Photothermally-enabled Pyro-catalysis Of BaTiO₃ Nanoparticles Composite Membrane At Liquid/Air Interface

Pyroelectric materials have been widely used as electricity generators to harvest thermal energy and convert it into electrical energy.The harvesting process is based on pyroelectric effect,which is owing to the generation of surface charges induced by the temperature oscillation-dependent spontaneous polarization.Recently,pyroelectric materials were studied as pyro-catalysts by thermal excitation in the aqueous environments,which provides hydroxyl radical?·OH?for disinfection and degradation.In the aforementioned systems,dispersed nanoparticles?NPs?solutions exhibit high surface area for catalytic reactions.Their thermal design with the bulk solution degradation,however,results in overall low efficiency due to the relatively low rate of temperature change.The high thermal heat capacity of water intrinsically limits the heating and cooling rate of the bulk solution,which subsequently limits pyroelectric conversion process.As revealed by pyroelectric coefficient equation,both the increase in the surface area?A?of pyroelectric materials and the increase in the rate of temperature change?dT/dt?can result in large pyroelectric current and thus high catalytic efficiency.Hence,a rational and efficient thermal design for the pyro-catalysis system is needed for the continuous advancement in this field.This paper reports the highly efficient pyroelectric nanomaterials-based catalytic degradation of waste dye under rapid temperature oscillation achieved by periodical solar irradiation on the floating porous pyroelectric nanoparticles composite membrane at the liquid/air interface.Such composite membrane is consisted of the light-to-heat conversion carbon black film as top layer and the porous polyvinylidene fluoride?PVDF?film embedded with pyroelectric BaTiO₃ nanoparticles?BTO NPs?for pyro-catalysis as bottom layer.By applying optical chopper,solar light could be modulated to periodically irradiate on the floating membrane.Due to the photothermal effect and low thermal conductivity of PVDF polymer,the generated heat would be localized at the surface of membrane and dramatically increase the surface temperature within a short period of time.When the solar light is blocked by the chopper,interfacial evaporation through porous membrane along with convective air cooling and radiation cooling leads to heat dissipation and then the temperature of membrane is decreased.Such efficient thermal cycle?i.e.heating and cooling process?results in substantial variation rate of temperature gradient of membrane,which enhances its pyroelectric capability and subsequent pyro-catalysis.In contrast,the efficiency of pyro-catalysis through dispersed BTO NPs solution is about four times lower than that of BTO composite membrane,as demonstrated in our control experiment.Since the large heat capacity of aqueous solution and inevitable thermal loss due to bulk heating,the variation rate of temperature gradient of BTO NPs solution is much smaller than that of BTO composite membrane,and thus results in fair pryo-catalytic capability.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 involving in pyroelectric materials.