Smart Utilization of Carbon Dots in Semiconductor Photocatalysis

Heterogeneous photocatalysis and its potential applications in water and wastewater treatment: a review

There has been a considerable amount of research in the development of sustainable water treatment techniques capable of improving the quality of water. Unavailability of drinkable water is a crucial issue especially in regions where conventional drinking water treatment systems fail to eradicate aquatic pathogens, toxic metal ions and industrial waste. The research and development in this area have given rise to a new class of processes called advanced oxidation processes, particularly in the form of heterogeneous photocatalysis, which converts photon energy into chemical energy. Advances in nanotechnology have improved the ability to develop and specifically tailor the properties of photocatalytic materials used in this area. This paper discusses many of those photocatalytic nanomaterials, both metal-based and metal-free, which have been studied for water and waste water purification and treatment in recent years. It also discusses the design and performance of the recently studied photocatalytic reactors, along with the recent advancements in the visible-light photocatalysis. Additionally, the effects of the fundamental parameters such as temperature, pH, catalyst-loading and reaction time have also been reviewed. Moreover, different techniques that can increase the photocatalytic efficiency as well as recyclability have been systematically presented, followed by a discussion on the photocatalytic treatment of actual wastewater samples and the future challenges associated with it.

Photoinduced in Situ Deposition of Uniform and Well-Dispersed PtO2 Nanoparticles on ZnO Nanorods for Efficient Catalytic Reduction of 4-Nitrophenol

Based on the photochemical property of semiconductors, a light irradiation-assisted strategy has been designed using one-dimensional ZnO nanorods as carriers to synthesize the rod-type PtO₂/ZnO catalyst with a well-defined structure. The high crystallinity and uniform crystal structure of the ZnO matrix conduct the in situ deposition of PtO₂ nanoparticles with 1.1-2.1 nm, which are evenly and densely anchored on the surface. Those small-sized and well-dispersed PtO₂ nanoparticles endow the PtO₂/ZnO catalyst a superior catalytic performance for the reduction of 4-nitrophenol to 4-aminophenol, which can convert all the substrates within 6.25 min. It is demonstrated that the catalytic activity of the PtO₂/ZnO catalyst is 2.3 times as high as that of the sample obtained by traditional wet-oxidation method under the same reaction conditions. Moreover, the light-irradiation time has been found to greatly affect the structure and activity of PtO₂/ZnO catalysts, and the product with 30 min exhibits the best catalytic performance in this work, as well as the good stability for ten runs. In terms of the photoexcited process of ZnO and reactive species-trapped experiments, the formation mechanism of PtO₂/ZnO catalysts has been explored in detail, which will probably stimulate the design and study of other metal-supported catalysts.

Role of elemental carbon in the photochemical aging of soot

Soot, which consists of organic carbon (OC) and elemental carbon (EC), is a significant component of the total aerosol mass in the atmosphere. Photochemical oxidation is an important aging pathway for soot. It is commonly believed that OC is photoactive but EC, albeit its strong light absorption, is photochemically inert. Here, by taking advantage of the different light absorption properties of OC and EC, we provide direct experimental evidence that EC also plays an important role in the photochemical aging of soot by initiating the oxidation of OC, even under red light irradiation. We show that nascent soot, in addition to undergoing photochemical oxidation under blue light with a wavelength of 440 nm, undergoes similar oxidation under red light irradiation of λ = 648 nm (L₆₄₈). However, separated OC (extracted from soot by n-hexane) and EC exhibit little reactivity under L₆₄₈ These observations indicate that EC plays a pivotal role in photoaging of soot by adsorbing light to initiate the oxidation of OC. Comparison of in situ IR spectra and photoelectrochemical behaviors suggests that EC-initiated photooxidation of OC proceeds through an electron transfer pathway, which is distinct from the photoaging induced by light absorption of OC. Since the absorption spectra of EC have a much larger overlap with the solar spectra than those of OC, our results provide insight into the chemical mechanism leading to rapid soot aging by organic species observed from atmospheric field measurements.

