Synthesis and characterization of carbon aerogels doped with the anatase form of titanium oxide

TiO₂-doped carbon aerogels (CAs) were synthesized by sol–gel polymerization of a mixture of resorcinol, formaldehyde and tetrabutyl orthotitanate, followed by gelation and supercritical drying and carbonization in N₂ gas atmosphere. The morphology of these TiO₂-doped CAs was characterized by transmission electron microscopy. X-ray diffraction and Brunauer–Emmett–Teller methods were employed to determine the microstructure and surface characteristics of samples. It was found that the doped TiO₂ had no significant effect on the surface area of the samples, whereas the pore and mesopore volumes were increased by the addition of TiO₂. The TiO₂ particles were kept still as anatase in samples carbonized at 900 °C, and did not transform into rutile on heating. Electrochemical performance of the samples as electrode materials was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge/discharge measurements. The results showed that the specific capacitance of CA electrodes had been improved by TiO₂ doping, and the samples with wider pore diameters have higher capacitance values.     

Adsorption and antibacterial activity of silver‐dispersed carbon aerogels

Silver‐dispersed carbon aerogels (Ag/CAs) were obtained by the direct immersion of organic aerogels in aqueous AgNO₃ solutions and then carbonization of the resulting material under a nitrogen atmosphere. The adsorption and antibacterial activity of Escherichia coli and Staphylococcus aureus on Ag/CAs were studied by the measurement of the amount of viable bacteria in suspensions and scanning electron microscopy (SEM) observations. The adsorbed amount of bacteria on samples without silver increased with an increase in the carbonization temperature and contact time. SEM studies showed that the adsorption capacity of Ag/CAs decreased with an increase in the silver content; this was considered to be mainly due to the dissolution behavior of bacteria by silver ions. The antibacterial test showed that 2.5 mg of Ag/CAs with more than 3.6% Ag could inhibit the growth of 10⁵ cfu/mL E. coli in 10 mL of a Mueller–Hinton broth culture, but in the case of S. aureus, 10‐mg samples just got the same antibacterial effect. An antibacterial persistency test showed that 25 mg of Ag/CAs with 6.5% Ag could kill 50 mL of 10⁵ cfu/mL E. coli eight times. These results indicate that Ag/CAs possess strong and long‐term antibacterial activity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1030–1037, 2006     

Adsorption of VOC on modified activated carbon fiber

The surface chemistry of activated carbon fiber (ACF) was modified by CuSO₄. The static adsorption capacities of modified ACF for different volatile organic compounds (VOCs) were determined. The result indicates that ACF modified by CuSO₄ could get higher adsorption capacities for the vapors of benzene, toluene, methanol and ethanol than the untreated ACF. The increasing extent of the adsorption capacity of modified VACFs is different for various VOCs. The dynamic adsorption behavior of acetone vapor on modified ACF was also studied. The result confirms that the surface modification of ACF with CuSO₄ can enhance the affinity between ACF and acetone, which makes it possible to extract acetone of very low concentration from polluted air.     

Starch-derived carbon aerogels with high-performance for sorption of cationic dyes

Environmentally green carbon aerogels have been prepared as adsorbents for dye-containing wastewater. The aerogels were prepared by carbonization of starch aerogels synthesized from soluble starch through a sol-gel process followed by drying at ambient pressure. The Brunauer-Emmett-Teller (BET) surface areas and pore size distribution were measured by N₂ adsorption/desorption, and the surface zeta-potential and microstructure of carbon aerogels were characterized using a scanning electron microscope (SEM) and zeta-potential analyzer. SEM images indicate that the carbon aerogels consist of flakes with side length of 60-120 μm and thickness of 3-4 μm. The flakes are irregular in shape and composed of spherical carbon nanoparticles of 10-30 nm. The carbon aerogels have both microporous and mesoporous structures and exhibit high specific surface areas, the highest value is 1571 m²/g. The mean diameter of the micropores is 0.89 nm and that of the mesopores is 2-10 nm. At pH = 10, the carbon aerogels have a zeta-potential of −40 mV and exhibit high adsorption capacities for cationic dyes, such as crystal violet (CV), methyl violet (MV) and methylene blue (MB), from aqueous solution. The largest adsorption capacities for CV, MV and MB are 1515, 1423 and 1181 mg/g, respectively.     

