Development of regenerative dye impregnated mesoporous silica materials for assessing exposure to ammonia.

The mesostructured materials MCM-41 and SBA-15 were studied as possible supports of bromocresol green (BG) dye impregnation for the ammonia gas detection because of their large surface area, high regenerative property, and high thermal stability. X-ray diffraction, transmission electron microscopy, scanning electron microscope, and N2 adsorption analysis were used to characterize the prepared materials. These materials could sense ammonia via visible color change from yellowish-orange to blue color. The color change process of the nanostructured materials was fully reversible during 10 cyclic tests. The results indicated that the ammonia absorption responses of the two nanostructured materials were both very sensitive, and high linear correlation and high precision were achieved. As the gaseous ammonia concentrations were 50 and 5 ppmv, the response times for the SBA-15/BG were only 1 and 5 min, respectively. Moreover the BG dye-impregnated SBA-15 was less affected by the variation in the relative humidity. It also had faster response for the detection of NH3, as well as lower manufacturing price as compared to that of the dye-impregnated MCM-41. Such feature enables SBA-15/BG to be a very promising material for the detection of ammonia gas.

Bromocresol green/mesoporous silica adsorbent for ammonia gas sensing via an optical sensing instrument.

A meso-structured Al-MCM-41 material was impregnated with bromocresol green (BG) dye and then incorporated into a UV-Vis DRA spectroscopic instrument for the online detection of ammonia gas. The absorption response of the Al-MCM-41/BG ammonia sensing material was very sensitive at the optical absorption wavelength of 630 nm. A high linear correlation was achieved for ppmv and sub-ppmv levels of ammonia gas. The response time for the quantitative detection of ammonia gas concentrations ranging from 0.25 to 2.0 ppmv was only a few minutes. The lower detection limit achieved was 0.185 ppmv. The color change process was fully reversible during tens of cycling tests. These features together make this mesoporous Al-MCM-41 material very promising for optical sensing applications.

Copper loaded on sol-gel-derived alumina adsorbents for phosphine removal.

The hydride gas of phosphine (PH3) is commonly used for semiconductor and optoelectronic industries. The local scrubbers must immediately abate it because of its high toxicity. In this study, copper (Cu) loaded on the sol-gel-derived gamma-alumina (Al2O3) adsorbents are prepared and tested to investigate the possibility of PH3 removal and sorbent regeneration. Test results showed that during the breakthrough time of over 99% PH3 removal efficiency, the maximum adsorption capacity of Cu loaded on the sol-gel-derived gamma-Al2O3 adsorbent is 18 mg-PH3/g-adsorbent. This is much higher than that of Cu loaded on the commercial gamma-Al2O3 adsorbent--8.6 mg-PH3/g-adsorbent. The high specific surface area, narrow pore size distribution, and well dispersion of Cu loaded on the sol-gel-derived gamma-Al2O3 could be the reasons for its high PH3 adsorption capacity. The regeneration test shows that Cu loaded on the sol-gel-derived gamma-Al2O3 adsorbent can be regenerated after a simple air purging procedure. The cumulative adsorption capacity for five regeneration cycles is 65 mg-PH3/g-adsorbent, which is approximately double that of the Cu/zeolite adsorbent demonstrated in the literature.

Removal of volatile organic compounds by single-stage and two-stage plasma catalysis systems: a review of the performance enhancement mechanisms, current status, and suitable applications.

This paper provides a comprehensive review regarding the application of plasma catalysis, the integration of nonthermal plasma and catalysis, on VOC removal. This novel technique combinesthe advantages of fast ignition/response from nonthermal plasma and high selectivity from catalysis. It has been successfully demonstrated that plasma catalysis could serve as an effective solution to the major bottlenecks encountered by nonthermal plasma, i.e., the reduction of energy consumption and unwanted/hazardous byproducts. Instead of working independently, the combination could induce extra performance enhancement mechanisms either in a single-stage or a two-stage configuration, in which the catalyst is located inside and downstream from the nonthermal plasma reactor, respectively. These mechanisms are believed to be responsible for the higher energy efficiency and better CO2 selectivity achieved with plasma catalysis. A comprehensive discussion on the performance enhancement mechanisms is provided in this review paper. Moreover, the current status of the applications of two different plasma catalysis systems on VOC abatement are also given and compared. The catalyst plays an important role in both configurations. Especially for the single-stage type, depositing an inappropriate active component on catalytic support would decrease the VOC removal efficiency instead. To date, no definite conclusion on catalyst selection forthe single-stage plasma catalysis is available. However, MnO2 seems to be the best catalyst for two-stage configuration because it could effectively decompose ozone and generate active species toward VOC destruction. On the other hand, although the single-stage plasma catalysis has been proved to be superior to the two-stage configuration, it does not mean that the former is always the best choice. Considering the typical VOC concentrations from different sources and the characteristics of different plasma catalysis systems, the single-stage and two-stage configurations are suggested to be more suitable for industrial and indoor air applications, respectively.

