Copper Sulfate Pentahydrate

Preetha N et al. successfully cultivated an 80*13 square millimetre sized single crystal of copper sulphate pentahydrate (CSPH), in 60 days using the Sankaranarayanan-Ramasamy unidirectional method. UV-Vis-NIR spectroscopy revealed a transmission of 79% at 435 nm and the presence of a sharp band-pass window centred at 280-580 nm which demonstrated its application as UV order-sorting filters. The results of powder XRD showed an average crystallite size of 16 nm and a crystallinity of 41% while EDAX proved the expected Cu:S:O stoichiometry. Photoluminescence spectra excited at 320 nm showed a distinct greenish-yellow peak centered at 570 nm. A continuous increase in Vickers micro-hardness with load, up to 100 g with no crack formation, classified the material as soft with Meyer index n = 2.3. Thermal gravimetric analysis coupled with differential thermal analysis (TGA/DTA) under nitrogen showed two discrete steps of dehydration and concluded with an endothermic melt transition at 110 ℃ confirming the uppermost safe working temperature limit.
Synthesis and characterization of the CSPH crystal highlighted its potential as a leak-free solid-state alternative to liquid UV filters as well as a possible passive UV filter device for optical communication systems.

Fig. 1 Preparation of single crystal of copper sulphate pentahydrate (CSPH). (Preetha N.; et al. 2023)

Schmieder L et al. evaluated copper sulphate pentahydrate (CuSO₄·5H₂O) as a thermochemical energy-storage material operated in a stirred oil suspension. By dispersing 30-70 wt% salt in mineral, silicone, or high-oleic sunflower oil, the three-phase reactor eliminated the agglomeration and poor heat/mass transfer that normally limit salt hydrates. Dehydration (charging) could be driven at 90-130 ℃, and 98.7% conversion was obtained within 5 min in flash tests. Hydration (discharge) was accomplished by simply injecting liquid water; exothermic temperature lifts scaled linearly with solid content, rising from 12-18 K at 30 wt% to 66.5 K at 60 wt%. Thirty dehydration-hydration cycles in mineral-silicone oil and fifteen in sunflower oil showed stable conversion (>90%) and unchanged hydration rates. XRD confirmed 99.3% pentahydrate recovery. Only conventional rapeseed oil failed after ten cycles because of thermal breakdown and agglomeration. Particle cracking was observed, but oil dispersion prevented blockages and allowed repeatable reaction paths.
The study demonstrated that combining CuSO₄·5H₂O, liquid-water hydration, and an inert-oil suspension overcame the previously reported drawbacks of slow kinetics, low temperature lift, and poor cycle life, and offered a compact, seasonal thermochemical storage option for 90-145 ℃ waste-heat or renewable-energy applications.

Fig. 2 The lab-scale suspension reactor (a) and the setup for the flash dehydration (b). (Schmieder L.; et al. 2026)