An ordered and porous N-doped carbon dot-sensitized Bi2O3 inverse opal with enhanced photoelectrochemical performance and photocatalytic activity

Biomass Derived Biofluorescent Carbon Dots for Energy Applications: Current Progress and Prospects

Biomass resources are often disposed of inefficiently and it causes environmental degradation. These wastes can be turned into bio-products using effective conversion techniques. The synthesis of high-value bio-products from biomass adheres to the principles of a sustainable circular economy in a variety of industries, including agriculture. Recently, fluorescent carbon dots (C-dots) derived from biowastes have emerged as a breakthrough in the field, showcasing outstanding fluorescence properties and biocompatibility. The C-dots exhibit unique quantum confinement properties due to their small size, contributing to their exceptional fluorescence. The significance of their fluorescent properties lies in their versatile applications, particularly in bio-imaging and energy devices. Their rapid and straight-forward production using green/chemical precursors has further accelerated their adoption in diverse applications. The use of green precursors for C-dot not only addresses the biomass disposal issue through a scientific approach, but also establishes a path for a circular economy. This approach not only minimizes biowaste, which also harnesses the potential of fluorescent C-dots to contribute to sustainable practices in agriculture. This review explores recent developments and challenges in synthesizing high-quality C-dots from agro-residues, shedding light on their crucial role in advancing technologies for a cleaner and more sustainable future.

O2-Generating Fluorescent Carbon Dot-Decorated MnO2 Nanosheets for "Off/On" MR/Fluorescence Imaging and Enhanced Photodynamic Therapy

Imaging-guided photodynamic therapy (PDT) has emerged as a promising protocol for cancer theragnostic. However, facile preparation of such a theranostic system for simultaneously achieving tumor location, real-time monitoring, and high-performance reactive oxygen species generation is highly desirable but remains challenging. Herein, we developed a reasonable tumor-targeting strategy based on carbon dots (CDs)-decorated MnO2 nanosheets (HA-MnO2-CDs) with an active magnetic resonance (MR)/fluorescence imaging and enhanced PDT effect. Under light irradiation, the addition of HA-MnO2-CDs increased the production of 1O2 by 2.5 times compared with CDs, providing favorable conditions for the PDT treatment effect on breast cancer. Moreover, HA-MnO2-CDs exhibited excellent performance in producing O2 in the presence of endogenous H2O2, which alleviated hypoxia in tumors and improved the therapeutic effect of PDT. In the presence of glutathione (GSH), the degraded MnO2 nanosheets released CDs and Mn2+ from HA-MnO2-CDs, restoring their fluorescence imaging function and increasing T1 relaxivity (r1) by 23 times. In vivo fluorescence and MR imaging suggested the excellent tumor-targeting property of HA-MnO2-CDs. By combining the complementary properties of nanoprobes and tumor microenvironments, the in vivo PDT therapeutic effect was significantly improved under the action of HA-MnO2-CDs. Overall, our reasonably designed HA-MnO2-CDs may inspire the future development of the next generation of high-performance tumor-responsive diagnostic and therapeutic agents to further enhance the targeted therapy effect of tumors.

An Insight into Carbon Nanomaterial-Based Photocatalytic Water Splitting for Green Hydrogen Production

At present, the energy shortage and environmental pollution are the burning global issues. For centuries, fossil fuels have been used to meet worldwide energy demand. However, thousands of tons of greenhouse gases are released into the atmosphere when fossil fuels are burned, contributing to global warming. Therefore, green energy must replace fossil fuels, and hydrogen is a prime choice. Photocatalytic water splitting (PWS) under solar irradiation could address energy and environmental problems. In the past decade, solar photocatalysts have been used to manufacture sustainable fuels. Scientists are working to synthesize a reliable, affordable, and light-efficient photocatalyst. Developing efficient photocatalysts for water redox reactions in suspension is a key to solar energy conversion. Semiconductor nanoparticles can be used as photocatalysts to accelerate redox reactions to generate chemical fuel or electricity. Carbon materials are substantial photocatalysts for total WS under solar irradiation due to their high activity, high stability, low cost, easy production, and structural diversity. Carbon-based materials such as graphene, graphene oxide, graphitic carbon nitride, fullerenes, carbon nanotubes, and carbon quantum dots can be used as semiconductors, photosensitizers, cocatalysts, and support materials. This review comprehensively explains how carbon-based composite materials function as photocatalytic semiconductors for hydrogen production, the water-splitting mechanism, and the chemistry of redox reactions. Also, how heteroatom doping, defects and surface functionalities, etc., can influence the efficiency of carbon photocatalysts in H2 production. The challenges faced in the PWS process and future prospects are briefly discussed.

