Search

To effectively investigate the influence of activated carbon on the adsorption of volatile organic compounds (VOCs), physical and chemical factors of activated carbon including pore wall thickness, pore size, and functional groups were studied using grand canonical Monte Carlo (GCMC) simulation. In addition, benzene and acetone were taken as two representative components of VOCs. Simulation results was presented by the changes in characteristics of benzene and acetone. The results show that at the saturated vapor pressure (P0), the adsorption density hardly varies with the mentioned factors of activated carbon. Differently, the saturated adsorption capacity increases considerably with the rise of pore size or the reduction of pore wall thickness, and the rise of pore size also leads to a dramatic increase in adsorption layer and a subsequent fall in ordering. However, when the pressure is less than 0.001P0, the monomolecular interaction energy and the isosteric heat are strengthened greatly with the addition of carboxyl and amino groups, while the threshold pressure shows an opposite change to the monomolecular interaction energy. In the meantime, the decrease of pore size or the increase of pore wall thickness will result in the same results. Findings in this paper can provide valuable insights into the microscopic mechanisms of the adsorption between activated carbon and VOCs.

Four different kinds of metal–organic framework (MOF) materials Zn-BTC, Cu-BTC, Cr-BTC, and Fe-BTC are incorporated into alginate, forming various hydrogels for n-hexane vapor adsorption. The cross...

Organosiliceous nanotubes (OSNs) have been successfully prepared by a reverse micelle, then coated with mixed silica sources of tetraethylorthosilicate (TEOS) and 1,2-bis(triethoxysilyl)ethane, (BTSE). The OSNs were analyzed with different apparatuses and used for volatile organic compounds (VOCs) removal. The static pentane, hexane, benzene, toluene, 92# gasoline and water adsorption behaviors on OSNs and marketable activated carbon (AC) and silica gel (SG) were explored. Experimental results showed that the OSN-35% sample (mass ratio BTSE to (BTSE + TEOS) of 35% in feeding process) was uniform nanotubes with the biggest aspect ratio and pore volume had the best static VOCs adsorption capacity (1.35 g g− 1, pentane, 1.63 g g− 1, hexane, 1.68 g g− 1, benzene, 1.83 g g− 1, toluene and 0.973 g g− 1, oil vapor, respectively) and 0.247 g g− 1, water (the smallest). The dynamic monocomponent n-hexane and toluene adsorption performance on OSN-35% was evaluated via breakthrough curves, and the experimental results showed that OSN-35% had longer breakthrough times (tbs) and higher adsorption capacities compared with commercial adsorbents, and OSN-35% is water resistant under wet condition. For binary component (n-hexane and toluene) adsorption, the OSN-35% preferred to adsorb toluene. The larger VOCs capacity of OSNs was co-influenced by the introduction of organic groups, aspect ratio and pore volume. The OSNs with enhanced hydrophobicity and VOCs adsorption behaviors and excellent stability are potential for VOCs adsorption application.

The conventional Na-mordenite (Na-MOR) zeolite membranes prepared on α-Al2O3 tubes by secondary hydrothermal growth method. To improve membrane performances in dehydration of acetic acid by pervaporation, the Na+ as counter ions in MOR membranes were exchanged by a series of mono- and di-valent cations to adjusted the channel structure and water affinity. Langmuir surface areas for monovalent ion-exchanged MOR zeolites were consistent with the reverse order of ion radii as H+>Li+>Na+>K+>Cs+, while for those exchanged by divalent ions the zeolites surface areas followed the reverse order of hydrated ion radii instead of natural radii as Ba2+>Ca2+>Mg2+. The water adsorption of MOR by mono- and di-valent cations exchange were all disordered, and H+, K+ and Ca2+ exchanged MOR showed higher water capacity than that of Na-MOR. In pervaporation, monovalent ion-exchanged membranes with molecular sieving effect showed higher performances than those of divalent ion-exchanged membranes with augmented steric effect and weakened molecular sieving. Among these membranes, H-MOR showed the largest flux of 3.68 kg m−2 h−1 with a normal separation factor of 472 in pervaporation of 90 wt% acetic acid/water under 348 K due to a larger pore size and higher water adsorption, which were supplemented for acid-treated membranes. To get better separation ability, H+ exchange conditions on MOR membranes were investigated in detail. The optimized H-MOR membrane showed a flux of 1.52 kg m−2·h−1and separation factor of 1443 with good stability for 100 h. A simple water wash with a recovered performance proved a previously reported phenomenon that reduced flux with time was affected by acetic acid blockage.

