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A prototype air purifier (AP) module has been constructed using bismuth-doped titanium dioxide (Bix-P25: x(%) as Bi/Ti molar ratios of 1.1, 2.1, 3.3, 5.3, and 8.7). The reactive adsorption property of Bix-P25 materials is evaluated against H2S gas at a recirculation rate of 160 L min-1 in a 17 L closed chamber. The AP (Bi5.3-P25) exhibits superior performance against 10 ppm H2S in dry air under dark conditions (i.e., without light irradiation), with a removal efficiency (XH2S)= 99% in 5 mins, reaction kinetic rate (r (at X = 10%))= 7.3 mmol h-1g-1, and partition coefficient= 0.18 mol kg-1 Pa-1. As such, its superiority is evident over the reference AP (P25) filter with XH2S < 10%. The clean air delivery rate (CADR) of AP (Bi5.3-P25) increases noticeably from 9.9 to 17.8 L min-1 with increasing relative humidity (RH) from 0 to 80%, respectively. In contrast, the CADR decreases from 9.9 to 5.8 L min-1 as the H2S increases from 10 to 20 ppm. According to density functional theory (DFT), the presence of H2O vapor enhances the hydroxylation of Bix-P25 surface to promote H2S mineralization through the formation of TiS3 (i.e., thermodynamic reaction of S atom with the catalytic surface). Complete removal of H2S on the Bi5.3-P25 surface is also confirmed consistently through gas chromatography-mass spectrometry (GC-MS), in-situ diffuse reflection infrared spectroscopy (in-situ DRIFTS), and elemental analysis (EA). This work represents the first utilization of Bix-P25 materials fabricated on an AP platform toward the desulfurization of H2S at room temperature (RT). The practical utility of Bix-P25 is overall validated by its eminent role in reactive adsorption and catalytic oxidation (RACO) of H2S from the air.
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The preparation of nitrogen-doped TiO2 (i.e., N-TiO2) catalysts is a highly effective option to improve the photocatalytic activity of TiO2. Nonetheless, relatively little is known about the effects of dopant precursors selected for their preparation with regard to the photocatalytic efficacy. In this study, three types of dopants are selected and used as N sources (urea (U), melamine (M), and aqueous ammonia (A)) for N-TiO2 samples with the name codes of NTU, NTM, and NTA, respectively. The photocatalytic efficacy of these N-TiO2 samples is examined against toluene in a packed bed flow reactor. Under optimal conditions (e.g., relative humidity (RH) = 20% and gas hourly space velocity (GHSV) = 1698 h-1), the superiority of NTA is evident over others with a quantum efficiency (QE) of 7.03 × 10-4 molecules photon-1, a space time yield (STY) of 1.38 × 10-4 molecules photon-1 mg-1, and a specific clean air delivery rate (SCADR) of 1148.8 L g-1 h-1. The analysis based on in-situ diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography-mass spectrometry confirms the formation of several intermediates such as benzyl alcohol, benzaldehyde, benzoic acid, and alkane species through ring opening reactions. In addition, the prepared NTA photocatalyst exhibits the highest toluene photocatalytic degradation efficiency among all TiO2-based catalysts surveyed to date. Overall, this study offers as a valuable guideline for the development of advanced TiO2 catalytic systems (such as N-TiO2) for the treatment of aromatic hydrocarbons in indoor air.
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Materials Institute Lavoisier (MIL) metal organic frameworks (MOFs) are known for their potential to adsorb gaseous organic pollutants. This study explores the synergistic effects between the selection of central metals (e.g., titanium, iron, and aluminum) and the incorporation of -NH2 groups in terms of adsorption efficiency against gaseous formaldehyde (FA). A group of the pristine MIL MOFs is synthesized using three different metals (i.e., titanium, iron, and aluminum) and terephthalic acid along with their NH2 derivatives using 2-aminoterephthalic acid. Among the pristine forms, MIL-125(Ti) achieves the highest FA adsorption capacity (Q) of 26.96 mg g-1 and a partition coefficient (PC) of 0.0898 mol kg-1 Pa-1. Further, amination significantly improves the FA adsorption potential of NH2-MIL-125(Ti) with a Q value of 91.22 mg g-1 (PC = 0.3038 mol kg-1 Pa-1). In situ diffuse reflectance infrared Fourier-transform spectroscopy reveals that the FA adsorption of plain MILs should be governed primarily by physisorption. In contrast, FA adsorption of NH2-MILs appears to be regulated by both physisorption and chemisorption, while the latter being affected mainly through FA-NH2 interactions (Schiff base reactions). These findings provide valuable insights into the utility of aminated MIL sorbents, possibly toward the efficient management of indoor air quality.
