Carbon⁻phosphorus⁻titanium composites (CPT) were synthesized by Ti-impregnation and carbonization of cellulose. Microcrystalline cellulose used as carbon precursor was initially dissolved by ...phosphoric acid (H₃PO₄) to favor the Ti-dispersion and the simultaneous functionalization of the cellulose chains with phosphorus-containing groups, namely phosphates and polyphosphates. These groups interacted with the Ti-precursor during impregnation and determined the interface transformations during carbonization as a function of the Ti-content and carbonization temperature. Amorphous composites with high surface area and mesoporosity were obtained at low Ti-content (Ti:cellulose ratio = 1) and carbonization temperature (500 °C), while in composites with Ti:cellulose ratio = 12 and 800 °C, Ti-particles reacted with the cellulose groups leading to different Ti-crystalline polyphosphates and a marked loss of the porosity. The efficiency of composites in the removal of the Orange G dye in solution by adsorption and photocatalysis was discussed based on their physicochemical properties. These materials were more active than the benchmark TiO₂ material (Degussa P25), showing a clear synergism between phases.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Activated carbons from a mixture of olive-residue, oil and vegetable water, known as alperujo, OR, were prepared by KOH and H3PO4 activation. KOH activations were made following two different methods ...(carbonization-activation and impregnation-activation) with two different KOH/carbon ratios. Textural characterization with N2 and CO2 reveals that a prior carbonization of samples followed by the activation with KOH, produces samples with similar textural and chemical properties to the impregnated ones at low KOH ratio, while at high KOH ratio; more porous samples are obtained by carbonization. However, no differences are observed increasing the KOH ratio for the impregnated samples. As a consequence, similar or even more porous samples are obtained by using an easier preparation method such as carbonization-activation. On the other side, H3PO4 activation leads to samples with less surface area but with a more developed mesoporosity. In addition, the chemical surfaces of KOH and H3PO4 activated samples are very different as shown by XPS and TPD results. XPS data denote a similar chemical texture in KOH activated samples in spite of the different preparation methods and KOH ratio, whereas the H3PO4 method fixed different phosphorus surface groups. Analysing TPD data while on KOH activated samples, oxygenated surface groups (OSG) decompose mainly as CO2 (carboxylic acid, anhydrides, lactones, etc.) during the TPD experiments, on H3PO4 activated one those OSG ones evolve as CO (semiquinone, carbonyl, etc.) which has been attributed to the presence of COP species that decompose in the form of CO at around 860°C. As a consequence, similar electrochemical capacitances are obtained using KOH activated samples, which depend linearly on the surface area while the H3PO4 activated one presents higher capacitance value and capacitance stability in spite of its smaller surface area. This fact was related with the presence and nature of phosphorus surface groups.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
A series of adsorbents was developed by physical (CO2) and chemical (KOH) activation of two bio-residues: olive stones (OS) and wood from olive tree pruning (OTP). The physicochemical properties of ...such materials were determined and correlated with their adsorptive performance in the removal of phenolic compounds of olive mill wastewater (OMW). Adsorption isotherms and kinetics of single phenolic acids, as well as the kinetics for competitive multi-compound adsorption, were fitted by applying different models, though Langmuir and pseudo-second order models fitted better the experimental results, respectively. The intraparticle diffusion model pointed out that mesoporosity reduces the influence of phenolic compounds’ restrictions in the external film diffusion of the adsorbent particle–solution interphase, but adsorption capacity linearly increases with the micropore volume accessible to N2 at −196 °C (and also with BET surface area), while diffusion into ultramicropores (<0.7 nm, determined by CO2-adsorption) is slow and presents minor influence on the total adsorption capacity. After saturation, thermal regeneration of spent adsorbents allows the removal of adsorbed products, enabling the reuse of samples whilst maintaining a significant performance.
