Ferroelectric-semiconductor BaTiO3–Ag2O nanohybrid as an efficient piezo-photocatalytic material
Introduction
Nanostructured heterogeneous semiconductor photocatalyst is a unique process which offers the simple way to convert the solar energy to useful energy for environmental remediation applications (Ong et al., 2016). But, the current efficiency of the catalysts is not up to the expected level needed for practical or real time applications for pollution control (Fresno et al., 2014). Hence, optimizing these parameters like light harvesting/absorbing, quantum efficiency, promotion and separation of photo-induced electron hole and transportation via interfacial engineering of materials physics and chemistry can provide improved photocatalytic efficacy (Mohan et al., 2012). There are several reports on the development of new catalytic systems which primarily studied on the degradation of azo dyes (Nascimento et al., 2012). One of the crucial concerns in photocatalysis is examination of efficacy of the system against colorless standard pollutant such as phenol (Thangavel et al., 2015a). Moreover, there are several reports available in literature that several semiconductor materials catalyze the organic dyes, which are unable to degrade the colorless dye such as phenol (Zhang et al., 2013). Therefore, the improvement in the reaction rate as well as enhancement in the complete degradation efficiency of standard pollutants is primary concerns which determine the practical applications of the semiconductor photocatalysis system towards real time applications.
In this scenario, novel perovskite-type mixed oxides are recently emerged as high performance catalytic material upon light irradiation. Recently, some ferroelectric materials are used as photocatalytic materials due to the perfect aligned band position, and other works carried out towards the development of piezotronics and piezophotonics for environmental remediation applications (Cui et al., 2013). Further, novel systems such as piezophototronic effect are also developed via hybridizing two different aspects of basic science viz (i) photocatalysis and (ii) piezoelectric, respectively (Wang et al., 2016). A few of ABO3 non-centro symmetric oxides nanostructures with different morphology and combinations with other materials such as ZnO–Zn/CNT film, ZnO nanoparticle embedded MWCNT paper, LiNbO3, BaTiO3, KNbO3, ZnSnO3 in irregular, nanocubes, nanowires, and nanorods have been successfully utilized in environmental remediation sector (Li et al., 2013; Gao et al., 2014). The effect of ferroelectric-semiconductor hybrid system for catalysis reaction under the combination of ultrasound and light irradiation resulted in superior activity compared to conventional photocatalysis, sonocatalysis, and sono-photocatalysis, respectively.
Considering the works undertaken until now on this sector, the usefulness of the piezoelectric materials for catalysis applications via ultrasonics was examined initially and the results are not up to the level of expectation. Later on, Wang and co-workers demonstrated the novel approach to improve the photocatalytic activity via altering built-in field of the ferroelectric−semiconductor (BaTiO3–Ag2O) hybrid photocatalysts (Li et al., 2015). Following this, novel hybrid such as BaTiO3–Ag as a novel photocatalyst was reported by Su et al. which demonstrated the enhancement in catalytic properties of BaTiO3 via Ag loadings (Su et al., 2015). More recently, Hong et al., reported the efficiency of CuS/ZnO nanowires arrays for utilizing solar and mechanical energy towards degradation of organic dye (Duan et al., 2015). These literatures on the hybrid photocatalysis via piezophototronic effect clearly evidences the improvement in the separation of photogenerated electrons and holes by screening effect due to internal electric field in the ferroelectric materials under stress. And most of the studies reported that degradation of azo dyes (methylene blue or Rhodamine-B) via piezophototronic effect assisted hybrid photocatalytic system. Further, the mechanism of catalysis reaction relies on the production of reactive oxygen species like hydroxyl radicals which degrade the dye molecules in a time dependent manner. On the other hand, it is well known that only the hydroxyl radicals are not sufficient for the degradation of complex pollutant molecules from industrial