Adsorption behaviors of volatile organic compounds (VOCs) on porous clay heterostructures (PCH)

Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV-Vis (DRS), FT-IR, N2 adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH3-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV-Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.

A new attempt to control volatile organic compounds (VOCs) pollution - Modification technology of biomass for adsorption of VOCs gas

The detrimental impact of volatile organic compounds on the surroundings is widely acknowledged, and effective solutions must be sought to mitigate their pollution. Adsorption treatment is a cost-effective, energy-saving, and flexible solution that has gained popularity. Biomass is an inexpensive, naturally porous material with exceptional adsorbent properties. This article examines current research on volatile organic compounds adsorption using biomass, including the composition of these compounds and the physical (van der Waals) and chemical mechanisms (Chemical bonding) by which porous materials adsorb them. Specifically, the strategic modification of the surface chemical functional groups and pore structure is explored to facilitate optimal adsorption, including pyrolysis, activation, heteroatom doping and other methods. It is worth noting that biomass adsorbents are emerging as a highly promising strategy for green treatment of volatile organic compounds pollution in the future. Overall, the findings signify that biomass modification represents a viable and competent approach for eliminating volatile organic compounds from the environment.

Extensive comparison of methods for removal of organic halogen compounds from pharmaceutical process wastewaters with life cycle, PESTLE, and multi-criteria decision analyses

Recycling and disposing wastewater from the pharmaceutical industry are of utmost importance in mitigating chemical waste generation, where unmanaged hazardous waste fluxes could cause massive environmental damage. Air stripping, steam stripping, distillation, and incineration offer significant emission reduction potentials for pharmaceutical applications; however, selecting specific process units is a complicated task due to the high number of influencing screening criteria. The mentioned chemical processes are modelled with the Aspen Plus program. This study examines the environmental impacts of adsorbable organic halogens (AOX) containing pharmaceutical process wastewater disposal by conducting life cycle impact assessments using the Product Environmental Footprint (PEF), IMPACT World + Endpoint V1.01, and Recipe 2016 Endpoint (H) V1.06 methods. The results show that the distillation-based separation of AOX compounds is characterized by the most favourable climate change impact and outranks the PEF single score of air stripping, steam stripping, and incineration by 6.3%, 29.1%, 52.0%, respectively. The energy-intensive distillation technology is further evaluated by considering a wide selection of energy sources (i.e., fossil fuel, nuclear, solar, wind onshore, and wind offshore) using PESTLE (Political, Economic, Social, Technological, Legal, Environmental) analysis combined with multi-criteria decision support to determine the most beneficial AOX disposal scenario. The best overall AOX regeneration performance and lowest climate change impact (7.25 × 10-3 kg CO2-eq (1 kg purified wastewater)-1) are obtained by supplying variable renewable electricity from onshore wind turbines, reaching 64.87% carbon emission reduction compared to the baseline fossil fuel-based process alternative.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

Enhancement Properties of Zr Modified Porous Clay Heterostructures for Adsorption of Basic-Blue 41 Dye: Equilibrium, Regeneration, and Single Batch Design Adsorber

Zirconium porous clay heterostructures (Zr-PCH) were synthesized using intercalated clay minerals by zirconium species with different contents of zirconium. The presence of zirconium and silica species was confirmed by X-ray diffraction, X-ray fluorescence, and magic-angle spinning nuclear magnetic resonance. The insertion of zirconium improved the thermal stability, the specific surface area with a maximum of 950 m²/g, and the acidity concentration of 0.993 mol of protons per g of solid. These materials were used to adsorb the basic blue-41 from aqueous solution. The adsorption efficiency was examined at different conditions, with a maximum adsorbed amount of 346 mg/g as estimated from Langmuir model. This value was dependent on zirconium content in the PCHs. The adsorption process was found to be favorable and spontaneous. The efficiency of the spent materials was maintained after five reuse cycles with a decrease by 15% of the original value for a particular Zr-PCH material with a Zr content of 6.82%. Single stage batch adsorber was suggested using the mass balance equation and Langmuir isotherm model. The amount of PCH materials required depended on the target percentage of adsorption at specific volume and initial concentration of the basic-blue-41 dye solution.

