Facile one-pot low-temperature solid-state approach towards phase transformation of nanoCdS

Nanocadmium sulphide (CdS) has been prepared by the one-pot solid-state method from cadmium chloride (CdCl₂) and sodium sulphide (Na₂S) without any capping agent. The grinding period plays a major role in transforming CdS from the cubic (zinc blende) to the hexagonal (wurtzite) phase, hitherto unreported at the lowest temperature of 200°C by the solid-state approach. The compounds are characterised by powder X-ray diffraction, UV-visible absorption spectroscopy, scanning electron microscopy and high resolution transmission electron microscopy techniques. On the basis of the results, it has been observed that with only grinding and without subsequent heat treatment, the compounds named with their grinding period as subscript have either zinc blende - CdS_{(30 min)} or mixed zinc blende/wurtzite - CdS_{(2,4, 6 and 8 h)} structures. However, when subjected to heat treatment at 200°C, there is a complete phase transformation to the wurtzite structure achieved only with the CdS_{(8 h)} compound, while the rest of the compounds show similar phases as the compounds prepared without annealing. The photocatalytic efficiency of CdS compounds on methyl orange follows the order, CdS_(cubic)> CdS_{(mixed phase → cubic + hexagonal)}> CdS_(hexagonal), with cubic phase CdS showing greater efficiency than mixed and hexagonal phases.