Gaseous Benzene Research Articles

Evidence of the dominant role of particle size in controlling the dynamic adsorption breakthrough behavior of gaseous benzene in a microporous carbon bed system

To learn more about the competing roles of the key process variables (e.g., particle size vs. space velocity) in the adsorption of volatile organic compounds (VOCs), the breakthrough (BT) behavior of gaseous benzene (at 3 Pa) was investigated using microporous activated carbon (AC) beds built individually with each of four different particle size ranges (<0.6, 0.6–1.7, 1.7–2.36, and 2.36–5 mm) at three flow rates (300, 500, and 1000 mL min−1). The effects of each variable on AC performance were evaluated in relation to the occurrence patterns of BT. The key performance metrics (e.g., capacity and partition coefficient) generally increased with decreases in particle size and flow rate, reflecting the critical role of sorbent bed physical properties (e.g., surface area, space velocity, and residence time) in the adsorption process. The smallest particle group (<0.6 mm) exhibited the highest uptake rate in the initial BT stage in terms of breakthrough volume (BTV: L g−1) (e.g., BTV5% (5% BTV) = 424 L g−1). In contrast, the order for 100% BT was reversed to record the highest at the largest particle group (2.36 – 5 mm). The kinetic modeling suggests the dominant role of the pore-diffusion mechanism on the overall adsorption process with enhanced benzene uptake rate onto smaller carbon particle sizes at higher flow rates. Based on this work, we recommend accurate determination of the relative dominance between adsorbent particle size and space velocity to maximize the efficiency of air filtration systems for real-world applications.

Investigation on the gaseous benzene removed by photocatalysis employing TiO2 modified with cobalt and iodine as photocatalysts under visible light

ABSTRACT A new type of photocatalysts, nanocrystalline titanium dioxide (TiO2) doped with Co and I, were synthesized and modified via the sol-gel method to enhance the utilization of visible light. Herein, mono- and co-doped TiO2 (i.e. Co-TiO2, I-TiO2, Co-I-TiO2) were employed as the photocatalysts to investigate the photocatalytic performance on gaseous benzene removal. The prepared photocatalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET)-specific surface areas, Raman spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis-DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). Results indicated that both particle sizes and band gaps of TiO2 were significantly reduced by doping with Co/I. Also, the lattice defects and the specific surface areas of TiO2 were substantially augmented by adding Co/I because of the increase of oxygen vacancies, especially for Co-I-TiO2. Meanwhile, Co and I were distributed on the titanium base with the existence of multivalent states. The benzene treatment capacity of Co-I-TiO2, Co-TiO2, I-TiO2 and Pure TiO2 is 441.46, 424.36, 388.06, and 51.25 μgC6H6/(g·h), respectively. To sum up, photocatalytic degradation of gaseous benzene could be improved by doping with Co/I because of the extension of catalyst lifetime and light response range covering visible light.

Fabrication and characterization of photo-responsive metal–organic framework membrane for gas sensing using planar optical waveguide sensor

A facile, novel fabrication approach using UV light irradiation was proposed to fabricate a photo-responsive metal–organic framework (PR-MOF-1, [Zn2-(bdc)2-(dpNDI)]n, where bdc = benzene-1,4-dicarboxylic acid; dpNDI = N,N′-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxy diimide) membrane. The morphology of the PR-MOF-1 framework evolved from a honeycomb porous structure to a densified ladder-layered structure after 60 min of UV-light illumination. The as-grown film was optically transparent and exhibited a greater sensing response to ethylenediamine (EDA) gas in the presence of interfering substances such as ammonia and dimethylamine as well as benzene, toluene, xylene, and styrene gases, as measured using an asymmetric planar optical waveguide gas sensor. When the EDA gas molecule was adsorbed on the surface of the membrane, charge transfer between them preferably occurred, leading to a change in the membrane surface conformation. As an ideal sensing material for EDA gas detection, the PR-MOF-1 membrane showed a relatively high surface sensitivity (11,000 times cm-1) after 60 min of growth, and it could quickly (in less than 2 s) detect 1 ppb of EDA gas with a significant response (S/N = 3.45). During the static gas adsorption process, the EDA gas adsorption kinetics fit well with pseudo-second-order (PSO) model, and the adsorption capacity (qe) on a unit surface showed a high value of 33.91 μg cm−2 at 283 K. The high selectivity and sensitivity of the PR-MOF-1 membrane for EDA gas indicate the effectiveness of the light irradiation method for alteration of the metal– organic framework membrane structure and control of the gas sensing properties.

