This study developed an inexpensive and simple microsensor for detecting volatile organic compounds (VOCs). This developed VOC sensor is composed of a nano-porous polyimide (PI) film doped with carbon black (CB) as the sensing material. The conductivity of the PI/CB film changed after absorbing VOC contents in the air. In general, solid state based VOC sensors which use metal oxide as the sensing materials have to work at a temperature of about 300¡V350¢J. Alternatively, this research developed a VOC sensor capable of sensing VOCs at room temperature, resulting in a sensor system of low energy consumption. A post pore opening procedure by plasma etching is used to enhance the response of the sensor film. SEM images confirm that the micro-pores interconnect with their neighboring pores and also open to the outside air. The film prepared with pore opening procedure exhibit a response of 3 times faster than the film prepared without pore opening. Results indicate that the developed VOC sensor has a good repeatability for detecting VOCs. PI film with 1% (weight percent) of CB has the best sensitivity due to the well dispersion of CB. This research detected 100 ppm ethanol fifth times to show good reproducibility, and detected 10 ppm, 100 ppm, 1000 ppm benzene and ethanol for 24 hours to show long-term stability, and detected 101 ppm¡ã105 ppm widely VOCs concentration. Besides, this sensor has selectivity on specific gas like alcohol and aldehyde, the sensor material has special chemical bond that can connect with specific gas. Moreover, the sensitivity is about 155% at 25 oC and 80% at 60 oC, it is almost 2 times at 25 oC. The moisture can also be detected to avoid the impact on the sensor performance for detecting VOCs, the moisture capacitance changes is 16 times higher than VOCs. The sensor developed in this study provides a simple and straight forward method to fabricate low-cost VOC sensors.

Relative humidity (RH) is an important parameter associated with occupant comfort in buildings. However, the effects of RH on indoor source off-gassing and interactions between air pollutants and indoor materials are poorly understood. For this study, air samples were collected in residential buildings to characterize “background” concentrations of volatile organic compounds (VOCs) in air. The interior space was then humidified for several hours prior to collection of another air sample to characterize the effects of increased RH on VOC concentrations. Samples were analyzed by GC/FID with abundance “binning” by elution time. Some samples were also analyzed using GC/MS to identify specific VOCs. Results indicate that increasing RH is associated with increases in VOC concentrations in residential indoor air. Many of the chemicals that show enhanced off-gassing are associated with architectural coating, moth repellents, and cleaning agents. The results of this study are novel and may have implications with respect to health effects associated with damp buildings and increased respiratory effects of children during sleep in bedrooms with elevated RH. / text

No description available.

The recently discovered mesoporous molecular sieve MCM-41 was synthesized, modified, and characterized and proposed as an alternative adsorbent for VOC control. The synthesis conditions for pure-silica and aluminosilicate MCM-41 were optimized as follows: 4.5Na2O:30SiO2:5.2C16H33(CH3)3N + :2500H2O and 7.5Na2O:30SiO2:xAl2O3:7.2C16H33(CH3)3N + :3500H2O (x < 1), respectively, and at 373 K for 4 days. Our studies showed that MCM-41 is not stable in the presence of water vapor. For example, a hydrothermal treatment of MCM-41 at 723 K for 2 hour resulted in 50 % of structure collapses. Again, when a template-free MCM-41 sample was exposed to air with a relative humidity of 60 % for three months, almost total pore structure collapses were observed. Adsorption equilibrium results showed that MCM-41 has a narrow pore size distribution and exhibits extraordinary pore volume compared to the classical microporous adsorbents, such as molecular sieves and activated carbons. Despite the impressive adsorption capacities of this material, the Type IV isotherm behavior requires the VOCs, in the gas phase, to be at high partial pressure. This is not the case with most industrial VOC streams. A real VOC stream requires an adsorbent with not only a high adsorption capacity but also a high adsorption affinity at a low VOC concentration. To overcome the above mentioned two problems, both