Xerogel Composites Research Articles

Sound-Absorbing, Thermal-Insulating Material Based on Poly(methylsiloxane) Xerogel and Cellulose Nanofibers

The automotive industry needs to improve energy efficiency rapidly to achieve carbon neutrality while creating a safe, secure, and comfortable driving environment for customers. Porous sound-absorbing materials and porous thermal insulators are typically used to satisfy these requirements despite limitations in mass and space. While these porous materials are similar, the microstructures they offer for high performance differ in the size and connectivity of their fluid phases, which enhances the difficulty of achieving excellent sound absorption and thermal insulation in the same material. In this study, a hydrophobic cellulose nanofiber–poly(methylsiloxane) xerogel composite was developed using computational microstructure modeling. This porous material has high porosity and excellent thermal insulation and sound absorption properties.

Investigation of platelet activation and calcium store release by a topical hemostatic xerogel dressing for improved blood clotting

AbstractAdequate topical hemostatic dressings are required as first‐line approach for reduction of uncontrolled hemorrhage, a leading cause of mortalities. Platelets play a major role during blood clotting to prevent hemorrhage during injuries. Here, we demonstrate the mechanisms activated through protease activating receptor 1 (PAR1), a platelet membrane protein in response to a porous composite xerogel dressing incorporating SiNPs (size 122 ± 10 nm) and calcium (2.5 mM), characterized by scanning electron microscopy–energy dispersive x‐ray spectroscopy and Fourier transform infrared spectroscopy. The composite displayed 13.9‐fold improved blood clotting index in comparison to commercial dressing. The composite displayed increased platelet aggregation due to development of well‐formed pseudopodia as compared to bare xerogel, SFLLRN (a thrombin mimic), adenosine di‐phosphate (a platelet activator), and heparin (a thrombin inhibitor). Further, PAR1 gene was significantly upregulated in model A549 epithelial cell line (1.2‐fold) and human platelets (1.4‐fold). The composite enhanced calcium release and its extrusion in A549 cells. Upregulation of PAR1 on the platelet surface and calcium release are crucial for platelet shape change and aggregation. The data indicate that xerogel composite containing SiNPs and calcium enhanced blood clotting through activation of PAR1. Such dressings can provide a potential hemostatic solution to reduce blood loss, disability, and mortality during surgery and trauma care.

ZnO/CeO2/carbon xerogel composites with direct Z-scheme heterojunctions: Enhancing photocatalytic remediation of 4-chlorophenol under visible light

This paper aims to create visible light driven ternary photocatalysts using zinc oxide (ZnO), cerium (IV) oxide (CeO2), and carbon xerogel (CX) as constituent materials. The use of CeO2 is based on the creation of direct-Z-scheme heterojunctions with the ZnO and the consequent diminishing of charge recombination, whereas the carbon xerogel inclusion is predicted to minimize bandgap energy, decrease electron-hole recombination, and boost specific surface area. Furthermore, the choice of the black-wattle tannin as a carbonaceous precursor was targeted at the development of an environmentally friendly and affordable composite. The existence of the hexagonal phase of zinc oxide and cubic structure of the cerium (IV) oxide in the ternary material was confirmed by X-ray diffractometry and X-ray photoelectron spectroscopy, with the latter also suggesting chemical bonding between the ZnO and the CX due to the creation of zinc oxycarbide complexes. The inclusion of the carbon xerogel provokes a significant modification in the morphology of the ternary material, resulting in an increased surface area and smaller particle aggregates. The CX/ZnO–CeO2 ternary composite obtains the highest photocatalytic efficiency among all the materials studied, degrading 100% of 4-chlorophenol under simulated sunlight and 68% under visible radiation, after 5 h. The increased photocatalytic activity can be attributed to the formation of direct Z-scheme heterojunctions between the semiconductors, higher visible light response, and higher specific surface area, as evidenced by the results obtained by active radical scavenging, chronoamperometry, diffuse reflectance spectroscopy, and N2 adsorption–desorption isotherms.