Tricolor White-Light-Emitting Carbon Dots with Multiple-Cores@Shell Structure for WLED Application

The past few years have witnessed the rapid development of carbon dots (CDs) due to their outstanding optical properties and a wide range of applications. However, the design and control of CDs with long-wavelength multicolor emission are still huge challenges to be addressed for their practical use in different fields. Here, novel nitrogen-doped multiple-core@shell-structured AC-CDs with tricolor emissions of red, green, and blue were constructed via one-pot hydrothermal method from 5-amino-1,10-phenanthroline and citric acid as reactants and the growth process of AC-CDs was monitored with the reaction time in the synthetic system. The origin of different fluorescence emissions was explored using the unique coordination ability of the surface groups of AC-CDs. An obvious concentration dependence of fluorescent properties was observed for the as-prepared AC-CDs, and a highly fluorescent quantum yield (QY) of 67% for red emission at 630 nm can be obtained by adjusting concentration of AC-CDs. The pure white-light emission (0.33, 0.33; Commission Internationale de l'Elcairage coordinate) was carried out from single carbon dot with QY of 29% through regulation of the excitation and concentration of multiple-core@shell-structured AC-CDs. In addition, because of their excellent photoluminescent properties, the white-emitting AC-CDs as emitting phosphor can be easily used in the fabrication of white-light-emitting diode with good anti-photobleaching and temperature stability.

Highly Efficient Carbon Dots with Reversibly Switchable Green-Red Emissions for Trichromatic White Light-Emitting Diodes

Carbon dots (CDs) have potentials to be utilized in optoelectronic devices, bioimaging, and photocatalysis. The majority of the current CDs with high quantum yield to date were limited in the blue light emission region. Herein, on the basis of surface electron-state engineering, we report a kind of CDs with reversible switching ability between green and red photoluminescence with a quantum yield (QY) of both up to 80%. Highly efficient green and red solid-state luminescence is realized by doping CDs into a highly transparent matrix of methyltriethoxysilane and 3-triethoxysilylpropylamine to form CDs/gel glasses composites with QYs of 80 and 78%. The CDs/gel glasses show better transmittance in visible light bands and excellent thermal stability. A blue-pumped CDs/gel glasses phosphor-based trichromatic white light-emitting diode (WLED) is realized, whose color rendering index is 92.9. The WLED gets the highest luminous efficiency of 71.75 lm W^-1 in CDs-based trichromatic WLEDs. This work opens a door for developing highly efficient green- and red-emissive switching CDs which were used as phosphors for WLEDs and have the tendency for applications in other fields, such as sensing, bioimaging, and photocatalysis.

Self-Assembled Supramolecular Hybrid of Carbon Nanodots and Polyoxometalates for Visible-Light-Driven Water Oxidation

Water splitting is considered the most attractive pursuit in the field of solar energy conversion. In this study, we report the synthesis and application of a supramolecular hybrid of carbon nanodot (CD) and cobalt polyoxometalate (Co-POM) to solar water oxidation. The self-assembly of the alginate-based CD and Co-POM led to the formation of a spherical hybrid of CD/Co-POM. Owing to the facile transfer of photogenerated holes from CD under visible light irradiation, the hybrid donor-acceptor type of CD/Co-POM enabled the rapid scavenging of holes and accumulation of a long-lived oxidation state of Co-POM for efficient solar water oxidation, outperforming conventional [Ru(bpy)₃]²⁺-based systems. We believe that this study offers new insights into the development of CD-based nanocomposites with various photocatalytic and optoelectronic applications.

Supramolecular Cross-Link-Regulated Emission and Related Applications in Polymer Carbon Dots

Involvement of clear photoluminescence (PL) mechanism in specific chemical structure is at the forefront of carbon dots (CDs). Supramolecular interaction exists in plenty of materials, offering an inherent way to administrate the optical and photophysical properties, especially in terms of newly developed polymer carbon dots (PCDs). However, supramolecular-interaction-derived PL regulation is always ignored in the shadow of many kinds of PL factors, and we still have a limited understanding on the distinct chemical structure and mechanism of supramolecular effect in PCDs. Herein, several distinct photoluminescent phenomena of PCDs under aqueous and solid state are reviewed in terms of supramolecular cross-linking, with highly emphasizing the importance of supramolecular cross-link-enhanced emission (SCEE) effects, and the regulated function of supramolecular interaction's intensity and types between PCDs for special PL behaviors of PCDs. In addition, we categorize the photoluminescent phenomena in PCDs into the following aspects: supramolecular cross-link-enhanced dilute-solution-state emission, concentration-controlled multicolor emission, supramolecular regulation for quenching-resistant solid-state fluorescence, as well as supramolecular cross-link-assisted room-temperature- phosphorescence (RTP) under solid states. Furthermore, the applications of PCDs in light-emitting diodes (LED), solar cells, and anticounterfeiting and data encryption, etc., are presented, based on the distinct supramolecular cross-link-regulated photoluminescent phenomena, especially the solid-state emission. Finally, a brief outlook is given, highlighting the currently existing problems and development direction of supramolecular cross-link-regulated emission in PCDs.