Carbon-silica composites with nanoporous structures were synthesized for the adsorption of volatile organic compounds (VOCs), taking tetraethyl orthosilicate (TEOS) as the silicon source and activated carbon powder as the carbon source. The preparation conditions were as follows: the pH of the reaction system was 5.5, the hydrophobic modification time was 50 h, and the dosage of activated carbon was 2 wt%. Infrared spectrum analysis showed that the activated carbon was dispersed in the pores of aerogel to form the carbon-silica composites material. The static adsorption experiments, dynamic adsorption-desorption experiments, and regeneration experiments show that the prepared carbon-silica composites have microporous and mesoporous structures, the adsorption capacity for n-hexane is better than that of conventional hydrophobic silica gel, and the desorption performance is better than that of activated carbon. It still has a high retention rate of adsorption capacity after multiple adsorption-desorption cycles. The prepared carbon-silica composites material has good industrial application prospects in oil vapor recovery, providing a new alternative for solving organic waste gas pollution.

To overcome the shortage of conventional synthetic methods, such as long reaction time at high temperature and pressure (HTP) or poor performance at room temperature and pressure (RTP), a facile and economical strategy was employed to prepare high-performance ZIF-90 for the first time at RTP only by adding triethylamine (TEA). Herein, we successfully prepared ZIF-90 nanocrystals by a two-step stirring method within several minutes (5–30 min) and their structure parameters (e.g., BET surface areas, 916–1235 m2·g−1) were also tuned simultaneously, which were much better than reported samples prepared at RTP. Afterwards, by changing functional ligands, hydrophobic ZIF-90-CF3 with low surface energy was also designed. With the ligand side of aldehyde (–CHO) and trifluoromethyl (-CF3) groups on ZIF-90 and ZIF-90-CF3, the water vapor uptakes and adsorption heats decreased from 7.9 to 0.79 mmol·g−1 and 20.6 to 2.6 kJ·mmol−1, respectively. Additionally, a shaped ZIF-90-CF3/melamine foam (MF) composite with both hydrophobic and oleophilic properties exhibited extraordinary organic compounds (OCs)-water separation ability, including a high adsorption capacity (40.1–108.7 g‧g−1) towards various OCs. Furthermore, owing to its excellent compressibility and mechanical stability, the ZIF-90-CF3/MF composite can be regenerated by slightly squeezing the adsorbed OCs, indicating the potential for possible commercialisation of the derived MOF/MF composites for the efficient purification of wastewater.

Welan gum (WLG) has been reported being used in chemical flooding and hydraulic fracturing for high-temperature and high-salinity reservoir development due to its good temperature resistance and salt tolerance properties. The adsorption and retention of WLG in reservoir rocks will reduce the reservoir permeability and affect the economic development of oil and gas fields. However, there are no reports about the adsorption of WLG on quartz sand. Therefore, in this study, standard curve of absorbance-WLG concentration was established by anthrone colorimetry method. The adsorption behavior accorded with the Langmuir adsorption isotherm. The adsorption capacity was 4.01 mg/g. By means of Fourier transform infrared spectrum analysis, X-ray diffraction technology, thermogravimetric analysis, scanning electron microscope, optical microscope, and contact angle measurement, it is confirmed that the adsorption was physical adsorption and surface adsorption, and did not have obvious influence on crystal spacing and wettability of quartz sand. Based on this, the study of the influence of reservoir conditions showed that: the adsorption capacity decreased with the increase of temperature; pH value had little effect; the adsorption capacity first increased and then decreased with the increase of inorganic salt content, and this trend varied with the types of inorganic salts.

An ordinary silica gel (SG-1) was chosen as the raw material and hydrophobically modified with trimethylchlorosilane under different microwave exposure. The orthogonal experiment was designed to screen the optimized modification method. The hydrophobic properties modified silica gel (SG-2) was analyzed by comparing the difference changes of surface chemistries. Then, the adsorption capacities of SG-1 and SG-2 to the n-hexane vapor and water vapor, respectively, were investigated and compared with the capacities of activated carbon and SG-3 (hydrophobically modified using the same composite modifier without microwave exposure). Meanwhile, there cyclable adsorptions of SG-2 to the two vapors were conducted while the desorptions of vacuum and heat was observed. The results showed that the effect of hydrophobic modification to SG-1 under microwave exposure was obvious and SG-2 also had a very good effect of adsorption for the n-hexane vapor. The modified silica gel shows great potential and effect for the recovery of volatile organic compounds with high content of water.

