Crystallization of calcium sulfate dihydrate (CaSO4·2H2O, gypsum) in sodium chloride solutions has been studied in the presence of magnesium ion. It was shown that Mg2+ has an inhibiting effect on the two stages of precipitation: nucleation and growth. Kinetic results were explained on the basis of the strong effect of magnesium ions on gypsum solubility. In the studied range of the ionic strength (IS), it was found that in the presence of NaCl the solubility increase stops beyond IS = 0.31 mol·L–1 whereas it continues to rise in the presence of MgCl2. X-ray diffraction analyses showed that magnesium ions act by substituting the calcium ones or by insertion in the defects of the gypsum crystal lattice.

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Calcium sulphate dihydrate (gypsum) crystallization was studied under conditions, of supersaturation and temperature, simulating a brackish water desalination unit using solar energy. The effect of an commercial sodium salt of poly(acrylic acid), based compound known as RPI, on homogeneous nucleation and growth of gypsum was also examined. Gypsum was precipitated by mixing aqueous CaCl 2 and Na 2 SO 4 solutions. It was found that, with increasing temperature or supersaturation, the induction time decreases and the growth rate increases. By using classical nucleation theory, the interfacial tension and the nucleation rate values were estimated. It was shown that the interfacial tension is temperature dependent. The addition of increasing quantities of RPI, in the same conditions of temperature and supersaturation, prolongs the induction time, decreases the nucleation rate and increases the interfacial tension. The addition mode of RPI (in calcium or in sulphate solution) was found as an important parameter in controlling the inhibition process of gypsum crystallization. XRD and SEM analysis showed that RPI antiscalant strongly affected the texture and the morphology of the deposit gypsum.

Single-phase BiVO 4 (BV) powder was synthesized successfully at 600 • C within 4 h duration through the mechanochemical high energy ball milling method, and the combined photocatalytic and piezocatalytic activity was studied to exhibit piezo-photocatalytic efficiency. Monoclinic BV phase existence in the synthesized powder was affirmed through Raman spectroscopy and the X-ray diffraction techniques. The scanning electron microscopy affirmed the irregularshaped BV powder in the synthesized powders. X-ray photoelectron spectroscopy affirmed the existence of various oxidation states of the elements V, Bi, and O in BV powders. The piezocatalytic and photocatalytic methylene blue (MB) dye degradation efficiency using BV powdered sample was observed to be 28% and 60%, respectively, within 240 min. The piezo-photocatalytic MB dye degradation using BV powdered sample was observed to be 81% within 240 min. Effect of dye concentration on kinetic rate constant was also studied.

Ferroelectric materials with a spontaneous polarization are proven to be potential multicatalysts in water remediation applications. The composition of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Sr0.3)TiO3 (BST-BZT) was examined for photocatalysis, piezocatalysis, and piezo-photocatalysis processes by degrading an azo dye named methylene blue (MB). Generally, dis-aligned dipoles restrict the catalytic activities due to which the BST-BZT powder sample was poled by the corona poling technique. Coupled piezocatalysis and photocatalysis process, i.e., the piezo-photocatalysis process has shown maximum dye degradation. There was a significant improvement in degradation efficiency by using a poled BST-BZT sample compared to the unpoled sample in all processes, thus the results suggest an extensive scope of poled ferroelectric ceramic powder in the catalysis field.

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