Against the backdrop of the COVID-19 outbreak, an emergency policy initiative called "Suspending Classes Without Stopping Learning" was launched by the Chinese government to continue teaching ...activities as schools across the country were closed to contain the virus. However, there is ambiguity and disagreement about what to teach, how to teach, the workload of teachers and students, the teaching environment, and the implications for education equity. Possible difficulties that the policy faces include: the weakness of the online teaching infrastructure, the inexperience of teachers (including unequal learning outcomes caused by teachers' varied experience), the information gap, the complex environment at home, and so forth. To tackle the problems, we suggest that the government needs to further promote the construction of the educational information superhighway, consider equipping teachers and students with standardized home-based teaching/learning equipment, conduct online teacher training, include the development of massive online education in the national strategic plan, and support academic research into online education, especially education to help students with online learning difficulties.
The novel ternary Fe3N/Fe2O3/C3N4 photocatalyst was prepared by thermal pyrolysis of potassium ferricyanide in melamine. The structural, morphological and physico-chemical properties of the ...photocatalyst were characterized by a multi-technique approach. Photocatalytic experiments supported that 0.04 g of the photocatalyst was able to totally remove 5 ppm of rhodamine B (RhB) solution under acidic condition with the rate constant of 0.1 min−1 in less than 30 min. According to spin-trapping ESR analysis, •OH radicals play a key role in the RhB photodegradation implying Z-scheme mechanism is applicable to our system. Moreover, the evolution rate of CO and CH4 over the photocatalyst was 8.03 and 1.6 μmol g−1 h−1, respectively, which was much higher than the reference photocatalysts under the same conditions. The enhanced photocatalytic performance of this system is attributed to the unique ternary heterojunction between the interfaces of g-C3N4, Fe3N and Fe2O3, which effectively suppressed the charge carriers recombination.
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•A novel ternary Fe3N/Fe2O3/C3N4 photocatalyst was prepared from cheap raw materials.•The interfacial Fe3N regions act as electron mediator and bandgap modifier.•The mechanism of RhB photodegradation was well discussed based on EPR experiments.•The ternary Fe3N/Fe2O3/C3N4 photocatalyst showed efficient photocatalytic CH4 evolution performance.
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•Size-selected Pt modified g-C3N4 was fabricated by in-situ photoreduction method.•Pt0.1-CN with single-atom Pt shows pronounced photocatalytic hydrogen evolution.•Pt0.1-CN exhibits ...H2 generation up to 473.82 µmol mg−1 pt under visible light.•Enhanced performance is due to the synergistic effect of Pt single-atom.
Graphitic carbon nitride (g-C3N4) with Pt co-catalyst was synthesized by in-situ photoreduction and used as a visible light photocatalyst. The size of Pt co-catalyst can be controlled form single atoms to nano-clusters by the induced amount of Pt precursor. The results indicated that compared with nano-clusters, the Pt0.1-CN (with 0.1 wt% Pt loading amount) which is characterized as single-atom Pt exhibits a pronounced photocatalytic hydrogen evolution capability. For Pt0.1-CN with single-atom Pt as co-catalyst, the H2 generation is up to 473.82 µmol mg−1pt under visible light irradiation (λ > 420 nm). The enhanced photocatalytic performance is mainly attributed to the synergistic effect of high light adsorption efficiency, effective charge separation, and high dispersed active sites of Pt atoms. The results of this work highlighted that loading g-C3N4 with Pt single atoms will achieve a maximum utilization efficiency of Pt atoms and an improvement photocatalytic performance.
Current plasmonic photocatalysts are mainly based on noble metal nanoparticles and rarely work in the infrared (IR) light range. Herein, cost‐effective Bi2O3−x with oxygen vacancies was formed in ...situ on commercial bismuth powder by calcination at 453.15 K in atmosphere. Interestingly, defects introduced into Bi2O3−x simultaneously induced a localized surface plasmon resonance (LSPR) in the wavelength range of 600–1400 nm and enhanced the adsorption for CO2 molecules, which enabled efficient photocatalysis of CO2‐to‐CO (ca. 100 % selectivity) even under low‐intensity near‐IR light irradiation. Significantly, the apparent quantum yield for CO evolution at 940 nm reached 0.113 %, which is approximately 4 times that found at 450 nm. We also showed that the unique LSPR allows for the realization of a nearly linear dependence of photocatalytic CO production rate on light intensity and operating temperature. Finally, based on an IR spectroscopy study, an oxygen‐vacancy induced Mars‐van Krevlen mechanism was proposed to understand the CO2 reduction reactions.
Bifunctional oxygen defects were created on noble‐metal‐free Bi2O3−x, which enables noble‐metal‐like localized surface plasmon resonance and enhanced CO2 adsorption properties. As a result, photocatalytic CO2‐to‐CO conversion with approximately 100 % selectivity was realized even under low‐intensity light at 940 nm, showing a quantum efficiency of 0.113 % that is 4.0 times of that at 450 nm.