Polymer dots grafted TiO2 nanohybrids as high performance visible light photocatalysts

As a new member of carbon dots (CDs), Polymer dots (PDs) prepared by hydrothermal treatment of polymers, usually consist of the carbon core and the connected partially degraded polymer chains. This type of CDs might possess aqueous solubility, non-toxicity, excellent stability against photo-bleaching and high visible light activity. In this research, PDs were prepared by a moderate hydrothermal treatment of polyvinyl alcohol, and PDs grafted TiO₂ (PDs-TiO₂) nanohybrids with TiOC bonds were prepared by a facile in-situ hydrothermal treatment of PDs and Ti (SO₄)₂. Under visible light irradiation, the PDs-TiO₂ demonstrate excellent photocatalytic activity for methyl orange degradation, and the photocatalytic rate constant of PDs-TiO₂ is 3.6 and 9.5 times higher than that of pure TiO₂ and commercial P25, respectively. In addition, the PDs-TiO₂ exhibit good recycle stability under UV-Vis light irradiation. The interfacial TiOC bonds and the π-conjugated structures in PDs-TiO₂ can act as the pathways to quickly transfer the excited electrons between PDs and TiO₂, therefore contribute to the excellent photocatalytic activity.

Carbon dots as photosensitisers for solar-driven catalysis

Artificial photosynthesis is the mimicry of the natural process of solar energy conversion into chemical energy carriers. Photocatalytic systems that combine light-harvesting materials and catalysts in solution or suspension provide a promising route towards this goal. A key requirement for a sustainable solar fuel production system is a low-cost, stable and non-toxic light harvester. Photoluminescent carbon nanoparticles, carbon dots (CDs), are promising emerging light-harvesters for photocatalytic fuel production systems. CDs possess many desirable properties for this purpose, such as inexpensive, scalable synthetic routes, low-toxicity and tuneable surface chemistry. In this tutorial review, the integration of CDs in photocatalytic fuel generation systems with metallic, molecular and enzymatic catalysts is discussed. An overview of CD types, synthesis and properties is given along with a discussion of tuneable CD properties that can be optimised for applications in photocatalysis. Current understanding of the photophysical electron transfer processes present in CD photocatalytic systems is outlined and various avenues for their further development are highlighted.

A Magnetofluorescent Carbon Dot Assembly as an Acidic H2 O2 -Driven Oxygenerator to Regulate Tumor Hypoxia for Simultaneous Bimodal Imaging and Enhanced Photodynamic Therapy

Recent studies indicate that carbon dots (CDs) can efficiently generate singlet oxygen (¹ O₂ ) for photodynamic therapy (PDT) of cancer. However, the hypoxic tumor microenvironment and rapid consumption of oxygen in the PDT process will severely limit therapeutic effects of CDs due to the oxygen-dependent PDT. Thus, it is becoming particularly important to develop a novel CD as an in situ tumor oxygenerator for overcoming hypoxia and substantially enhancing the PDT efficacy. Herein, for the first time, magnetofluorescent Mn-CDs are successfully prepared using manganese(II) phthalocyanine as a precursor. After cooperative self-assembly with DSPE-PEG, the obtained Mn-CD assembly can be applied as a smart contrast agent for both near-infrared fluorescence (FL) (maximum peak at 745 nm) and T₁ -weighted magnetic resonance (MR) (relaxivity value of 6.97 mM^-1 s^-1 ) imaging. More interestingly, the Mn-CD assembly can not only effectively produce ¹ O₂ (quantum yield of 0.40) but also highly catalyze H₂ O₂ to generate oxygen. These collective properties of the Mn-CD assembly enable it to be utilized as an acidic H₂ O₂ -driven oxygenerator to increase the oxygen concentration in hypoxic solid tumors for simultaneous bimodal FL/MR imaging and enhanced PDT. This work explores a new biomedical use of CDs and provides a versatile carbon nanomaterial candidate for multifunctional nanotheranostic applications.

Induction of long-lived room temperature phosphorescence of carbon dots by water in hydrogen-bonded matrices

Phosphorescence shows great potential for application in bioimaging and ion detection because of its long-lived luminescence and high signal-to-noise ratio, but establishing phosphorescence emission in aqueous environments remains a challenge. Herein, we present a general design strategy that effectively promotes phosphorescence by utilising water molecules to construct hydrogen-bonded networks between carbon dots (CDs) and cyanuric acid (CA). Interestingly, water molecules not only cause no phosphorescence quenching but also greatly enhance the phosphorescence emission. This enhancement behaviour can be explained by the fact that the highly ordered bound water on the CA particle surface can construct robust bridge-like hydrogen-bonded networks between the CDs and CA, which not only effectively rigidifies the C=O bonds of the CDs but also greatly enhances the rigidity of the entire system. In addition, the CD-CA suspension exhibits a high phosphorescence lifetime (687 ms) and is successfully applied in ion detection based on its visible phosphorescence.

