Heteroatom-Doped Carbon Dots (CDs) as a Class of Metal-Free Photocatalysts for PET-RAFT Polymerization under Visible Light and Sunlight

Review of carbon dot-hydrogel composite material as a future water-environmental regulator

As water pollution and scarcity pose severe threats to the sustainable progress of human society, it is important to develop a method or materials that can accurately and efficiently detect pollutants and purify aquatic environments or exploit marine resources. The compositing of photoluminescent and hydrophilic carbon dots (CDs) with hydrogels bearing three-dimensional networks to form CD-hydrogel composites to protect aquatic environments is a "win-win" strategy. Herein, the feasibility of the aforementioned method has been demonstrated. This paper reviews the recent progress of CD-hydrogel materials used in aquatic environments. First, the synthesis methods for these composites are discussed, and then, the composites are categorized according to different methods of combining the raw materials. Thereafter, the progress in research on CD-hydrogel materials in the field of water quality detection and purification is reviewed in terms of the application of the mechanisms. Finally, the current challenges and prospects of CD-hydrogel materials are described. These results are expected to provide insights into the development of CD-hydrogel composites for researchers in this field.

Antimony-Based Halide Perovskite Nanoparticles as Lead-Free Photocatalysts for Controlled Radical Polymerization

Metal halide perovskites have emerged as versatile photocatalysts to convert solar energy for chemical processes. Perovskite photocatalyzed polymerization draws special attention due to its straightforward synthesis process and the ability to create advanced perovskite-polymer nanocomposites. Herein, this work employs Cs3Sb2Br9 perovskite nanoparticles (NPs) as a lead-free photocatalyst for light-controlled atom transfer radical polymerization (ATRP). Cs3Sb2Br9 NPs exhibit high reduction potential and interact with electronegative bromide initiator with Lewis acid Sb sites, enabling efficient photoinduced reduction of initiators and controlled polymerization under blue light irradiation. Methacrylate monomers with various functional groups are successfully polymerized, and the resulting polymer showcased a dispersity (Đ) as small as 1.27. The living nature of polymerization is confirmed by high chain end fidelity and kinetic studies. Moreover, Cs3Sb2Br9 NPs serve as heterogeneous photocatalysts, demonstrating recyclability and reusability for up to four cycles. This work presents a promising approach to overcome the limitations of lead-based perovskites in photoinduced controlled radical polymerization, offering a sustainable and efficient alternative for the synthesis of well-defined polymeric materials.

Confinement of Sustainable Carbon Dots Results in Long Afterglow Emitters and Photocatalyst for Radical Photopolymerization

Sustainable carbon dots based on cellulose, particularly carboxymethyl cellulose carbon dots (CMCCDs), were confined in an inorganic network resulting in CMCCDs@SiO2. This resulted in a material exhibiting long afterglow covering a time frame of several seconds also under air. Temperature-dependent emission spectra gave information on thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) while photocurrent experiments provided a deeper understanding of charge availability in the dark period, and therefore, its availability on the photocatalyst surface. The photo-ATRP initiator, ethyl α-bromophenylacetate (EBPA), quenched the emission from the millisecond to the nanosecond time frame indicating participation of the triplet state in photoinduced electron transfer (PET). Both free radical and controlled radical polymerization based on photo-ATRP protocol worked successfully. Metal-free photo-ATRP resulted in chain extendable macroinitiators based on a reductive mechanism with either MMA or in combination with styrene. Addition of 9 ppm Cu2+ resulted in Mw/Mn of 1.4 while an increase to 72 ppm improved uniformity of the polymers; that is Mw/Mn=1.03. Complementary experiments with kerria laca carbon dots confined materials, namely KCDs@SiO2, provided similar results. Deposition of Cu2+ (9 ppm) on the photocatalyst surface explains better uniformity of the polymers formed in the ATRP protocol.

