct oxidative pyrolysis were characterized by employing a range of spectroscopic and microscopic techniques. We found that the nano form can inhibit the assembly process and disintegrate preformed fibrils of HEWL much more effective than the bulk form of PFPS. Moreover, MTT-based cell viability and hemolysis assays showed the capacity of both bulk and nano forms of PFPS in attenuating HEWL amyloid fibril-induced toxicity, where the nano form was more effective. On the basis of thioflavin T results, a delay in the initiation of amyloid fibril assembly of HEWL appears to be the mechanism of action of PFPS nanosheets. We suggest that the improved efficiency of PFPS nanosheets in modulating the HEWL fibrillation process may be attributed to their increased surface area in accord with the surface-assistance model. Our results may present polyphenol-based nanosheets as a powerful approach for drug design against amyloid-related diseases.

PFPS nanosheets modulate the amyloid fibrillation of HEWL much more effective than the bulk form of PFPS. Based on the thioflavin T results, a delay in the initiation of the assembly process appears to be the mechanism of action of PFPS nanosheets.

Synthesis and Applications of Graphene Oxide

Thanks to the unique properties of graphite oxides and graphene oxide (GO), this material has become one of the most promising materials that are widely studied. Graphene oxide is not only a precursor for the synthesis of thermally or chemically reduced graphene: researchers revealed a huge amount of unique optical, electronic, and chemical properties of graphene oxide for many different applications. In this review, we focus on the structure and characterization of GO, graphene derivatives prepared from GO and GO applications. We describe GO utilization in environmental applications, medical and biological applications, freestanding membranes, and various composite systems.

Morphological and optical investigation of 2D material-based ternary nanocomposite: Bi2O3/MgO/GO synthesized by a co-precipitation technique

A ternary oxide nanocomposite based on Bi2O3/MgO/GO was prepared using a co-precipitation method taking into consideration of preparing the material for photoconductive device applications.

Graphene oxide mediated Fe(III) reduction for enhancing Fe(III)/H2O2 Fenton and photo-Fenton oxidation toward chloramphenicol degradation

Slow reduction of Fe(III) in iron-mediated Fenton-like systems strongly limits the decomposition of H₂O₂ to produce hydroxyl radicals (^•OH). Here, we report that graphene oxide (GO) possesses excellent reactivity to enhance the Fe(III)/H₂O₂ Fenton and photo-Fenton oxidation for degrading chloramphenicol (CAP). EPR analysis and quenching tests reveal that ^•OH is the primary oxidant for CAP degradation. The characterization analysis and iron species transformation experiments demonstrate that Fe(III) can combine with the functional groups on the GO surface to form GO-Fe(III) complexes. The chronopotentiometry and cyclic voltammogram suggest that GO can donate electrons to Fe(III) via intramolecular electron transfer and promote H₂O₂ induced Fe(III) reduction by increasing the oxidation capability of Fe(III) due to the formation of GO-Fe(III) complexes, resulting in the strong promotion of the Fe(III)/Fe(II) cycle for producing OH. Moreover, the dark- and vis-GO/Fe(III)/H₂O₂ systems can effectively degrade CAP at initial pH ranging from 2.0 to 4.7. The reusability and stability of GO were evaluated by performing the cyclic degradation experiments of CAP. The OH induced degradation pathway of CAP was proposed involving three stages, based on intermediates analysis of UPLC-QTOF-MS/MS system. Therefore, the GO/Fe(III)/H₂O₂ system with or without visible light shows high potential for application in environmental remediation.

Computational modelling of ammonia addition on partially reduced graphene oxide flakes

Density functional theory is employed to model the chemisorption of ammonia on epoxy-containing polycyclic aromatic hydrocarbons (PAHs) and understand the reaction mechanism of ammonia addition on partially reduced graphene oxide flakes. Coronene (C₂₄H₁₂) and ovalene (C₃₂H₁₄) based four-epoxy group containing molecules are used to mimic the RGO surface properties. The reaction mechanism changing effect of a second ammonia molecule as well as explicit water molecules is considered. The proposed reaction mechanism consists of two steps: the migration of one epoxy group out of the modelled four-epoxy group formation to a thermodynamically less stable one and the nucleophilic addition of the ammonia molecule. The second step involves forming an amine group and reducing an epoxy group to a hydroxyl one. Interestingly, the forming amine group bonds to the carbon atom with the smallest bond order among the available ones and not necessarily to the carbon atom of the opening epoxy ring. Incorporating a second ammonia molecule has a negligible effect on the overall reaction mechanism, while in the presence of one water molecule, the reaction goes through a different pathway involving a trimolecular state during the nucleophilic addition. Including more than one water molecule or applying an implicit solvent model does not cause further changes in the reaction.

