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A treatment of graphitic carbon nitride (GCN) with concentrated nitric acid imparts GCN with the photocatalytic activity in hydrogen evolution from aqueous solutions of hydrazine hydrate, unsymmetric dimethylhydrazine (DMH) and hydrazinium sulfate under illumination with the UV light and in the presence of a Pd/SiO 2 co-catalyst. The rate of photocatalytic water reduction was found to be maximal in the presence of 3–5 M DMH and 12–14 M hydrazine hydrate and comparable to the hydrogen evolution rate in similar systems based on TiO 2 Evonik P25. The X-ray photoelectron spectroscopy of the activated GCN revealed that the acid treatment results in the elimination of some of the nitrogen atoms in the heptazine building blocks of the GCN and formation of carboxylic groups, the modification extent increasing with an increase of both duration of the acid treatment and the GCN synthesis temperature. The activation effect observed after the acid treatment of the GCN is assumed to originate from the participation of the introduced defects in the trapping and interfacial transfer of the photogenerated charge carriers. The maximal photoactivity was observed for the activated GCN produced at 500 °C followed by a 2-h contact with the concentrated HNO 3 .

Nanocrystalline FTO/ZnO/ZnSe were prepared from electrodeposited zinc oxide films and then converted into FTO/ZnO/CuSe heterostructures via complete substitution of zinc(II) in zinc selenide by copper(II). The starting FTO/ZnO films contain a 5–6-μm layer of porous zinc oxide microplatelets with the lateral size of up to 3 μm and the thickness of up to 200 nm which are formed by loosely aggregated ZnO nanocrystals. Partial conversion of such films into ZnSe and CuSe does not induce considerable changes in the film morphology allowing to use the FTO/ZnO films as a template defining the morphology and composition of resulting FTO/ZnO/ZnSe and FTO/ZnO/CuSe films. The FTO/ZnO/ZnSe heterostructures were found to be efficient photoanodes of model liquid-junction solar cells with sulfide/polysulfide redox-couple under illumination with white light ( λ > 400 nm). The activity of FTO/ZnO/CuSe heterostructures as cathodes of such solar cells was demonstrated for the first time. A two-electrode solar cell based on the FTO/ZnO/ZnSe photoanode and the FTO/ZnO/CuSe cathode generates by an order of magnitude higher photocurrent density as compared with a similar cell based on a Pt foil cathode.