Preparation And Characterization Of Cellulose-Based Materials For Adsorption And Fluorescence Detection Of Contaminants In Aqueous Phase

With the rapid development of the economy,the water pollution has become one of the most serious environmental problems,posing a significant threat to human health and environmental ecosystems.Therefore,it is important to rapid detection and effective removal of pollutants in water in order to improve the quality of water environment and achieve environmentally sustainable development.Cellulose is the most abundant biomass material in nature,showing a non-toxic,non-polluting,good biocompatibility and biodegradability.Moreover,the surface of cellulose has a large number of hydroxyl groups,which endows it with a high reactivity and can be used for the preparation of multifunctional cellulose matrix materials.Therefore,the cellulose can be employed as a carrier to load various of fluorescent probes for preparing a variety of dual-functional cellulose membrane/gel-based fluorescent sensors for the detection and removal of pollutants,which can reduce the cost of conventional sensors as well as potential environmental hazard.To this end,four cellulose-based materials were prepared in this thesis work,which innovatively combined the characteristics of probes and adsorbents.The integrated performance of as-prepared green materials for detection and adsorption of pollutants in water were comprehensively characterization along with revealing the related mechanisms.The main research contents and findings in this dissertation are as follows:(1)The cellulose loaded with zero-valent iron(S-ZVI)was prepared using a liquid phase reduction method to investigate the adsorption performance of cellulose-based adsorbents.The cellulose as matrix can not only effectively reduce the agglomeration of zero-valent iron,improve the adsorption performance of the adsorbent,but also reduce the cost of the adsorbent and the secondary pollution of the environment caused by the release of Fe3+.The equilibrium adsorption data showed that the adsorption of arsenic ions and Cr(III)by S-ZVI followed the Langmuir model,and the maximum adsorption reached 111.4 and 197.24 mg/g,respectively,in aqueous solution system.In addition,the adsorption process followed the pseudo-second-order model,suggesting the domination of chemical adsorption.Meanwhile,the S-ZVI exhibited a good recyclability for the removal of arsenic ions.The spectral and mechanistical analyses revealed that the efficient adsorption of the adsorbents towards arsenic ions and Cr(III)is attributed to the chelation,electrostatic interaction and redox reaction.(2)The carboxymethylated nanocellulose(C-CNC)was used as a raw material to explore its luminescence properties,which would lay a foundation for the subsequent integrated research on the detection and adsorption of pollutants in water.The C-CNC is found to be practically nonluminescent in dilute solutions,while being highly emissive when aggregated as nanosuspensions,showing a typical clustering-triggered emission(CTE)property.The C-CNC exhibits good quantum yields of 7.8%and 12.3%in solid state and aqueous solution,respectively.In order to further improve the luminescent efficiency of cellulose nanomaterials,the amino-fluorescent carbon dots(CDS-NH2)were prepared using C-CNC as carbon source via hydrothermal method.The prepared CDS-NH2 showed an excellent luminescence property and a rapid response to Cr(VI).Subsequently,a porous fluorescent aerogel(CPC aerogel)was constructed by immersing amino-based carbon dots(CDS-NH2)into a polyethylenimine(PEI)/carboxymethylated cellulose(CMC)aerogel network for simultaneous detection and adsorption of Cr(VI).The experiments confirm that the CPC aerogel exhibits a great sensitivity and extraction capacity for the Cr(VI),and can reach a level that conforms with industrial water safety standards.In addition,the CPC aerogel can continuously detect and remove Cr(VI)at high flux.These results demonstrate that cellulose show a potential performance to prepare a fluorescent sensor,which can be combined with cellulose-based adsorbents to effectively recognize and remove Cr(VI).(3)In order to further improve the detection accuracy,a ratiometric fluorescent probe(CDs-Rho)was synthesized with cellulose carbon dots as energy donor and rhodamine moiety as energy acceptor via amide reaction for the detection of Hg2+.Meanwhile,a new cellulose based fluorescent hydrogel(CCR hydrogel)was prepared by loading CDs-Rho onto cellulose hydrogel.The CDs-Rho exhibits a sensitive and linear response to Hg2+over a wide range from 0-100 μM with a limit detection of 2.19 × 10-9 M and exhibits high selectivity for Hg2+.The CCR hydrogel exhibits good sensitivity and excellent adsorption capacity for Hg2+with～95%removal efficiency,meeting the requirements for sewage discharge.Moreover,the purified water was successfully used for cell culture and animal growth,demonstrating excellent biocompatibility.In addition,a series of cellulose-based fluorescent hydrogel slices containing CDs-Rho are continuously prepared using microtomy of a hydrogel,facilitating the large-scale fabrication of functionalized hydrogel slices with controlled thickness.This approach is expected to offer a novel concept for the construction of biocompatible fluorescent hydrogels for the detection and removal of various pollutants.(4)Based on the above studies,a novel sensor is developed using a pyrene boronic acid and carbon dots(CDs)for the selective detection of fluoride(F-)ion by simply replacing the probe molecules.This would confirm the general applicability of the research methods.The pyrene-boronic acid-based CDs(CDs-PyB)result in a sensor whose response is linear for F-concentrations over a range from 0 to 200 μM(R2=0.996)with a detection limit of 5.9 ×10-5 M.Moreover,CDs-PyB display a high selectivity for F-over other anions.In addition,an amino-modified cellulose membrane containing CDs-PyB(CPC membrane)has been prepared for sensing and removal of F-.The cellulose membrane-based sensor shows a rapid response and high sensitivity for the detection of F-.Adsorption experiments demonstrate that the CPC membrane shows an excellent Fadsorption and removal efficiency of 90.2%.Moreover,an MTT assay demonstrates that the CPC membrane have an excellent cytocompatibility.The strategy offers a promising direction for the construction of other sensors by simply swapping the current probe with suitable replacements for a variety of relevant applications using biocompatible and abundant naturally based materials.Overall,a range of cellulose adsorption materials,luminescent materials and dualfunctional detection/adsorption materials prepared in this thesis work show a sensitive detection and efficient adsorption for the pollutants from water.The spectral analysis and various characterization methods revealed the detection mechanism of the material towards pollutants,and clarified the synchronous adsorption mechanism in the process.The research findings provide an important theoretical reference for the preparation of dual-functional materials to treat the wastewater.