Role of intrinsic defects on carbon adsorbent for enhanced removal of Hg^(2+)in aqueous solution

Carbon is a normally used adsorbent for removal of heavy metal ion in aqueous solutions,but the efficient adsorbent needs intensive modification by heteroatom doped or supported noble metals that cause severe pollution and easy leaching of active components during use.In this paper,the role of intrinsic defects on Hg^(2+)adsorption for carbon adsorbent was investigated.The maximum adsorbing capacity of defectrich carbon has been improved up to 433 mg·g^(-1)which is comparable to most of the modified carbon adsorbents via supported metal chloride or noble metal components.The basicity is increased with the content of defective sites and the strong chemical bonding can be formed via electron transformation between the defect sites with adsorbed Hg^(2+).The present study gives a direction to explore cheap and easily scale-up high-performance mercury adsorbents by simply tuning the intrinsic defective structure of carbon without the necessity to support metal or other organic compounds.

Estimation of the Isotherms of Phenol on Activated Carbons and Polymeric Adsorbents under Supercritical Condition

A method named as 'volume-expanding and pressure-reducing adsorption' is proposed. It can be used to measure the isotherms under supercritical condition. The adsorption isotherms of phenol on activated carbons and polymeric adsorbents are estimated and compared respectively for the systems of 'phenol-activated carbon-supercritical fluid CO2' and 'phenol-polymeric adsorbent-supercritical fluid CO2'. The results show that the amount of phenol adsorbed on the activated carbons and the polymeric adsorbents under the supercritical condition is much less than that under the general condition, which can be utilized to develop a technology regenerating the activated carbon with supercritical fluid. Moreover, the effects of ethyl alcohol, used as the third component, on the isotherms of phenol on the activated carbons and polymeric adsorbents under the supercritical condition are also investigated.

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO_(2)/N_(2) and CH_(4)/N_(2) separation

Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In this regard,in order to assess the better adsorbent for separating CO_(2) from flue gas and CH_(4) from coal bed methane,adsorption isotherms of CO_(2),CH_(4) and N_(2) on activated carbon and carbon molecular sieve are measured at 303.15,318.15 and 333.15 K,and up to 250 kPa.The experimental data fit better with Langmuir 2 compared to Langmuir 3 and Langmuir-Freundlich models,and Clausius-Clapeyron equation was used to calculate the isosteric heat.Both the order of the adsorbed amount and the adsorption heat on the two adsorbents are CO_(2)>CH_(4)>N_(2).The adsorption kinetics are calculated by the pseudo-first kinetic model,and the order of adsorption rates on activated carbon is N_(2)-CH_(4)>CO_(2),while on carbon molecular sieve,it is CO_(2)-N_(2)>CH_(4).It is shown that relative molecular mass and adsorption heat are the primary effect on kinetics for activated carbon,while kinetic diameter is the main resistance factor for carbon molecular sieve.Moreover,the adsorption selectivity of CH_(4)/N_(2) and CO_(2)/N_(2) were estimated with the ideal adsorption solution theory,and carbon molecular sieve performed best at 318.15 K for both CO_(2) and CH_(4) separation.The study suggested that activated carbon is a better choice for separating flue gas and carbon molecular sieve can be a strong candidate for separating coal bed methane.

Nanoporous carbons as promising novel methane adsorbents for natural gas technology

Nanoporous carbons were synthesized using furfuryl alcohol and sucrose as precursors and MCM-41 and mordenite as nanoporous templates.The produced nanoporous carbons were used as adsorbent for methane storage.The average pore diameter of the samples varied from 3.9 nm to 5.9 nm and the BET surface area varied from 320m2/g to 824m2/g.The volumetric adsorption experiments revealed that MCM-41 and sucrose had better performance compared with mordenite and furfuryl alcohol,correspondingly.Also,the effect of precursor to template ratio on the structure of nanoporous carbons and their adsorption capacities was investigated.The nanoporous carbon produced from MCM-41 mesoporous molecular sieve partially filled by sucrose shows the best methane adsorption capacity among the tested samples.

