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After more than a decade of studying the ecotoxicity of graphene oxide nanomaterials (nGOs), it has been concluded that there is limited information available regarding the environmental risk of graphene-based materials. Since existing... more
After more than a decade of studying the ecotoxicity of graphene oxide nanomaterials (nGOs), it has been concluded that there is limited information available regarding the environmental risk of graphene-based materials. Since existing ecotoxicological studies of nanomaterials have produced contradictory results, it is recommended that case-by-case studies should be conducted to evaluate their effects. This can be carried out by employing several methods, testing species from different trophic levels, and conducting community studies. Our goal was to evaluate the toxicity effects of two GOs (AF 96/97 and PM 995) derived from different graphite precursors on various test organisms from diverse trophic levels (bacteria, protozoa, a freshwater microbial community, plants, and invertebrate animals) in aquatic environments. We compared the effects of both nGO types and estimated the predicted no-effect environmental concentration (PNEC) values to determine their potential environmental r...
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In this work, we study the influence of reduced graphene oxide (rGO) on the morphology and chemistry of highly porous N,S-doped carbon cryogels. Simultaneously, we propose an easily upscalable route to prepare such carbons by adding... more
In this work, we study the influence of reduced graphene oxide (rGO) on the morphology and chemistry of highly porous N,S-doped carbon cryogels. Simultaneously, we propose an easily upscalable route to prepare such carbons by adding graphene oxide (GO) in as-received suspended form to the aqueous solution of the ι-carrageenan and urea precursors. First, 1.25–5 wt% GO was incorporated into the dual-doped polymer matrix. The CO2, CO, and H2O emitted during the thermal treatments resulted in the multifaceted modification of the textural and chemical properties of the porous carbon. This facilitated the formation of micropores through self-activation and resulted in a substantial increase in the apparent surface area (up to 1780 m2/g) and pore volume (up to 1.72 cm3/g). However, adding 5 wt% GO led to overactivation. The incorporated rGO has an ordering effect on the carbon matrix. The evolving oxidative species influence the surface chemistry in a complex way, but sufficient N and S at...
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Az orvosbiologiai es elvalasztastechnikai celokra is elterjedten hasznalt reszponziv polimer alapu rendszerekben az anyagfelvetelt es -leadast iranyito kolcsonhatasokat meg mindig nem ismerjuk pontosan. Terhalos poli-N-izopropil-akrilamid... more
Az orvosbiologiai es elvalasztastechnikai celokra is elterjedten hasznalt reszponziv polimer alapu rendszerekben az anyagfelvetelt es -leadast iranyito kolcsonhatasokat meg mindig nem ismerjuk pontosan. Terhalos poli-N-izopropil-akrilamid (PNIPA) hidrogelek fazisatalakulasi tulajdonsagait kulonboző biologiailag relevans ionok, aromas molekulak, aminosavak es protein jelenleteben vizsgalva megallapitottuk, hogy hatasuk nemcsak az oldoszer ’josaganak’ modositasara vezethető vissza, hanem anyagi minőseguktől fuggően specialis kolcsonhatas(oka)t alakithatnak ki a PNIPA oldallancaval. A kolcsonhatasokat befolyasolo tenyezők felterkepezesere komplex megkozelitest alkalmaztunk (mikrokalorimetria, NMR, szorasi modszerek, duzzadasi vizsgalatok, mechanikai tulajdonsagok, porozitas, stb.). Az irodalomban elsőkent publikaltuk a kolcsonhato egysegek lehetseges konformacioit es az atomi tavolsagokat. Hidrofob modositasokkal kiserletet tettunk a PNIPA gel tobb tulajdonsaganak (mechanikai, szorpcio...