Active Controlling of Cabin Benzene from Front Dashboard for Driver Passenger Safety

The amount of toxic benzene gas is increasing rapidly due to development in plastic industries and also due to more amount of vehicle exhaust & gasoline production all over the world. These results not only develop the wealth of a nation, but it seriously affects the environment, human and other living beings. Through this project. We can detect high toxic benzene gas in the car cabin and industry on working condition. By this detection of benzene gas, exposure of passengers to such toxic gases inside vehicle cabin is considerably decreased.In this work, focus has been on car’s interior toxic gas detection due to which deformation taken place on dashboards, seats and other plastics on hot weather condition. By this it is also necessary to indicate the value of gas concentration in car’s interior in ppm reading. Thereby, a battery is fixed inside a car, and a GSM module and Arduino is powered. MQ135 gas sensor detects the benzene level inside of the car and it will be projected on an LCD display. When the benzene level is increased above 300 ppm, a message will be sent to the mobile as “GAS LEVEL HIGH” and we command a text through mobile as “*START#”, by this the exhaust fans and car blower starts, where the car blower blows air from environment to car interior cabin and the exhaust fans expels out the car’s interior benzene gas to the environment.When the ppm level is decreased to normal level which is below 286 ± 14 ppm, a message would be received through mobile phone as “GAS LEVEL LOW” and we command a text as “*STOP#”, thus within 7 min the ppm level decreases from 300 to 286 ± 14 ppm. By this, the exhaust fans and car blower stops. Hence higher level of safety is ensured from the toxic gas produced inside a car cabin and instead of manually opening the door glass to reduce the benzene level.

Self S-doping activated carbon derived from lignin-based pitch for removal of gaseous benzene

In this study, lignin-based pitch extracted from black liquor was used as the precursor for synthesis of activated carbon (AC) with high specific surface area and pore volume through chemical activation with potassium hydroxide (KOH). The effect of the activation temperature on AC properties was also explored. The optimized activated carbon (PAC-5-850-60) was prepared at the activation temperature of 850 °C. At this temperature, the specific surface area and total pore volume of PAC-5-850-60 reached the maximum values of 3652 m2·g−1 and 2.35 cm3·g−1, respectively. The physicochemical properties and structural characteristics of ACs were characterized by N2 adsorption/desorption, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and X-ray photoelectron spectroscopy (XPS). In the adsorption study, gaseous benzene was selected as the adsorbate. Dynamic adsorption experiment was carried out to explore the adsorption behavior and mechanism of PACs. Under 5000 ppm (or 500 Pa partial pressure), the adsorption capacity and partition coefficient for gaseous benzene on PAC-5-850-60 were 802.06 mg g−1, and 0.20 mol kg−1Pa−1 at 10% breakthrough level and 819.77 mg g−1, and 0.02 mol kg−1Pa−1 at 100% breakthrough level. PAC-5-850-60 exhibited favorable recycling adsorption performance and could be a good absorbent for removal of gaseous benzene.

A strategy for the enhancement of trapping efficiency of gaseous benzene on activated carbon (AC) through modification of their surface functionalities.

Facile modification is a common, but effective, option to improve the uptake removal capacity of of activated carbon (AC) against diverse target volatile organic compounds (VOCs; e.g., benzene) in gaseous streams. To help design the routes for such modification, this research built strategies to generate three types of modified ACs by incorporating amine/sulfur/amino-silane groups under solvothermal or microwave (MW) thermal conditions. The adsorption performance has been tested using a total of six types of AC sorbents (three modified+three pristine forms) for the capture of 1Pa benzene (1atm and 298K). The obtained results are evaluated in relation to their textural properties and surface functionalities. Accordingly, the enhancement of AC surface basicity (e.g., point of zero charge (PZC)=10.25), attained via the silylation process, is accompanied by the reduced adsorption of benzene (a weak base). In contrast, ACs amended with amine/sulfur (electron-donating) groups using the MW technique are found to acquire high surface acidity (PZC of 5.99-6.05) to exhibit significantly improved benzene capturing capability (relative to all others). Their uplifted performance is demonstrated in terms of key performance metrics such as breakthrough volume (BTV10%: 163→443Lg-1), adsorption capacity (Q10%: 4.82→13.6mgg-1), and partition coefficient (PC10%: 0.516→1.67molkg-1 Pa-1). Based on the kinetic analysis, the overall adsorption process is found to be governed by pore diffusion as the main rate-determining step, along with surface interaction mechanisms. The results of this research clearly support the critical role of surface chemistry of AC adsorbents and their textural properties in upgrading air/gas purification systems.

