Geopolymers are emerging as sustainable alternatives to Ordinary Portland Cement (OPC), offering high strength, lightweight properties, and a lower environmental impact, making them promising materials for green concrete technologies. In this study, we synthesized graphene-based geopolymer nanocomposites using various functional graphene derivatives, such as graphene oxide (GO), sulfonated graphene oxide (G-SO3H) thiographene (G-SH), and phosphate graphene (G-PO3H), along with alumina- and silica-rich waste materials, such as fly ash and dolomite, to enhance mechanical properties, including setting time, flowability, compressive strength, and water absorption. The functional groups on graphene derivatives improve the particle dispersion and matrix density, enhancing compressive strength, while Raman spectroscopy reveals spectral shifts at interfaces of phosphate graphene with dolomite and fly ash, indicating interactions. The resultant FDGP exhibits a significantly higher compressive strength of 45.60 MPa at 7 days and 50.20 MPa at 28 days compared to GO, G-SH, and G-SO3H. The high concentration of phosphate functional groups promotes strong interactions with the geopolymer matrix, improving its workability. Furthermore, density functional theory (DFT) calculations elucidate the role of functional groups in graphene-based geopolymer concrete, enhancing molecular interactions and promoting robust interfacial adhesion with the geopolymer matrix for a superior performance. We studied the time-dependent interactions of functionalized graphene oxide phosphate using DFT and other characterization methods, revealing strong hydrogen bonding that enhances dispersion and reinforcement within the geopolymer matrix.

• Klíčová slova
• compressive strength, density functional theory (DFT), fly ash (FA), functional graphene derivatives, geopolymers, interfacial chemistry, water absorption,
• Publikační typ
• časopisecké články MeSH

Polarons belong to a class of extensively studied quasiparticles that have found applications spanning diverse fields, including charge transport, colossal magnetoresistance, thermoelectricity, (multi)ferroism, optoelectronics, and photovoltaics. It is notable, though, that their interaction with the local environment has been overlooked so far. We report an unexpected phenomenon of the solvent-induced generation of polaronic spin active states in a two-dimensional (2D) material fluorographene under UV light. Furthermore, we present compelling evidence of the solvent-specific nature of this phenomenon. The generation of spin-active states is robust in acetone, moderate in benzene, and absent in cyclohexane. Continuous wave X-band electron paramagnetic resonance (EPR) spectroscopy experiments revealed a massive increase in the EPR signal for fluorographene dispersed in acetone under UV-light irradiation, while the system did not show any significant signal under dark conditions and without the solvent. The patterns appeared due to the generation of transient magnetic photoexcited states of polaronic character, which encompassed the net 1/2 spin moment detectable by EPR. Advanced ab initio calculations disclosed that polarons are plausibly formed at radical sites in fluorographene which interact strongly with acetone molecules in their vicinity. Additionally, we present a comprehensive scenario for multiplication of polaronic spin active species, highlighting the pivotal role of the photoinduced charge transfer from the solvent to the electrophilic radical centers in fluorographene. We believe that the solvent-tunable polaron formation with the use of UV light and an easily accessible 2D nanomaterial opens up a wide range of future applications, ranging from molecular sensing to magneto-optical devices.

• Publikační typ
• časopisecké články MeSH

Single-atom catalysts (SACs) based on graphene derivatives are an emerging and growing class of materials functioning as two-dimensional (2D) metal-coordination scaffolds with intriguing properties. Recently, owing to the rich chemistry of fluorographene, new avenues have opened toward graphene derivatives with selective, spacer-free, and dense functionalization, acting as in-plane or out-of-plane metal coordination ligands. The particular structural features give rise to intriguing phenomena occurring between the coordinated metals and the graphene backbone. These include redox processes, charge transfer, emergence, and stabilization of rare or otherwise unstable metal valence states, as well as metal-support and metal-metal synergism. The vast potential of such systems has been demonstrated as enzyme mimics for cooperative mixed-valence SACs, ethanol fuel cells, and CO2 fixation; however, it is anticipated that their impact will further expand toward diverse fields, e.g., advanced organic transformations, electrochemical energy storage, and energy harvesting.

• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Fluorographene has been recently shown to be a suitable platform for synthesizing numerous graphene derivatives with desired properties. In that respect, N-octylamine-modified fluorographenes with variable degrees of functionalization are studied and their nonlinear optical properties are assessed using 4 ns pulses. A very strong enhancement of the nonlinear optical response and a very efficient optical limiting action are observed, being strongly dependent on the degree of functionalization of fluorographene. The observed enhanced response is attributed to the increasing number of defects because of the incorporation of N-heteroatoms in the graphitic network upon functionalization with N-octylamine. The present work paves the way for the controlled covalent functionalization of graphene enabling a scalable access to a wide portfolio of graphene derivatives with custom-tailored properties.