Engineered inverse opal structured semiconductors for solar light-driven environmental catalysis

Inverse opal (IO) macroporous semiconductor materials with unique physicochemical advantages have been widely used in solar-related environmental areas. In this minireview, we first summarize the synthetic methods of IO materials, emphasizing the two-step and three-step approaches, with the typical physicochemical properties being compared where applicable. We subsequently discuss the application of IO semiconductors (e.g., TiO₂, ZnO, g-C₃N₄) in various photo-related environmental techniques, including photo- and photoelectro-catalytic organic pollutant degradation in water, optical sensors for environmental monitoring, and water disinfection. The engineering strategies of these hierarchical structures for optimizing the activities for different catalytic reactions are discussed, ranging from heterojunction construction, cocatalyst loading, and heteroatom doping, to surface defect construction. Structure-activity relationships are established correspondingly. With a systematic understanding of the unique properties and catalytic activities, this review is expected to orient the design and structure optimization of IO semiconductor materials for photo-related performance improvement in various environmental techniques. Finally, the challenges of emerging IO structured semiconductors and future development directions are proposed.

Manganese phosphorous trifulfide nanosheets and nitrogen doped carbon dot composites with manganese vacancies for a greatly enhanced hydrogen evolution

As a novel chalcogenide photocatalyst, MnPS₃ suffered from limited visible light absorption, high photogenerated electron-hole recombination, and low hole oxidation capability due to its high valence band (VB) potential. In this work, the novel MnPS₃ nanosheets-Nitrogen-doped carbon dots (NCDs) composites were fabricated by immobilizing NCDs with terminal amine groups on Na⁺ intercalated MnPS₃ nanosheets for a greatly enhanced photocatalytic hydrogen production activity. MnPS₃ nanosheets of 400 nm with Mn²⁺ vacancies are produced in high yield by NaCl intercalation and subsequent exfoliation in N-methylpyrrolidone (NMP). NCDs with 5 nm are evenly loaded on the surface of MnPS₃ nanosheets of 400 nm via strong chemical interactions of ammonium sulfate salts formed at the interface. The MnPS₃-NCDs composites exhibit enhanced light absorption at 500-600 nm, reduced charge recombination and notably promoted photocatalytic activity in relative to neat MnPS₃ nanosheets. MnPS₃-NCDs composite with the NCDs content of 16.5% possessed the highest photocatalytic hydrogen evolution rate of 339.63 μmol·g^-1·h^-1 with good cycling stability, which is 9.17 times that of exfoliated MnPS₃ nanosheets. The type-II MnPS₃-NCDs heterojunction is conducive to the efficient interfacial carrier transport and the significantly improved photocatalytic hydrogen generation activity. Our work confirmed that the non-toxic MnPS₃ could possess photocatalytic performance comparable to CdS, which will be promising to become an attractive visible-light driven photocatalyst in environmental purification and energy applications.

Facile synthesis of g-C3N4/Ag2C2O4 heterojunction composite membrane with efficient visible light photocatalytic activity for water disinfection

Water pollution, deriving from the contamination of pathogenic bacteria, has posed a threat to human's survival and development. Photocatalytic disinfection is being widely studied in decentralized drink water safety, as traditional disinfection technologies are limited by harmful disinfection by-product and excessive energy consumption. Herein, a novel composite membrane (PN/Ag) with plasmonic heterojunction was synthesized for the efficient photocatalytic disinfection through the combination of polyacrylonitrile (PAN), N-doped carbon dots (NCDs)/g-C₃N₄ and Ag₂C₂O₄ by electrospinning technique and successive ionic layer adsorption and reaction (SILAR) process. The surface plasmon resonance (SPR) effect of Ag nanoparticles and Schottky barrier formation between metal and semiconductor contributed to the efficient separation of electron-hole pairs and the generation of reactive species, resulting in outstanding photocatalytic disinfection of PN/Ag composite membranes (7.48 and 7.70 log inactivation of E. coli and S. aureus respectively in 80 min) and good reusability under visible light illumination. Moreover, the potential Z-scheme photocatalytic mechanisms were proposed for PN/Ag system according to the band structure and reactive species analysis. The as-proposed PN/Ag composite membranes may shed light on the design and application of materials in water purification.

