Haibo Hu

Invisible photonic printing: computer designing graphics, UV printing and shown by a magnetic field

Invisible photonic printing, an emerging printing technique, is particularly useful for steganography and watermarking for anti-counterfeiting purposes. However, many challenges exist in order to realize this technique. Herein, we describe a novel photonic printing strategy targeting to overcome these challenges and realize fast and convenient fabrication of invisible photonic prints with good tenability and reproducibility. With this novel photonic printing technique, a variety of graphics with brilliant colors can be perfectly hidden in a soft and waterproof photonic-paper. The showing and hiding of the latent photonic prints are instantaneous with magnet as the only required instrument. In addition, this strategy has excellent practicality and allows end-user control of the structural design utilizing simple software on a PC.

Visually readable and highly stable self-display photonic humidity sensor

A visually readable and highly stable self-display photonic humidity sensor has been fabricated through the fast magnetically induced self-assembly of carbon-encapsulated superparamagnetic colloidals, followed by an instant radical polymerization to fix the photonic crystal structures inside a polyacrylamide glycol gel matrix. Because of the use of magnetic assembly and radical-polymerization, we can quickly and conveniently prepare the photonic humidity sensor on a large scale with arbitrary shape which has an important significance in large-scale industrial production. The photonic humidity sensor can self-display brilliant colors from navy blue to light red as the relative humidity changes from 11% to 97%. The whole shift of the reflection wavelength is nearly 160 nm, which almost covers the whole visual region and its intensity is readable by the naked eye. In addition, cycle tests demonstrate that the photonic humidity sensor has a good stability and reproducibility in its diffraction signal. Therefore, coupled with low cost and no power consumption, the photonic humidity sensor system can realize colorimetric detection of humidity, similarly to pH indicator paper.

Manganese hexacyanoferrate/MnO2 composite nanostructures as a cathode material for supercapacitors

A composite of manganese hexacyanoferrate (MnHCF) coated by an amorphous manganese dioxide layer was synthesized by a facile co-precipitation method and a further step called “deep electro-oxidation”. The structure and components of the resulting MnHCF/MnO2 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Electrochemical testing showed a capacitance of 225.6 F g−1 at a sweep rate of 5 mV s−1 within a voltage range of 1.3 V and a high energy density of 74.5 W h kg−1 at a current density of 0.5 A g−1 during galvanostatic charge/discharge cycles, which is superior to most cathode materials, including some reported graphene/MnO2 nanocomposites. It is confirmed that the two components, manganese hexacyanoferrate and manganese dioxide, lead to an integrated electrochemical behavior and a capacitor with enhanced performance. The electrochemical testing and corresponding XPS analysis also demonstrated that the manganese coordinated by cyanide groups via nitrogen atoms in MnHCF did not get involved in the charge storage process during potential cycles.

Photonic anti-counterfeiting using structural colors derived from magnetic-responsive photonic crystals with double photonic bandgap heterostructures

Herein, based on the recently developed magnetic-induced self-assembly techniques, we designed a novel, simple and low-cost method to fabricate a special class of photonic crystals with double photonic band-gap hetero-structures, and eventually achieved the purpose of modulating the optical diffraction color of the structural colors. The method greatly simplifies the fabrication of photonic crystals with multiple photonic band-gap hetero-structures and extends the modulation means of the optical diffraction color of structural colors. Furthermore, it is worth noting that due to the resulting structural colors that are derived from the double photonic band-gap hetero-structures consisting of double diffraction peaks and presenting a magnetic switching effect through the application and withdrawal of the magnetic fields (0.05 T), which is more difficult to be imitated by those of chemical dyes and pigments, a kind of novel photonic anti-counterfeiting label has been prepared with these structural colors. Due to the widespread counterfeiting of various commercial objects and the urgent requirements of forgery protection, the photonic anti-counterfeiting label demonstrated in our work will undoubtedly find applications in meeting the growing anti-counterfeiting needs.

Magnetically responsive photonic watermarks on banknotes

A high performance photonic anti-counterfeiting watermark that can be incorporated into banknotes has been developed by combining a novel invisible photonic printing with a flexible, translucent and ultra-thin magnetic-responsive photonic display film. The photonic anti-counterfeiting watermark has latent colourful patterns that are lithographically printable and magnetically responsive, and can be easily perceived by the naked eye under magnetic fields. In addition, the distinct differences of the spectral characteristics between the invisible-form and the visible-form of the patterns can be accurately detected by using a special optical instrument, which makes the photonic anti-counterfeiting watermark provide double security information to identify the authenticity of banknotes. Moreover, the strategy allows accurate control of the optical diffraction colour and the structural design of the latent patterns. The fabrication process does not damage the banknotes and allows fast, convenient and scalable production at low-costs. The present work demonstrates that the fabrication of high performance photonic-crystal-based anti-counterfeiting devices on banknotes is possible.