the surface chemistry and the pore-opening sizes of MCM-41 were modified. To modify the surface chemistry, one has to better understand the surface chemistry. Our pioneering study of the surface chemistry of MCM-41 using FTIR, 29 Si CP/MAS NMR, pyridine-TPD, and TGA demonstrated that three types of silanol groups, i.e. single, (SiO)3Si-OH, hydrogen-bonded, (SiO)3Si-OH---OH-Si(SiO)3 and geminal, (SiO)2Si(OH)2 are distributed over the surface of MCM-41. The number of silanol groups per unit nm 2 , aOH, varies between 2.5 and 3.0 depending on the template-removal method. To improve the hydrothermal stability and enhance the hydrophobicity, the surface chemistry of MCM-41 was modified by silylation. Though both the free and hydrogen-bonded SiOH groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol -1 , respectively, only the free SiOH groups are highly accessible to the silylating agent, chlorotrimethylsilane. The surface coverage of the modifying agent was found to has a linear relationship with the surface free silanol groups which can be controlled by different heating temperatures. Modification by silyaltion can significantly improve hydrophobicity and stability. Rehydration/dehydration experiments demonstrate that the surface-silylated MCM-41 is highly tolerable to water vapor due to the complete replacement of surface-hydrophilic silanols. A novel modification method, namely selective tailoring (ST), was developed to tailor the pore-opening sizes of MCM-41 (rather than the entire pores). The novelty is that only the pore mouths at both ends of a cylindrical pore of MCM-41 was modified by deposition of some alkoxides. By doing so, the types of adsorption isotherms of VOCs can be changed from Type IV to Type I while the pore volume can be significantly preserved. This is of course significance in VOC removal since the adsorption affinity has been drastically enhanced. Adsorption equilibria and kinetics for VOCs in the pore-opening-modified MCM-41 materials were measured, modeled and compared to that of activated carbons and hydrophobic molecular sieves. The pore-modified MCM-41 has a much higher adsorption capacity than that of the traditional microporous adsorbents such as activated carbons and molecular sieves. The adsorption equilibrium data fit the Langmuir-Uniform distribution (Unilan) models very well. Upon the equilibrium parameters being obtained and considering the pore structure of our pore-modified MCM-41 adsorbents, the kinetic data were further modeled using the literature-existed models recently developed by Do and coworkers, i.e. the constant surface diffusivity macropore, surface and micropore diffusion (CMSMD) model and the macropore and surface diffusion (MSD) model. Results demonstrated that the CMSMD model can predict our kinetic uptake curves reasonably fine. Some key kinetic parameters including pore and surface diffusivities, apparent diffusivity, activation energy for adsorption, and pore tortuosity factor can be readily obtained. The porosity of the MCM-41 materials were primarily evaluated using the traditional methods based on nitrogen adsorption/desorption data. Results indicated that the BJH method always underestimates the true pore diameter of MCM-41. An comparison plot (t-plot or as-plot) method was suggested and improved. Plotting of nitrogen adsorption data at 77 K versus the statistical film thickness reveals three distinct stages, with a characteristic of two points of inflection. The steep intermediate stage is caused by capillary condensation occurred in the highly uniform mesopores. From the slope of the section after condensation, the external surface area can be obtained. Therefore, the true surface area of the mesopores is readily calculated. The linear portion of the last section is extrapolated to the adsorption axis of the comparison plot, and this intercept is used to obtain the volume of the mesopores. From the surface area and pore volume, average mesopore diameter is calculated, and the value thus obtained is in good agreement with the pore dimension obtained from powder X-ray diffraction measurements. The principle of pore size calculation, the thickness of adsorbed nitrogen film, and the problems associated with the BJH method were discussed in detail. It has been found that at a given relative pressure, the smaller the pore radius, the thicker the adsorbed film. Thermodynamics analysis established that the stability of the adsorbed film is determined by interface curvature and