Study On The Photocatalytic Reversible Transformation Of Organic Dyes By Zinc Oxide And Its Application In Inkless Reproducible Printing Paper

Writing materials are closely related to human life and learning.For thousands of years,most of the preservation and dissemination of human civilization have relied on paper media.The current printed materials are mostly one-time reading,and the printed materials come from plant fibers and non-plant fibers(inorganic fibers,chemical fibers,and metal fibers).At present,the raw materials for papermaking in the world are mainly plant fibers.Some economically developed countries use coniferous or hardwood timber to account for more than 95% of the total consumption,causing a serious waste of the earth’s forest resources,which not only increases production costs,but also causes environmental problems.Therefore,there is an urgent need to research and find a new,environmentally friendly and low-cost writing materials to replace traditional printed ones.The emergence of inkless reproducible printing paper makes it possible to solve these current problems.It can print repeatedly without adding any ink.In this way,the goal of saving forest resources and protecting the environment can be achieved.Inkless reprintable paper is a new,environmentally friendly and low-cost writing material.Traditional rewriteable paper prepared based on photonic crystals,fluorescent rare earth complexes or organic chromophores has disadvantages such as low visible contrast,high price,and poor light stability.At present,the concept of a new type of photocatalytic reproducible printing paper can solve the above-mentioned problems.It achieves multi-color and repeatable printing through the photo-isomerization color conversion of organic dyes and the good photocatalytic ability of inorganic nanocrystals(tin oxide and titanium dioxide).It is compatible with laser printing.Zinc oxide quantum dots(ZnO QDs)refer to zinc oxide with a size of less than 100 nm.Over the years,due to its good biocompatibility,low biological toxicity,rich surface functional groups,strong modifiers,diverse chemical properties,simple preparation methods and low synthesis costs,it has been widely used in the fields of electricity,optics,detection,etc.The attention of scientific researchers.In addition to the above fields,ZnO itself also has photocatalytic performance,especially after modification,water-soluble zinc oxide quantum dots(ZnO@APTES)can be obtained,which significantly improves the photocatalytic performance of water systems.Moreover,ZnO is considered to be a potential high-efficiency photocatalyst candidate material due to its fast mobility and overwhelming production capacity of active protons excited by the band gap.Therefore,it can be applied to the photocatalytic reduction of organic dyes.Although there have been some studies of ZnO used in the preparation of reproducible printing paper and photocatalytic degradation of organics,these studies have not yet met our actual needs.Because in most studies,strong corrosive acid-base reagents are used to quench and restore ZnO fluorescence to achieve a repeatable printing path;Secondly,the common ZnO QDs used have poor dispersibility in water and the photocatalytic reaction process is easy to agglomerate.These problems limit the large-scale application and promotion of traditional zinc oxide quantum dots in the preparation of reproducible printing paper.In order to solve the above problems,this study chose ligand-modified water-soluble ZnO QDs as a new type of photocatalytic material.Using ZnO QDs under ultraviolet light(UV)to reduce and decolor methylene blue(MB)and slowly oxidize and recolor in the air cycle process.The inkless reproducible printing paper that can perform fast and repeatable printing is prepared.It only takes 10 seconds to complete the color change,and it can be repeatedly printed for many times.The research results obtained in this paper are as follows:(1)ZnO@APTES with small particle size and uniform morphology was prepared by sol-gel method.Then the silane coupling agent(APTES)was used to modify the ZnO QDs,so the surface was modified with hydrophilic groups such as amino and silicon oxide.Therefore,ZnO@APTES is given good water solubility.Water-soluble zinc oxide quantum dots can be dispersed uniformly and stably in water,and can increase the contact area with methylene blue under ultraviolet light,thereby increasing the photocatalytic rate.(2)In the analysis of the mechanism of water-soluble zinc oxide quantum dots photocatalytic methylene blue dye,the electron paramagnetic resonance(EPR)spectroscopy showed that when the water-soluble zinc oxide quantum dots photocatalyzed methyl blue dye,electrons were transferred from the excited state of ZnO@APTES to the MB molecule.Therefore,it can be proved that MB is not photodegraded or produced by other substances in this experiment.However,under the irradiation of UV light,the blue MB will be converted into colorless methylene blue(LMB).It is also confirmed that water-soluble zinc oxide quantum dots can perform photocatalysis on methylene blue dye.(3)The inkless reproducible printing paper was prepared using ZnO@APTES,methylene blue,hydroxyethyl cellulose and other materials.In the course of the experiment,the reproducible printing paper achieved more than 20 printing cycles,and the printed information could maintain high resolution and readability.The reproducible printing paper can not only achieve a fast color conversion time of about10 s,but also can perform multiple repetitive printing.Therefore,the inkless reproducible printing paper has a good application prospect in fast printing,and it is also of great significance in environmental protection.