Carboxyl groups do not play the major role in binding metal cations by graphene oxide

In this study, we investigate the chemical interactions of Mn²⁺ ions with graphene oxides, prepared by Hummers' (HGO) and Brodie's (BGO) methods in aqueous solutions by means of NMR relaxation. Carboxyl groups, which are always present in HGO in significant quantities, are often considered as the main binding sites for metal ions. Here we demonstrate that metal ions are bound efficiently by BGO, containing a negligibly small quantity of carboxyl groups. The difference in the shape of the relaxation curves is due mostly to the difference in the solubility and exfoliation degree of the two GO samples in aqueous media. HGO binds Mn²⁺ in the broad pH range, including highly acidic solutions, while BGO binds only at pH > 6, since it is not dispersible in water at lower pH values. The ability of BGO to chemically bind Mn²⁺ despite lacking sulfate and carboxyl groups, coupled with our earlier published findings, strongly suggests that carboxyl groups do not play the main role in binding metal ions by GO, as is commonly believed. We propose that metal ions initiate a significant transformation in the GO structure to attain the most efficient coordination of metal ions. This reorganization might involve the metal cation induced C-C bond cleavage with the formation of enols at the newly formed edges.

A Label-Free DNA-Immunosensor Based on Aminated rGO Electrode for the Quantification of DNA Methylation

In this work, we developed a sandwich DNA-immunosensor for quantification of the methylated tumour suppressor gene O-6-methylguanine-DNA methyltransferase (MGMT), which is a potential biomarker for brain tumours and breast cancer. The biosensor is based on aminated reduced graphene oxide electrode, which is achieved by ammonium hydroxide chemisorption and anti-5-methylcytosine (anti-5mC) as a methylation bioreceptor. The target single-strand (ss) MGMT oligonucleotide is first recognised by its hybridisation with complementary DNA to form double-stranded (ds) MGMT, which is then captured by anti-5mC on the electrode surface due to the presence of methylation. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM) techniques were used to characterise the electrode surface. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were used for electrochemical measurements. Under optimised conditions, the proposed biosensor is able to quantify a linear range of concentrations of the MGMT gene from 50 fM to 100 pM with a limit of detection (LOD) of 12 fM. The sandwich design facilitates the simultaneous recognition and quantification of DNA methylation, and the amination significantly improves the sensitivity of the biosensor. This biosensor is label-, bisulfite- and PCR-free and has a simple design for cost-efficient production. It can also be tailor-made to detect other methylated genes, which makes it a promising detection platform for DNA methylation-related disease diagnosis and prognosis.

Graphene oxide/graphene hybrid film with ultrahigh ammonia sensing performance

In this paper, a novel ammonia detection hybrid film is proposed based on a graphene oxide (GO)/graphene stack, which shows excellent sensing characteristics at room temperature. It is attributed to the cooperation of GO layer serving as molecular capture layer while graphene serving as conductive layer. GO layer is obtained on chemical vapor deposited graphene film by a simple drop-casting method. The prepared GO/graphene hybrid film is directly transferred to the target substrate without any additional transfer vehicle to reduce possible contamination. The success of the transfer depends on the mechanical strength of GO layer. The thickness of GO layer can scale down to 55 nm while sustaining the transfer process. The best ammonia gas sensing performance is obtained at about 275 nm GO layer thickness and the ammonia detection limit is calculated to be 1.5 ppb. In conclusion, the ammonia gas sensing performance of GO/graphene hybrid film can be significantly improved through GO layer thickness optimization.

Opening the internal structure for transport of ions: improvement of the structural and chemical properties of single-walled carbon nanohorns for supercapacitor electrodes

We investigated the electrochemical performance of single-walled carbon nanohorns (SWCNHs) for use as supercapacitor electrodes. For the first time, we used acid-treatment for oxidation of SWCNHs and hole creation in their structure. A detailed study was performed on the correlation between the oxidation of SWCNHs via acid treatment and variable acid treatment times, the structural properties of the oxidized carbon nanostructures, and the specific capacitance of the SWCNH electrodes. We showed that simple functionalization of carbon nanostructures under controlled conditions leads to an almost 3-fold increase in their specific capacitance (from 65 to 180 F g⁻¹ in 0.1 M H₂SO₄). This phenomenon indicates higher accessibility of the surface area of the electrodes by electrolyte ions as a result of gradual opening of the SWCNH internal channels.

