VOC Degradation Research Articles

Surface Hydroxyl and Oxygen Vacancies Engineering in ZnSnAl LDH: Synergistic Promotion of Photocatalytic Oxidation of Aromatic VOCs.

Photocatalytic oxidation has gained great interest in environmental remediation, but it is still limited by its low efficiency and catalytic deactivation in the degradation of aromatic VOCs. In this study, we concurrently regulated the surface hydroxyl and oxygen vacancies by introducing Al into ZnSn layered double hydroxide (LDH). The presence of distorted Al species induced local charge redistribution, leading to the remarkable formation of oxygen vacancies. These oxygen vacancies subsequently increased the amount of surface hydroxyl and elongated its bond length. The synergistic effects of surface hydroxyl and oxygen vacancies greatly enhanced reactant adsorption-activation and facilitated charge transfer to generate •OH, •O2-, and 1O2, resulting in highly efficient oxidation and ring-opening of various aromatic VOCs. Compared with commercial TiO2, the optimized ZnSnAl-50 catalyst exhibited about 2-fold activity for the toluene and styrene degradation and 10-fold activity for the chlorobenzene degradation. Moreover, ZnSnAl-50 demonstrated exceptional stability in the photocatalytic oxidation of toluene under a wide humidity range of 0-75%. This work marvelously improves the photocatalytic efficiency, stability, and adaptability through a novel strategy of surface hydroxyl and oxygen vacancies engineering.

A novel macroporous biochar as a biocarrier for DMAC biodegradation: Preparation, performance and mechanism

We produced a new biochar composite from waste bamboo powder and used it as a carrier for N,N-dimethylacetamide (DMAC) biodegradation. Characterization results highlighted the biochar composite's macroporous structure, comprising 72.14% of its total pore volume, facilitating bacterial colonization and growth. In comparison to traditional biocarriers and bamboo charcoal-loaded polyurethane (BC-PU), the biochar composite exhibited faster biofilm formation and achieved stability by the 5th day. Due to the increased biomass on the biochar composite, the DMAC degradation rate reached 80.44%, which was 1.5 times greater than that of BC-PU, indicating its potential for treating DMAC in biofilters. The Fourier transform infrared spectroscopy revealed the presence of abundant oxygen-containing functional groups in the biochar composite, which strongly interacted with bacterial adhesion. Selective passivation of oxygen-containing functional groups extended the biofilm formation time from 5 to 10 days, while the introduction of carboxyl groups expedited it by 1 day. Kinetic studies and the Derjaguin–Landau–Verwey–Overbeek theory demonstrated that the oxygen-containing functional groups reduced the total interaction energy and improved the mass transfer capacity of the biochar surface, thereby promoting biofilm formation. This study introduces a macroporous biochar composite with enhanced biodegradation capabilities, outperforming traditional biocarriers in VOCs degradation in bioreactors. The process provides a new direction for future biocarrier preparation.

Non‐thermal Plasma for VOCs Abatement: Recent Advance

AbstractVolatile organic compounds (VOCs) emissions are a factor in a number of environmental issues. To reduce the associated negative consequences, it is crucial to develop efficient VOCs removal systems. Non‐thermal plasma (NTP) co‐catalytic technology has become a popular research topic in this field as a result of its ability to reduce the activation energy of the reaction while simultaneously improving product selectivity. Despite the huge number of studies synthesising the use of metals and their oxide catalysts in the degradation of VOCs, metal‐organic frameworks (MOFs) and MOF derivatives are the subject of comparatively few studies in this area. This paper reviews the basic principles and technological progress of NTP co‐catalytic VOCs degradation, with a focus on the use of MOFs and their derivatives in plasma VOCs degradation, as well as the use of other non‐metallic carbon materials in plasma VOCs degradation. It highlights the potential future development direction of NTP catalytic synergistic treatment of VOCs by focusing on the optimization of catalytic synergism on the treatment impact. In the end, the challenges faced, the prospects, and our personal perspective on future research directions are also estimated and elucidated.