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•Olive stone and tree pruning are used to synthesize a series of AC-biosorbents.•Single & competitive removal of olive mill wastewater phenolic compounds is studied.•Adsorption capacity and rate controlled by larger micropores and BET surface area.•Olive stone derived-AC capacity can be restored upon simple thermal regeneration.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
From the most classic carbon materials (CMs) to the advanced ones, all of them integrate a promising catalyst set in terms of sustainability and energy efficiency for a greener future. Different ...synthetic strategies concerning to the catalytic synthesis of relevant N‐containing heterocycles are herein described to address the great potential of the referred catalysts flying over what has been done and all that remains to be done. Current trends in this field involve structure‐activity relationships establishment also considering the reaction mechanisms understanding and the identification of active catalytic sites, as function of both experimental datasets, emphasizing on operando characterization techniques, and theoretical studies which will significantly contribute to the design of custom‐made catalysts as a new horizon.
Building N‐heterocycles by using CMs. Current trends for the sustainable synthesis of significant N‐containing heterocycles, considering both different synthetic approaches to construct the heterocyclic core, and the role of CMs used as catalysts and catalyst supports, are reviewed. Establishment of structure‐activity relationships and reaction mechanisms understanding can contribute, in the future, to the rational catalyst design as a new horizon.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Graphene oxide (GO) is used to enhance the photocatalytic activity of ZnO nanoparticles for the degradation of vanillic acid (VA) under simulated solar light and visible-LED (λ > 430 nm). ZnO-GO ...composites are prepared by a mixing and sonication process with different GO loadings (i.e., from 1.8 to 6.5 wt.%). The materials are extensively characterized by thermogravimetric analysis (TGA), physisorption of N2, X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), point of zero charge (pHPZC), and UV-Vis diffuse reflectance spectroscopy (DRUV). The presence of GO increases the photocatalytic activity of all the prepared composites in comparison with the pristine ZnO. The highest photocatalytic activity is found for the composite containing 5.5 wt.% of GO (i.e., ZnO-GO5.5), reaching a VA degradation of 99% and 35% under solar light and visible-LED, respectively. Higher TOC removal/VA degradation ratios are obtained from the experiments carried out under visible-LED, indicating a more effective process for the mineralization of VA than those observed under simulated solar light. The influence of hole, radical, and non-radical scavengers is studied in order to assess the occurrence of the reactive oxygen species (ROS) involved in the photocatalytic mechanism. The study of the photo-stability during three reuse experiments indicates that the presence of GO in the composites reduces the photocorrosion in comparison with pristine ZnO.
•Carbon gels are produced by the carbonization of resorcinol–formaldehyde polymers.•The conditions of gelation, drying and carbonization should be carefully controlled.•The porosity and surface ...chemistry of carbon gels can be tailored.•Supported or doped nanostructured carbon gels are prepared and successfully applied as catalysts.
Nanostructured carbon gels are prepared by sol–gel polymerization of resorcinol–formaldehyde. The flexibility of the sol–gel process permits the control of the morphology, porosity and surface chemistry of carbon gels, but a large amount of variables should be carefully fitted. Pure carbon gels used as supports or doped-carbon gels and organic–inorganic composites to be used as catalyst, can be prepared. When metal-doped carbon gels are prepared, metals are active in all synthesis steps: polymerization, carbonization and/or activation. Interactions between organic–inorganic phases determine the distribution/dispersion of metals, sintering resistance, porosity, graphitization, formation of different active phases, etc. thus offering a large amount of possibilities in catalysis because final metal particles are also active in many catalyzed processes. Metal-doped carbon gels are more resistant to sintering or leaching than impregnated catalysts, however, some metal particles are encapsulated by the organic matrix, being therefore inactive in catalysis. Relationships between chemical and physical parameters with catalysts characteristics: loading, accessibility, chemical nature, stability (leaching or sintering) and catalytic behavior of the supported active phases are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A series of Ni-doped carbon aerogels with different Ni loadings were prepared and extensively characterized from a textural, chemical and electro-chemical point of view. The formation of graphitic ...clusters on nickel particles was specially analysed by XPS and Raman spectroscopy. Electro-capacitive properties were studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy in a three and two-electrode cell, and in acidic media and non-aqueous aprotic electrolyte.
