Morphological evolution of PbS crystals under the control of l-lysine at different pH values: The ionization effect of the amino acid

PbS crystals were synthesized by a simple hydrothermal process with l-lysine as the crystal growth modifier. Depending on the initial pH value of the reaction solution, the morphologies of the PbS crystals varied and the crystals with shapes of truncated nanocube, star-shaped dendrite, comb-like dendrite were obtained. The morphological evolution of the PbS crystals was explained by the different state of the ionization equilibrium of l-lysine in the solution at different pH values. The presence of differently charged l-lysine molecules would influence the crystal growth rates along different directions and result in the final morphologies of PbS crystals. It is proposed that when amino acids are used as crystal growth modifiers, besides the types of amino acids, which have been regarded to influence the crystals' growth, the ionized state of the amino acids at different pH values would play an important role in the morphological control, and this point may have been neglected before.

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