Phenanthroline Derived N-Doped Carbon Dots as Robust Metal-Free Photocatalysts for PET-RAFT Polymerization and Polymerization-Induced Self-Assembly

Metal-free organic photocatalysts for photo-mediated reversible deactivation radical polymerization (photo-RDRP) are witnessed to make increasing advancement in the precise synthesis of polymers. However, challenges still exist in the development of high-efficiency and environmentally sustainable carbon dots (CDs)-based organocatalysts. Herein, N-doped CDs derived from phenanthroline derivative (Aphen) are prepared as metal-free photocatalysts for photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The introduction of phenanthroline structure enhances the excited state lifetime of CDs and expands the conjugated length of their internal structure to enable the light-absorption to reach green light region, thereby enhancing photocatalytic activity. The as-designed CDs exhibit unprecedented photocatalytic capacity in photopolymerization even in large-volume reaction (100 mL) with high monomer conversion and narrow polymer dispersity (Mw/Mn < 1.20) under green light. The photocatalytic system is compatible with PET-RAFT polymerization of numerous monomers and the production of high molecular weight polyacrylate (Mn >250 000) with exquisite spatiotemporal control. Above results confirm the potential of CDs as photocatalyst, which has not been achieved with other CDs catalysts used in photo-RDRP. In addition, the construction of fluorescent polymer nanoparticles using CDs as both photocatalyst and phosphor through photoinitiated polymerization-induced self-assembly (Photo-PISA) technology is successfully demonstrated for the first time.

Nanosheet-Assembled Zirconium-Porphyrin Frameworks Enabling Surface-Confined, Initiator-Free Photosynthesis of Ultrahigh Molecular Weight Polymers

Metal-organic frameworks with well-organized low-dimensional architectures provide significant thermodynamic and/or kinetic benefits for diverse applications. We present here the controlled synthesis of a novel class of hierarchical zirconium-porphyrin frameworks (ZrPHPs) with nanosheet-assembled hexagonal prism morphology. The crystal growth behaviors and structural evolution of ZrPHPs in an additive-modulated solvothermal synthesis are examined, showing an "assembly-hydrolysis-reassembly" mechanism towards the formation of 2D nanosheets with ordered arrangement. Because of the highly-accessible active sites harvesting broadband photons, ZrPHPs serve as adaptable photocatalysts to regulate macromolecular synthesis under full-range visible light and natural sunlight. An initiator-free, oxygen-tolerant photopolymerization system is established, following a distinctive mechanism involving direct photo-induced electron transfer to dormant species and hole-mediated reversible deactivation. Specifically, ZrPHPs provide a surface-confined effect towards the propagating chains which inhibits their recombination termination, enabling the highly-efficient synthesis of ultrahigh molecular weight polymers (Mn >1,500,000) with relatively low dispersity (Đ≈1.5).

Near-Infrared Light and Acid/Base Dual-Regulated Polymerization Utilizing Imidazole-Anion-Fused Perylene Diimides as Photocatalysts

This work presents the first example of acid/base-responsive and near-infrared (NIR)-absorbing photocatalysts based on imidazole-anion-fused perylene diimide chromophores. The photocatalysts were in situ generated by deprotonation of imidazole-fused perylene diimide under an alkaline environment. NIR (λ = 730 nm, 128 mW/cm2) photoinduced atom transfer radical polymerization (ATRP) was implemented, exhibiting high efficiency and excellent livingness under ppm level of photocatalysts (15 ppm relative to monomer) and Cu(II) complex (10 ppm relative to monomer) concentrations. The method showed capabilities to polymerize behind opaque barriers (i.e., paper and pig skin) and under aerobic condition. Notably, this work demonstrated a dual temporal control of polymerization by adding weak base/acid and switching NIR light on/off. The polymerization can even be halted by bubbling CO2 and was then fully recovered by adding triethylamine. The NIR photoATRP of acrylamide monomers in aqueous solution was also performed, which can be regulated by the change of pH.

