Carbon Surface Functional Groups Research Articles

Experimental study on modified fruit shell carbon for methane adsorption and decarbonization

Modification of activated carbon has the potential to improve its adsorption and separation capacity. Different concentrations of ammonia (6%, 9%, 12%, 15%) and treatment times (4 h, 6 h, 8 h, 10 h) were used to modify jujube shell carbon and coconut shell carbon in ultrasonic washing equipment. Biogas adsorption experiments were carried out with modified activated carbon to study the effect of adsorption and decarbonization on activated carbon surface functional groups. After modification, the surface alkaline functional groups of activated carbon increased, the acidic functional groups decreased, and the adsorption performance of CO2 was enhanced. In addition, the specific surface area and total pore volume of activated carbon decreased, the average pore size increased, and the degree of graphitization increased. In the experimental research range, under ultrasonic conditions, jujube shell carbon impregnated with 12% ammonia water for 4 h and coconut shell carbon impregnated with 9% ammonia water for 10 h had the best modification effect. The adsorption capacity for CO2 was 1.83 and 1.745 mmol/g, respectively, which increased by 0.8 mmol/g and 0.599 mmol/g, respectively, compared with the unmodified sample.

Ash‐Free Porous Carbon as the Negative Additive of Lead‐Acid Batteries and Supercapacitors

Herein, a simple method to prepare porous carbon that inhibits hydrogen evolution is used, which has enormous advantages for both capacitors and lead‐acid batteries. The quantitative filter paper spongy porous carbon (SQFPC) is successfully synthesized by the two‐step method. SQFPC displays a porous, spongy structure with a large specific surface area (1847 m2 g−1). In electrochemical tests, SQFPC exhibits high specific capacitance (244 F g−1 at 1 A g−1) and a capacitance retention rate of 72.5% at 40 A g−1. In addition, the capacity of the battery with 0.5 wt% SQFPC is improved by 57.6% at a discharge rate of 0.1C, and the cycle life under the high‐rate partial state of charge is 9.3 times that of the blank battery. The enhanced battery performance is related to the unique structure and surface functional groups of carbon, which speed up ion movement inside the battery and provide active sites for lead deposition.

Plastic litter fate and contaminant transport within the urban environment, photodegradation, fragmentation, and heavy metal uptake from storm runoff

A significant portion of urban litter is plastic which contaminates the environment and threatens ecological safety. The conversion of plastic litter into small fragments called microplastics (MPs) intensifies their critical risks by facilitating their transport and altering their physicochemical features. This study focuses on low density polyethylene (LDPE) and polyethylene terephthalate (PET) as the main components of urban litter. The photodegradation of LDPE and PET MPs due to the accelerated weathering experiments is investigated through surface chemistry and morphology analysis. The influence of MPs’ photodegradation on their fragmentation behavior is evaluated through the innovative accelerated mechanical weathering experiments that simulated the abrasion of MPs with the road deposits. Furthermore, the role of MPs as the vehicles to transport the heavy metals from the urban environment to the water resources is evaluated by studying the kinetics of lead (Pb) uptake by new and weathered MPs in synthetic stormwater. The surface morphology investigation revealed the formation of crazes and the crack networks onto the MPs due to the weathering experiments. The surface chemistry analysis revealed the generation of several oxidized carbon surface functional groups onto the photodegraded MPs and their increased susceptibility to fragmentation due to the abrasion with the road deposits. The photodegradation increased the Pb accumulation onto the LDPE and PET MPs from 467 μg/m2 and 21 μg/m2 to 2290 μg/m2 and 725 μg/m2, after five days of metal exposure. The fundamental knowledge developed in this research provides a better conceptual understanding of the mechanisms controlling MPs persistence and contaminant transport within the urban environment, which is crucial to estimate their negative impacts on the ecosystem.

