Complexes of SCN and dithiol ligands for solvothermal green synthesis of high indexed binary PbS and SnS semiconductor nanoparticles

Binary PbS and SnS nanoparticles have dominated materials chemistry research due to their optical and photocatalytic potentials. Hence, in this work, (E)-2-(1-(2-oxo-2h-chromen-3-yl) ethylidene) hydrazinecarbothioamide [H₃L³] was prepared by the reaction of an intermediate (3-acetylcoumarin) formed by cycloaddition and cyclocondensation of ethyl acetoacetate and salicyaldehyde with thiosemicarbazide in ethanol. The metal complexes were then successfully synthesised in ethanolic solution of N, N′-dicyclohexyldithiooxamide and [H₂L²] with the corresponding Pb(II) and Sn(II) salts. The products obtained were characterized by FT-IR spectroscopy and micro elemental analysis. IR frequencies of the corresponding complexes show significant shifts from the absorption frequencies of the ligand at 1721.31 cm⁻¹ (CO), 1671.72 cm⁻¹ (CN), 1282.00 cm⁻¹ (CS) and 1721.31 (CO), 1673.30 (CN), and 1281.30 (CS) due to coordination to Pb²⁺ or Sn²⁺, respectively. Thermogravimetric analysis indicated weight loss of about 60 %, subdivided into two weight loss stages: the first stage occurred in the temperature range 150–300 °C, accounting for 42 % loss related to the removal of hydrazinecarbothioamide derivative ligand, while the second occurred between 300 and 400 °C, 18 % weight loss accounting for the dicyclohexyl derivative. PbS and SnS nanoparticles were equally synthesised from their precursors metal complexes through solvothermal decomposition at 200, 240 and 250 °C in oleylamine and dodecanethiol. P-XRD, SEM-EDX, TEM and HRTEM were used to characterise the resulting stable nanoparticles. Pure cubic crystal phase of PbS NPs (galena) with a space group of F m −3 m and orthorhombic SnS NPs (Herzenbergite) with P b n m space group were obtained. The crystallite sizes varied with temperature, as the average diameter for PbS nanoparticles ranged from 16.34 nm to 19.34 nm, while the particle size varied from 21.30 to 38.00 nm. Similarly, the orthorhombic SnS NPs obtained have crystallite size ranging from 13.15 to 22.91 nm, while the agglomerated nanoparticles measured an average of 52.14 nm at 200 °C, and a triangular shape of 498.88 nm was formed at 240 °C. The energy bandgaps and optical emission of the PbS and SnS nanocrystals were found to be 2.18 eV (570.98 nm) and 2.32 eV (544.63 nm), respectively. These values are within the optimum range for photovoltaic applications.