Adsorption Of Polycyclic Aromatic Hydrocarbons On Functional Sba-15 And The Detection Of Polycyclic Aromatic Hydrocarbons By SERS

Polycyclic aromatic hydrocarbons?PAHs?are a group of organic compounds which are widespread in the environment and have a huge adverse impact to human health.Therefore,how to effectively detect and remove PAHs from the environment is a hot topic all around the world.Adsorption has become a prevailing technique to remove PAHs in environment due to its low cost,easy operation and easy recovery.The objective of this work is to explore the adsorption and enrichment-detection of PAHs from aqueous solution,and we have designed and prepared a series of novel adsorbents,including two parts in this work.In the first part,the adsorption properties of different functionalized SBA-15 on PAHs were investigated,and the adsorption mechanisms were compared and analyzed.In the second part,Au/Fe₃O₄/GO composites were designed and used to enrich and detect the trace PAHs via surface enhanced Raman spectroscopy?SERS?.In the first part,a series of SBA-15 materials with different modifications have been successfully prepared,including acid-modified SBA-15 with two alumina-incorporation methods?O-Al-SBA-15 and P-Al-SBA-15 prepared by a direct synthesis and post-grafting method,respectively?,hydrophobicity-modified SBA-15?CH₃-SBA-15?,surface-functionalized SBA-15 with phenyl groups?Ph-SBA-15?and BT-SBA-15 which contains phenyl groups both on the surface and in the framework.The characterization results show that,the morphology,textural and structural properties of the five chemically modified materials are all similar to SBA-15,but the surface chemical properties of these functional SBA-15 are very different from each other.Compared with pure SBA-15,there are homogeneous distribution of L acid sites in O-Al-SBA-15 and P-Al-SBA-15,and the former possesses more L acid sites than the latter.CH₃-SBA-15 shows the strongest hydrophobicity among the five materials.Ph-SBA-15 has a certain amount of phenyl groups on the surface and BT-SBA-15 has phenyl groups both on the surface and in the framework.Based on the above research,this series of functional SBA-15 were applied as adsorbents to remove naphthalene?Nap?,antheracene?Ant?and pyrene?Pyr?from aqueous solutions to investigate the adsorption behavior of different adsorbents and explore how the functional groups in the adsorbents affect the adsorption rate,balance and capacity.Kinetic studies reveal that the adsorption equilibrium can be achieved within 120 min for Nap and Ant while only 90 min for Pyr,and all the adsorption process follows a pseudo-second-order rate equation.The adsorption isotherms are all fit for Freundlich adsorption model.BT-SBA-15 exhits the highest adsorption capacity for Nap,Ant and Pyr?332.6,363.0 and 389.3 mg/g,respectively?,which indicates that the?-?interaction is the primary interaction between PAHs and adsorbents,and the hydrophobic effect also could improve the adsorption obviously.The presence of Lewis acid sites show a favor to the?-electrons and enhance the absorption capacity in a certain degree,but the enhancement is limited especially for the PAHs containing more benzene rings in the molecules.Our results are of great importance for deeply understanding the adsorption mechanism,which may provide a foundation on the tailored design and controllable synthesis of facile and efficient adsorbents for the enrichment and removal of PAHs from aqueous solution.In the second part,the SERS method was used to detect PAHs in aqueous solution.According to the adsorption mechanism results in the first part,we chose grapheme oxide?GO?as support because it has interconnected sp² network which could undergo?-?interaction with PAHs molecules.Au/Fe₃O₄/GO composites were prepared and used as SERS substrate to enrich and detect the organic molecules.The dependence of Au NPs diameters on SERS performance was investigated and the results show that the Au NPs with an average particle size of 40 nm have the best SERS effect.The contents of Au in this composites could influence the SERS performance significantly,and the optimal mass fraction of Au in GO/Au composites is 20%.In this composites,Au NPs play a major role in the enhancement of the Raman signal due to the electromagnetic enhancement mechanism.GO could enrich the PAHs through?-?interaction,and additionally,GO could also generate strong chemical enhancement to Raman signal.The existence of Fe₃O₄ is favor to the separation of substrate from matrix,which greatly improves the detection limit,simplifies the detection procedure and facilitates the cycle use of the substrate.The detection limit of Pry is 10^-88 mol/L significantly lower than that of ordinary Raman,and it is expected to be used for the enrichment and detection of trace PAHs in the environment.