Silane removal at ambient temperature by using alumina-supported metal oxide adsorbents.

Copper, zinc, and cerium oxide adsorbents supported on alumina were used to remove silane gas (SiH4). The adsorbents were prepared using a coprecipitation method and characterized by the inductively coupled plasma mass spectrometry, X-ray powder diffractometer, and Brunauer-Emmett-Teller method (BET). The silane removal efficiency and adsorption capacity of the adsorbents were investigated in this study. Test results showed that the adsorbents containing active species had a removal efficiency >99.9% for SiH4 before breakthrough. Adsorbents containing mixed oxides (CuO-CeO2/ Al2O3 and CuO-ZnO/Al2O3), which showed well-dispersed active species and high BET surface areas, had a greater adsorption capacity than the adsorbents containing single metal oxide. However, when the CuO-ZnO/ Al2O3 adsorbents contain >40 wt% of active metal oxides, the increase of active species lowered the BET surface area leading to a decrease of the adsorption capacity. Additionally, when the content of the active metal oxides was between 20% and 40%, the CuO-ZnO/Al2O3 adsorbents demonstrated higher adsorption capacity.

An efficient venturi scrubber system to remove submicron particles in exhaust gas.

An efficient venturi scrubber system making use of heterogeneous nucleation and condensational growth of particles was designed and tested to remove fine particles from the exhaust of a local scrubber where residual SiH4 gas was abated and lots of fine SiO2 particles were generated. In front of the venturi scrubber, normal-temperature fine-water mist mixes with high-temperature exhaust gas to cool it to the saturation temperature, allowing submicron particles to grow into micron sizes. The grown particles are then scrubbed efficiently in the venturi scrubber. Test results show that the present venturi scrubber system is effective for removing submicron particles. For SiO2 particles greater than 0.1microm, the removal efficiency is greater than 80-90%, depending on particle concentration. The corresponding pressure drop is relatively low. For example, the pressure drop of the venturi scrubber is approximately 15.4 +/- 2.4 cm H2O when the liquid-to-gas ratio is 1.50 L/m3. A theoretical calculation has been conducted to simulate particle growth process and the removal efficiency of the venturi scrubber. The theoretical results agree with the experimental data reasonably well when SiO2 particle diameter is greater than 0.1 microm.

A local scavenging system to remove waste anesthetic gases during general anesthesia.

BACKGROUND: A local scavenging system was constructed and tested in both the operating room and the laboratory to remove the waste anesthetic gases so as to lower the exposure risk of the anesthetic personnel. METHODS: A local scavenging system was developed to suck away the waste anesthetic gases (e.g., N2O and sevoflurane) escaping from the mouth and nostrils of a patient. The local scavenging system used was composed of an inlet funnel (with a diameter of 20 cm), a flexible connecting tubing, a high efficiency particulate air (HEPA) filter and a vacuum pump. To help evaluate the performance of the local scavenging system, a tracer gas (SF6) of a fixed concentration (= 200 ppm) and flow rate (= 5 l/min) was introduced around the nostrils of the patient during anesthesia. The concentrations of the gases (SF6, N2O and SEV) drawn away by the scavenging system were then determined by an extractive Fourier transform infrared (FTIR) spectrometer and those spreading around the breathing zone of the anesthesiologist were obtained by the other FTIR. In the laboratory tests, the relationship between the scavenging efficiency and the inlet funnel position was obtained using the aforementioned SF6-FTIR techniques. RESULTS: With the application of this local scavenging system, during three surgical operations, the average personnel exposure concentrations of N2O and sevoflurane (SEV) as measured were 8.7 and 0.06 ppm, respectively. Both measured concentrations were lower than the TWA values recommended by the US-NIOSH for N2O (= 25 ppm) and SEV (= 2 ppm). Based on the tracer gas (SF6) results, it was found that the average scavenging efficiency was equal to 87%, which was lower than the laboratory testing results of 95%. The (scavenging) efficiency difference between the laboratory and on-site tests could be due to the movement and action of the anesthesiologist during anesthesia. To optimize the performance of the local scavenging device, the inlet (funnel) should be placed close to the breathing region (e.g., noses and mouth) of the patient in the front direction. CONCLUSIONS: The application of the local scavenging system was found to greatly reduce the concentrations of the waste anesthetic gases (e.g., N2O and SEV) to the levels lower than those recommended by the US-NIOSH. With this scavenging device, the exposure health risk of the anesthesiologists could be greatly reduced.

