In this study, electrochemiluminescence (ECL) properties of carbon dots (CDs, less than 10 nm) have been investigated. Such CDs were fabricated via electrochemical etching strategy from graphite rods. Subsequently, a series of CDs were prepared through controlled surface engineering technique by a wet chemical method, including the oxidized-CDs (oCDs), partially reduced-CDs (rCDs), and fully reduced-CDs (F-rCDs). In-depth characterizations including UV–vis, FT-IR, Raman, XPS, etc. revealed significant differences in features of these CDs, especially the condition of surface grafted oxygen containing functional groups. ECL results suggested that all of the annihilation ECL of CDs, oCDs, and rCDs demonstrated a stable positively charged luminophore (R+•) and an unstable negatively charged luminophore (R–•) at the surface of GCE and possessed a 365 nm emission peak and consistent emission range from 550 to 850 nm. During further structural mode investigation and ECL properties simulation, the surface construction nature of CDs was speculated and the significant role of oxygen containing groups in ECL behavior of CDs was also verified. According to the ECL behavior from all of these samples, the probable ECL mechanism of CDs was then proposed, which further interpreted the indispensable contributions of oxygen containing functional groups to the ECL property of CDs.

•An ingenious Bi2MoO6/Bi2S3 photoelectrochemical platform has been established.•Such a facile photoelectrochemical sensor can selectively distinguish gallic acid.•This simple yet cogent method broadens possibility for some drug quality control.•Relevant mechanism was in-depth researched via theory and morphology analysis.Along with continuous growing widespread adulterations of botanical drugs, the necessity for drug quality monitoring has become more popular than ever. Considering that antioxidants are widely found in natural plant pharmaceuticals, gallic acid (GA) is often regarded as the reference standard to make sure whether these are up to grade as guided by Chinese Pharmacopeia. Herein, a novel Bi2MoO6/Bi2S3 photoelectrochemical sensor has been successfully involved toward selective GA analysis to supervise drug quality, in which γ-Bi2MoO6 nanobelts were treated as template nanocrystal and scaffold. Such Bi2S3 accommodated in Bi2MoO6 nanobelts render platform with excellent light-harvesting capability, selectivity and reproducibility. Concerned mechanism was in-depth pursued through theoretical computation and morphology speculation, inferring that two aspects mainly contribute to the findings: (1) engineering particular structure brings about surface dangling bonds, which raises the likelihood of electrostatic interaction with opposite charges; (2) appending Bi2S3 to the Bi2MoO6 nanobelts acted as a new avenue to mediate photoelectrochemical behavior, nearly devoid of interference effect. Our work opens up broad possibilities for finely distinguishing different antioxidants. As the extension of this simple and valid strategy, photoelectrochemistry will become a potent backing for quality guaranty in drug field, which offers an entry into ensuring good consistency in batch production.Since some officinal plants are full of antioxidants, these crude drugs often use gallic acid (GA) as the quality criterion in accordance with Chinese Pharmacopeia. An ingenious Bi2MoO6/Bi2S3 photoelectrochemical platform was successfully involved in selective GA analysis to guarantee drug safety.Download high-res image (214KB)Download full-size image

The discovery of graphene and other two-dimensional (2D) materials has set the foundation for exploring and designing novel single layered sheets. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table and they have the potential to play a fundamental role in the future of electronics, composite materials and energy technology. Therefore, searching for new 2D materials is a big challenge in materials science. In this work, we theoretically designed a monolayer of Ti3BN following the strategy of “atomic transmutation”. The Ti3BN monolayer can be considered as three Ti-atomic layers being interleaved with one N-atomic layer and one B-atomic layer, in the sequence of Ti1–N–Ti2–B–Ti3. The moderate cohesive energy, positive phonon frequencies and high melting point are the best guarantees for good stability of Ti3BN. Based on a global minimum structures search using the particle-swarm optimization (PSO) method, Ti3BN is the lowest energy structure in 2D space, which holds great promise for the realization of layered Ti3BN in experiment. Based on density functional theory (DFT) calculations, Ti3BN is intrinsically metallic and its electronic properties can be modulated by varying the surface groups, such as OH or F-termination. If realized in experiment, it may find applications in many aspects.

