Adsorption of volatile organic compounds by mesoporous graphitized carbon: Enhanced organophilicity, humidity resistance, and mass transfer

Promoted wet peroxide oxidation of chlorinated volatile organic compounds catalyzed by FeOCl supported on macro-microporous biomass-derived activated carbon

Chlorinated volatile organic compounds (CVOCs) are a recalcitrant class of air pollutants, and the strongly oxidizing reactive oxygen species (ROS) generated in advanced oxidation processes (AOPs) are promising to degrade them. In this study, a FeOCl-loaded biomass-derived activated carbon (BAC) has been used as an adsorbent for accumulating CVOCs and catalyst for activating H₂O₂ to construct a wet scrubber for the removal of airborne CVOCs. In addition to well-developed micropores, the BAC has macropores mimicking those of biostructures, which allows CVOCs to diffuse easily to its adsorption sites and catalytic sites. Probe experiments have revealed HO^• to be the dominant ROS in the FeOCl/BAC + H₂O₂ system. The wet scrubber performs well at pH 3 and H₂O₂ concentrations as low as a few mM. It is capable of removing over 90% of dichloroethane, trichloroethylene, dichloromethane and chlorobenzene from air. By applying pulsed dosing or continuous dosing to replenish H₂O₂ to maintain its appropriate concentration, the system achieves good long-term efficiency. A dichloroethane degradation pathway is proposed based on the analysis of intermediates. This work may provide inspiration for the design of catalyst exploiting the inherent structure of biomass for catalytic wet oxidation of CVOCs or other contaminants.

Anthracite based activated carbon impregnated with HMTA as an effectiveness adsorbent could significantly uptake gasoline vapors

In this study, we synthesized and employed the amine impregnated activated carbon as an efficacious adsorbent for uptaking gasoline vapor. For this regard, anthracite as activated carbon source and hexamethylenetetramine (HMTA) as amine were selected and utilized. Physiochemical characterization of made sorbents were evaluated and investigated using SEM, FESEM, BET, FTIR, XRD, zeta potential, and elemental analysis. The synthesized sorbents provided an excellent textural features as compared with the literature and other activated carbon based sorbents and impregnated with amine. Our findings also suggested that in addition to high surface area (up to 2150 m² / g), the micro- meso pores created (Vmeso / V micro = 0.79 Cm ³ / g) surface chemistry may significantly affect the gasoline sorption capacity, which here the role of mesoporous is further highlighted. V meso for amine impregnated sample and free activated carbon was 0.89 and 0.31 Cm ³ / g, respectively. According to the results, the prepared sorbents have a potential capability in uptaking gasoline vapor and with line this, we report a high sorption capacity of 572.56 mg / g. After, four cycles used the sorbent had a high durability and about 99.11% of the initial uptake was maintained. Taking together the synthesized adsorbents as an activated carbon provided an excellent and unique features and enhanced gasoline uptake, therefore its applicability in uptaking gasoline vapor can be substantially considered.

Adsorption and membrane separation for removal and recovery of volatile organic compounds

Volatile organic compounds (VOCs) are a crucial kind of pollutants in the environment due to their obvious features of severe toxicity, high volatility, and poor degradability. It is particularly urgent to control the emission of VOCs due to the persistent increase of concentration and the stringent regulations. In China, clear directions and requirements for reduction of VOCs have been given in the "national plan on environmental improvement for the 13th Five-Year Plan period". Therefore, the development of efficient technologies for removal and recovery of VOCs is of great significance. Recovery technologies are favored by researchers due to their advantages in both recycling VOCs and reducing carbon emissions. Among them, adsorption and membrane separation processes have been extensively studied due to their remarkable industrial prospects. This overview was to provide an up-to-date progress of adsorption and membrane separation for removal and recovery of VOCs. Firstly, adsorption and membrane separation were found to be the research hotspots through bibliometric analysis. Then, a comprehensive understanding of their mechanisms, factors, and current application statuses was discussed. Finally, the challenges and perspectives in this emerging field were briefly highlighted.

Evaluation of HKUST-1 as Volatile Organic Compound Adsorbents for Respiratory Filters