The dynamic competition in adsorption between gaseous benzene and moisture on metal-organic frameworks across their varying concentration levels

Metal-organic frameworks (MOFs) have opened a new path for the construction of air/gas purification systems through a number of technological routes (e.g., adsorption and/or catalysis). To develop MOFs with upgraded adsorption performance, the breakthrough (BT) behavior of two MOF sorbents (e.g., MOF-199 and UiO-66-NH 2 ) was investigated using gaseous benzene under the interactive conditions between the two key variables: (i) the inlet benzene vapor concentration (10 to 200 ppm) and (ii) relative humidity (RH = 0 to 100%). According to the comparison of adsorption performance derived using gaseous benzene, MOF-199 outperformed UiO-66-NH 2 by 2 to 16-fold when assessed at 10% BT and zero RH. This observation thus reflects the high reactivity of Cu-metal sites for interaction with benzene ring compared with Zr sites. The dynamic adsorption data for the two MOFs at various RH conditions also indicated the competitive inhibition effect of water vapor on benzene adsorption mechanism, especially at low benzene concentrations (< 100 ppm) and high RH level of > 50%. Adsorption kinetics of benzene onto the two MOFs showed good fitting with both pseudo-first and -second-order kinetics at low RH (0–20%) conditions, whereas the results at high RH (> 50%) failed to fit with both kinetics (e.g., R 2 ≤ 0.87) because of the high roll-up effect. The water vapor acted as a competitive component, reducing the performance of the MOF adsorbents in purifying humidified gaseous streams. That effect became more prominent as the benzene concentration decreased (≤ 50 ppm), reflecting the dynamic interaction between multiple adsorbates (water and benzene) and the adsorbent. In addition, the exothermic adsorption property was evident for both MOFs under the dry conditions, while the patterns were reversed under humid conditions (e.g., 100% RH). Overall, the adsorption properties of VOCs onto MOFs and their uptake mechanisms are affected sensitively by an interplay between the key variables (e.g., concentration levels of competing adsorbates) along with the structural stabilities of sorbents against water vapor. • The adsorption of VOCs is compared at varying RH levels for MOF-199 and UiO-66-NH 2. • The performance of MOFs is assessed w.r.t. competition between benzene and water vapor. • Their performance was evaluated using key metrics like breakthrough volumes. • MOF-199 displayed the better performance at all benzene concentration levels under dry condition. • Moisture had negative effects on benzene adsorption, especially MOF-199 at low benzene levels.

Imidazole-based ionogel as room temperature benzene and formaldehyde sensor.

A room temperature benzene and formaldehyde gas sensor system with an ionogel as sensing material is presented. The sensing layer is fabricated employing poly(N-isopropylacrylamide) polymerized in the presence of 1-ethyl-3-methylimidazolium ethyl sulfate ionic liquid onto gold interdigitated electrodes. When the ionogel is exposed to increasing formaldehyde concentrations employing N2 as a carrier gas, a more stable response is observed in comparison to the bare ionic liquid, but no difference in sensitivity occurs. On the other hand, when air is used as carrier gas the sensitivity of the system towards formaldehyde is decreased byone order of magnitude. At room temperature, the proposed sensor exhibited in air higher sensitivities to benzene, at concentrations ranging between 4 and 20ppm resulting, in a limit of detection of 47ppb, which is below the standard permitted concentrations. The selectivity of the IL towards HCHO and C6H6 is demonstrated by the absence of response when another IL is employed. Humidity from the ambient air slightly affects the resistance of the system proving the protective role of the polymeric matrix. Furthermore, the gas sensor system showed fast response/recovery times considering the thickness of the material, suggesting that ionogel materials can be used as novel and highly efficient volatile organic compounds sensors operating at room temperature.Graphical abstract.

Microhotplate gas sensors incorporated with Al electrodes and 3D hierarchical structured PdO/PdO2-SnO2:Sb materials for sensitive VOC detection

High-performance, low-power microhotplate (MHP) gas sensors loaded with 3D hierarchical structured PdO/PdO2-SnO2:Sb materials on a pair of Al gas sensing electrodes were fabricated through advanced high-accuracy electrohydrodynamic printing method. The PdO/PdO2-SnO2:Sb materials with various PdO/PdO2 concentrations were initially synthesized via a mild and simple hydrothermal reaction. Their micromorphology and chemical composition were characterized by SEM, XRD, TEM, and XPS, which proved the successful synthesis. The gas sensing performance of the sensors to benzene, ethanol, acetone, formaldehyde, and ethanol-acetone mixed gas (volume ratio 1:1) was tested. The sensing property of the materials is regulated with different content of PdO/PdO2. The identification of the VOCs is realized by two-step principal component analysis (PCA). Simulation calculations on the I–V characteristic of the MHP gas sensors reveal that carriers have to get through Al2O3 barriers by Poole-Frenkel emission, which significantly affects the carrier conduction as well as the gas sensing properties. The gas sensing mechanism is analyzed from the aspects of gas sensing material and electrodes.