Modification of kaolinite/muscovite clay for the removal of Pb(II) ions from aqueous media

Natural clay extracted from the Central Region of Ghana was used for this study. Energy dispersive X-ray and powder X-ray diffraction analysis showed the composition of the clay to be 67.5% kaolinite and 32.5% muscovite. The samples were successfully modified by H2SO4 and NaOH activation. They were also characterized by scanning electron microscopic and Fourier transformed-infrared spectrophotometric techniques. Batch adsorption studies revealed that the samples are effective adsorbents for the removal of Pb(II) ions from aqueous media. Factors studied include contact time, pH, effect of ionic strength and the mass of adsorbent. Generally, the alkali activated samples had the highest adsorptive capacity followed by the acid activated clay. The kinetics of the adsorption process fitted the pseudo-second order model and the adsorption isotherm conformed to the Langmuir as well as the Freundlich models. All the experiments were carried out at room temperature (303 K).

Alkylation modified pistachio shell-based biochar to promote the adsorption of VOCs in high humidity environment

The objective of this work was to evaluate the adsorption capacity of alkylated modified porous biochar prepared by esterification and etherification (PSAC-2) for low concentrate volatile organic compounds (VOCs, toluene and ethyl acetate) in high humidity environment by experiments and theoretical calculations. Results showed that PSAC-2 has a large specific surface area and weak surface polarity, at 80% relative humidity, its capacities for toluene and ethyl acetate adsorption could be maintained at 92% and 87% of the initial capacities (169.9 mg/g and 96.77 mg/g). The adsorption behaviors of toluene, ethyl acetate, and water vapor were studied by adsorption isotherms, and isosteric heat was obtained. The desorption activation energy was obtained by temperature programmed desorption experiment. The outcomes manifested that the PSAC-2 can achieve strong adsorption performance for weakly polar molecules. Through density functional theory (DFT) simulations, owing to the interaction of hydrogen bonds, oxygen-containing groups became a significant factor influencing the adsorption of VOCs in humid environments. These results could provide an important reference for VOCs control in a high humidity environment.

Renewable Activated Carbon Filters Bearing Photocatalytic Particles for Volatile Organic Compound Removal

As interest in improving indoor air quality has increased, the development of long-lasting adsorbents that effectively and economically remove volatile organic compounds (VOCs) has become critical. In this study, TiO2-bearing activated carbon is introduced as a photocatalytic adsorbent in a renewable VOC filter. The activated carbon filter bearing TiO2 particles is prepared using the sol-gel method, followed by a spraying method. VOC adsorption and photocatalytic activity of the TiO2-bearing activated carbon are analyzed using a Tedlar bag sampling technique, using toluene and acetaldehyde as sample of VOC gas. Under ultraviolet-C (UV-C) irradiation for 22 h, the photocatalytic activity of TiO2 regenerates the VOC filters by 99 %. In addition, under UV-A and light-emitting diode, the TiO2-bearing activated carbon filters are regenerated by 60 % and 58 %, respectively, after 22 h. This result establishes its practical applicability as a renewable indoor VOC filter.

Produced Water Treatment with Conventional Adsorbents and MOF as an Alternative: A Review

A large volume of produced water (PW) has been produced as a result of extensive industrialization and rising energy demands. PW comprises organic and inorganic pollutants, such as oil, heavy metals, aliphatic hydrocarbons, and radioactive materials. The increase in PW volume globally may result in irreversible environmental damage due to the pollutants' complex nature. Several conventional treatment methods, including physical, chemical, and biological methods, are available for produced water treatment that can reduce the environmental damages. Studies have shown that adsorption is a useful technique for PW treatment and may be more effective than conventional techniques. However, the application of adsorption when treating PW is not well recorded. In the current review, the removal efficiencies of adsorbents in PW treatment are critically analyzed. An overview is provided on the merits and demerits of the adsorption techniques, focusing on overall water composition, regulatory discharge limits, and the hazardous effects of the pollutants. Moreover, this review highlights a potential alternative to conventional technologies, namely, porous adsorbent materials known as metal-organic frameworks (MOFs), demonstrating their significance and efficiency in removing contaminants. This study suggests ways to overcome the existing limitations of conventional adsorbents, which include low surface area and issues with reuse and regeneration. Moreover, it is concluded that there is a need to develop highly porous, efficient, eco-friendly, cost-effective, mechanically stable, and sustainable MOF hybrids for produced water treatment.

