Build-in electric field in CuWO4/covalent organic frameworks S-scheme photocatalysts steer boosting charge transfer for photocatalytic CO2 reduction.

Covalent organic frameworks (COFs) are crystalline porous materials with enormous potential for realizing solar-driven CO2-to-fuel conversion, yet the sluggish transfer/separation of photoinduced electrons and holes remains a compelling challenge. Herein, a step (S)-scheme heterojunction photocatalyst (CuWO4-COF) was rationally fabricated by a thermal annealing method for boosting CO2 conversion to CO. The optimal CuWO4/COF composite sample, integrating 10 wt% CuWO4 with an olefin (C═C) linked COF (TTCOF), achieved a remarkable gas-solid phase CO yield as high as 7.17 ± 0.35 µmol g-1h-1 under visible light irradiation, which was significantly higher than the pure COF (1.6 ± 0.29 µmol g-1h-1). The enhanced CO2 conversion rate could be attributable to the interface engineering effect and the formation of internal electric field (IEF) directing from TTCOF to CuWO4 according to the theoretical calculation and experimental results, which also proves the electrons transfer from TTCOF to CuWO4 upon hybridization. In addition, driven by the IEF, the photoinduced electrons can be steered from CuWO4 to TTCOF under visible light irradiation as well-elucidated by in-situ irradiated X-ray photoelectron spectroscopy, verifying the S-scheme charge transfer pathway over CuWO4/COF composite heterojunctions, which greatly foster the photoreduction activity of CO2. The preparation technique of the S-scheme heterojunction photocatalyst in this study provides a paradigmatic protocol for photocatalytic solar fuel generation.

Interspersed Bi Promoting Hot Electron Transfer of Covalent Organic Frameworks Boosts Nitrogen Reduction to ammonia.

Seeking highly-efficient, non-pollutant, and chemically robust photocatalysts for visible-light-driven ammonia production still remained challenging, especially in pure water. The key bottle-necks closely correlate to the nitrogen activation, water oxidization, and hydrogen evolution reaction (HER) processes. In this study, a novel Bi decorated imine-linked COF-TaTp (Bi/COF-TaTp) through N-Bi-O coordination is reasonably designed to achieve a boosting solar-to-ammonia conversion of 61 µmol-1  g-1  h-1 in the sacrificial-free system. On basis of serial characterizations and DFT calculations, the incorporated Bi is conducive to the acceleration of charge carriers transfer and N2 activation through the donation and back-donation mode. The N2 adsorption energy of 5% Bi/COF-TaTp is calculated to be -0.19 eV in comparison with -0.09 eV of the pure COF-TaTp and the electron exchange between N2 and the modified catalyst is much more intensive. Moreover, the accompanied hydrogen production process is effectively inhibited by Bi modification, demonstrated by the higher energy barrier for HER over Bi/COF-TaTp (2.62 eV) than the pure COF-TaTp (2.31 eV) when using H binding free energy (ΔGH* ) as a descriptor. This work supplies novel insights for the design of photocatalysts for N2 reduction and intensifies the understanding of N2 adsorption and activation over covalent organic frameworks-based materials.

Interfacial engineering of novel inorganic-organic ß-Ga2O3/COF heterojunction for accelerated charge transfer towards artificial photosynthesis.

Semiconductor-based solar-driven CO2 to fuels has been widely reckoned as an ingenious approach to tackle energy crisis and climate change simultaneously. However, the high carrier recombination rate of the photocatalyst severely dampens their photocatalytic uses. Herein, an inorganic-organic heterojunction was constructed by in-situ growing a dioxin-linked covalent organic framework (COF) on the surface of rod-shaped ß-Ga2O3 for solar-driven CO2 to fuel. This novel heterojunction is featured with an ultra-narrow bandgap COF-318 (absorption edge = 760 nm), which is beneficial for fully utilizing the visible light spectrum, and a wide bandgap ß-Ga2O3 (absorption edge = 280 nm) to directional conduct electrons from COF to reduce CO2 without electron-hole recombination occurred. Results showed that the solar to fuels performance over ß-Ga2O3/COF was much superb than that of COF. The optimized Ga2O3/COF achieved an outstanding CO evolution rate of 85.8 µmol h-1·g-1 without the need of any sacrificial agent or cocatalyst, which was 15.6 times more efficient than COF. Moreover, the analyses of photoluminescence electrochemical characterizations and density functional theory (DFT) calculations revealed that the fascinate construction of ß-Ga2O3/COF heterojunction significantly favored charge separation and the directional transfer of photogenerated electrons from COF to ß-Ga2O3 followed by CO2. This study paves the way for developing effective COF-based semiconductor photocatalysts for solar-to-fuel conversion.