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The extensive use of engineered nanomaterials, such as graphene oxide (GO), is stimulating research about its potential environmental impacts on the aquatic ecosystem. This study is aimed to comprehensively assess the acute toxicity of a... more
The extensive use of engineered nanomaterials, such as graphene oxide (GO), is stimulating research about its potential environmental impacts on the aquatic ecosystem. This study is aimed to comprehensively assess the acute toxicity of a well-characterized GO suspension to Daphnia magna. Conventional ecotoxicological endpoints (lethality, immobilization) and more sensitive, sublethal endpoints (heartbeat rate, feeding activity, and reactive oxygen species (ROS)) production were used. The possible normalization of the heartbeat rate and feeding activity in clean test medium was also investigated. The fate, time-dependent, and concentration-dependent aggregation behaviour of GO was followed by dynamic light scattering, UV-Vis spectroscopy, and zeta potential measurement methods. The EC20 value for immobilization was 50 mg/L, while, for physiological and behavioural endpoints, it ranged from 8.1 mg/L (feeding activity) to 14.8 mg/L (immobilization). The most sensitive endpoint was the ...
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When graphene oxide is reduced, the functional groups are released and the structure becomes more ordered. The degree of reduction might be tunable with the process parameters. In our work, graphene oxide is prepared and the effect of... more
When graphene oxide is reduced, the functional groups are released and the structure becomes more ordered. The degree of reduction might be tunable with the process parameters. In our work, graphene oxide is prepared and the effect of thermal and chemical reduction is investigated. The samples are characterized with TG/DTA-MS, SEM-EDX, TEM, XPS, ATR-FTIR, Raman spectroscopy and XRD. Their electrical resistance, cyclic voltammetry and photocatalytic activity data are investigated. The conductivity can be varied by several orders of magnitude, offering a tool to match its electrical properties to certain applications. Low temperature reduction in air offers a material with the highest capacitance, which might be used in supercapacitors. The bare graphene oxide has considerably larger photocatalytic activity than P25 TiO2. Reduction decreases the activity, meaning that reduced graphene oxide can be used as an electron sink in composite photocatalysts, but does not contribute to the pho...
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Among microporous storage materials copper benzene-1,3,5-tricarboxylate (CuBTC MOF, Cu3(BTC)2 or HKUST-1) holds the greatest potential for clean energy gases. However, its usefulness is challenged by water vapor, either in the gas to be... more
Among microporous storage materials copper benzene-1,3,5-tricarboxylate (CuBTC MOF, Cu3(BTC)2 or HKUST-1) holds the greatest potential for clean energy gases. However, its usefulness is challenged by water vapor, either in the gas to be stored or in the environment. To determine the protection potential of graphene oxide (GO) HKUST-1@GO composites containing 0–25% GO were synthesized and studied. In the highest concentration, GO was found to strongly affect HKUST-1 crystal growth in solvothermal conditions by increasing the pH of the reaction mixture. Otherwise, the GO content had practically no influence on the H2, CH4 and CO2 storage capacities, which were very similar to those from the findings of other groups. The water vapor resistance of a selected composite was compared to that of HKUST-1. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG/DTG) and N2 adsorption techniques were used to monitor the ...
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Waste and low-cost lignocellulosic biomasses are well studied and widely used as raw materials for porous carbon adsorbents. Much less attention is given to the exploration of the potential of marine biomasses, though these materials... more
Waste and low-cost lignocellulosic biomasses are well studied and widely used as raw materials for porous carbon adsorbents. Much less attention is given to the exploration of the potential of marine biomasses, though these materials contain also nitrogen, which—if preserved during the processing—has a beneficial influence on the sorption properties of the porous carbon obtained. Here, we report a multi-technique investigation into the conversion of crab shell to porous carbon adsorbent. Thermogravimetry and pyrolysis-GC/MS studies were used to reveal the thermal degradation of this natural polymer and follow the decomposition process through the identification of the products. Almost 40 various volatile degradation products were distinguished released at 500 °C pyrolysis temperature. Based on the TGA/DTG results, two temperatures, 350 and 500 °C, were selected to obtain pyrolytic samples in macroscopic quantities in order to characterize the morphology and surface chemistry of the ...
