Oxygen evolution reaction (OER) plays a crucial role in developing energy conversion and adjusting electronic structure of the electrocatalysts can effectively improve the catalytic activity and stability. However, it is a challenge to adjust the electronic structure on two-dimensional iridium dioxide nanosheets (IrO₂ NS), which have the advantages of high atom utilization. Here, we regulate the surface properties of IrO₂ NS through sulfonated carbon dots (SCDs) to promote the OER catalytic process. The catalyst IrO₂ NS/SCDs-2 exhibited excellent catalytic activity with a lower overpotential of 180 mV than IrO₂ NS (230 mV) at the current density of 10 mA·cm⁻² in a 0.5 M H₂SO₄ solution. And after 160 h of stability testing, the overpotential of IrO₂ NS/SCDs-2 only decreased by 4 mV. Moreover, transient potential scanning test can visually demonstrate that the addition of SCDs improves the conductivity of the catalyst and increases the electron transfer rate.

Hydrogen peroxide (H₂O₂) photoproduction in seawater with metal-free photocatalysts derived from biomass materials is a green, sustainable, and ultra environmentally friendly way. However, most photocatalysts are always corroded or poisoned in seawater, resulting in a significantly reduced catalytic performance. Here, we report the metal-free photocatalysts (RUT-1 to RUT-5) with in-situ generated carbon dots (CDs) from biomass materials (Rutin) by a simple microwave-assisted pyrolysis method. Under visible light (λ ≥ 420 nm, 81.6 mW/cm²), the optimized catalyst of RUT-4 is stable and can achieve a high H₂O₂ yield of 330.36 μmol/L in seawater, 1.78 times higher than that in normal water. New transient potential scanning (TPS) tests are developed and operated to in-situ study the H₂O₂ photoproduction of RUT-4 under operation condition. RUT-4 has strong oxygen (O₂) absorption capacity, and the O₂ reduction rate in seawater is higher than that in water. Metal cations in seawater further promote the photo-charge separation and facilitate the photo-reduction reaction. For RUT-4, the conduction band level under operating conditions only satisfies the requirement of O₂ reduction but not for hydrogen (H₂) evolution. This work provides new insights for the in-situ study of photocatalyst under operation condition, and gives a green and sustainable path for the H₂O₂ photoproduction with metal-free catalysts in seawater.

Chiral catalysis is one of the most direct and effective approach to obtain pure optical enantiomers. Chiral carbon dots (CDs) as carbon-based chiral catalysts show great potential in chiral catalysis. Herein, we report a facile one step base-catalyzed aldol condensation to fabricate the chiral CDs from glucose at ambient temperature and pressure. The formation of chiral CDs involves the processes of isomerization and aldol condensation. These chiral CDs have been demonstrated that they have selective capacity for electrocatalytic oxidization of tryptophan enantiomers. L type of CDs (LCDs) is more likely to catalyze L-tryptophan (Trp) than D-Trp with the selective factor (I_L/I_D) of 1.60, whereas the D type of CDs (DCDs) tends to catalyze D-Trp (I_L/I_D: 0.63). Theoretical calculations combined with various contrast experiments (temperature and pH) demonstrate that the selectively electrocatalytic capacity of chiral CDs toward Trp isomers is due to the different hydrogen-bond interactions between chiral CDs and Trp.

The microstructure design of electrode material is a crucial point to optimize the supercapacitor’s electrochemical properties. In this work, a Bi-based nanocomposite with a three-layer structure (Bi–Bi₂O₃@carbon armour (CA)/carbon dots (CDs)) is synthesized and investigated. This material inherits high capacitance and high activity from bismuth-based materials, and the coated CA protects the structure from complete oxidization and improves surface hydrophilicity. Furthermore, CDs in CA can enhance the ion conduction efficiency between the catalyst, carbon membrane, and electrolyte. As a consequence, the specific capacitance of the electrode reaches 973 F·g⁻¹ under 1 A·g⁻¹, and the energy density achieves 32.5 Wh·kg⁻¹ with a power density of 266.9 W·kg⁻¹, with impressive electrochemical stability that Coulomb efficiency of the electrode remains about 100% after 5000 cycles. Furthermore, in-situ Fourier transformation infrared (FT-IR) analyzes the structure evolvement of the material during synthesis and finds that the annealing process of the material removes a great number of oxygen-containing groups of CA and CDs, generating oxygen vacancies, defects, and thus active sites, which enhance the capacitance of the material.

Carbon dots (CDs), as a unique zero-dimensional member of carbon materials, have attracted numerous attentions for their potential applications in optoelectronic, biological, and energy related fields. Recently, CDs as catalysts for energy conversion reactions under multi-physical conditions such as light and/or electricity have grown into a research frontier due to their advantages of high visible light utilization, fast migration of charge carriers, efficient surface redox reactions and good electrical conductivity. In this review, we summarize the fabrication methods of CDs and corresponding CD nanocomposites, including the strategies of surface modification and heteroatom doping. The properties of CDs that concerned to the photo- and electro-catalysis are highlighted and detailed corresponding applications are listed. More importantly, as new non-contact detection technologies, transient photo-induced voltage/current have been developed to detect and study the charge transfer kinetics, which can sensitively reflect the complex electron separation and transfer behavior in photo-/electro-catalysts. The development and application of the techniques are reviewed. Finally, we discuss and outline the major challenges and opportunities for future CD-based catalysts, and the needs and expectations for the development of novel characterization technologies.