Insights into Photocatalytic Degradation Pathways and Mechanism of Tetracycline by an Efficient Z-Scheme NiFe-LDH/CTF-1 Heterojunction.

Photocatalysis offers a sustainable approach for recalcitrant organic pollutants degradation, yet it is still challenging to seek robust photocatalysts for application purposes. Herein, a novel NiFe layered double hydroxide (LDH)/covalent triazine framework (CTF-1) Z-scheme heterojunction photocatalyst was rationally designed for antibiotics degradation under visible light irradiation. The NiFe-LDH/CTF-1 nanocomposites were readily obtained via in situ loading of NiFe-LDH on CTF-1 through covalent linking. The abundant coupling interfaces between two semiconductor counterparts lay the foundation for the formation of Z-scheme heterostructure, thereby effectively promoting the transfer of photogenerated electrons, inhibiting the recombination of carriers, as well as conferring the nanocomposites with stronger redox ability. Consequently, the optimal photocatalytic activity of the LDH/CTF heterojunction was significantly boosted for the degradation of a typical antibiotic, tetracycline (TC). Additionally, the photodegradation process and the mineralization of TC were further elucidated. These results envision that the LDH/CTF-1 can be a viable photocatalyst for long-term and sustainable wastewater treatment.

Interlayer Charge Transfer Over Graphitized Carbon Nitride Enabling Highly-Efficient Photocatalytic Nitrogen Fixation.

Exploiting cost-effective, high-efficiency, and contamination-free semiconductors for photocatalytic nitrogen reduction reaction (N2 RR) is still a great challenge, especially in sacrificial-free system. On basis of the electron "acceptance-donation" concept, a boron-doped and carbon-deficient g-C3 N4 (Bx CvN) is herein developed through precise dopant and defect engineering. The optimized B15 CvN exhibisted an NH3 production rate of 135.3 µmol h-1  g-1 in pure water with nine-fold enhancement to the pristine graphitic carbon nitride (g-C3 N4 ), on account of the markedly elevated visible-light harvesting, N2 activation, and multi-directional photoinduced carriers transfer. The decorated B atoms with coexistent occupied and empty sp3 hybridized orbitals are theoretically proved to be in charge of the increase of N2 adsorption energy from -0.08 to -0.26 eV and the change in N2 adsorption model from one-way to two-way end-on pattern. Noticeably, the elaborate coordination of doped B atoms and carbon vacancies greatly facilitated the interlayer interaction and vertical charge migration of Bx CvN, which is distinctly revealed through the charge density difference calculations. The current study provides an alternative groundbreaking perspective for advancing photocatalytic N2 RR through the targeted configuration of the defect and dopant sites.

Cobalt quantum dots as electron collectors in ultra-narrow bandgap dioxin linked covalent organic frameworks for boosting photocatalytic solar-to-fuel conversion.

Photocatalysis offers a sustainable paradigm for solar-to-fuel conversion because it conflates the merits of renewable solar energy and reusable catalysts. However, the seek for robust photocatalysts that can utilize the full visible light spectrum remains challenging. Herein, cobalt quantum dots (Co QDs) were integrated into ultra-narrow bandgap dioxin linked covalent organic frameworks (COF-318) for photocatalytic solar-to-fuel conversion under full spectrum of visible light irradiation. The optimal Co10-COF exhibited superior photocatalytic CO2 reduction performance, affording a CO yield of 4232 µmol∙g-1∙h-1 and H2 evolution of 6611 µmol∙g-1∙h-1. Specifically, Co QDs played a crucial role in boosting the photocatalytic performance, which acted as electron collectors to capture the photoinduced electrons and then conveyed them to CO2 molecules. Moreover, the Co QDs modification significantly improved the CO2 adsorption and activation capacity, as well as prolonging the lifetime of photogenerated carriers. This work reveals an operable pathway for fabricating promising photocatalyst for visible-light-driven solar-to-fuel generation and provides insight into the impact of the integration of Co QDs on COF-based photocatalysts.

An Artificial Photosystem of Metal-Insulator-CTF Nanoarchitectures for Highly Efficient and Selective CO2 Conversion to CO.

