J. Kou, C. Lu, J. Wang, Y. Chen, Z. Xu, R. S. Varma: Selectivity Enhancement in Heterogeneous Photocatalytic Transformations, CHEMICAL REVIEWS, Article ASAP, 2017.
DOI: 10.1021/acs.chemrev.6b00396, IF = 37.369
Abstract: Photocatalysis has been invariably considered as an unselective process (especially in water) for a fairly long period of time, and the investigation on selective photocatalysis has been largely neglected. In recent years, the field of selective photocatalysis is developing rapidly and now extended to several newer applications. This review focuses on the overall strategies which can improve the selectivity of photocatalysis encompassing a wide variety of photocatalysts, and modifications thereof, as well as the related vital processes of industrial significance such as reduction and oxidation of organics, inorganics, and CO2 transformation. Comprehensive and successful strategies for enhancing the selectivity in photocatalysis are abridged to reinvigorate and stimulate future investigations. In addition, nonsemiconductor type photocatalysts, such as Ti–Si molecular sieves and carbon quantum dots (CQDs), are also briefly appraised in view of their special role in special selective photocatalysis, namely epoxidation reactions, among others. In the end, a summary and outlook on the challenges and future directions in the research field are included in the comprehensive review.
K. Jayaramulu, F. Geyer, M. Petr, R. Zboril, D. Vollmer, R. A. Fischer: Shape Controlled Hierarchical Porous Hydrophobic/Oleophilic Metal-Organic Nanofibrous Gel Composites for Oil Adsorption, ADVANCED MATERIALS, Article in Press, 2017.
DOI: 10.1002/adma.201605307, IF = 18.96
Abstract: A versatile and facile synthetic route toward a ultralight hierarchical poroushybrid composed of metal-organic gels and fluorinated graphene oxide is reported. The composite gels show excellent absorbency of oil and various organic solvents due to their prominent meso/macropores, notable hydrophobicity, and superoleophilicity.
A. Bakandritsos, M. Pykal, P. Blonski, P. Jakubec, D. D. Chronopoulos, K. Polakova, V. Georgakilas, K. Čépe, O. Tomanec, V. Ranc, A. B. Bourlinos, R. Zboril, M. Otyepka: Cyanographene and Graphene Acid - Emerging Derivatives Enabling High-Yield and Selective Functionalization of Graphene, ACS NANO, Article in press, 2017.
DOI: 10.1021/acsnano.6b08449, IF = 13.334
Abstract: 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 non-selective 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 towards 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 towards a broad set of 2D materials through consequent chemistries on cyanographene and on the prepared carboxy-, amino-, sulphydryl-, and hydroxy- graphenes.
S. Kalytchuk, K. Poláková, Y. Wang, J. P. Froning, K. Cepe, A. L. Rogach, R. Zbořil: Carbon Dot Nanothermometry: Intracellular Photoluminescence Lifetime Thermal Sensing, ACS NANO, vol. 11, iss. 2, pp. 1432–1442, 2017.
DOI: 10.1021/acsnano.6b06670, IF = 13.334
Abstract: Nanoscale biocompatible photoluminescence (PL) thermometers that can be used to accurately and reliably monitor intracellular temperatures have many potential applications in biology and medicine. Ideally, such nanothermometers should be functional at physiological pH across a wide range of ionic strengths, probe concentrations, and local environments. Here, we show that water-soluble N,S-co-doped carbon dots (CDs) exhibit temperature-dependent photoluminescence lifetimes and can serve as highly sensitive and reliable intracellular nanothermometers. PL intensity measurements indicate that these CDs have many advantages over alternative semiconductor- and CD-based nanoscale temperature sensors. Importantly, their PL lifetimes remain constant over wide ranges of pH values (5–12), CD concentrations (1.5 × 10–5 to 0.5 mg/mL), and environmental ionic strengths (up to 0.7 mol·L–1 NaCl). Moreover, they are biocompatible and nontoxic, as demonstrated by cell viability and flow cytometry analyses using NIH/3T3 and HeLa cell lines. N,S-CD thermal sensors also exhibit good water dispersibility, superior photo- and thermostability, extraordinary environment and concentration independence, high storage stability, and reusability–their PL decay curves at temperatures between 15 and 45 °C remained unchanged over seven sequential experiments. In vitro PL lifetime-based temperature sensing performed with human cervical cancer HeLa cells demonstrated the great potential of these nanosensors in biomedicine. Overall, N,S-doped CDs exhibit excitation-independent emission with strongly temperature-dependent monoexponential decay, making them suitable for both in vitro and in vivo luminescence lifetime thermometry.
