The synthesis of carbon dots (CDs) from green precursors has received considerable attention recently. However, most of the natural biomass-derived products without further surface treatment usually have quite low quantum yield (QY) varying in the range of 2–30%. Herein, we report the sustainable fabrication of highly fluorescent CDs from food waste, turtle shells, and demonstrate their applications in the fields of multisignal coding and anti-counterfeiting with a combination of colloidal photonic crystals (CPCs). We utilized turtle shells as precursors to synthesize fluorescent CDs via a simple pyrolysis method. The resultant CDs without further surface treatment have an absolute photoluminescence (PL) QY of 45% and high dispersibility in various solvents. Then, we realized collective optical properties with a combination of CDs and CPCs, including diffractive light abilities and fluorescence. CPC/CD bead codes with a structural color and fluorescence were prepared via a microfluidic device. CPC/CD patterned films with PL and angular dependence of structural colors were also constructed via a 3D microfluidic printing technique, which are useful for multisignal anti-counterfeiting and various optoelectronic applications.

Carbon dots (CDs) present an enticing prospect for a variety of optical applications relying on their high photoluminescence (PL) quantum yield (QY). Herein, the synthesis, optical properties, structural characterizations, density‐functional theory (DFT) calculations, and potential applications of yellow‐emissive CDs (Y‐CDs) with ultra‐high PL QY are reported. Solvothermal treatment of citric acid and urea in toluene, followed by column chromatography, produces Y‐CDs exhibiting excitation‐independent PL emission at 553 nm with a high solution PL QY of 92%. A variety of optical and structural characterizations and DFT theoretical calculations are implemented to confirm the general structure and fluorescence origin of Y‐CDs, conjugated sp2‐carbon domains (fused rings) with edge groups. Significantly, transparent Y‐CDs/acrylic resin films with strong solid‐state emissions are fabricated. The Y‐CD films exhibit a high fluorescence with PL QY of 98%, good PL stability (no PL variation under continuous irradiation for 180 h), and large Stokes shift (129 nm). The potential applications of Y‐CDs for luminescent solar concentrators as well as yellow phosphors for lighting are also demonstrated. These findings thus promote the development of high‐performance CDs and their optoelectronic applications.

Solar-driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high-cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three-dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light-facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light-to-vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO 2 photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu 2 O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy-to-perform construction on-site, providing a promising opportunity for efficient and decentralized water and clean fuel production.

Janus structural interfacial vaporization by separating the solar absorber from the bulk working fluid has attracted tremendous attention due to its low heat losses and high solar conversion efficiency for desalination, water purification, energy generation, etc. However, a totally separated double-deck structure with a discontinuous interfacial transition and inefficient photothermic materials undermines its long-term use and large-scale practical exploitation. Herein, a low-cost Janus monolithic chitosan aerogel with continuous aligned run-through microchannels has been demonstrated to have a highly efficient photothermic effect on seawater desalination and wastewater purification. The top solar absorber layer enhances broadband light absorption and photothermal conversion efficiency via the multiple internal reflection of incident light in the aligned microchannels. Moreover, the insulating/hydrophilic bottom layer promotes water transportation and heat localization, and simultaneously prevents salt/fouling accumulation. As a result, a long-term solar vaporization rate of ∼1.76 kg m −2 h −1 is achieved, corresponding to a light-to-vapor efficiency of ∼91% under 1 sun irradiation. Notably, the large-vessel microchannels throughout the aerogel and favorable swelling property provide sufficient water replenishment and storage for completely isolating self-contained evaporation, illustrating an enhanced and time-extended selfcontained solar steam generation. Such a low-cost bilayer aerogel with remarkable cycling stability in various fluids offers potential opportunities for freshwater production in remote rural areas.

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