It is of pivotal significance to explore robust photocatalysts to promote the photoreduction of CO2 into solar fuels. Herein, an intelligent metal-insulator-semiconductor (MIS) nano-architectural photosystem was constructed by electrostatic self-assembly between cetyltrimethylammonium bromide (CTAB) insulator-capped metal Ni nanoparticles (NPs) and covalent triazine-based frameworks (CTF-1). The metal-insulator-CTF composites unveiled a substantially higher CO evolution rate (1254.15 µmol g-1 h-1 ) compared with primitive CTF-1 (1.08 µmol g-1 h-1 ) and reached considerable selectivity (98.9 %) under visible-light irradiation. The superior photocatalytic CO2 conversion activity over Ni-CTAB-CTF nanoarchitecture could be attributed to the larger surface area, reinforced visible-light response, and CO2 capture capacity. More importantly, the Ni-CTAB-CTF nanoarchitecture endowed the photoexcited electrons on CTF-1 with the ability to tunnel across the thin CTAB insulating layer, directionally migrating to Ni NPs and thereby leading to the efficient separation of photogenerated electrons and holes in the photosystem. In addition, isotope-labeled (13 CO2 ) tracer results verified that the reduction products come from CO2 rather than the decomposition of the photocatalysts. This study opens a new avenue for establishing a highly efficient and selective artificial photosystem for CO2 conversion.

Band Gap Tuning of Covalent Triazine-Based Frameworks through Iron Doping for Visible-Light-Driven Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen energy production through water splitting paves a promising pathway for alleviating the increasingly severe energy crisis. Seeking affordable, highly active, and stable photocatalysts is crucial to access the technology in a sustainable manner. Herein, a trivalent iron-doped covalent triazine-based framework (CTF-1) was elaborately designed in this study to finely tune the band structure and photocatalytic activity of CTF-1 for H2 production. With optimal doping amount, Fe10 /CTF-1 exhibited a satisfying H2 production activity of 1460 µmol h-1 g-1 , corresponding to 28-fold enhancement compared with pure CTF-1. The Fe3+ doping is responsible for a remarkedly broadened visible-light adsorption range, improved reduction ability and inhibited electron-hole recombination of CTF-1. Specifically, the doped Fe3+ could serve as photocatalytically active center and "electron relay" to accelerate charge separation and transformation. This study offers a feasible strategy to validly design and synthesize CTF-based photocatalytic materials to efficiently utilize solar energy.

A smart material built upon the photo-thermochromic effect and its use for managing indoor temperature.

We demonstrate a material by dispersing a thermochromic mixture of leuco dye, developer, and solvent as microspheres in a polymer matrix to improve the efficiency of building energy management. The smart, photo-thermochromic film can automatically switch between a colored and colorless state in response to climate temperature and light to realize photothermal heating and cooling.

Rational construction of Ni(OH)2 nanoparticles on covalent triazine-based framework for artificial CO2 reduction.

Artificial photoreduction of CO2 to chemical fuel is an intriguing and reliable strategy to tackle the issues of energy crisis and climate change simultaneously. In the present study, we rationally constructed a Ni(OH)2-modified covalent triazine-based framework (CTF-1) composites to serve as cocatalyst ensemble for superior photoreduction of CO2. In particular, the optimal Ni(OH)2-CTF-1 composites (loading ratio at 0.5 wt%) exhibited superior photocatalytic activity, which surpassed the bare CTF-1 by 33 times when irradiated by visible light. The mechanism for the enhancement was systematically investigated based on various instrumental analyses. The origin of the superior activity was attributable to the enhanced CO2 capture, more robust visible-light response, and improved charge carrier separation/transfer. This study offers an innovative pathway for the fabrication of noble-metal-free cocatalysts on CTF semiconductors and deepens the understanding of photocatalytic CO2 reduction.

Distribution behavior of arsenate into α-calcium sulfate hemihydrate transformed from gypsum in solution.

Transforming gypsum into α-calcium sulfate hemihydrate (α-HH) provides a promising utilization pathway for the abundant amount of chemical gypsum. The transformation follows the route of "dissolution-recrystallization", during which the arsenic pollutant in gypsum is released into the solution, and hence raises the possibility of being distributed into the product of α-HH, a potential harm that has always been neglected. Investigation of the transformation process at neutral pH revealed that the arsenate ions in solution were distributed into α-HH and generated an enrichment of arsenic by 4-6 times. Arsenate ions distributed into α-HH by substitution for lattice sulfate, adsorption on α-HH facets and occupation for surface sulfate sites. While at higher concentrations, calcium arsenate coprecipitated with α-HH or even crystallized independently. Increasing temperature accelerated the phase transformation and restrained arsenate migration into α-HH due to the lag of distribution balance. The pH of solution modulated the dominant arsenate species and decreasing pH weakened arsenate substitution capacity for sulfate in α-HH. This work uncovers arsenate distribution mechanism during the transformation of gypsum into α-HH and provides a feasible method to restrain arsenate distribution into product, which helps to understand arsenate behavior in hydrothermal solution with high concentration of sulfate minerals and provides a guidance for controlling pollutants distribution into product.