Abstract
Achieving CO
2
reduction with H
2
O on metal photocatalysts and understanding the corresponding mechanisms at the molecular level are challenging. Herein, we report that quantum-sized Au ...nanoparticles can photocatalytically reduce CO
2
to CO with the help of H
2
O by electron-hole pairs mainly originating from interband transitions. Notably, the Au photocatalyst shows a CO production rate of 4.73 mmol g
−1
h
−1
(~100% selectivity), ~2.5 times the rate during CO
2
reduction with H
2
under the same experimental conditions, under low-intensity irradiation at 420 nm. Theoretical and experimental studies reveal that the increased activity is induced by surface Au–O species formed from H
2
O decomposition, which synchronously optimizes the rate-determining steps in the CO
2
reduction and H
2
O oxidation reactions, lowers the energy barriers for the *CO desorption and *OOH formation, and facilitates CO and O
2
production. Our findings provide an in-depth mechanistic understanding for designing active metal photocatalysts for efficient CO
2
reduction with H
2
O.
Photocatalytic materials for photocatalysis is recently proposed as a promising strategy to address environmental remediation. Metal-free graphitic carbon nitride (g-C3N4), is an emerging ...photocatalyst in sulfate radical based advanced oxidation processes. The solar-driven electronic excitations in g-C3N4 are capable of peroxo (O‒O) bond dissociation in peroxymonosulfate/peroxydisulfate (PMS/PDS) and oxidants to generate reactive free radicals, namely SO4•− and OH• in addition to O2•− radical. The synergistic mechanism of g-C3N4 mediated PMS/PDS photocatalytic activation, could ensure the generation of OH• radicals to overcome the low reductive potential of g-C3N4 and fastens the degradation reaction rate. This article reviews recent work on heterojunction formation (type-II heterojunction and direct Z-scheme) to achieve the bandgap for extended visible light absorption and improved charge carrier separation for efficient photocatalytic efficiency. Focus is placed on the fundamental mechanistic routes followed for PMS/PDS photocatalytic activation over g-C3N4-based photocatalysts. A particular emphasis is given to the factors influencing the PMS/PDS photocatalytic activation mechanism and the contribution of SO4•− and OH• radicals that are not thoroughly investigated and require further studies. Concluding perspectives on the challenges and opportunities to design highly efficient persulfate-activated g-C3N4 based photocatalysts toward environmental remediation are also intensively highlighted.
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•Advantages of peroxymonosulfate/peroxydisulfate (PMS/PDS) photocatalytic activation are mentioned.•The synergistic heterojunction effect on PMS/PDS over g-C3N4-based photocatalysts is evaluated.•The role of sulfate (SO4•−) radicals for pollutant degradation application are elaborated.•Challenges and future prospects of the photocatalytic activation PMS/PDS are proposed.
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–BrX, X = 5, 10, 20, 30), where X is a percentage mole ratio of NH4Br 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–BrX (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.
Br-doped g-C3N4 exhibits improved photocatalytic activity for Cr(VI) reduction under visible light irradiation. The Br element was intercalated into g-C3N4 to form C-Br bonds, and photogenerated e−,•OH, and H2O2 play important roles in Cr(VI) reduction.
Photoreduction of N2 is among the most interesting and challenging methods for N2 fixation under mild conditions. In this study, we determined that nitrogen vacancies (NVs) could endow graphitic ...carbon nitride (g-C3N4) with the photocatalytic N2 fixation ability. Photocatalytic N2 fixation induced by NVs is free from the interference of other gases. The reason is that NVs could selectively adsorb and activate N2 because NVs have the same shape and size as the nitrogen atom in N2. In addition to this, NVs could also improve many other properties of g-C3N4 to support photocatalytic N2 fixation. These new findings could elucidate the design of efficient photocatalysts for photocatalytic N2 fixation.
Inspired by natural photosynthesis, a new series of Z-scheme CdxZn1-xS/Au/g-C3N4 photocatalysts were synthesized via depositing Au particles on g-C3N4, followed by anchoring CdxZnl xS solid solution ...on the pre-formed Au/g-C3N4 for photocatalytic hydrogen evolution. Their structure, morphology and optical property were investigated in detail. Photocatalytic activities of the developed photocatalysts for water splitting were evaluated under visible-light irradiation （2 〉 420 nm） using glucose as electron donor. The highest hydrogen evolution rate of 123 μmol g^-1 h^-1 is achieved by Cdo.sZno.2S/Au/g-C3N4, which is 52.2 and 8.63 times higher than that of Au/g-C3N4 and CdS/Au/g-C3N4, respectively. The results of pho- toluminescence spectra, photoelectrochemical and time-resolved photoluminescence spectra indicate that the improved photocatalytic activities for CdxZn1-xSAu/g-C3N4 are due to the efficient separation of photogenerated carriers. In addition, it is noteworthy that the undesired byproducts CO and CO2 are greatly reduced by introducing CdxZn1-xS over Au/g-C3N4 surface. In the photocatalytic process, gluconic acid originated from the reaction of photogenerated hydroxyl radical with glucose plays a vital role on suppressing the formation of the gas byproducts. The present work will provide a new strategy to design Z-scheme photocatalysts with enhanced efficiency for water splitting along with suppressing the byproducts.
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