Cyclohexane is a representative of volatile organic compounds (VOCs). VOCs can cause serious health problems in case of continuous exposure; therefore, it is essential to develop efficient personal protective equipment. Historically, activated carbons are used as VOC adsorbents. However, the emergence of promising novel adsorbents, such as metal-organic frameworks, has pushed the research to study their behavior under the same conditions. In this work, the use of the well-known HKUST-1 MOF of different particle sizes (20 μm, 300-600 μm, and 1-1.18 mm) for the adsorption of low-grade (5000 ppm) cyclohexane combined with different water concentrations (dry, 27 and 80% RH) in a fixed bed is proposed. The results were compared under the same conditions for a typically used activated carbon, PICACTIF TA 60. HKUST-1 has higher affinity to cyclohexane than PICACTIF for the whole pressure range studied, especially at low partial pressures. It begins to adsorb much earlier (0.0025 kPa) than the activated carbon (0.01 kPa). However, a different adsorption behavior is evidenced for both materials in the presence of water vapor since HKUST-1 is very hydrophilic in the zone near to the copper open metal sites, whereas PICACTIF is hydrophobic. After three consecutive cycles, good stability results were obtained for the MOF, comparable to activated carbon, even in the presence of water. As the main finding, although the unstability of HKUST-1 is well established under high humid conditions, the kinetic of degradation has not been established so far. Here, it is shown that the time usage of HKUST-1 as the adsorbent for respiratory mask (single pass) is not affected by the degradation of the structure, which may occur on a longer time scale. Finally, shaping by tableting provides good results since it is possible to increase the MOF density by around 69% with minor loss of adsorption capacity. The best fraction is 300-600 μm, reaching cyclohexane breakthrough times around 85 min/cm³ at 80% RH, comparable with PICACTIF-activated carbon and promising for practical applications.

Adsorption-enforced Fenton-like process using activated carbon-supported iron oxychloride catalyst for wet scrubbing of airborne dichloroethane

Wet scrubbing is a low-cost process for disposing of air pollutants. Nevertheless, this method is rarely used for the treatment of volatile organic compounds (VOCs) because of their poor water solubility. In this study, we used a unique wet scrubbing system containing H₂O₂ and activated carbon (AC)-supported iron oxychloride (FeOCl) nanoparticles to remove airborne dichloroethane (DCE). The operating conditions of the wet scrubber were optimized, and the mechanism was explored. The results showed that the adsorption of dissolved DCE onto AC promoted its transfer from air to water, while the accumulation of DCE on AC facilitated its oxidation by •OH generated on FeOCl catalyst. The wet scrubber performed well at pH 3 and low H₂O₂ concentrations. By pulsed or continuous dosing H₂O₂, the cooperative adsorption-catalytic oxidation allowed long-term DCE removal from air. Benefiting from satisfactory cost-effectiveness, avoidance of toxic byproduct formation, and less corrosion and catalyst poisoning, wet scrubbers coupled with cooperative adsorption and heterogeneous advanced oxidation processes could have broad application potentials in VOC control.

Effects of Nitrobenzene's mass transfer at water-air interface

As a volatile organic compound, nitrobenzene has high vapor pressure and low boiling point, and it is very volatile when it enters the water body and enters the air. The mass transfer of VOCs at the water-air interface is a complex process of transboundary transport. In this paper, the effects of water temperature, interface turbulence, surfactant concentration, and humic acid concentration on the volatilization of nitrobenzene at the water-air interface were investigated. Under the influence of temperature, the volatilization of nitrobenzene accorded with the first-order kinetic equation. When the temperature increased from 5 ℃ to 25 ℃, the volatilization rate of nitrobenzene increased by 2.03 times. Temperature for volatilization rate constant was in accordance with the Arrhenius equation. The water-gas distribution of volatile organic compounds was in accordance with the Boltzman equation. Under the same temperature conditions, when the agitating intensity increased from 0 r/min to 250 r/min, the volatilization rate constant of nitrobenzene increased by 1.51 times. When the surfactant is greater than the critical micelle concentration, the volatilization rate constant of nitrobenzene decreases with the increase of surfactant. When the concentration of humic acid increased from 100 mg/L to 500 mg/L, the half-life increased by 1.14 h, and the volatilization rate decreased by 1.14 h, reduced by 17%. The results showed that the increase of temperature and the intensification of stirring had a significant promoting effect on the volatilization of nitrobenzene, while the surfactant and humic acid both played an inhibitory effect on the volatilization of nitrobenzene.

Oxide of porous graphitized carbon as recoverable functional adsorbent that removes toxic metals from water

The numerous oxygenated functional groups on graphite oxide (GO) make it a promising adsorbent for toxic heavy metals in water. However, the GO prepared from natural graphite is water-soluble after exfoliation, making its recovery for reuse extremely difficult. In this study, porous graphitized carbon (PGC) was oxidized to fabricate a GO-like material, PGCO. The PGCO showed an O/C molar ratio of 0.63, and 8.4% of the surface carbon species were carboxyl, exhibiting enhanced oxidation degree compared to GO. The small PGCO sheets were intensely aggregated chemically, yielding an insoluble solid easily separable from water by sedimentation or filtration. Batch adsorption experiments demonstrated that the PGCO afforded significantly higher removal efficiencies for heavy metals than GO, owing to the former's greater functionalization with oxygenated groups. An isotherm study suggested that the adsorption obeyed the Langmuir model, and the derived maximum adsorption capacities for Cr³⁺, Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ni²⁺ were 119.6, 377.1, 99.1, 65.2, 53.0, and 58.1 mg/g, respectively. Furthermore, the spent PGCO was successively regenerated by acid treatment. The results of the study indicate that PGCO could be an alternative adsorbent for remediating toxic metal-contaminated waters.