Research application of K2CO3 activated coal coal and processing by HNO3 from cake shoulder to process Methylene Blue color

Macadamia is a tree that produces dried fruits, with each ton of macadamia seeds producing 70 - 77% of the shell. Annually, the grain processing companies in Vietnam produce thousands of tons of seeds and release tens of thousands of tons of shells. As the demand for macadamia nuts is constantly increasing in the market, more in-depth studies are needed to handle this agricultural residue. Macadamia shell has a higher surface area than other seed pods and their ash content is very low at only 0.22%, the cellulose content in the shell is about 41.2%, this shows that Macadamia shell has the potential to prepare activated carbon when burning at high temperatures. The activated carbon surface can be modified appropriately to change adsorption characteristics, forming different types of surface functional groups (oxygen functional groups, carbon surface functional groups, carbon functional groups, carbon - nitrogen, carbon - halogen) and make coal more suitable for special applications. Results of researching to prepare bio-denatured material from activated carbon K2CO3 by chemical method using HNO3 agent with optimal denaturing conditions such as concentration of 21%, denaturation time of 12 hours, degree MB adsorption reached 193.13 mg/g. The results of methylene blue adsorption adsorption tests at the optimal conditions show that at pH = 9.5 with the appropriate dose of coal is 1g/L in 120 minutes, it can be processed to reach 79.36% efficiency for water. Methylene Blue waste is 70 mg/L.

Unexpected High Rate Capability Enhancement By MnO2 Incorporation in Cellulose-Derived Carbon Nanofiber Electrodes for Electrochemical Capacitors

Electrochemical capacitors (ECs) can provide ultra-long cycle life and ultra-fast energy delivery, which are impossible to reach by most battery technologies. Therefore, ECs are irreplaceable in applications such as energy harvesting systems and grid power buffer [1, 2]. The compositing between carbon and manganese oxides (denoted here as carbon/MnO2) is a popular strategy in the materials research community for getting higher energy densities of EC electrodes [3, 4]. MnO2 is well acknowledged for its high pseudocapacitance due to surface-confined redox processes that take place during charging/discharging, but also known for its poor intrinsic electrical conductivity (0.1 to 1 mS/m) that restricts high power applications [5]. The combination of carbon and MnO2 circumvents the limitation of MnO2 by taking advantage of good rate capability endowed by superior electrical conductivity of carbon. Normally, the fast rate capability (in terms of a retention value of capacitance at high current density relative to that at low current density) of the composite is enhanced compared to pure MnO2, but still remains inferior to pure carbon [6]. However, a greatly enhanced rate capability (78.2%, the ratio of 15 A/g capacitance to 0.5 A/g capacitance) compared to the original carbon (10.2%) was observed after the incorporation of MnO2 into a cellulose-derived nitrogen-doped carbon nanofibers (NCNF) system presented here. In the present study, the composite material (NCNF/MnO2) was prepared via the carbonization of electrospun cellulose and subsequent reaction between carbon nanofibers and permanganate (MnO4 -) in a liquid phase under a hydrothermal condition. The above processes generate a physical blend of the supporting NCNF matrix and MnO2. The unexpected high rate capability enhancement in this system can be explained by a significant change in carbon surface functional groups, specifically, the increased fraction of phenolic groups and the decreased fraction of carboxylic groups. This study presents not only a high performance electrode material for ECs (over 110 F/g specific capacitance, 78.2% rate capability and 96.3% capacitance retention over 50 000 cycles), but also highlights the critical role of carbon surface modification that is induced by the compositing processes, especially in the process deployed in this work, i.e. the electroless deposition of MnO2 on carbon via reaction with MnO4 - in liquid media.

