VOC Degradation Research Articles

Photothermal Catalytic Degradation of VOCs: Mode, System and Application.

Human production and living processes emit excessive VOCs into the atmosphere, posing significant threats to both human health and the environment. The photothermal catalytic oxidation process is an organic combination of photocatalysis and thermocatalysis. Utilizing photothermal catalytic degradation of VOCs can achieve better catalytic activity at lower temperatures, resulting in more rapid and thorough degradation of these compounds. Photothermal catalysis has been increasingly applied in the treatment of atmospheric VOCs due to its many advantages. A brief introduction on the three modes of photothermal catalysis is presented. Depending on the main driving force of the reactions, they can be categorized into thermal-assisted photocatalysis (TAPC), photo-assisted thermal catalysis (PATC) and photo-driven thermal catalysis (PDTC). The commonly used catalyst design methods and reactor types for photothermal catalysis are also briefly introduced. This paper then focuses on recent developments in specific applications for photothermal catalytic oxidation of different types of VOCs and their corresponding principles. Finally, the problems and challenges facing VOC degradation through this method are summarized, along with prospects for future research.

Simultaneous Catalytic Oxidation of Benzene and Toluene over Pd-CeZrOx Catalysts

Since actual industrial emissions contain a wide range of volatile organic compounds, studies into the simultaneous catalytic degradation of multi-component VOCs are essential. This work developed Pd-CeZrOx samples for the simultaneous elimination of benzene and toluene. Firstly, CeZrOx supports were synthesized using several methods (co-precipitation, CTAB template co-precipitation, and sol–gel method). Pd active species were then added into the 1.0Pd-CeZrOx samples using the impregnation procedure. XRD, BET, NH3-TPD, Raman, EPR, XPS, and H2-TPR were utilized to analyze the as-prepared Pd-CeZrOx samples. The catalytic performance tests reveal that the performance of 1.0Pd-CeZrOx-CTAB outperforms that of 1.0Pd-CeZrOx-PM and 1.0Pd-CeZrOx-CASG, and 1.0Pd-CeZrOx-CTAB displays superior catalytic activity for both benzene and toluene oxidation. The improved redox properties, the abundant surface oxygen vacancies, and the surface Pd2+ species of the 1.0Pd-CeZrOx-CTAB sample may be responsible for the simultaneous degradation activity of benzene and toluene.

Synthesis of Heteromorphic Bi2WO6 Films With an Interpenetrate 1D/2D Network Structure for Efficient and Stable Photocatalytic Degradation of VOCs.

2D layered Bi2WO6 (BWO) is a widely used attractive photocatalyst for degrading VOCs, but the low visible-light utilization and the easy stacking 2D nanosheets(NSs) limit photocatalysis efficiency and stability. Here, inspired by Eucalyptus, a synergistic strategy of multiscale domain-confinement and electrostatic force action, based on electrospinning is proposed, for fabricating a heteromorphic BWO photocatalyst. It is found that BWO NSs can grow radially in an orderly spaced arrangement along BWO nanofibers (NFs) during sintering, thereby forming 1D/2D BWO junctions like eucalyptus leaves. This interpenetrating 1D/2D network structure not only solves the easy stacking problem of BWO NSs but also selectively exposes the {010} crystal planes that exhibit efficient hole oxidation. In addition, this peculiar structure enriches electrons at the 1D/2D interface to avoid carrier recombination, thus improving the photocatalytic activity. The photocatalyst material with a reduced bandgap width from 2.56 to 2.49eV can rapidly degrade 100% of acetaldehyde under visible light without using sacrificial agents and photosensitizers and shows superior stability for eight cycles without any decay. This study provides a feasible method to synthesize an efficient and stable BWO photocatalyst.