Carbon Dots: Bottom-Up Syntheses, Properties, and Light-Harvesting Applications

The development of cost-effective and environmentally friendly photocatalysts and photosensitizers has received tremendous attention because of their potential utilization in solar-light-harvesting applications. In this respect, carbon dots (CDs) prepared by bottom-up methods have been considered to be promising light-harvesting materials. Through their preparation from various molecular precursors and synthetic methods, CDs exhibit excellent optical and charge-transfer properties. Furthermore, their photophysical properties can be readily optimized and enhanced by means of doping, functionalization, and post-synthetic treatment. In this review, we summarize the recent progress in CDs synthesized using bottom-up approaches. These CDs exhibit strong light absorption and unique electron donor/acceptor capabilities for light-harvesting applications. We anticipate that this review will provide new insights into novel types of photosensitizers and photocatalysts for a wide range of applications.

Preparation of a BiVO4 nanoporous photoanode based on peroxovanadate reduction and conversion for efficient photoelectrochemical performance

A unique, controllable and facile method based on peroxovanadate reduction and conversion to prepare BiVO₄ nanoporous films is presented. In this method, a slow and controllable reduction of peroxovanadate with ethanol was used, which was the crucial step to ensure the uniform deposition of V₂O₅·xH₂O on an F-doped tin oxide substrate, and subsequently the annealed V₂O₅·xH₂O film was converted to a BiVO₄ film by a simple impregnation method with Bi³⁺ under the oriented effect of polyethylene glycol. The converted BiVO₄ film possessed a single monoclinic scheelite structure and exhibited an optimal water splitting photocurrent density of 1.10 mA cm^-2 at 1.23 V vs. RHE in 0.1 M KH₂PO₄ (pH 7) under AM 1.5G illumination with an incident photon-to-current conversion efficiency of ∼22.4% at 400 nm using an annealed V₂O₅·xH₂O film deposited for 3 hours. The BiVO₄ film also showed excellent water splitting performance and degradation efficiency in the PEC degradation of methylene blue and tetracycline hydrochloride with a rate constant of 0.63 h^-1 and 0.21 h^-1, respectively.

Cascaded photo-potential in a carbon dot-hematite system driving overall water splitting under visible light

Hematite is an earth-abundant and ubiquitous semiconductor with a suitable bandgap of 2.1 eV for solar water splitting. Unfortunately, it suffers from a low conduction band position compared to the H⁺/H₂ potential and typically an external bias has to be applied. Here, we demonstrate carbon dot-hematite (CD-Fe₂O₃) nanocomposites as photocatalysts for visible-light-driven overall water splitting without any external bias or scavenger. Notably, the CD-Fe₂O₃ nanocomposites (carbon dots, 5 wt%) show a hydrogen evolution rate of 0.390 μmol h^-1 and an oxygen evolution rate of 0.225 μmol h^-1 under visible light illumination. In our system, carbon dots have been well coupled with hematite and are detected to generate a photo-induced potential. This photo-potential can be combined with hematite to meet the requirement for overall water splitting. In addition, carbon dots can significantly improve the charge separation efficiency. Our finding may greatly enhance the practical application of hematite for solar water splitting.

Loading sulfur and nitrogen co-doped carbon dots onto g-C3N4 nanosheets for an efficient photocatalytic reduction of 4-nitrophenol

A favorable interface for hybrid photocatalysts makes an important contribution in enhancing photocatalytic reactions.

A simple, scalable approach for combining carbon dots with hexagonal nanoplates of nickel-based compounds for efficient photocatalytic reduction

The combination of carbon dots and hexagonal nanoplates of nickel-based compounds exhibits enhanced visible light absorption and excellent photocatalytic performance for the reduction of 4-nitrophenol to 4-aminophenol.