Porous Gold Nanocages: High Atom Utilization for Thiolated Aptamer Immobilization to Well Balance the Simplicity, Sensitivity, and Cost of Disposable Aptasensors.

Gold nanostructures such as nanospheres, nanorods, or nanowires have been extensively used for electrode surface modification because they not only can increase the overall electroactive surface but can also provide anchoring sites for thiolated aptamers through facile Au-S covalent bonds. However, all of those gold nanostructures used are solid and only the outer surface is attractive. In the aim to reduce the usage of precious gold, in this paper, porous gold nanocages (AuNCs) with both inner and outer walls for effective aptamer immobilization have been electrostatically adhered on a screen-printed carbon electrode (SPCE), to develop a highly sensitive aptasensor in a truly label-free manner. Specifically, the thiolated aptamers specific for aflatoxin B1 (AFB1) were chosen as the model aptamer and covalently bound to the inner and outer surface of AuNCs using Au-S chemistry. Exposing the sensing interface to targets could initiate the formation of the aptamer/target complex, resulting in an increased interfacial electron transfer resistance on the SPCE. Under optimal conditions, this aptasensor could detect AFB1 in a wide range of 0.1 pg mL-1 to 100 ng mL-1 with a high linear fit and has an ultralow detection limit of 0.03 pg mL-1 (S/N = 3). The developed aptasensor has remarkable merits such as simpler operation, more cost-effective, more sensitive, and less reagent consumption. We therefore provided a universal strategy to well balance the simplicity, sensitivity, and cost of disposable aptasensors for a large population of targets having specific aptamer strands.

Near-Infrared-Triggered Release of Ca2+ Ions for Potential Application in Combination Cancer Therapy.

Calcium ion (Ca2+ ), an abundant species in the body, is a potential therapeutic ion with manageable side effects. However, the delivery of such a highly charged species represents a great challenge. Here, a nanosystem based on Au nanocages (AuNCs) and a phase-change material (PCM) for delivering calcium chloride (CaCl2 ) into cancer cells and thereby triggering cell death upon near-infrared (NIR) irradiation is demonstrated. In the absence of NIR irradiation, the nanosystem, denoted CaCl2 -PCM-AuNC, shows negligible cytotoxicity because the Ca2+ ions are fully encapsulated in a solid matrix. Upon NIR irradiation, the Ca2+ ions are swiftly released due to the melting of PCM matrix in response to photothermal heating. The sudden increase in intracellular Ca2+ causes disruption to the mitochondrial Ca2+ homeostasis and thus the loss of mitochondrial membrane potential, subsequently resulting in cell apoptosis. This nanosystem provides a new method for cancer treatment by tightly managing the intracellular concentration of a physiologically essential element.

Continuous processing of phase-change materials into uniform nanoparticles for near-infrared-triggered drug release.

We report a method based on interfacial, anti-solvent-induced precipitation in a fluidic device for the continuous and scalable processing of phase-change materials (PCMs) into uniform nanoparticles with controlled diameters in the range of 10-100 nm. A eutectic mixture of lauric acid and stearic acid, with a well-defined melting point at 39 °C, serves as an example to demonstrate the concept. In the fluidic device, a coaxial flow is created by introducing a PCM solution in ethanol and a lipid solution in water (the anti-solvent) as the focused and focusing phases, respectively. The formation of lipid-capped PCM nanoparticles is governed by diffusion-controlled mixing of ethanol and water. During the production, both doxorubicin (DOX, an anticancer drug) and indocyanine green (ICG, a near-infrared dye) can be readily loaded into the PCM nanoparticles to give a smart drug release system. Upon irradiation with near-infrared light, the photothermal heating caused by ICG can melt the PCM and thereby trigger the release of DOX. This work not only provides a new technique for the continuous processing of PCMs and other soft materials into uniform nanoparticles with controlled sizes but also demonstrates a biocompatible system for controlled release and related applications.

A Eutectic Mixture of Natural Fatty Acids Can Serve as the Gating Material for Near-Infrared-Triggered Drug Release.

