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.

Implications: The detector tube is a convenient ambient ammonia detection device. However, almost all the commercial detector tubes can be used once only, which not only increases the purchase cost but also produces lots of waste. In this study, we developed two sensing materials that are sensitive for repeated usage. The two mesoporous silica-based materials, MCM-41 and SBA-15, are impregnated by an organic dye of bromocresol green to induce color change behavior that can be easily observed by the naked eye, and it is concluded that dye-impregnated SBA-15/BG is a very promising material for the detection of ammonia gas.     

Co3O4/介孔分子筛催化剂对苯催化完全氧化的研究

分别以介孔分子筛MCM-41、MCM-48、SBA-15为载体，采用等体积浸渍法制备了氧化钴/介孔分子筛催化剂，利用N₂吸附、X射线衍射、程序升温还原等技术对催化剂进行了表征，考察了Co₃O₄的负载量及载体的孔结构对催化剂完全催化氧化苯的性能的影响。结果表明，Co₃O₄的负载量为20%时，催化剂的催化活性最好；载体的孔径和催化剂的可还原性能是影响催化活性的主要因素，催化剂活性顺序为Co₃O₄ /SBA-15> Co₃O₄ /MCM41> Co₃O₄ /MCM-48。     

Adsorption of basic dyes onto MCM-41

The adsorption of two basic dyes, Basic Green 5 (BG5) and Basic Violet 10 (BV10), onto MCM-41 was studied to examine the possible effect of interactions between large adsorbates and MCM-41 on the pore structure stability of MCM-41 and the potential of MCM-41 for the removal of basic dyes from wastewater. The revolutions of surface characteristics and pore structure of MCM-41 induced by dyes adsorption were characterized based on the analyses of the nitrogen isotherms, the XRD patterns, and the FTIR spectra. It was experimentally concluded that when the effect of interactions between large dyes (such as BV10) and MCM-41 on the pore structure stability of MCM-41 was insignificant, MCM-41 might be a good adsorbent for the removal of basic dyes from wastewater. The adsorption of BV10 on MCM-41 with respect to contact time, pH, and temperature was then measured to provide more information about the adsorption characteristics of MCM-41. Both Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the pseudo-second-order kinetic model was used to describe the kinetic data, from which some adsorption thermodynamic parameters were also evaluated.     

Modified SBA-15 mesoporous silica for heavy metal ions remediation

N-Propylsalicylaldimino-functionalized SBA-15 mesoporous silica was prepared, characterized and used as an adsorbent for heavy metal ions. The organic-inorganic hybrid material was obtained using successive grafting procedures of SBA-15 silica with 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. For comparison an amorphous silica gel was functionalized using the same procedure. The structure and physicochemical properties of the materials were characterized by means of elemental analysis, X-ray diffraction (XRD), nitrogen adsorption-desorption, thermogravimetric analysis and FTIR spectroscopy. The organic functional groups were successfully grafted on the SBA-15 surfaces and the ordering of the support was not affected by the chemical modification. The behavior of the grafted solids for the adsorption of heavy metals ions from aqueous solutions was investigated. The hybrid materials showed high adsorption capacity and high selectivity for copper ions. Other ions, such as nickel, zinc, and cobalt were adsorbed by the modified SBA-15 material. The adsorbent can be regenerated by acid treatment without altering its properties.     

Evaluation of new surfactant expanded zirconium and titanium phosphates for polycyclic aromatic hydrocarbons extraction from waters

A newly synthesized family of materials prepared with surfactant as organic template were tested for the extraction of polycyclic aromatic hydrocarbons (PAHs) from water, using pyrene (Pyr) and benzo[a]pyrene (B[a]P) as PAHs representatives. Particular attention was paid to the evaluation of the recovery factors with dichloromethane as eluent in order to estimate their potential as adsorbing solid phases for PAH remediation or analysis. Eleven lamellar MCM-50 type materials incorporating n-alkyl- (n = 12, 16, 18) trimethylammonium bromide molecules with different concentrations and chain lengths and two hexagonal MCM-41 type materials incorporating octadecyl-trimethyl ammonium bromide were tested. Best results were obtained by preparing lamellar MCM-50 zirconium and titanium phosphates in the presence of n-dodecyl-trimethylammonium at a relative molar concentration (surfactant/phosphate) of 1.     