Structure and adsorption properties of activated carbon aerogels

Activated carbon aerogels (ACAs) with excellent microporosity (e.g., 0.44 cm³/g) and mesoporosity (e.g., 1.72 cm³/g) were prepared by CO₂ activation. Their structures were investigated with transmission electron microscopy and N₂ adsorption–desorption analysis. Subsequently, their adsorption properties toward organic vapors were studied with static and dynamic adsorption experiments. The micropores of the ACAs had stronger adsorption ability than those of normal porous carbons. Furthermore, the condensation of organic vapors in the mesopores of ACAs greatly enhanced their equilibrium adsorption at high relative pressures. As a result, the adsorption capacities of organic vapors on the typical ACAs prepared were about 2–3 times greater than those on normal porous carbons. In addition, they also possessed excellent adsorption dynamics and outstanding desorption and regeneration properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Preparation and characterization of antibacterial silver-dispersed activated carbon aerogels

Silver-dispersed carbon aerogels (CAs) were obtained by direct immersion of organic aerogels prepared by ambient pressure drying technique in AgNO₃ aqueous solution and then carbonization. The effect of preparation conditions such as the resorcinol/catalyst ratio, the feed AgNO₃ concentration, the ratio of aerogel mass/solution volume, immersion time and carbonization temperature on the bulk density and silver content as well as the BET surface area of the dispersed CAs was studied. The dispersion and structure of silver nanoparticles in obtained materials were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The Ag-dispersed CAs prepared exhibit strong and long-term antibacterial activity.     

Influence of Long-term Use of Fertilizers and Farmyard Manure on the Adsorption–Desorption Behaviour and Bioavailability of Phosphorus in Soils

An understanding of the adsorption–desorption behaviour of phosphate (P) in soils after three decades of long-term fertilization would be an invaluable supplement to our knowledge of the chemistry of P in soils and would assist in developing P application strategies for successive crops. With this objective and within the framework of a long-term experiment, we collected surface soil samples (0–0.15 m) from agricultural crop land on which a rotation of maize-wheat-cowpea (fodder) crops had been grown for 32 years. The soil samples were investigated for adsorption and desorption behaviour of P, and the buffering capacities of soil samples were computed from the adsorption data. Soils differed widely in their P supply characteristics. Phosphate adsorption increased while percentage P adsorbed decreased gradually with increasing levels of added P. Adsorption maxima and the extent of P adsorption was at its maximum in unfertilized soil, and P adsorption decreased with increased P applications. The incorporation of farmyard manure with optimal P levels decreased P adsorption even more than a super-optimal application of P fertilizers. Bonding energy and Freundlich constant ȁ8nȁ9 also decreased with increased P application and with the incorporation of farmyard manure. The adsorption and desorption of applied P were inversely related, and the soils that adsorbed P the most readily released it the least into the soil solution, and vice-versa. Computation of maximum buffering capacities (MBC) indicated that increased levels of P application decreased MBC and increased P supply in soil. The beneficial effects of an annual incorporation of farmyard manure with optimal P levels were clearly pronounced, and P availability in these soils was found to be even higher than the soil receiving the super-optimal application of P fertilizers. Various adsorption–desorption parameters were significantly related with the P uptake of different summer (rice, maize, soybean) and winter (wheat, berseem and raya) crops. Adsorption maxima, desorption maxima and maximum buffering capacity are the major parameters governing P availability in soils.     