A Smartphone-Integrated Molecularly Imprinted Fluorescence Sensor for Visual Detection of Chlortetracycline Based on N,P-Codoped Carbon Dots Decorated Iron-Based Metal-Organic Frameworks

The residue of chlortetracycline is potentially hazardous to human health; it is meaningful to exploit a portable, rapid, sensitive, and selective method for detection of chlortetracycline (CTC). In this study, a novel fluorescence bionic sensing probe (NH2-MIL-53&N,P-CDs@MIP) was successfully prepared based on the nitrogen and phosphorus codoped carbon dots decorated iron-based metal-organic frameworks combining with molecular imprinted polymer for the detection of CTC. A fluorescence intensity-responsive "on-off" detection of CTC on account of the inner-filter effect (IFE) was achieved by NH2-MIL-53&N,P-CDs@MIP. Under the optimal conditions, the fluorescence quenching degree of NH2-MIL-53&N,P-CDs@MIP presented a good linear relationship with the CTC concentration in the range 0.06-30 μg mL-1 and the limit of detection (LOD) was 0.019 μg mL-1. The fluorescent probe was applied to detect CTC in milk samples, and experimental results showed a good recovery rate (88.73%-96.28%). Additionally, a smartphone-integrated fluorescence sensing device based on NH2-MIL-53&N,P-CDs@MIP was exploited to replace the expensive and bulky fluorescence spectrophotometer for quantitative determination of CTC with the LOD of 0.033 μg mL-1. The sensing system showed high selectivity, strong stability, high specificity, and portability, which provide a great strategy for the quantitative detection of antibiotic residue.

Emulsion-Directed Synthesis of Poly-Porphyrin Nanoparticles as Heterogeneous Photocatalysts for PET-RAFT Polymerization

Heterogeneous photocatalysts have attracted extensive attention in photo-induced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization due to their remarkable advantages such as easy preparation, tunable photoelectric properties, and recyclability. In this study, zinc (II) 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (ZnTAPP)-based poly-porphyrin nanoparticles (PTAPP-Zn) are constructed by an emulsion-directed approach. It is investigated as a heterogeneous photocatalyst for PET-RAFT polymerization of various methacrylate monomers under visible light exposure, and the reactions show refined polymerization control with high monomer conversions. Furthermore, it is demonstrated that the PTAPP-Zn nanoparticles with the larger pore size enhance photocatalytic activity in PET-RAFT polymerization. In addition, the capabilities of oxygen tolerance and temporal control are demonstrated and PTAPP-Zn particles can be easily recycled and reused without an obvious decrease in catalytic efficiency.

Conjugated cross-linked phosphine as broadband light or sunlight-driven photocatalyst for large-scale atom transfer radical polymerization

The use of light to regulate photocatalyzed reversible deactivation radical polymerization (RDRP) under mild conditions, especially driven by broadband light or sunlight directly, is highly desired. But the development of a suitable photocatalyzed polymerization system for large-scale production of polymers, especially block copolymers, has remained a big challenge. Herein, we report the development of a phosphine-based conjugated hypercrosslinked polymer (PPh₃-CHCP) photocatalyst for an efficient large-scale photoinduced copper-catalyzed atom transfer radical polymerization (Cu-ATRP). Monomers including acrylates and methyl acrylates can achieve near-quantitative conversions under a wide range (450-940 nm) of radiations or sunlight directly. The photocatalyst could be easily recycled and reused. The sunlight-driven Cu-ATRP allowed the synthesis of homopolymers at 200 mL from various monomers, and monomer conversions approached 99% in clouds intermittency with good control over polydispersity. In addition, block copolymers at 400 mL scale can also be obtained, which demonstrates its great potential for industrial applications.

Carbon Dots Based Photoinduced Reactions: Advances and Perspective

Seeking clean energy as an alternative to traditional fossil fuels is the inevitable choice to realize the sustainable development of the society. Photocatalytic technique is considered a promising energy conversion approach to store the abundant solar energy into other wieldy energy carriers like chemical energy. Carbon dots, as a class of fascinating carbon nanomaterials, have already become the hotspots in numerous photoelectric researching fields and particularly drawn keen interests as metal-free photocatalysts owing to strong UV-vis optical absorption, tunable energy-level configuration, superior charge transfer ability, excellent physicochemical stability, facile fabrication, low toxicity, and high solubility. In this review, the classification, microstructures, general synthetic methods, optical and photoelectrical properties of carbon dots are systematically summarized. In addition, recent advances of carbon dots based photoinduced reactions including photodegradation, photocatalytic hydrogen generation, CO₂ conversion, N₂ fixation, and photochemical synthesis are highlighted in detail, deep insights into the roles of carbon dots in various systems combining with the photocatalytic mechanisms are provided. Finally, several critical issues remaining in photocatalysis field are also proposed.