Construction of CdS@g–C3N4 heterojunction photocatalyst for highly efficient degradation of gaseous toluene

Exploring efficient photocatalysts for the degradation of VOCs under visible light is a challenge. CdS@g–C3N4 heterojunction photocatalytic materials were developed in this study using a microwave-assisted sol-gel process. CdS@g–C3N4(0.2) photocatalyzed the maximum degradation of gaseous toluene under visible light irradiation, and the time required to achieve the same degradation rate was reduced by 270 min when compared to pure CdS. The morphological characterization, photoelectric property analysis, and DFT calculations all verified that the CdS nanoparticles were uniformly disseminated on the surface of g–C3N4, and that the interfaces were closely contacted to form a heterojunction interface with a built-in field. This enhances charge transfer from CdS to g–C3N4 while successfully decreasing electron-hole pair recombination caused by light. Furthermore, the energy band structure was altered to absorb longer wavelengths of light and extend the absorption spectral range, improving the photocatalytic material's efficacy for broad-spectrum light such as sunshine. This paper proposes methods for predicting and optimizing the surface structure of catalysts, as well as developing high-performance multi-heterojunction photocatalysts for the degradation of indoor VOCs.

MXene/CdS photothermal–photocatalytic hydrogels for efficient solar water evaporation and synergistic degradation of VOC

Synergistic effect of solar-driven evaporation and photocatalysis purification by Ti3C2 MXene/CdS hydrogels for sustainable clean water production.

By-product reduction for the non-thermal plasma removal of toluene using an α-MnO2/Cordierite honeycomb monolithic catalyst in a honeycomb structure

The practical implementation of non-thermal plasma (NTP) combined with catalysts still faces challenges due to the by-products, such as O3 and nanoparticles. In this study, α-MnO2/Cordierite honeycomb monolithic (CHM) catalyst was used to reduce the by-products for NTP degradation of toluene. The by-products analysis shows that using the α-MnO2/CHM catalyst not only improves the degradation efficiency up to 98% and COX selectivity to 50%, but also simultaneously and greatly reduces the release of three types of hazardous by-products, organic components, ozone, and particles. The mechanisms of toluene degradation and by-product formation were investigated through online monitoring which can be summarized in two ways: direct degradation by energetic electrons and reactive radicals in the discharge region, and deep oxidation by active oxygen species on the catalyst surface. This investigation can improve our understanding of VOC degradation by combining monolithic catalysts with plasma, and accelerate the implementation of plasma-catalyzed technology in real-world.

High-efficiency transformation of O3 into •OH via AgOx nanocatalysis in synergy with water falling film discharge for multicomponent VOCs degradation

In this paper, two kinds of AgOx/Ti catalysts for catalytic VOCs degradation, including S(AgOx-Na2SiO3)/Ti and G(AgOx-SiO2)/Ti, were prepared through deposition–precipitation and sol–gel method separately. The characterization of microstructure and surface properties of the two catalysts demonstrated that Ag nanoclusters on the surface of S(AgOx-Na2SiO3)/Ti were finer and more evenly distributed. The in-situ measurement of discharge parameters for the two catalysts indicated that the S(AgOx-Na2SiO3)/Ti significant enhanced the discharge intensity of the DBD reactor. It is found that the S(AgOx-Na2SiO3)/Ti could effectively enhance the energy yield and VOCs degradation efficiency of water falling film discharge. The synergistic use of the two AgOx/Ti catalysts further improved the removal rate of multicomponent VOCs. It is verified that altering the inlet concentration of tertiary-butyl alcohol could regulate the catalytic transformation of generated ozone into •OH and hence the VOCs removal rate. The possible mechanism of catalytic transformation of O3 into •OH was proposed. The study may offer a facile method to prepare high-performing catalyst and provide a new way to treat multicomponent VOCs.