Synthesis and photocatalytic CO2 reduction performance of aminated coal-based carbon nanoparticles

To obtain high-efficiency, low-cost, environmentally friendly carbon-based photocatalytic material, we synthesized coal-based carbon dots with sp² carbon structure and multilayer graphene lattice structure by the hydrogen peroxide (H₂O₂) oxidation method to strip nano-scale crystalline carbon in the coal structure and link with oxygen-containing groups such as the hydroxyl group. N, S co-doped aminated coal-based carbon nanoparticles (NH₂-CNPs) were then obtained by thionyl chloride chlorination and ethylenediamine passivation. The physical properties and chemical structure of the synthesized NH₂-CNPs were studied and the photocatalytic CO₂ reduction performance was tested. The results show that NH₂-CNPs are vesicle-type spherical particles with particle size of 42.16 ± 7.5 nm and have a mesoporous structure that is capable of adsorbing CO₂. A defect structure was formed on the surface of the NH₂-CNPs due to the doping of N and S elements, thereby significantly improving the ability to photogenerate electrons under visible light along with the ability to efficiently separate the photo-generated carriers. The photocatalytic reduction products of CO₂ over NH₂-CNPs were CH₃OH, CO, C₂H₅OH, H₂ and CH₄. After 10 hours of reaction, the total amount of products was 807.56 μmol g⁻¹ cat, the amount of CH₃OH was 618.7 μmol g⁻¹ cat, and the calculated selectivity for conversion of CO₂ to CH₃OH was up to 76.6%.

Aminated coal-based carbon nanoparticles (NH₂-CNPs) was fabricated. The physical properties and chemical structure of the NH₂-CNPs was studied. Photocatalytic CO₂ reduction activity of NH₂-CNPs were measured and the reaction mechanism was discussed.

Carbon dots prepared in different solvents with controllable structures: optical properties, cellular imaging and photocatalysis

The preparation of carbon dots (CDs) featuring almost the same structures in different solvents is beneficial for their direct applications in the desired media without additional treatment and for resource conservation.

Foxtail millet-derived highly fluorescent multi-heteroatom doped carbon quantum dots towards fluorescent inks and smart nanosensors for selective ion detection

Foxtail millet-derived highly fluorescent nitrogen/sulfur/phosphrous (N/S/P) co-doped CQDs were efficiently fabricated via a green strategy, and were found to hold potential towards fluorescent inks and smart detection.

Facile generation of carbon quantum dots in MIL-53(Fe) particles as localized electron acceptors for enhancing their photocatalytic Cr(vi) reduction

Carbon quantum dots are generated in MIL-53(Fe) pores, serving as localized electron acceptors for enhancing their activity for Cr(vi) reduction.

Sulfur vacancy-rich CdS loaded on filter paper-derived 3D nitrogen-doped mesoporous carbon carrier for photocatalytic VOC removal

A new strategy is explored to fabricate a sulfur vacancy-rich CdS composite photocatalyst with a nitrogen-doped 3D porous carbon matrix for VOC removal.

Exploring the optimal ratio of d-glucose/l-aspartic acid for targeting carbon dots toward brain tumor cells

Targeting imaging to the desired site of action can increase the accuracy and effectiveness of diagnostic and treatment. In this work, a series of fluorescent carbon dots (CDs) were prepared by varying molar ratios of d-glucose (Glu) to l-aspartic acid (Asp). Their photophysical properties, morphologies and structures were investigated in detail. More important, the targeting ability was screened by confocal laser scanning microscopy and flow cytometry. The results indicate that CDs prepared from the optimal molar ratio of Glu/Asp (7:3) exhibit the highest targeting ability on C6 glioma cells. This work highlights the interplay of molecular design and corresponding functions, and open new possibility of developing state-of-art nanoparticles for biomedical applications.

Steering Photoelectrons Excited in Carbon Dots into Platinum Cluster Catalyst for Solar-Driven Hydrogen Production

In composite photosynthetic systems, one most primary promise is to pursue the effect coupling among light harvesting, charge transfer, and catalytic kinetics. Herein, this study designs the reduced carbon dots (r-CDs) as both photon harvesters and photoelectron donors in combination with the platinum (Pt) clusters and fabricated the function-integrated r-CD/Pt photocatalyst through a photochemical route to control the anchoring of Pt clusters on r-CDs' surface for solar-driven hydrogen (H2) generation. In the obtained r-CD/Pt composite, the r-CDs absorb solar photons and transform them into energetic electrons, which transfer to the Pt clusters with favorable charge separation for H2 evolution reaction (HER). As a result, the efficient coupling of respective natures from r-CDs in photon harvesting and Pt in proton reduction is achieved through well-steered photoelectron transfer in the r-CD/Pt system to cultivate a remarkable and stable photocatalytic H2 evolution activity with an average rate of 681 µmol g-1 h-1. This work integrates two functional components into an effective HER photocatalyst and gains deep insights into the regulation of the function coupling in composite photosynthetic systems.

