Lyophilization strategy to synthesize ultrafine NaCl template for preparation of photocatalytic BiOCl nanoplates via chemical vapor deposition

• The lyophilization method provides the NaCl templates for massive CVD growth. • The oxygen vacancies of 2D BiOCl nanoplates can be tuned by NaCl templates. • The defective 2D BiOCl shows extended absorption to the visible region. • Our work inspires the design of templates for the synthesis of 2D photocatalysts. Two-dimensional (2D) bismuth oxychloride (BiOCl) has attracted increasing attention in nanoelectronics, catalysis, energy storage, and the environment, attributed to its wide indirect band gap and large surface area. However, the imprecise control of the catalytic site on the substrate makes it challenging to produce 2D BiOCl in large quantities economically. Here, we developed lyophilization to create ultrafine NaCl templates to obtain a higher yield of 2D BiOCl nanoplates than traditional substrates using a chemical vapor deposition (CVD) method. In contrast to ball milling or recrystallization, lyophilization can produce the sodium chloride (NaCl) in the ice lattice domain, resulting in ultrafine NaCl particles after removing water. Moreover, the NaCl particles synthesized by lyophilization showed lower crystallinity with partially distorted structures, such as twisted octahedral structures and the structure with Na + separated from other atoms by an ice lattice. In addition, our method offers an opportunity to introduce and engineer the oxygen vacancies (OVs) on 2D BiOCl to narrow the band gap, improve the separation of photogenerated carriers, and enhance their photocatalytic efficiency by 17.2 times. Thus, our work opens a new avenue to produce 2D BiOCl by tuning the substrate in CVD growth and inspires a new strategy to promote the performance of 2D photocatalysts.