Photocatalytic H2 evolution using particulate semiconductors is a potentially scalable and economically feasible technology to utilize solar energy. A wide absorption range, long-term stability, high charge-separation efficiency and strong redox ability are the key features for ideal H2 evolution photocatalyst. Composited photocatalytic systems are more favorable to improve the charge separation, and our work has been focused on the C3N4-W18O49 composite for visible-light-responsive H2 evolution semiconductor and the latter is a good visible-light-responsive oxidative semiconductor [1-6].
We tuned the morphology of W18O49 by the structure-directing role of solvent to improve the activity and stability [1-3]. Urchin- and nanowire-like W18O49 are prepared by using ethanol and n-propanol as solvent, and interestingly, when acetic acid is used as solvent and structure-directing agent, uniform porous W18O49 with hollow architecture is synthesized. The spheres exhibit enhanced light harvesting, high surface area and adsorption capability, and thus are most active in photocatalysis compared with other two morphologies.
We fabricated g-C3N4 with simultaneous novel porous network and controllable O-doping[4,5]. First melamine was pre-treated with H2O2 or hydrothermal treatment to form hydrogen bond-induced supramolecular aggregates, then g-C3N4 was obtained upon calcinations. O doping preferentially occurs on two-coordinated N position, and the porous network and O-doping synergistically promote the light harvesting and charge separation. So g-C3N4 synthesized from H2O2-treated and hydrothermal melamine shows 6.1 and 11.3 times HER activity than bulk g-C3N4.
We further demonstrated that C3N4-W18O49, the type-II composite, can be switched to direct Z-scheme via modulating the interfacial band bending . Adsorption of triethanolamine (TEOA) on C3N4 surface significantly uplifts its Femi level, inverses the continuous interfacial band bending to interrupted one, and thus switches the composite from type-II to Z-scheme, without the assistance of any electron shuttles. The Z-scheme C3N4/W18O49 composites exhibit superior H2 production compared with pure C3N4, and reaction rate of 8597 μmol h-1 g-1 (AQY of 39.1% at 420 nm) with Pt as cocatalyst and TEOA as hole scavenger .
1. Z.-F. Huang, J. J. Song, L. Pan, X. W. Zhang, L. Wang, J.-J. Zou, Adv. Mater. 27 (2015) 5309-5327.
2. Z.-F. Huang, J. J. Song, L. Pan, F. Lv, Q. Wang, J.-J. Zou, X.W. Zhang, L. Wang, Chem. Commun. 50 (2014) 10959-10962.
3. Z.-F. Huang, J.-J. Zou, L. Pan, S. Wang, X. W. Zhang, L. Wang, Appl. Catal. B: Environ. 147 (2014) 167-174.
4. Z.-F. Huang, J. J. Song, L. Pan, Z. Wang, X. Q. Zhang, J.-J. Zou, W. B. Mi, X. W. Zhang, L. Wang, Nano Energy 12 (2015) 646-656.
5. J.-W. Zhang, S. Gong, N. Mahmood, L. Pan, X. W. Zhang, J.-J. Zou, Appl. Catal. B: Environ. 221 (2018) 9-16.
6. Z.-F. Huang, J. J. Song, X. Wang, L. Pan, K. Li, X. W. Zhang, L. Wang, J.-J. Zou, Nano Energy (40) 2017 308-316.