Hierarchically porous graphitic carbon monoliths containing nickel nanoparticles as magnetically separable adsorbents for dyes

The hierarchically porous graphitic carbon monoliths containing nickel nanoparticles (HPGCM‐Ni) were fabricated via multi‐component co‐assembly in polyurethane (PU) foam scaffold associated with a direct carbonization process from triblock copolymer F127, diblock copolymer PDMS‐PEO, phenolic resol, and nickel nitrate and subsequent silicates removal with NaOH solution. The decomposable PU foam scaffold played important role in the process of multi‐component co‐assembly and macrostructure formation. The nickel salts were reduced to metallic Ni nanoparticles during the carbonization process. The obtained HPGCM‐Ni materials exhibited macropores of 100–450 μm, mesopore size of 7.2 nm, BET surface area of 725 m² g^?1, pore volume of 0.74 cm³ g^?1, and saturation magnetization of 2.3 emu g^?1. Using methyl orange as model dye pollutant in water, HPGCM‐Ni samples showed good adsorption capacity of 440 mg g^?1, exhibiting excellent adsorption characteristics desirable for the application in adsorption of dyes and separation under an external magnetic field. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41322.     

The performance of two adsorption ice making test units using activated carbon and a carbon composite as adsorbents

The available adsorption working pairs applied to adsorption refrigeration system, which utilize activated carbon as adsorbent, are mainly activated carbon-methanol, activated carbon-ammonia, and composite adsorbent-ammonia. The adsorption properties and refrigeration application of these three types of adsorption working pairs are investigated. For the physical adsorbents, consolidated activated carbon showed best heat transfer performance, and activated carbon-methanol showed the best adsorption property because of the large refrigerant amount that can be adsorbed. For the composite adsorbents, the consolidated composite adsorbent with mass ratio of 4:1 between CaCl₂ and activated carbon, showed the highest cooling density when compared to the granular composite adsorbent and to the merely chemical adsorbent. The physical adsorption icemaker that employs consolidated activated carbon-methanol as working pair had the optimum coefficient of refrigeration performance (COP), volume cooling power density (SCP_v) and specific cooling power per kilogram adsorbent (SCP) of 0.125, 9.25 kW/m³ and 32.6 W/kg, respectively. The composite adsorption system that employs the consolidated composite adsorbent had a maximum COP, SCP_v and SCP of 0.35, 52.68 kW/m³ and 493.2 W/kg, respectively, for ice making mode. These results are improved by 1.8, 4.7 and 14 times, respectively, when compared to the results of the physical adsorption icemaker.     

Adsorption and electrothermal desorption of organic vapors using activated carbon adsorbents with novel morphologies

Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal-swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal-swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.     

Carbonaceous adsorbents from sewage sludge and their application in a combined activated sludge-powdered activated carbon (AS-PAC) treatment

In this study, waste biological sludge is converted to an adsorbent by chemical activation with sulphuric acid. The adsorbent obtained is then applied to the aerated vessel of an activated sludge process treating glucose and phenol to improve the quality of the treated effluent. The sludge-based carbonaceous adsorbent was found to be mesoporous in nature, with a good adsorption capacity for large molecular weight compounds and limited removal efficiency for smaller molecules such as phenol. The addition of carbon, either sludge-based or commercial, enhanced phenol removal from 58% to 98.7% and from 87% to 93% the organic matter removal as measured by the chemical oxygen demand (COD) when operated with feed concentrations of 100 mg phenol/l and 2500 mg COD/l. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based adsorbents in spite of the higher adsorption capacity of the former. It is suggested that powdered adsorbent bioregeneration in the combined AS-PAC system may be impaired by the obstruction of pores due to bacterial growth, the effect being more important for the commercial activated carbon with a narrower pore size distribution.     