Construction of Z-scheme g-C3N4/Al:SrTiO3 heterojunction for enhanced VOCs degradation in asphalt through pyroelectric and photocatalytic coupling

The semiconductor photocatalysts are promising in the degradation of volatile organic compounds (VOCs) but limited by its poor light absorption ability and rapid recombination of photogenerated carriers. In this regard, the heterojunction composites composed of graphitic carbon nitride (CN) and Al-doped BaTiO3 (Al:STO) were constructed and its pyro-photocatalytic coupling degradation performance and mechanism of VOCs in asphalt were investigated in this study. The results show that the presence of a temperature difference outside triggers polarization potential on both sides of the pyroelectric Al:STO and induces built-in electric field, which can drive photogenerated electrons and holes to migrate to different polar domains and inhibit their recombination. The constructed CN/Al:STO heterojunctions significantly improve the separation efficiency of photogenerated carriers. The abundant hydroxyl groups generate on the surface of the heterojunction hybrids as reaction intermediate to enhance the degradation rate of VOCs. When the mass ratio of Al:STO to CN is 1:1, the degradation efficiency of VOCs can reach 72.05 % at 50 min. Besides, the temperature sweep test results demonstrate that the addition of this composite material enhances the rutting resistance of asphalt. This study presents the utilization of heterojunction composites as filler in asphalt for enhanced VOCs degradation during mixing and service.

Fabrication of core–shell Fe3O4@SiO2/graphite catalyst to improve the charge separation for enhanced photocatalytic toluene oxidation

Magnetite (Fe3O4) has been regarded as a potential photocatalyst for VOCs degradation. Nevertheless, the magnetism of Fe3O4 always leads to the aggregation of particles, which is adverse for gaseous VOCs degradation. Meanwhile, the fast charge recombination of Fe3O4 seriously limits the photocatalytic activity. Herein, a layer of SiO2 was coated on the surface of Fe3O4, and Fe3O4@SiO2 particles were combined with graphite to prepare the core–shell catalyst for photocatalytic toluene oxidation. Fe3O4@SiO2/G catalyst showed the toluene degradation efficiency of 85.09%, which was 3.2 and 1.3 times than those of Fe3O4 and Fe3O4/G. The coating of SiO2 prevented the aggregation of Fe3O4 and greatly enhanced the specific surface area. Experimental and theoretical calculation proved that the existence of SiO2 promoted the spatial charge separation and inhibited the charge recombination, resulting in the generation of abundant reactive oxygen species. These findings offered an insight into the catalyst design for photocatalytic VOCs oxidation.

Visible-light responsive photocatalytic fuel cell with gas-diffusion g-C3N4/TiO2 heterojunction photoanode for simultaneously degrading VOCs and generating electricity

The use of a gas diffusion photoanode for a photocatalytic fuel cell is promising to simultaneously degrade VOCs and generate electricity. However, conventional gas-diffusion photoanode faces the issues of inefficient solar energy utilization and serious electron-hole recombination. Herein, a visible-light-responsive gas-diffusion g-C3N4/TiO2 heterojunction photoanode is developed for simultaneous degradation of toluene and generation of electricity. In addition to the intrinsic feature of reduced mass transfer resistance of VOCs to the photocatalytic surface, such a gas-diffusion photoanode not only extends the photo-response spectrum, but also enhances charge separation. Accordingly, the photocatalytic fuel cell with the newly-developed photoanode demonstrates superior discharging performance and toluene removal efficiency over the gas-diffusion TiO2 and g-C3N4 photoanodes. The maximum power density achieved by the gas-diffusion g-C3N4/TiO2 heterojunction photoanode is 0.0375 mW/cm², while the maximum toluene removal efficiency reaches 43.8 %. This study has promoted the development of photocatalytic fuel cells for the degradation of VOCs and electricity generation.