Uranium extraction from seawater: material design, emerging technologies and marine engineering

Uranium extraction from seawater (UES), a potential approach to securing the long-term uranium supply and sustainability of nuclear energy, has experienced significant progress in the past decade. Promising adsorbents with record-high capacities have been developed by diverse innovative synthetic strategies, and scale-up marine field tests have been put forward by several countries. However, significant challenges remain in terms of the adsorbents' properties in complex marine environments, deployment methods, and the economic viability of current UES systems. This review presents an up-to-date overview of the latest advancements in the UES field, highlighting new insights into the mechanistic basis of UES and the methodologies towards the function-oriented development of uranium adsorbents with high adsorption capacity, selectivity, biofouling resistance, and durability. A distinctive emphasis is placed on emerging electrochemical and photochemical strategies that have been employed to develop efficient UES systems. The most recent achievements in marine tests by the major countries are summarized. Challenges and perspectives related to the fundamental, technical, and engineering aspects of UES are discussed. This review is envisaged to inspire innovative ideas and bring technical solutions towards the development of technically and economically viable UES systems.

Covalent Organic Frameworks as Efficient Photoinitiators and Cross-Linkers To Fabricate Highly Stretchable Hydrogels

In this work, two kinds of imine-type covalent organic framework (COF) nanoparticles are demonstrated as efficient photocatalytic initiators to trigger the free-radical polymerization of acrylamide (AM) to prepare polyacrylamide (PAM) hydrogels under visible light irradiation, without any assistance from the co-initiator. Simultaneously, the COF nanoparticles bearing vinyl side groups (COF-V) promote covalent cross-linking of the polymer chains, which significantly reinforces the mechanical properties of the nanocomposite hydrogel. The obtained PAM/COF-V hydrogel is highly stretchable with an extraordinary elongation up to 3300% strain. On the other hand, the COF nanoparticles modified with methoxy moieties (COF-OMe) endow the resulting PAM/COF-OMe hydrogel with a promising fluorescence feature. In addition, this strategy provides a visible-light-regulated photocatalytic polymerization approach with a simplified recipe to fabricate COF-based nanocomposite hydrogels or resins with diverse functions.

Visible light-controlled living cationic polymerization of methoxystyrene

Photo-controlled living polymerization has received great attention in recent years. However, despite the great success therein, the report on photo-controlled living cationic polymerization has been greatly limited. We demonstrate here a novel decolorable, metal-free and visible light-controlled living cationic polymerization system by using tris(2,4-dimethoxyphenyl)methylium tetrafluoroborate as the photocatalyst and phosphate as the chain transfer agent (CTA) for polymerization of 4-methoxystyrene. This polymerization reaction under green LED light irradiation shows clear living characteristics including predictable molar mass, low molar-mass dispersity (Đ = 1.25), and sequential polymerization capability. In addition, the photocatalytic system exits excellent "on-off" photo switchability and shows the longest "off period" of 36 h up to now for photo-controlled cationic polymerization. Furthermore, the residual photo-catalyst is easily deactivated and decolored with addition of a base after the polymerization. The present study has extended the photo-controlled living cationic polymerization systems with new organic photocatalysts, phosphate CTA and polymerizable monomer as well as the new properties of excellent photostability and in-situ decolored capacity.

Ultrafast Visible-Light-Induced ATRP in Aqueous Media with Carbon Quantum Dots as the Catalyst and Its Application for 3D Printing

Photoinduced atom transfer radical polymerization (ATRP) has been proved to be a versatile technique for polymer network formation. However, the slow polymerization rates of typical ATRP limited its application in the field of additive manufacturing (3D printing). In this work, we introduced carbon quantum dots (CQDs) for the first time to the ATRP in aqueous media and developed an ultrafast visible-light-induced polymerization system. After optimization, the polymerization could achieve a high monomer conversion (>90%) within 1 min, and the polydispersity index (PDI) of the polymer was lower than 1.25. This system was then applied as the first example of ATRP for the 3D printing of hydrogel through digital light processing (DLP), and the printed object exhibited good dimensional accuracy. Additionally, the excellent and stable optical properties of CQDs also provided interesting photoluminescence capabilities to the printed objects. We deduce this ATRP mediated 3D printing process would provide a new platform for the preparation of functional and stimuli-responsive hydrogel materials.