the potential of interaction between adsorbate and adsorbent. A semi-empirical equation is proposed to describe the state of stable adsorbed films in cylindrical mesopores. It is also shown to be useful in calculations of pore size distributions of mesoporous solids. The desorption of four representative volatile organic compounds (VOCs), i.e. n-hexane, cyclohexane, benzene, and methanol from MCM-41 were also investigated and compared with the hydrophobic zeolite, silicalite-1, using the technique of temperature programmed desorption (TPD). The desorption energies of these organics to MCM-41 were evaluated and compared with the adsorption isosteric heats. The affinity of organics to MCM-41 and silicalite-1, which represents surface hydrophobicity/hydrophilicity were studied and discussed. Results showed that only one desorption peak can be found for all organics from MCM-41, different from that from the microporous adsorbents (activated carbons and hydrophobic molecular sieves). The activation energies for desorption of non-polar molecules are slightly higher than their latent heats of evaporation, whereas the activation energy for desorption of methanol is well above its latent heat of evaporation. These results are consistent with those derived from the adsorption isotherm measurements. The very high activation energy for the desorption of methanol is due to the hydrogen bonds between methanol molecules and silanol groups over MCM-41 surfaces. The affinity of volatile organics to MCM-41 are in the order of methanol > n-hexane > benzene > cyclohexane.

<div>Researchers have shown links between various hydrocarbons and carbonyl compounds and diseases, such as cancer using exhaled breath analysis through gas chro</div><div>matography/mass spectroscopy (GC/MS) analysis of volatile organic compounds (VOCs). Trained canines can detect these VOCs and can differentiate a patient suffering from cancer from a healthy control patient. In this project, an attempt has been made to develop highly sensitive sensors for the detection of low concentrations of aldehyde VOCs, such as nonanal, using conductive polymer composites (CPCs) and functionalized gold nanoparticles (f-GNPs). Facile methods have been used to enhance the sensitivity and cross-selectivity of the fabricated sensors towards nonanal. Interdigitated electrodes (IDEs) are fabricated through a photolithography process. Sensors of PEI/carbon black (CB) composite were developed via spin-coating of the</div><div>material followed by the heat treatment process. Sensors of 1-Mercapto-(triethyleneglycol) methyl ether functionalized GNPs are developed via drop-casting of nanomaterial and f-GNP/PEI sensors are fabricated by spin casting PEI film on top of f-GNPs. Fourier Transform Infrared (FTIR) analysis, X-Ray Diffraction (XRD) analysis, contact angle measurement, and Field Emission Scanning Electron Microscopy (FESEM) analysis was conducted to characterize the fabricated devices. The fabricated sensors have been tested with a low concentration of nonanal, nonanone, dodecane, and 1-octanol in dry air. Multiple sensors are fabricated to ensure sensors reproducibility. The sensors have been exposed repeatedly to the targeting VOCs to assess the repeatability of the sensors. PEI/CB sensor degradation was studied over a period of 36 days.</div><div><br></div><div>The fabricated PEI/CB film could detect (1-80 ppm) of nonanal with higher selectivity, than the f-GNPs. The sensor0s sensitivity to nonanal was over fourteen times</div><div>higher than 2-nonanone, 1-octanol, and dodecane. This shows the high selectivity of the fabricated sensor toward nonanal. In addition, the proposed sensor maintained its</div><div>sensitivity to nonanal over time showing minimal degradation. The sensor response to nonanal at a relative humidity (RH) of 50% and 85% dropped less than 13% and</div><div>32% respectively. The Response of f-GNP sensors to nonanal (400 ppb - 15 ppm), dodecane (5 - 15 ppm), 1-octanol (5 - 15 ppm), and 2-nonanone (5 - 15 ppm) presented a sensitivity (∆R/R0) of 0.217%, 0.08%, 0.192% and 0.182% per ppm of the VOCs respectively. Despite the high sensitivity to the targeting VOCs, the fabricated</div><div>sensors were damaged in an environment with relative humidity (RH) at 45%. A thin layer of PEI over the film was developed to ensure the sensor could tolerate long</div><div>time exposure to water vapor in an environment with RH up to 85% and enhance the sensor selectivity towards nonanal. The f-GNP/PEI sensors with nonanal (400 ppb- 15 ppm), dodecane (100 -200 ppm), 1-octanol (5 - 15 ppm) and 2-nonanone (5 - 15 ppm) presented sensitivity (∆R/R0) of 0.21%, 0.017%, 0.0438% and 0.0035% per ppm of the VOCs respectively. The sensor fabrication, characterization, testing methods, and results are presented and discussed.</div>