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Poluentes Atmosféricos , Formaldeído , Estruturas Metalorgânicas , Formaldeído/química , Adsorção , Estruturas Metalorgânicas/química , Poluentes Atmosféricos/química , Titânio/química , Alumínio/química , Espectroscopia de Infravermelho com Transformada de Fourier , Ferro/químicaRESUMO
Although bag sampling is a common quantification tool for volatile organic compounds (VOCs), it can serve as a major source of experimental bias, when storing even over a short duration (<24 h). To learn more about the reliability of the bag sampling method, the temporal stability of 27 VOCs (classified into five groups (i.e., aldehydes, nonpolar aromatic hydrocarbons, aliphatic carboxylic acids, phenol and methylphenols, and miscellaneous odorants) is assessed using poly-ester aluminum (PEA) bags at five intervals over a day (0.17, 1, 2, 6, and 24 h). In terms of reproducibility (e.g., relative standard error [RSEt, %]), nonpolar aromatic hydrocarbons (BTXS) exhibit the highest consistency (e.g., average RSE <1.55%). Considerable loss of VOCs is observed in the preparation of gaseous standards from a liquid phase standard when assessed by gas/liquid (G/L) ratio. Further, VOCs with lower molecular weights (e.g., propionaldehyde: 77%-94.4%) and branched molecular structures (e.g., isovaleraldehyde: 67.2%-78.9%) tend to have high G/L ratio (e.g., relative to valeraldehyde: 55.1%-66%). The overall relative recovery (RR; %) values of VOCs indicate an exponential decrease over 24 h. BTXS maintain fairly good RR values (above 94.3% at all intervals), possibly due to the nonpolar structure with uniform distribution of π electrons. In contrast, indole and skatole show the least preservation after 24 h (e.g., RR4 values of 10.9% and 24.6%, respectively) due to their highly reactive characteristics. The storability of VOCs appears to be affected by a number of variables (e.g., molecular weight, presence of ethyl branch, and time: e.g., R2 > 0.9). The results of this study offer valuable guidelines for the accurate quantification of VOC levels in air.
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Monitoramento Ambiental , Compostos Orgânicos Voláteis , Compostos Orgânicos Voláteis/análise , Monitoramento Ambiental/métodos , Poluentes Atmosféricos/análise , Reprodutibilidade dos Testes , Fatores de TempoRESUMO
The deterioration in air quality caused by volatile organic compounds (VOCs) has become an important environmental issue. Here, activated carbon (AC) composites with manganese oxide (MnO2: 1 % to 50 %) are synthesized as MAC for the removal of formaldehyde (FA) and toluene in air through a combination of reactive adsorption and catalytic oxidation (RACO) at room temperature (RT). The best-performing composite (MAC-20: 20 % of MnO2) exhibits a 10 % breakthrough volume (BTV10%) of FA and toluene at 41.2 and 377 L g-1, respectively while realizing complete oxidation of FA and toluene into carbon dioxide (CO2) at 100 °C and 275 °C, respectively. The reaction kinetic rates (r) for 10 % removal efficiency of FA and toluene (XFA or T) at RT are estimated as 9.82E-02 and 3.20E-02 mmol g-1 h-1, respectively. The high performance of MAC-20 can be attributed to its enriched adsorption capacity of oxygen vacancy (OV) and the presence of adsorbed oxygen (OA), as shown by an Mn3+/Mn4+ ratio of 0.729 and an OA/latticeoxygen (OL) ratio of 1.50. The results of this study highlight the interactive roles of oxygen abundance and temperature in the generation of distinctive oxidation patterns for FA in reference to toluene. This study is expected to offer practical guidance for the implementation of RACO against diverse VOCs for efficient management of air quality.
