The homogeneous nucleation during fast cooling crystallization and the heterogeneous nucleation during the solution-mediated polymorphic transformation (SMPT) of p-nitrobenzoic acid (PNBA) were investigated to elucidate the connection between the molecular self-assembly and the nucleation process. Process analytical technology (PAT) tools, such as attenuated total reflection-Fourier-transform infrared (ATR-FTIR) spectroscopy were successfully applied to highlight the existence of solution-phase dimers and monomers. The combination of solubility measurements, measured nucleation induction time, polymorphic outcome and transformation, and computational chemistry was used to demonstrate the connection among solvation, molecular self-assembly in solution, and the nucleation pathway of PNBA. The orders of solubility and nucleation rates in different solvents were found to be consistent with those of solute–solvent binding energies. The dimerization of PNBA molecules in hydrogen-bonded dimers and stacked dimers through π–π interactions seem similar in all four solvents investigated in this study, which indicates that the desolvation of PNBA is the key step during the overall nucleation pathway.
A simultaneous denitrifying and mineralizing bacterium, Pseudomonas sp. WZ39 was isolated for fluoride (F − ), nitrate (NO 3 − -N), and calcium (Ca 2+ ) removal. Strain WZ39 exhibited a remarkable defluoridation efficiency of 87.49% under a pH of 6.90, F − and Ca 2+ concentration of 1.99 and 201.88 mg L −1 , respectively. EEM, SEM–EDS, XRD, and FTIR analyses elucidated the chemical adsorption and co-precipitation with calcium salt contributed to the removal of F − . The mechanisms of biomineralization were also investigated by determining the role of bound and unbound extracellular polymeric substances (EPS), cell wall, and calcium channel in nucleation. The results showed that bacteria can promote nucleation on the templates of cell walls or EPS through the electrostatic effect. The presence of the calcium channel blocker inhibited the transport of intracellular Ca 2+ to the extracellular environment. The outcome of the present research can provide a theoretical basis for the understanding of MICP phenomenon and the efficient treatment of F − containing groundwater.
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