Water–n-BuOH solvothermal synthesis of ZnAl–LDHs with different morphologies and its calcined product in efficient dyes removal

In this study, water–n-BuOH mixed solvents were used to synthesize the ZnAl–layered double hydroxides (ZnAl–LDHs) via hydrothermal method. The XRD, FT-IR, SEM, ICP and CHN analyses revealed that the type of intercalated anions, the layer Zn/Al ratios, and morphologies of the LDHs depended on the ratio of V(water)/V(n-BuOH) in the mixed solvents. When the ratio of V(water)/V(n-BuOH) is 3 or 0.3, the as-prepared LDHs had 3D “silk flowers” (ZnAl–LDH–3) or “Sedimentary rock” morphology (ZnAl–LDH–0.3). Adsorption properties of dyes on calcined LDHs were studied. Compared with ZnAl–LDO–0.3 and ZnAl–LDO–w (calcined from the LDHs obtained in pure water), ZnAl–LDO–3 showed much better adsorption efficiency for anionic dyes thanks to its much larger BET-specific surface area. The sorption kinetics for dyes was appropriately described by the pseudo–second–order model and sorption isotherms can be fitted more satisfactorily by the Langmuir model. With the increasing concentrations of dyes from 10 mg/L to 400 mg/L, the maximum absorption capacities of ZnAl–LDO–3 were 1540 mg/g (2.21 mmol/g) for congo red, 1153 mg/g (3.52 mmol/g) for methyl orange and 390 mg/g (0.63 mmol/g) for active red (X-3B), respectively. The adsorption dyes onto the external surface is still the main mechanism for LDO adsorbents. The ZnAl–LDO–3 was a potential adsorbent for dyeing wastewater treatment.

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