Effect of Fe3O4 nanoparticles on magnetic xerogel composites for enhanced removal of fluoride and arsenic from aqueous solution

Fe3O4 magnetic xerogel composites were prepared by polycondensation of resorcinol (R)–formaldehyde reaction via a sol–gel process in an aqueous solution through varying the molar ratio of Fe3O4 nanoparticles (MNPs), catalyst (C), and water (W) content. MNPs were obtained by co-precipitation (MC), oxidation of iron salts (MO), or solvothermal synthesis (MS). Both MNPs and magnetic xerogels were examined regarding the performance of arsenic and fluoride removal in a batch system. The MC-based MNPs had higher adsorption capacities for both fluoride (202.9 mg/g) and arsenic (3.2 mg/g) than other MNPs in optimum conditions. The X-ray diffraction, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy confirmed that Fe was composed into the polymeric matrix of magnetic xerogels that contained 0.59%–4.42% of Fe with a molar ratio of MNPs (M) to R between 0.01 and 0.10. With low R/C and optimum M/R ratios, an increase in the surface area of magnetic xerogels affected the fluoride and arsenic adsorption capacities. The magnetic xerogel composites with the MC-based MNPs prepared at a fixed R/C ratio (100) and at different R/W (0.05–0.06) and M/R (0.07–0.10) ratios had a high arsenic removal efficiency of 100% at an As(V) concentration of 0.1 mg/L and pH of 3.0. The maximum adsorption capacities of magnetic xerogels were approximately five times higher than those of the xerogels without MNP composites. Therefore, Fe3O4 nanoparticles enhanced the adsorption of arsenate and fluoride. The variations of alkaline catalyst and water content significantly affected the resulting properties of textural and surface chemistry of magnetic xerogel composites.

Analysis of phase transformations of modified silicate xerogels during heat treatment

The ways of obtaining glass for dental cements with low synthesis temperature were analyzed. The xerogels of the SiO2–CaO–P2O5 systems were synthesized by sol-gel technology from affordable raw materials. The physicochemical processes, temperature regions of phase transformations and intensity of their course, which occur during heat treatment of xerogels of two series of the system at the SiO2 content of 50 wt.% and 60 wt.% were investigated by the method of differential thermal analysis. Analysis of the obtained results allowed us to affirm that all regions of phase transformations in the xerogel powders with 50 wt.% SiO2 content shifted to the lower temperature range. It was established that an increase in the temperature during heat treatment of the xerogel powders with different compositions led to the phase transformations: from a loose powdered state through a sintered state to the formation of a glassy state. It was determined that all samples are X-ray amorphous up to the temperature of 6500C. It was shown that increasing the CaO content in the composition of xerogels up to 30 wt.%, and accordingly increasing the ratio CaO:P2O5 from 1 to 6, leads to the absence of glass phase. The optimal ratio CaO:P2O5 is 2. The influence of Li2O and BaO on a decrease in the glass formation temperature was substantiated and experimentally confirmed by thermal analysis.

Mesoporous xerogel cellulose composites from biorenewable natural cotton fibers

All-cellulose xerogel composites were fabricated using a facile, scalable three-step process—(1) partial ionic liquid dissolution, (2) non-solvent rinsing, and (3) drying. The xerogel composites are composed of two phases where the yarn center is non-porous highly crystalline cellulose I surrounded by mesoporous amorphous regenerated cellulose. The composite had high 149 m2 g−1 Brunauer-Emmett-Teller (BET) surface area with 11.7 nm average pore diameter. The porosity was calculated using density-based (ϕρ = 0.49) and volume-based (ϕV = 0.52) methods. The porosity evolution mechanism is attributed to non-solvent-induced polarity shifts, and these results are compared with non-porous morphologies produced by varying the choice in non-solvents. Although similar decrystallization behavior was measured for all samples, non-porous yarns had a smaller diameter and significantly reduced BET surface area (0.03 m2 g−1). The presented fabrication method offers controllable mesoporous phase formation along with freestanding structural capability towards the development of advanced functional cellulosic materials.