Effect of Nitrogen Doping Level on the Performance of N-Doped Carbon Quantum Dot/TiO2 Composites for Photocatalytic Hydrogen Evolution

Carbon quantum dots (CQDs) have attracted widespread interest for photocatalytic applications, owing to their low cost and excellent electron donor/acceptor properties. However, their advancement as visible-light photosensitizers in CQDs/semiconductor nanocomposites is currently impaired by their poor quantum yields (QYs). Herein, we describe the successful fabrication of a series of nitrogen-doped CQDs (NCDs) with N/C atomic ratios ranging from 0.14-0.30. NCDs with the highest N-doping level afforded a remarkable external QY of 66.8 % at 360 nm, and outstanding electron transfer properties and photosensitization efficiencies when physically adsorbed on P25 TiO₂ . A NCDs/P25-TiO₂ hybrid demonstrated excellent performance for hydrogen evolution in aqueous methanol under both UV and visible-light illumination relative to pristine P25 TiO₂ . Controlled nitrogen doping of CQDs therefore represents a very effective strategy for optimizing the performance of CQDs/semiconductor hybrid photocatalysts.

Effect of nitrogen atom positioning on the trade-off between emissive and photocatalytic properties of carbon dots

Carbon dots (CDs) are a versatile nanomaterial with attractive photoluminescent and photocatalytic properties. Here we show that these two functionalities can be easily tuned through a simple synthetic means, using a microwave irradiation, with citric acid and varying concentrations of nitrogen-containing branched polyethyleneimine (BPEI) as precursors. The amount of BPEI determines the degree of nitrogen incorporation and the different inclusion modes within the CDs. At intermediate levels of BPEI, domains grow containing mainly graphitic nitrogen, producing a high photoluminescence yield. For very high (and very low) BPEI content, the nitrogen atoms are located primarily at the edge sites of the aromatic domains. Accordingly, they attract photogenerated electrons, enabling efficient charge separation and enhanced photocatalytic hydrogen generation from water. The ensuing ability to switch between emissive and photocatalytic behavior of CDs is expected to bring substantial improvements on their efficiency for on-demand light emission or energy conversion applications.

Sonocatalytic degradation of methylene blue by a novel graphene quantum dots anchored CdSe nanocatalyst

Cadmium selenide/graphene quantum dots (CdSe/GQDs) nanocatalyst with small band gap energy and a large specific surface area was produced via a facile three-step sonochemical-hydrothermal process. The features of the as-prepared CdSe, GQDs and CdSe/GQDs samples were characterized by photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR), diffuse-reflectance spectrophotometer (DRS), and Brunauer-Emmett-Teller (BET) analysis. The sonocatalytic activity of the synthesized CdSe/GQDs was effectively accelerated compared with that of pure CdSe nanoparticles in degradation of methylene blue (MB). The influence of the CdSe/GQDs dosage (0.25-1.25g/L), initial MB concentration (20-30mg/L), initial solution pH (3-12), and ultrasonic output power (200-600W/L) were examined on the sonocatalytic treatment of MB aqueous solutions. The degradation efficiency (DE%) of 99% attained at 1g/L of CdSe/GQDs, 20mg/L of MB, pH of 9, and an output power of 200W/L at 90min of ultrasonic irradiation. Furthermore, DE% increased with addition of K₂S₂O₈ and H₂O₂ as the enhancers via producing more free radicals. However, addition of sulfate, carbonate, and chloride as radical sweeper decreased DE%. Furthermore, well-reusability of the CdSe/GQDs sonocatalyst was demonstrated for 5 successive runs and some of the sonocatalytic generated intermediates were indicated by GC-MS analysis.

The Promoting Role of Different Carbon Allotropes Cocatalysts for Semiconductors in Photocatalytic Energy Generation and Pollutants Degradation

Semiconductor based photocatalytic process is of great potential for solving the fossil fuels depletion and environmental pollution. Loading cocatalysts for the modification of semiconductors could increase the separation efficiency of the photogenerated hole-electron pairs, enhance the light absorption ability of semiconductors, and thus obtain new composite photocatalysts with high activities. Kinds of carbon allotropes, such as activated carbon, carbon nanotubes, graphene, and carbon quantum dots have been used as effective cocatalysts to enhance the photocatalytic activities of semiconductors, making them widely used for photocatalytic energy generation, and pollutants degradation. This review focuses on the loading of different carbon allotropes as cocatalysts in photocatalysis, and summarizes the recent progress of carbon materials based photocatalysts, including their synthesis methods, the typical applications, and the activity enhancement mechanism. Moreover, the cocatalytic effect among these carbon cocatalysts is also compared for different applications. We believe that our work can provide enriched information to harvest the excellent special properties of carbon materials as a platform to develop more efficient photocatalysts for solar energy utilization.