Low-Cost, Acid/Alkaline-Resistant, and Fluorine-Free Superhydrophobic Fabric Coating from Onionlike Carbon Microspheres Converted from Waste Polyethylene Terephthalate

Onionlike carbon microspheres composed of many nanoflakes have been prepared by pyrolyzing waste polyethylene terephthalate in supercritical carbon dioxide at 650 °C for 3 h followed by subsequent vacuum annealing at 1500 °C for 0.5 h. The obtained onionlike carbon microspheres have very high surface roughness and exhibit unique hydrophobic properties. Considering their structural similarities with a lotus leaf, we further developed a low-cost, acid/alkaline-resistant, and fluorine-free superhydrophobic coating strategy on fabrics by employing the onionlike carbon microspheres and polydimethylsiloxane as raw materials. This provides a novel technique to convert waste polyethylene terephthalate to valuable carbon materials. At the same time, we demonstrate a novel application direction of carbon materials by taking advantage of their unique structural properties. The combination of recycling waste solid materials as carbon feedstock for valuable carbon material production, with the generation of highly value-added products such as superhydrophobic fabrics, may provide a feasible solution for sustainable solid waste treatment.

Reusable photonic wordpad with water as ink prepared by radical polymerization

In this article, we report and demonstrate a novel photonic wordpad that is fabricated through the fast magnetically induced self-assembly of carbon-encapsulated superparamagnetic colloidals, followed by an instant radical polymerization to fix the photonic crystal structures inside a polyacrylamide glycol gel matrix. The photonic wordpad strongly diffracts blue light due to the colloids forming ordered chain-like structures in the solidified polymer matrix with uniform interparticle spacing under the induction of an external magnetic field. Distilled water is used as ink to write letters or Chinese characters with a different color on the wordpad because it can swell the polymer matrix and then increase the interparticle spacing within the chains, and as a result a red-shift in optical diffraction occurs. The photonic wordpad not only has an excellent reusability because the ink mark can be written or erased by introducing or removing the water in the surface layer of the photonic wordpad, but also is environmentally friendly and low-carbon owing to the reusability of the wordpad and non-toxicity of the ink. In addition, due to the use of the recent development of magnetically tunable assembly techniques, the processing time of this photonic wordpad is greatly reduced compared to using conventional assembly methods, which has an important significance in the large-scale industrial production in the future.

Magnetically controllable colloidal photonic crystals: unique features and intriguing applications

Magnetically induced self-assembly is a very powerful method that can quickly, efficiently and reversibly assemble magnetic colloidal particles into ordered structures with tunable photonic properties. The recent developments in the techniques have enabled convenient modulation of photonic properties and easy fabrication of sophisticated photonic structures. As a result, various practical applications such as magnetically controlled display units, photonic humidity sensors, reusable photonic paper/ink, photonic anti-counterfeiting, high resolution full-color photonic printing and invisible photonic printing have been demonstrated. In this feature article, we will describe these recent advances, with special focus on magnetically induced self-assembly of colloidal particles into 1D chainlike photonic structures, and discuss the emerging applications of this new technique.

One for Two: Conversion of Waste Chicken Feathers to Carbon Microspheres and (NH4)HCO3

Pyrolysis of 1 g of waste chicken feathers (quills and barbs) in supercritical carbon dioxide (sc-CO2) system at 600 °C for 3 h leads to the formation of 0.25 g well-shaped carbon microspheres with diameters of 1-5 μm and 0.26 g ammonium bicarbonate ((NH4)HCO3). The products were characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectroscopic, FT-IR spectrum, X-ray electron spectroscopy (XPS), and N2 adsorption/desorption measurements. The obtained carbon microspheres displayed great superhydrophobicity as fabric coatings materials, with the water contact angle of up to 165.2±2.5°. The strategy is simple, efficient, does not require any toxic chemicals or catalysts, and generates two valuable materials at the same time. Moreover, other nitrogen-containing materials (such as nylon and amino acids) can also be converted to carbon microspheres and (NH4)HCO3 in the sc-CO2 system. This provides a simple strategy to extract the nitrogen content from natural and man-made waste materials and generate (NH4)HCO3 as fertilizer.