Insight into the degradation mechanism of mixed VOCs oxidation over Pd/UiO-66(Ce) catalysts: Combination of operando spectroscopy and theoretical calculation

Herein, Pd/UiO-66(Ce) catalysts were successfully synthesized by N2H4, H2, and NaBH4 reduction methods with UiO-66(Ce) as support. The best catalyst was selected via utilizing o-xylene as the probe molecule, and its degradation performance of mixed VOCs was further investigated. It was found that the reduction methods greatly influenced the size of Pd nanoparticles, the state of surface Pd, and the support structure in the catalysts, which in turn affected their catalytic performance. Among them, Pd/UiO-66(Ce)-Na exhibited the best o-xylene degradation activity (T90 = 192 °C) due to its smaller average Pd particle size (Pd Average = 2.93 nm) and higher surface Pd0 content (Pd0/Pdtotal = 0.79). The performance and interaction of Pd/UiO-66(Ce)-Na catalyst for degradation of mixed VOCs (o-xylene and toluene/benzene) were investigated by DFT adsorption energy calculation, in situ DRIFTS and GC–MS. Results suggested that the single adsorption energy of o-xylene was −1.20 eV, while in the system with toluene/benzene, the adsorption energy decreased to −0.78 and −0.6 eV, respectively. This showed the competitive adsorption effect between benzene and o-xylene was stronger than that between benzene and o-xylene. Finally, combined with in situ DRIFTS and GC–MS, the degradation path of mixed components was analyzed and studied systematically, and the mechanism of intermolecular interaction of benzene in the degradation process of mixed components was further revealed.

Effect of NH2-functionalization of MIL-125 on photocatalytic degradation of o-xylene and acetaldehyde

Ligand functionalization of metal organic framework (MOF) is a great important strategy to enhance the various properties of pristine materials. In this study, MIL-125 with different extents of NH2-functionalization were synthesized by solvothermal method. The photocatalytic degradation efficiency of the optimal sample for o-xylene and acetaldehyde were 88 % and 49 %, respectively, which were much improved compared to pristine MIL-125 (56 % for o-xylene and 3 % for acetaldehyde). Compared to pristine MIL-125, NH2-functionlized MIL-125 were more easily photoexcited to form photogenerated carriers, which facilitated the formation of more OH and O2− radicals under visible light irradiation. In addition, NH2 groups as the adsorption site interacted with o-xylene and acetaldehyde by the H-bonding and the Lewis acid-base effect, respectively. The above results contribute to a deep understanding of the influence of ligand functionalization of MOF on the photocatalytic degradation of VOCs.

Investigation of Mn–Co oxides loaded ceramic structured catalyst for microwave enhanced catalytic degradation of benzene

Compared with traditional heating, microwave heating has unique advantage and can enhance the chemical reaction. It is a promising technology for catalytic degradation of VOCs gas. Here we prepared a structured catalyst (Mn–Co/SiC) suitable for VOCs degradation under microwave. The catalyst shown excellent stability under microwave heating and microwave empowered the catalyst with good water resistance. Microwave heating exhibits high energy efficiency. Density functional theory is employed to investigate the microwave-enhanced catalytic degradation of VOCs. The theoretical calculation results indicate that the adsorption energy is more negative under microwave electric field, suggesting that microwave electric field is conducive to the activation of benzene. The electrons on the adsorption surface of the catalyst are redistributed to different degrees under the action of different microwave electric fields, thus affecting the activation of adsorbed molecules and chemical reaction process. The local density of states further reveals that electric fields may facilitate the electron transport.

Light induced degradation of CIGS solar cells

Considering warranted lifetimes of PV modules of typically 20-30 years, the performance stability of PV modules is one of the most crucial factors regarding power generation and yield. Long term outdoor performance studies depict realistic operation conditions best, but the correlated nature of e.g. irradiance and temperature impedes the physical interpretation. The possibility to control and tune the conditions in laboratory experiments enables to decompose effects, that are typically overlayed in outdoor experiments. This way, laboratory are crucial to interpret the results obtained in outdoor degradation studies. One driving force of degradation of CIGS modules is light exposure. In literature the focus of light induced degradation (LID) of CIGS modules and solar cells is on metastable changes analyzed on time scales ranging from minutes to hours. In this work we expose industrially produced encapsulated CIGS solar cells for more than 1000 h to light with varied intensity under varied temperature conditions. Such, we aim to study temperature and light intensity dependencies of the observed performance changes. Furthermore, we study the influence of applied bias by comparing LID at short and open circuit. We demonstrate that LID under short circuit conditions leads to VOC degradation, while being temperature assisted and not dependent on the irradiance intensity. CIGS solar cells kept at open circuit conditions appear to be stable under illumination. Exploiting the one diode model, we further connect the observed temperature assisted performance loss to enhanced recombination with lower ideality factor, in comparison to the dominant recombination process before degradation.