The use of Ni as a polymerization catalyst slightly decreases the micropore volume of the carbon aerogels but on the contrary, a great increase in their mesopore volume was obtained. All samples present high gravimetric capacitances, ranging from 182 to 219 F g−1 in 1 M H2SO4, and from 49 to 63 F g−1 in 1 M tetraethylammonium tetrafluoroborate. Results show that the equivalent series resistances decrease as the Ni content increases and the capacitance increases in the same sense. This trend is directly related to the presence of a good developed mesopore network in Ni-doped carbon aerogels and a better electrical conductivity due to the formation of the graphitic clusters around the Ni particles. The stability of the charge-discharge cycles, studied by floating tests, showed a very good performance of the doped-carbon aerogels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
A series of adsorbents (activated carbons, ACs) were synthesized by physical and chemical activation of olive stones (OS) and their textural and chemical characteristics determined by complementary ...techniques such as N2 and CO2 physisorption, pH of the point zero of charge (pHPZC), HRSEM or XPS. Samples with a wide range of physicochemical properties were obtained by fitting the activation procedure. The performance of these adsorbents in filters working under dynamic conditions was studied by determining the corresponding breakthrough curves for the ethylene removal. The physicochemical transformations of OS during activation were related with the adsorptive performance of derivative ACs. Results were compared to those obtained using commercial carbons, in particular ACs, carbon black or carbon fibers, in order to identify the properties of these materials on influencing the adsorptive performance. In general, ACs from OS perform better than the commercial samples, being also easily regenerated and properly used during consecutive adsorption cycles. CO2-activation showed to be the best synthesis option, leading to granular ACs with a suitable microporosity and surface chemistry. These results could favour the integration of this type of inexpensive materials on devices for the preservation of climacteric fruits, in a clear example of circular economy by reusing the agricultural residues.
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•Activated carbons (ACs) were prepared from biomass by different activation methods.•Physical activation by steam leads to a larger and wider porosity than that by CO2.•Chemical activation with KOH was the most severe method developing porosity.•ACs by CO2 show the best physico-chemical properties for ethylene adsorption.•Ethylene adsorption is completely reversible, spent ACs being easily regenerated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Escherichia coli colonies were grown on different supports for the removal of nitrates from water. A carbon material and different commercial metal oxides, such as SiO2, TiO2 and Al2O3, and their ...corresponding carbon–metal oxide composites were studied. The physicochemical properties were analyzed by different techniques and the results were correlated with their performance in the denitrification process. Developed biofilms effectively adhere to the supports and always reach the complete reduction of nitrates to gaseous products. Nevertheless, faster processes occur when the biofilm is supported on mesoporous and non-acid materials (carbon and silica).
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Carbon-Ti nanocomposites were prepared by a controlled two-step method using microcrystalline cellulose as a raw material. The synthesis procedure involves the solubilization of cellulose by an acid ...treatment (H
PO
or HNO
) and the impregnation with the Ti precursor followed of a carbonization step at 500 or 800 °C. The type of acid treatment leads to a different functionalization of cellulose with phosphorus- or oxygen-containing surface groups, which are able to control the load, dispersion and crystalline phase of Ti during the composite preparation. Thus, phosphorus functionalities lead to amorphous carbon-Ti composites at 500 °C, while TiP
O
crystals are formed when prepared at 800 °C. On the contrary, oxygenated groups induce the formation of TiO
rutile at an unusually low temperature (500 °C), while an increase of carbonization temperature promotes a progressive crystal growth. The removal of Orange G (OG) azo dye in aqueous solution, as target pollutant, was used to determine the adsorptive and photocatalytic efficiencies, with all composites being more active than the benchmark TiO
material (Degussa P25). Carbon-Ti nanocomposites with a developed micro-mesoporosity, reduced band gap and TiO
rutile phase were the most active in the photodegradation of OG under ultraviolet irradiation.
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