Recyclable adsorbent of BiFeO_3/Carbon for purifying industrial dye wastewater via photocatalytic reproducible

It is essential to prepare highly-efficiency reproducible adsorbent for purifying industrial dye wastewater. In this work, biscuit with a layered porous structure as a template is applied to prepare a photocatalytic recyclable adsorbent of BiFeO3/Carbon nanocomposites for purifying simulative industrial dye wastewater. It is found that the structure of the prepared BiFeO3/Carbon nanocomposite is related to the natural structure of the biscuit, annealing temperatures and immersing times, demonstrated by XRD, TEM, UV-Vis and adsorptive activities. Kinetics data shows that the adsorption rate of the adsorbent to the dye is rapid and fitted well with the pseudo-second-order model, that more than 80% of dyes can be removed in the beginning 30 min. The adsorption isotherm can be perfectly described by the Langmuir model as well. It can be seen from the adsorption data that the adsorption performance can reach over 90% at pH ? 2–12, which can imply its universal utilization. The prepared BiFeO_3/Carbon nanocomposites have also displayed excellent capacities(over 90% within 30 min) for adsorption of seven different dyes and their mixed one. According to the five times photocatalytic reproducible experiments, it is proved that BiFeO_3/Carbon nanocomposites show the excellent stability and reproduction for purifying simulative industrial dyes, even the sample have been placed for one year. These research results indicate that the adsorbent BiFeO_3/Carbon can be a suitable material used in treating industrial dye wastewater potentially.

Graphene oxide based carbon composite as adsorbent for Hg removal:Preparation, characterization, kinetics and isotherm studies

The presence of Hg in the aqueous media is known to cause severe health issues in both humans and animals.Many technologies and especially adsorbents have been applied for its removal. In this study, a graphene oxide–carbon composite(GO–CC) as a new adsorbent was prepared by sol gel procedure and characterized using field emission scanning electron microscopy, BET and EDX. The effects of different variables including solution p H, contact time, adsorbent dose and GO ratio in adsorbent matrix on the removal capacity of Hg were studied. The isotherm data correlated well with the Langmuir isotherm model. Further analysis recommended that the Hg^(2+) adsorption process is governed by the intra-particle and external mass transfer, in which the film diffusion was the rate restrictive step. The presented composite has maximum absorption capacity, q_(max) of 68.8 mg·g^(-1), which is comparable with carbon based adsorbent reported in the previous publications.

Fabrication and Thermal Conductivity Improvement of Novel Composite Adsorbents adding with Nanoparticles

Thermal conductivity is one of key parameters of adsorbents, which will affect the overall system performance of adsorption chiller. To improve adsorbent＇s thermal conductivity is always one of research focuses in chemisorption field. A new chemical composite adsorbent is fabricated by adding carbon coated metal（Aluminum and Nickel） nanoparticles with three different addition amounts into the mixture of chloride salts and natural expanded graphite aiming to improve the thermal conductivity. The preparation processes and its thermal conductivity of this novel composite adsorbent are reported and summarized. Experimental results indicate that the nanoparticles are homogenously dispersed in the composite adsorbent by applying the reported preparation processes. The thermal conductivity of the composite adsorbent can averagely enlarge by 20% when the weight ratio of the added nanoparticles is 10 wt%. Moreover, carbon coated aluminum nanoparticles exhibit more effective enlargement in thermal conductivity than nickel nanoparticles. As for the composite adsorbent of CaCl2-NEG, there is a big reinforcement from 30% to 50% for Al@C nanoparticles, however only 10% in maximum caused by Ni@C nanoparticles. The proposed research provides a methodology to design and prepare thermal conductive chemical composite adsorbent.

Superhigh selective capture of volatile organic compounds exploiting cigarette butts-derived engineering carbonaceous adsorbent