Fabrication and characterization of 3,4-diaminobenzophenone-functionalized magnetic nanoadsorbent with enhanced VOC adsorption and desorption capacity.

The present study, for the first time, utilized 3,4-diaminobenzophenone (DABP)-functionalized Fe3O4/AC@SiO2 (Fe3O4/AC@SiO2@DABP) magnetic nanoparticles (MNPs) synthesized as a nanoadsorbent for enhancing adsorption and desorption capacity of gaseous benzene and toluene as volatile organic compounds (VOCs). The Fe3O4/AC@SiO2@DABP MNPs used in adsorption and desorption of benzene and toluene were synthesized by the co-precipitation and sol-gel methods. The synthesized MNPs were characterized by SEM, FTIR, TGA/DTA, and BET surface area analysis. Moreover, the optimization of the process parameters, namely contact time, initial VOC concentration, and temperature, was performed by applying response surface methodology (RSM). Adsorption results demonstrated that the Fe3O4/AC@SiO2@DABP MNPs had excellent adsorption capacity. The maximum adsorption capacities for benzene and toluene were found as 530.99 and 666.00 mg/g, respectively, under optimum process parameters (contact time 55.47 min, initial benzene concentration 17.57 ppm, and temperature 29.09 °C; and contact time 57.54 min, initial toluene concentration 17.83 ppm, and temperature 27.93 °C for benzene and toluene, respectively). In addition to the distinctive adsorptive behavior, the Fe3O4/AC@SiO2@DABP MNPs exhibited a high reproducibility adsorption and desorption capacity. After the fifth adsorption and desorption cycles, the Fe3O4/AC@SiO2@DABP MNPs retained 94.4% and 95.4% of its initial adsorption capacity for benzene and toluene, respectively. Kinetic and isotherm findings suggested that the adsorption mechanisms of benzene and toluene on the Fe3O4/AC@SiO2@DABP MNPs were physical processes. The results indicated that the successfully synthesized Fe3O4/AC@SiO2@DABP MNPs can be applied as an attractive, highly effective, reusable, and cost-effective adsorbent for the adsorption of VOC pollutants.Graphical abstract.

The potential utility of HKUST-1 for adsorptive removal of benzene vapor from gaseous streams using a denuder versus a packed-bed adsorption system

The feasibility of various sorption methods has been explored to remove volatile organic compounds from indoor air (e.g., a packed bed-based air filtration system). However, the large space velocity/pressure drop is a common operational challenge associated with the use of a packed-bed adsorber, especially when using fine powdery adsorbent. Accordingly, this research was carried out to evaluate the effectiveness of two contrasting adsorptive removal systems (i.e., denuder vs. packed-bed) using a metal-organic framework (MOF: Hong Kong University of Science and Technology (HKUST-1) as a model adsorbent) as the test media. In the denuder design, HKUST-1 was coated as a thin layer (thickness 90 μm) on the inner wall of a 90 mm length quartz tube (internal diameter ≈ 4 mm) with the help of a polyvinyl alcohol binder. Additionally, an identical quartz tube was prepared with a HKUST-1 packed bed. The potential applicability of the denuder versus packed-bed was evaluated using gaseous benzene (0.1–10 partial pressure) in a N2 inlet stream at near-ambient conditions (298 K and 1 atm). A comparison of the breakthrough volume and adsorption performance data (capacity and partition coefficient) revealed that the packed bed outperformed the denuder design by four to five-fold at all inlet benzene partial pressures (0.1–10 Pa). Better performance was seen in the denuder system when benzene uptake was conducted at high benzene partial pressures (5–10 Pa) rather than at low partial pressure (<5 Pa) in the inlet stream. The evaluation of pressure drop data indicated the efficacy of the denuder over a packed bed in terms of pressure/space velocity drop, especially at a high flow rate (e.g., 330 mL min-1). However, in terms of uptake rate and space time yield, the denuder was 25 times less efficient than the packed bed.