Characterization of Ceramic Membrane based on Calcium Carbonate from Onyx Stone and Its Application for Coconut Sap Treatment

In this study, the calcium carbonate from onyx stone used as a pore-forming agent in the ceramic membrane of kaolin, zeolite, and silica xerogel composites were investigated. Four different membrane samples were prepared with varying onyx stone content from 5 wt.% to 30 wt.% into composite and then the prepared samples were sintered at 1200oC. The structural properties of the prepared sample was investigated in detail using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and N2 adsorption-desorption isotherms. The removal performance of the membrane was successfully tested during coconut sap treatment. It has been found that the prepared samples have a porous structure made up of interconnected pores and their volume fraction depends on onyx stone content. The sample with the onyx stone content of 30 wt.% provides the largest volume fraction of homogeneously interconnected pores and its presence demontrates the largest value for sap permeate flux and the flux rate in the initial phase. The pores formed in this produced membrane provide favorable conditions for the removal of the non-sugar impurities in the coconut sap.

Polyethylene glycol/silica and carbon black/silica xerogel composites as an adsorbent for CO2 capture.

Mesoporous polyethylene glycol (PEG)/silica and carbon black (CB)/silica xerogel composites were prepared by the sol-gel method as an adsorbent for CO2 adsorption. The CO2 adsorption process was carried out under pure CO2 atmosphere at room temperature in addition to ambient air. The xerogel composites with high surface area and pore volume showed better CO2 adsorption capacity than the pure silica xerogel. After modifying samples with propylene diamine using the wet impregnation method, an increase in CO2 adsorption capacity was observed for the samples except CB/silica xerogel composite. The highest CO2 adsorption capacity was determined as approximately 0.80 mmol/g for amine modified PEG/silica xerogel composite under pure CO2 exposure. According to the adsorption-desorption cyclic stability test, it was clear that the stable samples were obtained, which is a desirable property for all CO2 adsorbents. The promising findings revealed that the xerogel composites can be efficiently used as a CO2 adsorbent instead of conventional materials in many CO2 adsorption applications. Additionally, it can be expected that the xerogel composites can provide an effective adsorption process without high-cost, complexity, corrosion, and toxicity problems.

Hierarchically porous metal hydroxide/metal–organic framework composite nanoarchitectures as broad-spectrum adsorbents for toxic chemical filtration

We demonstrate that the hierarchically porous metal hydroxide/metal–organic framework composite nanoarchitectures exhibit broad-spectrum removal activity for three chemically distinct toxic gases, viz. acid gases, base gases, and nitrogen oxides. A facile and general in-situ hydrolysis strategy combined with gentle ambient pressure drying (APD) was utilized to integrate both Zr(OH)4 and Ti(OH)4 with the amino-functionalized MOF-808 xerogel (G808-NH2). The M(OH)4/G808-NH2 xerogel composites manifested 3D crystalline porous networks and substantially hierarchical porosity, with controllable amounts of amorphous M(OH)4 nanoparticles residing at the edge of xerogel particles. Microbreakthrough tests were performed under both dry and moist conditions to evaluate the filtration capabilities of the composites against three representative compounds: SO2, NH3, and NO2. Compared with the pristine G808-NH2 xerogel, the incorporation of M(OH)4 effectively enhanced the broad-spectrum toxic chemical mitigation ability of the material, with the highest SO2, NH3, and NO2 breakthrough uptake reaching 74.5, 55.3, and 394.0 mg/g, respectively. Post-breakthrough characterization confirmed the abundant M-OH groups with diverse binding configurations, alongside the unsaturated M (IV) centers on the surface of M(OH)4 provided extra adsorption sites for irreversible toxic chemical capture besides Van der Waals driven physisorption. The ability to achieve high-capacity adsorption and strong retention for multiple contaminants is of great significance for real-world filtration applications.

Dispersion of pure silica xerogel vs NaYF4- xerogel nanomaterials in silica aerogel and their effect on the optical and structural properties

Upconversion materials, which have the ability to transfer light's intensity, have reliable implementations on instruments from which they can synthesize light spectrum to better efficiency fulfillment. It has become useful to isolate the transformed nanomaterials with low clarity in a medium with a low optical attenuation coefficient; this step helps attendees to arrive and enhances the contribution of individual particles. Silica aerogels are suitable for dispersing nanomaterials around the volume due to their high transparency and all open porosities. To investigate the impact of compounds on their respective structures, NaYF4-based nanocrystals are combined with various anabolic steroids in silica xerogel and aerogel. Although, the fact that the average surface area of the compounds was diminished, the phases of nanocrystals and forms were preserved during the xerogel treatment. As nanoparticles are integrated into xerogel composites, their luminescence increases. The improvement in the strength of the composite luminance is claimed to be attributable to the nanoparticles that shield it from the cooling effects of the silica matrix after measuring the effects of the assembly and composite drainage engineering.