The Cu-BTC, a widely studied metal-organic framework (MOF), has been applied in various fields such as gas adsorption, separation, storage, and catalysis. However, the Cu-BTC collapses due to the replacement of the organic linker by water molecules under humid conditions, which limits its practical application in industries. In consideration of the undesirable water effect on the framework stability of Cu-BTC, a stable activated carbon (AC) was incorporated into it by the in situ method to yield a composite material AC/Cu-BTC with high water stability. XRD and SEM patterns proved that the AC7%/Cu-BTC successfully retains its crystal structure after being exposed to water molecules. The adsorption amount of n-hexane vapor of the AC7%/Cu-BTC after water vapor adsorption-thermal desorption is 307% of that of the Cu-BTC. The addition of the AC changes the adsorption active sites and reduces the strong affinity of the Cu-BTC to water molecules, resulting in the AC7%/Cu-BTC having a much lower adsorption rate for water vapor than the Cu-BTC. Therefore, the AC7%/Cu-BTC can be protected from a large amount of water molecules and avoid structural collapse caused by the disconnection between the copper center and the organic linker. The composite displays a potential value for stable applications of MOF-based materials under ambient conditions.

Highly ordered hexagonal meso-structured, vesicles, and mesoporous ordered siliceous foams have been elaborately synthesized in weak HCl solution under static conditions without any organic additives by finely tuning reaction pH (3.0–5.0) and/or the amount of adding sodium sulfate (Na2SO4). Lower pH value is favorable for hexagonal structure and higher pH value and Na2SO4 concentration is beneficial for vesicles and foams. Siliceous materials with different morphologies (rod, vesicle and foam), structures (hexagonal, vesicle and foam) and pore sizes were used for volatile organic compounds (VOCs) removal. The adsorption and desorption performance of hexagonal mesostructure (S1), vesicles (S5) and macroporous ordered siliceous (S7) samples were investigated under static (water vapor, n-hexane and 93# gasoline) and dynamic (n-hexane) conditions. Compared with S1, S5, commercial silica gel (SG) and activated carbon (AC), S7 shows higher static adsorption capacity of n-hexane and 93# gasoline, more stable breakthrough time and larger n-hexane adsorption capacity under dynamic adsorption conditions. The designed siliceous materials with high VOCs removal capacity and recyclability show great potential for VOCs controlling.

Hydrophobic functionalized SBA-15 has been developed via postsynthesis modification with trimethylchlorosilane (TMCS) and used for volatile organic compounds (VOCs) removal. The adsorption and desorption performance of different SBA-15-TMCS under static and dynamic conditions were investigated. Experimental results indicated that all samples showed a highly ordered two dimensional hexagonal mesostructure, and the organic groups were chemically incorporated into the pore surface of SBA-15 substrate. Comparing with commercial silica gel and activated carbon, SBA-15-TMCS shows higher static adsorption capacities of n-hexane and 93# gasoline, good recyclability, lower water vapor adsorption capacity, higher dynamic adsorption capacity, and longer breakthrough time. The high adsorption efficiency and stability of SBA-15-TMCS are associated with their hydrophobic surface, uniform and large pore size, high surface area and pore volume. The designed SBA-15-TMCS with high VOC adsorption capacity and recyclability shows great potential for VOC removal.

Graphene assisted photoanodes are promising because of the high performance of the resulting dye sensitized solar cells (DSSCs). A photoanode with a three-layer structure is prepared in this study and the synergy between each layer was found to play a vital role in its photovoltaic properties. The influence of interface contact between the transport layer and work layer is revealed. After ameliorating the interface contact level (enhancing the electron transport ability), the functions of the adopted reduced graphene oxide (RGO) and three-dimensional graphene networks (3DGNs) in the transport layer and work layer, respectively, can be made full use of. In order to further enhance the scattering ability for the incident light and improve the adsorption ability for dye molecules, a scattering layer based on the RGO–TiO2 is added in the photoanode. After a comprehensive optimization (including the types of functional groups and mass fractions of the RGO in the work layer and scattering layer), the resulting power conversion efficiency reaches 11.8%, which is much higher than that of previous reported graphene modified DSSCs.

The compact ZIF-69 membranes have been prepared by seeded growth method for the recovery of gasoline vapor which is a major challenge in the petrochemical industry. The membrane performances for separating N2/n-alkane mixtures at various operating conditions (e.g. trans-membrane pressure difference, operating temperature, feed concentration, and stage cut) were systematically investigated. The highest separation factor was 2.60 with the corresponding permeance of 5.02 × 10−8 mol/(m2 s Pa) for the N2/n-C6H14 model mixtures. Moreover, the effects of n-alkane components (n-C5H12, n-C6H14, and n-C7H16) on the separation performances were studied, and the separation factors followed α(N2/n-C7H16) > α(N2/n-C6H14) > α(N2/n-C5H12), due to the different adsorption capacities of n-alkanes on ZIF-69 materials. The present work demonstrates that the ZIF-69 membrane is a highly promising candidate for the application in gasoline vapor recovery.

