| Not only does odor have characteristics of volatile organic compounds(VOCs)pollution,but also the specificity of human olfactory perception.The odor threshold of malodorous gases is extremely low,and when the concentration volume fraction is 10-9 or even 10-12,a strong unpleasant taste can still be produced.At present,existed emission standards of 8 odorous gases are higher 1 to 3 orders of magnitude than the olfactory threshold,far less than the purpose of eradicating odor.Except that,around 4,000 types of odorous gases have been found(including over 10 common odorous gases).In addition,the treatment technology of low-concentration malodorous gas(volume fraction less than 10×10-6)is rarely paid attention,though it is the key and obstacle to solve the problem of malodorous pollution.Adsorption treatment technology is one of the methods applied to environmental management.Mesoporous silica not only has high specific surface area,adjustable pore structure,large pore volume,etc.,but also has good physicochemical stability.The silanic hydroxyl groups in mesoporous pore interface facilitates functional modification,which ensures that can handl a wide variety of malodorous gases with various physicochemical properties.In this paper,tetraethyl orthosilicate(TEOS)was used as the silicon source,cetyltrimethylammonium bromide(CTAB)and polyethylene glycol(PEG 2000)as template to prepare mesoporous silica nanoparticles(MSN)by sol-gel method at room temperature.The high specific surface area MSN was functionalized by introduction of silane coupling agents(SCA)or metal salts.The adsorption properties of mesoporous silica on low concentrations of malodorous gases n-butyraldehyde(n-C4H8O)and methyl mercaptan(CH3SH)were investigated.The main research contents and results are as follows:(1)The effects of reaction temperature(7),amount of ammonia(CNH3),reaction time(tgel)and amount of ethyl acetate(CEtOAc)on the morphology of MSN were investigated.The samples were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction analysis(XRD)and specific surface analysis(BET).The results show that the specific surface area of the material is maintained between 948 m2·g-1 and 1305 m2·g-1,the pore volume is maintained between 0.73 mL·g-1 and 2.11 mL·g-1.The study found that these four factors had little effect on mesoporosity(Ocrystal),while the pore size(Dpore)was negatively correlated with CNH3 and positively correlated with T,tgel and CEtOAc.It was finally determined that at T=25 ℃,CNH3=5 mL,tget=24 h,CEtOAc=1.32 mL,the specific surface area and pore volume were high,the mesopores were well ordered,the particles were more uniform,which are good for gas adsorbed.(2)When different silane coupling agents are selected as the silicon source precursor,the leaving group of the silane coupling agent causes the difference in the decomposition-condensation rate of the silicon source precursor to affect the morphology of the mesoporous silica.The Ocrystal also changes due to the difference in decomposition-condensation rate;the functional group affects the size of the micelle and thus affects the morphology of the resulting particles.The pore blocking phenomenon in the grafting method does not occur over the experimental sample,and the amount of the functional group can be precisely regulated.The amino-functionalized mesoporous silica A-MSN-3 prepared by the co-condensation method can maintain the state of completely adsorbing 5 ppm of n-butyraldehyde at a high space velocity of 180,000 mL·g-1·h-1 for about 1200 minutes.The capacity is 62.92 mg n-butyraldehyde g-1 adsorbent.(3)The effects of different metal ions and anions on the morphology and mesoporous structure of metal-doped mesoporous silica molecular sieves(Me-MSN)and their adsorption properties were investigated.Metal ions affect the aspect ratio of micelles to form MSN with rods or spheres.Also metal ions change the gel-sol process of the silicon source precursors to change the surface roughness and pore size of the particles.The effect of anions on the material is not obvious.It can be seen from the n-butyraldehyde adsorption experiment that different metal element doping samples have certain selectivity to the adsorbed gas.At a space velocity of 180,000 mL·g-1·h-1,1Fe-N-MSN adsorbs n-butyraldehyde in the dried condition,which can maintain 100%adsorption accuracy for 500 minutes.As 1Ni-N-MSN,adsorption of n-butyraldehyde has the best moisture resistance,it can maintain adsorption accuracy of more than 80%for about 1800 minutes,which is 20 to 50 times that of other samples.The adsorption site for adsorbing n-butyraldehyde was determined to be a Me-O-Si structure.Through in-situ DRIFT(Diffuse Reflectance Infrared Fourier Transform),it was found that the water molecules retained the adsorption of n-butyraldehyde after forming complex ions with Ni3+in Ni-O-Si.(4)It was verified that the Me-O-Si structure has selectivity and moisture resistance as a site of adsorption of the malodorous gas.By adjusting the templating agent to inexpensive PEG 2000 and adjusting the pH of the reaction to be acidic,a copper-doped mesoporous silica having a specific non-closed pore structure with a specific surface area over 550 m2·g-1 or more was obtained.It was found that CuO nanoparticles and copper compounds(Si-O-Cu)present in silica play an important role in the removal of CH3SH.It is presumed that the water molecules cause the copper atoms on the surface of the CuO nanoparticles and the copper atoms in the Si-O-Cu group to become hydrated complexes,which is more effective for capturing CH3SH having an empty Cu-3d orbital.The Cu element bonded to the mesoporous silica interface tends to form a complex state similar to[Cu(H2O)62+]—this is the main adsorption site for adsorption with methyl mercaptan,while CuO particles are in water.Under the action of molecules,it tends to form a complex state similar to[Cu(H2O)42+]or it is difficult to form complex ions to weaken the chelation of Cu and sulfhydryl groups.Cu(Ⅱ)is distributed on the mesoporous wall of silica to form a highly efficient adsorption site(chemical adsorption).Under the action of water molecules,the adsorption breakthrough time is further extended,indicating that the performance of the prepared adsorbent material is greatly improved.In addition,the performance of the high-temperature regenerated adsorbent does not decay,exhibiting excellent cycle stability and thermal stability.Finally,the improved preparation method reduces material costs,improves moisture resistance and recyclability,and increases material preparation from milligrams to tens of grams. |
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