Fabrication Of Ferroferric Oxide/Cellulose Composite Materials And Their Applications In Sensing

As a medium between human beings and surrounding,sensor can perceive information from environment,and human may take advantage of these feedback to manipulate issue,which is benefit to people.Thus it is worthy of researching on the exploitation and utilization of the sensor,leading to that a large amount of sensors have been widely used in our daily life.Due to the soaring advance of portable and wearable devices,the magnetic sensors and UV sensors have gained substantial attentions among these various sensors.Magnetic sensors are widely used in the fields of medical diagnose,navigation and data storage,while UV sensors are significant in both commercial and scientific applications including image sensing,communication,day-/night-time surveillance,etc.Fe₃O₄ particles are extraordinary building blocks owing to their excellent magnetic/electrical properties,low toxicity and biocompatibility,and have been drastically investigated and widely utilized in the fields of electromagnetic wave absorption,catalysis and sensing.However,to seek the proper substrate to anchor the magnetic particles for broader and more thorough practicability still remains as a challenge,since the naked Fe₃O₄ NPs are difficult to handle due to the sensitivity to oxidation and easily aggregation.Cellulose is the most abundant natural polymer on earth,and has received extensive concerns due to its inborn merits,such as the renewability,environmental friendliness,low cost,non-toxicity,availability,biocompatibility and biodegradability,etc.And the cellulosed-based materials are endowed with characteristics like high porosity,thermal/chemical stability and good mechanical property.Both two make cellulose an ideal carrier for loading nanoparticles.Nevertheless,the high crystallinity and the massive inter-/intra-molecular interactions lead to the fact that cellulose hardly dissolves or melts,hampering its practical utilization.Recently,the quaternary ammonium hydroxide aqueous solutions are developed as novel and superior aqueous cellulose solvents,due to the hydrophobic interaction between cations and cellulose improved significantly the dispersion of cellulose chains in aqueous medium.To some degree,the method results in the more facile and efficient dissolution of cellulose,and promotes the development and applications of cellulose based functional materials.In the present thesis,we have fabricated the flexible Fe₃O₄/cellulose composite films as film-based sensor,by co-dispersing homemade Fe₃O₄ nanoparticles and cellulose successively in Bz Me₃NOH aqueous solution.By controlling the condition of regeneration of cellulose and the preparation process the structure of the composite films and sensing behaviors were controlled,to improve their performance and enhance their application potentials.Therefore,our work may open a door for the novel utilization of Fe₃O₄ and the“green conversion”of renewable resources.The two main innovations of this thesis are as follows:?1?A simple and facile dissolution,blending and regeneration process in aqueous medium is developed to prepare Fe₃O₄/cellulose composite films.Furthermore,we investigate the structure of the composite films and their sensing behaviors against UV and magnetic field and the mechanisms.And they have been used as UV sensors and magnetic sensors.?2?The Fe₃O₄/cellulose composite films with magnetic anisotropy are fabricated via magnetic orientation and mechanical stretching process.And we investigated their structure and the mechanical performance,as well as anisotropically magnetic sensing behavior.The main contents and conclusions of this thesis include the following part.Fe₃O₄/cellulose composite films were successfully prepared as magnetic sensors and UV sensors,by co-dispersing homemade Fe₃O₄ nanoparticles and cellulose successively in Bz Me₃NOH aqueous solution followed by regenerating in aqueous sucrose solution and hot-pressing.The magnetic particles were fixed in the cellulose matrix via coordinate bond between Fe₃O₄ and hydroxyl of cellulose.Fe₃O₄ clusters with average size ranged from 578 to 963 nm depending on Fe₃O₄content formed and embedded in the cellulose matrix.The composite films were thermal stable below 290^oC.The tensile strength and elongation at break of the film named CFe03 reached 49.4MPa and 9.7%,and it can be folded and bended without fracture,which guarantees the wide application as sensors and devices.It also presented an excellent saturated magnetization as 27.2 emu/g,superparamagnetic property,as well as strong UV shielding property.It is noted that the composite films exhibited extraordinary sensing capabilities against both UV exposure and magnetic field,with fast responsiveness within 0.5 s and 1.4 s and excellent reproducibility.The present work not only supplied a simple pathway to prepare sensors with excellent properties,but also utilized the renewable resources,demonstrating both sustainability and great potentials.Robust Fe₃O₄/cellulose composite film with anisotropic structure and property was fabricated via magnetic orientation and mechanical stretching process.Fe₃O₄/cellulose blend solution was prepared in Bz Me₃NOH aqueous solution.After casting,an external magnetic field was applied to induce the alignment of Fe₃O₄ NPs.Then the sample was subjected to regeneration and mechanical stretching along the magnetic orientation direction,which further immobilized the aligned NPs in the cellulose matrix forming the Fe₃O₄/cellulose composite film.Due to the obtained film with aligned Fe₃O₄whiskers/wires,it showed magnetic anisotropy with higher saturated magnetization and remanence along the direction parallel to the magnetic field.And it was also endowed with anisotropic mechanical property because of the structure anisotropy.Besides,it possessed sensitive responsiveness to the external magnetic field,and the anisotropic magnetic response in the direction parallel/perpendicular to the orientation direction,potential as sensors and smart devices.Our work took advantage of bioresource and broadened novel applications of Fe₃O₄-based composites,which showed great potentials and values.The thesis co-dispersed Fe₃O₄ particles and cellulose successively in Bz Me₃NOH aqueous solution,and successfully controlled the structure and performance of the Fe₃O₄/cellulose composite films by controlling the regeneration of cellulose,leading to the application of Fe₃O₄-based material in the field of the sensor.Moreover,we obtained the composite film with unique sensing behaviors by changing preparation process,to improve its application potentials in sensing.These researches effectively combined the merits of Fe₃O₄ and cellulose,which achieved the“green conversion”of renewable resources.Meantime,it came up with a novel application of the Fe₃O₄-based composites in the field of sensor,exhibiting scientific significance and application prospect.