Photothermally Enabled Pyro-Catalysis of a BaTiO₃ Nanoparticle Composite Membrane at the Liquid/Air Interface

This paper reports the highly efficient pyroelectric nanomaterial-based catalytic degradation of waste dye under rapid temperature oscillation, which was achieved by periodical solar irradiation on a porous pyroelectric membrane that was floating at the liquid/air interface. Such a membrane consists of the light-to-heat conversion carbon black film as the top layer and the porous poly(vinylidene difluoride) (PVDF) film embedded with pyroelectric barium titanate (BaTiO₃) nanoparticles (BTO NPs) as the bottom layer. By using an optical chopper, solar light can be modulated to periodically irradiate on the floating membrane. Because of the photothermal effect and low thermal conductivity of the PVDF polymer, the generated heat is localized at the surface of the membrane and substantially increases the surface temperature within a short period of time. When the solar light is blocked by the chopper, interfacial evaporation through the porous membrane along with convective air cooling and radiative cooling leads to heat dissipation, and then the temperature of the membrane is rapidly decreased. Such an efficient thermal cycle results in a substantial rate of temperature change of the membrane, which enhances its pyroelectric capability and subsequent pyro-catalysis. In contrast, the efficiency of pyro-catalysis through the dispersed BTO NP solution is about 4 times lower than that of the BTO composite membrane. With the large heat capacity of the aqueous solution and inevitable thermal loss because of bulk heating, the rate of temperature change of the BTO NP solution is much smaller than that of the BTO composite membrane and thus results in a relatively small pyro-catalytic capability. Furthermore, the reusability and transferability of this newly developed composite membrane make it amenable to practical use in treating contaminated water. The findings in our report not only offer a new design strategy for efficient solar-enabled pyro-catalysis but also pave a new way to rationally harvest solar-thermal energy in nature for various applications that involve pyroelectric materials.