Study on Cooling System for Parked Cars using Mini Air Cooler and Exhaust Fan

Deaths among children and pets, as well as damage to car interior components, have been widely reported as a result of parking under direct sunlight for a long time. Rising car cabin temperatures in this condition trigger the formation of benzene gas, but it is not possible to turn on the AC due to security and energy consumption. Therefore, this article reports the experimental study on cabin cooling system for parked car under direct sunlight by applying a mini air cooler and exhaust fan powered by a solar cell on small car Bajaj Qute RE60. Two thermocouples were installed inside and outside the cabin to monitor the temperature for 7 hours, expressing daytime heat conditions. The results showed that this cooling system could reduce the temperature to 10 K by removing 8982 kJ (0.356 kW) of heat. In conclusion, this prototype is very promising to be developed and if implemented on a larger scale will reduce car interior damage while parking under direct sunlight.

The morphology and photocatalytic performance of Zn(OH)F under different synthetic conditions

Metal hydroxyfluorides have been widely used in the development of new functional materials, due to their diverse preparation methods and easy controlled morphologies. As an important zinc-based nanomaterial, zinc hydroxy fluoride (Zn(OH)F) is not only an important precursor for the synthesis of zinc oxide (ZnO) nanomaterials with special morphology, but also an effective photocatalyst in the degradation of organic pollutants. In this article, many different morphologies of Zn(OH)F were synthesized by changing the synthetic conditions (temperatures, reactants, surfactants), such as barklike, rod, cluster, ribbon, criss-cross, cross-assembled network, thorn-ball and so on. Moreover, their photocatalytic performances were investigated and barklike Zn(OH)F-T250 displayed good photocatalytic performance for liquid degradation (salicylic acid, rhodamine B, methylene blue and phenol) and gaseous benzene removal under UV-light irradiation. Therefore, this study about morphology control for metal hydroxyfluorides not only provides important theoretical value, but also performs broad application prospects.

The interactive roles of space velocity and particle size in a microporous carbon bed system in controlling adsorptive removal of gaseous benzene under ambient conditions

The performance of an air filtration system is commonly evaluated using laboratory-scale studies under optimal, but unrealistic, experimental conditions (e.g., high pollutant loading, slow feeding rate, and fine particle size). It is, therefore, important to assess the role of key variables affecting performance from a practical perspective. To this end, a series of dynamic adsorption tests were carried out to evaluate the uptake behavior of gaseous benzene (at 1 Pa) by a filter bed system made of a commercial activated carbon (AC) in relation to two key variables: particle-size range (granular AC [GAC]: 0.212 to 5 mm vs. powdered AC [PAC]: 0.6 to 2.36 mm) and space velocity (flow rates: 100 to 3000 mL min−1). The effects of these two key variables on capturing of benzene were assessed in terms of key performance metrics (e.g., breakthrough volume [BTV]: L g−1 atm−1, partition coefficient [PC]: mol kg−1 Pa−1, and adsorption capacity [Q]: mg g−1). It was verified that GAC outperformed PAC at a low flow rate (100 to 500 mL min−1), in particular in the 5% BTV region. In contrast, PAC performed better at a 100 L BTV (PC: 0.49 to 0.98 mol kg−1 Pa−1) under high flow conditions (1000 to 3000 mL min−1). The results of isotherm/kinetic analysis revealed the dominant role of the surface/pore diffusion in the multilayer adsorption of benzene onto GAC adsorbent (relative to PAC adsorbent). With the increases in space velocity, the flow patterns crossed from a laminar to transitional mode to promote advection transport (relative to diffusion transport) of benzene molecules through the GAC-bed filter (relative to the PAC-bed filter). These findings are expected to help open new paths for optimization of air filtration system under real environmental conditions, particulary with respect to space velocity and particle diameter (of adsorbent).

A solar light-induced photo-thermal catalytic decontamination of gaseous benzene by using Ag/Ag3PO4/CeO2 heterojunction

The effectively decontamination for atmosphere VOCs is getting more important whereas it is general facing the issues such as technical difficulties and high energy consumption. In this work, a Z-scheme Ag/Ag3PO4/CeO2 heterojunction was prepared with a precipitation method and was applied to decompose gaseous benzene at very convenient ambient conditions. The prepared composite presents a 90.18% removal rate and 74.17% TOC efficiency within 3 h solar light irradiation at an initial 600 ppm benzene concentration. A photo-catalytic mechanism superimposed with solar light induced thermo-catalysis is proposed. Ag3PO4 that has great solar light absorptive capacity is used as the photocatalytic component and CeO2 is used as thermo-catalytic substrate due to its good thermo-conductivity in lower temperature. Ag0 produced from an in situ reduction of Ag3PO4 is used as an electronic relay platform to form a Z-type heterojunction together with Ag3PO4 and CeO2. Lots of vacancies of CeO2 contribute to the enhanced pre-adsorption towards to VOCs. The assembled Z-scheme Ag/Ag3PO4/CeO2 heterojunction is specially effectively for the separation of the photo-excited electrons and holes in space and maintains the highly redox potentials to decontaminate VOCs. Meanwhile, the composite is diverse, also having good oxidative power for HCHO, and thus could be a kind of promising material to purify VOCs in the convenient atmospheric environment.

