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Niobium sulvanites Cu3NbX4 (X = S, Se) have been theoretically predicted as promising candidates for solar photovoltaics and photocatalytic water splitting. This report outlines the first synthesis of Cu3NbS4 and Cu3NbSe4 in a nanocrystalline form. The crystal structures were investigated by X-ray diffraction, identity was confirmed by Raman spectroscopy, and the optoelectronic properties and morphology of Cu3NbS4 and Cu3NbSe4 nanocrystals were examined by UV–vis spectroscopy and transmission electron microscopy, respectively. To gain insight into the Cu3NbX4 formation, a mechanistic study was conducted for Cu3NbSe4 monitoring the nanoparticles’ formation as a function of reaction time. Methylene blue photodegradation tests were conducted to evaluate the photoactivity of Cu3NbS4 and Cu3NbSe4. The degradation rates, 2.81 × 10–2 min–1 and 1.22 × 10–2 min–1 proved the photocatalysts’ potential of nanoscale Cu3NbX4. 

Abstract Two-dimensional (2D) ternary materials recently generated interest in optoelectronics and energy-related applications, alongside their binary counterparts. To date, only a few naturally occurring layered 2D ternary materials have been explored. The plethora of benefits owed to reduced dimensionality prompted exploration of expanding non-layered ternary chalcogenides into the 2D realm. This work presents a templating method that uses 2D transition metal dichalcogenides as initiators to be converted into the corresponding ternary chalcogenide upon addition of copper, via a solution-phase synthesis, conducted in high boiling point solvents. The process starts with preparation of VSe 2 nanosheets, which are next converted into Cu 3 VSe 4 sulvanite nanosheets (NSs) which retain the 2D geometry while presenting an X-ray diffraction pattern identical with the one for the bulk Cu 3 VSe 4 . Both the scanning electron microscopy and transmission microscopy electron microscopy show the presence of quasi-2D morphology. Recent studies of the sulfur-containing sulvanite Cu 3 VS 4 highlight the presence of an intermediate bandgap, associated with enhanced photovoltaic (PV) performance. The Cu 3 VSe 4 nanosheets reported herein exhibit multiple UV–Vis absorption peaks, related to the intermediate bandgaps similar to Cu 3 VS 4 and Cu 3 VSe 4 nanocrystals. To test the potential of Cu 3 VSe 4 NSs as an absorber for solar photovoltaic devices, Cu 3 VSe 4 NSs thin-films deposited on FTO were subjected to photoelectrochemical testing, showing p-type behavior and stable photocurrents of up to ~ 0.036 mA/cm 2 . The photocurrent shows a ninefold increase in comparison to reported performance of Cu 3 VSe 4 nanocrystals. This proves that quasi-2D sulvanite nanosheets are amenable to thin-film deposition and could show superior PV performance in comparison to nanocrystal thin-films. The obtained electrical impedance spectroscopy signal of the Cu 3 VSe 4  NSs-FTO based electrochemical cell fits an equivalent circuit with the circuit elements of solution resistance (R s ), charge-transfer resistance (R ct ), double-layer capacitance (C dl ), and Warburg impedance (W). The estimated charge transfer resistance value of 300 Ω cm 2 obtained from the Nyquist plot provides an insight into the rate of charge transfer on the electrode/electrolyte interface. 

Sulvanites have the parent formula Cu3MCh4. The metal M belongs to group 5 and Ch is a chalcogen. The tantalum sulvanites Cu3TaS4 and Cu3TaSe4 are predicted to have wide band gaps and p-type conductivity and show promise in optoelectronic applications. Their potential as p-type transparent conductors or efficient photocatalysts for visible-light water splitting is a valuable incentive to explore these materials in their nanoscale form, toward bottom-up processing opportunities. Reported herein are the first syntheses of nanosized Cu3TaS4 and Cu3TaSe4 sulvanites, which preserve the parent cubic crystal structure but show that morphology at the nanoscale is dependent of the reaction conditions. The two solution-based methods for synthesizing the tantalum S and Se sulvanites result in Cu3TaS4 or Cu3TaSe4 nanocrystals (NCs) with prismatic morphology, or, in the case of Cu3TaSe4, could lead to core-shell spherical nanostructures. The Cu3TaS4 NCs and Cu3TaSe4 NCs have good absorption in the UV-Vis region, while the Cu3TaSe4 core-shell NCs possess broad absorption bands not only in the UV-Vis but also in the near-infrared region. Photoluminescence measurements of Cu3TaS4 and Cu3TaSe4 reveal optical bandgaps of 2.54 and 2.32 eV, respectively, consistent with the values measured in bulk. Additionally, the current–voltage (I-V) curve of Cu3TaS4 NCs proves its electrical conductivity. 

The class of ternary copper chalcogenides Cu3MX4 (M = V, Nb, Ta; X = S, Se, Te), also known as the sulvanite family, has attracted attention in the past decade as featuring promising materials for optoelectronic devices, including solar photovoltaics. Experimental and theoretical studies of these semiconductors have provided much insight into their properties, both in bulk and at the nanoscale. The recent realization of sulvanites at the nanoscale opens new avenues for the compounds toward printable electronics. This review is aimed at the consideration of synthesis methods, relevant properties and the recent developments of the most important sulvanites.