Adsorption of mesitylene via mesoporous adsorbents

Mesitylene (or 1,3,5-trimethylbenzene) is a volatile organic compound emitted from various industrial processes, e.g., spray coating. Its emissions have become a critical issue because mesitylene is toxic and cannot be removed using traditional adsorbents, e.g., zeolite (H-ZSM-5; the diameter of mesitylene molecules is greater than the pore size of H-ZSM-5). Hence, an adsorbent with a large pore size, MCM-41, is used in this study to investigate its adsorption capacity for mesitylene and compare with that of H-ZSM-5. Experimental results reveal that MCM-41 without Al₂O₃ exhibits a good adsorption capacity (184 mg/g) for the gas stream containing 100 ppm of mesitylene at a relative humidity of 10%. The adsorption kinetics is well described by the Freundlich isotherm. Furthermore, experimental results reveal that MCM-41 is effective for the adsorption of low concentrations (10 ppm) of mesitylene. In addition, adsorption–desorption tests revealed that the sample MCM-41-AS is stable to sustain the adsorption capacity after 10 adsorption–desorption cycles. After 10 adsorption–desorption cycles, MCM-41-AS retains 92.4% of its initial adsorption capacity (170 vs. 184 mg/g). Finally, MCM-41 and H-ZSM-5 in series are effective for the simultaneous removal of mesitylene and toluene in the gas stream.

Implications: This study aims to improve the performance of adsorbent for mesitylene, which is typically applied in the spray-coating industry. The zeolite MCM-41-AS is selected as a candidate for the investigation. Experimental results reveal that MCM-41-AS exhibits a good adsorption capacity for mesitylene and that it can be integrated with H-ZSM-5-25 for the simultaneous adsorption of mesitylene and toluene.     

MCM-41介孔分子筛的合成及其对铜离子的吸附性能

以微硅粉为硅源，CTAB和PEG-6000为模板剂，合成MCM-41介孔分子筛。采用XRD、N2吸附-脱附曲线、FT—IR以及TEM表征了其结构、比表面积、孔径分布及晶体形貌，并且以该样品为吸附剂，对含Cu2＋的溶液进行了静态吸附实验。结果表明，以微硅粉为硅源成功合成了具有典型六方排列孔道结构的MCM-41，其比表面积为869．5m。／g，孔容为0．97cm3／g，平均孔径为3．3nm；溶液pH为5—6时，MCM-41对Cu2＋的去除效果最好；MCM-41对Cu3＋的最大吸附吸附容量36．3mg／g；MCM-41对Cu2＋的吸附性能符合Langmuir吸附方程的特征。动力学研究表明，该过程符合准二级动力学模型。     

MCM-41介孔分子筛的合成及其对铜离子的吸附性能简

以微硅粉为硅源，CTAB和PEG-6000为模板剂，合成MCM-41介孔分子筛。采用XRD、N₂吸附-脱附曲线、FTIR以及TEM表征了其结构、比表面积、孔径分布及晶体形貌，并且以该样品为吸附剂，对含Cu²⁺的溶液进行了静态吸附实验。结果表明，以微硅粉为硅源成功合成了具有典型六方排列孔道结构的MCM-41，其比表面积为869.5 m²/g，孔容为0.97 cm³/g，平均孔径为3.3 nm；溶液pH为5~6时，MCM-41对Cu²⁺的去除效果最好；MCM-41对Cu²⁺的最大吸附吸附容量36.3 mg/g；MCM-41对Cu²⁺的吸附性能符合Langmuir吸附方程的特征。动力学研究表明，该过程符合准二级动力学模型。     

Eco-friendly synthesis of nanostructured mesoporous materials from natural source rice husk silica for environmental applications

Environmental Science and Pollution Research - Nanostructured mesoporous materials of MCM-41 type were synthesized using a natural, non-toxic, and cheap source of silica from rice husk. Then, this...     

