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.

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.

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.

Carbon dots (CDs) have uniquely structural, physicochemical and photochemical properties, suggesting a promising platform for catalysis applications. The in-depth understanding of the structure-activity relationship in the CDs-based catalyst system needs to know the effect of the crystalline core on their catalytic performance. The efficient catalytic oxidation of cyclohexane is an urgent challenge in current chemical industry, in which, adipic acid (AA) plays an important role in industry for synthesis of nylon-6 and nylon-66. Here, we fabricated the pristine CDs by electrochemical etching graphite rod method and derived CDs with high crystalline core (CD-600, CD-800, and CD-1100) through a thermal treatment method in tube furnace. Furthermore, these CDs performed an outstanding catalytic performance for one-step synthesis of AA from cyclohexane. With the help of machine learning (ML), the deep correlations between features (structures of CDs, catalytic conditions) and catalytic performances were investigated by XGBoost (XGB) model. Then under the optimization and prediction of XGB, it was found that high crystalline core preceded the other features and CD-1100 could get the best conversion of 30.696% and selectivity to AA of 92.52% at reaction conditions of 130 °C, 1.5 MPa, and 10 h. This work pioneered the application of ML in industrial issues and demonstrated a comprehensive understanding on CDs as catalyst to realize one-step synthesis of AA.

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.

The energy crisis has always been a widely concerned problem. It is an urgent need for green and renewable energy technologies to achieve sustainable development, and the photo-assisted charging energy storage devices provide a new way to realize the sustainable utilization of solar energy. Here, we fabricated a photo-assisted charging fibrous supercapacitor (NM₂P₁) with Ti₃C₂T_x-based hybrid fibre modified by nitrogen-doped carbon dots (NCDs). The NM₂P₁ fibre provides a volumetric capacitance of 1, 445 F·cm^-3 (630 F·g^-1) at 10 A·cm^-3 under photo-assisted charging, which increases by 35.9% than that of dark condition (1, 063 F·cm^-3/ 464 F·g^-1). Furthermore, the NM₂P₁ fibrous supercapacitor device shows that the maximum volumetric energy density and volumetric power density are 18.75 mWh·cm^-3 and 8, 382 mW·cm^-3. Notably, the transient photovoltage (TPV) test was used to further confirm that NCDs as a photosensitizer enhance the light absorption capacity and faster charge transfer kinetics of NM₂P₁ fibre. This work directly exploits solar energy to improve the overall performance of supercapacitor, which opens up opportunities for the utilization of renewable energy and the development of photosensitive energy equipment.

Highly efficient photo-assisted electrocatalysis for methanol oxidation reaction (MOR) realizes the conversion of solar and chemical energy into electric energy simultaneously. Here we report a Pt-MXene-TiO₂ composite for highly efficient MOR via a photoactive cascaded electro-catalytic process. With light (UV and visible light) irradiation, MXene-TiO₂ serves as the photo active centre (photoinduced hole) to activate the methanol molecules, while Pt particles are the active centre for the following electro-catalytic oxidation of those activated methanol molecules. Pt-MXene-TiO₂ catalyst exhibits a lower onset potential (0.33 V) and an impressive mass activity of 2,750.42 mA·mg^-1_Pt under light illumination. It represents the highest MOR activity ever reported for photo-assisted electrocatalysts. Pt-MXene-TiO₂ also shows excellent CO tolerance ability and stability, in which, after long-term (5,000 s) reaction, still keeps a high mass activity of 1,269.81 mA·mg^-1_Pt (62.66% of its initial activity). The photo-electro-catalytic system proposed in this work offers novel opportunities for exploiting photo-assisted enhancement of highly efficient and stable catalysts for MOR.

The ~ 5 nm degradable carbon dots (CDs) were synthesized directly from carbon rod by a one-step electrochemical method at room temperature. The as-prepared CDs can effectively enhance the ribulose bisphosphate carboxylase oxygenase (RuBisCO) activity, and then promote the dicotyledons growth (soybean, tomato, eggplant and so on) and finally increase their yields. Here, we used Arabidopsis thaliana and Trifolium repens L. as model plants to systematically study the beneficial effects of CDs on plant growth. These include: (i) accelerating seed germination; (ii) enlarging root elongation; (iii) increasing metal ions absorption and delivery; (iv) improving enzymes activity; (v) enhancing the carbohydrate content; (vi) degradation into plant hormone analogues and CO₂; and finally (vii) enhancing the grain production by about 20%.