Carbon Dots: An Excellent Fluorescent Probe for Contaminant Sensing and Remediation

Pollution-induced degradation of the environment is a serious problem for both developing and developed countries. Existing remediation methods are restricted, necessitating the development of novel remediation technologies. Nanomaterials with unique characteristics have recently been developed for remediation. Quantum dots (QDs) are semiconductor nanoparticles (1-10 nm) with optical and electrical characteristics that differ from bigger particles owing to quantum mechanics, making them intriguing for sensing and remediation applications. Carbon dots (CDs) offer better characteristics than typical QDs, such as, CdSe QDs in terms of contaminant sensing and remediation. Non-toxicity, chemical inertness, photo-induced electron transfer, good biocompatibility, and adjustable photoluminescence behavior are all characteristics of CDs. CDs are frequently made from sustainable raw materials as they are cost-effective, environmentally compactable, and excellent in reducing waste generation. The goal of this review article is to briefly describe CDs fabrication methods, to deeply investigate the criteria and properties of CDs that make them suitable for sensing and remediation of contaminants, and also to highlight recent advances in their use in sensing and remediation of contaminants.

Carbon Dots: Synthesis, Properties and Applications

Carbon dots (CDs) are known as the rising star of carbon-based nanomaterials and, by virtue of their unique structure and fascinating properties, they have attracted considerable interest in different fields such as biological sensing, drug delivery, photodynamic therapy, photocatalysis, and solar cells in recent years. Particularly, the outstanding electronic and optical properties of the CDs have attracted increasing attention in biomedical and photocatalytic applications owing to their low toxicity, biocompatibility, excellent photostability, tunable fluorescence, outstanding efficient up-converted photoluminescence behavior, and photo-induced electron transfer ability. This article reviews recent progress on the synthesis routes and optical properties of CDs as well as biomedical and photocatalytic applications. Furthermore, we discuss an outlook on future and potential development of the CDs based biosensor, biological dye, biological vehicle, and photocatalysts in this booming research field.

A review on the preparation, microstructure, and photocatalytic performance of Bi2O3 in polymorphs

In recent years, the semiconductor bismuth oxide (Bi₂O₃) has attracted increasing attention as a potential visible-light-driven photocatalyst due to its simple composition, relatively narrow bandgap (2.2-2.8 eV), and high oxidation ability with deep valence band levels. Owing to the symmetry of its unit cell, Bi₂O₃ exists in more than one crystal form and exhibits phase-dependent photocatalytic properties. However, the phase-selective synthesis of Bi₂O₃ is a complex process, and its phase transformation usually occurs in a wide temperature range. Therefore, the development of Bi₂O₃ phases with a controllable microstructure and good photocatalytic properties is a great challenge. Hundreds of articles have been reported on the phase-selective synthesis and photocatalytic performance of Bi₂O₃. However, an interacting and critical review has rarely been reported, and thus it is essential to fill the gap in the literature. In this review, the phase-dependent photocatalytic performance of Bi₂O₃ is presented in detail. The phase-selective synthesis and temperature-dependent phase stability of highly active Bi₂O₃ are explored. The phase junction in Bi₂O₃ is reviewed, and the future perspective with an outlook on contemporary challenges is provided finally.

Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi2O3 semiconductor

The importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi2O3 has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process is hitherto missing. Herein, we show through a combination of theoretical and experimental studies that the perceived heterogeneous photocatalysis with Bi2O3 in the presence of alkyl bromides involves a homogeneous BinBrm species, which is the true photocatalyst operative in the reaction. Hence, Bi2O3 can be regarded as a precatalyst which is slowly converted in an active homogeneous photocatalyst. This work can also be of importance to mechanistic studies involving other semiconductor-based photocatalytic processes.