Indiana University-Purdue University Indianapolis (IUPUI) / Researchers have shown links between various hydrocarbons and carbonyl compounds and diseases, such as cancer using exhaled breath analysis through gas chromatography/mass spectroscopy (GC/MS) analysis of volatile organic compounds (VOCs). Trained canines can detect these VOCs and can differentiate a patient suffering from cancer from a healthy control patient. In this project, an attempt has been made to develop highly sensitive sensors for the detection of low concentrations of aldehyde VOCs, such as nonanal, using conductive polymer composites (CPCs) and functionalized gold nanoparticles (f-GNPs). Facile methods have been used to enhance the sensitivity and cross-selectivity of the fabricated sensors towards nonanal. Interdigitated electrodes (IDEs) are fabricated through a photolithography process. Sensors of PEI/carbon black (CB) composite were developed via spin-coating of the material followed by the heat treatment process. Sensors of 1-Mercapto-(triethylene glycol) methyl ether functionalized GNPs are developed via drop-casting of nanomaterial and f-GNP/PEI sensors are fabricated by spin casting PEI film on top of f-GNPs. Fourier Transform Infrared (FTIR) analysis, X-Ray Diffraction (XRD) analysis, contact angle measurement, and Field Emission Scanning Electron Microscopy (FESEM) analysis was conducted to characterize the fabricated devices. The fabricated sensors have been tested with a low concentration of nonanal, nonanone, dodecane, and 1-octanol in dry air. Multiple sensors are fabricated to ensure sensors reproducibility. The sensors have been exposed repeatedly to the targeting VOC toxiv assess the repeatability of the sensors. PEI/CB sensor degradation was studied over a period of 36 days. The fabricated PEI/CB film could detect (1-80 ppm) of nonanal with higher selectivity, than the f-GNPs. The sensor0s sensitivity to nonanal was over fourteen times higher than 2-nonanone, 1-octanol, and dodecane. This shows the high selectivity of the fabricated sensor toward nonanal. In addition, the proposed sensor maintained its sensitivity to nonanal over time showing minimal degradation. The sensor response to nonanal at a relative humidity (RH) of 50% and 85% dropped less than 13% and 32% respectively. The Response of f-GNP sensors to nonanal (400 ppb - 15 ppm), dodecane (5 - 15 ppm), 1-octanol (5 - 15 ppm), and 2-nonanone (5 - 15 ppm) presented a sensitivity (∆R=R0) of 0.217%, 0.08%, 0.192% and 0.182% per ppm of the VOCs respectively. Despite the high sensitivity to the targeting VOCs, the fabricated sensors were damaged in an environment with relative humidity (RH) at 45%. A thin layer of PEI over the film was developed to ensure the sensor could tolerate longtime exposure to water vapor in an environment with RH up to 85% and enhance the sensor selectivity towards nonanal. The f-GNP/PEI sensors with nonanal (400 ppb- 15 ppm), dodecane (100 -200 ppm), 1-octanol (5 - 15 ppm) and 2-nonanone (5 - 15 ppm) presented sensitivity (∆R=R0) of 0.21%, 0.017%, 0.0438% and 0.0035% per ppm of the VOCs respectively. / 2021-04-24

Esta tesis estudia el impacto que tienen los COV presentes en los plásticos reciclados para la economía circular. Actualmente, la industria del reciclaje actual no puede cubrir la creciente demanda de plásticos reciclados de alta calidad en los últimos años. Hasta ahora, el reciclaje mecánico es la solución más utilizada a nivel mundial, y su eficacia y fiabilidad han sido demostradas para el tratamiento del residuo plástico post-industrial. Sin embargo, el mismo reciclaje mecánico aplicado a los residuos plásticos post-consumo da lugar a un material reciclado de menor calidad que solamente es apto para aplicaciones de bajo valor añadido, como son las tuberías de riego o cubos de basura. Por ello, esta tesis evalúa la influencia que tienen las sustancias orgánicas que aparecen en los plásticos reciclados post-consumo dentro el sector del plástico. / Investigación cofinanciada por el Vicerrectorado de Investigación y Transferencia de Conocimiento para el fomento de la I+D+i de la Universidad de Alicante y Cadel Deinking, S.L.