Herein,we develop cost-efficient superhigh-performance of engineering carbonaceous adsorbent from cigarette butts using combined wet-impregnated and re-dispersed method of KOH,which optimizes the implant approach of activator,breaking the restriction of selective capture of toluene using traditional activated carbon.The Brunauer-Emmett-Teller(BET)surface area and pore volume of targeted adsorbent can attain 3088 m^(2)·g^(-1) and 1.61 cm^(3)·g^(-1),respectively,by optimizing the temperaturedependent synthetic factor effect of the adsorbent.The adsorption capacity of resultant adsorbent for presenting volatile benzene and toluene shows a positive correlation with increasing carbonization temperature of carbon precursor.Besides,we demonstrated the unsmoked and smoked butts derived adsorbents afford feeble difference in saturated adsorbed capacity of volatile organic compounds(VOCs).The highest adsorption capacity of sample CF-800 for benzene and toluene in CF group is as high as 1268.1 and 1181.6 mg·g^(-1) respectively,slightly higher than that of sample UF-800,but far outperforming reported other adsorbents.The predicted adsorption selectivity of CF-800 and UF-800 for C_(7)H_(8)/H_(2)O(g)using the DIH(difference of isosteric heats)equation reach up to ca.3800 and 7500 respectively,indicating the weak adsorbability of water vapor on the developed adsorbent and greater superiority of the smoked butts derived adsorbents in selective capture of VOCs at low relative humidity in the competitive adsorption process for practical mixed VOCs.

Performance Evaluation of Palm Kernel Shell Adsorbents for the Removal of Phosphorus from Wastewater

Studies were carried out on Palm Kernel Shell, an agricultural waste available in large quantity in Nigeria, to evaluate its ability to remove phosphorus from wastewater. The adsorbents, which were prepared from Palm Kernel Shells (PKN), were characterized using Fourier Transform Infrared (FT-IR), Energy dispersive X-ray (EDX) and Scanning Electron Microscopy (SEM). Batch mode experiments were conducted to study the effects of adsorbent dosage and contact time on phosphorus adsorption. Equilibrium and Kinetic studies of the process were also carried out. Results obtained show that, FT-IR spectrum of the activated carbon displays a number of absorption peaks, reflecting the complex bio-mass structure and a variety of functional groups which explains its improved adsorption behaviour on the colloidal particles. SEM shows the spherical shape of the carbon particles with a wide range of sizes, EDX indicated the constituent elements in the adsorbent in which C and O were found to be the most abundant. Equilibrium data fitted well to the Freundlick and Langmuir models but the data were best described by Langmuir Isotherm model at the temperature of 313 K. Pseudo second order best described the kinetics of the adsorption process. Removal efficiency (E%) of 97% was attained within 120 minutes at 50 g/l adsorbent concentration, pH6 and 0.2mm particle size of the adsorbent.

Structural characteristics andoil-removal mechanisms of the adsorbentsmade from petrochemical sludge

A new type of carbon-inorganic absorbent with good oil-removing performance is prepared by sintering and activating petrochemical sludge. Of the absorbents prepared by three different methods (non-activated, vapor /840 ℃/6 h, CO2/1 000 ℃/2 h), the one prepared by the second method is the best in oil-removing, which can remove 60% of oil from petrochemical wastewater with a concentration of 76.42 mg/L. X-ray Diffraction (XRD) analysis shows that the constituents of the adsorbents are basically similar to those of inorganic granulating materials, such as SiO2, Al2O3, orthoclase feldspar, iron ore, etc. Composition analysis reveals that the activated absorbent has a large specific surface area with a high carbon content in activated compositions and a good oil-removing capability.

Adsorption behavior of activated carbon for the elimination of zearalenone during bleaching process of corn oil

Zearalenone is a mycotoxin produced by Fusarium species.It frequently contaminates cereals used for foods or animal feeds,especially deposited in crude corn oil.Certain amounts of zearalenone can be removed during refining processes.In this study,we studied the influence of activated carbon and six industial absorbents(zeolite,diatomite,attapulgite,perlite,montmorillonite and activated clay)on the elimination of zearalenone during bleaching process of corn oil and explored the absorption mechanism of activated carbon.Results showed that activated carbon had an excellent adsorption capacity of zearalenone compared with the other six industrial adsorbents.For activated carbon,a high removal rate of zearalenone(exceeding 83%)from heavily zearalenone-polluted corn oil was achieved and the removal rate of zearalenone was kept above 60%after five regeneration cycles.The research on the adsorption mechanism of activated carbon showed that Freundlich adsorption isotherm model and pseudo-second-order kinetic model could well described the adsorption process.The thermodynamic study demonstrated that adsorption process was spontaneous and exothermic.Fourier transform infrared spectroscopy and Raman spectroscopy further revealed that activated carbon was effectively combined with zearalenone viaπ-πinteraction.Thus,activated carbon is an efficient and suitable adsorbent to control the levels of zearalenone during bleaching process of corn oil.This study not only proposed a systematic research scheme for the mechanism study of activated carbon for the elimination of zearalenone in corn oil,but also provided the scientific basis for developing effective methods to eliminate zearalenone in refined vegetable oils.