Green and controllable synthesis of one-dimensional Bi2O3/BiOI heterojunction for highly efficient visible-light-driven photocatalytic reduction of Cr(VI)

BiOI nanosheets have been successfully deposited on the porous Bi₂O₃ nanorobs via a one-pot precipitation method. The physicochemical features of the as-prepared materials were characterized in detail by a series of techniques, and the results revealed that BiOI nanosheets were evenly distributed on the porous Bi₂O₃ nanorobs. Because of higher photogenerated electron-hole pairs separation efficiency and the larger specific surface area compared to the pristine Bi₂O₃ and BiOI, the 50%Bi₂O₃/BiOI composite exhibited significantly enhanced photocatalytic activity for Cr(VI) reduction under visible light irradiation, and the reduction rate constant was 0.02002 min^-1, which was about 27.4 and 2.6 times higher than that of pure Bi₂O₃ (0.00073 min^-1) and BiOI (0.00769 min^-1), respectively. Moreover, the 50%Bi₂O₃/BiOI composite also possessed the excellent photochemical stability and recyclability, thereby facilitating its wastewater treatment application.

Boosted photocatalytic decomposition of nocuous organic gases over tricomposites of N-doped carbon quantum dots, ZnFe2O4, and BiOBr with different junctions

Herein, the effect of material structure on photocatalytic activity in the decomposition of nocuous organic gases (1,3,5-trimethylbenzene (TMB) and o-xylene (XYL)) was investigated by synthesizing tricomposite photocatalysts of N-doped carbon quantum dots, ZnFe₂O₄, and BiOBr (NCQDs/ZFO/BOB) with different junctions. The NCQDs/ZFO/BOB material (NCQDs/ZFO/BOB1) synthesized using a one-pot method revealed the highest photocatalytic efficiency. The NCQDs in NCQDs/ZFO/BOB1 exhibited photoluminescence property that expanded the photo-absorption nature and acted as a mediator to enhance the Z-scheme charge transfer between ZFO and BOB. The photocatalytic activity exhibited by NCQDs/ZFO/BOB1 was higher than that exhibited by the selected reference materials (CQDs/ZFO/BOB, NCQDs/BOB, ZFO/BOB, BOB, NCQDs/ZFO, and ZFO). Results showed that the decomposition efficiencies of TMB and XYL in the presence of NCQDs/ZFO/BOB1 under specified operational conditions were 94.5% and 72.5%, respectively. Moreover, the synthesized NCQDs/ZFO/BOB photocatalysts displayed excellent stability. Herein, the conversion ratios of TMB and XYL into CO₂ with NCQDs/ZFO/BOB1 and the intermediates formed during photocatalysis were assessed. Furthermore, a potential mechanism for the NCQDs/ZFO/BOB1-catalyzed organic gas decomposition was proposed. The hybridization access introduced herein thus provides a method for the intelligent synthesis of a new type of multicomponent nanocomposites for environmental remediation.

Photo-derived fixation of dinitrogen into ammonia at ambient condition with water on ruthenium/coal-based carbon nanosheets

Photocatalytic synthesis of ammonia is a kind of compelling and challenging nitrogen fixation method. In this paper, we extract the small-sized graphite-like carbon layer in the coal by organic solvent extraction method using HNO3 pretreated coal as a precursor. Then the coal-based carbon nanosheets (CNs) containing with Ca²⁺, Ti⁴⁺, Fe²⁺, Al³⁺, Si⁴⁺, C, N, O and other metal/non-metal ions was obtained under the assistance of the ultrasonication. The composite catalyst Ru/CNs was prepared by in situ loading the ruthenium (Ru) nanoparticles reduced from RuCl3·3H2O onto the as prepared CNs. The structure was characterized and the photocatalytic nitrogen fixation into ammonia performance under ambient temperature and atmospheric pressure was studied. The results show that the composite catalyst Ru/CNs with uniform dispersion of Ru nanoparticles on CNs has excellent photocatalytic nitrogen fixation activity, and the NH3 yield reaches 221.3 μmol/L after the reaction for 4 h. At the same time, the as prepared catalyst had quite good stability, and the NH3 yield remained substantially unchanged in 5 cycle experiments.