Performance analysis of an adsorption refrigerator using activated carbon in a compound adsorbent

To improve the performance of the adsorption refrigeration of CaCl₂-ammonia adsorption system, activated carbon has been distributed uniformly in the mass of CaCl₂, thereby helping to enhance mass transfer and uplift the cooling power density. A multifunctional heat pipe adsorption refrigerator, in which activated carbon-CaCl₂ is used as compound adsorbent and ammonia as refrigerant, is designed. Water and acetone are used as working liquids for the heat pipe. This paper presents a study on the adsorption refrigeration performances of this adsorption refrigerator under two different working conditions, ice-maker for fishing boat driven by the waste heat from exhaust gases, and solar ice-maker driven by solar water heating. The obtained average SCP (specific cooling power) and the COP (coefficient of performance) of the refrigerator were measured to be 770.4 W/kg and 0.39 at about −20 °C of evaporating temperature for the former working condition, and they were 161.2 W/kg and 0.12 at about −15 °C of evaporating temperature for the later working condition.     

Adsorption of cationic-anionic surfactant mixtures on activated carbon

This paper reported the adsorption of cationic-anionic surfactant mixtures, such as octyltriethylammonium bromide/sodium dodecylbenzenesulfonate (OTEAB/SDBS) and dodecylpyridinium chloride/sodium octanesulfonate (DPC/SOS), on activated carbon (AC) in deionized water and in mineralized water systems. The AC surface chemistry was characterized by X-ray photoelectron spectroscopy and ζ-potential determinations. It was observed that in deionized water solution, the addition of SOS obviously promoted the adsorption of DPC, while the existence of OTEAB increased the adsorption of SDBS first and then decreased that slightly with increasing SDBS concentration. In mineralized water solution, the addition of cationic (anionic) surfactants reduced the adsorption of anionic (cationic) surfactants. It was shown that the adsorption of the surfactants on the AC was predominated mainly by the hydrophobic interaction between AC surface and surfactants because of the low oxygen content and very low ζ-potential on the AC surface. There might exist synergism between cationic and anionic surfactants when adsorbing on AC in deionized water due to the electrostatic interaction between oppositely charged surface active ions. Such synergism might be greatly weakened when a large number of inorganic salts exist owing to the “screen” effect of the counter ions of the salt on the electrostatic attraction of oppositely charged surface active ions.     

Preparation of hydrophilic activated carbon through alkaline hydrolysis of ester for effective water-vapor adsorption

Hydrophilic activated carbon was prepared by a novel ethyl acetate hydrolysis method. Surface area analysis, spectroscopies, and microscopy were used to examine characteristic differences between raw and hydrophilic activated carbons. Results showed that hydrophilic groups were introduced onto the surface of activated carbon through ethyl acetate hydrolysis in an alkaline environment. The modified activated carbon exhibited higher water vapor adsorption capacity because the hydrophilic groups on its surface bound with water molecules through H-bonding. Adsorption isotherms of water vapor were well fitted by an adsorption model. The optimal temperature for thermal regeneration was determined to be 398 K.     

Characterisation of the surface of oxidised carbon adsorbents

The surface reactivity and functional group content of a series of oxidised active carbons has been assessed by elemental analysis, electrophoretic mobility measurements and potentiometric titrations. Oxidation of carbons with hot air resulted in a greater proportion of relatively weak acidic surface functional groups (i.e., phenolic), whereas nitric acid modification produced a greater amount of carboxylic groups. Electrophoretic mobility measurements suggest that the carbon surface is negatively charged within the range of the pH values studied. pH titration results indicate that the surface acidity of active carbons is stronger than that of a commercial polymeric carboxylic acid ion exchange resin. Possible mechanisms of carbon surface oxidation are discussed.     

Hydrogen storage on nickel catalysts supported on amorphous activated carbon

We have studied the hydrogen storage at room temperature and high pressure on nickel catalysts impregnated on an amorphous commercial activated carbon. The catalysts were studied by means of the BET method, XRD, metal surface area and temperature programmed desorption. It was shown that the catalysts could store significant amounts of hydrogen at room temperature and high pressure (up to 0.53% at 30 bars against 0.1% for the activated carbon). Various factors influencing the level of hydrogen uptake were examined and discussed. The hydrogen spillover would be the driving force for the hydrogen storage. Two mechanisms of hydrogen uptake are proposed.     