The correlation between the oxidation of single-walled carbon nanohorns (SWCNHs) via acid treatment and the electrochemical properties of the SWCNH electrodes is presented.

Sequential Ammonia and Carbon Dioxide Adsorption on Pyrolyzed Biomass to Recover Waste Stream Nutrients

The amine-rich surfaces of pyrolyzed human solid waste (py-HSW) can be "primed" or "regenerated" with carbon dioxide (CO₂) to enhance their adsorption of ammonia (NH₃) for use as a soil amendment. To better understand the mechanism by which CO₂ exposure facilitates NH₃ adsorption to py-HSW, we artificially enriched a model sorbent, pyrolyzed, oxidized wood (py-ox wood) with amine functional groups through exposure to NH₃. We then exposed these N-enriched materials to CO₂ and then resorbed NH₃. The high heat of CO₂ adsorption (Q _st) on py-HSW, 49 kJ mol^-1, at low surface coverage, 0.4 mmol CO₂ g^-1, showed that the naturally occurring N compounds in py-HSW have a high affinity for CO₂. The Q _st of CO₂ on py-ox wood also increased after exposure to NH₃, reaching 50 kJ mol^-1 at 0.7 mmol CO₂ g^-1, demonstrating that the incorporation of N-rich functional groups by NH₃ adsorption is favorable for CO₂ uptake. Adsorption kinetics of py-ox wood revealed continued, albeit diminishing NH₃ uptake after each CO₂ treatment, averaging 5.9 mmol NH₃ g^-1 for the first NH₃ exposure event and 3.5 and 2.9 mmol NH₃ g^-1 for the second and third; the electrophilic character of CO₂ serves as a Lewis acid, enhancing surface affinity for NH₃ uptake. Furthermore, penetration of ¹⁵NH₃ and ¹³CO₂ measured by NanoSIMS reached over 7 μm deep into both materials, explaining the large NH₃ capture. We expected similar NH₃ uptake in py-HSW sorbed with CO₂ and py-ox wood because both materials, py-HSW and py-ox wood sorbed with NH₃, had similar N contents and similarly high CO₂ uptake. Yet NH₃ sorption in py-HSW was unexpectedly low, apparently from potassium (K) bicarbonate precipitation, reducing interactions between NH₃ and sorbed CO₂; 2-fold greater surface K in py-HSW was detected after exposure to CO₂ and NH₃ than before gas exposure. We show that amine-rich pyrolyzed waste materials have high CO₂ affinity, which facilitates NH₃ uptake. However, high ash contents as found in py-HSW hinder this mechanism.

Hummers' and Brodie's graphene oxides as photocatalysts for phenol degradation

Undoped metal-free graphene oxide (GO) materials prepared by either a modified Hummers' (GO-H) or a Brodie's (GO-B) method were tested as photocatalysts in aqueous solution for the oxidative conversion of phenol. In the dark, the adsorptive capacity of GO-B towards phenol (~35%) was higher than that of GO-H (~15%). Upon near-UV/Vis irradiation, GO-H was able to remove 21% of phenol after 180 min, mostly through adsorption. On the other hand, by using less energetic visible irradiation, GO-B removed as much as 95% in just 90 min. By thorough characterization of the prepared materials (SEM, HRTEM, TGA, TPD, Raman, XRD, XPS and photoluminescence) the observed performances could be explained in terms of their different surface chemistries. The GO-B presents the lower concentration of oxygen functional groups (in particular carbonyl groups as revealed by XPS) and it has a considerably higher photocatalytic activity compared to GO-H. Photoluminescence (PL) of liquid dispersions and XRD analysis of powders showed lower PL intensity and smaller interlayer distance for GO-B relative to GO-H, respectively: this suggests lower electron-hole recombination and enhanced electron transfer in GO-B, in support of its boosted photocatalytic activity. Reusability tests showed no efficiency loss after a second usage cycle and over three runs under visible irradiation, which was in line with the similarity of the XPS spectra of the fresh and used GO-B materials. Moreover, scavenging studies revealed that holes and hydroxyl radicals were the main reactive species in play during the photocatalytic process. The obtained results, establish for the first time, that GO prepared by Brodie's method is an active and stable undoped metal-free photocatalyst for phenol degradation in aqueous solutions, opening new paths for the application of more sustainable and metal-free materials for water treatment solutions.