Microwave-assisted construction of MXene/MOF aerogel via N-metal bonds for efficient photodegradation of vapor acetone under high humidity

Designing MOF aerogels possessing highly efficient photocatalytic performance for VOCs photodegradation is a significant but challenging task. Herein, a microwave-assisted bridging strategy was proposed to construct MXene/MOF aerogel photocatalysts based on the wave-absorbing hot-spots effect of MXene for efficient acetone photodegradation in high humidity. The MXene/MOF aerogel formed abundant and intimate nano-interfaces via N-metal (N-Ti[MXene] and N-Zr[NH2-UiO-66(Zr)] bi-bonding under microwave irradiation, which enhanced light absorption, OH/O2− radicals formation, photo-induced electron-hole (e–/h+) generation, and their separation. Consequently, it exhibited excellent acetone photodegradation (97.3%) in 80% high humidity, with 10–104 times higher apparent rate constants (k*) than those of state-of-the-art photocatalysts. Moreover, MXene/MOF aerogel photocatalyst realized ∼ 95% TOC removal of acetone within 60 min and exhibited remarkable photocatalytic stability after five cycling-runs. Considering these attributes, the newly designed MXene/MOF aerogel photocatalysts have the potential to provide a practical approach for the efficient degradation of VOCs under high humidity conditions.

A novel Z-scheme heterojunction Fe-BDC/TiO2 for efficient photocatalytic degradation of acetaldehyde

Constructing heterojunction structures is considered one of the effective methods to improve the activity of photocatalysts. A novel Z-Scheme heterojunction Fe-BDC/TiO2 was designed and synthesized by amorphous gel Fe-BDC and TiO2 nanoparticles with electrostatic self-assembly method. The introduction of Fe-BDC has been proved to expand the light absorption range and promote the separation and transfer of interface photo generated electrons and holes. Thus, the photocatalytic degradation efficiency of acetaldehyde by 5% Fe-BDC/TiO2 sample is 2.3 times than that of pure TiO2 sample. And the reaction rate is 2.5 times than that of pure TiO2 sample. The free radical capture experiment shows that O2− played a more important role in the degradation of acetaldehyde. In addition, in situ infrared analysis further reveals the surface species of the photocatalysts during adsorption and degradation processes. The acetaldehyde degradation route of Fe-BDC/TiO2 has been speculated. ‘1These findings provide valuable references for the design of metal oxide semiconductor/Fe based MOF heterojunctions and the efficient degradation of aldehyde VOCs.

S-scheme construction boosts highly active self-supporting CeO2/Cu2O photocatalyst for efficient degradation of indoor VOCs

Photocatalyst-governing degradation of VOCs emitted from household products is promising due to its high performance and long-term durability. In this study, unique hierarchical CeO2/Cu2O nanowire arrays with S-scheme construction grow on a Cu mesh through a simple wet chemical method. Abundant oxygen vacancies on CeO2 work as adsorption sites, and the effective separation of photogenerated carriers driven by built-in electric field in the S-scheme CeO2/Cu2O heterojunction generates mobile reactive oxygen radicals for oxidizing target VOCs. Spectra of Kelvin probe force microscopy (KPFM) reveal that the potential difference at the CeO2/Cu2O interface grows from 9 mV in dark to 29 mV under irradiation, demonstrating a powerful force for driving the migration of photoelectrons. Therefore, under simulated sunlight exposure, 50 ppm of toluene, xylene and formaldehyde can be completely degraded in 70, 50 and 6 min by 15 cm2 CeO2/Cu2O mesh, respectively. The elimination of actual indoor VOCs confirms the practicability of the self-supporting CeO2/Cu2O catalyst, which figures out new ideas for designing efficient photocatalysts for the removal of VOCs pollutants.

Enhancing catalytic oxidation of toluene over Ag/Co3O4 by regulating Ag-Co interaction

Tuning the interaction between Ag and its supporters has been well accepted as a desirable way that adjusting the physicochemical properties and the catalytic performance of Ag-based catalysts. In this work, an in-situ surface reaction strategy was proposed to prepare high-performance Ag/Co3O4 catalyst by controlling the Ag-Co interaction for the purpose of efficient degradation of aromatic VOCs. The results of characterizations confirmed that the unique surface reaction strategy was conducive to anchoring Ag on the surface of Co3O4 and significantly enhanced Ag-Co interaction, as a result, Co-O bond was weakened by charge transfer between Ag and Co species, which showed great advantages in improving the reactivity of lattice oxygen species and in accelerating the adsorption of gaseous oxygen. Benefiting from this, 1%Ag/Co3O4-R synthesized by surface reaction method exhibited the best catalytic efficiency (T90 = 238 °C), excellent stability and admirable cyclic stability. In-situ DRIFTS spectroscopy investigation revealed that the loading of Ag remained unchanged reaction path of the catalytic oxidation of toluene, and benzoate was deemed a decisive stage in the oxidation course of toluene.