Thermal reactivation of ammonia-tailored granular activated carbon exhausted with perchlorate

Thermal reactivation with CO₂ or NH₃ at temperatures higher than 700 °C effectively restored the perchlorate adsorption capacity of ammonia-tailored carbon. In contrast, steam regeneration restored only a portion of the perchlorate adsorption capacity, and these distinctions were attributed to the change in surface chemistry that was induced by regeneration. After perchlorate loading, regenerating the ammonia-tailored GAC via CO₂ or NH₃ preserved the nitrogen content and positive surface charge density of the initial ammonia-tailored activated carbon. In contrast, steam regeneration caused a decrease in nitrogen content and positive surface charge. Perchlorate breakthrough was monitored in rapid small-scale column test (RSSCT) operations with either CO₂ or NH₃ regeneration. 4000-4500 bed volumes of perchlorate adsorption life could be achieved through at least three cycles of RSSCT operation and regeneration. This compared favorably to the 4500 bed volumes that had been achieved when using the initial ammonia-tailored carbon.     

Role of localized graphitization on the electrical and magnetic properties of activated carbon

The correlation between the magnetic and electrical properties of activated carbon with its microstructure is studied. The changes in the microstructure of activated carbon, after activation at three different temperatures (800°C, 900°C, 1000°C) using different amounts of the activating agent, KOH (KOH/C ratio of 1:1, 2:1, 3:1 and 4:1), are studied using X‐ray diffraction and Raman spectroscopy. The results showed the formation of localized nanographitic domains, along with the changes in the surface area and porosity of the activated carbon. The changes in the microstructure are found to be directly correlated with the magnetic properties and electrical conductivity. The interplay between ordering and disordering parameters in the activated carbon is found to determine the electrical conductivity and magnetic properties.     

Methane storage in wet activated carbon: Studies on the charging/discharging process

The dynamic behavior of charging/discharging methane onto/from water-preloaded activated carbon was studied at different conditions. It was shown that methane hydrate could form quickly in the porous space of carbon at the condition of 275 K and pressures beginning with 4.12 MPa. The stored methane could be continuously released at a constant flowrate for the whole discharging process. The packing density of 0.6 g cm⁻³ seemed optimal for the wet carbon tested, which yielded 152 V/V of released methane at charging pressure of 8 MPa. The thermal effect observed on the charging/discharging process was low and did not affect the effective storage capacity.     

溶胶法在活性炭上负载金属纳米颗粒的参数和机理研究

使用正交实验法研究了溶胶-凝胶法在活性炭上负载金属纳米颗粒的工艺条件.在固定活性炭量和表面活性剂量的情况下,研究了金属负载量、乙二醇用量、碱性中和剂量和氢还原时间等四因素对负载产物的比表面积和负载效果的影响.通过直观分析和方差分析找出溶胶法在活性炭上负载金属纳米颗粒的最优工艺条件.对样品的氮吸附检测和扫描电镜(SEM)照片检测发现,当负载量在16%以下时,金属粒子分散良好,无明显聚集现象.实验结果表明,溶胶-凝胶法可以控制金属粒子主要附着在活性炭的外表面和大孔壁上,对微孔几乎没有影响.因此,可用于制备兼具高负载量和大比表面积特点的高性能金属/活性炭复合催化剂.     

Bituminous coal-based activated carbons modified with nitrogen as adsorbents of hydrogen sulfide

Bituminous coal-based activated carbon was modified by impregnation with melamine and heat treatment at 850 °C. Another sample was impregnated with melamine and urea and heat treated at 650 and 850 °C. Chemical and physical properties of the materials were determined using Boehm titration, thermal analysis, sorption of nitrogen and SEM with EDX. Then the H₂S breakthrough capacity tests were carried out and the sorption capacity was calculated. The results revealed that carbons modified with nitrogen-containing species and heat-treated at 850 °C have a hydrogen sulfide removal capacity exceeding more then 10 times the capacity of unmodified sample. H₂S on the surface of these materials is oxidized to sulfuric acid and elemental sulfur and stored in the pore system. New carbons are hypothesized to act as catalytic reactors promoting two different pathways of hydrogen sulfide oxidation in two different locations. In small micropores, where water is present, hydrogen sulfide dissociate to HS⁻ ions and those ions are oxidized to sulfur radicals and sulfur dioxide leading to the formation of sulfuric acid. In larger pores with incorporated nitrogen, basic sites promote dissociation and formation of sulfur polymers, which are resistant to further oxidation.