A novel fluorescence ratio probe based on dual-emission carbon dots for highly selective and sensitive detection of chlortetracycline and cell imaging

The novel dual-emission carbon dots (DECDs) for highly selective and sensitive recognition of chlortetracycline (CTC) and cell imaging were synthesized successfully by one-step synthesis. The obtained DECDs possessed two fluorescence peaks (345 nm and 450 nm) and showed specific response to CTC, resulting in a decrease in fluorescence intensity at 345 nm, a blue shift, and an increase in fluorescence intensity at 450 nm. The obtained DECDs exhibited highly selective response to CTC and not to its analogues, such as tetracycline, doxycycline, and oxytetracycline. Thus, an excellent ratiometric probe for the detection of CTC was fabricated successfully and used for the detection of CTC in real samples with the detection limit (LOD) of 16.45 nM. More importantly, the DECDs were used for quantitative detection of CTC in living cells, which demonstrated excellent biocompatibility and broad prospects in biomedicine application. Finally, the excellent selectivity of DECDs toward CTC was attributed to the FRET mechanism and the formation of complexes.

Photopatterning of Carbon Dots in Poly(vinyl alcohol) with Photoacid Generators

Carbon dots (CDs) have drawn considerable attention owing to their attractive photoluminescence, advantageous chemical tolerance, good biocompatibility, and so on. However, it remains challenging to tune their photoluminescence spatially and temporally due to their high photostability. Herein, a viable approach to in-situ dialing the photoluminescence of CDs by using light in the presence of a photoacid generator (PAG, e.g., diphenyliodonium hexafluorophosphate) is demonstrated. Fluorescence quenching occurs upon light irradiation due to the protonation of pyridine and amino nitrogen atoms of CDs according to X-ray photoelectron spectroscopy and cyclic voltammetry. As such, blue, green, and red color fluorescent patterns of CDs are ready to form in poly(vinyl alcohol) by light irradiation under photomask. These patterns not only show a controlled preservation time under room light, but also can be erased on demand by flood UV irradiation, which are promising for advanced anti-counterfeiting such as shelf-life based security and erasable encryption.

Dual Enhancement of Carrier Generation and Migration on Au/g-C3N4 photocatalysts for High-Efficient Broadband PET-RAFT Polymerization

Photo-induced electron/energy transfer RAFT (PET-RAFT) polymerization can produce well-defined polymers with spatio-temporal control. Semiconductor graphitic carbon nitride (g-C3N4) as thermally and chemically stable photocatalyst, has achieved PET-RAFT method under UV-irradiation...

Organocatalytic PET-RAFT polymerization with a low ppm of organic photocatalyst under visible light

The development of light-mediated controlled radical polymerization has benefited from the discovery of novel photocatalysts, which could allow precise light control over the polymerization process and the production of well-defined polymers.

Visible Light-Regulated Heterogeneous Catalytic PET-RAFT by High Crystallinity Covalent Organic Framework

Covalent organic frameworks (COFs) are a class of promising photocatalysts for conversing light energy into chemical energy. Based on the tunable building blocks, COFs can be well-designed as photocatalyst for mediating reversible addition-fragmentation chain-transfer (RAFT) polymerization. Herein, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2″-bipyridine-5,5″-diamine (Bpy) are chosen to construct imine-based TFPPy-Bpy-COFs for catalyzing RAFT polymerization of methacrylates under white light irradiation. The well-defined polymers with precise molecular weight and narrow molecular weight distribution are obtained. The switch on/off light experiments suggest excellent temporal control toward RAFT polymerization system and the chain-extension reaction indicates high chain-end fidelity of macro-initiators. Mechanism study clarifies that the electron transfer between excited state of TFPPy-Bpy-COFs and RAFT agent can form living radicals to mediate polymerization. This methodology provides a novel platform for reversible-deactivation radical polymerization using COFs as heterogeneous catalysts.