In an electrocatalytic hydrogen evolution reaction (HER) system, a cathodic H+ resource, an anodic sacrificial agent and a robust catalyst are three essential factors. Industry wastewater emissions, containing high levels of acidity and organic dyes, actually can satisfy the material requirements for the HER. Herein, a new HER method is proposed, taking acidic ions from wastewater as a cathodic resource to produce H2, while organic dye waste acts as an anodic sacrifice to balance the reaction. In such a way, a sustainable H2 energy source can be generated and clean water is obtained as well. For the HER catalyst, low cost and highly efficient graphene supported Fe1−xCoxS2 was synthesized with an onset overpotential of ∼50 mV and it demonstrated impressive HER performance in both practical industry wastewater and analogous wastewater simulations. Besides the cathodic H2 evolution, anodic organic dyes (MO, MB, RhB and industry waste organic dyes) were all entirely decomposed within 8 min, 18 min, 9 min and 4 h under oxidation potentials of ∼1.46, 1.50, 1.47 and 1.40 V. As verified both in practical industry wastewater and wastewater simulations in the laboratory, our approach for integrating the HER and wastewater treatment puts forward an attractive opportunity in energy and environmental research fields.

The zero band gap of pristine graphene hinders its application in high-performance field effect transistors (FETs) at room temperature. The symmetry breaking of the sub-lattice, originated from the influence of substrates such as silicon carbide, hexagonal boron nitride as well as graphitic carbon nitride (C3N4), can produce a band gap in graphene. Herein, another novel kind of substrate, C2N, is employed to break the symmetry of the graphene sub-lattice, resulting in a band gap of about 0.40 eV in graphene. In combination with C2N through the weak van der Waals (vdW) interaction, graphene keeps its structural integrity and charge mobility. A band opening as large as 0.72 eV could be achieved through reducing the layer spacing to 3.2 Å. This is because the amount of electron transfer from graphene to C2N and the interaction between C2N and graphene increase with the decreasing interlayer spacing. Moreover, though the band gap of C2N is slightly altered, its electronic properties especially the direct band gap in visible region and the band dispersions are almost preserved. Thus, our theoretical results predict the promising multifunctional applications of C2N/graphene (C2N/G) heterostructures, including high-performance FETs and metal-free photocatalytic materials for water splitting.

For a healthy diet, which is an extension of a high quality lifestyle, tremendous attention has been focused on using antioxidant capacity indicators for food inspections and health guides. Although photoelectrochemical transducers have broadened our horizons for global antioxidant activity analysis, a growing body of foods and beverages needs to be quantified in the visible region and the necessary photoelectrochemical instrumentalization is still in its infancy. Generally, BiVO4 is considered as an ideal starting material for antioxidant surveillance under visible light irradiation. However, it is subjected to unsatisfied charge collection and utilization in practical applications. Herein, we studied the effects of successive molybdenum substitution of vanadium on the photocatalytic behavior of BiMoxV(1−x)O4 under visible light illumination. A superior photocurrent density was obtained for BiMo0.015V0.985O4 due to the flower-like architecture and favorable crystalline form. At the same time, this superhybrid BiMo0.015V0.985O4 composite successfully acted as a sensing unit in a photoelectrochemical platform for antioxidant capacity evaluation in foodstuffs. The related mechanism was further unearthed and discussed in-depth. Such a straightforward yet cogent principle was also applied to our integrated device for the “smart” analysis of the global antioxidant capacity, whereby collected data can be treated as a nutritive value index for routine quality control in the food industry. On the basis of this achievement, it is anticipated that mobile app-based quantitative antioxidant capacity detection will soon be realized.

Herein, a novel photoelectrochemical platform with WS2/TiO2 composites as optoelectronic materials was designed for selective detection of o-diphenol and its derivatives without any biomolecule auxiliary. First, catechol was chosen as a model compound for the discrimination from resorcinol and hydroquinone; then several o-diphenol derivatives such as dopamine, caffeic acid, and catechin were also detected by employing this proposed photoelectrochemical sensor. Finally, the mechanism of such a selective detection has been elaborately explored. The excellent selectivity and high sensitivity should be attributed to two aspects: (i) chelate effect of adjacent double oxygen atoms in the o-diphenol with the Ti(IV) surface site to form a five/six-atom ring structure, which is considered as the key point for distinction and selective detection. (ii) This selected WS2/TiO2 composites with proper band level between WS2 and TiO2, which could make the photogenerated electron and hole easily separated and results in great improvement of sensitivity. By employing such a photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been successfully performed for dopamine detection. This biomolecule-free WS2/TiO2 based photoelectrochemical platform demonstrates excellent stability, reproducibility, remarkably convenient, and cost-effective advantages, as well as low detection limit (e.g., 0.32 μmol L–1 for dopamine). It holds great promise to be applied for detection of o-diphenol kind species in environment and food fields