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Adsorptive removal of heavy metal ions from water is an energy- and cost-effective water decontamination technology. Schiff base functionalities can be incorporated into the pore cages of metal-organic frameworks (MOFs) via direct synthesis, post-synthetic modification, and composite formation. Such incorporation can efficiently enhance the interactions between the MOF adsorbent and target heavy metal ions to promote the selective adsorption of the latter. Accordingly, Schiff base-functionalized MOFs have great potential to selectively remove a particular metal ion from the aqueous solutions in the presence of coexisting (interfering) metal ions through the binding sites within their pore cages. Schiff base-functionalized MOFs can bind divalent metal ions (e.g., Pb(II), Co(II), Cu(II), Cd (II), and Hg (II)) more strongly than trivalent metal ions (e.g., Cr(III)). The adsorption capacity range of Schiff base-functionalized MOFs for divalent ions is thus much more broad (22.4-713 mg g-1) than that of trivalent metal ions (118-127 mg g-1). To evaluate the adsorption performance between different adsorbents, the two parameters (i.e., adsorption capacity and partition coefficient (PC)) are derived and used for comparison. Further, the possible interactions between the Schiff base sites and the target heavy metal ions are discussed to help understand the associated removal mechanisms. This review delivers actionable knowledge for developing Schiff-base functionalized MOFs toward the adsorptive removal of heavy metal ions in water in line with their performance evaluation and associated removal mechanisms. Finally, this review highlights the challenges and forthcoming research and development needs of Schiff base-functionalized MOFs for diverse fields of operations.
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Estruturas Metalorgânicas , Metais Pesados , Poluentes Químicos da Água , Água , Bases de Schiff/química , Descontaminação , Metais Pesados/química , Adsorção , Poluentes Químicos da Água/análiseRESUMO
Formaldehyde (HCHO: FA) is one of the most abundant but hazardous gaseous pollutants. Transition metal oxide (TMO)-based thermocatalysts have gained much attention in its removal due to their excellent thermal stability and cost-effectiveness. Herein, a comprehensive review is offered to highlight the current progress in TMO-based thermocatalysts (e.g., manganese, cerium, cobalt, and their composites) in association with the strategies established for catalytic removal of FA. Efforts are hence made to describe the interactive role of key factors (e.g., exposed crystal facets, alkali metal/nitrogen modification, type of precursors, and alkali/acid treatment) governing the catalytic activity of TMO-based thermocatalysts against FA. Their performance has been evaluated further between two distinctive operation conditions (i.e., low versus high temperature) based on computational metrics such as reaction rate. Accordingly, the superiority of TMO-based composite catalysts over mono- and bi-metallic TMO catalysts is evident to reflect the abundant surface oxygen vacancies and enhanced FA adsorptivity of the former group. Finally, the present challenges and future prospects for TMO-based catalysts are discussed with respect to the catalytic oxidation of FA. This review is expected to offer valuable information to design and build high performance catalysts for the efficient degradation of volatile organic compounds.
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Aluminum is a relatively inexpensive and abundant metal for the mass production of metal-organic frameworks (MOFs). Aluminum-based MOFs (Al-MOFs) have drawn a good deal of research interest due to their unique properties for diverse applications (e.g., excellent chemical and structural stability). This review has been organized to highlight the current progress achieved in the synthesis/functionalization of Al-MOF materials with the special emphasis on their sensing application, especially toward metal ion pollutants in the liquid phase. To learn more about the utility of Al-MOF-based sensing systems, their performances have been evaluated for diverse metallic components in reference to many other types of sensing systems (in terms of the key quality assurance (QA) criteria such as limit of detection (LOD)). Finally, the challenges and outlook for Al-MOF-based sensing systems are discussed to help expand their real-world applications.
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A number of flavored capsule heat-not-burn (FC-HNB) tobacco products such as IQOS, Lil, and Glo have been introduced as a new generation of cigarettes. As they can release various types of volatile organic compounds (VOCs), it is important to assess the harmfulness associated with their use. Thus, the composition of VOCs in HNB cigarette vapor was evaluated to investigate the interactive roles of key variables controlling the relationships between VOC composition and capsule breaking, particularly the compositional changes induced by capsule breaking and release of flavor from FC-HNB cigarettes relative to regular products. As the capsules of FC-HNB cigarettes were broken, the total VOC concentrations increased by as high as eight times from 60.3 ± 0.48 to 488 ± 21.8 µg cig-1. The key VOC components released after breaking the flavored capsules were identified as ethyl butyrate (157 ± 13.6 µg cig-1; Lil), isoamyl acetate (76.9 ± 1.98 µg cig-1; Lil), and limonene (52.3 ± 3.29 µg cig-1; Glo). If the primary health risks of FC-HNB cigarette vapor are assessed using National Institute for Occupational Safety & Health (NIOSH) guidelines, 2,3-butanedinone exceeds the maximum daily intake limit (i.e., 0.05 mg day-1). Our study is expected to offer valuable insights into the harmful effects of direct and indirect exposure to various VOCs in FC-HNB products.