Potential applications of graphene-based nanomaterials as adsorbent for removal of volatile organic compounds

In recent years, graphene-based materials (GBMs) have been regarded as the core technology in diverse research fields. Consequently, the demand for large-scale synthesis of GBMs has been increasing continuously for various fields of industry. These materials have become a competitive adsorbent for the removal of environmental pollutants with improved adsorption capacity and cost effectiveness through hybridization or fabrication of various functionalities on their large surface. In particular, their applicability opens up new avenues for the adsorptive removal of volatile organic compounds (VOCs) (e.g., through the build-up of efficient air purification systems). This review explored the basic knowledge and synthesis approaches for GBMs and their performances as adsorbent for VOC removal. Moreover, the mechanisms associated with the VOC removal were explained in detail. The performance of GBMs has also been evaluated along with their present limitations and future perspectives.

A review on exfoliation, characterization, environmental and energy applications of graphene and graphene-based composites

Because of an atom-thick two-dimensional structure with sp² hybridization, large specific area, high thermal conductivity, superior electron mobility, and chemical stability, graphene (GN) has developed substantial interest among researchers, exponentially accelerating GN based research. GN and its derivatives are the potentially attractive materials to develop composites for energy and environmental applications. This review covered a general overview on physical and chemical properties of GN and based composite materials, briefly summarizing exfoliation methodologies and characterization techniques in the first section. The environmental applications of GN and GN composites in detection of gases, bacteria as well as in the removal of organic and inorganic pollutants were comprehensively addressed in the second section. Third section focused on recent progress associated with the applications of GN and its composites in solar energy conversion, electrochemical energy devices, storage and production of hydrogen. Finally, conclusive remarks emphasizing unresolved problems and major future challenges were covered in the last section. In addition, the prospects and further development of GN and GN composites in energy, environment and bioscience were discussed.

Nanoscale chemical mapping of oxygen functional groups on graphene oxide using atomic force microscopy-coupled infrared spectroscopy

The unambiguous determination of the chemical functionality over graphene oxide (GO) is important to unleash its potential applications. However, the mapping of oxygen functionalities distribution remains to be unequivocally determined because of highly inhomogeneous non-stoichiometric structures and ultra-thin layers of GO. In this study, we report an experimental observation of the spatial distribution of oxygen functional groups on monolayer and multilayer GO using AFM-IR, atomic force microscopy coupled with infrared spectroscopy. Overcoming conventional IR diffraction limit for several micrometers, the novel AFM-IR reaches high spatial resolution ∼20 nm and could detect IR absorption on ∼1 nm thickness of monolayer GO. With nanoscale chemical mapping, the distribution of different oxygen functional groups is distinguished with AFM-IR over the GO surface. It allows us to observe that these oxygen functional groups prefer to sit on the fold areas, in discrete domains and on the edges of GO, which gave more insights into its chemical nature. The determination of the position of functional groups through precise imaging contributes to our understanding of GO structure-properties relations and paves the way for targeted tethering of polymers, biomaterials, and other nanostructures.

Monitoring of Chemical Risk Factors for Sudden Infant Death Syndrome (SIDS) by Hydroxyapatite-Graphene-MWCNT Composite-Based Sensors

Sensing properties of chemical sensors based on ternary hydroxyapatite-graphene-multiwalled carbon nanotube (HA-GN-MWCNT) nanocomposite in the detection of chemical substances representing risk factors for sudden infant death syndrome (SIDS), have been evaluated. Characterization data of the synthesized composite have shown that the graphene-MWCNT network serves as a matrix to uniformly disperse the hydroxyapatite nanoparticles and provide suitable electrical properties required for developing novel electrochemical and conductometric sensors. A HA-GN-MWCNT composite-modified glassy carbon electrode (HA-GN-MWCNT/GCE) has been fabricated and tested for the simultaneous monitoring of nicotine and caffeine by cyclic voltammetry (CV) and square wave voltammetry (SWV), whereas a HA-GN-MWCNT conductive gas sensor has been tested for the detection of CO2 in ambient air. Reported results suggest that the synergic combination of the chemical properties of HA and electrical/electrochemical characteristics of the mixed graphene-MWCNT network play a prominent role in enhancing the electrochemical and gas sensing behavior of the ternary HA-GN-MWCNT hybrid nanostructure. The high performances of the developed sensors make them suitable for monitoring unhealthy actions (e. g. smoking, drinking coffee) in breastfeeding women and environmental factors (bad air quality), which are associated with an enhanced risk for SIDS.