An effective strategy to improve the photothermocatalytic activity of Co3O4 for VOCs degradation: Specifically enhancing the surface lattice oxygen activity

Co3O4 catalysts with active surface lattice oxygen were constructed via a simple solvothermal method by adopting isopropyl alcohol (IPA) or tert-butyl alcohol (TBA) as solvent. The obtained Co3O4-IPA and Co3O4-TBA exhibit flower-like structures with (112) planes exposed on the surface. Due to abundant unsaturated Co3+ sites existing on the (112) plane, the content and activity of surface lattice oxygen on Co3O4-IPA and Co3O4-TBA are much higher than that on Co3O4-MA and Co3O4-EA, which prepared with methyl alcohol or ethyl alcohol as a solvent. The robust surface lattice oxygen on Co3O4-IPA and Co3O4-TBA facilitates the ring-opening process during photothermocatalytic oxidation of toluene, significantly promoting the catalytic performance. In the static atmosphere, about 98% of toluene conversion and 80% of CO2 yield can be achieved on Co3O4-IPA and Co3O4-TBA under full-spectrum light irradiation of 325 mW/cm2, much higher than 89% and 73% of conversion, 50% and 26% of CO2 yield on Co3O4-EA and Co3O4-MA, respectively.

3D snowflake graphene modified α-MnO2 Catalyst: Enhancing the Low-Temperature catalytic activity for VOCs degradation

Manganese oxide is a promising catalyst for volatile organic compounds oxidation with merits of low cost, abundant valence states, diverse crystal forms and morphology, however, its catalytic activity at low temperature (<200 °C) is limited due to the poor dispersion and inferior electron transfer. To solve these problems, a novel 3D snowflake graphene is doped into α-MnO2 to fabricate rGO@α-MnO2 catalyst to enhance the catalytic activity at low temperature. Compared with α-MnO2, the rGO@α-MnO2 catalysts present larger specific surface area and pore volume, which facilitates the adequate contact reaction between active component and VOCs. The unique graphene electronic bridge promotes the electron transfer on rGO@α-MnO2, which results in higher concentration of surface defects and more surface adsorbed oxygen to the catalyst. The performance tests show that the catalyst doped with 4% 3D snowflake graphene has the best activity, which can achieve 90% toluene conversion at 155 °C, and even 100% toluene conversion with 80% CO2 selectivity at 200 °C. In particular, 4%rGO@α-MnO2 demonstrates excellent catalytic stability and moisture resistance, presenting similar catalytic performance after 5 cycles for both the dry and high relative humidity (RH = 85%) conditions. The excellent activity of 4%rGO@α-MnO2 can be attributed to the enhancement of toluene adsorption energy after graphene doping and the defect induced by the interface effect between graphene and (211) facet. In general, 3D snowflake graphene doping provides a convenient and cost-effective method to enhance the low-temperature activity of the α-MnO2 catalyst, presenting great application potential.

An ultra-long stability of lanthanum (La) modified molecular sieve for catalytic degradation of typical sulfur-containing VOCs in a near-real environment

The catalytic degradation of typical sulfur-containing VOCs, ethyl mercaptan (C2H5SH), in a near-real environment remains a challenge task. In this study, an ultra-long stability of 600 h for degradation of C2H5SH was obtained over La doped ZSM-5, and the corresponding catalytic performance, reaction and deactivation mechanism were investigated by a series of ex situ and in situ characterizations. Furthermore, the influence law of other low-carbon mercaptans, such as methyl mercaptan (CH3SH), propyl mercaptan (C3H7SH), and butyl mercaptan (C4H9SH) as well as the moisture on their stability were investigated. The slight deactivation by designed experiment revealed a distinguished reversible moisture-induced deactivation mechanism, where moisture promoted the formation of carbonate related species that covers the active sites, while this deactivation could be recovered by a simple temperature-lifting strategy. This work provides a theoretical guidance for catalytic degradation of mixed sulfur-containing VOCs under the presence of moisture.