P. Blonski, J. Tucek, Z. Sofer, V. Mazánek, M. Petr, M. Pumera, M. Otyepka, R. Zboril: Doping with Graphitic Nitrogen Triggers Ferromagnetism in Graphene, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 139, iss. 8, pp. 3171–3180, 2017.
DOI: 10.1021/jacs.6b12934, IF = 13.038
Abstract: Nitrogen doping opens possibilities for tailoring the electronic properties and band gap of graphene towards its applications, e.g., in spintronics and optoelectronics. One major obstacle is development of magnetically active N-doped graphene with spin-polarized conductive behavior. However, the effect of nitrogen on the magnetic properties of graphene has so far only been addressed theoretically and triggering of magnetism through N-doping has not yet been proved experimentally, except for systems containing a high amount of oxygen and thus decreased conductivity. Here, we report the first example of ferromagnetic graphene achieved by controlled doping with graphitic, pyridinic, and chemisorbed nitrogen. The magnetic properties were found to depend strongly on both the nitrogen concentration and type of structural N-motifs generated in the host lattice. Graphenes doped below 5 at.% of nitrogen were nonmagnetic; however, once doped at 5.1 at.% of nitrogen, N-doped graphene exhib-ited transition to a ferromagnetic state at ~69 K and displayed a saturation magnetization reaching 1.09 emu/g. Theoretical calculations were used to elucidate the effects of individual chemical forms of nitrogen on magnetic properties. Results showed that magnetic ef-fects were triggered by graphitic nitrogen, whereas pyridinic and chemisorbed nitrogen contributed much less to the overall ferromagnetic ground state. Calcula-tions further proved the existence of exchange coupling among the paramagnetic centers mediated by the con-duction electrons.
J. Tuček, K. Holá, A. B. Bourlinos, P. Błoński, A. Bakandritsos, J. Ugolotti, M. Dubecký, F. Karlický, V. Ranc, K. Čépe, M. Otyepka, R. Zbořil: Room temperature organic magnets derived from sp3 functionalized graphene, NATURE COMMUNICATIONS vol. 8, pp. 14525, 2017.
DOI: 10.1038/ncomms14525, IF = 11.329
Abstract: Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp2-conjugated diradical motifs embedded in an sp3 matrix and superexchange interactions via –OH functionalization.
S. Presolski, L. Wang, A. H. Loo, A. Ambrosi, P. Lazar, V. Ranc, M. Otyepka, R. Zboril, O. Tomanec, J. Ugolotti, Z. Sofer, M. Pumera: Functional Nanosheet Synthons by Covalent Modification of Transition-Metal Dichalcogenides, CHEMISTRY OF MATERIALS vol. 29, iss. 5, pp. 2066-2073, 2017.
DOI: 10.1021/acs.chemmater.6b04171, IF = 9.407
Abstract: We report on the facile preparation of versatile MoS2–thiobarbituric acid conjugates, which, in addition to excellent electrochemical behavior, can serve as nanosheet platforms for further functionalization in a multitude of applications. We show that chemically exfoliated MoS2 was extensively modified with up to 50% surface coverage, while maintaining its metallic character, and that the strategy can be extended to MoSe2, WS2, and WSe2. The covalent functionalization endowed the materials not only with good aqueous dispersibility, but also with improved hydrogen evolution reaction (HER) activity, as well as promise in the oxidative detection of DNA nucleobases in solution.
D. D. Chronopoulos, A. Bakandritsos, P. Lazar, M. Pykal, K. Čépe, R. Zbořil, M. Otyepka: High-Yield Alkylation and Arylation of Graphene via Grignard Reaction with Fluorographene, CHEMISTRY OF MATERIALS, vol. 29, iss. 3, pp. 926–930, 2017.
DOI: 10.1021/acs.chemmater.6b05040, IF = 9.407
J. P. Froning, P. Lazar, M. Pykal, Q. Li, M. Dong, R. Zbořil, M. Otyepka: Direct mapping of chemical oxidation of individual graphene sheets through dynamic force measurements at the nanoscale, NANOSCALE vol. 9, iss. 1, pp. 119-127, 2017.