3D Brochosomes-Like TiO2 /WO3 /BiVO4 Arrays as Photoanode for Photoelectrochemical Hydrogen Production

An ideal photoelectrochemical (PEC) anode should process effective light absorption, charge transport, and separation efficiency. Here, a novel 3D brochosomes-like TiO₂ /WO₃ /BiVO₄ array as an efficient photoanode by combining a colloid polystyrene sphere template and electrochemical deposition routes for PEC hydrogen generation is reported. The as-fabricated 3D TiO₂ /WO₃ /BiVO₄ brochosomes photoanode yields excellent PEC performance with photocurrent densities of ≈3.13 and ≈4.27 mA cm^-2 with FeOOH/NiOOH catalyst, respectively, measured in 0.5 m Na₂ SO₄ solution with 0.1 m Na₂ SO₃ at 1.23 V versus reversible hydrogen electrode (RHE) under simulated AM1.5 light illumination, which is ≈6 times the reference sample of a planar WO₃ /BiVO₄ film electrode. The significantly improved performance could be benefited from the ordered hollow porous structure that provides enhanced light absorption and efficient charge transport as well as improved charge separation efficiency by WO₃ /BiVO₄ "host-guest" heterojunctions.

Bismuth Oxide Faceted Structures as a Photocatalyst Produced Using an Atmospheric Pressure Plasma Jet

The photocatalyst bismuth oxide, which is active under visual light, was deposited using an atmospheric pressure plasma jet (APPJ). Sixteen different samples were generated under different parameters of the APPJ to investigate their catalytic activity. The prepared samples were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), laser scanning microscopy (LSM), and UV–vis diffuse reflectance absorption spectroscopy. The measured data, such as average sample thickness, coverage ratio, phase fraction, chemical composition, band gap, and photocatalytic performance were used for comparing the samples. The XRD analysis showed that the deposition process produced a mixed phase of monocline Bi2O3 and tetragonal Bi2O2.33. Using the Rietveld refinement method, phase fractions could be determined and compared with the XPS data. The non-stoichiometric phases were influenced by the introduction of nitrogen to the surface as a result of the deposition process. The band gap calculated from the diffuse absorption spectroscopy shows that Bi2O2.33 with 2.78 eV had a higher band gap compared to the phases with a high proportion of Bi2O3 (2.64 eV). Furthermore, it was shown that the band gap was dependent on the thickness of the sample and oxygen vacancies or loss of oxygen in the surface. All coatings had degraded methyl orange (MO) under irradiation by xenon lamps.

Novel metal doped carbon quantum dots/CdS composites for efficient photocatalytic hydrogen evolution

Carbon quantum dots (CDs) are rising stars for photocatalytic applications due to their low toxicity and excellent electron transfer characteristics. Doping with heteroatoms is expected to adjust the band levels and electron transfer properties of CDs, and understanding the effect of doping on CDs can aid the rational preparation of highly efficient CD-based photocatalysts. Herein, we prepared a series of metal atom (Zn, Co, Bi, Cd, or Ti) doped CDs by pyrolysis and explored the photocatalytic application of these metal doped CDs for the first time. The metal doped CDs were combined with CdS nanowires as a co-catalyst for photocatalytic hydrogen production. The Bi, Cd and Ti doped CDs/CdS composites show much better hydrogen production performance than the undoped CDs/CdS composite. Among these composites, Bi-CDs/CdS presents the optimal interfacial charge separation and the best hydrogen production performance. The hydrogen evolution rate of Bi-CDs/CdS is 4.2 times and almost one time higher than that of pure CdS and undoped CDs/CdS, respectively. Bi doping can make the CDs metallic and promote the charge transfer of CDs. Such a great enhancement originates from the outstanding electron transfer properties of Bi-doped CDs, as well as the effective charge separation between Bi-doped CDs and CdS. Bi doping was demonstrated to be an effective strategy for optimizing the photocatalytic activity of CD based composites.