In this study, ordered hexagonal mesostructure siliceous materials and macroporous ordered siliceous foams were synthesized in pH = 5 buffer solution by simply adjusting the reaction temperature with P123 (EO20PO70EO20) as a structure-directing agent and tetramethoxysilane (TMOS) as the silica source. Increasing the reaction temperature from 15 to 35 °C led to a structural evolution from ordered hexagonal mesostructure siliceous material with a pore size of 10 nm to macroporous ordered siliceous foam with a pore size of ∼100 nm. The adsorption and desorption performance of hexagonal mesostructure and macroporous ordered siliceous samples (HMS and MOSF) were investigated under static (water vapor, n-hexane and 93# gasoline) and dynamic (n-hexane) conditions. Compared with commercial silica gel (SG), activated carbon (AC) and HMS, MOSF show higher static adsorption capacity of n-hexane and 93# gasoline, higher dynamic n-hexane adsorption capacity, and more stable breakthrough time under dynamic adsorption conditions. The designed MOSF with highest volatile organic compounds (VOCs) removal capacity and recyclability show great potential for VOCs controlling.

High quality and naturally continuous structure of three-dimensional graphene network (3DGN) endow it a promising candidate to modify TiO2. Although the resulting composite photocatalysts display outstanding performances, the lacking of active sites of the 3DGN not only goes against a close contact between the graphene basal plane and TiO2 nanoparticles (weaken electron transport ability) but also limits the efficient adsorption of pollutant molecules. Similar with surface functional groups of the reduced graphene oxide (RGO) nanosheets, surface defects of the 3DGN can act as the adsorption sites. However, the defect density of the 3DGN is difficult to control (a strict cool rate of substrate and a strict flow of precursor gas are necessary) because of its growth approach (chemical vapor deposition method). In this study, to give full play to the functions of graphene, the RGO nanosheets and 3DGN co-modified TiO2 composite photocatalysts are prepared. After optimizing the mass fraction of the RGO nanosheets in the composite photocatalyst, the resulting chemical adsorption ability and yields of strong oxidizing free radicals increase significantly, indicating the synergy of the RGO nanosheets and 3DGN.

Functionalized hollow siliceous spheres (HSSs) have been prepared by surface modification with trimethylchlorosilane (TMCS) for the removal of volatile organic compounds (VOCs). The resultant HSSs-TMCS possesses a uniform and well-dispersed hollow spherical structure, high surface area, large total pore volume, high VOCs adsorption capacity, and small water vapor adsorption capacity. The adsorption and desorption performance of HSSs-TMCS under static (n-hexane and 93# gasoline) and dynamic (n-hexane) conditions was investigated. Compared with commercial silica gel (SG) and activated carbon (AC), HSSs-TMCS show higher capacity of adsorbing n-hexane and 93# gasoline with good stability and low water vapor adsorption capacity under static adsorption conditions, higher dynamic adsorption capacity and stable breakthrough time under dynamic adsorption conditions. The high efficiency and stability of functionalized HSSs are associated with their unique hollow morphology and structure parameters. The designed HSSs-TMCS with high VOCs removal capacity and recyclability are promising candidates for the treatment of air pollution.

Hollow organosiliceous sphere (HOS) materials have been successfully synthesized by a co-condensation method with tetraethylorthosilicate (TEOS) and organosilane (1,2-bis(triethoxysilyl)ethane, BTSE) as mixed silica sources under acidic conditions. The application of HOSs as adsorbents for the volatile organic compound (VOC) abatement was demonstrated. The HOSs were characterized by transmission electron microscopy (TEM), N2 sorption isotherms, FT-IR spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results indicated that all samples showed a uniform hollow mesostructure and the organic groups were chemically incorporated into the walls of HOSs. The static adsorption and stability behaviors of water vapor, n-hexane and 93# gasoline on HOSs were investigated, with commercial silica gel (SG) and activated carbon (AC) as references. It was found that the sample with an initial molar ratio BTSE/(BTSE + TEOS) of 25% (HOS-25%) had the largest VOC adsorption capacity (1.36 g g−1n-hexane and 1.35 g g−1 93# gasoline) and the smallest water vapor adsorption capacity (0.0120 g g−1) under static adsorption conditions. The dynamic adsorption behaviors of n-hexane on HOS-25% were evaluated via breakthrough curves. The dynamic adsorption capacities of n-hexane are in the following order: SG < AC < HOS-25% and the stability is in the order of AC < SG < HOS-25%. The larger dynamic VOC capacity of the HOSs may be attributed to the synergetic effect between the unique morphology and hybrid walls. The static and dynamic n-hexane and water vapor competitive adsorption results suggested that HOS-25% had a much higher adsorption tendency for VOCs over water vapor. The HOSs with high hydrophobicity, large VOC removal capacity and excellent recyclability show great potential for VOC controlling.