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In this study, Bi2WO6 was prepared by the hydrothermal method. The effects of reaction temperature (150/170/200 °C) and reaction time (6/12/24 h) were investigated. The role of strongly acidic pH (1 >) and the full range between 0.3... more
In this study, Bi2WO6 was prepared by the hydrothermal method. The effects of reaction temperature (150/170/200 °C) and reaction time (6/12/24 h) were investigated. The role of strongly acidic pH (1 >) and the full range between 0.3 and 13.5 were studied first. Every sample was studied by XRD and SEM; furthermore, the Bi2WO6 samples prepared at different temperatures were examined in detail by EDX and TEM, as well as FT-IR, Raman and UV-vis spectroscopies. It was found that changing the temperature and time slightly influenced the crystallinity and morphology of the products. The most crystallized product formed at 200 °C, 24 h. The pure, sheet-like Bi2WO6, prepared at 200 °C, 24 h, and 0.3 pH, gradually transformed into a mixture of Bi2WO6 and Bi3.84W0.16O6.24 with increasing pH. The nanosheets turned into a morphology of mixed shapes in the acidic range (fibers, sheets, irregular forms), and became homogenous cube- and octahedral-like shapes in the alkaline range. Their band ga...
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Resorcinol-formaldehyde based polymer hydrogels with various graphene oxide (GO) content were synthesized using Na2CO3 as catalyst at pH=6 conditions. After supercritical drying they were converted to carbon aerogels in nitrogen... more
Resorcinol-formaldehyde based polymer hydrogels with various graphene oxide (GO) content were synthesized using Na2CO3 as catalyst at pH=6 conditions. After supercritical drying they were converted to carbon aerogels in nitrogen atmosphere. The heat treatment not only pyrolysed the polymer gel, but also reduced GO. The GO added varied within 0-14% related to the mass of resorcinol which resulted in the reinforcement of the polymer matrix. The texture of the polymer and the carbon aerogels were characterized and compared in the nanoscale using SEM and TEM imaging, X-ray diffraction (XRD) and low temperature nitrogen adsorption measurements. The transition from polymer to carbon state was studied by thermogravimetry. In agreement with reference works in the GO range studied the morphology was not affected by the GO content either in the polymer or in the carbon form. The direct current (DC) conductivity however linearly increased with the added GO and already 10 % doubled the conducti...
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An immobilization engineering approach using bioinformatics and experimental design tools was applied to improve the sol–gel enzyme entrapment methodology.
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Rice husk derived activated carbons doped with nitrogen have been studied using low temperature nitrogen adsorption, scanning electron microscopy, mercury porosimetry, thermogravimetric analysis combined with mass-spectrometry,... more
Rice husk derived activated carbons doped with nitrogen have been studied using low temperature nitrogen adsorption, scanning electron microscopy, mercury porosimetry, thermogravimetric analysis combined with mass-spectrometry, differential scanning calorimetry and X-ray photoelectron spectroscopy. It has been shown that N-doped activated carbon produced by high temperature treatment of the starting material soaked with urea, has a significantly higher anion exchange capacity than the other samples studied, which correlates with its higher adsorption capacity towards nitrate ion removal from aqueous solutions with the initial concentration of 5 and 15 ppm.
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ABSTRACT
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The adsorption technique is widely used in water purification, and its efficiency can be significantly improved by target-specific adsorbent design. Research on iodine and its ion removal from water has attracted a great deal of interest... more
The adsorption technique is widely used in water purification, and its efficiency can be significantly improved by target-specific adsorbent design. Research on iodine and its ion removal from water has attracted a great deal of interest due to increased concentrations in the environment and acute toxic effects, e.g., in human thyroid cells. In this work, the iodide removal performance of two high-surface-area resorcinol–formaldehyde-based carbon aerogels was studied under acidic conditions. The BET surface area was 790 m2/g (RF_ac) and 375 m2/g (RMF-GO), with a corresponding micropore ratio of 36 and 26%, respectively. Both aerogels showed outstanding adsorption capacity, exceeding the reported performance of other carbons and Ag-doped materials. Owing to its basic nature, the RMF-GO carbon aerogel showed higher I− capacity, up to 97 mg/g, than the acidic RF_ac, which reached a capacity of 82 mg/g. The surface chemistry of the aerogels also played a distinct role in the removal. In...
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The quantities and relationships of capillary theory are summarized in a consistent formalism. Its constituents are the canonical thermostatics of the excess quantities, the interpretation of the surface tension according to deformation... more
The quantities and relationships of capillary theory are summarized in a consistent formalism. Its constituents are the canonical thermostatics of the excess quantities, the interpretation of the surface tension according to deformation theory, and the formalism of parametric theory. A generalized concept of surface excess quantities is established by introducing the factors νφ and defining the individual quantities. The deformation quantities can also be incorporated into the theory, but the changes in the phase volumes have to be restricted. The theoretical difficulties of the traditional hypotheses do not arise in this unified approach and quantities that are not open to measurement can be calculated.