Fe(II)/LXQ-10 bifunctional resin materials for boosting synergistic adsorption/oxidation of benzene in industrial waste gas.

A series of adsorption/oxidation bifunctional material with different Fe(II) loading amounts was prepared by using ultrahigh crosslinking adsorption resin (LXQ-10) as a carrier and FeCl2 as an impregnating solution. The bifunctional material was characterized by BET, SEM, XRD, XPS, and EPR. The effects of Fe loading, reaction temperature, and space velocity on benzene adsorption efficiency were investigated using self-made experimental equipment to explore the optimal reaction condition. The adsorption results were fitted and analyzed by using four typical models: the quasi-first-order kinetic model, the quasi-second-order kinetic model, Elovich's kinetic model, and the Weber and Morris kinetic model. The quasi-first-order kinetic model had the highest R2 value (0.998) and the best applicability. The fitting effect of the Freundlich equation (R2 = 0.997) was better than that of the Langmuir equation (R2 = 0.919). Furthermore, the effects of Fe loading, H2O2 concentration, benzene inlet concentration, and temperature on the catalytic oxidation efficiency of benzene were studied. The catalytic oxidation efficiency of 3-Fe(II)/LXQ-10 was maintained at about 95% at a temperature of 303 K and an H2O2 concentration of 150 mmol/L. Compared with the adsorption efficiency, the catalytic oxidation efficiency of bifunctional resin materials in a heterogeneous Fenton system was remarkably improved and had excellent stability. A possible migration and transformation path during benzene removal was proposed according to the results of the analysis of GC-MS intermediates. This study provided a novel process for the adsorption and oxidative degradation of VOCs.

Unraveling a trade-off between positive effect and poisoning mechanism of soot over low-dose PtCu/CeO2 for simultaneously photothermocatalytic removal of VOCs and soot

It is challenging for simultaneous removal of VOCs and soot as soot would aggravate coke formation, and the lack of a deep understanding of pollutant effect on catalyst textural properties seriously limit its application. Herein, efficiently photothermocatalytic simultaneous removal of VOCs and soot was achieved by optimizing coke resistance and Pt utilization of PtCu/CeO2 through alloy modification and oxygen vacancy engineering. The findings of our combined experimental and computational study on catalytic process unravel a trade-off between positive effect and poisoning mechanism of soot, as follow: the unique photothermal properties and enhanced VOCs adsorption of soot accelerate VOCs degradation, while partially degraded soot passivate surface-active site of PtCu/CeO2 and weaken OH/O2 adsorption, thus suppressing VOCs mineralization. These new insights into the interfacial mechanism will provide a promising strategy to catalytic performance optimization and practical application.

Biodegradation characteristics of mixed phenol and p-cresol contaminants from a swine farm using bacteria immobilized in calcium alginate beads

Phenol and p-cresol, major odorous gases in swine farms, pose significant health risks and require efficient elimination. This study screened biofilm-derived bacteria from a local swine farm for effective phenol and p-cresol degradation. Isolated bacteria were exposed to 1000 ppm of phenol and p-cresol and cultivated in Mineral salts medium (MSM). Morphology, degradation characteristics, and 16S rRNA analysis were employed for identification. The isolate Proteobacteria and Actinobacteria, completely degraded phenol and p-cresol in water, up to 500 ppm, within 12 h. The mixtures of Proteobacteria and Actinobacteria eliminated 500 ppm of each compound within 28 h. Additionally, immobilized bacteria in calcium alginate beads exhibited reusable degradation activity for at least 5 cycles, with no decline in performance or bacterial loss. and no bacterial loss. This study highlights the potential of these bacterial strains and immobilization technique for effective VOC degradation in swine farm environments, improving odor control and environmental well-being.