Amorphous carbon layer: An effective assistant for realizing near-infrared-activated photocatalysis

Carbon quantum dots (CQDs) were considered as desirable up-conversion luminescent materials. However, the reason leading to their up-conversion luminescence was not clear. In this paper, CQDs decorated ZnSn(OH)₆ was successfully synthesized by facile in situ hydrothermal method. Under NIR light irradiation, ciprofloxacin degradation efficiency of sample was 37.4%. Subsequently, reasons for the up-conversion effect of CQDs were investigated to some extent. An amorphous carbon layer around CQDs was observed in composite (ZnSn(OH)₆@CQDs@C) by HR-TEM and elemental mapping images. To study the effect of amorphous carbon layer on up-conversion performance, individual CQDs decorated ZnSn(OH)₆ (ZnSn(OH)₆@CQDs) was also fabricated by compositely coating. ZnSn(OH)₆@CQDs had no up-conversion luminescence under 980 nm laser light excitation and its photocatalytic activity was negligible, implying amorphous carbon layer played a crucial role for realizing of up-conversion luminescence. A comparison of the FTIR spectra of two composites, ZnSn(OH)₆@CQDs@C sample revealed greatly enhanced surface oxidation degree, polarity and hydrophilicity. Surface state of ZnSn(OH)₆@CQDs@C composite was controlled by adjusting hydrothermal time, and the results confirmed that up-conversion performance had a close relationship with surface states of samples. This work could provide a new insight into understanding the up-conversion effect of CQDs.

Multi-functional organosilane-polymerized carbon dot inverse opals

This paper demonstrates multi-functional optical properties of organosilane-polymerized carbon dot inverse opals, such as tricolor-fluorescence, fluorescence enhancement, multi-color micro-patterns for anti-fake applications and a thermally-induced blueshift of bandgaps. It is of significance for the design and fabrication of novel optical devices.

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.

Smart Utilization of Carbon Dots in Semiconductor Photocatalysis

Efficient capture of solar energy will be critical to meeting the energy needs of the future. Semiconductor photocatalysis is expected to make an important contribution in this regard, delivering both energy carriers (especially H₂ ) and valuable chemical feedstocks under direct sunlight. Over the past few years, carbon dots (CDs) have emerged as a promising new class of metal-free photocatalyst, displaying semiconductor-like photoelectric properties and showing excellent performance in a wide variety of photoelectrochemical and photocatalytic applications owing to their ease of synthesis, unique structure, adjustable composition, ease of surface functionalization, outstanding electron-transfer efficiency and tunable light-harvesting range (from deep UV to the near-infrared). Here, recent advances in the rational design of CDs-based photocatalysts are highlighted and their applications in photocatalytic environmental remediation, water splitting into hydrogen, CO₂ reduction, and organic synthesis are discussed.

New development in carbon quantum dots technical applications

As a newly emerged member in carbon nanomaterials family, carbon quantum dots (CQDs) attracted everincreasing attention owing to their ultracompact size, excellent photoluminescence, favorable biocompatibility, versatile surface and superior electron transfer ability. The past decade has witnessed continuous advancements in the production of CQDs with high photoluminescence quantum yields for various applications. Herein, we track the newest development of CQDs with advanced physicochemical properties and their applications in sensing, bioimaging, nanomedicine and catalysis, and propose the challenges and perspectives in this exciting and promising field.

Carbon quantum dots decorated Cu2S nanowire arrays for enhanced photoelectrochemical performance

The photoelectrochemical (PEC) performance of Cu2S nanowire arrays (NWAs) has been demonstrated to be greatly enhanced by dipping-assembly of carbon quantum dots (CQDs) on the surfaces of Cu2S NWAs. Experimental results show that the pristine Cu2S NWAs with higher aspect ratios exhibit better PEC performance due to the longer length scale for light absorption and the shorter length scale for minority carrier diffusion. Importantly, the CQDs decorated Cu2S NWAs exhibit remarkably enhanced photocurrent density, giving a photocurrent density of 1.05 mA cm(-2) at 0 V vs. NHE and an optimal photocathode efficiency of 0.148% under illumination of AM 1.5G (100 mW cm(-2)), which is 4 times higher than that of the pristine Cu2S NWAs. This can be attributed to the improved electron transfer and the energy-down-shift effect of CQDs. We believe that this inexpensive Cu2S/CQD photocathode with increased photocurrent density opens up new opportunities in PEC water splitting.