## 3 Synthesis of Transition-Metal-Sulfide-Based Nanomaterials
### Solvothermal Processes  
Solvothermal processes are typically used in two distinct cases, when the starting materials are reactive in water or very oxyphilic, such as titanium or vanadium chlorides or other high oxidation state transition metals; these materials can be used as the starting TM in the solvothermal process, which can react to give the metal oxide or hydroxide. Alternatively, when the synthesis temperature cannot be achieved using water, due to pressure constraints or temperature constraints of the reaction vessels, then alternative methods should be used to form the product. Large organic molecules give the advantage of high boiling points with low vapor pressure. An example of the limitation of water as a solvent at temperature is that, when heated to 300 \({}^{\circ}\)C it has a vapor pressure of 85 atm, and after heating to 360 \({}^{\circ}\)C water has a vapor pressure of approximately 184 atm. The vapor pressure of water becomes a limiting factor and alterative solvents are to be explored for high temperature syntheses. In addition, the solvothermal process allows for the control of the phase, particle size, and morphology [124; 125; 126; 127; 128; 129; 130; 131; 132; 133; 134; 135].  
Titanium sulfide nanomaterials have been synthesized using solvothermal processes using titanium tetrachloride with elemental sulfur in 1-octadec at 300 \({}^{\circ}\)C in one hour of reaction [124]. Nickel sulfides in the pyrite phase, NiS\({}_{2}\) and NiS, were successfully synthesized using the solvothermal process using ethanol and ethylenediamine as solvents, respectively [125; 126].  
Many of the iron sulfides have been synthesized using solvothermal processes, for example, [PERSON] and [PERSON] synthesized iron sulfide nanowires using ethylenediamine as the solvent at 180 \({}^{\circ}\)C for 12 h [127]. [PERSON] et al. used a mixture of ethylene glycol and water to synthesize an Fe\({}_{7}\)S\({}_{8}\) nanomaterial at 180 \({}^{\circ}\)C in 1 h [128]. [PERSON] et al. used solvothermal processes for the controlled synthesis of pyrite in ethylenediamine at 130 \({}^{\circ}\)C [129]. [PERSON] and [PERSON] et al. showed the successful synthesis of Fe\({}_{5}\)S\({}_{4}\) using ethylene glycol with iron(III) chloride and thiourea at 180 \({}^{\circ}\)C [130]. Copper sulfides and MnS\({}_{2}\) were successfully synthesized using solvothermal processes with ethanol as the solvent and thioacetamide as the sulfiding agent [131]. [PERSON] et al. have used ethylenediamine as the solvent at a temperature 130 \({}^{\circ}\)C for 12 h and phase-pure Cu\({}_{2}\)S was synthesized, which showed a dendritic-type structure [132]. While the region at 130 \({}^{\circ}\)C for 4-8 h showed a similar type of morphology. The study showed that heating the reaction mixture for 8 h at 130 \({}^{\circ}\)C resulted in Cu\({}_{31}\)S\({}_{16}\). [PERSON] et al. used a solvothermal process which resulted in 1T-2H MoS\({}_{2}\) nanoflowers with defects [133]. The authors used ammonium thiocyanate as the sulfursource and ammonium molybate with a mixture of ethane/water/glycerin as the solvent. [PERSON] et al. performed solvothermal syntheses using ethylenediamine and dodecanthiol to form CdS nanowires [134]. The authors successfully synthesized CdS nanowires at 180 \({}^{\circ}\)C, with diameters of 25 nm and lengths into the \(\upmu\)m ranges, which showed controlled synthesis of CdS nanomaterials. [PERSON] et al. on the other hand, synthesized nanosized CoMoS\({}_{2}\) doped with La ions for the desulfurization of fuels [135]. The authors prepared a CoMoS\({}_{4}\) precursor which was doped with different amounts of La ions to replace Co atoms from 5 to 25%. The precursor was converted to the sulfide in decalin at 350 \({}^{\circ}\)C in a sealed autoclave reactor. The catalysts showed high activity and some resistance to carbonization.