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Study on h-WO3/TiO2 nanowires as ALD nucleation of TiO2 was found to be influenced by the WO3 polymorphs.
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Flax and hemp fibres were treated by various combinations of water/diluted alkaline solution and stirring/ultrasound, respectively. Changes in the microstructure (scanning electron microscopy) and porous structure (low-temperature... more
Flax and hemp fibres were treated by various combinations of water/diluted alkaline solution and stirring/ultrasound, respectively. Changes in the microstructure (scanning electron microscopy) and porous structure (low-temperature nitrogen adsorption), removal of non-cellulosic materials (weight loss, FTIR), mean fibre diameter, and adhesion of the polypropylene matrix to the fibres (micro-bond test) were investigated. For both types of fibres, removal of (FTIR) was observed. The fibre diameter of hemp was decreased by several treatments, most of all by stirring in alkali and subsequent sonication in water, while the ultrasound applied in alkali solution did not change the fibre fineness. This can be attributed to the dual effect of ultra-sonication: the swelling effect of alkali combined with ultrasound energy probably served the sticking of inter-fibrillar material rather than their dissolution. Fibre diameter of flax did not change in any circumstances. The porosity of hemp in the mesopore range increased, while that of flax decreased by alkali treatment and subsequent sonication. The reason for this difference might be the dissimilar cell wall structures of the two bast fibres, the high arabinose content of the hemp, and/or the cottonisation of hemp. No treatments altered the fibre-matrix adhesion measured by pulling out the fibre from a micro-droplet of polypropylene.
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The cellular structure of Norway spruce (Picea abies) was transformed via a simple, single-step carbonization process into a carbon monolith with molecular-sieve properties. The monolith exhibited a genuine honeycomb structure derived... more
The cellular structure of Norway spruce (Picea abies) was transformed via a simple, single-step carbonization process into a carbon monolith with molecular-sieve properties. The monolith exhibited a genuine honeycomb structure derived from the original intrinsic H2O channels of the wood. The micropores formed during carbonization from the walls of the channels were shown to have a high adsorption capacity. The honeycomb monolith was tested for air separation. Micropore diffusion of N2 and O2 was found by the frequency-response (FR) technique to be the rate-controlling process of mass transport.
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We have developed an easy route to prepare (nano-ZrO2,nano-ZrCx)@C composites with varying ZrO2/ZrCx content. The process consists of preparing a zirconium-loaded, iminodiacetate-functionalized styrene-divinylbenzene (STY-DVB) copolymer,... more
We have developed an easy route to prepare (nano-ZrO2,nano-ZrCx)@C composites with varying ZrO2/ZrCx content. The process consists of preparing a zirconium-loaded, iminodiacetate-functionalized styrene-divinylbenzene (STY-DVB) copolymer, and its subsequent carbonization in a tube furnace and/or a thermal plasma reactor. Depending on the zirconium salt used (zirconyl chloride, zirconyl nitrate or zirconium (IV) sulfate) in the Zr loading, the Zr-loaded resins resulted in ZrO2@C pre-pyrolizates with C to Zr molar ratios of 5.8, 6.8 and 6.60. This carbon surplus is sufficient for the partial or even complete reduction of ZrO2 into ZrC0.58 at 1400 °C. The reaction products also contain 5 to 55 mass% residual free carbon. The plasma processing of the ZrO2@C composite formed at 1000 °C in a tube furnace led to ZrC0.94@C composites. The transformation of amorphous carbon content during the plasma treatment strongly depended on the atmosphere (He or H2) in the reactor and the anion type of ...