A smart release system responsive to near-infrared (NIR) light is developed for intracellular drug delivery. The concept is demonstrated by coencapsulating doxorubicin (DOX) (an anticancer drug) and IR780 iodide (IR780) (an NIR-absorbing dye) into nanoparticles made of a eutectic mixture of naturally occurring fatty acids. The eutectic mixture has a well-defined melting point at 39 °C, and can be used as a biocompatible phase-change material for NIR-triggered drug release. The resultant nanoparticles exhibit prominent photothermal effect and quick drug release in response to NIR irradiation. Fluorescence microscopy analysis indicates that the DOX trapped in the nanoparticles can be efficiently released into the cytosol under NIR irradiation, resulting in enhanced anticancer activity. A new platform is thus offered for designing effective intracellular drug-release systems, holding great promise for future cancer therapy.

α-Calcium Sulfate Hemihydrate Nanorods Synthesis: A Method for Nanoparticle Preparation by Mesocrystallization.

The past decades have witnessed great advances in nanotechnology since tremendous efforts have been devoted for the design, synthesis, and application of nanoparticles. However, for most mineral materials such as calcium sulfate, it is still a challenge to prepare their nanoparticles, especially with uniform size and high monodispersity. In this work, we report a route to regulate the morphology and structure of α-calcium sulfate hemihydrate (α-HH) and successfully synthesize and stabilize its mesocrystals for the first time. The ellipsoidal mesocrystals in length of 300-500 nm are composed by α-HH nanoparticles arranged in the same crystallographic fashion and interspaced with EDTA. The time-dependent experiments indicate the α-HH aggregates evolve from irregular structure to mesocrystal structure with the subsequent growth of subunits and then partially fuse into single crystals. Disorganizing the mesocrystal structure before the emergence of fusion reaps α-HH nanorods in a length of 30-80 nm and a width of 10-20 nm with high monodispersion. This ingenious concept paves an alternative way for nanoparticle preparation and is readily extended to other inorganic systems.

Reconfigurable nonblocking 4-port silicon thermo-optic optical router based on Mach-Zehnder optical switches.

We demonstrate a reconfigurable nonblocking 4-port silicon thermo-optic optical router based on Mach-Zehnder optical switches. For all optical links in its 9 routing states, the optical signal-to-noise ratios are larger than 15 dB in the wavelength range from 1525 to 1565 nm. Each optical link of the optical router can manipulate 50 wavelength-division-multiplexing channels with the data rate of 32 Gbps for each channel in the same wavelength range. Its average energy efficiency is about 16.3 fJ/bit, and its response time is about 19 µs.

Controlled synthesis of monodisperse α-calcium sulfate hemihydrate nanoellipsoids with a porous structure.

We report a facile and green chemical solution approach to synthesize monodisperse α-calcium sulfate hemihydrate (α-HH) nanoellipsoids with a length of 600 nm and a width of 300 nm by simply mixing Ca(2+) and SO4(2-) glycerol-water precursor solutions in the presence of Na2EDTA. The α-HH nanoellipsoid is formed through a Na2EDTA-mediated self-assembly of small primary building blocks (α-HH domains: ∼14 nm). The study on the morphological evolution of α-HH reveals that the controlled synergy of supersaturation (precursor concentration) and Na2EDTA is crucial for the development of α-HH into nanoellipsoids. Further thermal annealing of the nanoellipsoid could make the α-HH domains transit into calcium sulfate anhydrites and grow up, generating the gaps between them and resulting in a porous structure. This work paves a new way for preparing high-quality α-HH nanoellipsoids with a monodisperse nanosize and a porous structure, promising their future application in many fields such as biomedicine.

Reconfigurable non-blocking four-port optical router based on microring resonators.

A reconfigurable non-blocking four-port optical router with the least optical switches is demonstrated. The device is based on microring resonators tuned through thermo-optic effect. The optical signal-to-noise ratio of the device at its nine routing states is about 15 dB. A 25 Gbps data transmission has been performed on its whole 12 optical links, and 8-channel wavelength division multiplexing data transmission has been implemented to expand its communication capacity. The energy efficiency of the device is 23 fJ/bit, and the response time of the device is about 25 µs.

Demonstration of a 3-bit optical digital-to-analog converter based on silicon microring resonators.

We propose an N-bit optical digital-to-analog converter based on silicon microring resonators (MRRs), which can transform an N-bit electrical digital signal to an optical analog signal. A 3-bit optical digital-to-analog convertor is fabricated as proof of concept through a CMOS-compatible process on a silicon-on-insulator platform. The silicon MRRs are modulated through the electric-field-induced carrier injection in forward biased PN junctions embedded in the ring waveguides. The electro-optical 3-dB bandwidths of the silicon MRRs are approximately 800 MHz. The device works well at a speed of 500 MSample/s under driving voltage swings of 0.75 V.