Smart and precise sensing is very important for the protection of both environment and personal security in modern civilized society. There are numerous sensing devices for detecting physical and ...chemical changes such as temperature, humidity, pressure, and chemical species. In this regard, conducting polymers is at the core of attention for the fabrication of next-generation sensor applications. Polypyrrole (PPy), is one of the emerging intelligent materials with a wide range of applications in the field of optical, electronic, and electrochromic devices and sensors. The stability in a different environment, ease of deposition from aqueous and non-aqueous media, adherence to diverse substrates, and high electrical conductivity made PPy a unique choice for sensor development. In recent years, PPy has proven an excellent candidate for sensing volatile organic compounds (VOCs) due to its selectivity and sensitivity towards target gas molecules, and detection of inorganic gases and VOCs. Consequently, to develop outstanding sensing devices attempts have been dedicated to developing PPy-based sensors for excellent mechanical and electrochemical performance. This review aims to provide a recent overview of progress in PPy-based advanced sensing devices. This review aims to provide a recent overview of progress in PPy-based advanced sensing devices. We have systematically discussed the challenges and future development of various sensing devices. Furthermore, the current understanding and performance evaluation of gas sensing mechanisms in PPy-based sensors are discussed theoretically and experimentally. We have also identified gaps in the state-of-the-art and hope that this study would lead to further research works into using PPy to make gas sensors. Finally, the future directions of various sensors with advanced PPy-based sensing systems have been prospected.
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•Polypyrrole (PPy) was an excellent candidate for capturing a broad range of VOCs.•Doping, surface modification, side-chain selection, and PPy-chain-arrangements were reported.•The complementary roles of experimental and theoretical studies were clearly described.•Reported families of PPy and their current utilities were elaborated.•Gaps were identified both from fundamental and applied standpoints.
Allelopathy is an ecological phenomenon in which organisms interfere with each other. As a management strategy in agricultural systems, allelopathy can be mainly used to control weeds, resist pests, ...and disease and improve the interaction of soil nutrition and microorganisms. Volatile organic compounds (VOCs) are allelochemicals volatilized from plants and have been widely demonstrated to have different ecological functions. This review provides the recent advance in the allelopathic effects of VOCs on plants, such as growth, competition, dormancy, resistance of diseases and insect pests, content of reactive oxygen species (ROS), enzyme activity, respiration, and photosynthesis. VOCs also participate in plant-to-plant communication as a signaling substance. The main methods of collection and identification of VOCs are briefly summarized in this article. It also points out the disadvantages of VOCs and suggests potential directions to enhance research and solve mysteries in this emerging area. It is necessary to study the allelopathic mechanisms of plant VOCs so as to provide a theoretical basis for VOC applications. In conclusion, allelopathy of VOCs released by plants is a more economical, environmentally friendly, and effective measure to develop substantial agricultural industry by using the allelopathic effects of plant natural products.
Most of the volatile organic compounds (VOCs) and especially the chlorinated volatile organic compounds (Cl–VOCs), are regarded as major pollutants due to their properties of volatility, diffusivity ...and toxicity which pose a significant threat to human health and the eco-environment. Catalytic degradation of VOCs and Cl–VOCs to harmless products is a promising approach to mitigate the issues caused by VOCs and Cl–VOCs. Non-thermal plasma (NTP) assisted catalysis is a promising technology for the efficient degradation of VOCs and Cl–VOCs with higher selectivity under relatively mild conditions compared with conventional thermal catalysis. This review summarises state-of-the-art research of the in plasma catalysis (IPC) of VOCs degradation from three major aspects including: (i) the design of catalysts, (ii) the strategies of deep catalytic degradation and by-products inhibition, and (iii) the fundamental research into mechanisms of NTP activated catalytic VOCs degradation. Particular attention is also given to Cl–VOCs due to their characteristic properties of higher stability and toxicity. The catalysts used for the degradation Cl–VOCs, chlorinated by-products formation and the degradation mechanism of Cl–VOCs are systematically reviewed in each chapter. Finally, a perspective on future challenges and opportunities in the development of NTP assisted VOCs catalytic degradation were discussed.
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•Catalytic degradation of Cl–VOCs under NTP condition is systematically reviewed.•The different catalysts used in NTP for Cl-VOC control are covered.•Formation and control strategies of hazardous by-products are reviewed.•Techniques used for understanding the degradation mechanisms are reviewed.