Universality of mesoporous coal gasification slag for reinforcement and deodorization in four common polymers

Mesoporous adsorbents and polymer deodorants are difficult to implement on a large scale because of their complicated preparation methods. Herein, a mesoporous adsorbent (CGSA) with a specific surface area of 564 m²g^-1and a pore volume of 0.807 cm³g^-1was prepared from solid waste coal gasification slag using a simple acid leaching process. The adsorption thermodynamics and adsorption kinetics results verified that the adsorption mechanism of propane on CGSA was mainly physisorption. Then the universality of CGSA in different polymers was investigated by introducing CGSA and its commercialized counterparts (CaCO₃, and zeolite) into four common polymers. When the filler content was 30 wt%, the average reinforcement effect of CGSA on the tensile, flexural, and impact strengths of the four polymers was 46.68%, 83.62%, and 211.90% higher than that of CaCO₃, respectively. Gas chromatography results also showed that CGSA significantly decreased total volatile organic compound emissions from the composites, and its optimal deodorization performance reached 69.58%, 81.33%, and 91.09% for different polymers, respectively, far exceeding that of zeolite. Therefore, this study showed that low-cost, high-performance, and multifunctional mesoporous polymer fillers with excellent universality can be manufactured from solid contaminants.

The adsorption properties of microporous activated carbon prepared from pistachio nut shell for low-concentration VOCs under low-medium temperatures

The control of low-concentration VOCs in coal-fired flue gas is one of the research hotspots at present. In this work, K₂CO₃ and K₂CO₃-KCl were employed to activate the agricultural wastes (pistachio nut shell) to prepare activated carbon (AC), named PSAC-1 and PSAC-2, respectively. By testing the adsorption performance of the prepared AC and commercial activated carbon (CAC) for the five target VOCs, it was observed that the adsorption capacity of PSAC-2 was the best compared to the other two. Particularly, the adsorption capacity of PSAC-2 (225 mg·g^-1) for phenol was 3.8 times that of CAC (59 mg·g^-1). In addition, the pseudo-first-order model, pseudo-second-order model, and Elovich model all fitted the adsorption process well, which indicated that both physical adsorption and chemical adsorption existed simultaneously, in which physical adsorption played a dominant role and chemical adsorption played a minor role. Weber-Morris kinetic model was used to illustrate the rate-controlling mechanism; the results confirmed that the stage of external membrane mass transfer was the control stage of adsorption rate. The results of this study can provide some references for the commercial production of biomass-derived AC and the removal of VOCs in coal-fired flue gas.

Facile and scalable preparation of ZIF-67 decorated cotton fibers as recoverable and efficient adsorbents for removal of malachite green

Recently, metal–organic frameworks (MOFs) have received considerable attention as highly efficient adsorbents for dye wastewater remediation. However, the immobilization of MOFs on the substrate surfaces to fabricate easy recyclable adsorbents via a facile route is still a challenge. In this work, ZIF-67/cotton fibers as adsorbents for dye removal were prepared in a large-scale using a simple coordination replication method. The successful fabrication of the ZIF-67/cotton fibers was confirmed by FTIR, XRD, XPS, SEM and BET analysis, respectively. As expected, the as-prepared ZIF-67/cotton fibers exhibited high adsorption capacity of 3787 mg/g towards malachite green (MG). Meanwhile, the adsorption kinetics and isotherm obeyed the pseudo-second-order kinetics and Langmuir model, respectively. Moreover, its removal efficiency towards MG was not significantly influenced by the pH and ionic strength of aqueous solution. Most importantly, the ZIF-67/cotton fibers can remove MG from synthetic effluents, and it can be easily regenerated without filtration or centrifugation processes, with the regeneration efficiency remaining over 90% even after 10 cycles. Additionally, the ZIF-67/cotton fibers presented excellent antimicrobial performance against E. coli and S. aureus. Hence, the distinctive features of the as-prepared ZIF-67/cotton fibers make it promisingly applicable for the colored wastewater treatment.

Water Purification of Classical and Emerging Organic Pollutants: An Extensive Review

The main techniques used for organic pollutant removal from water are adsorption, reductive and oxidative processes, phytoremediation, bioremediation, separation by membranes and liquid–liquid extraction. In this review, strengths and weaknesses of the different purification techniques are discussed, with particular attention to the newest results published in the scientific literature. This study highlighted that adsorption is the most frequently used method for water purification, since it can balance high organic pollutants removal efficiency, it has the possibility to treat a large quantity of water in semi-continuous way and has acceptable costs.