A novel porous La2Zr2O7 ceramic aerogels with ultralow thermal conductivity and photocatalytic property

Porous La₂Zr₂O₇ ceramic aerogels (CAs) were prepared by sol-gel template method and thermal treated process. The microstructure and crystallisation behavior of the samples were systematically characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. The results indicated that the as-prepared porous La₂Zr₂O₇ CAs had a single-phase pyrochlore structure with typical three-dimensional (3-D) porous structure. Meanwhile, the formation mechanisms of the as-prepared porous La₂Zr₂O₇ CAs were investigated. At the same time, the as-prepared porous La₂Zr₂O₇ CAs presented an ultralow room-temperature thermal conductivity of 0.07 W/(m K), high specific surface areas of 325.17 m²/g, and a relatively high compressive strength of 11.95 MPa. What's more, the as-prepared porous La₂Zr₂O₇ CAs possessed ideal photocatalytic activities due to its high crystallinity, large surface area as well as unique 3-D porous structure. Therefore, the present work is proposing some new insight to prepare rare-earth zirconates CAs with porous structures for thermal insulation and dye degradation applications.     

Adsorption of carbon dioxide on ionic liquids-modified active carbons and amino-modified polymer

Active carbons with various particle sizes (38–150, 300–500 and 800–1,200 μm) were modified by ionic liquids (ILs), and organic polymer was modified by acrylamide using a simple procedure, and these materials were applied to capture carbon dioxide (CO₂). The CO₂ adsorption amounts were calculated using a mass balance equation at three different temperatures (298.15, 308.15 and 318.15 K), respectively, and the influences of gas pressure, particle size and temperature on adsorption were discussed. Experimental results showed that the CO₂ adsorption capacity of ILs-modified active carbons was better than amino-modified polymer, and the smaller particle size (38–150 μm) ILsmodified active carbons had the largest adsorption capacity at 298.15 K. Compared with previous research about polyethyleneimine (PEI)-modified silica gel, the adsorption amount of CO₂ on ILs-modified active carbons has been greatly improved with lower cost.     

Adsorption characteristics of methyl mercaptan, dimethyl disulfide, and trimethylamine on coconut-based activated carbons modified with acid and base

The influence of surface modification of activated carbon on the adsorption of methyl mercaptan (MM), dimethyl disulfide (DMDS), and trimethylamine (TMA) was investigated by treatments with 1N-HNO₃ solution and 1N-NaOH solution. The surface modifications changed the concentrations of functional groups on the surface of activated carbon. Also, the surface modifications changed breakthrough time and equilibrium adsorption capacity of MM, DMDS, and TMA. The adsorption capacities of MM and DMDS were increased by acid treatment, but decreased by base treatment. On the other hand, the adsorption capacity of TMA was decreased by both acid and base treatments. But the difference ranges of equilibrium adsorption capacities according to acidity and basicity of the surface were relatively small.     

Porous structure and liquid‐phase adsorption properties of activated carbon aerogels

In this article, activated carbon aerogels (ACAs) were prepared by CO₂ activation. Their pore structures were investigated by N₂ adsorption–desorption analysis. ACAs have excellent microporosity (e.g. 0.36 cm³/g) and mesoporosity (e.g. 1.72 cm³/g). Adsorption characteristics of phenol, methylene blue, I₂, and VB₁₂ on ACAs in the liquid phase were studied by static adsorption experiments. Results showed that CO₂ activation process is an effective way to introduce micropores in carbon aerogels, which is enhanced with the increase of activation time. As a result, the adsorption capacities of the four mentioned adsorbates on ACAs were improved gradually with the increase of activation time. However, mesopore volume is also a factor on improving adsorption properties for the relatively giant molecules methylene blue and VB₁₂. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Understanding the inhibitory effect of sodium oleate on the corrosion of Al and Al–Cu alloys in 1.0 M H<Subscript>3</Subscript>PO<Subscript>4</Subscript> solution—Polarization studies