Construction of hollow sphere MnOX with abundant oxygen vacancy for accelerating VOCs degradation: Investigation through operando spectroscopycombined with on-line mass spectrometry

To clarify the key role of oxygen vacancy defects on enhancing the oxidative activity of the catalysts, metal–organic frameworks (MOFs) derived MnOX catalysts with different morphologies and oxygen vacancy defects were successfully prepared using a facile in-situ self-assembly strategy with different alkali moderators. The obtained morphologies included three-dimensional (3D) triangular cone stacked MnOX hollow sphere (MnOX-H) and 3D nanoparticle stacked MnOX nanosphere (MnOX-N). Compared to MnOX-N, MnOX-H exhibited higher activity for the oxidation of toluene (T90 = 226 °C). This was mainly due to the large number of oxygen vacancy defects and Mn4+ species in the MnOX-H catalyst. In addition, the hollow structure of MnOX-H not only facilitated toluene adsorption and activation of toluene and also provided more active sites for toluene oxidation. Reaction mechanism studies showed that the conversion of toluene to benzoate could be realized over MnOX-H catalyst during toluene adsorption at room temperature. In addition, abundant oxygen vacancy defects can accelerate the activated oxidation of toluene and the formation of oxidation products during toluene oxidation.

Flexible Ag-AgCl/TiO2/cellulose biocomposite film for solar photocatalytic degradation of VOCs

Photocatalyst immobilization on biopolymers presents a promising avenue for air purification, yet achieving efficient immobilization and purification methods remains a challenge. In this study, we develop a novel, straightforward sequential coating technique to fabricate cellulose film embedded with uniformly dispersed TiO2 submicrospheres and Ag-AgCl nanoparticles (NPs), tailored for effective indoor air purification under sunlight exposure. The obtained Ag-AgCl/TiO2/cellulose film exhibit remarkable photocatalytic prowess in degrading various volatile organic compounds (VOCs, including ethanol, 1-propanol, 1-butanol, propylamine, and propanethiol) under simulated sunlight, owing to the enhanced separation of charge carriers facilitated by the presence of plasmonic Ag-AgCl NPs. Notably, the nature of the functional groups and the carbon atom count within the VOCs molecular structures exert significant influence on the overall photocatalytic performance. Furthermore, our investigation into the reusability of this biocomposite film confirms its durability, particularly in mineralizing alcoholic compounds during VOC oxidization, and the deactivation primarily occurs with VOCs containing heteroatoms that can be residual on biocomposite surface. This study represents a significant step towards practical applications of biocomposite films with efficient photocatalytic activities for real-world air purification and environmental remediation.

Visible Light Photocatalytic Degradation of Several VOCs (Ethyl Acetate, 2-Propanol, and Benzene) Over a Graphene/ZnO Composite

Visible Light Photocatalytic Degradation of Several VOCs (Ethyl Acetate, 2-Propanol, and Benzene) Over a Graphene/ZnO Composite

Oxygen-deficient WO3 for stable visible-light photocatalytic degradation of acetaldehyde within a wide humidity range