Effect of solvent exchange on the properties of carbon xerogel and carbon xerogel/polypyrrole composites for supercapacitors

Carbon xerogels (CXs) with three-dimensional (3D) structure, unusual surface, physical, electrical and mechanical properties and their electrically conductive polymer polypyrrole (PPy) composites were synthesized as electrode materials for supercapacitors. The effect of different resorcinol/formaldehyde (R/C) ratios, whether solvent exchange with or without acetone and polypyrrole addition on the physicochemical (FTIR, XRD, BET, SEM and TGA) and electrochemical properties (CV, 1000 cycles) of the synthesized materials were investigated. It was observed that the R/C ratio and the solvent exchange process prior to drying affect the specific surface areas and the pore size distributions, thereby positively affecting the specific capacitance. PPy film thickness was observed to be effective in the specific capacitance of the electrode in PPy composite synthesis. Among the synthesized materials, the highest specific capacitance values belong to polypyrrole/carbon xerogel composites. As a result of the analysis and calculations, it was found that the highest specific capacitance belongs to CX2/PPy composite with 599 Fg−1 at 5 mVs−1. CX2/PPy composite has been found to have a capacitance retention rate of 80.30% at the end of 1000 cycles.

Carbon Xerogel Nanostructures with Integrated Bi and Fe Components for Hydrogen Peroxide and Heavy Metal Detection.

Multifunctional Bi- and Fe-modified carbon xerogel composites (CXBiFe), with different Fe concentrations, were obtained by a resorcinol–formaldehyde sol–gel method, followed by drying in ambient conditions and pyrolysis treatment. The morphological and structural characterization performed by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption/desorption porosimetry, scanning electron microscopy (SEM) and scanning/transmission electron microscopy (STEM) analyses, indicates the formation of carbon-based nanocomposites with integrated Bi and Fe oxide nanoparticles. At higher Fe concentrations, Bi-Fe-O interactions lead to the formation of hybrid nanostructures and off-stoichiometric Bi2Fe4O9 mullite-like structures together with an excess of iron oxide nanoparticles. To examine the effect of the Fe content on the electrochemical performance of the CXBiFe composites, the obtained powders were initially dispersed in a chitosan solution and applied on the surface of glassy carbon electrodes. Then, the multifunctional character of the CXBiFe systems is assessed by involving the obtained modified electrodes for the detection of different analytes, such as biomarkers (hydrogen peroxide) and heavy metal ions (i.e., Pb2+). The achieved results indicate a drop in the detection limit for H2O2 as Fe content increases. Even though the current results suggest that the surface modifications of the Bi phase with Fe and O impurities lower Pb2+ detection efficiencies, Pb2+ sensing well below the admitted concentrations for drinkable water is also noticed.

Synergistic performance of simply fabricated polyaniline/carbon xerogel composite as supercapacitor electrode

Abstract This work involves preparation of loaded polyaniline (PANI)/carbon xerogel (CX) composites with different mass ratios. The effect of PANI loading on the porosity and electrochemical activity of the composites is studied. Surface characterization analysis of studied samples reveals that incorporation of PANI onto the CX network reduces its specific surface area with a simultaneous expansion of the average pore diameter from the microporous to the mesoporous range. The prepared composites are tested as supercapacitor electrodes, and their electro-capacitive properties are studied by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy in a two-electrode cell using 1 M H2SO4 electrolyte. Results show that introducing PANI into CX network enhances the gravimetric capacitance from 156 to 612 F ∙ g−1 at current density of 0.1 A ∙ g−1 with reasonable stability. For instance, sample composite of PANI:CX = 5:1 w/w displays a retention percentage of 87.6% after 1500 repetitive cycles. In general, this synergy between PANI and CX in the prepared composites is attributed to the development of mesoporosity and the lowering of electrode resistance.