DOI: 10.1039/c6nr05799c, IF = 7.76
Abstract: Graphene oxide is one of the most studied nanomaterials owing to its huge application potential in many fields, including biomedicine, sensing, drug delivery, optical and optoelectronic technologies. However, a detailed description of the chemical composition and the extent of oxidation in graphene oxide remains a key challenge affecting its applicability and further development of new applications. Here, we report direct monitoring of the chemical oxidation of an individual graphene flake during ultraviolet/ozone treatment through in situ atomic force microscopy based on dynamic force mapping. The results showed that graphene oxidation expanded from the graphene edges to the entire graphene surface. The interaction force mapping results correlated well with X-ray photoelectron spectroscopy data quantifying the degree of chemical oxidation. Density functional theory calculations confirmed the specific interaction forces measured between a silicon tip and graphene oxide. The developed methodology can be used as a simple protocol for evaluating the chemical functionalization of other two-dimensional materials with covalently attached functional groups.
H. Han, F. Riboni, F. Karlický , S. Kment, A. Goswami, P. . Sudhagar, J. Yoo, L. Wang, O. Tomanec, M. Petr, O. Haderka, C. Terashima, A. Fujishima, P. Schmuki, R. Zboril: α-Fe2O3/TiO2 3D Hierarchical Nanostructures for enhanced Photoelectrochemical Water Splitting, NANOSCALE, vol. 9, iss. 1, pp. 134-142, 2017.
DOI: 10.1039/c6nr06908h, IF = 7.76
Abstract: We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe2O3 nanoflakes branched on TiO2 nanotubes. The novel α-Fe2O3/TiO2 hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO2 nanotubes. An enhanced separation of photogenerated charge carriers is here proposed as main factor for the observed photo-activities: electrons photogenerated in TiO2 are efficiently collected at FTO, while holes are transferred to the α-Fe2O3 nanobranches that serve as charge mediator to the electrolyte. The morphology of α-Fe2O3 that varies from ultra-thin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-Fe2O3/TiO2 composites. In particular, it is shown that for an optimized photo-electrochemical structure a combination of critical factors should be achieved such as i) TiO2 light absorption and photo-activation vs. α-Fe2O3-induced shadowing effect and ii) the availability of free TiO2 surface vs. α-Fe2O3-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-Fe2O3/TiO2 hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.
V. Urbanová, A. Bakandritsos, P. Jakubec, T. Szambó, R. Zbořil: A facile graphene oxide based sensor for electrochemical detection of neonicotinoids, BIOSENSORS AND BIOELECTRONICS vol. 89, pp. 532-537, 2017.
DOI: 10.1016/j.bios.2016.03.039, IF = 7.476
Abstract: The increasing use of neonicotinoids in systematic seed treatment to crops is a serious cause of pollution of water resources and environment. Consequently, food sources can get eventually contaminated. To this end, it is desirable to develop suitable and effective platforms in order to obtain low-cost and sensitive sensors for neonicotinoids detection. In this work, graphene oxide modified electrodes were used as highly efficient electrochemical sensors for detection of two common insecticides – thiamethoxam and imidacloprid. The proposed sensor responded linearly in the concentration range of 10–200 µmol L−1 for both analytes and the detection limits were determined as low as 8.3 µmol L−1 and 7.9 µmol L−1 for thiamethoxam and imidacloprid, respectively. Analytical performance was also evaluated on spiked water and honey samples.
A. Goswami, A. K. Rathi, C. Aparicio, O. Tomanec, M. Petr, R. Pocklanova, M. B. Gawande, R. S. Varma, R. Zboril: In-situ Generation of Pd-Pt Core-shell Nanoparticles on Reduced Graphene Oxide (Pd@Pt/rGO) using Microwaves: Applications in Dehalogenation Reactions and Reduction of Olefins, ACS APPLIED MATERIALS & INTERFACES, vol. 9, iss. 3, pp. 2815-2824, 2017.
DOI: 10.1021/acsami.6b13138, IF = 7.145
Abstract: Core-shell nanocatalysts are distinctive class of nanomaterials with varied potential applications in view of their unique structure and composition-dependent physico-chemical properties and promising synergism among the individual components. A one-pot microwave (MW)-assisted approach is described to prepare the reduced graphene oxide (rGO)-supported Pd-Pt core-shell nanoparticles, (Pd@Pt/rGO); spherical core-shell nanomaterials (~95 nm) with Pd core (~80 nm) and 15 nm Pt shell were nicely distributed on the rGO matrix in view of the choice of reductant and reaction conditions. The well-characterized composite nanomaterials, endowed with synergism among its components and rGO support, served as catalysts in aromatic dehalogenation reactions and for the reduction of olefins with high yield (>98%), excellent selectivity (>98%) and recyclability (up to 5 times); both, Pt/rGO and Pd/rGO and even their physical mixtures showed considerably lower conversions (20 and 57%) in dehalogenation of 3-bromoaniline. Similarly, in the reduction of styrene to ethylbenzene, Pt@Pd core-shell nanoparticles (without rGO support) possess considerably lower conversion (60%), compared to Pd@Pt/rGO. The mechanism of dehalogenation reactions with Pd@Pt/rGO catalyst is discussed with the explicit premise that rGO matrix facilitates the adsorption of the reducing agent thus enhancing its local concentration and expediting the decomposition rate. The versatility of the catalyst has been validated via diverse substrate scope for both, the reduction and dehalogenation reactions.
