Facile synthesis of NiS2 nanoparticles ingrained in a sulfur-doped carbon nitride framework with enhanced visible light photocatalytic activity: two functional roles of thiourea

Abstract

A one-step, simple and low-cost strategy toward production of novel NiS₂/S-doped g-C₃N₄ (NiS₂/CNS) composites was successfully accomplished. The hybrid photocatalyst materials with different amounts of NiS₂ nanoparticles (NPs) were successfully in situ synthesized via thermal condensation of a mixture containing thiourea and nickel(II) nitrate. Interestingly, thiourea showed two very important roles: (i) thiourea not only acted as a precursor to in situ produce sulfur-doped carbon nitride materials, but also (ii) the sulfur atmosphere that originated from polycondensation of thiourea provided a sulfur source for in situ production of NiS₂ nanoparticles as a non-noble metal sulfide on the CNS sheets during the synthesis. Density functional theory (DFT) computations were carried out to estimate the preferred position of S atoms within the backbone of the CNS framework as well as to compare the band gaps and partial density of states (PDOS) spectra. The NiS₂ NPs ingrained in the CNS phase increased the efficient charge transport via a heterojunction interface and obviously decreased the recombination of electron–hole pairs evidenced by photoelectrochemical and photoluminescence measurements. Moreover, the band structures of NiS₂ as a Mott insulator were studied through electrochemical methods. It was also found that the optimal NiS₂ loading value in the NiS₂/CNS composites was 5.9 wt% having a reaction rate constant equal to 0.011 min⁻¹, which was about 3.1 and 26.1 times faster compared with those of the CNS (0.0035 min⁻¹) and bulk g-C₃N₄ (0.00042 min⁻¹) toward degradation of Rhodamine B (RhB) under visible light irradiation. The optimized photocatalyst was capable of showing a high efficiency for phenol photodegradation as a light insensitive pollutant. Hence, the synergistic effects originating from combining sulfur doping and in situ growing of NiS₂ NPs in one material enhanced the physicochemical properties of carbon nitride materials. Our results might offer new insight into the cost-effective and simple designing of a photocatalyst using a bi-functional precursor such as thiourea so that it could easily be used on a large scale and even in industrial catalyst production.