Design and synthesis of a new topical agent for halting blood loss rapidly: A multimodal chitosan-gelatin xerogel composite loaded with silica nanoparticles and calcium

Uncontrolled hemorrhage often causes death during traumatic injuries and halting exsanguination topically is a challenge. Here, an efficient multimodal topical hemostat was developed by (i) ionically crosslinking chitosan and gelatin with sodium tripolyphosphate for (ii) fabricating a robust, highly porous xerogel by lyophilization having 86.7 % porosity, by micro-CT and large pores ∼30 μm by SEM (iii) incorporating 0.5 mg synthesized silica nanoparticles (SiNPs, 120 nm size, −22 mV charge) and 2.5 mM calcium in xerogel composite that was confirmed by FTIR analysis with peaks at 3372, 986 and 788 cm−1, respectively. XPS analysis displayed the presence of SiNPs (Si2p peak for silicon) and calcium (Ca2p1, Ca2p3 transition peaks) in the composite. Interestingly, in silico percolation simulation for composite revealed interlinked 800 μm long-conduits predicting excellent absorption capacity and validated experimentally (640 % of composite dry weight). The composite achieved >16-fold improved blood clotting in vitro than commercial Celox and Gauze through multimodal interaction of its components with RBCs and platelets. The composite displayed good platelet activation and thrombin generation activities. It displayed high compressive strength (2.45 MPa) and withstood pressure during application. Moreover, xerogel composite showed high biocompatibility. In vivo application of xerogel composite to lethal femoral artery injury in rats achieved hemostasis (2.5 min) significantly faster than commercial Celox (3.3 min) and Gauze (4.6 min) and was easily removed from the wound. The gamma irradiated composite was stable till 1.5 yr. Therefore, the xerogel composite has potential for application as a rapid topical hemostatic agent.

Facile preparation of Bi-doped ZnO/β-Bi2O3/Carbon xerogel composites towards visible-light photocatalytic applications: Effect of calcination temperature and bismuth content

This work aimed to study the development and properties of Bi-doped ZnO/β-Bi2O3/Carbon xerogel composites towards visible light photocatalysis applications. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dispersive energy spectroscopy, infrared spectroscopy, nitrogen adsorption isotherms, Raman spectroscopy, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the developed composites was evaluated through the photodegradation of the 4-chlorophenol molecule and by chronoamperometry tests. The results obtained show that the calcination temperature poses a major influence in the final structure of the materials developed. The calcination temperature of 600 °C resulted in the formation of the β-Bi2O3 and Bi0 phases, consequently enhancing the photocatalytic activity of the composites due to the increased charge mobility provided by the heterojunctions between zinc oxide, carbon xerogel, bismuth oxide and metallic bismuth. The composite with intermediate bismuth composition (XC/ZnO–Bi2O3 5%) displayed the best photocatalytic response among the materials tested, which was confirmed by its increased photocurrent generation capability. The photocatalytic mechanism is highly dependent in the generation of hydroxyl radicals and the composite presents good reusability properties.

Zinc oxide/carbon xerogel composites for photocatalytic applications developed through acidic and alkaline synthesis routes: structural, morphological, and photocatalytic evaluations

This paper evaluates the influence of synthesis route (acidic or alkaline) on the structure, morphology, and photocatalytic properties of ZnO/Carbon xerogel composites. Structurally, both classes of materials present the wurtzite phase of zinc oxide. Composites derived from acidic route displayed facile thermal degradation of the zinc oxalate precursor when compared with pure zinc oxalate. Morphology-wise, materials produced through alkaline route are composed of nodular and plate-like particles, whereas acidic route composites are heterogeneously formed by large polyhedral particles and small particle agglomerates. Elemental distribution analysis confirms the heterogeneity of the acidic route composites, showing clear phase separation between the ZnO and the carbon xerogel. The composites prepared using the alkaline route are superior in the photodegradation of 4-chlorophenol, probably due to higher homogeneity and synergy between the semiconductor and carbonaceous phases. The superiority of alkaline route composites is confirmed by electrochemical impedance spectroscopy, which shows that such materials have enhanced charge separation capability.