V. B. Gade, A. K. Rathi, S. B. Bhalekar, J. Tucek, O. Tomanec, R. S. Varma, R. Zboril, S. N. Shelke, M. B. Gawande: Iron-Oxide-Supported Ultrasmall ZnO Nanoparticles: Applications for Transesterification, Amidation, and O-Acylation Reactions, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Article in press, 2017.
DOI: 10.1021/acssuschemeng.6b03167, IF = 5.267
Abstract: An efficient maghemite–ZnO nanocatalyst has been synthesized via a simple coprecipitation method, where ZnO nanoparticles are uniformly decorated on the maghemite core and characterized by XRD, SEM-EDS, ICP-AES, XPS, TEM, HRTEM, and Mössbauer spectroscopy; maghemite nanoparticles are in the typical size range 10–30 nm with ultrasmall (3–5 nm) ZnO nanoparticles. A competent and benign protocol is reported for various organic transformations, namely, transesterification, amidation, and O-acylation reaction in good to excellent yields (75–97%) using magnetically separable and reusable maghemite–ZnO nanocatalyst.
J. Tuček, R. Prucek, J. Kolařík, G. Zoppellaro, M. Petr, J. Filip, V. K. Sharma, R. Zbořil: Zero-Valent Iron Nanoparticles Reduce Arsenites and Arsenates to As(0) Firmly Embedded in Core–Shell Superstructure: Challenging Strategy of Arsenic Treatment under Anoxic Conditions, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Article in press, 2017.
DOI: 10.1021/acssuschemeng.6b02698, IF = 5.267
Abstract: Arsenites and arsenates are carcinogenic to humans and are typically removed from contaminated water using various sorbents. However, these treatment methods result in the secondary release of weakly bound As species and require large amounts of sorbents. Here, we introduce a groundbreaking method involving the use of oxidic-shell-free nanoscale zero-valent iron (OSF-nZVI) to treat arsenite/arsenate-polluted underground water. Under anoxic conditions, OSF-nZVI is capable to reduce As(III)/As(V) species to As(0) (up to 65% of total arsenic content). Thus, reduction synergistically contributes to sorption tuning suitably the chemical nature and isoelectric points of As species, thereby enhancing arsenic removal from an anoxic aqueous environment. More importantly, As species are locked between the Fe(0) core and iron(III) oxide outer shell. For comparison, the removal capability of OSF-nZVI is 2 times lower under oxic conditions, due to the complex redox mechanism resulting in exclusive sorption of As(III)/As(V) species onto the surface of oxidized OSF-nZVI particles. The unique strategy to treat arsenites/arsenates by their reduction to zero-valent arsenic with OSF-nZVI was also demonstrated in experiments with real polluted water. Results suggest that “green” reduction and firm immobilization of toxic As species through OSF-nZVI could provide environmentally friendly tool to treat arsenic-polluted underground water, a main source of highly contaminated drinking water worldwide.
D. S. Doke, S. B. Umbarkar, M. B. Gawande, R. Zboril, A. V. Biradar: Environmentally Benign Bio-derived Carbon Microspheres-supported Molybdena Nanoparticles as Catalyst for the Epoxidation Reaction, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, vol. 5, iss.1, pp. 904-910, 2017.
DOI: 10.1021/acssuschemeng.6b02229, IF = 5.267
Abstract: A one-pot synthesis of molybdenum oxide nanoparticles (NPs) supported on bio-derived carbon microspheres is reported. The catalyst was synthesized by the low temperature hydrothermal (LTH) method using D-glucose and bagasse as the car-bon source. The carbonization of bagasse resulted in the formation of non-uniform carbon microspheres while glucose re-sulted in uniform carbon spheres. SEM and STEM elemental mapping show the uniform distribution of molybdenum oxide NPs over the carbon microspheres. XPS spectroscopy confirmed that molybdenum was in Mo6+ oxidation state. The 1% MoO3 supported on carbon microspheres derived from D-glucose showed excellent catalytic activity up to 100% olefin con-version with 100% epoxide selectivity using organic tert-Butyl hydroperoxide as an oxidant. The catalyst was successfully used up to five cycles without losing substantial activity and selectivity.