Highly luminescent nitrogen-doped carbon dots for simultaneous determination of chlortetracycline and sulfasalazine

Here, we have presented a green and facile strategy to fabricate nitrogen-doped carbon dots (N-CDs) and their applications for determination of chlortetracycline (CTC) and sulfasalazine (SSZ). The fluorescent N-CDs, prepared by one-step hydrothermal reaction of citric acid and l-arginine, manifested numerous excellent features containing strong blue fluorescence, good water-solubility, narrow size distribution, and a high fluorescence quantum yield (QY) of 38.8%. Based on the fluorescence quenching effects, the as-synthesized N-CDs as a fluorescent nanosensor exhibited superior analytical performances for quantifying CTC and SSZ. The linear range for CTC was calculated to be from 0.85 to 20.38 μg ml^-1 with a low detection limit of 0.078 μg ml^-1 . Meanwhile, the linear range for SSZ was estimated to be from 0.34 to 6.76 μg ml^-1 with a low detection limit of 0.032 μg ml^-1 . Therefore, the N-CDs hold admirable application potential for constructing a fluorescent sensor for pharmaceutical analysis.

Conjugated Microporous Polymer Nanosheets for Overall Water Splitting Using Visible Light

Direct water splitting into H₂ and O₂ using photocatalysts by harnessing sunlight is very appealing to produce storable chemical fuels. Conjugated polymers, which have tunable molecular structures and optoelectronic properties, are promising alternatives to inorganic semiconductors for water splitting. Unfortunately, conjugated polymers that are able to efficiently split pure water under visible light (400 nm) via a four-electron pathway have not been previously reported. This study demonstrates that 1,3-diyne-linked conjugated microporous polymer nanosheets (CMPNs) prepared by oxidative coupling of terminal alkynes such as 1,3,5-tris-(4-ethynylphenyl)-benzene (TEPB) and 1,3,5-triethynylbenzene (TEB) can act as highly efficient photocatalysts for splitting pure water (pH ≈ 7) into stoichiometric amounts of H₂ and O₂ under visible light. The apparent quantum efficiencies at 420 nm are 10.3% and 7.6% for CMPNs synthesized from TEPB and TEB, respectively; the measured solar-to-hydrogen conversion efficiency using the full solar spectrum can reach 0.6%, surpassing photosynthetic plants in converting solar energy to biomass (globally average ≈0.10%). First-principles calculations reveal that photocatalytic H₂ and O₂ evolution reactions are energetically feasible for CMPNs under visible light irradiation. The findings suggest that organic polymers hold great potential for stable and scalable solar-fuel generation.

Carbon Nanodot-Sensitized Modulation of Alzheimer's β-Amyloid Self-Assembly, Disassembly, and Toxicity

The self-assembly of amyloidogenic peptides into β-sheet-rich aggregates is a general feature of many neurodegenerative diseases, including Alzheimer's disease, which signifies the need for the effective attenuation of amyloid aggregation toward alleviating amyloid-associated neurotoxicity. This study reports that photoluminescent carbon nanodots (CDs) can effectively suppress Alzheimer's β-amyloid (Aβ) self-assembly and function as a β-sheet breaker disintegrating preformed Aβ aggregates. This study synthesizes CDs using ammonium citrate through one-pot hydrothermal treatment and passivates their surface with branched polyethylenimine (bPEI). The bPEI-coated CDs (bPEI@CDs) exhibit hydrophilic and cationic surface characteristics, which interact with the negatively charged residues of Aβ peptides, suppressing the aggregation of Aβ peptides. Under light illumination, bPEI@CDs display a more pronounced effect on Aβ aggregation and on the dissociation of β-sheet-rich assemblies through the generation of reactive oxygen species from photoactivated bPEI@CDs. The light-triggered attenuation effect of Aβ aggregation using a series of experiments, including photochemical and microscopic analysis, is verified. Furthermore, the cell viability test confirms the ability of photoactivated bPEI@CDs for the suppression of Aβ-mediated cytotoxicity, indicating bPEI@CDs' potency as an effective anti-Aβ neurotoxin agent.

Efficient synthesis of highly fluorescent carbon dots by microreactor method and their application in Fe3+ ion detection

Rapidly obtaining strong photoluminescence (PL) of carbon dots with high stability is crucial in all practical applications of carbon dots, such as cell imaging and biological detection. In this study, we proposed a rapid, continuous carbon dots synthesis technique by using a microreactor method. By taking advantage of the microreactor, we were able to rapidly synthesized CDs at a large scale in less than 5min, and a high quantum yield of 60.1% was achieved. This method is faster and more efficient than most of the previously reported methods. To explore the relationship between the microreactor structure and CDs PL properties, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were carried out. The results show the surface functional groups and element contents influence the PL emission. Subsequent ion detection experiments indicated that CDs are very suitable for use as nanoprobes for Fe³⁺ ion detection, and the lowest detection limit for Fe³⁺ is 0.239μM, which is superior to many other research studies. This rapid and simple synthesis method will not only aid the development of the quantum dots industrialization but also provide a powerful and portable tool for the rapid and continuous online synthesis of quantum dots supporting their application in cell imaging and safety detection.

