At present, the actual mechanism of the photoluminescence (PL) of fluorescent carbon dots (CDs) is still an open debate among researchers. Because of the variety of CDs, it is highly important to summarize the PL mechanism for these kinds of carbon materials; doing so can guide the development of effective synthesis routes and novel applications. This review will focus on the PL mechanism of CDs. Three types of fluorescent CDs were involved: graphene quantum dots (GQDs), carbon nanodots (CNDs), and polymer dots (PDs). Four reasonable PL mechanisms have been confirmed: the quantum confinement effect or conjugated π-domains, which are determined by the carbon core; the surface state, which is determined by hybridization of the carbon backbone and the connected chemical groups; the molecule state, which is determined solely by the fluorescent molecules connected on the surface or interior of the CDs; and the crosslink-enhanced emission (CEE) effect. To give a thorough summary, the category and synthesis routes, as well as the chemical/physical properties for the CDs, are briefly introduced in advance.

The photoluminescence mechanism in carbon dots (graphene quantum dots, carbon nanodots, and polymer dots): current state and future perspective

Design, and Applications Shutao Wang,†,‡ Kesong Liu, Xi Yao, and Lei Jiang*,†,‡,§ †Laboratory of Bio-inspired Smart Interface Science, Technical Institute of Physics and Chemistry, and ‡Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, BeiHang University, Beijing 100191, People’s Republic of China Department of Biomedical Sciences, City University of Hong Kong, Hong Kong P6903, People’s Republic of China

Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications

In the last few decades, pharmaceuticals, credited with saving millions of lives, have emerged as a new class of environmental contaminant. These compounds can have both chronic and acute harmful effects on natural flora and fauna. The presence of pharmaceutical contaminants in ground waters, surface waters (lakes, rivers, and streams), sea water, wastewater treatment plants (influents and effluents), soils, and sludges has been well doccumented. A range of methods including oxidation, photolysis, UV-degradation, nanofiltration, reverse osmosis, and adsorption has been used for their remediation from aqueous systems. Many methods have been commercially limited by toxic sludge generation, incomplete removal, high capital and operating costs, and the need for skilled operating and maintenance personnel. Adsorption technologies are a low-cost alternative, easily used in developing countries where there is a dearth of advanced technologies, skilled personnel, and available capital, and adsorption appears to be the most broadly feasible pharmaceutical removal method. Adsorption remediation methods are easily integrated with wastewater treatment plants (WWTPs). Herein, we have reviewed the literature (1990-2018) illustrating the rising environmental pharmaceutical contamination concerns as well as remediation efforts emphasizing adsorption.

Pharmaceuticals of Emerging Concern in Aquatic Systems: Chemistry, Occurrence, Effects, and Removal Methods.

Graphene-based materials are gaining heightened attention as novel materials for environmental applications The unique physicochemical properties of graphene, notably its exceptionally high surface area, electron mobility, thermal conductivity, and mechanical strength, can lead to novel or improved technologies to address the pressing global environmental challenges This critical review assesses the recent developments in the use of graphene-based materials as sorbent or photocatalytic materials for environmental decontamination, as building blocks for next generation water treatment and desalination membranes, and as electrode materials for contaminant monitoring or removal The most promising areas of research are highlighted, with a discussion of the main challenges that we need to overcome in order to fully realize the exceptional properties of graphene in environmental applications

Environmental applications of graphene-based nanomaterials.

Role of nanomaterials in water treatment applications: a review.

Significant concerns have been raised over pollution of antibiotics including tetracyclines in aquatic environments in recent years. Graphene oxide (GO) is a potential effective absorbent for tetracycline antibiotics and can be used to remove them from aqueous solution. Tetracycline strongly deposited on the GO surface via π-π interaction and cation-π bonding. The adsorption isotherm fits Langmuir and Temkin models well, and the theoretical maximum of adsorption capacity calculated by Langmuir model is 313 mg g(-1), which is approximately in a close agreement with the measured data. The kinetics of adsorption fits pseudo-second-order model perfectly, and it has a better rate constant of sorption (k), 0.065 g mg(-1) h(-1), than other adsorbents. The adsorption capacities of tetracycline on GO decreased with the increase in pH or Na(+) concentration. The adsorption isotherms of oxytetracycline and doxycycline on GO were discussed and compared.

Adsorption and removal of tetracycline antibiotics from aqueous solution by graphene oxide