Photocontrolled RAFT Polymerization Catalyzed by Conjugated Polymers under Aerobic Aqueous Conditions

Photocontrolled polymerization offers a convenient way to direct the reaction progress and tailor the polymer structures. Nevertheless, conjugated polymers are yet to be utilized as the photocatalyst in associated reactions. Herein, we employed poly(boron dipyrromethene-alt-fluorene) (PBF), a conjugated polymer with better photostability than eosin Y, as the photocatalyst for photo-RAFT polymerizations of acrylic monomers, and the polymers were obtained with moderately narrow molecular weight distributions. The reaction progress was effectively controlled by switching irradiation conditions, and the block copolymers were prepared from chain extension of a macroinitiator. As electron spin resonance (ESR) and optical spectra results suggested, the reductive quenching of PBF* by ascorbate was the key step leading to the reduction of a chain transfer agent (CTA), whereas the hydroxyl radical derived from superoxide was considered as a byproduct of deoxygenation.

Assemblies of Polyacrylonitrile-Derived Photoactive Polymers as Blue and Green Light Photo-Cocatalysts for Cu-Catalyzed ATRP in Water and Organic Solvents

Photoluminescent nanosized quasi-spherical polymeric assemblies prepared by the hydrothermal reaction of polyacrylonitrile (PAN), ht-PLPPAN, were demonstrated to have the ability to photo-induce atom transfer radical polymerization (ATRP) catalyzed by low, parts per million concentrations of CuII complex with tris(2-pyridylmethyl)amine (TPMA). Such photo induced ATRP reactions of acrylate and methacrylate monomers were performed in water or organic solvents, using ht-PLPPAN as the photo-cocatalyst under blue or green light irradiation. Mechanistic studies indicate that ht-PLPPAN helps to sustain the polymerization by facilitating the activation of alkyl bromide species by two modes: 1) green or blue light-driven photoreduction of the CuII catalyst to the activating CuI form, and 2) direct activation of dormant alkyl bromide species which occurs only under blue light. The photoreduction of the CuII complex by ht-PLPPAN was confirmed by linear sweep voltammetry performed under illumination. Analysis of the polymerization kinetics in aqueous media indicated even though CuI complexes comprised only 1-1.4% of all Cu species at equilibrium, they exhibited high activation rate constant and activated the alkyl bromide initiators five to six orders of magnitude faster than ht-PLPPAN.

Tunable Quantum Photoinitiators for Radical Photopolymerization

This review describes the use of nanocrystal-based photocatalysts as quantum photoinitiators, including semiconductor nanocrystals (e.g., metal oxides, metal sulfides, quantum dots), carbon dots, graphene-based nanohybrids, plasmonic nanocomposites with organic photoinitiators, and tunable upconverting nanocomposites. The optoelectronic properties, cross-linking behavior, and mechanism of action of quantum photoinitiators are considered. The challenges and prospects associated with the use of quantum photoinitiators for processes such as radical polymerization, reversible deactivation radical polymerization, and photoinduced atom transfer radical polymerization are reviewed. Due to their unique capabilities, we forsee a growing role for quantum photoinitiators over the coming years.

Light-Mediated Polymerization Induced by Semiconducting Nanomaterials: State-of-the-Art and Future Perspectives

Direct capture of solar energy for chemical transformation via photocatalysis proves to be a cost-effective and energy-saving approach to construct organic compounds. With the recent growth in photosynthesis, photopolymerization has been established as a robust strategy for the production of specialty polymers with complex structures, precise molecular weight, and narrow dispersity. A key challenge in photopolymerization is the scarcity of effective photomediators (photoinitiators, photocatalysts, etc.) that can provide polymerization with high yield and well-defined polymer products. Current efforts on developing photomediators have mainly focused on organic dyes and metal complexes. On the other hand, nanomaterials (NMs), particularly semiconducting nanomaterials (SNMs), are suitable candidates for photochemical reactions due to their unique optical and electrical properties, such as high absorption coefficients, large charge diffusion lengths, and broad absorption spectra. This review provides a comprehensive insight into SNMs' photomediated polymerizations and highlights the roles SNMs play in photopolymerizations, types of polymerizations, applications in producing advanced materials, and the future directions.