Improving Indoor Air Quality through Standardization

Human beings experience a large fraction of their exposure to air pollutants in indoor environments. Air pollution is a large environmental health risk, and exposure to ambient air pollution and indoor air pollution contribute equally to the total number of fatalities worldwide. Although legislative authorities have established limit values for ambient outdoor air and stack emissions, there are inconsistent and variable national and regional limit values for gaseous substances and airborne particulate matter in the built environment (schools, homes, healthcare facilities, offices, and other public spaces). This lack of regulation is unsurprising, because indoor spaces are characterized by complex air chemistry, and their construction materials and types of activities vary significantly. The current understanding of indoor pollutants, including short-lived oxidants, degradation of VOCs, particle formation, and particle composition, is incomplete. It is necessary to identify and assess emerging pollutants and their toxicity, and to consider new consumer products and green construction materials and their impact on indoor air quality (IAQ). Learning from IAQ surveys and audit protocols, research methodologies should be regularized for cross-research comparisons. Some indoor air quality guidance and standards have been written, and several more are in development, with the international ISO 16000 series of indoor standards leading the way for improving indoor air data quality. The WHO has established some ambient air limit values which can mostly be translated into indoor limit values. The built environment needs to harmonize energy efficiency, thermal comfort and air quality standards and guidance. In this review, we discuss the next steps for improving international, regional and national standards and guidance, leading to better and more complete indoor air quality regulations.

Efficient process of VOC degradation from the high airflow in conical fluidized photocatalytic reactor by mesoporous C-N doped -ZnO powder under visible light

Mesoporous carbon–nitrogen, doped ZnO powders were synthesized from the zeolite imidazolate framework (ZIF-8) by a facile thermal decomposition in the atmosphere of nitrogen and air, respectively. The prepared material was used as the photocatalyst in a conical fluidized photocatalytic reactor under visible light irradiation for degradation of acetaldehyde (as a model molecule of indoor volatile organic compounds). The synthesized samples were characterized by DRS, BET, EDAX, FTIR, XRD, TGA, and FESEM analysis. DRS analysis revealed that the absorption edge of the prepared samples from ZIF-8 was significantly shifted to the visible range. The band gap and absorption edge of the bare ZIF-8 was changed from 5.1(eV) and 243(nm), respectively, to almost 3(eV) and 400 (nm) in the prepared C-N doped ZnO. FTIR analysis confirmed the existence of carbon and nitrogen in the surface of the prepared material. The N2 adsorption–desorption analysis revealed the IV-type isotherm confirming mesoporous structure with improved specific pore volume. The photocatalytic activity of the samples was evaluated from the airflow polluted with a trace amount of acetaldehyde, under an alkali metal halide lamp in the conical fluidized reactor, and the outlet flow was analyzed by the online GC versus the time. According to the results, all samples exhibited significant photocatalytic activity compared with the bare ZIF-8, and commercial ZnO powder. Almost 90% acetaldehyde removal occurred by the sample prepared by N2 thermal decomposition of ZIF-8 at 600 °C for 120 min, followed by air annealing at 450 °C for 90 min. Subsequently, the reaction rate was investigated and modeled on the base of Langmuir-Hinshelwood type equation as a function of acetaldehyde concentration and light intensity.

Critical role of reactive species in the degradation of VOC in a plasma honeycomb catalyst reactor

This paper reports the nature of the reactive species formed and their role in the degradation of methyl ethyl ketone (MEK) using plasma catalysis in a honeycomb monolith reactor. A series of experiments were performed using plasma with different discharge gases (i.e., N2, O2, or air) in the presence of the honeycomb catalyst. A novel method is introduced to identify the reactive species that form during the plasma process and their contribution. We found the role of O atoms to be dominant compared with that of other reactive species in the plasma catalytic removal of MEK. In addition, the effect of introducing O3 over the catalyst surface was investigated, with oxygen activation resulting from surface chemisorption mainly contributing to MEK oxidation. Analysis of the byproducts enabled us to propose possible reaction mechanisms for the oxidation of MEK in the air plasma catalytic reactor.