Study on the indoor volatile organic compound treatment and performance assessment with TiO2/MCM-41 and TiO2/quartz photoreactor under ultraviolet irradiation

Volatile organic compounds (VOCs) are the cause of indoor air pollution and are readily emitted from furniture and cleaning agents. In Taiwan, the concentrations of indoor VOCs range roughly from 1 to 10 ppm. It is important to effectively reduce indoor VOC emissions and establish the implementation of long-term, low-cost, controlled techniques such as those found in the ultraviolet/titanium dioxide (UV/TiO2) control systems. This study evaluates the performance of a photoreactor activated by visible irradiation and packed with TiO2/quartz or TiO2/mobile catalytic material number 41 (MCM-41). The photocatalysts tested include commercial TiO2 (Degussa P-25) and synthesized TiO2 with a modified sol-gel process. The UV light had a wavelength of 365 nm and contained an 8-W, low-pressure mercury lamp. Reactants and products were analyzed quantitatively by using gas chromatography with a flame-ionization detector. It is important to understand the influence of such operational parameters, such as concentration of pollutant, temperature, and retention time of processing. The indoor concentrations of VOCs varied from 2 to 10 ppm. Additionally, the temperatures ranged from 15 to 35 degrees C and the retention time tested from 2 to 8.2 sec. The results show that quartz with TiO2 had a better photoreductive efficiency than quartz with MCM-41. The toluene degradation efficiency of 77.4% with UV/TiO2/quartz was larger than that of 54.4% with the UV/TiO2/MCM-41 system under 10-min reaction time. The degradation efficiency of the UV/TiO2 system decreased with the increasing concentrations of indoor VOCs. The toluene degradation efficiency at 2 ppm was approximately 5 times greater than that at 10 ppm. The photoreduction rate of the VOCs was also evaluated with the Langmuir-Hinshewood model and was shown to be pseudo-first-order kinetics.     

Oxidation of volatile organic compounds on SBA-15 mesoporous molecular sieves modified with manganese

Catalytic combustion of volatile organic compounds, such as propene, has been studied on manganese modified mesoporous molecular sieves. Powder X-ray diffraction, (29)Si nuclear magnetic resonance, nitrogen sorption and transmission electron microscopy show that the SBA-15 mesoporous silica molecular sieve can be modified with manganese using Mn(2)(CO)(10) or Mn(O(2)CMe)(2) without significant distortion of the host structure. The two products were catalytically active in propene oxidation, with SBA-15 modified with Mn(2)(CO)(10) showing significantly higher activity, possibly due to higher Mn content, than SBA-15 modified with Mn(O(2)CMe)(2).     

Ba/TiO2/MCM-41光催化降解对硝基苯甲酸

以钛酸丁酯为钛源、MCM-41分子筛为载体,采用溶胶-凝胶法制备了掺杂与负载相结合的光催化剂Ba/TiO2/MCM-41。结果表明:Ba/TiO2/MCM-41是一种比表面积高达341.2 m2/g的介孔材料,主要晶相为锐钛矿相,比P25有更强的紫外光吸收。将Ba/TiO2/MCM-41用于光催化氧化水中的对硝基苯甲酸,当催化剂投加量为0.5 g/L,对硝基苯甲酸初始pH为4、浓度为2×10-4mol/L时,紫外光照30 min后,对硝基苯甲酸降解率达到96.0%。用紫外光谱、红外光谱和高效液相色谱分析对硝基苯甲酸降解前后的变化,发现随着光照时间延长,苯环上的硝基、羧基吸收峰逐渐减弱;对硝基苯甲酸首先被降解为一些中间小分子产物,随着反应进行,小分子物质也逐渐被降解。     

Gaseous ammonia uptake in compost biofilters as related to compost water content

Sewage sludge and yard waste compost were used as biofilter materials and tested with respect to their capacity for removing ammonia from air at different water contents. Ammonia removal was measured in biofilters containing compost wetted to different moisture contents ranging from air dry to field capacity (maximum water holding capacity). Filters were operated for 15 days and subsequently analyzed for NH3/NH4+, NO2-, and NO3-. The measured nitrogen species concentration profiles inside the filters were used to calculate ammonia removal rates. The results showed that ammonia removal is strongly dependent on the water content in the filter material. At gravimetric water contents below 0.25 g H2O g solids(-1) for the yard waste compost and 0.5 g H2O g solids(-1) ammonia removal rates were very low but increased rapidly above these values. The sewage sludge compost filters yielded more than twice the ammonia removal rate observed for yard waste compost likely because of a high initial concentration of nitrifying bacteria originating from the wastewater treatment process and a high airwater interphase surface area that facilitates effective ammonia dissolution and transport to the biofilm.     

A tunable diode laser system for ammonia flux measurements over multiple plots

This paper reports on the field testing of a tunable diode laser trace gas analyzer system for micrometeorological monitoring of ammonia fluxes. This system uses infrared absorption spectroscopy to measure atmospheric ammonia concentrations and the fluxgradient method to relate the measured concentration gradient to a flux of ammonia. For the field tests, we monitored ammonia fuxes over three plots receiving different manure applications. Each plot was sampled for 15 or 30 min of each hour, producing a high-temporal resolution data set. Analysis of the system response showed that ammonia adsorption to the tubing walls was greatly reduced by the system design and did not interfere with the flux measurement.     

Microbial degradation of livestock-generated ammonia using biofilters at typical ambient temperatures

The purpose of this research was to neutralize livestock-generated ammonia by using biofilters packed with inexpensive inorganic and organic packing material combined with multicultural microbial load at typical ambient temperatures. Peat and inorganic supporting materials were used as biofiltration matrix packed in a perfusion column through which gas was transfused. Results show the ammonia removal significantly fell in between 99 and 100% when ammonia concentration of 200 ppmv was used at different gas flow rates ranged from 0.030 to 0.060 m3 h(-1) at a fluctuating room temperature of 27.5 +/- 4.5 C (Mean +/- SD). Under these conditions, the emission concentration of ammonia that is liberated after biofiltration is less than 1 ppmv (0.707 mg m(-3)) over the period of our study, suggesting the usage of low-cost biofiltration systems for long-term function is effective at wider ranges of temperature fluctuations. The maximum (100%) ammonia removal efficiency was obtained in this biofilter was having an elimination capacity of 2.217 g m(-3) h(-1). This biofilter had high nitrification efficiencies and hence controlled ammonia levels with the reduced backpressure. The response of this biofilter to shut down and start up operation showed that the biofilm has a superior stability.     

Heavy metals removal from electroplating wastewater by aminopropyl-Si MCM-41

The potential of removing nickel and copper from industrial electroplating wastewaters by using mesoporous materials with MCM-41 type structure functionalised with different ratios of aminopropyl groups, namely Na50, Na25 and Na5, were evaluated. The synthesised solids sorbents obtained were characterised by X-ray diffraction, elemental chemical analysis and IR spectroscopy. In preliminary experiments, studies were carried out to determine the optimal experimental conditions for the retention of heavy ions. Effects of concentration, optimal pH, interference with humic substances and other metals were studied for Na5, which showed the best capacity of absorption determined by the corresponding isotherm. This material has a greater selectivity against sodium, indicating that ionic strength does not affect the extraction. Results of an application of this material to remove nickel and copper in synthetic and real industrial wastewater samples from an electrochemical industry area are shown with successful results. The lowest level of nickel and copper were observed when Na5 was used. This observation suggests that reactive aminopropyl-Si MCM-41 and similar materials may be a promising and provide for alternative environmental technologies in the future.     

