Br-doping of g-C3N4 towards enhanced photocatalytic performance in Cr(Ⅵ)reduction

Semiconductor photocatalytic technology is widely recognized as one of the most promising technologies to solve current energy and environmental crisis, due to its ability to make effective use of solar energy. In recent years, graphite carbon nitride(g-C3N4), a new type of non-metallic polymer semiconductor photocatalyst, has rapidly become the focus of intense research in the field of photocatalysis because of its suitable bandgap energy, unique structure, and excellent chemical stability. In order to improve its intrinsic shortages of small specific surface area, narrow visible light response range, high electron-hole pair recombination rate, and low photon quantum efficiency, a simple method was utilized to synthesize Br-doped g-C3N4(CN–Br X, X = 5, 10, 20, 30), where X is a percentage mole ratio of NH4 Br to melamine. Experimental results showed that Br atoms were doped into the g-C3N4 lattice by replacing the bonded N atoms in the form of C–N=C, while the derived material retained the original framework of g-C3N4. The interaction of Br element with the g-C3N4 skeleton not only broadened the visible-light response of g-C3N4 to 800 nm with an adjustable band gap, but also greatly promoted the separation efficiency of the photogenerated charge carrier and the surface area. The photocurrent intensity of bare CN and CN–Br X(X = 5, 10, 20, 30) catalysts is calculated to be 1.5, 2.0, 3.1, 6.5, and 1.9 μA, respectively. And their specific surface area is measured to be 9.086, 9.326, 15.137, 13.397, and 6.932 m2/g. As a result, this Br-doped g-C3N4 gives significantly enhanced photocatalytic reduction of Cr(VI), achieving a twice enhancement over g-C3N4, with high stability during prolonged photocatalytic operation compared to bare g-C3N4 under visible light irradiation. Furthermore, an underlying photocatalytic reduction mechanism was proposed based on control experiments using radical scavengers.

Enhanced photocatalytic NO removal and toxic NO2 production inhibition over ZIF‐8‐derived ZnO nanoparticles with controllable amount of oxygen vacancies

The controlled introduction of oxygen vacancies(OVs)in photocatalysts has been demonstrated to be an efficient approach for improving the separation of photogenerated charge carriers,and thus,for enhancing the photocatalytic performance of photocatalysts.In this study,a two‐step calcination method where ZIF‐8 was used as the precursor was explored for the synthesis of ZIF‐8‐derived ZnO nanoparticles with gradient distribution of OVs.Electron paramagnetic resonance measurements indicated that the concentration of OVs in the samples depended on the temperature treatment process.Ultraviolet–visible spectra supported that the two‐step calcined samples presented excellent light‐harvesting ability in the ultraviolet‐to‐visible light range.Moreover,it was determined that the two‐step calcined samples presented superior photocatalytic performance for the removal of NO,and inhibited the generation of NO2.These properties could be attributed to the contribution of the OVs present in the two‐step calcined samples to their photocatalytic performance.The electrons confined by the OVs could be transferred to O2 to generate superoxide radicals,which could oxidize NO to the final product,nitrate.In particular,the NO removal efficiency of Z 350‐400(which was a sample first calcined at 350℃ for 2 h,then at 400℃ for 1 h)was 1.5 and 4.6 times higher than that of Z 400(which was one‐step directly calcined at 400℃)and commercial ZnO,respectively.These findings suggested that OV‐containing metal oxides that derived from metal‐organic framework materials hold great promise as highly efficient photocatalysts for the removal of NO.

The photocatalytic performance and active sites of g-C3N4 effected by the coordination doping of Fe(Ⅲ)

Element doping is a simple and effective method to improve photocatalytic activity of g-C3N4. However, the doping model and mechanism of metal elements are still uncharacterized. In this study, we found that Fe(Ⅲ) can be doped into g-C3N4 through the coordination between amidogen and Fe(Ⅲ). After activity tests, it was found that this coordination doping of Fe(Ⅲ) could enhance the Rh B oxidation and Cr(Ⅵ) reduction activities of g-C3N4 in interesting ways, but it is not helpful for the NO-removal performance of g-C3N4. Characterization and calculation results show that the coordination of Fe(Ⅲ) can not only improve the transfer of photogenerated electrons, but it also can passivate the carbon site of triazine rings, which is the active site of NO-removal. This study revealed some doping mechanisms and effect mechanisms of elemental metal in photocatalysis.