An eco-environmental assessment of harmful algal bloom mitigation using modified clay

The application of modified clay (MC) to mitigate harmful algal blooms (HABs) is becoming a widespread practice in China because of its low cost, high efficiency and environmental friendliness. Due to its success in China, this technology has also gained international recognition in recent years. Nevertheless, the eco-environmental impacts of this technology still remain to be a concern to many customers and government agencies, which has motivated scientists in both China and many other countries to evaluate its potential effects on nontarget aquatic organisms, water quality and the benthic environment. This paper reviews the results from these studies both in the laboratory and in the field, which showed that MC does not harm nontarget aquatic organisms and has no negative impact on water quality or the benthic environment. Additionally, findings show that MC can alter nutrient cycling and reduce algal toxins in water bodies. Furthermore, researchers also found that MC affects cyst formation and germination in sedimentary environments. This review is expected to provide scientific guidance for mitigating HABs in China and worldwide using clay or MC.

Porous Clay Heterostructure with Alginate Encapsulation for Toluene Removal

A volatile organic compound adsorbent based on a porous clay heterostructure (PCH) with alginate biopolymer was successfully prepared. From N₂ adsorption-desorption analysis, the specific surface area, pore volume, and pore size of bentonite were dramatically increased after introducing the porous structure. Following complexation with alginate (Alg-PCH), the pore volume and pore size were not significantly affected by pore structure. The thermal stability of Alg-PCH shows enhanced thermal stability compared to alginate and alginate beads. The morphology layered structure of Alg-PCH was carried out by transmission electron microscopy (TEM), suggesting the disorder and re-order of the c-axis layer stacking by porous structure and complexation with alginate, respectively, which was well-matched with X-ray diffraction results. To optimize the preparation of Alg-PCH, various reaction conditions (alginate, CaCl₂ concentration, bead size, and weight ratio between alginate and PCH) were utilized. According to the toluene adsorption-desorption experiments, the preparation conditions for Alg-PCH were selected as a 2 mm extrusion tip, 0.5% of alginate, and 2% of CaCl₂ solution with a 1:50 alginate:PCH weight ratio. Additionally, it shows 61.63 mg/g adsorption capacity with around 49% desorption efficacy under atmospheric temperature and pressure.

Isotherm, kinetic, and thermodynamic studies for dynamic adsorption of toluene in gas phase onto porous Fe-MIL-101/OAC composite

In the present paper, micro-mesoporous Fe-MIL-101/OAC composite using in situ incorporation of Fe-MIL-101 into oxidized activated carbon was synthesized and characterized by XRD, FT-IR, SEM, EDS, and BET techniques. The adsorption performances of toluene onto adsorbents in the gas phase were studied using a laboratory-scale dynamic adsorption system under moist ambience. The toluene adsorption capacity of Fe-MIL-101/OAC composite and Fe-MIL-101 were 127 and 97.6 mg g^-1, severally. Results revealed that the larger pores in micro-mesoporous Fe-MIL-101/OAC enhanced the molecular diffusion rate. The findings indicated that micro-mesoporous structures played key roles in the capture of toluene molecules. The initial toluene concentration positively affected on toluene adsorption capacity while temperature and humidity negatively affected on toluene adsorption capacity. The Langmuir model and the pseudo-second-order kinetics model described better adsorption process of Fe-MIL-101/OAC composite. Thermodynamic findings determined that toluene adsorption over Fe-MIL-101/OAC was spontaneous, exothermic physisorption. The regeneration of the composite was still up to 72.6% after six cycles. The micro-mesoporous Fe-MIL-101/OAC composite proposes a promising support for the high toluene removal for future. Graphical abstract.

Surface modified and activated waste bone char for rapid and efficient VOCs adsorption

In this work, very efficient VOCs adsorbent was developed from waste bovine bone. After pyrolysis at 450 °C, the bone char was treated by H₃PO₄ for surface modification and activated by K₂CO₃ respectively. The prepared materials were characterized by N₂ adsorption isotherms, SEM, FT-IR, and XPS. Adsorption/desorption and regeneration behavior of VOCs were also studied. Results showed that H₃PO₄ modification can effectively accelerate the adsorption process and after K₂CO₃ activation, a new hierarchical pore structure was found with an ultrahigh total pore volume of 2.807 cm³/g. The specific adsorption capacity for typical VOC reached ∼13.03 mmol/g which is much higher than literature data under the same condition. Static toluene adsorption test on the prepared activated bone-char revealed that the hierarchical structure has provided abundant adsorption sites and the adsorption behavior can be well described by the pseudo-second-order model. The dynamic/static adsorption ratio increased from 70.31% to 78.62% due to less mass transfer resistance by surface modification.

