Research article
Green synthesis of spongy Nano-ZnO productive of hydroxyl radicals for unconventional solar-driven photocatalytic remediation of antibiotic enriched wastewater

https://doi.org/10.1016/j.jenvman.2020.110961Get rights and content

Highlights

  • Facile one pot green route is successfully employed to prepare spongy ZnO NPs.

  • These ZnO NPs is of better response and narrowed band gab to absorb visible photons.

  • Moreover, it has oxygen vacancies defective morphology and high surface area.

  • It produces separable photogenerated e/h+ and high productivity of .OH radicals.

  • The spongy ZnO is potent/durable in solar-driven degrading of flumequine antibiotic.

Abstract

Herein, novel green/facile approach to synthesize spongy defective zinc oxide nanoparticles (ZnONPs) is presented using for the first time pomegranate seeds molasses as a green capping fuel/reducing mediator during an aqueous solution combustion process. The developed ZnONPs is characterized by UV–Vis. Spectrophotometry and fluorimetry, XRD, Raman spectroscopy, SEM, TEM and BET. Interestingly, pomegranate seeds molasses within a viable content of bio-capping molecules reveal a defective nanoporous ZnO NPs of smaller particle size, greater pore size/volume, and higher surface area compared to the bulky non-biogenic ZnONPs. Moreover, the biosynthesized defective ZnONPs showed narrowed band gap and higher absorption of visible photons that breed higher density of hydroxyl radicals (OH) under Solar-illumination. Even further, the bulk ZnO and the biosynthesized ZnO photocatalysts were examined in photodegrading flumequine (FL) antibiotic. The bulk ZnO gives 41.46% photodegradation efficiency compared to 97.6% for the biosynthesized ZnO. In highly acidic or highly alkaline media, FL photodegradability is greatly retarded. Scavenging experiment infers considerable contribution of holes over electrons in photodegradation reaction. The biosynthesized ZnO shows high durability in FL photodegradation after four reusing cycles. These promising findings highlight new insights for biogenic synthesis of tuned size/controlled morphology semiconductor NPs relevant to environmental remediation applications.

Introduction

Due to continuous exploration of new characteristics within promising diverse applications, nanotechnology has been capturing more and more attention, especially in dealing with semiconductor materials for several decades. High-surface-to-volume semiconductor nanoparticles and other exceptional physicochemical characteristics make them a leading contender in materials that have been renovated.

Zinc oxide (ZnO) nanoparticles were described among the various semiconductors as functionally promising and versatile inorganic materials with unparalleled optical and electrical properties that can be adjusted by modifying the size and morphology (Ma et al., 2019). Accordingly, ZnO displays a wide variety of appealing applications in the optoelectronics, piezoelectrical devices, transparent electronics, chemical sensors (Saito et al., 2018; Zou et al., 2018; Li et al., 2018), environmental protection, pharmaceutical, cosmetic, agricultural and food industries (Espitia et al., 2012). In addition, ZnO NPs demonstrated tremendous efficacy in biological and medical areas such as biological labeling, bio-sensing, gene delivery, drug delivery, nanomedicine and cosmetic sectors owing to their anti-microbial, anti-diabetic and wound healing capabilities (Dastjerdi and Montazer, 2010; Radzimska and Jesionowski, 2014; Mishra et al., 2017; Moezzi et al., 2012). ZnO nanoparticles have a wurtzite structure and belong to the family of semiconductors category II-IV, which has a covalence between ionic and covalent semiconductors (Ngoepe et al., 2018). Moreover, advanced oxidation process (AOPs) and the field of photocatalysis utilize ZnO to aid in remediating environment from hazardous contaminants more efficiently compared to conventional methods. Recently, wide utilization of antibiotics to confront infectious diseases and maintain the body health for human, fauna and flora (Kummerer, 2009) could be accompanied by abusing or inconvenient disposal. The antimicrobial agent, flumequine (FL), is one of the fluoroquinolone antiobiotics (Fig. 1) frequently detected within 6.9 μg/g in soil and 2.5–50 ng/L in aquatic media (Rodrigues-Silva et al., 2013; Feng et al., 2015a, 2015b). Unfortunately, the presence of trace amounts of FL in environment may result in resistive microbes and distressed organisms. Therefore, its presence in the aquatic life exhibits serious environmental issues that pave the way to an inevitable need for its save and efficient removal.