2D Porphyrinic Metal-Organic Framework Nanosheets as Multidimensional Photocatalysts for Functional Materials

Ultrathin porphyrinic 2D MOFs, ZnTCPP nanosheets (TCPP: 5,10,15,20-(tetra-4-carboxyphenyl) porphyrin) were employed as heterogeneous photocatalysts to activate PET-RAFT polymerization under various wavelengths ranging from violet to orange light. High polymerization rates, oxygen tolerance, and precise temporal control were achieved. The polymers showed narrow molecular weight distributions and good chain-end fidelity. The 2D ZnTCPP nanosheets were applied as photocatalysts in stereolithographic 3D printing in an open-air environment under blue light to yield well-defined 3D printed objects. Apart from providing an efficient catalytic system, 2D ZnTCPP nanosheets reinforced the mechanical properties of the 3D printed materials. The presence of ZnTCPP embedded in the materials conferred effective antimicrobial activity under visible light by production of singlet oxygen, affording 98 % and 93 % anti-bacterial efficiency against Gram-positive and Gram-negative bacteria, respectively.

Synthesis of carbon dots with high photocatalytic reactivity by tailoring heteroatom doping

The photocatalytic degradation of organic pollutant by carbon-based materials is still a challenge. Herein, xylose-derived carbon dots (X-CDs) and chitosan-derived CDs (C-CDs) were synthesized by heteroatoms-doping strategy. Although there is almost no difference in fluorescence emission behaviors, the two types of CDs demonstrated different advantages in photocatalysis and peroxymonosulfate (PMS) activation. Comparative research revealed that the X-CDs with doping of heteroatom S was superior in the separation of electron-hole pairs, resulting in a higher catalytic performance, while the S, N co-doped C-CDs can only exhibit high photocatalytic reactivity when they were coupled with PMS. The underlying reason is that the N-related functional groups with strong electron-donating property weakened the electron-trapping capacity of S-related energy level, but surface state resulting from this doping structures were conducive to promoting photo-generated electron transfer from C-CDs to PMS and played the primary role in organic oxidation. Thanks to the doping effect, both the X-CDs and C-CDs/PMS system displayed high photocatalytic performance for methylene blue removal under sunlight irradiation, showing almost 100% degradation efficiency in a 30 min period. The present study provides a valuable insight for the synthesis of CDs-based catalysts but also establishes a very promising catalytic oxidation system.

Enhancing the efficiency of semiconducting quantum dot photocatalyzed atom transfer radical polymerization by ligand shell engineering

Manipulating the ligand shell of semiconducting quantum dots (QDs) has proven to be a promising strategy to enhance their photocatalytic performance for small molecule transformations, such as H₂ evolution and CO₂ reduction. However, ligand-controlled catalysis for macromolecules, which differ from small molecules in penetrability and charge transfer behavior due to their bulky sizes, still remains undiscovered. Here, we systematically investigate the role of surface ligands in the photocatalytic performance of cadmium selenide (CdSe) QDs in light-induced atom transfer radical polymerization (ATRP) by using thiol-based ligands with various polarities and chain lengths. A highly enhanced polymerization efficiency was observed when 3-mercapto propionic acid (MPA), a short-chain and polar ligand, was used to modify the CdSe QDs' surface, achieving high chain-end fidelity, good temporal control, and a dispersity of 1.18, while also tolerating a wide-range of functional monomers ranging from acrylates to methacrylates and fluorinated monomers. Transient absorption spectroscopy and time-resolved photoluminescence studies reveal interesting mechanistic details of electron and hole transfers from the excited QDs to the initiators and 3-MPA capping ligands, respectively, providing key mechanistic insight of these ligand controlled and QD photocatalyzed ATRP processes. The thiolate ligands were found to serve as an efficient hole acceptor for QDs, which facilitates the formation of a charge-separated state, followed by electron transfer from the conduction band edge to initiators and ultimately suppressing charge recombination within the QD.