A critical review on VOCs adsorption by different porous materials: Species, mechanisms and modification methods

Volatile organic compounds (VOCs) have attracted world-wide attention regarding their serious hazards on ecological environment and human health. Industrial processes such as fossil fuel combustion, petrochemicals, painting, coatings, pesticides, plastics, contributed to the large proportion of anthropogenic VOCs emission. Destructive methods (catalysis oxidation and biofiltration) and recovery methods (absorption, adsorption, condensation and membrane separation) have been developed for VOCs removal. Adsorption is established as one of the most promising strategies for VOCs abatement thanks to its characteristics of cost-effectiveness, simplicity and low energy consumption. The prominent progress in VOCs adsorption by different kinds of porous materials (such as carbon-based materials, oxygen-contained materials, organic polymers and composites is carefully summarized in this work, concerning the mechanism of adsorbate-adsorbent interactions, modification methods for the mentioned porous materials, and enhancement of VOCs adsorption capacity. This overview is to provide a comprehensive understanding of VOCs adsorption mechanisms and up-to-date progress of modification technologies for different porous materials.

Highly efficient decomposition of toluene using a high-temperature plasma-catalysis reactor

Plasma-catalysis technologies (PCTs) have the potential to control the emissions of volatile organic compounds, although their low-energy efficiency is a bottleneck for their practical applications. A plasma-catalyst reactor filled with a CeO₂/γ-Al₂O₃ catalyst was developed to decompose toluene with a high-energy efficiency enhanced by the elevating reaction temperature. When the reaction temperature was raised from 50 °C to 250 °C, toluene conversion dramatically increased from 45.3% to 95.5% and the energy efficiency increased from 53.5 g/kWh to 113.0 g/kWh. Conversely, the toluene conversion using a thermal catalysis technology (TCT) exhibited a maximum of 16.7%. The activation energy of toluene decomposition using PCTs is 14.0 kJ/mol, which is far lower than those of toluene decomposition using TCTs, which implies that toluene decomposition using PCT differs from that using TCT. The experimental results revealed that the Ce³⁺/Ce⁴⁺ ratio decreased and O_ads/O_latt ratio increased after the 40-h evaluation experiment, suggesting that CeO₂ promoted the formation of the reactive oxygen species that is beneficial for toluene decomposition.

Adsorption of acetone and cyclohexane onto CO2 activated hydrochars

Most of the volatile organic compounds (VOCs) are toxic and harmful to human health and environment. In this study, hydrochars activated with CO₂ were applied to remove VOCs. Two typical VOCs, acetone and cyclohexane, were used as the 'model' adsorbates to evaluate hydrochars' performance. Specific surface areas of pristine hydrochars were small (<8 m²/g), whereas activated hydrochars showed much higher values (up to 1308 m²/g). As a result, the adsorption of VOCs onto the pristine hydrochars (13.24-24.64 mg/g) was lower than that of the activated ones (39.42-121.74 mg/g). The adsorption of the two VOCs onto the hydrochars was exothermal. In addition, there were significant correlations (R² > 0.91) between the VOC removal and hydrochars' specific surface area. These results suggest that the governing mechanism was mainly physical adsorption. Increasing experimental temperature (80-139 °C) desorbed the VOCs from the hydrochars. Due to its higher boiling point, cyclohexane desorption required a higher temperature than acetone desorption. The reusability of the activated hydrochars to the two VOCs was confirmed by five continuous adsorption-desorption cycles. The overall results indicated that hydrochars, particularly after CO₂ activation, are sufficient for VOC abatement.