• Klíčová slova
• N-doped graphene, graphene functionalization, nonlinear optical response, optical limiting,
• Publikační typ
• časopisecké články MeSH

Our recent experience of the COVID-19 pandemic has highlighted the importance of easy-to-use, quick, cheap, sensitive and selective detection of virus pathogens for the efficient monitoring and treatment of virus diseases. Early detection of viruses provides essential information about possible efficient and targeted treatments, prolongs the therapeutic window and hence reduces morbidity. Graphene is a lightweight, chemically stable and conductive material that can be successfully utilized for the detection of various virus strains. The sensitivity and selectivity of graphene can be enhanced by its functionalization or combination with other materials. Introducing suitable functional groups and/or counterparts in the hybrid structure enables tuning of the optical and electrical properties, which is particularly attractive for rapid and easy-to-use virus detection. In this review, we cover all the different types of graphene-based sensors available for virus detection, including, e.g., photoluminescence and colorimetric sensors, and surface plasmon resonance biosensors. Various strategies of electrochemical detection of viruses based on, e.g., DNA hybridization or antigen-antibody interactions, are also discussed. We summarize the current state-of-the-art applications of graphene-based systems for sensing a variety of viruses, e.g., SARS-CoV-2, influenza, dengue fever, hepatitis C virus, HIV, rotavirus and Zika virus. General principles, mechanisms of action, advantages and drawbacks are presented to provide useful information for the further development and construction of advanced virus biosensors. We highlight that the unique and tunable physicochemical properties of graphene-based nanomaterials make them ideal candidates for engineering and miniaturization of biosensors.

• Klíčová slova
• Biosensor, Graphene, Nanocomposite, SARS-CoV-2, Virus,
• MeSH
• Betacoronavirus genetika   izolace a purifikace   patogenita   MeSH
• biosenzitivní techniky * přístrojové vybavení   metody   trendy   MeSH
• COVID-19 MeSH
• design vybavení MeSH
• DNA virů analýza   genetika   MeSH
• elektrochemické techniky MeSH
• grafit * chemie   MeSH
• hybridizace nukleových kyselin MeSH
• klinické laboratorní techniky * přístrojové vybavení   metody   statistika a číselné údaje   MeSH
• kolorimetrie MeSH
• koronavirové infekce diagnóza   epidemiologie   virologie   MeSH
• kvantové tečky chemie   MeSH
• lidé MeSH
• luminiscence MeSH
• nanostruktury chemie   MeSH
• pandemie MeSH
• povrchová plasmonová rezonance MeSH
• Ramanova spektroskopie MeSH
• reakce antigenu s protilátkou MeSH
• SARS-CoV-2 MeSH
• testování na COVID-19 MeSH
• virologie metody   MeSH
• virová pneumonie diagnóza   epidemiologie   virologie   MeSH
• viry genetika   izolace a purifikace   patogenita   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• DNA virů MeSH
• grafit * MeSH

Using enzymes as bioelectrocatalysts is an important step toward the next level of biotechnology for energy production. In such biocatalysts, a sacrificial cofactor as an electron and proton source is needed. This is a great obstacle for upscaling, due to cofactor instability and product separation issues, which increase the costs. Here, we report a cofactor-free electroreduction of CO2 to a high energy density chemical (methanol) catalyzed by enzyme-graphene hybrids. The biocatalyst consists of dehydrogenases covalently bound on a well-defined carboxyl graphene derivative, serving the role of a conductive nanoplatform. This nanobiocatalyst achieves reduction of CO2 to methanol at high current densities, which remain unchanged for at least 20 h of operation, without production of other soluble byproducts. It is thus shown that critical improvements on the stability and rate of methanol production at a high Faradaic efficiency of 12% are possible, due to the effective electrochemical process from the electrode to the enzymes via the graphene platform.