Photocatalytic reduction of carbon dioxide into valuable chemicals is a sustainable and promising technology that alleviates the greenhouse effect and energy crisis. In this study, the Mn₃O₄/FeNbO₄ type II heterojunction photocatalyst with a core-satellite structure was synthesized by the facile soft chemical method. The formation of a nano-heterojunction is supposed to effectively improve light capture, charge transfer, and interfacial charge separation in the photochemical reaction. Meanwhile, the heterojunction has a good ability to capture and activate CO₂. Our results show that the prepared Mn₃O₄/FeNbO₄ photocatalyst exhibit obvious enhanced catalytic properties in the photocatalytic CO₂ reduction reaction, where the CH₄ yielding rate is 1.96 and 9.81 times those of FeNbO₄ and Mn₃O₄, respectively. The transient photovoltage test (TPV) shows that the low frequency electrons are crucial to the effective transfer of photogenerated electrons and holes in the Mn₃O₄/FeNbO₄ nano heterojunctions. Analysis of in situ Fourier transform infrared spectroscopy (FTIR) verifies the effective CO₂ adsorption on the Mn₃O₄/FeNbO₄ surface and the high selectivity of CH₄ products. These properties of the Mn₃O₄/FeNbO₄ photocatalyst infer its broad prospects in the fields of carbon fixation and energy conservation.

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent psychiatric disorders in children, and ADHD patients always display circadian abnormalities. While, the ADHD drugs currently used in clinic have strong side effects, such as psychosis, allergic reactions, and heart problems. Here, we demonstrated carbon dots derived from the ascorbic acid (VCDs) could strongly rescue the hyperactive and impulsive behaviour of a zebrafish ADHD disease model caused by per1b mutation. VCDs prolonged the circadian period of zebrafish for more than half an hour. In addition, the amplitude and circadian phase were also changed. The dopamine level was specifically increased, which may be caused by stimulation of the dopaminergic neuron development in the midbrain. Notably, it was found that the serotonin level was not altered by VCDs treatments. Also, the gene transcriptome effects of VCDs were discussed in present work. Our results provided the dynamic interactions of carbon dots with circadian system and dopamine signaling pathway, which illustrates a potential application of degradable and bio-safe VCDs for the treatment of the attention deficient and hyperactive disorder through circadian intervention.

Ammonia plays a vital role in the development of modern agriculture and industry. Compared to the conventional Haber–Bosch ammonia synthesis in industry, electrocatalytic nitrogen reduction reaction (NRR) is considered as a promising and environmental friendly strategy to synthesize ammonia. Here, inspired by biological nitrogenase, we designed iron doped tin oxide (Fe-doped SnO₂) for nitrogen reduction. In this work, iron can optimize the interface electron transfer and improve the poor conductivity of the pure SnO₂, meanwhile, the synergistic effect between iron and Sn ions improves the catalyst activity. In the electrocatalytic NRR test, Fe-doped SnO₂ exhibits a NH₃ yield of 28.45 μg·h⁻¹·mg_cat⁻¹, which is 2.1 times that of pure SnO₂, and Faradaic efficiency of 6.54% at −0.8 V vs. RHE in 0.1 M Na₂SO₄. It also shows good stability during a 12-h long-term stability test. Density functional theory calculations show that doped Fe atoms in SnO₂ enhance catalysis performance of some Sn sites by strengthening N–Sn interaction and lowering the energy barrier of the rate-limiting step of NRR. The transient photovoltage test reveals that electrons in the low-frequency region are the key to determining the electron transfer ability of Fe-doped SnO₂.

Great attention has been paid to green procedures and technologies for the design of environmental catalytic systems. Biomass-derived catalysts represent one of the greener alternatives for green catalysis. Photocatalytic production of hydrogen peroxide (H₂O₂) from O₂ and H₂O is an ideal green way and has attracted widespread attention. Here, we show a metal-free photocatalyst from cellulose, which has a high photocatalytic activity for the photoproduction of H₂O₂ with the reaction rate up to 2,093 μmol/(h·g) and the apparent quantum efficiency of 2.33%. Importantly, a machine learning model was constructed to guide the synthesis of this metal-free photocatalyst. With the help of transient photovoltage (TPV) tests, we optimized their fabrication and catalytic activity, and clearly showed that the formation of carbon dots (CDs) facilitates the generation, separation, and transfer of photo-induced charges on the catalyst surface. This work provides a green way for the highly efficient metal-free photocatalyst design and study from biomass materials with the machine learning and TPV technology.

Photocatalytic hydrogen production by overall water solar-splitting is a prospective strategy to solve energy crisis. However, the rapid recombination of photogenerated electron–hole pairs deeply restricts photocatalytic activity of catalysts. Here, the in-situ transient photovoltage (TPV) technique was developed to investigate the interfacial photogenerated carrier extraction, photogenerated carrier recombination and the interfacial electron delivery kinetics of the photocatalyst. The carbon dots/NiCo₂O₄ (CDs/NiCo₂O₄) composite shows weakened recombination rate of photogenerated carriers due to charge storage of CDs, which enhances the photocatalytic water decomposition activity without any scavenger. CDs can accelerate the interface electron extraction about 0.09 ms, while the maximum electron storage time by CDs is up to 0.7 ms. The optimal CDs/NiCo₂O₄ composite (5 wt.% CDs) displays the hydrogen production of 62 µmol·h⁻¹·g⁻¹ and oxygen production of 29 µmol·h⁻¹·g⁻¹ at normal atmosphere, which is about 4 times greater than that of pristine NiCo₂O₄. This work provides sufficient evidence on the charge storage of CDs and the interfacial charge kinetics of photocatalysts on the basis of in-situ TPV tests.