The selective and sensitive detection of chemical agents is demanded by a wide range of practical applications. In particular, sensing of volatile organic compounds (VOCs) at parts-per-billion level ...is critical for environmental monitoring, process control, and early diagnosis of human diseases. In this report, we demonstrate a specific and highly sensitive detection of ketone compounds using two-dimensional (2D) molybdenum ditelluride (MoTe
). We investigated the effects of UV activation on the sensing performance to a variety of VOCs. It is found that the MoTe
field-effect transistor (FET) exhibits an opposite sensing response to ketone compounds before and after UV light activation, whereas the responses to other types of VOCs remain in the same direction regardless of the illumination. This unique behavior enables the discriminative detection of ketone molecules including acetone and pentanone from other VOCs in a gas mixture. The activation of UV light also results in a very high sensitivity and low detection limit toward acetone (∼0.2 ppm). Moreover, the MoTe
FET shows a stable sensing performance in a high humidity environment. The results demonstrate the potential of MoTe
as a promising candidate for high-performance acetone sensors in important applications such as human breath analysis. The scheme of light-tunable sensing can be applied to a broad range of sensing platforms based on 2D materials.
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•The VOCs adsorption performance of different adsorbents were summarized.•The controlling factors of VOCs adsorption on adsorbent materials were explored.•Methods for increasing the ...adsorption capacity were demonstrated.•ACs and MOFs are good adsorption materials for the reduction of VOCs emission.
Volatile organic compounds are harmful to the environment and human health. Adsorption technology has been used to VOCs abatement for over 30 years and has proven to be an effective technology. This work provides a critical review of the recent research developments of VOCs adsorption materials and the key factors controlling the VOCs adsorption process. The average specific surface area, pore volume and VOCs adsorption capacity of different adsorption materials are metal organic frameworks (MOFs) > activated carbons (ACs) > hypercrosslinked polymeric resin (HPR) > zeolites. The mechanism of VOCs adsorption in adsorbent mainly includes electrostatic attraction, interaction between polar VOCs and hydrophilic sites, interaction between non-polar VOCs and hydrophobic sites, and partition in non-carbonized portion. With the specific surface area, pore volume, and surface chemical functional groups increase and the pore size decreases, the adsorption capacity increases. The volume of narrow micropores (size < 0.7 nm) controls the adsorption of VOCs. In addition, methods of activation and surface modification for improving the adsorption capacity of VOCs are discussed. The development of targeted modified adsorption materials and new adsorption materials and reduction of production costs of adsorption materials are especially important in future research.
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•V-Cu bimetallic catalysts with different supports were developed.•V-Cu/TiO2 showed excellent activity of removing toluene and NOx simultaneously.•The formation of acidic sites and ...oxygen vacancies was promoted on V-Cu/TiO2.•The synergistic effect of Cu and TiO2 played a key role in the activation of O2−.•V-Cu/TiO2 showed prominent flue gas tolerance to SO2 and H2O.
It is a major challenge to achieve effective synergistic reduction of NOx and VOCs in coal-fired flue gas under complex working conditions. In this work, V-Cu bimetallic oxide catalysts with different supports were designed. V1-Cu5 bimetallic oxide supported on TiO2 showed significantly higher activity for simultaneous toluene oxidation and NOx reduction than that supported on ZSM-5, SiO2 and γ-Al2O3. Meanwhile, it exhibited excellent stability and anti-poisoning performance, and could block the formation of toxic polycyclic aromatic hydrocarbons in by-products. Compared with ZSM-5, SiO2 and γ-Al2O3, TiO2 as support was conducive to the formation of abundant acidic sites and oxygen vacancies. In addition, the strong interaction between the metal active sites and TiO2 accelerated the electron transfer from Cu to adsorbed O2, thus promoting the formation of active O2−. This work can provide guidance for the development of catalysts designed for the simultaneous catalytic removal of NOx and VOCs.