Effect of Time, Temperature and Potential on Pre-Conditioning of Supercapacitors

One unique property of supercapacitors relative to other energy storage devices is their exceptional lifetime, often reported in commercial devices as being over 1 million cycles. This cycle life is most often accompanied with a lifetime relating to a float at maximum voltage for a time of 1000 (or more) hours at a particular temperature, which gives a more practical indication of lifetime in terms of both time to assess and real life application. The end of life for such devices is taken as the point where the capacitance has decreased by 20% and/or the ESR has increased by 100%. In the early stages of use for a supercapacitor, a significant drop in capacitance and an accompanying increase in ESR, along with an increased level of gas generation are observed, the result of which would be a reduced lifetime by the conditions defined above. In order to maximise the lifetime and performance of supercapacitors, this early stage is taken care of through a pre-conditioning or ‘burn in’ stage during manufacture. The causes of the early stage issues mentioned are varied and include decomposition of carbon surface functional groups, solvent splitting (electrochemical decomposition, hydrogen and oxygen evolution reactions including decomposition of trace water) with gas evolution and current collector corrosion[1,2]. The typical burn-in procedure requires the cells to be held at a specific potential and temperature for an extended period of time, during which the capacitance fade, ESR increase and gas generation plateau, allowing the device to then exhibit excellent lifetime characteristics. Whilst the need for this step is clear, it is also costly and can be time consuming, requiring significant Capex and energy costs and also tying up significant inventory during the manufacturing process. Improvements and greater understanding of this process presents clear benefits to the manufacturing process and cost reductions. In this work, the burn-in process has been investigated at various scales, from coin cells through to 100F pouch cells, with differences in the requirements as the cell size increases discussed. Coin cells and small format pouch cells (70x50mm) have been constructed with YP50-F (Kuraray, Japan) activated carbon electrodes and TEABF4 in acetonitrile electrolyte and have been conditioned at 25oC and floating at 2.7V for 72 hours to ensure a lifetime of over 1000 hours. The temperature and potential of the burn-in has then been varied to shorten the process time and also reduce the total electrical energy required to achieve the same lifetime of device in terms of capacitance and ESR. Furthermore, the effect of water content of the electrolyte on the performance and burn-in process has been investigated. [1] S. Phadke, S. Amara and M. Anouti, Chem Phys Chem., 18, 2364, 2017 [2] M. He, K. Fic, E. Frackowaik, P. Novak and E. J. Berg, Energy Environ. Sci., 9, 623, 2016

Kinetic study of methyl orange adsorption on activated carbon derived from pine (Pinus strobus) sawdust

Pine (Pinus strobus) sawdust (PSD), a sawmill waste, was used as a precursor for the preparation of activated carbon through a chemical activation technique with phosphoric acid at 600 °C (100 min). Phosphoric acid pine sawdust activated carbon (PSDP) was characterized and used for the adsorption of methyl orange (MO). The textural examination was applied to determine the total pore volume and specific surface area of PSDP. Carbon surface functional groups were identified utilizing Fourier transform infrared spectroscopy. The effects of pH, contact time, and adsorbent mass on the sorption were investigated in a batch procedure mode. Kinetic information was studied that followed the pseudo-second-order model. The results showed that PSDP could be used as a low-cost adsorbent for MO adsorption from waste effluents.

A self-powered flexibly-arranged gas monitoring system with evaporating rainwater as fuel for building atmosphere big data

The atmosphere big data technique can provide data support for scientific decision-making for industry and people's life. Here, a novel self-powered flexibly-arranged gas monitoring system has been presented basing on a new water-evaporation/gas-sensing coupling effect. The rainwater evaporation along the device can convert natural energy into electricity for powering the whole system. And the outputting voltage/current is significantly dependent on the environmental atmosphere, acting as the gas sensing signal. The surface functional groups of carbon can bind to gas molecules, which changes the zeta potential of carbon and thus affects the electric output. The self-powered gas monitoring systems can be flexibly fixed out of doors, actively detect the air quality of different locations, and wirelessly transmit the sensing information to external platforms for building big data. The present results can open a new possible research direction for self-powered gas sensor and will further promote the development of environmental big data.

Characterization of Carbon Derived from Water Hyacinth as a Renewable Energy Sources

An alternative renewable energy sources, such as biomass, can be produced using the combustion process inside the furnace. In this work, carbon derived from water hyacinth be produced through carbonization process. The carbonization of water hyacinth was carried out at different temperature i.e. 400°C, 500°C and 600°C and subsequently analyzed with the SEM-EDX to determine the microstructure and atomic percentage of present elements. While the FTIR analysis was conducted to qualitatively verify the surface functional groups of carbon. The results of SEM-EDX analysis showed that the pores began to form at a carbonization temperature of 600°C and carbon content increased with increased temperature of carbonization process. FTIR analysis results showed that the functional groups in the carbon derived from water hyacinth had an absorption pattern with OH, C-H, C-O, and C=C bonds.