Periodic optical microstructures are abundant in biological systems, and have provided enormous inspiration for scientists to mimic them for optical applications. Some nocturnal insects use arrays of non-close-packed nipples of sub-300-nm size as antireflective structures (ARS) to reduce reflection from their compound eyes. The ARS on the corneas of these insects can also increase light transmission in dark conditions, which improves sensitivity of light vision. In practical applications, simultaneously suppressing surface reflection and increasing transmission of light is crucial to the performance of an optical system, especially when there are several optical components involved. For flat-panel displays, antireflective surfaces are usually employed to increase transmission and eliminate ghost image or veil glare due to reflection from the optical surfaces. Despite the technical importance, actual material solutions for improved performance are limited, especially in the ultraviolet spectral region. To date, two kinds of approaches are available for fabricating antireflective surfaces. One is coating porous or multilayered films on the surface of devices. The other is fabricating subwavelength ARS (moth’s eye structures) directly on the surface of devices. The ARS surfaces exhibit distinct advantages compared to coatings. First, the ARS surfaces exhibit higher mechanical stability and better durability than coatings because no foreign materials are involved when they are used over a broad thermal range. Second, the material of the ARS surfaces is the same as that of devices, while coating materials with appropriate refractive index are rare in nature. Last, the ARS surfaces have many tunable factors, such as the spacing, depth and cross-sectional geometry. Similar to the nipple arrays in insects’ compound eyes and wings, the ARS surfaces with nipple-like or tapered profiles exhibit a gradient in refractive index between air and substrate. Therefore, they can dramatically suppress the reflection losses at the interface over a large range of wavelengths and a large field of view. Many techniques based on top-down lithography, such as electron-beam etching, fast atom beam and interference lithography have been applied to fabricated ARS surfaces. To avoid scattering from the optical interface, the structure dimension at an optical interface has to be smaller than the wavelength of the incident light. For ultraviolet and visible light applications, feature sizes below 200 nm are always necessary. In such small size ranges, conventional top-down lithographic technologies require sophisticated equipment, are timeconsuming and expensive to fabricate over the large areas required for practical applications. Moreover, processing of non-planar lenses, especially with a small curvature radius, is almost impossible due to the difficulty of fabricating masks on non-planar surfaces. Recently, ARS surfaces on silicon prepared by nanosphere lithography have been reported, but there are few ARS surfaces on fused silica or on non-planar lenses. Spatz and co-workers have prepared fused silica hollow pillar arrays; such arrays exhibit high performance antireflective properties in the deep ultraviolet region, although the antireflective properties in the visible region is suboptimal due to the pillars having a smaller spacing than the wavelength of visible light. The nipple arrays on the compound eyes of insects exhibit both antireflective and self-cleaning properties. Recently, multifunctional antireflective surfaces have attracted a lot of interest because the additional functions can improve the performance of optical devices. For instance, we have successfully prepared high aspect ratio silicon hollow-tip arrays for antireflective and water-repellent surfaces. Such antireflective surfaces with water-repellent properties enable applications in humid environments. In practical applications, the high transmission and antifogging surfaces are highly desired, such as eyeglass, swimming goggles, and lens in laparoscopic surgery. Superhydrophilic coatings can significantly suppress fogging behavior by rapid spread and flow of water droplets on their surfaces and eliminate light scattering caused by water droplets. Nowadays, antifogging and antireflective surfaces based on porous films have been prepared by LBL technology, which is usually used as a general means to create multifunctional coatings. In this Communication, we report a simple and time-efficient method to prepare large area fused silica cone arrays on planar fused silica substrates and planconvex lenses for high performance ARS and antifogging surfaces. The ARS surfaces introduce a gradient in the refractive index between air and the silica substrate, which dramatically suppresses the surface reflective loss from the ultraviolet to near-infrared regions with an incidence angle up to 458. Besides, such surfaces exhibit high performance antifogging properties. The antifogging and ARS surfaces exhibit higher mechanical stability and better durability than coatings because no foreign materials are involved.

Biomimetic Surfaces for High‐Performance Optics

In this paper, we report a kind of bioinspired high performance near-infrared improved transmittance silica surfaces with superhydrophobic properties by colloidal lithography, with transmittance about 99% from 1300 to 2000 nm. Meanwhile, the optical properties of such surfaces can be controlled by the antireflective structure morphologies resulting from the different reactive ion etching conditions. Using proper microspheres as mask, the high-performance near-infrared telecommunication optics can be achieved. Besides, the antireflective surfaces possess superhydrophobic properties after modified by fluorosilane. Such antireflective surfaces are promising for fabrication of highly light transmissive, antireflective, and superhydrophobic near-infrared optical materials to be used in many important fields.

Bioinspired Silica Surfaces with Near-Infrared Improved Transmittance and Superhydrophobicity by Colloidal Lithography

High refractive index organic–inorganic hybrid coatings with TiO2 nanocrystals

Polymer 1D photonic crystals with perfect optical tuning and distinctive brilliant colors are successfully fabricated through alternating thin films of PMMA and PNIPAM-co-PGMA, which can be easily processed as photonic paper by combining with top-down assisted photolithograph. The photonic paper is prewritten by ultraviolet light cross-linking with a photo mask and read with water as ink. The writing and erasing process is smoothly reversible by repeatedly exposing the material to water and air. The color of letters written on the paper can be modulated by tuning the cross-linking density and ink temperature. Moreover, multicolors can be integrated onto the photonic paper simultaneously by making the degree of cross-linking of different regions of the photonic paper different. The fabrication method is simple and low-cost, and the photonic paper can be easily manufactured in large areas. The integrated multicolor and its diverse change with external stimuli promises the photonic paper lots of potential applications, such as colorful sensors, security labels, full-color printing, displays and so on.

/pdf/polymer-bragg-stack-as-color-tunable-photonic-paper-1fi5staho6.pdf

Liang Zhang

Papers

Adsorption and removal of tetracycline antibiotics from aqueous solution by graphene oxide

Biomimetic Surfaces for High‐Performance Optics

Bioinspired Silica Surfaces with Near-Infrared Improved Transmittance and Superhydrophobicity by Colloidal Lithography

High refractive index organic–inorganic hybrid coatings with TiO2 nanocrystals

Polymer Bragg stack as color tunable photonic paper