Herein, we report the synthesis and characterization of Cu₃N nanocrystals using two single-source precursors, bis (pyrrole-2-carbalpropyliminato) Cu(ii) (PPC) and Cu(NO₃)₂·3H₂O.

Millions of people worldwide are affected by diabetes, a chronic disease that continuously grows due to abnormal glucose concentration levels present in the blood. Monitoring blood glucose concentrations is therefore an essential diabetes indicator to aid in the management of the disease. Enzymatic electrochemical glucose sensors presently account for the bulk of glucose sensors on the market. However, their disadvantages are that they are expensive and dependent on environmental conditions, hence affecting their performance and sensitivity. To meet the increasing demand, non-enzymatic glucose sensors based on chemically modified electrodes for the direct electrocatalytic oxidation of glucose are a good alternative to the costly enzymatic-based sensors currently on the market, and the research thereof continues to grow. Nanotechnology-based biosensors have been explored for their electronic and mechanical properties, resulting in enhanced biological signaling through the direct oxidation of glucose. Copper oxide and copper sulfide exhibit attractive attributes for sensor applications, due to their non-toxic nature, abundance, and unique properties. Thus, in this review, copper oxide and copper sulfide-based materials are evaluated based on their chemical structure, morphology, and fast electron mobility as suitable electrode materials for non-enzymatic glucose sensors. The review highlights the present challenges of non-enzymatic glucose sensors that have limited their deployment into the market.

Noble transition metal chalcogenide gold selenide is a relatively unexplored layered material. Herein, we report on the synthesis and characterization of polymorphic mixed-valence AuSe (Au¹⁺Au³⁺Se₂) by varying the sequence of the addition of the precursors in a colloidal synthesis. Despite the variations, all produced materials showed the co-existence of α- and β-AuSe. Although both polymorphs were observed, XRD showed that the addition of the gold precursor at higher temperatures resulted in α-AuSe being the dominant phase while the addition at lower temperatures resulted in β-AuSe being preferred. The crystal structures of both α- and β-AuSe consist of repeating units of a linearly bonded Au¹⁺ ion to two Se atoms and a Au³⁺ ion bonded to four Se atoms in a square planar geometry. The Au4f core level spectrum of XPS showed only the Au⁺¹ oxidation state, however, using the Se3d core level spectrum, the formation of AuSe (Au¹⁺Au³⁺Se₂) was evident. Using DFT calculations, the Raman spectra of α- and β-AuSe were simulated and only the square planar geometry was found to be Raman active. The square planar geometry (Au³⁺Se₄)⁻ ions belonging to the D_4h point group produced three Raman active vibrational modes, namely, a symmetric stretch (A_1g), a planar bend (B_1g) and an asymmetric stretch (B_2g) for α-AuSe as well as A_1g and B_1g for β-AuSe. Experimentally, all samples showed Raman vibrational lines from both phases. Moreover, Raman spectroscopy confirmed the presence of Au³⁺ in AuSe which was not detected using XPS. From the TEM and SEM results, it was evident that the morphologies of the predominantly α-AuSe samples were nanobelts while the predominantly β-AuSe samples showed plate-like structures. The predominantly α-AuSe samples showed a broad absorption band with a maximum at 853 nm while the predominantly β-AuSe samples showed evidence of absorption however with no defined excitonic peak.

Studies to improve the efficiency of dye-sensitized solar cells (DSSCs) include, but are not limited to, finding alternatives such as 2D layered materials as replacement counter electrodes (CEs) to the commonly used Pt. Herein, we report for the first time, the use of AuSe as a counter electrode for the reduction of triiodide ions (I₃ ⁻) to iodide ions (I⁻). The colloidal synthesis of gold selenide nanostructures produced α-AuSe and β-AuSe dominated products as determined by XRD. Electron microscopy showed α-AuSe having belt-like structures while β-AuSe had a plate-like morphology. EDS mapping confirmed the elemental composition and homogeneity of the AuSe CEs. Cyclic voltammetry curves of the AuSe CEs displayed the double set of reduction–oxidation peaks associated with the reactions in the I₃ ⁻/I⁻ electrolyte and therefore were comparable to the Pt CV curve. The α-AuSe CE showed better electrocatalytic activity with a reduction current of 6.1 mA than that of β-AuSe and Pt CEs, which were 4.2 mA and 4.8 mA, respectively. The peak-to-peak separation (ΔE_pp) for the α-AuSe CE was also more favourable with a value of 532 mV over that of the β-AuSe CE of 739 mV however, both values were larger than that of the Pt CE, which was found to be 468 mV. The EIS and Tafel plot data showed that α-AuSe had the best catalytic activity compared to β-AuSe and was comparable to Pt. The DSSC using α-AuSe as a CE had the highest PCE (6.94%) as compared to Pt (4.89%) and β-AuSe (3.47%). The lower efficiency for Pt was attributed to the poorer fill factor. With these novel results, α-AuSe is an excellent candidate to be used as an alternative CE to Pt in DSSCs.