In-Situ Quantification of Gas Evolution in Pouch Cell Supercapacitors and Its Effect on Device Performance and Operation

Valuable insight into the degradation mechanisms, lifetimes and state of health of supercapacitor devices can be obtained through the understanding and quantification of gas evolution during use. In typical commercial cylindrical devices, the hard casing can withstand the pressure build up resulting from the evolution of gases to pressures as high as 8-12 bar, but with detrimental effects on ESR and capacitance observed through the lifetime of device. In typical pouch cells, a small increase in pressure can result in the ballooning of cells and significant loss of performance. This is managed in some cases by the inclusion of pressure release valves and the like. Although supercapacitors typically produce gas throughout their lifetime, the rate of gas production varies significantly depending on the point in their lifetime and the potentials and charge/discharge rates that they experience. In order to maximise the lifetime and performance of supercapacitor devices, a “burn-in“ period is usually applied, during which time the evolution of gases is likely to be at its highest. After such a burn-in for pouch cells, this gas can be removed with ease before performing a final seal on cells, as is common with battery devices, and can have a significant positive effect on the cell lifetime. The evolution (and consumption) of gas in supercapacitors can be attributed to various processes including decomposition of carbon-surface functional groups, solvent splitting (hydrogen and oxygen evolution reactions, including decomposition of trace water) and chemical/electrochemical gas consumption[1,2]. In this work, the rate and amount of gas evolved in pouch cell supercapacitors and its effect on device performance has been studied through the use of calibrated mass load cells. Small format pouch cells (70x50mm) constructed in-house, consisting of YP50-F (Kuraray, Japan) activated carbon electrodes and TEABF4 in acetonitrile electrolyte have been suspended from calibrated load cells into oil and have been subjected to various charge–discharge conditions and floating at different potentials over different temperatures. The buoyancy of the cells as derived from the load cell has been used to calculate the gas evolved at various potentials / conditions. Through observation of the rate and quantity of gas evolved, insight into the optimal burn-in conditions (float potential, time and temperature) for new cells and impact on performance in operation have been observed. Furthermore, the effect of contaminant water concentration in electrolyte on gas production has been investigated at various points in the cell lifetime. [1] S. Phadke, S. Amara and M. Anouti, Chem Phys Chem., 18, 2364, 2017 [2] M. He, K. Fic. E. Frackowiak, P. Novak and E. J. Berg, Energy Environ. Sci., 9, 623, 2016

Preparation of Activated Carbons from Walnut Shell by Fast Activation with H3PO4: Influence of Fluidization of Particles

AbstractActivated carbons were produced from walnut shell by fast activation with H3PO4in a spouted bed, and the influence of particles fluidization had been investigated. Experimental results showed that walnut shell particles with higher H3PO4impregnation ratios would be agglomerated in spouted bed, and difficult to fluidize. Therefore, an amount of quartz sands were added to assist fluidization of H3PO4impregnated walnut shell particles. The BET surface area of activated carbon prepared under fluidization would be obviously increased with H3PO4impregnation ratio, reaching 1549.6 m2/g for the mass ratio of H3PO4to walnut shell particles of 2 and activation temperature of 700°C. Meanwhile, both of the micro- and meso- pore volumes were increased. In addition, fluidization of particles had very little influence on activated carbon surface functional groups forming. It was found that the activated carbons contained more carbonyl groups (C = O), carboxyl groups (COOH) and some P-containing functional group.

Cadmium ion adsorption by amine-modified activated carbon.

Cadmium (Cd) is one of the most toxic metals found in water and sediments. In the effort to develop an effective adsorbent for aqueous Cd removal, activated carbon (AC) was modified with an amino-terminated organosilicon (3-aminopropyltrimethoxysilane, APS). Response surface methodology was used to optimize selected operational parameters of adsorption of aqueous Cd by considering a central composite design with three input variables, temperature of the mixture solution, the contact time and feed ratio (APS/AC), on the surface modification. Results demonstrated that the strong Cd-binding amine ligands were effectively introduced onto the AC surfaces through the silanol reaction between carbon surface functional groups (-COOH, -COH) and APS molecules. The optimized preparation condition is 77 °C, 4 h and 2.1 ratio. The adsorbent presented a favorable adsorption of the aqueous Cd(II).