No description available.

The following investigation stems from the idea of using metabolic byproducts produced by mold as indicators of its presence in indoor environments in place of investigating airborne fungi by traditional particulate sampling techniques. VOCs and carbon dioxide are both examined in order to evaluate their usefulness as possible metabolic indicators of mold growth. A specially designed purge and trap laboratory setup was built and operated for the study of molds growing on specific media. Key variables for the operation of the apparatus include sampling time and sampling flow rate as well as other environmental conditions such as temperature. Carbon dioxide serves as a good marker for fungal activity, but is difficult to attribute to mold growth when studying non-closed loop systems. Many VOCs were collected but detection limits were often too high for the quantities collected. / Master of Science

Processos metabólicos naturais no organismo humano levam à formação de substâncias como compostos orgânicos voláteis (VOCs), de modo que, em um quadro patológico, processos diferenciados podem ocorrer nas células, fazendo com que um conjunto diferente de compostos seja produzido. Com esta hipótese, VOCs podem ser analisados em amostras biológicas com a intenção de se verificar alterações em seus perfis que sejam indicativos de certas patologias. No presente estudo, foi selecionado o suor como matriz, amostra de coleta simples e não-invasiva, de composição menos complexa e relacionada aos níveis sanguíneos e emanações da pele. Adicionalmente, foram também analisadas amostras de urina, para obtenção de dados comparativos. O presente estudo compreendeu amostras de voluntários saudáveis (grupo controle-C) e com diagnóstico de câncer confirmado (grupo positivo- P). As amostras de suor foram coletadas com o dispositivo PharmChek®, após, o patch foi removido, inserido em frasco e os VOCs isolados com emprego de técnica otimizada de Headspace estático (HS). Para as amostras de urina, estas foram analisadas com e sem tratamento por ?-glucuronidase. Perfis de VOCs foram obtidos por análise por cromatografia gasosa acoplada a espectrometria de massas (GC-MS) para todas amostras. A tentativa de identificação dos compostos detectados foi feita por busca na biblioteca NIST08 e uso do software AMDIS32. Diferenças qualitativas (teste chi-quadrado, p<<0,01) e quantitativas (teste U de Mann-Whitney, p<<0,01) foram avaliadas entre os perfis do grupo controle e positivo. Para o suor foram selecionados os potenciais biomarcadores pentanal, hexanal, heptanal, octanal, limoneno, 2-etil-1-hexanol, 1-undeceno, fenol, 2,6-dimetil-7-octen-2-ol (DMOL), nonanal, decanal e tridecano; para a urina, fenol e DMOL, hidrólise-dependentes, foram selecionados. Método HS-GC-FID (acoplado a detector por ionização de chama) foi desenvolvido e validado segundo a RDC 27/2012 da ANVISA, para ambas amostras. No suor, os analitos apresentaram limites inferiores de quantificação (LIQ) de 1 ng/adesivo, 5 ng/adesivo para o fenol; na urina foram de 2 ng mL-1 para o DMOL e 10 ng mL-1 para o fenol. Linearidade foi observada para faixa de 2 a 150 ng/adesivo e, 2 e 5 a 400 ng mL-1 na urina. No suor, a precisão variou de 0,08 a 12,35% e os analitos foram demonstrados estáveis para os ensaios realizados. Curvas ROC (Receiver Operating Characteristic) foram avaliadas e áreas sob a curva foram todas próximas a 1, com valores cut-off de 1,71 a 35,44 ng/adesivo no suor e 8,71 e 52,86 ng mL-1 na urina. 