Processable dispersions of photocatalytically active nanosheets derived from titanium diboride: self assembly into hydrogels and paper-like macrostructures.

Titanium diboride (TiB), a layered ceramic material, is well-known for its ultrahigh strength, wear resistance, and chemical inertness. In this work, we present a simple one-pot chemical approach that yields sheet-like nanostructures from TiB. We serendipitously found that TiB crystals can undergo complete dissolution in a mild aqueous solution of HO under ambient conditions. This unexpected dissolution of TiB is followed by non-classical recrystallization that results in nanostructures with sheet-like morphology exhibiting Ti-O and B-O functional groups. We show that this pathway can be used to obtain an aqueous dispersion of nanosheets with concentrations ≥3 mg mL. Interestingly, these nanosheets tend to transform into a hydrogel without the need of any additives. We found that the degree of gelation depends on the ratio of TiB to HO, which can be tuned to achieve gels with a shear modulus of 0.35 kPa. We also show this aqueous dispersion of nanosheets is processable and forms hierarchical paper-like macrostructures upon vacuum filtration. Such an ability to assemble into free-standing 3D structures would enable a leap to practical applications. We also show that the high surface area and presence of oxy-functional groups on these nanosheets endow them a superior photocatalytic activity to degrade organic pollutants. This exemplifies the rich potential that TiB offers upon nanoscaling. The results presented here not only add a novel material to the 2D flatland but also urge the scientific community to revisit the chemistry of metal borides, that have been traditionally considered as relatively inert ceramics.