Continuous-Flow Process for Glycerol Conversion to Solketal Using a Brönsted Acid Functionalized Carbon-Based Catalyst

The acetalization of glycerol with acetone represents a strategy for its valorization into solketal as a fuel additive component. Thus, acid carbon-based structured catalyst (SO3H-C) has been prepared, characterized and tested in this reaction. The structured catalyst (L = 5 cm, d = 1 cm) showed a high surface density of acidic sites (2.9 mmol H+ g−1) and a high surface area. This catalyst is highly active and stable in the solketal reaction production in a batch reactor system and in a continuous downflow reactor, where several parameters were studied such as the variation of time of reaction, temperature, acetone/glycerol molar ratio (A/G) and weight hourly space velocity (WHSV). A complete glycerol conversion and 100% of solketal selectivity were achieved working in the continuous flow reactor equipped with distillation equipment when WHSV is 2.9 h−1, A/G = 8 at 57 °C in a co-solvent free operation. The catalyst maintained its activity under continuous flow even after 300 min of reaction.

Fire-derived organic matter retains ammonia through covalent bond formation

Fire-derived organic matter, often referred to as pyrogenic organic matter (PyOM), is present in the Earth's soil, sediment, atmosphere, and water. We investigated interactions of PyOM with ammonia (NH3) gas, which makes up much of the Earth's reactive nitrogen (N) pool. Here we show that PyOM's NH3 retention capacity under ambient conditions can exceed 180 mg N g-1 PyOM-carbon, resulting in a material with a higher N content than any unprocessed plant material and most animal manures. As PyOM is weathered, NH3 retention increases sixfold, with more than half of the N retained through chemisorption rather than physisorption. Near-edge X-ray absorption fine structure and nuclear magnetic resonance spectroscopy reveal that a variety of covalent bonds form between NH3-N and PyOM, more than 10% of which contained heterocyclic structures. We estimate that through these mechanisms soil PyOM stocks could retain more than 600-fold annual NH3 emissions from agriculture, exerting an important control on global N cycling.

Proton Transfer at the Interaction Interface of Graphene Oxide

Proton transfer plays a crucial role in a variety of biological phenomena. The transformation of nanomaterials in the environment and biology makes probing the potential proton transfer between nanomaterials and biomolecules a crucial issue, but it still remains a significant challenge. Here, we report proton transfer at the interface of graphene oxide (GO) by studying the GO-induced vibrational changes of interfacial water and carboxyl-terminated self-assembled monolayer (SAM) with surface-enhanced infrared absorption spectroscopy. In addition to simply acting as a macromolecular buffer in solution, the GO sheet behaves as a two-dimensional hydrogen-bonded exchangeable proton pool to dissociate and transfer protons at the interface with a suitable Brønsted base pair, which may bear a significant potential toxic origin for biological systems with proton-coupled reactions.

Surface Pore Engineering of Covalent Organic Frameworks for Ammonia Capture through Synergistic Multivariate and Open Metal Site Approaches

Ammonia (NH₃) is a commonly used industrial gas, but its corrosiveness and toxicity are hazardous to human health. Although many adsorbents have been investigated for NH₃ sorption, limited ammonia uptake remains an urgent issue yet to be solved. In this article, a series of multivariate covalent organic frameworks (COFs) are explored which are densely functionalized with various active groups, such as -N-H, -C=O, and carboxyl group. Then, a metal ion (Ca²⁺, Mn²⁺, and Sr²⁺) is integrated into the carboxylated structure achieving the first case of an open metal site in COF architecture. X-ray photoelectron spectroscopy reveals conclusive evidence for the multiple binding interactions with ammonia in the modified COF materials. Infrared spectroscopy indicates a general trend of binding capability from weak to strong along with -N-H, -C=O, carboxyl group, and metal ion. Through the synergistic multivariate and open metal site, the COF materials show excellent adsorption capacities (14.3 and 19.8 mmol g^-1 at 298 and 283 K, respectively) and isosteric heat (Q_st) of 91.2 kJ mol^-1 for ammonia molecules. This novel approach enables the development of tailor-made porous materials with tunable pore-engineered surface for ammonia uptake.