To attain highly effaceable ZnO-photocatalyzed processes, it is important to devote research for morphology evolution to material characteristics. Thereby, tremendous attempts have been produced with distinct morphologies in ZnO's preparation techniques. Methods employing physical, chemical and green synthetic routes have been successfully presented. In recent years, researchers are remarkably interested in achieving advancement in the green technicalities for synthesizing semiconductor nanoparticles. This is due to advantages of safety, rapidity, positive economic and eco-friendly large scale productivity as compared with physical and chemical approaches Joseph and Mathew (2015); Kaushal et al. (2016). In such fascinating area of green biosynthesis of nanoparticles, microorganisms, enzymes, alga and plant extracts are used. The plant extracts contain various types of phenolic and flavonoid compounds that help in nanoparticles formation (Khan et al., 2016; Tahir et al., 2016). For example, from the extracts of various plants (Jafarirad et al., 2016; Ngoepe et al., 2018; Haritha et al., 2016; Kalaiselvi et al., 2015; Essawy, 2018; Kumar et al., 2015; Elango et al., 2016), ZnO and other nanomaterials were synthesized.

In the field of photocatalysis, ZnO is a wide band gap semiconductor with a band gap of 3.37 eV that unfortunately displays a lower compatibility to utilize solar energy (Essawy et al., 2018). In 2011, in Science, Chen et al. reported on a technique to reduce the band gap of TiO2 semiconductor materials that opened the door for scientists to a new globe (Chen et al., 2011; Liu et al., 2017; Essawy et al., 2017). In fabricating solar-responsive ZnO NPs with high performance, factors of porosity and surface oxygen defects are greatly crucial in exploring merits of ZnO in photocatalysis. The porous structure could exhibit higher adsorption potentiality, and the oxygen vacancies act as capture centers for photogenerated electrons. Accordingly, the reassemble of photogenerated electron-hole pairs is prohibited and more electrons reach the surface producing high density of reactive oxidizing species (Khan et al., 2014; Zhang et al., 2016). Furthermore, a defect level will be generated plausibly narrowing the band gap and enhances the electrical properties (Xu et al., 2015).

The recent bio-inspired green synthetic routes offer a uniquely flexible growth of nanoparticles of controlled shape and size (Narayanan and Sakthivel, 2010; Thakkar et al., 2010; Katata-Seru et al., 2018). Herein, the pomegranate seeds extract is presented as biogenic reducing and capping fuel during a novel one pot aqueous solution combustion reaction for the fabrication of a nanoporous defective ZnO nanoparticles. The amount of pomegranate extract added to the reaction course confers an interesting structural features of the prepared ZnO enabling highly efficient harvesting of solar energy. Furthermore, stunning Solar-sensitization for extensive productivity of reactive oxidizing species urgently required for a potent confronting of aquatic toxification by FL. To date, ZnO-photocatalyzed degradation of FL wastewater is markedly delimited in literature. Even further, to the best of our knowledge, the Solar-driven photocatalytic degradation of FL wastewater has not been reported.

Section snippets

Materials

A fresh pomegranate fruits were supplied from local market in Aljouf region, City of Sakaka, Saudi Arabia. Zinc nitrate hexahydrate (Zn(NO3)2.6H2O) of analytical grade, ethanol, terephthalic acid, zinc oxide, sodium hydroxide and Flumequine were obtained from Sigma Aldrich. The physico-chemical characteristics of flumequine are listed in Table 1 (Sotelo et al., 2013; Santoke et al., 2009). Deionized (DI) water was performed to prepare all the working aqueous solutions.

Preparation of pomegranate seeds extract (PMSE)

Fresh Pomegranate fruits

X- ray diffraction, XRD

The XRD patterns of the 0MSCBZnO and the different biosynthesized 1MSCDZnO, 2MSCDZnO, 3MSCDZnO and 4MSCDZnO NPs are shown in Fig. 3. The diffraction pattern (a) corresponds to 0MSCBZnO confirms the formation of pure ZnO of hexagonal wurtzite structure (JCPDS No. 36–1451) where the features peaks at 2θ = 31.6°, 34.4°, 36.2°, 47.4°, 56.6°, 62.9°, 66.4°, 67.8°, 69.0°, 72.6° and 77.0° can be attributed to the corresponding crystal surfaces of the (100), (002), (101), (102), (110), (103), (200),

Conclusions

In the present work, a facile one pot green and sustainable synthetic route is successfully employed to prepare ZnO NPs using pomegranate seeds extract as a biogenic reducing and capping fuel during a novel solution combustion process. The biosynthesized ZnO in comparison with the bulky one prepared in absence of the biogenic reagent is of better response and narrowed band gab to absorb visible photons of solar light. Also, the biosynthesized ZnO is characterized by a nanoporous oxygen

CRediT authorship contribution statement

Amr A. Essawy: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing - original draft, Writing - review & editing. Ibrahim Hotan Alsohaimi: Conceptualization, Funding acquisition, Investigation, Project administration, Resources, Software, Supervision, Visualization, Writing - review & editing. Mosaed S. Alhumaimess: Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors appreciate the financial aid of Jouf University for research group 40/G/02.

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