Zeolitic imidazolate framework-90 (ZIF-90) synthesized by solvothermal method reveals large BET surface area and high n-hexane vapor adsorption capacity. However, the adsorption rate and efficiency for n-hexane vapor are far from expectation, which affect the industrial applications. Thus, a green and efficient method using triethylamine (TEA) was developed to prepare a new ZIF-90 with large pore diameter to increase the adsorption rate and efficiency dramatically. Notably, the average pore diameter of the new ZIF-90 was up to 3.66 nm, which was more than twice larger than that reported one using previous method. On the other hand, the resulting samples with larger pore limited the adsorption capacity for n-hexane vapor. Therefore, graphene oxide (GO) was further employed as filler to modify the ZIF-90 based on its high BET surface area and thermal conductivity. The resulting ZIF-90/GO composite with both higher adsorption capacity and rate for n-hexane vapor was optimized, which was 72% and 11% higher than that of the pristine ZIF-90, respectively. More importantly, the ZIF-90/GO composite possessed a more stable structure for n-hexane vapor adsorption, which endowed it a potential prospect in the purification field.

MIL-101(Cr)/AC was synthesized by in situ incorporation of activated carbon powder via hydrothermal method. The water stability, n-hexane adsorption and regeneration of the MIL-101(Cr)/AC were experimentally measured. The results showed that the MIL-101(Cr)/AC exhibited the larger surface area (3319.3[Formula: see text]m2/g) than that of MIL-101(Cr) and AC, respectively. The addition of activated carbon was beneficial to improve the yield of MIL-101(Cr)/AC. The pore structure parameter and XRD of the MIL-101(Cr)/AC changed little after in water for 24[Formula: see text]h. Furthermore, the adsorption capacity of MIL-101(Cr)/AC for n-hexane was 786[Formula: see text]mg/g, which increased to 23.0% and 27.7% compared with MIL-101(Cr) and AC, respectively. Kinetic fitting of data indicated that the pseudo-first order model can more accurately describe the adsorption process of n-hexane on MIL-101(Cr)/AC and the intraparticle diffusion was not the sole rate-controlling step. Besides, the regeneration efficiency of MIL-101(Cr)/AC was over 92% after 10 consecutive n-hexane adsorption/desorption cycles.

Hierarchical N-doped carbon nanotubes (NCTs) with controllable aspect ratios were developed for CO2 adsorption. In this work, NCTs were synthesized by coating different amounts of 3-aminophenol/formaldehyde resin (APF) on the outer layer of silica nanotubes, carbonizing in N2 at 700∘C and removing the silica and Ni template by hydrofluoric acid etching. The obtained NCTs were activated by K2CO3. After activation, micropores on the activated N-doped carbon nanotubes (ANCTs) were enriched, the micro-surface area and pore volume of ANCT-1.0 reached 1195[Formula: see text]m2[Formula: see text]g[Formula: see text] and 0.45[Formula: see text]cm3[Formula: see text]g[Formula: see text], respectively, and the corresponding adsorption capacity increased by 50% (4.50[Formula: see text]mmol[Formula: see text]g[Formula: see text] at 0∘C and 1 bar). Moreover, ANCT-1.0 maintained a high stability throughout consecutive adsorption–desorption cycles. The advantages of hierarchical N-doped carbon nanotubes, including their meso–microporous structures, high geometric aspect ratio and good stability, make them valuable and promising materials to capture carbon dioxide.

There are many oil vapours to discharge from oil containers into the atmosphere in oil operations (such as storage and loading). Two basic concepts are discussed regarding the control of oil vapour emission (OVE). The first is to invent active methods to restrain the OVE. The second is to develop passive tail-end remediation technologies to control the released vapour. Oil vapour recovery technology (OVRT), as the typical remediation method, is introduced to separate the vapour-air mixture and recover valuable hydrocarbons. Four major OVRTs, using the separation methods of absorption, adsorption, condensation, and membrane, are compared, and the integrated technology of various separation methods is recommended as the preferred application, easing to meet increasingly stringent emission standards for volatile organic compounds (VOCs). Two typical integrated technologies of absorption-adsorption and condensation-adsorption are investigated for gasoline vapour recovery in China, with their vapour recovery efficiencies of 99%.