Polarization measurements were employed, as a first step towards studying the corrosion behaviour of Al and two Al–Cu alloys, namely Al–4.5%Cu, and Al–7.5%Cu alloys in deaerated stirred 1.0 M H₃PO₄ solution at 25 °C. Inhibition of Al and Al–Cu alloys corrosion in 1.0 M H₃PO₄ solution, using sodium oleate (SO) as an anionic surfactant inhibitor, was also studied. Polarization curves showed that SO acted as a mixed-type inhibitor to Al corrosion, while it acted mainly as a cathodic inhibitor to the acid corrosion of Al–4.5%Cu, and Al–7.5%Cu alloys. Inhibition is accomplished by inhibitor adsorption on the electrode surface without detectable changes in the chemistry of corrosion. The relationship between surfactant concentration, surfactant critical micellar concentration (CMC), and corrosion inhibition is also discussed based on the Langmuir isotherm assumption, commonly applied in corrosion inhibition evaluations. The protection efficiency increases with increase in surfactant concentration and %Cu in Al samples. Maximum protection efficiency of the surfactant is observed at concentrations around its CMC. The mechanism of adsorption is discussed based on the surface charge of the electrode surface.     

Investigation of the supercritical deposition of platinum nanoparticles into carbon aerogels

The preparation of platinum/carbon aerogel (CA) nanocomposites by the supercritical deposition method was investigated. CAs were impregnated with dimethyl(cyclooctadiene)platinum, CODPtMe₂, from supercritical carbon dioxide (scCO₂) solutions and the resulting CODPtMe₂/CA composites were converted to Pt/CA composites. The adsorption isotherms of CODPtMe₂ on CAs were measured and could be represented by the Langmuir model. The results indicated a strong interaction between CODPtMe₂ molecules and the CA surface and that a substantial fraction of the surface of the CAs was covered with CODPtMe₂ molecules at relatively low concentrations. Four different reduction methods were used to convert the CODPtMe₂ impregnated CAs which were: (1) thermal reduction at atmospheric pressure in an inert atmosphere; (2) thermal reduction in scCO₂; (3) chemical reduction in scCO₂ with hydrogen; and (4) chemical reduction at atmospheric pressure with hydrogen. Method 1 gave highly dispersed Pt nanoparticles (1–3 nm) at loadings ranging from 10 to 40 wt.%. The use of hydrogen in Method 4 increased the average particle size by a factor of 2 over Method 1 at the same Pt loading, but the particles still had a narrow unimodal size distribution. When the thermal reduction was carried out in scCO₂, loadings as high as 73% could be obtained. Method 3 generated a composite having a disordered columnar Pt coating and equiaxed particles ≈1 μm in diameter on the external surface of the monolith and dispersed Pt nanoparticles in the interior. The analysis of the reaction products in scCO₂ indicated an autocatalytic reaction. Increasing the Pt loading was found to decrease the surface area of the CA, primarily through blockage of the micropores.     

石墨烯基气凝胶对有机物的饱和吸附能力

以Pickering乳液法进行了石墨烯基气凝胶(GA)的制备,并以纯有机物和水中乳化油分为吸附对象,对其饱和吸附能力进行了评价,综合对比了不同研究者利用碳纳米材料所制备碳基气凝胶对纯有机化合物的吸附能力,发现包含本文所制备的GA在内的各种碳基气凝胶对不同的有机物的吸附能力与有机物的密度成正比,表明单位质量碳基气凝胶吸附有机物的体积(cm³?g^?1)为定值,与具体的被吸附有机物的种类无关。推断有机物在气凝胶材料中的吸附是一种体积填充行为,气凝胶孔隙体积的大小对于其吸附有机物的能力具有重要影响,但孔隙的占有率也是决定实际吸附有机物能力的关键因素。所制备的GA对水中油分的吸附能力低于其对纯油分的吸附能力,应与水的竞争吸附、有机物的扩散阻力等有关。     

Grafting of molecularly imprinted polymers from the surface of Fe3O4 nanoparticles containing double bond via suspension polymerization in aqueous environment: A selective sorbent for theophylline

