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Photocatalytic water splitting converts solar energy to storable hydrogen molecules which has the highest energy per mass. Most catalysts for photocatalytic water splitting utilize noble metals or precious metals. Organic photocatalysts are attracting more attention owing to several advantages like light weight, low cost, defined structure and tunability. In this study, the synthesis of several dibenzo[b,f][1,5]- diazocines via microwave irradiation for water splitting application is reported. Microwave irradiation facilitates fast, safe and simple synthesis in green reaction conditions. Mini library of dibenzo[b,f][1,5]diazocines were created in order to understand substituents effect on the photocatalytic activity.

In this study, we propose dibenzo[b,f][1,5]diazocine/ZnO organic/inorganic hybrid photoanode for application in the photoelectrochemical water splitting. The electrode consisting of inorganic ZnO nanorod (ZnO NR) array structures and organic diazocine derivative film with or without platinum nanoparticle (Pt NP) cocatalyst was examined. The morphology characterization was performed by FESEM. UV-vis absorbance spectra showed enhanced absorbance in the visible light spectrum for the hybrid sample. Photoluminescence analysis of a hybrid sample showed a significant decrease in charge recombination and enhanced charge separation. Photoelectrochemical measurements revealed an increase in current density for the organic/inorganic hybrid photoanode reaching 1.256 mA/cm2 at 1.23 V vs. RHE which is almost two times higher than bare ZnO NR arrays (0.716 mA/cm2 at 1.23 V vs. RHE). The addition of the Pt NP cocatalyst further enhanced the photocurrent density up to 1.636 mA/cm2. Therefore, proposed organic/inorganic hybrid photoelectrode is a promising candidate for the efficient solar water splitting.

We prepared ZnO nanocomposites with WO3 or CuO nanostructures to improve the photocatalytic performance of ZnO nanostructures. Characterization of the nanocomposites using scanning electron microscopy, x-ray diffraction, UV–vis spectrometry and photoluminescence revealed the morphologies and wide light absorption range of the materials. The highest current densities of WO3/ZnO and CuO/ZnO nanocomposites were 1.28 mA cm−2 and 2.49 mA cm−2 at 1.23 V (versus a reversible hydrogen electrode) under AM 1.5 100 mW cm−2, which are ~1.2- and 3.5-fold greater than those of bare ZnO nanostructures, respectively. The easy fabrication process suggests that nanocomposites with narrow bandgap materials, such as WO3 and CuO, will improve the performance of electrochemical and optoelectrical devices such as dye-sensitized solar cells and biosensors.

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