Preparation of a new high-efficiency resin deodorant from coal gasification fine slag and its application in the removal of volatile organic compounds in polypropylene composites

Deodorizing materials are often restricted from large-scale industrial production due to the high preparation cost. By utilizing the simple acid leaching technology, this study made use of the coal gasification fine slag (FS) as raw material to prepare a cost effective FS-based deodorant (FSD) with a specific surface area of 393 m² g^-1 and a pore volume of 0.405 cm³  g^-1. The propane adsorption test on FSD showed the maximum adsorption capacity to be as high as 121.61 mg g^-1 at 273 K. The partition coefficient values at 10% and 100% breakthrough (BT) for FSD to adsorb propane were 1.5 × 10^-3 and 3.2 × 10^-4 mol kg^-1 Pa^-1, respectively. Furthermore, the FSD was applied in the removal of volatile organic compounds (VOCs) pollutants from polypropylene resin (PP). It showed that the deodorizing effect of the FSD was nearly three times as good as the commonly used zeolite deodorants, which was able to decrease 50 percent of the VOCs volatilization amount in PP resin. Moreover, the FSD can better strengthen the mechanical properties of PP resin. This work provides a new method for the industrial production of deodorants as well as a new direction for the recycle of coal gasification wastes.

Adsorption and Oxidative Desorption of Acetaldehyde over Mesoporous Fe x O y H z /Al2O3

Fe _x O _y H _z nanostructures were incorporated into commercially available and highly porous alumina using the temperature-regulated chemical vapor deposition method with ferrocene as an Fe precursor and subsequent annealing. All processes were conducted under ambient pressure conditions without using any high-vacuum equipment. The entire internal micro- and mesopores of the Al₂O₃ substrate with a bead diameter of ∼2 mm were evenly decorated with Fe _x O _y H _z nanoparticles. The Fe _x O _y H _z /Al₂O₃ structures showed substantially high activity for acetaldehyde oxidation. Most importantly, Fe _x O _y H _z /Al₂O₃ with a high surface area (∼200 m²/g) and abundant mesopores was found to uptake a large amount of acetaldehyde at room temperature, and subsequent thermal regeneration of Fe _x O _y H _z /Al₂O₃ in air resulted in the emission of CO₂ with only a negligibly small amount of acetaldehyde because Fe _x O _y H _z nanoparticles can catalyze total oxidation of adsorbed acetaldehyde during the thermal treatment. Increase in the humidity of the atmosphere decreased the amount of acetaldehyde adsorbed on the surface due to the competitive adsorption of acetaldehyde and water molecules, although the adsorptive removal of acetaldehyde and total oxidative regeneration were verified under a broad range of humidity conditions (0-70%). Combinatory use of room-temperature adsorption and catalytic oxidation of adsorbed volatile organic compounds using Fe _x O _y H _z /Al₂O₃ can be of potential application in indoor and outdoor pollution treatments.

Chemically activated hydrochar as an effective adsorbent for volatile organic compounds (VOCs)

Hydrochars derived from hickory wood and peanut hull through hydrothermal carbonization were activated with H₃PO₄ and KOH to improve their performance as a volatile organic compound (VOC) adsorbent. Polar acetone and nonpolar cyclohexane were used as representative VOCs. The VOC adsorptive capacities of the activated hydrochars (50.57-159.66 mg⋅g^-1) were greater than that of the nonactivated hydrochars (15.98-25.36 mg⋅g^-1), which was mainly caused by the enlargement of surface area. The significant linear correlation (R² = 0.984 on acetone, and R² = 0.869 on cyclohexane) between BET surface areas of hydrochars and their VOC adsorption capacities, together with the obvious adsorption exothermal peak of differential scanning calorimetry curve confirmed physical adsorption as the dominating mechanism. Finally, the reusability of activated hydrochar was tested on H₃PO₄ activated hickory hydrochar (HHP), which had higher acetone and cyclohexane adsorption capacities. After five continuous adsorption desorption cycles, the adsorptive capacities of acetone and cyclohexane on HHP decreased by 6.2% and 7.8%, respectively. The slight decline in adsorption capacity confirmed the reusability of activated hydrochar as a VOC sorbent.