Indoor VOCs pollution has attracted broad attention for its harm to mankind’s health recent years. Photocatalytic degradation of indoor VOCs holds great prospects in addressing these health concerns in daily life. However, traditional photocatalysts have a large recombination rate of charge carriers and a decrease of the photocatalytic degradation efficiency under high relative humidity. Herein, uniform tungsten oxide nanoparticles with enriched oxygen vacancies (WO3-U) were synthesized by a direct annealing method with urea addition, which exhibited superior performance in the visible-light photocatalysis. The reaction rate constant value of photocatalytic acetaldehyde degradation over WO3-U catalyst was above 3 times higher than that of pristine WO3 sample. More importantly, the WO3-U catalyst maintained stable and excellent photocatalytic performance at relative humidity range of 25–100 %. Except for the enhanced photogenerated charges separation, abundant oxygen vacancies could effectively accelerate O2 activation to generate •O2−, which accounted mainly for the initial conversion of acetaldehyde. Then the subsequent transformation of •O2− into •OH to promoted the final mineralization of acetaldehyde. In addition, the presence of oxygen vacancies also facilitated H2O dissociation to form surface hydroxyl groups, which increased the adsorption of acetaldehyde, resulting in the consistent photocatalytic performance of WO3-U catalyst within a wide humidity range. This work provides guidelines to design visible-light responsive photocatalysts with efficient activity at high humidity conditions for indoor VOCs degradation.

Synthesis of tungsten iron-oxide zeolite composites and their catalytic degradation in VOC from rubber powder modified asphalt

Tungsten iron-oxide zeolite composites with different Fe and W loadings were synthesized over NaY zeolite supports using a wet impregnation method. The composites exhibited suitable textural properties, light absorption, redox sites and acidity for photocatalytic VOC degradation. The photocatalytic activity for degrading acetaldehyde and o-xylene VOCs emitted from rubber powder modified asphalt was evaluated under solar irradiation. The 5Fe-10 W-NaY(2.8) composite achieved the highest VOC removal of 80% for acetaldehyde and 76% for o-xylene after 6 hours. Increasing Fe and W loading up to 5 wt% and 10 wt%, respectively, significantly enhanced the VOC degradation efficiency. Higher zeolite content and stronger acidity also boosted the photocatalytic performance. The degradation occurred via redox mechanisms involving photo-generated electrons, holes and reactive oxygen species, facilitated by the zeolite acid sites. The 5Fe-10 W-NaY(2.8) composite exhibited good stability over 5 reuse cycles, indicating its potential for mitigating VOC emissions from rubber powder modified asphalt pavements.

Carbon-supported g-C3N4 photocatalyst for the treatment of vapor isobutanol as odorous VOC

Graphitic carbon nitride (g-C3N4) is a metal-free photocatalyst active under visible light but exhibits low photocatalytic activity due to its low specific surface area and fast recombination rates. However, it is possible to enhance its effectiveness and performance can be significantly improved by preparing composites of g-C3N4 with activated carbon (AC). In this manuscript, agave bagasse was employed as a precursor for activated carbon ranging from relatively low, medium and high porosity. The ability of the g-C3N4/activated carbon composite to degrade isobutanol as a model odorous VOC was evaluated under visible light. Different activation/deactivation phenomena were observed at different operation times. It was found that materials with higher porosity presented a higher level of degradation of the model VOC. However, synergy between the materials was demonstrated for the dynamic removal of isobutanol. These results demonstrate the synthesis of a composite with photocatalytic and adsorption properties based on g-C3N4 supported on activated carbon obtained from agave bagasse, which could contribute to the development of green photocatalytic materials and serve as an alternative for managing waste from the tequila industry.

Co3O4‐Based Catalysts for the Low‐Temperature Catalytic Oxidation of VOCs

AbstractVolatile organic compounds (VOCs) are a significant source of environmental pollution, posing threats to human safety. With growing concerns about environmental degradation, catalytic oxidation technology emerges as a paramount and widely adopted approach for VOC elimination, renowned for its operational simplicity, energy efficiency, and environmental friendliness. As a representative transition metal catalyst, cobalt‐based catalysts have garnered widespread use in VOC catalytic oxidation due to their cost‐effectiveness, versatility, and distinctive physicochemical properties. This paper provides a detailed exposition of the construction strategies and structure‐activity relationship of Co3O4‐based catalysts in VOCs oxidation reaction, encompassing both monometallic Co3O4 and multimetallic cobalt‐based catalysts. Furthermore, it offers a comprehensive summary and discussion of the latest research progress concerning Co3O4‐based catalysts in practical applications. Concluding with a meticulous analysis, the paper addresses the technical challenges inherent in developing Co3O4‐based catalysts for VOCs degradation. Additionally, it proposes research directions aimed at overcoming these challenges, contributing to the ongoing discourse on environmental sustainability.

