Pyroelectrically Driven •OH Generation by Barium Titanate and Palladium Nanoparticles

Abstract

The disinfection of bacteria by thermally excited pyroelectric materials in aqueous environments provides opportunities for the development of new means of sanitization. However, little is known about the formation of reactive oxygen species (ROS) at the surface of the thermally excited pyroelectric materials. To investigate the pyroelectrically driven ROS generation we performed OH radical specific measurements of thermally stimulated barium titanate nanoparticles in contact with palladium nanoparticles. Through electron spin resonance measurements with the spin trap BMPO (5-tert-butoxycarbonyl 5-methyl-1-pyrroline n-oxide) and fluorescence spectroscopy of 7-hydroxycoumarin, OH radical generation was detected, which confirms the hypothesis of pyroelectric ROS production. Since pyroelectric potential changes are insufficient for direct electrochemical OH radical generation, we propose a two-step chargetransfer model facilitated by intermittent contact between the palladium and the pyroelectric nanoparticles and the pyroelectric effect as the driving force for charge transfer. ■ INTRODUCTIONCommercial water disinfection currently relies on chemical methods using chlorine-or ozone-based chemicals, whereas physical methods like thermal disinfection or ultraviolet radiation are less often employed. Due to their high oxidative potential, reactive oxygen species (ROS) are well suited as a physical means of disinfection. A completely new approach for creating ROS is the utilization of the pyroelectric effect, 1 which seems favorable when naturally occurring temperature changes can be employed for the excitation of the pyroelectric materials and, thus, offer an environmentally friendly method of water disinfection.In an aqueous solution the spontaneous polarization at the surface of a ferroelectric is screened, for example, by dissolved ions or dissociated water molecules. Changes in temperature trigger the pyroelectric effect. The imbalance of polarization and screening charges changes the effective surface potential. It was shown that these potential changes whether they stem from changes in temperature or strain can be used to drive electrochemistry between physisorbed molecular species. 1,2 For example Hong et al. demonstrated water splitting on mechanically excited surfaces of BaTiO 3 and ZnO. Gutmann et al. proposed that the observed water disinfection with thermally stimulated LiNbO 3 and LiTaO 3 is facilitated by production of ROS at the surface of the pyroelectric materials.Free radicals have high oxidation potentials, especially the OH radical whose oxidation potential is twice that of chlorine which is commonly used for disinfection. It is known that OH radicals can pull H atoms from C−H and S−H bonds and split aromatic rings. Living cells are damaged by radicals reacting with amino acids and DNA molecules. 3 Photocatalytic E. coli inactivation with TiO 2 showed cell damage caused by various ROS, such as OH radicals, hyperoxide radicals, and H 2 O 2 . 4 Basically ROS react immediately at the place of their ori...

Macroscopic Polarization Enhancement Promoting Photo‐ and Piezoelectric‐Induced Charge Separation and Molecular Oxygen Activation

“…To inspect if COH was generated in the piezoelectric-induced process,t erephthalic acid (TA)-photoluminescence (PL) method is employed, as COH could react with TA in equal proportion to produce highly fluorescent 2hydroxyterephthalic acid at 425 nm. [5] Drastic PL peak intensity increase occurs with increasing the ultrasonic time (Supporting Information, Figure S15), suggesting the continuous production of COH. Thep lot of COH concentration vs. ultrasonic irradiation time is illustrated in Figure 4f.The COH concentration generated by BiOI 0.926 V 0.074 O 3 far exceeds that by BiOIO 3 ,a nd the average production rates are 1.2 and 3.9 mmol L À1 h À1 for BiOIO 3 Figure S16), further verifying the piezoelectric induced ROSe volution process.…”

“…Therefore, the superimposition of microscopic polyhedral distortion contributes to the large macroscopic polarization of BiOI 0.926 V 0.074 O 3 . [5] Drastic PL peak intensity increase occurs with increasing the ultrasonic time (Supporting Information, Figure S15), suggesting the continuous production of COH. Here,u ltrasonic agitation was employed as as table irradiation source to provide stress,and NBT was used as aprobe to quantify the CO 2 À concentration.…”

“…[3] As the fast carrier recombination (several ps) occurred in photocatalytic process,R OS evolution efficiency through photocatalysis is limited. [5] Thus,p romoting photocatalytic ROS evolution as well as exploration of new channels to production of ROS, particularly realized by asingle material, are of significance and challenge.P iezoelectrics reversibly convert-ing stress into electricity,a re widely applied in optoelectronics.T he stress-induced polarization potential can act as alternating built-in electric field to separate photoinduced carriers. [5] Thus,p romoting photocatalytic ROS evolution as well as exploration of new channels to production of ROS, particularly realized by asingle material, are of significance and challenge.P iezoelectrics reversibly convert-ing stress into electricity,a re widely applied in optoelectronics.T he stress-induced polarization potential can act as alternating built-in electric field to separate photoinduced carriers.…”

“…[4] Recently,pyroelectrically driven COH generation was achieved by synergism of ferroelectric BaTiO 3 and superficial Pd nanoparticles,b ut its efficiency is still low. [5] Thus,p romoting photocatalytic ROS evolution as well as exploration of new channels to production of ROS, particularly realized by asingle material, are of significance and challenge.P iezoelectrics reversibly convert-ing stress into electricity,a re widely applied in optoelectronics.T he stress-induced polarization potential can act as alternating built-in electric field to separate photoinduced carriers. [6] BiOIO 3 as an oncentrosymmetric (NCS) polar material presents strong second-harmonic generation (SHG, ca.…”

Enabling PIEZOpotential in PIEZOelectric Semiconductors for Enhanced Catalytic Activities

“…Benke et al were the first to verify hydroxyl radicals generated by thermally excited pyroelectric BaTiO 3 -Pd nanoparticles, [35] uncovering the possible pyrocatalytic mechanism and signifying the potential application of pyroelectric effect in catalysis.Ayear later, Jia et al reported the successful pyrocatalytic degradation of RhB,m ethyl orange (MO), and MB using BiFeO 3 as catalysts. [29] Thep yroelectric effect was also applied in the disinfection of 2',7'-dichlorodihydrogluorescin (DCFH) with LiNbO 3 and LiTaO 3 particles as catalysts.…”