The antioxidants in biological organisms can scavenge excess free radicals and effectively reduce oxidative stress, which protects DNA, protein and lipids in the human body from damage, thus preventing diseases from being induced. Therefore, it is particularly significant to assay the antioxidant capacities of our habitual foods during dietary evaluation. Herein, ultrathin graphitic carbon nitride (utg-C3N4)/TiO2 composites have been introduced as sensing elements into a photoelectrochemical platform with a thin layer structured flow-cell, for the real-time assay of the global antioxidant capacity in practical samples. In this system, the two-dimensional utg-C3N4 nanosheet/TiO2 nanoparticle composite material provided a much better optoelectronic function than the individual materials. In comparison with previous reports, this photoelectrochemical strategy shows considerable advantages, including excellent anti-interference properties, a high level of stability and reproducibility, and it is also proved to be the most prompt, convenient and cost-effective method for antioxidant capacity detection up to now. Moreover, utilizing theoretical and experimental examinations, we revealed its photoelectrochemical sensing mechanism in depth. It is proposed that the developed method will pave the way for the development of excellent antioxidant assays with the advantages of photoelectrochemistry and fluidic cells . It is expected to be further applied in food quality inspections and health guides, as well as in other fields.

TiO2 is an abundant and environmentally benign material, but has a wide band gap, which greatly confines its applications in photocatalysis. Doping and modifying the material composition are both generally used to change and control the photocatalytic activity of semiconductors. Herein, we describe a method and resulting activity of depositing Ce-/S-codoped TiO2 nanoparticles (NPs) on water-soluble sulfonated graphene (SGE) sheets, which guarantees a direct contact and satisfactory electron transfer between the semiconductor and graphene. The Ce/S–TiO2 NPs are homogeneously fixed on the surface of SGE sheets with an average particle size of ∼7 nm. The resulting composite showed noticeable activity in photodegrading methyl orange (κ = 0.425 h−1). This improved performance can be attributed to the synergistic effects of Ce- and S-codoping toward TiO2 and the composite action between TiO2 NPs and SGE. This type of novel composite is expected to stimulate the development of doped and graphene-involved photocatalysts for addressing environmental problems.

Promotion of the catalytic efficiency and reduction of the usage amount of Pd are crucial to developing effective and low-cost catalysts for catalytic reduction of organic aromatic nitro pollutant compound at present. Herein, we report a hybrid material of ultrafine Pd nanocrystals (PdNCs) grown on an excellent support of SnO2-decorated graphene nanosheets (SnO2-GNS) for a highly efficient reduction of a representative aromatic nitro compound (4-nitrophenol). The supporting material of SnO2-GNS was prepared simply by one step of homogeneous reaction with a positively charged polymer as stabilizer and active site for absorption of the PdNCs precursor. Transmittance electronic images demonstrate that the PdNCs are densely and well covered on the SnO2-GNS with a uniform size of 3.4 nm. This nanohybrid exhibits the fastest reduction time (4 minutes) compared to other controlled materials. Moreover, it shows high kinetic responses with an apparent kinetic rate constant (kapp) of 2.03 × 10−2 s−1 and turnover frequency (TOF) of 1.70 s−1. The cycle performance (10 times) experiments demonstrate that this nanohybrid also displays a good anti-poisoning capability. Thanks to the ultrafine PdNCs, this as-prepared PdNCs/SnO2-GNS nanohybrid may have broad potential in other catalytic fields, for example, organic synthesis, fuel cells and electrochemical biosensors.