residues (Thangavel et al., 2015b). Sulfate radicals with high oxidation potential involved advanced oxidation processes (AOPs) have received great attention recently. The AOPs can destroy different contaminates like dyes (Ghauch et al., 2012a), pharmaceutical compounds like Ibuprofen (Ghauch et al., 2012b), Naproxen (Ghauch et al., 2015), Ketoprofen (Amasha et al., 2018b). Sulfate radicals can be produced through persulfate activation (PS). At ambient atmosphere, PS is a stable and PS can be activated through various routes such as heat (Ghauch and Tuqan, 2012), UV-light (UVC and UVA/UVB) (Ghauch et al., 2017; Amasha et al., 2018a), homogeneous (El Asmar et al., 2021), heterogeneous (Ayoub and Ghauch, 2014) medium using MOF and iron based material (Ghauch et al., 2013; Naim and Ghauch, 2016; Al Hakim et al., 2019). Hence, it is beneficial to provide sufficient additional reactive oxygen species in the piezo-photocatalysis system via other methods such as persulfate activation which introduces the sulfate radicals in this system and thereby enable us to achieve high reaction rates as well as degradation of complex pollutants. Hence, the present work aimed at understanding the efficiency of a ferroelectric-semiconductor based nanohybrid system (BaTiO3–Ag2O) against general organic dye (Rhodamine B) as well as their performance in the catalytic degradation of standard pollutant, Phenol. Further, improvements in the piezo-photocatalysis were achieved via persulfate activation.
Section snippets
Materials
The precursor materials such as barium titanate (BaTiO3, >99.0%) and chemicals silver nitrate (AgNO3, >99.8%) sodium hydroxide (NaOH, >98.0%), phenol (C6H6OH, >99.0%), and common oxidant as potassium persulfate were purchased from Dae-Jung chemicals & metals Co Ltd, Korea. The azo dye Rhodamine-B (RhB, >99.0%) was obtained from Merck Chemicals Ltd., India. All chemicals and materials used in this work are of research purity and used as received without further purification. Doubly deionized
Results and discussion
The XRD pattern of bare BaTiO3 and sonochemically prepared Ag2O nanocrystals were shown in Fig. 1(a). The observed diffraction pattern and inter-planar spacing were matched well with the JCPDS card No: 75–1606 for BaTiO3 and JCPDS card No-75-1532 for Ag2O nanoparticles respectively (Shen et al., 2015; Chen et al., 2016). The powder diffraction pattern of sonochemically prepared BaTiO3–Ag2O nanohybrid was represent in Fig. 1(a) which evidences the presence of both BaTiO3, and Ag2O, thus,
Conclusion
The key findings of this work suggested the significance of ferroelectric-semiconductor (BaTiO3–Ag2O) nanohybrid catalyst towards degrading the pollutant dye and their improvements via persulfate activation. The series of experimental analysis using bare materials and their hybrid components evidenced that the prepared BaTiO3–Ag2O nanohybrid catalyst possess superior catalytic activity towards the degradation of a model dye RhB as well as standard pollutant (phenol) which showed its high
Author contributions statement
Sakthivel Thangavel: Formal analysis, Methodology, Investigation, Software, Writing – original draft. Parthiban Pazhamalai: Validation, Karthikeyan Krishnamoorthy: Investigation, Yuvaraj Sivalingam: Data curation, Durairaj Arulappan: Resources, Vigneshwaran Mohan: Resources, Sang-Jae Kim: Project administration, Funding acquisition, Gunasekaran Venugopal: Conceptualization, Visualization, Writing – review & editing, Supervision, Funding acquisition, Project administration
Declaration of competing interest
We certify that the manuscript, or any part of it, has not been published and will not be submitted elsewhere for publication while being considered in Chemosphere.
There is no conflict of interest in the work.
Acknowledgements
The author G. V. thankfully acknowledges the financial support from DST-SERB project grant (Grant no. ECR/2016/001798) and UGC-BSR research grant (Grant no. F.30-396/2017 [BSR]), New Delhi. Also the corresponding author extends his kind acknowledgement for the selection of his research scholar and subsequent financial support from Indo-Korea Research Internship (IKRI) program granted by DST, Govt. of India, New Delhi, in order to visit South Korea for one year research internship. A part of
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The first two authors contributed equally.