Solvent-free mechanochemically synthesized Zn layered hydroxide salts for the adsorption of naphtholate AS dye

Solvent-free synthesis through a mechanochemical method is one of the most promising benign methodologies in the recent decades. In this study, a very simple solvent-free mechanochemical method for the synthesis of Zn layered hydroxide salts (Zn LHSs) by manual grinding in a mortar was reported in detail. With a single step grinding for fifteen minutes at ambient temperature, Zn LHSs were successfully synthesized from Zn(NO3)2·4H2O and NaOH with OH/Zn molar ratio 0.6. Based on the characterization results using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermal analysis (TGA/DTA) and scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS), the as-synthesized Zn LHSs (mechano-Zn LHSs) showed similar characteristics as Zn LHSs prepared by conventional coprecipitation method (copre-Zn LHSs) but with slightly worse crystallinity and lower dehydroxylation temperature. Mechano-Zn LHSs were highly pure with only insignificant noticeable contamination from other phases. Adsorption of naphtholate AS dye on mechano-Zn LHSs and copre-Zn LHSs was optimum at pH 9.14 and matched well in Langmuir isotherm model with capacity and energy of adsorptions were 0.67 × 10−3 mol/g and 23.79 kJ/mol for mechano-Zn LHSs which were slightly higher than those of copre-Zn LHSs, i.e. 0.62 × 10−3 mol/g and 23.18 kJ/mol, respectively.