## 7 Synthesis of Two-Dimensional SnS
have synthesised SnS nanosheets with large lateral sizes of 5 \(\upmu\)m to 20 \(\upmu\)m and thicknesses of 100 nm with no impurities. The reaction involved the addition of octadecene into an aqueous SnCl\({}_{4}\).5H\({}_{2}\)O solution in a three-necked flask. This was degassed and heated to 130 \({}^{\circ}\)C before being heated to 280 \({}^{\circ}\)C, followed by the addition of S in oleylamine, and was then maintained at 280 \({}^{\circ}\)C for 30 min. This was then centrifuged and purified via washing in ethanol and cyclohexane. The SnS produced was used for ethanol sensing [117]. [PERSON] et al. have synthesised SnS nanosheets for a reduced graphene oxide (rGO)-SnS composite. The SnS nanosheets were synthesised onto rGO prepared via the Hummers method. The rGO in ethanol dispersion had tin(II) acetate and thioacetamide added before stirring and sonication. The mixture was then added to an SUS 316 reactor and heated in a molten salt bath for 10 min at 400 \({}^{\circ}\)C. The samples were then cooled and washed. The bare SnS produced had a thickness of 100 nm with lateral sizes of 0.5-2 \(\upmu\)m. Smaller, irregular nanosheets with lateral sizes around 100 nm were obtained for high precursor concentrations. The two sizes of SnS produced were due to the differing homogeneous and heterogeneous nucleation mechanisms. The smaller SnS produced by heterogenous nucleation occurred on the basal plane of graphene oxide, with the larger SnS nanosheets being produced in the fluid phase via homogeneous nucleation [118]. Hot injection synthesis methods are useful, because one can precisely control the size, shape, and composition by controlling synthesis conditions including reaction time and temperature, solvent, precursor types, and concentrations. The main parameters, which have to be controlled during nanocrystal synthesis, are size (emission colour), size dispersion (photoluminescence line width), and surface passivation (photoluminescence quantum yield, PLQY). Surface ligands play a very important role in tuning nanocrystal properties such as processability, reactivity, and stability. They also help to prevent nanocrystal agglomeration and facilitate the dispersion in a variety of solvents but deteriorate the performance of solar cells. [PERSON] et al. have synthesised SnS nanocrystals of different dimensions (0D, 1D, and 2D) using a facile colloidal route and studied their photoelectrochemical performance. A hot-injection method was used to synthesise 0D SnS nanoparticles (NPs), whilst a temperature-controlled cool-injection method was used to fabricate 1D SnS nanorods (NRs) and 2D SnS NSs. It was found that the order of injection of 1-Dodecanethiol (DDT) and thioacetamide is crucial to control the dimension of SnS nanocrystals. In the cool-injected method, the pre-injected thioacetamide not only served as a S source to form SnS seeds, but also coordinates to the tin centre to form Sn(I18 hioinidate, favouring the anisotropic growth of SnS NRs and NSs (Figure 10) [119]. [PERSON] et al. have reported the colloidal synthesis of different shaped SnS compounds, including nanosheets, and studied their photocatalytic degradation behaviour with methylene blue (MB). In-depth crystallographic analysis was performed on as-obtained SnS systems. For nanosheet synthesis, tin acetate, oleylamine, and sulfur were used with the reaction occurring in a three-necked flask at 180 \({}^{\circ}\)C. The nanosheets produced were of the order of 270 nm lateral size. Kubelka-Munck functions determined the SnS nanosheets to have an indirect and direct band gap of 1.1 eV and 1.3 eV, respectively [120]. [PERSON] et al. have reported a new synthetic method for the synthesis of well-calibrated square SnS nanoplatelets showing comparable small dimensions--thickness 4-15 nm and edge length 15-100 nm--where oleylamine, trioctylphosphine and oleic acid are used as ligands. A long-term colloidal stability (several years in chloroform) was observed.