The Ti3+ self-doping B-TiO2/g-C3N4 hollow core-shell nano-heterojunction is synthesized via the continuous hydrothermal deposition and sculpture-reduction processes. The results of SEM, XRD, TEM, XPS and FT-IR imply that the B-TiO2/g-C3N4 hollow core-shell nanospheres have been prepared successfully. The photocatalytic activity of the B-TiO2/g-C3N4 nano-heterojunctions remarkably exhibits an enhancement of 18 times and 65 times than that of normal TiO2 and g-C3N4, respectively. Further, the photocatalytic process and the mechanism of the photocatalytic hydrogen production enhancement have been studied, which could be ascribed to the Ov-Ti3+ in the B-TiO2 and interface nano-heterojunction, that have been proved by the transient photocurrent, PL, EIS and Mott-Schottky plots.

The enhancement of photocatalytic hydrogen production via Ti3+ self-doping black TiO2/g-C3N4 hollow core-shell nano-heterojunction

A A novel three-dimensional microspheres mediator-free Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst was successfully obtained for the first time. The photocatalytic performance of the as-prepared photocatalyst was systematically examined via the photocatalytic reduction of Cr6+ and oxidation of Bisphenol S under visible-light irradiation. Among these samples, 0.24-Ag3VO4/BiVO4 exhibits the highest photocatalytic performances, the photocatalytic reduction and oxidation efficiency of 74.9 and 94.8%, respectively, can be achieved. The enhanced photocatalytic performance is attributed to the build-in electric field assisted charge transfer between the Ag3VO4 and BiVO4, and the increasing lifetime of the charge carrier confirmed by the results of time-resolved fluorescence spectra and photoelectrochemical measures. Moreover, based on the results of free radical scavenging activity test, and EPR experiments, it has been verified that the Ag3VO4/BiVO4 heterostructures follow a typical Z-scheme charge transfer mechanism rather than conventional type-II heterojunction charge transfer mechanism. Furthermore, the theoretical understanding of the underlying mechanism was also supported, while the energy band structure, and Fermi level were systematically calculated using the density functional theory approach. The results show that a built-in electric field directed from Ag3VO4 to BiVO4 surface was established as an equalized Fermi level was reached, which benefits the separation of photogenerated charge carriers in the way of a Z-scheme charge transfer mechanism. The strategy to form the three-dimensional microspheres Z-scheme heterojunction photocatalyst may offer new insight into the Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.

A novel Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst: study on the excellent photocatalytic performance and photocatalytic mechanism

Fabrication of ternary Ag3PO4/Co3(PO4)2/g-C3N4 heterostructure with following Type II and Z-Scheme dual pathways for enhanced visible-light photocatalytic activity

We herein demonstrate the unusual effectiveness of two strategies in combination to enhance photoelectrochemical water splitting. First, the work function adjustment via molybdenum (Mo) doping significantly reduces the interfacial energy loss and increases the open-circuit photovoltage of bismuth vanadate (BiVO4) photoelectrochemical cells. Second, the creation and optimization of the heterojunction of boron (B) doping carbon nitride (C3N4) and Mo doping BiVO4 to enforce directional charge transfer, accomplished by work function adjustment via B doping for C3N4, substantially boost the charge separation of photo-generated electron-hole pairs at the B-C3N4 and Mo-BiVO4 interface. The synergy between the above efforts have significantly reduced the onset potential, and enhanced charge separation and optical properties of the BiVO4-based photoanode, culminating in achieving a record applied bias photon-to-current efficiency of 2.67% at 0.54 V vs. the reversible hydrogen electrode. This work sheds light on designing and fabricating the semiconductor structures for the next-generation photoelectrodes. While photoelectrodes represent a promising solar-to-fuel conversion technology, material challenges limit performances. Here, authors improve the onset potential and charge separation of bismuth vanadate photoanode water splitting performances by work function tuning and heterojunction engineering.

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Enhancing photoelectrochemical water splitting by combining work function tuning and heterojunction engineering.

Graphitic carbon nitride (g-C3N4) has emerged as one of the most promising photocatalysts due to its metal-free nature, abundance of raw material, and thermal physical–chemical stability. The breakthrough research studies in recent years have mostly been concentrated on the engineering of the intrinsic and morphological properties of g-C3N4-based photocatalysts in the framework of powder suspensions for artificial photosynthesis and environmental remediation. However, practical applications of g-C3N4-based electrodes and devices are still in the early stages of development due to challenging fabrication methods of g-C3N4 thin films. This review addresses the classification of diverse techniques to deposit g-C3N4-based thin films and explores a broad spectrum of applications pertinent to g-C3N4-based electrodes. Although this paper is principally focused on photoelectrochemical water splitting, other emerging applications of g-C3N4 in solar cells, electrocatalysts and supercapacitors are also reviewed. Lastly, further suggestions are posited for other potential applications, challenges and future orientations.

Graphitic carbon nitride (g-C3N4) electrodes for energy conversion and storage: a review on photoelectrochemical water splitting, solar cells and supercapacitors

BiVO4 is a considerably promising semiconductor for photoelectrochemical water splitting due to its stability, low cost and moderate band gap. In this research, g-C3N4 was proposed in Z-scheme configuration which boosted the performance of BiVO4 up to four times. The experimental observations were counterchecked with Density Functional Theory (DFT) simulations. A TiO2/BiVO4 heterojunction was developed and its performance was compared with that of g-C3N4/BiVO4. The photocurrent for g-C3N4/BiVO4 was 0.42 mAcm−2 at 1.23 V vs. RHE which was the highest among g-C3N4 based Z-scheme heterojunction devices. Lower charge transfer resistance, higher light absorption and more oxygen vacancy sites were observed for the g-C3N4 based heterojunction. The simulated results attested that g-C3N4 and BiVO4 formed a van der Waals type heterojunction, where an internal electric ﬁeld facilitated the separation of electron/hole pair at g-C3N4/BiVO4 interface which further restrained the carrier recombination. Both the valence and conduction band edge positions of g-C3N4 and BiVO4 changed with the Fermi energy level. The resulted heterojunction had small effective masses of electrons (0.01 me) and holes (0.10 me) with ideal band edge positions where both CBM and VBM were well above and below the redox potential of water.

Mohd Fairus Soh

Papers

Enhanced photoelectrochemical performance of Z-scheme g-C3N4/BiVO4 photocatalyst