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Sistemas Eletrônicos de Liberação de Nicotina , Produtos do Tabaco , Compostos Orgânicos Voláteis , Temperatura Alta , FumarRESUMO
Chemical sensors that can detect volatile organic compounds (VOCs) are the subject of extensive research efforts. Among various sensing technologies, molecularly imprinted polymers (MIPs) are regarded as a highly promising option for their detection with many advantageous properties, e.g., specific binding-site for template molecules, high recognition specificity, ease of preparation, and chemical stability. This review covers recent advances in the sensing application of MIPs toward various types of VOCs (e.g., aliphatic and aromatic compounds). Particular emphasis has been placed on multiple approaches to the synthesis of MIP-based VOC sensors in association with their performance and sensing mechanisms. Current challenges and opportunities for new VOC-sensing applications are also discussed based on MIP technology.
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Impressão Molecular , Compostos Orgânicos Voláteis , Gases , Polímeros Molecularmente Impressos , Polímeros/químicaRESUMO
This paper investigates how carbon taxes affect emissions by examining British Columbia's revenue-neutral carbon tax in the manufacturing sector. We theoretically demonstrate that carbon taxes can achieve emission reductions while increasing production. Recycling carbon tax revenues to lower corporate income tax rates encourages investments, allowing plants to emit less per unit of output. Using detailed confidential plant-level data, we evaluate this theoretical prediction by exploiting the treatment intensity through plants' emission intensity. We find that the carbon tax lowers emissions by 4 percent. Furthermore, we find that the policy had a positive output effect and negative emission intensity effect, suggesting that the carbon tax encouraged plants to produce more with less energy. We provide initial evidence showing how a revenue-neutral carbon tax may achieve emission reductions while stimulating the economy.
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Mycotoxin is toxic secondary metabolite formed by certain filamentous fungi. This toxic compound can enter the food chain through contamination of food (e.g., by colonization of toxigenic fungi on food). In light of the growing concerns on the health hazards posed by mycotoxins, it is desirable to develop reliable analytical tools for their detection in food products in both sensitive and efficient manner. For this purpose, the potential utility of molecularly imprinted polymers (MIPs) has been explored due to their meritful properties (e.g., large number of tailor-made binding sites, sensitive template molecules, high recognition specificity, and structure predictability). This review addresses the recent advances in the application of MIPs toward the sensing of various mycotoxins (e.g., aflatoxins and patulin) along with their fabrication strategies. Then, performance evaluation is made for various types of MIP- and non-MIP-based sensing platforms built for the listed target mycotoxins in terms of quality assurance such as limit of detection (LOD). Further, the present challenges in the MIP-based sensing application of mycotoxins are discussed along with the future outlook in this research field.
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Impressão Molecular , Micotoxinas , Fungos , Polímeros Molecularmente Impressos , Polímeros/químicaRESUMO
The effective control on environmental pollutants is crucial for the proper management of diverse environmental systems (e.g., soil, water, and air). In this respect, the utility of various functional materials such as hyperbranched polymers (HPs) has been recognized due to their great potentil as adsorbent for the mitigation of numerous environmental pollutants. Here, we highlight the latest progress achieved in the design and construction of HPs with high adsorption potentials. We focus on adsorption mechanisms, functionalization methods, the role of functional groups in adsorption capacity, and the choice of HPs in adsorption of cationic and anionic dyes. Recent published reports are reviewed to quantify and qualify the removal efficiency of pollutants through adsorption. We also evaluate the adsorbing efficiency of the constructed HPs and compared their performance with other such systems. The utilization potential of new materials (magnetic, polar, and biological) is highlighted along with the methods needed for their preparation and/or modification (surface, end-group, and zwitterionic) for the construction of efficient adsorbing systems. Finally, the advantages and limitations of adsorbing systems are described along with the existing challenges to help establish guidelines for future research. This article is thus expected to offer new path and guidance for developing advanced HP-based adsorbents.
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Poluentes Químicos da Água , Purificação da Água , Adsorção , Corantes , Polímeros , Água , Purificação da Água/métodosRESUMO
The abatement of airborne pathogens such as bacteria, viruses, and fungi has become an important goal of air-quality management. Efficient and effective treatment techniques such as photocatalysis are essential for disinfection of airborne microorganisms. This review focuses on recent advances in the formulation and development of photocatalytic disinfection, design of efficient photocatalysts, choice of photocatalytic reactor, removal and/or disinfection mechanisms, and the role of reactive ion species. Data from recent studies are analyzed to accurately assess the efficacy of such disinfection approaches. This review also highlights the application of innovative materials in individual and combined abatement systems against airborne bacterial, viral, and fungal pathogens. We discuss the efficiency and benefits presented by such systems, address the challenges, and provide a perspective for future research.