Pengju Yang

Construction of Z-scheme carbon nanodots/WO3 with highly enhanced photocatalytic hydrogen production

Carbon nanodots without any modification can drive photocatalytic hydrogen evolution. More importantly, we found that Z-scheme is an effective strategy to improve the photocatalytic performance of carbon nanodots. The photocatalytic H2-evolution rates improve from 4.65 μmol g−1 h−1 to 1330 μmol g−1 h−1 under xenon lamp irradiation.

Intramolecular hydrogen bonds quench photoluminescence and enhance photocatalytic activity of carbon nanodots.

Understanding the photoluminescence (PL) and photocatalytic properties of carbon nanodots (CNDs) induced by environmental factors such as pH through surface groups is significantly important to rationally tune the emission and photodriven catalysis of CNDs. Through adjusting the pH of an aqueous solution of CNDs, it was found that the PL of CNDs prepared by ultrasonic treatment of glucose is strongly quenched at pH 1 because of the formation of intramolecular hydrogen bonds among the oxygen-containing surface groups. The position of the strongest PL peak and its corresponding excitation wavelength strongly depend on the surface groups. The origins of the blue and green emissions of CNDs are closely related to the carboxyl and hydroxyl groups, respectively. The deprotonated COO(-) and CO(-) groups weaken the PL peak of the CNDs and shift it to the red. CNDs alone exhibit photocatalytic activity towards degradation of Rhodamine B at different pH values under UV irradiation. The photocatalytic activity of the CNDs is the highest at pH 1 because of the strong intramolecular hydrogen bonds formed among the oxygen-containing groups.

Pure carbon nanodots for excellent photocatalytic hydrogen generation

Pure carbon nanodots (CNDs) without any modification and co-catalyst can drive photocatalytic hydrogen generation. The hydrogen generation rate of CNDs reaches 3615.3 μmol g−1 h−1 when methanol was used as the sacrificial donor, which is 34.8 times higher than that of commercial Degussa P25 photocatalyst under the same conditions. Moreover, the CNDs show good stability; the hydrogen generation rate has negligible change even after four cycles of testing.

Light-induced synthesis of photoluminescent carbon nanoparticles for Fe3+ sensing and photocatalytic hydrogen evolution

We report a new method to prepare photoluminescent carbon nanoparticles (CNPs) by a light-induced process. The obtained CNPs are sensitive to the specific detection of Fe3+ with a detection limit of 0.55 ppm. CNPs also show excellent photocatalytic hydrogen production under xenon lamp irradiation. The hydrogen evolution rate is up to 4.89 μmol h−1 over 2.1 mg CNPs.

Understanding the Formation Mechanism of Graphene Frameworks Synthesized by Solvothermal and Rapid Pyrolytic Processes Based on an Alcohol–Sodium Hydroxide System

The determination of ways to facilitate the 2D-oriented assembly of carbons into graphene instead of other carbon structures while restraining the π-π stacking interaction is a challenge for the controllable bulk synthesis of graphene, which is vital both scientifically and technically. In this study, graphene frameworks (GFs) are synthesized by solvothermal and rapid pyrolytic processes based on an alcohol-sodium hydroxide system. The evolution mechanism of GFs is investigated systematically. Under sodium catalysis, the abundant carbon atoms produced by the fast decomposition of solvothermal intermediate self-assembled to graphene. The existence of abundant ether bonds may be favorable for 3D graphene formation. More importantly, GFs were successfully obtained using acetic acid as the carbon source in the synthetic process, suggesting the reasonability of analyzing the formation mechanism. It is quite possible to determine more favorable routes to synthesize graphene under this cognition. The electrochemical energy storage capacity of GFs was also studied, which revealed a high supercapacitor performance with a specific capacitance of 310.7 F/g at the current density of 0.2 A/g.