Insights into the role of nanostructure in the sensing properties of carbon nanodots for improved sensitivity to reactive oxygen species in living cells

The surface states of carbon nanodots (CDs) were engineered by controlling the chemical structure on the surface of the CDs, which play an important role in the chemiluminescence sensing properties of CDs towards peroxynitrite. Their application in monitoring exogenous and endogenous release of peroxynitrite in living cells is demonstrated.

Solvent-assisted thermal reduction of microcrystalline graphene oxide with excellent microwave absorption performance

To prepare a new kind of electromagnetic wave absorber, and improve the processing technology and accessional value of natural microcrystalline graphite minerals (NMGMs), reduced microcrystalline graphene oxide (rGO-M), a novel absorber with high absorption, low reflection and a wide absorption band, was prepared from NMGMs using a solvent-assisted thermal reduction method. Moreover, the as-produced rGO-M with adjustable electrical resistivity can be easily transferred into well distributed bulk materials by freeze-drying technology. These unique structures and compositions make a great contribution to the impedance match, and cause strong conductive loss and various dipole polarization effects which greatly enhance the absorption. Meanwhile, the effective bandwidths below −5 dB and −10 dB are 11.7 GHz and 3.32 GHz respectively, and the reflection loss can reach −42.68 dB. The study will be beneficial to the development of carbon resources and carbon materials research. Besides, it can provide a scientific basis for the further improvement of the comprehensive utilization and the level of deep processing technology of NMGM resources.

Reduced microcrystalline graphene oxide (rGO-M), a novel absorber with high absorption, low reflection and a wide absorption band, was prepared from NMGMs using a solvent-assisted thermal reduction method.

Nut-like MOF/hydroxylated graphene hybrid materials for adsorptive desulfurization of thiophene

A series of novel metal–organic framework/hydroxylated graphene hybrid materials were successfully designed and synthesized with different ratios of Cu-BTC and hydroxylated graphene and their adsorption performances for thiophene from oils were evaluated.

Investigation of Pristine Graphite Oxide as Room-Temperature Chemiresistive Ammonia Gas Sensing Material

Graphite oxide has been investigated as a possible room-temperature chemiresistive sensor of ammonia in a gas phase. Graphite oxide was synthesized from high purity graphite using the modified Hummers method. The graphite oxide sample was investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetry and differential scanning calorimetry. Sensing properties were tested in a wide range of ammonia concentrations in air (10-1000 ppm) and under different relative humidity levels (3%-65%). It was concluded that the graphite oxide-based sensor possessed a good response to NH₃ in dry synthetic air (ΔR/R₀ ranged from 2.5% to 7.4% for concentrations of 100-500 ppm and 3% relative humidity) with negligible cross-sensitivity towards H₂ and CH₄. It was determined that the sensor recovery rate was improved with ammonia concentration growth. Increasing the ambient relative humidity led to an increase of the sensor response. The highest response of 22.2% for 100 ppm of ammonia was achieved at a 65% relative humidity level.

Differential cytotoxic effects of graphene and graphene oxide on skin keratinocytes

Impressive properties make graphene-based materials (GBMs) promising tools for nanoelectronics and biomedicine. However, safety concerns need to be cleared before mass production of GBMs starts. As skin, together with lungs, displays the highest exposure to GBMs, it is of fundamental importance to understand what happens when GBMs get in contact with skin cells. The present study was carried out on HaCaT keratinocytes, an in vitro model of skin toxicity, on which the effects of four GBMs were evaluated: a few layer graphene, prepared by ball-milling treatment (FLG), and three samples of graphene oxide (GOs, a research-grade GO1, and two commercial GOs, GO2 and GO3). Even though no significant effects were observed after 24 h, after 72 h the less oxidized compound (FLG) was the less cytotoxic, inducing mitochondrial and plasma-membrane damages with EC₅₀s of 62.8 μg/mL (WST-8 assay) and 45.5 μg/mL (propidium iodide uptake), respectively. By contrast, the largest and most oxidized compound, GO3, was the most cytotoxic, inducing mitochondrial and plasma-membrane damages with EC₅₀s of 5.4 and 2.9 μg/mL, respectively. These results suggest that only high concentrations and long exposure times to FLG and GOs could impair mitochondrial activity associated with plasma membrane damage, suggesting low cytotoxic effects at the skin level.

Vertically aligned PANI nanorod arrays grown on graphene oxide nanosheets for a high-performance NH3 gas sensor

Vertically aligned PANI nanorod arrays uniformly distributed on GO nanosheets for a highly sensitive ammonia sensor.