Enhancing benzene removal by Chlorophytum comosum under simulation microgravity system: Effect of light-dark conditions and indole-3-acetic acid

Air phytoremediation technology has been reported as a high potential technology for indoor air pollution treatment. Since 1996, NASA has supported this technology for application in the international space station. However, changes in plant physiology and hormone levels under microgravity (μG) conditions might affect air phytoremediation efficiency, especially changes of auxin hormone transportation in plants. In this study, the application of Chlorophytum comosum, high benzene removal plant species, to remove 100 ppm gaseous benzene under μG condition was studied. The experiment was operated for three days in a random positioning machine generate 6.44 × 10−4 G within 1 h. The results showed that under μG, benzene removal efficiency by C. comosum was significantly increased, with a remove more than 80% within three days under both 24 h light and dark conditions. In contrast, C. comosum growing under normal gravity (1G) can remove about 75% and 50% benzene under 24 h light and 24 h dark conditions, respectively. Surprisingly, μG conditions seem to maintain open stomata of a plant open under both 24 h light and dark conditions, and this plant will normally have closed stomata in the dark. In this case, shoot auxin hormone in the form of Indole-3-acetic acid was highly increased in the plant growing under μG. This result suggested that under μG, auxin hormone might be accumulated in the shoot part of plant. This auxin accumulation effect of maintaining open plant stomata can enhance benzene phytoremediation efficiency since stomata are the major benzene uptake pathway. Therefore, this study is the first report presenting the possibility of applying air phytoremediation technology under μG conditions.

Mo-ion doping evoked visible light response in TiO2 nanocrystals for highly-efficient removal of benzene

In this work, Mo ions were employed to evoke the visible light response of TiO2 nanocrystals to enhance its photocatalytic removal ability of indoor gaseous benzene. The photocatalytic reaction rate constant of the optimal Mo-TiO2 was 0.0065 min−1, which was 4.81 times higher than that of undoped TiO2. Density functional theory (DFT) calculations using a novelty charge compensation structure model were performed to investigate the effect of Mo-doping on the electronic structure of TiO2. The theoretical results indicated that the reduction of bandgap energy could be attributed to the introduced Mo-d states. PL and I-t results showed that Mo ions with proper concentration could suppress the recombination of carriers. The feasible reaction pathways were also revealed based on the detected intermediates. The catalysts also exhibited good long-term stability in the recycling experiments for 6 runs. Furthermore, 1 kg of Mo-TiO2 nanocrystals could be produced with uniform morphology and clean surface by one batch synthesis. These promising results not only provide a facile synthesis route of Mo-TiO2 but also can promote the practical application of TiO2-based photocatalysts in environmental remediation.

Ultra-Sensitive Benzene Detection and Gas Sensing Mechanism of (C4H9NH3)2PbI2Br2 Organic-Inorganic Perovskite