• Klíčová slova
• bioelectrocatalysis, carbon dioxide reduction, enzyme catalysis, enzyme immobilization, graphene, methanol,
• MeSH
• biokatalýza * MeSH
• enzymy imobilizované chemie   MeSH
• grafit chemie   MeSH
• methanol chemická syntéza   MeSH
• oxid uhličitý chemie   MeSH
• oxidace-redukce MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• enzymy imobilizované MeSH
• grafit MeSH
• methanol MeSH
• oxid uhličitý MeSH

Controllable synthesis of graphene derivatives with defined composition and properties represents the holy grail of graphene chemistry, especially in view of the low reactivity of graphene. Recent progress in fluorographene (FG) chemistry has opened up new routes for synthesizing a plethora of graphene derivatives with widely applicable properties, but they are often difficult to control. We explored nucleophilic substitution on FG combining density functional theory calculations with experiments to achieve accurate control over the functionalization process. In-depth analysis revealed the complexity of the reaction and identified basic rules for controlling the 2D chemistry. Their application, that is, choice of solvent and reaction time, enabled facile control over the reaction of FG with N-octylamine to form graphene derivatives with tailored content of the alkylamine functional group (2.5-7.5% N atomic content) and F atoms (31.5-3.5% F atomic content). This work substantially extends prospects for the controlled covalent functionalization of graphene.

• Publikační typ
• časopisecké články MeSH

Preparation of graphene derivatives using fluorographene (FG) as a precursor has become a key strategy for the large-scale synthesis of new 2-D materials (e.g. graphene acid, cyanographene, allyl-graphene) with tailored physicochemical properties. However, to gain full control over the derivatization process, it is essential to understand the reaction mechanisms and accompanying processes that affect the composition and structure of the final products. Despite the strength of C-F bonds and high chemical stability of perfluorinated hydrocarbons, FG is surprisingly susceptible to reactions under ambient conditions. There is clear evidence that nucleophilic substitution on FG is accompanied by spontaneous defluorination, and solvent-induced defluorination can occur even in the absence of any nucleophilic agent. Here, we show that distributed radical centers (fluorine vacancies) on the FG surface need to be taken into account in order to rationalize the defluorination mechanism. Depending on the environment, these radical centers can react as electron acceptors, electrophilic sites and/or cause homolytic bond cleavages. We also propose a new radical mechanism of FG defluorination in the presence of N,N'-dimethylformamide (DMF) solvent. Spin-trap experiments as well as 19F NMR measurements unambiguously confirmed formation of N,N'-dimethylformyl radicals and also showed that N,N'-dimethylcarbamoyl fluoride plays a key role in the proposed mechanism. These findings imply that point defects in 2D materials should be considered as key factor determining their chemical properties and reactivity.

• Publikační typ
• časopisecké články MeSH

Fluorographene, formally a two-dimensional stoichiometric graphene derivative, attracted remarkable attention of the scientific community due to its extraordinary physical and chemical properties. We overview the strategies for the preparation of fluorinated graphene derivatives, based on top-down and bottom-up approaches. The physical and chemical properties of fluorographene, which is considered as one of the thinnest insulators with a wide electronic band gap, are presented. Special attention is paid to the rapidly developing chemistry of fluorographene, which was advanced in the last few years. The unusually high reactivity of fluorographene, which can be chemically considered perfluorinated hydrocarbon, enables facile and scalable access to a wide portfolio of graphene derivatives, such as graphene acid, cyanographene and allyl-graphene. Finally, we summarize the so far reported applications of fluorographene and fluorinated graphenes, spanning from sensing and bioimaging to separation, electronics and energy technologies.

• Klíčová slova
• Chemistry, Covalent functionalization, Fluorographene, Graphene derivatives,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Efficient and selective methods for covalent derivatization of graphene are needed because they enable tuning of graphene's surface and electronic properties, thus expanding its application potential. However, existing approaches based mainly on chemistry of graphene and graphene oxide achieve only limited level of functionalization due to chemical inertness of the surface and nonselective simultaneous attachment of different functional groups, respectively. Here we present a conceptually different route based on synthesis of cyanographene via the controllable substitution and defluorination of fluorographene. The highly conductive and hydrophilic cyanographene allows exploiting the complex chemistry of -CN groups toward a broad scale of graphene derivatives with very high functionalization degree. The consequent hydrolysis of cyanographene results in graphene acid, a 2D carboxylic acid with pKa of 5.2, showing excellent biocompatibility, conductivity and dispersibility in water and 3D supramolecular assemblies after drying. Further, the carboxyl groups enable simple, tailored and widely accessible 2D chemistry onto graphene, as demonstrated via the covalent conjugation with a diamine, an aminothiol and an aminoalcohol. The developed methodology represents the most controllable, universal and easy to use approach toward a broad set of 2D materials through consequent chemistries on cyanographene and on the prepared carboxy-, amino-, sulphydryl-, and hydroxy- graphenes.

• Klíčová slova
• 2D acid, fluorographene chemistry, graphene acid, graphene nitrile, nucleophilic substitution,
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH