Preparation of hydrophobic hierarchical pore carbon–silica composite and its adsorption performance toward volatile organic compounds

Carbon–silica materials with hierarchical pores consisting of micropores and mesopores were prepared by introducing nanocarbon microspheres derived from biomass sugar into silica gel channels in a hydrothermal environment.The physicochemical properties of the materials were characterized by nitrogen physical adsorption(BET),scanning electron microscopy(SEM),and thermogravimetric(TG),and the adsorption properties of various organic waste gases were investigated.The results showed that microporous carbon materials were introduced successfully into the silica gel channels,thus showing the high adsorption capacity of activated carbon in high humidity organic waste gas,and the high stability and mechanical strength of the silica gel.The dynamic adsorption behavior confirmed that the carbon–silica material had excellent adsorption capacity for different volatile organic compounds(VOCs).Furthermore,the carbon–silica material exhibited excellent desorption characteristics:adsorbed toluene was completely desorbed at 150℃,thereby showing superior regeneration characteristics.Both features were attributed to the formation of hierarchical pores.     

Aerosol optical properties under different pollution levels in the Pearl River Delta (PRD) region of China

To clarify the aerosol hygroscopic growth and optical properties of the Pearl River Delta(PRD)region,integrated observations were conducted in Heshan City of Guangdong Province from October 19 to November 17,2014.The concentrations and chemical compositions of PM_(2.5),aerosol optical properties and meteorological parameters were measured.The mean value of PM_(2.5) increased from less than 35(excellent) to 35-75 μg/m~3(good) and then to greater than 75 μg/m~3(pollution),corresponding to mean PM_(2.5) values of 24.9,51.2,and 93.3 μg/m~3,respectively.The aerosol scattering hygroscopic growth factor(f(RH = 80%)) values were 2.0,2.12,and 2.18 for the excellent,good,and pollution levels,respectively.The atmospheric extinction coefficient(σext)and the absorption coefficient of aerosols(σ_(ap)) increased,and the single scattering albedo(SSA)decreased from the excellent to the pollution levels.For different air mass sources,under excellent and good levels,the land air mass from northern Heshan had lower f(RH) and σ_(sp) values.In addition,the mixed aerosol from the sea and coastal cities had lower f(RH) and showed that the local sources of coastal cities have higher scattering characteristics in pollution periods.     

Tuning the fill percentage in the hydrothermal synthesis process to increase catalyst performance for ozone decomposition

The performance of Ce-OMS-2 catalysts was improved by tuning the fill percentage in the hydrothermal synthesis process to increase the oxygen vacancy density. The Ce-OMS-2 samples were prepared with different fill percentages by means of a hydrothermal approach (i.e. 80%, 70%, 50% and 30%). Ce-OMS-2 with 80% fill percentage (Ce-OMS-2-80%) showed ozone conversion of 97%, and a lifetime experiment carried out for more than 20?days showed that the activity of the catalyst still remained satisfactorily high (91%). For Ce-OMS-2-80%, Mn ions in the framework as well as K ions in the tunnel sites were replaced by Ce⁴⁺, while for the others only Mn ions were replaced. O₂-TPD and H₂-TPR measurements proved that the Ce-OMS-2-80% catalyst possessed the greatest number of mobile surface oxygen species. XPS and XAFS showed that increasing the fill percentage can reduce the AOS of Mn and augment the amount of oxygen vacancies. The active sites, which accelerate the elimination of O₃, can be enriched by increasing the oxygen vacancies. These findings indicate that increasing ozone removal can be achieved by tuning the fill percentage in the hydrothermal synthesis process.     

Acceleration of floc-water separation and floc reduction with magnetic nanoparticles during demulsification of complex waste cutting emulsions

Waste cutting emulsions are difficult to treat efficiently owing to their complex composition and stable emulsified structure. As an important treatment method for emulsions, chemical demulsification is faced with challenges such as low flocs–water separation rates and high sludge production. Hence, in this study, Fe₃O₄ magnetic nanoparticles (MNPs) were used to enhance chemical demulsification performance for treating waste cutting emulsions under a magnetic field. The addition of MNPs significantly decreased the time required to attain sludge–water separation and sludge compression equilibrium, from 210 to 20 min. In addition, the volume percentage of sludge produced at the equilibrium state was reduced from 45% to 10%. This excellent flocculation–separation performance was stable over a pH range of 3–11. The magnetization of the flocculants and oil droplets to form a flocculant–MNP–oil droplet composite, and the magnetic transfer of the composite were two key processes that enhanced the separation of cutting emulsions. Specifically, the interactions among MNPs, flocculants, and oil droplets were important in the magnetization process, which was controlled by the structures and properties of the three components. Under the magnetic field, the magnetized flocculant–MNP–oil droplet composites were considerably accelerated and separated from water, and the sludge was simultaneously compressed. Thus, this study expands the applicability of magnetic separation techniques in the treatment of complex waste cutting emulsions.     

Hygroscopicity measurement of sodium carbonate, β-alanine and internally mixed β-alanine/Na2CO3 particles by ATR-FTIR

Water-uptakes of pure sodium carbonate(Na_2CO_3),pure β-alanine and internally mixedβ-alanine/Na_2CO_3 aerosol particles with different mole ratios are first monitored using attenuated total reflectance Fourier transform infrared spectroscopy(ATR-FTIR) technique.For pure Na_2CO_3 aerosol particles,combining the absorptions at 877 and 1422 cm-1 with abrupt water loss shows the efflorescence relative humidity(ERH) of 62.9%–51.9%.Upon humidifying,solid Na_2CO_3 firstly absorbs water to from Na_2CO_3·H2 O crystal at 72.0% RH and then deliquesces at 84.5% RH(DRH).As for pure β-alanine particles,the crystallization takes place in the range of 42.4%–33.2% RH and becomes droplets at ～ 88.2% RH.When β-alanine is mixed with Na_2CO_3 at various mole ratios,it shows no efflorescence of Na_2CO_3 whenβ-alanine to Na_2CO_3 mole ratio(OIR) is 2:1.For 1:1 and 1:2 β-alanine/Na_2CO_3 aerosols,the ERHs of Na_2CO_3 are 51.8%–42.3% and 57.1%–42.3%,respectively.While β-alanine crystal appears from 62.7% RH for 2:1 and 59.4% RH for both 1:1 and 1:2 particles and lasts to driest state.On hydration,the DRH is 44.7%–75.2% for Na_2CO_3 with the OIR of 1:1 and 44.7%–69.0%for 1:2 mixture,and those of β-alanine are 74.8% for 2:1 mixture and 68.9% for two others.After the first dehumidification–humidification,all the water contents decrease despite of constituent fraction.And at ～ 92% RH,the remaining water contents are 92%,89% and 82%at ～ 92% RH,corresponding to OIR of 2:1,1:1 and 1:2 mixed system,respectively.     

Dynamic nano-Ag colloids cytotoxicity to and accumulation by Escherichia coli: Effects of Fe3+, ionic strength and humic acid

Released Ag ions or/and Ag particles are believed to contribute to the cytotoxicity of Ag nanomaterials, and thus, the cytotoxicity and mechanism of Ag nanomaterials should be dynamic in water due to unfixed Ag particle:Ag⁺ ratios. Our recent research found that the cytotoxicity of PVP-Ag nanoparticles is attributable to Ag particles alone in 3 hr bioassays, and shifts to both Ag particles and released Ag⁺ in 48 hr bioassays. Herein, as a continued study, the cytotoxicity and accumulation of 50 and 100 nm Ag colloids in Escherichia coli were determined dynamically. The cytotoxicity and mechanisms of nano-Ag colloids are dynamic throughout exposure and are derived from both Ag ions and particles. Ag accumulation by E. coli is derived mainly from extracellular Ag particles during the initial 12 hr of exposure, and thereafter mainly from intracellular Ag ions. Fe³⁺ accelerates the oxidative dissolution of nano-Ag colloids, which results in decreasing amounts of Ag particles and particle-related toxicity. Na⁺ stabilizes nano-Ag colloids, thereby decreasing the bioavailability of Ag particles and particle-related toxicity. Humic acid (HA) binds Ag⁺ to form Ag⁺-HA, decreasing ion-related toxicity and binding to the E. coli surface, decreasing particle-related toxicity. HA in complex conditions showed a stronger relative contribution to toxicity and accumulation than Na⁺ or Fe³⁺. The results highlighted the cytotoxicity and mechanism of nano-Ag colloids are dynamic and affected by environmental factors, and therefore exposure duration and water chemistry should be seriously considered in environmental and health risk assessments.     

Development of a static test apparatus for evaluating the performance of three PM2.5 separators commonly used in China

PM_(2.5) separator directly affects the accuracy of PM_(2.5) sampling.The specification testing and evaluation for PM_(2.5) separator is particularly important,especially under China's wide variation of terrain and climate.In this study,first a static test apparatus based on polydisperse aerosol was established and calibrated to evaluate the performance of the PM_(2.5) separators.A uniform mixing chamber was developed to make particles mix completely.The aerosol concentration relative standard deviations of three test points at the same horizontal chamber position were less than 0.57%,and the particle size distribution obeyed logarithmic normal distribution with an R~2 of 0.996.The flow rate deviation between the measurement and the set point flow rate agreed to within ± 1.0% in the range of -40 to 50℃.Secondly,the separation,flow and loading characteristics of three cyclone separators(VSCC-A,SCC-A and SCC112) were evaluated using this system.The results showed that the 50% cutoff sizes(D_(50)) of the three cyclones were 2.48,2.47 and 2.44 μm when worked at the manufacturer's recommended flow rates,respectively.The geometric standard deviation(GSD) of the capture efficiency of VSCCA was 1.23,showed a slightly sharper than SCC-A(GSD = 1.27),while the SCC112 did not meet the relevant indicator(GSD = 1.2 ± 0.1) with a GSD = 1.44.The flow rate and loading test had a great effect on D_(50),while the GSD remained almost the same as before.In addition,the maintenance frequency under different air pollution conditions of the cyclones was summarized according to the loading test.     

Cytotoxicity of the soluble and insoluble fractions of atmospheric fine particulate matter

Inhaled atmospheric fine particulate matter(PM_(2.5)) includes soluble and insoluble fractions,and each fraction can interact with cells and cause adverse effects.PM_(2.5) samples were collected in Jinan,China,and the soluble and insoluble fractions were separated.According to physiochemical characterization,the soluble fraction mainly contains watersoluble ions and organic acids,and the insoluble fraction mainly contains kaolinite,calcium carbonate and some organic carbon.The interaction between PM_(2.5) and model cell membranes was examined with a quartz crystal microbalance with dissipation(QCM-D) to quantify PM_(2.5) attachment on membranes and membrane disruption.The cytotoxicity of the total PM_(2.5) and the soluble and insoluble fractions,was investigated.Negatively charged PM_(2.5) can adhere to the positively charged membranes and disrupt them.PM_(2.5)also adheres to negatively charged membranes but does not cause membrane rupture.Therefore,electrostatic repulsion does not prevent PM_(2.5) attachment,but electrostatic attraction induces remarkable membrane rupture.The human lung epithelial cell line A549 was used for cytotoxicity assessment.The detected membrane leakage,cellular swelling and blebbing indicated a cell necrosis process.Moreover,the insoluble PM_(2.5) fraction caused a higher cell mortality and more serious cell membrane damage than the soluble fraction.The levels of reactive oxygen species(ROS) enhanced by the two fractions were not significantly different.The findings provide more information to better understand the mechanism of PM_(2.5) cytotoxicity and the effect of PM_(2.5) solubility on cytotoxicity.     

Mechanism and catalytic performance for direct dimethyl ether synthesis by CO2 hydrogenation over CuZnZr/ferrierite hybrid catalyst

Direct synthesis of dimethyl ether(DME) by CO_2 hydrogenation has been investigated over three hybrid catalysts prepared by different methods:co-precipitation,sol-gel,and solid grinding to produce mixed Cu,ZnO,ZrO_2 catalysts that were physically mixed with a commercial ferrierite(FER) zeolite.The catalysts were characterized by N_2 physisorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),temperature programmed desorption of CO_2(CO_2-TPD),temperature programmed desorption of NH_3(NH_3-TPD),and temperature programmed H2 reduction(H_2-TPR).The results demonstrate that smaller CuO and Cu crystallite sizes resulting in better dispersion of the active phases,higher surface area,and lower reduction temperature are all favorable for catalytic activity.The reaction mechanism has been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS).Methanol appears to be formed via the bidentate-formate(b-HCOO) species undergoing stepwise hydrogenation,while DME formation occurs from methanol dehydration and reaction of two surface methoxy groups.