High surface area microporous carbons as photoreactors for the catalytic photodegradation of methylene blue under UV–vis irradiation

High surface area (ca. 1700–3400m2g−1) activated carbons (ACs) were prepared from Chinese anthracite by chemical activation with KOH using KOH/Anthracite weight ratios (WKOH/WAnthracite) ranging from 1.6 to 5. The photocatalytic degradation of methylene blue (MB) at high concentration conditions up to 25ppm under UV–vis irradiation was performed on AC and on TiO2-AC mixtures prepared by slurry methodology. The highest values of both BET surface area and of micropore volume to total pore volume ratio were found with a WKOH/WAnthracite ratio of 4. It was found that ACs developed photocatalytic activity and an important synergistic effect with TiO2. TiO2-AC mixtures showed enhancements in the photocatalytic activity up to 6 times higher than commercial TiO2. The photocatalytic activity of ACs and binary materials was discussed with respect to textural properties and surface functional groups of carbons. The ratio of micropore volume to total pore volume and the surface pH of the ACs play important roles upon the photocatalytic activity of TiO2-AC, and the combination of adsorption followed by photodegradation clearly contributed to the treatment of highly concentrated methylene blue. It was concluded that photochemical reactive microporous ACs have a beneficial influence upon the photocatalytic activity of TiO2.

Effect of activated carbon surface functional groups on nano-lead electrodeposition and hydrogen evolution and its applications in lead-carbon batteries

The effect of activated carbon (AC) surface functional groups on the cycle performance of lead-carbon batteries was studied from hydrogen evolution and nano-lead electrodeposition on the surface of the AC. AC materials were modified by oxidation methods (hot air or acid treatment) to increase acidic groups and reduction processes (alkaline treatment or heat treatment in N2) to increase alkaline groups. The surface functional groups were characterized by X-ray photoelectron spectroscopy and Boehm titration method. We used cyclic voltammetry and a three-electrode system to prepare nano-lead deposits on the surface of the AC, and studied its influence on hydrogen evolution of AC. The results show that acidic groups are beneficial to lead electrodeposition. In addition, the lead deposits with high activity covering the surface of AC could inhibit hydrogen evolution and the irreversible sulfation in lead-carbon batteries, and then result in longer cycle life under High-rate Partial-state-of-Charge conditions.

Biochar of corn stover: Microwave-assisted pyrolysis condition induced changes in surface functional groups and characteristics

Biochar was prepared by microwave-assisted pyrolysis of corn stover at atmospheric pressure and different reaction temperatures and time. A central composite experimental design was used in the optimization of volatiles (bio-oil and syngas), biochar production, and the amount of carbon surface functional groups. Various types of oxygenated functional groups on the biochar were quantified by means of titrimetric techniques using a modified Boehm's method. The range of surface carbonyl groups amount was from 0.27 to 1.70mmol/g carbon. The produced biochars were also characterized in terms of the elemental composition, BET surface area and chemical structure. The maximum surface area of the biochar was 45m2/g. The result indicates that the surface functional groups of biochar were significantly influenced by the pyrolysis temperature and residence time. An adequate prediction model was developed to describe the development of carbon surface functional groups. Modification and characterization of biochar surface functional groups is a new way to improve or extend their catalytic application in biomass conversion and bio-oil upgrading.