Distinct Sustainable Carbon Nanodots Enable Free Radical Photopolymerization, Photo-ATRP and Photo-CuAAC Chemistry

Carbon nanodots (CDs) originating from different biomass result in different activities to sensitize photo-ATRP and photo-CuAAC reaction protocols with visible light. Free radical polymerization of tri(propylene glycol)diacrylate also exhibited a good efficiency using CDs in combination with an iodonium salt employing LEDs emitting either at 405 nm, 525 nm or 660 nm. Photo-ATRP experiments confirmed controlled polymerization conditions using CuII at the ppm scale resulting in dispersities between 1.06 to 1.10. Chain end fidelity was successfully provided by chain extension and block copolymerization additionally approving the living feature of polymerization using a CD synthesized from lac dye comprising olefinic moieties in the originating biomass. By global analysis, time resolved fluorescence measurements indicated the appearance of several emitting species contributing to the reactivity of the excited states. Different cytotoxic response appeared following the answer of MCF-10A cells in a flow cytometry assay; that is 400 μg mL-1 . Thus, cell viability was greater 80 % in the case of CD-2-CD-5 while that of CD-1 was close to 70 %.

Quantum Photoinitiators: Toward Emerging Photocuring Applications

Semiconductor nanocrystals are promising photocatalysts for a wide range of applications, ranging from alternative fuel generation to biomedical and environmental applications. This stems from their diverse properties, including flexible spectral tunability, stability, and photocatalytic efficiencies. Their functionality depends on the complex influence of multiple parameters, including their composition, dimensions, architecture, surface coating, and environmental conditions. A particularly promising direction for rapid adoption of these nanoparticles as photocatalysts is their ability to act as photoinitiators (PIs) for radical polymerization. Previous studies served to demonstrate the proof of concept for the use of quantum confined semiconductor nanocrystals as photoinitiators, coining the term Quantum PIs, and provided insights for their photocatalytic mechanism of action. However, these early reports suffered from low efficiencies while requiring purging with inert gases, use of additives, and irradiation by high light intensities with very long excitation durations, which limited their potential for real-life applications. The progress in nanocrystal syntheses and surface engineering has opened the way to the introduction of the next generation of Quantum PIs. Herein, we introduce the research area of nanocrystal photocatalysts, review their studies as Quantum PIs for radical polymerization, from suspension polymerization to novel printing, as well as in a new family of polymerization techniques, of reversible deactivation radical polymerization, and provide a forward-looking view for the challenges and prospects of this field.

The in situ “grafting from” approach for the synthesis of polymer brushes on upconversion nanoparticles via NIR-mediated RAFT polymerization

Through NIR-mediated RAFT polymerization, surface growth of polymer brushes on UCNPs was realized based on an efficient in situ ligand exchange.

Visible light-regulated organocatalytic ring-opening polymerization of lactones by harnessing excited state acidity

A metal-free ring-opening polymerization of lactones has been developed using PyOH as a photocatalyst under visible light mediation.

Ultrafast, green and recyclable photoRDRP in an ionic liquid towards multi-stimuli responsive amphiphilic copolymers

A simple and inexpensive method for ultrafast and recyclable photoRDRP in an ionic liquid is developed, yielding low dispersity poly(glycidyl methacrylate) and well-defined amphiphilic multi-stimuli responsive diblock copolymers thereof.

New horizons for carbon dots: quantum nano-photoinitiating catalysts for cationic photopolymerization and three-dimensional (3D) printing under visible light

Citric acid-based carbon dots (CDs) as nano-photoinitiating catalysts for 3D printing.

Thiol ligand capped quantum dot as an efficient and oxygen tolerance photoinitiator for aqueous phase radical polymerization and 3D printing under visible light

We report here a rapid visible-light-induced radical polymerization in aqueous media photoinitiated by only ppm level thiol ligand capped cadmium selenide quantum dots. The photoinitiation system could be readily employed for photo 3D printing.

A covalent organic framework as a photocatalyst for atom transfer radical polymerization under white light irradiation

TFPPy-Td-COFs have been synthesized to serve as heterogeneous photocatalysts for mediating photo-induced ATRP with copper as a co-catalyst under white light irradiation.

Heterogeneous photocatalytic reversible deactivation radical polymerization

Photocatalytic reversible deactivation radical polymerization (RDRP) permits the use of sustainable solar light for spatiotemporal regulation of radical polymerization under mild conditions.