Ba/TiO_2/MCM-41光催化降解对硝基苯甲酸

以钛酸丁酯为钛源、MCM-41分子筛为载体,采用溶胶-凝胶法制备了掺杂与负载相结合的光催化剂Ba/TiO2/MCM-41。结果表明：Ba/TiO2/MCM-41是一种比表面积高达341.2 m2/g的介孔材料,主要晶相为锐钛矿相,比P25有更强的紫外光吸收。将Ba/TiO2/MCM-41用于光催化氧化水中的对硝基苯甲酸,当催化剂投加量为0.5 g/L,对硝基苯甲酸初始pH为4、浓度为2×10-4mol/L时,紫外光照30 min后,对硝基苯甲酸降解率达到96.0%。用紫外光谱、红外光谱和高效液相色谱分析对硝基苯甲酸降解前后的变化,发现随着光照时间延长,苯环上的硝基、羧基吸收峰逐渐减弱;对硝基苯甲酸首先被降解为一些中间小分子产物,随着反应进行,小分子物质也逐渐被降解。     

生物滤池处理城市污水工艺中恶臭和微生物气溶胶的填料选择

采用实验室规模的生物滤池对含硫化氢、氨和微生物气溶胶的气体进行处理，并对海绵、陶粒、堆肥和空心塑料小球4种物质作为反应器填料的性能进行比较。结果表明，不同填料生物滤池对硫化氢、氨和微生物气溶胶的去除效率明显不同，去除效率从高到低的顺序依次为海绵、陶粒、堆肥和空心塑料小球生物滤池。海绵和陶粒生物滤池出气异养细菌和真菌主要以小粒径粒子为主。在同样的进气和运行条件下，堆肥填料层的压力降最大，其次是陶粒和空心塑料小球填料层，海绵填料层的压力降最小。对4种填料的性能进行综合比较，海绵和陶粒较适宜作为处理硫化氢、氨和微生物气溶胶的生物滤池填料。     

生物滤池处理城市污水工艺中恶臭和微生物气溶胶的填料选择简

采用实验室规模的生物滤池对含硫化氢、氨和微生物气溶胶的气体进行处理，并对海绵、陶粒、堆肥和空心塑料小球4种物质作为反应器填料的性能进行比较。结果表明，不同填料生物滤池对硫化氢、氨和微生物气溶胶的去除效率明显不同，去除效率从高到低的顺序依次为海绵、陶粒、堆肥和空心塑料小球生物滤池。海绵和陶粒生物滤池出气异养细菌和真菌主要以小粒径粒子为主。在同样的进气和运行条件下，堆肥填料层的压力降最大，其次是陶粒和空心塑料小球填料层，海绵填料层的压力降最小。对4种填料的性能进行综合比较，海绵和陶粒较适宜作为处理硫化氢、氨和微生物气溶胶的生物滤池填料。     

Instrument development and application in studies and monitoring of ambient ammonia

During recent years, it has become clear that ammonia is an important gas in relation to different environmental issues, such as acidification, eutrophication, human health and climate change (through particle formation). Therefore, there is a growing need to develop and apply instrumentation suitable for research into emission, dispersion, conversion and deposition of ammonia and ammonium. Recently, several instruments were developed suitable for measuring concentrations in ambient conditions even at very low levels, such as ammonia sensors suitable for monitoring and research, deposition measuring systems and aerosol samplers for on-line measurement of aerosol composition. These instruments have been tested and applied in a number of field studies. These studies include dry deposition measurements, ammonium nitrate studies in relation to the (in)direct aerosol effect, emission studies and policy evaluation with concentration and deposition monitoring data. The policy evaluation study showed that the measures to reduce ammonia emissions were not as successful as projected beforehand by statistical studies.