Spray drying as feasible processing technique to enhance the photocatalytic activity of the Nb2O5/carbon xerogel composite

This work aimed to study the effect of the spray drying technique on the morphological, structural, optical and photocatalytic properties of the Nb2O5/carbon xerogel composite. The results obtained show that the spray drying technique causes a significant change in the morphology of the composites, resulting in spherical and uniform particles. Structurally wise, the composite produced using spray drying has the hexagonal structure of the niobium oxide, whereas the material produced using evaporative drying has an amorphous structure. The optical properties of the composite were also affected, as the bandgap energy of the spray dried material is lower than the one obtained for the composite obtained through evaporative drying. The spray dried material presented superior adsorption capacity and photocatalytic efficiency, indicating that the modifications introduced by the spray drying are suitable to enhance the photocatalytic efficiency of the Nb2O5/carbon xerogel composite.

Effect of the residual water content in gels on solution combustion synthesis temperature

The composition of gels and xerogels, as well as their transformation during heating and dehydration, determine the thermochemistry of solution combustion synthesis reactions. An improved descriptive thermodynamic model of combustion processes was formulated on the basis of the investigated formation of complex compounds of metal ions with organic fuel (glycine, citric acid, urea, and PVA) in nitrate solutions. The intensity of SCS reactions was found to depend on the strength of Ni2+–ligand complexes. The effect of heat loss during combustion on the ΔTmax value was analyzed for the model system Ni(NO3)2·nH2O–Fuel–H2O. It was found the heat loss occurs due to the presence of various amounts of structurally-bound water in gels and xerogels before the combustion.

Effect of synthesis medium on structural and photocatalytic properties of ZnO/carbon xerogel composites for solar and visible light degradation of 4-chlorophenol and bisphenol A

The effect of synthesis medium (ethanol and water) on ZnO/Carbon xerogel photocatalysts was studied in order to increase the efficiency of the photocatalytic degradation of 4-chlorophenol and bisphenol A. The use of carbon xerogel is justified due to its excellent electrical conductivity, high surface area and porosity. The effect of the carbon content in the composites was also evaluated. The composites were characterized using scanning electron microscopy, transmission electron microscopy, dispersive energy spectrometry, X-ray diffractometry, infrared spectroscopy, nitrogen isotherms, differential scanning calorimetry, thermogravimetry, electrochemical impedance spectroscopy and Raman spectroscopy. All materials present the hexagonal crystalline structure of zinc oxide. Materials without carbon in their composition also presented the zinc hydroxychloride monohydrate phase. X-ray diffractograms and bandgap values obtained confirm the incorporation of carbon in the crystalline structure of zinc oxide. Materials produced in ethanol medium have lower values of crystallite and particle size, as well as higher graphite contents in their composition and higher specific surface area. All materials displayed photocatalytic activity when subjected to visible and solar radiation. Materials produced in ethanol displayed superior performance when compared to those synthesized in aqueous medium. The maximum values found for the degradation of 4-chlorophenol and bisphenol A were 88% and 78%, respectively, after 5 h. The mechanism of photocatalysis is strongly influenced by the generation of hydroxyl radicals and the materials were stable for three cycles of reuse. The electrochemical impedance spectroscopy confirms that the charge separation efficiency was optimized in the presence of the carbon xerogel and when the composite was produced in ethanol medium.

Reduction of NO with new vanadium-carbon xerogel composites. Effect of the oxidation state of vanadium species

Vanadium-carbon composites were successfully prepared by sol-gel methods, and their behaviour as NOx-reduction catalysts was tested. Two different synthesis approaches were employed: the distribution of VOx (i) along the carbon matrix and (ii) on the carbon spheres surface. This allows to modify the carbon-VOx interaction and thus, evaluate the role of vanadium oxidation state in the NOx abatement. The distribution of VOx along the carbon matrix favours the dispersion and reducibility of VOx nanoparticles and improves the carbon-VOx contact stabilizing vanadium low oxidation states (V2+), however part of the VOx particles were embedded on the carbon matrix becoming inactive. The distribution of those species on the carbon spheres surface improves the accessibility to the VOx active sites but at the expense of the decrease of the carbon-VOx interaction and VOx dispersion and reducibility. The oxidation state of the active phase is related with the global synthesis procedure and that reducibility depends on the interactions between phases. Catalytic results evidence that the NO reduction is strongly influenced by the oxidation state of vanadium. Commercial V2O5 and carbon-V2O5 physical mixture are poorly reactive whereas a stronger activity improvement activity was observed for C-VOx composites reaching conversion higher than 91% at 450 °C.