Using an extractive Fourier transform infrared spectrometer for improving cleanroom air quality in a semiconductor manufacturing plant.

A mobile extractive Fourier transform infrared (FTIR) spectrometer was successfully used to locate, identify, and quantify the "odor" sources inside the cleanroom of a semiconductor manufacturing plant. It was found that ozone (O(3)) gas with a peak concentration of 120 ppm was unexpectedly releasing from a headspace of a drain for transporting used ozonized water and that silicon tetrafluoride (SiF(4)) with a peak concentration of 3 ppm was off-gassed from silicon wafers after dry-etching processing. When the sources of the odors was pinpointed by the FTIR, engineering control measures were applied. For O(3) control, a water-sealed pipeline was added to prevent the O(3) gas (emitting from the ozonized water) from entering the mixing unit. A ventilation system also was applied to the mixing unit in case of O(3) release. For SiF(4) mitigation, before the wafer-out chamber was opened, N(2) gas with a flow rate of 150 L/min was used for 100 sec to purge the wafer-out chamber, and a vacuum system was simultaneously activated to pump away the purging N(2). The effectiveness of the control measures was assured by using the FTIR. In addition, the FTIR was used to monitor the potential hazardous gas emissions during preventative maintenance of the semiconductor manufacturing equipment.

The effect of environmental conditions and electrical charge on the weighing accuracy of different filter materials.

Different filter materials and electrical charge elimination methods were used to investigate the weighing accuracy of filter papers under different environmental conditions. The results show that the standard deviations (S.D.) of weight data for glass fiber and MCE filters were substantial without environmental control, whether or not the electrical charge eliminators were used. Values of 0.157 and 0.349 mg were determined for glass and MCE filters, respectively. The accuracy of weighing was substantially improved and the S.D. was reduced to 0.01 and 0.09 mg for glass fiber and MCE filters, respectively, after applying the environmental control conditions. For PVC and Teflon filters, the accuracy of weighing was good, even in the uncontrolled environmental conditions, whether or not the electrical charge eliminators were used. The S.D. values of weighing data of PVC and Teflon filters were 0.007 and 0.011 mg, respectively.

Personnel exposure to waste sevoflurane and nitrous oxide during general anesthesia with cuffed endotracheal tube.

BACKGROUND: Waste anesthetic gases may have adverse effects on the health of operating room personnel. To reduce the risk of exposure, the United States National Institute of Occupational Safety and Health (US-NIOSH) recommends a time-weighted average (TWA) of 25 ppm (part-per-million) for nitrous oxide (N2O) and a ceiling of 2 ppm for sevoflurane (SEV). This study investigated the concentrations of these two gases in the atmosphere of operating room to which the working personnel (anesthetists) were exposed during anesthetic practice. METHODS: An extractive Fourier transform infrared (FTIR) spectrometer, with an optical path length of 10 meters, was used to monitor the concentrations of waste general anesthetics in the operating rooms. The FTIR in application could simultaneously determine the concentrations of several gases in a near real-time manner, which helped to accurately obtain the varying concentrations of gases in different anesthetic condition. The sampling Teflon tube of the FTIR was conveniently installed in the breathing zone of the anesthetic personnel to obtain the personal exposure concentrations of N2O and SEV. RESULTS: Nitrous oxide (N2O) and sevoflurane (SEV) concentrations for five surgeries in four different operating rooms were determined. In normal condition during maintenance, the SEV concentrations as measured were less than 2 ppm but the average N2O concentration was greater than 25 ppm. In addition, in three abnormal or specific conditions, the N2O and SEV concentrations increased dramatically. Firstly, at the end of maintenance (right before emergence), peak concentrations of 751 ppm for N2O and 26 ppm for SEV were measured. These unusually high concentrations resulted from flushing the tubing of the anesthetic machine to speed up the emergence of wakefulness of the patient from anesthesia. Secondly, when the cuff of the endotracheal tube was not well inflated or unserviceable, peak concentrations of 631 ppm for N2O and 32 ppm for SEV were measured. Thirdly, malfunction of or loose connection (or disconnection) between the anesthetic machine and the exhaust venting system of operating theater almost doubled the N2O and SEV concentrations. CONCLUSIONS: To decrease the exposure of the operating personnel to waste anesthetics, minimization of the use of N2O is recommended. Besides, the three extraordinary conditions as disclosed in this study were tubing flushing, illy managed endotracheal tube cuff and disconnection of scarvenging system, the first of which sometimes is unavoidable but the last two of which should be avoided.