Rewritable Painting Realized from Ambient-Sensitive Fluorescence of ZnO Nanoparticles

Abstract

Paper, as one of the most important information carriers, has contributed to the development and transmission of human civilization greatly. Meanwhile, a serious problem of environmental sustainable development caused by the production and utilization of paper has been resulted to modern society. Therefore, a simple and green route is urgently demanded to realize rewritable painting on paper. Herein, a simple route to rewritable painting on copy paper has been demonstrated by using eco-friendly ZnO nanoparticles (NPs) as fluorescent ink, and vinegar and soda that are frequently used in kitchen as erasing and neutralizing agents. Words or patterns written using the ZnO NPs as ink can be erased by vinegar vapour within five seconds, and after a neutralizing process in the ambient of soda vapour, the paper can be used for writing again. It is worth noting that the resolution and precision of the patterns produced via the above route degrade little after ten rewriting cycles, and the quality of the patterns produced using the ZnO NPs as ink fades little after being storage for several months, which promises the versatile potential applications of the rewriting route proposed in this paper.

Figure 1

(a) TEM image of the ZnO NPs; (b) High-resolution TEM image of the NPs; (c) XRD pattern of the ZnO NPs; (d) FTIR spectrum of the ZnO NPs.

Figure 2

(a) The fluorescence spectra of the ZnO NP solution with concentrations ranging from 0.05 to 0.3 mol/L; (b) Absorption spectra of the ZnO NPs with different concentrations, and the inset shows the fluorescence image of solid NPs evaporated from the NP solution; (c) The images of the NPs and the written words using NP solution as ink under indoor lighting conditions and (d) UV lighting conditions. (The photographs of hand was taken by Ruo-Qiu Wang).

Figure 3

(a) The fluorescent spectra of the ZnO NPs under different pH value; (b) The histogram diagram of the fluorescence intensity of the ZnO NPs under various pH values; (c) Absorption spectra of the ZnO NPs with pH value of 4.3, 5.3, 6.8, and 10.5 respectively; (d) The schematic illustration of the writing, erasing, neutralizing, and rewriting process using the ZnO NP solution as ink, vinegar as eraser, and soda solution as neutralizer.

Figure 4

(a) A 4 × 4 grey scale pattern printed by using ZnO NP solution as ink; (b) The variation of grey value of each square, and the inset is the grey value along the yellow line marked in (a); (c) The printed night-time image of the earth pictured by NASA; (d) Simulated image of (c) with MATLAB; (e) Schematic illustration of the rewriting process in a printer employing the ZnO NPs as fluorescent ink.

Figure 5

(a) The printed images and MATLAB treated patterns of three circles placed above vinegar vapor for 0 second, 2, and 5 seconds; (b) The intensity of the circles calculated with MATLAB along the diagonal line marked in (a); (c) The images and MATLAB treated patterns of the reprinted circles using ZnO NPs as ink after a neutralization process; (d) The intensity of the circles calculated with MATLAB along the diagonal line marked in (c).

Figure 6

(a) The image printed onto a piece of paper for the 1^st cycle; (b) The image printed on the paper for the 10^th cycle; The grey value distribution of each pixel in the 1^st image (c) and that of the 10^th image (d); (e) A plot of the averaged grey values for the image in the ten cycles (Scale bar = 1 cm).

Figure 7

The image of the as-printed pattern (a) and that of the pattern after being stored in air ambient for six months (b); (c) The grey value along the lines marked in (a) and (b); (d) The magnified version of the rectangle marked in (c).