Molecularly imprinted polymers (MIPs) were grafted from the surface of Fe₃O₄ nanoparticles containing double bond via suspension polymerization in aqueous environment, and the leakage of Fe₃O₄ nanoparticles from MIPs was overcome in this study. The effect of different cross‐linker on adsorption capacity of the resultant magnetic MIPs was investigated using pure trimethylolpropane trimethacrylate (TRIM) or the mixture of TRIM and divinylbenzene (DVB) as cross‐linker. Both magnetic MIPs exhibited higher adsorption capacity for the template theophylline than the corresponding non‐imprinted polymer, and Freundlich model fitted reasonably well for theophylline adsorption on both magnetic MIPs. In addition, both magnetic MIPs exhibited good recognition properties for the template theophylline versus caffeine, and the selectivity of magnetic MIPs using pure TRIM as cross‐linker (mag‐MIP‐TRIM) was much higher than those using the mixture of TRIM and DVB as cross‐linker (mag‐MIP‐TRIM and DVB). The adsorption dynamics of theophylline on both magnetic MIPs fitted well with the first‐order kinetic model, but the adsorption equilibrium on mag‐MIP‐TRIM and DVB reached faster than that on mag‐MIP‐TRIM. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Adsorption removal of thiophene and dibenzothiophene from oils with activated carbon as adsorbent: effect of surface chemistry

Commercial coconut-based activated carbons (AC), before and after being treated using 65 wt% HNO₃ at different temperatures (termed as AC–Hs), were used as adsorbents to remove thiophene (T) or dibenzothiophene (DBT) from model oils. The fresh AC sample and all of the AC–Hs samples were characterized by Boehm titration, Fourier-transform infrared spectroscopy, and thermal analysis, which yield the information of the surface chemistry properties of the carbon materials. The results show that in comparison to the fresh AC sample, the quantity of oxygen-containing functional groups on the surface of AC–Hs samples increases as the pretreatment temperature of the fresh AC sample increases. The adsorption capabilities of the AC samples for removal of T and DBT from model oils were evaluated in a batch-type reactor. It has been found that the refractory DBT can be removed easily over the untreated commercial AC with the removal efficiency even being higher than that of T. In the case of acid modified AC–Hs samples, the efficiency for removal of T has been greatly improved, but this is not the case for the removal of DBT. The possible mechanism for adsorption removal of T and DBT over activated carbons is discussed in terms of the quantity of surface oxygen-containing functional groups of adsorbents and the chemical structure of sulfur compounds. The effect of olefin (1-octene) and aromatic hydrocarbons (benzene) in the model oils on the selective adsorption DBT over AC is also evaluated, revealing that in the case of DBT, the competitive adsorption is involved in the process, and the removal efficiency levels off at a level over 80%.     

Adsorption and reaction of CO on CuO–CeO2 catalysts prepared by the combustion method

Temperature-programmed techniques were employed to investigate the interaction of CO with CuO–CeO₂ prepared by the urea-nitrates combustion method. These catalysts exhibited high and stable CO oxidation activity at relatively low reaction temperatures (< 150 °C). The CO adsorption capacity and catalytic activity of the catalysts was analogous to the concentration of easily-reduced copper oxide surface species. TPD and TPSR results can be explained by a dual scheme of CO adsorption: (i) on oxidized sites, which get reduced with simultaneous formation of surface CO₂ and (ii) on reduced sites created by the former interaction. 10–20% of adsorbed CO desorbs molecularly in the absence of gas-phase O₂, but reacts totally towards CO₂ in the presence of gas-phase O₂. Inhibition by CO₂ observed under steady-state CO oxidation conditions is due to CO₂ adsorption as found by CO₂-TPD.     