Multifunctional Nitrogen-Doped carbon nanodots for photoluminescence,sensor, and visible-Light-Induced H2 production

Herein, multifunctional N-doped carbon nanodots (NCNDs) were prepared through the one-step hydrothermal treatment of yeast. Results show that the NCNDs can be used as a new photocatalyst to drive the water-splitting reaction under UV light. Moreover, the NCNDs can efficiently catalyze the hydrogen evolution reaction. Under visible-light irradiation, Eosin Y-sensitized NCNDs exhibit excellent activity for hydrogen evolution. The hydrogen evolution rate of NCNDs (without any modification and co-catalyst) reaches 107.1 μmol h(-1) (2142 μmol g(-1)  h(-1) ). When Pt is loaded on the NCNDs, the hydrogen evolution rate reaches 491.2 μmol h(-1) (9824 μmol g(-1)  h(-1)) under visible-light irradiation. In addition, the NCNDs show excellent fluorescent properties and can be applied as a fluorescent probe for the sensitive and selective detection of Fe(3+) .

Chlorine-Induced In Situ Regulation to Synthesize Graphene Frameworks with Large Specific Area for Excellent Supercapacitor Performance

Three-dimensional (3D) graphene frameworks are usually limited by a complicated preparation process and a low specific surface area. This paper presents a facile suitable approach to effectively synthesize 3D graphene frameworks (GFs) with large specific surface area (up to 1018 m(2) g(-1)) through quick thermal decomposition from sodium chloroacetate, which are considerably larger than those of sodium acetate reported in our recent study. The chlorine element in sodium chloroacetate may possess a strong capability to induce in situ activation and regulate graphene formation during pyrolysis in one step. These GFs can be applied as excellent electrode materials for supercapacitors and can achieve an enhanced supercapacitor performance with a specific capacitance of 266 F g(-1) at a current density of 0.5 A g(-1).

Cooperative Dehydrogenation Coupling of Isopropanol and Hydrogenation Coupling of Acetone Over a Sodium Tantalate Photocatalyst

Photocatalytic organic syntheses are often limited by their low system efficiency and product selectivity. We demonstrate herein that intermolecular hydrogen transfer from isopropanol to acetone can be achieved efficiently on the surfaces of NaTaO3 photocatalysts, on which 2‐hydroxyisopropyl radicals are produced selectively from both oxidation and reduction half‐reactions and then coupled to form 2,3‐dimethyl‐2,3‐butanediol. Such a process effectively increases the total reaction efficiency. We also found that the two half‐reactions occur at different crystal facets and display a remarkably promotive interaction, which dramatically speeds up the reactions by one order of magnitude and significantly restrains side reactions. The sodium ions on the NaTaO3 surfaces play an important role in the promotive effect, likely facilitating the proton transfer between the oxidation and reduction sites. These factors make the production rate of 2,3‐dimethyl‐2,3‐butanediol reach a very high level (10.87 mmol g−1 h−1), emphasizing the potential of photocatalytic hydrogenation and dehydrogenation in improving system efficiency of photocatalytic organic syntheses.

Direct C–C coupling of bio-ethanol into 2,3-butanediol by photochemical and photocatalytic oxidation with hydrogen peroxide

Theoretically, selective C–H manipulation in ethanol can result in a direct C–C coupling synthesis of 2,3-butanediol (2,3-BDO). However, this process is typically extremely difficult to achieve because of the high complexity of the involved chemical bonds. In this work, we determine that hydroxide radicals generated from the photolysis of H2O2 can selectively attack the α-hydrogen atom in ethanol aqueous solutions and crack the C–H bond to produce hydroxyethyl radicals, which subsequently undergo C–C coupling to form 2,3-BDO. This selective C–H breakage is determined by the reaction rate, which is primarily controlled by the local H2O2 concentration at a given irradiation intensity. At a moderate reaction rate of ethanol (37 mmol h−1), the 2,3-BDO selectivity reaching as high as 91% can be obtained. The introduction of a catalyst can further increase ethanol conversion and enhance the 2,3-BDO formation rate by controlling the reaction rate. This result provides an environment-friendly approach to convert bio-ethanol directly to 2,3-BDO and to manipulate a single bond selectively in complex bonding situations.

Green oxidation of bio-lactic acid with H2O2 into tartronic acid under UV irradiation

Tartronic acid (TA) is a high value-added chemical widely used as a pharmaceutical product and a preservative; however, its synthesis technology is complicated and high cost. In this study, aqueous solutions of lactic acid were photochemically converted into TA via green oxidation by using hydrogen peroxide (H2O2).