Synergetic degradation of VOCs by vacuum ultraviolet photolysis and catalytic ozonation over Mn-xCe/ZSM-5

Volatile organic compounds (VOCs) are one of the most important precursors to form the fine particulate matter and photochemical smog, and should be strictly controlled. Vacuum ultraviolet (VUV) photolysis has provided a facile and an effective way to remove VOCs due to its powerful oxidation capability under mild reaction conditions. However, VUV irradiation would generate ozone which brings about secondary pollution. In this study, ZSM-5 supported Mn-Ce mixed oxides (Mn-xCe/ZSM-5) were fabricated as efficient catalysts for ozone catalytic oxidation (OZCO) process, which were applied in combination with VUV photolysis to remove O₃ byproduct and simultaneously facilitate toluene oxidation. The results indicated that the Mn-3Ce/ZSM-5 catalyst considerably enhanced the catalytic degradation efficiency up to 93% for the gas-phase toluene, one of the hazardous VOCs. Meanwhile, almost all the O₃ by-product could be eliminated in the process. It was found that the strong interaction of the MnOCe bond and the variable chemical valence of Mn and Ce based species in the mixed oxides would tune the redox capacity of Mn-xCe /ZSM-5. An increase in surface Ce³⁺ species and surface density of oxygen vacancies would benefit the adsorption and catalytic transformation of O₃ which eventually form the reactive oxygen species over Mn-xCe/ZSM-5.

Adsorption of volatile organic compounds onto natural porous minerals

The abundance of natural porous minerals and their low cost make them the potential adsorbents for VOCs (volatile organic compounds). In this paper, three natural minerals (diatomite, stellerite and vitric tuff) and their corresponding acid-treated minerals were used as adsorbents. The adsorption performances of minerals were investigated by the adsorption breakthrough curves of VOCs. The results indicated that the properties of organic compounds such as boiling point and polarity and the surface area and pore volume of minerals had obvious effects on the adsorption of VOCs over minerals. Increasing adsorption temperature and relative humidity would have negative effects on the VOC adsorption of minerals. The adsorption capacity of 2-heptanone over acid stellerite decreased by 7.2% as the temperature rose from 25°C to 45°C. The adsorption capacity of acid stellerite for 2-heptanone reduced by 60.9% when relative humidity increased from 0% to 75%. Minerals were tested for five adsorption-regeneration cycles to study the reusability. Better fittings of Thomas model, pseudo-first order kinetics model, and Freundlich model were showed in fitting the adsorption. Overall, porous minerals with high specific surface area and pore volume have promising prospect in VOCs adsorption.

Metal organic frameworks as potent treatment media for odorants and volatiles in air

The presence of odorants/volatiles in the air exerted various types of negative impacts on the surrounding environment. Their concentrations in indoor/outdoor air, if exceeding the threshold level, may not only affect human health but also deteriorate living standards. To maintain and enhance the quality of life, a better tool for the removal of these molecules is in great demand. Metal-organic frameworks (MOFs) and their associated materials offer an excellent platform for the treatment of odorants/volatiles in air (and water) systems. The diversity of ligands and metal ions in their frame imparts large loading capacities and excellent selectivity for a variety of targetable VOCs and/or odorants. This review discusses the use of MOFs and their composites to treat odorants/volatile molecules in gaseous media, with extensive discussion of their adsorptive uptakes, along with methods for their synthesis and regeneration. Moreover, the progression of odorant/volatile removal by MOFs is considered, with a special note on future directions in this emerging research field.

Development of Sustainable Technology to Mitigate VOCs Pollution from Air Using a Continuous System Composed of Fe-ZSM-5 Coated on Polypropylene Tubes Coupled with UV Irradiation at the Pilot Scale

In this work, the efficacy of volatile organic compounds (VOCs), such as benzene, toluene, ethylbenzene, and xylene, for the removal of indoor air in a heterogeneous photo-Fenton catalytic semi pilot reactor was investigated at room temperature. Fe-zeolite socony mobil (ZSM)-5 was used as the adsorptive catalytic material, which was coated on the polyethylene tubes as a solid support. The response of Fe-ZSM-5 to UV dry irradiation was investigated in terms of VOC degradation from the indoor air. Different coating materials were tested in order to achieve better binding and less pore blockage. Scanning electron microscope (SEM) micrographs of the Fe-ZSM-5 coated tubes were used for the morphological analysis of the tubes. A complete modular semi pilot reactor (12.51 L) was designed to accommodate the Fe-ZSM-5 coated tubes and UV lamps for UV irradiation, in order to achieve the degradation for VOC and the regeneration of the catalytic material. After completion of the setup, the plant design parameters, such as the linear velocity, surface volume loading rate (SVL), and space retention time (SRT), were calculated.