K-doped Mo–V–Sb–O crystalline catalysts for propane selective oxidation to acrylic acid

Mo–V–Sb–O complex metal oxide catalysts were synthesized hydrothermally and potassium was doped to the catalysts either during the hydrothermal synthesis or by ion-exchange method. The obtained catalysts were characterized by ammonia TPD and tested for propane selective oxidation to acrylic acid (AA) in order to investigate relationship between surface acid property and catalytic properties. The K-doped catalysts showed higher selectivity to AA than the un-doped catalyst but poorer in the propane conversion. It was observed that potassium clearly decreased the ammonia adsorption capacity on the surface without affecting bulk structural phases and furthermore a linear relationship was obtained between the reaction rate of propane and the ammonia adsorption capacity. The results strongly suggest that surface protonic acid sites involve in the oxidative activation step of propane which is regarded as the rate-determining step. On the basis of a demonstrative test using the K-doping by ion-exchange and the grinding procedure, it is concluded that the selectivity increase by the K-doping was due to the less influence of potassium on the rate of propene selective oxidation. We discuss a multi-functional character derived from high dimensional structures of the catalysts and mechanism of the selective oxidation of propane.     

Hydrogen sorption characteristics of Zonguldak region coal activated by physical and chemical methods

Hydrogen sorption characteristics of activated carbons (ACs) produced by physical and chemical activations from two coal mines (Kilimli and Armutcuk) in the Zonguldak region, Turkey were investigated by a volumetric technique at 77 K. H₂ adsorption isotherms were obtained on the samples exposed to pyrolytic thermal treatments in a temperature range of 600–900 °C under N₂ flow and chemical activation using different chemical agents such as KOH, NH₄Cl, ZnCl₂ from the two mines. Experimental hydrogen adsorption isotherm data at 77 K were used for the evaluation of the adsorption isotherm constants of the Brunauer-Emmett-Teller (BET) and the Langmuir models, and also the amount of hydrogen adsorbed on the various samples was evaluated by using the adsorption isotherm data. Higher hydrogen adsorption capacity values were obtained for all the heat and the chemically treated activated carbon samples from the Kilimli coal samples than Armutcuk. The amount of H₂ adsorbed on the original Kilimli coal samples was 0.020 wt%, and it was increased to 0.89 wt% on the samples pyrolyzed at 800 °C. The highest value of hydrogen adsorption obtained was 1.2 wt% for the samples treated with KOH+NH₄Cl mixture at 750 °C followed by oxidation with ZnCl₂. It was shown that chemical activations were much more effective than physical activations in increasing the surface area, pore volume and the hydrogen sorption capacities of the samples.     

Physico-chemical properties of silica aerogels prepared from TMOS/MTMS mixtures

In the present work, results on the physico-chemical properties of the silica aerogels prepared by sol–gel process using mixtures of TMOS and MTMS as precursor are reported. The wide range of precursor mixture was studied with ratio of MTMS/TMOS in precursor mixtures as 0:100, 25:75, 50:50, 75:25, and 100:0 by volume. The gels with these precursor mixtures were successfully prepared using two step acid–base catalysis for gelation. Acetic acid (0.001 M) and NH₄OH (1.5 M) were used for catalysis and resulting alcogels were subsequently dried by supercritical solvent extraction method. FTIR spectroscopy revealed that the aerogels show more intense peak at 1,260 and 790 cm⁻¹ attributed to Si–CH₃ resulting in more hydrophobic nature and these results were concurrent with adsorbed water content measurements made using Karl Fischer’s titration technique. The resulted aerogels were characterized using differential thermal analysis, thermo gravimetric analysis and surface area measurements. The surface area measurements showed an interesting trend that the surface area increased from 395 to 1,037 m²/g with increase in MTMS content in the precursor mixture from 0 to 50% and then again decreased to 512 m²/g for further increase in MTMS content from 50 to 100% in the precursor mixture. It was observed from our studies that silica aerogels prepared using a starting mixture of 50% TMOS and 50% MTMS resulted in high moisture resistance (adsorbed water content of 0.721% w/w), low density of 90 kg/m³ and the highest surface area of 1,037 m²/g, which has great potential for catalysis support applications.