INFLUENCE OF PHYSICAL-CHEMICAL PROPERTIES OF ACTIVE CARBONS ON GALLIC ACID ADSORPTION

The adsorption of gallic acid on active carbons of different ranks with different pore structure and chemical state of the surface is investigated. The regularities and features of the adsorption process are established. It is revealed that the adsorption isotherm of gallic acid from the aqueous solution with activated carbon of AG-OB-1 rank refers to the L-type isotherms by Giles's classification, and AC adsorption isotherm of ABG and Purolat-Standard ranks - to the S-type isotherms. L-type isotherm gives evidence concerning the flow of physical adsorption. With S-type isotherm is the adsorption described, at which the strength of the interaction between the solute and the adsorbent is less than the force of interaction between the adsorbed molecules, which can be explained by the formation of hydrogen bonds. It was found that the maximum adsorption of gallic acid with carbon sorbents changes in the following sequence - Purolat-standard > ABG > AG-OV-1. The mechanism of adsorption of gallic acid on active carbons is offered. Proceeding from the structure, the chemical state and the main adsorption parameters of active carbon, we can assume that the adsorption of gallic acid has physical nature. It can take place in pores, both due to dispersion interaction (of van der Waals forces) and due to the interaction between the active carbon surface functional groups, containing oxygen with carboxyl and hydroxyl groups of gallic acid. The values of adsorptive capacity testify to the dependence of the adsorption efficiency on the structure and physical-chemical properties of the sorbent. It has been determined that by the absorption of gallic acid specific interaction makes greater contribution. It is shown that the results obtained can be applied to create adsorption technologies on removing gallic acid from the sewage containing individual components and from the mixture with other polyphenols, including beer wort.

Effect of carbon surface functional groups on the synthesis of Ru/C catalysts for supercritical water gasification

A carbon support was treated with HNO3 to create surface functional groups (e.g. –COOH, –OH), which were then characterized by TGA, TPD, CNS elemental analysis, and Boehm titration.

KOH Activation of Thermally Modified Carbon as a Support of Ru Catalysts for Ammonia Synthesis

AbstractCarbon supports with a low ratio of micropore volume to total pore volume can be prepared by KOH activation of thermally modified carbon. KOH treatment of carbons in nitrogen led to the creation of basic sites as well as acidic surface groups, whereas KOH treatment in air resulted in more acidic groups. Steam treatment quickly increased the surface area and pore volume, but did not create surface‐reactive groups. The increase in surface areas, micropores, and surface functional groups of carbon supports led to a decrease of the particle sizes, which not only improved the ability of hydrogen to migrate from Ru metal to the remote promoter precursors, but also increased the amount of adsorbed hydrogen and nitrogen. The properties of carbon combined with the size of the Ru particles affected the ammonia‐synthesis activity.

Two stage thermal regeneration of exhausted activated carbons. Steam gasification of effluents

This work studies the thermal regeneration of p-nitrophenol exhausted activated carbons by a novel method in which two reactors are connected in series in order to minimize the emission of the hazardous adsorbate and other heavy hydrocarbon molecules to the environment. For this task, previous one-stage runs were made, in which the ACs were thermally treated, studying the influence of heating rate and temperature on: (a) the final porosity properties of regenerated ACs, as well as the regeneration efficiency, and (b) the gas profiles (H2, CO and CO2) evolved during the process. It was found that these compounds were mainly released at high temperatures (above 450°C), corresponding to the removal of the carbon surface functional groups and/or cracking of chemisorbed products.The use of a second reactor gave rise to a significant modification in the gas patterns, in comparison with one step experiments. H2, CO and CO2 where identified at higher quantities and their emission started at lower temperatures. These results allowed to conclude that the use of this additional gas treatment promotes the steam cracking of the physisorbed p-nitrophenol molecule, which is removed during the first stages of the regeneration process.

Iron and Nitrogen containing Carbon Catalysts with Enhanced Activity for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

Iron and nitrogen containing carbon catalysts were prepared by the pyrolysis of iron (III) tetramethoxyphenylporphyrin complex adsorbed on as-received as well as nitric acid treated carbon black and employed them as oxygen reduction electrodes for hydrogen-oxygen PEM fuel cells. The influence of carbon surface functional groups on the dispersion of active species and electrocatalytic performance is investigated using electron microscopic and electrochemical techniques. The existence of quinone functional groups on the nitric acid treated carbon was evident from X-ray photoelectron spectroscopy and cyclic voltammetry. Rotating disk electrode voltammetry results affirmed the good electrocatalytic activity and stability of pyrolyzed macrocyclic complex adsorbed on nitric acid treated carbon compared to that of as-received carbon. This is ascribed to the greater number of Fe/N active species as well as good dispersion of metal clusters over nitric acid treated carbon support. Fuel cell tests depicted the comparable performance of pyrolyzed complex adsorbed on nitric acid treated carbon with commercial Pt/C at 353 K. Durability measurements performed under fuel cell operating conditions for 120 h indicate the good stability of the catalysts.