2-etil-1-hexanol se demonstrou negativamente correlacionado com o estágio clínico em adenocarcinomas (rô= -0,527) e DMOL, no suor, e aldeídos C5-C8 positivamente relacionados ao estágio do câncer de próstata (rô= 0,779 e 0,684, respectivamente). Conclui-se, portanto, que o método apresentado se mostrou eficiente, contudo, prático e de baixo custo, e os resultados obtidos corroboram para ideia da determinação de VOCs como promissora ferramenta auxiliar de diagnóstico no câncer. / Natural metabolic processes in the human body lead to the formation of substances such as volatile organic compounds (VOCs), so that, in a pathological context, differentiated processes can occur in the cells, causing a different set of compounds to be produced. With this hypothesis, VOCs can be analyzed in biological samples with the intention to verify changes in their profiles that are indicative of certain pathologies. In the present study, sweat was selected as the matrix, due simple and non-invasive collection, with lower complexity composition and related to blood levels and skin emanations. In addition, urine samples were also analyzed to obtain comparative data. The present study comprised samples from healthy volunteers (control-C group) and individuals with confirmed cancer diagnosis (positive-P group). The sweat samples were collected with PharmChek® device, next, the patch was removed, inserted in a vial and the VOCs were isolated using an optimized Static Headspace (HS) technique. For urine samples, these were analyzed with and without ?-glucuronidase treatment. VOC profiles were obtained by gas chromatography coupled to mass spectrometry (GC-MS) for all samples. The attempt to identify the detected compounds was made by searching the NIST08 library and using the AMDIS32 software. Qualitative differences (chi-square test, p << 0.01) and quantitative tests (Mann-Whitney U test, p << 0.01) were evaluated between the profiles of the control and positive groups. For the sweat, the potential biomarkers pentanal, hexanal, heptanal, octanal, limonene, 2-ethyl-1-hexanol, 1-undecene, phenol, 2,6-dimethyl-7-octen-2-ol (DMOL), nonanal, decanal and tridecane; for urine, phenol and DMOL, both hydrolysis-dependent, were selected. HS-GC-FID (coupled to flame ionization detector) method was developed and validated according to RDC 27/2012- ANVISA, for both samples. In sweat, the analytes presented limits of quantification (LOQ) of 1 ng/patch, 5 ng/patch for phenol; in urine were 2 ng mL-1 for DMOL and 10 ng mL-1 for phenol. Linearity was observed for the range of 2 to 150 ng/patch and, 2 and 5 to 400 ng mL-1 in urine. In sweat, the precision ranged from 0.08 to 12.35% and the analytes were shown to be stable for the assays performed. Receiver Operating Characteristic (ROC) curves were evaluated and areas under the curve were all near to 1, with cut-off values of 1.71 to 35.44 ng/patch in sweat and 8.71 and 52.86 ng mL-1 in urine. 2-ethyl-1-hexanol was shown to be negatively correlated with the clinical stage in adenocarcinomas (rho= -0.527) and DMOL, in sweat, and C5-C8 aldehydes sum, positively related to the stage of prostate cancer (rho= 0.779 and 0.684, respectively). It was concluded, therefore, that the method presented proved to be efficient, however, practical and low cost, and the results corroborate to the idea of VOCs determination as a promising diagnostic tool for cancer diagnosis.