Morphology and photocatalytic tetracycline degradation of g-C_(3)N_(4) optimized by the coal gangue

Coal gangue(CG),a solid waste from coal mining and processing,has raised concerns about its environmental impact.Graphitic carbon nitride(g-C_(3)N_(4))is promising for photocatalytic decomposition of organic pollutants,but its performance is hampered by its inherent defects.In this study,the compound of coal gangue and g-C_(3)N_(4)was formed by in-situ loading g-C_(3)N_(4)on the surface of coal gangue.After recombination,the morphology of g-C_(3)N_(4)changes from block structure to tremella nanosheet.This change not only increases the specific surface area of g-C_(3)N_(4),but also broadens the light absorption spectrum of g-C_(3)N_(4).Compared with original g-C_(3)N_(4),the photo-current of the complex in visible light is increased twice,and the tetracycline(TC)degradation rate is 2.1 times faster.The structure,optical properties,band structure,morphology and charge transfer mechanism of the composite were analyzed by a series of characterization techniques.It is found that coal gangue can promote the space charge transfer and separation of g-C_(3)N_(4),and the cyclic test compound has good activity stability.In this paper,a strategy of comprehensive utilization of coal gangue is proposed,which can not only reduce the envi-ronmental risk of coal gangue,but also provide carbon nitride(CN)based photocatalytic materials with superior photocatalytic properties.

The photocatalytic ·OH production activity of g-C_(3)N_(4) improved by the introduction of NO

The efficiency of photocatalytic pollutant removal largely depends on the ability of the photocatalytic system to produce hydroxyl radicals(·OH).However,the capability of photocatalyst to produce·OH is not strong at present.Advancing the capacity of photocatalytic system to produce·OH has always been a tough problem and challenge in the field of environmental science.In this research,it was found that introducing nitric oxide(NO)into the graphitic carbon nitride(g-C_(3)N_(4))photocatalytic system could memorably enhance the ability of producing·OH group.This study provides a new idea for improving the capacity of photocatalytic·OH production.

First-principles study on Fe_(2)B_(2)as efficient catalyst for nitrogen reduction reaction

[18_(T)D$IF]Ammonia(NH_(3))is considered an attractive candidate as a clean,highly efficient energy carrier.The electrocatalytic nitrogen reduction reaction(NRR)can reduce energy input and carbon footprint;therefore,rational design of effective electrocatalysts is essential for achieving high-efficiency electrocatalytic NH_(3)synthesis.Herein,we report that the enzymatic mechanism is the more favourable pathway for NRR,due to lower limiting potential(-0.44 V),lower free energy(only 0.02 eV)of the first hydrogenation step(*N–N to*NH–N),and more electron transfer from Fe_(2)B_(2)to the reaction species.In addition,both vacancies and dopants can be helpful in reducing the reaction energy barrier of the potential-determining step.Therefore,we have demonstrated that Fe_(2)B_(2)is a potential new candidate for effective NRR and highlighted its potential for applications in electrocatalytic NH_(3)synthesis.

Measuring fine molecular structures with luminescence signal from an alternating current scanning tunneling microscope

In scanning tunneling microscopy-induced luminescence(STML),the photon count is measured to reflect single-molecule properties,e.g.,the first molecular excited state.The energy of the first excited state is typically shown by a rise of the photon count as a function of the bias voltage between the tip and the substrate.It remains a challenge to determine the precise rise position of the current due to possible experimental noise.In this work,we propose an alternating current version of STML to resolve the fine structures in the photon count measurement.The measured photon count and the current at the long-time limit show a sinusoidal oscillation.The zero-frequency component of the current shows knee points at the precise voltage as the fraction of the detuning between the molecular gap and the DC component of the bias voltage.We propose to measure the energy level with discontinuity of the first derivative of such a zero-frequency component.The current method will extend the application of STML in terms of measuring molecular properties.