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H_2

Activated carbon （AC） supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation （PROX） in excess H2 was evaluated. Ag/AC catalysts, after reduction in H2 at low temperatures （≤200 ℃） following heat treatment in He at 200 ℃ （He200H200）, exhibited the best catalytic properties. Temperature-programmed desorption （TPD）, X-ray diffraction （XRD） and temperature-programmed reduction （TPR） results indicated that silver oxides were produced during heat treatment in He at 200 ℃ which were reduced to metal silver nanoparticles in H2 at low temperatures （≤200 ℃）, simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 ℃. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H200 treatment displayed similar PROX of CO reaction properties to Ag/SiO2. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.

Abnormal IR Spectra of CO Adsorbed on the Surface of Glass Carbon Electrode Modified with Polypyrrole Film with Platinum Microparticles

Abnormal IR spectra of CO adsorbed at the surface of glass carbon electrode modified with polypyrrole film with Pt microparticles are reported.

Innovation of experimental methodology for adsorbed gases on hydrocarbon-source rocks

As compared to the device developed by our predecessors, the newly developed adsorbed gas degasification-collection device has a series of advantages such as wide sample application range, large sample inlet, high vacuum, short-time sample smashing, low crushing temperature and water-free gas collection, which ensure the geochemical characteristics of acquired adsorbed gas samples to be the same as those of the adsorbed gases on corresponding hydrocarbon-source rocks. The results showed that the acquired adsorbed gases are composed mainly of hydrocarbon gas and carbon dioxide gas, with the hydrocarbon gas accounting for more than 80%, and can be measured reliably for their δ13C1-δ13C3 data, even δ13C4-δ13C5 data. The results of carbon isotope test and analysis satisfy the needs for the geochemical study and application of adsorbed gases. The above new techniques of experimental geochemistry are helpful for establishing the new direct natural gas-source correlation method, proving that the previous usual method of indirect natural gas-source correlation is scientific and authentic, thus providing the experimental basis for the study and application of adsorbed gases on hydrocarbon-source rocks.

Tailoring the separation performance of a carbon nanotube-based mixed matrix membrane decorated with metal–organic framework

Synthesis of mixed matrix membranes(MMM)using carbon nanotubes(CNTs)has shown great prospects for achieving excellent selective separation because of its special structure.Nevertheless,the preparation of highly selective MMM faces challenges,which is attributed to the obstacles encountered by CNTs dispersion in polymer matrix and elimination of interface defects.A novel CNT-based composite decorated with metal–organic framework(MOF)was synthesized and applied to the preparation of MMM.MOF was post modified,and then carboxyl groups were inserted on the outer surface of CNTs.The synthetic MMM(Cu-MOF-en@MWCNT)not only has selective adsorption on dyes,but also has selective photodegradation on dyes.The method of using CNTs to wrap the outside of MOF has great potential in dye separation.The performance of MMM was further improved by decorating MOF on the filler to improve the selectivity to the designated dye.

A Simple Method for Preparing CuCl/Activated Carbon for Selective CO Adsorption from Hydrogen

Carbon monoxide(CO)is an impurity gas that can poison the precious metal catalysts of hydrogen fuel cells,so it is necessary to separate CO from hydrogen.In this paper,an isovolumetric impregnation method was developed to prepare Cu(I)-supported activated carbon(AC),which is simple and easy to industrialize.The prepared cuprous chloride CuCl/AC adsorbent displayed a high CO adsorption capacity of 82.1 cm^(3)/g and a high CO/H_(2) separation factor of 20 at 20 bar and 298 K.This material can adsorb and remove CO from CO/H_(2) mixed gas(5μL/L CO-balanced H_(2))to less than 0.2μL/L under dynamic flow conditions,and showed excellent regeneration performance.The results show that CuCl/AC is an effective adsorbent for separating trace CO in high-purity hydrogen.