Dietary antioxidants as health promoters for human beings have attracted much attention and triggered tremendous efforts in evaluation of the antioxidant capacity. Unfortunately, no versatile detection system has been designed to date. Due to the possible synergistic effect among antioxidant components in a diversified system, to isolate and quantify an individual antioxidant via a chromatography approach limits the scope for global antioxidant activity assay. Quality inspections with a spectroscopy strategy to any colored food are far from satisfactory. Herein, a photoelectrochemical (PEC) platform with an ultrasensitive titanium dioxide decorated sulfonated graphene (SGE-TiO2) based transducer was introduced for antioxidant monitoring. Under an open circuit potential (zero potential), with extraordinary response, excellent reproducibility and stability, this PEC sensor could be successfully applied for rational analysis of the global antioxidant capacity. Such a highly efficient strategy showed advantages such as simplicity, convenience, high sensitivity and universality, which were also applicable to the detection of colored system. Moreover, the PEC sensor could be employed for practical evaluation of antioxidant capacity of teas. The concerned mechanism was further proposed and adequately discussed. This straightforward yet powerful approach provides a general format for dietary antioxidant assessment in foodstuff industries.

Manipulating the electronic structure of semiconductor photocatalysts represents an ideal approach for the exploration and development of photocatalysis. However, it still remains a challenge in terms of silver halide photocatalysts. Herein, we report ternary alloyed AgClxBr1−x nanocrystals (NCs) synthesized by controlling the crystal growth process within a facile microemulsion system. The alloyed NCs crystallize in a homogeneous rock-salt crystal structure and possess tunable bandgaps from 2.5 to 3.0 eV obtained by varying the halogen mole ratios (Cl/Br). Their photocatalytic activities for dye degradation and CO2 reduction are found to depend strongly on the chemical compositions, and among them, the AgCl0.75Br0.25 sample exhibits the highest activity (about 2–4 times higher than AgCl and AgBr). Further theoretical calculations demonstrate that a decrease of the ratios of Cl/Br lowers the levels of the conduction band minimum and thereby narrows the bandgaps. Combining the theoretical and experimental results, the highest activity can be rationally ascribed to the optimum conduction band levels, which balances the overall effect of bandgap, electronic coupling and redox potential. This methodological exploration of engineering the bandgap of silver halide materials is a step forward toward the development of advanced photocatalysts and will shed light on devising various semiconductor photocatalytic systems.

The antioxidants in biological organisms can scavenge excess free radicals and effectively reduce oxidative stress, which protects DNA, protein and lipids in the human body from damage, thus preventing diseases from being induced. Therefore, it is particularly significant to assay the antioxidant capacities of our habitual foods during dietary evaluation. Herein, ultrathin graphitic carbon nitride (utg-C3N4)/TiO2 composites have been introduced as sensing elements into a photoelectrochemical platform with a thin layer structured flow-cell, for the real-time assay of the global antioxidant capacity in practical samples. In this system, the two-dimensional utg-C3N4 nanosheet/TiO2 nanoparticle composite material provided a much better optoelectronic function than the individual materials. In comparison with previous reports, this photoelectrochemical strategy shows considerable advantages, including excellent anti-interference properties, a high level of stability and reproducibility, and it is also proved to be the most prompt, convenient and cost-effective method for antioxidant capacity detection up to now. Moreover, utilizing theoretical and experimental examinations, we revealed its photoelectrochemical sensing mechanism in depth. It is proposed that the developed method will pave the way for the development of excellent antioxidant assays with the advantages of photoelectrochemistry and fluidic cells . It is expected to be further applied in food quality inspections and health guides, as well as in other fields.

TiO2 is an abundant and environmentally benign material, but has a wide band gap, which greatly confines its applications in photocatalysis. Doping and modifying the material composition are both generally used to change and control the photocatalytic activity of semiconductors. Herein, we describe a method and resulting activity of depositing Ce-/S-codoped TiO2 nanoparticles (NPs) on water-soluble sulfonated graphene (SGE) sheets, which guarantees a direct contact and satisfactory electron transfer between the semiconductor and graphene. The Ce/S–TiO2 NPs are homogeneously fixed on the surface of SGE sheets with an average particle size of ∼7 nm. The resulting composite showed noticeable activity in photodegrading methyl orange (κ = 0.425 h−1). This improved performance can be attributed to the synergistic effects of Ce- and S-codoping toward TiO2 and the composite action between TiO2 NPs and SGE. This type of novel composite is expected to stimulate the development of doped and graphene-involved photocatalysts for addressing environmental problems.