Catalytic oxidation of VOCs over Mn/TiO2/activated carbon under 185 nm VUV irradiation

Volatile organic compounds (VOCs) are regarded as the major contributors to air pollution, and should be strictly regulated. Photocatalytic oxidation (PCO) is of great interest for the removal of VOCs owing to its strong oxidation capability. However, its application is greatly limited by catalytic deactivation. Vacuum Ultraviolet (VUV) irradiation provides a novel way to improve the photocatalytic activity while much O₃ will be generated which may cause secondary pollution. In this study, a multi-functional catalyst of Mn/TiO₂/activated carbon (AC) was developed to eliminate and utilize O₃, as well as enhance catalytic oxidation of VOC degradation via ozone-assisted catalytic oxidation (OZCO). The results indicate that Mn modified TiO₂/AC (i.e. 0.1%Mn/20%TiO₂/AC) achieved a toluene removal efficiency of nearly 86% with 100% elimination rate of O₃. With the help of Mn/TiO₂/AC catalyst, O₃ was catalytically decomposed and transformed into active species of O (¹D) and OH, thus enhancing toluene removal. The combination of VUV irradiation with multi-functional catalyst provides a novel and efficient way for the degradation of VOCs.

Plasma-catalyst hybrid reactor with CeO2/γ-Al2O3 for benzene decomposition with synergetic effect and nano particle by-product reduction

A dielectric barrier discharge (DBD) catalyst hybrid reactor with CeO₂/γ-Al₂O₃ catalyst balls was investigated for benzene decomposition at atmospheric pressure and 30 °C. At an energy density of 37-40 J/L, benzene decomposition was as high as 92.5% when using the hybrid reactor with 5.0wt%CeO₂/γ-Al₂O₃; while it was 10%-20% when using a normal DBD reactor without a catalyst. Benzene decomposition using the hybrid reactor was almost the same as that using an O₃ catalyst reactor with the same CeO₂/γ-Al₂O₃ catalyst, indicating that O₃ plays a key role in the benzene decomposition. Fourier transform infrared spectroscopy analysis showed that O₃ adsorption on CeO₂/γ-Al₂O₃ promotes the production of adsorbed O₂^- and O₂^2‒, which contribute benzene decomposition over heterogeneous catalysts. Nano particles as by-products (phenol and 1,4-benzoquinone) from benzene decomposition can be significantly reduced using the CeO₂/γ-Al₂O₃ catalyst. H₂O inhibits benzene decomposition; however, it improves CO₂ selectivity. The deactivated CeO₂/γ-Al₂O₃ catalyst can be regenerated by performing discharges at 100 °C and 192-204 J/L. The decomposition mechanism of benzene over CeO₂/γ-Al₂O₃ catalyst was proposed.

Synergistic effect of UV pretreated Fe-ZSM-5 catalysts for heterogeneous catalytic complete oxidation of VOC: A technology development for sustainable use

In this work, the performance of benzene, toluene, ethylbenzene, and xylene (BTEX) removal and degradation from gas, air streams on UV pretreated Fe-ZSM-5 in a batch reactor at room temperature were studied. The Fe-ZSM-5 zeolite catalyst was prepared by hydrothermal reaction method. The influence of UV pre-irradiation time on the removal of BTEX were assessed by varying the time, ranging from 15min to 60smin. Then, sustainability of the activation of the catalyst resulted by UV pretreatment was studied by the four-cycle experiment with one time UV irradiation and after each cycle irradiation followed by BTEX removal after every cycle respectively. The results of BTEX removal depicted that 30min of UV pretreatment was sufficient for complete organics removal. The UV pretreatment effect on the catalytic oxidation and the stability of the catalyst were studied by modern instrumental techniques. The novelty of the process was the sustainable reuse of catalyst with persistent VOC removal, which works on the -adsorption-oxidation-regeneration-adsorption- cycle, which was confirmed by the characterization studies of the catalyst after four runs. The results revealed that the change in the structure, stability, morphology, and removal efficiency of the catalyst during the experiments was negligible. The VOC degradation mechanism studies showed that the oxidation occurs due to the formation of free radicals as well as hydroxyl ions, so named it heterogeneous photo-Fenton oxidation. The residual materials analysis showed the complete mineralization of VOC except small amount of acetone as oxidation product. Lastly, the kinetics of the VOC removal was studied.