Porous carbon materials for CO_(2)capture,storage and electrochemical conversion

Continuous accumulation and emission into the atmosphere of anthropogenic carbon dioxide(CO_(2)),a major greenhouse gas,has been recognized as a primary contributor to climate change associated with the global warming and acidification of oceans.This has led to drastic changes in the natural ecosystem,and hence an unhealthy ecological environment for human society.Thus,the effective mitigation of the ever increasing CO_(2)emission has been recognized as the most important global challenge.To achieve zero carbon footprint,novel materials and approaches are required for potentially reducing the CO_(2)release,while our current fossil-fuel-based energy must be replaced by renewable energy free from emissions.In this paper,porous carbons with hierarchical pore structures are promising for CO_(2)adsorption and electrochemical CO_(2)reduction owing to their high specific surface area,excellent catalytic performance,low cost and long-term stability.Since efficient gas-phased(electro)catalysis involves the access of reactants to active sites at the gas-liquid-solid triple phase,the hierarchical porous carbon materials possess multiple advantages for various CO_(2)-related applications with enhanced volumetric and gravimetric activities(e.g.,CO_(2)uptake and current density)for practical operations.Recent studies have demonstrated that porous carbon materials exhibited notable activities as CO_(2)adsorbents and provided facile conducting pathways and mass diffusion channels for efficient electrochemical CO_(2)reduction even under the high current operation conditions.Herein,we summarize recent advances in porous carbon materials for CO_(2)capture,storage,and electrochemical conversion.Prospectives and challenges on the rational design of porous carbon materials for scalable and practical CO_(2)capture and conversion are also discussed.

Adsorption of Anionic and Cationic Dyes from Textile Effluents by Activated Carbon Prepared from Sawdust and Fish Scale

In Bangladesh, there are thousands of textile-dying industries spread across the country’s many regions, the majority of which involve knitting and dying. The dyeing industry uses an enormous quantity of water, as well as colors and chemicals. After the dying process has been completed, they also release a significant amount of wastewater. Cotton, wool, and polyester fiber are typically dyed with textile dyes such as reactive, acid, and disperse dyes. These dyes are utilized most frequently in the respective sectors. The dyes’ colorants are extremely poisonous and dangerous to all forms of life, including aquatic life and living things. The present work has been intended to investigate whether or not it is practicable to remove commonly used textile dyes simultaneously from an aqueous dye solution using an adsorption technique that makes use of a variety of different adsorbents. This study focuses on the removal of color from two distinct types of dyes—Methylene Blue and Reactive Blue-250 which are cationic and anionic in nature respectively, using two different types of activated carbon adsorbents prepared from sawdust and fish scale. Dye removal capacity was tested as a function of contact time, the dosage of the adsorbent, pH during the treatment process, temperature and initial concentration of dye. The applicability of the Langmuir and Freundlich adsorption isotherms in describing experimental data was investigated. The micro and mesoporous activated carbon prepared from sawdust and fish scale identified by Scanning Electron Microscopy (SEM) images indicated that such adsorbents with a large surface area have more dye adsorption potential whereas the variation in dye adsorption occurs due to variation in surface area. From the overall experimental data, maximum removal of 95.39% and 87.92% was found for Methylene Blue and Reactive Blue-250 respectively by sawdust, and 90.64% removal of Methylene Blue by using fish scale.

The decisive role of adsorbed OH^(*)in low‐potential CO electro‐oxidation on single‐atom catalytic sites

CO impurity-induced catalyst deactivation has long been one of the biggest challenges in proton-exchange membrane fuel cells,with the poisoning phenomenon mainly attributed to the overly strong adsorption on the catalytic site.Here,we present a mechanistic study that overturns this understanding by using Rh-based single-atom catalysis centers as model catalysts.We precisely modulated the chelation structure of the Rh catalyst by coordinating Rh with C or N atoms,and probed the reaction mechanism by surface-enhanced Raman spectroscopy.Direct spectroscopic evidence for intermediates indicates that the reactivity of adsorbed OH^(*),rather than the adsorption strength of CO^(*),dictates the CO electrocatalytic oxidation behavior.The RhN_(4)sites,which adsorb the OH^(*)intermediate more weakly than RhC4 sites,showed prominent CO oxidation activity that not only far exceeded the traditional Pt/C but also the RhC4 sites with similar CO adsorption strength.From this study,it is clear that a paradigm shift in future research should be considered to rationally design high-performance CO electro-oxidation reaction catalysts by sufficiently considering the water-related reaction intermediate during catalysis.