Modulating the steric effect over high-index facet of MnOx catalysts to enhance toluene oxidation

Engineering surface structures of metal-oxide catalysts are of utmost significance for boosting their catalytic performances. In this work, we reported the high-index (310) facets catalysts (MnOx-AAUS) with oxygen vacancies for VOCs degradation, which was synthesized via an ultrasonic-assisted redox precipitation process. Interestingly, the excellent catalytic performance of MnOx-AAUS catalysts was due to the steric effect between high-index facet with reactants and the simultaneous adsorption-activation of toluene and gaseous oxygen on the high-index (310) facets with oxygen vacancies. The T90% value of the (310) facets catalysts (600 ppm toluene, GHSV = 60,000 mL/g·h, 21 % O2/N2) was significantly lower than that of the previous (001) facets catalysts. Density functional theory (DFT) calculations, along with in-situ FT-IR spectra, revealed that the tilted adsorption configuration of toluene was conducive to simultaneous reaction with the surrounding activated oxygen species. Such the adsorption configuration of toluene/oxygen contributed to the substantially enhanced catalytic activity of the MnOx-AAUS catalyst for VOCs oxidation. This work provides new insights into the roles of high-index facets with oxygen vacancies of MnOx catalysts in the toluene oxidation and paves new avenues for the rational design of highly efficient catalysts for oxidation reactions.

Efficient Photothermal Catalytic Oxidation Enabled by Three-Dimensional Nanochannel Substrates.

Photothermal catalysis exhibits promising prospects to overcome the shortcomings of high-energy consumption of traditional thermal catalysis and the low efficiency of photocatalysis. However, there is still a challenge to develop catalysts with outstanding light absorption capability and photothermal conversion efficiency for the degradation of atmospheric pollutants. Herein, we introduced the Co3O4 layer and Pt nanoclusters into the three-dimensional (3D) porous membrane through the atomic layer deposition (ALD) technique, leading to a Pt/Co3O4/AAO monolithic catalyst. The 3D ordered nanochannel structure can significantly enhance the solar absorption capacity through the light-trapping effect. Therefore, the embedded Pt/Co3O4 catalyst can be rapidly heated and the O2 adsorbed on the Pt clusters can be activated to generate sufficient O2- species, exhibiting outstanding activity for the diverse VOCs (toluene, acetone, and formaldehyde) degradation. Optical characterization and simulation calculation confirmed that Pt/Co3O4/AAO exhibited state-of-the-art light absorption and a notable localized surface plasmon resonance (LSPR) effect. In situ diffuse reflectance infrared Fourier transform spectrometry (in situ DRIFTS) studies demonstrated that light irradiation can accelerate the conversion of intermediates during toluene and acetone oxidation, thereby inhibiting byproduct accumulation. Our finding extends the application of AAO's optical properties in photothermal catalytic degradation of air pollutants.

A novel CeO2 nanowire catalyst prepared by the freeze-drying method with significantly improved catalytic performance for toluene oxidation

A wire like CeO2 catalyst (CeO2-w) was obtained after the calcination of the precursor at 400 °C, which was prepared by the freeze-drying method for the first time. It shows good performance for catalytic oxidation of toluene with T90 of 220 °C, which is much better than the CeO2 catalysts with other structures prepared by the different methods. The good performance of CeO2-w is due to the bigger pore volume, more active oxygen species, more oxygen vacancies, better low temperature reducibility, higher surface area normalized reaction rates and lower Ea value. Additionally, the CeO2-w catalyst exhibits good water resistance and catalyst stability. In situ DRIFTS indicates the catalytic oxidation of toluene on CeO2-w undergoes the progress of toluene → benzaldehyde → benzoic acid → maleic acid → CO2 and H2O. This work affords a new idea to prepare high active CeO2 nanowire catalysts for catalytic oxidation of toluene, and open an efficient way for the construction of CeO2 based composite catalysts for VOCs degradation.