Developing efficient sensing materials with superior sensing capabilities of sensitive, fast, selective detection of volatile organic compounds (VOCs) is necessary for fields like environmental gas ...monitoring and non-invasive disease diagnosis. Recently, carbon nanotubes, graphene, MXene, and other carbon-based nanomaterials have been paid much attention for possible use as high-performance VOCs sensing materials due to unique physical structures and excellent electric properties. The tunability of the chemical character and surface properties of the carbon-based nanomaterials increases their potential in constructing selective sensors targeting VOCs gases. Besides, the mechanical flexibility of the carbon-based nanomaterials allows the new designs of gas sensing platforms and puts the carbon-based nanomaterials at the forefront of other sensing materials for wearable applications. In this review, we highlight the most recent progress of the carbon-based nanomaterials in the detection of VOCs gases with an emphasis on the available strategies for the construction of these VOCs gas sensors. These strategies are proved by addressing some representative paradigms, and their suitability in applications like environmental gas monitoring and non-invasive disease diagnosis is assessed. This review is intended to offer timely sources of information and provide insight for future research works on designing high-performance VOCs gas sensors by utilizing carbon-based materials.
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•Ball milling improved the physicochemical characteristics of biochar.•Ball-milled biochars showed enhanced adsorption of VOCs.•VOC adsorption onto ball-milled biochars was controlled ...by surface adsorption and partition mechanisms.•Adsorbed VOCs were completely desorbed from ball-milled biochars.
Hickory wood was pyrolyzed at 300 °C, 450 °C, and 600 °C to produce biochars, which were then modified by ball milling. The pristine and ball-milled biochars were used to remove volatile organic compounds (VOCs) including acetone, ethanol, chloroform, cyclohexane, and toluene. Compared with the corresponding pristine one, each ball-milled biochar showed significantly improved structural characteristics. Their specific surface area (SSA) increased by 1.4–29.1 times, average pore size (APS) decreased slightly, and the hydrophilicity and polarity were also enhanced according to the elemental analysis. The adsorption of VOCs by ball-milled biochar increased by 1.3–13.0 folds, and the maximum adsorption capacity of acetone was up to 103.4 mg/g. The adsorption of polar VOCs (acetone, ethanol, and chloroform) onto ball-milled biochars was mainly controlled by surface adsorption process, which was affected by the SSA, APS, and volatile organic matter of the biochars, as well as the properties of the VOCs. The adsorbed VOCs were completely desorbed from the ball-milled biochars at relatively low temperature (≤115.2 °C). Reusability experiments with five adsorption-desorption cycles showed that ball-milled biochar had an excellent reusability for all VOCs. Ball-milled biochars can therefore be used as an effective and regenerable adsorbent for the removal of VOCs.
Spatiotemporal change patterns of China's industrial VOCs emissions were explored in response to integrated air quality control policies during 2013–2019, and future emissions predicted under the two ...different scenarios targeting 2030. China's industrial VOCs emissions were decreased to 15.72 Tg in 2019, of which chemical industry, industrial painting, petroleum industry, coal-coking industry, and other industries respectively accounted for 31.0%, 23.9%, 15.6%, and 13.0%, 16.3%, after peaking at 16.40 Tg in 2016. VOC emissions from the petroleum industry and industrial painting showed a continuous increase, with emissions increasing by 0.46 Tg and 0.71 Tg. VOC emissions from the chemical industries increased by 0.91 Tg during 2013–2016 and decreased by 0.72 Tg during 2016–2019. Industrial VOCs emissions in the Beijing-Tianjin-Hebei, Shandong Peninsula, and Central Plain in 2019 respectively reduced by 12.0%, 3.2%, and 8.7% compared to 2013 due to stringent control measures and closure/relocation of highly polluting enterprises. By contrast, industrial VOCs emissions in the West Coast of the Strait and the Central Guizhou increased by 38.1% and 31.8% during 2013–2019. In summary, China's industrial high VOCs emission areas were shifting from key areas to its surrounding areas, resulting in little change in total VOCs emissions. The coal-coking industry, architectural painting, petroleum refining, and pharmaceutical industry will have the most considerable reduction responsibility to reduce VOCs emissions in the future. Guangdong, Jiangsu, Shandong, and Zhejiang will share the highest reduction responsibility, accounting for approximately 40% of national emission reduction.
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•Spatiotemporal trends of China's industrial VOCs were analyzed during 2013–2019•China's industrial VOCs showed decreasing after peaking at 2016 with 16 Tg emissions•High industrial VOCs emission area were shifting from key areas to surrounding areas•Coking and oil refining will have the largest reduction responsibility in the future
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