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An aerial humidity-induced solid-phase hydrolytic transformation of the [Zn(NH3)4]MoO4@2H2O (compound 1@2H2O) with the formation of [(NH4)xH(1−x)Zn(OH)(MoO4)]n (x = 0.92–0.94) coordination polymer (formally NH4Zn(OH)MoO4, compound 2) is... more
An aerial humidity-induced solid-phase hydrolytic transformation of the [Zn(NH3)4]MoO4@2H2O (compound 1@2H2O) with the formation of [(NH4)xH(1−x)Zn(OH)(MoO4)]n (x = 0.92–0.94) coordination polymer (formally NH4Zn(OH)MoO4, compound 2) is described. Based on the isostructural relationship, the powder XRD indicates that the crystal lattice of compound 1@2H2O contains a hydrogen-bonded network of tetraamminezinc (2+) and molybdate (2−) ions, and there are cavities (O4N4(μ-H12) cube) occupied by the two water molecules, which stabilize the crystal structure. Several observations indicate that the water molecules have no fixed positions in the lattice voids; instead, the cavity provides a neighborhood similar to those in clathrates. The @ symbol in the notation is intended to emphasize that the H2O in this compound is enclathrated rather than being water of crystallization. Yet, signs of temperature-dependent dynamic interactions with the wall of the cages can be detected, and 1@2H2O easi...
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TiO2 and ZnO single and multilayers were deposited on hydroxyl functionalized multi-walled carbon nanotubes using atomic layer deposition. The bare carbon nanotubes and the resulting heterostructures were characterized by TG/DTA, Raman,... more
TiO2 and ZnO single and multilayers were deposited on hydroxyl functionalized multi-walled carbon nanotubes using atomic layer deposition. The bare carbon nanotubes and the resulting heterostructures were characterized by TG/DTA, Raman, XRD, SEM-EDX, XPS, TEM-EELS-SAED and low temperature nitrogen adsorption techniques, and their photocatalytic and gas sensing activities were also studied. The carbon nanotubes (CNTs) were uniformly covered with anatase TiO2 and wurtzite ZnO layers and with their combinations. In the photocatalytic degradation of methyl orange, the most beneficial structures are those where ZnO is the external layer, both in the case of single and double oxide layer covered CNTs (CNT-ZnO and CNT-TiO2-ZnO). The samples with multilayer oxides (CNT-ZnO-TiO2 and CNT-TiO2-ZnO) have lower catalytic activity due to their larger average densities, and consequently lower surface areas, compared to single oxide layer coated CNTs (CNT-ZnO and CNT-TiO2). In contrast, in gas sens...
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The potential applications of mesoporous carbon aerogels are wide-ranging. These gels are often obtained from resorcinol-formaldehyde (RF) hydrogel precursors. The sol-gel method in this synthesis provides an efficient and versatile means... more
The potential applications of mesoporous carbon aerogels are wide-ranging. These gels are often obtained from resorcinol-formaldehyde (RF) hydrogel precursors. The sol-gel method in this synthesis provides an efficient and versatile means of product control through systematic variation of process conditions, such as pH, stoichiometry, concentration, catalyst, further additives, etc., in addition to the drying and pyrolytic conditions. Here, a novel means of tuning the texture of carbon aerogels is proposed. Water-1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4] mixtures constitutes a polycondensation medium that requires no added catalyst, thus yielding an intrinsically metal-free carbon aerogel after pyrolysis. We also show that the carbon morphology is tailored by the supramolecular structure of the aqueous ionic liquid. The results of scanning electron micrographs, low-temperature nitrogen adsorption/desorption isotherms, and small-angle X-ray scattering (SAXS) confirm th...
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Concurrent equilibrium adsorption on a highly porous activated carbon of both water vapour and toluene was studied to determine the extent and the location of toluene adsorption in the presence of water. We report small angle neutron... more
Concurrent equilibrium adsorption on a highly porous activated carbon of both water vapour and toluene was studied to determine the extent and the location of toluene adsorption in the presence of water. We report small angle neutron scattering (SANS) measurements in which the H/D ratio of both the water and toluene components is varied. Measurements are made both in the lower transfer wave vector region (5 × 10−2 ≤ q ≤ 1 Å−1) and in the high q region >1 Å−1. Just below the Porod scattering region (0.3–1 Å−1), the liquid/vapour interface contributes significantly. To solve the intrinsic ternary character of the signal in this region, contrast variation measurements with H2O/D2O mixtures alone and with toluene-D and toluene-H mixtures alone at constant relative pressure were performed. The carbon samples, of commercial origin (Norit R1), were previously treated with nitric acid to reduce the ash content, which simplifies the data treatment in the diffraction region at hig...