Promotion of the catalytic efficiency and reduction of the usage amount of Pd are crucial to developing effective and low-cost catalysts for catalytic reduction of organic aromatic nitro pollutant compound at present. Herein, we report a hybrid material of ultrafine Pd nanocrystals (PdNCs) grown on an excellent support of SnO2-decorated graphene nanosheets (SnO2-GNS) for a highly efficient reduction of a representative aromatic nitro compound (4-nitrophenol). The supporting material of SnO2-GNS was prepared simply by one step of homogeneous reaction with a positively charged polymer as stabilizer and active site for absorption of the PdNCs precursor. Transmittance electronic images demonstrate that the PdNCs are densely and well covered on the SnO2-GNS with a uniform size of 3.4 nm. This nanohybrid exhibits the fastest reduction time (4 minutes) compared to other controlled materials. Moreover, it shows high kinetic responses with an apparent kinetic rate constant (kapp) of 2.03 × 10−2 s−1 and turnover frequency (TOF) of 1.70 s−1. The cycle performance (10 times) experiments demonstrate that this nanohybrid also displays a good anti-poisoning capability. Thanks to the ultrafine PdNCs, this as-prepared PdNCs/SnO2-GNS nanohybrid may have broad potential in other catalytic fields, for example, organic synthesis, fuel cells and electrochemical biosensors.

For a healthy diet, which is an extension of a high quality lifestyle, tremendous attention has been focused on using antioxidant capacity indicators for food inspections and health guides. Although photoelectrochemical transducers have broadened our horizons for global antioxidant activity analysis, a growing body of foods and beverages needs to be quantified in the visible region and the necessary photoelectrochemical instrumentalization is still in its infancy. Generally, BiVO4 is considered as an ideal starting material for antioxidant surveillance under visible light irradiation. However, it is subjected to unsatisfied charge collection and utilization in practical applications. Herein, we studied the effects of successive molybdenum substitution of vanadium on the photocatalytic behavior of BiMoxV(1−x)O4 under visible light illumination. A superior photocurrent density was obtained for BiMo0.015V0.985O4 due to the flower-like architecture and favorable crystalline form. At the same time, this superhybrid BiMo0.015V0.985O4 composite successfully acted as a sensing unit in a photoelectrochemical platform for antioxidant capacity evaluation in foodstuffs. The related mechanism was further unearthed and discussed in-depth. Such a straightforward yet cogent principle was also applied to our integrated device for the “smart” analysis of the global antioxidant capacity, whereby collected data can be treated as a nutritive value index for routine quality control in the food industry. On the basis of this achievement, it is anticipated that mobile app-based quantitative antioxidant capacity detection will soon be realized.

The on-line detection and treatment of atmospheric formaldehyde (HCHO) at real-time levels, especially in indoor environments, is becoming more and more important. Herein, by first principles calculations, a highly active sub-stoichiometric WO2.9 (010) surface for HCHO sensing and treatment has been demonstrated. The exposed one-coordinated terminal O atoms (O1c), two-coordinated bridge O atoms (O2c) and five-coordinated W atoms (W5c) at the surface are found to be active sites for HCHO adsorption. HCHO molecules can anchor on the WO2.9 (010) surface through newly formed OF–W5c and/or CF–O1c/O2c/W5c bonds, forming ‘ridge-like’/’hobbyhorse-like’ or slantwise adsorption configurations. The absorbed HCHO molecules may exchange electrons with the WO2.9 (010) surface and change the conductivity of the surface, which is the working mechanism of WO2.9 based sensors. Furthermore, Cl-NEB results suggest that the absorbed HCHO molecules tend to dissociate under moderate excitation (for example, solar visible light) at room temperature due to the minimum energy barrier of only 0.54 eV. The HCHO dissociation results in an H adatom bond to a surface O1c atom and a formate or formyl group chemisorbed to the surface with elongated OF–W5c and CF–W5c bonds, which means that OF–W5c and CF–W5c bonds are active and prone to breaking. These results demonstrate the potential of WO2.9 in HCHO sensing and elimination.