Surface engineering of graphitic carbon nitride polymers with cocatalysts for photocatalytic overall water splitting

Overall water splitting for the stoichiometric generation of H₂ and O₂ has been achieved by rational cocatalyst modification of g-C₃N₄ polymers to modulate the surface redox reaction kinetics.

Graphitic carbon nitride based polymers, being metal-free, accessible, environmentally benign and sustainable, have been widely investigated for artificial photosynthesis in recent years for the photocatalytic splitting of water to produce hydrogen fuel. However, the photocatalytic stoichiometric splitting of pure water into H₂ and O₂ with a molecular ratio of 2 : 1 is far from easy, and is usually hindered by the huge activation energy barrier and sluggish surface redox reaction kinetics. Herein, we provide a concise overview of cocatalyst modified graphitic carbon nitride based photocatalysts, with our main focus on the modulation of the water splitting redox reaction kinetics. We believe that a timely and concise review on this promising but challenging research topic will certainly be beneficial for general readers and researchers in order to better understand the property–activity relationship towards overall water splitting, which could also trigger the development of new organic architectures for photocatalytic overall water splitting through the rational control of surface chemistry.

Self-Assembled Carbon Dot Nanosphere: A Robust, Near-Infrared Light-Responsive, and Vein Injectable Photosensitizer

Self-assembly "activated" carbon dot photosensitizer: a robust, NIR-light responsive, and vein injectable carbon dot nanosphere (CDNS) photosensitizer with ¹ O₂ quantum yield of 0.45 under 671 nm laser irradiation has been developed through self-assembly using individual CD as building units. This study develops the biomedical applications of CD, highlights the self-assembly for designing well-defined CD-based photosensitizers, and promotes future explorations of this CDNS photosensitizer in nanomedical and clinical applications.

Lasing behavior of surface functionalized carbon quantum dot/RhB composites

Random lasers have been extensively and intensively investigated due to their fundamental importance and promising applications. Here, we explored the lasing behavior of carbon quantum dot (CQD)/Rhodamine B (RhB) composites. CQDs exhibited a broad emission spectrum which overlapped with the absorption spectrum of the RhB dye. We investigated an approach wherein the -OH, -NH₂ and -PO₄ group functionalized CQD/RhB composites showed lasing behavior. The optical pumping of functionalized CQD/RhB composites exhibited lasing emission which is dynamically tunable as a function of the surface properties of CQDs at the laser wavelength of 532 nm by varying the pump energy. The PO₄-CQD/RhB composites showed a typical lasing emission with a linewidth of 3.2 nm at 587 nm at 1.86 mJ pump energy. We also demonstrated that the pH value of CQD solution played a key role on the lasing behavior of CQD/composites.

Photocatalytic oxygen evolution from low-bandgap conjugated microporous polymer nanosheets: a combined first-principles calculation and experimental study

Nanostructured semiconducting polymers have emerged as a very promising class of metal-free photocatalytic materials for solar water splitting. However, they generally exhibit low efficiency and lack the ability to utilize long-wavelength photons in a photocatalytic oxygen evolution reaction (OER). Here, based on first-principles calculations, we reveal that the two-dimensional (2D) aza-fused conjugated microporous polymer (aza-CMP) with a honeycomb network is a semiconductor with novel layer-dependent electronic properties. The bandgap of the as-synthesized aza-CMP nanosheets is measured to be 1.22 eV, suggesting that they can effectively boost light absorption in the visible and near infrared (NIR) region. More importantly, aza-CMP also possesses a valence band margin suitable for a photocatalytic OER. Taking advantage of the 2D layered nanostructure, we further show that the exfoliated ultrathin aza-CMP nanosheets can exhibit a three-fold enhancement in the photocatalytic OER. After deposition of a Co(OH)₂ cocatalyst, the hybrid Co(OH)₂/aza-CMP photocatalyst exhibits a markedly improved performance for photocatalytic O₂ evolution. Furthermore, first-principles calculations reveal that the photocatalytic O₂ evolution reaction is energetically feasible for aza-CMP nanosheets under visible light irradiation. Our findings reveal that nanostructured polymers hold great potential for photocatalytic applications with efficient solar energy utilization.