Introduction Benzene vapour is one of the general hazardous air pollutants, as well as a typical lung cancer marker, hence the permissible environment limit value has been regulated to be ~1.6 ppb (part per billion) in Europe. It is interesting to develop a portable device for detection ultra-low concentration benzene. Chemiresistive gas sensors to detect benzene have been widely investigated, however, most detection limits are in ppm level,while only a few reports are in ppb level (100 ppb)[1]. Organic-inorganic hybrid perovskites combine the excellent performance of organic materials and inorganic semiconductors, so one compound was utilized as a gas sensing material in this work. Synthesis and benzene detecting application of (C4H9NH3)2PbI2Br2 are reported, and the gas sensing mechanism is also discussed using in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRFT-IR). Synthesis of (C4H9NH3)2PbI2Br2 Perovskite (C4H9NH3)2PbI2Br2 was synthesized through a facile mixed solution method [2]. N-butylamine (30 ml) was dissolved in 47 wt% hydroiodic acid (35 ml) and absolute ethanol (15 ml) solution under ice-water bath. The pomegranate red solution was maintained at 70 °C for 2 h in a water bath kettle, resulting in light yellow solution. Then, white powders were obtained via vacuum distillation at 90 °C for 20 min. The powders were then collected with the suction filter, washed several times with ether, and dried at 70 °C in a vacuum oven for 12 h. PbBr2 (0.8808 g) and as-obtained C4H9NH3I (0.9651 g) were mixed in 47 wt% hydroiodic acid (10 ml), 48 wt% hydrobromic acid (10 ml) and absolute ethanol (10 ml) solution. The solution was kept at 90 °C for 2 h in a water bath kettle, resulting in light yellow solution. Then, light yellow powders were obtained via vacuum distillation at 70 °C for 20 min. The powders were collected with the suction filter, washed several times with ether, and dried at 70 °C in a vacuum oven for 24 h. S ensor F abrication and Measurement The perovskite was fabricated into a traditional resistive sensor device [3]. The sensing performance was conducted on a NS-4000 Smart Sensor Analyser (Beijing Zhong Ke Micro-Nano Networking Technology Ltd., China). The response was defined as the ratio of sensor resistance in air (Ra) to that in a target gas (Rg): Sr = Ra/Rg. Results and Conclusions The perovskite (C4H9NH3)2PbI2Br2 exhibits the highest response at the optimum operating temperature of 160 °C, indicating excellent selectivity, as shown in Fig. 1 (a). This gas sensor shows such ultra-high response for ppt-level benzene that has never been reported before. As can be seen in the response-recovery curves in Fig. 1 (b), the response increases fast to an equilibrium value and then decreases rapidly to the baseline in each cycle at 160 °C. The in-situ DRFT-IR spectra of (C4H9NH3)2PbI2Br2 in air and benzene at room temperature (RT) and 160 °C, respectively, confirming the gas sensing mechanism is originated from the physical adsorption-desorption of benzene molecules on the (C4H9NH3)2PbI2Br2 surface, charge transfer model of which is quite different from that of conventional metal oxides. Fig. 1 (a) Response of the (C4H9NH3)2PbI2Br2 sensor to 500 ppt benzene, toluene, ethanol, ortho-xylene, and para-xylene gases at various operating temperatures. (b) Response-recovery curves of the gas sensor to 1–500 ppt benzene at 160 °C. (c) In-situ DRFT-IR spectra of (C4H9NH3)2PbI2Br2 in air and benzene at RT and 160 °C, respectively.

Highly Sensitive Acetone Gas Sensors Using Nanocomposites of CuO Hollow Nanocubes Decorated on TiO2

Introduction There has been considerable effort to detect volatile organic compounds (VOCs) by metal oxide semiconductor gas sensors for their high sensitivity, low cost, easy production, and compact size [1]. In recent times, acetone in exhaled breath have studied for biomarkers more than hazardous air pollutants. According to the previous studies, breath acetone may be correlated with fat burning [2-3] not only a specific breath marker for type-1 diabetes [4]. However, there are many drawbacks of metal oxide based acetone sensors to apply diet monitoring since the concentration of breath acetone for healthy humans are from 300 to 900 ppb, which require to develop highly sensitive sensing materials and systems. From this point of view, addition of noble metals for catalytic effect, formation of p-n heterojunction and synthesis of hierarchical and hollow nanostructures for high surface area are suggested to improve the sensing performances. In this study, we describe the novel nanostructure of hollow CuO nanocubes decorated on hollow TiO2 nanosphere and investigate their acetone gas response properties. Method TEM images of the nanoparticles were obtained by FEI Tecnai G2 F30 S-Twin (300 kV, KAIST). For the preparation of gas sensing devices based on TiO2-CuO nanocomposites, interdigitated electrodes on 8-inch oxidized silicon wafers were formed using conventional photo lithographic techniques. A sub micrometer layer of the photoresist was spin-coated onto the silicon oxide wafer at 5000 rpm and baked at 90 ℃ for 3 min before ultraviolet (UV) exposure in a photo mask aligner. After the exposure, the wafer was developed for 30 s in a developing solution. The Au electrode with 10 μm gaps on silicon substrate were successfully patterned with thin films (10 nm Cr/100 nm Au) deposited by e-beam evaporation and a metal lift-off process in acetone. Then, TiO2-CuO dispersed in ethanol spin-coated onto interdigitated electrodes. The dynamic sensing responses were measured using a data-acquisition system consisting of Agilent 34970A and BenchLink Data logger program, and the sensor devices were located in a temperature-controlled chamber. Dry air was used as a balance gas at a flow rate of 1000 cc/min. In addition, the acetone gas was used as an analyte (obtained from RIGAS Co. in Korea) at a concentration of 10 ppm/100ppm and blended with a balance gas to achieve the desired analyte concentrations of 20 ppb to 10 ppm by using mass-flow controllers. The gas response was measured by allowing the concentration-controlled acetone gas to flow into the reaction chamber, and then allowing only the balance gas to flow into the chamber for recovering the gas sensor. Results and Conclusions Figure 1 shows the TEM images of the formation of TiO2-CuO hollow nanocubes. First, 300 nm of hollow TiO2 nanosphere was synthesized as shown in figure 1 (a). Then, Cu2O nanocubes were decorated on TiO2 (figure 1 (b)) and diameter of nanocubes was approximately 20 nm. For the TiO2-CuO hollow nanocubes, TiO2-Cu2O need additional thermal oxidation process and the oxidized CuO hollow nanocubes are shown in figure 1 (c-d). Acetone-sensing properties of TiO2-CuO hollow nanocubes were studied at optimized operating temperature, 200 ℃, under a dry condition. Figure 2 shows the response curve of TiO2-CuO hollow nanocubes for acetone 1 ppm and the response value is estimated to 12.1. Here, TiO2-CuO hollow nanocubes shows the p-type semiconductor properties even TiO2 is typical n-type semiconductor because p-type CuO hollow nanocubes are covered the surface of TiO2 hollow nanosphere so that the ratio of p-p contact becomes higher and therefore, its electrical property is dominated by p-type. Figure 3 shows the abbreviation curve of sensitivity as a function of acetone concentration from 20 ppb to 500 ppb. The response values were increased with increasing acetone concentration and limit of detection was calculated as 2.23 ppb using the noise of base resistance [5]. And the responses of TiO2-CuO hollow nanocubes toward other gases existing in VOCs was also examined. As shown in figure 4, response of 1 ppm acetone, formaldehyde, benzene and ammonia gas at 200 ℃ were measured and TiO2-CuO showed the highest response to acetone gas among the tested gases.

Natural rubber modification as a pre-vulcanized latex impregnated with TiO2 for photo-catalytic degradation of gaseous benzene

Photocatalytic oxidation purposes an economical and environmental friendly process to remove benzene from indoor air pollution. However, the process efficiency is primarily dependent on catalytic-film. The main purpose of this study is to synthesize pre-vulcanized latex impregnated with TiO2 (PVL-TiO2 thin film) from natural rubber to be used in photo-catalytic oxidation for benzene removal in a reactor. PVL-TiO2 thin films were synthesized for 3 different dosages of TiO2, which were 5%, 15%, and 25% The outcome of this study offers the new application of modified natural rubber in terms of environmental and health care protection. Morphology of the synthesized films was analyzed by SEM. The results showed that TiO2 particles could be well dispersed all over the surface of the film, in which the best distribution could be found for the PVL-TiO2 15% thin film. Tensile stress of the films was analyzed using ASTM D412. Results showed that the stress of the films got higher with the increasing amount of TiO2 content. This indicates that TiO2 strengthened the PVL-TiO2 film because the uniformly distribution of TiO2 on the inner surface increased the strength of the film. The decomposition of PVL and PVL-TiO2 thin films was analyzed using thermo gravimetric analysis. The maximum weight loss rates in the range of 1.536–1.145 wt%/°C attained at between 380 - 382 °C TiO2 particles enhanced thermal stability of PVL-TiO2 thin films due to the high decomposition temperature of its properties and also acted as barrier for the heat transfer of the films. Specific surface area (SSA) of the films was analyzed using Brunauer-Emmett-Teller. Specific surface area increased as the increasing content of TiO2, which corresponded to the morphology analysis by SEM. The analysis of chemical functional group of thin films was performed using ATR-FTIR. The results of Crystal identification using XRD clearly showed good attachment of rutile TiO2 on the films. Finally, results of absorbance spectrums and band gap energy showed that PVL not only peg TiO2 particles but also reducing band gap energy which induced by S and ZnO. Therefore, PVL-TiO2 thin films could be used under visible light condition. The films were then used in the study of benzene removal in annular reactor. The highest removal efficiency (83%)for the PVL-TiO2 15% thin film was obtained. Comparing to the maximum removal efficiency for PVL film (28%), roughly 60% increase in efficiency was achieved. The PCO kinetics were well fit by a first order Langmuir-Hinshelwood model. The calculation of oxidation rate and percentage of residual intermediates indicated that accumulation of residual intermediates can occur on the active site and the gas phase, resulting in increasing of residual intermediates. The successful synthesis of PVL-TiO2 thin film provides new opportunity to use natural rubber in terms of environmental and health care protection.